新疆古块体的形成与演化

在中亚造山带南缘中国新疆地区划分出塔里木—库鲁克塔格、中天山、伊犁、柯坪四个古块体。塔里木—库鲁克塔格和中天山块体具有一致的前南华纪基底、相似的岩石组合与构造-岩浆演化过程,反映彼此间密切的亲缘性。推测库鲁克塔格在深部可能与塔里木相连,属于塔里木克拉通的一部分。研究表明,中天山是从塔里木克拉通裂解出去的块体,位于两者之间的是通过弧后引张作用而形成的古生代南天山洋盆。伊犁块体在新元古代岩石组合、地层序列、构造环境与演化历史等方面与塔里木块体相似;南华纪裂解以来,差异逐渐明显,并逐渐朝中亚地区的巴尔喀什块体方向运移,到志留纪时增生到哈萨克斯坦板块上,成为巴尔喀什山弯构造带的南部成员。柯坪块体在岩石构造组合、岩层时代、构造环境与演化历史等方面和塔里木—库鲁克塔格、伊犁、中天山三个块体均存在较大差异,属于新元古代洋壳块体。地质证据、岩浆岩年代学证据和碎屑锆石U-Pb年龄谱表明,新疆地区的前寒武纪块体记录了地球早期演化过程中丰富的地壳活动与岩浆作用信息,对全球多期构造-岩浆事件响应积极,包括全球古陆核生长事件、哥伦比亚超大陆聚合事件、罗迪尼亚超大陆聚合与裂解事件。柯坪块体保留了冈瓦纳大陆聚合的信息。     

塔里木北缘库鲁克塔格地区古元古界——祝贺芮行健先生90华诞

库鲁克塔格地区出露了塔里木克拉通最完整的前寒武纪基底,其中新太古界—古元古界构成了塔里木早前寒武纪结晶基底。本文详细总结了该区古元古界岩石组成及变质变形特征,并获得其中的变质火山岩锆石U-Pb年龄为(1 965±13) Ma,代表了该区古元古界沉积年龄。结合区域地层格架、变质事件的研究,认为古元古界沉积时代为2.0~1.8 Ga,并在1.8 Ga发生角闪岩相变质。该变质事件是对北塔里木地体哥伦比亚超大陆汇聚的构造响应。依据岩石组合、前寒武纪大陆地壳生长过程及变质事件综合分析,推测北塔里木地体在中元古代之前属于印度—华北克拉通的一部分,哥伦比亚超大陆裂解过程中与印度—华北克拉通分离,形成一个独立的微陆块,并在罗迪尼亚超大陆汇聚过程中,与南塔里木地体拼合形成了统一的塔里木克拉通前南华纪基底。     

中天山北缘华力西期造山作用——变质岩锆石U-Pb年代学限定

笔者对中天山微陆块北缘托克逊干沟地区角闪岩相变质岩中的锆石进行了U-Pb年代学研究,结果证明变质沉积岩中的碎屑锆石记录了从太古宙至元古宙(3320～530 Ma)的源区岩浆热事件,变质火成岩中的岩浆锆石记录了新元古代晚期(550 Ma)的岩浆作用,而变质锆石记录了晚泥盆纪(385～360 Ma)的变质作用。这一定年结果表明,中天山微陆块北缘的造山作用很可能发生在华力西期,中天山微陆块形成于新元古代以前,但并没有经历前寒武纪变质作用,具有与塔里木克拉通明显不同的前寒武纪构造演化历史。因此,中天山微陆块很可能是一个独立的块体,并不支持其是从塔里木板块分离出来的观点。     

黔东南新元古代清水江组碎屑锆石U-Pb年代学研究及其地质意义

采用LA-ICP-MS方法,对黔东南雷山地区新元古代清水江组郎德剖面碎屑锆石进行U-Pb同位素测定,以建立清水江组碎屑锆石U-Pb年龄谱。从获得的56组单颗锆石有效U-Pb年龄结果反映,清水江组碎屑锆石U-Pb年龄主要分布区间为934 Ma~931Ma,855 Ma~847 Ma,827 Ma~825 Ma,805 Ma~798 Ma,785 Ma~776 Ma和767 Ma~763 Ma,最小年龄加权平均值为766 Ma,幕式分布特征明显,峰值突出,充分反映扬子陆块与华夏陆块拼合以来的构造岩浆热事件。U-Pb年龄谱对比结果表明,其U-Pb年龄谱与扬子西缘、扬子北缘U-Pb年龄谱基本一致,代表了扬子陆块的U-Pb年龄谱基本特征。U-Pb年龄谱相似性分析显示,扬子陆块与塔里木陆块亲缘关系密切,而与华北陆块关系疏远,与华夏陆块自1 000 Ma汇聚以来才开始有很好的亲缘性。     

扬子东南缘两界河组碎屑锆石U-Pb年龄及其对Sturtian冰川作用的启示

扬子东南缘两界河组的岩性以岩屑砂岩和石英砂岩为主,代表了长安冰期和古城冰期之间的间冰期沉积,其沉积时限的厘定对认识华南Sturtian冰期地层的时空分布特征具有重要意义.对黔东地区两界河组碎屑锆石进行了系统的形态学和U-Pb年代学研究,大多数锆石为典型的岩浆锆石,锆石U-Pb年龄主要分布于740~900 Ma,另有少量古元古代和太古宙年龄,主要峰值为~760 Ma、~780 Ma、~800 Ma、~820 Ma和880~900 Ma.在两界河组底部获得最年轻的单颗粒锆石年龄为708±15 Ma,在上部获得最年轻的单颗粒锆石年龄为703±22 Ma,结合区域上相当地层渫水河组的顶部年龄（~690 Ma）,认为黔东地区两界河组的沉积时代应在708~690 Ma之间.两界河组碎屑锆石U-Pb年龄谱记录了扬子陆块新元古代幕式岩浆事件及早期地壳演化的信息,结合锆石形态认为其物质来源可能包括下伏新元古代岩浆岩及沉积地层、扬子西北缘和西南缘的基底岩石.研究区两界河组底部碎屑锆石年龄约束了江口间冰期沉积晚于~708 Ma,考虑到南华纪早期地层分布在一定程度上受控于盆地构造活动,不排除长安冰期沉积物在黔东地区局部存在的可能性.      

扬子北缘南华系武当群锆石U-Pb年龄: 对扬子北缘南华纪裂解模式的启示

扬子北缘出露的武当群是南秦岭地区最重要的基底组成物质, 记录了南秦岭最古老的物质信息。为探讨扬子北缘南华纪的地层序列与裂谷演化模式, 对湖北随州地区武当群典型剖面上的碎屑岩和火山岩进行锆石U-Pb测年, 确定了武当群的沉积层序, 并结合武当、随州地区的武当群锆石年龄, 认为武当地区武当群年龄较随州地区老30 Ma左右, 显示扬子北缘的南华纪裂谷具有自西向东逐渐打开的"剪刀式"裂解特征。武当群碎屑锆石主要峰值年龄为722 Ma、759 Ma、820 Ma、2014 Ma和2445 Ma, 与扬子陆块碎屑锆石的峰值具有较好的对应, 指示了武当群与扬子陆块强烈的亲缘性, 峰值2014 Ma则反映武当群可能有来自桐柏—大别地区的物源信息; 722~759 Ma的峰值代表扬子北缘南华纪早期裂解最强烈的时期, 该裂解事件可能是扬子北缘Rodinia超大陆裂解过程的体现。     

Zircons LA-ICP-MS U-Pb Dating on the Baluntai Deformed Granitoids,Central Tianshan Block, Northwest China,and Its Tectonic Implications

本文对巴仑台地区中天山南北边缘的变形花岗岩体进行了详细的锆石LA-ICP-MS U-Pb年代学研究.中天山北缘花岗质麻岩中岩浆锆石结晶年龄为630.0±5.0Ma,代表了中天山微陆基底的新元古代岩浆事件年龄;其变质增生锆石边的年龄为440.9±3.3Ma,精确限定了中天山北缘洋盆闭合与碰撞造山作用的时代为早志留世.中天山南缘糜棱岩化花岗闪长岩中岩浆锆石结晶年龄为389.5±3.2Ma,指示出中天山南缘洋壳在中泥盆世向北俯冲形成陆缘岩浆弧;其变质增生锆石边的年龄为362.1±4.3Ma,精确限定了中天山南缘洋盆闭合与碰撞造山作用的时代为晚泥盆世末期.研究结果还表明中天山微陆块具有年龄为2.5Ga和1.8Ga的古老结晶基底.     

新疆兴地断裂带前寒武纪构造—岩浆—变形作用特征及其年龄

本文分析了发生在塔里木北缘兴地断裂带的多期构造—岩浆演化特征。在此基础上,对三件前寒武纪火成岩样品进行了LA-ICP-MS锆石U-Pb定年,对兴地断裂带韧性变形构造进行了运动学分析。研究表明,兴地断裂带至少经历了4期地质构造演化; 其中,前寒武纪有两期。第一期发生在前南华纪,以强烈的挤压褶皱、韧性剪切变形和岩浆活动为特色; 第二期发生在南华纪—震旦纪,以广泛发育的双峰式火成岩、复式岩流和基性岩墙群为特征,伴随大规模冰川作用和地壳沉陷,对应Rodinia超大陆的裂解。LA-ICP-MS法锆石U-Pb年龄测定表明,辉长岩中的俘获锆石保留了3114±20Ma、2509±42Ma、1916±36Ma等多期古构造演化和岩浆活动信息,揭示研究区深部存在一个中-新太古代和古元古代的基底。双峰式火成岩测年数据证实,区内在820~800Ma(花岗岩脉,798±7Ma; 辉长辉绿岩墙,816±15Ma)发生过强烈的裂谷—岩浆活动。根据构造交切关系,兴地断裂带发生过两期前南华纪韧性变形;变形时代尚不清楚。运动学分析表明,第一期为朝北逆冲的推覆变形,第二期为右旋走滑变形。南华纪以来,区域变质和韧性变形微弱,为韧脆性变形。     

新疆库鲁克塔格北部现代河流沉积物源分析：碎屑锆石U-Pb年代学的证据

古生代时期塔里木北缘是否为主动大陆边缘对于了解南天山洋俯冲方式及塔里木北缘地质演化具有极其重要的意义。本文对取自乌斯腾高勒河沟的69粒碎屑锆石进行阴极发光和LA-ICP-MSU-Pb定年,获得的50组U-Pb有效年龄数据表明:1)物源主要集中在库鲁克塔格北部379～466 Ma、651～817 Ma及1844～2122 Ma的岩石;2)碎屑锆石U-Pb有效年龄记录了至少3期构造热事件,其中,锆石年龄379～466 Ma的碎屑锆石表明,在古生代中期库鲁克塔格地区发育大规模岩浆作用,经对比研究发现,这些事件可能与该期南天山洋向南俯冲,塔里木北缘为主动大陆边缘有关,晚元古代的岩浆作用可能记录了罗迪尼亚超大陆裂解事件,早元古代变质锆石的存在可能与哥伦比亚超大陆有关。     

桂西南凭祥火山岩年代学、地球化学及Hf同位素研究——对古特提斯洋最晚北向俯冲事件的启示

华南西南缘凭祥地区位于特提斯构造域东端,华南与印支陆块碰撞缝合带的北部,该区出露的三叠纪中酸性火山岩是古特提斯洋俯冲过程中在华南陆块边缘形成的大陆弧产物,这些火山岩同时携带的大量来自华南陆块基底的捕获锆石为华南陆块的构造热事件研究将提供重要的信息。对凭祥地区三叠系北泗组英安岩进行了同位素年代学、地球化学及锆石Hf同位素研究,获得了一个英安岩样品的加权平均年龄为（227.8±1）Ma,这些英安岩具有高SiO₂、K₂O含量,极低的MgO、MnO和CaO含量,富集大离子亲石元素（Rb、Ba、Th和U）和亏损高场强元素（Nb、Ta）的特点,显示了典型的岛弧岩浆作用特征,代表古特提斯洋向北俯冲至华南陆块之下形成的大陆弧产物。其余两个英安岩样品中的70粒锆石主要为来自华南陆块基底的捕获锆石,其年龄数据变化区间较大,为1010~231 Ma,这些捕获锆石U-Pb年龄频谱分布主要集中在四个区间:11010~800 Ma（峰值900 Ma）,其锆石的ε_Hf（t）值为4.5~15.1,响应扬子和华夏陆块之间聚合-裂解-再聚合的构造演化事件,反应了其幔源岩浆的广泛参与;2720~620 Ma（峰值680 Ma）响应南华纪已拼合的扬子-华夏陆块的再次发生裂解;3490~400 Ma（峰值450 Ma）,其锆石的ε_Hf（t）值为2.2~-7.8,响应华南早古生代加里东运动有关的壳-幔相互作用岩浆事件;4280~230 Ma（峰值250 Ma）,其锆石ε_Hf（t）值为-13.6~-16.5,地壳模式年龄为2.3~2.1 Ga,代表了印支与华南陆块之间古特提斯洋俯冲闭合的岩浆事件。文章的研究结果揭示了凭祥北泗组英安岩与华南陆块的亲缘性,其结晶年龄限定了华南与印支陆块之间的古特提斯洋俯冲结束、陆-陆开始碰撞的最晚时限为中-晚三叠纪。      

南秦岭随枣地块耀岭河组双峰式火山岩: 对扬子克拉通北缘大陆裂解过程的约束

长期以来,扬子克拉通北缘新元古代地质构造演化一直是地学界研究的热点。在南秦岭随州地区耀岭河组中新识别出一套双峰式变火山岩,对其开展锆石U-Pb年代学研究结果表明,变玄武岩中锆石较少,且多为捕获锆石,年龄组成特征与下伏武当岩群顶部岩石中碎屑锆石基本一致;白云母千枚岩中锆石年龄集中,获得的U-Pb年龄为623±3 Ma,代表了南秦岭随枣地区耀岭河组的形成时代,该结果与侵入武当岩群中的基性岩墙年龄650~600 Ma一致,两者应为同时期不同产出相的岩浆作用的产物。结合区域研究成果,扬子克拉通北缘裂解可能经历了更长期且复杂的地质构造过程,西部裂解较早,东部（现今方向）较晚,总体呈"拉链式"裂解模式。     

塔里木盆地塔中志留系柯坪塔格组物源示踪:碎屑锆石U-Pb年代学证据

目前对塔中志留系物源的认识仍存在不确定性.利用LA-ICP-MS分析技术对塔里木盆地塔中地区志留系柯坪塔格组2件样品开展碎屑锆石U-Pb年代学研究.结果表明塔中志留系碎屑锆石主要为岩浆结晶成因,锆石年龄主要分布在早古生代460～490 Ma、新元古代760～1000 Ma、古元古代1600～2200 Ma及新太古代晚期...     

Detrital zircons from Neoproterozoic sedimentary rocks in the Yili Block: Constraints on the affinity of microcontinents in the southern Central Asian Orogenic Belt

The Yili Block is one of the Precambrian microcontinents dispersed in the Central Asian Orogenic Belt (CAOB). Detrital zircon U–Pb ages and Hf isotopic data of Neoproterozoic meta-sedimentary rocks (the Wenquan Group) are presented to constrain the tectonic affinity and early history of the Yili Block. The dating of detrital zircons indicates that both the lower and upper Wenquan Groups have two major populations with ages at 950–880 Ma and 1600–1370 Ma. Moreover, the upper Wenquan Group has two minor populations at ~ 1100 Ma and 1850–1720 Ma. According to the youngest age peaks of meta-sedimentary rocks and the ages of related granitoids, the lower Wenquan Group is considered to have been deposited during the early Neoproterozoic (900–845 Ma), whereas the upper Wenquan Group was deposited at 880–857 Ma. The zircon ε_Hf (t) values suggest that the 1.85–1.72 Ga source rocks for the upper Wenquan Group were dominated by juvenile crustal material, whereas those for the lower Wenquan Group involved more ancient crustal material. For the 1.60–1.37 Ga source rocks, however, juvenile material was a significant input into both the upper and lower Wenquan Groups. Therefore, two synchronous crustal growth and reworking events were identified in the northern Yili Block at ca. 1.8–1.7 Ga and 1.6–1.3 Ga, respectively. After the last growth and reworking event, continuous crustal reworking took place in the northern Yili Block until the early Neoproterozoic. Comparing the age patterns and Hf isotopic compositions of detrital zircons from the Yili Block and the surrounding tectonic units indicates that the Yili Block has a close tectonic affinity to the Chinese Central Tianshan Block in the Precambrian. The Precambrian crustal evolution of the Yili Block is distinct from that of the Siberian, North China and Tarim Cratons. Such difference therefore suggests that the Yili Block and the Chinese Central Tianshan Block may have been united in an isolated Precambrian microcontinent within the CAOB rather than representing two different blocks rifted from old cratons on both sides of the Paleo-Asian Ocean.     

Provenance of the early to mid-Paleozoic sediments in the northern Alxa area: Implications for tectonic evolution of the southwestern Central Asian Orogenic Belt

The continental fragments in Northwest China are key to revealing the tectonic and crustal evolution of the Central Asian Orogenic Belt (CAOB). However, their tectonic correlation, affinity and implications have not been well defined. The early to mid-Paleozoic sediments in the northern Alxa area can help to understand this question. These sediments were deposited in a deep to shallow marine environment during a regression. The southeast paleocurrent attributes their provenance to the northwest. Detrital zircons from the collected sandstones record peak ages of approximately 1726 Ma, 1462 Ma, 915 Ma and 438 Ma. The zircon ε_Hf(t) values are negative to positive at 1726 Ma, 915 Ma and 438 Ma, but only positive at 1462 Ma. The detrital zircon U–Pb ages and Hf isotopes suggest the provenance to be the blocks in Central Tianshan and Southern Beishan or their analogs, rather than the Tarim Craton. The source blocks show no tectonic affinity to the Tarim Craton but might be accreted to it in the Neoproterozoic Rodinia. The provenance analyses show tectonic correlation among the northern Alxa, Tianshan and Beishan orogenic belts. The Late Devonian molasse deposits, geochemical shifting to continental margins and suddenly increased early Paleozoic zircons indicate an arc-continent collision. The discovery of more indicators for continental fragments advocates a multiterrane model and dominant crustal reworking/contamination for the tectonocrustal evolution of the CAOB at least during the early to mid-Paleozoic.     

Provenance of latest Mesoproterozoic to early Neoproterozoic (meta)-sedimentary rocks and implications for paleographic reconstruction of the Yili Block

The Yili Block is one of the major Precambrian microcontinents of the Central Asian Orogenic Belt (CAOB). Detrital zircon U-Pb ages and Hf isotopic data of the Meso-Neoproterozoic (meta)-sedimentary units within the Yili Block constrain the tectonic affinity and early history of the block. Detrital zircon U-Pb ages, in combination with related magmatic age data, indicate that the Tekesi and Kusitai groups were deposited during the latest Mesoproterozoic-earliest Neoproterozoic (1040–960 Ma) and early Neoproterozoic (<926 Ma), respectively. Zircons from the Kusitai Group yield major age groups at 941–910 Ma and 1887–1122 Ma, whereas the Tekesi Group have a dominant age group at ca. 2.0–1.1 Ga with age peaks at ca. 1.9 Ga, 1.8 Ga, 1.75–1.70 Ga, 1.58 Ga, 1.5 Ga, 1.47–1.43 Ga and 1.27–1.20 Ga. A minor age peak of ca. 2.5 Ga is also recognized in the middle part of the Tekesi Group. Early Neoproterozoic detrital zircons with relatively uniform ε_Hf(t) values (+0.7 to +3.2) were mainly derived from contemporaneous magmatic rocks in the Yili Block. The Central Tianshan Block provides a likely source for detritus with ages of ca. 1.7–1.4 and 2.5 Ga. The predominant late Paleoproterozoic to latest Mesoproterozoic detrital zircons with positive ε_Hf(t) values (+0.5 to +12.0) in the Yili Block were probably derived primarily from regions exhumed during collisional assembly of Rodinia. These populations are consistent with those from the late Mesoproterozoic-early Neoproterozoic (meta)-sedimentary successions in the Central Tianshan, Kokchetav-North Tianshan and Erementau-Niyaz blocks, and Southeast Siberia and northeastern Laurentia cratons. The Yili Block, together with the Precambrian microcontinents in the southwestern Central Asian Orogenic Belt, was likely located at the margin of Rodinia supercontinent, between the southeast Siberia and northeast Laurentia during the early Neoproterozoic.     

The tectonic evolution of the Tianshan Orogenic Belt: Evidence from U–Pb dating of detrital zircons from the Chinese southwestern Tianshan accretionary mélange

The Tianshan Orogenic Belt, which is located in the southwestern part of the Central Asian Orogenic Belt (CAOB), is an important component in the reconstruction of the tectonic evolution of the CAOB. In order to examine the evolution of the Tianshan Orogenic Belt, we performed detrital zircon U–Pb dating analyses of sediments from the accretionary mélange from Chinese southwestern Tianshan in this study. A total of 542 analyzed spots on 541 zircon grains from five samples yield Paleoarchean to Devonian ages. The major age groups are 2520–2400 Ma, 1890–1600 Ma, 1168–651 Ma, and 490–390 Ma. Provenance analysis indicates that, the Precambrian detrital zircons were probably mainly derived from the paleo-Kazakhstan continent formed before the Early Silurian by amalgamation of the Kazakhstan–Yili microplate, the Chinese central Tianshan terrane and the Kyrgyz North and Middle Tianshan blocks, while detrital zircons with Paleozoic ages mainly from igneous rocks of the continental arc generated by the northward subduction of the south Tianshan paleocean. The age data correspond to four tectono-thermal events that took place in these small blocks, i.e., the continental nucleus growth during the Late Neoarchean–early Paleoproterozoic (~ 2.5 Ga), the evolution of the supercontinents Columbia (2.1–1.6 Ga) and Rodinia (1.3–0.57 Ga), and the arc magmatism related with the Phanerozoic orogeny. The Precambrian zircons show a similar age pattern as the Tarim and the Cathaysia cratons and the Eastern India–Eastern Antarctica block but differ from those of Siberia distinctly. Therefore, the Tianshan region blocks and the Kazakhstan–Yili microplate have a close affinity to the eastern paleo-Gondwana fragments, but were not derived from the Siberia craton as proposed by some previous researchers. These blocks were likely generated by rifting accompanying Rodinia break-up in late Precambrian times.The youngest ages of the detrital zircons from the subduction mélange show a maximum depositional age of ca. 390 Ma. It is coeval with the end of an earlier arc magmatic pulse (440–390 Ma) but a bit older than a younger one at 360–320 Ma and nearly 70–80 Ma older than the HP–UHP metamorphism in the subduction zone (320–310 Ma).     

The provenance and tectonic affinity of the Paleozoic meta-sedimentary rocks in the Chinese Tianshan belt: New insights from detrital zircon U–Pb geochronology and Hf–isotope analysis

The tectonic evolution of the Chinese Tianshan Belt which is located in the southern margin of the Central Asian Orogenic Belt remains controversial. In order to reveal the evolutionary history of this belt, we investigate metasedimentary rocks from the Tianshanmiao of Harlik domain and Xingxingxia area of central Tianshan domain in this study. The Permian siltstones from Xingxingxia contain six zircon populations with ages peak at 280, 815 and 910, 1590, 1855 and 2340 Ma, suggesting a diverse provenance. The 2544–2294 Ma ages correlate with the generation of continental nuclei in Tarim. The tectonothermal events during 1855, 1590, 910 and 815 Ma may correspond to the assembly and breakup of the Columbia and Rodinia supercontinents, respectively. Similar Precambrian age spectra and “event signature” curves suggest that the central Tianshan was most likely a part of the Tarim block in the Proterozoic. The detrital zircon U–Pb ages of Ordovician meta-greywackes from the Tianshanmiao sequence reveal six zircon populations with peaks at 460, 933, 1382, 1850, 2000 and 2462 Ma, among which the zircons with dominant age peaks (460 Ma and 930 Ma, more than 70%) are euhedral, low sphericity and exhibit clear oscillatory zoning, suggesting local derivation from the proximal Ordovician and Neoproterozoic granitoids. The range of εHf(t) values (−5.4 to +21) of zircon grains from Ordovician rocks suggests that these were derived from depleted mantle or through partial melting of juvenile crust, similar to the case for the Early Paleozoic magmatism in Chinese Altai. Our detrital zircon data suggest that the provenance of the Harlik was neither the Tarim nor the Junggar, and instead, we propose a connection with the Chinese Altai-Tuva–Mongol Arc along the southern margin of the Siberia craton at ∼500 Ma. The Harlik domain drifted southward and then collided with the central Tianshan in the Carboniferous-Permian as a result of the closure of Paleo-Tianshan Ocean.     

中天山巴仑台地区变形花岗岩类LA-ICP-MS-U-Pb年代学及其构造意义

本文对巴仑台地区中天山南北边缘的变形花岗岩体进行了详细的锆石LA-ICP-MS-U-Pb年代学研究。中天山北缘花岗质片麻岩中岩浆锆石结晶年龄为630.0±5.0 Ma,代表了中天山微陆基底的新元古代岩浆事件年龄;其变质增生锆石边的年龄为440.9±3.3 Ma,精确限定了中天山北缘洋盆闭合与碰撞造山作用的时代为早志留世。中天山南缘糜棱岩化花岗闪长岩中岩浆锆石结晶年龄为389.5±3.2 Ma,指示出中天山南缘洋壳在中泥盆世向北俯冲形成陆缘岩浆弧;其变质增生锆石边的年龄为362.1±4.3 Ma,精确限定了中天山南缘洋盆闭合与碰撞造山作用的时代为晚泥盆世末期。研究结果还表明中天山微陆块具有年龄为2.5Ga和1.8Ga的古老结晶基底。     

Detrital and xenocrystic zircon ages from Neoproterozoic to Palaeozoic arc terranes of Mongolia: Significance for the origin of crustal fragments in the Central Asian Orogenic Belt

The Central Asian Orogenic Belt contains many Precambrian crustal fragments whose origin is unknown, and previous speculations suggested these to be derived from either Siberia, Tarim or northern Gondwana. We present an age pattern for detrital and xenocrystic zircons from Neoproterozoic to Palaeozoic arc and microcontinental terranes in Mongolia and compare this with patterns for Precambrian rocks in southern Siberia, the North China craton, the Tarim craton and northeastern Gondwana in order to define the most likely source region for the Mongolian zircons. Our data were obtained by SHRIMP II, LA-ICP-MS and single zircon evaporation and predominantly represent arc-related low-grade volcanic rocks and clastic sediments but also accretionary wedges and ophiolitic environments.The Mongolian pattern is dominated by zircons in the age range ca. 350–600 and 700–1020 Ma as well as minor peaks between ca. 1240 and 2570 Ma. The youngest group reflects cannibalistic reworking of the Palaeozoic arc terranes, whereas the Neoproterozoic to late Mesoproterozoic peak reflects both reworking of the arc terranes as well as Neoproterozoic rifting and a Grenville-age crust-formation event.The 700–1020 Ma peak does not exist in the age spectra of the Siberian and North China cratons and thus effectively rules out these basement blocks as potential source areas for the Mongolian zircons. The best agreement is with the Tarim craton where a major Grenville-age orogenic event and early Neoproterozoic rifting have been identified. The age spectra also do not entirely exclude northeastern Gondwana as a source for the Mongolian zircons, but here the Neoproterozoic age peak is related to the Pan-African orogeny, and a minor Grenville-age peak may reflect a controversial orogenic event in NW India.Our Mongolian detrital and xenocrystic age spectrum suggests that the Tarim craton was the main source, and we favour a tectonic scenario similar to the present southwestern Pacific where fragments of Australia are rifted off and become incorporated into the Indonesian arc and microcontinent amalgamation that will evolve into a future orogenic belt.     

再论塔里木北缘阿克苏蓝片岩的时代和成因环境:来自锆石U-Pb年龄、Hf同位素的新证据

阿克苏蓝片岩和基性岩墙形成时代和构造背景对认识塔里木地块前寒武纪构造演化以及新元古代超大陆重建具有重要意义.本文通过对含蓝片岩的阿克苏群中变质碎屑岩和侵入阿克苏群的基性岩墙的锆石U-Pb定年及Hf同位素分析表明,(长石)石英片岩中碎屑锆石出现2个明显的统计峰值,较老一组锆石²⁰⁷Pb/²⁰⁶Pb的表面年龄集中在~1.9Ga,并有少量太古代的年龄信息;另一组较年轻锆石²⁰⁶Pb/²³⁸U表面年龄峰值为~820Ma,代表阿克苏群的最大沉积年龄.侵入阿克苏群的基性岩墙锆石U-Pb年龄为~760Ma.阿克苏蓝片岩相变质的时间被严格限定在820~760Ma区间内.碎屑锆石Hf同位素地壳模式年龄峰值出现在2.2~2.3Ga,2.6Ga和3.2~3.3Ga.综合本次工作及前人研究成果,表明阿克苏蓝片岩地体是塔里木早前寒武纪基底之上发育起来的大陆边缘岩浆弧.