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1.
The Borborema Province is a complex neoproterozoic orogen in northeastern Brazil, made of a mosaic of fault-bounded terrains and several metassedimentary sequences. In the present work, new zircon U–Pb provenance data for metasedimentary rocks in the Western Pernambuco-Alagoas Domain, southern part of the Province, are reported. Detrital zircon ages range from Archean to Neoproterozoic. Three samples of the Cabrobó Complex were investigated: (i) sillimanite-kyanite-garnet-biotite schist, which presented mostly Ediacaran and Cryogenian detrital zircon ages (youngest zircon at ca. 554 Ma) indicating erosion of neoproterozoic sources, (ii) garnet-biotite schist, which has a dominant Tonian/Stenian population, a less abundant Cryogenian (youngest zircon age at ca. 643 Ma) as well as Paleoproterozoic and Archean zircon grains, and (iii) tourmaline-muscovite quartzite, which contains detrital zircon varying in age between ca. 2.08 Ga and 1.57 Ga, and an abundant population close to the Meso/Paleoproterozoic boundary, possibly associated with the erosion of rocks formed during the Statherian taphrogenesis, known in the central part of the São Francisco Craton as well as in other areas of the Borborema Province. Two samples of the Riacho Seco Metasedimentary Complex were also investigated: (i) a biotite schist with a dominant population presenting ages mostly between 2.3 and 2.7 Ga (youngest zircon age at ca. 2023 Ma) and (ii) a magnetite-biotite-muscovite quartzite, having detrital zircon grains with ages ranging between ca. 1.9 and 2.7 Ga. The sedimentary rocks of the Riacho Seco Complex may have their origin related to the erosion of sources within the São Francisco Craton. The data for the Riacho Seco metasedimentary rocks, however, are not conclusive with respect to the depositional age of the original sedimentary rocks. The sequence might represent exposure of an old (Paleoproterozoic) sedimentary pile or, alternatively, it comprises a neoproterozoic passive margin sequence, with the original sediments derived from the erosion of the cratonic areas to the south.  相似文献   

2.
廖鑫  张晓晖  金胜贤  朴雄  郑哲寿 《岩石学报》2016,32(10):2981-2992
克拉通内部活动带变质沉积建造蕴藏了早期超大陆形成中地体聚-散动力学过程的重要信息,碎屑锆石年代学则是揭示这种信息的最佳工具之一。针对华北(中-朝)克拉通最具代表性的古元古代活动带(辽-吉-朝活动带)中巨量沉积建造精细表征方面的空白区域,本文开展了朝鲜半岛检德地区摩天岭群的碎屑锆石年代学研究。SIMS U-Pb定年结果显示,北大川组变火山碎屑岩样品的锆石年龄谱记录了约2.53Ga的主要年龄峰值和约2.19Ga的最年轻峰值,说明北大川组开始沉积的时代应该晚于2.2Ga。南大川组变沉积岩样品碎屑锆石记录的最年轻峰值年龄为约2.02Ga,说明南大川组的沉积时代应该不早于2.02Ga;其锆石年龄谱记录了一个主要年龄峰值区域(2.02~2.18Ga)、一个次要年龄峰值(约2.46Ga)和一些2.78~3.30 Ga的古老年龄,指示其物质源区主要为同区古元古代地质体和邻近地体上的太古宙变质基底。区域对比表明,摩天岭群与中国境内辽吉活动带中的辽河群及集安群/老岭群具有基本一致的碎屑锆石年龄谱,说明它们不仅是同一时代的产物,而且分享类似的物质源区。这些时代一致、物源相近的沉积建造可以为甄别古元古代辽-吉-朝活动带的大地构造属性提供重要参考。与沉积年龄相近的碎屑锆石占据主导的碎屑锆石年龄谱反映了汇聚板块边缘各类盆地的典型特征,而相悖于大部分碎屑锆石年龄远大于地层沉积年龄的裂谷型盆地。  相似文献   

3.
The Serrinha magmatic suite (Mineiro belt) crops out in the southern edge of the São Francisco craton, comprising the Brito quartz-diorite, Brumado de Cima and Brumado de Baixo granodiorites, granophyres and felsic sub-volcanic and volcanic rocks, part of which intruded into the Nazareno greenstone belt. The suite rocks have petrographic features that are consistent with magma supercooling due to the low water content combined with volatile loss, leading to crystallization of quartz and alkaline feldspar at the rims of plagioclase phenocrysts (granophyric intergrowth). The investigated rocks are sub-alkaline, calc-alkaline and show low content in rare earth elements. The U–Pb zircon crystallization ages for the Brumado de Cima granodiorite [2227 ± 22 (23) Ma] and a coeval granophyre [2211 ± 22 (23) Ma], coupled with available single-zircon Pb evaporation ages for the Brito and Brumado de Baixo plutons, are significantly older than the “Minas orogeny” (ca. 2100–2050 Ga) of Quadrilátero Ferrífero area, eastward from the Serrinha suite. Our data establish an early Rhyacian event tectonically linked with the evolution of the Mineiro belt. The bulk Nd isotopic signature [low negative to positive εNd(t) values] of the Serrinha samples are consistent with the important role of Paleoproterozoic mantle components in the magma genesis. The integrated geologic, geochemical and isotopic information suggests that Paleoproterozoic evolution of the Mineiro belt initiated in a passive continental margin basin with deposition of the Minas Supergroup at ca. 2500 Ma. This stage was succeeded by outboard rupture of the oceanic lithosphere with development and coalescence of progressively younger magmatic arcs during Rhyacian time. One of the earliest arcs formed the Serrinha suite. The tectonic collage of the Serrinha and Ritápolis (2190–2120 Ma) arcs produced the NE–SW Lenheiro shear zone, resulting in mylonitization and recrystallization of both the granitoid intrusions and host rocks. As a matter of fact juxtaposition of distinct magmatic units in age and origin took place along the Lenheiros structure in this sector of the Mineiro belt.  相似文献   

4.
华北克拉通中部造山带早元古代盆地演化   总被引：3，自引：1，他引：2  
刘超辉  刘福来  赵国春 《岩石学报》2012,28(9):2770-2784
华北克拉通中部造山带被认为是由东、西部陆块碰撞而产生的陆陆碰撞带。然而,关于两个陆块碰撞的时间以及方式还存在着争议。其中一个模式认为俯冲方向是向西的,两个陆块最终碰撞的时间是在2.5Ga左右,而另一个模式则认为俯冲方向是向东的,并且存在着2.1Ga和1.85Ga两期碰撞事件,第三个模式则认为俯冲方向是向东的,而最终的碰撞拼合发生在1.85Ga左右。近几年来,对于中部造山带中浅变质表壳岩系的研究取得了很大进展,为解决以上争议提供了进一步的资料。根据岩石组合和表壳岩中的不整合接触关系,位于中部造山带中段五台杂岩中的滹沱群和吕梁杂岩中的野鸡山群被分成了上下两个部分。其中,两个群的下部以及位于中部造山带南段中条杂岩中的绛县群和下中条群主要由类似于弧后盆地沉积的变质碎屑岩、碳酸盐岩和火山岩组成,而滹沱群和野鸡山群的上部以及上中条群和担山石群的岩石组合则是类似于山前磨拉石建造的变质砾岩和砂岩。来自于这些浅变质碎屑岩中碎屑锆石的年龄为我们提供了源区以及最大沉积年龄的信息。滹沱群和野鸡山群中的碎屑锆石具有两个峰值年龄,2.5Ga和2.15Ga,它们分别对应于中部造山带中段两期重要的岩浆事件。中条杂岩中的碎屑锆石年龄图谱则较为复杂,除了具有2.5Ga和2.15Ga这两个峰值,还具有2.7Ga这个较低和较老的峰值,这些较老的锆石可能来自中部造山带最南端太华杂岩中的古老岩石。弧后盆地沉积中最年轻的碎屑锆石年龄在2.1Ga左右,而山前磨拉石中最年轻的碎屑锆石在1.85Ga左右。结合前人的研究成果,我们给出了一个华北克拉通中部造山带早元古代沉积盆地的演化模式。从2.1Ga左右开始,一系列弧后盆地在"安第斯型"大陆边缘弧之后产生,在之后的东西陆块碰撞过程中他们成为了中部造山带的一部分。从1.85Ga左右开始,东西陆块沿着中部造山带碰撞,导致了陆壳加厚以及随后的快速抬升和剥蚀,从而形成了周缘前陆盆地中的山前磨拉石建造。发生在早元古代晚期的由弧后盆地向周缘前陆盆地的转化支持了华北的最终克拉通化发生在1.85Ga的构造演化模式。  相似文献   

5.
The Paulistana and Santa Filomena Complexes are situated in the southern part of the Borborema Province (northeastern Brazil), in the Riacho do Pontal Orogen, and represent meta-volcano-sedimentary sequences. We present compositional variations in the metasedimentary rocks and new U–Pb detrital zircon data. Major and trace elements indicate that the metasedimentary rocks from the Paulistana and Santa Filomena Complexes are composed mostly of immature to mature sediments derived from felsic-intermediate sources with moderate to slightly high chemical weathering. The geochemical signatures of the sediment protoliths for both complexes are characteristic of continental magmatic arc settings with minor contribution from recycled sediment sources. The source area for the Paulistana Complex rocks follow the compositional trend between calc-alkaline granites and granodiorites, whereas the Santa Filomena Complex rocks have a more restricted composition trending to more granodioritic sources. For the Paulistana Complex, two main source ages were identified: (1) Tonian (ca. 950 Ma – sample RPE-58) and Tonian–Stenian (ca. 1.0 Ga – sample RPE-103). These data coupled with geochemical information suggest that the Cariris Velhos arc system was the main source area for the Paulistana Complex. Regarding the Santa Filomena metasedimentary rocks, potential source-areas include: (1) Neoarchaean rocks (~2.6 Ga) represented by the adjacent basement rocks of the Riacho do Pontal Orogen; (2) Rhyacian–Orosirian rocks (2.2–2.0 Ga) of the Riacho do Pontal Orogen and the Pernambuco–Alagoas terrain, which include an augen-gneiss with arc-related geochemical signature; (3) Statherian granites (1.7–1.6 Ga); and (4) Cariris Velhos crust (1000–920 Ma). The metasedimentary rocks of the Paulistana Complex were deposited in a rift stage (ca. 900 Ma), which is related to the break-up of the Rodinia supercontinent. The metasedimentary rocks of the Santa Filomena Complex most probably were deposited in another rift stage (ca. 750–700 Ma) and could be correlatives of the rift formation of the Canindé Domain (Sergipano Orogen).  相似文献   

6.
We present results of study of the trace-element and Lu–Hf isotope compositions of zircons from Paleoproterozoic high-grade metasedimentary rocks (paragneisses) of the southwestern margin of the Siberian craton (Irkut terrane of the Sharyzhalgai uplift). Metamorphic zircons are represented by rims and multifaceted crystals dated at ~ 1.85 Ga. They are depleted in either LREE or HREE as a result of subsolidus recrystallization and/or synchronous formation with REE-concentrating garnet or monazite. In contrast to the metamorphic zircons, the detrital cores are enriched in HREE and have high (Lu/Gd)n ratios, which is typical of igneous zircon. The weak positive correlation between 176Lu/177Hf and 176Hf/177Hf in the zircon cores evidences that their Hf isotope composition evolved through radioactive decay in Hf = the closed system. Therefore, the isotope parameters of these zircons can give an insight into the provenance of metasedimentary rocks. The Paleoproterozoic detrital zircon cores from paragneisses, dated at ~ 2.3–2.4 and 2.0–1.95 Ga, are characterized by a wide range of εHf values (from + 9.8 to –3.3) and model age T C 2.8–2.0 Ga. The provenance of these detrital zircons included both rocks with juvenile isotope Hf parameters and rocks resulted from the recycling of the Archean crust with a varying contribution of juvenile material. Zircons with high positive εHf values were derived from the juvenile Paleoproterozoic crustal sources, whereas the lower εHf and higher T C values for zircons suggest the contribution of the Archean crustal source to the formation of their magmatic precursors. Thus, at the Paleoproterozoic stage of evolution of the southwestern margin of the Siberian craton, both crustal recycling and crustal growth through the contribution of juvenile material took place. On the southwestern margin of the Siberian craton, detrital zircons with ages of ~ 2.3–2.4 and 1.95–2.0 Ga are widespread in Paleoproterozoic paragneisses of the Irkut and Angara–Kan terranes and in terrigenous rocks of the Urik–Iya graben, which argues for their common and, most likely, proximal provenances. In the time of metamorphism (1.88–1.85 Ga), the age of Paleoproterozoic detrital zircons (2.4–2.0 Ga), and their Lu–Hf isotope composition (εHf values ranging from positive to negative values) the paragneisses of the southwestern margin of the Siberian craton are similar to the metasedimentary rocks of the Paleoproterozoic orogenic belts of the North China Craton. In the above two regions, the sources of detrital zircons formed by both the reworking of the Archean crust and the contribution of juvenile material, which is evidence for the crustal growth in the period 2.4–2.0 Ga.  相似文献   

7.
Archean basement gneisses and supracrustal rocks, together with Neoproterozoic (Sinian) metasedimentary rocks (the Penglai Group) occur in the Jiaobei Terrane at the southeastern margin of the North China Craton. SHRIMP U–Pb zircon dating of an Archean TTG gneiss gave an age of 2541 ± 5 Ma, whereas metasedimentary rocks from the Neoproterozoic Penglai Group yielded a range in zircon ages from 2.9 to 1.8 Ga. The zircons can be broadly divided into three age populations, at: 2.0–1.8 Ga, 2.45–2.1 Ga and >2.5 Ga. Detrital zircon grains with ages >2.6 Ga are few in number and there are none with ages <1.8 Ga. These results indicate that most of the detrital material comes from a Paleoproterozoic source, most likely from the Jianshan and Fenzishan groups, with some material coming from Archean gneisses in the Jiaobei Terrane. An age of 1866 ± 4 Ma for amphibolite-facies hornblende–plagioclase gneiss, forming part of a supracrustal sequence within the Archean TTG gneiss, indicates Late Paleoproterozoic metamorphism. Both the Archean gneiss complex and Penglai metasedimentary rocks resemble previously described components of the Jiao-Liao-Ji orogenic belt and suggest that the Jiaobei Terrane has a North China Craton affinity; they also suggest that the time of collision along the Jiao-Liao-Ji Belt was at 1865 Ma.  相似文献   

8.
Thick quartzites record significant information on cratonic environments during long geological periods. The capacity to resist weathering and deformation turn the quartzite covers especially useful in the provenance studies of Precambrian basins. Provenance of 194 detrital zircon grains from two samples of thick quartzite cover on the Paleoproterozoic Encantadas Complex displays mostly Paleoproterozoic (95%) and minor Archean (5%) sources. The results indicate that sediments were derived from the La Plata Craton with the maximum depositional age at 2.03 Ga possibly up to 1.7 Ga. In comparison, the adjacent Porongos Group has provenance data of 61 detrital zircon grains indicating mostly Mesoproterozoic (69%), subordinately Paleoproterozoic (26%) and minor Archean ages (5%). Considering previous published data, the Porongos Group is Ediacaran in age and probably chronocorrelated with sedimentary basins from the Tandilia Belt (Argentina). Therefore, the quartzite cover and the Porongos Group require distinct evolution in time and in tectonic environment.  相似文献   

9.
运用碎屑锆石LA-ICP-MS U-Pb测年和地球化学方法,对内蒙古狼山东升庙和义和久地区侏罗系石拐群物源进行了探讨。通过对111颗有效锆石年龄统计分析可知,年龄峰值以晚古生代(259~308Ma)为主,其次为古元古代(1.74~2.18Ga)和早古元古代—新太古代(2.39~2.58Ga)。晚古生代年龄与狼山大规模出露的海西期岩浆岩年龄一致,古元古代—新太古代年龄与狼山地区古元古代岩浆岩、孔兹岩带年龄分布特征相近。侏罗系砂岩稀土元素配分特征与海西期岩浆岩、乌拉山群、孔兹岩系相似。结合石拐群样品薄片和砾岩分析,认为侏罗系为近源沉积,其物源主要为狼山地区大规模海西期岩浆岩,其次来自河套地区孔兹岩带,狼山地区太古宙乌拉山群、古元古代岩浆岩和早—中三叠世岩浆岩可能提供了部分物源。另外,根据碎屑锆石最年轻年龄为243Ma(中三叠世),结合前人植物化石组合研究及狼山地区整体缺失三叠纪地层的特点,认为该套地层的时代应为早—中侏罗世。狼山地区侏罗系沉积物源模式为南北两侧为隆起物源区,主要物源为北侧狼山隆起,南侧河套隆起向北提供部分物源,不同地区物源存在一定差异。  相似文献   

10.
The provenance of Neoproterozoic to Early Paleozoic sedimentary rocks in the Sierras Pampeanas has been established using U–Pb SHRIMP age determination of detrital zircons in twelve metasedimentary samples, with supplementary Hf and O isotope analyses of selected samples. The detrital zircon age patterns show that the western and eastern sectors of the Sierras Pampeanas are derived from different sources, and were juxtaposed during the Early Cambrian ‘Pampean’ collision orogeny, thus defining initiation of the supercontinent stage of southwestern Gondwana. The Western Sierras Pampeanas (WSP), which extend northwards to the southern Puna (Antofalla) and the Arequipa Massif (Peru), constitute a single large continental basement of Paleoproterozoic age — the MARA block — that was reworked during the Grenvillian orogeny. The MARA block probably extends eastwards to include the Río Apa block (southern Brazil), but in this case without a Mesoproterozoic overprint. Detrital zircons from the WSP and Antofalla yield age peaks between 1330 and 1030 Ma, remarkably similar to the range of ages in the Grenville province of eastern Laurentia. The WSP Neoproterozoic sedimentary cover to this basement shows the same 1330–1030 component, but also includes important 1430–1380 Ma zircons whose juvenile Hf and O isotopic signatures strongly suggest derivation from the Grenville and the Southern Granite–Rhyolite provinces of eastern Laurentia. In contrast the Eastern Sierras Pampeanas metasedimentary rocks have a typically bimodal detrital zircon pattern with peaks at ca. 1000 and 600 Ma, which respectively indicate sources in the Natal–Namaqua belt and the East African orogen and/or the Dom Feliciano belt of SE Brazil and Uruguay. Sedimentary rocks in the Eastern Sierras Pampeanas and Patagonia deposited during the Late Early Cambrian–Early Ordovician interval, after the Pampean orogeny, have detrital patterns common to many sectors along the Terra Australis orogen, reflecting increasingly dominant input to the Paleozoic basins from the Neoproterozoic to Early Cambrian orogenic belts of the Gondwana margin.  相似文献   

11.
The eastern margin of Sarmatia comprises the Paleoproterozoic (2.1–2.05 Ga) rock associations of the eastern Voronezh Crystalline Massif, including the Lipetsk-Losevo volcanic-plutonic belt and the adjacent East Voronezh lithotectonic zone composed of metasedimentary rocks of the Vorontsovka Group. The isotopic and geochemical study of the available drill cores that characterize the main rock associations of the Lipetsk-Losevo belt and its nearest framework allowed us to furnish evidence for the formation of this belt in the regime of an island arc at the active margin of the Archean continent above a low-angle subduction zone. The juvenile isotopic and geochemical signatures of metaturbidites of the Vorontsovka Group indicate that only a fast growing mountain edifice with the Lipetsk-Losevo Belt in its highest part (foreland) could have been a provenance of the flysch basin. It is proposed to name this Paleoproterozoic mountain system the East Sarmatian Orogen. The hinterland of this orogen embraced the megablock of the Kursk Magnetic Anomaly as a part of the Voronezh Massif and the Azov Block of the Ukrainian Shield. It has been shown that the East Sarmatian Orogen was formed in the same way as accretionary orogens of the Cordilleran type.  相似文献   

12.
合肥盆地位于华北板块东南缘,形成于华南、华北板块碰撞过程中。合肥盆地形成时表现为大别造山带向北逆冲形成的前陆挠曲盆地,早白垩世在区域伸展背景下转变为断陷盆地。中侏罗统圆筒山组是合肥盆地前陆挠曲阶段的沉积地层之一,主要表现为湖泊相沉积,与下伏的防虎山组典型的河流相沉积明显不同。为了获得圆筒山组更详细的物源信息,对肥西地区出露的圆筒山组紫红色粉砂岩开展了碎屑锆石LA-ICP MS U-Pb定年。定年结果显示,两个粉砂岩样品均获得了约2.0 Ga和约770 Ma两个主要峰值以及约2.4 Ga次要峰值。该特征与扬子板块锆石年龄分布特征几乎完全一致,指示圆筒山组物源应来自扬子板块。考虑到盆地地层的物源不应来自其周边隆起区分水岭的另一侧,因而推测圆筒山组物源应来自张八岭隆起中侏罗世时地表出露岩石。在燕山运动A幕影响下,下扬子地区发生逆冲褶皱活动,张八岭隆起发生明显隆升,上部岩石被剥蚀殆尽,仅保留现今出露的新元古代张八岭群及肥东杂岩,被剥蚀的岩石搬运沉积于合肥盆地内,形成圆筒山组。  相似文献   

13.
《地学前缘(英文版)》2020,11(5):1763-1787
The southern portion of the Sao Francisco Palaeocontinent in Brazil is denoted by Archean nuclei and Paleoproterozoic magmatic arcs that were amalgamated during Siderian to Orosirian orogenic processes(ca.2.4-2.1 Ga).New isotopic U-Pb in zircon and Sm-Nd whole rock combined with major and trace element composition analyses constrain the crystallization history of the Neoarchean Piedade block(at ca.2.6 Ga) and the Paleoproterozoic Mantiqueira Complex(ca.2.1-1.9 Ga).These therefore display quite different magmatic histories prior to their amalgamation at ca.2.05 Ga.Sm-Nd and Rb-Sr isotopes imply a mixed mantle-crustal origin for the samples in both units.A complete Palaeoproterozoic orogenic cycle,from subduction to collision and collapse,is recorded in the Piedade Block and the Mantiqueira Complex.Rhyacian to Orosirian subduction processes(ca.2.2-2.1 Ga) led to the generation of coeval(ca.2.16 Ga)TTG suites and sanukitoids,followed by late(2.10-2.02 Ga) high-K granitoids that mark the collisional stage.The collisional accretion of the Mantiqueira Complex against the Piedade Block at 2.08-2.04 Ga is also recorded by granulite facies metamorphism in the latter terrane,along the Ponte Nova suture zone.The collisional stage was closely followed by the emplacement of within-plate tholeiites at ca.2.04 Ga and by alkaline rocks(syenites and enriched basic rocks) at ca.1.98 Ga,marking the transition to an extensional tectonic regime.The discovery of two episodes of TTG and sanukitoid magmatism,one during the Neoarchean in the Piedade Complex and another during the Rhyacian in the Mantiqueira Complex,indicates that the onset of subduction-related melting of metasomatized mantle was not restricted to Neoarchean times,as generally believed,but persisted much later into the Paleoproterozoic.  相似文献   

14.
近年来,锆石的晶体形态、内部结构、年龄和Hf-O同位素分析已经成为盆地沉积物源区示踪的重要探针。渣尔泰群和白云鄂博群中碎屑锆石年龄主要集中在新太古代末期（～2.50 Ga）与古元古代末期（～1.90 Ga）两组,这两组碎屑锆石的相对丰度在层序上出现“振荡性”变化,这种变化特征与经典的源汇系统中构造—沉积响应的年代记录明显不一致。为研究渣尔泰群、白云鄂博群沉积层序中碎屑锆石年龄分布特征与源区构造演化之间的关系。本文系统总结了区域内大量相关的锆石U-Pb年龄数据,同时对渣尔泰群书记沟组和增隆昌组进行碎屑锆石LA-ICP-MS U-Pb年代学研究。研究表明这两组年龄与南部大青山—乌拉山造山带中基底岩石记录的构造热事件年龄相一致,同时根据锆石结构特征认为～2.50 Ga的锆石来源于造山带内新太古代岩浆—变质地体,～1.90 Ga的锆石来源于高级变质—深熔地体。大青山—乌拉山造山带与这套中-新元古代沉积地层构成源汇系统。源区造山带下地壳新太古代与古元古代变质岩系近水平互层叠置是大青山—乌拉山造山带下地壳结构的基本特征,岩性变化率在垂向上远大于水平方向,是控制盆地中碎屑锆石组合变化的直接原因。  相似文献   

15.
We present data on the composition of metasedimentary rocks from the greenstone belt of the Onot terrane (Sharyzhalgay uplift) and results of U–Pb dating (SHRIMP II) and Lu–Hf isotope study of detrital zircon from garnet–staurolite schists. The metasedimentary rocks of the Onot greenstone belt are dominated by garnet- and staurolite-bearing schists alternating with amphibolites (metabasalts) in the upper part of the section. Compositionally the protoliths of garnet–staurolite schists correspond to sedimentary rocks, ranging from siltstone to pelitic mudstone. The trace-element characteristics of the garnet–staurolite schists indicate that the terrigenous material was derived from three different rock types, such as tonalite–trondhjemite plagiogneisses (elevated Gd/Yb ratios), mafic rocks (elevated Cr/Th ratios and reduced Th/Sc ratios), and felsic igneous rocks formed by crustal melting (the presence of a Eu minimum), which agrees with the set of potential source rocks from the Onot terrane. The age of predominant detrital zircon reflects the erosion of mainly Neoarchean igneous rocks; this fact, combined with the poor rounding of zircon and tectonically active sedimentation conditions accompanied by mafic volcanism, suggests that the probably depositional age is ca. 2.7 Ga. Older source rocks (2.80–3.35 Ga) contributed to the sediment deposition along with the Neoarchean ones. According to the Hf isotope composition of detrital zircon from the garnet–staurolite schists, the source provenances had different crustal prehistories. The source provenances include Paleoarchean and juvenile Neoarchean crust and rocks formed by the mixing of melts from ancient and juvenile crustal sources.  相似文献   

16.
The Lützow-Holm Complex (LHC) of East Antarctica has been regarded as a collage of Neoarchean (ca. 2.5 Ga), Paleoproterozoic (ca. 1.8 Ga), and Neoproterozoic (ca. 1.0 Ga) magmatic arcs which were amalgamated through the latest Neoproterozoic collisional events during the assembly of Gondwana supercontinent. Here, we report new geochronological data on detrital zircons in metasediments associated with the magmatic rocks from the LHC, and compare the age spectra with those in the adjacent terranes for evaluating the tectonic correlation of East Antarctica and Sri Lanka. Cores of detrital zircon grains with high Th/U ratio in eight metasediment samples can be subdivided into two dominant groups: (1) late Meso- to Neoproterozoic (1.1–0.63 Ga) zircons from the northeastern part of the LHC in Prince Olav Coast and northern Sôya Coast areas, and (2) dominantly Neoarchean to Paleoproterozoic (2.8–2.4 Ga) zircons from the southwestern part of the LHC in southern Lützow-Holm Bay area. The ca. 1.0 Ga and ca. 2.5 Ga magmatic suites in the LHC could be proximal provenances of the detrital zircons in the northeastern and southwestern LHC, respectively. Subordinate middle to late Mesoproterozoic (1.3–1.2 Ga) detrital zircons obtained from Akarui Point and Langhovde could have been derived from adjacent Gondwana fragments (e.g., Rayner Complex, Eastern Ghats Belt). Meso- to Neoproterozoic domains such as Vijayan and Wanni Complexes of Sri Lanka, the southern Madurai Block of southern India, and the central-western Madagascar could be alternative distal sources of the late Meso- to Neoproterozoic zircons. Paleo- to Mesoarchean domains in India, Africa, and Antarctica might also be distal sources for the minor ∼2.8 Ga detrital zircons from Skallevikshalsen. The detrital zircons from the Highland Complex of Sri Lanka show similar Neoarchean to Paleoproterozoic (ca. 2.5 Ga) and Neoproterozoic (ca. 1.0 Ga) ages, which are comparable with those of the LHC, suggesting that the two complexes might have formed under similar tectonic regimes. We consider that the Highland Complex and metasedimentary unit of the LHC formed a unified latest Neoproterozoic suture zone with a large block of northern LH–Vijayan Complex caught up as remnant of the ca. 1.0 Ga magmatic arc.  相似文献   

17.
From the Archean to the end of the Neoproterozoic the Borborema Province, northeast Brazil went through a complex polycyclic geologic evolution, ending, between 660 and 570 Ma, with the Brasiliano/Pan-African orogeny that led to West Gondwana amalgamation. Evolution of the metasedimentary covers of the Province, from the beginning of their deposition up to their involvement in the Brasiliano/Pan-African collision, is a key element in understanding formation of Gondwana and in attempts in pre-drift correlation between South America and West Africa. One of these covers, the Ceará Group, is exposed in the Ceará Central domain. Aiming to unravel the history of the Ceará Group, we carried out a geochronologic study of representative samples, combining Sm–Nd isotopic data, conventional U–Pb TIMS dating of zircon and U–Pb SHRIMP age determination of detrital zircon grains. Our results show that sedimentation of the Ceará Group started around 750 Ma, following rifting of the Archean/Paleoproterozoic basement, associated with bimodal volcanism. The interlayered basic volcanic rocks, re-crystallized into garnet amphibolites, show a concordant age of 749 ± 5 Ma interpreted as the age of crystallization. About 90% of calculated Sm–Nd TDM model ages of metasedimentary rocks are Paleoproterozoic and more than 50% of the analyzed samples have TDM between 1.95 and 2.4 Ma, with strongly negative ɛNd, consistent with provenance mainly from the Paleoproterozoic basement. Strong contrast between Paleoproterozoic TDM with negative ɛNd and young TDM (Mesoproterozoic) with slightly positive ɛNd is interpreted as a consequence of changes in detritus provenance induced by geomorphologic alterations resulting from tectonic activity during rifting. Ages of detrital zircon grains obtained by SHRIMP U–Pb analyses show three main groups: about 1800 Ma, 1000–1100 Ma and ca. 800 Ma which corresponds to the bimodal magmatism associated, respectively to the Orós-Jaguaribe domain, Cariris Velhos event and Independência Group.  相似文献   

18.
《International Geology Review》2012,54(14):1806-1824
In this article, we present in situ U–Pb and Lu–Hf isotope data for Upper Triassic detritus in the Sichuan region of northwestern South China, which was a foreland basin during the Late Triassic. The aim is to determine the provenance of sediments in the foreland basin and to constrain the evolution of the surrounding mountain belts. U–Pb age data for the Late Triassic detrital zircons generally show populations at 2.4–2.6 Ga, 1.7–1.9 Ga, 710–860 Ma, 410–460 Ma, and 210–300 Ma. By fitting the zircon data into the tectonic, sedimentologic, and palaeographic framework, we propose that the north Yangtze Block and South Qinling–Dabie Orogen were the important source areas of sediments in the northern part of the foreland basin, whereas the Longmen Shan thrust-fold belt was the main source region for detritus in other parts of the foreland basin. The South Qinling–Dabie Orogen could also have served as a physical barrier to block most detritus shed from the southern North China Block into the foreland basin during the sedimentation of the Xujiahe Formation. Our results also reveal that part of the flysch from the eastern margin of the Songpan–Ganzi region had been displaced into the Longmen Shan thrust-fold belt before the deposition of the foreland basin sediments. In addition, the Lu-Hf data indicate that Phanerozoic igneous rocks in central China show insignificant formation of the juvenile crust.  相似文献   

19.
The global plate tectonic regime in early Paleoproterozoic times is highly debated. The interval 2.45–2.2 Ga is known for a minima in juvenile magmatism, but this is not a global phenomenon. New results of whole-rock geochemistry and U–Pb-Hf analysis in igneous and detrital zircons, allied with existing isotopic and geophysical data, allow to identify and constrain the duration of magmatic flare-up and quiescence events in the western São Francisco Paleoplate. Igneous samples yield ages indicating three accretionary magmatic events, an older with ages ca. 2476.4 ± 9 Ma to 2462 ± 13 Ma, an intermediate at 2390 ± 14 Ma, and a younger from 2235 ± 26 Ma to 2201 ± 5 Ma, all presenting magmatic arc geochemical signatures. Xenoliths of quartzite and volcanic tuff from the upper greenstone sequence (Morro do Carneiro Fm.) are hosted in the 2211 ± 9 Ma tonalite and the maximum depositional age of the Morro do Carneiro basin is dated 2234 ± 12 Ma, indicating a syn-orogenic setting for this basin. Detrital zircon UPb age distribution for quartzites of the greenstone sequence shows peaks at 2.65, 2.47, 2.39, 2.27 and 2.23 Ga. Altogether, the studied rocks record an accretionary orogeny with four distinct episodes: Episode S1: 2.52–2.46 Ga, ɛHf(t) values from +0.57 to +6.36; Episode S2: 2.43–2.37 Ga, ɛHf(t) values from +0.10 to +4.30; Episode R1: 2.32–2.26 Ga, ɛHf(t) values from +1.61 to −7.23 (from detrital zircons); Episode R2: 2.24–2.20 Ga, ɛHf(t) values from +0.39 to −2.73. These early Paleoproterozoic accretionary orogenies mark the onset of amalgamation of the São Francisco continental paleoplate that surrounds the craton, with accretions of an exotic micro-block and continental magmatic arcs, indicating evolution from dominant Siderian juvenile magmatism to Rhyacian crustal magmatism. These patterns show striking similarities to the orogenies in the Mineiro Belt and North China Craton.  相似文献   

20.
Paleoproterozoic orogens of the North Australian Craton are related to the assembly of the Columbia Supercontinent. The roles of the distinct orogens in the Paleoproterozoic craton amalgamation are poorly understood due to the lack of surface exposure. The age and isotopic systematics of detrital zircon grains hosted in Paleoproterozoic sedimentary sequences are used to unravel the geological history of the craton, in terms of paleogeography and tectonic setting. The oldest (Early Paleoproterozoic) metasedimentary units are characterised by detrital zircon ages peaking at ca. 2500 Ma. The zircon εHf values show large variations in the different orogens and range from −18 to +6. The overlaying youngest turbiditic units show minor accumulation of Archean detritus. Units from apparently different metasedimentary sequences have a major detrital zircon age population at ca. 1865 Ma, and a relatively restricted range of zircon εHf values between −7.3 and +2.6. The isotopic distinctiveness of the oldest units is attributed to local variations in the depositional environment, probably due to horst-graben architecture of the early Paleoproterozoic basin. The youngest turbiditic units blanketed this early horst-graben architecture and in part have a local provenance. Potential detritus sources include South Australian Craton, Dharwar Craton and Aravalli-Lesser Himalayan terrains in India, South China, and Madagascar (Africa). This finding indicates that these regions might have been connected before the Columbia Supercontinent was formed. The ubiquitous ca. 2500 Ma magmatic event records the assembly of these cratonic fragments in a previous supercontinent called Kernorland. In addition, the data do not support a proximity of the North Australian Craton with the North China Block, Western Laurentia (North America), and Kaapvaal Craton (Africa) during Columbia amalgamation.  相似文献   

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