Genesis of Cr-bearing hydrogrossular-rich veins in a chromitite boulder from Ayios Stefanos, West Othris, Greece: A paradigm of microrodingites formation at the late stages of oceanic slab emplacement
Genesis of Cr-bearing hydrogrossular-rich veins in a chromitite boulder from Ayios Stefanos, West Othris, Greece: A paradigm of microrodingites formation at the late stages of oceanic slab emplacement
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希腊西奥里斯 Ayios Stefanos 铬铁矿巨石中含铬富水钙石矿脉的成因：大洋板片侵位后期微罗丁岩形成的范例
DOI：
10.1016/j.oregeorev.2017
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发表时间：
2017
影响因子：
3.3
通讯作者：
Aspasia Antonelou
中科院分区：
文献类型：
--
作者：
Argyrios Kapsiotis;Anne Ewing Rassios;Giovanni Grieco;Aspasia Antonelou
已废弃的Ayios Stefanos Chrome矿位于希腊中部Othris蛇绿岩西部的变形和蛇纹化地幔橄榄岩中。Chrome矿石由暴露在构造衰减纯橄榄岩内的m级透镜状至豆荚状铬铁矿体组成。我们研究了一个糜棱岩化的矿石巨石。（体积为2 m3），由几个蚀变辉长岩脉（15-20 cm厚）侵入的具有浅成结构的铬铁矿岩组成。这个铬铁岩巨石包括以前未描述的水石榴石轴承微静脉几乎肉眼可见。细脉彼此隔离，由未变形的富铬水钙铝榴石（球粒）、斜绿泥石、蛇纹石、硅灰石、火山灰岩、水镁石和从属量的其他相组成。侵入辉长岩的纹理观察表明，作为透闪石取代透辉石有生产的氧化富钙水介质。这是能够浸出铬，铝和铁2+从铬尖晶石碎片分散在细脉。由此产生的热液流体输送所需的成分沉淀的矿物组合类似的钙铝榴石。细脉中的氢钙铝榴石球显示出化学分带，其特征是Cr2 O3和Fe 2 O3的丰度增加，H2O浓度向其边界降低。微杆柱岩“动脉”的雁行结构与细脉矿物的未应变性质相结合，表明它们填充了糜棱岩化铬铁岩体中晚期伸展冷却裂隙。总的来说，细脉的结构矿物化学特征可以充分解释一般T减少仰冲板并发运输远离扩展中心。
The retired Ayios Stefanos chrome mine is hosted by deformed and serpentinized mantle peridotites of the western Othris ophiolite of central Greece. Chrome ores consist of m-scale lenticular to podiform chromitite bodies exposed within a tectonically attenuated dunite. We studied a mylonitized ore boulder.(2 m3 in volume) that consists of massive-textured chromitite intruded by several altered gabbroic.veins (15–20 cm thick). This chromitite boulder includes previously undescribed hydrogarnet-bearing microveins barely visible to the naked eye. The veinlets are isolated from each other and composed of undeformed Cr-rich hydrogrossular (spherules), clinochlore, serpentine, wollastonite, vesuvianite, brucite and subordinate amounts of other phases. Textural observations of the intruding gabbros indicate that as tremolite substituted for diopside there was production of an oxidizing Ca-rich aqueous medium. This was capable of leaching Cr, Al and Fe2+ from Cr-spinel fragments dispersed within the veinlets. The resultant hydrothermal fluids transported components required to precipitate a mineral assemblage resembling that of rodingite. Hydrogrossular globules in the veinlets display chemical zoning characterized by increasing abundances of Cr2O3 and Fe2O3 and decreasing H2O concentration toward their boundaries. The en echelon structure of the micro-rodingite ‘‘arteries” combined with the unstrained nature of the.veinlet minerals suggests that they filled late extensional cooling fractures in a mylonitized chromitite body. Overall, the structural-minerochemical characteristics of the veinlets can be adequately explained by general T decrease in the obducting slab concurrent to transport away from the spreading center.