关于华北元古宙富钾、富稀土沉积岩是白云鄂博大型稀土矿床矿源层的讨论

文章对大连、北京元古宙沉积岩及白云鄂博稀土矿围岩的岩石化学成分、独居石形态和稀土元素特征等进行了分析与总结,结果显示三者特征相似.因此认为白云鄂博的稀土矿不是来自地幔岩而是源于大陆增生,华北元古宙富钾、富稀土沉积岩可能是白云鄂博巨型稀土矿的矿源层.文章还提出了一个白云鄂博稀土矿的理想大陆增生成矿模式图.     

Pb-Pb age of Jatulian carbonate rocks: The Tulomozero Formation of southeast Karelia

The U-Pb systematics of 25 carbonate samples collected from the Upper Jatulian Tulomozero Formation in southeastern area of the Baltic shield has been studied. The U-Pb systems of Jatulian carbonates metamorphosed here under conditions of the greenschist facies likely have not been reset completely. Samples have been collected from core sections recovered by drilling 60 to 70 km apart from each other in western and eastern areas of the Onega Lake region. In majority, the rocks sampled characterize a thick upper member of the Tulomozero Formation, and a few samples have been collected in addition from its middle and lower members. The analyzed dolomitic rocks (Mg/Ca=0.60–0.68) have variable Mn (54–1450 ppm) and Sr (31–438 ppm) concentrations. Powdered dolomite samples have been treated preliminary in 1 N solution of ammonium acetate in order to get material for analysis enriched in pre-metamorphic carbonate phases in terms of U-Pb systematics. Five samples have been subjected to stepwise dissolution in 0.5 N HBr to analyze their carbonate phases L-1, L-2, L-3 and siliciclastic fraction for getting a deeper insight into the U-Pb systematics. The U-Pb characteristics of carbonate and siliciclastic fractions suggest deposition of studied carbonate sediments in two different paleobasins. In addition, they show for same samples the partial Pb redistribution between carbonate and siliciclastic components in the course of metamorphism and Pb gain from allogenic metamorphic fluids. The Pb-Pb date of 2090 ± 70 Ma (MSWD = 2.0) is estimated for the least altered dolomite samples from upper member of the Tulomozero Formation, which represent marine sediments of a paleobasin and contain a minimum of siliciclastic material, being the least-contaminated by gained Pb. The date obtained is well consistent with U-Pb and Sm-Nd ages established for the Jatulian volcanogenic rocks in northern and western areas of the Baltic shield.     

Neoproterozoic India within East Gondwana: Constraints from recent geochronologic data from Himalaya

Recent geochronologic data of detrital zircons and neodymium isotopic signatures of the Himalaya, Arabian–Nubian Shield, and Western Australia–East Antarctica (the Pinjarra Orogen/Circum-East Antarctic Orogen) are assessed to estimate the location of Neoproterozoic basement of the Himalaya.

The protolith of the Higher Himalayan Gneisses is considered to have been derived from the Pinjarra Orogen/Circum-East Antarctic Orogen of Western Australia–East Antarctica, and not from the Indian Craton to the south. This conclusion strongly suggests the juxtaposition of the Indian Craton, which forms the basement of the Himalaya, with the Circum-East Antarctic Orogen during the Neoproterozoic when the protolith of the Higher Himalayan Gneisses deposited.     

内蒙古拜仁达坝维拉斯托 超大型银铅锌矿的发现及找矿意义

大兴安岭中南段西坡新近发现的拜仁达坝维拉斯托超大型银铅锌矿,是内蒙古地矿局最新勘查成果,也是自20世纪50年代开展物化探工作以来,应用综合物化探方法找到超大型矿床的典型案例。拜仁达坝矿区银的远景规模大于8000t,铅锌远景规模可达300万t;维拉斯托矿区银的远景规模大于2000t,铅锌铜可达300万t。两矿区可能会发展成为超大型银多金属矿田。为大兴安岭中南段地质矿产勘查和矿产资源评价开创了美好的前景。     

Rb-Sr, K-Ar, H-and O-Isotope systematics of the Middle Riphean shales from the Debengda Formation, the Olenek Uplift, North Sibera

Clay subfractions (SFs) of <0.1, 0.1–0.2, 0.2–0.3, 0.3–0.6, 0.6–2 and 2–5 μm separated from Middle Riphean shales of the Debengda Formation are studied using the TEM, XRD, K-Ar and Rb-Sr isotopic methods. The oxygen and hydrogen isotope compositions in the SFs are studied as well. The low-temperature illite-smectite is dominant mineral in all the SFs except for the coarsest ones. The XRD, chemical and isotopic data imply that two generations of authigenic illite-smectite different in age are mixed in the SFs. The illite crystallinity index decreases in parallel with size diminishing of clay particles. As compared to coarser SFs, illite of fine-grained subfractions is enriched in Al relative to Fe and Mg, contains more K, and reveals higher K/Rb and Rb/Sr ratios. The Rb-Sr age calculated by means of the leachochron (“inner isochron”) method declines gradually from 1254-1272 Ma in the coarsest SFs to 1038-1044 Ma in finest ones, while the K-Ar age decreases simultaneously from 1225–1240 to 1080 Ma. The established positive correlation of δ¹⁸O and δD values with dimensions of clay particles in the SFs seems to be also consistent with the mixing systematics. The isotopic systematics along with data on mineral composition and morphology lead to the conclusion that mixedlayer illite-smectite was formed in the Debengda shales during two periods 1211–1272 and 1038–1080 Ma ago. The first period is likely close to the deposition time of sediments and corresponds to events of burial catagenesis, whereas the second one is correlative with the regional uplift and changes in hydrological regime during the pre-Khaipakh break in sedimentation.     

Tectonostratigraphy and base-metal mineralization controls, Aravalli province (western India): New interpretations from geophysical data analysis

Analysis and synthesis of multi-disciplinary geoscience information from geological literature/maps and from digitally-processed aeromagnetic and gravity data pertinent to the Aravalli province were carried out to address some hitherto unresolved questions about the tectonostratigraphy of this Archaean–Proterozoic metallogenic province. Based on the magnetic anomalies, several tectonic domains were identified. These domains, bounded by regional-scale geophysical lineaments, have distinct crustal, lithological, metamorphic, and metallogenic characteristics and correlate broadly with lithostratigraphic belts identified by several earlier workers. New interpretations on the tectonostratigraphy and the base-metal mineralization controls in the Aravalli province are as follows. The Hindoli sequences, in the eastern parts of the province, constitute an independent Palaeo–Proterozoic tectonic domain and do not form part of the Archaean basement complex. The base-metal-bearing metasedimentary enclaves in the central parts of the province also constitute an independent Palaeo–Proterozoic tectonic domain, which is quite distinct from the surrounding (basement complex?) rocks. The base-metal-bearing metavolcano-sedimentary sequences in the western parts of the province constitute an independent Neo–Proterozoic tectonic domain. The base-metal deposits in the province are spatially associated with the regional-scale lineaments and with the mafic metavolcanic rocks deduced from the aeromagnetic data. The regional-scale lineaments, which possibly represent Proterozoic crustal-scale faults, are plausible structural controls on the base-metal mineralization in the province. The mafic metavolcanic rocks are plausible heat-source controls on the SEDEX- and/or VMS-type base-metal mineralizations and are possible metal-source controls on the VMS-type base-metal mineralization in the province.     

The Rayner Complex of East Antarctica: complex isotopic systematics within a Proterozoic mobile belt

Abstract New isotopic (Rb–Sr, U–Pb zircon and Sm–Nd) and petrological data are presented for part of an extensive Proterozoic mobile belt (locally known as the Rayner Complex) in East Antarctica. Much of the belt is the product of Mid-Proterozoic (∼ 1800–2000 Ma) juvenile crustal formation. Melting of this crust at about 1500 Ma ago produced the felsic magmas from which the dominant orthogneisses of this terrain were subsequently derived. Deformation and transitional granulite-amphibolite facies conditions (which peaked at 750 ± 50°C and 7–8 kbar (0.7–0.8 GPa) produced open to tight folding about E–W axes and syn-tectonic granitoids about 960 Ma ago. Subsequent felsic magmatism occurred at about 770 Ma and not, as has been widely advocated, at 500–550 Ma, which appears to have been a time of widespread upper greenschist facies (400–500°C) metamorphism, localized shearing and faulting. Sm-Nd model ages of 1.65–2.18 Ga disprove a previously favoured hypothesis that the Rayner Complex mostly represents reworked Archaean rocks from the neighbouring craton (Napier Complex). Models that involve rehydration of the Napier Complex are no longer required, since the Rayner Complex was its own source of water. Two episodes of Proterozoic crustal growth are identified, the later of which occurred between about 1200 Ma and 1000 Ma, and was relatively minor. Sedimentation took place only shortly before Late Proterozoic orogenesis. The multiphase history of the Rayner Complex has resulted in complex isotopic behaviour. Three temporally discrete episodes of Pb loss from zircon have been identified, the earliest two of which are responses to the c. 960 Ma and 540 Ma tectonothermal events. Fluid leaching was operative during the later event for there is a good correlation between degree of isotopic discordance and secondary mineral growth. Pb loss during the high-grade event was probably governed by the same process or by lattice annealing. Some zircon suites also document recent Pb loss. Most lower concordia intercepts have no direct geological meaning and are explicable as mixed ages produced by incomplete Pb loss during two or more secondary events. Whereas all zircon separates from the orthogneisses produce U–Pb isotopic alignments, zircons from the only analysed paragneiss produce scattered data, in part reflecting a range of provenance. The 960 Ma event was also associated with the growth of a characteristically low U zircon (∼ 300 μg/g) in rocks of inferred high Zr content. There is ubiquitous evidence for the resetting of Rb–Sr total-rock isochrons. Even samples separated by up to 10 km fail to produce igneous crystallization ages. Minor mineralogical changes produced by the 540 Ma upper greenschist-facies metamorphism were sufficient to almost completely reset some Rb–Sr isochrons and to produce open system conditions on outcrop scale, at least in one location.     

石鼓群的划分及变质特征探讨

石鼓群位于云南西北部,面积约1 600km2,为甘孜一理塘板块的结晶基底.据现有资料,分为古元古代黎明岩群、中元古代新主岩群、新元古代巨甸岩群.黎明岩群为云母石英片岩、云母片岩,夹斜长片麻岩、斜长角闪岩.泥质岩石中具铁铝榴石、十字石、蓝晶石组合,基性岩中具铁铝榴石、普通角闪石组合,为中压低角闪岩相.黎明岩群后期抬升减压,叠加低压低角闪岩相变质,新生红柱石,部分原生蓝晶石退变成红柱石.于侵入其中的斜长角闪岩中获得Nd同位素模式年龄1 369.8Ma和1 343.8Ma,绿泥石英片岩中获得1 896.6Ma和2 161MaNd同位素模式年龄,故将黎明岩群时代置于古元古代.新主岩群分哈吉洛岩组和路西岩组,岩性为云母石英片岩、云母片岩、大理岩夹片麻岩及斜长角闪岩,部分岩石具糜棱岩化.哈吉洛岩组为低压低角闪岩相,具红柱石、十字石、铁铝榴石组合,路西岩组为高绿片岩相.于侵入新主岩群中的变质变形花岗质岩脉中获得锆石铅同位素年龄811 ±2Ma、820±1Ma、823±1Ma,故将新主岩群时代置于中元古代.巨甸岩群分陇巴岩组和塔城岩组,岩性为千枚岩、板岩,夹一层变质杏仁状玄武岩,为低绿片岩相.     

北祁连山西段螯油沟蛇绿岩SHRIMP分析结果及其地质意义

本文通过对北祁连山西段熬油蛇绿岩中辉绿岩岩墙的锆石SHRIMP法年龄 的测定，确定出熬油的沟蛇绿岩形成于中元古代早期（约1777Ma)，这是迄今为止我国发现的最古老的蛇绿岩。该年龄测定的结果还暗示了本区在1466Ma和507Ma各有一次地质事件，前者可能代表了中元古代早期的洋盆闭合的下限年龄，后者代表一次加里东期区域变质事件，并且本区可能还存在未出露的新太古结晶基底（2561Ma)。     

辽宁太子河盆地元古宙—古生代层序地层

太子河盆地元古宇-古生界划分为23个三级层序,归并为3个二级超层序,分别命名为偏岭超层序(Qn)、太子河超层序(∈-O)和牛心台超层序(C-P).本文对各层序的特征、界面性质、沉积相和相序等作了较详细的描述;对石炭-二叠纪陆相地层,尝试使用不同于海相地层的层序地层学术语;对太子河盆地的演化阶段及其特征作了划分和总结.这是首次对太子河盆地进行的层序地层学研究.