喜馬拉雅造山帶東段上三疊統(tǒng)復(fù)理石沉積地質(zhì)研究
發(fā)布時(shí)間：2018-07-24 18:11
【摘要】：西藏南部大面積分布上三疊統(tǒng)復(fù)理石(即山南地體郎杰學(xué)群),它位于喜馬拉雅造山帶東段,構(gòu)造-地層上多歸屬特提斯喜馬拉雅北亞帶,被認(rèn)為系印度大陸北部被動(dòng)大陸邊緣(半)深海沉積；或者與修康群一起被劃為雅魯藏布江縫合帶內(nèi)的構(gòu)造增生楔。這兩種不同構(gòu)造歸屬不僅有礙于其自身物源和沉積盆地分析,而且對(duì)晚三疊世特提斯古地理(如基末利大陸、新特提斯、岡瓦納大陸北緣)、古構(gòu)造格局及其演化的重建有重要影響。近年來,郎杰學(xué)群受到了越來越多的關(guān)注,盡管業(yè)已取得了較多研究成果,但是一些重要的科學(xué)問題尚未得到很好的解決或達(dá)成共識(shí)。這些問題主要涉及沉積體系、物源、盆地性質(zhì)、古地理位置、構(gòu)造演化等方面。本文對(duì)17條地質(zhì)路線及32條地層剖面進(jìn)行了觀測(cè)記錄,對(duì)70余個(gè)觀察點(diǎn)的巖性厚度、90余組近千數(shù)據(jù)的古水流進(jìn)行了測(cè)量和統(tǒng)計(jì),對(duì)30余件砂巖樣品的碎屑組分、近60件重礦物組合及其指數(shù)等進(jìn)行了統(tǒng)計(jì)、計(jì)算分析；重點(diǎn)對(duì)20件砂巖的近1600枚碎屑鋯石、6件輝綠巖的80余枚鋯石進(jìn)行了U-Pb同位素定年,并測(cè)試分析了170余枚碎屑鋯石的Hf同位素和140余枚碎屑鉻尖晶石的地球化學(xué)。在上述大量野外資料和室內(nèi)測(cè)試數(shù)據(jù)基礎(chǔ)上,作者綜合研究了微相、巖相、沉積物分散樣式、沉積體系和物源,并試圖對(duì)沉積盆地性質(zhì)、古地理和構(gòu)造演化進(jìn)行了探討,初步獲得以下結(jié)果和認(rèn)識(shí)：沉積物分散樣式方面,重礦物指數(shù)ZTR值、S/M(砂／泥)比值和古水流流向結(jié)果均指示沉積物主體由北向南供給。其中,古水流流向平均205°,復(fù)原后平均185°,并顯示有多組向西南、東南方向的物源供給。三種參數(shù)組合呈現(xiàn)弧形-放射狀沉積物分散樣式,暗示郎杰學(xué)群的碎屑組分可能是通過分支水道在中扇和外扇區(qū)域扇狀分散開堆積沉積,同時(shí)也可能反映了海底扇水道系統(tǒng)的分布形式。巖相和沉積體系方面,共識(shí)別出水道(A)、舌狀體(B)、天然堤-水道間(C)和盆地平原(D)4種相,以及相應(yīng)的9個(gè)亞相單元(A1-3,B1-3和C1-3)。它們構(gòu)筑了海底扇6個(gè)相組合,分別是水道-水道間、漫灘-天然堤、決口扇、外扇舌狀體、扇緣和盆地平原。通過巖相和沉積物分散樣式分析,在原始地層分布恢復(fù)基礎(chǔ)上,提出郎杰學(xué)群由一個(gè)以海底扇為主的深海沉積體系組成。該沉積體系規(guī)模可達(dá)400-500 km×600-700 km大小或更大,是目前報(bào)道的前新生代最大海底扇之一；它由4個(gè)橫向分布、至少6次垂向疊加的海底扇體聯(lián)合組成,發(fā)育中扇和外扇亞沉積體系,缺失內(nèi)扇記錄；垂向疊加格局顯示為從進(jìn)積到退積樣式,指示海底扇的發(fā)育可能受海平面上升或區(qū)域構(gòu)造沉降加劇控制；砂巖和板巖比例關(guān)系顯示海底扇屬于富泥-砂型,指示沉積物從源區(qū)經(jīng)歷了中-遠(yuǎn)距離(可達(dá)400-600 km)的搬運(yùn)。物源分析結(jié)果顯示,郎杰學(xué)群的母源區(qū)存在各種不同的巖性。重礦物組合表現(xiàn)出沉積巖、花崗巖、變質(zhì)巖等多種原巖類型,其中輝石和鉻尖晶石說明存在基性和超基性的物源。重礦物指數(shù)RuZi顯示研究區(qū)東西兩側(cè)存在不同,可能是源區(qū)巖石類型變化所致,暗示至少存在兩個(gè)以上不同的源區(qū)。砂巖碎屑組分比例Dickinson三角圖解投點(diǎn)大多落入再旋回造山帶,次為巖漿弧和混合區(qū),說明物源區(qū)可能有多種構(gòu)造背景。鉻尖晶石地球化學(xué)成分指示源區(qū)母巖存在玄武巖、橄欖巖和玻安巖,它們可能由洋中脊和／或洋島／海山提供。上述結(jié)果證明郎杰學(xué)群由多個(gè)母源區(qū)提供碎屑物質(zhì)。多物源還進(jìn)一步得到碎屑鋯石U-Pb同位素年齡不同分布主值區(qū)間的證實(shí)。分析結(jié)果顯示,這套上三疊統(tǒng)復(fù)理石砂巖中的鋯石有兩組年齡,分別是600-460 Ma(峰值大約520 Ma)和260-200 Ma(峰值大約240 Ma)。更為重要的是,前者與泛非造山帶有關(guān),同時(shí)表明為山南盆地提供碎屑的源區(qū)可能是拉薩地體、西澳大利亞、羌塘地體和岡瓦納大陸其它地塊,或是其中某一個(gè)或某二個(gè)以上。后者強(qiáng)烈支持山南地體與特提斯喜馬拉雅無親緣性的觀點(diǎn)。特殊的碎屑鋯石年齡分布區(qū)間260-200 Ma(峰值大約240Ma)、400-290 Ma的碎屑鋯石較正的εHf (t)值、鉻尖晶石的存在和～130 Ma的大量輝綠巖巖脈侵入體,說明山南地體與拉薩地體存在較大物源差異,至少證明拉薩地體不是山南地體的唯一物源區(qū)�；诙辔镌垂┙o特性、物源區(qū)多構(gòu)造背景特征,在與錯(cuò)美-班伯里大型火成巖省有關(guān)的早白堊世中期(大約140-128 Ma)的輝綠巖脈古地理限制下,本次工作提出,郎杰學(xué)群很可能沉積于岡瓦納北側(cè)的一個(gè)殘留洋盆,它位于印度東部與澳大利亞西部之間。從物源區(qū)方向和巖性特征判斷,北側(cè)拉薩地體及其南北側(cè)的巖漿弧與弧后區(qū)、新特提斯洋南側(cè)的古海山和洋中脊可能是主要的物源區(qū),西澳大利亞和印度東部可能會(huì)提供少量物源或者提供了其中部分泛非期相關(guān)的物源。在這種盆地模式和古地理格局下,本文推測(cè)了山南地體古地理和構(gòu)造演化過程：三疊紀(jì)末期,山南盆地隨著拉薩地體(弧后擴(kuò)張和洋脊增生)北向漂移(構(gòu)造格局發(fā)生變化)而快速終結(jié)不再接受其物源供給,隨后被構(gòu)造上馱在大印度東北部；侏羅紀(jì)-早白堊世早期,山南地體可能成為了大印度東北邊緣部分盆地基底保持在這個(gè)位置；早白堊世中期(132 Ma以后)開始,隨著印度洋打開,山南地體與印度大陸一起向北漂移,直到印度與亞洲的碰撞、隆升；始新世-至今,它與特提斯喜馬拉雅一起變形變質(zhì),接受侵蝕和剝蝕。這種古地理和古構(gòu)造演化暗示,山南地體可能不是雅魯藏布江縫合帶內(nèi)侏羅紀(jì)-白堊紀(jì)的增生楔。
[Abstract]:The large area of the three stack complex in southern Tibet, which is located in the eastern section of the Himalaya orogenic belt, is located in the eastern section of the Himalaya orogenic belt. It is considered as the northern subzone of the Tethys of Himalaya, which is considered to be a passive continental margin (half) deep sea deposit in the northern part of the mainland of India, or in the Yarlung Zangbo Suture belt together with the Kacang group. The two types of tectonic settings not only impede the analysis of their own source and sedimentary basins, but also have important effects on the paleogeography of the late three Triassic Tethys, such as the base Continental, the new Tethys, the northern margin of the Gondwana continent, and the reconstruction of the paleotectonic pattern and its evolution. Although many research achievements have been achieved, some important scientific problems have not been well solved or reached consensus. These problems are mainly related to sedimentary system, source, basin nature, paleogeographic position and tectonic evolution. This paper has recorded 17 geological routes and 32 stratigraphic sections, and more than 70 observation points. The lithology thickness and more than 90 groups of paleo currents of nearly 1000 data were measured and counted. The debris components of more than 30 sandstone samples, nearly 60 pieces of heavy mineral assemblages and their index were calculated and analyzed. The emphasis was on the nearly 1600 detrital zircon of 20 sandstone and more than 80 zircons of 6 diabase rocks, and the test scores were tested. The geochemistry of more than 170 detrital zircon Hf isotopes and more than 140 clastic chromite spinel are analyzed. On the basis of a large amount of field data and indoor test data, the authors have studied the microfacies, lithofacies, sediment dispersion patterns, depositional systems and provenances, and tried to explore the nature, paleogeography and tectonic evolution of the sedimentary basins. The following results and understanding are obtained: the sediment dispersion style, the ZTR value of heavy mineral index, the ratio of S/M (sand / mud) and the result of paleo flow direction all indicate that the sediment main body is supplied from north to south, of which the average flow direction is 205 degrees, the average 185 degree after recovery, and the supply of many groups to the south-west and southeastern sources. Three parameter combinations The scattered patterns of arc - Radial sediments suggest that the debris components of the Lang Jiro group may be dispersed and deposited in the middle fan and outer fan area by the branch channel, and may also reflect the distribution of the seabed fan channel system. In the aspects of lithofacies and depositional systems, the A, the tongue (B), the natural dike and the waterway are identified. 4 phases (C) and basin plain (D), and the corresponding 9 subfacies units (A1-3, B1-3 and C1-3). They construct 6 facies combinations of the seabed fan, which are waterways and waterways, floodplain - natural levee, crevasse fan, outer fan tongue, fan margin and basin plain. Based on the distribution pattern of lithofacies and sediments, it is based on the restoration of the distribution of the original strata. The Jie Xue group is composed of a deep-sea sedimentary system dominated by seabed fan. The size of the sedimentary system can reach 400-500 km x 600-700 km size or larger. It is one of the largest subsea fans in the pre Cenozoic. It is composed of 4 horizontal distribution, at least 6 vertical superimposed subsea fans, and the middle and outer fan subfacies. The vertical superposition pattern shows that the development of the submarine fan may be controlled by the rise of sea level or the regional tectonic subsidence, and the relation between the sandstone and the slate shows that the seabed fan belongs to the rich mud sand type, indicating the sediment transport from the source area to the medium distance (up to 400-600 km). The results show that there are various types of lithology in the parent source area of the Lang Jie group. The combination of heavy minerals shows sedimentary rocks, granites and metamorphic rocks, among which pyroxene and chrome spinel indicate the existence of basic and ultrabasic source. The heavy mineral index RuZi shows that the East and west sides of the study area are different and may be the change of the source rock types. The result indicates that there are at least two different source regions. The Dickinson triangle diagram of sandstone debris components falls mostly into the re gyratory orogenic belt, which is the magma arc and the mixed area, indicating that there may be a variety of tectonic settings in the source area. The geochemical composition of chromium spinel indicates that the parent rock of the source region is basalt, peridotite and Bosite. It may be provided by the mid ocean ridge and / or ocean island / seamount. The results show that the Lang Jie group is provided with detrital materials from multiple parent sources. The source of U-Pb isotopes of detrital zircons is further confirmed by the main range of the main value range of different distribution of zircon. The results show that the zircon in this set of upper three series of complex stone sandstone has two groups of ages, respectively, 60 0-460 Ma (peak about 520 Ma) and 260-200 Ma (peak about 240 Ma). More importantly, the former is related to the Pan African orogenic belt, and indicates that the source area for Shannan basins may be Lhasa, Western Australia, Qiangtang, and other blocks of the Gondwana continent, or one or more of one or more of them. The latter is strongly supported. The special detrital zircon age distribution is 260-200 Ma (peak 240Ma), the 400-290 Ma detrital zircon is more than positive epsilon Hf (T), the presence of chromium spinel and a large number of diabase vein intrusions to 130 Ma, indicating that there is a great difference between the Sannan and the Lhasa terrain. At least, it is proved that Lhasa is not the only source area in the south of Shannan. Based on the supply characteristics of multi source source and the multi tectonic setting of the source area, under the restriction of the palaeogeography of the Middle Early Cretaceous (about 140-128 Ma) in the Middle Early Cretaceous (about 140-128) in the large igneous province of the wrong United States, this work suggests that the Lang Jie group is likely to be deposited in Gondwana. A residual oceanic basin on the north side, located between eastern India and Western Australia. Judging from the direction and lithologic characteristics of the source area, the magma arc and the back arc of the north side of Lhasa and its north and south sides, the ancient seamounts and mid ocean ridges on the southern side of the new Tethys ocean may be the main source areas, and a small amount may be provided in Western Australia and Eastern India. In this basin model and palaeogeographic pattern, this paper deduces the process of paleogeography and tectonic evolution in this basin: at the end of the Triassic, the Sannan basin was no longer quickly terminated with the northern drift of the Lhasa ground (after the expansion of the arc and the ridge of the ocean ridge). In the early period of the Jurassic Early Cretaceous, the southern part of the northeastern part of the great India may be maintained at this position, and in the early Cretaceous period of the early Cretaceous (132 Ma after the early Cretaceous), with the opening of the India ocean, the Sannan was drifting northward along with the mainland of India. The paleogeography and Paleogeographic Evolution suggested that the Sannan earth may not be a Jurassic Cretaceous accretionary wedge in the Yarlung Zangbo Suture Zone, which is deformed and metamorphosed together with Tethys Himalaya.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：P534.51
，
本文編號(hào)：2142226
[Abstract]:The large area of the three stack complex in southern Tibet, which is located in the eastern section of the Himalaya orogenic belt, is located in the eastern section of the Himalaya orogenic belt. It is considered as the northern subzone of the Tethys of Himalaya, which is considered to be a passive continental margin (half) deep sea deposit in the northern part of the mainland of India, or in the Yarlung Zangbo Suture belt together with the Kacang group. The two types of tectonic settings not only impede the analysis of their own source and sedimentary basins, but also have important effects on the paleogeography of the late three Triassic Tethys, such as the base Continental, the new Tethys, the northern margin of the Gondwana continent, and the reconstruction of the paleotectonic pattern and its evolution. Although many research achievements have been achieved, some important scientific problems have not been well solved or reached consensus. These problems are mainly related to sedimentary system, source, basin nature, paleogeographic position and tectonic evolution. This paper has recorded 17 geological routes and 32 stratigraphic sections, and more than 70 observation points. The lithology thickness and more than 90 groups of paleo currents of nearly 1000 data were measured and counted. The debris components of more than 30 sandstone samples, nearly 60 pieces of heavy mineral assemblages and their index were calculated and analyzed. The emphasis was on the nearly 1600 detrital zircon of 20 sandstone and more than 80 zircons of 6 diabase rocks, and the test scores were tested. The geochemistry of more than 170 detrital zircon Hf isotopes and more than 140 clastic chromite spinel are analyzed. On the basis of a large amount of field data and indoor test data, the authors have studied the microfacies, lithofacies, sediment dispersion patterns, depositional systems and provenances, and tried to explore the nature, paleogeography and tectonic evolution of the sedimentary basins. The following results and understanding are obtained: the sediment dispersion style, the ZTR value of heavy mineral index, the ratio of S/M (sand / mud) and the result of paleo flow direction all indicate that the sediment main body is supplied from north to south, of which the average flow direction is 205 degrees, the average 185 degree after recovery, and the supply of many groups to the south-west and southeastern sources. Three parameter combinations The scattered patterns of arc - Radial sediments suggest that the debris components of the Lang Jiro group may be dispersed and deposited in the middle fan and outer fan area by the branch channel, and may also reflect the distribution of the seabed fan channel system. In the aspects of lithofacies and depositional systems, the A, the tongue (B), the natural dike and the waterway are identified. 4 phases (C) and basin plain (D), and the corresponding 9 subfacies units (A1-3, B1-3 and C1-3). They construct 6 facies combinations of the seabed fan, which are waterways and waterways, floodplain - natural levee, crevasse fan, outer fan tongue, fan margin and basin plain. Based on the distribution pattern of lithofacies and sediments, it is based on the restoration of the distribution of the original strata. The Jie Xue group is composed of a deep-sea sedimentary system dominated by seabed fan. The size of the sedimentary system can reach 400-500 km x 600-700 km size or larger. It is one of the largest subsea fans in the pre Cenozoic. It is composed of 4 horizontal distribution, at least 6 vertical superimposed subsea fans, and the middle and outer fan subfacies. The vertical superposition pattern shows that the development of the submarine fan may be controlled by the rise of sea level or the regional tectonic subsidence, and the relation between the sandstone and the slate shows that the seabed fan belongs to the rich mud sand type, indicating the sediment transport from the source area to the medium distance (up to 400-600 km). The results show that there are various types of lithology in the parent source area of the Lang Jie group. The combination of heavy minerals shows sedimentary rocks, granites and metamorphic rocks, among which pyroxene and chrome spinel indicate the existence of basic and ultrabasic source. The heavy mineral index RuZi shows that the East and west sides of the study area are different and may be the change of the source rock types. The result indicates that there are at least two different source regions. The Dickinson triangle diagram of sandstone debris components falls mostly into the re gyratory orogenic belt, which is the magma arc and the mixed area, indicating that there may be a variety of tectonic settings in the source area. The geochemical composition of chromium spinel indicates that the parent rock of the source region is basalt, peridotite and Bosite. It may be provided by the mid ocean ridge and / or ocean island / seamount. The results show that the Lang Jie group is provided with detrital materials from multiple parent sources. The source of U-Pb isotopes of detrital zircons is further confirmed by the main range of the main value range of different distribution of zircon. The results show that the zircon in this set of upper three series of complex stone sandstone has two groups of ages, respectively, 60 0-460 Ma (peak about 520 Ma) and 260-200 Ma (peak about 240 Ma). More importantly, the former is related to the Pan African orogenic belt, and indicates that the source area for Shannan basins may be Lhasa, Western Australia, Qiangtang, and other blocks of the Gondwana continent, or one or more of one or more of them. The latter is strongly supported. The special detrital zircon age distribution is 260-200 Ma (peak 240Ma), the 400-290 Ma detrital zircon is more than positive epsilon Hf (T), the presence of chromium spinel and a large number of diabase vein intrusions to 130 Ma, indicating that there is a great difference between the Sannan and the Lhasa terrain. At least, it is proved that Lhasa is not the only source area in the south of Shannan. Based on the supply characteristics of multi source source and the multi tectonic setting of the source area, under the restriction of the palaeogeography of the Middle Early Cretaceous (about 140-128 Ma) in the Middle Early Cretaceous (about 140-128) in the large igneous province of the wrong United States, this work suggests that the Lang Jie group is likely to be deposited in Gondwana. A residual oceanic basin on the north side, located between eastern India and Western Australia. Judging from the direction and lithologic characteristics of the source area, the magma arc and the back arc of the north side of Lhasa and its north and south sides, the ancient seamounts and mid ocean ridges on the southern side of the new Tethys ocean may be the main source areas, and a small amount may be provided in Western Australia and Eastern India. In this basin model and palaeogeographic pattern, this paper deduces the process of paleogeography and tectonic evolution in this basin: at the end of the Triassic, the Sannan basin was no longer quickly terminated with the northern drift of the Lhasa ground (after the expansion of the arc and the ridge of the ocean ridge). In the early period of the Jurassic Early Cretaceous, the southern part of the northeastern part of the great India may be maintained at this position, and in the early Cretaceous period of the early Cretaceous (132 Ma after the early Cretaceous), with the opening of the India ocean, the Sannan was drifting northward along with the mainland of India. The paleogeography and Paleogeographic Evolution suggested that the Sannan earth may not be a Jurassic Cretaceous accretionary wedge in the Yarlung Zangbo Suture Zone, which is deformed and metamorphosed together with Tethys Himalaya.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：P534.51
，
本文編號(hào)：2142226
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