内蒙古赵井沟新元古代花岗岩成因：年代学、地球化学及Sr-Nd-Pb-Hf同位素约束

为研究内蒙古中部新元古代的地质作用过程与岩浆演化,在详细的野外调查和岩相学观察的基础上,对华北板块北缘大青山赵井沟地区发现的新元古代花岗岩开展了全岩主微量元素、锆石年代学及Sr-Nd-Pb-Hf同位素分析。分析结果显示,该区域新元古代花岗岩具有高硅(72.54%～75.67%)、富碱(8.70%～10.15%),贫Ca及低Fe、Mg的特点,Ga/Al(2.90～3.44)较高,具有明显的负Eu异常,其稀土配分曲线呈"海鸥型"展布,Rb、Th、U、Ta等元素较为富集,Ba、Sr、P和Ti等元素强烈亏损,显示出造山后A型花岗岩的地球化学特征;具有震荡环带结构的岩浆成因锆石的LA-ICP-MS谐和年龄为(765±5.0) Ma,表明该花岗岩为新元古代岩浆结晶演化的产物;样品ε_(Nd)(t)变化于-7.3～-2.7,ε_(Hf)(t)为-15.9～-6.3,与负的ε_(Hf)(t)对应的T_(DM2)(地壳二阶段模式年龄)介于2 045～2 662 Ma,暗示该花岗岩的初始物质源于较为古老的地壳物质,但存在幔源混入,这可能是伸展构造背景下地幔岩浆上涌所致。综合区域研究成果及地球化学特征,内蒙古赵井沟新元古代A型花岗岩的形成主要与华北板块北缘古元古代地壳物质的部分熔融有关,是对Rodinia超大陆裂解的岩浆响应。     

Sinian-Cambrian stratigraphic framework for shallow- to deep-water environments of the Yangtze Platform: an integrated approach

The Sinian (Terminal Proterozoic) and Early Cambrian shallow- to deep-water sequences of the Yangtze Platform were investigated. Based on integrated lithostratigraphic, biostratigraphic, and other approaches, the shallow-water sequence from the base of the Sinian (base of the Doushantuo Formation) to the top of the Qiongzhusian (top of the Yu'anshan Formation) was subdivided into 12 stratigraphic intervals. These 12 intervals were applied in turn to the subdivision and correlation of the sequences present in various facies of the Yangtze Platform. The high-resolution stratigraphic framework here developed can serve as a time frame for ongoing multidisciplinary analyses of the "Cambrian explosion".     

新元古代九里桥组中的风暴活动记录及生物学响应

安徽淮南地区新元古代九里桥组主要由砂质、泥质灰岩,叠层石灰岩和白云质灰岩组成.该组沉积物中保存了特征明显的海洋风暴活动记录.对该组风暴沉积序列的岩性和沉积构造的不同组合特征的研究表明,这一时期发生的风暴活动作用过程经历了平静期、强盛期、减弱期和消亡期四个阶段.在不同的作用阶段,风暴活动发生的频率与强度有所不同,对沉积物的改造和破坏作用也不同,与之相关的岩层中叠层石、微体浮游生物化石和宏体生物化石的分布和保存也各具特色,这些迹象表明长期的风暴活动作用对区域性的生物生存和发展具有显著的影响.     

New evidence of deposition under cold climate for the Xieshuihe Formation of the Nanhua System in northwestern Hunan,China

Yangjiaping section is located in Hupingshan Town, Shimen County, Hunan Province. The section has been intensively studied since 1980. However, The paleoclimate during the deposition of the Xieshuihe Formation remains controversial. Based on chemical analysis of sedimentary clastic rocks of the unit, the resulting CIA (the chemical index of alteration) values of the Xieshuihe Formation are similar to those of the overlying Gucheng Formation (also called the Dongshanfeng Formation). It indicates that the sedimentary rocks of the Xieshuihe Formation and Gucheng Formation underwent the similar degrees of chemical weathering before deposition. Therefore, the Xieshnihe Formation was also likely to be deposited under a cold climatic condition, which probably belongs to a part of the record of glaciations.     

Pyritization in the Gaojiashan Biota

The Late Sinian (Ediacaran) Gaojiashan Biota was a soft-bodied fossil-Lagersttte dominated by sub-stantial pyritized, three-dimensionally preserved tubular and conotubular fossils. Soft-tissue pyritiza-tion is extremely scarce in the fossil records, especially in the Precambrian, therefore it has very im-portant and unique significance for the study of pyritization in the Gaojiashan Biota. Early pyritization played a pivotal role in the fossil preservation and two main factors ensured the successful pyritization of the fossils, namely rapid burial and permineralization. The former was controlled by secular storm deposition, and the latter was achieved by sufficient supply of available iron from sediments. SEM data of Conotubus demonstrate two types of preservation of the tubes (defined as type A and type B, re-spectively). In type A, pyritization took place relatively earlier and completely preserved both tube wall and coelom, but no detailed structure. While in type B, pyritization took place somewhat later and pre-served the integrated tube wall, but partially the coelom. The size frequency distribution of the pyrite framboids suggests that pyritization took place in two different environments with entire different oxygen content.     

Zircon U–Pb and Hf isotopic study of Neoproterozoic granitic gneisses from the Alatage area,Xinjiang:constraints on the Precambrian crustal evolution in the Central Tianshan Block

The architecture and growth history of Precambrian crustal basements in the Central Tianshan Block play a key role in understanding the tectonic evolution of the Chinese Tianshan Orogenic Belt.In this study,we present precise LA-ICP-MS zircon U–Pb dating and LAMC-ICPMS zircon Hf isotopic data for two granitic gneisses from Alatage area in the Central Tianshan Block.The magmatic zircons from both samples yield similar protolith ages of 945±6 and 942±6 Ma,indicating that the early Neoproterozoic magmatism is prevailed in the Alatage area.These zircons have crustal Hf model ages of1.82–2.22 and 1.70–2.03 Ga,respectively,which are significantly older than their crystallization ages.It indicates that their parental magmas were derived from the reworking of ancient crust.However,we suggest that these Paleoproterozoic Hf model ages might result from mixing of continental materials with different ages in the Neoproterozoic crust.The inherited(detrital)zircon cores not only yield a wide age range of ca.989–1617 Ma,but also exhibit large Hf-isotope variations with Hf model ages of1.54–2.30 Ga.In particular,some 1.4–1.6 Ga zircons show high initial176Hf/177Hf ratios,consistent with those of depleted mantle,which indicates that the Mesoproterozoic event involved both reworking of older crust and generation of juvenile crust.The Central Tianshan Block has different Precambrian crustal growth history from the Tarim Craton.Therefore,it would not be a fragment of the Precambrian basement of the Tarim Craton.     

粤西新元古代蛇绿岩的发现及其地质意义

粤西信宜贵子、茶山和陆川石窝一带浅变质云开群底部层状、似层状变基性超基性岩的研究表明,变基性岩以变辉长岩、变玄武岩、细碧岩、斜长角闪岩为主,伴生一套细碧角斑岩及少量硅质岩,变超基性岩则以蛇纹石化橄榄岩零星出露为特征,它们是遭受后期构造变形变质作用强烈改造的蛇绿混杂岩。变基性岩的岩石地球化学和同位素地球化学特征显示为E-MORB和N-MORB构造环境形成的大洋拉斑玄武岩。变基性岩、斜长角闪岩中获得的Sm-Nd全岩同位素等时线年龄为(824±77)Ma和(815±75)Ma,这为华南存在新元古大洋提供了重要证据。     

贵州瓮安新元古代陡山沱组磷块岩中的有机化合物

对保存有多细胞藻类原植体、细菌和疑原类化石的贵州瓮安陡山沱组磷块岩所作的地球化学分析表明,磷块岩有机质演化程度较高,最高热解温度t_max达597℃。岩石抽提物中以非烃化合物和沥青质为主要成分,烃类含量不足20%。色谱-质谱(GC-MS)分析图谱显示正烷烃的碳数范围很宽,有显著的高碳数正烷烃峰群(C₁₉—C₃₁),奇偶优势明显,烃类有机组分中除正烷烃外还包含有萜烷、甾烷、芳香烃和类异戊二烯烃等。其中生物标记化合物及其组成特征指示了有机物的主要来源是当时生存的真核的多细胞藻类、细菌和古细菌,这与所观察到的磷块岩中保存的古生物化石组成相吻合。某些特征有机物和生物标记物还指示了磷块岩沉积环境特征：强还原性、高盐度、低陆源输入以及与水热活动相关的局部高温。这与沉积学和岩石学的观察相符。     

Finding of Neoproterozoic （～775 Ma） magmatism recorded in metamorphic complexes from the North Qilian orogen： Evidence from SHRIMP zircon U-Pb dating

The Qilian Mountain is considered a part of the Cen- tral Orogenic Belt of China[1]. The Central Orogenic Belt of China, extending for a distance of about 4000 km long in the E-W direction from the east coast west- ward through the mainland China all the …     

Zircon U-Pb dating for the earliest Neoproterozoic mafic magmatism in the southern margin of the North China Block

Geological records of Neoproterozoic magmaticevents have recently been identified in the central Phanerozoic orogenic belts of China[1]. In regions of east Qinling orogen[2], Dabie-Sulu orogen[3], north Qaidam Basin orogen[4―6], and southwest Tarim Basin…