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1.
Early Paleozoic evolution of the northern Gondwana margin is interpreted from integrated in situ U-Pb and Hf-isotope analyses on detrital zircons that constrain depositional ages and provenance of the Lancang Group, previously assigned to the Simao Block, and the Mengtong and Mengdingjie groups of the Baoshan Block. A meta-felsic volcanic rock from the Mengtong Group yields a weighted mean 206Pb/238U age of 462 ± 2 Ma. The depositional age for the previously inferred Neoproterozoic Lancang and Mengtong groups is re-interpreted as Early Paleozoic based on youngest detrital zircons and meta-volcanic age. Detrital U-Pb zircon analyses from the Baoshan Block define three distinctive age peaks at older Grenvillian (1200–1060 Ma), younger Grenvillian (~ 960 Ma) and Pan-African (650–500 Ma), with εHf(t) values for each group similar to coeval detrital zircons from western Australia and northern India. This suggests that the Baoshan Block was situated in the transitional zone between northeast Greater India and northwest Australia on the Gondwana margin and received detritus from both these cratons. The Lancang Group yields a very similar detrital zircon age spectrum to that of the Baoshan Block but contrasts with that for the Simao Block. This suggests that the Lancang Group is underlain by a separate Lancang Block. Similar detrital zircon age spectra suggest that the Baoshan Block and the Lancang Block share common sources and that they were situated close to one another along the northern margin of East Gondwana during the Early Paleozoic. The new detrital zircon data in combination with previously published data for East Gondwana margin blocks suggests the Early Paleozoic Proto-Tethys represents a narrow ocean basin separating an “Asian Hun superterrane” (North China, South China, Tarim, Indochina and North Qiangtang blocks) from the northern margin of Gondwana during the Late Neoproterozoic-Early Paleozoic. The Proto-Tethys closed in the Silurian at ca. 440–420 Ma when this “Asian Hun superterrane” collided with the northern Gondwana margin. Subsequently, the Lancang Block is interpreted to have separated from the Baoshan Block during the Early Devonian when the Paleo-Tethys opened as a back-arc basin. 相似文献
2.
We present the first evidence of an early Paleozoic terrane in the southern Yanbian region, NE China. We used LA-ICP-MS zircon U–Pb and Hf isotope techniques to analyze one plagioclase gneiss and two garnet-bearing two-mica quartz schists from the early Paleozoic Jiangyu Group, as well as two tonalites that intruded the Jiangyu Group. The tonalites yield weighted mean 206Pb/238U zircon crystallization ages of 423 and 422 Ma. Zircons from the Jiangyu Group gneiss and two schist samples yield maximum depositional ages of 439 ± 4, 443 ± 2, and 443 ± 5 Ma, respectively. These constraints, together with the age of the tonalite intrusion, indicate that the Jiangyu Group was deposited between 443 and 423 Ma (i.e., Silurian). In addition, detrital zircon age spectra of the three Jiangyu Group samples exhibit prominent age peaks at 442, 473, 513, 565, 600, 635, 671, 740, 1000, and 1162 Ma, as well as secondary peaks between 1344 and 3329 Ma. The occurrence of the prominent Meso- and Neoproterozoic detrital zircon age populations for the Jiangyu Group, combined with the corresponding zircon Hf isotopic data, reveals that the Jiangyu Terrane has a tectonic affinity with northeastern Gondwana. The early Paleozoic magmatism, as suggested by the medium-K calc-alkaline I-type tonalite intrusion and Jiangyu Group detrital zircon age spectra, corresponds to coeval subduction–accretion events along the southern margin of the eastern Central Asian Orogenic Belt (CAOB). Accordingly, we propose that the Jiangyu Group is part of an exotic terrane that rifted from northeastern Gondwana, drifted northward, and ultimately became involved in the early Paleozoic tectonic evolution of the southern margin of the eastern CAOB after the Early Cambrian. 相似文献
3.
《Journal of South American Earth Sciences》2009,27(4):343-354
U–Pb detrital zircon studies in the Rio Fuerte Group, NW Mexico, establish its depositional tectonic setting and its exotic nature in relation to the North American craton. Two metasedimentary samples of the Rio Fuerte Formation yield major age clusters at 453–508 Ma, 547–579 Ma, 726–606 Ma, and sparse quantities of older zircons. The cumulative age plots are quite different from those arising from lower Paleozoic miogeoclinal rocks of southwestern North America and of Cordilleran Paleozoic exotic terranes such as Golconda and Robert Mountains. The relative age-probability plots are similar to some reported from the Mixteco terrane in southern Mexico and from some lower Paleozoic Gondwanan sequences, but they differ from those in the Gondwanan-affinity Oaxaca terrane. Major zircon age clusters indicate deposition in an intraoceanic basin located between a Late Ordovician magmatic arc and either a peri-Gondwanan terrane or northern Gondwanaland. The U–Pb magmatic ages of 151 ± 3 Ma from a granitic pluton and 155 ± 4 Ma from a granitic sill permit a revision of the stratigraphic and tectonic evolution of the Rio Fuerte Group. A regional metamorphism event predating the Late Jurassic magmatism is preliminarily ascribed to the Late Permian amalgamation of Laurentia and Gondwana. The Late Jurassic magmatism, deformation, and regional metamorphism are related to the Nevadan Orogeny. 相似文献
4.
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
5.
The Danubian domain basement of the South Carpathians, Romania, comprises two Neoproterozoic continental crustal fragments, the Dr?g?an and Lainici-P?iu? terranes, which were sutured by the closure of an intervening oceanic domain, the Ti?ovi?a terrane. Magmatic and detrital zircons extracted from an orthogneiss, four granitoid plutons, two metasedimentary units, and a Liassic sandstone were dated by zircon U/Pb LA-ICP-MS. The F?ge?el augen gneiss from the Dr?g?an terrane basement yielded an age of 803.2 ± 4.4 Ma, the oldest well-constrained crystallization age reported from the Romanian Carpathians basement. The Tismana, ?u?i?a, Novaci and Olte? granitoid plutons, which intrude the Lainici-P?iu? terrane basement, yielded ages of 600.5 ± 4.4, 591.0 ± 3.5, 592.7 ± 4.9, and 588 ± 2.9 Ma, respectively. The Tismana granitoid age of 600 Ma and the youngest detrital zircon ages of 637–622 Ma from a metaquartzite within the Lainici-Paiu? terrane, constrain the deposition of the metaquartzite protolith to ca. 620–600 Ma. The 803 Ma age represents an old Pan-African age, whereas the younger Neoproterozoic ages suggest Pan-African/Cadomian thermotectonic events. Detrital and inherited zircon ages within the Dr?g?an and Lainici-Paiu? terranes attest to a peri-Amazonian, Avalonian-type provenance for the Dr?g?an terrane and possibly a Ganderian-type provenance for the Lainici-P?iu? terrane. The Lainici-P?iu? terrane rifted off Gondwana before the Dr?g?an terrane. Both terranes were attached to Moesia during the Early Paleozoic. 相似文献
6.
We present new U–Pb isotopic age data for detrital zircons from 16 deformed sandstones of the Ross Supergroup in north Victoria Land, Antarctica. Zircon U/Th ratios primarily point to dominantly igneous parent rocks with subordinate contributions from metamorphic sources. Comparative analysis of detrital zircon age populations indicates that inboard stratigraphic successions (Wilson Terrane) and those located outboard of the East Antarctic craton (the Bowers and Robertson Bay terranes) have similar ~ 1200–950 Ma (Mesoproterozoic–Neoproterozoic) and ~ 700–490 Ma (late Neoproterozoic–Cambrian, Furongian) age populations. The affinity of the age populations of the sandstones to each other, as well as Gondwana sources and Pacific-Gondwana marginal stratigraphic belts, challenges the notion that the outboard successions form exotic terranes that docked with Gondwana during the Ross orogeny and instead places the terranes in proximity to each other and within the peri-Gondwana realm during the late Neoproterozoic to Cambrian. The cumulative zircon age suite from north Victoria Land yields a polymodal age spectra with a younger, primary 700–480 Ma age population that peaks at ~ 580 Ma. Cumulative analysis of zircons with elevated U/Th ratios (> 20) indicating metamorphic heritage yield ~ 657–532 Ma age probability peaks, which overlap with the younger dominantly igneous zircon population. The data are interpreted to give important new evidence that is consistent with ongoing convergent arc magmatism by ~ 626 Ma, which provided the dominant zircon-rich igneous rocks and subordinate metamorphic rocks. Maximum depositional ages as young as ~ 493–481 Ma yielded by deformed sequences in the outboard Bowers and Robertson Bay terrane samples provide new support for late Cambrian to Ordovician deformation in outboard sectors of the orogen, consistent with tectonic models that call for cyclic phases of contraction along the north Victoria Land sector of the Ross–Delamerian orogen. 相似文献
7.
LA-ICPMS U-Pb geochronology of detrital rutile from North Gondwana Cambro-Ordovician sandstones is reported for the first time. Our sampling sites in Israel, Jordan and Ethiopia are situated thousands of kilometers apart thus providing a continental-scale perspective on the cooling and unroofing history of the provenance of the great Cambro-Ordovician sandstone sheet.Detrital rutiles in the Cambrian sandstone of Israel and Jordan define a unimodal age concentration at 0.59–0.58 Ga, preceding the timing of major orogenic sutures and predating the final assembly of Gondwana. Cooling to below the rutile U-Pb closure temperature followed continental-scale Pan-African granitoid intrusion at 0.63–0.60 Ga, signifying that rather than representing high-grade metamorphism the detrital rutile age spectra reflect widespread resetting, cooling and exhumation associated with late to post-tectonic igneous activity. The unimodal 0.59–0.58 Ga age spectra do not change significantly up the Cambrian sequence, implying exhumation prior to Cambrian sedimentation generated ample crustal material with an almost uniform U-Pb rutile signature that was prone to deliver immense amounts of detritus. Therefore, rather than reflecting progressive erosion of Cambrian Supermountains, the North Gondwana Cambrian sandstone represents secondary denudation of an already-exhumed metamorphic basement.Alongside the older (0.59–0.58 Ga) detrital rutile population, which dominates the Cambrian sequence, 0.55 Ga detrital rutiles first appear in the Ordovician of Jordan while 0.54 Ga rutile locally dominates the Ordovician from Ethiopia, some 2000 km upstream the Cambro-Ordovician fluvial system, close to its headwaters. The Ordovician drainage basin has thus been extended to include crustal vestiges that were exhumed coeval with Gondwana consolidation, but it is likely that most of the rock carapace that has been eroded from consolidating Cambrian orogenic sutures has been delivered to the south (modern coordinates). 相似文献
8.
The Charysh–Terekta–Ulagan–Sayan suture zone was regarded as a tectonic boundary separating two distinct subduction–accretion systems in the Central Asian Orogenic Belt (CAOB). In the north, magmatic arcs, such as the Gorny Altai terrane, formed in the southwestern periphery of the Siberian continent, whereas in the south, arc-prism systems, such as the Altai–Mongolian terrane, formed around the so-called Kazakhstan–Baikal composite continent with Gondwana affinity. When did these two systems amalgamate and whether the metamorphic complexes in the suture zone represent Precambrian micro-continental slivers are critical for our understanding of the accretionary orogenesis and crustal growth rate in the CAOB. A combined geochemical and detrital zircon U–Pb–Hf isotopic study was conducted on the meta-sedimentary rocks from the Ulagan (also referred to Bashkaus) and Teletsk Complexes in the suture zone. The results indicate that the protoliths of these rocks were dominated by immature sediments deposited in a time period between 500 and 420 Ma. Thus, Precambrian micro-continental slivers may not exist in the suture zone and even in the whole Altai Orogen.The meta-sedimentary rocks from the Ulagan Complex yield geochemical compositions between those of common intermediate and felsic igneous rocks, implying that these kinds of rocks possibly served as dominant sources. Detrital zircons from this complex consist of a major population of ca. 620–500 Ma, a subordinate one of ca. 931–671 Ma and rare grains of ca. 2899–1428 Ma. This age spectrum is compatible with the magmatic records of the western Mongolia. We propose that the Ulagan Complex possibly represents part of a subduction–accretion complex built upon an active continental margin of the western Mongolia in the early Paleozoic. The remarkable similarities in source nature, provenance, and depositional setting to the early Paleozoic meta-sedimentary rocks from the northern Altai–Mongolian terrane imply that the Ulagan Complex was possibly fragmented from this terrane.The meta-sedimentary rocks from the Teletsk Complex show similar detrital zircon populations but contain higher proportions of mafic sediments and have more depleted whole-rock Nd isotopic compositions. Our data suggest that the detritus mostly came from the same source as that for the Ulagan Complex but those from the Gorny Altai terrane also contributed. This implies that the Gorny Altai and Altai-Mongolian terranes possibly amalgamated prior to the early Devonian rather than in the middle Devonian to early Carboniferous as previously thought. Thus, the widespread Devonian to early Carboniferous magmatism within these two terranes was possibly generated in a similar tectonic setting. Moreover, the dominant Neoproterozoic to early Paleozoic detrital zircons from the Teletsk Complex yield largely varied ɛHf(t) values of − 23.8 to 12.4, indicating that crustal growth and reworking are both important in the accretionary orogenesis. 相似文献
9.
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
10.
In most of the rocks of the Fuping Complex in the Trans-North China Orogen, a large quantity of leucocratic veins, dykes and granitic intrusions are present as migmatites. The incongruent partial melting of biotite to hornblende suggests the water-fluxed anatexis of the migmatization of which the melt is manifested by the euhedral crystallization of some quartzofeldspathic minerals and presence of albite rim on earlier plagioclase or K-feldspar. Importantly, some melt may be segregated in the sillimanite gneisses or extracted and injected as faint dispersed melt into the competent metasedimentary quartzite of the Wanzi series rocks. The quartzite has plenty of zircon ages cluster at c 2.5 Ga and some at c 2.1–2.0 Ga, the former may be detrital zircon age, while the latter represents the age of migmatization or crystallization of the injected melt, not detrital zircon ages as conventionally believed. The data have constrained that the sedimentation time of the protolith of the quartzite of the Wanzi series was between c 2.5 Ga and c 2.1–2.0 Ga, not younger than c 2.1–2.0 Ga as once proposed. Therefore it must be cautious in applying detrital zircon ages in constraining the time of sedimentation if the rocks have undergone middle-high grade metamorphism, especially when migmatization was involved in the metamorphism process. 相似文献
11.
We present a synopsis of detrital zircon U–Pb ages of sandstones from North Africa and neighboring Israel and Jordan, which allows us to identify zones with characteristic sediment provenance along the northern Gondwana margin (in present-day coordinates) in Cambrian–Ordovician times, and helps us to unravel the peri-Gondwana jigsaw puzzle. A special feature of the early Paleozoic cover sequence of North Africa is the eastward increase of 1.1–0.95 Ga detrital zircons, which become ubiquitous in the early Paleozoic sandstones of the Saharan Metacraton. Detrital zircons aged about 2.7–2.5, 2.15–1.75 and 0.75–0.53 Ga are also present. Early Paleozoic sandstones with similar provenance are known from peri-Gondwana terranes in the Eastern and Western Mediterranean and from NW Iberia. These terranes need not be transported from western Gondwana (Amazonia) as suggested previously. They were likely located to the north of the Saharan Metacraton during the early Paleozoic before they rifted off from Gondwana. Furthermore, we recognize an increase, as stratigraphic ages get younger, of ca. 1.0 Ga detrital zircons at some point between the Late Cambrian and late Middle Ordovician. We speculate that this might be linked to far-field tectonics and regional uplift in central Gondwana related to plate-tectonic reorganization along the Gondwana margin, leading to erosion of ca. 1.0 Ga basement and country rocks of the Transgondwanan supermountain and fluvial dispersal of detritus toward the Gondwana margin. 相似文献
12.
Kerstin Drost Axel Gerdes Teresa Jeffries Ulf Linnemann Craig Storey 《Gondwana Research》2011,19(1):213-231
New LA-ICP-MS U–Pb detrital zircon ages from Ediacaran and Paleozoic siliciclastic rocks are used to constrain provenance and paleogeographic affinities of the Teplá-Barrandian unit (TBU) in the centre of the Bohemian Massif (Central Europe, Czech Republic). The samples taken span the period from ≤ 635 Ma to ～ 385 Ma and permit recognition of provenance changes that reflect changes in geotectonic regime. Detrital zircon age spectra of two Ediacaran, one Lower Cambrian and three Upper Ordovician samples resemble the ages known from the NW African proportion of Gondwana, particularly the Trans-Saharan belt, while three rocks from higher Lower Cambrian to Lowermost Ordovician strata contain detritus that may have been derived exclusively from local sources. The age spectrum of the Devonian rock is a combination of the NW Gondwanan and local features. These new findings in combination with a wide range of published data are in agreement with a Neoproterozoic subduction-related setting at the margin of Gondwana followed by a Cambrian/Early Ordovician rifting stage and an Ordovician passive margin setting. Furthermore the data are in favour of a position of the TBU at the Gondwanan margin throughout pre-Variscan times. 相似文献
13.
Detrital zircons from the upper Cambrian-Devonian sandstones (Crashsite Group; n = 485) and Carboniferous tillite (Whiteout Conglomerate; n = 81) of the Ellsworth Mountains, Antarctica record a steady supply of Neoproterozoic (“Pan-African”) orogeny (~ 550–600 Ma), Grenville (~ 1000 Ma) and Neoarchean (~ 3000–3500 Ma) zircons into the northern marginal basin of Gondwana. The overlying Permian Glossopteris-bearing Polarstar Formation shales (n = 85) have the same zircon provenance as underlying units but also include a dominance of depositional-age (263 Ma) euhedral zircons which are interpreted to be of local, volcanic arc origin. Modeling of detrital zircon provenance suggests that source areas were present in Pan-African and Laurentian crust throughout the Paleozoic. We also report calcite twinning strain results (12 strain analyses; n = 398 twins) for the Cambrian Minaret Fm. in the Heritage range which is predominantly a layer-parallel shortening strain in the direction (WSW-ENE) of Permian Gondwanide orogen thrust transport. There is a secondary, sub-vertical twinning strain overprint. The initiation of localized lower-middle Cambrian rifting (Heritage Group deposition) in Grenville-aged crust as Gondwana amalgamated and the subsequent Jurassic counterclockwise rotation of the Ellsworth-Whitmore terrane out of the Permian Gondwanide belt into central Antarctica each remain tectonic curiosities. 相似文献
14.
M. Naipauer G.I. Vujovich C.A. Cingolani W.C. McClelland 《Journal of South American Earth Sciences》2010,29(2):306-326
Metamorphic basement and its Neoproterozoic to Cambrian cover exposed in the Sierra de Pie de Palo, a basement block of the Sierras Pampeanas in Argentina, lie within the Cuyania terrane. Detrital zircon analysis of the cover sequence which includes, in ascending order, the El Quemado, La Paz, El Desecho, and Angacos Formations of the Caucete Group indicate a Laurentian origin for the Cuyania terrane. The lower section represented by the El Quemado and La Paz Formations is interpreted as having an igneous source related to a rift setting similar to that envisioned for the southern and eastern margins of Laurentia at approximately 550 Ma. The younger strata of the El Desecho Formation are correlative with the Cerro Totora Formation of the Precordillera, and both are products of rift sedimentation. Finally, the Angacos Formation and the correlative La Laja Formation of the Precordillera were deposited on the passive margin developed on the Cuyania terrane. The maximum depositional ages for the Caucete Group include ca. 550 Ma for the El Quemado Formation and ca. 531 Ma for the El Desecho Formation. Four different sediment sources areas were interpreted in the provenance analysis. The main source is crystalline basement dominated by early Mesoproterozoic igneous rocks related to the Granite-Rhyolite province of central and eastern Laurentia. Possible source areas for 1600 Ma metamorphic detrital zircons of the Caucete Group include the Yavapai-Mazatzal province (ca. 1800–1600 Ma) of south-central to southwestern Laurentia. Younger Mesoproterozoic zircon is likely derived from Grenville-age medium- to high-grade metamorphic rocks and subordinate igneous rocks that form the basement of Cuyania as well as the southern Grenville province of Laurentia itself. Finally, Neoproterozoic igneous zircon in the Caucete Group records different magmatic pulses along the southern Laurentian margin during opening of Iapetus and break-up of Rodinia. Northwestern Cuyania terrane includes a small basement component derived from the Granite-Rhyolite province of Laurentia, which was the source for detrital zircons found in the middle Cambrian passive margin sediments of Cuyania. 相似文献
15.
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
16.
《Russian Geology and Geophysics》2014,55(11):1249-1263
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
17.
U–Pb dating of detrital zircons was performed on mélange-hosted lithic and basaltic sandstones from the Inthanon Zone in northern Thailand to determine the timing of accretion and arc activity associated with Paleo-Tethys subduction. The detrital zircons have peak ages at 3400–3200, 2600–2400, 1000–700, 600–400, and 300–250 Ma, similar to the peaks ages of detrital zircons associated with other circum-Paleo-Tethys subduction zones. We identified two types of sandstone in the study area based on the youngest detrital zircon ages: Type 1 sandstones have Late Carboniferous youngest zircon U–Pb ages of 308 ± 14 and 300 ± 16 Ma, older than associated radiolarian chert blocks within the same outcrop. In contrast, Type 2 sandstones have youngest zircon U–Pb ages of 238 ± 10 and 236 ± 15 Ma, suggesting a Middle Triassic maximum depositional age. The youngest detrital zircons in Type 1 sandstones were derived from a Late Carboniferous–Early Permian ‘missing’ arc, suggesting that the Sukhothai Arc was active during sedimentation. The data presented within this study provide information on the development of the Sukhothai Arc, and further suggest that subduction of the Paleo-Tethyan oceanic plate beneath the Indochina Block had already commenced by the Late Carboniferous. Significant Middle Triassic arc magmatism, following the Late Carboniferous–Early Permian arc activity, is inferred from the presence of conspicuous detrital zircon U–Pb age peaks in Type 2 sandstones and the igneous rock record of the Sukhothai Arc. In contrast, only minimal arc activity occurred during the Middle Permian–earliest Triassic. Type 1 sandstones were deposited between the Late Permian and the earliest Triassic, after the deposition of associated Middle–Late Permian cherts that occur in the same mélanges and during a hiatus in Sukhothai Arc magmatism. In contrast, Type 2 sandstones were deposited during the Middle Triassic, coincident with the timing of maximum magmatism in the Sukhothai Arc, as evidenced by the presence of abundant Middle Triassic detrital zircons. These two types of sandstone were probably derived from discrete accretionary units in an original accretionary prism that was located along the western margin of the Sukhothai Arc. 相似文献
18.
We have investigated the petrography, geochemistry, and detrital zircon U–Pb LA-ICPMS dating of sandstone from the Gorkhi Formation of the Khangai–Khentei belt in the Ulaanbaatar area, central Mongolia. These data are used to constrain the provenance and source rock composition of the accretionary complex, which is linked to subduction of the Paleo-Asian Ocean within the Central Asian Orogenic Belt during the Middle Devonian to Early Carboniferous. Field and microscopic observations of the modal composition of sandstone and constituent mineral chemistry indicate that the sandstone of the Gorkhi Formation is feldspathic arenite, enriched in saussuritized plagioclase. Geochemical data show that most of the sandstone and shale were derived from a continental margin to continental island arc setting, with plutonic rocks being the source rocks. Detrital zircon 206Pb/238U ages of two sandstones yields age peaks of 322 ± 3 and 346 ± 3 Ma. The zircon 206Pb/238U age of a quartz–pumpellyite vein that cuts sandstone has a weighted mean age of 339 ± 3 Ma. Based on these zircon ages, we infer that the depositional age of sandstone within the Gorkhi Formation ranges from 320 to 340 Ma (i.e., Early Carboniferous). The provenance and depositional age of the Gorkhi Formation suggest that the evolution of the accretionary complex was influenced by the intrusion and erosion of plutonic rocks during the Early Carboniferous. We also suggest that spatial and temporal changes in the provenance of the accretionary complex in the Khangai–Khentei belt, which developed aound the southern continental margin of the Siberian Craton in relation to island arc activity, were influenced by northward subduction of the Paleo-Asian Ocean plate. 相似文献
19.
New combined U–Pb and Lu–Hf isotope analyses on zircon from three turbidite deposits, and petrologic data for associated igneous rocks were used to study the evolution of the Paleozoic basement of Eastern Cordillera, NW Argentina. Maximum and minimum ages for turbidite deposits, considered to be part of the Puncoviscana Fm., are reported. In the Tastil area, turbidites were deposited in a fore-arc setting after 560 Ma and intruded at 534 Ma by the Tastil batholith. In the El Niño Muerto Hill area turbidites with maximum depositional age of 496 ± 11 Ma were intruded by high-K dacites at 483 ± 3 Ma. In the Río Blanco Valley, the turbiditic/hemipelagitic sediments, with maximum depositional age of 463 ± 11 Ma were contemporaneous with E-MORB/OIB volcanism. The U–Pb and Lu–Hf data permitted to distinguish two major periods of magmatic activity during Late Mesoproterozoic–Early Neoproterozoic (0.95 to 1.2 Ga) and Late Neoproterozoic–Early Paleozoic (0.75 to 0.46 Ga) times, the former dominated by the input of juvenile crust and the latter by arc magmatism and recycling of Meso- to Paleoproterozoic crust. On the basis of new data we suggest that western margin of Gondwana was controlled by subduction processes and accretion of small terrains during Neoproterozoic–Early Paleozoic times. 相似文献
20.
This paper reports LA–ICP–MS U–Pb dates and in situ Hf isotope analyses of detrital zircons from the Mesozoic basins in western Shandong, China, with the aim to constrain the depositional ages and provenances of the Mesozoic strata as well as the Mesozoic tectonic evolution of the eastern North China Block (NCB). The Mesozoic strata in western Shandong, from bottom to top, include the Fenghuangshan, Fangzi, Santai and Wennan formations. Most of the analyzed zircon grains exhibit oscillatory growth zoning and have relatively high Th/U ratios (generally 0.2–3.4), suggesting a magmatic origin. Zircons from the Fenghuangshan Formation in the Zhoucun Basin yield six main age populations (2489, 1854, 331, 305, 282, and 247 Ma). Zircons from the Fangzi Formation in the Zhoucun and Mengyin basins yield eight main age populations (2494, 1844, 927, 465, 323, 273, 223, and 159 Ma) and ten main age populations (2498, 1847, 932, 808, 540, 431, 315, 282, 227, and 175 Ma), respectively, whereas zircons from the Santai Formation in the Zhoucun and Mengyin basins yield nine main age populations (2519, 1845, 433, 325, 271, 237, 192, 161, and 146 Ma) and six main age populations (2464, 1845, 853, 277, 191, and 150 Ma), respectively. Five main age populations (2558, 1330, 609, 181, and 136 Ma) are detected for zircons from the Wennan Formation in the Pingyi Basin. Based on the youngest age, together with the contact relationships among formations, we propose that the Fenghuangshan Formation formed in the Early–Middle Triassic, the Fangzi Formation in the Middle–Late Jurassic, the Santai Formation after the Late Jurassic, and the Wennan Formation after the Early Cretaceous. These results, together with previously published data, indicate that: (1) the sediments of the Fenghuangshan Formation were sourced from the Precambrian basement and from late Paleozoic to early Mesozoic igneous rocks in the northern part of the NCB; (2) the sediments of the Fangzi and Santai formations were sourced from the Precambrian basement, late Paleozoic to early Mesozoic igneous rocks in the northern part of the NCB, and the Sulu terrane, as well as from Middle–Late Jurassic igneous rocks in the southeastern part of the NCB; and (3) the Wennan Formation was sourced from the Tongshi intrusive complex, the Sulu terrane, and minor Precambrian basement and Early Cretaceous igneous rocks. The evolution of detrital provenance indicates that in the Early–Middle Triassic, the northern part of the NCB was higher than its interior; during the Late Triassic to Early Jurassic, the eastern NCB was uplifted, resulting in a period of non-deposition; and an important transition from a compressional to an extensional tectonic regime occurred during the Middle–Late Jurassic. The presence of Neoproterozoic and Triassic detrital zircons in the Fangzi Formation sourced from the Sulu terrane suggests that large-scale sinistral strike-slip movement along the Tan-Lu Fault Zone did not occur after the Middle Jurassic (ca. 175 Ma). 相似文献