Hydro-uvarovite from Mantle Peridotites of Naga Hills Ophiolite:A Mineral Tracer for Neo-Tethyan Mantle Wedge MetasomatismOACSTPCD
Hydro-uvarovite from Mantle Peridotites of Naga Hills Ophiolite:A Mineral Tracer for Neo-Tethyan Mantle Wedge Metasomatism
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 Cr2O3 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-pH 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.
Anisha VERENCAR;Abhishek SAHA;Nilanjana SORCAR;Sohini GANGULY;Pankaj KUMAR;Atul Kumar SINGH
CSIR-National Institute of Oceanography,Dona Paula,Goa 403004,India||School of Earth,Ocean and Atmospheric Sciences,Goa University,Taleigão Plateau,Goa 403206,IndiaCSIR-National Institute of Oceanography,Dona Paula,Goa 403004,IndiaNational Centre for Earth Science Studies,Thiruvananthapuram,Kerala,IndiaSchool of Earth,Ocean and Atmospheric Sciences,Goa University,Taleigão Plateau,Goa 403206,IndiaInter University Accelerator Centre(IUAC),New Delhi 110067,IndiaInter University Accelerator Centre(IUAC),New Delhi 110067,India||North-Eastern Hill University,Shillong,Meghalaya 793022,India
uvarovitehydroxylmetasomatic alterationlow-Cr diopsidesserpentinizationmantle peridotite
《地质学报（英文版）》 2024 (004)
867-877 / 11
AS and AV are grateful to the Director,CSIR-National Institute of Oceanography,Goa for his encouragement,support and permission to publish this work.AV sincerely acknowledges Dr.A.J.Locock for insightful discussion on the hydrous garnet.AS acknowledges the funding received from the Science and Engineering Research Board(SERB),Govt.of India under GAP 3291.The Secretary,MoES,Govt of India and Director,National Centre for Earth Science Studies,Thiruvananthapuram are thanked for providing analytical support to carry out the work.NS thanks Dr.Sneha Mukherjee for help during EPMA analyses.Authors are thankful to IUAC for extending LA-HR-ICPMS established under National Geochronology Facility funded by Ministry of Earth Science(MoES)with project reference number MoES/P.O.(Seismic)8(09)-Geochron/2012.We thankfully acknowledge the Editor-in-Chief and two anonymous reviewers for their constructive comments.This study is a part of Ph.D.work of AV.This is NIO's contribution no.7256.
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