Origin of the Diamonds within Chromitite from the Mirdita Ophiolite(Albania) and its Geological Significance  

作　　者：WU Weiwei YANG Jingsui ZHENG Jianping LIAN Dongyang QIU Tian RUI Huichao 

机构地区：[1]College of Marine Science and Technology,China University of Geosciences(Wuhan),No.388 Lumo Road,Wuhan 430074,China [2]CARMA,Key Laboratory of Deep-Earth Dynamics of MLR,Institute of Geology,Chinese Academy of Geological Sciences,No.26 Baiwanzhuang Road,Beijing 100037,China [3]School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China

出　　处：《Acta Geologica Sinica(English Edition)》2020年第S01期64-65,共2页地质学报（英文版）

基　　金：funded by grants from the International Geoscience Programme(IGCP 649,2015–2020);the Natural Science Foundation of China(41802055 and 41802034);the project from the China Postdoctoral Science Foundation(2018M632942);the Natural Science Foundation of Jiangsu(BK20180349);the Research Founding from Chinese Academy of Geological Sciences(J1903);the fund from the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources

摘　　要：Geophysical investigations and laboratory experiments show evidence for possible subduction of ancient oceanic crust.Geological and mineralogical observations suggest that subducted oceanic crust is recycled into the upper mantle.The subduction is supported by the recovery of superdeep diamonds from kimberlites and the presence of crustal materials in ophiolitic chromitites and their host peridotites.What is the mechanism?Here we report the new discovery of ophiolite-hosted diamonds in the podiform chromitites within the Skenderbeu massif from the Mirdita ophiolite in the western part of Neo-Tethys(Fig.1).The diamonds are characterized by exceedingly light C isotopes(δ13CPDB^-25‰),which can be interpreted as evidence for subduction of organic carbon from Earth’s surface.The diamonds are also characterized by an exceptionally large range inδ15Nair(-12.9‰to+25.5‰),accompanied by a low N aggregation state(Fig.2).On the other hand,materials sparsely included in diamonds include amorphous material,Ni-Mn-Co alloy,nanocrystals(20 nm×20 nm)of calcium silicate with an orthorhombic perovskite structure(Ca-Pv),and fluids(Fig.3).We consider that the Skenderbeu diamonds nucleated and grew from a C-saturated,NiMnCo-rich melt derived from a subducted slab of ocean crust and lithosphere in the deep mantle environment.The environment is in the diamond stability field or near the top of the mantle transition zone.The new discovery of diamonds from the Mirdita ophiolite provides a valuable opportunity to understand deep cycling of subducted oceanic crust and mantle(i.e.,composition and process).

关 键 词：Mirdita ophiolite DIAMOND NiMnCo alloy calcium silicate perovskite carbon and nitrogen isotopes SUBDUCTION West Albania 

分 类 号：P57[天文地球—矿物学]