Plate tectonics in the Eastern Alps

Earth and Planetary Science Letters, 24 (1975) 405-413 [ - ~ © North-Holland Publishing Company, Amsterdam - Printed in The Netherlands l.___d

PLATE TECTONICS IN THE EASTERN ALPS

CA. HAWKESWORTH, D.J. WATERS and M.J. BICKLE*

Department of Geology and Mineralogy, University of Oxford (Great BritainJ

Received September 20, 1974 Revised version received November 11, 1974

The weight of the geological evidence, which includes the recognition of a late Cretaceous paired metamorphic belt, suggests that a southward dipping subduction zone existed in the Eastern Alps. On this basis a new plate tectonic model is presented for the post-Palaeozoic evolution of that orogen.

1. Introduction

The concept of flake tectonics [1] has signifi- cantly reduced the number of criteria by which the polarity of subduction may be established in ancient collision-type orogens which involve the mechanical emplacement of large sheets of continental material. The direction of tectonic emplacement, the age re- lations within flysch deposits [2], and the direction of pressure increase within pumpellyite-blueschist metamorphic belts, may no longer be unambiguously related to the direction of subduction, with the result that arguments on subduction polarity in such orogens should ideally be based on the recognition of paired metamorphic belts [3] and their associated igneous rock suites.

In the Eastern Alps, however, the occurrence of three metamorphic events during the Late Cretaceous and Early Tertiary coupled with a paucity of andesitic igneous activity complicates such an approach. No single piece of evidence provides an unambiguous in- dication of subduction polarity and it therefore be- comes necessary to set up alternative models for the East Alpine orogen in which the direction of subduction is varied. Oxburgh [1] has outlined such a model

* Present ad&ess: Department of Geology, University of Rl,od,..~La, R.h,~desia.

(flake tectonics) in which subduction occurred in a northerly direction; this paper suggests that more of the available geological evidence is consistent with a southerly dipping subduction zone (see also [4-6]) . We emphasise that the nature of the evidence is such that neither model may yet be ruled out, but we suggest that together they provide a balanced frame- work for further discussion and research.

A evaluation of the geological evidence for subduction polarity in the Eastern Alps is followed by a discussion of the post-Palaeozoic history of the area.

2. Subduction polarity

It is initially assumed that the subduction polarity in the Eastern Alps must be the same as that in the Western Alps. Events occur at similar times in both segments of the Alpine Chain and the mechanical problems inherent in a change of polarity along strike make such a change unlikely. Consequently, by com- parison with the convex nature of many destructive plate margins today we may infer that subduction is more likely to have taken place towards the interior of the Alps in the south and east.

The first Mesozoic metamorphic event recognised

406 CJ. HAWKESWORTH ET AL

Fig. 1. Geological map of the Eastern Alps. 1 = pre-Mesozoic basement of the Pennine Zone and the Bohemian Massif; 2 --" Sehiefer- htiUe, largely Biindnerschiefer; 3 = Unterostatpin; 4 = pre-Mesozoic Austroalpine basement, the AltkristaUin; 5 = Palaeozoic and Mesozoic cover to the Austioalpine basement; 6 = the Flysch and Helvetic Zones; 7 = molasse; 8 = the Southern Alps; 9 = peri- Adriatic intrusives. P = Pr~itigau

in the Alps is confined to the Austroalpine basement (the Mtkristallin) along the southern margins of the Tauern Window (Fig. 1), where it apparently just postdates an extensive east-west trending deformation. An andalusite/sillimanite isograd in the aluminium silicate-staurolite-two mica schists exists about 4 km above the postulated base of the Altkristallin and the radiometric mica systems (Rb/Sr and K/Ar) have been locally reset at least to within 1 km of the top of the AltkristaUin [7,8]. Assuming the presence of a hydrous fluid phase in those rocks we infer conditions at that isograd of a maximum of 5 kbars at a minimum temperature of 620°0 [9,10]. Average near-surface thermal gradients in excess of 35°C/kin are indicated and this is consequently a low-pressure/high-tempera-

ture type of metamorphism. The peak of metamorphism is thought to have occurred at ca. 105 m.y. [11], although cooling ages as young as 70-65 m.y. have been reported [7,12,13].

The second metamorphic event is of high-pressure/ low-temperature facies and it is preserved in the g!aucophane rocks of Zermatt and the Sesia.Lanzo Zone in the Western Atps [6] and perhaps in the un- dated eclogitic fragments in the Btindnerschiefer of the Tauern Window [14].Dal Piaz et al. [6] discuss the radiometric evidence from the Western Alps and conclude that the glaucophane from Zermatt reached temperatures low enough to permit the accumulation of radiogenic 40Ar at ca. 83 m.y., while phengites from the Sesia-Lanzo Zone remained open to Rb diffusion

PLATE TECTONICS IN THE EASTERN ALPS 407

until 52 m.y. In addition, they point out that pressure, as indicated by the mineral assemblages of the Sesia- Lanzo Zone, increases in a southerly direction.

The third, and the only metamorphic event to post-date the emplacement of the Austroalpine units onto the Penninic domain, is the thermal metamorphism best developed in the Hohe Tauern and the Lepontine Alps: the peak of metamorphism in these areas is estimated to have occurred at ca. 3 5 - 4 0 m.y. (see below) and 38 -+ 2 m.y. [15], respectively. Two attempts have recently been made to investigate quantitatively whether the metamorphism in the Hohe Tauern is due solely to burial beneath the Austroalpine nappes [16], or whether additional heat was added from below implying subduction beneath the Pennine Zone [17]. Unfortunately a rea- sonable case may still be made for each argument (de- pending on the parameters adopted) and consequently this metamorphism does not yet help in establishing the direction of subduction.

Oxburgh and Turcotte [17] point out that the temperatures beneath the Austroalpine sheets may have been low enough, for a short time after thrusting, for blueschist metamorphism; although whether the Austroalpine units provide a sufficient overburden for the observed eclogitic and jadeite-bearing assemblages is still doubtful. Thus the flake tectonic model can explain both the early high-pressure/low-temperature and the younger thermal metamorphic event. Subduction towards the south, however, provides an explanation for all three metamorphic events: blueschist metamorphism parallel to, but on the oceanic side of, the low-pressure/high-temperature metamorphism in the Altkristallin, followed by a post-emplacement burial metamorphism in the rocks of the Pennine Zone. Such a model is consistent with the geophysical evidence that the present East Alpine crust reaches a maximum thickness of ca. 45 km to the south of the Tauern Window ([18] and Fig. 2). Moreover, in agreement with the relative ages of paired metamorphic belts in Japan [19], the blueschist rocks yield similar but slightly younger mineral ages than the parallel coexisting low-pressure/high- temperature metamorphics [6,20].

Finally, polarity is indicated by the available palinspastic reconstructions o f the Btindnerschiefer*.

* For the purposes of this paper Biindnerschiefer is regarded as synonymous with Schistes Lustr6s.

S

B U NCA G SA i

\M cQ.100

ISOTHERM

H F U NCA

ca.80 my \ \ " ~

O SA

H F U NCA G SA

\ "-. --. ZG ,\

M

co.65mv - - ~ \ \

\ x \

H,F NCA t'~U B \ \ G S, 6, MO

PRESENT DAY 3 0 k m t

Fig. 2. The proposed model for the late Mesozoic and Tertiary history of the Eastern Alps. A = Altkristallin; B = Biindner- schiefer; BM = Bohemian Massif; F = Flysch Zone; G = Gailtal Line (which marks the northern boundary of the Southern Alps); H = Helvetic Zone; Mo = molasse; NCA = Northern Calcareous Alps; SA = Southern Alps; U = Unterostalpin; ZG = Zentralgneis, the granitic basement of the Pennine Zone as exposed in the Tauern Window; M = Mohorovidi6 discon- tinuity, whose present-day position is as described by Angen- heister et al. [18].

408 C.J. HAWKESWORTH ET AL.

The allochthonous Biinderschiefer lithologies exposed around the southeast corner of the Tauern Window have been recently interpreted as a tectonic m~lange [21 ], the formation of which apparently pre-dates their emplacement onto the Penninic Basement (Bickle and Hawkesworth, in prep.). The m~lange consists of fragments of ocean-floor tholeiites [22], serpentinites, and eclogites [23] caught up in a matrix of usually calcareous meta-sediments, and it is reasonably interpreted as a fossil subduction m~lange. The fact that the amount of mafic and ultramafic material tectoni- cally intermixed with the deep-water calcareous sediments increases markedly towards the south in the generally accepted palinspastic reconstructions of the Pr~itigau [24] and Central Tauern [25] areas is therefore consistent with the presence of a subduction trench along the southern (or internal) margin of the Biindnershiefer ocean.

Thus we maintain that subduction took place in a southerly direction along this segment of the Alpine Chain and in the following discussion we show how this model places new constraints on the Mesozoic and Tertiary plate tectonic history of the Eastern Alps.

3. The Mesozoic and Tertiary history of the Eastern Alps

The Mesozoic and Tertiary history of the Eastern Alps is considered in terms of three phases.

(1) A tensional phase in which oceanic lithosphere was created.

(2) A compressional phase, partly coeval with phase 1, which is subdivided into two distinct periods of large-scale horizontal movement: (a) the destruction of the Alpine ocean created in phase 1 ; and (b) the emplacement of the Austroalpine units.

(3) A final phase of vertical uplift and associated gravity tectonics.

3.1. Phases i and 2a

Phase 1 is reflected in the deep-water sediments and ophiolitic rocks of the Biindnerschiefer. Primary ages on Tethyan ophiolitic fragments are as old as 180 m.y. [25] so that this phase had started by the beginning of the Jurassic, and sedimentation in the

deep-water environment continued at least until the middle Cretaceous [27,28]. Moreover, since the Austroalpine nappes were probably emplaced at around the Cretaceous/Palaeocene boundary [ 11,13 ], destruction of the oceanic lithosphere (i.e. phase 2a) must have started before the middle Cretaceous, assuming similar rates for the creation and destruction of that ocean.

The timing of phase 2 is further constrained by the recognition of a Late Cretaceous paired metamorphic belt in and below the Austroalpine basement and the likelihood that during phase 2 subduction took place in a southerly direction (Fig. 2). To allow time for the upward transfer of heat to the structural levels exposed today, subduction must have commenced some time (probably at least 20 m.y.) before the peak of the low-pressure/high-temperature metamorphism at ca. 105 m.y. [ 11 ]. Furthermore, the Alt- kristallin, at least around the southern margins of the Tauern Window, was deformed about E-W axes just prior to the peak of this Cretaceous metamorphism. The intensity of this deformation increases markedly with depth and, although the coarse mineral fabric which yields the 100-65-m.y. radiometric ages is largely post-tectonic [13], where deformation is most intense some of the minerals define an axial planar foliation indicating that nucleation occurred in that stress field. There is no evidence that these minerals are mimetic on a pre-existing axial planar foliation. It is" of interest that this E-W deformation in the Eastern Alps apparently occurred at about the same time as the early Alpine tectonic movements demonstrated by Rb/Sr whole rock ages from the front of the Monte Rosa nappe (125 -+ 20 m.y.) in the Western Alps [15], and from the mylonite zones in Alpine Greece (C. Barton, personal communication).

The stratigraphic evidence from the sedimentary sequences apparently deposited on the Altkristallin (the interpretation of such sequences in Fig. 2 follows Kober [29]) is consistent with the proposed timing of phases 1 and 2a. In the Unterostalpin and the Northern Calcareous Alps stable shallow-water car- bonate conditions in the Triassic are followed by signs of increasing tectonic instability during the Jurassic and the Lower Cretaceous [30-32]. During the Neocomian, at about the time the deeper regions of the altkristallin were undergoing deformation about E-W trending axes, the end of largely pelagic post-


Triassic sedimentation in the Northern Calcareous Alps was marked by an extensive coarse clastic deposit (the Rossfeld Beds), while deposition in the Unter- ostalpin apparently ceased [30].

3.2. Events marking the transition from phase 2a-2b

Little is known about how glaucophane schist facies rocks are brought up to high enough levels in the crust to allow their metastable preservation. It is difficult to see how upward movement of such rocks could occur while subduction was in progress [33], and consequently it is suggested that the 83-m.y. glaucophane from Zermatt represents an age of isostatic readjustment of subducted material due to a temporary halt in subduction at about that time. Oberhauser [28] points out that sedimentation in what he decribes as the Ophiolite Zone ceased in or soon after the Turonian, so that the temporary halt in subduction may be due to the initial collision of the Austroalpine and Penninic continental margins. This coincides with the main phase of deformation within the Northern Calcareous Alps which took place in the Upper Turonian (ca. 90 m.y.) [28,34].

The presence of detrital glaucophane and chromite in rocks of Cenomanian age [28] (i.e. older than the postulated time of continental collision) may indicate that obduction [35] of oceanic and trench material occurred near the end of phase 2a.

The increase in stress due to the temporarily locked plate margin, perhaps aided by the isostatic uplift of the subducted material beneath the Austroalpine basement, then resulted in the emplacement of the Austroalpine nappes onto the Penninic domain by renewed subduction of the latter towards the south. This proposed period of isostatic uplift along the temporarily locked plate margin is reflected in the cluster of K/Ar mineral ages at 90-80 m.y. in the Altkristallin (Fig. 3), in the first occurrence of detrital metamorphic minerals in the shallow-water sediments of the Lower Campanian (ca. 76 m.y.) [36] as well as in the mineral ages from the glaucophane-bearing rocks in the Western Alps.

3. 3. Phase 2b: emplacement of the Austroalpine units

In the model proposed here overthrusting cannot have started until after uplift of glaucophane schists

Muscovite

20

10

o 50 ~o 70 ~o 90 t;o tlO t~o t3o

Age [Millions of years)

Fig. 3. Distribution of K/Ar mica ages from the Altkristallin around the southern and eastern margins of the Tauern Window. The tailing effect to the right is largely due to the presence of excess 4°Ar in those micas. Data from Oxburgh et al. [12] Brewer [11] and Waters (unpublished).

in the Western Alps at about 83 m.y.: to assess when it may have finished, the available radiometric and stratigraphic evidence is considered.

Recent structural and petrofabric work across the southeast margins of the Tauern Window (Bickle and Hawkesworth, in prep.) indicates that two main phases of deformation are associated with the emplacement of the Austroalpine units. Bickle [16] suggests that about 4/5ths of the 100-150 km estimated northward movement of these units took place during the earlier deformation; and Rb/Sr ages on muscovite that apparently post-date it and pre-date later deforma- tions indicate that the main phase of overthrusting had finished by ca. 65 m.y. [13].

Stratigraphic evidence for the timing of phase 2b comes mainly from the Pditigau area (Fig. 1) where it has been possible to establish a fairly detailed history in rocks which elsewhere lack fossils and are intensely deformed [27].

Sedimentation in the Pratigau area occurred on the northern margin of the proposed oceanic region and the rocks change from calcareous clastics, deposited in water of intermediate depth, into true flysch near the end of the Cretaceous [27]. Classically the start of flysch sedimentation is interpreted as being coin- cident with the uprising of a cordillera to the south [24], but the observation that the site of flysch deposition moved northwards during the Tertiary [27] and that similar sediments are found along destructive

15

Frequency


plate margins today [37] suggests that the flysch belt marks the northerly advance of the Austroalpine nappe fronts. It is very noticeable that the flysch facies sediments of only phase 2b are preserved: similar rocks presumed to have been deposited during phase 2a along the destructive plate margin of the Alpine oceanic area were either destroyed by subduction, or they are unrecognisable within the tectonic mglange of the Biindnerschiefer.

The Pr~itigau flysch is thought to be of Turonian to Lower Eocene age [27] so that initial continental collision and the closure of the oceanic region must have occurred in or before the Turonian, and the Austroalpine units did not over-ride the Pr/itigau area until the Lower Eocene. Since this area lies near the northern edge of the Altkristallin Sheet it may only have been covered during the second, relatively minor, phase of overthrusting recognised in the Hohe Tauern.

Stratigraphic evidence in the Pratigau area is thus consistent with the radiometric evidence from the Hohe Tauern, and suggests the end of phase 2a at ca. 90 m.y. (Turonian), that the bulk of overthrusting had occurred by the end of the Cretaceous (65 m.y.), and that the final phase of emplacement was before the end of the Eocene (40 m.y.).

3. 4. The compressional phase 2 in the Swiss A lps

Austria indicates that the oceanic region with its associated ophiotitic rocks was closed at the end of phase 2a in the early Upper Cretaceous*. Where we differ from TrUmpy is in ascribing the overthrusting of the Austroalpine (phase 2b) largely to the Late Cretaceous rather than to the Late Eocene. The stratigraphic evidence from the Swiss Alps that coarse flysch was finally overridden at about 40 m.y. may, we suggest, be accommodated by late pulses of movements such as those described in the Hohe Tauern (Bickle and Hawkesworth, in prep.), but the critical evidence for Cretaceous overriding in Switzerland lies in the interpretation of the metamorphism in the Lepontine Alps. In Triimpy's model only 2 m.y. elapse between overriding (40 m.y.) and the peak of Lepon- tine metamorphism [39]. If the metamorphism is interpreted as a consequence of burial under the overriding Austroalpine units [40] this 2-m.y. time inter- val is drastically insufficient for the build up of heat in the overridden pile. We suggest instead that part of (perhaps, by analogy with the Eastern Alps, most of) the movement occurred 25-30 m.y. before the peak of metamorphism and interpret the Lepontine region as analogous with the Hohe Tauern where metamorphism has been quantitatively described as a burial metamorphism (Bickle, Hawkesworth, England and Athey, in prep.).

Trtimpy [38] has recently discussed the timing of the orogenic events in the Swiss Alps and pointed out that the Cretaceous deformation seen in the Dent Blanche and the Piemont Trough may have culminated in the closure of the latter during the Cretaceous. He also suggested that the peak of deformation associated with the emplacement of the Austroalpine nappes occurred at the end of the Eocene (on the basis of stratigraphic evidence from Pr5tigau and Oberhalbstein), and that this was followed 2 m.y. later by the peak of the Lepontine metamorphism. Thus there would appear to be large differences in the timing of the major events during the late Mesozoic and Tertiary between the Austrian and the Swiss Alps. We believe that these differences are greater than may satisfactorily be explained by a diachronous movement of events along the Alpine Chain (e.g. both reconstructions drawn on the same evidence from the Prgtigau area), and we suggest that the disparities have no reality.

The evidence from both Switzerland [38] and

3.5. A mechanism for the emplacement of the Austro- alpine units

In this discussion the mechanical problem of em- placing slices of continental crust has so far been neglected. The observed thickness of Austroalpine units (ca. 20 km on the south side of the Tauern Window, from the position of the kyanite/andalusite isograd discussed earlier) represents little more than half the thickness of normal continental crust. By the time of its emplacement the Altkristallin had cooled consider- ably from the 105-m.y. event and it is difficult to see how a sub-horizontal brittle fracture could occur at that time.

Armstrong and Dick [41] outline a model for de-

* We visualise the Valais and the Piemont sequences as merely different structural units of rock tectonicaUy transported from within and beside the same oceanic region. It is unlikely that they represent two palaeogeographically distinct deep-water basins in which oceanic crust was being created.


taching thin Slices of continental crust along a horizon parallel to isotherms in the area of high heat flow behind a volcanic arc. However, the apparent lack of any island arc volcanics in the Eastern Alps suggests that the Altkristallin lay over a relatively short-lived subduction zone rather than behind a volcanic arc. Nonetheless it is possible that the detachment of the Altkristallin from its base occurred during that 105- m.y. metamorphism along a horizon which must have been at about 700°C, rather close to the solidus of hydrous pelitic rocks. We envisage this horizon as one where extensive deformation by plastic flow could have occurred in a stress field Of no great magnitude (fig. 2a in Armstrong and Dick [41]). The E-W deformation in the Altkristallin is seen as coeval with the separation of the upper continental slice: deformation increases markedly in intensity towards the present base of the Altkristallin and occurred at a time of high heat flow just prior to the peak of Cretaceous metamorphism. It is therefore suggested that the break between the Altkristallin and the lower crust may have been initiated as a subhorizontal shear zone as early as the Lower Cretaceous and that during subduction (phase 2a) the Altkristallin was gradually separated from its lower crust (Fig. 2).

3. 6. Phase 3: vertical uplift and associated tectonics

The peak of the post-emplacement metamorphism in the Eastern Alps is estimated to have occurred at ca. 35 -40 m.y. (35 m.y. is the oldest Alpine Rb/Sr mineral age recorded [13]) and the subsequent cooling reflects the regional uplift of the Hohe Tauern. The Northern Calcareous Alps and their underlying Palaeozoic rocks (the Grauwackenzone) are thought to have slid north at about this time causing the end of deposition in the Flysch Zone, and subsequently in the Helvetic Zone (a parautochthonous unit in which fairly slow sedimentation took place from the Lower Jurassic to the Eocene, Figs. 1 and 2). Evidence from the Molasse Basin also confirms that this northwards movement of the Northern Calcareous Alps, with its associated deformation of the underlying units, did not stop until the Lower Miocene [30].

4. Conclusions

The Mesozoic and Tertiary history of the Eastern

Alps has been considered in terms of three phases. After an initial tensional phase in which oceanic crust was created and which must have already been present at the beginning of the Jurassic, some change in the regional pattern of plate movements resulted in the onset of a compressional regime in the Lower Cretace- ous. The local occurrence of middle Cretaceous ophiolites [42] emphasises that phase 2 was in part coeval with phase 1.

We believe that the curvature of the Central Alpine Chain, the distribution of mafic and ultramafic material in the Btindnerschiefer m61ange, and the recognition of an Upper Cretaceous paired metamorphic belt, indicate that the destruction of oceanic crust during phase 2 occurred in a southerly direction. An E-W deformation in the Altkristallin, which increases in intensity downwards and which only just pre-dates the low-pressure/high-temperature Cretaceous metamorphism, reflects the initiation of a subhorizontal separation of the Altkristallin from its lower crust.

The oceanic ridge appears to have closed in or soon after the Turonian and it is suggested that a temporary halt in subduction at this time, due to the initial collision of the Austroalpine and the Penninic continental margins, permitted the isostatic rise of the previously subducted high-pressure/low-temperature metamorphic rocks and the overlying Altkristallin. Most of the emplacement of the Austroalpine units (phase 2b) had been completed by 65 m.y. but, as indicated by the flysch deposition along the front of the advancing Austroalpine units, some overthrusting movements continued until the late Eocene.

The final phase (phase 3) was one of vertical uplift along the Axial Zone of both the Austrian and the Swiss Alps which induced cooling of the post-tectonic thermal metamorphism and which was accompanied by tectonic movements involving the sedimentary cover during the Oligocene and the Miocene [30,43].

Finally, we emphasise that our model differs in detail from the two recent plate tectonic reconstructions of the post-Palaeozoic history of the Mediter- ranean region [44,45]. The major change in regional plate movements, as reflected in our model of the geology of the Eastern/Ups, apparently occurred in the Lower Cretaceous, a time which is coeval with the opening of the Southern [46,47] and not the Northern Atlantic ocean.


A c k n o w l e d g e m e n t s

The ideas ou t l i ned he re have arisen f r o m discussions

wi th m a n y people . K. Cox, E.R. Oxburgh , S.W.

R icha rdson , E.T.C. Spooner , R.C. Wright , and P.C.

England have great ly improved earlier d ra f t s o f the

manusc r ip t , and we are par t icu la r ly i n d e b t e d to

S.W. R icha rdson for his e n t h u s i a s m and advice dur ing

the f inal p r epa ra t i on o f th is paper .

M.J.B. and D.J.W. acknowledge N.E.R.C. s tuden t -

ship, and C.I .H. acknowledges the rece ip t o f a g ran t

f rom the Burde t t Cou t t s Trus t .

Refe rences

1 E.R. Oxburgh, Flake tectonics and continental collision, Nature 239 (1972) 202.

2 A.H.G. Mitchell, Flysch-ophiolite successions: polarity indicators in arc and collision-type orogens, Nature 248 (1974) 747.

3 A. Miyashiro. Evolution of metamorphic belts, J. Petrol. 2 (1961) 277.

4 W.G. Ernst, Metamorphic zonation on presumably subducted lithospheric plates from Japan, California and the. Alps, Contrib. Mineral. Petrol. 34 (1971) 43.

5 W.G. Ernst, Interpretive synthesis of metamorphism in the Alps, Geol. Soc. Am. Bull. 84 (1973) 2053.

6 V. Dal Piaz, J.C. Hunziker and G. Martinotti, La zona Sesia-Lanzo e L'evolutione tettonico-metamorfica delle Alpi nordoccidental interne, Mem. Geol. Soc. It. 11 (1972) 433.

7 M.S. Brewer, Excess radiogenic argon in metamorphic micas from the Eastern Alps, Austria, Earth Planet. Sci.

Lett. 6 (1969) 321. 8 CJ. Hawkesworth, Unpublished D. Ph. Thesis, Oxford

(1974). 9 S.W. Richardson, Staurolite stability in a part of the

system F e - A 1 - S i - O - H , J. Petrol. 9 (1968) 467. 10 S.W. Richardson, M.C. Gilbert and P.M. Bell, Experimental

determination of kyanite-andalusite and andalusite-sll- limanite equilibria; the aluminium silicate triple point, Am. J. Sci. 267 (1969) 259.

11 M.S. Brewer, Unpublished D. Ph. Thesis, Oxford (1970). 12 E.R. Oxburgh, R.St.J. Lambert, H. Baadsgaard and J.G.

Simons, Potassium-argon studies across the southeast margin of the Tauern Window, the Eastern Alps, Verh. Geol. Bund. 1/2 (1966) 17.

13 C.J. Hawkesworth, Geochronological traverse across the margin of the Tauern Window (abstr.), Third European Colloquium of Geochronology, Oxford (1973).

14 H. Scharbert, Die eklogitischen Gesteine des siidlichen Grossvenedigergebietes (Osttirol), Jb. Geol. B-A. Wien 97 (1954) 39.

15 J.C. Hunziker, Polymetamorphism in the Monte Rosa, Western Alps, Eclog. Geol. Helv. 63 (1970) 151.

16 M.J. Bickle, Unpublished D. Ph. Thesis, Oxford (1973). 17 E.R. Oxburgh and D.L. Turcotte, Thermal gradients and

regional metamorphism in overthrust terrains with special reference to the Eastern Alps, Schweiz. Mineral. Pet. Mitt. 54 (1974) 641.

18 G. Angenheister, H. B~Sgel, H. Gebrande, P. Giese, P. Schmidt-Thomd and W. Zeil, Recent investigations of surfieial and deeper crustal structures of the Eastern and Southern Alps, Geol. Rundsch. 61 (1972) 349.

19 A. Miyashiro, Metamorphism and Metamorphic Belts (Allen and Unwin, 1973).

20 J. Bocquet, M. Delaloye, J.C. Hunziker and D. Krummen- acher, K-Ar and Rb-Sr dating of blue amphiboles, micas, and associated minerals from the Western Alps, Contrib. Mineral. Petrol. 47 (1974) 7.

21 R.A. Cliff, R.J. Norris, E.R. Oxburgh and R.C..Wright, Structural, metamorphic and geochronological studies in the Reisseck and southern Ankogel Groups, in: E.R. Ox- burgh ed., Jb. Geol. B-A 114 (1971) 121.

22 M.J. Bickle and E.G. Nisbet, The oceanic affinities of some Alpine mafic rocks based on their T i - Z r - Y contents, J. Geol. Soc. Lond. 128 (1972) 267.

23 H.P. Cornelius and E. Clar, Geologic des Grossglocknerge- bietes, Abh. Reichsstelle Bodenforsch. Zweigst. Wien 25 (1939) 1.

24 J. Debelmas and M. Lemoine, The Western Alps: palaeo- geography and structure, Earth. Sci. Rev. 6 (1970) 221.

25 G. Frasl and W. Frank, Einfiihrung in die Geologic und Petrographic des Penninikums im Tauernfenster (Vereini- gung der Freunde der Mineralogie und Geologic (VFMG) e G., Heidelberg, 1966).

26 G. Bigazzi, F.P. Bonadona, G. Ferrara and G. Innocenti, Fission track ages of zircons and apatites from North Apennine ophiolites, Fortschr. Mineral. 50 (1972) 51.

27 R. Triimpy, Palaeotectonic evolution of the Central and Western ~ps , Geolo Soc. Am. Bull. 71 (1960) 843.

28 R. Oberliauser, Beitr~ige zur Kenntnis der Tektonik und der Pal//ographie wLhrend der Oberkreide und dem Pal~iogen im Ostalpeuraum, Jb. Geol. B-A. Wien 11 (1968) 115.

29 L. Kober, Bau und Entstehung der Alpen (Deuticke, Wien, 1955).

30 E.R. Oxburgh, An outline of the geology of the Central Eastern Alps, Proc. Geol. Assoc. 76 (1968) 1.

31 R.E. Garrison and A.G. Fischer, Deep water limestones and radiolarites of the Alpine Jurassic, Soc. Econ. Palaeontol. Mineral., Spec. Pub. 14 (1969) 20.

32 D. Bernoulli and H. Jenkyns, Alpine, Mediterranean, and Central Atlantic Mesozoic facies in relation to the early evolution of the Tethys, Soc. Econ. Palaeontol. Mineral., Spec. Publ. 19 (1974) 129.

33 E.R. Oxburgh and D.L Turcotte, Origin of paired metamorphic belts and crustal dilation in island are regions, J. Geophys. Res. 76 (1971) 1315.

34 K. Muller, Das "Randcenoman" der N6rdlichen Kalkalpen und seine Bedeutung fiir den Ablauf der ostalpin Decken- iiberschiebungen und ihrer Schubweiten, Geol. Rundsch. 62 (1973) 54.

35 E.M. Moores, Ultramafics and orogeny, with models of the U.S. Cordillera and the Tethys, Nature 228 (1970) 837.


36 G. Woletz, Schwermineralvergesellschaftungen aus ostalpin Sedimentationsbecken der Kreidezeit, Geol. Rundsch. 56 (1967) 308.

37 A.H.G. Mitchell and H.G. Reading, Continental margins, geosynclines and ocean-floor spreading, J. Geol. 77 (1969) 629.

38 R. Triimpy, L'evolution de l'orogenbse dans les Alpes Centrales: interpretation des donndes stratigraphiques et tectoniques, Eclog. Geol. Helv. 66 (1973) 1.

39 E. J~er , Die Alpine Orogenese im Lichte der radiometrischen Altersbestimmung, Eclog. Geol. Helv. 66 (1973) 11.

40 E. Niggli, Alpine Metamorphose und alpine Gebirgsbildung, Fortschr. Miner. 47 (1970) 16.

41 R.L Armstrong and H.J.B. Dick, A model for the develop- ment of thin overthrust sheets of crystalline rock, Geology 2, 1 (1974) 35.

42 V. Dietrich, Geosynclinaler Vulkanismus in den Oberen penninischen Decken Graubiindens (Schweiz), Geol. Rundsch. 55 (1967) 246.

43 R. Trtimpy, Die helvetischen Decken der Ostschweiz: Versuch einer palinspastischen Korrelation und Ans//tze zu einer kinematischen Analyse, Eclog. Geol. Helv. 62 (1969) 105.

44 A.G. Smith, Alpine deformation and the oceanic areas of the Tethys, Mediterranean and Atlantic, Geol. Soc. Am. Bull. 82 (1971) 2039.

45 J.F. Dewey, W.C. Pitman III, W.B. Ryan and J. Bonnin, Plate tectonics and the evolution of the Alpine System, Geol. Soe. Am. Bull. 84 (1973) 3137.

46 G~ Siedner and J.A. Miller, K-Ar determinations on basalt- ic rocks from southwest Africa and their bearing on continental drift, Earth Planet. Sci. Lett. 4 (1968) 451.

47 R.A. Reyment and E.A. Tait. Biostratigraphical dating of the early history of the South Atlantic Ocean, Phil. Trans. R. Soc. London 264 (1972) 55.

Plate tectonics in the Eastern Alps

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