Elevated magma fluxes deliver high-Cu magmas to the upper crust
Elevated magma fluxes deliver high-Cu magmas to the upper crust
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DOI：
10.1130/g47562.1
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发表时间：
2020-10-01
期刊：
影响因子：
5.8
通讯作者：
Kunz, Barbara E.
中科院分区：
文献类型：
--
作者：
Cox, Daniel;Watt, Sebastian F. L.;Kunz, Barbara E.
斑岩型铜金矿床在全球范围内都与会聚边缘伴生。然而，控制亲硫元素的加工和分布（例如，Cu）存在争议。在这里，我们表明，岩浆喂养许多智利成层火山fractured硫化物与高铜/银比在其地壳演化的早期。这些岩浆显示出下地壳石榴子石和角闪石结晶的证据，其硫化物分馏和Cu贫化的程度与地壳厚度和石榴子石分馏的程度增加。然而，样品从一小部分的火山喷发通量升高离开这个铜耗尽的趋势，而不是喷发富铜岩浆。这意味着，在这些非典型的网站，提高岩浆生产力和地壳吞吐量，潜在的促进“途径”利用主要的地壳断层系统，使快速岩浆过境，避免低地壳铜贫化硫化物分馏和潜在的斑岩矿石成因中发挥重要作用。
Porphyry Cu-Au ore deposits are globally associated with convergent margins. However, controls on the processing and distribution of the chalcophile elements (e.g., Cu) during convergent margin magmatism remain disputed. Here, we show that magmas feeding many Chilean stratovolcanoes fractionate sulfides with a high-Cu/Ag ratio early in their crustal evolution. These magmas show evidence of lower-crustal garnet and amphibole crystallization, and their degree of sulfide fractionation and Cu depletion increase with both crustal thickness and the extent of garnet fractionation. However, samples from a small proportion of volcanoes with elevated eruptive fluxes depart from this Cu-depleting trend, instead erupting Cu-rich magmas. This implies that at these atypical sites, elevated magma productivity and crustal throughput, potentially facilitated by "pathways" exploiting major crustal fault systems, enable rapid magma transit, avoiding lower-crustal Cu-depleting sulfide fractionation and potentially playing an important role in porphyry ore genesis.