Geochemical constraints on the link between volcanism and plutonism at the Yunshan caldera complex, SE China
Geochemical constraints on the link between volcanism and plutonism at the Yunshan caldera complex, SE China
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DOI：
10.1007/s00410-017-1430-5
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发表时间：
2017
影响因子：
3.5
通讯作者：
Lili Yan;Zhengjun He;C. Beier;R. Klemd
中科院分区：
文献类型：
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作者：
Lili Yan;Zhengjun He;C. Beier;R. Klemd
云山火山口复合体是一个规模更大的火山口群的一部分，约1000年。中国东南沿海长达2000公里的火山岩杂岩带.火山口复合体中的火山岩的特征是高硅过铝质和过碱性流纹岩，与火山口内斑状石英二长岩体相关。在这项研究中，我们提供了锆石 U-Pb、Hf 和稳定 O 同位素以及火山岩和深成岩的地球化学数据，以评估云山破火山口杂岩中火山活动和深成岩活动之间潜在的岩石成因联系。火山岩和深成岩的 SHRIMP 锆石 U-Pb 地质年代学得出几乎相同的年龄，范围为 95.6 至 93.1 Ma。过铝质和过碱性流纹岩显示出 Sr、P、Ti 和 Ba 的负异常，以及较小程度的 Nb 和 Ta 负异常，以及 Rb 正异常和具有负 Eu 异常和低 (La/Yb)N 比的“海鸥状”稀土元素 (REE) 模式。火山口内斑状石英二长岩显示出轻微的负 Rb、Nb、Ta、Sr、P 和 Ti 异常和正 Ba 异常，稀土元素模式的特征是相对较高的 (La/Yb)N 比，但缺乏明显的 Eu 异常。过铝质和过碱性流纹岩以及斑状石英二长岩表现出一致的εNd(t) 值为- 3.7 至- 2.2，锆石εHf(t) 值为- 2.1 至3.7。它们还具有类似地幔的锆石氧同位素组成（δ18OVSMOW主要 = 4.63至5.76‰）。我们对这些观测结果的解释与晶体糊状模型一致，在该模型中，云山破火山口杂岩的火山岩和深成岩的母岩浆可能是由软流圈熔体与受俯冲影响的富集地幔楔相互作用产生的。过碱性流纹岩被解释为代表了分化程度最高的岩浆，随后经历了显着的流体-熔体相互作用，而斑状石英二长岩可能代表了残留的晶体糊状物。云山流纹岩典型地符合“干热还原”流纹岩的地球化学特征，表明晚白垩世，中国东南部的构造环境从挤压环境转变为伸展环境，即从弧状环境转变为弧后环境。我们的结果表明，火山口系统中的火山岩和深成岩可能对岩浆系统的演化提供独特的限制，在岩浆系统中，喷发的熔体和残留的结晶物质都被保存下来。
The Yunshan caldera complex is part of a larger scale, ca. 2000-km-long volcanic–plutonic complex belt in the coastal region of SE China. The volcanic rocks in the caldera complex are characterized by high-silica peraluminous and peralkaline rhyolites associated with an intracaldera porphyritic quartz monzonite pluton. In this study, we present zircon U–Pb, Hf and stable O isotopes along with geochemical data of both volcanic and plutonic rocks to evaluate the potential petrogenetic link between volcanism and plutonism in the Yunshan caldera complex. SHRIMP zircon U–Pb geochronology of both volcanic and plutonic rocks yields almost identical ages ranging from 95.6 to 93.1 Ma. The peraluminous and peralkaline rhyolites show negative anomalies of Sr, P, Ti and Ba and to a lesser extent negative Nb and Ta anomalies, along with positive Rb anomalies and ‘seagull-like’ rare earth element (REE) patterns with negative Eu anomalies and low (La/Yb)Nratios. The intracaldera porphyritic quartz monzonite displays minor negative Rb, Nb, Ta, Sr, P and Ti anomalies and a positive Ba anomaly with REE patterns characterized by relatively high (La/Yb)Nratios and lack significant Eu anomalies. The peraluminous and peralkaline rhyolites and the porphyritic quartz monzonite exhibit consistentεNd(t) of − 3.7 to − 2.2 and display zirconεHf(t) values of − 2.1 to 3.7. They further have similar, mantle-like, zircon oxygen isotopic compositions (δ18OVSMOWmainly = 4.63 to 5.76‰). We interpret these observations to be in agreement with a crystal mush model in which the parental magma of the volcanic and plutonic rocks of the Yunshan caldera complex was likely produced by interaction of asthenosphere melts with subduction-influenced enriched mantle wedge. The peralkaline rhyolites are interpreted to represent the most differentiated magma that has subsequently experienced significant fluid–melt interactions, whereas the porphyritic quartz monzonite may be representative of the residual crystal mush. The Yunshan rhyolites typically match the geochemical characteristics of ‘hot-dry-reduced’ rhyolites indicating that, during the late Cretaceous, the tectonic setting of SE China changed from a compressional environment to an extensional environment, i.e., from an arc into a back-arc setting. Our results imply that volcanic and plutonic rocks in caldera systems may provide unique constraints on the evolution of the magmatic system in which both the erupting melt and the residual crystalline material are being preserved.