Early Cretaceous adakite from the Atlas porphyry Cu-Au deposit in Cebu Island, Central Philippines: Partial melting of subducted oceanic crust
Early Cretaceous adakite from the Atlas porphyry Cu-Au deposit in Cebu Island, Central Philippines: Partial melting of subducted oceanic crust
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菲律宾中部宿雾岛阿特拉斯斑岩铜金矿床的早白垩世埃达克岩：俯冲洋壳的部分熔融
DOI：
10.1016/j.oregeorev.2019.102937
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发表时间：
2019
影响因子：
3.3
通讯作者：
Sun Weidong
中科院分区：
文献类型：
--
作者：
Deng Jianghong;Yang Xiaoyong;Qi Huasheng;Zhang Zhao-feng;Mastoi Abdul Shakoor;Berador Al Emil G.;Sun Weidong
菲律宾岛弧系广泛发育新生代弧火山岩、埃达克岩和大型铜金矿床。此外，迄今为止，整个菲律宾仅发现两个早白垩世埃达克质侵入体，菲律宾中部宿务岛的卢托潘闪长岩和邻近的坎西闪长岩。卢托潘闪长岩（岩性为闪长岩至石英闪长岩）是菲律宾唯一的白垩纪巨型阿特拉斯斑岩型铜金存款的成矿侵入体。通过对阿特拉斯斑岩型铜金存款卡门坑中的卢托潘闪长岩进行年代学和地球化学研究，并与宿务岛早白垩世坎西闪长岩和弧火山岩进行对比，揭示了岩石成因和岩浆来源。卡门闪长岩具有中等SiO2和MgO含量、高Na 2 O和低K2 O含量、LREE富集和铲状REE配分模式、低Yb和Y含量、高Sr含量和高Sr/Y比值、低（87 Sr/86 Sr）i（0.7037-0.7038）等现代岛弧埃达克岩的特征。卡门闪长岩早白垩世锆石U-Pb年龄为109 Ma-107 Ma，与北部坎西闪长岩的U-Pb年龄在误差范围内一致。卡门闪长岩和坎西闪长岩都形成于洋内岛弧环境。卡门闪长岩的稀土配分模式为板状，Nb/Ta比值低，Zr/Sm比值高，表明其形成于角闪岩相的俯冲洋壳部分熔融，不同于坎西闪长岩的石榴角闪岩-角闪榴辉岩熔融成因。卡门闪长岩岩浆源区存在少量俯冲沉积物，εNd（t）（+7.1 ~+10.6）、锆石εHf（t）（+3.3 ~+3.9）值和低Th/U比值进一步揭示了这一点。Carmen埃达克质岩浆在岩浆上升过程中没有与地幔橄榄岩发生明显的相互作用，表现为MgO含量和Mg#值适中，Cr和Ni含量较低，与具有高MgO、Mg#和Cr、Ni含量的Kansi埃达克岩（高镁埃达克岩）不同。我们认为，几乎同时代的Lutopan闪长岩和Kansi闪长岩是两个独立的早白垩世埃达克质侵入体在宿务岛，虽然他们都与铜，金矿化密切相关。陆陀盘闪长岩的板熔成因和高氧逸度是导致岩浆中Cu富集的重要因素，是形成巨型阿特拉斯斑岩型Cu-Au存款的必要条件。
In the Philippine island arc system, there are widely developed Cenozoic arc volcanic rocks, adakites and large Cu-Au deposits. Besides, only two early Cretaceous adakitic intrusions have been found in the entire Philippines so far, i.e., the Lutopan Diorite and the adjacent Kansi diorites in Cebu Island, Central Philippines. The Lutopan Diorite (diorite to quartz diorite in lithology) is the ore-forming intrusion of the giant Atlas porphyry Cu-Au deposit, which is the only Cretaceous porphyry deposit in the Philippines. In this study, geochronology and geochemistry of the Lutopan Diorite in the Carmen pit of Atlas porphyry Cu-Au deposit are investigated in detail, by comparing them with the previously studied Early Cretaceous Kansi diorites and arc volcanic rocks in Cebu Island, to reveal the petrogenesis and magma sources. The Carmen diorites are characterized by moderate SiO2and MgO contents, coupled with high Na2O and low K2O contents, LREE-enriched and listric REE distribution patterns, low Yb and Y contents, high Sr contents and thereby high Sr/Y ratios, and low (87Sr/86Sr)i (0.7037–0.7038), typical of modern island arc adakites. Zircon U-Pb ages of the Carmen diorites are 109 Ma − 107 Ma in the Early Cretaceous, which is identical with that of the Kansi diorite in the north within error. Both the Carmen and Kansi diorites were formed in intra-oceanic island arc settings. The Carmen diorites show listric REE patterns and low Nb/Ta, high Zr/Sm ratios, suggesting they are formed by partial melting of subducted oceanic crust in amphibolite facies, which is different from the garnet amphibolite- to amphibole eclogite-melting genesis of the Kansi diorites. There is a small amount of subducted sediments in the magma source of Carmen diorite, as further revealed by εNd(t) (+7.1 to +10.6), zircon εHf(t) (+3.3 to +3.9) values, and low Th/U ratios. The Carmen adakitic magma did not undergo significant interaction with mantle peridotite during magma ascent as indicated by the moderate MgO content and Mg# value, and quite low Cr and Ni contents, distinguished from the Kansi diorite (high-Mg adakite) that have high MgO, Mg#, and Cr and Ni contents. We suggest that the nearly contemporary Lutopan Diorite and Kansi diorite are two independent Early Cretaceous adakitic intrusions in Cebu Island, although they are both closely associated with Cu-Au mineralization. The slab-melting genesis and high oxygen fugacities of the Lutopan Diorite are the most important factors to cause Cu enrichment in the magma, which is necessary to form the giant Atlas porphyry Cu-Au deposit.