Grain-size reduction of feldspar and flow of deformed granites within the Gaoligong shear zone, southwestern Yunnan, China

作     者：Yanlong DONG Shuyun CAO Xuemei CHENG Junlai LIU Hanchen CAO 

作者机构：State Key Laboratory of Geological Processes and Mineral Resources School of Earth Sciences China University of Geosciences Wuhan 430074 China State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences Beijing 100083 China 

出 版 物：《Science China Earth Sciences》 (中国科学（地球科学英文版）)

年 卷 期：2019年第62卷第9期

页      面：1379-1398页

核心收录：

学科分类：07[理学] 

基　　金：supported by the Excellent Youth Fund of National Natural Science Foundation of China (Grant No. 41722207) the National Key Research and Development Program (Grant No. 2017YFC0602401) the National Natural Science Foundation of China (Grant Nos. 41472188 & 41430211) 

主　　题：Feldspar Grain-size reduction EBSD fabric Fluid Myrmekite Mylonite Ultramylonite 

摘      要：Mineral deformation and rock flow mechanism in the lithosphere are related to the rheological behavior and weakening mechanism of the continent. Natural deformation behaviors of feldspars are not well understood due to the complexity of their mineral compositions, crystal structures, as well as changing deformation conditions. The refined microstructure,fabric and composition of major minerals in the deformed granitic rocks within the Gaoligong shear zone(GLGSZ), southwestern Yunnan, China, were studied. With increasing mylonitization, two fabric types of end-members have been distinguished(type-I banded granitic mylonite and type-II banded ultramylonite). The two types of deformed granitic rocks have the same mineral assemblage, but different mineral modes. The type-I banded granitic mylonite has a greater proportion of K-feldspar(mostly present as porphyroclasts)plagioclasequartz±biotite, however, the type-II banded ultramylonite has a greater proportion of fine-grained plagioclaseK-feldsparquartz±biotite. The crystallographic preferred orientation(CPO) patterns of quartz combined with two-feldspar geothermometer, confirm that the quartz grains in the type-I and type-II granitic rock have undergone high-temperature dislocation creep deformation. The K-feldspar grains in the matrix of type-II banded ultramylonite show a dominant(100)[010] slip system with dislocation creep recrystallization, while the fine-grained plagioclase grains present a weak CPO pattern with superplastic flow. The K-feldspar porphyroclasts show grain-size reduction associated with mineral composition and fabric transformation. The myrmekite formation with the fine-grained neocrystallization of plagioclase and quartz significally replaced the K-feldspar porphyroclasts. Finally, the fine-grained neocrystallization plagioclases were formed further into the high strain localized ultramylonites with superplastic flow.