Petrological evidence for shock-induced high-Pmetamorphism in a gabbro

Autor: Meng-Xi Huang, A.-P. Chen, Jun Yang, Huan Zhang
Rok vydání: 2016
Předmět:
Zdroj: Journal of Metamorphic Geology. 35:121-140
ISSN: 0263-4929
DOI: 10.1111/jmg.12223
Popis: Microlites (minute spherulitic, dendritic, skeletal, acicular and poikilitic crystals) diagnostic of crystallization in quenched melt or glass in fault rocks have been used to infer fossil earthquakes. High-pressure microlites and crystallites are described here in a variably eclogitized gabbro, the wallrock to the coesite-bearing eclogite breccia at Yangkou in the Chinese Su-Lu high-pressure metamorphic belt. The studied hand specimens are free of discernible shear deformation, although microfractures are not uncommon under the microscope. In the least eclogitized gabbro, the metagabbro, stellate growths of high-pressure minerals on the relict igneous minerals are common. Dendritic garnet crystals ( 2 GPa between the metagabbro and the coesite-bearing eclogite about 20 m apart cannot be explained by the subduction hypothesis because this would require a depth difference of >60 km. The microlites and crystallites are evidence for rapid crystallization due to rapid cooling because constitutional supercooling was unlikely for the plagioclase pseudomorphs. Therefore, the eclogitization of the wallrock to a eclogite breccia was also coseismic, as proposed earlier for the eclogite-facies fault rocks. The lack of annealing of the broken biotite and augite overgrown by strain free skeletal garnet is consistent with a transient high-P-T event at a low ambient temperature (
Databáze: OpenAIRE
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