�������� ����� ��

The Watonga Formation and Tacking Point Gabbro, Port Macquarie, Aus-tralia: Insights into crustal growth mechanisms on the eastern margin ofGondwana

Solomon Buckman, Allen P. Nutman, Jonathan Aitchison, Joseph Parker,Sarah Bembrick, Tom Line, Hiroshi Hidaka, Tomoyuki Kamiichi

PII: S1342-937X(14)00097-5DOI: doi: 10.1016/j.gr.2014.02.013Reference: GR 1239

To appear in: Gondwana Research

Received date: 9 August 2013Revised date: 28 February 2014Accepted date: 28 February 2014

Please cite this article as: Buckman, Solomon, Nutman, Allen P., Aitchison, Jonathan,Parker, Joseph, Bembrick, Sarah, Line, Tom, Hidaka, Hiroshi, Kamiichi, Tomoyuki, TheWatonga Formation and Tacking Point Gabbro, Port Macquarie, Australia: Insightsinto crustal growth mechanisms on the eastern margin of Gondwana, Gondwana Research(2014), doi: 10.1016/j.gr.2014.02.013

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

1

The Watonga Formation and Tacking Point Gabbro, Port

Macquarie, Australia: Insights into crustal growth

mechanisms on the eastern margin of Gondwana

Solomon Buckman1*

, Allen P. Nutman1, Jonathan Aitchison

2, Joseph Parker

3, Sarah

Bembrick1,2

, Tom Line4, Hiroshi Hidaka

5 and Tomoyuki Kamiichi

5

1 GeoQuEST Research Centre, School of Earth and Environmental Sciences,

University of Wollongong, Wollongong, NSW 2522, Australia

2 School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia

3 Mount Isa Mines, Mount Isa, Queensland 4825, Australia

4 Arrium Mining, Whyalla, South Australia 5600, Australia

5 Department of Earth and Planetary Systems Sciences, University of Hiroshima,

1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan

*Corresponding author: Solomon Buckman email: solomon@uow.edu.au

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

2

Abstract

A diverse assemblage of accretionary complex, island-arc, ophiolitic and high-

pressure, low-temperature metamorphic rocks occurs within the serpentinite mélange

at Port Macquarie on the eastern extremity of the New England Orogen of eastern

Australia. New field observations, U-Pb zircon dating, petrography and geochemistry

presented here establish a more robust chronology and interpretation of these rocks.

Previously, all basalt, chert and volcaniclastic sandstones at Port Macquarie were

grouped into the Watonga Formation. Ordovician to middle Devonian radiolarians

and conodonts from ‘Watonga’ chert-basalt associations shows that they are older

than, and unrelated to, ‘Watonga’ volcaniclastic rocks like those at Green Mound

which contain volcanic/detrital zircons as young as 335 Ma that were derived from a

Carboniferous arc. Volcanic detritus with pillow lava forming a block within the

serpentinite mélange yielded 452±10 Ma igneous zircons, indicating an Ordovician

age. The Tacking Point Gabbro has an age of 390±7 Ma (Devonian) and geochemical

affinities with intra-oceanic arc igneous suites. It was intruded into deformed cherts of

the Watonga Formation giving a spatial link between an Ordovician-Devonian?

accretionary complex and adjacent Devonian island-arc. The MORB-like basalt-chert

association of the Watonga Formation and the Devonian Tacking Point gabbro

represent a mid-Paleozoic assemblage allochthonous to Gondwana, which possibly

correlate with the Djungati and Gamilaroi terranes respectively located further west in

the New England Orogen. Zircon dating shows that post-serpentinite mafic-felsic

dykes were emplaced into the Port Macquarie serpentinite at 247±20 Ma and further

disrupted. Therefore, tectonism affecting the serpentinite continued into the Early

Triassic, with final movement during the Hunter-Bowen Orogeny. Our results from

Port Macquarie are compatible with a tectonic model for the New England Orogen

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

3

that involves episodic island-arc collisional events (Gamilaroi and Gympie terranes)

interspersed with periods of continental margin “Andean-type” magmatism and

accretion along eastern Gondwana.

Keywords: Serpentinite mélange; Watonga Formation; Tacking Point Gabbro; Port

Macquarie; New England Orogen

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

4

1. Introduction

The New England Orogen (NEO) of Australia (Figure 1) developed along the

eastern margin of Gondwana by convergent margin accretion and amalgamation of

terranes during the Paleozoic and earliest Mesozoic (Cawood and Buchan, 2007;

Cawood et al., 2011a; Flood and Aitchison, 1988; Murray et al., 1987). Widespread

intrusion of granite plutons occurred episodically within the NEO from the latest

Carboniferous (~300 Ma) through to the Triassic (~220 Ma). The Hunter-Bowen

Orogeny is the main deformation event within the NEO (Collins, 1991) and broadly

corresponds with a magmatic hiatus from the latest Permian to Early Triassic

(Holcombe et al., 1997; Li et al., 2012). Together these resulted in the complex

tectonic collage now observed in the NEO.

For the eastern Gondwanan margin, there is considerable debate whether crustal

accretion was entirely over a single long-lived, westerly-dipping, easterly migrating

subduction zone (Cawood and Buchan, 2007; Cawood et al., 2011a) or if there were

changes of subduction polarity, with rafting-in of intra-oceanic island-arc domains of

Panthalassan origin onto the Gondwanan margin (Aitchison and Ireland, 1995;

Aitchison et al., 1992; Murray, 2007; Offler and Gamble, 2002). Furthermore, the

timing of these events is much debated. Some studies argue that most crustal

development, including the emplacement of serpentinites with blocks preserving

eclogite and blueschist facies metamorphism, occurred entirely in the early-middle

Paleozoic (Fukui et al., 1995; Och et al., 2003; Phillips and Offler, 2011), whereas

more recent dating suggests that some important crustal development as well as some

high-pressure metamorphism could have occurred as late as ~250 Ma, perhaps early

in the Hunter-Bowen Orogeny (Nutman et al., 2013).

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

5

In this paper these controversies are explored further by U-Pb zircon dating,

petrographic and geochemical studies of the Watonga Formation, the Tacking Point

Gabbro and syn-kinematic intrusions (Leitch, 1974; Och, 2007) at Port Macquarie in

northern New South Wales (Figures 1 and 2). The Watonga Formation is one of the

easternmost occurrences of basalt-chert-turbidite associations in the NEO, and

sedimentary petrology and the dating of detrital zircons can test to what degree it was

derived from a simple (intra-oceanic) volcaniclastic source or from a complex early

Paleozoic to Precambrian Gondwanan source. The Tacking Point Gabbro is

important, because it is the easternmost body of its type in the NEO, and its age,

geochemistry and the nature of its country rocks can establish whether or not it

formed remote from the Gondwana margin. Results of our study, suggest it is possible

for the first time, to correlate key lithologies within the Port Macquarie Block with

other terranes further west in the NEO and provide a simpler and more accurate

tectonostratigraphic framework with which to advance our understanding of Paleozoic

to Mesozoic continental growth mechanisms along the eastern margin of Gondwana.

1. The New England Orogen (NEO)

The NEO extends approximately 1300 km along eastern Australia from

Bowen (20˚ S) to Newcastle (33˚ S) and has been divided into three regional

provinces; northern New England (Yarrol), southern New England and Gympie

(Figure 1). The western limit of the orogen is marked by the Hunter-Mooki fault

system, a low angle thrust fault dipping east, with the footwall containing early

Triassic rocks of the Sydney Basin (Korsch et al., 1993).

Continental rifting of Rodinia during the Neoproterozic formed the eastern

margin of Gondwana and opened the Paleo-Pacific (Panthalassan) Ocean. The closure

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

6

of this ocean basin began in the late Neoproterozoic (~570 Ma) building the

Tasmanides or Terra Australis Orogen (Cawood, 2005) that contains a mixture of

both exotic and Gondwana margin terranes. Plate convergence and terrane accretion

along eastern Gondwana resulted in multiple orogenic events from the Cambrian to

Triassic after which New Zealand rifted away to open up the Tasman Sea.

Examination of the NEO from a tectonostratigraphic perspective (Cawood and Leitch,

1985; Flood and Aitchison, 1988; Scheibner, 1985) showed that several discrete

terranes exist, suggesting that the NEO may not have evolved as a simple,

continuously west-dipping subduction system throughout the Paleozoic, and that

exotic island arc terranes may have periodically collided and accreted to eastern

Gondwana. This occurred before evolving into an Andean-type continental margin in

the Carboniferous producing the characteristic felsic volcanic lithologies of the

Tamworth Belt (arc to fore-arc basin) and the overlapping and interleaved

Carboniferous accretionary complex known as the Anaiwan terrane or Tablelands

Complex. In this way the quantum addition of juvenile island arc material may

represent a significant component of continental growth (Aitchison and Buckman,

2012) within the Terra Australis Orogen as opposed to purely accretionary orogen

models (Cawood and Buchan, 2007; Cawood et al., 2011a). Tectonostratigraphic

nomenclature introduced by Aitchison and Flood (1990) are used here to describe the

geology.

2. Port Macquarie Geology

The Port Macquarie “Block” (Figure 1) refers to a small tract of Paleozoic rocks

which comprises a serpentinite-matrix mélange containing and associated with

lithologies that superficially resemble a dismembered ophiolitic sequence with chert,

shale, pillowed and brecciated basic extrusive rocks, mafic and ultramafic dykes,

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

7

blueschist facies blocks and felsic dykes (Barron et al., 1976; Och et al., 2007a).

Apart from the rocky coastline, exposure is very limited and of poor quality, hence all

our information is derived from coastal outcrops. Oceanic-derived basalt, ribbon

chert, and argillite represent the majority of blocks within the mélange (Aitchison et

al., 1994). Wilkinson (in Voisey (1969)) recorded mantle protoliths such as

harzburgite, lherzolite and orthopyroxenite from blocks within the serpentinite matrix

at Port Macquarie, typical of the “alpine” ultramafic suite. To the south the Port

Macquarie Block is overlain by Triassic fluvial sedimentary rocks and acid volcanic

rocks of the Lorne Basin (Pratt, 2010; Tonkin, 1998), which are intruded by Triassic

granites. The volcanic rocks and granites yield U-Pb ages of ca. 220 and 210 Ma

respectively (Richardson, 2013).

3.1. Port Macquarie serpentinite mélange

Eight masses of serpentinite occur along the coastal tract at Port Macquarie and are

referred to collectively as the Port Macquarie Serpentinite (Och et al., 2007a) (Figure

2). The serpentinite ranges from large linear masses, as at Town Beach (Figure 1,

Inset 1), to narrow lenses of limited lateral extent, as at northern Miners Beach. Fresh

outcrop exposures are poor away from the coast due to the development of a deep

regolith. The serpentinite matrix in some localities is highly schistose and contains

blocks of highly altered mantle protoliths such as serpentinised harzburgite/dunite,

rodingite and massive serpentinite (Och et al., 2007a). Although they are highly

modified, relict layering structure is preserved in the larger blocks (Figure 3A). Other

lithologies enveloped in the serpentinite include blueschists/eclogites (Barron et al.,

1976; Och et al., 2007a) of likely Carboniferous to-Permo-Triassic age (Nutman et

al., 2013), chert (Figure 3E) and pillow basalt interbedded with volcaniclastic

sandstones (Figure 3B). Basaltic and felsic dykes intrude the serpentinite and locally

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

8

display an intermingled, pillowed form between the mafic and felsic melts (e.g. Town

Beach and southern headland of Oxley Beach and Tacking Point - Figure 3C). These

dykes are themselves further sheared and disrupted (Figure 3G). This suggests they

were intruded during serpentinite emplacement (synkinematic) but were disrupted by

continuing shearing within the serpentinite.

3.2. Watonga Formation

The Watonga Formation (Leitch, 1980) as currently defined, embraces a basalt-chert-

volcaniclastic sedimentary rock sequence at Port Macquarie, which has been

disrupted extensively by shearing and isoclinal folding. Its lack of stratal continuity is

typical of accretionary complexes (Leitch, 1980; Och, 2007; Och et al., 2007a). It

outcrops east of the Lake Innes Fault across to the Town Beach-Tacking Point coastal

tract (Figure 2). Chert occurs in isoclinally folded, thin ribbon beds, ranging from 1-

10 cm thick intercalated with thinner recessive dark mudstone units. Red and grey

cherts dominate but white, green and black varieties are also found. Pockets of red,

interpillow chert are common within larger basalt blocks (such as at the northern end

of Flynn’s Beach). Volcaniclastic sandstones crop out at Green Mound, east of Town

Beach, in the footwall of the Town Beach serpentinite. These are isolated from

occurrences of cherts and basalts that are assigned to the Watonga Formation. Ishiga

et al. (1988) reported Upper Silurian to Upper Devonian conodonts (Belodella spp.)

from Tacking Point and to Upper Devonian radiolarians (undescribed palaeosceniids)

from cherts of the Watonga Formation at Watonga Rock on the beach just south of

Tacking Point. However, doubts exist as to the identification of the Upper Devonian

fauna, which appear to be sponge spicules, as outlined in a discussion by Aitchison

(1989). Och et al. (2007b) extracted Middle to Late Ordovician conodonts from cherts

at Town Beach, Flynns Beach and near Tacking Point. With the exception of

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

9

sedimentary units of Middle to Late Cambrian age (Murrawong Creek and Pipeclay

Creek formations as documented by Percival et al. (2011)) west of the Peel Fault at

Copes Creek, the Ordovician cherts at Port Macquarie represent some of the oldest

biostratigraphically dated sediments within the NEO.

The dominance of ribbon-bedded radiolarian chert overlying pillow basalts of

typical MORB geochemical character (Figure 9) as well as the absence of limestone

and only minor volcaniclastic material and pillow interstices filled with chert rather

than carbonate, indicate that these portions of the formation initially developed in a

deep marine, ocean-floor environment. The volcaniclastic sedimentary rocks

overlying or structurally adjacent the basalt-chert sequences are typically immature,

greywackes containing abundant basaltic lithic fragments and feldspar with little or no

quartz (Parker, 2010) typical of volcanic arc environments (Dickinson and Suczek,

1979).

3.3. Tacking Point Gabbro

The Tacking Point Gabbro (Och et al., 2007a) (Figure 2) is a polyphase intrusion,

with medium to coarse-grained hornblende-bearing gabbro, leucogabbro and tonalitic

suites (Parker, 2010). Although predominantly massive, some zones exhibit evidence

of compositional layering between leuco- and melano-gabbroic phases as well as

signs of magmatic mingling (Figure 3D) suggesting there were repeated injections of

mafic melt into a more felsic, fractionating magma chamber. Small patches of

pegmatitic, amphibole-rich gabbro occur within the massive gabbro indicating a

relatively hydrous magma or by interaction of an anhydrous magma with circulating

seawater (Figure 3F). The Tacking Point Gabbro contains isoclinally folded pendants

of Watonga Formation chert and basalt which in some cases have been completely

bleached and recrystallised with the original iron in the chert being reduced to

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

10

magnetite or native iron. The intrusive rocks are only weakly deformed, with an

overprint of epidote amphibolite to greenschist facies assemblages (Parker, 2010). A

K-Ar age of 359 ± 11 Ma was obtained for actinolite in the Tacking Point Gabbro (E.

Scheibner, Geological Survey of New South Wales, personal communication, in

Aitchison and Ireland, 1995). The actinolite is a secondary mineral, thus 359 Ma

represents a minimum age of emplacement.

3.4. Post-serpentinite mafic-felsic intrusions

Barron et al. (1976) noted that the basement rocks of Port Macquarie are cut

by complex suites of felsic and basic intrusions. At Town Beach and Oxley’s Beach

the serpentinite is intruded by post-serpentinite felsic dykes, also locally with basic

components. These display a variety of relationships with the serpentinite and the

tectonic blocks within them. At Oxleys Beach (Figure 2) intrusive sheets have

irregular form with lobate chilled margins and have incorporated fragments of the

adjacent serpentinite (Figure 3G). Some of these have been disrupted by extensional

shear zones, or distorted into sigmoidal shapes by late movement in the serpentinite.

At Town Beach blocks of gabbro within the serpentinite are cut by pegmatitic felsic

sheets (Figure 2 Inset 1). The form of the intrusions indicates their emplacement was

coeval with ductile flow of the serpentinites. At Tacking Point, the gabbro is cut by

younger, polyphase, felsic-basic sheets that occupy anastomosing steep and shallow-

dipping extensional fractures (Figure 3C). Zircon dating for one of these sheets (TP1)

is reported below. The complex internal form of these sheets displaying no

transitional zone of mixing between the two melts indicates coeval emplacement of

mafic and felsic magmas and rapid cooling. Wholerock geochemistry of these

intermingled felsic and mafic sheets is shown in Table 1 and plotted in Figure 9.

These composite bodies cutting the Tacking Point Gabbro are synonymous with the

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

11

felsic intrusive phases referred to as plagiogranites and reported in the zircon U-Pb

dating study of Aitchison and Ireland (1995). Given that field relations clearly show

that these mafic-felsic intrusions intrude and therefore post-date the schistose

serpentinite at Town Beach and the zircon populations indicate a Permo-Triassic age,

it is clear that these felsic portions are not plagiogranites in the strict definition of an

ophiolitic plagiogranite and have no direct genetic relationship to the ophiolitic

peridotite blocks within the melange. The composition of these felsic intrusions is

similar to that of an ophiolitic plagiogranite due to the melt being derived from partial

melting of components within the serpentinite melange during extension in the latter

stages of emplacement. However, to avoid confusion, we will refer to these magmatic

rocks as post-serpentinite mafic-felsic intrusions rather than plagiogranites.

4. Zircon U-Pb dating

4.1. Analytical methods and data appraisal

Zircons were handpicked and mounted with standard zircons in epoxy resin discs and

then polished to present grain cross sections for analysis. Prior to analysis,

cathodoluminescence images of the grains were acquired, in order to ascertain their

internal structure. U-Th-Pb measurements were carried out on SHRIMP II

instruments at Geoscience Australia and the University of Hiroshima. Analytical

procedures, including U-Th-Pb calibration methods, follow Williams (1998) and

Stern (1998). U abundance was calibrated using a fragment of the single crystal SL13

zircon standard (U=238 ppm). 206

Pb/238

U ratios for all samples, apart from the Town

Beach felsic intrusion zircon mount (first analysed by Aitchison and Ireland, 1995),

were calibrated using Temora 2, with a 206

Pb/238

U age of 417 Ma (Black et al., 2003).

For the re-analysis of the Aitchison and Ireland (1995) Town Beach felsic intrusion

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

12

zircon mount, 206

Pb/238

U ratios were calibrated using SL13, with a 206

Pb/238

U age of

572 Ma (Claoué-Long et al., 1995). All errors also take into account non-linear

fluctuations in ion counting rates beyond that expected from counting statistics (e.g.,

Stern, 1998). Data were corrected for common Pb based on measured 204

Pb and

Cumming and Richards (1975) common Pb composition for the likely age of the rock.

Finalised data were appraised and plotted using ISOPLOT/EX (Ludwig, 2003).

Weighted mean 206

Pb/238

U ages are reported at the 95% confidence level and are

rounded to the nearest million years. The analytical results are shown in the Tera-

Wasserburg diagrams of Figure 5 and 7, and are summarised in

Table 2.

4.2. Volcaniclastic sandstone block within serpentinite, Town Beach

At Town Beach (Figure 2) a volcaniclastic sandstone (sample 21-01; -31.42973°S

152.92256°E) associated with pillow lava was sampled from a <10 m broad block that

occurs within the serpentinite. The sample yielded 6 small, oscillatory zoned,

euhedral, prismatic zircons (Figure 4). These grains have high Th/U values typical of

igneous zircons. Seven analyses on four grains yielded close to concordant, mutually

indistinguishable ages (Figure 5A), with a weighted mean 206

Pb/238

U age of 455±10

Ma (MSWD=0.26; upper-middle Ordovician). This is interpreted as giving the age of

the volcaniclastic sandstone.

4.3. Green Mound volcaniclastic sandstone ascribed to the Watonga Formation

At Green Mound at the eastern end of Town Beach, quartzo-feldspathic volcaniclastic

sandstone (Parker, 2010) forms the entire headland, and tectonically underlies the

Town Beach serpentinite unit (Figure 2). Sample 21-02 (-31.43041°S, 152.92395°E)

of the Green Mound, volcaniclastic sandstone yielded only 15 grains. Based on CL

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

13

imaging, ten of these were most suitable for U-Pb dating. Thirteen analyses were

undertaken, with the duplicate analyses performed on the some of the apparently

younger grains, to check for any loss of radiogenic Pb (Figure 5B). The youngest

grains are Carboniferous in age (360-330 Ma; grains 2, 3, 5, 6), and are oscillatory

zoned with only minor sedimentary abrasion (Figure 4). The first analysis on grain 3

has a 206

Pb/238

U age of ~283 Ma, whereas analysis 2 has an age of ~335 Ma. This

grain might have suffered local loss of radiogenic Pb, and an age of ~335 Ma is

proposed for this grain. In all other cases, duplicate analyses agreed within analytical

error. Pre-Carboniferous grains have 450-400 Ma, 550-500 Ma and Neoproterozoic

ages and tend to be more rounded (Figure 4), pointing to recycling in sedimentary

systems. The results suggest that the sediment formed proximal to a Carboniferous

(Visean?) arc, but received some influx from earlier Palaeozoic and Gondwanan

sources.

4.4. Tacking Point Gabbro

A tonalitic facies of the Tacking Point Gabbro (sample TP208/JP44; -31.472677°S

152.937647°) gave a small yield of oscillatory-zoned zircons devoid of inherited

cores and overgrowths (Figure 6). Eight analyses on five grains have high Th/U, have

mutually indistinguishable concordant ages (Figure 7B), with a weighted mean

206Pb/

238U age of 390±7 Ma. This is interpreted as the age of intrusion (Eifelian-

Emsian; Middle Devonian).

4.5. Post-serpentinite felsic-mafic intrusions

Aitchison and Ireland (1995) reported zircon dating from Town Beach for a sample

with field characteristics of a plagiogranite and also on an intrusion cutting cherts and

pillow lavas, from just north of Tacking Point. Samples from both localities yielded a

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

14

diverse zircon population, with ages between ~3000 Ma and 250 Ma. These results

were enigmatic, because other ophiolitic plagiogranite blocks collected along the Peel

Fault gave Cambrian to Devonian ages, hence neither inherited Precambrian zircons

nor ones as young as 250 Ma were anticipated (Aitchison et al., 1994). The Aitchison

and Ireland (1995) samples were dated prior to the routine application of CL imaging

in SHRIMP U-Pb zircon dating, meaning that without detailed information on the

internal structure of these grains, these results were hard to interpret. We have

undertaken CL imaging and extra dating of the Town Beach sample zircons (Figure 6

and 7A). A minority of the grains are euhedral and prismatic, with well developed

igneous oscillatory zoning parallel to the euhedral grain margins. These yield ages of

~250 Ma (Figure 7A). Most of the grains are more rounded, with truncated internal

zoning and/or structures. Those analysed in the restudy yielded ages between ~350

and 1000 Ma. These results indicate that the intrusion probably has an age of ~250

Ma, but contains abundant inherited grains. The pattern of ages obtained by the CL-

guided analyses is congruent with the larger Aitchison and Ireland (1995) data set

from both the Town Beach and Tacking Point samples (Figure 8).

A small sample (<500 g) was taken from a thin, felsic sheet cutting the

Tacking Point Gabbro and had a low zircon yield of 30 grains. The grains are all

somewhat rounded or have been fragmented in mineral separation (Figure 6). Nine

analyses were undertaken on 7 least recrystallised grains. All have high Th/U ratios,

indicating igneous origins, and 5 have ages of 360-330 Ma, with the remaining 2

grains being Precambrian (Figure 7). None of the few grains recovered from this

sample appear to be euhedral magmatic grains, and thus the 360-330 Ma grains are

initially interpreted as the youngest inherited component.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

15

5. Whole rock geochemistry

5.1. XRF analytical methods

Fifteen representative gabbro samples were collected from the Tacking Point

Gabbro and cross-cutting felsic-mafic dykes (Table 1) and five samples of Watonga

Formation basalt. Samples were crushed using a TEMA chromium ring mill. Fused

buttons were made for X-ray fluorescence (XRF) major element analysis. Depending

on elemental concentrations estimated in trace element analysis, different types of

flux were used. Pure metaborate was used for high silica samples, 57% tetraborate to

43% metaborate was used for ultramafic samples, and 12% tetraborate to 22%

metaborate was used for mafic samples. 400 mg of sample was added to each flux

(300 mg for pure metaborate). Samples JP22, JP35 and JP44 were oxidised before

being fused in the furnace by adding 5 ml of lithium nitrate solution and left at 60°C

overnight. Press pellets for trace element analysis were created by mixing ~5 g of

sample with a polyvinyl acetate (PVA) binder and pressed into an aluminium cup

using a hydraulic hand press. Trace element pressed pellets were then oven dried at

60°C for 12 hours. Whole rock geochemical analysis was conducted using a

SPECTRO XEPOS energy dispersive polarisation X-ray fluorescence spectrometer at

the University of Wollongong.

A Niton 3XLt GOLDD+ handheld XRF was used to collect trace element

compositions of igneous rocks in the field to compliment the XRF data obtained from

crushed samples outlined above. Detection limits vary according to the sample

medium but for the trace elements used in tectonic discrimation plots of Figure 9 the

detection limits were; V (~40ppm), Ti (~60ppm), Zr (~3ppm) and Sr (~2ppm) which

was sufficient to discriminate using those diagrams. The analysis window of the Niton

XRF is ~6 mm making it suitable for fine-grained volcanic rocks such as the Watonga

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

16

Formation basalts. For coarse-grained gabbros, as at Tacking Point, a single analysis

consisted of the average of three separate analyses within a 10 cm diameter. The

handheld XRF trace element data is included in Table 1 and in geochemical plots

(Figure 9) but represented as a hollow symbol rather than the solid symbols for the

standard laboratory XRF data.

5.2. Tacking Point Gabbro

The Tacking Point gabbros have a compositional range from gabbro to quartz-

dioritic compositions with SiO2 ranging from 40-49 wt.% (Table 1). They are

characterised by variable but typically high MgO (6-23 wt%), Ni (12-828 ppm) and

Cr (11-3000 ppm) concentrations. Major element compositions indicate the gabbros

are typical of a high-Mg tholeiitic suite which is also reflected in V, TiO2 and P2O5

concentrations which show a negative correlation with Mg#, suggesting increased

compatibility during fractionation (Parker, 2010). Ni, Co and Cr show a positive

correlation with Mg# which is consistent with fractional crystallisation involving

olivine and pyroxene. The high-field strength element concentrations (Nb, Zr, Ga and

Y) are low to moderate and according to various classification schemes (Pearce, 1982;

Pearce and Cann, 1973; Shervais, 1982) the Tacking Point gabbros plot well within

the typical range of island arc igneous rocks (Figure 9).

5.3. Watonga Formation basalts

Basalts collected from the Watonga Formation at Town Beach, Flynns Beach

and pendants within the Tacking Point Gabbro plot as mostly basalts to basaltic

andesites with silica values usually between 45-50 wt.% but up to 62 wt.% which

probably represent locallised alteration and silicification. The various basaltic

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

17

discrimination diagrams (Figure 9) show that they plot in the MORB to within plate

basalt field with the exception of the Ordovician pillow basalt at Town Beach

interbedded with the volcaniclastic sandstone. It plots closer to the island-arc tholeiite

field.

5.4. Post-serpentinite mafic-felsic dykes

Barron et al. (1976) described as lamprohyric the earliest mafic intrusions

common to all basement lithologies along the Port Macquarie Town Beach to

Tacking Point tract. However, subsequent geochemical studies point to a more

boninitic affinity for similar intrusions at Tacking Point (Aitchison et al. (1994), see

analysis TP1 in Table 1). These magnesian, low titanium mafic rocks are intimately

associated with the late felsic intrusions described here (see Figure 3D). The mafic

intrusions of boninitic affinity, hint at a convergent plate boundary setting for their

formation, however the wide spread of inherited zircons within the associated felsic

sheets indicates contamination from Gondwana-derived Tablelands Complex.

Tectonic discrimination plots of a limited number of samples (Figure 9) are

inconclusive with respect to the origins of the mafic-felsic dykes intruded into

serpentinite and more work on these is needed to determine the source and

mechanisms of Permo-Triassic magma formation at Port Macquarie.

6. Discussion

6.1.Redefining the Watonga Formation

The Green Mound sedimentary rocks ascribed to the Watonga Formation, are arc-

derived greywackes (Parker, 2010). They contain euhedral, 355-335 Ma zircons of

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

18

igneous appearance likely derived from a Carboniferous arc. They also contain

generally more rounded Early Paleozoic and Precambrian zircons. This is the age

signature seen in the inherited zircon populations of the felsic sheets dated by

Aitchison and Ireland (1995). The zircon age spectrum in all these samples matches

that of Carboniferous arc-derived subduction complex assemblages throughout the

New England Orogen (Korsch et al., 2009). This links these clastic sedimentary

rocks, previously assigned to the Watonga Formation, with a regional sequence of

Carboniferous arc-related rocks – the Anaiwan terrane or more broadly the

“Tablelands Complex”, which includes anything east of the Peel-Manning Fault. As

pointed out by several researchers (e.g., (Cawood et al., 2011a; Cawood et al., 2011b)

and references therein) the Tablelands Complex developed in response to continental

‘Andean-style’ convergence which gave rise to an extensive Carboniferous

accretionary complex within the New England Orogen.

Cherts of the Watonga Formation contain Upper Ordovician conodonts (Och et

al., 2007b) and Devonian? radiolarians (Ishiga et al., 1988) and thus are clearly older

than the Green Mound (Carboniferous) volcaniclastic rocks. The extended age range

of cherts within the Watonga Formation is typical of accretionary complexes in which

progressively younger oceanic material has been off-scraped over the life-time of the

subduction complex. Furthermore, a block of pillow lava and attached volcaniclastic

sandstone within the serpentinite at Town Beach has a Late Ordovician age of 455±10

Ma, contrasting with the nearby Green Mound volcaniclastic sandstone with a

depositional age of ≤335 Ma. Kimbrough et al. (1993) reported a U-Pb zircon age of

436±9 Ma from the Pola Fogal hornblende-tonalite suite associated with serpentinites

in the Piga Barney area (Figure 1), at the southern end of the Peel Manning fault

system. This age is close to that of the 455±10 Ma arc-related volcaniclastic

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

19

sandstone block in the serpentinite at Town Beach and hints at the presence of

Ordovician island-arc material within serpentinite mélange of the NEO. Thus

combining the U-Pb zircon dating and paleontological studies, the Watonga

Formation appears to embrace rocks of different age (455 to ≤330 Ma) and

provenance. Most of the Watonga Formation basalts that appear to underlie the cherts

plot as MORB or intra-plate basalts with occasional island-arc tholeiites. This, along

with an absence of terrigenous material interbedded with the cherts, indicates that the

Watonga Formation represents oceanic crust that was off-scraped into a sediment-

starved trench far from any continental sediment source. We suggest that the

definition of the Watonga Formation should be refined to include only the

Ordovician-Devonian? basalt-chert-siltstone associations, and thereby it can be

correlated with Djungati terrane rocks further west (Figure 1). Consequently,

Carboniferous volcaniclastic sandstones such as at Green Mound should be excluded

from the Watonga Formation, and represent either a distinct Carboniferous overlap

assemblage or accretionary complex, that can be broadly correlated with the Anaiwan

terrane (Tablelands Complex).

6.2.Tacking Point Gabbro

The Tacking Point Gabbro with a U-Pb zircon age of 390±7 Ma is Middle

Devonian. It was correlated with the Permian Clarence River Supersuite based on

geochemical similarities before any isotopic geochronology was available (Och et al.,

2007a). Instead, its age agrees within error with a 377±8 Ma U-Pb igneous zircon age

for Yarras Complex plagiogranite/tonalite (Aitchison and Ireland, 1995), ca. 60 km

west of Port Macquarie (Figure 1). As with the Tacking Point Gabbro, the Yarras

Complex is proximal to a strand of serpentinite mélange in the New England Orogen.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

20

The igneous age of the Tacking Point Gabbro is also close to the 394±5 Ma K-Ar age

(Sano et al., 2004) for igneous hornblende in an arc-affinity diorite block in

serpentinite of the Peel Manning fault system at Glenrock Station, ~140 km west of

Port Macquarie (Figure 1).

6.3. Ages of post-serpentinite mafic-felsic intrusions and the tectonic history of the

Port Macquarie serpentinite

The Port Macquarie area late felsic intrusions dated by Aitchison and Ireland

(1995) and studied further in this paper have an age of ~250 Ma. With their bulk

compositions (Table 1 and Figure 9) and their abundance of inherited zircons, they

are clearly not ophiolitic plagiogranites, but are low temperature partial melts

incorporating sedimentary sources. Their inheritance pattern matches that of siliceous

varieties of Carboniferous arc-related sedimentary rocks throughout the New England

Orogen (Korsch et al., 2009), including the Green Mound sample 21-02 presented

here (Figure 8). At least some of these felsic sheets were emplaced into gently-

inclined extensional fractures and are coeval with mafic mantle-derived magma

(Figure 3C). Furthermore, in the Port Macquarie serpentinite, some of these sheets

show evidence of having been sheared by subsequent movement within the

serpentinite. This indicates that ductile deformation of the serpentinite continued until

≤250 Ma. This reaffirms conclusions of Aitchison et al. (1994) that tectonic

movements in the serpentinite continued until ≤250 Ma.

The main serpentinite belts further west in the New England Orogen are all

associated with, or contain tectonic blocks of Cambrian ophiolite (Weraerai terrane),

Ordovician to Devonian island arc-related assemblages (Gamilaroi terrane) and

Ordovician to Devonian basalt-chert accretionary complex rocks (Djungati terrane).

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

21

The Upper Carboniferous to Upper Permian zircon ages obtained for the Port

Macquarie eclogites by Nutman et al. (2013) reveal that eclogite-blueschist

metamorphism is much younger than the Ordovician K-Ar phengite ages originally

obtained by Fukui et al. (1995). This is in accord with final serpentinite emplacement

occurring at ≤250 Ma, as revealed by the U-Pb zircon dating of post-serpentinite

felsic dykes. U-Pb ages and REE chemistry of zircons from an eclogite occurrence at

Attunga (Buckman and Nutman, in prep.) indicates an upper Cambrian (~490 Ma)

age for high-pressure metamorphism in contrast to the Neoproterozoic age of

Watanabe et al. (1999). Thus the proposed Cambro-Ordovician or even late

Neoproterozoic age (Phillips and Offler, 2011; Watanabe et al., 1999) for HP/LT

metamorphism and serpentinite formation followed by prolonged (~200 Ma)

residence of HP-LT metamorphic rocks in the upper crust is untenable. These ages

indicate there is probably more than one episode of HP metamorphism preserved in

the NEO and raise serious doubts as to the validity of interpretation of previous K-Ar

ages obtained from micas. A complete re-evaluation of the tectonic history of the

New England Orogen is warranted.

6.4. Regional settings and correlations in the New England Orogen

To the west, the Port Macquarie Block is in faulted contact with the Devonian to

Carboniferous Birpai terrane (Flood and Aitchison, 1988) or Hastings terrane

(Roberts et al., 1993), which include rocks of the Yarras Complex. Following the

methodology associated with tectonostratigraphy and the discrimination of terranes,

Flood and Aitchison (1988) separated the Port Macquarie Block as a separate

tectonostratigraphic unit (the Ngamba terrane) because it could not be directly

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

22

correlated with terranes found further west in the NEO. However our results suggest

linkages can be made.

The Tacking Point gabbro is Middle Devonian in age (390±7 Ma) and has island

arc geochemical characteristics. This suggests that it is equivalent to plutonic rocks of

the Gamilaroi terrane found further west (Figure 1). This is in accord with its

intrusion into Ordovician-Silurian oceanic cherts of similar age to those seen in the

Djungati terrane. Basalts and dolerites of the Yarras Complex display typical island

arc tholeiite characteristics (Aitchison et al., 1994) and SHRIMP U-Pb dating of

zircons from a trondhjemite intruding gabbro indicates a Late Devonian (374±8 Ma)

age. This is consistent with the nature and timing of arc-rift basalts of the Gamilaroi

terrane (Aitchison and Flood, 1994) with which the Birpai terrane can most likely be

correlated (Aitchison et al., 1994). Again, there appears to be enough similarities in

age and composition to group rocks of the Birpai terrane (Yarras Complex) with the

Gamilaroi terrane (Aitchison et al., 1999). Thus the Ngamba (Port Macquarie Block)

and Birpai (Yarras Complex) terranes are possible correlatives with the Gamilaroi

terrane and if so should be grouped together accordingly. If correct, this correlation

simplifies the nomenclature and understanding of older components in the NEO

(Figure 1).

The intrusive relationship of the Tacking Point Gabbro into the Watonga

Formation demonstrates a spatial relationship between a Devonian island-arc complex

and an adjacent accretionary complex, which had not previously been recognized. We

tentatively suggest that the Tacking Point Gabbro correlates with the Gamilaroi

terrane and the Watonga Formation with the Djungati terrane elsewhere in the NEO

based on the similarities in age and composition. The east-dipping polarity of

subduction beneath the Gamilaroi terrane initially proposed by Aitchison and Flood

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

23

(1994) and further corroborated by Offler and Gamble (2002), provides a valid

mechanism of accreting and preserving an intra-oceanic island arc into an upper plate

position. We suggest that slab-rollback beneath the evolving Gamilaroi terrane could

explain the migration of the active portion of the island-arc (Tacking Point Gabbro)

into an older portion of the accretionary wedge (Watonga Formation or Djungati

terrane) as illustrated in Figure 10B.

From Green Mound, we identify fragments of Carboniferous volcaniclastic

sedimentary rocks associated with the serpentinite mélange at Port Macquarie. The

Green Mound rocks are similar to units broadly correlated with the Carboniferous

Tablelands Complex (Fergusson, 1984) to the north, or correlatives such as the

Anaiwan terrane (or Yarrowitch Block - (Leitch et al., 1990) to the west, and the

Myall Block to the south (Roberts and Engel, 1987; Skilbeck and Cawood, 1994). As

with the Hastings Block, a distinct change in provenance occurs between the

predominantly basaltic Silurian-Devonian units to andesitic to felsic provenance at the

Devonian-Carboniferous boundary (Roberts et al., 1995). The first evidence of

Gamilaroi terrane arrival at the margin of Gondwana is the observation made by

Flood and Aitchison (1992) of Lachlan-derived quartzite clasts within the latest

Devonian Keepit Conglomerate which overlies the youngest unit in the Gamilaroi

terrane - the Baldwin Formation. This is consistent with a switch from an oceanic

island arc to a continental arc tectonic setting (Figure 10C-D).

In terms of the overall northward displacement of the Port Macquarie serpentinite

relative to the Weraerai terrane bodies at the southern end of the Peel Fault system,

Cawood and Leitch (1985) suggested that the Hastings (Birpai) terrane was once

connected with the southern end of the Tamworth belt (Gamilaroi terrane) and

Roberts et al. (1993) suggested the block underwent 130° dextral rotation and

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

24

northward displacement via sinistral faulting. Collins et al. (1993) further developed

this model to include a phase of oroclinal bending to accompany the sinistral faulting.

Skilbeck and Cawood (1994) reverted to a model involving syn-subduction, dextral

strike-slip activity along an irregular continental margin during the Late Devonian to

Carboniferous in order to shift the Tamworth Belt from an intra-oceanic position

outboard of the Gondwana continental margin to be juxtaposed with the margin. The

underlying assumption with all of these models is that the dislocation is due to lateral,

horizontal displacements alone. Here we introduce a new hypothesis to explain

apparent oroclines within the New England Orogen involving vertical rather than

lateral displacements. We follow on from the model of Aitchison and Flood (1994)

which proposed that the exotic, Panthalassan, Cambrian-Devonian terranes

(Gamilaroi + Djungati + Weraerai) were accreted westward over the Gondwanan

continental margin by the latest Devonian (Figure 10A-C). Following the collision

and flip in subduction polarity in the latest Devonian, eastern Gondwana developed as

a continental ‘Andean’-style convergent margin (Figure 10D). Subsequently an

accretionary complex (Anaiwan terrane) grew on top of the previously obducted

Weraerai + Gamilaroi + Djungati terranes throughout the Carboniferous. The

collision of the Permo-Triassic Gympie terrane (Figure 10E-F) initiated the Hunter-

Bowen Orogeny at about the Permo-Triassic boundary (~251 Ma) (Aitchison and

Buckman, 2012; Harrington and Korsch, 1985; Nutman et al., 2013). Although the

Gympie terrane only crops out along a small portion of the Australian eastern

seaboard it has been correlated with similar age and composition rocks of island arc

affinity in both New Zealand and New Caledonia (Aitchison, 1993; Spandler et al.,

2005). This suggests that the Gympie terrane was laterally extensive and that the

collision and accretion of this island-arc was a major tectonic event that was driving

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

25

mechanism for the Hunter-Bowen Orogeny. We propose that the Hunter-Bowen

compressional event is responsible for exhuming portions of the Weraerai +

Gamilaroi + Djungati terranes from under their Carboniferous carapace, along thrust

zones such as the one observed at Town Beach. Thus, the northward (sinistral)

displacement of the Port Macquarie and Hastings Blocks and the apparently

contradictory dextral displacement of the Coffs Harbour Block, is apparent only, and

due more in part to vertical displacements of an extensive, thin-skinned sheet of

oceanic plus island arc crust that underlies the Tablelands Complex, rather than

extensive lateral movements with the opposite sense of motion. In this way there is no

need to invoke large-scale ‘oroclinal’ folding (Cawood et al., 2011; Li and

Rosenbaum, in press; Offler and Foster, 2008; Rosenbaum et al., 2012) or significant

sinistral faulting (Schmidt et al., 1994) to explain the repetition of Hastings and Port

Macquarie blocks in the southern New England. Indeed, a simple geological section

across the postulated Texas or Manning oroclines would show that the steeply dipping

limbs several hundred kilometres either side of the megafold axis must extend to a

depth of many hundreds of kilometres. Given that the maximum thickness of

continental crust is ~70 km beneath continental collision zones, these oroclines must

be detached along a low-angle décollement rather than be a simple series of mega-

synclines and anticlines extending several hundreds of kilometres below the surface.

The orocline concept was initially proposed (Korsch, 1981; Korsch and Harrington,

1987) to explain apparent large scale bending of lineaments observed in regional

magnetic surveys. However, strong geological evidence for such a mega-fold is

lacking and the entire concept of an orocline in the NEO raises many questions as

raised by Lennox et al. (2013). One critical question revolves around a valid

mechanism for oroclinal folding. In the Himalaya there is an obvious mechanism of

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

26

collision of two continents with an irregular continental margin boundary to produce

the large indent and oroclinal mountain belts either side of the Indian continent. No

such continent-continent collision has occurred within the New England or Lachlan

orogens. For these reasons, we look to a simpler, alternative and testable model that

can be supported by modern-day analogues.

Our results support the interpretation of Aitchison and Buckman (2012), that the

eastern margin of Gondwana grew by a combination of; (a) the addition of exotic

island arc complexes (i.e. the exotic Macquarie Arc in the latest Ordovician to Early

Silurian the Gamilaroi terrane in the latest Devonian and finally the Gympie terrane at

about the Permo-Triassic boundary) plus; (b) coeval or interspersed Andean-style arcs

at the continental margin. Each island-arc collision is associated with a major

contractional deformation event – the Benambran, Kanimblan and Hunter-Bowen

orogenies respectively. A switch in subduction polarity follows arc accretion and this

marks the onset of classic continental-margin accretionary orogenesis and the

intrusion of voluminous S- and I-type granites.

This style of episodic continental growth via arc-continent collisions is observed

in Phanerozoic systems, such as, Taiwan (Huang et al., 2008), Oman (Searle et al.,

2004), the ancient southern margin of Tethys in Ladakh (Corfield et al., 1999), and

Cyprus (Robertson, 2004) or on the Kamchatka Peninsula in the NW Pacific

(Hourigan et al., 2009). In these examples, intra-oceanic island arcs are drawn

towards continental margins via the consumption of intervening oceanic crust and

emplaced onto continents due to their position on the overriding plate. Evidence of

supra-subduction zone rocks in upper plate positions that have over-ridden continental

margins are recorded not only in the Phanerozoic but also within Precambian terranes

such as the Paleoproterozoic Nagssugtoqidian Orogen, Greenland (Kalsbeek and

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

27

Nutman, 1996; Nutman et al., 2008). Obducted intra-oceanic arc systems are thin-

skinned or rootless systems commonly accompanied by a basal melange structurally

overlying a continental margin sequence. Oblique convergence can result in lateral

translations and duplexing of portions of these tectonic packages (McCaffrey, 1992).

Widespread strike-slip faulting during the Early Permian was introduced by Aitchison

and Flood (1992) to help explain the development of strike-slip basin deposits

(Manning Group) along the Peel-Manning Fault System. Strike-slip faulting may have

some influence on the apparent northward (sinistral) translation of the Hastings and

Port Macquarie blocks (Manning orocline) in the southern NEO but it is at odds with

the large-scale dextral Demon Fault associated with the Texas orocline to the north.

This structural contradiction is difficult to reconcile via oroclinal bending or strike-

slip faulting alone. However, compression and vertical movements along thrust faults

can result in complex, doubly plunging outcrop patterns that have an apparent

opposite sense of displacement in plan view. We suggest that the Weraerai, Gamilaroi

and Djungati terranes are thin-skinned terranes overlain by a Carboniferous to

Permian accretionary complex but in places like Port Macquarie and Coffs Harbour

these terranes have been exhumed during the Hunter-Bowen Orogeny and the

Carboniferous carapace eroded away.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

28

7. Conclusions

(1) The Tacking Point Gabbro has a middle Devonian age of 390±7 Ma and

geochemical affinities with intra-oceanic arc igneous suites. Therefore, along with its

chert and basalt country rocks, it represents a mid-Paleozoic assemblage

allochthonous to Gondwana (Gamilaroi + Djungati terrane affinity).

(2) The Watonga Formation, as it is currently defined, contains rocks of different age

and origin including an Ordovician, MORB-like basalt-chert-volcaniclastic

association to a Carboniferous volcaniclastic sequence. We conclude that the

Watonga chert-basalt associations are older than, and unrelated to, the Carboniferous

arc-derived volcaniclastic rocks like those at Green Mound. We propose that the name

Watonga Formation should be reserved for only the older chert + basalt components

while the Carboniferous Green Mound rocks be grouped with the Tablelands

Complex (Anaiwan terrane).

(3) Felsic dykes intruded the Port Macquarie serpentinite at 247±20 Ma. These post-

date serpentinite melange emplacement but are late- to syn-kinematic. This, along

with the revised younger Upper Carboniferous to Upper Permian age (probably

≤251±6 Ma) of the Port Macquarie eclogites (Nutman et al., 2013) indicates that the

tectonic evolution of the serpentinite at Port Macquarie continued into the early

Triassic during the Hunter-Bowen Orogeny.

(4) The accrued data enable correlations between the Port Macquarie Block and the

more extensive terranes of the NEO further west. We propose that the NEO contains a

large, far-travelled oceanic and island arc terrane that was emplaced over the

Gondwanan margin during the latest Devonian to Early Carboniferous.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

29

(5) It is likely that HP-LT metamorphism and serpentinite emplacement at Port

Macquarie and in the Great Serpentinite Belt to the west occurred at different times

and are unrelated.

Acknowledgments

Support to S. Buckman and A.P. Nutman was via the University of Wollongong

GeoQuEST Research Centre, a Japan travel grant to Allen Nutman from the

Australian Academy of Sciences, the University of Hiroshima, University of

Wollongong support for Honours students J. Parker, T. Line and S. Bembrick. We

thank S. Meffre and P-F. Li for their constructive comments in the review process.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

30

Table Captions

Table 1 Whole rock XRF geochemical analyses of Port Macquarie rocks. Date

sources: Parker (2010).

Table 2 SHRIMP U-Th-Pb summary data.

Figure captions

Figure 1 Geology of the New England Orogen grouping units into the terrane scheme

of Aitchison and Flood (1990) and showing the location of the Port Macquarie study

area.

Figure 2 Geological outcrop map of the Port Macquarie Town Beach to Tacking Point

coastal tract showing the occurrence of major lithologies. Inset 1 shows the detailed

geological mapping of the Town Beach/Green Mound area.

Figure 3 Field relations showing:

A) Layered peridotite and pillow basalt blocks within the serpentinite mélange at

Town Beach. The pillow basalt block is interbedded with interpillow volcaniclastic

material ascribed to the Watonga Formation from which zircons were extracted

(sample 21-01, 152.92256°E, 31.42973°S).

B) Volaniclastic sandstone (21-02) taken from Green Mount Point east of Town

Beach (152.92395°E, 31.43041°S).

C) Mafic-felsic sheet cutting the Tacking Point Gabbro which itself is cut by dolerite

dykes (31°28'24" S 152°56'15" E).

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

31

D) Tacking Point gabbro showing evidence of magmatic mingling between coarse-

grained leucocratic- and melanocratic-gabbro components (31.473544°S

152°937352). Note the younger (~250 Ma) composite mafic-felsic sheet at the top of

the outcrop.

E) Highly deformed chert of the Watonga Formation forming inclusions within the

Tacking Point Gabbro (-31.474043°S 152.937351°). These attest to pre-Devonian

deformation, probably during accretion.

F) Pegmatitic gabbro patches within the Tacking Point Gabbro similar to the sample

from which Devonian zircons were extracted (TP208/JP44; -31.472677°S

152.937647°).

G) Felsic intrusion cutting through the schistose serpentinite mélange which is itself

sheared, indicating syn-kinematic emplacement with the serpentinite (-31.433160°S

152.924380°).

H) A low-angle mylonitic shear zone (looking south) on the contact between the

Town Beach serpentinite mélange to the west and cherts of the Watonga Formation to

the east. S-C fabrics show a clear west over east sense of motion suggesting the

serpentinite mélange has been thrust over the Carboniferous volcaniclastic rocks

found to the east at Green Mound.

Figure 4 Cathodoluminescence images of zircons extracted from (A) volcano-

sedimentary block 21-01 within the Port Macquarie serpentinite mélange and (B)

from Green Mound sedimentary rock 21-02.

Figure 5 238

U/206

Pb – 207

Pb/206

Pb (radiogenic) plots, with analytical errors depicted at

the 2 σ level. (A) Sample 21-01 and (B) sample 21-02.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

32

Figure 6 Cathodoluminescence images of zircons extracted from (A) Tacking point

Gabbro sample TP, (B) Town Beach late felsic sheet sample ‘Town Beach’ and (C)

Tacking Point late felsic sheet sample 12-01.

Figure 7 238

U/206

Pb – 207

Pb/206

Pb (radiogenic) plots, with analytical errors depicted at

the 2 σ level. (A) Tacking Point Gabbro sample TP, (B) late felsic sheet sample

‘Town Beach’ and (C) late felsic sheet sample 12-01.

Figure 8 Zircon age histograms for regional New England Orogen quartz rich ‘broken

formation’ samples (n=815 from (Korsch et al., 2009)), Green Mound sample 21-02

and for the Port Macquarie and Tacking Point felsic igneous rocks, using data

presented here and by Aitchison and Ireland (1995).

Figure 9 A) Ti/V diagram of Shervais (1982); B) Zr-Ti diagram of Pearce (1982); C)

Ti-Zr-Sr and D) Ti/Zr diagrams of Pearce and Cann (1973). Data sourced from Table

1 (Parker, 2010) and Aitchison et al. (1994). *Portable XRF trace element data shown

in Appendix A.

Figure 10 A schematic tectonic reconstruction of the eastern margin of Gondwana

from the Cambrian to the Triassic highlighting the episodic nature of island arc

collision events.

A) Ordovician initiation of island arc development (possible proto-Gamilaroi terrane)

on top of Late Cambrian ophiolitic basement (possible Weraerai terrane). During the

Early Silurian eastern Gondwana is experiencing widespread deformation

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

33

(Benambran Orogeny) associated with collision of the Macquarie Arc (Aitchison and

Buckman, 2012).

B) Active island arc development in the Gamilaroi terrane including the intrusion of

the Tacking Point Gabbro into the Ordovician cherts of the Watonga Formation.

During the same time (Upper Silurian to Middle Devonian) the continental margin of

Gondwana is experiencing widespread intrusion of voluminous S- and I-type granites

indicating that subduction was occurring contemporaneously beneath eastern

Gondwana and the Gamilaroi terrane. While the polarity of subduction beneath

Gondwana could only have been to the west, subduction beneath the Gamilaroi

terrane is not fully understood, however it’s preservation in an upper plate position in

the NEO suggests it was situated on the overriding plate and therefore subduction was

to the east beneath it.

C) The west dipping subduction zone beneath Gondwana stalls by the Middle

Devonian as the Gamilaroi terrane arrives at the Gondwana margin, thus switching off

production of granites in the Lachlan Orogen. Accretion of the Gamilaroi terrane onto

Gondwana in the latest Devonian results in a subduction flip and a brief continental

magmatic hiatus (Late Devonian to Early Carboniferous).

D) An Andean-type continental margin developed along eastern Gondwana

throughout the Carboniferous. The magmatic core of the continental arc is marked by

the Bathurst Granite suite within the eastern Lachlan Orogen and the felsic volcanics

of the Currabubula-Connors-Auburn arc and Tamworth Belt (fore arc basin) in the

western NEO. The Tablelands Complex develops as a continental accretionary

complex dominated by volcanic detritus shed off the Carboniferous continental arc

but with a significant Gondwanan inheritance.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

34

E) The island arc Gympie terrane docks onto Gondwana at about the Permo-Triassic

boundary initiating the Hunter-Bowen Orogeny and thrusting elements of the NEO

over the Permo-Triassic Sydeny Basin and possibly emplacing the serpentinite

mélange and associated eclogites at Port Macquarie.

F) Another subduction flip follows the Hunter-Bowen Orogeny resulting in another

eastward magmatic jump before the continental subduction zone resulted in

emplacement of the Triassic coastal suite granites (220-210 Ma).

References

Aitchison, J. C. (1993). Evolution of the eastern margin of Australian Plate: possible

correlatives in Australia, New Caledonia and New Zealand. New England Orogen,

Eastern Australia. Department of Geology and Geophysics, University of New

England, Armidale, Australia, 665-669.

Aitchison, J. C., Flood, P. G. (1992). Early Permian transform margin development of

the southern New England Orogen, eastern Australia (eastern Gondwana).

Tectonics, 11(6), 1385-1391.

Aitchison, J., Flood, P., 1994. Gamilaroi Terrane: A Devonian rifted intra-oceanic

island-arc assemblage, NSW, Australia, In: Smellie, J.L. (Ed.), Volcanism

Associated With Extension at Consuming Plate Margins. Geological Society,

London, Special Publications, London, pp. 155-168.

Aitchison, J., Ireland, T.R., 1995. Age profile of ophiolitic rocks across the late

Palaeozoic New England Orogen, New South Wales; implications for tectonic

models. Australian Journal of Earth Sciences 42, 11-23.

Aitchison, J.C., 1989. Radiolarian and Conodont Biostratigraphy of Siliceous Rocks

from the New-England Fold Belt - Discussion. Australian Journal of Earth Sciences

36, 141-142.

Aitchison, J.C., Blake, M.C., Jr., Flood, P.G., Jayko, A.S., 1994. Paleozoic ophiolitic

assemblages within the southern New England Orogen of eastern Australia;

implications for growth of the Gondwana margin. Tectonics 13, 1135-1149.

Aitchison, J.C., Buckman, S., 2012. Accordion vs. quantum tectonics: Insights into

continental growth processes from the Paleozoic of eastern Gondwana. Gondwana

Research 22, 674-680.

Aitchison, J.C., Davis, A.M., Stratford, J.M.C., Spiller, F.C.P., 1999. Lower and

Middle Devonian radiolarian biozonation of the Gamilaroi Terrane New England

Orogen, eastern Australia. Micropaleontology 45, 138-162.

Aitchison, J.C., Flood, P.G., 1990. Preliminary tectonostratigraphic terrane map of the

southern part of the New England Orogen, eastern Australia. Earth Science Series

13, 81-85.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

35

Aitchison, J.C., Ireland, T.R., Blake, M.C., Jr., Flood, P.G., 1992. 530 Ma zircon age

for ophiolite from the New England Orogen; oldest rocks known from eastern

Australia. Geology Boulder 20, 125-128.

Barron, B.J., Scheibner, E., Slansky, E., 1976. A dismembered ophiolite suite at Port

Macquarie, New South Wales. Records of the Geological Survey of New South

Wales 18, 69-102.

Black, L.P., Kamo, S.L., Allen, C.M., Aleinikoff, J.N., Davis, D.W., Korsch, R.J.,

Foudoulis, C., 2003. TEMORA 1: a new zircon standard for Phanerozoic U-Pb

geochronology. Chem. Geol. 200, 155-170.

Cawood, P.A., 2005. Terra Australis Orogen: Rodinia breakup and development of

the Pacific and Iapetus margins of Gondwana during the Neoproterozoic and

Paleozoic. Earth Science Reviews, 69, 249-279.

Cawood, P.A., Buchan, C., 2007. Linking accretionary orogenesis with

supercontinent assembly. Earth-Science Reviews 82, 217-256.

Cawood, P.A., Leitch, E.C., 1985. Accretion and dispersal tectonics of the southern

New England fold belt, eastern Australia, In: Howell, D.G. (Ed.),

Tectonostratigraphic Terranes of the Circum-Pacific Region. Circum-Pacific

Council for Energy and Mineral Resources Houston, Texas, United States, pp. 481-

492.

Cawood, P.A., Pisarevsky, S.A., Leitch, E.C., 2011. Unraveling the New England

orocline, east Gondwana accretionary margin. Tectonics 30.

Cawood, P.A., Leitch, E.C., Merle, R.E., Nemchin, A.A., 2011a. Orogenesis without

collision: Stabilizing the Terra Australis accretionary orogen, eastern Australia.

Geol. Soc. Am. Bull. 123, 2240-2255.

Cawood, P.A., Pisarevsky, S.A., Leitch, E.C., 2011b. Unraveling the New England

orocline, east Gondwana accretionary margin. Tectonics 30.

Claoué-Long, J.C., Compston, W., Roberts, J., Fanning, M., 1995. Two

Carboniferous ages: a comparison of SHRIMP zircon dating with conventional

zircon ages and 40Ar/39Ar analysis, In: Berggren, W.A., Kent, D.V., Aubrey, M.-

P., Hardenbol, J. (Eds.), Geochronology, Time Scales and Stratigraphic Correlation.

SEPM (Society for Sedimentary Geology) Special Publication, pp. 3-21.

Collins, W., 1991. A reassessment of the "Hunter-Bowen" Orogeny: Tectonic

implications for the southern New England fold belt. Australian Journal of Earth

Sciences 38, 409-423.

Collins, W.J., Offler, R., Farrell, T.R., Landenberger, B., 1993. A revised Late

Palaeozoic-Early Mesozoic tectonic history for the southern New England Fold Belt,

In: Flood, P.G., Aitchison, J.C. (Eds.), New England Orogen, eastern Australia.

University of New England, Department of Geology and Geophysics Armidale,

N.S.W., Australia, pp. 69-84.

Corfield, R.I., Searle, M.P., Green, O.R., 1999. Photang thrust sheet; an accretionary

complex structurally below the Spontang Ophiolite constraining timing and tectonic

environment of ophiolite obduction, Ladakh Himalaya, NW India. Journal of the

Geological Society, London 156, 1031-1044.

Cumming, G.L., Richards, J.R., 1975. Ore lead isotope ratios in a continuously

changing earth. Earth Planet. Sci. Lett. 28, 155-171.

Dickinson, W.R., Suczek, C.A., 1979. Plate tectonics and sandstone compositions.

American Association of Petroleum Geologists Bulletin 63, 2164-2182.

Fergusson, C.L., 1984. Tectono-stratigraphy of a Palaeozoic subduction complex in

the central Coffs Harbour Block of north-eastern New South Wales. Australian

Journal of Earth Sciences 31, 217-236.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

36

Flood, P.G., Aitchison, J.C., 1988. Tectonostratigraphic terranes of the southern part

of the New England Orogen, In: Kleeman, J.D. (Ed.), New England Orogen:

Tectonics and Metallogenesis. Univ. N. Engl., Dep. Geol. and Geophys., Armidale,

pp. 7-10.

Flood, P.G., Aitchison, J.C., 1992. Late Devonian Accretion of the Gamilaroi Terrane

to Eastern Gondwana - Provenance Linkage Suggested by the 1st Appearance of

Lachlan Fold Belt-Derived Quartzarenite. Australian Journal of Earth Sciences 39,

539-544.

Fukui, S., Watanabe, T., Itaya, T., Leitch, E.C., 1995. Middle Ordovician high PT

metamorphic rocks in eastern Australia; evidence from K-Ar ages. Tectonics 14,

1014-1020.

Harrington, H.J., Korsch, R.J., 1985. Deformation associated with the accretion of the

Gympie terrane in eastern Australia, In: Leitch, E.C. (Ed.), Third circum-Pacific

terrane conference, extended abstracts. Geological Society of Australia, Abstracts

14, pp. 104-108.

Holcombe, R.J., Stephens, C.J., Fielding, C.R., Gust, D., Little, T.A., Sliwa, R.,

Kassan, J., McPhie, J., Ewart, A., 1997. Tectonic evolution of the northern New

England Fold Belt: the Permian-Triassic Hunter-Bowen Event, In: Ashley, P.M.,

Flood, P.G. (Eds.), Tectonics and metallogenesis of the New England orogen.

Special Publication Geological Society of Australia, Armidale, pp. 52-65.

Hourigan, J.K., Brandon, M.T., Soloviev, A.V., Kirmasov, A.B., Garver, J.I.,

Stevenson, J.A., Reiners, P.W., 2009. Eocene arc-continent collision and crustal

consolidation in Kamchatka, Russian Far East. Am J Sci 309, 333–396.

Huang, C.Y., Chien, C.W., Yao, B., Chang, C.P., 2008. The Lichi Mélange: A

collision mélange formation along early arcward backthrusts during forearc basin

closure, Taiwan arc-continent collision, In: Draut, A.E., Clift, P.D., Scholl, D.W.

(Eds.), Formation and Applications of the Sedimentary Record in Arc Collision

Zones. Geological Society of America Special Paper 436, pp. 127–154.

Ishiga, H., Leitch, E.C., Watanabe, T., Naka, T., Iwasaki, M., 1988. Radiolarian and

conodont biostratigraphy of siliceous rocks from the New England fold belt.

Australian Journal of Earth Sciences 35, 73-80.

Kalsbeek, F., Nutman, A.P., 1996. Anatomy of the early Proterozoic Nagssugtoqidian

orogen, west Greenland, explored by reconnaissance SHRIMP U-Pb zircon dating.

Geology 24, 515-518.

Kimbrough, D.L., Cross, K.C., Korsch, R.J., 1993. U-Pb isotopic ages for zircons

from the Pola Fogal and Nundle granite suites, southern New England Orogen, In:

Flood, P.G., Aitchison, J.C. (Eds.), New England Orogen, eastern Australia.

University of New England, Department of Geology and Geophysics Armidale,

N.S.W., Australia, pp. 403-412.

Korsch, R.J., 1981, Deformational history of the Coffs Harbour Block: Royal Society

of New South Wales, Journal and Proceedings, v. 114, 17–22.

Korsch, R.J. and Harrington, H.J., 1987, Oroclinal bending, fragmentation and

deformation of terranes in the New England Orogen, eastern Australia: American

Geophysical Union, Geodynamics Series, v. 19, pp. 129–139.

Korsch, R.J., Adams, C.J., Black, L.P., Foster, D.A., Fraser, G.L., Murray, C.G.,

Foudoulis, C., Griffin, W.L., 2009. Geochronology and provenance of the late

Paleozoic accretionary wedge and Gympie Terrane, New England Orogen, eastern

Australia. Australian Journal of Earth Sciences 56, 655-685.

Korsch, R.J., Wake-Dyster, K.D., Johnstone, D.W., 1993. The Gunnedah Basin-New

England Orogen deep seismic reflection profile: implications for New England

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

37

tectonics, In: Flood, P.G.A., J.C. (Ed.), New England Orogen, eastern Australia.

University of New England, Department of Geology and Geophysics, Armidale,

N.S.W., Australia, pp. 85-100.

Leitch, E.C., 1974. The geological development of the southern part of the New

England Fold Belt. Journal of the Geological Society of Australia 21, 133-156.

Leitch, E.C., 1980. Rock units, structure, and metamorphism of the Port Macquaire

Block, eastern New England fold belt. Proceedings of the Linnean Society of New

South Wales 104, 3-4.

Leitch, E.C., Watanabe, T., Iwasaki, M., Ishiga, H., Iszumi, S., Honma, H., Kawachi,

Y., 1990. Terranes of the southern part of the New England fold belt; a critical

review, In: Wiley, T.J., Howell, D.G., Wong, F.L. (Eds.), Terrane analysis of China

and the Pacific Rim. Circum-Pacific Council for Energy and Mineral Resources

Houston, Texas, United States, pp. 95-101.

Lennox, P.G., Offler, R., Yan, J., 2013. Discussion of Glen R.A. and Roberts J. 2012:

Formation of Oroclines in the New England Orogen, Eastern Australia. Journal of

the Virtual Explorer, 44, paper 1.

Li, P., Rosenbaum, G., 2013 In Press. Does the Manning Orocline exist? New

structural evidence from the inner hinge of the Manning Orocline (eastern

Australia). Gondwana Research.

Li, P., Rosenbaum, G., Rubatto, D., 2012. Triassic asymmetric subduction rollback in

the southern New England Orogen (eastern Australia): the end of the Hunter-Bowen

Orogeny. Australian Journal of Earth Sciences 59, 965-981.

Offler, R., Foster, D.A., 2008. Timing and development of oroclines in the southern

New England Orogen, New South Wales. Australian Journal of Earth Sciences 55,

331-340.

Ludwig, K.R., 2003. Isoplot/Ex. Berkeley Geochronology Center, Publication 1.

McCaffrey, R., 1992. Oblique plate convergence, slip vectors, and forearc

deformation. Journal of Geophysical Research 97, 8905-8915.

Murray, C.G., 2007. Devonian supra-subduction zone setting for the Princhester and

Northumberland Serpentinites: implications for the tectonic evolution of the

northern New England Orogen. Australian Journal of Earth Sciences 54, 899-925.

Murray, C.G., Fergusson, C.L., Flood, P.G., Whitaker, W.G., Korsch, R.J., 1987.

Plate tectonic model for the Carboniferous evolution of the New England fold belt.

Australian Journal of Earth Sciences 34, 213-236.

Nutman, A.P., Buckman, S., Hidaka, H., Kamiichi, T., Belousova, E., Aitchison, J.,

2013. Middle Carboniferous-Early Triassic eclogite–blueschist blocks within a

serpentinite mélange at Port Macquarie, eastern Australia: Implications for the

evolution of Gondwana's eastern margin. Gondwana Research.

Nutman, A.P., Kalsbeek, F., Friend, C.R.L., 2008. The Nagssugtoqidian orogen in

South-East Greenland: Evidence for Paleoproterozoic collision and plate assembly.

Am J Sci 308, 529-572.

Och, D.J., 2007. Eclogite, serpentinite, mélange and mafic intrusive rocks:

manifestation of long-lived Palaeozoic convergent margin activity, Port Macquarie,

eastern Australia, Faculty of Science. University of Technology, Sydney, p. 244.

Och, D.J., Leitch, E.C., Caprarelli, G., 2007a. Geological units of the Port Macquarie-

Tacking Point tract, north-eastern Port Macquarie Block, mid north coast region of

New South Wales. Quarterly Notes Geological Survey of New South Wales. Pages,

126.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

38

Och, D.J., Leitch, E.C., Caprarelli, G., Watanabe, T., 2003. Blueschist and eclogite in

tectonic melange, Port Macquarie, New South Wales, Australia. Mineralogical

Magazine 67, 609-624.

Och, D.J., Percival, I.G., Leitch, E.C., 2007b. Ordovician conodonts from the

Watonga Formation, Port Macquarie, northeast New South Wales. Proceedings of

the Linnean Society of New South Wales 128, 209-216.

Offler, R., Gamble, J., 2002. Evolution of an intra-oceanic island arc during the Late

Silurian to Late Devonian, New England Fold Belt. Australian Journal of Earth

Sciences 49, 349-366.

Parker, J., 2010. Analysis of the Port Macquarie serpentinite mélange. University of

Wollongong Honours Thesis (unpublished), Wollongong, p. 100.

Pearce, J.A., 1982. Trace element characteristics of lavas from destructive plate

boundaries, In: Thorpe, R.S. (Ed.), Orogenic andesites and related rocks. John Wiley

and Sons, Chichester, England, pp. 528-548.

Pearce, J.A., Cann, J.R., 1973. Tectonic setting of basic volcanic rocks determined

using trace element analyses. Earth Planet. Sci. Lett. 19, 290-300.

Percival, I.G., Quinn, C.D., Glen, R.A., 2011. A review of Cambrian and Ordovician

stratigraphy in NSW. Quarterly Notes Geological Survey of New South Wales, 41.

Phillips, G., Offler, R., 2011. Contrasting modes of eclogite and blueschist

exhumation in a retreating subduction system; the Tasmanides, Australia. Gondwana

Research 19, 800-811.

Pratt, G.W., 2010. A revised Triassic stratigraphy for the Lorne Basin, NSW.

Quarterly Notes Geological Survey of New South Wales 134, 1-35.

Richardson, J., 2013. Geochemistry and geochronology of the igneous rocks within

the Lorne Basin, NSW, School of Earth and Environmental Sciences. University of

Wollongong, Wollongong, p. 152.

Roberts, J., Engel, B.A., 1987. Depositional and tectonic history of the southern New

England Orogen. Australian Journal of Earth Sciences 34, 1-20.

Roberts, J., Leitch, E.C., Lennox, P.G., Offler, R., 1995. Devonian-Carboniferous

stratigraphy of the southern Hastings Block, New England Orogen, eastern

Australia. Australian Journal of Earth Sciences 42, 609-633.

Roberts, J., Lennox, P.G., Offler, R., 1993. The geological development of the

Hastings Terrane - displaced forearc fragments of the Tamworth Belt, In: Flood,

P.G., Aitchison, J.C. (Eds.), New England Orogen, eastern Australia. University of

New England, Department of Geology and Geophysics Armidale, N.S.W.,

Australia, pp. 231-242.

Robertson, A., 2004. Development of concepts concerning the genesis and

emplacement of Tethyan ophiolites in the Eastern Mediterranean and Oman regions.

Earth-Science Reviews 66, 331-387.

Rosenbaum, G., Li, P.F., Rubatto, D., 2012. The contorted New England Orogen

(eastern Australia): New evidence from U-Pb geochronology of early Permian

granitoids. Tectonics 31.

Sano, S., Offler, R., Hyodo, H., Watanabe, T., 2004. Geochemistry and chronology of

Tectonic blocks in serpentinite melange of the southern New England Fold Belt,

NSW, Australia. Gondwana Research 7, 817-831.

Scheibner, E., 1985. Suspect terranes in the Tasman fold belt system, eastern

Australia, In: Howell, D.G. (Ed.), Tectonostratigraphic terranes of the Circum-

Pacific Region. Circum-Pacific Council for Energy and Mineral Resources, pp. 493-

514.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

39

Schmidt, P.W., Aubourg, C., Lennox, P.G., Roberts, J., 1994. Paleomagnetism and

Tectonic Rotation of the Hastings Terrane, Eastern Australia. Australian Journal of

Earth Sciences 41, 547-560.

Searle, M.P., Warren, C.J., Waters, D.J., Parrish, R.R., 2004. Structural evolution,

metamorphism and restoration of the Arabian continental margin, Saih Hatat region,

Oman Mountains. Journal of Structural Geology 26, 451-473.

Shervais, J.W., 1982. Ti-V plots and the petrogenesis of modern and ophiolitic lavas.

Earth Planet. Sci. Lett. 59, 101-118.

Skilbeck, C.G., Cawood, P.A., 1994. Provenance history of a Carboniferous

Gondwana margin forearc basin, New England Fold Belt, eastern Australia: modal

and geochemical constraints. Sedimentary Geology 93, 107-133.

Spandler, C., Worden, K., Arculus, R., & Eggins, S. (2005). Igneous rocks of the

Brook Street Terrane, New Zealand: Implications for Permian tectonics of eastern

Gondwana and magma genesis in modern intra‐oceanic volcanic arcs. New Zealand

Journal of Geology and Geophysics, 48(1), 167-183.

Stern, R.A., 1998. High-resolution SIMS determination of radiogenic trace-isotope

ratios in minerals, In: Cabri, L.J., Vaughan, D.J. (Eds.), Modern approaches to ore

and environmental mineralogy. Mineralogical Association of Canada, Short course,

pp. 241-268.

Tonkin, P.C., 1998. Lorne Basin, New South Wales; evidence for a possible impact

origin? Australian Journal of Earth Sciences 45, 669-671.

Voisey, A.H., 1969. IV The New England region. Journal of the Geological Society

of Australia 16, 227-310.

Watanabe, T., Fanning, C.M., Leitch, E., Morita, T., 1999. Neoproterozoic Attunga

Eclogite in eastern Australia margin. Gondwana Research 2, 616.

Williams, I.S., 1998. U–Th–Pb geochronology by ion microprobe, In: McKibben,

M.A., Shanks III, W.C., Ridley, W.I. (Eds.), Applications of Microanalytical

Techniques to Understanding Mineralizing Processes. Reviews in Economic

Geology, pp. 1-35.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

40

Figure 1

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

41

Figure 2

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

42

Figure 3

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

43

Figure 4

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

44

Figure 5

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

45

Figure 6

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

46

Figure 7

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

47

Figure 8

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

48

Figure 9

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

49

Figure 10

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

50

Table 1. Whole rock XRF geochemical analyses of Port Macquarie rocks. Data sources: Parker (2010).

Sample# JP40 JP39 JP21 JP15 0821-01 JP44 JP17 JP23 JP24 JP32 JP34

Lat. S 152.9267 152.9266 152.9370 152.9256 152.9226 152.9376 152.9376 152.9376 152.9376 152.9376 152.9376

Long. E -31.4407 -31.4411 -31.4748 -31.4378 -31.4297 -31.4727 -31.4727 -31.4727 -31.4727 -31.4727 -31.4727

Location

Flynns

B.

Flynns

B.

Flynns

B.

Flynns

B.

Flynns B.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Rocktype

Wat. Fm.

Basalt

Wat. Fm.

Basalt

Wat. Fm.

Basalt

Wat. Fm.

Basalt

Wat. Fm.

volcanicl. Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro

SiO2 45.6 46.4 48.7 61.8 50.5 39.4 41.6 43.1 44.4 44.9 45.3

TiO2 0.9 1.9 1.4 0.9 0.7 1.8 0.2 0.3 0.2 0.5 0.5

Al2O3 17.2 15.0 17.9 13.9 14.1 13.9 17.0 11.3 14.3 12.4 18.9

Fe2O3 9.0 13.0 9.3 9.5 8.7 20.1 9.0 9.6 7.8 10.1 8.1

MnO 0.2 0.2 0.2 0.1 0.1 0.3 0.2 0.2 0.1 0.2 0.1

MgO 6.8 7.5 7.1 3.2 3.5 6.4 12.3 16.7 14.5 14.6 6.9

CaO 11.8 8.0 10.0 1.2 9.1 9.4 12.3 13.1 10.9 9.6 13.8

Na2O 2.5 3.7 3.4 5.5 6.3 1.6 1.0 0.2 0.7 1.3 2.0

K2O 0.3 0.4 0.9 0.3 0.2 0.7 0.4 0.0 0.6 0.9 1.3

P2O5 0.1 0.2 0.2 0.2 0.2 0.1 0.0 0.1 0.1 0.2 0.1

SO3 0.1 0.3 0.1 0.9 0.1 1.5 0.0 0.0 0.0 0.0 0.1

LOI 5.8 4.1 2.3 2.9 6.7 3.9 3.7 4.9 3.5 2.9 4.0

TOT. 100.1 100.6 101.2 100.3 100.2 99.1 97.7 99.6 97.3 97.8 101.1

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

51

S <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

Cl 178.0 234.0 402.0 174.0 39.0 158.1 42.3 25.0 23.6 60.1 59.8

V 234.0 382.0 269.0 262.0 243.0 966.0 122.0 164.0 137.0 210.0 334.0

Cr 331.0 231.0 328.0 64.0 73.0 11.0 760.0 1250.0 957.0 1381.0 203.0

Co 55.0 58.0 45.0 35.0 21.0 < 3.0 68.0 105.0 80.0 85.0 40.0

Ni 78.0 61.0 56.0 52.0 15.0 12.0 269.0 450.0 366.0 410.0 45.0

Cu 88.0 80.0 45.0 137.0 292.0 231.0 16.0 8.0 11.0 17.0 100.0

Zn 57.0 99.0 55.0 108.0 58.0 116.0 64.0 55.0 46.0 75.0 50.0

Ga 11.0 16.0 15.0 14.0 12.0 19.0 12.0 9.0 9.0 12.0 15.0

As < 1 2.0 < 1 14.0 < 1 4.0 1.0 < 0.5 < 0.2 1.0 0.0

Br < 1 < 1 1.0 1.0 < 1 1.0 0.0 < 0.5 < 0.5 < 0.5 < 0.5

Rb 4.0 6.0 17.0 4.0 2.0 19.0 9.0 1.0 17.0 21.0 28.0

Sr 101.0 77.0 260.0 87.0 913.0 268.0 355.0 204.0 219.0 264.0 445.0

Y 20.0 33.0 22.0 24.0 19.0 14.0 7.0 7.0 5.0 10.0 9.0

Zr 51.0 121.0 84.0 92.0 61.0 25.0 < 1.0 15.0 9.0 18.0 19.0

Nb 3.0 9.0 8.0 3.0 2.0 2.0 < 0.2 1.0 0.0 1.0 1.0

Mo < 1 < 1 < 1 < 1 < 1 <1 <1 <1 <1 <1 <1

Sn < 3 < 3 < 3 < 3 < 3 < 3.0 < 3.0 0.0 2.0 < 3.0 0.0

Sb < 3 < 3 < 3 < 3 < 3 <1 <1 <1 <1 <1 <1

Cs < 3 < 3 < 3 < 3 < 3 <1 <1 <1 <1 <1 <1

Ba 38.0 57.0 270.0 62.0 115.0 128.0 76.0 13.0 91.0 210.0 173.0

La < 2 12.0 < 2 24.0 19.0 < 2.0 12.0 16.0 11.0 < 2.0 14.0

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

52

Ce < 2 16.0 < 2 < 2 15.0 < 2.0 < 2.0 < 2.0 14.0 < 2.0 < 2.0

Hf 4.0 5.0 3.0 4.0 0.0 <1 <1 <1 <1 <1 <1

Ta 6.0 5.0 3.0 9.0 27.0 2.0 < 1.5 4.0 4.0 < 1.0 < 1.0

W 72.0 54.0 70.0 69.0 2.0 2.0 < 1.0 2.0 < 1.0 0.0 1.0

Pb 2.0 1.0 1.0 6.0 8.0 3.0 3.0 2.0 1.0 0.0 2.0

Th < 1 1.3 < 1 1.4 2.1 < 1.0 < 1.0 1.4 < 1.0 0.7 < 1.0

U < 1 < 1 < 1 < 1 < 1 0.5 < 1.0 0.9 0.8 0.8 0.6

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

53

Table 1 cont.

Sample# JP26 JP43 JP28 JP22 JP38 JP25 JP33 JP35 HONS240 JP36a JP36b

Lat. S 152.9376 152.9376 152.9376 152.9376 152.9376 152.9376 152.9376 152.9376 152.9237 152.9376 152.9376

Long. E -31.4727 -31.4727 -31.4727 -31.4727 -31.4727 -31.4727 -31.4727 -31.4727 -31.4314 -31.4727 -31.4727

Location

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Tacking

Pt.

Rocktype Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro

Post-serp.

bas. dyke

Post-serp.

bas. dyke

Post-serp.

fels. dyke

SiO2 45.4 45.6 45.8 46.2 46.6 46.7 46.8 48.8 40.7 52.0 70.9

TiO2 0.5 0.5 0.5 0.4 0.5 0.2 0.3 0.8 0.6 0.9 0.3

Al2O3 14.4 20.8 13.1 16.1 6.8 24.3 6.1 11.2 12.8 14.4 14.7

Fe2O3 7.9 7.1 8.8 7.7 10.8 3.4 8.8 9.0 10.5 9.4 2.4

MnO 0.2 0.1 0.2 0.1 0.2 0.1 0.1 0.2 0.5 0.2 0.0

MgO 10.7 6.2 12.2 9.1 15.8 5.5 22.5 8.6 16.2 7.1 0.8

CaO 9.8 14.0 9.1 11.8 15.1 11.9 8.9 10.9 14.2 7.2 3.5

Na2O 2.1 2.6 2.1 1.6 0.6 1.5 0.2 2.3 0.2 5.1 6.5

K2O 1.2 0.5 1.0 0.8 0.1 3.1 0.1 0.5 0.1 0.3 0.1

P2O5 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.3 0.2 0.3 0.1

SO3 0.0 0.5 0.0 1.2 0.0 0.1 0.0 0.4 0.0 0.0 0.0

LOI 1.0 4.4 1.9 4.1 4.1 2.5 2.9 2.9 5.1 4.5 4.4

TOT. 93.4 102.3 94.8 99.2 100.9 99.2 97.3 96.0 101.0 97.7 103.9

S <1 <1 <1 <1 <1 <1 <1 <1 23.2 <1 <1

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

54

Cl 128.9 138.6 151.1 19.4 233.3 22.8 161.0 226.1 507.6 198.2 6.9

V 228.0 376.0 240.0 301.0 363.0 105.0 123.0 399.0 296.4 332.0 54.0

Cr 691.0 164.0 664.0 400.0 1124.0 268.0 2995.0 471.0 770.0 190.0 109.0

Co 54.0 14.0 56.0 46.0 90.0 14.0 130.0 < 3.0 61.8 37.0 < 3.0

Ni 287.0 46.0 241.0 122.0 234.0 72.0 828.0 157.0 200.9 68.0 9.0

Cu 64.0 91.0 54.0 146.0 142.0 12.0 64.0 1434.0 89.2 113.0 65.0

Zn 58.0 35.0 63.0 50.0 71.0 23.0 47.0 77.0 89.7 70.0 12.0

Ga 11.0 15.0 11.0 13.0 6.0 16.0 5.0 16.0 11.7 11.0 13.0

As 1.0 < 0.5 1.0 < 0.2 1.0 1.0 19.0 1.0 1.4 1.0 < 0.5

Br 1.0 1.0 0.0 < 0.5 < 0.5 0.0 < 0.5 1.0 <1 < 0.5 0.0

Rb 28.0 11.0 23.0 20.0 2.0 76.0 5.0 10.0 <1 2.0 1.0

Sr 532.0 621.0 478.0 356.0 69.0 470.0 28.0 535.0 804.1 253.0 338.0

Y 13.0 6.0 12.0 9.0 14.0 5.0 7.0 26.0 15.7 24.0 20.0

Zr 22.0 10.0 20.0 12.0 16.0 9.0 13.0 64.0 34.7 72.0 156.0

Nb 1.0 1.0 1.0 1.0 1.0 0.0 0.0 2.0 1.3 4.0 5.0

Mo <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

Sn 1.0 1.0 1.0 1.0 < 3.0 3.0 2.0 1.0 <3 5.0 10.0

Sb <1 <1 <1 <1 <1 <1 <1 <1 <3 <1 <1

Cs <1 <1 <1 <1 <1 <1 <1 <1 <4 <1 <1

Ba 314.0 75.0 294.0 147.0 < 2.0 562.0 < 2.0 123.0 <2 48.0 47.0

La 10.0 < 2.0 < 2.0 < 2.0 < 2.0 6.0 < 2.0 < 2.0 8.4 < 2.0 18.0

Ce < 2.0 < 2.0 < 2.0 17.0 < 2.0 14.0 < 2.0 18.0 <2 34.0 29.0

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

55

Hf <1 <1 <1 <1 <1 <1 <1 <1 1.3 <1 <1

Ta 56.0 1.0 < 1.0 2.0 6.0 < 1.0 5.0 < 1.0 <1 10.0 < 1.0

W 1.0 1.0 < 0.8 1.0 < 0.8 1.0 < 0.1 6.0 <1 1.0 3.0

Pb 2.0 5.0 2.0 2.0 0.0 2.0 1.0 4.0 <1 < 0.3 2.0

Th < 1.0 < 1.0 < 0.6 1.1 < 1.0 1.1 < 1.0 1.7 1.6 1.8 3.7

U 0.4 < 0.5 1.1 < 0.5 < 1.0 1.4 < 1.0 < 1.0 <1 0.7 0.6

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

56

Table 2 SHRIMP U-Th-Pb summary data

Labels site U/ppm Th/ppm Th/U 204Pb/206Pb f206% 238U/206Pb 207Pb/206Pb age (Ma)* %disc

21-01 volcaniclastic block within serpentinite, Town Beach

1.1 e,osc,p 211 102 0.49 0.0004 ± 0.0003 0.672 14.052 ± 0.395 0.0518 ± 0.0047 443 ± 12

1.2 e,osc,p 176 58 0.33 <0.0001 ± 0.0011 0.002 13.405 ± 0.425 0.0563 ± 0.0166 464 ± 14

2.1 e,osc,p 561 243 0.43 0.0001 ± 0.0001 0.171 13.701 ± 0.327 0.0546 ± 0.0020 454 ± 10

2.2 e,osc,p 398 117 0.29 <0.0001 ± 0.0002 0.002 13.881 ± 0.484 0.0557 ± 0.0027 448 ± 15

3.1 e,osc/rex,p 120 37 0.31 0.0008 ± 0.0005 1.204 13.987 ± 0.526 0.0481 ± 0.0080 445 ± 16

4.1 e,osc,p 317 163 0.51 <0.0001 ± 0.0003 0.002 13.662 ± 0.538 0.0572 ± 0.0052 455 ± 17

4.2 e,osc,p 186 80 0.43 <0.0001 ± 0.0002 0.002 13.728 ± 0.430 0.0551 ± 0.0039 453 ± 14

21-02 volcaniclastic Watonga Formation, Green Point

1.1 e,osc,p 832 142 0.17 0.0001 ± 0.0001 0.114 14.959 ± 0.448 0.0555 ± 0.0014 417 ± 12

1.2 e,osc,p,fr 641 176 0.27 <0.0001 ± 0.0001 0.002 14.326 ± 0.262 0.0555 ± 0.0018 435 ± 8

2.1 e,osc,p 265 132 0.50 <0.0001 ± 0.0000 0.002 18.326 ± 0.504 0.0553 ± 0.0015 343 ± 9

2.2 e,osc,p,fr 311 248 0.80 <0.0001 ± 0.0000 0.002 18.011 ± 0.523 0.0553 ± 0.0020 348 ± 10

3.1 e,osc,p 810 621 0.77 0.0005 ± 0.0002 0.877 22.282 ± 0.927 0.0517 ± 0.0039 283 ± 12

3.2 m,osc,p 215 127 0.59 <0.0001 ± 0.0001 0.002 18.701 ± 0.637 0.0541 ± 0.0019 336 ± 11

4.1 e,osc,p 433 297 0.68 <0.0001 ± 0.0000 0.067 11.718 ± 0.267 0.0608 ± 0.0011 528 ± 12

5.1 m/c,hb,ov 274 225 0.82 <0.0001 ± 0.0000 0.002 9.203 ± 0.250 0.0619 ± 0.0012 665 ± 17

6.1 e,osc,p,fr 824 247 0.30 0.0004 ± 0.0000 0.635 6.324 ± 0.123 0.0738 ± 0.0010 1035 ± 27 -9

7.1 m/c,osc,p,fr 329 432 1.31 0.0002 ± 0.0002 0.387 17.679 ± 0.688 0.0496 ± 0.0031 355 ± 13

8.1 m,osc,p 202 198 0.98 0.0002 ± 0.0002 0.317 18.124 ± 0.625 0.0519 ± 0.0029 346 ± 12

9.1 e,osc,p 225 155 0.69 0.0002 ± 0.0002 0.323 15.100 ± 0.492 0.0533 ± 0.0032 413 ± 13

10.1 e,osc,p,fr 199 42 0.21 0.0001 ± 0.0000 0.096 11.303 ± 0.569 0.0581 ± 0.0025 546 ± 26

TP208 Tacking Point Gabbro tonalite, north of Tacking Point

1.1 m,osc,p 598 858 1.43 0.0001 ± 0.0000 0.152 16.381 ± 0.414 0.0526 ± 0.0012 382 ± 9

1.2 e,osc,p 458 580 1.27 <0.0001 ± 0.0000 0.011 15.985 ± 0.361 0.0535 ± 0.0014 391 ± 9

2.1 m,osc,p,fr 166 128 0.77 0.0002 ± 0.0004 0.246 15.950 ± 0.479 0.0523 ± 0.0062 392 ± 11

2.2 e,osc,p,fr 239 125 0.53 <0.0001 ± 0.0002 0.002 16.181 ± 0.497 0.0547 ± 0.0040 387 ± 12

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

57

3.1 m,osc,p,fr 409 395 0.97 0.0001 ± 0.0001 0.194 16.187 ± 0.597 0.0532 ± 0.0020 386 ± 14

4.1 m,osc,eq,fr 130 68 0.52 <0.0001 ± 0.0001 0.034 15.920 ± 0.381 0.0581 ± 0.0021 393 ± 9

5.1 e,osc,p,fr 431 402 0.93 0.0002 ± 0.0001 0.354 16.219 ± 0.676 0.0528 ± 0.0020 386 ± 16

5.2 m,osc,p,fr 368 339 0.92 0.0000 ± 0.0001 0.002 16.178 ± 0.405 0.0552 ± 0.0018 387 ± 9

Town Beach' felsic sheet cutting gabbro in the serpentinite (extra CL-guided analyses of Aitchison and Ireland (1995)

sample) 1.1† r,osc,p 2268 3225 1.42 0.0071 ± 0.0003 13.106 32.450 ± 0.563 0.0492 ± 0.0059 196 ± 3

1.2† r,osc,p 984 723 0.73 0.0059 ± 0.0004 10.892 24.422 ± 0.678 0.0451 ± 0.0071 259 ± 7

1.3† c,osc,p 498 313 0.63 0.0024 ± 0.0002 4.449 19.027 ± 0.254 0.0527 ± 0.0032 330 ± 4

1.4† r,osc,p 843 726 0.86 0.0047 ± 0.0003 8.558 25.836 ± 0.486 0.0599 ± 0.0050 245 ± 5

2.1 r,h,ov 298 49 0.17 0.0001 ± 0.0001 0.148 12.176 ± 0.168 0.0561 ± 0.0014 509 ± 7

2.2 c,osc,ov 491 386 0.79 <0.0001 ± 0.0000 0.011 5.986 ± 0.137 0.0785 ± 0.0010 1159 ± 26 -14

2.3 r,h,ov 356 66 0.18 0.0005 ± 0.0002 0.915 12.273 ± 0.222 0.0567 ± 0.0025 505 ± 9

3.1 e,osc,fr 5 20 3.80 0.0024 ± 0.0007 4.504 1.712 ± 0.103 0.1247 ± 0.0140 2024 ± 214 47

4.1 m,osc,p 412 146 0.35 0.0001 ± 0.0000 0.131 9.877 ± 0.148 0.0606 ± 0.0010 622 ± 9

4.2 e,osc,p 434 57 0.13 0.0001 ± 0.0000 0.153 10.458 ± 0.150 0.0587 ± 0.0008 589 ± 8

5.1 e,osc,p,fr 462 518 1.12 0.0003 ± 0.0001 0.518 20.236 ± 0.386 0.0538 ± 0.0023 311 ± 6

6.1 m,osc,p 309 168 0.54 0.0002 ± 0.0001 0.307 26.109 ± 0.408 0.0511 ± 0.0016 242 ± 4

12-01 felsic sheet cutting Tacking Point Gabbro, north of Tacking Point

1.1 e,osc,p 128 80 0.63 0.0005 ± 0.0004 0.897 15.191 ± 0.377 0.0545 ± 0.0060 411 ± 10

2.1 m,osc,p,fr 408 554 1.36 0.0018 ± 0.0003 3.213 16.934 ± 0.368 0.0302 ± 0.0047 370 ± 8

3.1 c?osc,p 959 796 0.83 0.0015 ± 0.0001 2.647 21.130 ± 0.431 0.0401 ± 0.0021 298 ± 6

3.2 c?osc,p 678 304 0.45 0.0004 ± 0.0002 0.641 18.653 ± 0.344 0.0493 ± 0.0027 337 ± 6

4.1 e,osc,eq 524 120 0.23 0.0001 ± 0.0000 0.221 9.745 ± 0.194 0.0614 ± 0.0014 630 ± 12

5.1 m,osc/h,p 177 162 0.91 0.0005 ± 0.0002 0.974 18.423 ± 0.383 0.0505 ± 0.0042 341 ± 7

5.2 m.osc/h,p 211 181 0.86 0.0008 ± 0.0002 1.446 18.924 ± 0.428 0.0482 ± 0.0029 332 ± 7

6.1 m,osc/h,p 494 193 0.39 0.0026 ± 0.0004 4.717 17.842 ± 0.402 0.0311 ± 0.0058 352 ± 8

7.1 c,osc,ov 155 121 0.78 <0.0001 ± 0.0002 0.002 3.900 ± 0.236 0.1519 ± 0.0088 2367 ± 102 -38 grain analytical sites: e=end, m=middle, r=rim, c=structural core, p=prism, eq=equant, ov=oval, fr=grain fragment

cathodoluminescence petrography: osc=oscillatory zoning, h=homogeneous, hb=homogeneous and bright, hd=dull homogeneous, rex=recrystallised

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

58

f206% is the percentage of 206Pb of non in situ radiogenic origin, based on measured 204Pb and Cumming & Richards (1975) common Pb compositions

all analytical errors are given at the 1σ level

* ages are given after correction for common Pb. For Neoproterozoic and Phanerozoic grains 206Pb/238U ages are given. For pre-Neoproterozoic grains are given 207Pb/206Pb ages (in italics) and the degree of discordance (%disc)

between the 206Pb/238U and 207Pb/206Pb ages † sites with overestimated common Pb due to isobaric interference under the 204Pb measuring position

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

59

Graphical abstract

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

60

Highlights

Tacking Point Gabbro is Devonian not Permian and Watonga Formation is

confirmed as Ordovician.

Sandstone at Green Mound is Carboniferous and therefore not a part of the

Watonga Formation.

Dykes cutting the serpentinite are ~250 Ma constraining the emplacement age

of the mélange.