Metasomatic origin of garnet xenocrysts from the *** kimberlite pipe,Arkhangelsk region,NW Russia

作     者：E.V.Shchukina A.M.Agashev N.P.Pokhilenko 

作者机构：Sobolev Institute of Geology and MineralogySiberian Branch Russian Academy of Sciences 

出 版 物：《Geoscience Frontiers》 (地学前缘（英文版）)

年 卷 期：2017年第8卷第4期

页      面：641-651页

核心收录：

学科分类：070904[理学-构造地质学] 0709[理学-地质学] 07[理学] 070901[理学-矿物学、岩石学、矿床学] 0708[理学-地球物理学] 0704[理学-天文学] 

基　　金：supported by the FBRF(Grants No.15-05-07758) by state assignment project No.Ⅷ.72.1.1 

主　　题：Lithospheric mantle Mantle xenolith Lherzolite harzburgite wehrlite megacryst paragenesis Trace element Major element Kimberlite 

摘      要：This paper presents new major and trace element data from 150 garnet xenocrysts from the *** kimberlite pipe located in the central part of the Arkhangelsk diamondiferous province（ADP）.Based on the concentrations of Cr_2O_3,CaO,TiO_2 and rare earth elements（REE） the garnets were divided into seven groups：（1） lherzolitic ＂depleted＂ garnets（ ＂Lz 1＂）,（2） lherzolitic garnets with normal REE patterns（ ＂Lz2＂）,（3） lherzolitic garnets with weakly sinusoidal REE patterns（ ＂Lz 3＂）,（4） lherzolitic garnets with strongly sinusoidal REE patterns（ ＂Lz 4＂）,（5） harzburgitic garnets with sinusoidal REE patterns（ ＂Hz＂）,（6）wehrlitic garnets with weakly sinusoidal REE patterns（ ＂W＂）,（7） garnets of megacryst paragenesis with normal REE patterns（ ＂Meg＂）.Detailed mineralogical and geochemical garnet studies and modeling results suggest several stages of mantle metasomatism influenced by carbonatite and silicate *** metasomatism at the first stage resulted in refertilization of the lithospheric mantle,which is evidenced by a nearly vertical CaO-Cr_2O_3 trend from harzburgitic（ ＂Hz＂） to lherzolitic（ ＂Lz 4＂） garnet *** garnets（ ＂Hz＂） have probably been formed by interactions between carbonatite melts and exsolved garnets in high-degree melt extraction *** the second stage of metasomatism,garnets with weakly sinusoidal REE patterns（ ＂Lz 3＂, ＂W＂） were affected by a silicate melt possessing a REE composition similar to that of ADP alkaline mica-poor *** the last stage,the garnets interacted with basaltic melts,which resulted in the decrease CaO-Cr_2O_3 trend of ＂Lz 2＂ garnet ***-poor garnets of megacryst paragenesis（ ＂Meg＂） could crystallize directly from the silicate melt which has a REE composition close to that of ADP alkaline mica-poor picrites.P-T estimates of the garnet xenocrysts indicate that the interval of-60-110 km of the lithospheric mantle beneath the *** pipe was predominantly affected by the silicate melts,wherea