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首页> 外文期刊>Journal of Asian earth sciences >Compositional variation of the late Cretaceous-Paleogene plutons from southwest Japan and its implication for ore genesis and continental growth
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Compositional variation of the late Cretaceous-Paleogene plutons from southwest Japan and its implication for ore genesis and continental growth

机译：日本西南部晚白垩世-古近系云母的组成变化及其对成因和大陆生长的影响

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摘要

During the late Cretaceous-Paleogene period, the fluids liberated from the subducting slab along Japanese-arc subduction zone could have triggered the partial melting of the mantle wedge, whose composition was similar to the fertile primitive mantle. Underplating of the produced basaltic magmas beneath the continental crust could further facilitate the partial melting of the lower continental crusts. The primary magmas produced by the mixing of resultant partial melts underwent various degrees of fractional crystallization processes to produce the late Cretaceous-Paleogene plutons in southwest Japan, and have contributed to the growth of continental crust with new, non-recycled materials during the Phanerozoic. The factor analysis of chemical data from ore-barren Ryoke and W-Sn-ore-rich Sanyo plutonic rocks identifies three major groups of elements: the mafic group (Al, Fe, Mg, Mn, Ca, Sr, Zn, Co, V, P, Cu, Ni, and Cr); the felsic group (Si, K, Rb, Cs, Tl, Pb, Y, Nb, Ta, Hf, Ge, Sn, W, Th, U, and HREE); and the LREE + Zr group (Ba, La, Ce, Pr, Nd, Eu, Zr, and Hf). Mafic group and felsic group elements are inversely correlated. The concentrations of LREE + Zr group elements increase first, then, decrease with increasing SiO_2 content. Therefore, the high silica samples of the Ryoke + Sanyo belts are low in LREE + Zr group elements. In the Ryoke samples Mo behaves like Zr, which results in the lowest Mo content in the Ryoke samples with high silica. The high Mo and Si contents in some Sanyo samples suggest that the zircon-compatible Mo~(4+) may be converted to incompatible Mo~(6+) under a relatively high oxygen fugacity condition at the late stage of magmatic differentiation. W and Sn behave as the felsic group elements in the Ryoke + Sanyo samples. Thus, their concentrations are high in the high silica granitoids, especially rock samples from the Sanyo belt, which are often associated with W-Sn ores. The factor analysis of the Sanin plutonic samples indicates that W still belongs to the felsic group, but Sn no longer correlates with W and behaves more like Zr due to the conversion of incompatible Sn~(2+) to zircon-compatible Sn~(4+) under a relatively high oxygen fugacity condition in the Sanin belt. Therefore, Sn content is low in high silica granitoids from Sanin belt. The high silica Sanin samples are often enriched in Mo, again suggesting the conversion of zircon-compatible Mo~(4+) into incompatible Mo~(6+) in the magmas of those samples. The high Mo granitoids from the Sanin belt are probable source rocks for the associated Mo ores in the area.
机译：在白垩纪-古近纪晚期，沿着日本弧俯冲带从俯冲板释放的流体可能触发了地幔楔的部分融化，其成分类似于肥沃的原始地幔。在大陆壳之下对产生的玄武岩浆进行底盘作用可以进一步促进下部大陆壳的部分融化。由混合产生的部分熔体产生的初级岩浆经历了不同程度的分步结晶过程，以在日本西南部生产晚白垩世-古近系云母，并在新生代期间利用新的不可回收材料促进了陆壳的生长。来自贫矿性的Ryoke和富含W-Sn矿石的三洋矿床的化学数据的因子分析确定了三大元素组：铁镁质组（Al，Fe，Mg，Mn，Ca，Sr，Zn，Co，V ，P，Cu，Ni和Cr）；长素族（Si，K，Rb，Cs，Tl，Pb，Y，Nb，Ta，Hf，Ge，Sn，W，Th，U和HREE）；和LREE + Zr组（Ba，La，Ce，Pr，Nd，Eu，Zr和Hf）。镁铁质族和非铁质族元素成反比。 LREE + Zr族元素的浓度先增加，然后随着SiO_2含量的增加而降低。因此，Ryooke + Sanyo带的高二氧化硅样品的LREE + Zr组元素含量低。在Ryoke样品中，Mo的行为类似于Zr，这导致具有高二氧化硅的Ryoke样品中的Mo含量最低。一些三洋样品中较高的Mo和Si含量表明，在岩浆分化后期，在相对较高的氧气逸度条件下，锆石相容的Mo〜（4+）可能会转变为不相容的Mo〜（6+）。 W和Sn充当Ryoke + Sanyo样本中的长素族元素。因此，它们在高硅质花岗岩中的浓度很高，尤其是来自三洋带的岩石样品，这些样品通常与W-Sn矿石有关。 Sanin岩体样品的因子分析表明，W仍然属于长英质族，但是由于不相容的Sn〜（2+）转变为锆石相容的Sn〜（4），Sn不再与W相关并且表现得更像Zr。 +）在萨宁带的相对较高的氧气逸度条件下。因此，来自萨宁带的高硅质花岗岩中的锡含量低。硅含量较高的Sanin样品通常富含Mo，再次表明在这些样品的岩浆中，锆石相容的Mo〜（4+）转变为不相容的Mo〜（6+）。 Sanin带的高Mo花岗岩是该地区相关Mo矿石的可能烃源岩。

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