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首页> 外文期刊>Lithos: An International Journal of Mineralogy, Petrology, and Geochemistry >Anatomy of the Cretaceous Hobenzan pluton, SW Japan: Internal structure of a small zoned pluton, and its genesis
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Anatomy of the Cretaceous Hobenzan pluton, SW Japan: Internal structure of a small zoned pluton, and its genesis

机译：日本西南部白垩纪霍本赞岩体的解剖：小带状岩体的内部结构及其成因

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摘要

Field, petrographic, geochemical, and K-Ar and U-Pb age data were used to elucidate the internal structure of the Cretaceous Hobenzan pluton, SW Japan, and the processes which generated that structure. The pluton is elongated E-W with dimensions of about 6.5 x 2.0 km (13 km2), and was emplaced at -95 Ma as a pluton in accretionary complexes. The pluton contains an early tonalite, but most of the body consists of later granitoids that show a continuous differentiation series from biotite-hornblende granodiorite (GD) to hornblende-biotite granite (HBG) and biotite granite (BG). The contacts between the GD and HBG are gradational. The pluton provides an exceptional cross-sectional view of a simple cooling magma body. The GD shows no vertical variations in modal and chemical compositions, whereas the HBG displays differentiation from the lowermost exposure to the top of the pluton. Initial Sr isotope ratios (SrI) in the HBG increase from the lower part to the top of the pluton. The granitoids show continuous compositional variations from 65 to 79 wt% SiO2 (anhydrous basis), and mag-matic differentiation was dominantly controlled by crystal fractionation of hornblende and plagioclase. Field, elemental and Sr-Nd isotope data are consistent with limited operation of assimilation with pelitic rocks and fractional crystallization (AFC), in which assimilation increased with higher degrees of differentiation. The Hobenzan pluton retains a history of granitoid magma evolution in a subvolcanic magma reservoir. The GD formed as a rigid sponge, and melt fraction increases inwards from the walls, forming the HBG mush by fractional crystallization, coupled with small degrees of assimilation of adjacent schists. A more evolved and enriched low-density melt segregated from the mushy cumulate of the HBG by incomplete crystal-melt separation, and moved upwards with the assistance of gas-driven filter pressing, as indicated by the presence of miarolitic cavities, thus forming the BG at the roof of the pluton.
机译：野外，岩相，地球化学以及K-Ar和U-Pb年龄数据被用来阐明日本西南部白垩纪Hobenzan岩体的内部结构以及产生该结构的过程。质子是细长的E-W，尺寸约为6.5 x 2.0 km（13 km2），并作为增生性化合物中的质子放置在-95 Ma处。岩体包含早期的角质岩，但主体的大部分由较晚的花岗石组成，这些花岗石显示出从黑云母-角闪石花岗闪长花岗岩（GD）到角闪石-黑云母花岗岩（HBG）和黑云母花岗岩（BG）的连续分化系列。 GD和HBG之间的接触是渐变的。插头提供了一个简单的冷却岩浆体的特殊剖面图。 GD在模态和化学组成上没有显示出垂直变化，而HBG从最低暴露到to的顶部显示出差异。 HBG中的初始Sr同位素比（SrI）从轻子的下部到顶部增加。花岗岩显示出从65％到79％（重量）SiO2（无水）的连续组成变化，岩浆分化主要由角闪石和斜长石的晶体分级控制。场，元素和Sr-Nd同位素数据与与粉质岩的同化作用和部分结晶（AFC）的局限性一致，其中同化作用随着分化程度的提高而增加。霍本赞岩体保留了火山岩下岩浆储层中花岗岩类岩浆演化的历史。 GD形成为刚性海绵，熔体分数从壁向内增加，通过分步结晶以及相邻片岩的少量同化作用形成HBG糊状物。通过不完全的晶体-熔体分离，从HBG的糊状堆积中分离出的更多析出和富集的低密度熔体，并在气体驱动压滤的帮助下向上移动（如微孔洞的存在所示），从而形成了BG。在云母的屋顶。

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