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1.
The formation environments of stratiform ore deposits in the Neoproterozoic Baikal–Patom region (BPR) have been considered. A model for the formation of the Sukhoi Log gold ore deposit in the Bodaibo zone has been put forward. The first stage is gold concentration by a chemolithotrophic bacterial community. Independently established facts suggest that bacterial communities may also have contributed to initial metal accumulation in the sediments of the Kholodnaya Pb–Zn deposit. The ore beds occur in the high-carbon sediments of the side and trough of a back-arc basin. Sedimentation (Dal’nyaya Taiga and Zhuya regional horizons) took place during the “back-arc basin–foreland basin” transition. This transition is characterized by increased sediment bioproductivity, which is clearly evidenced from the increased biophile-element content and taxonomic diversity of organic remains. Hundreds of microfossil sites in the Neoproterozoic BPR host littoral benthos (cyanobacteria and brown algae) and plankton (green algae). Most microfossils in the outer shelf, on the basin side, and in its trough belong to chemolithotrophic bacteria. These bacteria are assumed to have accumulated metals in the vent field of the back-arc basin. Studies showed the ability of microorganisms (bacteria, algae, fungi, etc.) to accumulate Fe, Mn, Au, Pb, Zn, and other metals. Bacterial communities are particularly important for metal accumulation in the vent fields of rift zones and areas of arc volcanism. All these conditions were observed in the Neoproterozoic BPR.  相似文献   

2.
The Guarguaraz Complex, in western Argentina, comprises a metasedimentary assemblage, associated with mafic sills and ultramafic bodies intruded by basaltic dikes, which are interpreted as Ordovician dismembered ophiolites. Two kinds of dikes are recognized, a group associated with the metasediments and the other ophiolite-related. Both have N-MORB signatures, with εNd between +3.5 and +8.2, indicating a depleted source, and Grenville model ages between 0.99 and 1.62 Ga. A whole-rock Sm–Nd isochron yielded an age of 655 ± 76 Ma for these mafic rocks, which is compatible with cianobacteria and acritarchae recognized in the clastic metasedimentary platform sequences, that indicate a Neoproterozoic (Vendian)–Cambrian age of deposition.The Guarguaraz metasedimentary–ophiolitic complex represents, therefore, a remnant of an oceanic basin developed to the west of the Grenville-aged Cuyania terrane during the Neoproterozoic. The southernmost extension of these metasedimentary sequences in Cordón del Portillo might represent part of this platform and not fragments of the Chilenia terrane. An extensional event related to the fragmentation of Rodinia is represented by the mafic and ultramafic rocks. The Devonian docking of Chilenia emplaced remnants of ocean floor and slices of the Cuyania terrane (Las Yaretas Gneisses) in tectonic contact with the Neoproterozoic metasediments, marking the Devonian western border of Gondwana.  相似文献   

3.
<正>1 Introduction The Songnen–Zhangguangcai Range Massif(SZRM)crops out over an extensive part of NE China and was thought to contain Precambrian crystalline basement material,as evidenced by the presence of what appears to bePaleoproterozoicbasementmaterialwithin exploration drillholes(Pei et al.,2007).An alternative view is that the basement within the SZRM is  相似文献   

4.
The South Oman Salt Basin (SOSB) is host to the world’s oldest known commercial deposits. Most of the South Oman oils have been proven to be associated with the source rocks of the Neoproterozoic to Cambrian Huqf Supergroup, but the assignment of oils to specific Huqf intervals or facies has been hampered by the geochemical similarity of the organic matter across the entire Huqf sequence, possibly as a consequence of limited change in the local palaeoenvironment and biota over the time of its deposition. This study was conducted to establish improved correlations between organic-rich rock units and reservoir fluids in the SOSB through detailed molecular and isotopic analysis of the Huqf Supergroup, with special emphasis directed towards understanding the Ara carbonate stringer play.Unusual biomarkers, tentatively identified as A-norsteranes, show distinctive patterns among carbonate stringer oils and rocks different from those observed in Nafun sediments and Ara rocks from the Athel basin. These putative A-norsteranes form the basis for new oil-source correlations in the SOSB and provide for the first time geochemical evidence of a self-charging mechanism for the carbonate stringer play. The paucity of markers specific to the Nafun Group (Shuram, Buah and Masirah Bay formations) confounds attempts to quantify their respective contributions to Huqf oil accumulations. Nafun inputs can only be determined on the basis of subtle differences between Nafun and Ara biomarker ratios. The most useful geochemical characteristics delineating Nafun Group organic matter from Ara Group intra-salt source rocks included: low relative abundance of mid-chain monomethyl alkanes (X-compounds); low relative abundance of gammacerane, 28,30-dinorhopane, 25,28,30-trinorhopane and 2-methylhopanes; low C22T/C21T and high C23T/C24T cheilanthanes ratio values. Based on these parameters, molecular evidence for major contributions of liquid hydrocarbons from Nafun Group sediments (Shuram, Buah and Masirah Bay formations) is lacking. Our results suggest that the majority of SOSB hydrocarbon accumulations originate from within the Ara group, either from the carbonate stringers or from the package of sediments that comprises the Thuleilat, Athel Silicilyte and U shale formations. Subtle aspects of the composition of some carbonate stringer and post-salt Huqf oils could suggest some degree of sourcing from the Nafun rocks but stronger evidence is needed to confirm this.  相似文献   

5.
In this article, we report whole-rock and mineral Sm–Nd isotopic and whole-rock elemental and Sr–Nd isotopic data of Xingdi No. 1 mafic–ultramafic intrusion in the western Kuluketage block, north-eastern Tarim. Xingdi No. 1 mafic–ultramafic intrusion is the largest in the Xingdi mafic–ultramafic belt, with an exposed area of ca. 20 km2. It intruded into the Palaeoproterozoic basement. Gabbro is the major rock type and there is minor olivine pyroxenite. Sm–Nd geochronometry of the gabbro gives an isochron age of 761.2 ± 31.2 million years, identical to the intrusive age of Xingdi No. 2 pluton (760 ± 6 million years). The gabbro is systematically enriched in large ion lithosphile elements and light rare earth elements and depleted in high field strength elements and heavy rare earth elements. The studied rocks are characterized by low whole-rock and mineral ?Nd(t) values (?7.8 to??7.1) and elevated (87Sr/86Sr) i values (0.7066–0.7073). These geochemical characteristics, together with the presence of abundant hornblende, biotite, bladed biotite enclosed in amphibole, and crescent-shaped Palaeoproterozoic wall-rock xenoliths in the intrusion, are key features of magma mixing in the source or assimilation during its emplacement. The rocks have a Zr/Y ratio of 3.81–13, which falls in the within-plate basalt area. As Xingdi No. 1 and No. 2 plutons formed at the same period and display similar geochemical characteristics, we propose that they formed within the same tectonic setting and were derived from the same source, but No. 1 pluton experienced a higher extent of evolution and contamination. Previous studies have shown that the Neoproterozoic tectonic and magmatic events in Kuluketage comprise syn-collisional granite around TC (ca. 1.0–0.9 Ga), post-collisional K-rich granite and alkaline mafic–ultramafic intrusions (ca. 830–800 Ma), and rifting-related mafic–ultramafic plutons, dikes, and bimodal volcanic rocks (ca. 774–744 Ma).  相似文献   

6.
《Gondwana Research》2011,19(4):583-595
Ophiolites are key components of the Neoproterozoic Arabian–Nubian Shield (ANS). Understanding when they formed and were emplaced is crucial for understanding the evolution of the ANS because their ages tell when seafloor spreading and terrane accretion occurred. The Yanbu–Onib–Sol Hamed–Gerf–Allaqi–Heiani (YOSHGAH) suture and ophiolite belt can be traced ∼ 600 km across the Nubian and Arabian shields. We report five new SHRIMP U–Pb zircon ages from igneous rocks along the Allaqi segment of the YOSHGAH suture in southernmost Egypt and use these data in conjunction with other age constraints to evaluate YOSHGAH suture evolution. Ophiolitic layered gabbro gave a concordia age of 730 ± 6 Ma, and a metadacite from overlying arc-type metavolcanic rocks yielded a weighted mean 206Pb/238U age of 733 ± 7 Ma, indicating ophiolite formation at ∼ 730 Ma. Ophiolite emplacement is also constrained by intrusive bodies: a gabbro yielded a concordia age of 697 ± 5 Ma, and a quartz-diorite yielded a concordia age of 709 ± 4 Ma. Cessation of deformation is constrained by syn- to post-tectonic granite with a concordia age of 629 ± 5 Ma. These new data, combined with published zircon ages for ophiolites and stitching plutons from the YOSHGAH suture zone, suggest a 2-stage evolution for the YOSHGAH ophiolite belt (∼ 810–780 Ma and ∼ 730–750 Ma) and indicate that accretion between the Gabgaba–Gebeit–Hijaz terranes to the south and the SE Desert–Midyan terranes to the north occurred as early as 730 Ma and no later than 709 ± 4 Ma.  相似文献   

7.
The South China Block was built up by the assembly of the Yangtze and Cathaysia blocks along the Neoproterozoic Jiangnan Orogenic Belt. The timing of the Jiangnan Orogeny remains controversial. The widespread orogeny–related Neoproterozoic angular unconformity that separates the underlying folded Sibao (ca.1000–820 Ma) and overlying Danzhou (ca.800–720 Ma) Groups was investigated. Six sedimentary samples, below and above the unconformity in three distal localities (Fanjingshan, Madiyi, and Sibao) yield detrital zircon with UPb ages ranging from 779 ± 16 Ma to 3006 ± 36 Ma, with a prominent peak at ca. 852 Ma. The youngest ages of 832 ± 11 Ma and 779 ± 16 Ma are revealed for the underlying Sibao and overlying Danzhou Groups, respectively. The detrital zircon UPb age relative probability plot of the Jiangnan Orogen matches well with those of the Yangtze and Cathaysia blocks since ca. 865 Ma. Integrating geological, geochemical and geochronological results, we suggest that the Paleo–South China Ocean began to subduct under the Yangtze block at ca. 1000 Ma, and was partly closed at ca. 865 Ma. Afterwards, the Yangtze and Cathaysia blocks initially collide at 865 Ma, forming the Jiangnan Orogen. This collision resulted in not only the folding of the Sibao Group, but also sediment deposition in a syn-collisional setting, which makes the upper part of the Sibao Group. The youngest S-type granite dated at ca. 820 Ma that intruded in the Sibao Group marks the late stage of the Jiangnan Orogeny.  相似文献   

8.
The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation.  相似文献   

9.
Investigation of the petrogenesis and the origin of zircons from the volcanic rocks of the Liujiaping Group of the back-Longmenshan tectonic belt in the northwest margin of the Yangtze Block is conducted by analysis of U–Pb geochronology and geochemistry. Results show that selected zircons are characterized by internal oscillatory zonings and high Th/U ratios(0.43–1.18), indicating an igneous origin. Geochronological results of LA–ICP–MS U–Pb dating of the Liujiaping Group zircons yield an age of 809 ± 11 Ma(MSWD = 2.2), implying that the volcanic rocks were formed in the Late Neoproterozoic. Geochemical analysis shows that the rocks are calc-alkaline, supersaturated in Al, and metaluminous to weakly peraluminous. Rare-earth elements are present at high concentrations(96.04–265.48 ppm) and show a rightward incline and a moderately negative Eu anomaly, similar to that of continental rift rhyolite. Trace element geochemistry is characterized by evident negative anomalies of Nb, Ta, P, Th, Ti, inter alia, and strong negative anomalies of K, Rb, Sr, et al. We conclude that the Liujiaping Group volcanic rocks resulted from typical continental crust source petrogenesis and were formed in a continental margin setting, which had no relation to subduction, and thus, were the products of partial melting of the lower crust due to crustal thickening caused by active continental margin subduction and arc–continent collision orogeny in the northwestern Yangtze Block and were triggered by the breakup of the Rodinia supercontinent during the Neoproterozoic.  相似文献   

10.
The Shilu Fe–Co–Cu ore district is situated in the western Hainan Province of south China. This district consists of the upper Fe-rich layers and the lower Co–Cu ores, which are mainly hosted within the Neoproterozoic Shilu Group, a dominantly submarine siliciclastic and carbonate sedimentary succession that generally has been metamorphosed to greenschist facies. Three facies of metamorphosed BIFs, the oxide, the silicate–oxide and the sulfide–carbonate–silicate, have been identified within the Shilu Group. The oxide banded iron formation (BIF) facies (quartz itabirites or Fe-rich ores) consists of alternating hematite-rich and quartz-rich microbands. The silicate–oxide BIF facies (amphibolitic itabirites or Fe-poor ores) comprises alternating millimeter to tens of meter scale, magnetite–hematite-rich bands with calc-silicate-rich macro- to microbands. The sulfide–carbonate–silicate BIF facies (Co–Cu ores) contain alternating cobaltiferous pyrite, cobaltiferous pyrrhotite and chalcopyrite macrobands to microbands mainly with dolomite–calcite, but also with minor sericite–quartz bands. Blasto-oolitic, pelletoidal, colloidal, psammitic, and cryptocrystalline to microcrystalline textures, and blasto-bedding structures, which likely represent primary sedimentation, are often observed in the Shilu BIF facies.The Shilu BIFs and interbedded host rocks are generally characterized by relatively low but variable ∑ REE concentrations, LREE depletion and/or MREE enrichment relative to HREE, and no Ce, Gd and Eu anomalies to strongly positive Ce, Gd and Eu anomalies in the upward-convex PAAS-normalized REY patterns, except for both the banded or impure dolostones with nil Ce anomaly to negative Ce anomalies and negative La anomalies, and the minor sulfide–carbonate–silicate BIF facies with moderately negative Eu anomalies. They also contain relatively low but variable HFSE abundances as Zr, Nb, Hf, Th and Ti, and relatively high but variable abundances of Cu, Co, Ni, Pb, As, Mn and Ba. The consistently negative εNd(t) values range from − 4.8 to − 8.5, with a TDM age of ca. 2.0 Ga. In line with the covariations between Al2O3 and TiO2, Fe2O3 + FeO and SiO2, Mn and Fe, Zr and Y/Ho and REE, and Sc and LREE, the geochemical and Sm–Nd isotopic features suggest that the precursors to the Shilu BIFs formed from a source dominated by seafloor-derived, high- to low temperature, acidic and reducing hydrothermal fluids but with variable input of detrital components in a seawater environment. Moreover, the involved detrital materials were sourced dominantly from an unknown, Paleoproterozoic or older crust, with lesser involvement from the Paleo- to Mesoproterozoic Baoban Group underlying the Shilu Group.The Shilu BIFs of various facies are interpreted to have formed in a shallow marine, restricted or sheltered basin near the rifted continental margin most likely associated with the break-up of Rodinia as the result of mantle superplume activity in South China. The seafloor-derived, periodically upwelling metalliferous hydrothermal plume/vent fluids under anoxic but sulfidic to anoxic but Fe2 +-rich conditions were removed from the plume/vent and accumulated in the basin, and then variably mixed with terrigenous detrital components, which finally led to rhythmic deposition of the Shilu BIFs.  相似文献   

11.
Much work at A.A. Trofimuk Institute of Petroleum Geology and Geophysics (Novosibirsk) has been done to synthesize geological and geophysical data from the Siberian Arctic and Arctic shelf. Namely, seismic-geological modeling and petroleum potential assessment have been performed for the Neoproterozoic–Phanerozoic section of the Anabar–Lena province in the northern Sakha Republic (Yakutia). The results include seismic-geological division, a set of structural maps, and structural, paleotectonic, and facies analysis. The study shows that Riphean, Vendian, Cambrian, and Permian sequences are of interest in terms of petroleum potential; oil and gas may accumulate in traps of different types.  相似文献   

12.
Doklady Earth Sciences - The metamorphosed iron ore volcanogenic–sedimentary strata of the Karsakpai series in the eastern Ulutau Precambrian terrane of Central Kazakhstan are studied. The...  相似文献   

13.
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14.
Investigation of the petrogenesis and the origin of zircons from the volcanic rocks of the Liujiaping Group of the back-Longmenshan tectonic belt in the northwest margin of the Yangtze Block is conducted by analysis of U–Pb geochronology and geochemistry. Results show that selected zircons are characterized by internal oscillatory zonings and high Th/U ratios (0.43–1.18), indicating an igneous origin. Geochronological results of LA–ICP–MS U–Pb dating of the Liujiaping Group zircons yield an age of 809 ± 11 Ma (MSWD = 2.2), implying that the volcanic rocks were formed in the Late Neoproterozoic. Geochemical analysis shows that the rocks are calc-alkaline, supersaturated in Al, and metaluminous to weakly peraluminous. Rare-earth elements are present at high concentrations (96.04–265.48 ppm) and show a rightward incline and a moderately negative Eu anomaly, similar to that of continental rift rhyolite. Trace element geochemistry is characterized by evident negative anomalies of Nb, Ta, P, Th, Ti, inter alia, and strong negative anomalies of K, Rb, Sr, et al. We conclude that the Liujiaping Group volcanic rocks resulted from typical continental crust source petrogenesis and were formed in a continental margin setting, which had no relation to subduction, and thus, were the products of partial melting of the lower crust due to crustal thickening caused by active continental margin subduction and arc–continent collision orogeny in the northwestern Yangtze Block and were triggered by the breakup of the Rodinia supercontinent during the Neoproterozoic.  相似文献   

15.
The Borborema Province is the western part of a major Brasiliano belt that extends from Brazil through NW Africa in pre-drift reconstructions. This province resulted from convergence and collision among the West African, Congo-São Francisco, and Amazonian cratons about 600 Ma. This study focuses on the Pernambuco–Alagoas (PEAL) domain, which is a complex of magmatic, migmatitic, and metamorphic rocks, located in the southern part of the Borborema Province. U–Pb geochronology and Sm–Nd data for metasedimentary sequences (Rio Una, Inhapi) of the PEAL domain and a sample from a sequence of the Transversal Zone domain suggest that their deposition occurred during a Cryogenian extensional event, within the interval 850–631 Ma (or slightly younger). This extensional event occurred in the PEAL, Transversal Zone, and Sergipano domains before the onset of the Brasiliano collision and was followed by syn- and post-collisional magmatism. The Rio Una sequence and the sequence from Transversal Zone domain were deposited over a Rhyacian (ca. 2.0–2.2) basement having a juvenile Palaeoproterozoic Nd signature, whereas the Inhapi sequence was deposited over an Early Neoproterozoic (Tonian) basement. The deposition of the studied sequences is coeval with metasedimentary sequences to the north and south in other domains of the Borborema Province. However, differences in Nd isotopic signatures between the sequences from PEAL, Transversal Zone, and Sergipano domains suggest that they were formed in distinct basins. Metasedimentary sequences from the PEAL domain have Meso- and Palaeoproterozoic T DM model ages. These data suggest that the orogens where the metasedimentary sequences are located have a strong ensialic component. T DM model ages of ca. 1.0 Ga and εNd (0.6 Ga) values around zero recorded in granites from the southern part of the PEAL, suggesting that juvenile material was accreted to the southern part of the PEAL domain crust during the Tonian. The migmatites from the PEAL domain have a wide range of T DM ages along with a wide range of εNd (0.6 Ga) values. The transition between the northern and southern parts of the PEAL domain denotes the approximate northern margin of a Late Mesoproterozoic to Early Neoproterozoic rift.  相似文献   

16.
The Vazante Group show varied U–Pb provenance patterns along the basin. Zircon ages range from 936 to 3409 Ma, but Paleo- and Mesoproterozoic terrains constitute the main sources of the original sediments. The youngest population (~ 930 Ma) establishes the maximum depositional age of the group. Sm–Nd TDM data show the predominance of Paleoproterozoic ages (1.90–2.08 Ga) and also indicate some input from younger sources in rocks of the Lapa Formation (1.67 to 2.0 Ga) in the upper part of the group, whereas rocks of the Serra do Garrote Formation present the oldest model ages (2.03 to 2.76 Ga). Hf isotopic compositions of the detrital zircons indicate that they were derived mainly from recycled Paleoproterozoic crust with a minor Mesoproteroic juvenile component. Terranes within the São Francisco Craton represent the main sources of detrital sediments of this group and reinforce the interpretation that it may be a passive margin sequence developed along the western margin of the original continent. However, the origin of Mesoproterozoic grains remains uncertain. Slightly younger Sm–Nd model ages in the Lapa Formation, however, are not entirely consistent with derivation solely from the craton and may indicate contribution from younger sources, such as the Neoproterozoic Goiás Magmatic Arc.  相似文献   

17.
The relationship of the Yangtze Block with other continental blocks of the Rodinia and Gondwana supercontinents is hotly debated. Here we report U–Pb and Lu–Hf isotopic data for zircons from the latest Neoproterozoic Yanjing Group and the overlying Silurian–Devonian rocks on the western margin of Yangtze Block, which provide critical constraints on the provenance of these sediments and further shed light on the crustal evolution and tectonic affinity of the western Yangtze Block in the context of Rodinia and the subsequent Gondwanaland. Mica schist from the middle part of the Yanjing Group contains dominant Neoproterozoic detrital zircons (0.72–0.80 Ga) with a pronounced age peak at 0.75 Ga. Based on the euhedral to subhedral shapes, high Th/U ratios and exclusively positive εHf(t) values (+ 6 to + 14) for the zircon crystals, and the lack of ancient zircons, we consider the sediments as products of proximal deposition near a Neoproterozoic subduction system in western Yangtze. Combined with the age of rhyolite from the lower part of the Yanjing Group, these strata were estimated to have been deposited in a period between 0.72 and 0.63 Ga. In contrast, the Silurian–Devonian sediments exhibit dominant Grenvillian ages (0.9–1.0 Ga), with middle Neoproterozoic (0.73–0.85 Ga), Pan-African (0.49–0.67 Ga) and Neoarchean (~ 2.5 Ga) age populations, suggesting a significant change of sedimentary provenance and thus a different tectonic setting. Although the shift occurred in the Silurian, the age spectra turn to be consistent along the western margin of the Yangtze Block until the Devonian, indicating persistence of the same sedimentary environment. However, the related provenance of these Paleozoic sediments cannot be found in South China. The presence of abundant Grenvillian, Pan-African and Neoarchean ages, along with their moderately to highly rounded shapes, indicates the possibility of exotic continental terrane(s) as a possible sedimentary provenance. Considering the potential source areas around the Yangtze Block when it was part of the Rodinia or Gondwana, we suggest that the source of these Paleozoic sediments had typical Gondwana affinities such as the Himalaya region, north India, which is also supported by their stratigraphic similarity, newly published paleomagnetic data and the tectono-thermal events of northwestern fragments of Gondwana. This implies that after a prolonged subduction in the Neoproterozoic, the western margin of the Yangtze Block began to incorporate into the assembly of the Gondwana supercontinent and was able to accept sediments from northwestern margin of Gondwanaland as a result of early Paleozoic orogeny.  相似文献   

18.
ForaPrecambriancratoncomposedofcompositeterranes,orblocks,andbelts,whichexperiencedcomplexpolyphasedeformationandmetamorphism,thefinaltectonothermaleventismoresignificantthantheearlieronesinthelightofplatetectonics,becausethefinaltectonothermaleventresultedfromamalga-mationofthecraton.Although,generally,aworkinghypothesisofpolyphasedeformationandmetamorphismiswidelyappliedtoahigh-gradeterrane,dis-cernmentofitsfinaltectonothermalepisodeisvitaltounderstandingitsgeologicalhistory.Inrecentyears,an…  相似文献   

19.
The Central Taimyr accretionary belt includes two granite-metamorphic terranes: Faddey and Mamont-Shrenk, which include the oldest igneous formations of the Taimyr folded area in the Arctic framing of the Siberian craton—granitoids and granite-gneisses with U–Pb zircon ages of 900–830 Ma. The [FeO*/(FeO* + MgO)]-enriched granitoids of these terranes are products of highly fractionated I-type magmas. This paper presents results of new petrographic, geochemical, geochronological, and paleomagnetic investigations of acid rocks from a volcanic-plutonic association (in the region of the Leningradskaya River) in the Faddey terrane in the northeastern Taimyr area. These rocks formed during the final stage of continent–island arc accretion and collision that occurred at approximately 870–820 Ma. We established that the studied rocks belong to a long granitoid belt extending from Mamont-Shrenk to Faddey terrane, where all the igneous bodies are deformed and oriented uniformly. The paleomagnetic pole we calculated differs significantly from the apparent polar-wander path interval of corresponding age for Siberia. The 33.8°±5.4° angular distance between the poles indicates that the formation of this volcanic-plutonic association took place at a significant distance from the Taimyr margin of the Siberian paleocontinent.  相似文献   

20.
The Sergipano Belt is the outcome of collision between the Pernambuco–Alagoas Massif and the São Francisco Craton during Neoproterozoic assembly of West Gondwana. Field relationships and U–Pb geochronology of granites intruded in garnet micaschists of the Macururé Domain are used to constrain the main collisional event (D2) in the belt. The granites are divided into two groups, the pre-collisional granites (pre- to early-D2) and the syn-collisional granites (syn- to tardi-D2), the latter were emplaced as sheets along the S2 axial plane foliation or they were collected at the hinge zones of F2 folds. A U–Pb SHRIMP zircon age of 628 ± 12 Ma was obtained for the pre-collisional Camará tonalite. Two U–Pb TIMS titanite ages were obtained for the syn-collisional granites, 584 ± 10 Ma for the Angico granite and 571 ± 9 Ma for the Pedra Furada granite, and these ages are close to the garnet-whole rock Sm–Nd isochron of 570 Ma found for the peak of metamorphism in the Sergipano Belt. The ages of the Camará tonalite (628 Ma) and the Pedra Furada granite (571 Ma) mark respectively the maximum age for beginning of the D2 event and minimum age for the end in the Macururé Domain. Using these ages, the main Neoproterozoic D2 collisional event has been in operation in the Sergipano Belt for at least 57 million years. Correlation with coeval granitoids farther north in the Borborema Province indicate that while in the Sergipano Belt the syn-D2 granites (ca. 590–570 Ma) were emplaced under compression, in the Borborema Province they emplaced under extensional conditions related to regional strike-slip shear zones. These contrasting emplacement settings for contemporaneous Neoproterozoic granitoids are explained by a combination of continent–continent collision and extrusion tectonics.  相似文献   

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