Sodic-calcic alteration and transpressional shear along the Atacama fault system during IOCG mineralization, Copiapó, Chile

IF 4.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
N. M. Seymour, J. S. Singleton, R. Gomila, G. Arancibia, J. Ridley, M. L. Gevedon, D. F. Stockli, S. M. Seman
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Abstract

The Punta del Cobre district near Copiapó is a center of iron oxide-copper–gold (IOCG) mineralization spatially and temporally associated with regional sodic-calcic hydrothermal alteration, the Atacama fault system (AFS), and two phases of Early Cretaceous magmatism. Here, we investigate the spatiotemporal and geochemical relationships between magmatism, ductile deformation, and hydrothermal alteration along the ~ 200 to 300-m-thick steeply NW-dipping Sierra Chicharra shear zone, interpreted to be the major strand of the AFS. Mylonitic fabrics and oblique sinistral-reverse kinematic indicators together record coaxial flattening in a transpressional regime. Deformation on the AFS took place before, during, and after intrusion of the synkinematic Sierra Chicharra quartz diorite of the Coastal Cordillera arc at ~ 122 Ma and terminated before intrusion of the unstrained ~ 114 Ma Sierra Atacama diorite of the Copiapó batholith. Geochemical data show that the Copiapó batholith was more mafic and more K-rich than the calc-alkaline Coastal Cordillera arc. This time period thus overlaps IOCG mineralization in the Punta del Cobre district (~ 120 to 110 Ma). Multiple phases of sodic-calcic alteration in and around the AFS shear zone are recognized. Textures of altered rock in the shear zone show both synkinematic assemblages and post-kinematic hydrothermal oligoclase. A ~ 775-m-long andradite vein that cuts the shear zone formed broadly at the end of magmatism in the district (~ 95 Ma). Oxygen isotope ratios from the vein indicate that hydrothermal fluids were likely magmatically derived. Together, this work shows the AFS-related shear zone and nearby IOCG mineralization developed in a regional transpressional regime produced by SE-directed oblique convergence across a NE-striking shear zone. IOCG-related magmatic-hydrothermal fluids exploited this transcrustal shear zone to produce multiple episodes of regional sodic-calcic alteration formed from fluids exsolved from magmas or driven by the heat of the Coastal Cordillera arc and Copiapó batholith.

Abstract Image

智利科皮亚波 IOCG 成矿过程中沿阿塔卡马断层系统的钠钙质蚀变和转位剪切作用
科皮亚波(Copiapó)附近的科布雷角(Punta del Cobre)地区是氧化铁-铜-金(IOCG)矿化中心,在空间和时间上与区域钠钙热液蚀变、阿塔卡马断层系统(Atacama fault system,AFS)以及早白垩世岩浆活动的两个阶段有关。在此,我们研究了岩浆活动、韧性变形和热液蚀变之间的时空和地球化学关系,这些活动沿约 200 至 300 米厚的陡峭西北倾 Sierra Chicharra 剪切带进行,该剪切带被解释为 AFS 的主要地段。麦饭石质构造和斜向正弦反向运动指标共同记录了转压机制下的同轴扁平化。AFS上的变形发生在海岸科迪勒拉弧的Sierra Chicharra石英闪长岩侵入之前、期间和之后(约122 Ma),并在科皮亚波浴岩的Sierra Atacama闪长岩侵入之前(约114 Ma)终止。地球化学数据显示,与钙碱性海岸科迪勒拉弧相比,科皮亚波浴岩的岩浆含量更高,钾含量更丰富。因此,这一时期与 Punta del Cobre 地区的 IOCG 成矿期(约 120 至 110 Ma)重叠。AFS剪切带及其周围的钠钙质蚀变有多个阶段。剪切带中的蚀变岩的纹理显示了同生组合和热液后低凝灰岩。切割剪切带的一条长约 775 米的安山岩脉大致形成于该地区岩浆活动的末期(约 95 Ma)。矿脉中的氧同位素比率表明热液很可能是岩浆流体。总之,这项研究表明,AFS 相关剪切带和附近的 IOCG 矿化是在一个区域性的换位体系中形成的,该换位体系是由穿越东北向切变带的东南向斜向辐合产生的。与 IOCG 相关的岩浆-热液利用这条横贯地壳的剪切带产生了多次区域性钠钙质蚀变,这些蚀变是由岩浆中溶解出来的流体或由海岸科迪勒拉弧和科皮亚波熔岩的热量驱动形成的。
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来源期刊
Mineralium Deposita
Mineralium Deposita 地学-地球化学与地球物理
CiteScore
11.00
自引率
6.20%
发文量
61
审稿时长
6 months
期刊介绍: The journal Mineralium Deposita introduces new observations, principles, and interpretations from the field of economic geology, including nonmetallic mineral deposits, experimental and applied geochemistry, with emphasis on mineral deposits. It offers short and comprehensive articles, review papers, brief original papers, scientific discussions and news, as well as reports on meetings of importance to mineral research. The emphasis is on high-quality content and form for all articles and on international coverage of subject matter.
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