GEOCHRONOLOGY, PETROGEOCHEMISTRY AND GEOLOGIC IMPLICATION OF THE YUESHANDONG DIORITE PLUTON IN YANBIAN AREA, JILIN PROVINCE
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摘要: 月山洞岩体位于吉林省延边地区，大地构造位置位于龙岗地块与吉黑造山带的交界处，岩性主要为闪长岩.LA-ICP-MS锆石U-Pb测年结果显示，月山洞岩体样品P3B6-2加权平均年龄为178.4±1.2 Ma，表明其岩体侵位时代为早侏罗世晚期.岩石地球化学特征上，月山洞岩体具有高Al富Na的特点，样品的Na2O、K2O、Al2O3、CaO、MgO、FeOt、P2O5和TiO2与SiO2均呈明显的线性关系，表明在成岩过程中存在着辉石、磷灰石、磁铁矿等矿物的分离结晶作用.月山洞样品稀土含量中等，具有轻稀土元素相对富集，重稀土元素相对亏损的特点，且δEu值为0.67~1.04，显示出微弱的Eu负异常到微弱的正Eu异常.月山洞岩体亏损Nb、Ta、P和Ti等高场强元素，富集Cs、Rb、Ba和K等大离子亲石元素.其Nb/Ta、La/Nb和Th/Nb比值介于地壳和地幔平均值之间，显示了月山洞岩体岩浆具有壳幔混源的特点.结合月山洞岩体岩石地球化学特点和区域构造背景，认为该岩体构造背景应受到了太平洋板块俯冲的影响，同时也可能受到了古亚洲洋闭合后南北大陆持续碰撞的叠加影响.
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关键词:
- LA-ICP-MS 锆石 U-Pb 测年 /
- 环太平洋构造体系 /
- 闪长岩 /
- 岩石地球化学 /
- 吉林延边
Abstract: The Yueshandong diorite pluton in Yanbian area, Jilin Province is tectonically located the boundary between the Longgang block and Ji-Hei orogenic zone. The LA-ICP-MS zircon U-Pb dating and geochemical data yield weighted mean 206Pb/238U ages of 178.4 ±1.2 Ma, indicating that the pluton was formed during the late of Early Jurassic. The petrogeochemistry is characterized by high Al and Na. The main oxides (Na2O, K2O, Al2O3, CaO, MgO, FeOt, P2O5 and TiO2) show a linear relation to SiO2 from, which indicate that the magma experienced a fractional crystallization of pyroxene, apatite and magnetite. The rare earth contents of samples display similarly fractionated REE patterns, with enrichment in LREEs and depletion in HREEs. The ratios of δEu range from 0.67 to 1.04, with negative to slightly positive Eu anomalies. The trace element spider diagram shows that the rocks are enriched in large ion lithophile elements(LILEs, such as CS, Rb, Ba and K), whereas depleted in high field strength elements (HFSE, such as Nb, Ta, Ti and P). The ratios of Nb/Ta, La/Nb and Th/Nb are between the data of curst and mantle, showing that the magma is derived from crustmantle mixing source. From the geochemical charateristics and regional tectonic setting, the pluton is tectonically related to the subduction of the circum-Pacific tectonic system beneath the Eurasian continent and, at the same time, might be influenced by the collision between North China Plate and Siberia Plate. -
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