扬子板块西缘石棉安顺场新元古代钾长花岗岩地球化学特征及其地质意义

发布时间：2019-01-16 09:16

【摘要】：扬子板块西缘新元古代岩浆活动强烈,其成因研究对探讨Rodinia超大陆的演化有着重要意义。本文对石棉安顺场钾长花岗岩形成年龄及其地球化学特征研究,结果表明锆石~(206)Pb/~(238)U年龄加权平均值为777.3±4.8 Ma(MSWD=0.23,2σ),代表花岗岩的结晶年龄。岩石SiO_2含量高(72.64%~76.27%),铝饱和指数A/CNK大于1(1.06~1.24),K_2O/Na_2O在1.40~2.22之间,里特曼指数σ小于3.3(2.08~2.74)。岩石轻稀土元素(LREE)富集,Nb、Ta轻微亏损,Eu负异常明显(δEu=018~0.23)。岩石的ε_(Nd)(t)为0.5~3.3(平均值为2.1),T_(DM)在1.19~1.61Ga之间,反映其源区以古老地壳物质为主。铅的初始同位素比值分别为[n(~(206)Pb)/n(~(204)Pb)]i=15.4103~17.2707,[n(~(207)Pb)/n(~(204)Pb)]i=15.4265~15.5479,[n(~(208)Pb)/n(~(204)Pb)]i=33.3518~35.8641。此外,岩石具有高的Rb/Sr比值和低的Ca O/Na2O比值、较低的Al_2O_3/TiO_2比值和低的Rb/Ba比值,表明其起源于泥质岩石的部分熔融。综合地球化学、同位素特征和区域地质资料,我们认为石棉安顺场钾长花岗岩为过铝质高钾钙碱性S型花岗岩,它是地壳泥质源岩部分熔融的产物,形成于挤压的构造环境中。
[Abstract]:The Neoproterozoic magma activity in the western margin of Yangtze plate is very strong, and the study of its genesis is of great significance to the study of the evolution of Rodinia supercontinent. The age of formation and geochemical characteristics of asbestosite in Anshunchang potassium feldspar is studied. The results show that the weighted average of zircon ~ (206) Pb/~ _ (238) U age is 777.3 卤4.8 Ma (MSWD=0.23,2 蟽), which represents the age of crystallization of the granite. The SiO_2 content of the rock is high (72.64%), the aluminum saturation index (A/CNK) is greater than 1 (1.061.24), the K_2O/Na_2O is between 1.40 and 2.22, and the Ritman index 蟽 is less than 3.3 (2.08 ~ 2.74). The rocks are enriched in light rare earth elements (LREE), slightly depleted in Nb,Ta, and obviously abnormal in Eu (未 Eu=018~0.23). The 蔚 _ (Nd) (t) of the rocks is 0.5 ~ 3. 3 (mean value is 2. 1), and the T _ (DM) is between 1.19~1.61Ga, indicating that the source region is dominated by the ancient crustal material. The initial isotopic ratios of lead are [n (~ (206) Pb) / n) (~ (204) Pb) ihe 15.4103) 17.2707, [n (~ (207) Pb) / n (~ (204) Pb) ihe 15.4265n] 15.5479, respectively. [n (~ (208) Pb) / n) (~ (204) Pb)] I) 33.3518 (35.8641). In addition, the rock has high Rb/Sr ratio and low Ca O/Na2O ratio, low Al_2O_3/TiO_2 ratio and low Rb/Ba ratio, which indicates that the rocks originated from partial melting of muddy rocks. Based on geochemistry, isotopic characteristics and regional geological data, we consider that asbestosite Anshunchang potassium feldspar is a peraluminous high-potassium calc-alkaline S-type granite, which is the product of partial melting of crustal argillaceous source rocks and formed in a compressional tectonic environment.
【作者单位】：西北大学大陆动力学国家重点实验室/地质学系;
【基金】：国家自然科学基金资助项目(批准号:41372067,41102037) 国家自然科学基金委创新群体项目(批准号:41421002)的成果~~
【分类号】：P588.121

【相似文献】