�������� ����� ��

Magmatic and metamorphic imprints in 2.9 Ga chromitites from the Sittam-pundi Layered Complex, Tamil Nadu, India

Upama Dutta, Uttam K. Bhui, Pulak Sengupta, Sanjoy Sanyal,D.Mukhopadhyay

PII: S0169-1368(11)00052-7DOI: doi: 10.1016/j.oregeorev.2011.05.004Reference: OREGEO 856

To appear in: Ore Geology Reviews

Received date: 28 December 2009Revised date: 12 May 2011Accepted date: 15 May 2011

Please cite this article as: Dutta, Upama, Bhui, Uttam K., Sengupta, Pulak, Sanyal,Sanjoy, D.Mukhopadhyay, Magmatic and metamorphic imprints in 2.9 Ga chromititesfrom the Sittampundi Layered Complex, Tamil Nadu, India, Ore Geology Reviews (2011),doi: 10.1016/j.oregeorev.2011.05.004

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

Magmatic and metamorphic imprints in 2.9 Ga chromitites from the Sittampundi

Layered Complex, Tamil Nadu, India

Upama Dutta1, Uttam K. Bhui1, Pulak Sengupta1,**, Sanjoy Sanyal1, D.Mukhopadhyay2

1Department of Geological Sciences, Jadavpur University, Kolkata 700032, India

2Department of Geology, University of Calcutta, 29, Ballygunge Circular Road, Kolkata 700019, India

Abstract

The c.2.9 Ga old Sittampundi layered complex (SLC) of South India belongs to a special group of

deformed and metamorphosed Archaean rocks where chromitites are interlayered with anorthosite.

Detailed field studies have revealed that the SLC comprises of a sequence of magmatic rocks

consisting of clinopyroxenite, anorthosite and mafic rocks of tholeiitic composition. Minor BIF

(Banded Iron Formations) intercalated with the mafic rocks are the only sedimentary rock within the

SLC. Chromitite occurs as continuous to discontinuous bands (a few mm up to 6 m thick) within

clinopyroxenite and highly calcic anorthosite (An 99-100) but never in the enclosing mafic rocks.

Chromite occurs broadly in three textural types: (a) cumulus grains in chromitite layers; (b)

disseminated grains in clinopyroxenite and anorthosite; and (c) small grains included in clinopyroxene

and plagioclase. A suite of felsic magma intruded the SLC at c.2.51 Ga. Subsequently the entire rock

sequence underwent polyphase deformation and metamorphism at c.2.50-2.45 Ga (granulite facies) and

at 0.72–0.50 Ga (amphibolite facies). During the latter event, extensive alteration of clinopyroxene to

amphibole and chlorite, of plagioclase to clinozoisite and of chromite to Cr-poor green spinel took

place.

* Corresponding author. Tel.: +91 33 24152782. E-mail addresses: pulaksg@gmail.com

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Chromite compositions show large variations (Cr# = 26-60, Mg# = 4-45, Fe3+# = 2-24) depending

upon textural type and nature of the associated phases. The most conspicuous compositional variation

took place when chromite was metasomatically replaced by green spinel (Cr# = 3-21; Mg# 45-61)

during amphibolite facies metamorphism. On a Cr# vs. Mg# plot, pristine magmatic compositions of

chromite define an array that suggest increasing Cr# with concomitant decrease in Mg#, presumably

during magmatic fractionation. Highly calcic plagioclase in anorthosite and Fe-Al rich chromite in

chromitite in the SLC are consistent with a hydrous parental magma of tholeiitic composition. This

hydrous magma was generated in an oceanic arc environment and crystallized close to the surface of

the earth. In terms of mineralogy and field relations, chromitite-bearing rocks of the SLC show

remarkable similarity with the Archaean anorthosite-hosted chromitite deposits in layered magmatic

complexes at Fiskenaesset (Greenland) and Messina (South Africa) but contrasts sharply with the

chromitite deposits of Proterozoic and Phanerozoic age. A change in the style of arc magmatism

appears to be the controlling factor for marked change in chromite compositions across the Archaean-

Proterozoic boundary.

Keywords: Chromitite; Anorthosite; Archaean; Sittampundi layered complex; Arc magma.

1. Introduction

Studies in the past two decades have revealed that the Earth’s mantle has undergone significant

physical and chemical changes over geological time (reviewed in Rollinson, 2007). Episodic melting,

extraction of melts from the mantle and contamination of materials from the subducted slab to the

overlying mantle wedge are considered to be primarily responsible for chemical evolution of the mantle

(Rollinson, 2007). Because of slow mixing rates and slow rates of diffusion, mantle heterogeneities are

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

preserved over a long time (≥1 Ga, Rollinson; 2007). This observation makes mantle-derived magmas a

potential tool for deciphering chemical evolution of the mantle. Anorthosite-bearing layered magmatic

complexes represent an important component of mantle-derived magmatic rocks that range in age from

Archaean to Phanerozoic (Ashwal, 1993). On the basis of form, structure and plagioclase composition,

Precambrian anorthosites are broadly divided into layered- and massif-types (reviewed in Ashwal,

1993). The Archaean layered anorthosite complexes are hosted in high-grade metamorphic terrains, and

are complexly deformed and metamorphosed along with their host rocks (Windley et al., 1981). Most

post-Archaean layered complexes (e.g., Bushveld complex, Stillwater complex), on the other hand,

occur as sill like bodies, and are mostly undeformed and unmetamorphosed (Hatton and von

Gruenewaldt, 1990; Ashwal, 1993; Stowe, 1994). Chromite, which is considered to be an important

petrogenetic indicator (Irvine, 1965, 1967), occurs in many of the Precambrian layered anorthosite

complexes (Hatton and von Gruenewaldt, 1990; Ashwal, 1993; Stowe, 1994; Rollinson et al., 2002).

Detailed petrological characterization of chromite deposits in Archaean layered complexes should,

therefore, provide invaluable information about the enigmatic mantle processes in early Earth history.

Existing information has indicated that chromite in Archaen layered complexes has distinct

compositions that contrast sharply with the chromite compositions in Proterozoic and Phanerozoic

rocks (Rollinson et al., 2002). Plagioclase in Archaen layered complexes is also highly calcic compared

to their younger counterpart (Ashwal, 1993). However, examples of Archaean layered complexes are

limited, and detailed information on chromite is hitherto available only from two complexes: 1)

Fiskenaesset, Greenland and 2) Messina, South Africa (Windley et al., 1981; Ashwal, 1993; Rollinson

et al., 2002).

Highly deformed and metamorphosed layered complexes of Bhavani (BLC) and Sittampundi (SLC)

of south India have been known for their anorthosite and chromitite for a long time (Subramanium,

1956; Ramadurai et al., 1975; Windley et al., 1981; Srikantappa et al., 2003). Recent geochronological

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

studies have unequivocally demonstrated that both the layered complexes were formed within late

Archaean time (ca. 2.9-2.8 Ga; Bhaskar Rao et al., 1996; Ghosh et al., 2004). Detailed study on this

important Archaean chromite deposit in the light of recent advances of the subject is lacking and is the

subject of this communication. Here we present field relations, textural features and compositional

characteristics of chromite deposits from the SLC. Interpreting the petrological features of SLC and the

rocks of a wider area, an attempt has been made to (a) compute composition and depth of emplacement

of parental magma from which magmatic rocks of the SLC were formed (b) constrain the probable

tectonic setting where the SLC might have been emplaced, (c) asses the nature and extent of

compositional modifications of magmatic chromite during fluid-induced metamorphism and (d)

compare and contrast the geological history of the SLC with other well studied chromite deposits

associated with Achaean layered magmatic complexes.

2. Geological background

The granulite terrain of south India is considered to be a mosaic of crustal domains with distinctive

geological and geochronological characteristics (Braun and Kriegsman, 2003; Bhaskar Rao et al., 2003;

Ghosh et al., 2004). A number of crustal-scale shear zones are presumed to have divided the entire

granulite belt into three major domains (Fig. 1). The northernmost domain, the northern granulite

terrains (NGT), exposes an assemblage of mafic, ultramafic and volumetrically major felsic

orthogneisses that underwent a latest high-grade event at ca. 2.6-2.5 Ga whereas the southernmost

domain (Madurai Block or MB) shows a latest high-grade event at a much younger age (ca. 0.6-0.5 Ga;

Chetty, 1996; Braun and Kriegsman, 2003; Bhaskar Rao et al., 2003; Chetty et al., 2003; Ghosh et al.,

2004). The NGT and MB are separated by a roughly E-W trending belt. The rock associations in this

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

belt show complex magmatic, metamorphic and deformational history over a protracted period from

2.9 Ga to 0.5 Ga (Braun and Kriegsman, 2003; Bhaskar Rao et al., 2003; Mukhopadhyay et al., 2003;

Ghosh et al., 2004, Raith et al., 2010). Several crustal-scale shear zones are believed to have affected

the rocks of this linear belt for which is often referred to as the Cauvery Shear System (CSS, Chetty,

1996; Fig. 1). The CSS that is dissected by ductile to brittle shears is believed to have a protracted

geological history with major reactivation at ca. 0.6-0.5 Ga (Meissner et al., 2002; Srikantappa et al.,

2003). An assemblage of mafic-ultramafic-anorthosite-felsic orthogneisses is the dominant rock

association of the CSS.

A number of layered magmatic complexes with or without economically viable chromite deposits

are located in the CSS, of which the layered complexes of Bhavani (BLC) and Sittampundi (SLC) have

been studied in some details (Fig. 1; Subramanium, 1956, Janardhan and Leake, 1975, Anbarasu et al.

2011, Bhaskar Rao et al., 1996, 2003; Ghosh et al., 2004). The first systematic study on the rocks of

SLC was done by Subramanium (1956). Existing geochronological data indicate that the layered

complexes were emplaced at c. 2.9 Ga (Subramanium, 1956; Bhaskar Rao et al., 1996; Ghosh et al.,

2004). A suite of felsic magmas now represented by enderbite and charnockite (felsic orthogneiss)

subsequently intruded the members of the SLC. The entire ensemble of mafic, ultramafic and felsic

rocks underwent deformation accompanied by high-grade metamorphism at ca. 2.450-2.45 Ga and by

amphibolite facies metamorphism during ca. 0.72-0.50Ga (Bhaskar Rao et al., 1996; Meissner et al.,

2002; Ghosh et al., 2004). Late Archaean and Neoproterozoic tectonothermal activities obliterated the

primary magmatic features of the layered complexes in most places although vestiges of rhythmic

interlayering among anorthosite, chromitite and clinopyroxenite are present and are considered to be of

magmatic origin (Subramanium, 1956). The BLC locally shows nearly complete magmatic stratigraphy

(see Fig. 2b). The sequence starts with a unit of olivine-rich ultramafic rocks e.g., harzburgite, wehrlite

and dunite (now extensively altered to serpentinite and magnesite) which is overlain successively by

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

clinopyroxenite, leucogabbro / anorthosite and basaltic rocks (now garnetiferous mafic granulites) (Fig.

2b). Chromite occurs as thin layers and disseminated grains within the olivine-rich ultramafic rocks.

BIF is intercalated with the top mafic unit of the sequence in a few places (Fig. 2b). Extant geological

and geochronological information have shown that the late Archaean high-grade rock ensemble of the

CSS remained undisturbed for a protracted period until these rocks were polydeformed, intruded by

voluminous granitoids and were extensively retrogressed during the Pan-African tectonothermal events

(ca. 0.72-0.5 Ga: Bhaskar Rao et al., 2003; Ghosh et al., 2004). Proximal to the boundary with the MB,

the CSS exposes a packet of young supracrustal rocks (now represented by marble, calc-silicate rocks

and metapelites) having an average crustal residence age of 1.9 Ga (Fig. 1; Meissner et al., 2002).

Locally the metapelites contain blocks of granulite-grade BIF suggesting that the sediments were

deposited on the ca. 2.5 Ga granulite basement (Ghosh et al., 2004). These supracrustal rocks

underwent prograde metamorphism that culminated at 9±1 kbar and 700±50 °C on a clockwise P-T

trajectory (Meissner et al., 2002; Sengupta et al., 2009a). Geochronological data bracket the age of

metamorphism of these supracrustal rocks within ca. 0.61-0.52 Ga (Meissner et al., 2002; Raith and

Srikantappa, 2008).

3. The Sittampundi layered complex (SLC)

3.1. Magmatic and metamorphic events in the SLC and the enclosing rocks

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

The generalized geological map of the SLC showing dispositions of the different lithologies is

presented in Fig. 2a. The rocks of this magmatic complex and the adjoining areas have been studied by

a number of authors (Subramanium, 1956; Ramadurai et al., 1975; Bhaskar Rao et al., 1996, 2003;

Mukhopadhyay et al., 2003; Ghosh et al., 2004; John et al., 2005; Shimpo et al., 2006; Sengupta et al.

2009 a, b, among others). The SLC comprises an intercalated sequence of clinopyroxenite, anorthosite

and a suite of mafic rocks now represented as mafic granulite with the mineralogy clinopyroxene +

plagioclase ± orthopyroxene ± garnet ± amphibole (Bhaskar Rao et al., 1996; Ghosh et al., 2004; our

unpublished data). Although dm to cm-thick chromitite layers are present in clinopyroxenite and

anorthosite, thick bands (up to 6 meter thick, Subramanium, 1956) of economic-grade chromite occur

only in clinopyroxenite (now extensively retrograded to amphibolite).

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Extant geochemical and Nd-isotope data indicate that the mafic–ultramafic rocks of the SLC are co-

genetic and show a fractionation trend akin to that of tholeiitic magma (Bhaskar Rao et al., 1996). A ca.

2.9 Ga emplacement age for the SLC has been established by whole-rock Sm-Nd isochron and U-Pb

dating of zircon (Bhaskar Rao et al., 1996; Ghosh et al., 2004). Vestiges of Banded Iron Formation

(BIF), which represent the sole sedimentary component in the magmatic sequence and are intimately

associated with the mafic rocks of the SLC, show cm to mm thick compositional layers alternatively

rich in magnetite + pyroxene and quartz (Fig. 3a, b). The compositional banding of BIF, that

presumably represent primary sedimentary layering can be traced laterally for several meters. Owing to

repeated folding actual number of BIF layers in the mafic host cannot be determined. The SLC is

surrounded by felsic orthogneiss (Fig. 2; ca. 2.51 Ga emplacement age; Ghosh et al., 2004), which

contains fragments of mafic-ultramafic rocks including xenoliths of dunite, harzburzite and wherlite

(Fig. 3c), and sends apophyses into the rocks of the magmatic complex. Field studies together with

extant geochronological data indicate that subsequent to the emplacement of felsic magma, the

ensemble of ca. 2.9-2.51 Ga rocks underwent polyphase deformation at ca. 2.50-2.45 Ga (granulite

facies) and at ca. 0.72-0.50 Ga (amphibolite facies) (Bhaskar Rao et al., 1996; Ghosh et al., 2004; Raith

et al., 1999). The high-grade metamorphism that produced garnet and orthopyroxene-bearing

leucosomes in felsic rocks and megacrystic garnet in mafic rocks and BIF were culminated at 9.5 ± 1

kbar and 800 ± 50 oC (Bhaskar Rao et al., 1996; our unpublished data). Recently, from one locality

near SLC, Sajeev et al. (2009) reported mafic rocks that shows ultra-high pressure metamorphism (>20

kbar) and interpreted it as slices of mantle rocks that exhumed during Neoproterozoic metamorphism.

During the Neoproterozoic (ca. 0.72-0.50 Ga) events voluminous granitoid batholiths intruded the high

grade Archaean rocks. Extensive retrogression of high-grade rocks particularly at the contact of these

granitoid batholiths transformed the granulites facies pyroxenes and feldspars to secondary minerals

principally amphibole, chlorite, epidote and biotite at distinctly lower P-T conditions (650 ± 50 °C, 6-7

kbar, Bhaskar Rao et al., 1996; Sengupta et al., 2009 a, b). Prismatic amphibole and megacrystic

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

corundum (ruby) with coronitic green spinel having variable thickness (Fig. 3d) were developed in

anorthosite during this retrogressive event. Randomly oriented amphibole and chlorite grains and

preservation of delicate corona of green spinel around corundum suggest static condition at the time of

growth of these secondary minerals. ca. 540 Ma concordant U-Pb zircon date from one small granitoid

pluton fixes the age of emplacement of these granitoids (Ghosh et al., 2004). In most places, the

original magmatic relations among the rocks of the SLC are obscured due to superposed deformation

and polyphase metamorphism and hydration. Nevertheless, a generalized magmatic stratigraphy has

been developed integrating all the field features (Fig. 2b). Except for the presence of thick chromite

seams and lack of olivine-rich ultramafic rocks the magmatic stratigraphy and the age of emplacement

of the SLC bear striking resemblance with the BLC (Fig. 2b). However, the possibility that olivine-rich

rocks may occur beneath the exposed section of the SLC cannot be ruled out in view of the presence of

dunite and wehrlite xenoliths in the felsic gneiss whose protolith intruded the magmatic complex, and

might have sampled the lower part of the complex. Features such as (a) occurrence of chromite-bearing

ultramafic enclave in mafic rocks, and (b) presence of tongues of mafic rocks in anorthosite corroborate

the view that mafic rocks represent the uppermost part of the SLC. Intimate association of mafic rocks

with BIF which is presumed to have deposited as chemical sediments also corroborates this view.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Chromite occurs in a number of forms in the SLC. In the most abundant mode, thin to thick chromitite

(up to 6 meter thick) seams are present within clinopyroxenite layers (Fig. 3e). These banded

sequences of chromitite and pyroxenite that can be traced laterally for a distance of more than

500 meters are presumed to be of magmatic origin. In another mode, mm to cm thick

chromitite layers occur within anorthosite (Fig. 3f, g). Intense post-crystallization deformation

affected the chromitite layers and its host clinopyroxenite and anorthosite. There is pinch and

swell and boudin structure in the competent chromitite layers (Fig. 3f). Intense Neoproterozoic

deformation also caused intricate folding of interlayered anorthosite and chromitite (Fig. 3g).

In places, green-spinel rich veins (confirmed by petrography) were found along the extension

direction of deformed chromite seams (Fig. 3d). Chromite layers are absent in the adjoining

mafic rocks.

3.2. Mutual relations between chromite and associated phases

Detailed petrographic study of anorthosite and clinopyroxenite are beyond the purview of this

communication. In the following sections, salient petrographic features of these rocks that have direct

relation on the formation and alteration of chromite will be described.

3.2.1. Chromite in thick chromitite layers and in host clinopyroxenite

In the thick chromitite layers, coarse chromite grains show a typical cumulus texture (Fig. 4a),

which is partially modified by superposed deformation. However this texture will be referred to as

cumulate texture. Commonly, volume of cumulus chromite exceeds 90 vol.%. Minor (<10 vol.%)

secondary amphibole and chlorite (Fig. 4a) occupy the interstitial spaces of coarse chromite grains.

Locally, inclusions of corroded clinopyroxene were found in secondary amphibole. Secondary chlorite

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

grains replace secondary amphibole and rarely coexist with calcite. Cumulus chromite grains show

minor (≤2 vol.%, estimated from visual inspection and image analyses) crystallographically oriented

fine needles of rutile (Fig. 4b). Granular rutile grains locally surround cumulus chromite grains in a few

places (Fig. 4a). These features indicate that rutile was “exsolved” from and migrated out of the host

chromite grains during cooling (Subramanium, 1956, Mitra and Samanta, 1996). In the host

clinopyroxenite, small chromite grains are either included in the cumulus clinopyroxene (Fig. 4c) or

disseminated in the interstitial space formed by cumulus clinopyroxene grains. Alteration of

clinopyroxene to amphibole (Fig. 4c) is a common feature in these rocks.

3.2.2. Chromite in anorthosite

In thin chromitite layers in anorthosite, small grains of plagioclase and clinopyroxene that are in

different stages of alteration to amphibole and chlorite occur in the interstitial space formed by cumulus

chromite grains (Fig. 4d). The proportion of interstitial silicate minerals is distinctly higher (10-30 vol.

%) than in the thick chromitite layers in clinopyroxenite. In the host anorthosite, recrystallization of

magmatic plagioclase develops a polygonal grain mosaic (Fig. 4e). A few megacrystic plagioclase

grains that are set in polygonal matrix grains show impress of deformation manifested by kinked twin

lamellae, undulose extinction and formation of polygonal sub-grains. All these features suggest that the

grain size of magmatic plagioclase in anorthosite was much larger than what is seen now. Disseminated

chromite grains occur at the triple-point junctions of the polygonal plagioclase grains as well as

inclusions within clinopyroxene (Fig. 4f). Aggregates of the secondary minerals amphibole, chlorite,

calcite and clinozoisite partially replace polygonal grains of clinopyroxene, plagioclase and

disseminated chromite grains. Large stumpy grains of corundum (corundum 1) are embedded in a

matrix made up of polygonal plagioclase grains (Fig. 4g). These corundum grains developed coronitic

green spinel of variable thickness (Fig. 4g). Green spinel protrudes into the adjacent polygonal

plagioclase grains (Fig. 4g). The coronitic green spinel breaks down to an aggregate of granular

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

corundum (corundum 2), magnetite and chlorite (Fig. 4g). Green spinel that occurs in veins in stretched

chromitite layers contains relics of chromite at the core of it and replaced the latter mineral to different

extent (Fig. 4h-i). Appel et al. (2002) described a similar feature from Greenland and attributed it to

melt-chromite interaction at a late stage of magmatic evolution. However, microstructural features

described before corroborate the view that replacement of chromite by green spinel in the SLC

occurred during or after regional deformation (see also below).

4. Mineral chemistry

4.1. Compositional variation of chromite in the SLC

Compositions of chromite from different textural types are presented in Fig. 5a, b and Table 1a.

Spot analyses of chromite show uniformly low TiO2 (≤0.43 wt.%) and Fe3+ (0.05 to 0.47 atom per

formula unit; a.p.f.u.) contents, irrespective of its association and textural type (Table 1a). The presence

of rutile as fine exsolution lamellae in as well as granules along the periphery of cumulus chromite

grains suggest that the primary (magmatic) chromite had higher TiO2 content than those represented by

spot analyses. Considering low volume of the exsolved rutile, TiO2 content of cumulus chromite never

exceeded 0.5 wt.%. Depending on the textural types, chromite grains marked variation on Cr#

(100×Cr/(Cr+Al)) vs. Mg# (100×Mg/(Mg+Fe2+)) plot (Fig. 5a). Cumulus chromite grains from

chromitite layers in clinopyroxenite and in anorthosite define an array, which is characterized by

reverse relation between Mg# and Cr# with larger range of the former compared to the latter (Fig. 5a).

No significant compositional variation was noted between core and rim compositions in individual

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

cumulus chromite grains in the chromitite layers (Table 1a). Even when the cumulus chromite grains

coexist with volumetrically minor silicate grains, compositional profile in the former show only minor

change in terms of Mg#, Cr# and Fe3+# on few microns in the rim whereas the core regions have

virtually uniform compositions (Fig. 5b). All these features attest to the view that the primary

composition of cumulus chromite, particularly at the core region of these grains, did not change

significantly during subsolidus and metamorphic processes. Volumetrically minor and disseminated

chromite grains, on the other hand, show significant post-magmatic compositional modification. At the

contact with metamorphic amphibole, disseminated chromite grains show the highest Cr# and lowest

Mg# (Fig. 5a). This may be attributed to the loss of Al (relative to Cr) and Mg (relative to Fe2+) in

chromite due to exchange of elements between amphibole and chromite during amphibolite facies

metamorphism (Beeson and Jackson, 1969; Murck and Campbell, 1986; Kimball, 1990; Rollinson,

1995; Rollinson et al., 2002). The most conspicuous compositional variation was observed in chromite

grains that coexist with green spinel (Fig. 5a). Compositions of these chromite grains define a positive

array showing reverse relation between their Mg# and Cr# (Fig. 5a). This compositional trend is

steeper than the ‘magmatic crystallization’ trend defined by cumulus chromite, and the two trends meet

at Cr#~50 and Mg#~25 (Fig. 5a). This compositional variation trend that is associated with

replacement of chromite by green spinel is consistent with the coupled substitutions of the types

MgFe2+-1 and AlCr-1 (Fig. 5a).

This trend of compositional variation in the chromite in spinel-rich veins has marked resemblance

with the ‘replacement trend’ described by Rollinson et al. (2002) from the Fiskenaesset complex. The

authors attributed this ‘replacement trend’ to melt-chromite interaction during the late stage of

magmatic history of the layered complex of Fiskenaesset, Greenland. However, the following features

support that in the studied area replacement of chromite by green spinel occurred during amphibolite

facies metamorphism:

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

a) Cumulus chromite grains were replaced by green spinel in the extensional fractures in the deformed

chromitite layers in anorthosite (Figs. 3d and 4i-h).

b) Corona of green spinel also formed around the stumpy corundum crystals that were set in the

recrystallized polygonal aggregates of plagioclase in anorthosite (Figs. 3d and 4g). Existing

petrological and geochronological information suggest that the deformation of anorthosite and

chromitite occurred during Pan-African (0.72-0.50 Ga) tectonothermal events (Bhaskar Rao et al.,

1996; Ghosh et al., 2004). Composition of coronitic green spinel over corundum 1 effectively lies along

the hercynite-pleonaste join (Mg#=45-61, Cr#=3-21) with insignificant Ti and Fe3+. Estimated

temperature of 650 ± 50 °C ( Bhaskar Rao et al., 1996; Srikantappa et al., 2003; Sengupta et al., 2009a,

b) during the Pan-African metamorphism in the area is suitable for coexistence of Al- and Cr-rich

spinels (Sack and Ghiorso, 1991).

4.2. Compositions of the associated phases

In clinopyroxenite and anorthosite, the clinopyroxene is diopside (Mg#=85 to 90, Table 1b).

Clinopyroxene (diopside) in clinopyroxenite is distinctly lower in Al2O3 (<0.56 wt.%) than the

clinopyroxene in anorthosite (0.76 to 6.67 wt.%, Table 1b). This difference in the Al2O3 content of

clinopyroxene possibly mimics the bulk Al2O3 content of rocks in which clinopyroxene grew. Cr2O3

(<0.62 wt.%) and TiO2 (0.03-1.09 wt.%) content of clinopyroxene are low (Table 1b). The CaSiO3

component of diopside ranges between 0.46-0.52 (Table 1b). Individual grains do not show any

significant compositional zoning. Irrespective of the mode of occurrence, plagioclase is almost end-

member anorthite (≥99 mol.%, Table 1c).

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Secondary amphibole shows marked compositional variation depending upon the associated

phases. Amphibole from the thick chromitite and clinopyroxenite is less aluminous (3.9-12.9 wt.%

Al2O3 and 0.65 to 2.15 Al a.p.f.u.) and slightly more magnesian (Mg#=82-91) compared to amphibole

in anorthosite (11.8-14.8 wt.% Al2O3; 2.00 to 2.52 Al a.p.f.u., Mg#=76-85, Table 1d). TiO2, Na2O and

Cr2O3 contents of amphibole varies in different association. TiO2 varies within the range 0.33-1.20 wt.

%; whereas Na2O and Cr2O3 varies in the range of 0.59-2.14 wt.% and 0.04-1.79-wt.%, respectively

(Table 1d). Amphibole in anorthosite has higher TiO2 and Na2O compared to amphibole in

clinopyroxenite and chromitite (Table 1d). According to the amphibole nomenclature of Leake et al.

(1997), the composition ranges from magnesio hornblende to pargasite to tschermakite (Table 1d).

Chlorite is the most magnesian phase in the rock (Mg#>90, Al2O3 ~20-22 wt.% Table 1e). Cr2O3

content of chlorite varies from 1.54 to 3.85 wt.%. The most Cr-rich chlorite grains are at physical

contact with chromite. This mineral contains insignificant TiO2.

Corundum contains 0.33-0.75 wt.% Fe2O3 and 0.05-0.12 wt.% Cr2O3 (Table 1f) whereas clinozoisite

contains ~5 mol.% pistacite molecule (Table 1f). Carbonate is almost pure CaCO3.

5. Physico-chemical conditions during crystallization of chromite in the SLC

5.1. Nature of the parental melt of the chromitite-bearing rocks of Sittampundi

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

In the absence of chilled margin and the presence of high variant chromite-bearing assemblages

estimation of parental melt composition of the SLC is not very straightforward. Nevertheless, certain

mineral-chemical observations made in this study in combination with results of the existing

experimental studies shed some light on the composition of melt from which the chromitite-bearing

rocks of the studied area might have crystallized. This study has demonstrated that highly calcic

plagioclase (>An98), clinopyroxene and Fe-Al rich chromite were the liquidus phases in anorthosite

(clinopyroxene and Fe-Al chromite in case of clinopyroxenite). Compositions of the liquidus phases are

consistent with the view that the melt from which these minerals were formed was rich in Al, Fe and Cr

and poorer in silica, alkalis, Ti and Mg (Rollinson et al., 2010). Composition of chromite has long been

used as a proxy for the composition of the melt that deposited the chromite (Maurel and Maurel, 1982;

Kamenetsky et al., 2001). In the Cr# vs. Mg# plot, the chromites of SLC follow a trend with

progressive Fe and Cr enrichment (Fig. 5a). When the graphical methods of Kamenetsky et al. (2001)

are used, the most primitive compositions of chromite (having the highest Mg#) that represent core

compositions of cumulus chromite not in physical contact with any other Fe-Mg bearing minerals,

suggest that the parental melt contained up to 18 wt.% Al2O3 and low TiO2 (<0.6 wt.%) (Fig. 6)

Integration of small volume proportion of exsolved rutile lamellae with their host chromite composition

would marginally enhance the TiO2 content of the estimated melt composition. It is to be noted that the

most primitive chromite compositions of the SLC are aluminous that evolved to more Fe- and Cr- rich

composition presumably during crystal fractionation. The compositional array of the chromite in the

SLC follows the same trend that is defined by the anorthosite hosted chromites of the Fiskenaesset

complex of Greenland (Rollinson et al., 2010). REE pattern of the anorthosite and mafic granulites of

the SLC (Bhaskar Rao et al., 1996) and Fiskenaesset complex (Polat et al., 2009) are similar. In view of

similarity in terms of chromite chemistry and the REE pattern of enclosing mafic rocks and anorthosite

between the SLC and Fiskenaesset complex, it is presumed that both the complexes share a similar

petrogenetic history. This involved early fractionation of magnesian phases (olivine, orthopyroxene)

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

from a tholeiitic parental magma that depleted the residual liquid in Mg and silica and enriched in Ca,

Cr, Al and Fe The evolved composition of the melt then triggered the precipitation of Fe-Al rich

chromite and highly calcic plagioclase (Polat et al., 2009; Rollinson et al., 2010). Presence of dunite,

wehlite and harzburzite xenoliths in younger felsic magma (protoliths of enderbite) further corroborates

this view.

5.2. Depth and crystallization history of chromitite in the SLC: significance of highly calcic

plagioclase

Lack of contact aureole and the presence of high variant primary mineral assemblage make

estimation of the depth of emplacement of chromitite seams difficult. Nevertheless, intimate

association of BIF with the mafic rocks suggests that SLC were emplaced at a relatively shallow depth.

Further insight about the depth of emplacement of the magmatic rocks can be achieved from the

stability of highly calcic plagioclase (>An98) in the anorthosite of the SLC.

Experimental studies have demonstrated that the KD Ca-Na (plag-melt) increase abruptly with a small

increase in H2O in the basaltic melt (Sisson and Grove, 1993; Berndt et al., 2005; Takagi et al., 2005;

Feig et al., 2006). Total pressure was shown to have little or no effect on this distribution coefficient

(Sisson and Grove, 1993). In view of these factors, the parental melts of the chromite-bearing

clinopyroxenite and anorthosite of the SLC are presumed to be hydrous. The highly calcic plagioclase

(>An90) that are reported by Takagi et al. (2005) and Arculus and Wills (1980) from hydrous arc basalts

justify our presumption. Recent experimental data of Feig et al. (2006) demonstrate the influence of

H2O on the crystallization sequence of a tholeiitic melt, a likely analogue of the parental melt of the

SLC. The phase diagrams of Feig et al. (2006) are shown in figure 7a-d. It is evident from Fig. 7a-b

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

that clinopyroxene can crystallize before plagioclase at low pressure (≤2 kbar) if the melt has more than

3 wt.% H2O. For water saturated melt, clinopyroxene touches liquidus before plagioclase at pressure

close to only 1 kbar (Fig.7d). Enlargement of the stability field of clinopyroxene at higher H2O content

was also documented by Hamada and Fujii (2008). Olivine always crystallizes before clinopyroxene

irrespective of the H2O content of the melt at least up to 5 kbar (Fig. 7a-c). At ≥2 kbar, field of

orthopyroxene expands so much that this mineral will be a liquidus phase at all temperatures above

1100 °C (Fig. 7c). The absence of orthopyroxene in the anorthosite and chromitite-bearing pyroxenite

in the SLC, therefore, seems to be consistent with the fact that the parental magma(s) of the SLC was

emplaced at shallow depth (<2 kbar, corresponding to a maximum depth of ca. 6 km). Figures 7a-c also

demonstrate that amphibole does not appear as a liquidus phase unless H2O content of the melt exceeds

2 wt.% and temperature of crystallization is below 1000 °C. This then follows that hydrous basaltic

melt will crystallize amphibole if the crystallization temperature drops below 1000 oC. Textural

features in the chromitite-bearing rocks of the SLC indicate that amphiboles replaced clinopyroxene.

This evidence, however, does not completely rule out the possibility of crystallization of magmatic

amphibole in SLC. However, in the absence of any clue in support of magmatic amphibole, it is

presumed that higher crystallization temperature (>1000 oC) rather than H2O-undersaturation of the

parental melt was instrumental for non appearance of magmatic amphibole in the SLC.

On the basis of the foregoing analyses a generalized crystallizing sequence can be developed for the

SLC. A parental melt having the composition of hydrous tholeiitic magma crystallized combination of

dunite, wehrlite and hurzburgite. These early-crystallized rocks plausibly lie beneath the exposed level

and was sampled by the intruding felsic magma. Continued crystallization of the evolved melt

produced an alternate sequence of clinopyroxene- and chromite-rich layers at pressure <2 kbar. Since,

Mg is preferentially partitioned to clinopyroxene than the coexisting melt, crystallization of large

volumes of clinopyroxene (to form clinopyroxenite) would enrich the parental melt with Cr, Fe and Al

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

which then triggered the crystallization of Fe-Al-rich chromite to form thick to thin chromite seams in

clinopyroxenite. Crystallization of Fe-Al-rich chromite, in turn, enriched the magma in Mg and paved

the way for crystallization of clinopyroxene. Continuation of this process can explain formation of

several layers of chromitite in clinopyroxenite. This process eventually enriched the residual melt with

Ca, Al and H2O from which anorthosite with highly calcic plagioclase was crystallized. Crystallization

of large volume of calcic plagioclase increased Cr concentration of the melt, which when reached a

critical value, deposited thin chromite seams in anorthosite. High PH2O of the evolved melt could also

help crystallization of chromite in the anorthosite (Matveev and Ballhaus, 2002). Temperatures during

the entire crystallization sequence were above 1000 °C in order to suppress crystallization of magmatic

amphibole.

6. Discussion

6.1. Tectonic setting of the SLC

The tectonic setting in which Archaean layered anorthosite with highly calcic plagioclase and Fe-Al

rich chromite have been studied in great detail for the occurrences of Greenland (Weaver et al., 1981;

Ashwal, 1993; Dymek and Owens, 2001; Polat et al., 2009; Rollinson et al., 2010). Although the

compositions of plagioclase and chromite are remarkably similar between the Fiskenaesset Complex of

Greenland and the SLC, absence of quality geochemical and isotopic data is the main impediment for

precise delineation of the tectonic setting in which the SLC was emplaced. Nevertheless a number of

features suggest that the SLC represents fragments of oceanic crust. These are:

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

1. The rock ensemble of the SLC is enclosed by mafic-ultramafic rocks (now mafic granulites

with or without garnet). BIF constitutes the only sedimentary rocks in the complex. The

voluminous felsic rocks (enderbite) that occurs in wider areas are intrusive into the SLC and

their enclosing mafic-ultramafic rocks.

2. The pseudomagmatic stratigraphy developed for the SLC and its temporally equivalent BLC

(Fig. 2b) matches well with the ultramafic-mafic-chert/BIF association of many well-studied

ophiolites of Phanerozoic (Kusky et al., 2001) and Precambrian (Harper, 1984, 1986; Kusky et

al., 2001; Slabunov et al., 2003; Dilek and Polat, 2008) ages.

These observations corroborate the view that Archaean high-grade complexes with layered

anorthosite are remnants of the oceanic crust (Weaver et al., 1981; Polat et al., 2009). Presence of

highly calcic plagioclase in anorthosite indicates that the melts that deposited plagioclase and Fe-Al

rich chromites in the SLC were hydrous in nature. A number of studies have indicated that hydrous

basaltic magmas are generated in arc setting from Archaen to present day where these magmas

precipitate highly calcic plagioclase (>An90, Arculus and Wills, 1980; Takagi et al., 2005; Polat et al.,

2009). Furthermore, some primitive arc basalts also have chromites with low Mg# (<0.6) and low Cr#

(0.4-0.6), which overlaps with the compositions of chromites from SLC and Fiskenaesset Complex

Greenland (Grove et al., 2003; Righter et al., 2008; Rollinson et al., 2010).

On the basis of REE patterns and Nd-Sm isotope compositions, Bhaskar Rao et al. (1996) opined

that the mafic rocks and the chromitite-bearing rocks of the SLC are genetically linked. To put some

additional constraints on the tectonic setting, bulk compositions of some mafic rocks from SLC and the

adjoining BLC were analyzed with XRF (Table 2). Figure 8 shows some tectonic discriminant plots

that separate basalts from spreading centers (MORB), Island Arc (IAB) and within plate continental

flood basalts (WPB). In these diagrams, most compositions of basic rocks are plotted in the field of

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

IAB with a data straddle the boundary between MORB and IAB (Fig. 8). Mafic rocks of the

Fiskenaesset Complex also show similar trend although more rigorous geochemical analyses were done

in this complex. The compositional plots of Fig. 8, together with the inferred high PH2O of the parental

liquids are consistent with parental liquid of the SLC being derived from Neoarchaean (c.2.9 Ga) upper

mantle that was metasomatized by subduction-derived components during formation of oceanic arc

system (Polat et al., 2009). However, compared to the compositions of chromites that are formed in

modern arc basalts, chromites from the Neoarchaean layered magmatic complexes of Fiskenaesset and

Sittampundi are distinctly aluminous at similar Mg# (Fig. 5a). This difference has been attributed to the

fact that Neoarchaean mantle wedge that occurred above the subducting oceanic plate was more

aluminous owing to percolation of Al-rich melt derived from melting of subducting oceanic crust (Polat

et al., 2009; Rollinson et al., 2010).

In summary, mineralogy of the chromitite-bearing rocks together with geochemical signatures of the

enclosing mafic rocks support the view that the magmatic rocks of the SLC were emplaced in an arc

setting and the rock ensemble presumably represents a fossil suprasubduction zone in Neoarchaean

time (Dielek and Polat 2008). Excluding ultramafic rocks of upper mantle affinity, the rock ensembles

of SLC and BLC and their reconstructed stratigraphy bear remarkable similarity with several ophiolite

complexes of of Archaean age (Harper, 1984, 1986; Kusky et al., 2001; Slabunov et al., 2003; Dilek

and Polat, 2008). The absence of upper mantle rocks in the SLC and BLC may be attributed either to a

lack of exposure of the lowermost parts of the magmatic sequence or to detachment at crustal level

rather than within the mantle, during emplacement (Harper, 1984, 1986). Absence of mantle xenoliths

in the younger felsic intrusive rocks (protoliths of felsic granulites) tends to support the second option.

A high thermal gradient in the oceanic lithosphere and/or a thicker oceanic crust in the Archaean time

may help decoupling of oceanic crust from its mantle root (Harper, 1984, 1986). Detailed geological,

geochemical and isotopic studies on the fragments of the Archaean layered magmatic complexes of the

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

CSS will help unravel the enigmatic crust-mantle interactions and tectonic patterns during the early part

of the Earth’s history.

6.2. Comparison between the chromite deposits in the SLC and other layered complexes in Archaean

high-grade terrains

Archaean high-grade terrains expose polydeformed and polymetamorphosed middle to lower

continental crust (Windley et al., 1981; Ashwal, 1993; Harley et al., 1998). Only a few of these

Archaean terrains contain chromite-bearing mafic-ultramafic-anorthosite complexes (Windley et al.,

1981; Hatton and von Gruenewaldt, 1990; Ashwal, 1993; Harley et al., 1998; Rollinson et al., 2002;

Rollinson, 2008). Although superposed deformation and high-grade metamorphism obliterated, to a

great extent, the original magmatic stratigraphy and mineralogy of the chromite-bearing rocks, detail

studies on the layered magmatic complexes of Messina, S. Africa (Hor et al., 1975; Barton et al., 1979)

and Fiskenaesset, Greenland (Windley et al., 1981; Ashwal, 1993; Peck and Valley, 1996; Rollinson,

2008; Polat et al., 2009; Rollinson et al., 2010) provide a wealth of information about the magmatic

history and metamorphic reconstitution of the rocks of these complexes. In the following sections we

present similarity and contrast in terms of salient geological features among the three chromitite-

anorthosite occurrences (Fiskenaesset, Messina and the SLC) that are hosted in the Archaean high-

grade terrines.

Similar to the layered complexes of Fiskenaesset and Messina, the SLC shows a lower ultramafic

unit, which grades upward to leucogabbro to anorthosite to mafic rocks (Fig. 2b). Olivine-rich rocks

(dunite/harzburgite) that form the lower part of the magmatic sequences of Fiskenaesset complex and

Messina complex are also observed in BLC and their presence is inferred from the xenoliths in the

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

younger felsic intrusive in the SLC. In all the four complexes, anorthosite and the co-genetic

pyroxenite are interlayered with chromitite seams and underwent polyphase deformation and upper

amphibolite to granulite-facies metamorphism (Windley and Smith, 1976; Windley et al., 1981;

Ashwal, 1993; Windley and Garde, 2009; Rollinson et al., 2010). In Fiskenaesset Complex and SLC,

anorthosite and chromite-bearing rocks are enclosed by mafic rocks of ocean floor affinity and were

subsequently intruded by voluminous felsic rocks of TTG affinity. Emplacement of Messina complex

within a sequence BIF, quartzite and pelite supports its continental affinity (Windley et al., 1981).

Highly calcic plagioclase (XAn>0.8) and Fe-Al-rich chromitite are the unique features of the

magmatic complexes of Messina, Fiskenaesset and SLC (Windley et al., 1981; this study).

Tschermakitic amphibole, which is considered as “primary’ magmatic mineral in the Fiskenaesset

complex (Rollinson et al., 2010), has metamorphic origin in the SLC.

Figure 5a shows that chromite compositions from Neoarchaen layered complexes of Fiskenaesset

and Sittampundi define an array showing decreasing Mg# and increasing Cr#. This array of chromite

compositions contrasts with the compositions of chromite from other occurrences that show distinctly

higher Cr# and Mg# than the layered anorthosite hosted chromitite (Fig. 5a).

Detail petrological, geochemical and stable isotopic data show that layered anorthosite of

Fiskenaesset Complex, Greenland was emplaced at or close to the oceanic surface (Weaver et al., 1981;

Windley et al., 1981; Peck and Valley, 1996; Rollinson et al., 2010). Shallow level intrusion

presumably in a stable shelf region is also considered for Messina complex from their intercalated

rocks (Windley et al., 1981). Geological features of SLC indicate that like the other two Neoarchaean

magmatic complexes, SLC were also emplaced at or close to the sea surface.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

In summary, chromite-bearing rocks of Achaean high-grade terrains share a number of geological

features that contrast sharply with their younger counterparts. Anorthosite with highly calcic

plagioclase and chromite with Fe-Al rich compositions that are key to the features of Neoarchaean

anorthosite hosted chromitite deposits are attributed to hydrous and aluminous nature of the parental

melt compositions from which these magmatic complexes were formed. Dwindling of these hydrous

magmas in the post Archaean may be related to a number of factors such as desiccation of mantle

through repeated discharge of hydrous magmas during the Archaean, dominance of slab dehydration in

place of slab melting at reduced geothermal gradient in the post Archaean time and melting of mantle

wedge in place of slab melting during post Archaean era (Rollinson, 2007; Rollinson et al., 2010).

Acknowledgements

We are thankful to the Department of Science and Technology (DST), New Delhi, India, DAAD-DST PPP

and CAS, Department of Geological Sciences, Jadavpur for financial assistance. Most of the analyses were done

during the stay of P.S., U.K.B. and U.D.in the Mineralogisch-Petrologisch Institute, Bonn as a part of the DST-

DAAD PPP programme. We are indebted to Professor M.M. and Prof. C. Ballhaus, Directors, Mineralogisch

Petrologisches Institut, Bonn, Germany, for extending the analytical facilities of the institute. D.M.

acknowledges support from Senior Scientist Project from the Indian National Science Academy. The final draft

of this manuscript was prepared when P.S. was visiting the Mineralogy and Geology Department of University

of Cologne, Germany as a AvH Fellow. P.S. thanks Prof. C. Muenker and Prof. R. Kleinschrodt of Mineralogy

and Geology Department, University of Cologne for many stimulating discussions. We thank Profs. H.

Rollinson and P. Page for their critical but extremely useful comments on an earlier draft of the manuscript. This

manuscript is greatly benefitted from the erudite comments from the journal reviewers Prof. H. Rollinson, Prof.

B.F. Windley, Prof. G. Grieco and Associate Editor Prof. S. Rowins. We thank Prof. N.J. Cook for through

editorial corrections and additional comments that improved the clarity of the manuscript.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

References:

Anbarasu, K. , Dar,A.M., A. Karthikeyan,A.,2011. Geochemistry and petrographyof pyroxenites from

Mettupalayam ultramafic Complex, Tamil Nadu. Recent Research in Science and Technology 3(4): 66-70.

Appel, C.C., Appel, P.W.U., Rollinson, H.R., 2002. Complex chromite textures unravel the history of an early

Archaean layered ultramafic body in west Greenland. Mineralogical Magazine 66, 1029-1041.

Arculus, R.J., Wills, K.J.A., 1980. The petrology of plutonic blocks and inclusions from the Irsser Antilles island

arc. Journal of Petrology 21, 743-799.

Ashwal, L.D., 1993. Anorthosites. Springer, Berlin, 422 pp.

Barton, J.M. Jr., Fripp, R.E.P., Horrocks, P.C., McLean, N., 1979. The geology, age, and tectonic setting of the

Messina Layered Intrusion, Limpopo Mobile Belt, southern Africa. American Journal of Science 279, 1108–

1134.

Beeson, M.H., Jackson, E.D., 1969. Chemical composition of altered chromites from the Stillwater complex,

Montana. American Mineralogist 54, 1084-1100.

Berndt, J., Koepke, J., Holtz, F., 2005. An experimental investigation of the influence of water and oxygen

fugacity on differentiation of MORB at 200 MPa. Journal of Petrology 46, 135-167.

Bhaskar Rao, Y.J., Chetty, T.R.K., Janardhan, A.S., Gopalan, K., 1996. Sm-Nd and Rb-Sr ages and P-T history

of the Archaean Sitampundi and Bhavani layered meta-anorthosite complexes in Cauvery Shear Zone, South

India: evidence for Late Proterozoic reworking of Archaean crust. Contributions to Mineralogy and Petrology

125, 237–250.

Bhaskar Rao, Y.J., Janardhan, A.S., Vijaya Kumar, T., Narayan, B.L., Dayal, A. M., Taylor, P.N., Chetty,

T.R.K., 2003. Sm-Nd model ages and Rb-Sr isotopic systematics of charnockites and gneisses across the

Cauvery Shear zones, Southern India: implications for the Archaean-Neoproterozoic terrane boundary in the

Southern Granulite terrane. In: Ramakrishna, M. (Ed.), Tectonics of Southern Granulite terrain. Geological

Society of India Memoir 50, p. 297–317.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Braun, I., Kriegsman, L.M., 2003. Proterozoic crustal evolution of southernmost India and Sri Lanka In:

Yoshida, M., Windley, B.F., Dasgupta, S. (Eds.), Proterozoic East Gondwana: Supercontinent Assembly and

Breakup. Geological Society of London Special Publication 206, p. 169–202.

Chetty, T.R.K., 1996. Proterozoic shear zones in southern granulite terrain, India. In: Santosh, M, Yoshida, M

(Eds.), The Archaean and Proterozoic terrains in Southern India within east Gondwana, Gondwana Research

Group Memoir 3, p. 77-89.

Chetty, T.R.K., Bhaskar Rao, Y.J., Narayana, B.L., 2003. A structural cross section along Krishnagiri-Palani

corridor, Southern Granulite terrain of India. In: Ramakrishna, M. (Ed.), Tectonics of Southern Granulite

terrain. Geological Society of India Memoir 50, p. 225–253.

Dilek, Y., Polat, A., 2008. Suprasubduction zone ophiolites and Archaean tectonics. Geology 36, 431-432.

Dymek, R.F., Owens, B.R., 2001. Chemical assembly of Archean anorthosites from amphibolite- and granulite-

facies terrains, SW Greenland. Contributions to Mineralogy and Petrology 141, 513–528.

Feig, S.T., Koepke, J., Snow, J.E., 2006. Effect of water on tholeiitic basalt phase equilibria: an experimental

study under oxidizing conditions. Contributions to Mineralogy and Petrology 152, 611–638.

Geological quadrangle map of Tamil Nadu. 1995. Geological Survey of India, Kolkata.

Ghosh, J.G., De Wit, M.J., Zartman, R.E., 2004. Age and tectonic evolution of Neoproterozoic ductile shear

zones in the southern granulite terrain of India with implications for Gondwana studies. Tectonics 23, 1-38.

Grove, T. L., Elkins-Tanton, L. T., Parman, S. W., Chatterjee, N., Muntener, O., Gaetani, G. A., 2003. Fractional

crystallization and mantle-melting controls on calcalkaline differentiation trends. Contributions to Mineralogy

and Petrology 145, 515–533.

Hamada, M., Fujii, T., 2008. Experimental constraints on the effects of pressure and H2O on the fractional

crystallization of high-Mg island arc basalt. Contributions to Mineralogy and Petrology 155, 767-790.

Harley, S.L., Snape, I., Black, L.P., 1998. The evolution of a layered meta-igneous complex in the Rauer Group,

East Antarctica: evidence for a distinct Archaean terrane. Precambrian Research 89, 175-205.

Harper, G.D., 1984. The Josephine Ophiolite, northwestern California. Geological Society of America Bulletin

95, 1009-1026.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Harper, G.D., 1986. Dismembered Archaean ophiolite in the southeastern Wind River Mountains, Wyoming:

Remains of Archaean oceanic crust. In: Lunar and Planetary Institute, Workshop on the Tectonic Evolution of

Greenstone Belts, 47-49 (SEE N86-23089 13-46).

Hatton, C.J. von Gruenewaldt, G., 1990. Early Precambrian layered intrusions. In: Hall, R.P., Hughes, D.J.

(Eds.), Early Precambrian Basic Magmatism. Blackie, London, p. 56-81.

Hor, A.K., Hutt, D.K., Smith, J.V., Wakefield, J., Windley, B.F., 1975. Petrochemistry and mineralogy of early

Precambrian anorthositic rocks of the Limpopo Belt, southern Africa. Lithos 8, 297-310.

Irvine, T.N., 1965. Chromian spinel as a petrogenetic indicator. Part 1. Theory. Canadian Journal of Earth

Sciences 2, 648-672.

Irvine, T.N., 1967. Chromian spinel as a petrogenetic indicator. Part 2. Petrologic implications. Canadian Journal

of Earth Sciences 4, 71-103.

Janardhanan, A.S., Leake, B.E., 1975. The origin of the meta-anorthositic gabbros and garnetiferous granulites

of the Sittampundi Complex, Madras, India. Journal of Geological Society of India 16, 391-408.

John, M.M., Balakrishnan, S., Bhadra, B.K., 2005. Contrasting metamorphism across Cauvery shear zone, south

India. Journal of Earth System Science 114, 143-158.

Kamenetsky, V.S., Crawford, A.J., Meffre, S., 2001. Factors controlling chemistry of magmatic spinel: an

empirical study of associated olivine, Cr-spinel and melt inclusions from primitive rocks. Journal of Petrology

42, 655-671.

Kimball, K.L., 1990. Effects of hydrothermal alteration on the compositions of chromian spinels. Contributions

to Mineralogy and Petrology 105, 337-346.

Kretz, R., 1983. Symbols for rock-forming minerals. American Mineralogist 68, 277–279.

Kusky, T.M., Li, J.H., Tucker, R.D., 2001. The Archaean Dongwanzi Ophiolite Complex, North China Craton:

2.505-Billion-Year-Old Oceanic Crust and Mantle. Science 292, 1142-1145.

Leake, B.E. and 21 co-authors, 1997. Nomenclature of amphiboles: Report of the subcommittee on amphiboles

of the International Mineralogical Association, Commission on new minerals and mineral names. American

Mineralogist 82, 1019-1037.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Matveev, S., Ballhaus, C., 2002. Role of water in the origin of podiform chromite deposits. Earth and Planetary

Science Letters 203, 235-243.

Maurel, C., Maurel, P., 1982. Etude experimentale de la distribution del’aluminium entre bain silicate basique et

spinelle chromifere. Implications petrogenetiques: teneur en chrome des spinelles. Bulletin de Minéralogie

105, 197-202.

Mondal, S.K., Ripley, E.M., Li, C., Frei, R. (2006): The genesis of Archaean chromitites from the

Nuasahi and Sukinda massifs in the Singhbhum craton, India. Precambrian Research 148, 45-66

Murck, B.W., Campbell, I.H., 1986. The effects of temperature, oxygen fugacity and melt composition on the

behavior of chromium in basic and ultrabasic melts. Geochimica et Cosmochimica Acta 50, 1871–1887.

Meissner, B., Deters, P., Srikantappa, C., Kohler, H., 2002. Geological evolution of the Moyer, Bhavani and

Palghat shear zones of southern India: implications for Gondwana correlation. Precambrian Research 114,

149-175.

Mitra, S., Samanta, A.K., 1996. Rutile exsolution in Fe3+-chromites: A case study from layered granulitic

complex of Sittampundi, S. India. Journal of Geological Society of India 47, 75-82.

Mukhopadhyay, D., Senthil Kumar, P., Srinivasan, R., Bhattacharya, T., 2003. Nature of Palghat-Cauvery

lineament in the region south of Namakkal, Tamil Nadu: Implication for terrane assembly in the South Indian

granulite province In: Ramakrishna, M. (Ed.) Tectonics of Southern Granulite terrain. Geological Society of

India Memoir 50, p. 279–296.

Pearce, J., 1982. Trace element characteristics of lavas from destructive plate boundaries. In: Thorpe, R.S. (Ed.),

Andesites. Wiley, New York, p. 525-548.

Pearce, J.A., Norry, M.J., 1979. Petrogenetic implications of Ti, Zr. Y, and Nb variations in volcanic rocks.

Contributions to Mineralogy and Petrology 69, 33-47.

Peck, W.H., Valley W.J., 1996. The Fiskenaesset Anorthosite Complex: Stable isotope evidence for shallow

emplacement into Archean ocean crust. Geology 24, 523-526.

Polat, A., Appel, P.W.U., Fryer, B., Windley, B., Frei, R., Samson, I.M., Huang, H., 2009. Trace element

systematics of the Neoarchean Fiskenæsset anorthosite complex and associated meta-volcanic rocks, SW

Greenland: Evidence for a magmatic arc origin. Precambrian Research 175, 87-115.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Pouchou, J.L., Pichoir, F., 1984. A new model for quantitative X-ray microanalysis, Part I: Application to the

analysis of homogeneous samples. La Recherche Aerospatiale 3, 162–192.

Prame, W.K.B.N., 1997. Geochemistry and genesis of granitoid rocks from Southern Sri Lanka. Mineralogy and

Petrology 60, 245-265.

Raith, M., Srikantappa, C., Köhler, H., Buhl, D., 1999. The Nilgiri enderbites: nature and age constraints on

protolith formation, high-grade metamorphism and cooling history. Precambrian Research 98, 129-150.

Raith, M.M., Srikantappa, C., 2008. Corundum–leucosome-bearing aluminous gneiss from Ayyarmalai,

Southern Granulite Terrain, India: a textbook example of vapour phase-absent muscovite melting in silica-

undersaturated pelitic rocks, 86th Annual meeting of DMG, p. 14–17.

Raith, M.M., Srikantappa, C., Sengupta, P., Kooijman, E., Upadhyay D., 2010. Corundum–leucosome-bearing

aluminous gneiss from Ayyarmalai, Southern Granulite Terrain, India: A textbook example of vapor phase-

absent muscovite-melting in silica-undersaturated aluminous rocks. American Mineralogist 95, 897–907.

Ramadurai, S., Sankaran, M., Selvan, T.A., Windley, B.F., 1975. The stratigraphy and structure of the

Sittampundi complex, Tamil Nadu, India. Journal of Geological Society of India 16, 409–414.

Righter, K., Chesley, J.T., Caiazza, C.M., Gibson, E.K., Jr., Ruiz, J., 2008. Re and Os concentrations in arc

basalts: the roles of volatility and source region fO2 variations. Geochimica et Cosmochimica Acta 72, 926–

947.

Rollinson, H. R., 1995. Composition and tectonic settings of chromite deposits through time – a discussion.

Economic Geology 90, 2091-2092.

Rollinson, H., 2007. Early Earth system: a geochemical approach. Blackwell Publishing, 285 pp.

Rollinson, H., 2008. The geochemistry of mantle chromitites from the northern part of the Oman ophiolite –

inferred parental melt compositions. Contributions to Mineralogy and Petrology 156, 273-288.

Rollinson, H.R., Appel, P.W.U., Frei, R., 2002. A metamorphosed, early Archaean chromitite from west

Greenland: Implications for the genesis of Archaean anorthositic chromitites. Journal of Petrology 43, 2143–

2170.

Rollinson, H., Reid, C., Windley, B., 2010. Chromitites from the Fiskenæsset anorthositic complex, West

Greenland: clues to late Archaean mantle processes. In: Kusky, T.M., Zhai, M.-G., Xiao, W. (Eds.), The

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Evolving Continents: Understanding Processes of Continental Growth. Geological Society, London, Special

Publication 338, p. 197–212.

Sack, R.O., Ghiorso, M.S. 1991. Chromite as a petrogenetic indicator, in, Lindsley DH ed., Oxide

Minerals: Petrologic and Magnetic Significance, Mineralogical Society of America Reviews in

Mineralogy 25, 323-353.

Sajeev, K., Windley, B.F., Connolly, J.A.D., Kon, Y., 2009. Retrogressed eclogite (20 kbar, 1020°C). from the

Neoproterozoic Palghat-Cauvery suture zone, southern India. Precambrian Research 171, 23-36.

Sengupta, P., Dutta, U., Bhui, U., Mukhopadhyay, D., 2009a. Genesis of wollastonite- and grandite-rich skarns

in a suite of marble-calc-silicate rocks from Sittampundi, Tamil Nadu: constraints on the P–T–fluid regime in

parts of the Pan-African mobile belt of South India. Mineralogy and Petrology 95, 179-200.

Sengupta, P., Bhui, U.K., Braun, I., Dutta, U., Mukhopadhyay, D., 2009b. Chemical substitutions and

paragenetic relations of högbomite in Sittampundi layered anorthosite complex, south India and their

implications. American Mineralogist 94, 1520-1534.

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

Science Letters 59, 101-l18.

Shimpo, M., Tsunogae, T., Santosh, M., 2006. First report of garnet-corundum rocks from southern India:

Implications for prograde high-pressure (eclogite-facies?) metamorphism. Earth and Planetary Science

Letters 242, 111-129.

Sisson, T.W., Grove, T.L., 1993. Temperature and H2O contents of low-MgO high-alumina basalts.

Contributions to Mineralogy and Petrology 113, 167-184.

Slabunov, A.I., Volodichev, O.I., Bibikova, E.V., Shchipansky, A.A., Stepanov, V.S., Konilov, A.N., 2003.

Archaean ophiolotic Sequences and eclogites of the Baltic/Fennoscandian shield. Geophysical Research

Abstracts 5, 01072.

Srikantappa, C., Srinivas, G., Basavarajappa, H.T., Prakash Narasimha, K.N., asavalingu, B., 2003.

Metamorphic evolution and fluid regime in the deep continental crust along the N-S Geotransect from Vellar

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

to Dharapuram, Southern India. In: Ramakrishna, M. (Ed.), Tectonics of Southern Granulite terrain.

Geological Society of India Memoir 50, p. 319-373.

Stowe, C.W., 1994. Compositions and tectonic settings of chromite deposits through time. Economic Geology

89, 528-546.

Subramanium, A.P., 1956. Mineralogy and petrology of the Sittampundi complex, Salem district, Madras State,

India. Geological Society of America Bulletin 67, 317-390.

Takagi, D., Sato, H., Nakagaoa, M., 2005. Experimental study of low alkali tholeiite at 1-5 kbar: optimal

condition for the crystallization of high-An plagioclase in hydrous arc tholeiite. Contributions to Mineralogy

and Petrology 149, 527–540.

Weaver, B.L., Tarney, J., Windley, B., 1981. Geochemistry and petrogenesis of the Fiskenæsset anorthosite

complex, southern West Greenland: nature of the parent magma. Geochimica et Cosmochimica Acta 45,

771–725.

Windley, B.F., Garde, A.A., 2009. Arc-generated blocks with crustal sections in the North Atlantic craton of

West Greenland: Crustal growth in the Archean with modern analogues. Earth-Science Reviews 93, 1–30.

Windley, B.F., Smith, J.V., 1974. The Fiskenæsset Complex, West Greenland, part 2 General mineral chemistry

from Qeqertarssuatsiaq. Grønlands Geologiske Undersøgelse Bulletin 108, 54.

Windley, B.F., Bishop, F.C., Smith, J.V., 1981. Metamorphosed layered igneous complexes in Archaean

granulite-gneiss belts. Annual Review of Earth and Planetary Sciences 9, 175–198.

Figure captions

Fig. 1. Generalized geological map of Cauvery Shear System (CSS) modified after the geological quadrangle

map of Tamil Nadu (Geological Survey of India, 1995). Different shear zones in CSS and adjoining areas are

shown in the inset. DC: Granite-greenstone belt of Dharwar Craton, FL: Fermore line separating DC from the

South Indian granulite terrane, NGT: Northern Granulite Terrane, CSS: Cauvery Shear System (Chetty,

1996), MSZ: Moyar shear zone, BSZ: Bhavani shear zone, MBASZ: Moyar-Bhavani Attur shear zone,

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

PCSZ: Palghat-Cauvery shear zone, MB: Madurai Block, KKPTSZ, Karur-Kumbum-Panivu-Trichur shear

zone (Ghosh et al., 2004), ACSZ: Achankovil shear zone, KKB: Kerala khondalite belt, BLC: Bhavani

layered complex, SLC: Sittampundi layered complex.

Fig. 2. (a) Detailed lithological map of the studied area showing the sample locations. (b) Schematic

stratigraphic sections of the layered complexes of (i) Bhavani (BLC) and (ii) Sittampundi (SLC). Mafic rocks

now represented by mafic granulites with or without garnet. These granulites are partly altered to

amphibolites. Thickness of units is not to scale. See text for detail.

Fig. 3. Field photos showing lithological relationships among different rock units in and around the SLC. (a)

Alternation of thin layers rich in magnetite and silica in the Banded Iron Formation (BIF). (b) Sharp contact

between BIF and the enclosing garnetiferous mafic granulites (GMG). Note the tight folding of magnetite-

rich layers within BIF. (c) Dunite xenolith within felsic (enderbitic) gneiss. Note the swerving of foliation of

the host gneiss around the dunite xenolith. (d) Corundum (ruby) with coronitic green spinel in anorthite-rich

layers close to chromitite layer. Note the occurrence of thin green spinel-rich veins in chromitite at high angle

to the compositional layers. (e) Alternate layering of clinopyroxenite and chromitite. (f) Deformed chromitite

layers within anorthosite. Note the pinch and swell structure and boudinage in viscous chromitite layer. (g)

Folds defined by alternate layers of anorthosite and chromite-bearing pyroxenite/chromitite.

Fig. 4. Photomicrographs showing textural relationship among minerals within chromitite, clinopyroxenite and

anorthosite. (a) Cumulus chromite (Chr) with interstitial amphibole (Hbl) and chlorite (Chl). Note the

presence of rutile (Rt) along the grain boundary of chromite. Thick chromitite layer in clinopyroxenite. BSE

image. (b) Cumulus chromite (Chr) with fine exsolved lamellae of rutile (Rt). Thick chromitite layer in

clinopyroxenite. BSE image. (c) Cumulus clinopyroxene (Cpx) grains partially altered to amphibole (Hbl)

along the grain boundary. Chromite-bearing clinopyroxenite.Length of the photo 1.72 mm. polarized light (d)

Chlorite (Chl) grains replace cumulus chromite (Chr) and retrograde amphibole (Hbl) in anorthosite. BSE

image. (e) Recrystalized and polygonal aggregates consisting of plagioclase (Pl) and clinopyroxene (Cpx)

grains. Anorthosite. Length of the photo = 1.72 mm. crossed polars. (f) Chromite (Chr) inclusion within

clinopyroxene (Cpx) in anorthosite. Note the development of clinozoisite (Czo) over clinopyroxene and

plagioclase grain. Length of the photo = 1.72 mm. crossed polars. (g) Green spinel (Spl) rims coarse

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

corundum (Crn 1) against plagioclase (Pl). The green spinel (Spl) breaks down to aggregates of granular

corundum (Crn 2), magnetite (Mag, highly reflecting) and chlorite (Chl). BSE image. (h) Vein of green spinel

(Spl) in chromitite at high angle to the compositional layering (see Fig. 3d). Note the relics of chromite (dark)

within green spinel (Spl). Length of the photo = 1.72 mm. polarized light (i) Irregular veins of green spinel

(shades of gray) replacing chromite (bright). Reflectivity increases with Cr2O3 content of spinel. Also note the

plagioclase (Pl) in the interstitial space. Anorthosite. BSE image. Abbreviations after Kretz (1983).

Fig. 5a. Comparison of chromite compositions of the studied area (symbols) with the compositions of chromite

from other Archaean and younger deposits. 1 = Picrites, 2 = Komatiites, 3 = MORB (Rollinson et al., 2002);

4 = Layered complexes (Windley et al., 1981); 5-6= Chromite in Archaean chromitite associated with

ultramafic rocks. Nuasahi and Sukinda massifs, Singhbhum, India (Mondal et al., 2006); Arrows with “M”

and “R” indicate the magmatic crystallization trends of the magmatic crystallization and replacement of

chromite from Ujaragssuit nunat area, west Greenland (Rollinson et al., 2002). Compositional spread of

‘magmatic’ and metasomatically altered chromite from the studied area. ● = chromite from thick chromitite

in clinopyroxenite, ■ = chromite from thin chromitite in anorthosite, ○ = Disseminated chromite within

anorthosite, ∆ = small chromite grains included in clinopyroxene, anorthosite, ▲ = compositional variation

of chromite due to replacement by green spinel. Light and deep shaded regions represent cluster of chromite

compositions (core) from Fiskenaesset Complex, Greenlan and the chromite compositions (core) from the

modern arc basalts respectively (Rollinson et al., 2010). Note that the composition of cumulus chromite from

the SLC and Greenland show similar magmatic differentiation trend. See text.

Fig. 5b. Variation of Cr#(Cr/Cr+Al), Mg# (Mg/Mg+Fe2+) and Fe3+# (Fe3+ + Al+Cr) from rim to core of a

cumulus chromite in a thick chromitite layer in clinopyroxenite. Note that barring first few microns on the

rim, the composition of chromite remain virtually constant (see text).

Fig. 6 (a)-(b). Al2O3 and TiO2 contents of parental melt calculated from the chromite compositions of the studied

area following the procedure of Kamenetsky et al. (2001). The solid lines represent the best fit lines through

all the data of Kamenetsky et al. (2001). Symbols are same as in figure 5.

Fig. 7 (a)–(d). Experimentally determined stability field of some magmatic minerals in hydrous basaltic melts

(after Feig et al., 2006). Note the enlargement of the stability field of clinopyroxene (Cpx) with increasing

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

H2O content of the melt. Filled circles represent crossover point of crystallization of clinopyroxene (Cpx) and

plagioclase (Pl). See text.

Fig. 8. Tectonic discrimination diagram for mafic rocks (a) Cr vs. Y discrimination diagram for basalt (after

Pearce, 1982). (b) Ti vs. Zr discrimination diagram of Pearce (1982). (c) V-Ti discrimination diagram of

Shervais (1982). (d) Zr/Y vs. Zr discrimination diagram of Pearce and Norry (1979). IAB= island-arc basalt;

MORB= mid-ocean ridge basalt; WPB= within-plate basalt; IAT= island-arc t

Appendix A

Analytical details. Chemical compositions of the minerals were determined with a CAMECA CAMEBAX

MICROBEAM electron microprobe at the University of Bonn, Germany. The instrument was operated at 15 kV

accelerating voltage, 2 microns beam diameter and 15 nA current. Natural mineral standard were used and the

raw data were corrected by PAP procedure (Pouchou and Pichoir, 1984). Details of the analytical procedures are

described in Raith et al. (2010). Detection limit for the electron microproble analyses are different for different

elements depending on several factors. Considering all the factors, detection limit of the measured

concentrations has been set at 0.02 wt%. Mineral abbreviations are according to Kretz (1983).

The samples of mafic rocks were analyzed for their major and trace element composition (i.e., bulk chemical

analysis) by PHILIPS X-RAY FLUORESCENCE at University of Bonn, Germany. Details of the analytical

procedures and the analytical precision are described in Prame (1997). Following Prame (1997), trace element

concentrations that measure 2 ppm or less are excluded from Table-2.

Backscattered electron images were obtained from the JEOL JSA 6490 Electron Microprobe at the

Department of Geology and Geophysics, Indian Institute of Technology, Khargapur, West Bengal.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT