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1.
The Permian Cape Fold Belt (CFB) of South Africa forms part of a major orogenic belt that originally extended from Argentina, across southern Africa and into Antarctica. The CFB is dominated by complexly folded and faulted rocks of the siliciclastic Cape Supergroup that were deposited in the Cape Basin. The provenance of the Cape Supergroup, timing of deformation and tectonic setting are poorly constrained. U-Pb detrital zircon provenance studies suggest that the Cape Basin received sedimentary detritus from the African Mesoproterozoic Namaqua-Natal Metamorphic Belt, Neoproterozoic-Cambrian Pan-African Belts and the Brasiliano orogenic belts of South America, Africa and Antarctica. However, as zircon is able to survive multiple orogenic and sedimentary transport cycles, complementary provenance tools are required to confirm Cape Supergroup provenance. Previous studies have suggested both uni-modal and multi-modal models for the timing of CFB orogenesis. In the current study, structurally controlled, muscovite-bearing samples were collected along several north-south traverses across the CFB. Detailed textural and mineral chemistry analyses identified multiple muscovite populations, commonly with complex intergrowth features. High precision 40Ar/39Ar analyses reveal a dominant 490–465 Ma detrital muscovite population, lending support to a largely South American provenance for the Cape Supergroup. Lesser detrital muscovite populations in the range 650–500 Ma and >730 Ma, corroborate previous zircon provenance studies suggesting Pan-African/Brasiliano terranes and the Namaqua-Natal Metamorphic Belt as significant sediment sources, respectively. Detailed 40Ar/39Ar analyses of multiple neo-crystallised muscovite samples are consistent with a single major phase of CFB deformation occurring between 253.4 and 249.6 Ma. This age is interpreted to represent either the peak or final dominant phase of CFB deformation.  相似文献   

2.
The age and Precambrian history of the Moine Supergroup within the Caledonide belt of north-west Scotland have long been contentious issues. The Ardgour granite gneiss is essentially an in situ anatectic granite formed during deformation and regional high-grade metamorphism from Moine metasediments. High-precision TIMS and SHRIMP U-Pb zircon dating shows that the age of the anatectic Ardgour granite gneiss and its enclosed segregation pegmatites is 873 ± 7 Ma. This demonstrates the reality of a Neoproterozoic episode of high-grade metamorphism in the Glenfinnan Group Moine and, contrary to previous evidence, the absence of Grenvillian-aged metamorphism. This conclusion places constraints on Neoproterozoic palaeogeographic reconstructions of the North Atlantic region, indicating that the Moine rocks cannot be used as a link between the Grenvillian belt of North America and the Sveconorwegian orogen in Scandinavia. SHRIMP ages of between c. 1100 and 1900 Ma were obtained from detrital, inherited zircons and reflect the provenance of the Glenfinnan Group Moine sediments which must, therefore, have been deposited between c. 1100 and 870 Ma. Potential sources are found as relatively minor, tectonically bounded basement inliers within the British Caledonides, although more widespread source areas occur outside Britain in both Laurentia and Baltica. The most important feature of the provenance is the absence of detrital Archaean grains. This suggests that the Archaean Lewisian gneiss complex, which forms the basement component of the western foreland to the Caledonides in Britain, was not a major contributor to the Glenfinnan Group basin. Received: 16 June 1996 / Accepted: 29 January 1997  相似文献   

3.
The Neoproterozoic sedimentary cover deposited across the interface of several Pan-African/Brasiliano fold-thrust belts with their respective cratons is strongly similar and has been widely correlated throughout Gondwana. In particular, the upper part of the cratonic cover of the São Francisco Craton has been interpreted as a ring of foreland basin sediments. However, detailed studies carried out around the southern-central part of the Sergipano Belt (NE Brazil) and its interface with the northern margin of the São Francisco Craton demonstrate that: (1) sedimentation records the evolution of a passive continental margin and is divided into two cycles (I and II), each one comprising a basal siliciclastic megasequence overlain by a carbonate megasequence; (2) the cratonic cover comprises cycle I and part of the basal megasequence of cycle II; (3) all of these rocks spread continuously across the craton margin into the Sergipano Belt, where they occur around basement domes and are overlain by a metadiamictite formation and a metacarbonate formation that complete cycle II; and (4) basement and cover underwent the same Brasiliano (670–600 Ma) compressive deformation under sub-greenschist metamorphic conditions. These data deny the foreland basin model for the cratonic sediments to the south of the Sergipano Belt and, coupled with recent data on the evolution of other margins of the craton, indicate that the Neoproterozoic sedimentary cover derives from highs existing close to the centre of the ancient São Francisco Plate. This sedimentary cover was also influenced by highs of an Andean-type margin that evolved ca 900–640 Ma along the western side of the plate. Such evolution also applies to the Neoproterozoic cover of other cratons of the Pan-African/Brasiliano orogeny.  相似文献   

4.
The Punta del Este Terrane (eastern Uruguay) lies in a complex Neoproterozoic (Brasiliano/Pan-African) orogenic zone considered to contain a suture between South American terranes to the west of Major Gercino?CSierra Ballena Suture Zone and eastern African affinities terranes. Zircon cores from Punta del Este Terrane basement orthogneisses have U?CPb ages of ca. 1,000?Ma, which indicate an lineage with the Namaqua Belt in Southwestern Africa. U?CPb zircon ages also provide the following information on the Punta del Este terrane: the orthogneisses containing the ca. 1,000?Ma inheritance formed at ca. 750?Ma; in contrast to the related terranes now in Africa, reworking of the Punta del Este Terrane during Brasiliano/Pan-African orogenesis was very intense, reaching granulite facies at ca. 640?Ma. The termination of the Brasiliano/Pan-African orogeny is marked by formation of acid volcanic and volcanoclastic rocks at ca. 570?Ma (Sierra de Aguirre Formation), formation of late sedimentary basins (San Carlos Formation) and then intrusion at ca. 535?Ma of post-tectonic granitoids (Santa Teresa and José Ignacio batholiths). The Punta del Este Terrane and unrelated western terranes represented by the Dom Feliciano Belt and the Río de La Plata Craton were in their present positions by ca. 535?Ma.  相似文献   

5.
The Palaeoproterozoic Magondi Supergroup lies unconformably on the Archaean granitoid-greenstone terrain of the Zimbabwe Craton and experienced deformation and metamorphism at 2.06–1.96 Ga to form the Magondi Mobile Belt. The Magondi Supergroup comprises three lithostratigraphic units. Volcano-sedimentary rift deposits (Deweras Group) are unconformably overlain by passive margin, back-arc, and foreland basin sedimentary successions, including shallow-marine sedimentary rocks (Lomagundi Group) in the east, and deeper-water shelf to continental slope deposits in the west (Piriwiri Group). Based on the upward-coarsening trend and presence of volcanic rocks at the top of the Piriwiri and Lomagundi groups, the Piriwiri Group is considered to be a distal, deeper-water time-equivalent of the Lomagundi Group. The Magondi Supergroup experienced low-grade metamorphism in the southeastern zone, but the grade increases to upper greenschist and amphibolite facies grade to the north along strike and, more dramatically, across strike to the west, reaching upper amphibolite to granulite facies in the Piriwiri Group.  相似文献   

6.
《Gondwana Research》2001,4(3):289-306
The Neoproterozoic geological history in western Rajasthan, northwest Indian Shield began with the intrusion of anorogenic bodies of diorites at ca. 1000 Ma. Recently available single zircon dates indicate possible continuity of the “Grenville belt” beyond Eastern Ghats through the Satpura Orogenic Belt into the Aravalli Mountains. Closely following this tectono-thermal event at the Meso-Neoproterozoic boundary, some narrow basins opened west of the Aravalli Mountains. The basin closing related to the tectonic inversion and associated magmatism at ca. 835 Ma completed the cratonisation process of the Precambrian Aravalli crust. Subsequent geological events witnessed over a wide region to the southwest of the Aravalli Mountains, were in the form of “plume-related” magmatism of the Malani Group, which comprises bimodal volcanics (dominantly felsic and minor mafic), minor sediments, and peraluminous and peralkaline granitoids. An unconformity indicating a hiatus is noticed at the base of the Malani Group. The final phase of the Neoproterozoic cratonic history is associated with thick platformal deposits of the Marwar Supergroup. The Marwar basins show a clear sedimentological affiliation with the sub-Himalayan basin of “Saline Series” in Pakistan.The beginning of the Neoproterozoic history in the northwestern Indian Shield is correlated with the events related to the possible break up of the Rodinia Supercontinent. Much of the later phases of the Neoproterozoic geological events witnessed in the Indian Shield are traditionally described as the “Pan-African”. However, the geological events recorded in the northwestern part of Indian Shield are neither strictly coeval nor are tectonically correlatable with the ‘orogeny and fabric-forming contemporary events’ of the East African Orogeny (EAO), which is undoubtedly the type terrane of the Pan-African Tectono-thermal Belt. The evolution of the northwestern Indian Shield during the Neoproterozoic does not appear to be related in any way with the Pan-African events observed in EAO. Further, the most talked about ‘Pan-African’ dates at ca. 500±50 Ma, are manifestations of anorogenic thermal event, which possibly marks an aborted attempt to fragment the ‘Greater Gondwana’ during the early Palaeozoic.  相似文献   

7.
塔里木盆地巴楚隆起西缘的同1井(TX1)在寒武系之下钻遇一套火山岩,本文对该套火山岩的岩石类型、形成时代、岩石成因及构造环境进行了详细研究。结果显示,这套火山岩可分为上下两段,分别为杏仁状辉石安山岩和角闪石英安岩,属于钙碱性系列火山岩,形成于大陆边缘弧构造环境。安山岩锆石U-Pb年龄(747±12Ma)表明该岩浆弧发育时代为新元古代。同1井钻揭的火山岩与卡塔克隆起上塔参1井(TC1)钻揭的闪长岩(744.0±9.3Ma~790.0±22.1Ma)和花岗闪长岩(757.4±6.2Ma)成岩时代一致、形成环境相同,表明横亘塔里木盆地中部的古隆起带(巴楚隆起-卡塔克隆起-古城虚隆起)起源于一条新元古代陆缘岩浆弧,塔里木盆地的基底是由新元古代造山作用拼合的基底。以中央隆起带为界,南、北塔里木的基底性质和成盆演化过程可能有所差异。  相似文献   

8.
The Damara Orogen is composed of the Damara, Kaoko and Gariep belts developed during the Neoproterozoic Pan-African Orogeny. The Damara Belt contains Neoproterozoic siliciclastic and carbonate successions of the Damara Supergroup that record rift to proto-ocean depositional phases during the Rodinia supercontinent break up. There are two conflicting interpretations of the geotectonic framework of the Damara Supergroup basin: i) as one major basin, composed of the Outjo and Khomas basins, related to rifting in the Angola-Congo-Kalahari paleocontinent or, ii) as two independent passive margin basins, one related to the Angola-Congo and the other to the Kalahari proto-cratons. Detrital zircon provenance studies linked to field geology were used to solve this controversy. U-Pb zircon age data were analyzed in order to characterize depositional ages and provenance of the sediments and evolution of the succession in the northern part of the Outjo Basin. The basal Nabis Formation (Nosib Group) and the base of the Chuos Formation were deposited between ca. 870 Ma and 760 Ma. The upper Chuos, Berg Aukas, Gauss, Auros and lower Brak River formations formed between ca. 760 Ma and 635 Ma. It also includes the time span recorded by the unconformity between the Auros and lower Brak River formations. The Ghaub, upper Brak River, Karibib and Kuiseb formations were deposited between 663 Ma and 590 Ma. The geochronological data indicate that the main source areas are related to: i) the Angola-Congo Craton, ii) rift-related intrabasinal igneous rocks of the Naauwpoort Formation, iii) an intrabasinal basement structural high (Abbabis High), and iv) the Coastal Terrane of the Kaoko Belt. The Kalahari Craton units apparently did not constitute a main source area for the studied succession. This is possibly due to the position of the succession in the northern part of the Outjo Basin, at the southern margin of the Congo Craton. Comparison of the obtained geochronological data with those from the literature shows that the Abbabis High forms part of the Kalahari proto-craton and that Angola-Congo and Kalahari cratons were part of the same paleocontinent in Rodinia times.  相似文献   

9.
The Neoproterozoic to Early Cambrian amalgamation of SW Gondwana through the Brasiliano/Pan-African orogeny is reviewed with emphasis on the role of the Río de la Plata craton of South America in the light of new evidence from a borehole at the eastern end of the Tandilia belt (38°S). U–Pb, Hf and O isotope data on zircon indicate that this un-reworked Palaeoproterozoic craton abuts against a distinct continental terrane to the east (Mar del Plata terrane). The craton is bounded everywhere by transcurrent faults and there is no evidence to relate it to the Neoproterozoic mobile belts now seen on either side. The Punta Mogotes Formation at the bottom of the borehole contains 740–840 Ma detrital zircons that are assigned to a widespread Neoproterozoic rifting event. The data suggest that the Mar del Plata terrane rifted away from the southwestern corner of the Angola block at c. 780 Ma. Negative εHft values and δ18O > 6.5‰ suggest derivation by melting of old crust during a protracted extensional episode. Other continental terranes may have formed in a similar way in Uruguay (Nico Pérez) and southeastern Brazil, where the Schist Belt of the Dom Feliciano orogenic belt is probably a correlative of the Punta Mogotes sequence, implying that the Dom Feliciano belt must extend at least as far as 38°S. A new geodynamic scenario for West Gondwana assembly includes at least two major oblique collisional orogenies: Kaoko–Dom Feliciano (580–680 Ma) and Gariep–Saldania (480–580 Ma), the latter resulting from oblique impingement of the Rio de la Plata craton against the Kalahari craton. Assembly of this part of South-West Gondwana was accomplished before the Ordovician (to Silurian?) siliciclastic platform sediments of the Balcarce Formation in the Tandilia Belt covered the southern sector of Río de la Plata craton.  相似文献   

10.
The Neoproterozoic Katangan Supergroup comprises a thick sedimentary rock succession subdivided into the Roan, Nguba, and Kundelungu Groups, from bottom to top. Deposition of both Nguba and Kundelungu Groups began with diamictites, the Mwale/Grand Conglomérat and Kyandamu/Petit Conglomérat Formations, respectively, correlated with the 750 Ma Sturtian and (supposedly) 620 Ma Marinoan/Varanger glacial events. The Kaponda, Kakontwe, Kipushi and Lusele Formations are interpreted as cap-carbonates overlying the diamictites. Petrographical features of the Nguba and Kundelungu siliciclastic rocks indicate a proximal facies in the northern areas and a basin open to the south. The carbonate deposits increase southward in the Nguba basin. In the southern region, the Kyandamu Formation contains clasts from the underlying rocks, indicating an exhumation and erosion of these rocks to the south of the basin. It is inferred that this formation deposited in a foreland basin, dating the inversion from extensional to compressional tectonics, and the northward thrusting. Sampwe and Biano sedimentary rocks were deposited in the northernmost foreland basin at the end of the thrusting. The Zn–Pb–Cu and Cu–Ag–Au epigenetic, hypogene deposits occurring in Nguba carbonates and Kundelungu clastic rocks probably originate from hydrothermal resetting and remobilization of pre-existing stratiform base metal mineralisations in the Roan Group.  相似文献   

11.
In order to facilitate the understanding of the geological evolution of the Kalahari Craton and its relation to South America, the provenance of the first large-scale cratonic cover sequence of the craton, namely the Ordovician to Carboniferous Cape Supergroup was studied through geochemical analyses of the siliciclastics, and age determinations of detrital zircon. The Cape Supergroup comprises mainly quartz-arenites and a Hirnantian tillite in the basal Table Mountain Group, subgreywackes and mudrocks in the overlying Bokkeveld Group, while siltstones, interbedded shales and quartz-arenites are typical for the Witteberg Group at the top of the Cape Supergroup. Palaeocurrent analyses indicate transport of sediment mainly from northerly directions, off the interior of the Kalahari Craton with subordinate transport from a westerly source in the southwestern part of the basin near Cape Town. Geochemical provenance data suggest mainly sources from passive to active continental margin settings. The reconnaissance study of detrital zircons reveals a major contribution of Mesoproterozoic sources throughout the basin, reflecting the dominance of the Namaqua-Natal Metamorphic Belt, situated immediately north of the preserved strata of Cape Supergroup, as a source with Archaean-aged zircons being extremely rare. We interpret the Namaqua-Natal Metamorphic Belt to have been a large morphological divide at the time of deposition of the Cape Supergroup that prevented input of detrital zircons from the interior early Archaean Kaapvaal cratonic block of the Kalahari Craton. Neoproterozoic and Cambrian zircons are abundant and reflect the basement geology of the outcrops of Cape strata. Exposures close to Cape Town must have received sediment from a cratonic fragment that was situated off the Kalahari Craton to the west and that has subsequently drifted away. This cratonic fragment predominantly supplied Meso- to Neoproterozoic, and Cambrian-aged zircon grains in addition to minor Silurian to Lower Devonian zircons and very rare Archaean (2.5?Ga) and late Palaeoproterozoic (1.8-2.0?Ga) ones. No Siluro-Devonian source has yet been identified on the Kalahari Craton, but there are indications for such a source in southern Patagonia. Palaeozoic successions in eastern Argentina carry a similar detrital zircon population to that found here, including evidence of a Silurian to Lower Devonian magmatic event. The Kalahari and Río de la Plata Cratons were thus in all likelihood in close proximity until at least the Carboniferous.  相似文献   

12.
Detrital zircon and monazite dating of clastic rocks in the Mesozoic Kutch Basin at the western continental margin of India reveals predominant sediment derivation from rocks of Neoproterozoic Pan-African orogeny, followed by those of Cambro-Ordovician Bhimphedian (or Kurgiakh) orogeny and 850–1000 Ma rocks, with subordinate input from rocks of 700–800 Ma, 1500–1600 Ma, 2400–2500 Ma and 2800–3300 Ma. This finding refutes the existing idea regarding the predominant Mesoproterozoic source inferred for this basin. The dominance of southwesterly palaeocurrent data of Mesozoic rocks in Kutch Basin rules out sediment supply from south or west. Th/U ratios of detrital zircon grains indicate predominantly magmatic and subordinately metamorphic source rock. Petrographic data, particularly the QFR plot supports this interpretation of source rock. Rocks belonging to the Pan-African orogeny are poorly exposed in northwestern India while isolated outcrops of peralkaline granites in the Himalayan region bear testimony of the Bhimphedian orogeny. While the paucity of records of the Pan-African orogeny in western India possibly relates to either burial under the Deccan Flood Basalts or extensive erosion during Mesozoic greenhouse climate, the dearth of rocks of Bhimphedian orogeny results from its occurrence along the present-day Himalayan thrust belt. The absence of detrital zircon grains younger than 458 Ma indicates that post-Ordovician tectono-thermal events skipped the source area. The large gap between youngest detrital zircon and the depositional age of the Mesozoic sediments, suggests long-distance sediment transport as well as sediment recycling. This study, therefore, indicates the existence of widespread younger magmatic rocks to the north during the deposition of Mesozoic of Kutch.  相似文献   

13.
The Menderes Massif, exposed in western Anatolia, is a metamorphic complex cropping out in the Alpine orogenic belt. The metamorphic rock succession of the Massif is made up of a Precambrian basement and overlying Paleozoic-early Tertiary cover series. The Pan-African basement is composed of late Proterozoic metasedimentary rocks consisting of partially migmatized paragneisses and conformably overlying medium- to high-grade mica schists, intruded by orthogneisses and metagabbros. Along the southern flank of the southern submassif, we recognized well-preserved primary contact relationship between biotite and leucocratic tourmaline orthogneisses and country rocks as the orthogneisses represent numerous large plutons, stocks and vein rocks intruded into a basement of garnet mica schists. Based on the radiometric data, the primary deposition age of the precursors of the country rocks, garnet mica schist, can be constrained between 600 and 550?Ma (latest Neoproterozoic). The North Africa–Arabian-Nubian Shield in the Mozambique Belt can be suggested as the possible provenance of these metaclastics. The intrusion ages of the leucocratic tourmaline orthogneisses and biotite orthogneisses were dated at 550–540?Ma (latest Neoproterozoic–earliest Cambrian) by zircon U/Pb and Pb/Pb geochronology. These granitoids represent the products of the widespread Pan-African acidic magmatic activity, which can be attributed to the closure of the Mozambique Ocean during the final collision of East and West Gondwana. Detrital zircon ages at about 550?Ma in the Paleozoic muscovite-quartz schists show that these Pan-African granitoids in the basement form the source rocks of the cover series of the Menderes Massif.  相似文献   

14.
新元古代江南造山带远离晚中生代活动大陆边缘,是研究华南地区新元古代至早中生代多期造山作用的理想对象。文章通过对江南造山带东段沉积建造、岩浆活动、构造变形以及同位素年代学数据的综合分析,总结了其晋宁期、广西期以及印支期造山作用的特征。江南造山带东段在晋宁期经历了南北两侧大洋俯冲和两期碰撞造山作用。新元古代早期(880~860 Ma)双溪坞岛弧与扬子陆块东南缘发生弧-陆碰撞作用,形成淡色花岗岩、高压蓝片岩、NNE向褶皱-逆冲构造以及弧后前陆盆地。新元古代中期(约850 Ma),扬子陆块北缘开始发育由北向南的大洋俯冲。随着俯冲作用的进行,弧后盆地发生关闭,扬子陆块与华夏陆块发生陆-陆碰撞并形成新元古代(820~810Ma)江南造山带,导致近E-W走向褶皱-逆冲构造、韧性变形以及过铝质花岗岩的发育。江南造山带东段在约810Ma开始发生后造山垮塌和裂谷作用,以发育南华纪早期(805~750 Ma)花岗岩、中酸性火山岩、基性岩以及裂谷盆地为特征。江南造山带东段万载—南昌—景德镇—歙县断裂带以南地区卷入了华南广西期造山作用,发育近E-W走向由南向北的逆冲构造(465~450 Ma)、NNE向正花状构造(449~430 Ma)以及后造山近E-W走向韧性走滑剪切带(429~380 Ma)。印支期造山作用导致了NNE向褶皱-逆冲构造和花岗岩的发育,并奠定了江南造山带东段的基本构造面貌。  相似文献   

15.
塔里木克拉通基底古隆起构造-热事件及其结构与演化   总被引：10，自引：4，他引：6  
通过盆地内部锆石U-Pb测年分析表明,塔里木克拉通基底存在2950～ 3100Ma、2100 ～ 2400Ma、1900～2000Ma、1300～1600Ma、900 ～ 950Ma、700～800Ma、540 ～ 560Ma、400～ 500Ma和270～290Ma等9期构造-热事件.中央航磁异常带井下花岗岩锆石SHRIMP U-Pb年龄测定发现1908.2±8.6Ma前寒武纪基底,表明盆地内部可能存在古元古代构造-热事件形成的古老花岗岩基底.结合新的地质与地球物理资料综合分析,塔里木盆地前寒武纪具有不同年代、不同类型的基底结构,北部为中-新元古代中浅变质岩基底、中部为古元古代花岗岩基底、南部为新元古代早-中期岩浆岩与变质岩基底、东南部为遭受早志留纪区域变质改造的变质岩基底.井震结合发现塔里木盆地寒武系/前寒武系发育广泛分布的大型不整合,形成塔北与塔南两大前寒武纪基底古隆起,可能与550Ma“泛非运动”相关.塔里木盆地基底古隆起主要经历5期演化,古元古代中期形成克拉通化基底,新元古代早期形成统一的变质结晶基底,寒武纪沉积前两大基底古隆起形成,加里东晚期五大基底古隆起基本定型,海西期以来发生局部调整改造.  相似文献   

16.
华北克拉通南缘豫西地区保存有较为完整的变质结晶基底和中-新元古代沉积盖层,记录了重要的前寒武纪构造演化信息。近年来的年龄研究结果表明原认为是中-新元古代的汝阳群-洛峪群可能形成于中元古代早期(1. 75～1. 60Ga),而沿着华北克拉通南缘与秦岭造山带的拼合带(洛南-栾川断裂带)分布的新元古代盖层(主要为栾川群)的形成时代尚不明确。华北南缘新元古代栾川群主要由大理岩、片岩、千枚岩和碱性火山岩组成,其上部大红口组火山岩以碱性粗面质岩石为主,高硅富钾,与侵入到栾川群中下部的辉长岩构成典型的双峰式岩石组合。栾川群大红口组三个粗面岩样品的锆石U-Pb年龄分别为840±4Ma、845±5Ma和846±6Ma,结合已有的栾川群下伏地层最年轻的碎屑锆石年龄结果(～1000Ma),限定栾川群归属于新元古代早期(1000～840Ma)。大红口组岩浆岩的岩石组合和地球化学特征表明其形成于板内裂谷环境,根据区域构造资料以及前人的研究成果,栾川群火山岩与北秦岭同时期的岩浆活动共同指示了华北南缘与北秦岭在～845Ma均处于板内拉张阶段。  相似文献   

17.
The Satpura Mountain Belt (also referred as Central Indian Tectonic Zone in recent literature) forms an important morphotectonic unit in the central part of India. Some of the recent workers have reported an orogenic event at ∼1000–900 Ma (termed “Sausar orogeny”) which led to amalgamation of the North Indian Block and the South Indian Block and formation of the Satpura Mountain Belt. In this model the stratigraphic relations of two important lithostratigraphic units on either side of the Satpura Mountain Belt (the Sausar Group in the south and the Vindhyan Supergroup on the north) are suggested to be revised from previously held ideas. Critical analyses of available published work in the region to assess the status of the Sausar Group vis a vis the Vindhyan Supergroup was carried out. It is found that the ideas proposed by the recent workers stem from an earlier interpretation that the Sausar Group has monocyclic evolution and the earliest fabric in the Sausar Group is marked by a schistosity with EW strike. Re-mapping of the gneissic rocks and adjacent matasedimentary rocks of Khawasa, Deolapar, and Kandri–Mansar areas revealed presence of gneissic rocks and granulites of two generations, and of four phases of superposed deformations in the metasediments and gneisses. The older gneisses and granulites constitute the basement over which the rocks of the Sausar Group were deposited; and the younger gneisses developed by metamorphism and migmatisation of the rocks of the Sausar Group. The latter types are found in the Khawasa–Ramakona areas. Contrary to the belief of the recent workers that no volcanic activity is present in the Sausar Group, volcanic rocks marked by amygdular basic flows and tuffs have been mapped from different parts of the Sausar Group. Migmatisation and metamorphism of these volcanic rocks (of the Sausar Group) have given rise to amphibolites and granulites in Khawasa and Ramakona areas. Therefore, the use of fabric patterns in these areas to suggest that the granulite facies metamorphism in the Ramakona–Katangi granulite domain was pre-Sausar in age is debatable.Available geochronological data of the Satpura Mountain Belt and its eastward continuation into the Chhotanagpur Gneiss terrain indicate that the basement and cover rocks of these areas were subjected to multiple deformation and metamorphic episodes of similar style and nature. The earliest deformation and metamorphism of the rocks of the Sausar Group and its equivalent rocks to the east took place at ∼2100–1900 Ma. The regional EW trend of the belt developed during the second deformation at ∼1800–1700 Ma and again at ∼1600–1500 Ma. This deformation was accompanied by migmatisation and granulite facies metamorphism in the northern domain of the Sausar Belt and in the Chhotanagpur Gneiss region. Late phase low intensity deformations in the region were associated with thermal events at ∼1100–1000 Ma and ∼900–800 Ma.The ∼EW trending fabric, referred as “Satpura orogenic trend” in Indian literature marks a major compressional tectonic event, developed during the second deformation of the Sausar Group. This has its counter part in Western Australia as the Capricorn orogeny (∼1780–1830 Ma). The development of the Satpura Mountain Belt during the Grenvillian orogeny is ruled out from the synthesis of event stratigraphic data of the region and from its comparison with the Western Australian Craton.  相似文献   

18.
The itabirite-bearing metasedimentary sequence from Morro Escuro Ridge comprises the basal units of the Espinhaço Supergroup and makes up a small tectonic inlier developed during one of the Brasiliano orogenic events (800-500 Ma), amongst horses of the Archean TTG gneisses, including sheared granites of the anorogenic Borrachudos Suite (∼1700 Ma). The metasedimentary rocks are comprised of low-to intermediate-amphibolite facies schists, quartzites, conglomerates and banded iron formation (itabirite) correlatable with the sequences of the Serro Group, which underlies the metasedimentary rocks of the Espinhaço Supergroup in the Serra da Serpentina Ridge. A maximum Statherian deposition age (1668 Ma) was established using SHRIMP U–Pb isotopic constraints on zircon grains from conglomerate and quartzite units overlying the itabirite. The itabirite is predominantly hematitic and its geochemical characteristics are typical of a Lake Superior-type BIF deposited in a platformal, suboxic to anoxic environment distant from Fe-bearing hydrothermal vents. Close to the contact zone with amphibolites of the Early Neoproterozoic Pedro Lessa mafic suite, an increase of the magnetite content and crystallization of metasomatic Mg-hornblende and Ce-allanite can be observed. These mineralogical changes developed preferentially along the igneous contact zone but are probably co-genetic with the formation of alteration haloes in zircon grains during the Neoproterozoic Brasiliano orogeny (506 ± 6 Ma).  相似文献   

19.
The Dom Feliciano Belt evolution is reviewed based on cross-sections, space–time diagrams, P-T paths, and Sr–Nd isotopic data of pre-collisional metaigneous rocks. The belt is divided into northern, central and southern sectors, subdivided into tectonic domains, developed at Neoproterozoic pre-, syn- and post-collisional stages. The northern sector foreland pre-collisional setting represents a rift, with tholeiitic (meta)volcanic rocks (∼800 Ma) chronocorrelated to hinterland intermediate and acidic orthogneisses of high-K calc-alkaline arc signature. In contrast, the central sector records a complete section from the forearc towards the back-arc region during pre-collisional times. In the western domain, ophiolites (∼920 Ma) are associated with arc-related orthogneisses and metavolcanic rocks (880–830 Ma; 760–730 Ma). At back-arc position, continental arc-related magmatism (800–780 Ma) is registered by hinterland orthogneisses and central foreland metavolcanic rocks. Ophiolites on the hinterland opposite side comprise two compositional groups, with N-MORB and supra subduction signature, interpreted as a back-arc basin record (∼750 Ma). The pre-Neoproterozoic basement of the whole belt is correlated with the Nico Perez Terrane and Luis Alves Block (Archean to Mesoproterozoic, with Congo Craton affinity). This contrasts with the Piedra Alta Terrane (Rio de La Plata Craton, only Paleoproterozoic), westernmost Uruguay. The suture between the Piedra Alta and Nico Perez terranes is correlated with the suture zone in the westernmost central sector. Transpression affected both foreland and hinterland during collision (660–640 Ma), with high-T/low-P hinterland progressive exhumation, whilst foreland low- to medium-grade correlated sequences record underthrusting. Post-collisional processes included magmatism throughout the belt (640–580 Ma), strain partitioning along strike-slip shear zones, and foreland basin fill. Late tectono-metamorphic and magmatic processes (560–540 Ma) were attributed to the Kalahari Craton collision. Arc magmatism migration due to subduction angle variations suggests modern-style plate tectonics during Gondwana amalgamation. Diachronism and kinematic inversion are characteristic of an oblique convergent multi-plate orogenic system.  相似文献   

20.
秦岭岩群被认为是出露于北秦岭地体内最古老的前寒武纪基底岩石,记录了北秦岭造山带的地壳形成和演化历史。本文报道丹凤-西峡地区五件秦岭岩群片麻岩锆石U-Pb年龄结果,限定其形成和变质时代,探讨北秦岭地体的构造归属。定年结果表明,岩浆成因锆石颗粒的年龄集中在1400～1600Ma左右和850～950Ma左右,记录两期主要岩浆活动。6粒锆石具有变质成因特征,低Th/U比值(0.03),206Pb/238U年龄变化在510～465Ma之间,加权平均值477±18Ma。这一古生代变质叠加时代与北秦岭地体南北缘高压变质作用时代基本一致,说明秦岭岩群遭受到北秦岭造山带俯冲-碰撞造山过程的变质作用。秦岭岩群主要形成于中元古代晚期至新元古代早期,基底岩石缺乏早元古代和太古代岩浆活动的记录。在岩浆作用时代上,北秦岭地体与广泛发育新元古代中-晚期岩浆作用的扬子陆块北缘有差别,也不同于晚太古代-早元古代的华北陆块南缘,可能是中-新元古代形成的独立微陆块。  相似文献   

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