Petrology, geochronology, and tectonics of shear zones in the Zermatt–Saas and Combin zones of the Western Alps

Journal of Metamorphic Geology - Tập 20 Số 2 - Trang 263-281 - 2002
Ian Cartwright1, A. C. Barnicoat1
11 Victorian Institute of Earth and Planetary Sciences, School of Geoscience, Clayton, Vic. 3800,Australia ([email protected])2School of Earth Sciences, The University, Leeds, LS2 9JT, UK

Tóm tắt

AbstractMetre to tens‐of‐metre wide, steeply dipping, greenschist facies shear zones that cut blueschists and eclogites of the Combin and Zermatt–Saas Zones at Täschalp and in adjacent areas of the western Alps were sites of extensive recrystallization driven by fluid flow and deformation. Rb–Sr data imply that these shear zones formed at 42–37 Ma with a systematic younging of structures northward toward, and into, the hangingwall of the Mischabel Structure. Shearing commenced at 400–475 °C and 400–500 MPa and continued as pressures and temperatures fell to 300–350 °C and 300–350 MPa. Individual shear zones were active for 2–3 Myr with later lower grade stages of shearing concentrated into narrow zones. Fluids that infiltrated the shear zones were water rich (XH2O > 0.9). Alteration zones around albite veins and at the margins of serpentinite bodies are penecontemporaneous with these shear zones and formed at approximately the same conditions. The eclogites were exhumed from c. 64 km at 44 Ma to 14–16 km at 42–41 Ma implying exhumation rates of 2–5 cm yr−1. Rapid exhumation was probably achieved by extension aided by buoyancy, following subduction of continental crust, and rapid erosion. The shear zones form part of a regional‐scale extensional system responsible for a significant portion of the exhumation of the subducted oceanic crust.

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Tài liệu tham khảo

10.1016/S0012-821X(99)00161-2

Ballevre M., 1993, The Combin fault: compressional reactivation of a Late Cretaceous‐Early Tertiary detachment fault in the Western Alps, Schweizerische Mineralogische und Petrographische Mitteilungen, 73, 205

10.1111/j.1525-1314.1988.tb00439.x

Barnicoat A. C., 1995, Sea‐floor hydrothermal alteration in metabasites from high‐pressure ophiolites of the Zermatt‐Aosta area of the western Alps, Museo Regionale Di Scienze Naturali Di Torino, Bolletino, 13, 191

10.1016/0012-821X(95)00040-J

10.1111/j.1525-1314.1997.00058.x

10.1144/gsjgs.143.4.0607

10.1029/94TC02017

Bearth P., 1953, Geologischer Atlas der Schweiz

Bearth P., 1967, Beitraege Zur Geologischen Karte der Schweiz, 132

10.1080/09853111.1988.11105157

10.1111/j.1525-1314.1994.tb00013.x

10.1007/s005310050261

10.1046/j.1525-1314.1999.00205.x

10.1046/j.1525-1314.2000.00280.x

10.1016/S0009-2541(96)00068-X

Coward M. P., 1989, Alpine Tectonics, Special Publication 45, 1

Deblemas J. 1980.Annecy — Carte Geologique de la France a 1/250 000.Bureau de Recherches Géologiques et Minières Orléans.

10.1007/BF00310451

10.1038/42446

Ellis C., 1989, Alpine Tectonics, Special Publication 45, 265

10.1029/96TC02477

10.1016/0040-1951(79)90155-0

Gebauer D., 1997, 35 Ma old ultrahigh‐pressure metamorphism and evidence for very rapid exhumation in the Dora Maira Massif, Western Alps, Lithos, 41, 5, 10.1016/S0024-4937(97)82002-6

10.1007/BF00371156

10.1007/s004100000218

10.1130/0091-7613(1992)020<0907:UOAMCC>2.3.CO;2

10.1111/j.1525-1314.1998.00140.x

Hunziker J. C., 1969, Rb–Sr–Altersbestimmungen aus den Walliser Alpen; hellglimmer‐ und Gesmatgesteinsalterswerte, Eclogae Geologicae Helvetiae, 62, 527

10.1111/j.1525-1314.1994.tb00052.x

Marthaler M., 1989, Les schistes lustrés a ophiolites de la nappe du Tsate; un ancien prisme d'accretion issu de la marge active Apulienne?, Schweizerische Mineralogische und Petrographische Mitteilungen, 69, 211

McCaig A. M., 1997, Deformation‐Enhanced Fluid Transport in the Earth's Crust and Mantle, 227

Miller J. A., 1998, Proceedings of Water–Rock Interaction 9, 789

Miller J. A. Cartwright I.&Barnicoat A. C. 2001.The formation of albite veins during exhumation of high‐pressure terranes: a case study from the Corsican and Zermatt‐Saas ophiolites Western European Alps.Journal of Metamorphic Geology 20 in press.

10.1016/0191-8141(81)90041-9

Moiné P., 1989, Mise en évidence de l'âge Eocene Moyen du métamorphism de haute‐pression dans la nappe ophilitique du Monviso (Alpes Occidentales) par la méthode 40Ar–39Ar, Comptes Rendus de l'Academie Des Sciences, Série II, 309, 245

Oberhänsli R., 1982, The P–T history of some pillow lavas from Zermatt, Ofioliti, 7, 432

10.1111/j.1365-3121.1993.tb00237.x

10.1130/0016-7606(1986)97<1037:DOOWAT>2.0.CO;2

Pognante U., 1989, Early alpine eclogitisation in talc‐chloritoid‐bearing Mg–metagabbros and in jadeite–Fe omphacite‐bearing metatrondhjeimites from the ophiolites of the western Alps, Rendiconti Della Società Italiana Di Minerlaogia E Petrologia, 43, 687

Powell R., 1989, An internally consistent thermodynamic dataset with uncertainties and correlations: 3: Applications to geobarometry, worked examples and a computer program, Journal of Metamorphic Geology, 9, 173

10.1046/j.1525-1314.1999.00220.x

10.1127/ejm/3/1/0007

10.1007/s005310050044

Ring U., 1999, Exhumation Processes: Normal Faulting, Ductile Flow and Erosion, Special Publication 154, 1

10.1130/0016-7606(1992)104<0901:FBALGE>2.3.CO;2

10.1007/s004100050421

Sperlich R., 1988, The transition from crossite to actinolite in metabasites of the Combin unit in Vallee St. Barthelemy (Aosta, Italy), Schweizerische Mineralogische und Petrographische Mitteilungen, 68, 215

Trumpy R., 1980, An Outline of the Geology of Switzerland. Part A

10.1144/gsjgs.148.6.1101

10.1016/0012-821X(93)90097-S

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Journal of Metamorphic Geology

Tập 20 Số 2

263-281

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