EOCENE AGE OF ECLOGITE METAMORPHISM IN PAKISTAN HIMALAYA - IMPLICATIONS FOR INDIA EURASIA COLLISION

被引：205

作者：

TONARINI, S

VILLA, IM

OBERLI, F

MEIER, M

SPENCER, DA

POGNANTE, U

RAMSAY, JG

机构：

[1] Istituto di Geocronologia E Geochimica Isotopica, Cnr, Pisa, 56127

[2] Universität Bern, MPI-Isotopengeologie, Bern, 3012

[3] Labor Für Isotopengeochemie, Eth-Zentrum, Zürich

[4] Geologisches Institut, ETH-Zentrum, Zürich

[5] Dipartimento di Scienza Mineralogiche E Petrologiche, Torino, 10125

来源：

TERRA NOVA | 1993年 / 5卷 / 01期

关键词：

D O I：

10.1111/j.1365-3121.1993.tb00221.x

中图分类号：

P [天文学、地球科学];

学科分类号：

07 ;

摘要：

A geochronological investigation of two rocks with an eclogitic assemblage (omphacite-garnet-quartz-rutile) from the High Himalaya using the Sm/Nd, Rb/Sr, U/Pb and Ar/Ar methods is presented here. The first three methods outline a cooling history from the time of peak metamorphism at 49+/-6 Ma recorded by Sm/Nd in garnet-clinopyroxene to the closure of Rb/Sr in phengite at 43+/-1 Ma and U/Pb in rutile at 39-40 Ma. The Sm/Nd isotopic system was fully equilibrated during eclogitization and has not been disturbed since; its mineral ages may date the peak metamorphic conditions (650+/-50-degrees-C at 13-18 kbar: Pognante and Spencer, 1991). The Ar/Ar data reveal the presence of substantial amounts of excess Ar-40 in hornblende, and yield a statistically acceptable but geologically meaningless phengite plateau age of 81.4+/-0.2 Ma, inconsistent with Sm/Nd, Rb/Sr and U/Pb. This questions the use of such a chronometer for the dating of high-pressure assemblages. The results imply a Late Palaeocene or Early Eocene subduction of the northern Indian plate margin in NW Himalaya. The fact that eclogites are restricted to NW Himalaya may be the result of a peculiar p-T-t path associated with a high convergence rate during the first indentation, in contrast to the later and slow subduction in Central and Eastern Himalaya.

引用

页码：13 / 20

页数：8

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