藏南错那淡色花岗岩LA-MC-ICP-MS锆石U-Pb年龄、岩石地球化学及其地质意义

发布时间：2018-03-17 07:31

本文选题：错那淡色花岗岩　切入点：LA-MC-ICP-MS　出处：《地质通报》2016年01期 　论文类型：期刊论文

【摘要】：藏南错那淡色花岗岩位于喜马拉雅造山带的东部。对其进行LA-MC-ICP-MS锆石U-Pb定年,结果显示,结晶年龄为17.7±0.3Ma,代表中新世的地壳深熔作用。淡色花岗岩样品具有高的Si O2(74.46%~75.57%)、Al2O3(14.07%~14.64%)和K2O(4.19%~4.85%)含量,高的K2O/Na2O值(1.09~1.31)和A/CNK值(1.15~1.25),富集Rb、Th和U,亏损Ba、Nb、Sr、Zr等元素,显示高的Rb/Sr值(17.75~29.50)和强烈的负Eu异常(δEu=0.18~0.26),属于壳源成因的高钾钙碱性过铝质S型花岗岩。样品具有高的Isr值(0.78982~0.79276)和低的εNd(t)值(-19.5~-18.2),可与大喜马拉雅结晶杂岩(GHC)中的变泥质岩对比,暗示其来自变泥质岩的部分熔融。样品的Isr值较高,而Sr浓度较低,且随着Ba浓度的增加,Rb/Sr值逐渐降低,表明淡色花岗岩是无水条件下白云母部分熔融的产物,部分熔融可能与藏南拆离系(STDS)伸展拆离导致的构造减压有关。错那淡色花岗岩的形成反映了地壳伸展减薄背景下,构造减压导致的中下地壳中含水矿物脱水熔融,并沿STDS上升侵位的动力学过程。
[Abstract]:The results of LA-MC-ICP-MS zircon U-Pb dating show that the crystal age is 17.7 卤0.3 Ma, which represents the deep melting of the crust in Miocene. The samples of pale granite have high contents of Sio _ 2, 74.46, 75.57, Al _ 2O _ 314.07 and K _ 2O _ (4.19) and 4.85), respectively, in the eastern part of the Himalayan orogenic belt, and the results show that the age of crystallization is 17.7 卤0.3 Ma, representing the deep melting of the crust of the Miocene. The high K _ 2O / Na _ 2O value of 1.09 ~ 1.31) and the A / C _ (K) value of 1.15 ~ 1.25% enriched RbN Th and U, and depleted the elements such as BaNbSr, Sr, Zr, etc. The results show that the samples have high Rb/Sr value of 17.75 ~ 29.50 and strong negative EU anomalies (未 EU ~ (0.18) ~ (0.26)), which belong to the crust-origin high-potassium calc-alkaline peraluminous S-type granite. The samples have a high Isr value of 0.78982 ~ 0.79276 and a low 蔚 -Ndtt value of -19.5- 18.2g, which can be compared with the argillaceous rocks in the great Himalayan crystalline complex. It is suggested that the samples come from the partial melting of argillaceous rocks. The Isr value of the samples is higher, but the Sr concentration is lower, and with the increase of Ba concentration, the RB / Sr value decreases gradually, which indicates that the pale granite is the product of partial melting of Muscovite under anhydrous condition. The partial melting may be related to the structural decompression caused by the extensional detachment of STDS in southern Tibet. The formation of tinted granite reflects the dehydration and melting of water-bearing minerals in the middle and lower crust caused by tectonic decompression in the context of crustal extensional thinning. And the dynamic process of emplacement along the rise of STDS.
【作者单位】：地壳动力学重点实验室/中国地震局地壳应力研究所;造山带与地壳演化教育部重点实验室/北京大学地球与空间科学学院;中国地质调查局西安地质调查中心;
【基金】：中国地震局地壳应力研究所中央级公益性科研院所基本科研业务专项(编号:ZDJ2014-09) 国家自然科学基金项目(批准号:41402175、41172176)
【分类号】：P588.121;P597.3

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