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1.
We present new zircon U–Pb–Hf and whole-rock geochemical data for volcanic rocks along the eastern margin of the Xing'an Massif of NE China in order to further our understanding of the history of subduction towards the SE and the spatial extent of the Mongol–Okhotsk tectonic regime. Zircon U–Pb dating indicates that the Triassic volcanism in the Xing'an Massif occurred in two stages during the Middle (ca. 242 Ma) and Late (ca. 223–228 Ma) Triassic. Middle Triassic basaltic andesites in the Heihe area have an affinity to arc-type volcanic rocks. The zircon εHf(t) values (+ 8.5 to + 12.7) suggest that the primary magma was generated by the partial melting of a relatively depleted mantle wedge that had been metasomatized by subduction-related fluids. The Late Triassic andesites in the Handaqi area exhibit geochemical affinities to high-Mg adakitic andesites. Their zircon εHf(t) values (+ 11.5 to + 14.5) and TDM2 ages (313–484 Ma) indicate that their primary magma was derived from the partial melting of a young subducted oceanic crust, followed by interaction with melts derived from mantle peridotite. The Late Triassic basaltic andesites, andesites, and dacites in the Zhalantun–Moguqi area have features similar to those of igneous rocks formed in subduction zones. Their zircon εHf(t) values (+ 8.4 to + 15.4) and TDM1 ages (260–542 Ma) indicate that their primary magma was derived from the partial melting of a depleted mantle wedge that had been metasomatized by subduction-related fluids. These data suggest that the Triassic volcanic rocks of the Xing'an Massif formed in an active continental margin setting associated with the southward subduction of the Mongol–Okhotsk oceanic plate towards the SE. We conclude that the Mongol–Okhotsk tectonic regime extended at least as far as the eastern margin of the Xing'an Massif, and that the tectonism spanned the period from the late Permian to early Early-Cretaceous. 相似文献
2.
《Gondwana Research》2014,25(3-4):865-885
Exhumation of middle and lower crustal rocks during the 450–320 Ma intraplate Alice Springs Orogeny in central Australia provides an opportunity to examine the deep burial of sedimentary successions leading to regional high-grade metamorphism. SIMS zircon U–Pb geochronology shows that high-grade metasedimentary units recording lower crustal pressures share a depositional history with unmetamorphosed sedimentary successions in surrounding sedimentary basins. These surrounding basins constitute parts of a large and formerly contiguous intraplate basin that covered much of Neoproterozoic to early Palaeozoic Australia. Within the highly metamorphosed Harts Range Group, metamorphic zircon growth at 480–460 Ma records mid-to-lower crustal (~ 0.9–1.0 GPa) metamorphism. Similarities in detrital zircon age spectra between the Harts Range Group and Late Neoproterozoic–Cambrian sequences in the surrounding Amadeus and Georgina basins imply that the Harts Range Group is a highly metamorphosed equivalent of the same successions. Maximum depositional ages for parts of the Harts Range Group are as low as ~ 520–500 Ma indicating that burial to depths approaching 30 km occurred ~ 20–40 Ma after deposition. Palaeogeographic reconstructions based on well-preserved sedimentary records indicate that throughout the Cambro–Ordovician central Australia was covered by a shallow, gently subsiding epicratonic marine basin, and provide a context for the deep burial of the Harts Range Group. Sedimentation and burial coincided with voluminous mafic magmatism that is absent from the surrounding unmetamorphosed basinal successions, suggesting that the Harts Range Group accumulated in a localised sub-basin associated with sufficient lithospheric extension to generate mantle partial melting. The presently preserved axial extent of this sub-basin is > 200 km. Its width has been modified by subsequent shortening associated with the Alice Springs Orogeny, but must have been > 80 km. Seismic reflection data suggest that the Harts Range Group is preserved within an inverted crustal-scale half graben structure, lending further support to the notion that it accumulated in a discrete sub-basin. Based on palaeogeographic constraints we suggest that burial of the Harts Range Group to lower crustal depths occurred primarily via sediment loading in an exceptionally deep Late Cambrian to Early Ordovician intraplate rift basin. High-temperature Ordovician deformation within the Harts Range Group formed a regional low angle foliation associated with ongoing mafic magmatism that was coeval with deepening of the overlying marine basin, suggesting that metamorphism of the Harts Range Group was associated with ongoing extension. The resulting lower crustal metamorphic terrain is therefore interpreted to represent high-temperature deformation in the lower levels of a deep sedimentary basin during continued basin development. If this model is correct, it indicates that regional-scale moderate- to high-pressure metamorphism of supracrustal rocks need not necessarily reflect compressional thickening of the crust, an assumption commonly made in studies of many metamorphic terrains that lack a palaeogeographic context. 相似文献
3.
Post-rift fault activities were often observed in deepwater basins, which have great contributions to oil and gas migration and accumulation. The main causes for post-rift fault activities include tectonic events, mud or salt diapirs, and gravitational collapse. In the South China Sea continental margin, post-rift fault activities are widely distributed, especially in Baiyun sag, one of the largest deepwater sag with its main body located beneath present continental slope. During the post-rift stage, large population of faults kept active for a long time from 32 Ma (T70) till 5.5 Ma (T10). Seismic interpretation, fault analysis and analogue modeling experiments indicate that the post-rift fault activities in Baiyun sag between 32 Ma (T70) and 13.8 Ma (T30) was mainly controlled by gravity pointing to the Main Baiyun sag, which caused the faults extensive on the side facing Main Baiyun sag and the back side compressive. Around 32 Ma (T70), the breakup of the continental margin and the spreading of the South China Sea shed a combined effect of weak compression toward Baiyun sag. The gravity during post-rift stage might be caused by discrepant subsidence and sedimentation between strongly thinned sag center and wing areas. This is supported by positive relationship between sedimentation rate and fault growth index. After 13.8 Ma (T30), fault activity shows negative relationship with sedimentation rate. Compressive uplift and erosion in seismic profiles as well as negative tectonic subsiding rates suggest that the fault activity from 13.8 Ma (T30) to 5.5 Ma (T10) might be controlled by the subductive compression from the Philippine plate in the east. 相似文献
4.
The Western Foothills of Taiwan was known to be composed of Late Oligocene to Pleistocene shallow marine strata continuously deposited on the stable passive Chinese continental margin without significant stratigraphic break. Here we present multiple micropaleontological evidences, including occurrence of larger foraminifera Discocyclina dispansa ex. interc. sella-dispansa and calcareous nannoplanktons, to show that there are Middle Eocene marine strata (first named as the Chungliao Formation) exposed in the Tsukeng anticline of the Western Foothills, central Taiwan. Occurrences of intact tests with thin delicate outer rims and well-preserved embryonic chambers suggest that the Discocyclina dispansa ex. interc. sella-dispansa (Lutetian to Bartonian in the Tethys region) are buried indigenously on shallow inner shelf during an episodic transgression in the Early Middle Eocene. The conclusion is consistent with a biostratigraphy study of calcareous nannoplanktons (Zones NP14–15) in the shale/sandstone alternations overlying the Discocyclina-bearing bed of the Chungliao Formation and calcareous nannofossils of Zone NP16 integrated with an age dating of 38.8 ± 1 Ma (Late Middle Eocene) on zircon grains of the overlying Pinglin Tuff. The Middle Eocene syn-rift sequences (Chungliao Formation and Pinglin Tuff) exposed along the Tsukeng anticline are unconformably covered by the latest Oligocene–Miocene post-rift sequence, a scenario similar to what have been drilled in the East China Sea-Taiwan Strait-South China Sea. This rift basin (named as the Nantou Basin) is sitting on the Peikang Basement High margin which further extends southwestward to the Central Uplift of the Pearl River Mouth Basin in the northern slope of the South China Sea. The present work documents a hitherto unknown occurrence of the exposed early Tertiary marine rift basin sequence in the Western Foothills of Taiwan. The study extends our knowledge of the Western Foothills geohistory from the Late Oligocene downward to the Early Middle Eocene. The occurrence of the Paleogene Nantou rift basin in the Western Foothills may also suggest that there could have similar Paleogene rift sequences exposed in other parts of the Taiwan mountain belt like the Hsüehshan Range and the Central Range east of the Western Foothills. 相似文献
5.
Microfossils and a U–Pb age dating on zircon grains in the tuff beds exposed in the axial part of the Tsukeng anticline along the Pinglin River in the Western Foothills near Nantou, central Taiwan, show an occurrence of the Eocene volcanics unconformably beneath the uppermost part of the Latest Oligocene Wuchihshan Formation. This is the first discovery of the Eocene tuff exposed in the Western Foothills.The proposed Miocene “Tsukeng Formation” and “Takeng Formation” of Ho et al. (1956) named for sequences exposed in the Nantou area, Western Foothills, have to be abandoned and the standard Oligocene–Miocene lithostratigraphy used commonly in the Western Foothills of northern Taiwan is properly applicable in central Taiwan. The thick pink–brown–green colored volcanics unconformably beneath the uppermost Wuchihshan Formation is named for the first time as the Pinglin Tuff which contains Late Middle Eocene calcareous nannofossils (Zone NP16) consistent with a U–Pb age dating (38.8 ± 1 Ma) on zircon grains in the tuff. The Pinglin Tuff is overlying the Middle Eocene Chungliao Formation which contains indigenous larger foraminifera Discocyclina dispansa ex. interc. sella-dispansa and calcareous nannofossils of Zones NP14–15. The Middle Eocene Pinglin Tuff and Chungliao Formation represent the Paleogene syn-rift sequence unconformably overlain by the Latest Oligocene–Miocene post-rift sequence. This is the first document with conclusive paleontological data and age dating showing an occurrence of Paleogene marine rift basin exposed in the Western Foothills. This study also confirms similar Tertiary basin architecture between the Taiwan Strait–Pearl River Mouth Basin in the NE South China Sea and the Western Foothills onland central Taiwan. 相似文献
6.
U–Pb detrital zircon geochronology has been used to identify provenance and document sediment delivery systems during the deposition of the early Late Triassic Yanchang Formation in the south Ordos Basin. Two outcrop samples of the Yanchang Formation were collected from the southern and southwestern basin margin respectively. U–Pb detrital zircon geochronology of 158 single grains (out of 258 analyzed grains) shows that there are six distinct age populations, 250–300 Ma, 320–380 Ma, 380–420 Ma, 420–500 Ma, 1.7–2.1 Ga, and 2.3–2.6 Ga. The majority of grains with the two oldest age populations are interpreted as recycled from previous sediments. Multiple sources match the Paleozoic age populations of 380–420 and 420–500 Ma, including the Qilian–Qaidam terranes and the North Qilian orogenic belt to the west, and the Qinling orogenic belt to the south. However, the fact that both samples do not have the Neoproterozoic age populations, which are ubiquitous in these above source areas, suggests that the Late Triassic Yanchang Formation in the south Ordos Basin was not derived from the Qilian–Qaidam terranes, the North Qilian orogenic belt, and the Qinling orogenic belt. Very similar age distribution between the Proterozoic to Paleozoic sedimentary rocks and the early Late Triassic Yanchang Formation in the south Ordos Basin suggests that it was most likely recycled from previous sedimentary rocks from the North China block instead of sediments directly from two basin marginal deformation belts. 相似文献
7.
The Bianjiadayuan Pb–Zn–Ag deposit in the Southern Great Xing'an Range consists of quartz-sulfide vein-type and breccia-type mineralization related to granite. Vein orebodies are localized in NW-trending extensional faults. Hydrothermal alteration is well developed and includes silicification, potassic alteration, chloritization and sericitization. Three stages of mineralization are recognized based on field evidence and petrographic observation and are marked by assemblages of quartz–arsenopyrite–pyrite (stage I), quartz–pyrrhotite–chalcopyrite–sphalerite (stage II) and quartz–galena–silver minerals (stage III). The granite, with a zircon age of 143.2 ± 1.5 Ma (n = 14, MSWD = 0.93), is subalkaline, peraluminous and is classified as A2-type granite originating in a post-orogenic extensional setting during the opening of suture zone between the North China Craton and the Siberia Craton from the Late Jurassic to the Early Cretaceous. The δ34SCDT values of sulfides, ranging from 3.19 to 10.65‰, are not consistent with the majority of magmatic hydrothermal deposits in the SGXR, possibly implying accessory source in addition to magmatic source. Microthermometric measurements show that ore minerals were deposited at intermediate temperatures (347.8–136.4 °C) with moderate salinities (2.9–14.4 wt.% NaCl). Ore-forming fluids were derived largely from magmatic hydrothermal processes, with the addition of meteoric water in late stage. Successive precipitation of Pb, Zn and Ag occurred with changes of physicochemical conditions. Overall considering mineralization features, ore-forming fluids and materials and tectonic setting and comparing with adjacent deposits, the Bianjiadayuan deposit is a mesothermal magmatic hydrothermal vein-type Pb–Zn–Ag deposit controlled by fractures and related to A2-type granite in response to the tectonic/magmatic/hydrothermal activity in late Jurassic. Besides, the explosive breccias in the west area require more attention in future exploration. 相似文献
8.
《Comptes Rendus Geoscience》2018,350(6):267-278
This study uses field observations and new U–Pb ages of detrital zircon grains from three samples to question the stratigraphic position of the Firgoun and Niamey siliciclastic sediments, presumed to be Neoproterozoic in age. Sharing several lithological similarities with the Late Cryogenian “Triad” of the Taoudenni, Gourma, and Volta basins, the uppermost siliciclastic sediments of the Firgoun and Niamey areas were likely also deposited during this period. This is corroborated by matrix-supported diamictites with faceted or striated pebbles as well as by structures resembling cryoturbation processes. However, the detrital zircon U–Pb age record that we present here for the lowermost deposits of Firgoun and Niamey provides mainly Paleoproterozoic ages, and very few Archean ages, altogether in a range from 1822 ± 9 to 3392 ± 9 Ma. Therefore, the new data only show that the Firgoun and Niamey sediments were deposited before about 1800 Ma. Nevertheless, the U–Th–Pb zircon age data allows examining the possible provenance of the sediments. We show that the latter was likely in the westerly close vicinity of the studied areas. The Archean zircons are likely inherited, and possibly originating from a more westerly source. The nearby source of the Niamey and Firgoun sediments suggests that a high topographic relief was still existing in the south-central part of the West African Craton in the Mid Neoproterozoic. 相似文献
9.
The Qinling Orogen, central China, was constructed during the Mesozoic collision between the North China and Yangtze continental plates. The orogen includes four tectonic units, from north to south, the Huaxiong Block (reactivated southern margin of the North China Craton), North Qinling Accretion Belt, South Qinling Fold Belt (or block) and Songpan Fold Belt, evolved from the northernmost Paleo-Tethys Ocean separating the Gondwana and Laurentia supercontinents. Here we employ detrital zircons from the Early Cretaceous alluvial sediments within the Qinling Orogen to trace the tectonic evolution of the orogen. The U–Pb ages of the detrital zircon grains from the Early Cretaceous Donghe Group sediments in the South Qinling Fold Belt cluster around 2600–2300 Ma, 2050–1800 Ma, 1200–700 Ma, 650–400 Ma and 350–200 Ma, corresponding to the global Kenorland, Columbia, Rodinia, Gondwana and Pangaea supercontinent events, respectively. The distributions of ages and εHf(t) values of zircon grains show that the Donghe Group sediments have a complex source comprising components mainly recycled from the North Qinling Accretion Belt and the North China Craton, suggesting that the South Qinling Fold Belt was a part of the united Qinling–North China continental plate, rather than an isolated microcontinent, during the Devonian–Triassic. The youngest age peak of 350–200 Ma reflects the magmatic event related to subduction and termination of the Mian-Lue oceanic plate, followed by the collision between the Yangtze Craton and the united Qinling–North China continent that came into existence at the Triassic–Jurassic transition. The interval of 208–145 Ma between the sedimentation of the Early Cretaceous Donghe Group and the youngest age of detrital zircons was coeval with the post-subduction collision between the Yangtze and the North China continental plates in Jurassic. 相似文献
10.
《Gondwana Research》2014,26(4):1627-1643
The Tianshan Orogenic Belt, which is located in the southwestern part of the Central Asian Orogenic Belt (CAOB), is an important component in the reconstruction of the tectonic evolution of the CAOB. In order to examine the evolution of the Tianshan Orogenic Belt, we performed detrital zircon U–Pb dating analyses of sediments from the accretionary mélange from Chinese southwestern Tianshan in this study. A total of 542 analyzed spots on 541 zircon grains from five samples yield Paleoarchean to Devonian ages. The major age groups are 2520–2400 Ma, 1890–1600 Ma, 1168–651 Ma, and 490–390 Ma. Provenance analysis indicates that, the Precambrian detrital zircons were probably mainly derived from the paleo-Kazakhstan continent formed before the Early Silurian by amalgamation of the Kazakhstan–Yili microplate, the Chinese central Tianshan terrane and the Kyrgyz North and Middle Tianshan blocks, while detrital zircons with Paleozoic ages mainly from igneous rocks of the continental arc generated by the northward subduction of the south Tianshan paleocean. The age data correspond to four tectono-thermal events that took place in these small blocks, i.e., the continental nucleus growth during the Late Neoarchean–early Paleoproterozoic (~ 2.5 Ga), the evolution of the supercontinents Columbia (2.1–1.6 Ga) and Rodinia (1.3–0.57 Ga), and the arc magmatism related with the Phanerozoic orogeny. The Precambrian zircons show a similar age pattern as the Tarim and the Cathaysia cratons and the Eastern India–Eastern Antarctica block but differ from those of Siberia distinctly. Therefore, the Tianshan region blocks and the Kazakhstan–Yili microplate have a close affinity to the eastern paleo-Gondwana fragments, but were not derived from the Siberia craton as proposed by some previous researchers. These blocks were likely generated by rifting accompanying Rodinia break-up in late Precambrian times.The youngest ages of the detrital zircons from the subduction mélange show a maximum depositional age of ca. 390 Ma. It is coeval with the end of an earlier arc magmatic pulse (440–390 Ma) but a bit older than a younger one at 360–320 Ma and nearly 70–80 Ma older than the HP–UHP metamorphism in the subduction zone (320–310 Ma). 相似文献
11.
In the Menderes Massif (western Taurides) a Neoproterozoic basement comprising metasediments and intrusive granites is imbricated between Paleozoic platform sediments. U–Pb–Hf zircon analyses of Menderes rock units were performed by us using LA-ICP-MS. The U–Pb detrital zircon signal of the Neoproterozoic metasediments is largely consistent with a NE African (Gondwana) provenance. The oldest unit, a paragneiss, contains significant amounts (~ 30%) of Archean-aged zircons and εHf (t) values of about a half of its Neoproterozoic zircons are negative suggesting contribution from Pan-African terranes dominated by reworking of an old crust. In the overlying, mineralogically-immature Core schist (which is still Neoproterozoic), the majority of the detrital zircons are Neoproterozoic, portraying positive εHf (t) values indicating derivation from a proximal juvenile source, resembling the Arabian–Nubian Shield.The period of sedimentation of the analyzed metasediments, is constrained between 570 and 550 Ma (Late Ediacaran). The Core schist sediments, ~ 9 km thick, accumulated in less than 20 My implying a tectonic-controlled sedimentary basin evolved adjacent to the eroded juvenile terrane. Granites, now orthogneisses, intruded the basin fill at 550 Ma, they exhibit ± 0 εHf (t = 550 Ma) and TDM ages of 1.4 Ga consistent with anatexis of various admixtures of juvenile Neoproterozoic and Late Archean detrital components. Granites in the northern Arabian–Nubian Shield are no younger than 580 Ma and their εHf (t) are usually more positive. This implies that the Menderes does not represent a straightforward continuation of the Arabian–Nubian Shield.The lower part of the pre-Carboniferous silisiclastic cover of the Menderes basement, comprises a yellowish quartzite whose U–Pb–Hf detrital zircon signal resembles that of far-traveled Ordovician sandstones in Jordan (including 0.9–1.1 Ga detrital zircons), supporting pre-Triassic paleorestorations placing the Tauride with Afro-Arabia. The detrital signal of the overlying carbonate-bearing quartzitic sequence indicates contribution from a different source: the majority of its detrital zircons yielded 550 Ma and ± 0 εHf (t = 550 Ma) values identical to that of the underlying granitic gneiss implying exposure of Menderes-like granites in the provenance.260–250 Ma lead-loss and partial resetting of the U–Pb system of certain zircons in both basement and cover units was detected. It is interpreted as a consequence of a Permian–Early Triassic thermal event preceding known Triassic granitoid intrusions. 相似文献
12.
The North China Craton (NCC) is bounded by two Paleozoic accretionary arc terranes: the North Qinling terrane to the south and the Bainaimiao terrane to the north. The timing of arc accretion to the NCC and the architecture of the Bainaimiao arc remain unclear. During the building and accretion of the arcs along its margins, the NCC experienced a long sedimentary hiatus since the Ordovician, which ended with the deposition of bauxite-bearing sediments in the Late Carboniferous. In this paper we report the U–Pb and Hf isotopes of detrital zircons from the Late Carboniferous bauxite layer and use these data to constrain the tectonic evolution of the margin of the NCC. The detrital zircons yield a minimum U–Pb age of ca. 310 Ma and a prominent age peak at ca. 450 Ma. Zircon crystals with ages of ca. 330 Ma and ca. 1900 Ma are more common in the bauxite samples from the northern part of the NCC than in those from the central part. The εHf(t) values of the ca. 450 Ma detrital zircon crystals of the bauxite samples from the NCC are similar to those of the contemporaneous detrital zircon crystals from the North Qinling arc terrane to the south, but different from those of the contemporaneous detrital zircon crystals from the Bainaimiao arc terrane to the north. The ca. 450 Ma detrital zircon crystals in the ca. 310 Ma bauxite deposits are therefore interpreted to have been derived from the North Qinling arc terrane. The source of the ca. 330 Ma detrital zircon crystals of the bauxite deposits is interpreted to be the northern margin of the NCC, where intermediate-felsic plutons formed at ca. 330 Ma are common. The results from this study support the interpretation that the Paleozoic continental arc terranes and their concomitant back-arc basins were developed along the margins of the NCC before ca. 450 Ma, and the arc complexes were subsequently accreted to the craton in the Late Carboniferous. This was then followed by the formation of a walled continental basin within the NCC. 相似文献
13.
Xiaoping Long Chao Yuan Min Sun Wenjiao Xiao Guochun Zhao Yujing Wang Keda Cai Xiaoping Xia Liewen Xie 《Tectonophysics》2010,480(1-4):213-231
Subduction–accretion complexes occur widely in the Central Asian Orogenic Belt (CAOB). Due to the scarcity of fossils, the depositional timing of the Habahe flysch sequence of the subduction–accretion complex in the Chinese Altai is poorly constrained, which gave rise to much controversy in understanding the time of the basement and the tectonic evolution of the Chinese Altai. U–Pb dating of detrital zircons from the Habahe sequence in the northwestern Chinese Altai reveals a young zircon population with a mean 206Pb/238U age around 438 Ma which, together with a mean 206Pb/238U age of 411 ± 5 Ma for the overlying rhyolite of the Dongxileke Formation, brackets the time of deposition of the sequence between early Silurian and early Devonian. The age of the Dongxileke rhyolite also indicates that the overlying Baihaba Formation possibly began to be deposited in the early Devonian, though U–Pb dating of detrital zircons from this formation gave a maximum depositional age of ～ 438 Ma. The youngest detrital zircons and metamorphic grains of the Habahe sequence reveal different provenance to the sequence in the east. The youngest and metamorphic zircon grains, with early Paleozoic, Neoproterozoic and pre-Neoproterozoic populations, suggest a multi-source for the Habahe sequence. The predominantly early Paleozoic zircons, characterized by concentric zoning, high Th/U ratios and euhedral shapes, imply that the sediments of the sequence were mostly derived from a proximal magmatic source. Based on the age patterns of the Neoproterozoic and pre-Neoproterozoic populations, the Tuva–Mongol Massif, along with adjacent island arcs and metamorphic belts, may be an alternative source region for the Habahe sequence. In view of new geochemical and chronological data for granitoids and advancement in the study of regional metamorphism in the Chinese Altai, we suggest a tectonic model of subduction beneath a huge subduction–accretion complex for the evolution of the Chinese Altai in the early Paleozoic. 相似文献
14.
U–Pb detrital zircon ages are reported from Puncoviscana Formation (late Neoproterozoic–Early Cambrian) and Mesón Group (Late Cambrian) greywackes of northwest Argentina, to constrain provenance and depositional environment.The new data are combined with previously-published detrital zircon ages, to show that Puncoviscana Formation age patterns contain two broad groups: late Mesoproterozoic–early Neoproterozoic (1150–850 Ma) and late Neoproterozoic–Early Cambrian (650–520 Ma); with their relative proportions varying inversely with youngest component age. The 1150–850 Ma age components are dominant in greywackes with oldest late Neoproterozoic components > 600 Ma. The former diminish considerably when late Neoproteozoic components become dominant and younger, to 520 Ma. A northernmost greywacke sample from Purmamarca, Jujuy, is distinctive: whilst its zircon age pattern partly resembles other Puncoviscana Formation samples, it contains no Cambrian–late Neoproterozoic ages, the youngest ages being early Neoproterozoic. This may reflect an early, Neoproterozoic, passive-margin depocentre for the Formation, or an older (early Neoproterozoic) succession within it, which may predate the Brasiliano orogeny in Brazil. The youngest age components, c. 520 Ma, in a greywacke from Rancagua (Cachi, Salta province), dominate an almost unimodal pattern suggestive of contemporary volcanic sources at a late Early Cambrian depocentre. Detrital zircon age patterns of the Mesón Group (Lizoite Formation) have major Cambrian–latest Neoproterozoic components resembling those of the Puncoviscana Formation, but its Mesoproterozoic component is diminished, and there are no significant age components of this age. Small youngest components at c. 500 Ma suggest a maximum Late Cambrian stratigraphic age. The Puncoviscana Formation detrital zircon patterns suggest a provenance in a continental hinterland having a stabilised, extensive late Mesoproterozoic orogen (with minor Paleoproterozoic and Archean precursors), and a more variable late Neoproterozoic orogen containing an evolving sequence of less extensive subcomponents. A direct relationship with the Brazilian Shield is suggested; with sediment supplies originating within active-margin orogens of the interior and collisional orogens at the suture between African and South American cratons, but ultimate deposition in passive-margin environments of western Gondwanaland. 相似文献
15.
The tectonic evolution of the Chinese Tianshan Belt which is located in the southern margin of the Central Asian Orogenic Belt remains controversial. In order to reveal the evolutionary history of this belt, we investigate metasedimentary rocks from the Tianshanmiao of Harlik domain and Xingxingxia area of central Tianshan domain in this study. The Permian siltstones from Xingxingxia contain six zircon populations with ages peak at 280, 815 and 910, 1590, 1855 and 2340 Ma, suggesting a diverse provenance. The 2544–2294 Ma ages correlate with the generation of continental nuclei in Tarim. The tectonothermal events during 1855, 1590, 910 and 815 Ma may correspond to the assembly and breakup of the Columbia and Rodinia supercontinents, respectively. Similar Precambrian age spectra and “event signature” curves suggest that the central Tianshan was most likely a part of the Tarim block in the Proterozoic. The detrital zircon U–Pb ages of Ordovician meta-greywackes from the Tianshanmiao sequence reveal six zircon populations with peaks at 460, 933, 1382, 1850, 2000 and 2462 Ma, among which the zircons with dominant age peaks (460 Ma and 930 Ma, more than 70%) are euhedral, low sphericity and exhibit clear oscillatory zoning, suggesting local derivation from the proximal Ordovician and Neoproterozoic granitoids. The range of εHf(t) values (−5.4 to +21) of zircon grains from Ordovician rocks suggests that these were derived from depleted mantle or through partial melting of juvenile crust, similar to the case for the Early Paleozoic magmatism in Chinese Altai. Our detrital zircon data suggest that the provenance of the Harlik was neither the Tarim nor the Junggar, and instead, we propose a connection with the Chinese Altai-Tuva–Mongol Arc along the southern margin of the Siberia craton at ∼500 Ma. The Harlik domain drifted southward and then collided with the central Tianshan in the Carboniferous-Permian as a result of the closure of Paleo-Tianshan Ocean. 相似文献
16.
The Cambrian Maotianshan Shale in Yunnan Province, China contains the well-preserved soft-body fossils of the Chengjiang Biota. The high quality preservation of the non-mineralizing biota (soft tissues and whole carcasses) shows regional and temporal differences, suggesting that paleogeography and local environmental conditions might have contributed to the taphonomy of these fossils. In this paper we present new results from petrographic, geochemical and detrital zircon analyses, and provide a new interpretation about the provenance of the Maotianshan Shale, as well as add to the understanding of the paleogeography of the South China Block during the Cambrian Stage 3. Results from petrographic analysis indicate that the provenance of the Maotianshan Shale is a recycled orogen overall, bordering the western and southwestern margin on the Yangtze Block. The most likely source of the terrigenous material is an exhumed area extending from the Kangdian paleoland to the southeast, paralleling the Song Ma fault zone. Minor regional differences in geochemical and petrographic proxies between the northwestern Jianshan/Ercai area and the southeastern Maotianshan/Xiaolantian area suggest influence of local sources. Sediments of the southeastern province are less mature and samples include minor elements commonly associated with mafic sources. Sediments from the northwestern province are more mature, largely lack mafic components and are enriched in Zr and Hf. The major population of the Maotianshan Shale detrital zircons group at ~ 800 Ma. This crystallization age matches well with the age of a widely spread felsic volcanic and intrusive event associated with the Neoproterozoic Kangdian rift, suggesting that these igneous rocks are most likely a major provenance for the Maotianshan sediments. The youngest zircon population yields consistent Concordia ages of ~ 520 Ma, representing a maximum age constraint on the timing of deposition of the Maotianshan Shale. The zircon crystals of the ~ 520 Ma populations are euhedral with magmatic zoning, indicative of short-distance transport. Volcanic activity along the Song Ma suture zone is a potential source for the ~ 520 Ma detrital zircon suite. 相似文献
17.
The Xingshan porphyry Mo deposit is located in the Lesser Xing’an Range–Zhangguangcai Range metallogenic belt, NE China. Mineralization occurred in granodioritic porphyry and monzogranite, which have zircon U–Pb ages of 171.7 ± 2.2 Ma and 170.9 ± 4.6 Ma, respectively. Molybdenite Re–Os dating indicates that Mo mineralization occurred at 167.3 ± 2.5 Ma. These geochronological data suggest that the magmatic and hydrothermal activities of the Xingshan Mo deposit happened during the Middle Jurassic in Mesozoic. Positive εHf values (6.2–11.6) and young TDM2 (473–826 Ma) of the monzogranite (XS-3) and granodioritic porphyry (XS-5) indicate that the source materials of Xingshan ore-bearing rocks are the juvenile crust, which mainly accreted on the Songnen block during the Meso-Neoproterozoic. Xingshan porphyry Mo deposits resulted from the magmatism and tectonism induced by the subduction of Paleo-Pacific Ocean. 相似文献
18.
《Gondwana Research》2013,23(3-4):855-865
The ages of detrital zircon grains from one paragneiss and inherited zircon cores from two augen gneisses from the amphibolite facies basement of the Peloritani Mountains (southern Italy) measured by SHRIMP U–Pb constrain the previously unknown deposition age of the original sediments and help to elaborate a model for their provenance and subsequent evolution. The deposition age is latest Neoproterozoic to Cambrian (~ 545 Ma), bracketed by the combined ages of the youngest detrital/inherited zircon populations and of zircon from virtually coeval granitoids that intrude the metasediments. This is consistent with the subgreenschist facies Palaeozoic volcano–sedimentary sequences exposed in the southern Peloritani Mountains being the original cover rocks of the northern Peloritani late Neoproterozoic to early Cambrian basement. The age spectra of the detrital/inherited zircon grains show that the Neoproterozoic/Cambrian sediments were derived from the erosion of sources dominated by Neoproterozoic rocks with ages in the range of 0.85–0.54 Ga, with other main components aged 1.1–0.9 and ~ 2.7–2.4 Ga, and a minor one aged ~ 1.6 Ga, as typically found in peri-Gondwanan terranes. The presence of a large amount of Grenvillian-aged zircon contradicts previous models that propose a West African affinity for the Calabria–Peloritani Terrane, and the absence of 2.2–1.9 Ga Trans Amazonian/Tapajós–Parima/Eburnean zircon rules out an Amazonian provenance. The age spectra are more consistent with the basement sediments having an East African origin, similar to that of the early Palaeozoic sandstones in southern Israel and Jordan, part of a “provenance regionality” shared with other terranes currently located in the eastern Mediterranean area. 相似文献
19.
The newly discovered Chalukou giant porphyry Mo deposit, located in the northern Great Xing’an Range, is the biggest Mo deposit in northeast China. The Chalukou Mo deposit occurs in an intermediate-acid complex and Jurassic volcano-sedimentary rocks, of which granite porphyry, quartz porphyry, and fine-grained granite are closely associated with Mo mineralization. However, the ages of the igneous rocks and Mo mineralization are poorly constrained. In this paper, we report precise in situ LA-ICP-MS zircon U–Pb dates for the monzogranite, granite porphyry, quartz porphyry, fine grained granite, rhyolite porphyry, diorite porphyry, and andesite porphyry in the Chalukou deposit, corresponding with ages of 162 ± 2 Ma, 149 ± 5 Ma, 148 ± 2 Ma, 148 ± 1 Ma, 137 ± 3 Ma, 133 ± 2 Ma, and 132 ± 2 Ma, respectively. Analyses of six molybdenite samples yielded a Re–Os isochron age of 148 ± 1 Ma. These data indicate that the sequence of the magmatic activity in the Chalukou deposit ranges from Jurassic volcano-sedimentary rocks and monzogranite, through late Jurassic granite porphyry, quartz porphyry, and fine-grained granite, to early Cretaceous rhyolite porphyry, diorite porphyry, and andesite porphyry. The Chalukou porphyry Mo deposit was formed in the late Jurassic, and occurred in a transitional tectonic setting from compression to extension caused by subduction of the Paleo-Pacific oceanic plate. 相似文献
20.
To constrain the provenance of the Ordos Basin and the evolution history of the Qinling Orogen Belt from the Triassic to the Jurassic, 10 samples from the Dongsheng area and 28 samples from the Yan’an area were analyzed for U–Pb ages and Lu–Hf and Sm–Nd isotopic compositions. The results indicate that Middle Jurassic sediments in the Dongsheng area were derived from the Khondalite Belt, Langshan Mountain and the Yinshan Terrane. Mesozoic sediments in the Yan’an area consist of two parts. One part is derived from the North China Craton (NCC), which has U–Pb age groups of ∼1.8 Ga and ∼2.5 Ga, and Hf model ages of ∼2.8 Ga. The other part is derived from the Qilian–Qinling Orogenic Belt, which has U–Pb age groups of 600–1500 Ma and 100–500 Ma, and Nd and Hf isotopic model ages of less than 2.2 Ga. Combining the U–Pb ages with the Hf and Nd isotopic model ages, Mesozoic detrital zircons with U–Pb age groups of ∼1.8 Ga and ∼2.5 Ga in the Yan’an area are found to also be derived from the Khondalite Belt, Langshan Mountain and the Yinshan Terrane, not from the Trans-China Orogen Belt. From the late–Late Triassic sediments of the Yan’an area, the low average values of the Hf (2.03 Ga) and Nd (2.03 Ga) model ages and the characteristic age population of 600–1500 Ma reveal that the main collision or continental subduction between the NCC and the South China Craton (SCC) occurred in the late–Late Triassic. After the main collision or continental subduction, the proportion of sediments from the Qinling–Qilian Orogenic Belt began to decrease (recorded in the early Jurassic samples), which may be in response to the gradual slowing of the uplift speed of the Qinling Orogenic Belt. In the early-middle Jurassic, the sediments have a main U–Pb age population of 100–500 Ma, low detrital zircon Hf model ages (average value is 1.17 Ga) and low whole rock Nd model ages (average value is 1.13 Ga), which suggests that the Qilian–Qinling Orogenic Belt may have a fast uplift history in the early-middle Jurassic. 相似文献