Hydro-uvarovite from Mantle Peridotites of Naga Hills Ophiolite: A Mineral Tracer for Neo-Tethyan Mantle Wedge Metasomatism  

作　　者：Anisha VERENCAR Abhishek SAHA Nilanjana SORCAR Sohini GANGULY Pankaj KUMAR Atul Kumar SINGH 

机构地区：[1]CSIR-National Institute of Oceanography,Dona Paula,Goa 403004,India [2]School of Earth,Ocean and Atmospheric Sciences,Goa University,Taleigao Plateau,Goa 403206,India [3]National Centre for Earth Science Studies,Thiruvananthapuram,Kerala,India [4]Inter University Accelerator Centre(IUAC),New Delhi 110067,India [5]North-Eastern Hill University,Shillong,Meghalaya 793022,India

出　　处：《Acta Geologica Sinica(English Edition)》2024年第4期867-877,共11页地质学报（英文版）

基　　金：the funding received from the Science and Engineering Research Board (SERB), Govt. of India under GAP 3291;funded by Ministry of Earth Science (MoES) with project reference number Mo ES/ P.O. (Seismic) 8 (09)-Geochron/2012。

摘　　要：Hydrous Cr-bearing uvarovite garnets are rare in natural occurrences and belong to the ugrandite series and exist in binary solid solutions with grossular and andradite garnets. Here, we report the occurrence of hydrous uvarovite garnet having Cr_(2)O_(3) upto 19.66 wt% and CaO of 32.12–35.14 wt% in the serpentinized mantle peridotites of Naga Hills Ophiolite(NHO), India. They occur in association with low-Cr diopsides. They are enriched in LILE(Ba, Sr), LREEs, with fractionating LREE-MREE [avg.(La/Sm)_(N) = 2.16] with flat MREE/HREE patterns [avg.(Sm/Yb)_(N) = 0.95]. Raman spectra indicate the presence of hydroxyl(OH^(–)) peaks from 3500 to 3700 cm^(-1). Relative abundances in fluid mobile elements and their close association with clinopyroxenes are suggestive of the formation of uvarovite garnets through low temperature metasomatic alteration of low-Cr diopsides by hydrothermal slab fluids. The high LREE concentration and absence of Eu anomaly in the garnet further attest to alkaline nature of the transporting slab dehydrated fluid rather the involvement of low-p H solution. The chemical characteristics of the hydroxyl bearing uvarovite hosted by the mantle peridotite of NHO deviate from the classical features of uvarovite garnet, and their origin is attributed to the fluid-induced metasomatism of the sub arc mantle wedge in a suprasubduction zone regime.

关 键 词：UVAROVITE HYDROXYL metasomatic alteration low-Cr diopsides SERPENTINIZATION mantle peridotite 

分 类 号：P542.5[天文地球—构造地质学] P588.125[天文地球—地质学]