辽宁早前寒武纪变质岩元素地球化学特征及富集模式

早前寒武纪变质岩系是辽宁地区古老变质岩系的重要组成部分,变质程度高于绿片岩相,局部可达麻粒岩相.通过研究辽宁早前寒武纪变质岩系元素地球化学特征,计算了辽宁地区早前寒武纪变质岩系元素原始浓集系数,建立了不同构造单元和地层单元元素的原始浓集模型.     

云开地区加里东期花岗岩锆石U-Pb年龄及其地质意义

对云开地区1∶25万区调中划归前寒武纪或新元古代的(片麻状)花岗岩进行了锆石LA-ICP-MS U-Pb定年,获得的年龄分别为(443.3±2.6)Ma(样品1009,陆川县陆透水库东南)、(445.7±2.3)Ma(样品1010,陆川县月垌村)、(441.1±2.0) Ma(样品1012,高州市谢鸡镇)和(443.7±1.7)Ma(样品10108,信宜市朱砂镇),表明它们属于加里东期的产物而不是以往认为的前寒武纪基底或新元古代岩石.结合前人的研究表明,这些花岗岩主要由元古宙基底岩石发生深熔作用而成,是华南地区加里东期陆内造山作用的响应.随着云开地区前寒武纪基底中大量加里东期年龄的发现,说明加里东运动对该区的影响非常强烈,1∶25万区调中划归前寒武纪基底或新元古代的部分片麻状花岗岩应归属加里东期.云开地区前寒武纪基底主要是以片麻岩类为代表的高州杂岩和以变沉积岩类为代表的云开群,高州杂岩形成时代为中新元古代,云开群形成时代可能为新元古代.从整个华夏地块来看,存在古-中元古代结晶基底,但出露可能并不像以往认为的那么广泛.     

Correlation of the lower devonian rocks of australasia

Alkali basaltic rocks from the Southern Highlands, N.S.W., contain oxide phases of both high and low pressure origin. The two phases are readily distinguished using chemical and textural criteria.

Chemical data for low‐pressure Fe‐Ti oxides indicate that oxygen fugacities of the host lavas range from 10‐^12.8 to 10‐⁸ atm at 950° to 1110°C. In most cases, the oxygen fugacities of the individual lava flows appear to be principally a function of temperature and intrinsic chemical equilibria existing at the time of formation of the basaltic liquid. However, some relatively differentiated flows shows a high degree of oxidation due to volatile enrichment with fractionation. Rare glassy flows show dendritic crystallization of Fe‐Ti oxides. Most flows in which abundant olivine was the first phase to be precipitated also contain Cr‐rich spinels associated, and apparently coeval, with the earliest‐crystallizing olivine.     

Resolution of foraminiferal biotopes in Broken Bay,N.S.W.

A recent benthonic foraminiferal population consisting of 144 species from an interacting marine‐estuarine environment has been analysed by Q‐mode cluster analysis to reveal biotopes. Simplification of the total populations, both in terms of abundance and occurrence, discloses that the more significant subpopulation is composed of the widely‐occurring species. Subpopulations based on rarely occurring but locally abundant species do not define meaningful biotopes.     

Gold-Plationoid Mineralization of Metasomatically Altered Ultramafites in Precambrian Protrusions of Mamynsky Geoblok

On the contiguous territories of Russia and China, along the left and right banks of the Amur River (Heilongjiang Province of China, and Amur Oblast′ of Russia), several Precambrian protrusions (Gonzhinsk, Mamynsk, Amurkhe, and Khumakhe) are known. On the Russian territory, along the setting and on the area of the protrusions, lode manifestations, precious-metal deposits, and gold-platinoid placers are known having the industrial imponance. Ultramafites are metasomatically altered more likely by the action of the kate Paleozoic intrusions and produced by them hydrothermae, and are transformed into listvenites. It can be concluded that as one of the sources of precious metals in the placers were the aureoles of listvenitization. This is evidenced by the presence of talc (typomorphic mineral of apoultrabasites) inclusions together with Pt-, Pd- and Ir-bearing gold in the corrosive coatings of the primary platinoids. This conclusion requires the revision of the work strategy of prospecting the lode gold and PGE manifestations within the ore-placer node because apoultrabasites before were considered non-promising for precious metals.     

The Precambrian supercontinent Palaeopangaea: two billion years of quasi-integrity and an appraisal of geological evidence

The Protopangaea-Palaeopangaea model for the Precambrian continental crust predicts quasi-integrity reflecting a dominant Lid Tectonics defined by a palaeomagnetic record showing prolonged near-static polar behaviour during very long time intervals (~2.7–2.2, 1.5–1.2, and 0.75–0.6 Ga). Intervening times show polar loops radiating from the geometric centre of the crust explaining the anomalous Precambrian magnetic inclination bias. The crustal lid was a symmetrical crescent-shaped body confined to a single hemisphere on the globe comparable in form to the Phanerozoic supercontinent (Neo)Pangaea. There were two major transitions in the tectonic regime when prolonged near-static motion was succeeded by widespread tectonic-magmatic activity, and each coincided with the major isotopic/geochemical signatures in the Precambrian record. The first comprised a ~90° reconfiguration of crust and mantle at ~2.2 Ga terminating the long 2.7–2.2 Ga static interval; the second was the largest continental break-up event in geological history and is constrained to the Ediacaran Period at ~0.6 Ga by multiple isotopic and geochemical signatures and the subsidence history of marine passive margins. Break-up of the lid at ~0.6 Ga defines a transition from dominant Lid Tectonics to dominant Plate Tectonics and is the primary cause of contrasts between the Precambrian and Phanerozoic aeons of geological times. The long interval of minimal continental motion in the mid-Proterozoic correlates with extensive emplacement of anorogenic anorthosite-rapakivi plutons unique to these times, and high-level emplacement was probably caused by blanketing of the mantle and comprehensive thermal weakening of the crust. Continental velocities were low during the two Proterozoic intervals characterized by profound glaciation (~2.4–2.2 and ~0.75–0.6 Ga) when partial or complete magmatic shutdown is likely to have reduced volcanic greenhouse gas production. Specific implications of Protopangaea-Palaeopangaea include: (i) support for recent evidence that 60–70% of the present continental crust had accreted by ~2.5 Ga; (ii) recognition from spatially constrained mineral provinces that sub-crustal lithosphere was already chemically differentiated by mid-Archaean times; (iii) strong axial alignment of younger greenstone belts, major Palaeoproterozoic shear zones, and later Meso–Neoproterozoic mobile/orogenic belts; (iv) concentration of anorogenic magmatism and progressive contraction of activity towards the orogenic margin subsequently to become the focus of Grenville (~1.1 Ga) orogenesis; and (v) late Neoproterozoic arc magmatism/tectonics at the instep margin of the continental crescent persisting until the Ediacaran continental break-up.     

Neoarchean Magmatic Events in the Western Songnen Massif,Central Asian Orogenic Belt: Timing and Tectonic Significance

Whether a Neoarchean basement existing in the Songnen massif is currently debated. Identification of Archean magmatism from the Songnen Massif is helpful to resolve this issue. Here, we report newly discovered Neoarchean Shanquan pluton in the Western Songnen Massif. These Neoarchean Shanquan pluton are mainly composed of granites that are exposed near the town of Shanquan in Heilongjiang Province. LA-ICP-MS zircon U-Pb dating reveals that the sample 2015TW1 has an upper intercept age of 2801 ± ...     

Neoproterozoic(750–711 Ma) Tectonics of the South Qinling Belt,Central China: New Insights from Geochemical,Zircon U-Pb Geochronological,and Sr-Nd Isotopic Data from the Niushan Complex

The Xiejiaba and Fuqiangbei plutons form part of the newly identified Neoproterozoic Niushan complex, which is located in the southern South Qinling belt(SQB). The plutons are compositionally similar, were emplaced at 750–711Ma, and provide insights into Neoproterozoic tectonism within the South Qinling belt. The Xiejiaba pluton contains diorite,quartz diorite, granodiorite, and granite phases, all of which are sub-alkaline and have variable major element compositions with negative correlations ...     

Detrital Zircon Geochronology and Provenance of Metasedimentary Rocks from the Susong Complex Zone in the Dabie Orogen

The Susong complex zone is a relatively low-grade metamorphic unit located in the southern part of the Dabie orogen and preserves a variety of metasedimentary rocks, mostly with epidote–amphibolite facies. However, their depositional age, provenance and tectonic setting of sedimentary protolith remain controversial due to the lack of fossils, precise dating and integrated geochemical investigation. This study has conducted whole-rock elemental, and zircon U-Pb SHRIMP dating and Lu-Hf isotope ana...