北秦岭太白花岗岩体年代学和成因研究

发布时间：2018-02-03 15:03

本文关键词： 北秦岭太白花岗岩体锆石U-Pb年龄地球化学 Sr-Nd-Hf同位素　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：太白花岗岩体位于秦岭造山带商丹断裂带北侧,野外侵入关系和锆石U-Pb定年表明,该岩体由早志留世的五里峡岩体、晚三叠世的红崖河岩体与早白垩世的下板寺岩体组成。五里峡岩体的主要岩石类型为片麻状似斑状黑云母二长花岗岩和片麻状黑云母二长花岗岩,其中片麻状似斑状黑云母二长花岗岩锆石U-Pb年龄为431±2Ma;红崖河岩体的主要岩石类型为黑云母二长花岗岩和细粒黑云母花岗闪长岩,其锆石U-Pb年龄分别为214±2Ma和212±3Ma;下板寺岩体岩性比较简单,为粗粒黑云母花岗岩,锆石U-Pb年龄为130±1Ma。五里峡片麻状似斑状黑云母二长花岗岩和片麻状黑云母二长花岗岩具富硅、碱、高铝的特点,属高钾钙碱性系列,弱过铝质I-A过渡型花岗岩;红崖河黑云母二长花岗岩具富硅、碱、高铝的特点,属高钾钙碱性系列,弱过铝质I-A过渡型花岗岩,细粒黑云母花岗闪长岩Si O2含量相对较低,富碱、高铝,属于高钾钙碱性系列,准铝质I-A过渡型花岗岩;下板寺粗粒黑云母花岗岩具有富硅、碱、高铝的特点,属于钾玄岩系列,弱过铝质I型花岗岩,具有高分异的特点。太白花岗岩体的花岗质岩石属于准铝质-弱过铝质和高钾钙碱性/钾玄岩系列;球粒陨石标准化曲线表现为轻稀土相对富集的右倾特征,轻、重稀土元素分馏明显[(La/Yb)N=9.05~107.33],具有较弱的铕异常(δEu=0.38~1.21);原始地幔标准化微量元素蛛网图显示,各岩石具有相似的微量元素配分模式,富集K、Rb、Ba、Sr、Pb等大离子亲石元素,亏损Nb、Ta、P等高场强元素。在同位素组成上,五里峡岩体全岩ISr=0.701935,εNd(t)=-4.98,tDM2=1.58Ga,锆石的εHf(t)=2.93~8.18,平均值为4.83,两阶段模式年龄tDM2=0.90~1.23Ga,平均年龄为1.11Ga;红崖河岩体全岩ISr=0.702754,εNd(t)=-8.02,tDM2=1.65Ga,锆石的εHf(t)=-7.10~-0.74,平均值为-3.52,两阶段模式年龄tDM2=1.29~1.70Ga,平均值年龄为1.47Ga;下板寺岩体全岩ISr=0.705506,εNd(t)=-6.00,tDM2=1.41Ga,锆石的εHf(t)=-10.21~-1.11,平均值为-5.54,两阶段模式年龄tDM2=1.26~1.84Ga,平均年龄为1.54Ga。元素地球化学与Sr-Nd-Hf同位素组成特征显示,组成太白花岗岩体的五里峡岩体、红崖河岩体和下板寺岩体的成岩物质以元古界地壳物质(宽坪群和秦岭群)为主,同时还有较多年轻组分的加入,并且从早到晚(五里峡岩体→红崖河岩体→下板寺岩体),年轻组分参与程度减小。结合区域构造和岩浆演化特征分析,五里峡岩体形成于秦岭古生代造山作用中的碰撞阶段,形成于块体碰撞挤出过程及略后的抬升环境;红崖河岩体可能是扬子地块与华北地块后碰撞阶段岩浆作用的产物;下板寺岩体形成于挤压向伸展转换的构造环境,是板内岩浆作用的产物,可能和太平洋板块向欧亚板块俯冲导致岩石圈伸展减薄有关。
[Abstract]:The Taibai granite body is located on the northern side of the Shangdan fault zone of the Qinling orogenic belt. The field intrusive relationship and zircon U-Pb dating indicate that the body is from the early Silurian Wuli Gorge rock body. The late Triassic Hongyahe rock body and the early Cretaceous Xiabansi rock body are composed of the main rock types of the Wuli Gorge body: the granitic porphyritic biotite monzogranite and the granitic biotite monzomorphic granite. The zircon U-Pb age of porphyritic biotite monzonitic granites is 431 卤2Ma. The main rock types of Hongyahe pluton are biotite monzonitic granite and fine-grained biotite granodiorite with U-Pb zircon ages of 214 卤2Ma and 212 卤3Marespectively. The lithology of the Xiabansi rock mass is relatively simple, and it is a coarse biotite granite. The zircon U-Pb age is 130 卤1 Ma.Wulixia granitic porphyritic biotite monzonitic granite and granitic biotite monzomorphic granite are characterized by rich in silicon, alkali and aluminum, and belong to high potassium calc-alkaline series. Weakly peraluminous I-A transitional granite; Hongyahe biotite monzogranite is characterized by rich in silicon, alkali and high aluminum. It belongs to high potassium calc-alkaline series, weakly peraluminous I-A transitional granite and relatively low Sio _ 2 content in fine-grained biotite granodiorite. Alkali rich, high aluminum, belongs to high-potassium calc-alkaline series, quasi-aluminous I-A transitional granite; Xiabansi coarse-grained biotite granite has the characteristics of rich in silicon, alkali and high aluminum. It belongs to the series of potash rocks and weakly peraluminous I-type granite. The granitic rocks of the Taibai granite body belong to the series of quasi-aluminite-weakly peraluminous and high-potassium calc-alkaline / kaliacite; The normalized curve of chondrites shows a right-dip characteristic of relative enrichment of light rare earth elements, and the fractionation of light and heavy rare earth elements is obvious. [La / YbN 9.05 (107.33), with weak europium anomaly (未 EU ~ (2 +) 0.38 ~ (1.21) ~ (-1) ~ (-1) ~ (-1) ~ (-1) ~ (-1)); The primitive mantle standardized trace element cobweb shows that the rocks have similar microelement distribution patterns, enriched in large ion lithophile elements, such as K _ (Rb) _ (B _ (B) _ (B) _ (B) _ (B) _ (Ba) _ S _ (Sr) _ (Pb), etc. The isotopic composition of the Wulixia body is 0.701935 for the whole rock, and 1.58 Ga for the 蔚 Ndndltzhui-4.98 TDM2Ga, and the isotopic composition of the isophoric field strength element of P is 0.701935 and 4.98 TDM2Ga, respectively. For zircon, the average value is 4.83, and the mean value is 4.83. The two-stage model age (tDM2 + 0.90) is 1.23Ga, with an average age of 1.11Ga. The whole rock of Hongyahe pluton is 0.702754, 蔚 -8.02tDM2Ga-1.65Ga. 蔚 Hf(t)=-7.10~-0.74 of zircon. The average value is -3.52, the two-stage model age is 1.291.70Ga, and the average age is 1.47Ga. The whole rock of Xiabansi rock is 0.705506, 蔚 Ndndltzhu-6.00 tDM2O1.41 Ga, 蔚 Hf(t)=-10.21~-1.11 of zircon. The mean value was -5.54, and the age of two-stage model was tDM2=1.26~1.84Ga. The average age is 1.54Ga.Elemental geochemistry and Sr-Nd-Hf isotopic composition show that the Wuli Gorge body is composed of Taibai granite. The diagenetic materials of Hongyahe and Xiabansi rock bodies are mainly Proterozoic crustal materials (Kuanping Group and Qinling Group), with the addition of many young components, and from morning to night (Wuli Gorge rock mass). 鈫扝ongyahe rock body. 鈫扐ccording to the analysis of regional tectonics and magmatic evolution, the Wulixia rock body was formed in the collision stage of the Qinling Paleozoic orogeny. It was formed in the extrusion process of block collision and the uplift environment. The Hongyahe pluton may be the product of magmatism in the post-collision stage of the Yangtze block and the North China block. The Xiabansi rock body was formed in the tectonic environment of compression-to-extensional transformation, which is the product of intraplate magmatism, and may be related to the extensional thinning of lithosphere caused by the subduction of the Pacific plate to the Eurasian plate.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121;P597.3

【相似文献】