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The Shanderman eclogites: A Late Carboniferous high-pressure event in the NW Talesh Mountains (NW Iran)

By
Stefano Zanchetta
Stefano Zanchetta
1
Dipartimento Scienze Geologiche e Geotecnologie
,
Università di Milano-Bicocca
,
Piazza della Scienza 4, Milano, 20126
Italy
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Andrea Zanchi
Andrea Zanchi
1
Dipartimento Scienze Geologiche e Geotecnologie
,
Università di Milano-Bicocca
,
Piazza della Scienza 4, Milano, 20126
Italy
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Igor Villa
Igor Villa
1
Dipartimento Scienze Geologiche e Geotecnologie
,
Università di Milano-Bicocca
,
Piazza della Scienza 4, Milano, 20126
Italy
3
Institut für Geologie
,
Universität Bern
,
3012 Bern
,
Switzerland
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Stefano Poli
Stefano Poli
2
Dipartimento di Scienze della Terra
,
Università di Milano
,
Via Mangiagalli 34, 20133 Milano
,
Italy
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Giovanni Muttoni
Giovanni Muttoni
2
Dipartimento di Scienze della Terra
,
Università di Milano
,
Via Mangiagalli 34, 20133 Milano
,
Italy
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Published:
January 01, 2009

Abstract

The Shanderman Metamorphic Complex, exposed along the Caspian foothills of the Talesh Mountain, western Alborz, Iran, has always been interpreted as an ophiolitic fragment of the Palaeotethys Ocean. According to our new data, this unit consists of metamorphic rocks mainly represented by garnet–staurolite micaschists with large bodies of metabasites containing well-preserved eclogitic-phase assemblages. The Shanderman Complex (SC) was later intruded at middle crustal levels by intermediate–basic intrusive bodies. New Ar/Ar ages of paragonitic white micas in equilibrium with the high-pressure assemblages have given a Late Carboniferous age (315±9 Ma). Our new data suggest that the SC was equilibrated in high-pressure conditions during an orogenic event that predates the Eo-Cimmerian orogeny by more than 100 Ma and that may be tentatively ascribed to the Variscan orogeny sensu latu. We suggest that the Shanderman Complex represents a fragment of the Upper Palaeozoic European continental crust. The occurrence of eclogites in these regions can be explained by two different hypotheses: (1) the SC high-pressure rocks can be related to the accretion of Gondwana-related Transcauscasian–Moesian microplate to the southern margin of Eurasia; or (2) the SC eclogites can represent a fragment of the Late Palaeozoic ‘Variscan belt’ sensu latu of central Europe, which has been translated eastwards during Permian along a dextral megashear zone taking from a Pangea-B to a Pangea-A plate configuration. This metamorphic unit was stacked southwards on the northern edge of the Iran Plate during the Eo-Cimmerian events occurring at the end of the Triassic. The eclogite-bearing basement of the SC was finally exhumed at the end of the Eo-Cimmerian orogeny, as suggested by the composition of the basal layers of the Shemshak Group dated here Middle Jurassic, that cover the crystalline rocks of the SC along a regional non-conformity. The SC was probably displaced further southwards during the Mesozoic opening of the South Caspian Basin and the Tertiary thrust stacking and dextral shearing accompanying the formation of the Alborz intracontinental belt.

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Contents

Geological Society, London, Special Publications

South Caspian to Central Iran Basins

M.-F. Brunet
M.-F. Brunet
CNRS-INSU and Université Pierre et Marie Curie, France
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M. Wilmsen
M. Wilmsen
Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Germany
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J. W. Granath
J. W. Granath
Granath & Associates Consulting Geology, USA
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Geological Society of London
Volume
312
ISBN electronic:
9781862395602
Publication date:
January 01, 2009

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