336 From Shallow to Deep: Recent Advances in Metamorphic Petrology (Posters)

Wednesday, 28 September 2016
9:00 AM - 6:30 PM
Exhibit Hall E/F

METAMORPHIC EVOLUTION OF A KYANITE ECLOGITE, NORTH QAIDAM TERRANE, WESTERN CHINA

Paper number: 336-13
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The North Qaidam Mountains of western China near Dulan house areas of UHP terranes, these terranes contain lenses of kyanite-bearing eclogite.

A kyanite eclogite sample exhibits a mineral assemblage of garnet, omphacite, kyanite, amphibole, zoisite and quartz. Garnet occurs as inclusion rich porphyroblasts within a foliated matrix defined by kyanite, omphacite and zoisite. Idiomorphic garnets are zoned with increasing Ca and Mg content from core to rim, as well as a decreasing content of Fe and Mn from core to rim. Omphacite and quartz are present as inclusions in garnet. Omphacite (Xjd =0.31) is partially replaced by fine grained symplectite making rims. Xenomorphic kyanite is also partially replaced by symplectite of fine grained margarite and zoisite.

Rutile grains of ~60 µm contain Zr concentrations of 84-140 ppm, leading to an average of 117 ±13 ppm. These concentrations yielded temperatures of 622-660 ºC with an average of 647 ºC ± 8 ºC calculated at 30 kbar.

Phase equilibria modeling predicts that the stability field that best fits the observed mineral assemblage (garnet, omphacite, kyanite and quartz) is within a temperature range of 620-800 ºC and a pressure range of 19-30 kbar. However, amphibole and zoisite are present at 500-800 ºC and less than 23 kbar.

Preliminary phase equilibrium diagrams as well as Zr-in-rutile thermometry indicate that this sample reached peak P-T conditions within the lawsonite stability field. Also these models suggest that the amphibole and zoisite grew during the early retrograde path.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-287719

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