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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Copper-mineralised porphyries sample the evolution of a large-volume silicic magma reservoir from rapid assembly to solidification
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Copper-mineralised porphyries sample the evolution of a large-volume silicic magma reservoir from rapid assembly to solidification

机译：铜矿化卟啉样样本从快速组装到凝固的大批量硅状岩浆储层的演变

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Volatile-rich intermediate to silicic magmatic systems can feed devastating volcanic eruptions but also generate valuable magmatic-hydrothermal ore deposits that supply most of the world's copper. Understanding the geometry, dynamics and timescales of these magmatic systems is critical in developing models for predicting the occurrence of ore deposits and future large volcanic eruptions. Here, we use zircon petrochronology from an equigranular monzonite and successively emplaced porphyry dykes to reconstruct the time - temperature - composition evolution of the magma that sourced the giant Cu-MoAu deposit at Bingham Canyon (USA). Combining high-precision CA-ID-TIMS geochronology with in-situ trace element analyses by LA-ICP-MS shows the intra-grain, inter-sample and temporal geochemical changes recording the evolution of the magmatic system over 817 +/- 62 kyr. Systematic variation of zircon chemistry with time indicates crystallisation from a coherent magma reservoir. After reservoir assembly its thermal and chemical state was controlled by protracted monotonous crystallisation over similar to 650 kyr with rapid cooling over the first 200 kyr followed by a longer period approaching the granite solidus. Porphyry Cu-Au ore formation occurred after the early drop in magma temperature that resulted in large-scale fluid saturation and expulsion into the sub-volcanic environment but main Momineralisation occurred after protracted low-temperature magma storage and the emplacement of the last porphyry. Zircons do not quantify the depth of this reservoir but integrating independent geophysical evidence with 2-D thermal modelling indicates that the time - temperature evolution recorded by the zircons is consistent with rapid incremental assembly of this large pluton (magma emplacement rate greater than or similar to 0.0065km3/yr) by initially zircon-undersaturated monzonitic magma into pre-heated upper crust. Our results indicate that massive fluid expulsion from rapidly-formed, large magma reservoirs containing mobile but mushy magma (>40 wt.% melt) can occur in the upper crust, favouring the formation of giant porphyry copper deposits. (C) 2021 The Author(s). Published by Elsevier B.V.
机译：富含挥发性的中硅岩浆系统可以引发毁灭性的火山喷发，但也会产生宝贵的岩浆热液矿床，供应世界上大部分的铜。了解这些岩浆系统的几何、动力学和时间尺度，对于开发预测矿床产状和未来大型火山喷发的模型至关重要。在这里，我们使用等粒二长岩和连续侵位的斑岩脉的锆石岩石年代学来重建岩浆的时间-温度-成分演化，该岩浆是宾厄姆峡谷（美国）巨大Cu MoAu矿床的来源。将高精度CA-ID-TIMS地质年代学与LA-ICP-MS原位微量元素分析相结合，显示了粒内、样品间和时间地球化学变化，记录了817+/-62 kyr以上岩浆系统的演化。锆石化学随时间的系统变化表明，从连贯的岩浆储层结晶。储层组装后，其热状态和化学状态由类似于650 kyr的长时间单调结晶控制，在最初200 kyr内快速冷却，然后经过更长时间接近花岗岩固相线。斑岩型铜金矿的形成发生在岩浆温度早期下降之后，这导致了大规模的流体饱和并被排到次火山环境中，但主要的成矿作用发生在长期的低温岩浆储存和最后一个斑岩的侵位之后。锆石没有量化该储层的深度，但将独立的地球物理证据与二维热模拟相结合表明，锆石记录的时间-温度演化与该大型深成岩体（岩浆侵位速率大于或类似于0.0065km3/yr）的快速增量组合相一致，最初，锆石未饱和二长岩岩浆进入预热状态上地壳。我们的研究结果表明，上地壳中可能会出现大量流体从快速形成的大型岩浆储层中排出，这些岩浆储层中含有流动但呈糊状的岩浆（>40 wt.%熔体），有利于形成巨型斑岩铜矿。（c）2021作者。由Elsevier B.V.出版。

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