本文關(guān)鍵詞：老撾瑯勃拉邦及黎府構(gòu)造帶古特提斯構(gòu)造演化　出處：《中國地質(zhì)大學(xué)》2016年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 古特提斯 黎府構(gòu)造帶 瑯勃拉邦構(gòu)造帶 巖漿巖 地球化學(xué)

【摘要】：泰國和老撾均位于東古特提斯構(gòu)造域,是由數(shù)個(gè)微陸塊并由其間的縫合帶／構(gòu)造帶拼接而成的復(fù)雜結(jié)合帶,同時(shí)也是西部的Sibumasu板塊和東部的印支板塊的結(jié)合部位。國內(nèi)及外國地質(zhì)學(xué)者對東南亞地區(qū)特提斯的研究主要集中在云南省境內(nèi)“三江”地區(qū),而對與之相連的泰國老撾的研究較少,尤其是缺少對老撾境內(nèi)的研究工作,而這也是造成現(xiàn)今東南亞地區(qū)構(gòu)造帶劃分沒有統(tǒng)一的關(guān)鍵。因此,本文選擇了老撾境內(nèi)黎府構(gòu)造帶和瑯勃拉邦構(gòu)造帶內(nèi)的巖漿巖及硅質(zhì)巖為研究對象,開展了詳盡的野外地質(zhì)考察和系統(tǒng)的巖相學(xué)研究,通過詳細(xì)的全巖地球化學(xué)、鋯石U-Pb年代學(xué)、Sr-Nd同位素地球化學(xué)以及放射蟲硅質(zhì)巖的綜合研究,以求揭示這些巖漿巖及硅質(zhì)巖的時(shí)空分布和巖石成因,探討其構(gòu)造背景,進(jìn)而探討這兩個(gè)構(gòu)造帶的古特提斯構(gòu)造演化及南北銜接,取得了以下主要成果和認(rèn)識：1、限定了黎府弧后盆地的俯沖時(shí)限及其南北延伸老撾西北部Muang Feuang和巴菜地區(qū)識別出2套主要的火山巖。其中Muang Feuang地區(qū)識別出的安山巖、流紋巖及凝灰?guī)r鋯石U-Pb年齡分別為330.4 Ma、334.9 Ma和349.6Ma,巴萊地區(qū)的玄武巖及玄武安山巖鋯石年齡314.6 Ma到315.4 Ma,并非之前區(qū)域地質(zhì)圖上認(rèn)為的二疊紀(jì)-早三疊世。對這兩個(gè)地方的玄武巖、玄武安山巖和流紋巖樣品的地球化學(xué)研究表明,Muang Feuang和巴萊地區(qū)的火山巖都具有低TiO2、Ni、Cr和高A1203含量,其中Muang Feuang地區(qū)的火山巖富集輕稀土元素,同時(shí)富集大離子親石元素,虧損高場強(qiáng)元素(Nb、Ta、Ti),具有Eu負(fù)異常(Eu/Eu*=0.45-0.91),類似瀾滄江構(gòu)造帶內(nèi)的陸緣弧火山巖。巴萊地區(qū)的玄武巖及玄武安山巖具有輕稀土元素的弱富集,具有微弱的Eu負(fù)異常(Eu/Eu*=0.92-0.97),富集大離子親石元素,而虧損高場強(qiáng)元素(Nb、Ta、Ti),地球化學(xué)表明這兩個(gè)地方的火山巖均應(yīng)來自一個(gè)富集的地幔源區(qū),為俯沖板片流體交代地幔楔所形成的,而沉積物的參與較少。根據(jù)各類構(gòu)造環(huán)境判別圖表明,該套火山巖為一套陸緣弧火山巖,可以和泰國碧彩汶構(gòu)造帶內(nèi)的石炭紀(jì)巖漿巖進(jìn)行對比,說明黎府弧后盆地的俯沖應(yīng)為早石炭世。相對的,沙耶武里地區(qū)的玄武安山巖鋯石U-Pb年齡為237.7+1.7 Ma,并不同于Muang Feuang和巴萊地區(qū)的石炭紀(jì)陸緣弧火山巖,而屬于另一個(gè)洋盆或弧后的俯沖所形成。對其中的玄武巖、玄武安山巖和安山巖的地化研究表明,該地區(qū)的火山巖具有低TiO2、Ni、Cr和高A1203含量,都富集輕稀土元素和大離子親石元素,不具有明顯的Eu正負(fù)異常(Eu/Eu*=0.91-1.13),虧損高場強(qiáng)元素(Nb和Ta),同樣來自一個(gè)富集的地幔源區(qū),以俯沖板片流體交代地幔楔形成的,而沉積物的參與較少。根據(jù)對比研究,發(fā)現(xiàn)沙耶武里地區(qū)的這套火山巖與泰國境內(nèi)碧彩汶構(gòu)造帶內(nèi)二疊-三疊紀(jì)弧火山巖類似,說明該套弧火山巖應(yīng)形成于難河弧后盆地向印支板塊西緣的俯沖過程。2、在瑯勃拉邦構(gòu)造帶識別出了石炭紀(jì)弧后盆地的基性巖漿巖老撾瑯勃拉邦構(gòu)造帶為新識別出的一個(gè)巖漿巖帶,該帶位于思茅板塊和印支板塊之間,大致平行奠邊府?dāng)嗔褞?帶內(nèi)存在兩套主要的巖漿巖。其中Nam Ou河邊的粗粒玄武巖及輝綠巖鋯石U-Pb年齡分別為304.5 Ma和335.5 Ma。地球化學(xué)研究表明輝綠巖樣品呈現(xiàn)近似平行的“右傾型”分異,輕稀土相對重稀土輕微富集,具有類似E-MORB的特征,富集高度不相容元素(Rb、Bb和Th),具有弱的Nb-Ta的負(fù)異常和Sr的正異常,其87Sr/86Sr (t)值為0.7052,ENd (t)值為+5.16,鋯石εHf(t)值為+11.6-+13.3,因此我們認(rèn)為,輝綠巖主要源自類似E-MORB的源區(qū),受到新生的俯沖物質(zhì)加入形成的。玄武巖樣品虧損輕稀土元素,無明顯的Eu異常(Eu/Eu*=0.99-1.04),富集Rb、Ba和U,虧損高場強(qiáng)元素Nb,具Sr的正異常,類似N-MORB、哀牢山縫合帶鎂鐵質(zhì)巖石及現(xiàn)代東勞弧后盆地玄武巖,具有低的87Sr/86Sr (t)值(0.7032-0.7052)和正的εNd (t)值(+6.57-+6.93),地球化學(xué)顯示其源區(qū)主要來自N-MORB類似的源區(qū),同時(shí)受到俯沖板片脫水流體交代作用,并且有一定比例的俯沖沉積物參與。我們認(rèn)為瑯勃拉邦構(gòu)造帶這套基性巖漿巖應(yīng)為形成于石炭紀(jì)的陸源弧后盆地環(huán)境。3、在瑯勃拉邦構(gòu)造帶識別出晚二疊世-中三疊世俯沖有關(guān)的巖漿巖Pak Ou和瑯勃拉邦南部地區(qū)的巖漿巖都具有島弧火山巖的特點(diǎn)。同時(shí)富集高度了不相容元素,虧損高場強(qiáng)元素Nb和Ta。其中Pak Ou地區(qū)的巖漿巖形成于晚二疊世(～257Ma),具有輕稀土的富集,無明顯的Eu異常,富集高度不相容元素(Rb、Bb和Th),具有Sr的正異常,全巖的初始87Sr/86Sr (t)比值為0.7047-0.7056,SNd (t)為+5.95-+7.33,地球化學(xué)顯示主要來自MORB類似的源區(qū)(地幔橄欖巖區(qū))同時(shí)受到俯沖板片熔體的交代作用形成的產(chǎn)物,而瑯勃拉邦南部地區(qū)的輝長巖樣品鋯石U-Pb年齡為中三疊世(238-242Ma),其稀土元素配分模式呈現(xiàn)近平行的特征,無明顯Eu異常,類似E-MORB稀土配分模式,這些輝長巖樣品富集大離子親石元素,具有Nb-Ta的負(fù)異常,全巖87Sr/86Sr (t)比值為0.7042-0.7046,ENd (t)為+6.40-+7.96。地球化學(xué)顯示是受到年輕板片流體交代過的難熔地幔楔部分熔融的產(chǎn)物,Pak Ou和瑯勃拉邦南部地區(qū)的巖漿巖均形成于與俯沖有關(guān)的島弧環(huán)境,這兩個(gè)地區(qū)的巖漿巖鋯石年齡與泰國境內(nèi)的黎府構(gòu)造帶西亞帶、碧彩汶構(gòu)造帶和老撾沙耶武里地區(qū)的弧火山巖年齡一致,根據(jù)區(qū)域?qū)Ρ妊芯空J(rèn)為應(yīng)屬于瑯勃拉邦-難河構(gòu)造帶/縫合帶向印支西北緣俯沖形成的。4、在瑯勃拉邦構(gòu)造帶識別出早石炭世的遠(yuǎn)洋放射蟲硅質(zhì)巖瑯勃拉邦構(gòu)造帶內(nèi)放射蟲硅質(zhì)巖含有放射蟲Entactinia vulgaris Won, Entactinosphaera palimpola Foreman 和 Belowea variabilis (Ormiston et Lane),時(shí)代為早石炭世。,硅質(zhì)巖樣品具有很高的Si02含量(95.29-98.17 wt.%%%),大部分樣品表現(xiàn)出相類似的稀土配分模式,部分樣品配分模式圖表現(xiàn)為上凸?fàn)?具有中稀土富集,均具有明顯的Ce負(fù)異常,Ce/Ce*值為0.64-0.74,其中部分樣品具有Eu的負(fù)異常,為0.58-0.68。Y/Ho比值為31.05-40.96,類似日本Sasayama中-晚二疊世的遠(yuǎn)洋硅質(zhì)巖。地球化學(xué)顯示其為含酸性火山碎屑非熱液成因的遠(yuǎn)洋硅質(zhì)巖,應(yīng)形成于一個(gè)開闊的弧后盆地環(huán)境。5、提出兩條構(gòu)造帶的演化模型和延伸黎府弧后盆地的俯沖應(yīng)始于早石炭世,在碧彩汶構(gòu)造帶內(nèi)的石炭紀(jì)巖漿巖和火山碎屑巖應(yīng)為老撾西北部地區(qū)石炭紀(jì)火山巖向南的延伸,進(jìn)而證實(shí)黎府構(gòu)造帶可以一直延伸至老撾境內(nèi)�，槻顦�(gòu)造帶可以與難河和金沙江-哀牢山縫合帶相連,同時(shí)其晚二疊世-中三疊世的島弧巖漿巖可以與碧彩汶構(gòu)造帶、黎府西亞帶、沙耶武里地區(qū)和哀牢山縫合帶內(nèi)的俯沖有關(guān)的巖漿巖進(jìn)行對比,證明了瑯勃拉邦構(gòu)造帶可以與難河縫合帶和哀牢山縫合帶相連,說明在印支板塊西北緣和素可泰/思茅板塊之間存在一個(gè)石炭紀(jì)時(shí)期的弧后盆地,其俯沖時(shí)間應(yīng)該為二疊紀(jì)。
[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
【學(xué)位授予單位】：中國地質(zhì)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：P542
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本文編號：1345181