Multiple generations of forearc mafic–ultramafic rocks in the Timor–Tanimbar ophiolite, eastern Indonesia
Multiple generations of forearc mafic–ultramafic rocks in the Timor–Tanimbar ophiolite, eastern Indonesia
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DOI：
10.1016/j.gr.2006.04.007
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发表时间：
2007
影响因子：
6.1
通讯作者：
A. Ishikawa;Y. Kaneko;A. Kadarusman;T. Ota
中科院分区：
文献类型：
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作者：
A. Ishikawa;Y. Kaneko;A. Kadarusman;T. Ota
我们调查了镁铁质-超镁铁质岩石分布在东帝汶Tanimbar地区作为一个可能的现代类似的地中海型蛇绿岩在特提斯系统。地质产状表明，澳大利亚大陆的浮力俯冲作用抬升了新形成的幔-壳剖面的碎片，并延伸到邻近的先侵位弧前边缘盆地。然而，我们认识到大量的各种火成岩的功能，这是一致的，缺乏完整的继承和存在丰富的横切结构。帝汶（Mutis、Atapupu和Dili）的所有橄榄岩体的成分大多是肥沃的（二辉橄榄岩）。此外，我们还发现，亏损方辉橄榄岩、高耐火纯橄榄岩和橄榄石二辉橄榄岩作为次要成分出现，与二辉橄榄岩的成分形成对比。结构上覆Ocussi火山岩类似岛弧拉斑玄武岩的微量元素特征，显然不符合与帝汶二辉橄榄岩群众的成因关系。在东部的小岛屿（Moa和Dai），所有类型的蛇绿岩显示不同程度的岛弧亲和力。傣族伟氏岩和辉长岩的堆积成因以单斜辉石结晶早、高钙斜长石普遍产出为标志。相对于Ocussi火山岩，切割辉长岩序列的岩脉具有较弱的岛弧特征。Moa中等亏损的二辉橄榄-方辉橄榄岩被高镁安山质岩浆侵入，结晶出含高镁斜方辉石的角闪石辉长岩。这些岩石学和地球化学的变化可以用（1）可能与弧前盆地的发展有关的岩浆活动的时间变化和（2）在每个地点空间上不同的弧前区的侵位来解释。异常发生肥沃的二辉橄榄岩在弧前设置，代高镁安山岩岩浆，反转变质等级记录从相关的变质岩，和边缘盆地的形成可能与高温软流圈物质注入地幔楔。
We investigated mafic–ultramafic rocks distributed in the Timor–Tanimbar region as a possible modern analogue for the Mediterranean-type ophiolites in the Tethyan system. The geological occurrence suggests that the buoyant subduction of Australian continent uplifted the fragments of newly formed mantle–crust section, which extends to the neighboring preemplaced forearc marginal basins. However, we recognized a large variety of igneous features, which is consistent with the lack of complete succession and the presence of abundant crosscutting structures. All peridotite masses in Timor (Mutis, Atapupu and Dili) are mostly fertile (lherzolitic) in compositions. In addition, we found depleted harzburgite, highly refractory dunite and olivine websterite to occur as minor constituents, which display compositional contrast to those of the lherzolites. Structurally overlying Ocussi volcanics resemble island–arc tholeiite in terms of trace element characteristics, apparently inconsistent with genetic relationship with Timor lherzolite masses. In eastern small islands (Moa and Dai), all types of ophiolitic rocks display varying degrees of island–arc affinities. Cumulate origin of wehrlite and gabbroic rocks in Dai is marked by early crystallization of clinopyroxene and common occurrence of high-calcic plagioclase. Dikes cutting the gabbro sequence have weak island–arc signatures relative to those of Ocussi volcanics. Mildly depleted lherzolite–harzburgite in Moa was intruded by high-Mg andesitic magma, which crystallized hornblende gabbro containing high-Mg orthopyroxene. These petrological and geochemical variations can be best explained by the combination of (1) a temporal change of igneous activity possibly associated with development of forearc basin and (2) the emplacement of spatially different forearc regions in each locality. Unusual occurrence of fertile lherzolite in the forearc setting, generation of high-Mg andesite magmatism, inverted metamorphic grade recorded from associated metamorphic rocks, and formation of marginal basins may be linked to the injection of high-temperature asthenospheric materials into the mantle wedge.