首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
The Qinling Orogenic Belt, linking the Kunlun and Qilian Mountains to the west and continuing farther east to the Dabie Mountain, was assembled by the convergence and collision between the Greater South China and the North China blocks. The precise timing of the subduction and collision processes between these continental blocks and tectonic regime switchover is very equivocal. Zircon in-situ LA-ICP-MS U–Pb dating in this contribution indicates that the biotite monzogranite and monzogranite phases of the Dangchuan complex were crystallized at ca. 239.8 ± 2.3 Ma and 227.8 ± 1.2 Ma, respectively. The ca. 240 Ma biotite monzogranite displays εHf(t) values ranging from −2.4 to +2.9, and corresponding TDM2 of 1.72–1.94 Ga and TDM1 of 0.77–0.88 Ga. The ca. 228 Ma monzogranite exhibits εHf(t) values ranging from −4.3 to +1.9, and corresponding TDM2 of 1.73–2.08 Ga and TDM1 of 0.81–0.88 Ga. Lutetium–Hf isotopic composition indicates that the biotite monzogranite and monzogranite probably have the same parental magmas which were originated from hybrid sources of both reworking of Paleoproterozoic ancient crust and partial melting of the Neoproterozoic juvenile crust. The more negative εHf(t) values of the monzogranite suggest more contribution of the ancient crust during the source contamination, or more possible crustal assimilation during their crystallization at ca. 228 Ma than precursor biotite monzogranite. Integrated with previous research and our detailed petrography, we propose that the Dangchuan complex underwent an episodic growth documenting the tectonic regime switchover from early Paleozoic to Triassic. The ca. 439 Ma inherited zircon recorded the persistent subduction of the oceanic crust, the ca. 240 Ma biotite monzogranite emplaced during the northward subduction of the Mianlue oceanic crust beneath the South Qinling block, and the ca. 228 Ma monzogranite emplaced during the syn-collisional process in a compressional setting.  相似文献   

2.
New insights on the Paleozoic evolution of the continental crust in the North Patagonian Massif are presented based on the analysis of Sm–Nd systematics. New evidence is presented to constrain tectonic models for the origin of Patagonia and its relations with the South American crustal blocks. Geologic, isotopic and tectonic characterization of the North Patagonian Massif and comparison of the Nd parameters lead us to conclude that: (1) The North Patagonian Massif is a crustal block with bulk crustal average ages between 2.1 and 1.6 Ga TDM (Nd) and (2) At least three metamorphic episodes could be identified in the Paleozoic rocks of the North Patagonian Massif. In the northeastern corner, Famatinian metamorphism is widely identified. However field and petrographic evidence indicate a Middle to Late Cambrian metamorphism pre-dating the emplacement of the ca. 475 Ma granitoids. In the southwestern area, are apparent 425–420 Ma (?) and 380–360 Ma metamorphic peaks. The latter episode might have resulted from the collision of the Antonia terrane; and (3) Early Paleozoic magmatism in the northeastern area is coeval with the Famatinian arc. Nd isotopic compositions reveal that Ordovician magmatism was associated with attenuated crust. On the southwestern border, the first magmatic recycling record is Devonian. Nd data shows a step by step melting of different levels of the continental crust in the Late Palaeozoic. Between 330 and 295 Ma magmatism was likely the product of a crustal source with an average 1.5 Ga TDM (Nd). Widespread magmatism represented by the 295–260 Ma granitoids involved a lower crustal mafic source, and continued with massive shallower-acid plutono volcanic complexes which might have recycled an upper crustal segment of the Proterozoic continental basement, resulting in a more felsic crust until the Triassic. (4) Sm–Nd parameters and detrital zircon age patterns of Early Paleozoic (meta)-sedimentary rocks from the North Patagonian Massif and those from the neighboring blocks, suggest crustal continuity between Eastern Sierras Pampeanas, southern Arequipa-Antofalla and the northeastern sector of the North Patagonian Massif by the Early Paleozoic. This evidence suggests that, at least, this corner of the North Patagonian Massif is not allochthonous to Gondwana. A Late Paleozoic frontal collision with the southwestern margin of Gondwana can be reconcilied in a para-autochthonous model including a rifting event from a similar or neighbouring position to its post-collision location. Possible Proterozoic or Early Paleozoic connections of the NPM with the Kalahari craton or the western Antartic blocks should be investigated.  相似文献   

3.
《Gondwana Research》2014,25(1):170-189
The Lhasa terrane in southern Tibet is composed of Precambrian crystalline basement, Paleozoic to Mesozoic sedimentary strata and Paleozoic to Cenozoic magmatic rocks. This terrane has long been accepted as the last crustal block to be accreted with Eurasia prior to its collision with the northward drifting Indian continent in the Cenozoic. Thus, the Lhasa terrane is the key for revealing the origin and evolutionary history of the Himalayan–Tibetan orogen. Although previous models on the tectonic development of the orogen have much evidence from the Lhasa terrane, the metamorphic history of this terrane was rarely considered. This paper provides an overview of the temporal and spatial characteristics of metamorphism in the Lhasa terrane based mostly on the recent results from our group, and evaluates the geodynamic settings and tectonic significance. The Lhasa terrane experienced multistage metamorphism, including the Neoproterozoic and Late Paleozoic HP metamorphism in the oceanic subduction realm, the Early Paleozoic and Early Mesozoic MP metamorphism in the continent–continent collisional zone, the Late Cretaceous HT/MP metamorphism in the mid-oceanic ridge subduction zone, and two stages of Cenozoic MP metamorphism in the thickened crust above the continental subduction zone. These metamorphic and associated magmatic events reveal that the Lhasa terrane experienced a complex tectonic evolution from the Neoproterozoic to Cenozoic. The main conclusions arising from our synthesis are as follows: (1) The Lhasa block consists of the North and South Lhasa terranes, separated by the Paleo-Tethys Ocean and the subsequent Late Paleozoic suture zone. (2) The crystalline basement of the North Lhasa terrane includes Neoproterozoic oceanic crustal rocks, representing probably the remnants of the Mozambique Ocean derived from the break-up of the Rodinia supercontinent. (3) The oceanic crustal basement of North Lhasa witnessed a Late Cryogenian (~ 650 Ma) HP metamorphism and an Early Paleozoic (~ 485 Ma) MP metamorphism in the subduction realm associated with the closure of the Mozambique Ocean and the final amalgamation of Eastern and Western Gondwana, suggesting that the North Lhasa terrane might have been partly derived from the northern segment of the East African Orogen. (4) The northern margin of Indian continent, including the North and South Lhasa, and Qiangtang terranes, experienced Early Paleozoic magmatism, indicating an Andean-type orogeny that resulted from the subduction of the Proto-Tethys Ocean after the final amalgamation of Gondwana. (5) The Lhasa and Qiangtang terranes witnessed Middle Paleozoic (~ 360 Ma) magmatism, suggesting an Andean-type orogeny derived from the subduction of the Paleo-Tethys Ocean. (6) The closure of Paleo-Tethys Ocean between the North and South Lhasa terranes and subsequent terrane collision resulted in the formation of Late Permian (~ 260 Ma) HP metamorphic belt and Triassic (220 Ma) MP metamorphic belt. (7) The South Lhasa terrane experienced Late Cretaceous (~ 90 Ma) Andean-type orogeny, characterized by the regional HT/MP metamorphism and coeval intrusion of the voluminous Gangdese batholith during the northward subduction of the Neo-Tethyan Ocean. (8) During the Early Cenozoic (55–45 Ma), the continent–continent collisional orogeny has led to the thickened crust of the South Lhasa terrane experiencing MP amphibolite-facies metamorphism and syn-collisional magmatism. (9) Following the continuous continent convergence, the South Lhasa terrane also experienced MP metamorphism during Late Eocene (40–30 Ma). (10) During Mesozoic and Cenozoic, two different stages of paired metamorphic belts were formed in the oceanic or continental subduction zones and the middle and lower crust of the hanging wall of the subduction zone. The tectonic imprints from the Lhasa terrane provide excellent examples for understanding metamorphic processes and geodynamics at convergent plate boundaries.  相似文献   

4.
《Precambrian Research》2007,152(1-2):48-82
Tectonic affinity of tectono-lithological units close to ultrahigh-pressure metamorphic belt is a key issue for understanding the geodynamics of continental collision. This is particularly so for the Jiaobei terrane northeast of the Dabie-Sulu orogenic belt in China. New data from LA-ICPMS zircon U–Pb dating, whole-rock elements and Nd–Sr isotopes, and mineral O isotopes are presented for metamorphic rocks from this terrane. The results place geochronological and geochemical constraints on their protolith nature and metamorphic timing and thus on its tectonic affinity to one of the two Triassic collided continents, the North and the South China Blocks. Protolith ages for TTG gneiss, amphibolite and mafic granulite are ∼2.7, ∼2.5 and ∼2.4 Ga, respectively; regional metamorphism took place extensively at ∼1.76 Ga. Protolith of the TTG gneiss was generated by partial melting of mantle-derived rocks at the root of a thickened crust. Protolith of the amphibolite was probably a product of arc-like magmatism; protolith of the mafic granulite was derived from a depleted mantle source. Both of them were locally contaminated by supracrustal materials. Protoliths of paragneiss and schist in the Fenzishan Group were mostly derived from supracrustal sources, but protolith of amphibolite in the Fenzishan Group is of mantle-derived signature. Unlike the UHP metaigneous rocks in the Dabie-Sulu orogenic belt that show unusual 18O-depletion, the Jiaobei metamorphic rocks have basically preserved their original mantle-like O isotope compositions. In general, the nature and timing of geological events recorded in the metamorphic rocks from the Jiaobei terrane are comparable with those from the North China Block rather than the South China Block. Thus, the Jiaobei terrane is concluded to have tectonic affinity to the former, but behave like a micro-continent during the Triassic continental collision. The ∼1.76 Ga regional metamorphism in the Jiaobei terrane is likely related to reworking of the arc-continent collisional orogen in the periphery of the North China Block rather than the ∼1.85 Ga collision event between the eastern and western North China Blocks. The present study lends support to the common assumption that the suture boundary between the North and South China Blocks in the Sulu orogen is located along the Wulian-Yantai fault. Tectonic mingling along the Wulian-Yantai fault is probably related to subduction erosion during the continental collision.  相似文献   

5.
The Trans-Amazonian cycle was an important rock-forming event in South America, generating voluminous juvenile and reworked fractions of continental crust. The Bacajá domain, in the southern sector of the Maroni-Itacaiúnas Province in the Amazonian craton, is an example of the Trans-Amazonian terranes adjacent to the Archean Carajás block. Zircon Pb-evaporation and whole-rock Sm–Nd analyses were carried out on representative samples of six lithological units, and allowed the proposal of a comprehensive tectonic-magmatic evolutionary sequence for the central and eastern parts of this domain, from the Neoarchean to the Rhyacian. Gneisses with ages of ca. 2.67 and 2.44 Ga are the oldest rocks recorded in the region, and probably represent remnants of island and continental arcs. The Três Palmeiras succession, emplaced between 2.36 and 2.34 Ga, hosts gold deposits and represents the first record of Siderian supracrustal rocks in the Amazonian craton. It was probably part of an island arc/ocean floor accreted to a craton margin. Rhyacian granitogenesis lasted for ca. 140 My (2.22–2.08 Ga), marking different stages of the Trans-Amazonian cycle. The first stage is represented by continental arc granitoids formed by melting of Archean crust at 2.22–2.18 Ga. The second is characterized by the production of juvenile material between 2.16 and 2.13 Ga. The third and final stage at ca. 2.08 Ga is represented by a large volume of granitoids originated from either juvenile material or reworked crust during compressive stresses. Nd isotopes reveal that juvenile rocks dominated in the northern part of the domain, whereas those formed from reworked crust predominate in the south. The present-day configuration of the Bacajá domain results from collision against the Archean Carajás block at the end of the Trans-Amazonian cycle.  相似文献   

6.
《Gondwana Research》2014,25(2):561-584
The aim of this paper is to review the main features of the Meso-Neoarchaean Belomorian eclogite province (BEP) in the northeastern Fennoscandian Shield, including regional and local geology, geochemistry, petrology and geochronology and to compare the Belomorian eclogites with Precambrian eclogites elsewhere. Two eclogite associations have been recognized within Belomorian TTG gneisses: (1) the subduction-type Salma association and (2) Gridino eclogitized mafic dykes. Protoliths of the Salma eclogites represent a sequence comprising gabbro, Fe–Ti gabbro and troctolites, formed at ~ 2.9 Ga in a slow-spreading ridge setting (like the Southwest Indian Ridge). The main subduction and eclogite-facies events occurred between ~ 2.87 and ~ 2.82 Ga. Injection of mafic magma into an active continental margin setting, recorded by the Gridino dyke swarm, is attributed to subduction of a mid-ocean ridge, commencing at 2.87 Ga. Crustal delamination of the active margin and subsequent involvement of the lower crust in subduction between 2.87 and 2.82 Ga ago caused high-pressure metamorphism of the Gridino dykes, culminating in eclogite-facies conditions between 2.82 and 2.78 Ga and accompanying amalgamation of the Karelia, Kola and Khetolamba blocks and formation of the Mesoarchaean Belomorian accretionary–collisional orogen. The clockwise P–T paths of the Salma and Gridino associations cross the granulite-facies P–T field. Detailed metamorphic studies indicate a complicated post-eclogite history with thermal events and fluid infiltration, related to plume activity at 2.72–2.70, ~ 2.4 and ~ 1.9 Ga. The eclogite assemblages were exhumed to mid-to-lower crustal depths at ~ 1.7 Ga, while erosion or younger tectonic events were responsible for final exhumation to the surface. Comparison of P–T–t paths and data for peak metamorphic parameters demonstrates the general similarity of the Archaean and Palaeoproterozoic eclogites worldwide and their association with anomalously “hot” environments. The occurrence of high-T conditions during eclogite-facies metamorphism can be attributed to either subduction of a mid-ocean ridge (Archaean, BEP) or to interaction with mantle plumes (Proterozoic).  相似文献   

7.
《Gondwana Research》2016,29(4):1516-1529
Voluminous Proterozoic (~ 1700 Ma) rapakivi granites occur in several cratons, especially in the northern hemisphere. Similar Proterozoic rapakivi granites have recently been recognized in the Paleozoic North Qaidam orogen, western segment of the China Central Orogenic System (CCOS). SHRIMP zircon U–Pb dating of these granites yielded ages of 1778 ± 17 and 1778 ± 12 Ma. These granites exhibit typical rapakivi textures. They are ferroan, alkalic to alkalic-calc, metaluminous to peraluminous and characterized by high Ga/Al ratios, Na2O + K2O and rare earth elements (apart from Eu) contents, but low MgO, CaO and Sr contents. These are typical A-type granite features. Whole-rock εNd(t) values of the granites range from − 6.09 to − 5.74 with Nd model ages of 2762 to 2733 Ma, and their zircon εHf(t) values are from − 8.3 to − 5.2 with two-stage Hf model ages of 2944 to 2800 Ma, suggesting that these rocks were derived from old continental crust. The ages, rapakivi texture and geochemical features suggest that these granites are very close to typical Proterozoic (~ 1700 Ma) rapakivi granites within the North China Craton (NCC) and belong to the group of Proterozoic rapakivi granites of the northern hemisphere. These indicate that part of the basement of the North Qaidam orogen in the western CCOS is similar to that of the NCC or was probably derived from it, and then became involved in the CCOS. This provides new data to solve the dispute on the basement origin in this orogen.  相似文献   

8.
《Gondwana Research》2015,27(3-4):888-906
The Ongole Domain in the southern Eastern Ghats Belt of India formed during the final stages of Columbia amalgamation at ca. 1600 Ma. Yet very little is known about the protolith ages, tectonic evolution or geographic affinity of the region. We present new detrital and igneous U–Pb–Hf zircon data and in-situ monazite data to further understand the tectonic evolution of this Columbia-forming orogen.Detrital zircon patterns from the metasedimentary rocks are dominated by major populations of Palaeoproterozoic grains (ca. 2460, 2320, 2260, 2200–2100, 2080–2010, 1980–1920, 1850 and 1750 Ma), and minor Archaean grains (ca. 2850, 2740, 2600 and 2550 Ma). Combined U–Pb ages and Lu–Hf zircon isotopic data suggest that the sedimentary protoliths were not sourced from the adjacent Dharwar Craton. Instead they were likely derived from East Antarctica, possibly the same source as parts of Proterozoic Australia. Magmatism occurred episodically between 1.64 and 1.57 Ga in the Ongole Domain, forming felsic orthopyroxene-bearing granitoids. Isotopically, the granitoids are evolved, producing εHf values between − 2 and − 12. The magmatism is interpreted to have been derived from the reworking of Archaean crust with only a minor juvenile input. Metamorphism between 1.68 and 1.60 Ga resulted in the partial to complete resetting of detrital zircon grains, as well as the growth of new metamorphic zircon at 1.67 and 1.63 Ga. In-situ monazite geochronology indicates metamorphism occurred between 1.68 and 1.59 Ga.The Ongole Domain is interpreted to represent part of an exotic terrane, which was transferred to proto-India in the late Palaeoproterozoic as part of a linear accretionary orogenic belt that may also have included south-west Baltica and south-eastern Laurentia. Given the isotopic, geological and geochemical similarities, the proposed exotic terrane is interpreted to be an extension of the Napier Complex, Antarctica, and may also have been connected to Proterozoic Australia (North Australian Craton and Gawler Craton).  相似文献   

9.
The Qinling Orogen, central China, was constructed during the Mesozoic collision between the North China and Yangtze continental plates. The orogen includes four tectonic units, from north to south, the Huaxiong Block (reactivated southern margin of the North China Craton), North Qinling Accretion Belt, South Qinling Fold Belt (or block) and Songpan Fold Belt, evolved from the northernmost Paleo-Tethys Ocean separating the Gondwana and Laurentia supercontinents. Here we employ detrital zircons from the Early Cretaceous alluvial sediments within the Qinling Orogen to trace the tectonic evolution of the orogen. The U–Pb ages of the detrital zircon grains from the Early Cretaceous Donghe Group sediments in the South Qinling Fold Belt cluster around 2600–2300 Ma, 2050–1800 Ma, 1200–700 Ma, 650–400 Ma and 350–200 Ma, corresponding to the global Kenorland, Columbia, Rodinia, Gondwana and Pangaea supercontinent events, respectively. The distributions of ages and εHf(t) values of zircon grains show that the Donghe Group sediments have a complex source comprising components mainly recycled from the North Qinling Accretion Belt and the North China Craton, suggesting that the South Qinling Fold Belt was a part of the united Qinling–North China continental plate, rather than an isolated microcontinent, during the Devonian–Triassic. The youngest age peak of 350–200 Ma reflects the magmatic event related to subduction and termination of the Mian-Lue oceanic plate, followed by the collision between the Yangtze Craton and the united Qinling–North China continent that came into existence at the Triassic–Jurassic transition. The interval of 208–145 Ma between the sedimentation of the Early Cretaceous Donghe Group and the youngest age of detrital zircons was coeval with the post-subduction collision between the Yangtze and the North China continental plates in Jurassic.  相似文献   

10.
U-Pb data from the Rinkian fold Belt, western Greenland, provide new constraints on provenance and timing of deposition of the Karrat Group, the emplacement interval of the Prøven Igneous Complex, and the tectonic setting of west Greenland during the interval 2.03–1.83 Ga. U-Pb detrital data establish the entire Karrat Group metasedimentary succession as Paleoproterozoic in age, initiated after ca. 2029 Ma (Qeqertarssuaq Formation), with deeper water deposition after 1953 ± 31 Ma and 1905 ± 20 Ma (Nûkavsak Formation). The detrital age profiles highlight a profound change in source region after ca. 1.95 Ga that we attribute to thickening, uplift, and exhumation related to collision of a juvenile magmatic arc with the northwest margin of Rae craton at ca. 1.97–1.95 Ga (Thelon Orogen). Accordingly, the Karrat Group is viewed as having initiated as an extensional rift basin(s) that received ca. 3.00–2.95 Ga detritus from local basement sources, and which evolved into a deeper water foreland-basin succession derived from the north. This foreland basin was intruded by the Prøven Igneous Complex, for which new U-Pb data establish emplacement between 1.90 and 1.87 Ga in a within-(Rae) plate setting. Prøven plutonism is coeval with lower-plate mantle magmatism elsewhere across NE Laurentia which may have been triggered by asthenospheric thinning due to plume-induced extension of lower-plate Rae craton at 1.95–1.92 Ga. Our data refute a direct link between the Prøven Igneous Complex and the voluminous 1.86–1.845 Ga Cumberland Batholith, Baffin Island, long considered its counterpart.  相似文献   

11.
Glacigenic diamictite successions of the Macaúbas Group are widespread in the western domain of the Araçuaí orogen, east of the São Francisco craton (Brazil). Diamictites also occur on this craton and in the African counterpart of the Araçuaí orogen, the West Congo belt. Detrital zircon grains from the matrix of diamictites and sandstones from the Macaúbas Group were dated by the U–Pb SHRIMP technique. The geochronological study sets the maximum depositional age of the glacial diamictites at 900 Ma, and indicates multiple sources for the Macaúbas basin with ages ranging from 900 to 2800 Ma. Sm–Nd TDM model ages, determined on whole rock samples, range from 1.8 Ga to 2.5 Ga and get older up-section. Comparison of our data with those from the cratonic area suggest that these glacial deposits can be correlated to the Jequitaí and Carrancas diamictites in the São Francisco craton, and to the Lower Mixtite Formation of the West Congolian Group, exposed in Africa. The 900–1000 Ma source is most probably represented by the Zadinian–Mayumbian volcanic rocks and related granites from the West Congo belt. However, one of the most voluminous sources, with ages in the 1.1–1.3 Ga interval, has not been detected in the São Francisco-Congo craton. Possible sources for these grains could occur elsewhere in Africa, or possibly from within the Brasília Belt in western central Brazil.  相似文献   

12.
《Gondwana Research》2013,24(4):1241-1260
An overview is presented for the formation and evolution of Precambrian continental lithosphere in South China. This is primarily based on an integrated study of zircon U–Pb ages and Lu–Hf isotopes in crustal rocks, with additional constraints from Re–Os isotopes in mantle-derived rocks. Available Re–Os isotope data on xenolith peridotites suggest that the oldest subcontinental lithospheric mantle beneath South China is primarily of Paleoproterozoic age. The zircon U–Pb ages and Lu–Hf isotope studies reveal growth and reworking of the juvenile crust at different ages. Both the Yangtze and Cathaysia terranes contain crustal materials of Archean U–Pb ages. Nevertheless, zircon U–Pb ages exhibit two peaks at 2.9–3.0 Ga and ~ 2.5 Ga in Yangtze but only one peak at ~ 2.5 Ga in Cathaysia. Both massive rocks and crustal remnants (i.e., zircon) of Archean U–Pb ages occur in Yangtze, but only crustal remnants of Archean U–Pb ages occur in Cathaysia. Zircon U–Pb and Lu–Hf isotopes in the Kongling complex of Yangtze suggest the earliest episode of crustal growth in the Paleoarchean and two episodes of crustal reworking at 3.1–3.3 Ga and 2.8–3.0 Ga. Both negative and positive εHf(t) values are associated with Archean U–Pb ages of zircon in South China, indicating both the growth of juvenile crust and the reworking of ancient crust in the Archean. Paleoproterozoic rocks in Yangtze exhibit four groups of U–Pb ages at 2.1 Ga, 1.9–2.0 Ga, ~ 1.85 Ga and ~ 1.7 Ga, respectively. They are associated not only with reworking of the ancient Archean crust in the interior of Yangtze, but also with the growth of the contemporaneous juvenile crust in the periphery of Yangtze. In contrast, Paleoproterozoic rocks in Cathaysia were primarily derived from reworking of Archean crust at 1.8–1.9 Ga. The exposure of Mesoproterozoic rocks are very limited in South China, but zircon Hf model ages suggest the growth of juvenile crust in this period due to island arc magmatism of the Grenvillian oceanic subduction. Magmatic rocks of middle Neoproterozoic U–Pb ages are widespread in South China, exhibiting two peaks at about 830–800 Ma and 780–740 Ma, respectively. Both negative and positive εHf(t) values are associated with the middle Neoproterozoic U–Pb ages of zircon, suggesting not only growth and reworking of the juvenile Mesoproterozoic crust but also reworking of the ancient Archean and Paleoproterozoic crust in the middle Neoproterozoic. The tectonic setting for this period of magmatism would be transformed from arc–continent collision to continental rifting with reference to the plate tectonic regime in South China.  相似文献   

13.
High-Mg# peridotite xenoliths in the Cenozoic Hebi basalts from the North China Craton have refractory mineral compositions (Fo > 91.5) and highly heterogeneous Sr–Nd isotopic compositions (87Sr/86Sr = 0.7031–0.7048, 143Nd/144Nd = 0.5130–0.5118) ranging from MORB-like to EM1-type mantle, which are similar to those of peridotites from Archean cratons. Thus, the high-Mg# peridotites may represent relics of the ancient lithospheric mantle. Published Re–Os isotopic data for Cenozoic basalt-borne xenoliths show TRD ages of 3.0–1.5 Ga for the peridotites from Hebi (the center of the craton), 2.2–0 Ga for those from Hannuoba and Jining (north margin of the craton), and 2.6–0 Ga for those from Fanshi and Yangyuan (midway between the center and north margin of the craton). In situ Re–Os data of sulfides in Hannuoba peridotites suggest that whole-rock Re–Os model ages represent mixtures of multiple generations of sulfides with varying Os isotopic compositions. These observations indicate that initial lithospheric mantle beneath the Central Zone of the North China Craton formed during the Archean and was refertilized by multiple melt additions after its formation. The refertilization became more intensive from the interior to the margin of the craton, leading to the high heterogeneity of the lithospheric mantle: more ancient and refractory peridotites with highly variable Sr–Nd isotopic compositions in the interior, and more young and fertile peridotites with depleted Sr–Nd isotopic composition in the margin. Our data, coupled with published petrological and geochemical data of peridotites from the Central Zone of the North China Craton, suggest that the lithospheric mantle beneath this region is highly heterogeneous, likely produced by refertilization of Archean mantle via multiple additions of melts/fluids, which were closely related to the Paleoproterozoic collision between the Eastern and the Western Blocks and subsequent circum-craton subduction events.  相似文献   

14.
Northern Sweden is currently experiencing active exploration within a new gold ore province, the so called Gold Line, situated southwest of the well-known Skellefte VMS District. The largest known deposit in the Gold Line is the hypozonal Fäboliden orogenic gold deposit. Mineralization at Fäboliden is hosted by arsenopyrite-rich quartz veins, in a reverse, mainly dip-slip, high-angle shear zone, in amphibolite facies supracrustal host rocks. The timing of mineralization is estimated, from field relationships, at ca. 1.8 Ga.The gold mineralization is hosted by two sets of mineralized quartz veins, one steep fault–fill vein set and one relatively flat-lying extensional vein set. Ore shoots occur at the intersections between the two vein sets, and both sets could have been generated from the same stress field, during the late stages of the Svecofennian orogen.The tectonic evolution during the 1.9–1.8 Ga Svecofennian orogen is complex, as features typical of both internal and external orogens are indicated. The similarity in geodynamic setting between the contemporary Svecofennian and Trans-Hudson orogens indicates a potential for world-class orogenic gold provinces also in the Svecofennian domain.The Swedish deposits discussed in this paper are all structurally associated with roughly N–S striking shear zones that were active at around 1.8 Ga, when gold-bearing fluids infiltrated structures related to conditions of E–W shortening.  相似文献   

15.
The Paleoproterozoic cover sequence at the 100–150 km wide western margin of the Archean Karelian Province is dominated by deep water Lower and Upper Kaleva metasediments. We present here an interpretation of Sm–Nd isotope and geochemical data on 36 samples, TIMS multi-grain U–Pb zircon analyses on nine samples, and ca. 100 SIMS analysis of detrital zircon grains from four Upper Kaleva and one Lower Kaleva samples.The Lower Kaleva is characterized by autochthonous–parautochthonous, lithologically heterogeneous metaturbidites showing common enrichment in quartz. All the analysed detrital zircons are of a local Neoarchean source but tDM variation up to 2.4 Ga combined with geochemical data indicate abundant mixing of Paleoproterozoic mafic material, presumably from 2.1 Ga plateau lavas and dykes, in most of the Lower Kaleva samples.The Upper Kaleva is dominantly allochthonous with tectonically enclosed fragments of ophiolite bodies, and it is characterized by lithological and geochemical-isotopic homogeneity. Geochemical, isotopic and detrital zircon data favour material derived from an orogenic domain, comprising both Archean and Proterozoic units, followed by effective mixing during the transport. The Archean zircon grains (25%) are mostly Neoarchean. The Paleoproterozoic grains lack zircons at 2.5–2.2 Ga and plot dominantly (92%) between 1.92 and 2.05 Ga. The indicated maximum deposition ages vary from 1.95–1.94 Ga to 1.92 Ga. The main source area proposed is the Himalaya-type Lapland-Kola orogen (now) in the northeast, which experienced mountain building and erosion at 1.95–1.91 Ga.The western margin of the Karelian Province shows evidence of rifting and lithosphere thinning from 2.1 to 1.95 Ga but it is still under debate whether the craton breakup occurred at 2.06 Ga in a volcanic or later at 1.95 Ga in a non-volcanic margin setting. One hypothesis is that the onset of collision in the northeast changed plate motion and lead to a new spreading within the pre-existing passive margin at 1.97–1.95 Ga. Thus, both a volcanic margin at 2.06 Ga and a non-volcanic margin at ca. 1.95 Ga could have been operated at the western margin of the Karelian Province.  相似文献   

16.
The Sunsás–Aguapeí province (1.20–0.95 Ga), SW Amazonian Craton, is a key area to study the heterogeneous effects of collisional events with Laurentia, which shows evidence of the Grenvillian and Sunsás orogens. The Sunsás orogen, characterized by an allochthonous collisional-type belt (1.11–1.00 Ga), is the youngest and southwesternmost of the events recorded along the cratonic fringe. Its evolution occurred after a period of long quiescence and erosion of the already cratonized provinces (>1.30 Ga), that led to sedimentation of the Sunsás and Vibosi groups in a passive margin setting. The passive margin stage was roughly contemporary with intraplate tectonics that produced the Nova Brasilândia proto-oceanic basin (<1.21 Ga), the reactivation of the Ji-Paraná shear zone network (1.18–1.12 Ga) and a system of aborted rifts that evolved to the Huanchaca–Aguapeí basin (1.17–1.15 Ga). The Sunsás belt is comprised by the metamorphosed Sunsás and Vibosi sequences, the Rincón del Tigre mafic–ultramafic sill and granitic intrusive suites. The latter rocks yield εNd(t) signatures (?0.5 to ?4.5) and geochemistry (S, I, A-types) suggesting their origin associated with a continental arc setting. The Sunsás belt evolution is marked by “tectonic fronts” with sinistral offsets that was active from c. 1.08 to 1.05 Ga, along the southern edge of the Paraguá microcontinent where K/Ar ages (1.27–1.34 Ga) and the Huanchaca–Aguapeí flat-lying cover attest to the earliest tectonic stability at the time of the orogen. The Sunsás dynamics is coeval with inboard crustal shortening, transpression and magmatism in the Nova Brasilândia belt (1.13–1.00 Ga). Conversely, the Aguapeí aulacogen (0.96–0.91 Ga) and nearby shear zones (0.93–0.91 Ga) are the late tectonic offshoots over the cratonic margin. The post-tectonic to anorogenic stages took place after ca. 1.00 Ga, evidenced by the occurrences of intra-plate A-type granites, pegmatites, mafic dikes and sills, as well as of graben basins. Integrated interpretation of the available data related to the Sunsás orogen supports the idea that the main nucleus of Rodinia incorporated the terrains forming the SW corner of Amazonia and most of the Grenvillian margin, as a result of two independent collisional events, as indicated in the Amazon region by the Ji-Paraná shear zone event and the Sunsás belt, respectively.  相似文献   

17.
《Gondwana Research》2013,24(4):1342-1364
Based mainly on field geological observation and geochronologic data, six tectonic units have been recognized in western Inner Mongolia (China), including, from south to north: North China Craton (NCC), Southern Orogenic Belt (SOB), Hunshandake Block (HB), Northern Orogenic Belt (NOB), South Mongolia microcontinent (SMM), and Southern margin of Ergun Block (SME), suggesting that the tectonic framework of the CAOB in western Inner Mongolia is characterized by an accretion of different blocks and orogenic belts. The SOB includes, from north to south, fold belt, mélange, arc-pluton belt, and retroarc foreland basin, representing a southern subduction–collision system between the NCC and HB blocks during 500–440 Ma. The NOB consists also of four units: arc-pluton belt, mélange, foreland molasse basin, and fold belt, from north to south, representing a northern subduction–collision system between the HB and SMM blocks during 500–380 Ma. From the early Paleozoic, the Paleo-Asian oceanic domains subducted to the north and the south, resulting in the forming of the SOB and the NOB in 410 Ma and 380 Ma, respectively. This convergent orogenic system, therefore, constrained the consumption process of the Paleo-Asian Ocean in western Inner Mongolia. A double subduction–collision accretionary process is the dominant geodynamic feature for the eastern part of the CAOB during the early to middle Paleozoic.  相似文献   

18.
《Precambrian Research》2006,144(1-2):92-125
This paper presents a plate tectonic model for the evolution of the Australian continent between ca. 1800 and 1100 Ma. Between ca. 1800 and 1600 Ma episodic orogenesis occurred along the southern margin of the continent above a north-dipping subduction system. During this interval multiple orogenic events occurred. The West Australian Craton collided with the North Australian Craton (ca. 1790–1770 Ma), the Archaean nucleus of the Gawler Craton amalgamated with the North Australian Craton (ca. 1740–1690 Ma), and numerous smaller terranes accreted along the western Gawler Craton and the southern Arunta Inlier (ca. 1690–1640 Ma). The pattern of accretion suggests southward migration of the plate margin, which occurred due to a combination of slab rollback and back stepping of a subduction system behind the accreted continental blocks. Coeval with subduction a series of continental back-arc basins formed in the interior of the North Australian Craton and parts of the South Australian Craton, which were attached to the North Australian Craton prior to 1500 Ma. Extension of the North Australian Craton led to the opening of an oceanic basin along the eastern margin of the continent at ca. 1660 Ma. Continuing divergence was accommodated by oceanic spreading whereas the continental basins thermally subsided resulting in the development of sag-phase basins throughout the North Australian Craton. This oceanic basin was subsequently consumed during convergence, which ultimately led to development of a ca. 1600–1500 Ma orogenic belt along the eastern margin of Proterozoic Australia. Between ca. 1470 and 1100 Ma, the South Australian Craton, consisting of the Curnamona Province and the Gawler Craton rifted from the North Australian Craton and was re-attached in its present configuration during episodic ca. 1330–1100 Ma orogenesis, which is preserved in the Albany-Fraser Belt and the Musgrave Block.  相似文献   

19.
《Gondwana Research》2013,24(4):1402-1428
The formation of collisional orogens is a prominent feature in convergent plate margins. It is generally a complex process involving multistage tectonism of compression and extension due to continental subduction and collision. The Paleozoic convergence between the South China Block (SCB) and the North China Block (NCB) is associated with a series of tectonic processes such as oceanic subduction, terrane accretion and continental collision, resulting in the Qinling–Tongbai–Hong'an–Dabie–Sulu orogenic belt. While the arc–continent collision orogeny is significant during the Paleozoic in the Qinling–Tongbai–Hong'an orogens of central China, the continent–continent collision orogeny is prominent during the early Mesozoic in the Dabie–Sulu orogens of east-central China. This article presents an overview of regional geology, geochronology and geochemistry for the composite orogenic belt. The Qinling–Tongbai–Hong'an orogens exhibit the early Paleozoic HP–UHP metamorphism, the Carboniferous HP metamorphism and the Paleozoic arc-type magmatism, but the three tectonothermal events are absent in the Dabie–Sulu orogens. The Triassic UHP metamorphism is prominent in the Dabie–Sulu orogens, but it is absent in the Qinling–Tongbai orogens. The Hong'an orogen records both the HP and UHP metamorphism of Triassic age, and collided continental margins contain both the juvenile and ancient crustal rocks. So do in the Qinling and Tongbai orogens. In contrast, only ancient crustal rocks were involved in the UHP metamorphism in the Dabie–Sulu orogenic belt, without involvement of the juvenile arc crust. On the other hand, the deformed and low-grade metamorphosed accretionary wedge was developed on the passive continental margin during subduction in the late Permian to early Triassic along the northern margin of the Dabie–Sulu orogenic belt, and it was developed on the passive oceanic margin during subduction in the early Paleozoic along the northern margin of the Qinling orogen.Three episodes of arc–continent collision are suggested to occur during the Paleozoic continental convergence between the SCB and NCB. The first episode of arc–continent collision is caused by northward subduction of the North Qinling unit beneath the Erlangping unit, resulting in UHP metamorphism at ca. 480–490 Ma and the accretion of the North Qinling unit to the NCB. The second episode of arc–continent collision is caused by northward subduction of the Prototethyan oceanic crust beneath an Andes-type continental arc, leading to granulite-facies metamorphism at ca. 420–430 Ma and the accretion of the Shangdan arc terrane to the NCB and reworking of the North Qinling, Erlangping and Kuanping units. The third episode of arc–continent collision is caused by northward subduction of the Paleotethyan oceanic crust, resulting in the HP eclogite-facies metamorphism at ca. 310 Ma in the Hong'an orogen and low-P metamorphism in the Qinling–Tongbai orogens as well as crustal accretion to the NCB. The closure of backarc basins is also associated with the arc–continent collision processes, with the possible cause for granulite-facies metamorphism. The massive continental subduction of the SCB beneath the NCB took place in the Triassic with the final continent–continent collision and UHP metamorphism at ca. 225–240 Ma. Therefore, the Qinling–Tongbai–Hong'an–Dabie–Sulu orogenic belt records the development of plate tectonics from oceanic subduction and arc-type magmatism to arc–continent and continent–continent collision.  相似文献   

20.
《Precambrian Research》2005,136(2):159-175
Juvenile Neoproterozoic dioritic, tonalitic, trondhjemitic and granodioritic gneisses in the São Gabriel block, southern Brazil, have been identified by geochronologic studies. Age proposals for associated (ultra-)mafic metavolcanic and metasedimentary rocks, however, range from Archean to Neoproterozoic. Whole rock Sm–Nd analyses presented here support a Neoproterozoic age for these rocks. TDM model ages of the (ultra-)mafic metavolcanic rocks range between 0.65 and 1.35 Ga with ɛNd(t) positive values between 3.16 and 6.87; TDM model ages of metasedimentary and metavolcanoclastic rocks vary between 0.77 and 1.19 Ga with ɛNd(t) values between 1.2 and 6.23; tonalitic calc-alkaline gneisses show ɛNd(t) values of 4.34 and 6.3 and TDM model ages of 0.89 and 0.72 Ga, respectively. A late-kinematic granite (Santa Zélia granite) display slightly negative ɛNd(t) values (−1.6) and a higher TDM model age of about 1.4 Ga. These data support the existence of Meso/Neoproterozoic juvenile oceanic crust and island arc rocks during the Brasiliano orogenic events. The main source rocks of the metasedimentary units are previously formed juvenile rocks. The data also indicate minor assimilation of older crustal material and/or contamination of the melts by radiogenic Nd released from older rocks on the subducting slab. Existence of widespread old sialic crust in the subduction zone environment, however, can be ruled out indicating important orogenic accretion between 0.9 and 0.7 Ga. A geotectonic model for the São Gabriel block and the eastern margin of the Rio de la Plata craton comprises eastward subduction and following accretion of an intra-oceanic island arc between 0.9 and 0.8 Ga and a subsequent westward subduction with formation of an active continental margin at the eastern margin of the Rio de la Plata craton between 0.8 and 0.7 Ga. We postulate that the juvenile rocks of São Gabriel block represent relics of a Neoproterozoic ocean between the Rio de la Plata craton and a continental block (Encantadas block) possibly derived from the Kalahari craton. Subduction and arc accretion began roughly coeval with the initial stages of the break-up of Rodinia (0.9 Ga) and indicate a peripheric Rio de la Plata craton in relation to the Rodinia supercontinent with evolution from a passive margin to an active margin in the beginning of the Neoproterozoic Brasiliano orogenic events.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号