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1.
U–Pb dating and oxygen and Lu–Hf isotope analyses are applied to ~ 400 detrital zircon grains from the Neoproterozoic–Cambrian Kahar, Bayandor and Zaigun sandstones. The results reveal the evolutionary history of the Central Iranian continental crust in the northern margin of Gondwana during the Neoproterozoic–Cambrian. The U–Pb dating produces major peaks of crystallization ages at 0.5–0.7 Ga and minor peaks around the Tonian, Paleoproterozoic and Neoarchean. The zircon population in the Zaigun sandstone is dominated by long-transported grains and exhibits slightly different zircon distribution patterns than those from the older Kahar and Bayandor units. The zircon population ages and Hf isotopes of the Zaigun sample are very similar to the Neoproterozoic–Early Palaeozoic siliciclastic units in the Arabian Nubian shield (ANS) and Turkey, which suggests the late to post–Pan-African unroofing of the Afro–Arabia realm as the main process for detritus accumulation in Central Iran during the early Palaeozoic. A significant proportion of the Tonian-aged zircons (~ 64%) in the Kahar and Bayandor samples show positive εHf(t) values, whereas those with late Cryogenian–Ediacaran ages have high δ18O and variable εHf(t) values (~− 30‰ to + 17‰), suggesting that the crustal evolution of provenance of the Tonian-aged zircons commenced in an island arc setting and continued in an active continental margin. All the samples contain pre-Neoproterozoic zircons that are ca 1.9–2.3 Ga or 2.5–3.2 Ga, which are much older than the known Neoproterozoic igneous rocks in Iran and are more consistent with pre-Neoproterozoic igneous-metamorphic rocks in the eastern ANS and northern Africa. These ages support the eastern sector of the Afro–Arabia margin as a provenance for the detrital zircons in the oldest sedimentary sequences of Iran during the late Neoproterozoic–Cambrian. The Hf model ages of zircons with mantle-like δ18O values suggest that a significant amount of continental crust in the provenance of the detrital zircons was generated at around 1.0–2.0 and 3.0–3.5 Ga, likely by mantle-derived mafic magmas, and subsequently reworked during crustal differentiation into younger, more felsic crust with varying crustal residence times. 相似文献
2.
U–Pb–Hf of detrital zircons from diverse Cambrian units in Morocco and Sardinia were investigated in order to clarify the sandstone provenance and how it evolved with time, to assess whether the detrital spectra mirror basement crustal composition and whether they are a reliable pointer on the ancestry of peri-Gondwanan terranes. Coupled with Hf isotopes, the detrital age spectra allow a unique perspective on crustal growth and recycling in North Africa, much of which is concealed below Phanerozoic sediments.In Morocco, the detrital signal of Lower Cambrian arkose records local crustal evolution dominated by Ediacaran (0.54–0.63 Ga) and Late-Paleoproterozoic (1.9–2.2 Ga; Eburnian) igneous activity. A preponderance of the Neoproterozoic detrital zircons possess positive εHf(t) values and their respective Hf model ages (TDM) concentrate at 1.15 Ga. In contrast, rather than by Ediacaran, the Neoproterozoic detrital signal from the Moroccan Middle Cambrian quartz-rich sandstone is dominated by Cryogenian-aged detrital zircons peaking at 0.65 Ga alongside a noteworthy early Tonian (0.95 Ga) peak; a few Stenian-age (1.0–1.1 Ga) detrital zircons are also distinguished. The majority of the Neoproterozoic zircons displays negative εHf(t), indicating the provenance migrated onto distal Pan-African terranes dominated by crustal reworking. Terranes such as the Tuareg Shield were a likely provenance. The detrital signal of quartz–arenites from the Lower and Middle Cambrian of SW Sardinia resembles the Moroccan Middle Cambrian, but 1.0–1.1 Ga as well as ~ 2.5 Ga detrital zircons are more common. Therefore, Cambrian Sardinia may have been fed from different sources possibly located farther to the east along the north Gondwana margin. 1.0–1.1 Ga detrital zircons abundant in Sardinia generally display negative εHf(t) values while 0.99–0.95 Ga detrital zircons (abundant in Morocco) possess positive εHf(t), attesting for two petrologically-different Grenvillian sources. A paucity of detrital zircons younger than 0.6 Ga is a remarkable feature of the detrital spectra of the Moroccan and Sardinian quartz-rich sandstones. It indicates that late Cadomian orogens fringing the northern margin of North Africa were low-lying by the time the Cambrian platform was deposited. About a quarter of the Neoproterozoic-aged detrital zircons in the quartz-rich sandstones of Morocco (and a double proportion in Sardinia) display positive εHf(t) values indicating considerable juvenile crust addition in North Africa, likely via island arc magmatism. A substantial fraction of the remaining Neoproterozoic zircons which possess negative εHf(t) values bears evidence for mixing of old crust with juvenile magmas, implying crustal growth in an Andean-type setting was also significant in this region. 相似文献
3.
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
4.
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
5.
《Gondwana Research》2013,24(4):1261-1272
A combined study of Lu–Hf isotopes and U–Pb ages for detrital zircons from sedimentary rocks can provide information on the crustal evolution of sedimentary provenances, and comparisons with potential source regions can constrain interpretations of paleogeographic settings. Detailed isotopic data on detrital zircons from Neoproterozoic sedimentary rocks in the northern part of the Yangtze Block suggest that these rocks have the maximum depositional ages of ~ 750 Ma, and share a similar provenance. In their source area, units of late Archean (2.45 to 2.55 Ga) to Paleoproterozoic (1.9 to 2.0 Ga) U–Pb ages made up the basement, and were overlain or intruded by magmatic rocks of Neoproterozoic U–Pb ages (740 to 900 Ma). Hf isotopic signatures of the detrital zircons indicate that a little juvenile crust formed in the Neoarchean; reworking of old crust dominates the magmatic activity during the Archean to Paleoproterozoic, while the most significant juvenile addition to the crust occurred in the Neoproterozoic. Only the Neoproterozoic zircon U–Pb ages can be matched with known magmatism in the northern Yangtze Block, while other age peaks cannot be correlated with known provenance areas. Similar zircon U–Pb ages have been obtained previously from sediments along the southeastern and western margins of the Yangtze Block. Thus, it is suggested that an unexposed old basement is widespread beneath the Yangtze Block and was the major contributor to the Neoproterozoic sediments. This basement had a magmatic activity at ~ 2.5 Ga, similar to that in North China; but zircon Hf isotopes suggest significant differences in the overall evolutionary histories between the Yangtze and North China. 相似文献
6.
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
7.
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
8.
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
9.
《Gondwana Research》2014,25(3):1202-1215
The South China Block, consisting of the Yangtze and the Cathaysia blocks, is one of the largest Precambrian blocks in eastern Asia. However, the early history of the Cathaysia Block is poorly understood due largely to intensive and extensive reworking by Phanerozoic polyphase orogenesis and magmatism which strongly overprinted and obscured much of the Precambrian geological record. In this paper, we use the detrital zircon U–Pb age and Hf isotope datasets as an alternative approach to delineate the early history of the Cathaysia Block. Compilation of published 4041 Precambrian detrital zircon ages from a number of (meta)sedimentary samples and river sands exhibits a broad age spectrum, with three major peaks at ~ 2485 Ma, ~ 1853 Ma and ~ 970 Ma (counting for ~ 10%, ~ 16% and ~ 24% of all analyses, respectively), and four subordinate peaks at ~ 1426 Ma, ~ 1074 Ma, ~ 780 Ma and ~ 588 Ma. Five of seven detrital zircon age peaks are broadly coincident with the crystallisation ages of ~ 1.89–1.83 Ga, ~ 1.43 Ga, ~ 1.0–0.98 Ga and ~ 0.82–0.72 Ga for known igneous rocks exposed in Cathaysia, whereas, igneous rocks with ages of ~ 2.49 Ga and ~ 0.59 Ga have not yet been found. The Hf isotopic data from 1085 detrital zircons yield Hf model ages (TDMC) between ~ 4.19 Ga and ~ 0.81 Ga, and the calculated εHf(t) values between − 40.2 and 14.4. The Archean detrital zircons are exclusively oval in shape with complicated internal textures, indicating that they were sourced by long distance transportations and strong abrasion from an exotic Archean continent. In contrast, the majority of detrital zircons in age between ~ 1.9 and ~ 0.8 Ga are euhedral to subhedral crystals, indicative of local derivation by short distance transportations from their sources. The oldest crustal basement rocks in Cathaysia were most likely formed by generation of juvenile crust and reworking of recycled Archean components in Late Paleoproterozoic at ~ 1.9–1.8 Ga, rather than in the Archean as previously speculated. Reworking and recycling of the continental crust are likely the dominant processes for the crustal evolution of Cathaysia during the Mesoproterozoic to Neoproterozoic time, with an intervenient period of significant generation of juvenile crust at ~ 1.0 Ga.Precambrian crustal evolutions of the Cathaysia Block are genetically related to the supercontinent cycles. By comparing detrital zircon data from Cathaysia with those for other continents, and integrating multiple lines of geological evidence, we interpret the Cathaysia Block as an orogenic belt located between East Antarctica, Laurentia and Australia during the assembly of supercontinent Columbia/Nuna at ~ 1.9–1.8 Ga. The Cathaysia Block amalgamated with the Yangtze Block to form the united South China Block during the Sibao Orogeny at ~ 1.0–0.89 Ga. The Laurentia–Cathaysia–Yangtze–Australia–East Antarctica connection gives the best solution to the paleo-position of Cathaysia in supercontinent Rodinia. The significant amount of ~ 0.6–0.55 Ga detrital zircons in Cathaysia and West Yangtze have exclusively high crustal incubation time of > 300 Ma, indicating crystallisation from magmas generated dominantly by crustal reworking. This detrital zircon population compares well with the similar-aged zircon populations from a number of Gondwana-derived terranes including Tethyan Himalaya, High Himalaya, Qiangtang and Indochina. The united South China–Indochina continent was likely once an integral part of Gondwanaland, connected to northern India by a “Pan-African” collisional orogen. 相似文献
10.
《Gondwana Research》2013,24(4):1241-1260
An overview is presented for the formation and evolution of Precambrian continental lithosphere in South China. This is primarily based on an integrated study of zircon U–Pb ages and Lu–Hf isotopes in crustal rocks, with additional constraints from Re–Os isotopes in mantle-derived rocks. Available Re–Os isotope data on xenolith peridotites suggest that the oldest subcontinental lithospheric mantle beneath South China is primarily of Paleoproterozoic age. The zircon U–Pb ages and Lu–Hf isotope studies reveal growth and reworking of the juvenile crust at different ages. Both the Yangtze and Cathaysia terranes contain crustal materials of Archean U–Pb ages. Nevertheless, zircon U–Pb ages exhibit two peaks at 2.9–3.0 Ga and ~ 2.5 Ga in Yangtze but only one peak at ~ 2.5 Ga in Cathaysia. Both massive rocks and crustal remnants (i.e., zircon) of Archean U–Pb ages occur in Yangtze, but only crustal remnants of Archean U–Pb ages occur in Cathaysia. Zircon U–Pb and Lu–Hf isotopes in the Kongling complex of Yangtze suggest the earliest episode of crustal growth in the Paleoarchean and two episodes of crustal reworking at 3.1–3.3 Ga and 2.8–3.0 Ga. Both negative and positive εHf(t) values are associated with Archean U–Pb ages of zircon in South China, indicating both the growth of juvenile crust and the reworking of ancient crust in the Archean. Paleoproterozoic rocks in Yangtze exhibit four groups of U–Pb ages at 2.1 Ga, 1.9–2.0 Ga, ~ 1.85 Ga and ~ 1.7 Ga, respectively. They are associated not only with reworking of the ancient Archean crust in the interior of Yangtze, but also with the growth of the contemporaneous juvenile crust in the periphery of Yangtze. In contrast, Paleoproterozoic rocks in Cathaysia were primarily derived from reworking of Archean crust at 1.8–1.9 Ga. The exposure of Mesoproterozoic rocks are very limited in South China, but zircon Hf model ages suggest the growth of juvenile crust in this period due to island arc magmatism of the Grenvillian oceanic subduction. Magmatic rocks of middle Neoproterozoic U–Pb ages are widespread in South China, exhibiting two peaks at about 830–800 Ma and 780–740 Ma, respectively. Both negative and positive εHf(t) values are associated with the middle Neoproterozoic U–Pb ages of zircon, suggesting not only growth and reworking of the juvenile Mesoproterozoic crust but also reworking of the ancient Archean and Paleoproterozoic crust in the middle Neoproterozoic. The tectonic setting for this period of magmatism would be transformed from arc–continent collision to continental rifting with reference to the plate tectonic regime in South China. 相似文献
11.
Detrital zircons from the Ordovician and Devonian sedimentary cover of the Siberian Craton were analyzed for U/Pb geochronology to understand their sediment provenances. Five main age-peaks were identified in the zircon U/Pb age-spectra: (1) Neoarchaean – early Palaeoproterozoic (2.7–2.4 Ga); (2) late Palaeoproterozoic (2.0–1.65 Ga); (3) minor early Neoproterozoic (1.0–0.75 Ga); (4) Ediacaran (0.65–0.60 Ga) and (5) Cambrian – Early Ordovician (0.54–0.47 Ga), reflecting the main magmatic events in the sediment source regions. The oldest zircons (groups 1 and 2) are derived from the Siberian Craton which amalgamated during the Neoarchean – Palaeoproterozoic. The Neoproterozoic zircons (groups 3 and 4) likely sourced from southwestern basement uplifts and Neoproterozoic belts of the Siberian margin such as the Yenisey Ridge and Baikal-Muya region. The provenance of the youngest zircons (group 5) can be traced to the Altai–Sayan fold-belt, where peri-Gondwanan microcontinents and island-arcs accreted to Siberia during late Neoproterozoic – early Palaeozoic progressive consumption of the Palaeo-Asian Ocean. 相似文献
12.
New U–Pb detrital zircon ages from (meta-)graywackes of the Blovice accretionary complex, Bohemian Massif, provide an intriguing record of expansion of the northern active margin of Gondwana during late Neoproterozoic and Cambrian. The late Neoproterozoic (meta-)graywackes typically contain a smaller proportion of Archean and Paleoproterozoic zircons and show a 1.6–1.0 Ga age gap and a prominent late Cryogenian to early Ediacaran age peak. The respective zircon age spectra match those described from other correlative Cadomian terranes with a West African provenance. On the other hand, some samples were dominated by Cambrian zircons with concordia ages as young as 499 Ma. The age spectra obtained from these samples mostly reflect input from juvenile volcanic arcs whereas the late Cambrian samples are interpreted as representing relics of forearc basins that overlay the accretionary wedge.The new U–Pb zircon ages suggest that the Cadomian orogeny, at least in the Bohemian Massif, was not restricted to the Neoproterozoic but should be rather viewed as a continuum of multiple accretion, deformation, magmatic and basin development events governed by oceanic subduction until late Cambrian times. Our new U–Pb ages also indicate that the Cadomian margin was largely non-accretionary since its initiation at ~ 650–635 Ma and that most of the material accreted during a short time span at around 527 Ma, closely followed by a major pulse of pluton emplacement. Based on the new detrital zircon ages, we argue for an unsteady, cyclic evolution of the Cadomian active margin which had much in common with modern Andean and Cordilleran continental-margin arc systems. The newly recognized episodic magmatic arc activity is interpreted as linked to increased erosion–deposition–accretion events, perhaps driven by feedbacks among the changing subducted slab angle, overriding plate deformation, surface erosion, and gravitational foundering of arc roots. These Cadomian active-margin processes were terminated by slab break-off and/or slab rollback and by a switch from convergent to divergent plate motions related to opening of the Rheic Ocean at around 490–480 Ma.The proposed tectonic evolution of the Teplá–Barrandian unit is rather similar to that of the Ossa Morena Zone in Iberia but shows significant differences to that of the North Armorican Massif and Saxothuringian unit in Western and Central Europe. This suggests that the Cadomian orogenic zoning was complexly disrupted during early Ordovician opening of the Rheic Ocean and Late Paleozoic Variscan orogeny so that the originally outboard tectonic elements are now in the Variscan orogen's interior and vice versa. 相似文献
13.
The Ordovician Ponón Trehué Formation is the only early Palaeozoic sedimentary sequence known to record a primary contact with the Grenvillian-age basement of the Argentinean Cuyania terrane, in its southwards extension named the San Rafael block. Petrographic and geochemical data indicate contributions from a dominantly upper continental crustal component and a subordinated depleted component. Nd isotopes indicate εNd of ? 4.6, ?Sm/Nd ? 0.36 and TDM 1.47 Ga in average. Pb-isotope ratios display average values for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb of 19.15, 15.69 and 38.94 respectively. U–Pb detrital zircon ages from the Ponón Trehué Formation cluster around values of 1.2 Ga, indicating a main derivation from a local basement source (Cerro La Ventana Formation). The Upper Ordovician Pavón Formation records a younger episode of clastic sedimentation within the San Rafael block, and it shows a more complex detrital zircon age population (peaks at 1.1 and 1.4 Ga as well as Palaeoproterozoic and Neoproterozoic detrital grains). Detailed comparison between the two Ordovician clastic units indicates a shift with time in provenance from localized basement to more regional sources. Middle to early Upper Ordovician age is inferred for accretion of the Cuyania terrane to the proto-Andean margin of Gondwana. 相似文献
14.
《Gondwana Research》2013,23(3-4):828-842
Whether any Grenvillian magmatic records are preserved in the North China Craton (NCC) is a key issue to understand the Proterozoic tectonic evolution of the NCC and its correlation to the supercontinent Rodinia. Meso- to Neo-proterozoic sedimentary series is well exposed in the NCC, but magmatic events in this period, especially of 1.3–1.0 Ga, have seldom been reported. New U–Pb isotopic dating and Hf isotopic composition analyses have been carried out in this study using SIMS and LA–ICP-MS methods on detrital zircons from sandstones of the Tumen Group in the Shandong Peninsula and quartz sandstones of the Sangwon System in the Phyongnam Basin, North Korea. The age populations of the detrital zircons of the Tumen Group are at ~ 2.5 Ga, ~ 1.85 Ga, ~ 1.7 Ga, ~ 1.58 Ga, ~ 1.5 Ga, ~ 1.36 Ga and ~ 1.2 Ga and those of the Sangwon System are at 1.88–1.86 Ga, ~ 1.78 Ga, 1.62–1.58 Ga, 1.46–1.41 Ga, ~ 1.32 Ga, ~ 1.17 Ga and ~ 980 Ma. Most of the age peaks of Neoarchean and Proterozoic correspond to the significant tectonic-magmatic-thermal events previously recognized in the NCC, revealing that the main provenances of the Tumen Group and the Sangwon System are Early Precambrian basement and Late Paleo- to Meso-proterozoic magmatic rocks of the NCC. Furthermore, the youngest detrital zircon ages of ~ 1.1 Ga from the Tumen Group and 984 Ma from the Sangwon System, as well as 910 Ma Rb–Sr whole rock isochron age of a limestone from the Tumen Group and 899 Ma mafic sills intruding the Sangwon System suggest that both groups were deposited in the Neoproterozoic, coevally with the Qingbaikou System in the Yanliao Aulacogen. The common zircon ages of 1.3–1.0 Ga from the Tumen Group and the Sangwon System, as well as the contemporaneous Penglai and Yushulazi Group in the eastern margin of the NCC, indicate that during the deposition of these sediments there have been significant contributions from Grenvillian magmatic rocks in the eastern NCC. This may provide clues to understand the possible relationship of the NCC and the supercontinent Rodinia. Moreover, the positive εHf (t) and ~ 2.8 Ga crust model ages of detrital magmatic zircons of 2.8–2.4 Ga suggest that there have been significant crustal growth at ~ 2.8 Ga in the eastern margin of the NCC, same as in other areas of the NCC. 相似文献
15.
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
16.
《Gondwana Research》2014,26(4):1484-1500
The southern Rheinisches Schiefergebirge, which is part of the Rhenohercynian zone of the Central European Variscides, exhibits several allochthonous units: the Gießen-, and the Hörre nappe, and parts of the Frankenbach imbrication zone. These units were thrust over autochthonous and par-autochthonous volcano-sedimentary complexes of the Lahn and Dill–Eder synclines. This paper reports a representative data set of U–Pb LA–SF–ICP–MS ages of 1067 detrital zircon grains from Devonian and Lower Carboniferous siliciclastic sediments of the autochthonous and the allochthonous areas, respectively. The cluster of U–Pb ages from the allochthonous units points to a provenance in the Saxothuringian zone. Zircon populations from the Saxothuringian zone are representative of a Gondwanan hinterland and are characterized by age clusters of ~ 530–700 Ma, ~ 1.8–2.2 Ga, ~ 2.5–2.7 Ga, and ~ 3.0–3.4 Ga. Further samples were taken from the autochthonous and par-autochthonous units of the Lahn–Dill and Kellerwald areas. A Lower Devonian sandstone sample from the Siegen anticline provides a reference for siliciclastic sediments derived from the Old Red Continent. These samples show a provenance representative of Laurussia with debris primarily derived from Baltica and Avalonia. U–Pb zircon age clusters occur at ~ 400–450 Ma, 540–650 Ma, 1.0–1.2 Ga, ~ 1.4–1.5 Ga, ~ 1.7–2.2 Ga, and 2.3–2.9 Ga. Provenance analysis and geochemical data of the Rhenohercynian zone provide new information on the evolution of magmatic arcs in the Mid-Paleozoic. The data set constrains top-SE and top-NW directed subduction of the oceanic crust of the Rheic Ocean. Subduction-related volcanism lasted from the Early Devonian to the Early Carboniferous and thus confirms the existence of the Rheic Ocean until the Early Carboniferous. The tectonic model outlined for the Rhenohercynian zone suggests a wide Rheic Ocean. 相似文献
17.
The origin of the Greater Himalayan Sequence in the Himalaya and the paleogeographic position of the Lhasa terrane within Gondwanaland remain controversial. In the Eastern Himalayan syntaxis, the basement complexes of the northeastern Indian plate (Namche Barwa Complex) and the South Lhasa terrane (Nyingchi Complex) can be studied to explore these issues. Detrital zircons from the metasedimentary rocks in the Namche Barwa Complex and Nyingchi Complex yield similar U–Pb age spectra, with major age populations of 1.00–1.20 Ga, 1.30–1.45 Ga, 1.50–1.65 Ga and 1.70–1.80 Ga. The maximum depositional ages for their sedimentary protoliths are ~ 1.0 Ga based on the mean ages of the youngest three detrital zircons. Their minimum depositional ages are ~ 477 Ma for the Namche Barwa Complex and ~ 499 Ma for the Nyingchi Complex. Detrital zircons from the Namche Barwa Complex and Nyingchi Complex also display similar trace-element signatures and Hf isotopic composition, indicating that they were derived from common provenance. The trace-element signatures of 1.30–1.45 Ga detrital zircons indicate that the 1.3–1.5 Ga alkalic and mafic rocks belt in the southeastern India is a potential provenance. Most 1.50–1.65 Ga zircons have positive εHf(t) values (+ 1.2 to + 9.0), and most 1.70–1.80 Ga zircons have negative εHf(t) values (− 7.1 to − 1.9), which are compatible with those of the Paleo- to Mesoproterozoic orthogneisses in the Namche Barwa Complex. Provenance analysis indicates that the southern Indian Shield, South Lhasa terrane and probably Eastern Antarctica were the potential detrital sources. Combined with previous studies, our results suggest that: (1) the Namche Barwa Complex is the northeastern extension of the Greater Himalaya Sequence; (2) the metasedimentary rocks in the Namche Barwa Complex represent distal deposits of the northern Indian margin relative to the Lesser Himalaya; (3) the South Lhasa terrane was tectonically linked to northern India before the Cambrian. 相似文献
18.
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
19.
Y. Rojas-Agramonte A. Kröner A. Demoux X. Xia W. Wang T. Donskaya D. Liu M. Sun 《Gondwana Research》2011,19(3):751-763
The Central Asian Orogenic Belt contains many Precambrian crustal fragments whose origin is unknown, and previous speculations suggested these to be derived from either Siberia, Tarim or northern Gondwana. We present an age pattern for detrital and xenocrystic zircons from Neoproterozoic to Palaeozoic arc and microcontinental terranes in Mongolia and compare this with patterns for Precambrian rocks in southern Siberia, the North China craton, the Tarim craton and northeastern Gondwana in order to define the most likely source region for the Mongolian zircons. Our data were obtained by SHRIMP II, LA-ICP-MS and single zircon evaporation and predominantly represent arc-related low-grade volcanic rocks and clastic sediments but also accretionary wedges and ophiolitic environments.The Mongolian pattern is dominated by zircons in the age range ca. 350–600 and 700–1020 Ma as well as minor peaks between ca. 1240 and 2570 Ma. The youngest group reflects cannibalistic reworking of the Palaeozoic arc terranes, whereas the Neoproterozoic to late Mesoproterozoic peak reflects both reworking of the arc terranes as well as Neoproterozoic rifting and a Grenville-age crust-formation event.The 700–1020 Ma peak does not exist in the age spectra of the Siberian and North China cratons and thus effectively rules out these basement blocks as potential source areas for the Mongolian zircons. The best agreement is with the Tarim craton where a major Grenville-age orogenic event and early Neoproterozoic rifting have been identified. The age spectra also do not entirely exclude northeastern Gondwana as a source for the Mongolian zircons, but here the Neoproterozoic age peak is related to the Pan-African orogeny, and a minor Grenville-age peak may reflect a controversial orogenic event in NW India.Our Mongolian detrital and xenocrystic age spectrum suggests that the Tarim craton was the main source, and we favour a tectonic scenario similar to the present southwestern Pacific where fragments of Australia are rifted off and become incorporated into the Indonesian arc and microcontinent amalgamation that will evolve into a future orogenic belt. 相似文献
20.
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