High water content of arc magmas recorded in cumulates from subduction zone lower crust
High water content of arc magmas recorded in cumulates from subduction zone lower crust
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DOI：
10.1038/s41561-022-00947-w
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发表时间：
2022-05
影响因子：
18.3
通讯作者：
B. Urann;V. Le Roux;O. Jagoutz;O. Müntener;M. Behn;E. Chin
中科院分区：
文献类型：
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作者：
B. Urann;V. Le Roux;O. Jagoutz;O. Müntener;M. Behn;E. Chin
岩浆挥发分（如水）在弧熔体中含量丰富，对岩浆演化、喷发动力学和经济矿床的形成起着根本性的控制作用。为了限制弧岩浆的H2O含量，大多数研究都依赖于测量喷出产物和矿物熔融包裹体。然而，这些方法具有固有的局限性，混淆了弧岩浆中的H2O的全范围。在这里，我们报告二次离子质谱测量的挥发性（H2O，F，P，S，Cl）丰度下地壳堆积矿物从科希斯坦古弧（巴基斯坦西北部）和确定H2O丰度的熔体从堆积结晶。辉石保留岩浆H2O丰度和记录潮湿（小于1重量% H2O）含水（高达10重量% H2O）原始熔体。随后的晶体分馏导致形成超水熔体约12-20重量% H2O，预测岩石学，但实际上没有从熔体包裹体记录。斑岩铜矿很可能是超含水熔体流体出溶的自然结果，越来越多的证据证实了这一点。
Magmatic volatiles (for example, water) are abundant in arc melts and exert fundamental controls on magma evolution, eruption dynamics and the formation of economic ore deposits. To constrain the H2O content of arc magmas, most studies have relied on measuring extrusive products and mineral-hosted melt inclusions. However, these methods have inherent limitations that obfuscate the full range of H2O in arc magmas. Here, we report secondary-ion mass spectrometry measurements of volatile (H2O, F, P, S, Cl) abundances in lower-crustal cumulate minerals from the Kohistan palaeo-arc (northwestern Pakistan) and determine H2O abundances of melts from which the cumulates crystallized. Pyroxenes retained magmatic H2O abundances and record damp (less than 1 wt% H2O) to hydrous (up to 10 wt% H2O) primitive melts. Subsequent crystal fractionation led to formation of super-hydrous melts with approximately 12–20 wt% H2O, predicted petrologically yet virtually absent from the melt-inclusion record. Porphyry copper deposits are probably a natural eventuality of fluid exsolution from super-hydrous melts, corroborating a growing body of evidence.