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1.
Abstract

Re-evaluation of geochemical and geophysical datasets, and analysis of magmatic and detrital zircons from drill-core samples extracted from the Louth region of the southern Thomson Orogen (STO), augmented by limited field samples, has shown that two temporally and compositionally distinct igneous groups exist. The older Lower Devonian, calc-alkaline group corresponds to complexly folded, high-intensity curvilinear magnetic anomalies in the Louth region (Louth Volcanics) and are probable equivalents to Lower Devonian volcanics in the northern Lachlan Orogen. A younger Permo-Triassic alkaline assemblage forms part of an E–W corridor of diatremes that appears to relate to focussed lithospheric extension associated with the later stages of the Hunter–Bowen Orogeny in the New England Orogen. The alkaline group includes gabbros previously considered as Neoproterozoic, but all magmatic rocks, including alkaline basalts, contain an unusual number of xenocrystic zircons. The age spectra of the xenocrystic zircons mimic detrital zircons from Cobar Basin sedimentary rocks and/or underlying Ordovician turbidites, suggesting incorporation of upper crustal zircons into the alkaline basaltic magmas. A distinct difference of detrital zircon age spectra from central Thomson Orogen metasediments indicates the STO metasediments have greater affinities to the Lachlan Orogen, but both orogens probably began in the Early Ordovician during widespread backarc extension and deposition of turbidites in the Tasmanides. A surprising result is that Ordovician, Devonian and Permo-Triassic basaltic rocks from the STO and elsewhere in the Tasmanides, all yield the same Nd-model ages of ca 960–830 Ma, suggesting that Neoproterozoic subcontinental lithospheric mantle persisted throughout the evolution of the Tasmanide orogenic system.  相似文献   

2.
Detrital zircon from the Carboniferous Girrakool Beds in the central Tablelands Complex of the southern New England Orogen, Australia, is dominated by ca 350–320 Ma grains with a peak at ca 330 Ma; there are very few Proterozoic or Archean grains. A maximum deposition age for the Girrakool Beds of ca 309 Ma is identified. These data overlap the age of the Carboniferous Keepit arc, a continental volcanic arc along the western margin of the Tamworth Belt. Zircon trace-element and isotopic compositions support petrographic evidence of a volcanic arc provenance for sedimentary and metasedimentary rocks of the central Tablelands Complex. Zircon Hf isotope data for ca 350–320 Ma detrital grains become less radiogenic over the 30 million-year record. This pattern is observed with maturation of continental volcanic arcs but is opposite to the longer-term pattern documented in extensional accretionary orogens, such as the New England Orogen. Volcanic activity in the Keepit arc is inferred to decrease rapidly at ca 320 Ma, based on a major change in the detrital zircon age distribution. Although subduction continues, this decrease is inferred to coincide with the onset of trench retreat, slab rollback and the eastward migration of the magmatic arc that led to the Late Carboniferous to early Permian period of extension, S-type granite production and intrusion into the forearc basin, high-temperature–low-pressure metamorphism, and development of rift basins such as the Sydney–Gunnedah–Bowen system.  相似文献   

3.
秦岭造山带东段秦岭岩群的年代学和地球化学研究   总被引：20，自引：14，他引：6  
时毓  于津海  徐夕生  邱检生  陈立辉 《岩石学报》2009,25(10):2651-2670
对东秦岭地区的陕西省洛南县、宁陕县、长安县和河南省淅川县出露的四个秦岭岩群变质岩进行的岩石学和地球化学研究表明,样品主要由变质火山岩和变质沉积岩组成.详细的锆石U-Pb定年结果显示三个正变质岩均形成于新元古代早期(971～843Ma),而副变质岩中富集大量新元古代碎屑锆石,根据最年轻的谐和年龄(859Ma)和早古生代的变质年龄,推测其沉积时代为新元古代中晚期.因此,北秦岭南部的秦岭岩群的变质岩主要由新元古代早期的火成岩和新元古代中晚期的沉积岩组成.变质作用主要发生在加里东期,局部有燕山期的变质作用叠加.指示北秦岭的造山作用主要发生在早古生代.岩石地球化学研究还显示秦岭岩群的新元古代火山岩均形成于火山弧构造环境,沉积岩沉积于大陆弧-活动大陆边缘环境,指示秦岭造山带在新元古代早期是一个火山弧.秦岭岩群的火山岩和沉积岩在形成时代和构造环境方面与扬子克拉通西缘的特征非常相似,表明位于北秦岭造山带的秦岭岩群应归属于扬子克拉通陆块,是扬子北缘的一个大陆边缘弧.  相似文献   

4.
The late Carboniferous to Triassic tectonic history of eastern Australia includes important periods of regional-scale crustal extension and contraction. Evidence for these periods of tectonism is recorded by the extensive Pennsylvanian (late Carboniferous) to Triassic basin system of eastern Australia. In this study, we investigate the use of U–Pb dating of detrital zircons in reconstructing the tectonic development of one of these basins, the eastern Galilee Basin of Queensland. U–Pb detrital zircon ages were obtained from samples of stratigraphically well-constrained Cisuralian and Lopingian (early and late Permian, respectively) sandstone in the Galilee Basin. Detrital zircons in these sandstones are dominated by a population with ages in the range of 300–250 Ma, and ages from the youngest detrital zircons closely approximate depositional ages. We attribute these two fundamental findings to (1) appreciable derivation of detrital zircons in the Galilee Basin from the New England Orogen of easternmost Australia and (2) syndepositional magmatism. Furthermore, Cisuralian sandstone of the Galilee Basin contains significantly more >300 Ma detrital zircons than Lopingian sandstone. The transition in detrital zircon population, which is bracketed between 296 and 252 Ma based on previous high-precision U–Pb zircon ages from Permian ash beds in the Galilee Basin, corresponds with the Hunter–Bowen Orogeny and reflects a change in the Galilee Basin from an earlier extensional setting to a later foreland basin environment. During the Lopingian foreland basin phase, the individual depocentres of the Galilee and Bowen basins were linked to form a single and enormous foreland basin that covered >300 000 km2 in central and eastern Queensland.  相似文献   

5.
The New England Orogen (NEO), the youngest of the orogens of the Tasmanides of eastern Australia, is defined by two main cycles of compression–extension. The compression component involves thrust tectonics and advance of the arc towards the continental plate, while extension is characterised by rifting, basin formation, thermal relaxation and retreat of the arc towards the oceanic plate. A compilation of 623 records of U–Pb zircon geochronology rock ages from Geoscience Australia, the geological surveys of Queensland and New South Wales and other published research throughout the orogen, has helped to clarify its complex tectonic history. This contribution focuses on the entire NEO and is aimed at those who are unfamiliar with the details of the orogen and who could benefit from a summary of current knowledge. It aims to fill a gap in recent literature between broad-scale overviews of the orogen incorporated as part of wider research on the Tasmanides and detailed studies usually specific to either the northern or southern parts of the orogen. Within the two main cycles of compression–extension, six accepted and distinct tectonic phases are defined and reviewed. Maps of geological processes active during each phase reveal the centres of activity during each tectonic phase, and the range in U–Pb zircon ages highlights the degree of diachronicity along the length of the NEO. In addition, remnants of the early Permian offshore arc formed during extensive slab rollback, are identified by the available geochronology. Estimates of the beginning of the Hunter-Bowen phase of compression, generally thought to commence around 265?Ma are complicated by the presence of extensional-type magmatism in eastern Queensland that occurred between 270 and 260?Ma.  相似文献   

6.
Abstract

The Charters Towers Province, of the northern Thomson Orogen, records conversion from a Neoproterozoic passive margin to a Cambrian active margin, as characteristic of the Tasmanides. The passive margin succession includes a thick metasedimentary unit derived from Mesoproterozoic rocks. The Cambrian active margin is represented by upper Cambrian–Lower Ordovician (500–460?Ma) basinal development (Seventy Mile Range Group), plutonism and metamorphism resulting from an enduring episode of arc–backarc crustal extension. Detrital zircon age spectra indicate that parts of the metamorphic basement of the Charters Towers Province (elements of the Argentine Metamorphics and Charters Towers Metamorphics) overlap in protolith age with the basal part of the Seventy Mile Range Group and thus were associated with extensional basin development. Detrital zircon age data from the extensional basin succession indicate it was derived from a far-field (Pacific-Gondwana) primary source. However, a young cluster (<510?Ma) is interpreted as reflecting a local igneous source related to active margin tectonism. Relict zircon in a tonalite phase of the Fat Hen Creek Complex suggests that active margin plutonism may have extended back to ca 530?Ma. Syntectonic plutonism in the western Charters Towers Province is dated at ca 485–480?Ma, close to timing of metamorphism (477–467?Ma) and plutonism more generally (508–455?Ma). The dominant structures in the metamorphic basement formed with gentle to subhorizontal dips and are inferred to have formed by extensional ductile deformation, while normal faulting developed at shallower depths, associated with heat advection by plutonism. Lower Silurian (Benambran) shortening, which affected metamorphic basement and extensional basin units, resulted in the dominant east–west-structural trends of the province. We consider that these trends reflect localised north–south shortening rather than rotation of the province as is consistent with the north–south paleogeographic alignment of extensional basin successions.
  1. KEY POINTS

  2. Northern Tasmanide transition from passive to active margin tectonic mode had occurred by ca 510?Ma, perhaps as early as ca 530?Ma.

  3. Cambro-Ordovician active margin tectonism of the Charters Towers Province (northern Thomson Orogen) was characterised by crustal extension.

  4. Crustal extension resulted in the development of coeval (500–460?Ma) basin fill, granitic plutonism and metamorphism with rock assemblages as exposed across the Charters Towers Province developed at a wide range of crustal levels and expressing heterogeneous exhumation.

  5. Protoliths of metasedimentary assemblages of the Charters Towers Province include both Proterozoic passive margin successions and those emplaced as Cambrian extensional basin fill.

  相似文献   

7.
Abstract

The Jurassic–Cretaceous Great Artesian Basin is the most extensive, and largest volume, sedimentary feature of continental Australia. The source of its mud-dominated Cretaceous infill is attributed largely to contemporary magmatism along the continental margin to the east, but the source of its Jurassic infill, dominated by quartz sandstone, remains unconstrained. This paper investigates the question of a Jurassic sediment source for the northern part of the basin. Jurassic uplift and exhumation of the continental margin crustal sector to the east provided the primary Jurassic sediment source. (U–Th)/He data are presented for zircon and apatite from Pennsylvanian to mid Permian granitoids of the Kennedy Igneous Association distributed within the northern Tasmanides between the Townsville and Cairns regions and for coeval granites of the Urannha batholith from the Mount Carlton district (N Bowen Basin), also within the northern Tasmanides. The data from zircon indicate widespread Jurassic exhumation of a crustal tract located to the east of the northern Great Artesian Basin and largely occupied by rocks of the Tasmanides. Detrital zircon age spectra for samples of the Jurassic Hutton and Blantyre sandstones from the northeastern margin of the Great Artesian Basin show their derivation to be largely from rocks of the northern Tasmanides. In combination, the detrital age spectra and (U–Th)/He data from zircon indicate exhumation owing to uplift generating appreciable physiographic relief along the north Queensland continental margin during the Jurassic, shedding sediment westward into the Great Artesian Basin during its early development. A portion of (U–Th)/He data for zircon are consistent with late Permian–mid Triassic exhumation within the Tasmanides, attributable to the influence of the Hunter--Bowen Orogeny. Evidence of Cretaceous and Paleocene exhumation episodes is also indicated for some samples, mainly by apatite (U–Th)/He analysis, consistent with data previously published from fission track studies. Overall, new data from the present study reveal that the exhumation related to Jurassic regional uplift and the subsequent erosional reworking of the northeast Australian continental margin is critical for the evolution and development of the northern side of the Great Artesian Basin in eastern Australia. Apart from this, another two previously suggested Permian–Triassic and Cretaceous exhumation and uplift episodes along the northeast Australian continental margin are also confirmed by the dataset of this study.
  1. KEY POINTS

  2. U–Pb detrital zircon ages of sandstone samples from the northeastern Eromanga Basin reveal Paleozoic (480–280 Ma) and Proterozoic (1800–1400 Ma) age clusters.

  3. (U–Th)/He zircon and apatite dating results of granitoids samples from Cairns, Townsville and the Mount Carlton districts are dominated by Jurassic (198–164 Ma) and Permian–Triassic (272–238 Ma) age clusters.

  4. Combination of above two datasets proves the regional uplift-driving Jurassic exhumation episode in the northeast Australian continental is vital for the development of the northern Great Artesian Basin.

  相似文献   

8.
《International Geology Review》2012,54(16):2036-2056
ABSTRACT

The Chinese Southwest Tianshan Orogenic Belt is located along the boundary between the Central Asian Orogenic Belt (CAOB) and the Tarim Block (TB), NW China. It records the convergence of the Tarim Block and the Middle Tianshan, and is, therefore, a crucial region for understanding the Eurasia continental growth and evolution. The Wulagen (geographical name) metasedimentary rocks of the Wuqia area (mainly metamorphic sandstones and mica schists) form one of the metamorphic terranes in the Southwestern Tianshan Orogenic Belt. The geochronology of these rocks is poorly known, which hampers our understanding of the tectonic evolution of the belt. We analyzed 517 zircon grains for detrital zircon U–Pb dating and 93 zircon grains for in situ Lu–Hf isotopic compositions from the Wulagen metasedimentary rocks. The analyzed zircon grains yield Neoarchean to late Paleozoic U–Pb ages with major age peaks at ~2543 Ma, 1814 Ma, 830 Ma, 460 Ma, and the youngest cluster of zircon (magmatogene) ages is 395 Ma. The zircon U–Pb data show that the late Paleozoic (Early Devonian) is the maximum depositional age of the Wulagen metasedimentary rocks, rather than the previously considered Precambrian period. The zircons with Paleozoic ages yield εHf(t) values of ?22.0 to +11.3 and two-stage model ages (TDM2) of 3.95 to 1.30 Ga, suggesting that the parental magmas were formed from partial melting of pre-existing crustal rocks. Our zircon U–Pb geochronology and Hf isotopic data indicate the major source regions for the Wulagen metasedimentary rocks was the Kyrgyzstan North Tianshan. The zircon age population of 600–400 Ma (peak at ~460 Ma) has negative εHf(t) values (?15.0 to ?0.6) and Mesoproterozoic two-stage model ages, suggesting that the early Paleozoic magmatism resulted mainly from the melting of ancient crust, which played an important role in crustal evolution in the southern CAOB.  相似文献   

9.
The southern part of the Korean Peninsula preserves important records of the Paleozoic evolutionary history of East Asia. Here we present SHRIMP U–Pb ages of detrital zircon grains from Paleozoic metasedimentary successions (Okcheon and Joseon Supergroups, Yeoncheon Group, Taean Formation, and Pyeongan Supergroup) that are incorporated into the major Phanerozoic mountain belts (Okcheon and Hongseong-Imjingang Belts) in South Korea, providing new insights for provenances and paleotectonic evolution of the South Korean Peninsula during Paleozoic time. The zircon ages from our samples display two distinct spectra patterns in their presence/absence of Neoproterozoic and/or Paleozoic populations. Our results, together with the available data from the Korean Peninsula, suggest that: (1) the Early to Middle Paleozoic successions in the Okcheon Belt were deposited in continental margin setting(s) formed by Neoproterozoic intracratonic rifting, (2) the Middle Paleozoic metasedimentary rocks in the Imjingang belt can be interpreted as molasse and flysch sediments along an active continental margin, (3) the Late Paleozoic to Early Triassic Taean Formation along the western Gyeonggi Massif represents a syn- to post-collision deltaic complex of a remnant oceanic basin, and (4) the Late Paleozoic to possibly Early Triassic Pyeongan Supergroup in the Okcheon Belt might represent a wedge-top and/or foreland basin. The spatial and temporal discrepancy between the South Korean Peninsula and the Central China Orogenic Belt during Paleozoic might reflect lateral variations in crustal evolution history along the East Asian continental margin during the Paleo-Tethyan Ocean closure.  相似文献   

10.
Zircon U-Pb LA-ICPMS ages were obtained from three metasedimentary and two metavolcanic samples from the Monte Cavallino (South Tyrol) and the Cima Vallona (Carnic Alps) tectono-metamorphic groups from the eastern South Alpine crystalline basement in NE Italy. These analyses were performed to constrain the maximum depositional ages of the South Alpine domain, and to compare the spatial and temporal provenance variations with those of adjacent terranes. The detrital zircon dataset from the metasedimentary rocks (416 grains) yield populations with age peaks at 2.7–2.9 Ga, 1.8–2.1 Ga, 1.2–0.85 Ga, and 0.65–0.45 Ga, with maximum depositional ages ranging from the latest Neoproterozoic to the Silurian. The metavolcanic zircon dataset (209 grains) documents the presence of a two Ordovician volcanic events in the South Alpine domain. The detrital zircon dataset implies that the clastic units of the South Alpine crystalline basement were (a) deposited on the peri-Gondwanan active continental margin and (b) were originally sourced from the Proterozoic and Paleozoic units of NW Gondwana and hence should no longer be considered as exotic elements. The age spectra of the three metasedimentary units highlight differences between the Ediacaran basement gneiss, the Ordovician greywacke, and the Silurian metaconglomerate, suggesting up-section age variations due to a temporal change in provenance. Collectively, these new detrital zircon U-Pb ages imply that the clastic units within the South Alpine domain recorded sedimentation at c. 550 Ma on the peri-Gondwanan active continental margin, followed by rift-related continental and marine sedimentation in a back-arc basin setting until at least the Silurian. The South Alpine domain ultimately rifted off from Gondwana due to back-arc spreading, and subsequently underwent Variscan metamorphism during accretion onto the Laurussia margin, which started at c. 380 Ma and lasted until at least c. 320 Ma.  相似文献   

11.
The Paulistana and Santa Filomena Complexes are situated in the southern part of the Borborema Province (northeastern Brazil), in the Riacho do Pontal Orogen, and represent meta-volcano-sedimentary sequences. We present compositional variations in the metasedimentary rocks and new U–Pb detrital zircon data. Major and trace elements indicate that the metasedimentary rocks from the Paulistana and Santa Filomena Complexes are composed mostly of immature to mature sediments derived from felsic-intermediate sources with moderate to slightly high chemical weathering. The geochemical signatures of the sediment protoliths for both complexes are characteristic of continental magmatic arc settings with minor contribution from recycled sediment sources. The source area for the Paulistana Complex rocks follow the compositional trend between calc-alkaline granites and granodiorites, whereas the Santa Filomena Complex rocks have a more restricted composition trending to more granodioritic sources. For the Paulistana Complex, two main source ages were identified: (1) Tonian (ca. 950 Ma – sample RPE-58) and Tonian–Stenian (ca. 1.0 Ga – sample RPE-103). These data coupled with geochemical information suggest that the Cariris Velhos arc system was the main source area for the Paulistana Complex. Regarding the Santa Filomena metasedimentary rocks, potential source-areas include: (1) Neoarchaean rocks (~2.6 Ga) represented by the adjacent basement rocks of the Riacho do Pontal Orogen; (2) Rhyacian–Orosirian rocks (2.2–2.0 Ga) of the Riacho do Pontal Orogen and the Pernambuco–Alagoas terrain, which include an augen-gneiss with arc-related geochemical signature; (3) Statherian granites (1.7–1.6 Ga); and (4) Cariris Velhos crust (1000–920 Ma). The metasedimentary rocks of the Paulistana Complex were deposited in a rift stage (ca. 900 Ma), which is related to the break-up of the Rodinia supercontinent. The metasedimentary rocks of the Santa Filomena Complex most probably were deposited in another rift stage (ca. 750–700 Ma) and could be correlatives of the rift formation of the Canindé Domain (Sergipano Orogen).  相似文献   

12.
The well-known southwest-to-northeast younging of stratigraphy over a present-day cross strike distance of >1500 km in the southern Tasmanides of eastern Australia has been used to argue for models of accretionary orogenesis behind a continually eastwards-rolling paleo-Pacific plate. However, these accretionary models need modification, since the oldest (ca 530 Ma) outcrops of Cambrian supra-subduction zone rocks occur in the outboard New England Orogen, now ～900 km east of the next oldest (520–510 Ma) supra-subduction zone rocks. This is not consistent with simple, continuous easterly rollback. Instead, the southern Tasmanides contain an early history characterised by a westwards-migrating margin between ca 530 and ca 520 Ma, followed by rapid eastwards rollback of the paleo-Pacific plate from 520 to 502 Ma that opened a vast backarc basin ～2000 km across that has never been closed. From the Ordovician through to the end of the Carboniferous, the almost vertical stacking of continental margin arcs (within a hundred kilometres of each other) in the New England Orogen indicates a constant west-dipping plate boundary in a Gondwana reference frame. Although the actual position of the boundary is inferred to have undergone contraction-related advances and extension-related retreats, these movements are estimated to be ～250 km or less. Rollback in the early Permian was never completely reversed, so that late Permian–Triassic to Cretaceous arcs lie farther east, in the very eastern part of eastern Australia, with rifted fragments occurring in the Lord Howe Rise and in New Zealand. The northern Tasmanides are even more anomalous, since they missed out on the middle Cambrian plate boundary retreat seen in the south. As a result, their Cambrian-to-Devonian history is concentrated in a ～300 km wide strip immediately west of Precambrian cratonic Australia and above Precambrian basement. The presence in this narrow region of Ordovician to Carboniferous continental margin arcs and backarc basins also implies a virtually stationary plate boundary in a Gondwana frame of reference. This bipolar character of the Tasmanides suggests the presence of a segmented paleo-Pacific Plate, with major transform faults propagating into the Tasmanides as tear faults that were favourably oriented for the formation of local supra-subduction zone systems and for subsequent intraplate north–south shortening. In this interpretation of the Tasmanides, Lower–Middle Ordovician quartz-rich turbidites accumulated as submarine fan sequences, and do not represent multiple subduction complexes developed above subduction zones lying behind the plate boundary. Indeed, the Tasmanides are characterised by the general absence of material accreted from the paleo-Pacific plate and by the dominance of craton-derived, recycled sedimentary rocks.  相似文献   

13.
U–Pb (SHRIMP) detrital zircon age patterns are reported for 12 samples of Permian to Cretaceous turbiditic quartzo‐feldspathic sandstone from the Torlesse and Waipapa suspect terranes of New Zealand. Their major Permian to Triassic, and minor Early Palaeozoic and Mesoproterozoic, age components indicate that most sediment was probably derived from the Carboniferous to Triassic New England Orogen in northeastern Australia. Rapid deposition of voluminous Torlesse/Waipapa turbidite fans during the Late Permian to Late Triassic appears to have been directly linked to uplift and exhumation of the magmatically active orogen during the 265–230 Ma Hunter‐Bowen event. This period of cordilleran‐type orogeny allowed transport of large volumes of quartzo‐feldspathic sediment across the convergent Gondwanaland margin. Post‐Triassic depocentres also received (recycled?) sediment from the relict orogen as well as from Jurassic and Cretaceous volcanic provinces now offshore from southern Queensland and northern New South Wales. The detailed provenance‐age fingerprints provided by the detrital zircon data are also consistent with progressive southward derivation of sediment: from northeastern Queensland during the Permian, southeastern Queensland during the Triassic, and northeastern New South Wales — Lord Howe Rise — Norfolk Ridge during the Jurassic to Cretaceous. Although the dextral sense of displacement is consistent with the tectonic regime during this period, detailed characterisation of source terranes at this scale is hindered by the scarcity of published zircon age data for igneous and sedimentary rocks in Queensland and northern New South Wales. Mesoproterozoic and Neoproterozoic age components cannot be adequately matched with likely source terranes in the Australian‐Antarctic Precambrian craton, and it is possible they originated in the Proterozoic cores of the Cathaysia and Yangtze Blocks of southeast China.  相似文献   

14.
Abstract

Cambrian deformation associated with the Delamerian Orogeny is most evident in the Delamerian Orogen (southwestern Tasmanides) but has also been documented in the Thomson Orogen (northern Tasmanides). The tectonic evolution of the Thomson Orogen in the context of the Delamerian Orogeny is poorly understood. In particular, tectonostratigraphic relationships between the different parts of the Thomson Orogen (Anakie Inlier, Nebine Ridge, and southern Thomson Orogen) are still unclear. New detrital zircon data from the Nebine Ridge revealed an age spectrum that is consistent with published geochronological data from the Anakie Inlier. These results, in conjunction with petrographic observations and the interpretation of geophysical data, suggest that along the eastern part of the Thomson Orogen, the?～?NNE-trending Nebine Ridge represents the southward continuation of the?～?N–S-trending Anakie Inlier. New detrital zircon geochronological data are also presented for metasedimentary rocks from both sides of the Thomson–Lachlan boundary. The results constrain the maximum age of deposition (Ordovician–Devonian), and show that both sides of the Thomson–Lachlan boundary received detritus from a similar provenance. This might suggest that the Thomson–Lachlan boundary did not play a major role as a crustal-scale boundary prior to the Devonian. We speculate that transpressional deformation along this?～?E–W boundary, during the Early Devonian, was responsible for disrupting the original belt that connected the Delamerian Orogen (Koonenberry Belt) with the eastern Thomson Orogen (Nebine Ridge and Anakie Inlier).
  1. Highlights

  2. The Nebine Ridge is the southward continuation of the Anakie Inlier.

  3. The Anakie Inlier and Nebine Ridge represent a northern segment of the Cambrian Delamerian–Thomson Belt.

  4. ～E–W-trending crustal-scale structures at the southern Thomson Orogen were active during Devonian.

  相似文献   

15.
The Pine Creek Orogen, located on the exposed northern periphery of the North Australian Craton, comprises a thick succession of variably metamorphosed Palaeoproterozoic siliciclastic and carbonate sedimentary and volcanic rocks, which were extensively intruded by mafic and granitic rocks. Exposed Neoarchean basement is rare in the Pine Creek Orogen and the North Australian Craton in general. However, recent field mapping, in conjunction with new SHRIMP U–Pb zircon data for six granitic gneiss samples, have identified previously unrecognised Neoarchean crystalline crust in the Nimbuwah Domain, the eastern-most region of the Pine Creek Orogen. Four samples from the Myra Falls and Caramal Inliers, the Cobourg Peninsula, and the Kakadu region have magmatic crystallisation ages in the range 2527–2510 Ma. An additional sample, from northeast Myra Falls Inlier, yielded a magmatic crystallisation age of 2671 ± 3 Ma, the oldest exposed Archean basement yet recognised in the North Australian Craton. These results are consistent with previously determined magmatic ages for known outcropping and subcropping crystalline basement some 200 km to the west. A sixth sample yielded a magmatic crystallisation age of 2640 ± 4 Ma. The ca. 2670 Ma and ca. 2640 Ma samples have ca. 2500 Ma metamorphic zircon rims, consistent with metamorphism broadly coeval with emplacement of the volumetrically dominant ca. 2530–2510 Ma granites and granitic gneisses. Neoarchean zircon detritus, particularly in the ca. 2530–2510 Ma and ca. 2670–2640 Ma age span, are an almost ubiquitous feature of detrital zircon spectra of unconformably overlying metamorphosed Palaeoproterozoic strata of the Pine Creek Orogen, and of local post-tectonic Proterozoic sequences, consistent with this local provenance. Neoarchean zircon is also a common detrital component in Palaeoproterozoic sedimentary units across much of the North Australian Craton suggesting the existence of an extensive, if not contiguous, Neoarchean crystalline basement underlying not only a large part of the Pine Creek Orogen, but also much of the North Australian Craton.  相似文献   

16.
We document new U-Pb detrital zircon LA-MC-ICP-MS data for seven metavolcanic-sedimentary successions and metasedimentary sequences and reassess additional dates of five siliciclastic samples toward their tectonic significance in the context of the Mineiro belt, Southern São Francisco Craton. This belt represents a crustal segment of the 2.47–2.00 Ga Minas Orogen, classically known by its Siderian and Rhyacian juvenile rocks with important implications in the Earth's geodynamics. The new and compiled detrital provenance constraints unravel the long-lived magmatic and sedimentary history of the studied basins, lasting ca. 230–220 Myr. The maximum depositional dates around 2.1 Ga reflect the renewed sediment budget with the subsequent metamorphic episode ca. 2.0 Ga. Most of the unmixed relative probability diagrams are consistent with sourcing from the Siderian and Rhyacian arcs of the Mineiro belt, determining a detrital provenance change in time and space for the precursor basins. Alternative potential sources could be the youngest rocks of the Mantiqueira and Juiz de Fora terranes that constitute the other segments of the Minas Orogen, given the age match. The overall detrital fingerprints determine the study basins resumed mainly in Rhyacian fore-arc and/or back-arc settings, i.e., akin to a subduction-related system that evolved to a collisional (foreland) environment. Few samples show fingerprints of primary extensional settings, determined by major Archean detrital populations sourced from areas outside the Mineiro belt beside the Paleoproterozoic detritus. The working model considers the collage between the Mineiro belt and the ancient foreland around 2.10 Ga and eventual interaction with other crustal segments of the Minas Orogen, generating the ca. 2.0 Ga metamorphism over the metasedimentary samples. The more complete isotopic repository in detrital and igneous zircon grains for the studied supracrustal successions and the associated rocks allows new insights into the Rhyacian–Orosirian dynamics of the Minas orogeny. In a broader perspective, the juvenile nature of the Mineiro belt reinforces the paradigm of uninterrupted continental growth during the Paleoproterozoic Earth.  相似文献   

17.
Lower to upper Middle Ordovician quartz-rich turbidites form the bedrock of the Lachlan Orogen in the southern Tasmanides of eastern Australia and occupy a present-day deformed volume of ～2–3 million km3. We have used U–Pb and Hf-isotope analyses of detrital zircons in biostratigraphically constrained turbiditic sandstones from three separate terranes of the Lachlan Orogen to investigate possible source regions and to compare similarities and differences in zircon populations. Comparison with shallow-water Lower Ordovician sandstones deposited on the subsiding margin of the Gondwana craton suggests different source regions, with Grenvillian zircons in shelf sandstones derived from the Musgrave Province in central Australia, and Panafrican sources in shelf sandstones possibly locally derived. All Ordovician turbiditic sandstone samples in the Lachlan Orogen are dominated by ca 490–620 Ma (late Panafrican) and ca 950–1120 Ma (late Grenvillian) zircons that are sourced mainly from East Antarctica. Subtle differences between samples point to different sources. In particular, the age consistency of late Panafrican zircon data from the most inboard of our terranes (Castlemaine Group, Bendigo Terrane) suggests they may have emanated directly from late Grenvillian East Antarctic belts, such as in Dronning Maud Land and subglacial extensions that were reworked in the late Panafrican. Changes in zircon data in the more outboard Hermidale and Albury-Bega terranes are more consistent with derivation from the youngest of four sedimentary sequences of the Ross Orogen of Antarctica (Cambrian–Ordovician upper Byrd Group, Liv Group and correlatives referred to here as sequence 4) and/or from the same mixture of sources that supplied that sequence. These sources include uncommon ca 650 Ma rift volcanics, late Panafrican Ross arc volcanics, now largely eroded, and some <545 Ma Granite Harbour Intrusives, representing the roots of the Ross Orogen continental-margin arc. Unlike farther north, Granite Harbour Intrusives between the Queen Maud and Pensacola mountains of the southern Ross Orogen contain late Grenvillian zircon xenocrysts (derived from underlying relatively juvenile basement), as well as late Panafrican magmatic zircons, and are thus able to supply sequence 4 and the Lachlan Ordovician turbidites with both these populations. Other zircons and detrital muscovites in the Lachlan Ordovician turbidites were derived from relatively juvenile inland Antarctic sources external to the orogen (e.g. Dronning Maud Land, Sør Rondane and a possible extension of the Pinjarra Orogen) either directly or recycled through older sedimentary sequences 2 (Beardmore and Skelton groups) and 3 (e.g. Hannah Ridge Formation) in the Ross Orogen. Shallow-water, forearc basin sequence 4 sediments (or their sources) fed turbidity currents into outboard, deeper-water parts of the forearc basin and led to deposition of the Ordovician turbidites ～2500–3400 km to the north in backarc-basin settings of the Lachlan Orogen.  相似文献   

18.
Abstract

The turbidite-filled, Lower Devonian Cobar Basin is characterised through a detrital zircon study. Uranium–Pb age data for six samples were combined with published data to show the basin has a unique age spectrum characterised by a subordinate Middle Ordovician (ca 470?Ma) peak superimposed on a dominant ca 500?Ma peak. Maximum depositional ages for 3 samples were ca 425?Ma, close to the published Lower Devonian (Lochkovian 419–411?Ma) biostratigraphic ages. A minor ca 1000?Ma zircon population was also identified. The major source of the 500?Ma zircons was probably the local Ordovician metasedimentary basement, which was folded, thickened and presumably exposed during the ca 440?Ma Benambran Orogeny. The ca 470?Ma age peak reflects derivation from Middle Ordovician (Phase 2) rocks of the Macquarie Arc to the east. The I-type Florida Volcanics, located ～50?km eastward from the Cobar Basin, contains distinctive Middle and Late Ordovician zircon populations, considered to be derived from deeply underthrust Macquarie Arc crust. Protracted silicic magmatism occurred before, during and after Cobar Basin deposition, indicating that the basin formed by subduction-related processes in a back-arc setting, rather than as a continental rift.  相似文献   

19.
The high-temperature–low-pressure Wongwibinda Metamorphic Complex of the southern New England Orogen is bound by S-type granite plutons of the Hillgrove Supersuite to the north, east and south. New U–Pb geochronology of five samples of the Hillgrove Supersuite demonstrates that plutonism in the complex involved two pulses: ca 300 Ma and ca 292 Ma. This indicates that plutonism partially overlaps the age of high-T–low-P metamorphism (296.8 ± 1.5 Ma), but also postdates it. Zircon grains identified as xenocrysts based on age (≥310 Ma) have U–Pb–Hf isotopic character that largely overlaps detrital grains in the host Girrakool Beds, indicating that accretionary complex crust is the likely source of these xenocrysts. The 176Hf/177Hf initial character for zircon for the ca 300 Ma plutons (three samples) is less radiogenic than those in the ca 292 Ma plutons (two samples). The progression in 176Hf/177Hf initial character for zircon infers an increasing mantle component in the Hillgrove Supersuite with time. These data are evidence of a rift tectonic setting, where mantle-derived magmas are predicted to more readily migrate to shallower crustal levels as the crust thins and becomes hotter. Additionally, early episodes of partial melting in the system melt-depleted the metasedimentary sources, thus reducing the S-type component as anatexis progressed. The evolution of the Hillgrove Supersuite coincides with a period of early Permian slab roll back and extension accompanied by crustal rifting and thinning, leading to high-T–low-P metamorphism, anatexis and S-type granite production and the development of rift basins such as the Sydney–Gunnedah–Bowen system.  相似文献   

20.
锆石U-Pb定年及Hf同位素测定结果表明,鄂尔多斯盆地周缘的华北板块北缘、兴蒙造山系及扬子板块-秦岭-大别-苏鲁造山带等构造单元系统具有明显不同的形成与演化历史。华北板块北缘锆石年龄平均值为1 837 Ma,最强烈的岩浆活动出现于2 200~1 800 Ma,该期锆石约占全部的40%;次为强烈的岩浆活动在2 800~2 200 Ma,其众数在全部锆石中约占30%;1 500~1 200 Ma、500~100 Ma这两个阶段形成的锆石在全区所占比例各约为15%。华北板块北缘最突出的特征是基本不含1 000~700 Ma期间形成的锆石,>3 000 Ma的锆石在全区分布极为有限。锆石Hf同位素亏损地幔模式年龄表明华北板块北缘平均值为2.55 Ga,较U-Pb平均年龄老,说明2 200~1 800 Ma期间形成的锆石含有较多的古老地壳再循环组分。Hf亏损地幔模式年龄最强峰值约为2.8 Ga,与全岩Nd亏损地幔模式年龄的峰值相一致,Hf模式年龄为3.0~2.25 Ga的颗粒占全部的近95%,证明华北板块北缘的地壳增生主要在太古宙至古元古代期间。Hf同位素亏损地幔模式年龄>3.0 Ga的锆石颗粒所占比例不到0.1%,另外近5%锆石的模式年龄分布于中元古代。晚古生代-中生代所形成的锆石均是先存地壳组分,尤其是中元古代增生地壳的熔融作用形成。兴蒙造山系中锆石U-Pb年龄平均值为497 Ma,最强峰分布于石炭纪(约320 Ma),石炭纪-二叠纪末(350~250 Ma)形成的锆石所占比例达30%以上。新元古代至早古生代(600~440 Ma)形成的锆石占全部锆石的55%以上,而中元古代末-新元古代期间(1 200~600 Ma)形成的锆石在全区仅占4%。中元古代以前形成的锆石非常有限,说明该区最早形成的地壳组分在兴蒙造山系的形成过程中较充分地参与到后期的岩浆作用过程中。兴蒙造山系中锆石相应的Hf同位素亏损地幔模式年龄平均为1.13 Ga,明显较相应的U-Pb年龄老,最强峰值出现于约0.6 Ga。Hf亏损地幔模式年龄为0.7~0.28 Ga的颗粒在兴蒙造山系所占比例达57%,证明该区最强烈的地壳增生发生于新元古代至古生代期间。Hf同位素亏损地幔模式年龄分布于1.5~0.7 Ga的锆石在全区约占38%,说明此期间也是该区地壳较强烈的增生期。Hf亏损地幔模式年龄大于1.5 Ga的锆石所占比例不到5%,古生代以后兴蒙造山系也基本没有明显的地壳增生。扬子与秦岭-大别-苏鲁造山带构造单元中的锆石U-Pb年龄平均为799 Ma,年龄为1 300~750 Ma的锆石在全部锆石中约占70%。晚古生代-燕山期形成的锆石约占20%。年龄在3 500~2 650 Ma、2 118~1 680 Ma的锆石在该区各约占5%。结合扬子与秦岭-大别-苏鲁造山带平均为1.56 Ga的Nd亏损地幔模式年龄特征,说明1 300~750 Ma期间该区较强烈的岩浆作用事件中有较多的古老地壳组分加入其中。锆石U-Pb年龄及Hf同位素组成均说明鄂尔多斯盆地周缘各构造单元具有不同的形成演化历史。地壳是幕式增长的,但各构造单元每幕发生的时间、强度存在明显差别。因此,由盆地中不同时代地层中碎屑锆石U-Pb年龄及Hf同位素组成及全岩Nd同位素特征的系统研究可反演盆地物源供给与周围构造单元之间的关系。  相似文献   

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