扬子地块北缘大汉山地区新元古代花岗岩岩石学、地球化学、锆石年代学及其地质意义

发布时间：2018-05-11 10:27

本文选题：扬子北缘 + 汉南杂岩　；参考：《西北大学》2015年硕士论文

【摘要】：扬子地块北缘空间上向北楔入南秦岭,东临巴山弧,西临龙门山推覆构造带和松藩-甘孜造山带。大汉山地区位于扬子北缘米仓山北麓,区内广泛发育一套新元古代基性-酸性侵入杂岩体,它们构成汉南杂岩的重要组成部分。此外,新元古代岩浆活动还广泛分布于扬子地块西缘(攀西地区)、东南缘(桂北地区)以及黄陵地区。目前,由这些岩浆活动引出的超大陆构造模式和岛弧模式之争掀起了研究热潮,引发许多学者的广泛关注。本项研究旨在通过对大汉山地区4个不同岩石类型的新元古代花岗岩体进行野外地质调查、岩石学、地球化学、锆石U-Pb年代学及Hf同位素研究,确定研究区新元古代花岗岩类的时空分布特征、岩浆作用期次、岩石成因及源区特征,探讨这套花岗岩的大地构造意义。研究获得了如下主要进展和认识：(1)野外地质调查及岩相学研究表明,大汉山地区花岗岩岩体具有多种类型。本项研究包括喜神坝含暗色微粒包体的黑云母花岗岩(GQ)、黄官钾长花岗斑岩(NH-7)、红庙镇钾长花岗岩(XSB和NH-3)及祖师店奥长花岗岩(EL-1)。各岩体岩石新鲜,未发生明显变形和变质。(2)通过详细的锆石原位U-Pb定年工作,获得喜神坝黑云母花岗岩岩体(GQ)的成岩年龄为886.5±6.8 Ma;黄官钾长花岗斑岩岩体(NH-7)的成岩年龄为814±25 Ma；红庙镇钾长花岗岩岩体中的两个样品(XSB、NH-3)分别获得了802.1±4.3 Ma和790.5±5.7 Ma的年龄,在误差范围内这两个样品的年龄基本一致；祖师店奥长花岗岩岩体(EL-1)的成岩年龄为728±3 Ma。(3)经过系统的地球化学研究,判断喜神坝黑云母花岗岩岩体和祖师店奥长花岗岩岩体具有岛弧花岗岩特征,二者具有Nb、Ta、Ti负异常的地球化学特征,形成于俯冲挤压环境；红庙镇岩体和黄官岩体代表伸展构造背景下的产物。(4)结合前人研究成果,提出大汉山地区新元古代岩浆活动可划分为3个阶段：-880 Ma,代表一期与板块俯冲汇聚相关的的岛弧岩浆作用,对应本研究的喜神坝黑云母花岗岩岩体；～800 Ma,代表伸展构造背景,对应红庙镇钾长花岗岩岩体和黄官钾长花岗斑岩岩体；790Ma之后,发生另一期俯冲汇聚事件下的岛弧岩浆作用,对应于大汉山辉长岩岩体(790～780Ma)和祖师店奥长花岗岩岩体。(5)锆石Hf同位素研究显示,喜神坝岩体的锆石εHf(t)值为-25～-3,对应的锆石两阶段Hf模式年龄(TDM2)集中于2.4Ga；红庙镇岩体的锆石εHf值为-26～-4,对应的锆石两阶段Hf模式年龄(TDM2)集中于2.2Ga;祖师店岩体的锆石εHf(t)值为+5.0～-+12.2,对应的两阶段锆石Hf模式年龄集中于1.1 Ga。可以看出,喜神坝岩体指示了俯冲背景下古老地壳物质的再造；红庙镇岩体指示了伸展背景下古老地壳物质的再造；而祖师店岩体则指示了新元古代地壳生长事件。因此,汉南杂岩并非来自同一源区同一期次的岩浆作用,代表了新元古代扬子北缘地壳演化历史。(6)综合区域大地构造,推测880Ma的岩浆活动可能代表了扬子北缘对全球性格林威尔造山运动最晚期活动的响应；830～790 Ma的岩浆活动可能与Rodinia超大陆裂解相关；而790～720Ma代表扬子北缘与南秦岭碰撞拼合的时间。自此以后,扬子和南秦岭拼贴在一起,处于相对稳定的状态。
[Abstract]:The northern margin of the Yangtze block is wedged northward in the southern Qinling Mountains, the East is the Bashan arc, the Longmen mountain nappe structure belt and the pine fan Ganzi orogenic belt in the west, and the Da Han Shan area is located at the northern foot of the Yangtze River in the north of the Yangtze River, and a set of Neoproterozoic basic acid intrusive complex is widely developed in the northern margin of the Yangtze River. The magmatic activity is also widely distributed in the western margin of the Yangtze block (Panxi area), the southeast margin (north of Guangxi) and the Huangling area. At present, the controversy over the supercontinental tectonic model and the island arc model caused by these magma activities has aroused a lot of research upsurge, which has caused extensive attention by many scholars. This study is aimed at 4 different rocks in the Great Han mountain area. The Neoproterozoic granitoids of the stone type are investigated in the field, petrology, geochemistry, zircon U-Pb chronology and Hf isotopes, to determine the temporal and spatial distribution characteristics of the Neoproterozoic granitoids in the study area, the stages of magmatism, the petrogenesis and the characteristics of the source area, and to discuss the tectonic significance of the granites. Progress and understanding: (1) the field geological survey and petrographic study show that the granitoid rock mass in the Great Han mountain area has a variety of types. This study includes the dark mica granite (GQ), the Yellow official potassium long granite porphyry (NH-7), the potassium feldspar granite (XSB and NH-3) of the red temple town and the ancestor division granitic granite (EL-1). The body rock is fresh, without obvious deformation and metamorphism. (2) through the detailed zircon in-situ U-Pb dating, the age of diagenesis of the biotite granitoid granite rock mass (GQ) is 886.5 + 6.8 Ma, and the age of diagenesis of the Huang Guan potassium long granite porphyry rock mass (NH-7) is 814 + 25 Ma, and two samples (XSB, NH-3) in the potash granite rock mass of the red temple town are divided. The age of 802.1 + 4.3 Ma and 790.5 + 5.7 Ma is not obtained. The age of the two samples is basically the same in the range of error; the age of the diagenesis of the AUD granitic granite (EL-1) is 728 + 3 Ma. (3) through systematic geochemical study. It is determined that the rock mass of the black mica granite and the Oracle granite rock of the Heisan dam are island arc granite. Rock characteristics, two of which have the geochemical characteristics of Nb, Ta, Ti negative anomalies, formed in the subduction and extrusion environment; the red temple rock mass and the Huang Guan rock mass represent the product of the extensional tectonic setting. (4) the Neoproterozoic magmatic activity in the Great Han mountain area can be divided into 3 stages: -880 Ma, representing the first stage and the subduction and convergence of the plate subduction. The related island arc magmatism corresponds to the biotite granite rock mass of the joy God dam of this study; to 800 Ma, representing the extensional tectonic setting, corresponding to the red temple granite rock mass and the Yellow official potassium long granite porphyry rock mass; after 790Ma, the island arc magmatism under another subduction event occurs, corresponding to the Great Han mountain gabbro rock mass (790). (5) the zircon Hf isotopes of the zircon. (5) the zircon Hf (T) value of the zircon is -25 to -3, and the corresponding zircon two stage Hf mode age (TDM2) is concentrated in 2.4Ga; the zircon - Hf values of the red temple rock mass are -26 to -4, the two phase of the zircon is concentrated in the ancestor Dian Yan The zircon epsilon Hf (T) value of the body is +5.0 to -+12.2, and the corresponding two stage zircon Hf mode age is concentrated at 1.1 Ga., it can be seen that the Xinshen dam rock indicates the reengineering of ancient crustal material under the subduction background, and the red temple rock mass indicates the reengineering of ancient crustal material under the extensional background, while the zutodian rock mass indicates the Neoproterozoic crust growth. Therefore, the Hannan complex does not come from the same stage of magmatism in the same source area and represents the evolution history of the northern margin of the Neoproterozoic Yangtze River. (6) comprehensive regional tectonics, and it is presumed that the magmatic activity of 880Ma may represent the response of the northern margin of the Yangtze to the most advanced activity of the orogenic movement of the global character Lin Wei, and 830~790 Ma of magma activity. The movement may be associated with the Rodinia supercontinental fragmentation, while 790 ~ 720Ma represents the time of collision and integration of the northern margin of the Yangtze and southern Qinling Mountains. Since then, the Yangtze and southern Qinling Mountains collages together in a relatively stable state.

【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121;P597.3

【参考文献】