Nature of the Precambrian metamorphic blocks in the eastern segment of Central Tianshan: Constraint from geochronology and Nd isotopic geochemistry

The Central Tianshan Tectonic Zone (CTTZ) is anarrow domain between an early Paleozoic southernTianshan passive continental margin and a late Paleo-zoic northern Tianshan arc zone, which is character-ized by the presence of numerous Precambrian meta-morphic basement blocks. Proterozoic granitoidgneisses and metamorphic sedimentary rocks,namely Xingxingxia and Kawabulag and Tianhugroups, are the most important lithological assem-blages in these metamorphic basement blocks, and alittle of …     

试论中国古大陆中-新元古代汇聚与裂解的地质记录

自1990年新元古Rodinia超大陆提出后,现已发展成地学研究热点之一。在全球新元古代超大陆旋回的汇聚与裂解机制影响下,中国古大陆也随之变化。中元古代末一新元古代初的汇聚和新元古代晚期的裂解是最重要的两次地质事件。塔里木、华北、华南古陆都有它的地质记录。晋宁事件应是中元古代晚期-新元古代早期,北秦岭地块与中秦岭地块俯冲一碰撞造山作用和新元古代时期Rodinia超大陆形成的主要地质事件;华南的武陵运动,使华夏古陆与扬子地块发生碰撞形成统一的“华南古陆”。在塔里木古陆与哈萨克斯坦一伊犁古陆之间的那拉提南缘碰撞带,甘肃北山南带柳园及青海柴达木盆地北部边缘的榴辉岩一花岗岩带的发现都是最新的研究成果。     

梵净山区格林威尔期造山带与Rodinia超大陆

贵州梵净山区有保存完好、发育齐全的中元古代的地质记录 ,是扬子陆块晚前寒武地质研究的理想场所和重要窗口。现有地质和同位素年代学等资料表明 ,该区存在格林威尔期造山带 ,其形成时间为ca 10 0 0Ma±。它同原始江南造山带一起成为华南Rodinia超大陆的组成部分 ;对其进行探讨 ,必将促进我国Rodinia超大陆聚合、裂解及其演化的研究 ,并具有重大的科学意义。     

Rodinia超大陆构造演化研究的新进展和主要目标

概略评述了1997年以来国际上有关Rodinia超大陆构造演化问题的研究成果，并提出今后工作的主要目标。Rodinia超大陆的聚合造山发生在1300－1000Ma，基本形式表现为早期弧一陆碰撞和晚期陆－陆碰撞，并在1000－900Ma继以伸展作用。Rodinia超大陆的裂解发生于830Ma之后，但其过程具有明显的时，空分布不均一性，地幔柱可能是导致超大陆裂解的主要机制，大火成岩省”是地幔柱发育的关键性标志，已经初步证实裂解过程影响地球大气圈和水圈中二氧化碳的循环，进而改变晚前寒武纪的全球气候，控制生物圈的兴衰和岩石圈表层的碳酸盐，铁，锰和磷等沉积，这些现象可用“雪球化地球”（Snowball Earth)模式概括。     

Paleogeographic maps of the Japanese Islands: Plate tectonic synthesis from 750 Ma to the present

Abstract A series of paleogeographic maps of the Japanese Islands, from their birth at ca 750–700 Ma to the present, is newly compiled from the viewpoint of plate tectonics. This series consists of 20 maps that cover all of the major events in the geotectonic evolution of Japan. These include the birth of Japan at the rifted continental margin of the Yangtze craton ( ca 750-700 Ma), the tectonic inversion of the continental margin from passive to active ( ca 500 Ma), the Paleozoic accretionary growth incorporating fragments from seamounts and oceanic plateaux ( ca 480-250 Ma), the collision between Sino-Korea and Yangtze (250–210 Ma), the Mesozoic to Cenozoic accretionary growth (210 Ma-present) including the formation of the Cretaceous paired metamorphic belts (90 Ma), and the Miocene back-arc opening of the Japan Sea that separated Japan as an island arc (25-15 Ma).     

桂北地区丹洲群碎屑锆石LA-ICP-MS U-Pb年龄和Hf同位素特征及其地质意义

桂北丹洲群顶部拱洞组粉砂岩的碎屑锆石的阴极发光图像和Th/U(0.2~2.4)值显示,它们均为岩浆成因的锆石。锆石~(206)Pb/~(238)Pb年龄分布在730~769Ma和771~850Ma之间,这些锆石的Hf同位素成分范围较大,ε_(Hf)(t)值和二阶段Hf模式年龄(T_(DM2))分别为-18.4~11.4和1020~2812Ma。此外,样品中还有一些年龄较老的锆石颗粒,~(207)Pb/~(206)Pb年龄为1910~3140Ma,ε_(Hf)(t)值和二阶段Hf模式年龄(T_(DM2))分别为-13.6~3.4和2740~3635Ma。结合前人的研究推测,桂北丹洲群拱洞组沉积年龄小于等于706±10Ma,物源主要由扬子板块新元古代岩浆岩组成,也有少量太古宙岩浆岩的加入。推测中国华南地区存在对应于Rodinia超大陆聚合相关的格林威尔运动的响应。根据已测锆石的ε_(Hf)(t)值和Hf二阶段模式年龄推断,研究区地壳生长主要经历3个阶段:(1)3.64~3.25Ga,初生地壳出现在3.64Ga;(2)2.98~2.37Ga;(3)2.19~1.28Ga,地壳生长的主要时期。     

扬子板块北缘花山群沉积时代及其对Rodinia超大陆裂解的制约

出露于扬子板块北缘大洪山地区的花山群自下而上由一套以砾岩为主的粗碎屑沉积和一套以砂质板岩为主的细碎屑沉积组成,伴随有拉斑玄武质岩浆活动。花山群整体变质程度不高,形成构造环境复杂,对其构造属性及其与区内所谓的花山"蛇绿混杂岩"的时空关系一直存有争议,它们对新元古代Rodinia超大陆在扬子板块北缘的汇聚-裂解响应具有重要的制约意义。笔者在花山群六房咀组下部细砂岩中采集玄武质熔结凝灰岩夹层样品1件,碎屑岩样品2件,在上覆地层南华系莲沱组采集碎屑岩样品1件;对玄武质熔结凝灰岩进行了SHRIMP锆石U-Pb同位素测年,对碎屑岩样品进行了LA-MC-ICPMS锆石U-Pb同位素测年。获得玄武质熔结凝灰岩锆石U-Pb年龄814.7±7.3 Ma;花山群的碎屑锆石U-Pb年龄谱存在三个明显的峰值:~900 Ma、~2050Ma和~2650 Ma,最显著峰值为~2650 Ma,上覆莲沱组碎屑岩年龄谱的三个峰值为:~900 Ma、~2050 Ma和~2500 Ma,最显著峰值为~2050Ma,三件碎屑岩样品均与扬子板块的碎屑锆石U-Pb年龄统计峰值一致。花山群的碎屑源区可能包括下伏中元古代打鼓石群、太古宙鱼洞子杂岩以及崆岭杂岩。结合前人年代学研究资料和区域构造成果分析,花山群沉积时代应为820~815Ma,形成于伸展构造背景,与花山"蛇绿混杂岩"不是同期同构造背景的产物;花山"蛇绿混杂岩"与花山群沉积建造依次反映了扬子板块北缘由挤压构造背景向伸展构造背景的转换过程。花山群中的碎屑沉积物与基性火山岩、火山碎屑岩属于裂解背景下形成的同时代沉积-火山建造;结合前人在扬子板块周缘发现的大量约820 Ma酸性—基性岩浆活动记录以及同时代(820~800 Ma)的沉积地层,推测花山群形成于Rodinia超大陆裂解背景之下,与超级地幔柱活动有关。     

新元古代重大地质事件及其与生物演化的耦合关系

新元古代的地球表层系统经历了超大陆裂解与重组、大规模冰期、古海洋氧化、埃迪卡拉生物群辐射与灭绝、后生动物兴起等一系列重大变革,这些地质事件与生物演化在时空上的耦合关系长期受多学科交叉研究领域的广泛关注。Rodinia超大陆的裂解伴随有超级地幔柱活动、古地磁真极移等复杂响应,裂解过程影响了大气圈和水圈中氧气和二氧化碳的循环,并可能直接导致了新元古代极端的气候条件。构造格局的变动对生物的影响主要体现在物质来源和生存环境的改变上,强上升洋流和强地表径流区域的富营养化促使生物大量繁盛。“雪球地球”期间巨大的选择压力为生物的多样化演变提供了可能,而其后冰川的快速消融则促进了生产力的爆发式增长及多种沉积矿产的形成。与此同时,大气-海洋氧气含量的增加和海水化学结构的改变使得多项元素及同位素指标发生了地质历史上最大幅度的波动,这种特殊的地质背景可能最终对生物演化产生了极为深刻的影响。     

扬子克拉通西缘1.73Ga非造山型花岗斑岩的发现及其地质意义

首次发现扬子克拉通西缘古元古代晚期海孜斜长花岗斑岩岩体.本文报道了其锆石的LA-ICP-MS U-Pb年龄,为1730±15Ma(MSWD=4.0,n=15).岩石具有高SiO2(69.77％～73.83％)、高碱(ALK=5.46～6.65)、低钾(K2O/Na2O=0.02～0.14)含量.里特曼指数1.04～1.65,A/CNK值为1.11～1.25,平均值为1.18(＞1.1),10000 Ga/Al=3.96～7.34(均值为5.18＞2.6),较高的含铁指数[FeO/(FeO+MgO) =0.95～0.99],总体显示了低钾钙碱性过铝质(SP)铁质A型花岗岩的特点.岩石富集Nb、Ta、Zr和Hf等高场强元素,强烈亏损K、Sr和Ba等大离子亲石元素,稀土元素总量∑REE=390.70×10-6～674.91×10-6,LREE/HREE=1.74～3.29(均值2.18),轻稀土分异作用明显,相对富集,表现出强烈的负Eu异常.地球化学特征显示,海孜花岗斑岩岩体为形成于板内伸展构造环境,可能与同期基性岩浆活动的底侵作用相关.海孜花岗岩的年龄和地球化学表明,扬子克拉通西缘存在古元古代晚期与全球性Columbia超级大陆裂解同期的双峰式岩浆岩组合.     

Paleoproterozoic crustal evolution of the Tarim Craton: Constrained by zircon U–Pb and Hf isotopes of meta-igneous rocks from Korla and Dunhuang

The Tarim Craton is one of three large cratons in China. Presently, there is only scant information concerning its crustal evolutionary history because most of the existing geochronological studies have lacked a combined isotopic analysis, especially an in situ Lu–Hf isotope analysis of zircon. In this study, Precambrian basement rocks from the Kuluketage and Dunhuang Blocks in the northeastern portion of the Tarim Craton have been analyzed for combined in situ laser ablation ICP-(MC)-MS zircon U–Pb and Lu–Hf isotopic analyses, as well as whole rock elements, to constrain their protoliths, forming ages and magma sources. Two magmatic events from the Kuluketage Block at ∼2.4 Ga and ∼1.85 Ga are revealed, and three stages of magmatic events are detected in the Dunhuang Block, i.e., ∼2.0 Ga, ∼1.85 Ga and ∼1.75 Ga. The ∼1.85 Ga magmatic rocks from both areas were derived from an isotopically similar crustal source under the same tectonic settings, suggesting that the Kuluketage and Dunhuang Blocks are part of the uniform Precambrian basement of the Tarim Craton. Zircon Hf model ages of the ∼2.4 Ga magmatism indicate that the crust of the Tarim Craton may have been formed as early as the Paleoarchean period. The ∼2.0 Ga mafic rock from the Dunhuang Block was formed in an active continental margin setting, representing an important crustal growth event of the Tarim Craton in the mid-Paleoproterozoic that coincides with the global episode of crust formation during the assembly of the Columbia supercontinent. The ∼1.85 Ga event in the Kuluketage and Dunhuang Blocks primarily involved the reworking of the old crust and most likely related to the collisional event associated with the assembly of the Columbia supercontinent, while the ∼1.75 Ga magmatism in the Dunhuang Block resulted from a mixture of the reworked Archean crust with juvenile magmas and was most likely related to a post-collisional episode.