The genetic association of adakites and Cu–Au ore deposits
The genetic association of adakites and Cu–Au ore deposits
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DOI：
10.1080/00206814.2010.507362
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发表时间：
2011-02
影响因子：
2.6
通讯作者：
Weidong Sun;Hong Zhang;M. Ling;Xing Ding;Sun‐Lin Chung;Jibin Zhou;Xiaoyong Yang;W. Fan
中科院分区：
文献类型：
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作者：
Weidong Sun;Hong Zhang;M. Ling;Xing Ding;Sun‐Lin Chung;Jibin Zhou;Xiaoyong Yang;W. Fan
埃达克岩可能是俯冲洋壳岩石圈或陆壳下部部分熔融形成的。利用La/Yb、Sr/Y比值、MgO和Na_2 O含量及Sr-Nd同位素特征，可区分这两种岩浆类型。鉴于玄武质地壳的铜浓度比下陆壳和地幔楔高两倍以上，由大洋板片熔融产生的“原始”埃达克岩应含有明显高于来自大陆地壳的埃达克岩，以及正常弧安山岩的铜含量。一个全球汇编的数据集显示，埃达克岩中的铜含量普遍低于正常弧岩。我们将这种低铜含量归因于埃达克质岩浆分异过程中硫酸盐还原导致的岩浆流体损失，而这又是由对矿化至关重要的铁钛氧化物结晶引起的。因此，下溢的大洋板片衍生的埃达克岩，可以释放大量的铜（可能是Au以及）的晶体分馏导致更高的潜力，铜，金矿化沿着会聚边缘，通常与脊俯冲。这种玄武质板片熔体最初具有相当高的Cu含量，因此特别是在相对封闭的岩浆系统中起着至关重要的作用，该岩浆系统负责生成斑岩Cu矿床。
Adakites may form by partial melting of either the subducting oceanic lithosphere or the lower part of the continental crust. These two magma types can be discriminated geochemically using a combination of La/Yb, Sr/Y ratios, MgO and Na2O contents, and Sr–Nd isotopes. Given that the basaltic crust has Cu concentrations more than two times higher than the lower continental crust and the mantle wedge, ‘primitive’ adakites produced by oceanic slab melting should contain significantly higher Cu contents than adakites derived from the continental crust, as well as normal arc andesites. A globally compiled dataset shows that Cu concentrations in adakites are generally lower than that in normal arc rocks. We attribute this low copper content to loss of magmatic fluids as a result of sulphate reduction during adakitic magma differentiation, in turn induced by the crystallization of Fe–Ti oxides, essential to mineralization. Therefore, the underflow of oceanic-slab-derived adakites that can release larger amounts of Cu (presumably Au as well) by crystal fractionation leads to higher potential for Cu–Au mineralization along convergent margins, usually associated with ridge subduction. Such basaltic slab melts initially have considerably higher Cu contents and thus play a crucial role particularly in the relatively closed magma system responsible for generating porphyry Cu deposits.