Basement framework and geodynamic evolution of the Palaeoproterozoic superbasins of north‐central Australia: An integrated review of geochemical,geochronological and geophysical data

A largely convergent setting is proposed for crustal, tectonic and basin evolution of the intracratonic regions of north‐central Australia between 1800 and 1575 Ma. The new geodynamic model contrasts with previous proposals of widespread extension during the Leichhardt, Calvert and Isa intervals. Local transtensional to extensional structures exist, but these are best explained by a combination of flexural, thermal and dynamic processes related to an active southern margin. The development of thick accumulations of sediments (superbasins) is linked geodynamically to interpreted active margin processes (subduction and magmatic arcs) in central Australia. A synthesis of geochemical data from the 1870–1575 Ma igneous units from the Arnhem, McArthur and Mt Isa regions of north‐central Australia confirms the intracratonic setting of these units and suggests that a long‐lived thermal anomaly was responsible for the generation of both mafic and felsic magmas. The geochemical characteristics suggest the igneous units are derived from the lithospheric mantle and are not typical rift‐ or plume‐related melts. A review of the U–Pb SHRIMP ages for the entire region demonstrates the minimum distribution of correlative igneous rocks was widespread. Exotic populations in the ²⁰⁷Pb/²⁰⁶Pb isotopic data provide insights into the nature and evolution of the crust throughout north‐central Australia. Archaean inheritance is found to be nearly ubiquitous. The data support the temporal subdivision of north‐central Australia into the Leichhardt (1800–1750 Ma), Calvert (1750–1690 Ma) and Isa (1690–1575 Ma) intervals which are marked by superbasins and concomitant episodes of igneous activity. A highly heterogeneous pre‐superbasin crust is interpreted from regional, newly processed geophysical data. The cratonic portion of north‐central Australia is interpreted to consist of three broad northwest‐trending belts or elements that are further distinguished into western, central and eastern geophysically distinct provinces. A map of the superbasin distribution is derived and integrated with structural and stratigraphic data to assess the evolution of the basins and the crust through time. The superbasin successions of north‐central Australia are synchronous and widespread, although not necessarily interconnected. The tectonic model incorporates dynamic tilting of the craton during episodes of subduction and transmission of compressive intraplate stresses through the craton during intervening episodes of orogeny. These processes resulted in flexure, strike‐slip deformation and a complex thermal structure. These mechanisms account for the subsidence and basin evolution that results in widespread ramp and strike‐slip basins. The model also accounts for the thermal history recorded by magmatic events. The proposed geodynamical model provides a unifying crustal evolution scenario for central and northern Australia for approximately 225 million years of the Proterozoic.     

Tectonic and eustatic control on the distribution of black-shale source beds in the Wufeng and Longmaxi formations (Ordovician-Silurian),South China

It is known that high-quality, black-shale source rocks occur in the uppermost Ordovician Wufeng Formation and in the lowermost Silurian Longmaxi Formation in South China. Hence, it is important to understand their lithostratigraphy and the controls on their deposition. A review of lithostratigraphic criteria for subdividing the two adjacent formations provides new regional correlations between the formations and related stratigraphic successions and facies. Both the black shales and the related, overlying flysch deposits at the Ordovician-Silurian transition in South China appear to have migrated northwestward in time and space, reflecting probable flexural control in a foreland basin that developed in response to subduction-type orogeny southeast of the Yangtze block. The black shales also contain K-bentonites from explosive, felsic-intermediate volcanism, the distribution of which also supports orogeny to the southeast. Finally, the analysis of sequence stratigraphy, which shows that the initiation of transgressive system tracts (TST) and condensed section (CS) in the related third-order sequences coincided with the two black-shale horizons respectively, indicates that the main controlling factors for the deposition of the Ordovician-Silurian black shales in South China are (1) northwestwardly migrating, foreland-basin subsidence caused by deformational loading related to episodic accretion of the Cathaysia block to the Yangtze block during this period, and (2) the anoxic, sediment-starved water column caused by rapid rise of the sea-level during the two successive phases of third-order global sea-level rise near the Ordovician-Silurian transition in South China. In future exploration for hydrocarbon source rocks in the area, it is important to consider likely flexural and eustatic causes for subsiding, deep, anoxic seas in recognizing other source rock intervals, and our understanding of the Wufeng and Longmaxi formations may serve as models for future source rock exploration. __________ Translated from Earth Science—Journal of China University of Geosciences, 2007, 32(6): 818–827 [译自: 地球科学—中国地质大学学报]     

克拉通内盆地研究中的几个重要问题

克拉通内盆地不仅记录了克拉通在显生宙的演化历史，而且是油气富集的重要场所。本文提出了在克拉通内盆地研究中的几个重要问题：（１）克拉通内盆地基底的非均一性；（２）克拉通内盆地地层层序及其边界不整合分析；（３）克拉通内盆地沉降史分析；（４）克拉通内盆地成因探讨；（５）克拉通内盆地演化与板块构造作用的关系。通过对这些问题的研究，可以深入理解克拉通内盆地形成、充填、改造作用及其对油气分布的控制。     

TECTONIC EVOLUTION OF THE GARZE—LITANG PLATE JUNCTION, WITH PARTICULAR REFERENCE TO THE GOLD DEPOSITS

TECTONIC EVOLUTION OF THE GARZE—LITANG PLATE JUNCTION, WITH PARTICULAR REFERENCE TO THE GOLD DEPOSITS     

陕西南秦岭地质组成及其演化

综合分析南秦岭地质组成与构造特征，显示出区内经历了太古－早、中元古代基底形成阶段，晚元古－早古生代统一扬子大陆北缘演化阶段，古生代勉略－石泉海槽的形成、闭合造山阶段和燕山以来的陆内造山4个大的演化阶段，并形成了相应的岩石建造与构造变形组合。     

“磨拉石建造”和“不整合”在地层对比中的意义——以扬子地块及其北缘晚前寒武纪地层为例

扬子地块及其北缘晚前寒武纪地层划分对比争议较大,主要是对“地层不整合”和“磨拉石建造”存在认识上的分歧,笔者据现代构造理论,对地壳变形和沉积建造的控制作用认为,地层不整合可以发育在被动大陆边缘形成初始阶段的裂谷期和裂谷期后,又可产生于造山作用过程;磨拉石建造应按构造动力学背景划分为拉张型、挤压型和剪切型三类;它们分别代表了威尔逊旋回不同阶段的产物。     

内蒙古大青山太古宙麻粒岩带的板块构造演化模式

太古宙末期在全球范围内出现的麻粒岩带是地壳早期地质演化历史中的一个重大事件，可能意味着地壳构造演化机制的重大转变。越来越多的地质事实表明，太古宙晚期大陆地壳已具有足够的刚性和稳定性。太古宙时期地幔存在强烈的热对流，具备发生板块运动的条件。太古宙麻粒岩带就是太古宙地壳发生刚性板块运动的直接产物。内蒙古大青山太古宙麻粒岩带呈东西向连续出露于大青山地区达２３０余公里，由中晚太古代乌拉山群麻粒岩相组成，其     

赣北前震旦纪构造变形特征及其动力学意义

赣北存在近南北向(D1)、近东西向(D2)、北北西-北北东向(D3)三个世代的叠加褶皱.它们是华夏板块与扬子板块缓慢拼贴过程中应力向板内传递的结果,均形成于前震旦纪.从发生的时间来看,应与格林威尔造成山运动相当.     

Petrogenesis of granitic rocks of the Jabal Sabir area,South Taiz City,Yemen Republic

The Tertiary granitic intrusive body(～21 Ma) of the Jabal Sabir area was emplaced during the early stages of the Red Sea opening.This intrusive body occupies the southern sector of Taiz City.It is triangular in shape,affected by two major faults,one of which is in parallel to the Gulf of Aden,and the other is in parallel to the eastern margin of the Red Sea coast.The petrogenesis of such a type of intrusion provides additional information on the origin of the Oligo-Miocene magmatic activity in relation to the rifting tectonics and evolution of this part of the Arabian Shield.The granitic body of Jabal Sabir belongs to the alkaline or peralkaline suite of A-type granites.It is enriched in the REE.The tight bundle plot of its REE pattern reflects neither tectonism nor metamorphism.This granite body is characterized by high alkali(8.7%-10.13%),high-field strength elements(HFSE),but low Sr and Ba and high Zn contents.The abundance of xenoliths from the neighboring country rocks and prophyritic texture of the Jabal Sabir granite body indicate shallow depths of intrusion.The major and trace elements data revealed a fractional crystallization origin,probably with small amounts of crustal contamination.It is interpreted that the Jabal Sabir intrusion represents an anorogenic granite pertaining to the A-type,formed in a within-plate environment under an extensional tectonic setting pertaining to rift-related granites.     

Two Types of Archaean Grey Gneiss in North China and Their Geological Significance

Grey gneisses are tonalitic intrusive rocks that have Archaean characteristics and tectonic significance. Archaean grey gneisses in North China may be classified into two types: the Zunhua type and the Heagshan type. Grey gneisses of the Zunhua type alternate with basic granulites, forming a bimodal migmatitic suite. The rock is characterized by complex mineral composition, highly varied REE patterns and positive Eu anomaly and originated from autochthonous or partly autochthonous deep-level migmatization with a high degree (30%±) of fusion. As the sub-stratum in the root of the early-stage high-grade greenstone belt, they prevented basic rocks from sinking. Grey gneisses of the Hengshan type are characterized by a relatively distinct intrusion form, large-amplitude upward emplacement, rather simple mineral composition, only slight/changes of REE patterns and absence of Eu anomaly. The rock is a product of subduction and underthrusting of the high-grade greenstone belt and then fusion and emplacement w