川西义敦岛弧稻城花岗岩体和海子山花岗岩体锆石U-Pb年代学、Hf同位素特征及地质意义

发布时间：2018-12-16 18:10

【摘要】：义敦岛弧形成于晚三叠世大规模俯冲造山作用过程中,位于松潘-甘孜褶皱带和羌塘地体之间。稻城岩体和海子山岩体分别为义敦岛弧上出露的晚三叠世和白垩纪花岗质岩体。结合野外考察,本文对上述岩体进行岩相学、锆石U-Pb年代学和Hf同位素的研究,结果表明,1稻城岩体和海子山岩体主要矿物为斜长石、钾长石、石英和黑云母,副矿物为锆石、榍石、磁铁矿和磷灰石等;钠质斜长石颗粒,以及钾长石和石英不连续出现,表明二者均属于低熔线花岗岩,是含水条件下,在与造山事件有关的环境中形成。2稻城岩体的侵位年龄为217.4Ma,属晚三叠世花岗岩侵入体,εHf(t)为-7.1~-0.1,二阶段模式年龄(tDM2)为1.26~1.7Ga,表明在中元古代与扬子克拉通经历了共同的地壳演化历史;海子山岩体的形成时代为98.3 Ma,为白垩纪时期产物,εHf(t)变化于-12.1~+2.5,二阶段模式年龄(tDM2)变化于1.0~1.93Ga。3结合前人研究成果,本文认为稻城岩体源岩可能是与扬子克拉通有关的中元古代的下地壳物质,在甘孜-理塘洋俯冲闭合后的同碰撞造山阶段,因地幔岩浆底侵作用而发生了部分熔融,同时伴有少量的亏损地幔成分加入,之后上升侵位于中—上地壳,并且侵位后经历了快速的冷却过程。海子山岩体是与俯冲有关的造山后伸展环境下形成的A2型花岗岩,源岩主要为中元古代地壳物质,同样有少量地幔物质加入,在白垩纪时侵位于地壳较浅部位,之后亦同样经历了快速的冷却过程。
[Abstract]:The Yidun island arc was formed during the late Triassic large-scale subduction orogeny between the Songpan-Ganzi fold belt and the Qiangtang terrane. The Daocheng and Haizishan intrusions are late Triassic and Cretaceous granitic rocks respectively. Combined with field investigation, the authors have studied the lithofacies, zircon U-Pb chronology and Hf isotopes of the abovementioned rocks. The results show that the main minerals of the Daocheng and Haizishan pluton are plagioclase, potash feldspar, quartz and biotite, and the main minerals are plagioclase, potassium feldspar, quartz and biotite. The accessory minerals are zircon sphene magnetite and apatite etc. The occurrence of sodium plagioclase particles, as well as potassium feldspar and quartz discontinuities, indicate that both of them belong to low-melting-line granites and are formed in an environment related to orogenic events under water-bearing conditions. 2 the emplacement age of the Daocheng rock body is 217.4 Ma. It belongs to the late Triassic granite intrusion, 蔚 Hf (t) is -7.1 ~ (-1) -0.1, and the two-stage model age (tDM2) is 1.26 ~ 1.7Ga, which indicates that the Mesoproterozoic and Yangtze craton experienced a common history of crustal evolution. The age of formation of the Haizi mountain body is 98.3 Ma, which is the product of Cretaceous period, 蔚 Hf (t) changes from -12.1-2.5, and the two-stage model age (tDM2) changes with 1.0~1.93Ga.3 combined with previous research results. In this paper, it is suggested that the source rocks of the Daocheng rock body may be the lower crust material of the Mesoproterozoic associated with the Yangtze craton. During the syncollision orogenic stage after the subduction of the Ganzi-Litang Ocean, partial melting occurred due to the mantle magmatic underthrust. At the same time, it is accompanied by a small amount of depleted mantle composition, and then rises and transgressions are located in the mid-upper crust and undergo a rapid cooling process after emplacement. The Haizishan rock body is an A2 type granite formed in the post-orogenic extensional environment related to subduction. The source rocks are mainly of the Mesoproterozoic crustal material, with a small amount of mantle material added, and transgression in the shallow part of the crust during the Cretaceous period. Also experienced the same rapid cooling process.
【作者单位】：中国地质科学院地质研究所中国地质调查局大陆动力学研究中心;中国地质大学地球科学学院地质过程与矿产资源国家重点实验室;中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室;
【基金】：中国地质调查局项目(编号12120114061701、121201102000150005-06和12120115027001)联合资助成果
【分类号】：P597.3;P588.121

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