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1.
Paleoproterozoic orogens of the North Australian Craton are related to the assembly of the Columbia Supercontinent. The roles of the distinct orogens in the Paleoproterozoic craton amalgamation are poorly understood due to the lack of surface exposure. The age and isotopic systematics of detrital zircon grains hosted in Paleoproterozoic sedimentary sequences are used to unravel the geological history of the craton, in terms of paleogeography and tectonic setting. The oldest (Early Paleoproterozoic) metasedimentary units are characterised by detrital zircon ages peaking at ca. 2500 Ma. The zircon εHf values show large variations in the different orogens and range from −18 to +6. The overlaying youngest turbiditic units show minor accumulation of Archean detritus. Units from apparently different metasedimentary sequences have a major detrital zircon age population at ca. 1865 Ma, and a relatively restricted range of zircon εHf values between −7.3 and +2.6. The isotopic distinctiveness of the oldest units is attributed to local variations in the depositional environment, probably due to horst-graben architecture of the early Paleoproterozoic basin. The youngest turbiditic units blanketed this early horst-graben architecture and in part have a local provenance. Potential detritus sources include South Australian Craton, Dharwar Craton and Aravalli-Lesser Himalayan terrains in India, South China, and Madagascar (Africa). This finding indicates that these regions might have been connected before the Columbia Supercontinent was formed. The ubiquitous ca. 2500 Ma magmatic event records the assembly of these cratonic fragments in a previous supercontinent called Kernorland. In addition, the data do not support a proximity of the North Australian Craton with the North China Block, Western Laurentia (North America), and Kaapvaal Craton (Africa) during Columbia amalgamation. 相似文献
2.
We present new data on the highly fractionated Late Triassic I-type Liyuantang granite, which is located in the middle segment of the South Qinling Subzone of central China and is associated with molybdenum mineralization. Zircon U–Pb dating indicates that the granite was emplaced at 210.1 ± 1.9 Ma, with a single zircon containing an inherited core that yielded an age of 449.8 ± 7.1 Ma. Magmatic zircons from the granite have εHf(t) values of − 4.0 to + 1.5, whereas the inherited zircon core has a εHf(t) value of − 5.3. Calculated Hf model ages of crust formation are indicative of substantial contributions from melting of Proterozoic crust that ranges in age from 1501 to 1155 Ma. The granite contains high concentrations of Si, Al, Na, and K, is enriched in Rb, Th, and U, has elevated Rb/Sr and Ga/Al ratios, and is depleted in Ti, Fe, Mn, Mg, Ca, and P, with significantly negative Eu anomalies (δEu = 0.33–0.50), similar to other highly fractionated I-type granites. These data indicate that the magmas that formed the Liyuantang pluton were produced during partial melting of Proterozoic garnet-absent quartz amphibolites. The magmas then fractionated apatite, feldspar, Ti-bearing phases, biotite, and hornblende prior to emplacement.Re–Os isotope analysis of molybdenite from the study area yields a mineralization age of 200.9 ± 6.2 Ma, suggesting that the Liyuantang molybdenum deposit formed during a previously unrecognized mineralization event. The present results, together with previous data, demonstrate that highly fractionated I-type granites associated with the second pulse of magmatism in the South Qinling subzone should be considered highly prospective for mineral exploration, focusing on Triassic–Early Jurassic granitoids. 相似文献
3.
小土尔根是近年来阿尔泰诺尔特盆地发现的首例斑岩铜矿床,其成岩成矿年代学的研究可以对矿床模型构建、区域成矿规律的总结提供制约。矿区侵入岩发育,矿化受花岗闪长斑岩控制,少部分赋存在地层中。文章利用LA-ICP-MS锆石U-Pb测年法对矿区岩体进行了成岩年代学研究。含矿花岗闪长斑岩、黑云二长花岗岩和花岗斑岩中锆石的206Pb/238U年龄的加权平均值分别为(401.0±2.9)Ma、(398.1±2.2)Ma和(400.5±2.0)Ma,为早泥盆世同一岩浆侵入活动形成的不同侵入岩。侵入岩年龄结合凝灰岩年龄,将矿区地层划归早泥盆世诺尔特组。含矿花岗闪长斑岩锆石U-Pb年龄限定小土尔根斑岩铜矿床成矿时代略晚于401 Ma,即矿床形成于早泥盆世。 相似文献
4.
Chen Wanfeng Guo Gang Miao Xiuquan Wang Jinrong Hu Wanlong Zhao Binbin Fan Lifei 《地球科学进展》2016,31(2):180-191
Shanlianglishi Formation strata volcanic rocks are widely distributed in western fault zone of Kalamaili. Studies show that the rocks are basalt, andesite and basaltic andesite, calc-alkaline series with SiO2 content of samples ranging from 49.43% to 59.08%, TiO2 (1.18%~2.49%), P2O5 (0.21%~0.92%) and MgO (3.81%~6.28%). Samples have relatively high HFSE content (Ti, Zr, Y) and also high La/Nb (2.98~1.96), Zr/Y (9.36~4.01) ratio. The primitive mantle normalized trace element spider shows samples enriched LILE (Rb, Ba, K, U) and Pb, but relatively depleted Nb, Ta and Ti. Rare earth element distribution of REE shows slightly enriched LREE, (La/Yb)N=1.93~9.59, and that Eu is weakly negative anomaly (δEu=0.87~0.95). Combined with geochemical characteristics of WPB and VAB. Shanlianglishi Formation strata formed in the stretched after collision environmen. After partial melting of the enriched mantle that was previously metasomatized by the subduction fluid and with participation of the subduction sediment, magma experienced a certain degree of fractional crystallization and contamination by earth crust, and then erupted to form the Shanlianglishi Formation strata volcanic rocks. In eraly Late-Carboniferous, extensional movement was the most intense volcanic activity, which reached its peak in this area. 相似文献
5.
小土尔根是近年来诺尔特地区新发现的斑岩铜矿。矿区内发育花岗斑岩、花岗闪长斑岩、黑云母二长花岗岩,其中与成矿作用密切相关的岩体为花岗闪长斑岩。为了确定矿区侵入岩成因及其与铜矿化的内在关系,对矿区内发育的岩体开展了岩相学和地球化学研究。结果表明,所有岩石富硅和碱,铝含量中等,属高钾钙碱性和钾玄质系列岩石。所有样品富集Rb、Ba等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、Ti、P、Sr和重稀土元素,指示其为同源岩浆分异演化的产物,形成于陆缘弧环境。结合区域地质背景,推测这些岩体是俯冲洋壳发生部分熔融并交代上覆地幔楔后,在上升过程中经分离结晶作用后的产物。与典型的还原性斑岩型铜矿形成条件进行对比研究后,认为小土尔根地区有形成斑岩型矿床的潜力。 相似文献
6.
《Russian Geology and Geophysics》2016,57(5):809-821
We have revealed the spatio-temporal regularities of distribution of platinum group elements (PGE) in basaltoids related to the activity of the Siberian mantle plume. As objects of study, we chose rift and flood basalts from the Norilsk district (sampled from the SD-9 borehole), flood basalts from the central part of the Tunguska syneclise (Lower Tunguska), Kuznetsk Basin traps, and subalkalic basalt from the Semeitau volcanoplutonic structure in eastern Kazakhstan. Based on the PGE patterns of basaltoids related to the activity of the Permo-Triassic Siberian plume, we have shown that the rocks that formed in the central part of the Siberian Large Igneous Province (LIP) at the early rift stage have low contents of PGE, whereas picrites and tholeiitic flood basalts have high contents. The rift (Semeitau structure) and flood (Kuznetsk Basin traps) basalts from the peripheral regions are characterized by extremely low PGE contents. The high PGE contents in magmas of the plume head are responsible for the high productivity of ultramafic-mafic trap magmatism. The elevated K contents in magmas and the high PGE contents in the mantle plume head are probably due to the ascent of deep-seated material from the core-lower-mantle boundary, as follows from the thermochemical model of the Siberian plume. 相似文献
7.
《Journal of Asian Earth Sciences》2007,29(1):127-135
Lower Devonian corals and stromatoporoids have recently been discovered in limestones among low grade metamorphic rocks on the western margin of the Kon Tum Block (South Viet Nam). This unit has been identified as the Cu Brei Formation. Coral and stromatoporoid species have been described including Squameofavosites aff. spongiosus, Parallelostroma cf. multicolumnum, Amphipora cf. rasilis, A. cf. raritalis, Simplexodictyon cf. artyschtense, Stromatopora cf. boriarchinovi and Stromatopora sp. indet. The Cu Brei Formation is exposed in a small area 6 km in length and 3 km wide at the foot of Cu Brei Mountain (Sa Thay District, Kon Tum Province). As this formation is in marine shelf facies it is probable that further exposures of Lower Devonian sediments may be discovered in the Kon Tum Block. This discovery raises the question of the tectonic history of the metamorphic Kon Tum Block. It is possible that the block was not an area of positive uplift from the beginning of Paleozoic as has been supposed, but was submerged in a marine environment, at least on its outer margins, in the Devonian, and possibly even earlier, in Early Paleozoic. 相似文献
8.
阿尔泰山南缘东段玛因鄂博韧性剪切带特征及运动学、动力学分析 总被引：2，自引：0，他引：2
玛因鄂博韧性剪切带位于阿尔泰山南缘额尔齐斯大断裂东段,玛因鄂博断裂以北,带内岩石糜棱岩化强烈,线理、面理构造发育,局部剪切变形明显部位发育S-C组构、σ型和δ型残碎长石斑晶系,均指示为左行韧性剪切变形.带内变形岩石宏、微观特征显示:玛因鄂博韧性剪切带是以压扁变形为主的左行剪切变形,韧性变形深度相当于地壳10～15km深处,温度约300～450℃,压力在0.25～0.40GPa,是一种发生在地壳中-浅构造层次和中-低温度、中等压力条件下的韧性-脆性变形,其变形变质作用相当于中低绿片岩相,局部达高绿片岩相;剪切主应力方向为NEE向,约83°.剪切位移量和剪切带宽度大致相当,总剪切位移量约9.2～11.5km.该韧性剪切带的剪切活动持续时间较长,高峰期为290～270Ma,而其最后结束时间为230Ma左右. 相似文献
9.
Here we examined the light hydrocarbon and nitrogen content and isotopic signatures of eleven gaseous samples in order to evaluate lateral intra-reservoir continuity in a Venezuelan reservoir in the central area of Lake Maracaibo Basin. At least three single compartments, located in the northern-central and southern parts of the reservoir, are revealed by nitrogen concentrations showing clear step-like compositional breaks. The occurrence of step-breaks was also supported by the isotopic signature of individual hydrocarbon compounds in the range of C1–C4 alkanes. Samples presented only slight differences in N2 and hydrocarbon gas compositions within the central and northern parts of the reservoir, and therefore it was not possible to infer structural barriers in coherence with the geological section. Some oil bulk parameters corroborate gradual changes that provide additional information on the reservoir-filling history, thus suggesting that the lateral physical–chemical equilibrium of fluids was not reached in this reservoir. 相似文献
10.
红石金矿床是新疆东天山康古尔塔格金矿带中的代表性矿床之一。通过对其地表、已开采中段及部分钻孔的岩石系统采样分析和计算统计,研究了各指示元素在不同位置的组合特征。结果表明:指示元素中Au、Ag密切相关,其他元素组合复杂多变,反映了成矿成晕的多期性、多阶段特点。结合实际勘查资料,采用多种计算方法,建立了矿床原生晕轴向分带模式,即矿床轴向分带(自上而下)为Bi-Mo-Hg-Zn-Pb-Ag-As-Cu-Sb-Au。利用不同中段的7个分带评价值指标确定了矿体的叠加模型。 相似文献