Abstract
Diopside, an important component of the crustal and upper mantle, plays an important role in the formation of nephrite. Polysynthetic twinning in natural diopside, especially from skarns, has rarely been systematically researched. Here, the polysynthetic twinning of natural diopside was investigated in two skarn-type nephrite deposits (Niewang and Tatliksu) in Qiemo, Xinjiang, China. Petrographic observations revealed periodic alternations of dark–light lamellae under cross-polarized light and parallel striations under plane-polarized light, whereas backscattered electron images indicated high homogeneity, which suggested a type of mechanical polysynthetic twinning. According to the optical indicatrix, twins were predominantly oriented as a (100)[100] system. Raman spectra and chemical data show that pyroxenes in nephrite are close to the Di end-member with 0.90–1.04 a.p.f.u. Mg and 0.98–1.05 a.p.f.u. Ca. Both diopside and tremolite from Tatliksu contain slightly higher Fe than those from Niewang. Given the seismic origin of mechanical clinopyroxenes twins, twins of studied diopsides are likely to be attributed to Paleozoic-Mesozoic paleoearthquakes in the Altyn Mountain. A shear stress ≥ 140 MPa and a differential stress greater than 280 MPa are suggested as conditions linked to generation of the twinning of diopsides in the nephrite deposits. The replacement of diopside by tremolite along its twin planes highlights the potential gemological implications, as such replacement by tremolite probably facilitated the formation of dense, fine fibre textures in the nephrites.
Funder
National Key R&D Program of China
Second Tibetan Plateau Scientific Expedition and Research Program
National Science Foundation of China
Subject
Geology,Geotechnical Engineering and Engineering Geology
Reference56 articles.
1. Geochemistry, mineralogy and genesis of the Ayazmant Fe-Cu skarn deposit in Ayvalik, (Balikesir), Turkey;Oyman;Ore Geol. Rev.,2010
2. Geochemistry and petrology of nephrite from Alamas, Xinjiang, NW China;Liu;J. Asian Earth Sci.,2011
3. The Tashisayi nephrite deposit from South Altyn Tagh, Xinjiang, northwest China;Gao;Geosci. Front.,2019
4. Jiang, Y., Shi, G., Xu, L., and Li, X. (2020). Mineralogy and Geochemistry of Nephrite Jade from Yinggelike Deposit, Altyn Tagh (Xinjiang, NW China). Minerals, 10.
5. Formation of the nephrite deposit with five mineral assemblage zones in the Central Western Kunlun Mountains, China;Zhang;J. Petrol.,2022
Cited by
1 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
1. Dolomite type nephrite processing wastes and their application;Gornye nauki i tekhnologii = Mining Science and Technology (Russia);2023-07-24