柴达木盆地北缘西端埃达克质花岗岩的发现及地质意义
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The discovery of Adakitic granit in the west segment of the north margin of Qaidam and its geological significance
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    摘要:

    盐场北山英云闪长岩位于柴北缘西端青海冷湖地区。岩体Si2O>56%(62.86%~64.83%),A12O3>15%,MgO<3%(含量介于1.73%~1.96%),Mg#=33.4~37.0,小于50。Sr>400×10-6(平均为409×10-6),Y<18×10-6(Y=3.09~6.6×10-6),Yb<1.9×10-6(Yb=0.4~0.58×10-6),具有埃达克岩地球化学特征;Na2O/K2O=2.39~2.73,富Na贫K,Eu、Sr正异常(δEu=1.22~1.44),属O型埃达克岩。岩体富集大离子亲石元素(K、Rb、Sr、Ba),亏损高场强元素(Nb、Ta、P),具弧型花岗岩特征。LA-ICP-MS锆石U-Pb测年结果表明,岩体形成于263±2Ma。结合区域地质背景和岩石地球化学特征,认为柴北缘西端埃达克质花岗岩可能产于与俯冲有关的活动大陆边缘火山弧环境,是俯冲板片直接熔融的产物。进而揭示早二叠世末柴北缘地区处于洋陆俯冲的构造演化阶段。

    Abstract:

    The Yanchangbeishan tonalite develop in Lenghu area of Qinghai, which located in the west segment of the north margin of Qaidam. A study of their petrochemical, geochemical shows that they have geochemical characteristics of adakite, such as: High Sr(>400×10-6,409μg/g in average), low Y(varies from 3.09 to 6.6μg/g ),Yb (varies from 0.4 to 0.58 μg/g), Si2O>56% ( ranging from 62.86% to 64.83%), A12O3>15% ( ranging from 17.25% to 18.15% ), MgO<3%(ranging from 1.73% to 1.96%),Mg#<50 (ranging from 33.4 to 37.0); meanwhile, they riched Na and depleted in K(Na2O/K2O=2.39~2.73), Eu and Sr positive anomaly, display characteristics of O-type adakitic rock. Moreover, These samples are depleted in HFSEs (Nb, Ta, P) intensively, riched LILEs (K, Rb, Rb, Ba), reflecting the characteristics of arc granite. LA-ICPMS zircon U–Pb dating shows that the formation age of the rock is 263±2Ma. Based on the regional geological backgroud and the geochemical characteristics of the masses, we consider the adakitic granite of the west segment of the north margin of Qaidam may formed in volcanic arc setting of active continental margin underneath subduction. it is believed that the adakitic magma originated by melting of subducting plate, and which indicated the north margin of Qaidam was in a tectonic evolution stage of oceanic crust subduction during middle Permian epoch

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邱士东,董增产,辜平阳.2015.柴达木盆地北缘西端埃达克质花岗岩的发现及地质意义[J].地质学报,89(7):1231-1243.
Qiu shidong, Dong zengchan, GU PINGYANG.2015. The discovery of Adakitic granit in the west segment of the north margin of Qaidam and its geological significance[J]. Acta Geologica Sinica,89(7):1231-1243.

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  • 收稿日期:2014-11-24
  • 最后修改日期:2015-04-22
  • 录用日期:2015-05-04
  • 在线发布日期: 2015-07-09
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