老挝琅勃拉邦及黎府构造带古特提斯构造演化

发布时间：2017-12-28 07:39

  本文关键词：老挝琅勃拉邦及黎府构造带古特提斯构造演化　出处：《中国地质大学》2016年博士论文　论文类型：学位论文

  更多相关文章： 古特提斯 黎府构造带 琅勃拉邦构造带 岩浆岩 地球化学

【摘要】：泰国和老挝均位于东古特提斯构造域,是由数个微陆块并由其间的缝合带／构造带拼接而成的复杂结合带,同时也是西部的Sibumasu板块和东部的印支板块的结合部位。国内及外国地质学者对东南亚地区特提斯的研究主要集中在云南省境内“三江”地区,而对与之相连的泰国老挝的研究较少,尤其是缺少对老挝境内的研究工作,而这也是造成现今东南亚地区构造带划分没有统一的关键。因此,本文选择了老挝境内黎府构造带和琅勃拉邦构造带内的岩浆岩及硅质岩为研究对象,开展了详尽的野外地质考察和系统的岩相学研究,通过详细的全岩地球化学、锆石U-Pb年代学、Sr-Nd同位素地球化学以及放射虫硅质岩的综合研究,以求揭示这些岩浆岩及硅质岩的时空分布和岩石成因,探讨其构造背景,进而探讨这两个构造带的古特提斯构造演化及南北衔接,取得了以下主要成果和认识：1、限定了黎府弧后盆地的俯冲时限及其南北延伸老挝西北部Muang Feuang和巴菜地区识别出2套主要的火山岩。其中Muang Feuang地区识别出的安山岩、流纹岩及凝灰岩锆石U-Pb年龄分别为330.4 Ma、334.9 Ma和349.6Ma,巴莱地区的玄武岩及玄武安山岩锆石年龄314.6 Ma到315.4 Ma,并非之前区域地质图上认为的二叠纪-早三叠世。对这两个地方的玄武岩、玄武安山岩和流纹岩样品的地球化学研究表明,Muang Feuang和巴莱地区的火山岩都具有低TiO2、Ni、Cr和高A1203含量,其中Muang Feuang地区的火山岩富集轻稀土元素,同时富集大离子亲石元素,亏损高场强元素(Nb、Ta、Ti),具有Eu负异常(Eu/Eu*=0.45-0.91),类似澜沧江构造带内的陆缘弧火山岩。巴莱地区的玄武岩及玄武安山岩具有轻稀土元素的弱富集,具有微弱的Eu负异常(Eu/Eu*=0.92-0.97),富集大离子亲石元素,而亏损高场强元素(Nb、Ta、Ti),地球化学表明这两个地方的火山岩均应来自一个富集的地幔源区,为俯冲板片流体交代地幔楔所形成的,而沉积物的参与较少。根据各类构造环境判别图表明,该套火山岩为一套陆缘弧火山岩,可以和泰国碧彩汶构造带内的石炭纪岩浆岩进行对比,说明黎府弧后盆地的俯冲应为早石炭世。相对的,沙耶武里地区的玄武安山岩锆石U-Pb年龄为237.7+1.7 Ma,并不同于Muang Feuang和巴莱地区的石炭纪陆缘弧火山岩,而属于另一个洋盆或弧后的俯冲所形成。对其中的玄武岩、玄武安山岩和安山岩的地化研究表明,该地区的火山岩具有低TiO2、Ni、Cr和高A1203含量,都富集轻稀土元素和大离子亲石元素,不具有明显的Eu正负异常(Eu/Eu*=0.91-1.13),亏损高场强元素(Nb和Ta),同样来自一个富集的地幔源区,以俯冲板片流体交代地幔楔形成的,而沉积物的参与较少。根据对比研究,发现沙耶武里地区的这套火山岩与泰国境内碧彩汶构造带内二叠-三叠纪弧火山岩类似,说明该套弧火山岩应形成于难河弧后盆地向印支板块西缘的俯冲过程。2、在琅勃拉邦构造带识别出了石炭纪弧后盆地的基性岩浆岩老挝琅勃拉邦构造带为新识别出的一个岩浆岩带,该带位于思茅板块和印支板块之间,大致平行奠边府断裂带,带内存在两套主要的岩浆岩。其中Nam Ou河边的粗粒玄武岩及辉绿岩锆石U-Pb年龄分别为304.5 Ma和335.5 Ma。地球化学研究表明辉绿岩样品呈现近似平行的“右倾型”分异,轻稀土相对重稀土轻微富集,具有类似E-MORB的特征,富集高度不相容元素(Rb、Bb和Th),具有弱的Nb-Ta的负异常和Sr的正异常,其87Sr/86Sr (t)值为0.7052,ENd (t)值为+5.16,锆石εHf(t)值为+11.6-+13.3,因此我们认为,辉绿岩主要源自类似E-MORB的源区,受到新生的俯冲物质加入形成的。玄武岩样品亏损轻稀土元素,无明显的Eu异常(Eu/Eu*=0.99-1.04),富集Rb、Ba和U,亏损高场强元素Nb,具Sr的正异常,类似N-MORB、哀牢山缝合带镁铁质岩石及现代东劳弧后盆地玄武岩,具有低的87Sr/86Sr (t)值(0.7032-0.7052)和正的εNd (t)值(+6.57-+6.93),地球化学显示其源区主要来自N-MORB类似的源区,同时受到俯冲板片脱水流体交代作用,并且有一定比例的俯冲沉积物参与。我们认为琅勃拉邦构造带这套基性岩浆岩应为形成于石炭纪的陆源弧后盆地环境。3、在琅勃拉邦构造带识别出晚二叠世-中三叠世俯冲有关的岩浆岩Pak Ou和琅勃拉邦南部地区的岩浆岩都具有岛弧火山岩的特点。同时富集高度了不相容元素,亏损高场强元素Nb和Ta。其中Pak Ou地区的岩浆岩形成于晚二叠世(～257Ma),具有轻稀土的富集,无明显的Eu异常,富集高度不相容元素(Rb、Bb和Th),具有Sr的正异常,全岩的初始87Sr/86Sr (t)比值为0.7047-0.7056,SNd (t)为+5.95-+7.33,地球化学显示主要来自MORB类似的源区(地幔橄榄岩区)同时受到俯冲板片熔体的交代作用形成的产物,而琅勃拉邦南部地区的辉长岩样品锆石U-Pb年龄为中三叠世(238-242Ma),其稀土元素配分模式呈现近平行的特征,无明显Eu异常,类似E-MORB稀土配分模式,这些辉长岩样品富集大离子亲石元素,具有Nb-Ta的负异常,全岩87Sr/86Sr (t)比值为0.7042-0.7046,ENd (t)为+6.40-+7.96。地球化学显示是受到年轻板片流体交代过的难熔地幔楔部分熔融的产物,Pak Ou和琅勃拉邦南部地区的岩浆岩均形成于与俯冲有关的岛弧环境,这两个地区的岩浆岩锆石年龄与泰国境内的黎府构造带西亚带、碧彩汶构造带和老挝沙耶武里地区的弧火山岩年龄一致,根据区域对比研究认为应属于琅勃拉邦-难河构造带/缝合带向印支西北缘俯冲形成的。4、在琅勃拉邦构造带识别出早石炭世的远洋放射虫硅质岩琅勃拉邦构造带内放射虫硅质岩含有放射虫Entactinia vulgaris Won, Entactinosphaera palimpola Foreman 和 Belowea variabilis (Ormiston et Lane),时代为早石炭世。,硅质岩样品具有很高的Si02含量(95.29-98.17 wt.%%%),大部分样品表现出相类似的稀土配分模式,部分样品配分模式图表现为上凸状,具有中稀土富集,均具有明显的Ce负异常,Ce/Ce*值为0.64-0.74,其中部分样品具有Eu的负异常,为0.58-0.68。Y/Ho比值为31.05-40.96,类似日本Sasayama中-晚二叠世的远洋硅质岩。地球化学显示其为含酸性火山碎屑非热液成因的远洋硅质岩,应形成于一个开阔的弧后盆地环境。5、提出两条构造带的演化模型和延伸黎府弧后盆地的俯冲应始于早石炭世,在碧彩汶构造带内的石炭纪岩浆岩和火山碎屑岩应为老挝西北部地区石炭纪火山岩向南的延伸,进而证实黎府构造带可以一直延伸至老挝境内。琅勃拉邦构造带可以与难河和金沙江-哀牢山缝合带相连,同时其晚二叠世-中三叠世的岛弧岩浆岩可以与碧彩汶构造带、黎府西亚带、沙耶武里地区和哀牢山缝合带内的俯冲有关的岩浆岩进行对比,证明了琅勃拉邦构造带可以与难河缝合带和哀牢山缝合带相连,说明在印支板块西北缘和素可泰/思茅板块之间存在一个石炭纪时期的弧后盆地,其俯冲时间应该为二叠纪。
[Abstract]:Thailand and Laos are all located in the Don Gut Tis tectonic domain, which is a complex combination zone composed of several micro continental blocks and their suture Belts / structural belts. It is also the conjunction part of the western Sibumasu plate and the eastern Indosinian plate. The domestic and foreign scholars on the geology of Southeast Asia Tethys research mainly concentrated in the territory of Yunnan Province, Sanjiang area, and connected with the Thailand Laos study less, especially the lack of research work in Laos, which is caused by the tectonic belt of Southeast Asia Division has no unified key. Therefore, this paper chooses the Laos Loei tectonic belt and Luang Prabang tectonic belt in the magmatite and siliceous rocks as the research object, to carry out the study of petrography field geological investigation and detailed, through detailed whole rock geochemistry, zircon U-Pb geochronology and Sr-Nd isotope geochemistry and radiolarian siliceous rocks in the comprehensive study in order to reveal the spatial distribution and petrogenesis of magmatite and siliceous rocks, discusses its tectonic background, and then discusses the two tectonic belt of the Paleo Tethys tectonic evolution and North-South convergence, the main results are shown as following: 1, the limited time and the subduction of the north and south of Loei arc basin extension of northwestern Laos Muang and Feuang identification of Pakistan 2 main dish area volcano rock. The identification of Muang Feuang in the andesite, rhyolite and tuff of zircon U-Pb ages were 330.4 Ma, 334.9 Ma and 349.6Ma, baligh area basalts and basaltic andesite zircon Ma age of 314.6 to 315.4 Ma, not before the regional geological map as Permian Early Triassic three. Geochemical study of the two parts of the basalt, basaltic andesite and rhyolite samples showed that Muang Feuang and ballee area of the volcano rocks have lower TiO2, Ni, Cr and high A1203 content, the Muang Feuang area of the volcano rocks are rich in light rare earth elements, and the enrichment of lile and depletion of high field strength elements (Nb, Ta, Ti, Eu) with negative anomaly (Eu/Eu*=0.45-0.91), similar to the Lancang River tectonic belt in the continental margin arc volcano rock. The basalt and basaltic andesite baratei area with weak enrichment of light rare earth elements, with weak negative Eu anomaly (Eu/Eu*=0.92-0.97), enrichment of large ion lithophile elements and depleted in high field strength elements (Nb, Ta, Ti), geochemistry indicates that the two parts of the volcano rock shall be derived from an enriched mantle source District, formed by subduction fluid metasomatism of the mantle wedge, and sediment in less. According to various tectonicdiscrimination diagrams show that the volcano rocks is a continental margin arc volcano rock, can be compared to Thailand and Timor bicai tectonic belt in Carboniferous magmatic rocks, Loei arc basin subduction for early carboniferous. Relatively, Sayaboury area of basaltic andesite zircon U-Pb ages of 237.7+1.7 and Ma, Muang and Feuang in different regions of the bale Carboniferous epicontinental arc volcano rock, which belongs to the formation of another basin or back arc subduction. Study on the basalt, basaltic andesite and andesite that the area of the volcano rock has low TiO2, Ni, Cr and high A1203 content, are enriched in light rare earth elements and large ion lithophile elements, without obvious Eu negative anomalies (Eu/Eu*=0.91-1.13), depleted in high field strength elements (Nb and Ta) also, from an enriched mantle source region, by the subducting slab fluid mantle wedge formation, and less involved in sediments. According to the comparative study, found that the volcano rock Sayaboury region in Thailand and Timor bicai tectonic belt in two Triassic arc volcano rocks are similar, indicating that the set of arc volcano rocks should be formed in the back arc basin to the river to the western margin of the Indian plate subduction process. 2, in the Luang Prabang tectonic zone identified as a Laos Luang Prabang tectonic magmatite identified with mafic magmatite Carboniferous backarc basin zone, the zone is located in the Simao plate and the Indo China plate, roughly parallel to the Dien Bien Phu fault zone, there are two main sets of magmatite belt. The U-Pb ages of the coarse basalt and the zircons of the diabase on the Nam Ou River are 304.5 Ma and 335.5 Ma respectively. Geochemical studies indicate that the diabase samples exhibited approximately parallel to the "right" differentiation, LREE relative to heavy REE slightly enriched, features similar to E-MORB, enriched in highly incompatible elements (Rb, Bb and Th), Sr has a weak negative anomaly and Nb-Ta positive anomaly, the value of 87Sr/86Sr (T) 0.7052, ENd (T) = +5.16, epsilon Hf zircon (T) value of +11.6-+13.3, so we think, mainly from the source area of diabase is similar to the E-MORB, by adding new material formed by subduction. Basalt sample loss of light rare earth elements, no obvious abnormality of Eu (Eu/Eu*=0.99-1.04), Rb, Ba and U enrichment and depletion of high field strength elements Nb, Sr positive anomaly, similar to N-MORB, Ailaoshan suture zone of mafic rock and modern East Lo backarc basin basalts, with low 87Sr/ value 86Sr (T) (0.7032-0.7052) and Nd (T) positive epsilon value (+6.57-+6.93), geochemistry showed that the source area is mainly from N-MORB similar source area, at the same time by the subduction fluid metasomatism, and a certain proportion of the subducted sediment in. We believe that the Luang Prabang tectonic belt basic magmatite should be formed in the Carboniferous continental arc basin environment. 3, in the Luang Prabang tectonic belt identified late Permian Middle Triassic subduction related three magmatite and Pak Ou in the southern area of Luang Prabang magmatite with island arc volcanic rocks. At the same time, the incompatible elements are enriched and the high field and strong elements Nb and Ta are depleted. The Pak Ou area of magmatite formed in the Late Permian (~ 257Ma), with the enrichment of LREE, no obvious Eu anomaly, enriched in highly incompatible elements (Rb, Bb and Th), with positive Sr anomalies, initial whole rock 87Sr/86Sr (T) = 0.7047-0.7056 (T) for SNd +5.95-+7.33, geochemistry
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P542
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