Exhumation of blueschist-facies assemblages from western Turkey :

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" Exhumation of blueschist-facies assemblages from western Turkey : "
Sherlock, Sarah Christine

Document Type	:	Latin Dissertation
Record Number	:	828324
Doc. No	:	TLets326182
Main Entry	:	Sherlock, Sarah Christine
Title & Author	:	Exhumation of blueschist-facies assemblages from western Turkey :\ Sherlock, Sarah Christine
College	:	Open University
Date	:	1999
student score	:	1999
Degree	:	Thesis (Ph.D.)
Abstract	:	The Tavsanli Zone of northwest Turkey is a tract of metacherts, metapelites and metabasite lithologies that have undergone a single metamorphic cycle in the lawsonite-blueschist, epidote-blueschist and low-temperature eclogite sub-facies. These deeply subducted rocks which formed during late Cretaceous closure of the Tethys Ocean reached minimum pressures of 24 ± 2 kbar and temperatures of approximately 500° C in the eastern regions, and 20 ± 2 kbar and 400° C in the central and western regions. The difference in metamorphic pressures between the east and west regions of the Tavsanli Zone are attributed to different locations of the rocks within the subducting slab. Syn-subduction exhumation brought the rocks up from depths of 75 km to the base of the continental crust. Metamorphism took place under fluid-absent conditions, in part due to the incorporation of large quantities of water into the lawsonite. Subduction ended by approximately 70 Ma and the ensuing exhumation during continent-continent collision took place by thrusting. Rb-Sr and <sup>40</sup>Ar-<sup>39</sup>Ar geochronological techniques have been applied to phengites from the Tavsanli Zone and indicate that white mica crystallisation and the onset of exhumation occurred at 79 to 82 Ma. Ultra-violet laser, infra-red laser and furnace step-heating <sup>40</sup>Ar-<sup>39</sup>Ar techniques confirm that the rocks of the Tavsanli Zone contain excess argon, which has probably built up in the grain-boundary network during the single metamorphic cycle. The variable concentrations of excess argon correlate with lithological type, reflecting low mobility of argon. This is consistent with vapour-absent metamorphism as inferred from metamorphic petrology.
Subject	:	Tavsanli zone; Metamorphism; Tethys Ocean
Added Entry	:	Open University