本文關(guān)鍵詞： 岡底斯 花崗巖類(lèi) 韌性剪切帶 裂變徑跡 構(gòu)造演化　出處：《中國(guó)地質(zhì)科學(xué)院》2016年博士論文　論文類(lèi)型：學(xué)位論文

【摘要】：岡底斯巖漿帶位于拉薩地體南緣,是新特提斯洋盆演化和印度-亞洲陸陸碰撞的巖漿產(chǎn)物,對(duì)岡底斯巖漿帶的研究方興未艾,但一些基本問(wèn)題仍然存在著激烈的爭(zhēng)論(比如晚三疊到早-中侏羅世新特提斯洋演化的極性,岡底斯巖漿帶中大型韌性剪切帶形成的時(shí)代、動(dòng)力學(xué)機(jī)制以及岡底斯中段新生代的隆升-剝蝕模式等等),這都直接影響了對(duì)新特提斯域構(gòu)造和青藏高原形成演化的理解,以及對(duì)岡底斯構(gòu)造成礦帶的資源評(píng)價(jià)。本文選擇岡底斯巖漿帶中段南緣地區(qū)作為研究對(duì)象,開(kāi)展了詳細(xì)的野外地質(zhì)調(diào)查,首次在日喀則南木林和拉薩曲水地區(qū)發(fā)現(xiàn)和厘定了晚三疊紀(jì)的侵入巖體,并開(kāi)展了詳細(xì)的巖石學(xué)、礦物學(xué)、地球化學(xué)、鋯石Lu-Hf同位素分析和年代學(xué)研究；對(duì)早-中侏羅世的花崗巖類(lèi)及次火山巖開(kāi)展了巖石學(xué)、年代學(xué)和鋯石Lu-Hf同位素研究；對(duì)岡底斯中段高海拔地區(qū)的始新世花崗巖類(lèi)進(jìn)行了地球化學(xué)和年代學(xué)研究；對(duì)岡底斯中段謝通門(mén)-曲水韌性剪切帶和曲水地區(qū)色甫-雞公韌性剪切帶進(jìn)行了詳細(xì)的野外地質(zhì)調(diào)查、顯微薄片鑒定、EBSD研究、云母40Ar-39Ar和鋯石U-Pb定年等；在前人研究的基礎(chǔ)上,對(duì)岡底斯中段進(jìn)行選擇性采樣,補(bǔ)充了新的磷灰石裂變徑跡數(shù)據(jù)；綜合分析上述研究資料,并結(jié)合前人研究成果以及區(qū)域地質(zhì)特征,試圖建立和探討岡底斯中段南緣的構(gòu)造演化模式。1.南木林卡孜鄉(xiāng)糜棱質(zhì)花崗巖形成于206-212Ma之間,形成環(huán)境為活動(dòng)大陸邊緣,鋯石的εHf(t)值從8.95到12.91,一階段模式年齡326-486Ma;曲水其奴角閃輝長(zhǎng)巖侵位結(jié)晶年齡為-210Ma,鋯石的εHf(1)值從9.56到14.75,一階段模式年齡為256～459Ma;曲水達(dá)嘎花崗巖體的侵位結(jié)晶年齡為225-230Ma,具有正的εHf(t)值(13.91到15.54);地質(zhì)年代學(xué)、巖石學(xué)、礦物學(xué)、地球化學(xué)以及鋯石Lu-Hf同位素等顯示,晚三疊紀(jì)的花崗巖、角閃輝長(zhǎng)巖和新特提斯洋的向北俯沖有關(guān),其中角閃輝長(zhǎng)巖和俯沖板片流體交代地幔楔的部分熔融有關(guān),花崗質(zhì)巖石和初生地殼的部分熔融有關(guān),并且地幔物質(zhì)在花崗質(zhì)巖石的形成過(guò)程中扮演有重要的角色。晚三疊紀(jì)的巖漿作用暗示了新特提斯洋的俯沖應(yīng)該不晚于230Ma。2.通過(guò)對(duì)岡底斯中段南緣日喀則奴瑪?shù)貐^(qū)和尼木地區(qū)的閃長(zhǎng)巖、花崗閃長(zhǎng)巖、花崗巖以及次火山巖的地質(zhì)年代學(xué)、地球化學(xué)、礦物巖石學(xué)以及鋯石Lu-Hf同位素等綜合研究,獲得了如下認(rèn)識(shí)：花崗巖類(lèi)及次火山巖主要形成于169～191Ma,為早-中侏羅世晚期巖漿作用的產(chǎn)物;在化學(xué)組成上,花崗巖類(lèi)及次火山巖富集輕稀±(LREEs)和大離子親石元素(LILEs),強(qiáng)烈虧損Nb、Ta等高場(chǎng)強(qiáng)元素,具有島弧型花崗巖的地球化學(xué)特征；花崗巖類(lèi)為亞堿性,屬中鉀鈣堿性I型花崗巖類(lèi);樣品的εHf(t)值為10.10-15.44,具有明顯虧損鋯石的Hf同位素組成；綜合研究表明,早中侏羅世應(yīng)該和晚三疊紀(jì)具有一樣的大地構(gòu)造環(huán)境,即藏南岡底斯地區(qū)(活動(dòng)大陸邊緣)應(yīng)屬于新特提斯洋板片俯沖的構(gòu)造背景,花崗質(zhì)巖石的形成主要是來(lái)自中下地殼物質(zhì)的部分熔融。3.對(duì)岡底斯中段始新世的花崗巖類(lèi)(閃長(zhǎng)巖到花崗巖斑巖)進(jìn)行了鋯石U-Pb年代學(xué)、Lu-Hf同位素和地球化學(xué)分析。分析結(jié)果顯示,花崗巖類(lèi)鋯石的LA-ICP-MS U-Pb定年結(jié)果為40-55Ma之間,該年齡代表了花崗巖類(lèi)的侵位結(jié)晶年齡；在地球化學(xué)組成上,花崗巖類(lèi)富集輕稀土(HREEs)和大離子親石元素(LILEs),強(qiáng)烈虧損高場(chǎng)強(qiáng)元素Mb、Ta、P等,樣品顯示出島弧型花崗巖的特征。此外,分析樣品還表現(xiàn)為準(zhǔn)鋁質(zhì)I型花崗巖類(lèi)的特征,主要位于鈣堿性到高鉀鈣堿性系列區(qū)域。鋯石的Lu-Hf同位素分析結(jié)果顯示,多數(shù)樣品的εH(t)以正值為主,少數(shù)鋯石為負(fù)的εH(t)值,結(jié)合地球化學(xué)成分判別圖解,花崗巖類(lèi)主要是新生地殼的部分熔融一由變基性到變英云閃長(zhǎng)質(zhì)巖石的部分熔融以及變砂巖的部分熔融,在此過(guò)程中,底侵的地幔物質(zhì)也參與了花崗質(zhì)巖石的形成和演化。在Sr-Yb圖解上始新世的樣品表現(xiàn)為碰撞期花崗巖類(lèi)的地球化學(xué)特征,因此也暗示了印度-亞洲在始新世早期時(shí)已經(jīng)完全碰撞。始新世岡底斯地區(qū)的巖漿作用可能是由于新特提斯洋板片俯沖到歐亞板片之下,由于印度-亞洲大陸的碰撞,致使新特提斯洋板片俯沖角度變陡,并且發(fā)生了板片斷離(slab break off),引發(fā)了始新世岡底斯地區(qū)強(qiáng)烈的巖漿-火山作用。4.通過(guò)野外詳細(xì)的地質(zhì)調(diào)查、構(gòu)造解析以及室內(nèi)薄片鑒定和EBSD組構(gòu)分析,確定了謝通門(mén)-曲水韌性剪切帶的構(gòu)造屬性和演化特征。謝通門(mén)-曲水韌性剪切帶主要由強(qiáng)變形域和弱變形組成,包括面理化花崗巖、糜棱巖化花崗巖、初糜棱巖、糜棱巖組成,局部地區(qū)可見(jiàn)千糜巖。幾何學(xué)和運(yùn)動(dòng)學(xué)研究結(jié)果顯示謝通門(mén)-曲水韌性剪切帶具有一致的運(yùn)動(dòng)學(xué)特征,表現(xiàn)為以向北的正向滑覆為主。此外,運(yùn)動(dòng)學(xué)渦度顯示(Wk0.71)該剪切帶為典型的簡(jiǎn)單剪切為主的一般剪切,為伸展減薄型剪切帶,平均減薄量為20%。剪切帶的EBSD組構(gòu)分析顯示了謝通門(mén)-曲水韌性剪切帶主要滑移系以柱面a、菱面a和底面a滑移為主,變形主要以中低溫作用為主(550～300℃)。5.謝通門(mén)-曲水韌性剪切帶中的黑云母、絹云母40Ar-39Ar年代學(xué)以及鋯石U-Pb年代學(xué)共同限定了剪切帶活動(dòng)的時(shí)限。綜合年代學(xué)結(jié)果表明：謝通門(mén)-曲水韌性剪切帶形成于中新世早期21～24Ma之間。6.經(jīng)過(guò)詳細(xì)的野外地質(zhì)調(diào)查、室內(nèi)顯微薄片鑒定、EBSD組構(gòu)分析等研究認(rèn)為色甫-雞公韌性剪切帶以右行走滑為主。長(zhǎng)石-石英變形礦物對(duì)以及石英EBSD組構(gòu)研究結(jié)果顯示,雞公-曲水韌性剪切帶發(fā)生變形的溫度為500-550℃C。其次,通過(guò)對(duì)剪切帶中發(fā)育的同構(gòu)造長(zhǎng)英質(zhì)脈體的鋯石U-Pb年代學(xué)分析,獲得了色甫-雞公韌性剪切帶活動(dòng)的時(shí)限35～38Ma,即始新世晚期。7.通過(guò)對(duì)岡底斯中段11件磷灰石樣品的裂變徑跡分析,獲得了中段南緣的構(gòu)造隆升剝蝕史。研究結(jié)果顯示：岡底斯中段的隆升是多階段性的,漸新世以前的抬升、剝蝕和印度-亞洲板塊的碰撞有關(guān),23Ma以來(lái)的快速隆升和岡底斯地區(qū)逆沖斷裂的活動(dòng)有關(guān),并且在快速隆升階段也存在短暫的構(gòu)造平靜期。10Ma以來(lái)是岡底斯中段南緣地區(qū)又一次快速的隆升期,該次隆升和雅魯藏布江的快速下切侵蝕有關(guān)。第四紀(jì)以來(lái)在構(gòu)造活動(dòng)和氣候變化以及地表徑流的聯(lián)合作用下,共同塑造了現(xiàn)今的岡底斯。8.綜合結(jié)果表明：岡底斯巖漿帶經(jīng)歷了一個(gè)長(zhǎng)期的演化過(guò)程,從晚三疊紀(jì)開(kāi)始俯沖消減(230Ma),直到60～55Ma時(shí)印度-亞洲大陸的碰撞。始新世印度亞洲的碰撞導(dǎo)致了逆沖斷裂和大型走滑斷層的形成,并導(dǎo)致了新生代岡底斯巖基及鄰區(qū)的第一次整體的隆升剝蝕。23Ma以來(lái),由于藏南地區(qū)地殼側(cè)向增厚變化不均勻以及南北向應(yīng)力擠壓的松弛,導(dǎo)致了拉薩地體發(fā)生東西向的崩塌和南北向的伸展,此時(shí)大型正斷層以及拆離構(gòu)造應(yīng)用而生,同時(shí)加厚的地殼發(fā)生部分熔融而形成了具有特殊地球化學(xué)屬性的花崗質(zhì)斑巖,此時(shí)也是岡底斯地區(qū)成礦大爆發(fā)時(shí)期。
[Abstract]:The magmatic belt is located in the Lhasa terrane, is the magma evolution and Neo Tethyan ocean India Asia continental collision, the Gangdese magmatic belt just unfolding research, but some basic problems still exist controversy (such as late three to Early Triassic Middle Jurassic - polarity, Neo Tethys evolution of the Gangdise magmatic belt formation the ductile shear zone of the era, dynamic mechanism and the Middle Cenozoic uplift and erosion pattern and so on), which have a direct impact on the formation and evolution of the understanding of the new Tethys domain structure and the Qinghai Tibet Plateau, and the Gangdese metallogenic belt of the resource evaluation. This paper chooses the Gangdese magmatic belt in the South area as the research object. To carry out detailed geological survey, first found in Shigatse and Lhasa area and QUXU Namling determined the intrusive rock in Late Triassic period, were carried out. With the characteristics of petrology, mineralogy, geochemistry, zircon Lu-Hf geochronology and isotope analysis; in the early Middle Jurassic granitoids and volcano rock was carried out research on petrology, geochronology and Lu-Hf isotope; the central Gangdise high altitude Eocene granites of Geochemistry and geochronology of the mid Gangdise Xietongmen; - QUXU ductile shear zone and the area of color - Fu QUXU Jigongshan ductile shear zone of detailed geological survey, the research of optical microscope, EBSD, mica and 40Ar-39Ar zircon U-Pb dating; on the basis of previous research on mid Gangdise selective sampling, added the new apatite fission track data; comprehensive analysis the above research data, combined with the previous research, the regional geological features, trying to establish and study the southern central Gangdise tectonic evolution .1. card Namling Zi Xiang mylonitic granite formed in 206-212Ma, formed in the continental margin, epsilon Hf zircon (T) values from 8.95 to 12.91, a stage model of age 326-486Ma; the QUXU flash gabbro emplacement and crystallization age of slave Pt. -210Ma, epsilon Hf zircon (1) value from 9.56 to 14.75, a model age of 256 ~ 459Ma; Qushui granite Dagar emplacement and crystallization age of 225-230Ma, with epsilon Hf positive (T) value (13.91 to 15.54); geochronology, petrology, mineralogy, geochemistry and zircon Lu-Hf isotope show that late Triassic granite, northward subduction of bojite and the Neo Tethys ocean, the partial melting of hornblende gabbro and subduction fluid metasomatism of mantle wedge, granitic rocks and juvenile crust partial melting of the mantle, and played in the formation of granitic rocks in There is an important role. The Late Triassic magmatism that Neo Tethys subduction should not later than 230Ma.2. on the southern margin of the middle Shigatse area and the NUMA Nimu area diorite, granodiorite, granite and geochronology, geochemistry of volcano rock, a comprehensive study of mineral petrology and zircon Lu-Hf isotopes. The conclusions are as follows: Granite and volcano rock formed mainly in 169 ~ 191Ma, as a result of early Middle Jurassic late magmatism; in chemical composition, granite and volcano rock enrichment light rare + (LREEs) and large ion lithophile elements (LILEs), strong depletion of Nb, Ta. Field elements, geochemistry with arc type granite; granite sub alkaline, belong to calc alkaline I type granite; epsilon Hf samples (T) value is 10.10-15.44, with obvious loss of zircon Hf Isotopic composition; comprehensive study shows that the early Middle Jurassic and Late Triassic should have the same tectonic environment, namely Zangnan Gangdise area (active continental margin) should belong to the tectonic background of Neo Tethys subduction, granitic rocks are mainly formed from partial melting of.3. middle lower crust of middle Eocene Gangdise granite class (granodiorite to granite porphyry) of zircon U-Pb geochronology, geochemical and Lu-Hf isotopic analysis. Analysis results show that the granite zircon LA-ICP-MS U-Pb dating results for 40-55Ma, which represent the age of Granite Emplacement and crystallization age; in geochemical composition of granitoids, enrichment of LREE (HREEs) and large ion lithophile elements (LILEs), field strength elements Mb, Ta, P etc., the samples show characteristics of island arc granite. In addition, the analysis also shows the sample For the characteristics of quasi aluminous I type granite, mainly located in the calc alkaline to high potassium calc alkaline series. Lu-Hf isotope analysis results of zircon shows that most samples of the epsilon H (T) with positive and negative minority zircon as epsilon H (T) value, combined with the geochemical composition of granitoids mainly discrimination is the partial melting of juvenile crust partial melting of a mafic to tonalitic rock partial melting and sandstone, in this process, the mantle underplating is also involved in the formation and evolution of granitic rocks in Eocene. The Sr-Yb diagram of the sample showed the geochemical characteristics of syncollisional granite class, so it suggests that India - Asia in the early Eocene has completely collision magmatism. The Eocene Gangdise area may be due to the Neo Tethys subduction to Eurasian plate, the India Asia continental collision Hit, resulting in the Neo Tethys subduction angle becomes steeper, and the occurrence of slab break off (slab break off), triggered a strong magmatic Eocene in Gangdise volcano.4. through detailed field geological survey, structural analysis, thin section and EBSD fabric analysis, determine the xaitongmoin - Qushui ductile shear zone the tectonic setting and evolution. QUXU ductile shear mainly by strong deformation and weak deformation domain composed of Xietongmen zone, including foliated granite, mylonitize granite, protomylonite, mylonites, local area visible phyllonite. The geometry and kinematics of ductile shear belt - xaitongmoin QUXU display kinematic characteristics consistent with that is characterized by positive sliding northward. In addition, the kinematic vorticity (Wk0.71) showed that the shear zone is a typical general shear simple shear dominated, extensional thinning Shear zone, the average reduction of 20%. shear band of EBSD fabric analysis shows the xaitongmoin - Qushui ductile shear zones mainly slip in cylindrical a, rhombohedral A and bottom a slip, deformation mainly in low temperature effects (550 to 300 DEG C).5. - xaitongmoin QUXU ductile shear zone in the dark mica, mica and 40Ar-39Ar geochronology of zircon U-Pb geochronology together define the shear activity time. The results showed that the comprehensive chronology xaitongmoin - QUXU ductile shear zone formed in the early Miocene between 21 ~ 24Ma.6. through detailed geological survey, indoor insufficient sheet identification, EBSD fabric analysis of color - Fu chicken with dextral strike slip ductile shear zone. The deformation of feldspar quartz minerals and quartz EBSD fabric research results show that the ductile shear deformation with chicken - QUXU temperature of 500-550 C. followed by the shear zone Analysis of zircon U-Pb chronology isomorphism development in the making of felsic veins, the color of Fu - Jigongshan ductile shear zone activity time of 35 ~ 38Ma, the late Eocene.7. through the analysis of 11 samples of mid Gangdise apatite fission track, the southern margin of the middle of the tectonic uplift and denudation history. The research results show that: the middle uplift is the stage, before the Oligocene uplift, denudation and collision of India Asia plate, 23Ma since the rapid uplift of the Gangdise area and the thrust of the activities, and in the stage of rapid uplift since there are short quiet tectonic period is.10Ma and a southern central Gangdise area rapid uplift stage, the uplift and the Brahmaputra rapid downcutting. In Quaternary tectonic activity and climate change and surface runoff under the combined effect of mold together The results show that the.8. integrated Gangdise magmatic belt has undergone a long evolution process, from the Late Triassic to the subduction (230Ma), until 60 to the India Asia continental collision 55Ma. India Asia collision resulted in Eocene thrust faults and large strike slip faults, and caused the new Daigang Gangdese batholith and its adjacent areas, the first overall uplift since.23Ma, due to the relaxation of Zangnan regional crustal thickening and uneven lateral changes of North-South stress extrusion, resulted in the Lhasa terrane occurred east-west and North-South extensional collapse, the large normal fault and detachment structure application and at the same time. Partial melting of thickened crust formed has special geochemical properties of granitic porphyry mineralization, this is also the Gangdise area outbreak period.

【學(xué)位授予單位】：中國(guó)地質(zhì)科學(xué)院
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類(lèi)號(hào)】：P542

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