共查询到20条相似文献，搜索用时 625 毫秒
1.
Kent C.Condie 《地学前缘(英文版)》2018,9(1):51-60
Many geological and geochemical changes are recorded on Earth between 3 and 2 Ga.Among the more important of these are the following:(1)increasing proportion of basalts with"arc-like"mantle sources;(2)an increasing abundance of basalts derived from enriched(EM)and depleted(DM)mantle sources;(3)onset of a Great Thermal Divergence in the mantle;(4)a decrease in degree of melting of the mantle;(5)beginning of large lateral plate motions;(6)appearance of eclogite inclusions in diamonds;(7)appearance and rapid increase in frequency of collisional orogens;(8)rapid increase in the production rate of continental crust as recorded by zircon age peaks;(9)appearance of ophiolites in the geologic record,and(10)appearance of global LIP(large igneous province)events some of which correlate with global zircon age peaks.All of these changes may be tied directly or indirectly to cooling of Earth's mantle and corresponding changes in convective style and the strength of the lithosphere,and they may record the gradual onset and propagation of plate tectonics around the planet.To further understand the changes that occurred between 3 and 2 Ga,it is necessary to compare rocks,rock associations,tectonics and geochemistry during and between zircon age peaks.Geochemistry of peak and inter-peak basalts and TTGs needs to be evaluated in terms of geodynamic models that predict the existence of an episodic thermal regime between stagnant-lid and plate tectonic regimes in early planetary evolution. 相似文献
2.
Parampreet Kaur Naveen Chaudhri I. Raczek A. Kröner A.W. Hofmann M. Okrusch 《Gondwana Research》2011,19(4):1040-1053
The Khetri region forms a late Palaeoproterozoic igneous–metamorphic complex in NE Rajasthan, India. Seven granitoid plutons of the Khetri complex have been studied for zircon U–Pb and Pb–Pb dating along with whole-rock and Nd–Sr isotope geochemistry to provide new constraints on the Palaeoproterozoic magmatic activity in the Aravalli orogen of northwestern India. Most intrusives show evidence of moderate to extreme albitisation forming microcline–albite granite and albite granite, respectively. The rocks are metaluminous to weakly peraluminous, largely ferroan and intraplate A-type granites. The U–Pb zircon ages for four plutons cover a time span of 1732–1682 Ma, whereas Pb–Pb zircon evaporation data for three intrusives indicate minimum emplacement ages between 1671 and 1537 Ma. The Nd–Sr isotopic systematics suggest the involvement of Neoarchaean to Palaeoproterozoic crustal components in the petrogenesis of these granitoids. A regional survey of late Palaeoproterozoic ages in the Aravalli orogen provides evidence for a geographically widespread extension-related event in the northwestern Indian shield about 1720–1700 Ma ago. The record of comparable ages and the magmatic history reported in parts of North America and the North China Craton may indicate the significance of this event for the rift tectonics of the hypothetical supercontinent Columbia. 相似文献
3.
Evine Laure Tanko Njiosseu Jean-Paul Nzenti Théophile Njanko Badibanga Kapajika Anne Nédélec 《Comptes Rendus Geoscience》2005,337(6):551-562
The central domain of the Pan-African Belt in Cameroon is characterized by abundant porphyritic granitoids, which were emplaced synkinematically and variably orthogneissified in relation with ENE-striking steeply dipping transcurrent shear zones. These plutonic rocks have intermediate to felsic compositions and constitute a high-K calk-alkaline series. Conventional UPb zircon dating yields an age of 618 Ma for this syntectonic Pan-African magmatism in the Tonga area. The country rocks are made of metabasites (garnet amphibolites) and tonalitic to trondhjemitic gneisses, which suffered two distinct orogenic cycles: the first one is the Palaeoproterozoic Eburnean–Transamazonian cycle at 2.1 Ga and the second one is the Pan-African orogenesis. These new ages confirm the existence of an extensive Palaeoproterozoic crust in Cameroon and question the areal extent of the Congo–São Francisco craton towards the north. To cite this article: E.L. Tanko Njiosseu et al., C. R. Geoscience 337 (2005). 相似文献
4.
A.M. Mloszewska S.J. Mojzsis E. Pecoits D. Papineau N. Dauphas K.O. Konhauser 《Gondwana Research》2013,23(2):574-594
Analyses of chemical sedimentary precipitates such as banded iron formation (BIF) provide a direct means to explore the nature and composition of the early hydrosphere. The recently discovered > 3750 Myr old Nuvvuagittuq Supracrustal Belt (NSB) in the Northeast Superior Province (Québec, Canada) hosts a suite of iron oxide-rich (± pyroxene and amphibole) units that are interpreted to be the metamorphosed equivalents of Fe oxide-facies BIF, and a collection of BIF-like Ca–Fe–Mg silicate rocks. The NSB rocks provide a rare glimpse of trace metal availability in Eoarchean (ca. 3800 Ma) seawater. As they may be contemporaneous with the relatively well-studied Isua Supracrustal Belt of southern West Greenland, their comparison provides an opportunity to enhance our basic understanding of the Eoarchean oceans at a global scale. Work since the initial discovery of the NSB in 2001 has established the basic lithological, geochemical and petrographic characteristics of these BIF and BIF-like rocks. Here we review the current state of knowledge of NSB rocks of probable chemical sedimentary origin, including aspects of their geology, likely origin and age. We conclude by examining the implications of results thus far for our understanding of early seawater compositions, and for the emergence of life in the context of early metallo-enzyme evolution. 相似文献
5.
J.-M. Garnier C. Hurel J. Garnier V. Lenoble C. Garnier K.M. Ahmed J. Rose 《Applied Geochemistry》2011,26(9-10):1665-1672
6.
Ancient crustal rocks provide the only direct evidence for the processes and products of early Earth differentiation. SHRIMP
zircon U-Th-Pb dating has identified, amongst the Acasta gneisses of the western Slave Province, Canada, two metatonalites
and a metagranodiorite that have igneous ages of 4002 ± 4, 4012 ± 6 and 4031 ± 3 Ga respectively. These are the first identified
Priscoan terrestrial rocks. A record of metamorphic events at ∼3.75, ∼3.6 and ∼1.7 Ga also is preserved. These discoveries
approximately double, to ∼40 km2, the area over which ∼4.0 Ga gneisses are known to occur. A single older zircon core in one sample suggests that rocks as
old as 4.06 Ga might yet be found in the region. As early as 4.03 Ga, terrestrial differentiation was already producing tonalitic
magmas, probably by partial melting of pre-existing, less differentiated crust.
Received: 28 February 1997 / Accepted: 9 July 1998 相似文献
7.
This paper reports in situ observations on barite (0 0 1) surface dissolution behavior in 0.1–0.001 M NaCl solutions at 30 °C using atomic force microscopy (AFM). The step retreating on barite (0 0 1) surfaces changed with increasing NaCl solution concentrations. In solutions with a higher NaCl concentration (⩾0.01 M), many steps showed curved or irregular fronts during the later experimental stage, while almost all steps in solutions with a lower NaCl concentration exhibited straight or angular fronts, even during the late stage. The splitting phenomenon of the initial 〈h k 0〉 one-layer steps (7.2 Å) into two half-layer steps (3.6 Å) occurred in all NaCl solutions, while that of the initial [0 1 0] one-layer steps observed only in the 0.1 M NaCl solution. The step retreat rates increased with an increasing NaCl solution concentration. We observed triangular etch pit and deep etch pit formation in all NaCl solutions, which tended to form late in solutions with lower NaCl concentrations. The deep etch pit morphology changed with increasing NaCl solution concentrations. A hexagonal form elongated in the [0 1 0] direction was bounded by the {1 0 0}, {3 1 0}, and (0 0 1) faces in a 0.001 M NaCl solution, and a rhombic form was bounded by the {5 1 0} and (0 0 1) faces in 0.01 M and 0.1 M NaCl solutions. An intermediate form was observed in a 0.005 M NaCl solution, which was defined by {1 0 0}, a curved face tangent to the [0 1 0] direction, {3 1 0}, and (0 0 1) faces: the intermediate form appeared between the hexagonal and rhombic forms in solutions with lower and higher NaCl concentrations, respectively. The triangular etch pit and deep etch pit growth rates also increased with the NaCl solution concentration. Combining the step and face retreat rates in NaCl solutions estimated in this AFM study as well as the data on the effect of water temperature on the retreat rates reported in our earlier study, we produced two new findings. One finding is that the retreat rates increase by approximately two-fold when the NaCl solution concentration increases by one order of magnitude, and the other finding is that the retreat rate increase due to a one order of magnitude increase in the NaCl concentration corresponds to an increase of approximately 8 °C in water temperature. This correlation may help to understand and evaluate increasing dissolution kinetics induced by the different mechanisms where barite dissolution is promoted by the catalytic effect of Na+ and Cl− ions (through an increase in the NaCl solution concentration) or by an increase in the hydration of Ba2+ and SO42− (through an increase in water temperature). 相似文献
8.
一、对我国石油天然气工业发展历史、现状、前景的评估 1、世界天然气工业,从50年代以来迅速发展。1950年世界剩余探明储量为8.5万亿m~3,1988年初已达111.9万亿m~3。其探明储量大约每十年翻一番。据十二届世界石油大会(1987年,美国休斯敦)资料介绍,尚可寻找的储量为119万亿m~3。以目前年产约1.5～1.8万亿m~3(有人预测2020年年产可达2.0万亿m~3)计算,世界天然气储量可维持开采100年以上。从全球来看,在可望的未来,天然气仍是不可替代的重要能源和化工原料。天然气工业仍处于蓬勃发展的趋势。 相似文献
9.
10.
11.
Denis Thiéblemont Christine Flehoc Michel Ebang-Obiang Christophe Rigollet Jean-Pierre Prian François Prognon 《Comptes Rendus Geoscience》2013,345(7-8):272-283
We present new 14C data on charcoal fragments recovered from the lower (coarse-grained Stone Line) and upper (fine-grained Cover Horizon) portions of surficial formation profiles in Gabon. These data and others compiled from the literature enable a reconstruction of the Upper Holocene geological regional history of Gabon. The connection between the geological events recorded in the surficial formations and the Upper Holocene environmental crisis is discussed and a scenario connecting geological events with climatic and environmental changes is proposed. Such a scenario suggests that following the climatic crisis, the reconstitution of soils by aeolian sedimentation could have been an important factor of Bantu expansion. 相似文献
12.
W. David SINCLAIR 《地质学报》2014,88(Z2):463-465
Please refer to the attachment(s) for more details. 相似文献
13.
14.
15.
16.
Acta Geochimica - Kyanite is an important and slow-dissolving mineral. Earlier work has measured its dissolution rate at high temperature and acidic pH, but experimental measurements at low... 相似文献
17.
The Gangbian alkaline complex in the southeastern Yangtze Block (South China) is composed of Si-undersaturated pyroxene syenites and Si-saturated to -oversaturated syenites and quartz monzonites. SIMS zircon U–Pb analyses indicate that the complex was emplaced at 848 ± 4 Ma, during a previously-recognized interval of magmatic quiescence between the ca 1.0–0.89 Ga Sibaoan orogenic magmatism and the ca 0.83–0.78 Ga magmatic flare-up. The Gangbian rocks are characterized by wide, coherent variations in major and trace elements (SiO2 = 47.6–68.4%, K2O + Na2O = 4.5–10.5%, K2O/Na2O = 0.4–1.2, MgO = 1.2–8.5%, Cr = 4.5–239 ppm, and Ni = 4.5–143 ppm) and by enrichment in LIL and LREE and depletion in Nb, Ta and P in trace element spidergrams. Their whole-rock εNd(T) (? 6.5 to ? 0.4) and εHf(T) (? 10.7 to 0.4) are positively correlated, suggesting involvement of both metasomatized mantle and continental crust materials in their genesis. In situ zircon Hf–O isotopic measurements for the most evolved quartz monzonite sample yield a binary mixing trend between the mantle- and supracrustal-derived melts. It is suggested that the pyroxene syenites were derived by partial melting of metasomatized, phlogopite-bearing lithospheric mantle, and the parental magma experienced extensive fractionation of pyroxene and olivine associated with varying degrees of crustal contamination. Subsequent fractional crystallization of hornblende and minor amounts of plagioclase from the alkali basaltic magmas, accompanied by crustal contamination, produced the Si-saturated to -oversaturated syenites and quartz monzonites. These ca. 0.85 Ga alkaline rocks and neighboring contemporaneous dolerite dykes are the products of the anorogenic magmatism after the Sibao Orogeny. They post-date the final amalgamation between the Yangtze and Cathaysia Blocks, most likely manifesting the initial rifting of South China within the Rodinia supercontinent. 相似文献
18.
《地学前缘(英文版)》2022,13(2):101138
In paleogeographic reconstructions of the Columbia and Rodinia Supercontinents, the position of the Greater India landmass is ambiguous. This, coupled with a limited understanding of the tectonic evolution of the mobile belts along which the mosaic of crustal domains in India accreted, impedes precise correlation among the dispersed crustal fragments in supercontinent reconstructions. Using structural, metamorphic phase equilibria, chronological and geochemical investigations, this study aims to reconstruct the tectonic evolution of the Chottanagpur Gneiss Complex (CGC) as a distinct crustal block at the eastern end of the Greater Indian Proterozoic Fold Belt (GIPFOB) along which the North India Block (NIB) and the South India Block (SIB) accreted. The study focuses on two issues, e.g. dating the Early Neoproterozoic (0.92 Ga) accretion of the CGC with the NIB contemporaneous with the assembly of Rodinia, and documenting the widespread (>24,000 km2) plutonism of 1.5–1.4 Ga weakly peraluminous, calc-alkalic to alkali-calcic and ferroan A-type granitoids (± garnet) devoid of mafic microgrannular enclaves and coeval mafic emplacements in the crustal block. These dominantly within-plate granitoids arguably formed by asthenospheric upwelling induced partial melting of garnet-bearing anatectic quartzofeldspathic gneisses that dominate the Early Mesoproterozoic basement of the block. The major and trace element chemistry of the granitoids is similar to the 1.35–1.45 Ga A-type granitoids in Laurentia/Amazonia emplaced contemporaneous with the 1.5–1.3 Ga breakup of the Columbia Supercontinent.This study suggests the Chottanagpur Gneiss Complex occured as a fragmented crustal block following the breakup of the Columbia Supercontinent; the crustal block was subsequently integrated within India during the Early Neoproterozoic oblique accretion between the NIB and SIB contemporaneous with the Rodinia Supercontinent assembly. 相似文献
19.
The newly-discovered Shiyaogou molybdenum deposit is located in the eastern Qinling metallogenic belt in central China. The deposit contains at least 152,000 t of Mo metal and bears typical porphyry-type features in terms of its concentric alteration zonation, quartz vein-hosted Mo mineralization, veining sequence and the spatial association with concealed granite porphyries. Re–Os isotope analyses of molybdenite from the deposit yield an ore-forming age of 132.3 ± 2.8 Ma. LA-ICP-MS U–Pb zircon dating of ore-related porphyries yields crystallization ages from 135 Ma to 132 Ma, indicating a temporal link between granitic magmatism and Mo mineralization. A population of captured magmatic zircons indicates another pulse of magmatism at ~ 143 Ma. A barren granite intrusion near the deposit gives a zircon U–Pb age of 148.1 ± 1.1 Ma. These magmatic activities were concurrent with the emplacement of the nearby Heyu granitic batholith, a largely ore-barren intrusive complex formed from ~ 148 Ma to ~ 127 Ma. Zircon Ce4 +/Ce3 + ratios of ore-related porphyries are obviously higher than those of contemporaneous barren granitoids, implying an affinity between Mo mineralization and highly oxidized magmas. Moreover, zircons from these granitoids overall have decreasing Ce4 +/Ce3 + ratios from 148 Ma to 132 Ma, reflecting decreasing oxygen fugacities during magma evolution. Available geological, radiometric and stable isotopic evidence suggests that the decrease of magma oxygen fugacity was probably associated with an increase of mantle contribution to granitic magmatism and metallogenesis, which probably gave rise to successive mineralization of Mo and Au in the eastern Qinling. The intense magmatic–metallogenic events in the eastern Qinling during Late Jurassic to Early Cretaceous times are interpreted as a response to the large-scale lithosphere thinning and subsequent asthenosphere upwelling beneath the eastern part of the North China Craton. 相似文献
20.
《地学前缘(英文版)》2022,13(6):101431
Melt inclusions in kimberlitic minerals and diamonds indicate that chlorides are important constituents of mantle carbonatite melts. Besides, alkaline chlorides are important constituents of saline high-density fluids (HDFs) found in diamonds from kimberlites and placers around the world. Continuous compositional variations suggest that saline and carbonatitic HDFs could be genetically linked. However, the essence of this link remains unclear owing to the lack of data on phase relations in the chloride-carbonate systems under pressure. Here we studied subsolidus and melting phase relations in the system NaCl–CaCO3–MgCO3 at 6 GPa and 1000–1600 °C using a Kawai-type multianvil press. We found that at 1000 °C, subsolidus assemblage consists of halite, magnesite, and aragonite. At higher temperatures, the stabilization of dolomite splits the subsolidus area into two partial ternary fields: halite + magnesite + dolomite and halite + dolomite + aragonite. The minimum on the liquidus surface corresponds to the halite-dolomite-aragonite ternary eutectic, situated at 1100 °C. The eutectic melt has Ca# 89 and contains 30 wt.% NaCl (26 mol% 2NaCl). The system has two ternary peritectics: halite + dolomite = magnesite + liquid located near the ternary eutectic and magnesite + dolomite = Mg-dolomite + liquid situated between 1300 and 1400 °C. Although under dry conditions incipient melting yields carbonate-dominated melt, the addition of water facilitates the fusion of NaCl and expands the liquid field to NaCl-rich compositions with up to 70 wt.% NaCl. The obtained results favor the idea that hydrous saline melts/fluids (brines) found as inclusions in diamonds could be a lower temperature derivative of mantle carbonatite melts and disagree with the hypothesis on chloride melt generation owing to the chloride-carbonate liquid immiscibility since no such immiscibility was established. We also studied the interaction of the NaCl–CaCO3–MgCO3 system with iron metal and found that carbonate reduction produces C-bearing species (Fe0, Fe-C melt, Fe3C, Fe7C3, C0) and wüstite containing Na2O, CaO, and MgO. Besides, a carbonate chloride compound, Ca2Cl2CO3, was established among the reaction products. The interaction between NaCl-bearing carbonate melt shifts its composition toward Mg-poor and NaCl-rich. Given the above, an alternative hypothesis can be proposed, according to which the interaction of alkaline chloride-bearing carbonate melts formed in the subduction zones with the reduced mantle should be accompanied by diamond crystallization and shift the composition of the melt from carbonatitic to alkali-rich saline. 相似文献