藏南林周盆地设兴组砂岩及其中玄武岩夹层的地球化学与成因

印度与亚洲大陆的碰撞是青藏高原演化的重要构造事件,碰撞过程被记录在拉萨地块南部的晚白垩世到古新世的沉积-岩浆作用中。林周盆地的晚白垩世设兴组及其之后不整合覆盖的林子宗火山岩,是解析碰撞过程的重要记录。本文对设兴组最高层位的砂岩和玄武岩夹层进行了岩石学、地球化学和年代学研究,探讨了岩石成因和构造意义。设兴组砂岩属于杂砂岩,碎屑物质主要来自中酸性岩浆岩源区;锆石Hf同位素指示设兴组大部分碎屑物质来源于盆地北面的中部拉萨地块,少部分来自盆地南部的冈底斯岩基;砂岩中最年轻的碎屑锆石年龄指示林周盆地设兴组是在98Ma之后接受沉积的。以夹层产出在设兴组顶部的玄武岩和玄武安山岩,富集轻稀土元素、亏损重稀土元素、弱负Eu异常,强烈富集Ba、Th、U、Pb等大离子亲石元素,显著亏损Nb、Ta等高场强元素,属于高钾钙碱性玄武岩系列,与典型安第斯型玄武岩特征吻合。玄武岩和玄武安山岩的锆石均为捕获锆石,其最年轻碎屑锆石年龄限定了设兴组玄武岩的喷发晚于110Ma。综合分析表明,林周盆地晚白垩世时期为夹持在冈底斯岩浆弧与中部拉萨地块之间的弧后盆地,新特提斯洋壳晚白垩世俯冲到冈底斯弧和弧后盆地之下,大约在98～110Ma之后喷发到林周盆地的很少量中基性岩浆构成了设兴组顶部的玄武岩和玄武安山岩夹层,是新特提斯洋俯冲相关的幔源岩浆作用。林周盆地设兴组(晚于98Ma)与上覆的林子宗火山岩(底部约为65Ma)之间呈大约33Myr的构造间断,可能代表了冈底斯弧的碰撞之前的隆升剥蚀过程。     

Early Cretaceous sedimentary evolution of the northern Lhasa terrane and the timing of initial Lhasa-Qiangtang collision

Lower Cretaceous strata in the Baingoin basin of the northern Lhasa terrane record initial collision between the Lhasa and Qiangtang blocks, followed by the early uplift of central Tibet. North-south traverses across the Baingoin basin highlight major differences between the Duba Formation in the north and the quasi-coeval Duoni Formation in the south. The Duba Formation documents upward transition from shallow shelf and deltaic environments to coarse-grained siliciclastic fluvial sedimentation. Abundance of detrital zircons yielding Jurassic-Cretaceous ages with εHf(t) values mainly between −2 and +10, occurrence of chert, Cr-spinel, and pyroxene grains, together with southward paleocurrent directions indicate that the Duba Formation was sourced from the southern Qiangtang terrane and Bangong-Nujiang suture zone to the north. The Duoni Formation in the south was deposited in shelfal to fan-delta and fluvial environments. Abundant volcanic clasts, detrital zircons yielding Cretaceous ages with mainly negative εHf(t) values, and northward paleocurrents indicate an active volcanic source located in the central Lhasa terrane to the south, with minor input from the northern Lhasa terrane. Only the northern part of the Baingoin basin was directly controlled by the Lhasa-Qiangtang collision and may thus be considered a peripheral foreland basin, whereas the southern part was mainly influenced by tectonic processes related to the northward subduction of Neotethyan lithosphere, and may thus be comparable to a retroarc foreland basin. But these sedimentary features and the 139–79 Ma Baingoin plutonic intrusion do not fit well with classical foreland-basin models. Zircon chronostratigraphy constrains the final consumption of Bangong-Nujiang oceanic lithosphere and initial collision between the Lhasa and Qiangtang microcontinents to have taken place by 122 Ma, which has major implications for paleotectonic reconstructions of the Tibetan Plateau.     

西藏尼玛盆地南部古近系物源分析及地质意义

位于羌塘地体与拉萨地体之间的尼玛盆地包含有青藏高原演化过程中重要的沉积记录,恢复该地区的古地理特征及讨论其构造演化过程,具有重要地质意义。尼玛盆地南部古近系由古新世-始新世牛堡组与渐新世丁青湖组构成,主体为一套扇三角洲相与湖泊相碎屑沉积建造。采用沉积学、年代学方法,对该盆地南部古近系查昂巴剖面进行沉积特征、碎屑锆石U-Pb年代学及古地理研究,以确定其物源区,并分析构造作用对盆地的改造过程。从牛堡组到丁青湖组,稳定碎屑组分逐渐减少而不稳定组分增加,显示古近纪时盆地沉积过程中受到构造活动影响;碎屑锆石U-Pb年龄中存在36~70 Ma,100~130 Ma,500~550 Ma,750~900 Ma,1800~1900 Ma及~2500 Ma等年龄峰值。碎屑岩组分、锆石年龄特征及其他分析显示,拉萨地体、羌塘地体及缝合带内的逆冲带为其物源区,存在多向物源。在古近纪碰撞、挤压的构造条件下,伴随着地壳缩短、逆冲断层及造山系统的活动,尼玛盆地南部演化为一个受构造活动控制的独立沉积中心;挤压及逆冲变形决定了其古地理特征,沉积过程及物源与区域隆升、剥蚀活动联系密切。     

早侏罗世叶巴组与桑日群火山岩:特提斯洋俯冲过程中的陆缘弧与洋内弧?

雅鲁藏布特提斯洋的演化对研究青藏高原的形成具有重要的意义,一般认为广泛分布于拉萨地块南部叶巴组和桑日群火山-沉积岩系是该特提斯洋早期的俯冲岩浆产物。本研究选取了拉萨附近达孜地区叶巴组中的2个中基性火成岩样品进行了锆石LA-ICPMS U-Pb分析,结果显示其年龄分别为188±2Ma和175±2Ma,与已发表的叶巴组中酸性火成岩的形成时代(174~193Ma)一致,已发表的桑日群火山岩的年龄也在相同范围内,因此叶巴组和桑日群火山岩喷发时间主要为早侏罗世。叶巴组和桑日群基性及中酸性岩浆均类似岛弧型火山岩,但前者具有相对高的Nb、Zr含量,Th/Y比值及相对较低的La/Nb比值,呈现出大陆地壳组分增加的趋势,叶巴组火山岩表现为典型的大陆边缘弧特征而桑日群类似于洋内弧火山岩,桑日群火山岩分布于叶巴组南侧,并呈碎片似展布于拉萨地块南部,同时显示了与叶巴组不同的岩性组合,暗示同时代的叶巴组和桑日群火山-沉积岩可能分别代表特提斯洋俯冲过程中的形成的陆缘弧和洋内弧。     

Dating of detrital zircon grains and fossils from Late Palaeozoic sediments of the Baruo area,Tibet: constraints on the Late Palaeozoic evolution of the Lhasa terrane

ABSTRACT

To determine the Late Palaeozoic evolution of the Lhasa terrane, we report the results of field mapping, petrological and fossil investigations, and U–Pb dating of detrital zircon grains (n = 474) from lower-greenschist-facies clastic rocks of the Lagar Formation in the Baruo area, Tibet. Our results indicate that the Lagar Formation was deposited during the Late Carboniferous to Early Permian in a shallow-marine environment on the northern margin of Gondwana. Glacial marine diamictites are common within the Lagar Formation and record glaciation of Gondwana during the Late Palaeozoic. Moreover, the detrital materials of the Lagar formation originated mostly from the collision orogenic belt. The ages of detrital zircon grains from the Lagar Formation make up five main groups with ages of 410–540 Ma, 550–650 Ma, 800–1100 Ma, 1600–1800 Ma, and 2300–2500 Ma, which display three characteristic age peaks at ~1150, 2390 and 2648 Ma. We tentatively suggest that the Lhasa terrane was a shallow-marine basin under the influence of the Gondwanan glaciation during the Late Carboniferous–Early Permian.     

中新生代天山剥蚀与塔里木盆地北缘沉积耦合过程:新疆库车河剖面的低温热年代学证据

天山造山带中新生代快速剥露对于了解天山构造演化过程意义重大.然而,人们对于中新生代精确的冷却时间还一直存在争议.本文报道了塔里木盆地北缘库车河剖面中生界砂岩中碎屑磷灰石裂变径迹数据和早二叠世流纹岩热史演化模拟结果. 热年代学年龄趋势显示碎屑磷灰石裂变径迹的主要年龄组分为143.0~148.9 Ma和35.7~38.1 Ma,其中较年轻的组分已经完全重置,揭示了库车坳陷的剥露信息. 热史模拟结果显示了160~140 Ma的快速冷却事件. 结合库车河剖面前人的碎屑锆石U-Pb和重矿物数据,笔者认为欧亚南缘拉萨地体的拼贴是通过刚性的塔里木将挤压应力传递至天山,导致其在晚侏罗世?早白垩世强烈隆升剥蚀,大量碎屑被搬运沉积在塔里木盆地北缘,造成库车坳陷中广泛发育的早白垩世亚格列木组砾岩及其与晚侏罗世地层之间的角度不整合. 在欧亚板块南缘多块体持续拼贴的远程效应下,天山经历始新世快速隆升变形,变形持续向南扩展,导致库车坳陷在晚始新世遭受变形和抬升.      

四川新龙地区甘孜-理塘蛇绿混杂岩带侏罗系地层沉积学、地球化学和年代学研究及其构造背景分析SCIEI北大核心CSCD

甘孜-理塘蛇绿混杂岩带作为扬子板块与中咱地块的碰撞结合带,其对探讨西南“三江”多岛弧盆系构造演化具有重要意义。本文选取四川新龙地区瑞环山组进行沉积学、古生物学、地球化学和同位素年代学研究,限定其沉积时代及物质属性,探讨其沉积构造背景。新龙地区瑞环山组为碳酸盐岩夹碎屑岩岩石组合,其碎屑岩物源区为安山质火山岩及陆缘复理石,母岩构造背景为大洋岛弧环境。瑞环山组灰岩中珊瑚化石主要集中于晚侏罗世-早白垩世。碎屑锆石定年结果表明砂岩中锆石主要来源于扬子板块(435Ma、764Ma、1888Ma峰值)以及甘孜-理塘俯冲增生杂岩(229Ma峰值),锆石最新年龄为196±2Ma,指示其应沉积于早侏罗世之后的残留海盆地。研究结果表明,甘孜-理塘洋在晚三叠世末弧陆碰撞造山之后又经历了侏罗纪残留海阶段,在残留海盆地西侧临近甘孜-理塘俯冲增生杂岩浅海环境中沉积了瑞环山组碳酸盐岩夹碎屑岩建造,至早白垩世全面进入造山隆升阶段。     

藏北羌塘南部埃迪卡拉系达布热组的建立及其地质意义

羌塘位于青藏高原腹地,构造上处于冈瓦纳大陆北缘。因其特殊的构造位置,羌塘地体的起源及构造演化对于探讨青藏高原的早期形成演化、冈瓦纳大陆裂解,以及特提斯洋演化等关键科学问题至关重要。最近,在羌塘南部达布热地区发现一套碎屑岩夹玄武岩的岩石组合,碎屑岩具有低成分成熟度的特点,虽然岩石发生了低绿片岩相变质,但仍然保留了原岩类复理石沉积的特点。根据碎屑锆石定年结果,该套地层中碎屑锆石的最年轻年龄为550Ma左右。此外,该套地层中玄武岩夹层的测年结果表明,该套地层形成于埃迪卡拉纪(约550Ma)。结合地层剖面及区域地层对比,建立了埃迪卡拉纪达布热组。达布热组是羌塘地区首次发现的埃迪卡拉纪地层,该组地层的建立为探讨冈瓦纳大陆北缘构造演化提供了重要线索。     

Palaeomagnetism of late Cretaceous sediments from southern Tibet: Evidence for the consistent palaeolatitudes of the southern margin of Eurasia prior to the collision with India

Twenty sites were drilled in the late Cretaceous Shexing Formation for palaeomagnetic studies in the Lhasa terrane near the locality of Maxiang (29.9°N/90.7°E). The stepwise thermal demagnetizations successfully isolated high unblocking temperature characteristic directions. The tilt-corrected mean direction is D/I = 350.8°/32.1° with α₉₅ = 8.1° and N = 20 sites, corresponding to a paleopole at 75.0°N, 306.7°E with A₉₅ = 6.8°. Positive fold tests indicate a primary origin for the characteristic remanence. Based on previous Cretaceous data mainly from the Takena Formation and Paleocene data from the Linzizong volcanic rocks near the city of Lhasa, the latitude of the southern margin of Asia is located at about 15°N, and yields a stable position of the Lhasa terrane during Cretaceous and Paleocene. Compared with expected paleomagnetic directions from the stable India and Eurasia blocks, the collision palaeolatitude further implies the total latitudinal convergence was accommodated by 1700 ± 800 km (16.2 ± 7.6°) between southern Tibet and stable Eurasia and 1500 ± 830 km (14.4 ± 7.9°) between southern Tibet and stable India since the collision of India and Eurasia. A collision age between c. 54 and 47 Ma was determined using the results for the southern margin of Eurasia according to our new data and the extent of ‘Greater India’.     

柴北缘牦牛山地区牦牛山组沉积相组合特征

柴达木盆地北缘牦牛山地区出露的牦牛山组是一套由冲积扇和扇三角洲相共同构成的陆相沉积组合,冲积扇相砾岩-粗砂岩组合主要分布于研究区SE侧,扇三角洲相砂岩-泥岩组合主要分布于研究区NW侧。古水流分析表明牦牛山组沉积物主要来自其SE侧古隆起,但后期扇三角洲相包含少量来自NW和NE向的沉积物。该套沉积组合序列特征与区域上分布在牦牛山西侧同时期形成的湖泊相、滨浅海相沉积共同表明,柴达木盆地北缘在晚志留-早泥盆世时期存在一NW向倾斜的古斜坡,且晚期北侧发生抬升。砾岩和砂岩碎屑组成与区域岩石组合类型对比表明,牦牛山组沉积碎屑物主要来自于滩间山群。沉积组合序列特征、碎屑组成和区域构造背景综合研究表明,牦牛山组可能为柴达木板块向北俯冲过程中形成的局部断陷盆地的充填物。     

Sedimentary record of Jurassic northward subduction of the Bangong–Nujiang Ocean: insights from detrital zircons

The subduction polarity and related arc–magmatic evolutional history of the Bangong–Nujiang Ocean, which separated the South Qiangtang terrane to the north from the North Lhasa terrane to the south during the Mesozoic, remain debated. This study tries to reconstruct the subduction and evolution of the Bangong–Nujiang Ocean on the basis of U–Pb and Hf isotopic analyses of detrital zircons in samples from sedimentary rocks of the middle-western section of the Bangong–Nujiang suture zone in Gerze County, central Tibet. The Middle Jurassic Muggargangri Group in the Bangong–Nujiang suture zone was deposited in a deep-sea basin setting on an active continental margin. The Late Jurassic strata, such as the Sewa Formation, are widely distributed in the South Qiangtang terrane and represent deposition on a shelf. The Early Cretaceous Shamuluo Formation in the Bangong–Nujiang suture zone unconformably overlies the Muggargangri Group and was probably deposited in a residual marine basin setting. The detrital zircons of the Muggargangri Group contain seven U–Pb age populations: 2.6–2.4 Ga, 1.95–1.75 Ga, 950–900 Ma, 850–800 Ma, 650–550 Ma, 480–420 Ma, and 350–250 Ma, which is similar to the age populations in sedimentary rocks of the South Qiangtang terrane. In addition, the age spectra of the Shamuluo Formation are similar to those of the Muggargangri Group, indicating that both had a northern terrane provenance, which is conformed by the north-to-south palaeocurrent. This provenance indicates northward subduction of the Bangong–Nujiang oceanic crust. In contrast, two samples from the Sewa Formation yield variable age distributions: the lower sample has age populations similar to those of the South Qiangtang terrane, whereas the upper possesses only one age cluster with a peak at ca. 156 Ma. Moreover, the majority of the late Mesozoic detrital zircons are characterized by weakly positive εHf(t) values that are similar to those of magmatic zircons from arc magmatic rocks in the South Qiangtang terrane. The findings, together with information from the record of magmatism, indicate that the earliest prevalent arc magmatism occurred during the Early Jurassic (ca. 185 Ma) and that the principal arc–magmatic stage occurred during the Middle–Late Jurassic (ca. 170–150 Ma). The magmatic gap and scarcity of detrital zircons at ca. 140–130 Ma likely indicate collision between the Qiangtang and Lhasa terranes. The late Early Cretaceous (ca. 125–100 Ma) magmatism on both sides of the Bangong–Nujiang suture zone was probably related to slab break-off or lithospheric delamination after closure of the Bangong–Nujiang Ocean.     

Gangdese retroarc thrust belt and foreland basin deposits in the Damxung area,southern Tibet

Geologic mapping and U–Pb detrital zircon geochronologic studies of (meta)sedimentary rocks in the Damxung area (∼90 km north of Lhasa) of the southern Lhasa terrane in Tibet provide new insights into the history of deformation and clastic sedimentation prior to late Cenozoic extension. Cretaceous nonmarine clastic rocks ∼10 km southeast of Damxung are exposed as structural windows in the footwall of a thrust fault (the Damxung thrust) that carries Paleozoic strata in the hanging wall. To the north of Damxung in the southern part of the northern Nyainqentanglha Range (NNQTL), metaclastic rocks of previously inferred Paleozoic age are shown to range in depositional age from Late Cretaceous to Eocene. The metaclastic rocks regionally dip southward and are interpreted to have been structurally buried in the footwall of the Damxung thrust prior to being tectonized during late Cenozoic transtension. Along the northern flank of the NNQTL, Lower Eocene syncontractional redbeds were deposited in a triangle zone structural setting. All detrital zircon samples of Cretaceous–Eocene strata in the Damxung area include Early Cretaceous grains that were likely sourced from the Gangdese arc to the south. We suggest that the that newly recognized Late Cretaceous to Early Eocene (meta)clastic deposits and thrust faults represent the frontal and youngest part of a northward directed and propagating Gangdese retroarc thrust belt and foreland basin system that led to significant crustal thickening and elevation gain in southern Tibet prior to India-Asian collision.     

松潘地区尕海盆地上白垩统热鲁组物源分析及其意义

运用Dickinson三角图解和碎屑锆石年龄分析方法,对松潘地区白龙江隆起西段尕海盆地上白垩统热鲁组物源及沉积背景进行了研究。热鲁组砂岩岩屑以变质岩为主,碎屑物质成分和结构成熟度较低;Dickinson三角图解显示热鲁组砂岩物源主要来自再旋回造山带的石英再旋回和过渡再旋回带;碎屑锆石分析显示最新年龄为137Ma,指示该地层时代应晚于早白垩世早期;碎屑锆石U-Pb年龄基本上继承了区域上三叠纪地层的碎屑锆石年龄分布特征,说明热鲁组碎屑物质主要来自于区域上三叠纪地层,较少或几乎没有来自前三叠纪地层,而现今展布于盆地周围的下伏前三叠纪地层,晚白垩世时期尚未出露遭受剥蚀,同时这一结论也与松潘地区的热年代学数据揭示的构造背景相一致。     

西藏羌塘盆地白垩纪中期构造事件的磷灰石裂变径迹证据

拉萨与羌塘地块于白垩纪中期的碰撞造山对羌塘原型盆地的热体制和构造演化有着重要影响.运用磷灰石裂变径迹方法,对羌塘盆地隆鄂尼夏里组和托纳木雪山组砂岩分析表明,裂变径迹年龄集中在120～ 80Ma之间,表明在白垩纪中期,羌塘盆地普遍发生了一次构造抬升事件,该期构造事件的年龄与盆地内早白垩世的岩浆热事件、主要构造变形作用发生在晚白垩世以及雪山组和阿布山组角度不整合的时代(125～75Ma)较一致,是拉萨与羌塘地块碰撞造山事件的记录.热历史模拟表明,白垩纪中期构造事件对羌塘盆地南部和北部的热演化历史有着差异影响,羌塘盆地南部降温速率相对不大,抬升剥蚀厚度约1500m,而北部古地温迅速降温到近地表温度,抬升剥蚀厚度近4000m.这种差异抬升剥蚀可能与班公湖-怒江洋壳向南俯冲使得因拉萨地块构造负载而导致羌塘地块的挠曲有关.     

存在比桑日群弧火山岩更早的新特提斯洋俯冲记录么？

新特提斯洋的演化过程对于青藏高原的形成具有重要的意义,一直以来桑日群火山岩被认为是其俯冲作用的代表性岩浆记录.在拉萨以东发育的叶巴组火山岩,虽被认为早于桑日群的火山岩,但一直缺乏年代学的证据.本次研究选取了叶巴组的样品做了单颗粒锆石的LAM-ICP-MS定年,获得了174Ma左右的年龄,明显老于桑日群.同时,叶巴组火山岩具有与岛弧火成岩类似的地球化学特点：如大离子亲石元素相对富集,中基性火山岩表现明显的高场强元素HFSE的亏损.综合来看,叶巴组火山岩很可能是新特提斯洋向北俯冲作用的产物.如果这一点能够确证的话,新特提斯洋开始俯冲的时代将可以前推至早中侏罗纪或更早.     

Paleomagnetism of late Cretaceous dykes in the Gangdese belt: New constraints on the position and structure of the southern margin of Asia prior to the India-Asia collision

This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa. Our research goals are to provide further constraints on pre-collisional structure of the southern margin of Asia and the onset of the India-Asia collision. Magnetite is identified as the main magnetic carrier in our study. The magnetite shows no evidence of metamorphism or alteration as determined from optical and scanning electron microscope observations. A strong mineral orientation is revealed by anisotropy of magnetic susceptibility analysis both for the intruded dykes and the country rocks. The authors interpret this AMS fabric to have formed during intrusion rather than deformation. Fifteen of 23 sites yield acceptable site mean characteristic remanences with dual polarities. A scatter analysis of the virtual geomagnetic poles suggests that the mean result adequately averaged paleosecular variation. The paleomagnetic pole from the Gangdese dykes yields a paleolatitude of 14.3°N±5.8°N for the southern margin of Asia near Lhasa. The paleolatitude corresponds to an in-between position of the Lhasa terrane during about 130–60 Ma. Furthermore, the mean declination of the characteristic remanent magnetization reveals a significant counterclockwise rotation of 18°±9° for the sampling location since about 83 Ma. In the light of tectonic setting of the dykes, the strike of the southern margin of Asia near Lhasa is restored to trend approximately about 310°, which is compatible with the hypothesis that the southern margin of Eurasia had a quasi-linear structure prior to its collision with India.©2023 China Geology Editorial Office.     

西藏桑日县地区中生代火山岩地层层序——基于锆石U-Pb 年龄及地球化学数据

青藏高原中生代时期新特提斯洋演化及其相应的岩浆作用一直是高原基础研究的热点之一,其系统研究对新特提斯洋及拉萨地块的地质演化具有重要的意义。以桑日县地区出露的叶巴组、桑日群比马组、桑日群麻木下组、旦师庭组火山-沉积岩系为研究对象,在详细的野外调查及前人研究基础上,选择麻木下组安山岩和旦师庭组火山凝灰岩样品进行锆石U-Pb测年,对叶巴组和桑日群比马组火山岩进行地球化学对比研究。结果表明,桑日群上部比马组火山岩（189.0±3.0~195.0±3.0Ma）与叶巴组火山岩（174.2±3.6~192.7±1.3Ma）均形成于早侏罗世,且两者具有相似的地球化学特征,均为钙碱性岛弧火山岩,表明二者可能形成于相同的构造背景。因此,将比马组从原桑日群中解体出来与叶巴组合并为同一套火山岩地层,而桑日群下部麻木下组（99.9±0.7~136.5±1.7Ma）的形成时间明显晚于比马组,属早白垩世火山岩地层,且具有埃达克岩的地球化学特征,应单独建组;旦师庭组形成于93.7±1.2Ma,属晚白垩世地层,也单独成为一组。     

山东青岛地区灵山岛早白垩世碎屑岩锆石U-Pb-Hf同位素特征及其大地构造意义

苏鲁造山带东缘的灵山岛上发育有早白垩世碎屑岩,目前人们对其沉积的精确时代、成因机制和大地构造环境仍然存在着广泛的争议.利用LA-ICP-MS的方法对灵山岛上两套碎屑岩进行了锆石U-Pb测年,并对特征年龄谱中的代表性碎屑锆石进行了Lu-Hf同位素分析.结果表明:（1）碎屑锆石U-Pb测年结果显示,莱阳群法家茔组和青山群八亩地组下部的碎屑岩沉积时代分别为127±3 Ma和128±4 Ma,表明两套碎屑岩都是早白垩世中晚期的沉积产物;（2）灵山岛上两套碎屑岩具有完全相似的年龄谱以及锆石Hf同位素组成,表明发育软沉积变形的粉砂岩、泥岩和上覆的含砾粗砂岩具有相似的物源,并且源区组成较为单一,主要以亲华北的胶北地体为主,其次的物源区为苏鲁造山带;（3）胶莱盆地下白垩统莱阳群和灵山岛下白垩统莱阳群的碎屑锆石年龄谱对比表明,灵山岛上的莱阳群碎屑岩明显不同于胶莱盆地的莱阳群,暗示在早白垩世时,灵山岛上的两套碎屑岩可能受到区域断裂的控制,沉积于一个相对独立的盆地.综合结果表明,灵山岛地区莱阳群法家茔组可能沉积于断陷湖盆的萎缩期,早期的沉积以湖相为主,晚期主要以河流相为主,在此期间遭受到了强烈的火山地震作用,诱发了下部的湖相的砂泥岩发生大规模的滑塌和软沉积变形.      

青藏高原新生代火山作用与构造演化

青藏高原的新生代火山作用是印度-亚洲大陆碰撞的火山响应,它显示了系统的时、空变化。随着印度-亚洲大陆碰撞从~65 Ma的接触-碰撞(即"软碰撞")转变到~45 Ma的全面碰撞(即"硬碰撞"),火山作用也逐渐从钠质+钾质变为钾质-超钾质+埃达克质。65~40 Ma的钾质和钠质熔岩主要分布于藏南的拉萨地块,少量分布于藏中的羌塘地块。从45~26 Ma,在藏中的羌塘地块中广泛发育钾质-超钾质熔岩和少量埃达克岩。随后的碰撞后火山作用向南迁移,在拉萨地块中产生~26~10 Ma间的同时代超钾质和埃达克质熔岩。尔后,从~18 Ma始,钾质和少量埃达克质火山作用重新向北,在西羌塘和松潘-甘孜地块中呈广泛和半连续状分布。此种时-空变异对形成青藏高原的深部地球动力学过程提供了重要约束。该过程包括:已消减的新特提斯大洋板片的回转、断离及随后增厚拉萨岩石圈根的去根作用,及因此而造成的印度岩石圈向北下插。青藏高原的隆升是自南向北穿时发生的。高原南部被创建于渐新世晚期,并保持至今;直到中新世中期,由于下插印度岩石圈的持续向北推挤,西羌塘和松潘-甘孜岩石圈的下部开始塌陷和拆离,高原北部才达到其现今的高度和规模。     

Late Jurassic-Early Cretaceous Northern Qaidam Basin, NW China: Implications for the earliest Cretaceous intracontinental tectonism

Formation of Mesozoic western China, which was dominated by tectonic amalgamation along its southern margin and associated intracontinental tectonisms, holds a key for interpreting the succedent Cenozoic evolution. This paper presents new data including lithology, sedimentary facies, stratigraphic contact, seismic interpretation and paleo-structures within the Upper Jurassic-Lower Cretaceous strata in the northern Qaidam Basin, NW China. These data all account for a contractional tectonic deformation in the earliest Cretaceous. The South Qilian Shan, according to the sedimentary features and provenance analysis, reactivated and exhumated during the deformation, controlling the deposition of the Lower Cretaceous sequences. A simplified model for the Late Jurassic-Early Cretaceous paleogeography and tectonics of the northern Qaidam Basin is accordingly proposed. The results also support a ∼25° clockwise rotation of the Qaidam Basin since the Early Cretaceous and a more accurate Mesozoic evolution process for the basin. This earliest Cretaceous deformation, associated with the reactivation of the South Qilian Shan at the time, are part of the intracontinental tectonisms in central Asia during the Mesozoic, and probably driven by both the closure of the Mongol-Okhostk Ocean to the north and the collision of the Lhasa and the Qiangtang blocks to the south.