首页> 外文期刊>Lithos: An International Journal of Mineralogy, Petrology, and Geochemistry >Formation of the Yandangshan volcanic-plutonic complex (SE China) by melt extraction and crystal accumulation
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Formation of the Yandangshan volcanic-plutonic complex (SE China) by melt extraction and crystal accumulation

机译:通过熔体萃取和晶体堆积形成雁荡山火山-古生界复合体(中国东南)

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The association of volcanic and shallow plutonic rocks in caldera may provide important clues to the geochemical evolution of silicic magma systems. The Yandangshan caldera is a typical example of late Mesozoic volcanic plutonic complex in SE China. It is composed of a series of rhyolitic extrusives and subvolcanic intrusions of porphyritic quartz syenites. In this work, we conducted petrological and geochemical studies, as well as zircon dating, on the coexisting volcanic and plutonic rocks from the Yandangshan caldera. The results of SHRIMP and LA-ICP-MS zircon U-Pb dating revealed that the crystallization of the rhyolitic extrusives and subvolcanic intrusions was contemporaneous within analytical errors and in a short period (104-98 Ma). Geochemically, the volcanic rocks are characterized by high Rb/Sr and Rb/Ba ratios and depletion in Ba, Sr, P, Eu and Ti, while the shallow plutons show high K, Ba, Al, Fe and low Rb/Sr and Rb/Ba ratios with insignificant negative Eu anomalies. The volcanic and plutonic rocks have a similar range of zircon Hf isotopic compositions (epsilon(Hf)(t) = 10.0 to + 1.5) and TDm2 model ages of 2.10-1.23 Ga. They also have comparable whole-rock Sr and Nd isotopic compositions ((Sr-87/Sr-86)(t) = 0.7084-0.7090; epsilon(Nd)(t) = -7.8 to -6.5) and zircon oxygen isotopic compositions (delta O-18 mainly = 4.5 to 6.0%0). We argue that the volcanic-plutonic complex of the Yandangshan caldera was formed by reworking of Paleoproterozoic lower crusts in the eastern Cathaysia blocic, and that the complex could be linked by fractional crystallization and crystal accumulation in a shallow magma chamber. The volcanic rocks represent the highly fractionated end-member, whereas the subvolcanic intrusions of porphyritic quartz syenites could be the residual crystal mushes. This case study could have a general implication for the genetic relationship between volcanic and shallow plutonic rocks in calderas. (C) 2016 Elsevier B.V. All rights reserved.
机译:火山口中的火山岩和浅层的火山岩的联系可能为硅质岩浆系统的地球化学演化提供重要线索。雁荡山火山口是中国东南部晚中生代火山岩体的典型例子。它由一系列的斑岩石英正长岩的流变质挤出物和次火山岩侵入物组成。在这项工作中,我们对雁荡山火山口的火山岩和深成岩共存进行了岩石学和地球化学研究,以及锆石定年。 SHRIMP和LA-ICP-MS锆石U-Pb测年的结果表明,在分析误差范围内和短时间内(104-98 Ma),流纹岩挤出物和火山岩下侵入体的结晶同时发生。从地球化学上讲,火山岩的特征是高的Rb / Sr和Rb / Ba比值以及Ba,Sr,P,Eu和Ti的耗竭,而浅岩体显示出高的K,Ba,Al,Fe和低的Rb / Sr和Rb / Ba比值与负Eu异常无关紧要。火山岩和深成岩的锆石Hf同位素组成范围相似(ε(Hf)(t)= 10.0至+ 1.5),TDm2模型年龄为2.10-1.23 Ga。它们的全岩Sr和Nd同位素组成也相当((Sr-87 / Sr-86)(t)= 0.7084-0.7090; epsilon(Nd)(t)= -7.8至-6.5)和锆石氧同位素组成(δO-18主要为4.5至6.0%0) 。我们认为,雁荡山破火山口的火山—古生复合体是由东加泰罗尼亚东部古元古代下地壳的再造形成的,并且该复合体可能与浅层岩浆室内的部分结晶和晶体堆积有关。火山岩代表着高度分馏的端部,而斑岩石英正长岩的次火山岩侵入可能是残余的结晶糊。该案例研究可能对火山口中火山岩与浅层深部岩石的遗传关系具有普遍意义。 (C)2016 Elsevier B.V.保留所有权利。

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