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1.
O. M. Turkina L. N. Urmantseva N. G. Berezhnaya S. L. Presnyakov 《Stratigraphy and Geological Correlation》2010,18(1):16-30
The Early Precambrian granulite-gneiss complex of the Irkut Block (Sharyzhalgai salient of the Siberian Craton basement) with
the protoliths represented by a wide range of magmatic and sedimentary rocks, has a long-term history including several magmatic
and metamorphic stages. To estimate the age of sedimentation and metamorphism of the terrigenous deposits, the composition
of the garnet-biotite, hyper-sthene-biotite, and cordierite-bearing gneisses has been studied; their isotopic Sm-Nd values
have been revealed; and the U-Pb zircon dating has been performed using the SHRIMP II ion microprobe. The protoliths of the
terrigenous sediments metamorphosed under conditions of the granulite facies correspond to a rock series from siltstones and
graywackes to pelites. The Nd model ages of paragneisses range from 2.4 to 3.1 Ga. Zircons of the cordierite-bearing and hypersthene—biotite
gneisses show the presence of cores and rims. The clastic, smoothed, and irregular shape of the cores indicates their detrital
character and relicts of oscillatory zoning suggest the magmatic origin of zircon. The rim’s metamorphic genesis is indicated
by the lack of zoning and by the lower Th/U ratio compared to that of the cores. The age of the detrital cores (≥2.7, ~2.3,
and 1.95—2.0 Ga) and metamorphic rims (1.85–1.86 Ga) defines the time of sedimentation at 1.85–1.95 Ga ago. Potential sources
for the Archean detrital zircons were metamagmatic rocks of the granulite—gneiss complexes in the southwestern margin of the
Siberian Craton. The age of the dominant detrital cores at 1.95–2.0 Ga ago, together with the minimal TNd(DM) values, indicates the contribution of the juvenile Paleoproterozoic crust to the formation of sediments. The juvenile
Paleoproterozoic crust was likely represented by magmatic complexes similar to the volcanic and granitoid associations of
the Aldan shield, which were formed 1.99–2.0 Ga ago and showthe model age of 2.0—2.4 Ga. The isotopic Sm-Nd data show that
the Late Paleoproterozoic metasedimentary rocks occur not only in the Sharyzhalgai salient but in the Aldan and Anabar shields
of the Siberian Craton as well. 相似文献
2.
The eastern margin of the East European Craton (EEC) has a long lasting geological record of Precambrian age. Archaean and Proterozoic strata are exposed in the western fold-and-thrust belt of the Uralides and are known from drill cores and geophysical data below the Palaeozoic cover in the Uralides and its western foredeep. In the southern Uralides, sedimentary, metamorphic and magmatic rocks of Riphean and Vendian age occur in the Bashkirian Mega-anticlinorium (BMA) and the Beloretzk Terrane. In the eastern part of the BMA (Yamantau anticlinorium) and the Beloretzk Terrane, K-Ar ages of the <2-µm-size fraction of phyllites (potassic white mica) and slates (illite) give evidence for a complex pre-Uralian metamorphic and deformational history of the Precambrian basement at the southeastern margin of the EEC. Interpretation of the K-Ar ages considered the variation of secondary foliation and the diagenetic to metamorphic grade. In the Yamantau anticlinorium, the greenschist-facies metamorphism of the Mesoproterozoic siliciclastic rocks is of Early Neoproterozoic origin (about 970 Ma) and the S1 cleavage formation of Late Neoproterozoic (about 550 Ma). The second wide-spaced cleavage is of Uralian origin. In the central and western part of the BMA, the diagenetic to incipient metamorphic grade developed in Late Neoproterozoic time. In post-Uralian time, Proterozoic siliciclastic rocks with a cleavage of Uralian age have not been exhumed to the surface of the BMA. Late Neoproterozoic thrusts and faults within the eastern margin of the EEC are reactivated during the Uralian deformation. 相似文献
3.
Ivashchenko V. I. Bushmin S. A. Ruchyev A. M. Kornakov A. S. Bogomolov E. S. Savva E. V. Ivanov M. V. Tytyk V. M. Frolov P. V. 《Doklady Earth Sciences》2018,480(2):804-809
One unsolved problem of Archean metallogeny of the Russian part of the Fennoscandian Shield is related to the period of formation of orogenic gold deposits, the age of which was previously considered Early Proterozoic. Comprehensive studies identified the complex evolution of ores from the Novye Peski deposit and the first Neoarchean Sm–Nd isochron isotopic age (2583 ± 16 Ma) of the formation of orogenic gold of the Karelian Craton. A significant positive εNd(t) value of +4.7 of gold-bearing metasomatites probably points to the link between the ore-forming fluid and the deep mantle source.
相似文献4.
J. L. Payne M. Hand K. M. Barovich B. P. Wade 《Australian Journal of Earth Sciences》2013,60(5):623-640
LA-ICPMS U–Pb data from metamorphic monazite in upper amphibolite and granulite-grade metasedimentary rocks indicate that the Nawa Domain of the northern Gawler Craton in southern Australia underwent multiple high-grade metamorphic events in the Late Paleoproterozoic and Early Mesoproterozoic. Five of the six samples investigated here record metamorphic monazite growth during the period 1730–1690 Ma, coincident with the Kimban Orogeny, which shaped the crustal architecture of the southeastern Gawler Craton. Combined with existing detrital zircon U–Pb data, the metamorphic monazite ages constrain deposition of the northern Gawler metasedimentary protoliths to the interval ca 1750–1720 Ma. The new age data highlight the craton-wide nature of the 1730–1690 Ma Kimban Orogeny in the Gawler Craton. In the Mabel Creek Ridge region of the Nawa Domain, rocks metamorphosed during the Kimban Orogeny were reworked during the Kararan Orogeny (1570–1555 Ma). The obtained Kararan Orogeny monazite ages are within uncertainty of ca 1590–1575 Ma zircon U–Pb metamorphic ages from the Mt Woods Domain in the central-eastern Gawler Craton, which indicate that high-grade metamorphism and associated deformation were coeval with the craton-scale Hiltaba magmatic event. The timing of this deformation, and the implied compressional vector, is similar to the latter stages of the Olarian Orogeny in the adjacent Curnamona Province and appears to be part of a westward migration in the timing of deformation and metamorphism in the southern Australian Proterozoic over the interval 1600–1545 Ma. This pattern of westward-shifting tectonism is defined by the Olarian Orogeny (1600–1585 Ma, Curnamona Province), Mt Woods deformation (1590–1575 Ma), Mabel Creek Ridge deformation (1570–1555 Ma, Kararan Orogeny) and Fowler Domain deformation (1555–1545 Ma, Kararan Orogeny). This westward migration of deformation suggests the existence of a large evolving tectonic system that encompassed the emplacement of the voluminous Hiltaba Suite and associated volcanic and mineral systems. 相似文献
5.
Ali Elmas İsak Yılmaz Erdinç Yiğitbaş Thomas Ullrich 《International Journal of Earth Sciences》2011,100(6):1251-1263
In the eastern part of the Strandja Massif constituting the east end of the Rhodope Massif, the amphibolite facies basement
rocks intruded by Permian metagranites are juxtaposed against the greenschist facies cover metasediments of Triassic-Middle
Jurassic protolith age. The distinct metamorphic break between the basement and cover rocks requires a missing metamorphic
section. The boundary between the two groups of rocks is a ductile to brittle extensional shear zone with kinematic indicators
exhibiting a top to the E/NE shear sense. Footwall rocks are cut by weakly metamorphosed and foliated granite bodies which
are clearly distinguished from the Permian metagranites by their degree of deformation, cross-cutting relations and syn-tectonic/kinematic
character. Also, hangingwall rocks were intruded by unmetamorphosed and weakly foliated leucogranites. 40Ar/39Ar data indicate that the ductile deformation from 156.5 to 143.2 Ma (Middle Oxfordian-Earliest Berriasian) developed during
the syn-tectonic plutonism in the footwall. Deformation, and gradual/slower cooling-exhumation survived until to 123 Ma (Barremian).
The mylonitic and brittle deformation in the detachment zone developed during Oxfordian-Earliest Berriasian time (155.7–142.6 Ma)
and Early Valanginian-Aptian time (136–118.7 Ma), respectively. Our new field mapping and first 40Ar/39Ar ages demonstrate the existence of an extensional core complex of Late Jurassic-Early Cretaceous age not previously described
in the Rhodope/Strandja massifs. 相似文献
6.
The West Kunlun orogenic belt is located at the conjunction of the paleo-Asian tectonic system and the Tethys tectonic system.
Petrological and mineralogical studies of the Early Cambrian metamorphic surface crust in this region have shown that in case
the metamorphism reached low-temperature granulate facies, the typical mineral assemblage is biotite-garnet-silimanite-K feldspar-plagioclase-quartz.
The peak metamorphic temperatures are within the range of 720–740°C and the pressure is 0.6 GPa ±. Three types of metamorphic
zircon have been detected in the metamorphic rocks: the complex inclusion-bearing type ; the early relic zircon inclusion-bearing
type; and the inclusion-free type. SHRIMP age determination of these three types of metamorphic zircon have revealed that
these zircons were formed principally during 400–460 Ma, indicating that pre-Cambrian metamorphic surface crust rocks underwent
low-temperature granulite facies metamorphism during the Caledonian. In combination with the geological characteristics of
this region, it is considered that when the oceanic basin was closed, there occurred intense intracontinental subduction (type
A), bringing part of the Early Cambrian metamorphic basement in this region downwards to the lower crust. Meanwhile, there
were accompanied with tectonic deformation at deep levels and medium- to high-grade metamorphism. This study provided important
chronological and mineralogical evidence for the exploration of the evolutionary mechanism and process of the West Kunlun
Early Paleozoic.
Part of the results from the research project “ Research on the West Kunlun pre-Cambrian tectonic events” under the program
“ Research on the important geological problems of China’ s pre-Cambrian” (No. 200113900070) sponsored by the China National
Geological Surveying Bureau. 相似文献
7.
Summary The rocks of the crystalline basement of the East European Craton in southern Estonia show effects of partial melting under
granulite facies conditions. Zircons extracted from partial melting products (tonalite from the Tapa Zone – 1824 ± 26, tonalite
from the South Estonian Zone – 1788 ± 16 Ma and charnockite from the Tapa Zone – 1761 ± 11 Ma) yield U–Pb crystallisation
ages that span over approximately 80 Ma, suggesting a prolonged high-grade metamorphism or several separate events. U–Pb zircon
age of one sample of charnockite is concordant with the Nd model age of partial melting of its host mafic granulite facies
gneiss (intercept at 1.76 Ga). Linear geochemical trends and similar initial Nd isotopic compositions of mafic granulites
and charnockites suggest their possible genetic relationship. From our new and previously published data it follows that the
peak granulite metamorphic conditions and formation of tonalites and charnockites (850 °C and 6 kbar) in the Estonian basement
occurred at 1788–1778 Ma. Then, the rocks cooled down, passing through the garnet closure temperature of approximately 650–700 °C
at 1728 ± 24 Ma. The age of metamorphism of the Estonian granulites is lower than the metamorphic ages known from southern
Finland, but it is similar to the age of metamorphism reported from the Belarus-Baltic Granulite Belt in Latvia. 相似文献
8.
抚顺南部早前寒武纪变质杂岩的地质事件序列 总被引：8，自引：7，他引：1
抚顺南部早前寒武纪变质杂岩是华北克拉通北缘辽北-吉南早前寒武纪变质地块的一个重要组成部分,主要由浑南群石棚子组角闪岩相变质火山岩、火山碎屑岩及相伴生的沉积岩等表壳岩系和侵位于其中的石英闪长质片麻岩、英云闪长质-奥长花岗质-花岗闪长质(TTG)片麻岩和花岗闪长岩-二长花岗岩-钾长花岗岩岩石组合组成。LA-ICP-MS锆石U-Pb同位素分析结果显示,侵位于表壳岩中的石英闪长质片麻岩样品12LN39-3的岩浆结晶年龄为2571±7Ma,指示存在老于该年龄的表壳岩系。英云闪长质片麻岩样品12LN04-1和奥长花岗质片麻岩样品13LB49-3的岩浆结晶年龄分别为2544±4Ma和2550±10Ma,记录了一期重要的英云闪长质-奥长花岗质片麻岩侵位事件。斜长角闪岩(样品12LN25-2)的岩浆结晶的最小年龄为2530±5Ma,指示另一火山喷发阶段。晚期钾长花岗岩样品12LN01-1和奥长花岗质片麻岩样品12LN27-1分别侵位于2522±4Ma和2518±23Ma,说明它们的岩浆作用发生于同一时期。而采自于晚期未变形侵入体的石英闪长岩样品12LN30-2的岩浆结晶年龄为2496±18Ma,与上述表壳岩和深成侵入体的主要变质作用(2510~2470Ma)同期发生。这些年代学结果表明,抚顺南部地区新太古代大规模的铁镁质火山喷发作用在大于2571±7Ma已经发生,紧接着2571±7Ma发生石英闪长质岩浆侵位,在2550±10Ma~2544±4Ma之间发生英云闪长质-奥长花岗质岩浆侵位。接下来铁镁质火山再度喷发(~2530±5Ma),随后为钾长花岗岩和奥长花岗质岩浆的侵位(2522±4Ma~2518±23Ma)。晚期为角闪岩相变质作用时期(2510~2470Ma),伴随一定规模的石英闪长岩侵位。 相似文献
9.
华北克拉通是我国最大且最古老的克拉通,是研究太古宙岩浆活动和构造演化的理想区域,一直备受地质学家的关注。太华杂岩是华北克拉通的重要组成部分,主要分布在其南缘,总体呈近北西西-南东东向分布。在详细野外地质调查的基础上,对鲁山地区太华杂岩中的斜长角闪岩样品进行了LA-ICP-MS锆石U-Pb定年,以揭示其成岩及变质事件时代。样品的锆石U-Pb加权平均207Pb/206Pb年龄为2 788±16、2 714±12和1 920±18 Ma,分别代表斜长角闪岩成岩年龄、早期变质事件年龄及晚期变质事件年龄。综合梳理前人的锆石U-Pb年代学及Hf同位素研究数据,分析并讨论了3次地质事件的地质意义:2 850~2 700 Ma为一期重要的岩浆事件,代表了太古宙新生地壳的形成;2 800~2 600和~1 900 Ma为两期变质事件,期间太华杂岩分别遭受新太古代和古元古代两次变质变形改造。本次研究不仅可以解释太华杂岩的形成、变质时代及其地质意义,而且为进一步研究华北克拉通南缘乃至整个华北克拉通的形成与演化过程提供了新的数据资料。 相似文献
10.
N. E. Kozlov E. V. Martynov N. E. Kozlova T. V. Kaulina Yu. P. Smirnov 《Geochemistry International》2007,45(2):123-130
This paper addresses the problem of the systematization of amphibolites from the Archean part of the section of the SG-3 Kola
Superdeep Borehole. It was shown that a combined petrochemical and geochemical approach allows one to classify these rocks
with high confidence and to distinguish supposedly Archean and Proterozoic varieties among them. It was found that Proterozoic
rocks account for about 50–70% of basic rocks in the Archean section. Homologues of the basic metavolcanics of the Matert
Formation were detected among the Proterozoic metaigneous rocks of the Archean section of the SG-3, which casts doubt on the
conclusion of some authors on the allochthonous origin of the upper levels of the northern Pechenga section, including its
productive horizons. This result has very important metallogenic implications.
Original Russian Text N.E. Kozlov, E.V. Martynov, N.E. Kozlova, T.V. Kaulina, Yu.P. Smirnov, 2007, published in Geokhimiya,
2007, No. 2, pp. 150–158. 相似文献
11.
Qiugen Li Shuwen Liu Zongqi Wang Zhuyin Chu Biao Song Yanbin Wang Tao Wang 《International Journal of Earth Sciences》2008,97(3):443-458
Detrital zircon U–Pb ages, whole-rock Nd isotopic, and geochemical data of metasedimentary rocks from the Wutai Complex in
the Central Zone, North China Craton, have been determined. Compositionally, these rocks are characterized by a narrow variation
in SiO2/Al2O3 (2.78–3.96, except sample 2007-1), variable Eu anomalies, spanning a range from significantly negative Eu anomalies to slightly
positive anomalies (Eu/Eu* = 0.58–1.12), and positive ε
Nd (t) values (0.1–1.97). The 18 detrital zircons of one sample yielded age populations of 2.53 Ga, 2.60 Ga, and 2.70–2.85 Ga.
Geochemical data reveal intermediate source weathering, varying degrees of K-metasomatism in the majority of these metasedimentary
rocks, whereas other secondary disturbances seem to be negligible. Detailed analysis in detrital zircon U–Pb geochronology,
whole-rock Nd isotope, and geochemistry shows that these metasedimentary rocks are derived from a mixed provenance. The predominant
derivation is from the late Archean granitoids and metamorphic volcanics in the Wutai Complex, and there is also input of
older continental remnants, except TTG gneisses, from the Hengshan and Fuping Complexes. The sediments were probably deposited
in fore-arc or/and intra-arc basins within an arc system. 相似文献
12.
Chao Zhang Chang-Qian Ma Qun-An Liao Jin-Yang Zhang Zhen-Bing She 《International Journal of Earth Sciences》2011,100(7):1665-1684
Several major volcanic zones are distributed across the eastern North China Craton, from northwest to southeast: the Greater
Xing’an Range, Jibei-Liaoxi, Xishan, and Songliao Basins, and the Yanji, Huanghua, and Ludong volcanic zones. The Huanghua
depression within the Bohai Bay Basin was filled by middle Late Mesozoic volcanic rocks and abundant Cenozoic alkaline basalts.
Zircon LA-ICP-MS and SHRIMP U–Pb dating show that basic–intermediate volcanic rocks were extruded in the Early Cretaceous of 118.8 ± 1.0 Ma (weighted mean 206Pb/238U age), before Late Cretaceous acid lavas at 71.5 ± 2.6 Ma. An inherited zircon from andesite has a Paleoprotoerozoic core
crystallization age of 2,424 ± 22 Ma (206Pb/207Pb age) indicating that the basement of the Bohai Bay Basin is part of the North China Craton. Early Cretaceous basic and
intermediate lavas are characterized by strong enrichments in LREE and LILE and depletions in HREE and HFSE, indicating a
volcanic arc origin related to oceanic subduction. Depletion in Zr only occurs in basic and intermediate volcanic rocks, while
depletions in Sr and Ti exist only in acid samples, indicating that the acid series is not genetically related to the basic–intermediate
series. Formation ages and geochemical features indicate that the Late Cretaceous acid lavas are products of crustal remelting
in an extensional regime. Combined information from all these volcanic zones shows that subduction-related volcanic rocks
were generated in the Jibei-Liaoxi and Xishan volcanic zones during the Early Jurassic, about 60 Ma earlier than their analogues
extruded in the Huanghua and Ludong volcanic zones during the Early Cretaceous. This younging trend also exists in the youngest
extension-related volcanism in each of these zones: Early Cretaceous asthenosphere-derived alkaline basalts in the northwest
and Late Cretaceous in the southeast. A tectonic model of northwestward subduction and continuous oceanward retreat of the
Paleo-Pacific Plate is proposed to explain the migration pattern of both arc-related and post-subduction extension-related
volcanic rocks. As the subduction zone continuously migrated, active continental margin and backarc regimes successively played
their roles in different parts of North China during the Late Mesozoic (J1–K2). 相似文献
13.
Fukun Chen Xiang-Hui Li Xiu-Li Wang Qiu-Li Li Wolfgang Siebel 《International Journal of Earth Sciences》2007,96(6):1179-1194
The Baoshan block of the Tethyan Yunnan, southwestern China, is considered as northern part of the Sibumasu microcontinent.
Basement of this block that comprises presumably greenschist-facies Neoproterozoic metamorphic rocks is covered by Paleozoic
to Mesozoic low-grade metamorphic sedimentary rocks. This study presents zircon ages and Nd–Hf isotopic composition of granites
generated from crustal reworking to reveal geochemical feature of the underlying basement. Dating results obtained using the
single zircon U–Pb isotopic dilution method show that granites exposed in the study area formed in early Paleozoic (about
470 Ma; Pingdajie granite) and in late Yanshanian (about 78–61 Ma, Late Cretaceous to Early Tertiary; Huataolin granite).
The early Paleozoic granite contains Archean to Mesoproterozoic inherited zircons and the late Yanshanian granite contains
late Proterozoic to early Paleozoic zircon cores. Both granites have similar geochemical and Nd–Hf isotopic charateristics,
indicating similar magma sources. They have whole-rock T
DM(Nd) values of around 2,000 Ma and zircon T
DM(Hf) values clustering around 1,900–1,800 and 1,600–1,400 Ma. The Nd–Hf isotopic data imply Paleoproterozoic to Mesoproterozoic
crustal material as the major components of the underlying basement, being consistent with a derivation from Archean and Paleoproterozoic
terrains of India or NW Australia. Both granites formed in two different tectonic events similarly originated from intra-crustal
reworking. Temporally, the late Yanshanian magmatism is probably related to the closure of the Neotethys ocean. The early
Paleozoic magmatism traced in the Baoshan block indicates a comparable history of the basements during early Paleozoic between
the SE Asia and the western Tethyan belt, such as the basement outcrops in the Alpine belt and probably in the European Variscides
that are considered as continental blocks drifting from Gondwana prior to or simultaneously with those of the SE Asia. 相似文献
14.
Maria M. Bogina Valeriy L. Zlobin Michael V. Mints 《International Geology Review》2015,57(11-12):1433-1445
A combined study of major and trace elements, Nd isotopes, and U-Pb systematics has been conducted for the early Palaeoproterozoic (Sumian) volcanic rocks and granites localized in different portions of the Karelian Craton. SHRIMP dating of zircons from the Sumian basalts indicates an emplacement age of 2423 ± 31 Ma, which constrains the lower age boundary of the early Palaeoproterozoic sequence at the Karelian Craton. The early Palaeoproterozoic mafic volcanic rocks of the Karelian Craton show practically no lateral geochemical and isotope-geochemical variations. The rocks bear signs of crustal contamination, in particular Nb and Ti negative anomalies, light rare earth element (LREE) enrichment, and nonradiogenic Nd isotope composition. However, some correlations between incompatible element ratios suggest that the crustal signatures were mainly inherited from mantle sources metasomatized during a previous subduction event. En route to the surface, melts presumably experienced only insignificant contamination by crustal material. Felsic rocks do not define common trends with mafic rocks and were formed independently. They exhibit higher REE contents, large-ion lithophile element (LILE) enrichment, and extremely wide variations in Nd isotope composition, which clearly demonstrates a considerable contribution of heterogeneous basement to their formation. Geochemically, the felsic rocks of the Karelian Craton correspond to A2-type granites and were formed by melting of crustal rocks in an anorogenic setting. Their possible sources are Archaean sanukitoid-type granitoids and Archaean granite gneisses. The high Yb content and pronounced Eu anomaly imply that they were generated from a garnet-free pyroxene – plagioclase source at shallow depths. By the Palaeoproterozoic, the older Vodlozero block was colder than the Central Domain, which facilitated the development of the brittle deformations and faulting and, correspondingly, rapid magma ascent to the surface without melting of crustal rocks. This resulted in the absence of felsic rocks and the formation of more primitive basalts in this area. 相似文献
15.
B. Yu. Astaf’ev O. A. Levchenkov N. G. Rizvanova O. A. Voinova A. S. Voinov L. K. Levskii A. F. Makeev K. I. Lokhov 《Stratigraphy and Geological Correlation》2010,18(1):1-15
The geological structure, age, and genesis of sedimentary—volcanogenic, metamorphic, and metasomatic rocks from the Terskii
greenstone belt fringing the southern Imandra—Varzuga structure in the southeastern Kola Peninsula are discussed with defining
main stages in endogenic activity of the region in the Late Archean and Early Proterozoic. The U-Pb method (SHRIMP-II, ID-TIMS,
and Pb-LS techniques) was used to determine the age of volcano-sedimentary rocks of the Imandra Group as well as that of magmatic
and superimposed metamorphic and metasomatic processes. The basic—intermediate metavolcanics of the Imandra Group are dated
at 2.67 Ga, which corresponds to the Lopingian Gimol’skii Superhorizon (Late Archean). The Archean metavolcanics were subjected
to Early Proterozoic regional metamorphism 2.1 Ga ago and metasomatic processes in the period of 1.85 to 1.77 Ga ago. The
obtained data indicate multistage evolution of rock formation in the Terskii greenstone belt located in the southern flank
of the Imandra—Varzuga structure in the Kola Peninsula. 相似文献
16.
Y. J. Bhaskar Rao T. R. K. Chetty A. S. Janardhan K. Gopalan 《Contributions to Mineralogy and Petrology》1996,125(2-3):237-250
Sittampundi and Bhavani Archean layered meta-anorthosite complexes occur as tectonic lenses within the Cauvery shear zone
(CSZ), a crustal scale shear dividing the Precambrian granulite crust of south India into late Archean (> 2.5 Ga) and Proterozoic (c. 0.55 Ga) blocks. They and their host supracrustal-gneiss rocks record at least two stages of
tectonometamorphic history. The first is seen as regional scale refolded isoclinal folds and granulite metamorphism (D1-M1) while the second stage is associated with dominantly E–W dextral transcurrent shearing and metamorphic recrystallisation
(D2-MCSZ). Whole rock Sm-Nd isochrons for several comagmatic rocks of the layered complexes yield concordant ages: Sittampundi – 2935±60
Ma, ɛNd + 1.85±0.16 and Bhavani – 2899±28 Ma, ɛNd + 2.18±0.14 (2σ errors). Our Sm-Nd results suggest that: (1) the magmatic protoliths of the Sittampundi and Bhavani layered
complexes were extracted from similar uniform and LREE depleted mantle sources; (2) M1 metamorphism occurred soon after emplacement at c.3.0 Ga ago. P-T estimates on garnet granulites from the Sittampundi complex characterise the MCSZ as a high-P event with metamorphic peak conditions of c. 11.8 kbar and 830°C (minimum). The MCSZ is associated with significant isothermal decompression of the order of 4.5–3.5 kbar followed by static high-temperature
rehydration and retrogression around 600°C. The timing of MCSZ is inferred to be Neoproterozoic at c. 730 Ma based on a whole rock-garnet-plagioclase-hornblende Sm-Nd isochron age for
a garnet granulite from the Sittampundi complex and its agreement with the 800–600 Ma published age data on post-kinematic
plutonic rocks within the CSZ. These results demonstrate that the Cauvery shear zone is a zone of Neoproterozoic reworking
of Archean crust broadly similar to the interface between the Napier and Rayner complexes of the East Antarctic shield in
a model Proterozoic Gondwana supercontinent.
Received: 5 December 1995 / Accepted: 3 May 1996 相似文献
17.
F. Lucassen R. Becchio H. G. Wilke G. Franz M. F. Thirlwall J. Viramonte K. Wemmer 《Journal of South American Earth Sciences》2000,13(8):697
The Late Precambrian–Early Paleozoic metamorphic basement forms a volumetrically important part of the Andean crust. We investigated its evolution in order to subdivide the area between 18 and 26°S into crustal domains by means of petrological and age data (Sm–Nd isochrons, K–Ar). The metamorphic crystallization ages and tDM ages are not consistent with growth of the Pacific margin north of the Argentine Precordillera by accretion of exotic terranes, but favor a model of a mobile belt of the Pampean Cycle. Peak metamorphic conditions in all scattered outcrop areas between 18 and 26°S are similar and reached the upper amphibolite facies conditions indicated by mineral paragensis and the occurrence of migmatite. Sm–Nd mineral isochrons yielded 525±10, 505±6 and 509±1 Ma for the Chilean Coast Range, the Chilean Precordillera and the Argentine Puna, and 442±9 and 412±18 Ma for the Sierras Pampeanas. Conventional K–Ar cooling age data of amphibole and mica cluster around 400 Ma, but are frequently reset by Late Paleozoic and Jurassic magmatism. Final exhumation of the Early Paleozoic orogen is confirmed by Devonian erosional unconformities. Sm–Nd depleted mantle model ages of felsic rocks from the metamorphic basement range from 1.4 to 2.2 Ga, in northern Chile the average is 1.65±0.16 Ga (1σ; n=12), average tDM of both gneiss and metabasite in NW Argentina is 1.76±0.4 Ga (1σ; n=22), and the isotopic composition excludes major addition of juvenile mantle derived material during the Early Paleozoic metamorphic and magmatic cycle. These new data indicate a largely similar development of the metamorphic basement south of the Arequipa Massif at 18°S and north of the Argentine Precordillera at 28°S. Variations of metamorphic grade and of ages of peak metamorphism are of local importance. The protolith was derived from Early to Middle Proterozoic cratonic areas, similar to the Proterozoic rocks from the Arequipa Massif, which had undergone Grenvillian metamorphism at ca. 1.0 Ga. 相似文献
18.
内蒙古苏尼特右旗白乃庙地区徐尼乌苏组的形成时代及其地质意义 总被引：1，自引：1，他引：0
本文对白乃庙地区徐尼乌苏组沉积特征、原岩建造、变质火山岩及变质碎屑岩的年代学和地球化学进行了研究,探讨了白乃庙地区早古生代构造演化。本次研究采集了徐尼乌苏组中具有代表性的变质含砾粗粒杂砂岩、变质英安质晶屑凝灰岩和变质长石石英细砂岩样品,进行了锆石LA-ICP-MS U-Pb年代学和岩石地球化学分析。结果显示,2个变质英安质晶屑凝灰岩锆石的加权平均年龄分别为440.9±1.8Ma(MSWD=0.10)和440.9±1.7Ma(MSWD=0.15),锆石Th/U比值为0.46~1.59,自形程度较好,发育有典型的岩浆锆石振荡环带结构,显示为岩浆成因锆石的特点,表明徐尼乌苏组的形成时代为早志留世。变质含砾粗粒杂砂岩的碎屑锆石年龄在452.0±1.3Ma~535.0±1.0Ma之间,最高峰值年龄为490Ma左右;变质长石石英细砂岩碎屑锆石年龄则在440.1±5.7Ma~3268.9±57.7Ma之间,最小谐和年龄为440.1±5.7Ma,峰值年龄为490Ma左右,另有1.0Ga、1.6Ga、1.8Ga和2.5Ga四个明显的峰值年龄。根据研究区徐尼乌苏组岩性组合与结构构造,可将该组划分为3个不同的沉积旋回。结合白乃庙地区徐尼乌苏组测年结果、岩石地球化学特征、原岩建造及区域岩浆岩资料,白乃庙弧后盆地沉积可划分为三个演化阶段:早期快速堆积阶段(452.3~440.9Ma),形成了一套成熟度较低的粗碎屑岩建造,物源主要来源于白乃庙岩浆弧中的岩浆岩;中期火山喷发阶段(440.9~440.1Ma),以火山沉积作用为主,为火山碎屑岩建造夹有碳酸盐建造和少量碎屑岩建造,碎屑物质主要来源于该时期的火山活动;晚期稳定沉积阶段(440.1Ma),形成一套细碎屑岩建造和碳酸盐建造,为浅海相稳定沉积,此时物源广泛,分别来源于华北克拉通基底、兴蒙造山带和白乃庙早古生代火山弧。根据徐尼乌苏组的沉积建造和火山建造特征,结合白乃庙火山弧岩浆活动特征,认为徐尼乌苏组形成于早古生代弧后盆地中,此时华北板块北缘属于安第斯型活动大陆边缘。 相似文献
19.
鄂尔多斯盆地乌审旗地区上古生界砂岩碎屑锆石U-Pb年龄及其地质意义 总被引：1，自引：0，他引：1
通过LA-ICP-MS碎屑锆石的U-Pb测年和U、Th元素含量分析,结合邻区年龄数据和岩性特征,对鄂尔多斯盆地乌审旗地区上古生界山西组1段和下石盒子组8段砂岩进行了同位素定年物源示踪研究。研究揭示,盒8段和山1段源区母岩形成年龄属于太古代、古元古代、中元古代、晚古生代,分别与华北块体的形成、增生和克拉通化相关,是华北克拉通演化多阶段地质事件作用下的产物。沉积物源区主要为华北克拉通内部或盆地北缘,物源主要来自华北地台东部的早太古代基底古老变质岩系和新太古代的变质岩系、乌拉山和东部集宁地区的新太古代晚期的片麻状花岗岩、早元古代早期的古老的TTG片麻岩及麻粒岩和早元古代晚期的孔兹岩带,此外,阴山地块390～310 Ma岩浆岩也是重要物源之一。该项成果不仅查明了乌审旗地区上古生界山西组1段和下石盒子组8段碎屑锆石年龄与华北克拉通地质事件在时间上的对应关系,指明了年龄区间碎屑物质成分来源的归属性,而且对研究区可能存在的华北克拉通地质事件首次从岩性上提供了重要信息。 相似文献
20.
Ling-Ling Xiao Chun-Ming Wu Guo-Chun Zhao Jing-Hui Guo Liu-Dong Ren 《International Journal of Earth Sciences》2011,100(4):717-739
Garnet-bearing metapelites and amphibolites are exposed in the south and middle parts of the Zanhuang complex, which is located
in the central segment of the nearly NS-striking Trans-North China Orogen. These rocks preserve three metamorphic mineral
assemblages forming at the prograde, peak and post-peak decompression stages. The prograde metamorphic stage (M1) is represented by mineral inclusions within garnet porphyroblasts, the peak metamorphic stage (M2) is represented by garnet rims and matrix minerals, whereas the retrograde stage (M3) is represented by amphibole + plagioclase symplectite rimming garnet porphyroblasts in the amphibolites and biotite + plagioclase
symplectite rimming garnet porphyroblasts in the metapelites. All garnet porphyroblasts in the metapelites preserve prograde
chemical zoning except for the ubiquitous, quite narrow zones from the underwent post-peak decompression. It has been determined
through thermobarometric computation that the metamorphic conditions are 650–710°C at 8.2−9.2 kbar for the M1 (inclusion) assemblages, >810°C at >12.5 kbar for the metamorphic peak M2 (matrix) assemblages, and 660–680°C at 4.4–4.5 kbar for the retrograde M3 (symplectite) assemblages. These rocks are thus determined to have undergone metamorphism with clockwise P–T paths involving nearly isothermal decompression (ITD) segments, which is inferred to be related to the amalgamation of the
Eastern and Western Blocks to form the coherent basement of the North China Craton along the Trans-North China Orogen in the
late Paleoproterozoic (1.88–1.85 Ga). 相似文献