滇西南早古生代构造属性：岩浆与沉积作用限定

发布时间：2018-05-11 00:32

  本文选题：早古生代 + 花岗岩浆作用　； 参考：《中国科学院研究生院(广州地球化学研究所)》2016年博士论文

【摘要】：特提斯-喜马拉雅构造域内,如印度西北部、尼泊尔、藏南以及中国西南部发育有早古生代岩浆岩和沉积岩(~525-460 Ma),这些区域在早古生代时期位于冈瓦纳大陆北缘,朝向原特提斯洋。目前,不同学者对这些区域早古生代构造事件主要提出了两种动力学模型:(1)泛非造山运动。是与Rodinia超大陆裂解以及冈瓦纳大陆的聚合相关的造山运动;(2)安第斯型造山运动。随着冈瓦纳大陆的聚合,由原特提斯洋向印度克拉通以及邻区相关微陆块之下俯冲而引起的造山运动。然而,由于晚古生代岩浆作用记录的缺失、以及受到古特提斯洋关闭和喜马拉雅造山运动相关的热构造事件改造,相关区域的早古生代构造演化以及古地理位置尚未得到较好约束。滇西南地区是东特提斯构造带的重要组成部分,位于北西西向展布的喜马拉雅构造结向南北向伸展的东南亚构造结转换部位,并保存了大量早古生代岩浆活动和沉积作用证据,是我们研究早古生代原特提斯构造属性的天然实验室。本次研究选取研究对象为滇西南地区腾冲、保山和禅泰地块内的片麻状花岗岩、变火山岩以及碎屑岩并对其开展了系统的岩石学、岩相学、锆石U-Pb年代学、主量及微量元素地球化学和Lu-Hf及Sr-Nd同位素组成研究,以探讨滇西南地区早古生代岩浆岩的岩石成因、沉积物源性质及早古生代构造背景与动力学机制。结合前人研究成果,本文重建了早古生代冈瓦纳大陆边缘微陆块的地理位置,提出了相关区域的构造演化模型。主要获得了以下研究成果和认识:(1)腾冲、保山和禅泰地块早古生代花岗质岩石锆石U-Pb年代学、原位Lu-Hf同位素、全岩主微量元素和Sr-Nd同位素数据分析表明它们形成于早古生代时期的冈瓦纳大陆北缘。十二个样品厘定出的U-Pb锆石结晶年龄为492-460 Ma,主要矿物为石英、钾长石、斜长石和黑云母,次要矿物为白云母和石榴石等,A/CNK值为1.10-1.39,为强过铝质S型花岗岩。样品表现出高Si O2(53.57-69.10 wt.%),高Rb/Sr和Rb/Ba比值,低Al2O3(12.4-15.8 wt.%)、Mg O(0.2-1.0 wt.%)、Ti O2(0.02-0.55 wt.%)、Fe Ot(0.5-3.3 wt.%)和Ca O/Na2O比值,富集LILEs,亏损Nb、Sr、P、Eu和Ti。87Sr/86Sr初始比值为0.70839-0.72302,εNd(t)值介于-5.3和-8.1之间,Nd模式年龄为1.7-2.8 Ga,与已发表的藏南同期花岗质岩石一致。早古生代岩浆岩εHf(t)值变化为-0.37到-14.1,Hf模式年龄为1.49-2.35 Ga。源区以古老变质泥岩和含有少量比例变质火成岩(新元古代)组分为特征。研究认为滇西南腾冲、保山和禅泰地块早古生代过铝质S型花岗岩形成于与增生造山运动有关的活动大陆边缘背景。(2)腾冲-保山地块澜沧群惠民组两个变火山岩锆石U-Pb定年获得了晚奥陶世年龄,分别为462±6 Ma和454±27 Ma。结合同一地区已发表的地球化学数据表明,惠民组火山岩具有钙碱性特征,含较高Al2O3(13.04-18.77 wt.%)和较低Ti O2(0.64~1.00 wt.%)。Si O2含量为53.57-69.10 wt.%,mg#值变化于62~50,为高镁安山质岩石。样品表现出富集轻稀土元素(LREEs)和大离子亲石元素(LILEs),具有明显的Eu负异常(δEu=0.20~0.33),亏损高场强元素,与弧火山岩相似。初始87Sr/86Sr变化为0.72136~0.72252,εNd(t)值变化为-7.63~-7.62。研究认为滇西南地区早古生代火山岩形成于岛弧背景,为新元古代-早古生代冈瓦纳大陆北缘增生造山的产物。(3)对西盟群帕可组三个变质砂岩和澜沧群七个变质碎屑岩样品的激光U-Pb测年(394颗)和原位Lu-Hf同位素组成(246颗)研究表明,碎屑锆石年龄变化范围为3490-465 Ma,εHf(t)值变化为-35.45~26.3。不同样品给出的最小年龄分别为515±19 Ma、531±13 Ma、514±14 Ma、480±12 Ma、559±16 Ma、489±5 Ma、548±7 Ma、505±20 Ma、503±14 Ma和465±4 Ma。相应样品的最小年龄峰值分别为568 Ma、541 Ma、560 Ma、506 Ma、562 Ma、491 Ma、551 Ma、530 Ma、551Ma和614 Ma,约束它们的沉积年龄小于491 Ma。因此滇西南帕可组和澜沧群应该沉积于491-454 Ma间的晚寒武世-中奥陶世,而非以往所认为的前寒武纪地层。Lu-Hf同位素组成则显示变质碎屑岩样品物源为古老地壳物质的再循环和新生地壳组分,具有东冈瓦纳大陆亲缘性。(4)滇西南奥陶纪高镁质岩石和同期镁铁质及花岗质岩石为早古生代时期原特提斯洋沿东冈瓦纳大陆北缘俯冲的产物,代表了冈瓦纳大陆北缘早古生代岩浆岩带向南的延伸。沿土耳其西北部、伊朗中部、巴基斯坦西北部、印度和尼泊尔西北部到藏南及滇西南存在一个渐进穿时造山运动。(5)研究认为在冈瓦纳大陆奥陶纪(约460 Ma)重建图中,腾冲-保山及禅泰地块更可能靠近印度板块而不是澳大利亚板块。由此提出了滇西南地区构造演化模型,滇西南地区原特提斯洋的俯冲至少持续到450 Ma。
[Abstract]:The early Paleozoic magmatic rocks and sedimentary rocks (~525-460 Ma) developed in the Tethys Himalaya tectonic domain, such as Northwestern India, Nepal, Zangnan, and southwestern China, are located on the northern margin of Gondwana in the early Palaeozoic era and toward the original Tethys ocean. At present, different scholars have mainly raised the early Paleozoic tectonic events in these regions. Two dynamic models: (1) the Pan African orogeny. The orogenic movement associated with the Rodinia supercontinental cracking and the polymerization of the Gondwana continent; (2) the Andean orogeny. With the polymerization of the Gondwana continent, the orogenic movement caused by the subduction of the original Tethys ocean to the India Craton and the adjacent area. The lack of magmatism in the late Paleozoic, as well as the transformation of the thermal tectonic events related to the closure of the Paleo Tethys ocean and the Himalaya orogenic movement, has not been well constrained by the early Paleozoic tectonic evolution and palaeogeographic position in the related regions. The Himalaya tectonic knot extends to the North-South extension of the Southeast Asian tectonic junction, and preserves a large number of Early Paleozoic magmatic activities and depositional evidences. It is a natural laboratory for our study of the early Paleozoic original Tethys structural properties. This study selected the study object in Tengchong, Baoshan and Zen land block in southwestern Yunnan. The lithology, petrography, zircon U-Pb chronology, principal and trace element geochemistry, and Lu-Hf and Sr-Nd isotopic compositions of the main and trace elements are carried out to explore the petrogenesis of the early Paleozoic magmatic rocks in southwestern Yunnan, in order to explore the early Paleozoic tectonic background and motive force. Based on the previous research results, this paper reconstructs the geographical location of the continental margin of the gwana continental margin in the early Paleozoic and proposed the tectonic evolution model of the related regions. The main achievements are as follows: (1) the zircon U-Pb chronology of the early Paleozoic granitic rocks in Tengchong, Baoshan and Zen thay massif, in situ Lu-Hf isotopes and whole rocks The main trace elements and Sr-Nd isotopic data indicate that they formed in the northern margin of the Gondwana continent in the early Paleozoic era. The U-Pb zircon crystallization age of twelve samples is 492-460 Ma, the main minerals are quartz, potassium feldspar, plagioclase and biotite, and the secondary minerals are muscovite and garnet, and the A/CNK value is 1.10-1.39, which is a strong peralmite. The sample shows high Si O2 (53.57-69.10 wt.%), high Rb/Sr and Rb/Ba ratio, low Al2O3 (12.4-15.8 wt.%), Mg O. The age of 1.7-2.8 Ga is the same as that of the published granitic rocks in Zangnan. The epsilon Hf (T) value of the early Paleozoic magmatic rocks changed from -0.37 to -14.1, and the Hf mode age was 1.49-2.35 Ga. source area with ancient metamorphic mudstone and a small proportion of metamorphic igneous rocks (Neoproterozoic) components. It was considered that Tengchong, Baoshan and Chan Tai massif in southwestern Yunnan. The early Paleozoic peraluminous S type granites were formed in the active continental margin associated with the hyperplastic orogeny. (2) the U-Pb zircon U-Pb of the Huimin group of the Lancang group, Tengchong - Baoshan block, obtained the age of the late Ordovician, and the geochemical data of 462 + 6 Ma and 454 + 27 Ma. in the same area showed that the Huimin group fire The high Al2O3 (13.04-18.77 wt.%) and lower Ti O2 (0.64~1.00 wt.%).Si O2 content is 53.57-69.10 wt.%, and the mg# values are high magnesium an mountain rock. The samples show the enrichment of light rare earth elements and large ionic stone elements, which have obvious negative anomaly (delta) and high loss field. The strong element is similar to the arc volcanic rocks. The initial 87Sr/86Sr change is 0.72136~0.72252, and the change of Nd (T) value is -7.63~-7.62.. The early Paleozoic volcanic rocks in Southwest Yunnan are formed in the island arc background, which are the product of the hyperplastic orogeny in the northern margin of the Neoproterozoic Early Paleozoic Gondwana continent. (3) three metamorphic sandstone and Lancang group in the Ximeng group Palac group. The study of laser U-Pb dating (394) and in situ Lu-Hf isotopic composition (246) of seven metamorphic clastic rocks showed that the age range of detrital zircon was 3490-465 Ma, and the minimum age of Hf (T) values was 515 + 19 Ma, 531 + 13 Ma, 514 + 14 Ma, 480 + 12 Ma and 559 + Ma. The minimum age peaks of 5 + 20 Ma, 503 + 14 Ma and 465 + 4 Ma. respectively are 568 Ma, 541 Ma, 560 Ma, 506 Ma, 562 Ma, 491 Ma, 551 Ma, Ma, 551Ma, and Ma, which restrict their deposition age to be deposited in the late Cambrian Middle Ordovician between the Southwest Yunnan and Lancang The.Lu-Hf isotopic composition of the Precambrian strata shows that the metamorphic clastic rock samples were derived from the ancient crustal material recirculation and the new crustal component, and had the relationship between the East Gondwana continent. (4) the Ordovician high magnesia rocks in southwestern Yunnan and the same period of the mafic and granitic rocks were the north of the early Paleozoic to the north of the eastern Gondwana continent. The product of the marginal subduction represents the extension of the early Paleozoic magmatic rocks in the northern margin of the Gondwana. Along the northwestern part of Turkey, central Iran, northwest Pakistan, India and Nepal to Zangnan and southwestern Yunnan, there is a progressive orogenic orogenic movement. (5) the study was identified in the Ordovician (about 460 Ma) reconstruction of the Gondwana continent. Tengchong Baoshan and Chan Tai block are more likely to be near the India plate rather than the Australian plate. Thus the tectonic evolution model in southwestern Yunnan was put forward. The subduction of the original Tethys ocean in southwestern Yunnan lasted for at least 450 Ma..

【学位授予单位】：中国科学院研究生院(广州地球化学研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P542
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本文编号：1871632