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北喜马拉雅花岗岩位于特提斯喜马拉雅的中部,对其研究不仅有助于认识和理解碰撞造山过程中地壳物质的熔融行为和机制,而且对探讨部分熔融作用与相关构造的关系也具有重要意义.通过对北喜马拉雅佩枯花岗岩开展系统的LA-MCICP-MS锆石U-Pb年代学和地球化学研究,结果表明佩枯花岗岩的结晶时间较长,从23.9Ma持续到16.5Ma,并记录了22.3±0.6Ma和17.3±0.3Ma两期深熔作用.全岩地球化学分析结果显示,佩枯花岗岩具有高含量的SiO_2(71.87%~75.56%)、Al_2O_3(13.57%~15.49%)和K_2O(3.34%~4.59%),以及高的K_2O/Na_2O比值(1.02~1.39)和A/CNK值(1.21~1.23),属于高钾钙碱性过铝质花岗岩.岩石强烈富集大离子亲石元素Rb和放射性生热元素Th、U,亏损Ba、Nb、Sr、Zr等元素;轻重稀土元素分馏较强((La/Yb)N=10.76~16.60),几乎无或弱的负Eu异常(δEu=0.76~0.97).样品的(87Sr/86Sr)i值和εNd(t)值变化范围分别为0.736 184~0.741 258和-14.6~-14.3,与大喜马拉雅变质沉积岩的Sr-Nd同位素组成一致,表明其源岩可能为大喜马拉雅变质沉积岩.样品(87Sr/86Sr)i值较低而Sr浓度较高,且随着Ba浓度的增加,Rb/Sr比值基本不变,与水致白云母部分熔融的特征和趋势一致,表明佩枯花岗岩是水致白云母部分熔融的产物,部分熔融作用可能与藏南拆离系的活动密切相关.
The northern Himalayan granite is located in the middle of the Tethys Himalayas and its research not only helps to understand and understand the melting behavior and mechanism of crustal material during collision orogeny but also is of great significance for exploring the relationship between partial melting and related tectonics. The systematic LA-MCICP-MS zircon U-Pb geochronology and geochemistry of the northern Himalayan pegmatite granulite are carried out. The results show that the crystallization time of the pegmatite granite is relatively long, from 23.9Ma to 16.5Ma, and 22.3 ± 0.6Ma and 17.3 ± 0.3Ma.The whole rock geochemical analysis shows that the Permian granite has high contents of SiO 2 (71.87% -75.56%), Al 2 O 3 (13.57% -15.49%) and K 2 O (3.34% ~ 4.59%), high K 2 O / Na 2 O ratios (1.02-1.39) and A / CNK values (1.21-1.23), which are high K calc-alkaline peraluminous granites.The rocks are strongly enriched in large ion lithophile elements Rb and (La / Yb) N = 10.76 ~ 16.60), almost no or weak negative Eu anomaly (δEu = 0.76 ~ 0.97) .The values of (87Sr / 86Sr) i and εNd (t) of the samples range from 0.736 184 to 0.741 258 and -1 4.6 ~ -14.3, which is consistent with the Sr-Nd isotope composition of the Greater Himalayan metamorphic sedimentary rocks, indicating that the source rocks may be the Greater Himalayan metasedimentary rocks with lower (87Sr / 86Sr) i value and higher Sr concentration. With increasing Ba concentration , And the Rb / Sr ratio is basically the same, which is in agreement with the characteristics and tendency of partial melting of water-induced muscovite, indicating that the granite is the product of partial melting of hydrous muscovite and part of the melting may be related to the activity closely related.