Contrasting platinum-group mineral assemblages of the Kondyor massif (Russia): Implications for the sources of HSE in zoned-type ultramafic massifs
Contrasting platinum-group mineral assemblages of the Kondyor massif (Russia): Implications for the sources of HSE in zoned-type ultramafic massifs
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Kondyor 地块（俄罗斯）的铂族矿物组合对比：对分区型超镁铁地块中 HSE 来源的影响
DOI：
10.1016/j.lithos.2020.105800
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发表时间：
2020
期刊：
影响因子：
3.5
通讯作者：
Badanina, Inna Y.
中科院分区：
文献类型：
--
作者：
Malitch, Kreshimir N.;Puchtel, Igor S.;Belousova, Elena A.;Badanina, Inna Y.
本文报道了位于俄罗斯西伯利亚东部Kondyor带型超镁铁岩中第一高亲铁元素（HSE：Re，Os，Ir，Ru，Rh，Pt，Pd，Au）丰度和原生Pt-Fe矿物和富Os合金的Re-Os同位素数据。Kondyor Alzhef由三个带组成：（A）最古老的纯橄榄岩核，伴生铬铁矿，侵位年龄约为250 Ma;（B）较年轻的边缘，代表着与纯橄榄岩核有过渡接触的变结岩、韦尔岩、单斜辉石岩和暗色辉长岩;（C）出露于Alzhef西南部的最年轻的磷灰石-金云母-磁铁矿富集的单斜辉石岩网脉。它与纯橄榄岩核有侵入接触，形成于~125 Ma。在这项研究中分析的铬铁矿带（A）和单斜辉石带（C）的特点是不同的铂族矿物（PGM）的组合为主的Pt-Fe合金在前者和铜与sperrylite和Pt-Fe合金在后者，与从属量的Os-Ir合金存在于两个组合。Re-Os同位素结果表明，A带铬铁矿和铬铁矿本身的Os-Ir合金的初始187 Os/188 Os值（0.1249-0.1254）范围较窄（0.12466 ± 0.00005）。这种南极初始187 Os/188 Os值（γ 187 Os（T=250 Ma）介于-0.5和+0.1之间）表明，区域（A）中铬铁矿和PGM的HSE预算主要受地幔域的HSE预算控制，该地幔域与长期近南极Re/Os一起演化，这一观点也得到了Luguet等人（2019）的最新数据的支持。而C带单斜辉石中的Os合金的初始187 Os/188 Os值在0.1302 ~ 0.1308之间（初始γ 187 Os（T=125 Ma）= +3.2 ~+3.7），表明这些岩石的源岩为超球粒陨石的时间积分Re/Os。矿物学和同位素地球化学数据表明，研究的PGM和HSE的至少两个不同的来源，在Kondyor的超镁铁质岩石的高温起源。
This study presents the first highly siderophile element (HSE: Re, Os, Ir, Ru, Rh, Pt, Pd, Au) abundance and Re–Os isotopic data for primary Pt–Fe minerals and Os-rich alloys from the Kondyor zoned-type ultramafic massif located in the southeastern part of the Siberian Craton, Russia. The Kondyor massif is composed of three zones: (A) the oldest dunite core with associated chromitites, with an age of emplacement of ~250 Ma, (B) a younger rim represented by metadunite, wehrlite, clinopyroxenite, and melanocratic gabbro that has transitional contacts with the dunite core, and (C) the youngest apatite-phlogopite-magnetite-rich clinopyroxenite stockwork exposed in the southwestern part of the massif. It has intrusive contacts with the dunite core and formed at ~125 Ma. Chromitites from zone (A) and clinopyroxenites from zone (C) analyzed in this study are characterized by distinct platinum-group mineral (PGM) assemblages dominated by Pt–Fe alloys in the former and cooperite with sperrylite and Pt–Fe alloys in the latter, with subordinate amounts of Os–Ir alloys present in both assemblages. The Re–Os isotope results identify a narrow range of initial187Os/188Os values for Os–Ir alloys from the zone A chromitites (0.1249–0.1254) and the chromitites themselves (0.12466 ± 0.00005). Such chondritic initial187Os/188Os values (γ187Os(T=250 Ma)ranging between −0.5 and + 0.1) indicate that the HSE budget of the chromitites and PGM from zone (A) was largely controlled by that of the mantle domain that evolved with long-term near-chondritic Re/Os, a notion that is also supported by the recent data of Luguet et al. (2019). In contrast, Os alloys from the zone C clinopyroxenites have initial187Os/188Os values ranging between 0.1302 and 0.1308 (initial γ187Os(T=125 Ma)= +3.2 to +3.7), indicative of a suprachondritic time-integrated Re/Os in the source of these rocks. The mineralogical and isotope-geochemical data point to a high-temperature origin of the studied PGM and at least two distinct sources of HSE in the ultramafic rocks of the Kondyor massif.
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