Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites
Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites
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希腊奥特里斯地块 Ayios Stefanos 矿中含锆石铬铁矿的成因和多期蚀变：对蛇绿质铬铁矿中锆石起源的非常规假说的评估
DOI：
10.3390/min6040124
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发表时间：
2016-11
期刊：
影响因子：
2.5
通讯作者：
Evangelos Tzamos
中科院分区：
文献类型：
--
作者：
Argyrios Kapsiotis;Annie Ewing Rassios;Aspasia Antonelou;Evangelos Tzamos
在希腊西部Othris蛇绿岩杂岩的Ayios Stefanos退休矿山中，几个小型铬（Cr）矿体位于构造变薄的纯橄榄岩单元内。铬矿石由半块状至块状、豆荚状和透镜状铬铁矿的构造印记体组成，这些铬铁矿由高Cr# [Cr/（Cr + Al）= 0.51-0.66]和Mg# [Mg/（Mg + Fe 2+）= 0.58-0.76]、低Fe 3 +# [Fe 3 +/（Fe 3 + + Fe 2+）0.43]和低TiO 2含量（0.21重量%）。这种组合物的特点是铬尖晶石平衡与岛弧拉斑玄武岩（IAT）和洋中脊玄武岩（MORB）之间的中间亲和力的熔体。这些矿石中的几种铬尖晶石晶体表现出由镁硅酸盐的尖晶石托管定向层状结构（主要是尖晶石）组成的不完美区域，这些层状结构局部沿着晶界和裂缝过度生长。从Cr-尖晶石核心到富含片晶的边缘，Cr#、Mg#和Fe ~（3+）#一般增加（分别为0.68-0.87、0.78-0.88和0.55-0.80），而从核心或具有取向片晶的尖晶石区到多孔域，Mg#和Fe ~（3+）#一般减少（分别为0.45-0.74和0.51）。在氧化条件下形成的片层丰富的轮辋，而多孔轮辋导致从后来的还原事件。几个微小的（30米），半自形到非自形和细长的含锆硅酸盐矿物颗粒被发现，主要是沿着开放和愈合的裂缝切割铬尖晶石。大多数含锆硅酸盐矿物（35粒中有30粒）是在一个被复杂的辉长岩脉网络侵入的铬铁矿巨石中发现的。到目前为止，主要的含锆硅酸盐相是锆石，在阴极发光（CL）图像中显示出均匀的内部纹理。拉曼光谱数据表明，锆石经历了由于自辐照的结构损伤。其微量元素含量表明，从斜长岩轴承，低SiO2中间基性来源的衍生。结合微观结构和矿物化学数据重复锆石衍生有限体积的高T流体从辉长岩侵入体的可能性。一旦锆石在裂纹中沉淀，其可转变为富含Ca的含Zr硅酸盐相（即，钙镁铁榴石、钙针铁矿）。几乎所有的锆石在这些样品中的溶剂化合物（CaO，Al 2 O3和FeO）的收益的证据可能是由于再平衡与后期氘流体。
Several small chromium (Cr) ore bodies are hosted within a unit of tectonically thinned dunite in the retired Ayios Stefanos mine of the western Othris ophiolite complex in Greece. Chromium ores consist of tectonically imprinted bodies of semi-massive to massive, podiform and lenticular chromitites composed of chromian spinel [Cr-spinel] with high Cr# [Cr/(Cr + Al) = 0.51–0.66] and Mg# [Mg/(Mg + Fe2+) = 0.58–0.76], low Fe3+# [Fe3+/(Fe3+ + Fe2+) 0.43] and low TiO2 (0.21 wt %) content. This composition is characteristic of Cr-spinels in equilibrium with melts of intermediate affinity between island-arc tholeiites (IATs) and mid-ocean ridge basalts (MORBs). Several Cr-spinel crystals in these ores exhibit imperfect zones made up of spinel hosting oriented lamellae of Mg-silicates (mostly chlorite) locally overgrown by porous domains along grain boundaries and fractures. From the Cr-spinel core to the lamellae-rich rim Cr#, Mg# and Fe3+# generally increase (0.68–0.87, 0.78–0.88 and 0.55–0.80, respectively), whereas from the.core or the spinel zones with oriented lamellae to the porous domains Mg# and Fe3+# generally decrease (0.45–0.74 and 0.51, correspondingly). The lamellae-rich rims formed at oxidizing conditions, whereas the porous rims resulted from a later reducing event. Several tiny (30 m), subhedral to anhedral and elongated Zr-bearing silicate mineral grains were discovered mainly along open and healed fractures cutting Cr-spinel. Most of the Zr-bearing silicate minerals (30 out of 35 grains) were found in a chromitite boulder vastly intruded by a complex network of gabbroic dykes. The dominant Zr-bearing silicate phase is by far zircon displaying a homogeneous internal texture in cathodoluminescence (CL) images. Raman spectroscopy data indicate that zircons have experienced structural damage due to self-irradiation. Their trace-element contents suggest derivation from a plagioclase-bearing, low-SiO2 intermediate to mafic source. Combined micro-textural and minerochemical data repeat the possibility of zircon derivation from limited volumes of high-T fluids emanating from the gabbroic intrusions. Once zircon is precipitated in cracks, it may be altered to Ca-rich Zr-bearing silicate phases (i.e., armstrongite, calciocatapleiite). Almost all zircons in these samples show evidence of gains in solvent compounds (CaO, Al2O3 and FeO) possibly due to re-equilibration with late deuteric fluids.
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影响因子：
4.5
作者：
Geisler, Thorsten;Schaltegger, Urs;Tomaschek, Frank
通讯作者：
Tomaschek, Frank
影响因子：
1.3
作者：
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通讯作者：
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5.8
作者：
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通讯作者：
Nicole M. McGowan;W. Griffin;J. González-Jiménez;E. Belousova;J. Afonso;R. Shi;C. McCammon;N. Pear
影响因子：
2.7
作者：
T. Geisler;A. A. Rashwan-A.;M. Rahn;U. Poller;H. Zwingmann;R. Pidgeon;H. Schleicher;F. Tomaschek
通讯作者：
T. Geisler;A. A. Rashwan-A.;M. Rahn;U. Poller;H. Zwingmann;R. Pidgeon;H. Schleicher;F. Tomaschek
影响因子：
3.1
作者：
C. Palenik;L. Nasdala;R. Ewing
通讯作者：
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