The geochemical characteristics of Haiyang A-type granite complex in Shandong, eastern China
The geochemical characteristics of Haiyang A-type granite complex in Shandong, eastern China
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DOI：
10.1016/j.lithos.2014.04.014
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发表时间：
2014-07
期刊：
影响因子：
3.5
通讯作者：
He Li;M. Ling;Xing Ding;Hong Zhang;Cong-ying Li;Dunji Liu;Wei-dong Sun
中科院分区：
文献类型：
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作者：
He Li;M. Ling;Xing Ding;Hong Zhang;Cong-ying Li;Dunji Liu;Wei-dong Sun
海阳花岗岩杂岩由钾长花岗岩和正长岩组成，总出露面积约600 km 2。钾长花岗岩为偏铝质（A/CNK = 0.70 ~ 0.99），正长岩为稍过铝质（A/CNK = 1.01 ~ 1.10），具有高总碱含量和高FeOT/（FeOT+ MgO）比值的A型花岗岩的典型特征。钾长花岗岩和正长岩的锆石U-Pb年龄分别为116.8 ± 1.7Ma和115.8 ± 2.2Ma。这与野外观察到的正长岩侵入钾长花岗岩相一致。钾长花岗岩和正长岩的锆石O同位素组成变化较大（钾长花岗岩为5.65-7.78‰，正长岩为4.68-7.08‰），峰值略高于地幔锆石，反映了地幔的重要贡献。这些与钾长石花岗岩（− 22.4至− 15.6）和正长岩（− 24.6至− 13.5）的锆石εHf（t）值的巨大变化一起，可以通过至少两种成分的参与来最好地解释，例如，富集岩石圈地幔+/-俯冲物质和软流圈上涌。磷灰石具有右递减稀土配分模式。钾长花岗岩中磷灰石的Cl含量比正长岩中的高，说明钾长花岗岩源区受俯冲释放流体的影响较大。这种区别是支持系统较高的氧逸度的钾长石花岗岩所示的锆石Ce 4 +/Ce 3+的比例。在Yb/Ta-Y/Nb、Ce/Nb-Y/Nb图解中，钾长花岗岩和正长岩均为A1型，钾长花岗岩更接近A2型。在Nb-Y-3Ga和Nb-Y-Ce图中，正长岩位于A1和A2的分界线附近，而部分钾长花岗岩样品位于A2区，表明最初有从A2区向A1区过渡的趋势。一般来说，A1花岗岩形成于板内环境，而A2花岗岩形成于碰撞后环境。可能是俯冲释放流体交代的地幔组分更容易部分熔融，形成氧逸度较高的钾长花岗岩（接近A2型），从而消除俯冲特征，进而形成A1型正长岩。与下扬子带A1和A2群花岗岩出露于同一地区的情况相似，海阳花岗岩杂岩也可以用脊俯冲模式来解释，该模式被认为是控制华北陆块去克拉通化的机制。
Haiyang granite complex consists of K-feldspar granite and syenite, with a total exposure area of ~ 600 km2. The K-feldspar granite is metaluminous (A/CNK = 0.70 to 0.99) and the syenite is slightly peraluminous (A/CNK = 1.01 to 1.10), both of which have typical characteristics of A-type granite with high total alkali contents and FeOT/(FeOT+ MgO) ratios. Zircon U–Pb age are 116.8 ± 1.7 Ma and 115.8 ± 2.2 Ma, for the K-feldspar granite and the syenite, respectively. This is consistent with field observation that the syenite intruded into the K-feldspar granite. Varied zircon O isotope (5.65–7.78‰ for K-feldspar granite and 4.68–7.08‰ for syenite) with peak values that are marginally higher than those of mantle zircon reflects important mantle contributions. These together with large variation of zircon εHf(t) values of K-feldspar granite (− 22.4 to − 15.6) and syenite (− 24.6 to − 13.5), can best be explained by the involvement of at least two components, e.g., enriched lithospheric mantle +/− subducted materials, and upwelling asthenosphere. Apatite has right decline REE pattern. The apatite from K-feldspar granite has higher Cl contents than those of syenite, implying more influence from a subduction released fluid in K-feldspar granite source. This distinction is supported by the systematically higher oxygen fugacity of K-feldspar granite as indicated by zircon Ce4 +/Ce3 +ratios. In the Yb/Ta–Y/Nb, Ce/Nb–Y/Nb diagrams, both K-feldspar granite and syenite plot in A1-type, with K-feldspar granite plotting closer to A2. In the Nb–Y–3Ga and Nb–Y–Ce charts, syenite plots near the boundary between A1and A2, whereas some K-feldspar granite samples plot in A2field, indicating a tendency of transition originally from A2to A1. In general A1granites form in intraplate settings, whereas A2granite forms in post-collision. It is likely that mantle components metasomatized by subduction released fluids are easier to be partially melted, forming K-feldspar granite (closer to A2type) with higher oxygen fugacity, which consequently eliminated subduction signatures, and then followed by A1type syenite. Similar to the Lower Yangtze River belt, where both A1and A2group granites of similar ages outcropped in the same region, Haiyang granite complex may also be plausibly explained by a ridge subduction model, which has been proposed as the mechanism that controlled the decratonization of the North China Craton.