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1.
U–Pb zircon analyses from a series of orthogneisses sampled in drill core in the northern Gawler Craton provide crystallisation ages at ca 1775–1750 Ma, which is an uncommon age in the Gawler Craton. Metamorphic zircon and monazite give ages of ca 1730–1710 Ma indicating that the igneous protoliths underwent metamorphism during the craton-wide Kimban Orogeny. Isotopic Hf zircon data show that 1780–1750 Ma zircons are somewhat evolved with initial εHf values –4 to +0.9, and model ages of ca 2.3 to 2.2 Ga. Isotopic whole rock Sm–Nd values from most samples have relatively evolved initial εNd values of –3.7 to –1.4. In contrast, a mafic unit from drill hole Middle Bore 1 has a juvenile isotopic signature with initial εHf zircon values of ca +5.2 to +8.2, and initial εNd values of ～+3.5 to +3.8. The presence of 1775–1750 Ma zircon forming magmatic rocks in the northern Gawler Craton provides a possible source for similarly aged detrital zircons in Paleoproterozoic basin systems of the Gawler Craton and adjacent Curnamona Province. Previous provenance studies on these Paleoproterozoic basins have appealed to the Arunta Region of the North Australian Craton to provide 1780–1750 Ma detrital zircons, and isotopically and geochemically similar basin fill. The orthogneisses in the northern Gawler Craton also match the source criteria and display geochemical similarities between coeval magmatism in the Arunta Region of the North Australian Craton, providing further support for paleogeographic reconstructions that link the Gawler Craton and North Australian Craton during the Paleoproterozoic.  相似文献   

2.
The Dashiqiao Formation on the Liaodong Peninsula constitutes an important component within the Jiao–Liao–Ji Belt, North China Craton. It is composed dominantly of dolomitic marbles intercalated with minor carbonaceous slates and mica schists, hosting one of the largest magnesite deposits on Earth. This study presents zircon cathodoluminescence (CL) images and U–Pb–Hf isotope data, as well as single-mineral geochemical data for the staurolite–garnet–mica schist from the Dashiqiao Formation, in order to constrain its protolith age and provenance, and further to discuss the early Precambrian tectono-thermal events of the North China Craton. U–Pb isotopic dating using the LA–ICP–MS method on detrital zircons from the schist preserves at least three age populations ranging in age from 2.99 to 2.02 Ga, and grains as old as ca 4087 Ma. The dominant Neoarchean detrital zircons were most probably sourced from the basement within the Longgang and Nangrim blocks, while the minor Mesoarchean zircons were only sourced from the Longgang Block. The subordinate middle Paleoproterozoic zircons are consistent with ages of the regionally distributed coeval Liaoji granites and volcanics within the Jiao–Liao–Ji Belt. Zircon U–Pb dating yields a metamorphic age of 1930 Ma for the sample, interpreted to represent the peak stage of epidote amphibolite facies metamorphism. Thus, the depositional age for the protolith of the schist was proposed in the period between 2.01 and 1.93 Ga. LA–MC–ICP–MS Lu–Hf isotopic data show that all Archean (2.45–2.55) detrital zircons possess positive εHf(t) values from +?0.7 to +?7.5 with juvenile depleted mantle model ages, suggesting a significant crustal growth event during the Neoarchean in the North China Craton. The Paleoproterozoic detrital zircons possess variable εHf(t) values (??5.5–+?8.3) and depleted mantle model ages from Mesoarchean to Paleoproterozoic. The zircons with negative εHf(t) values implies the Mesoarchean to Neoarchean crust undergoing a recycling event in the period 2.40–2.01 Ga, while those with positive εHf(t) value suggest some indication of juvenile addition to the crust during the Paleoproterozoic. Using regional geological and new detrital zricon U–Pb–Hf isotopic data, the early Precambrian tectono-thermal events can be subdivided into the following episodes: Mesoarchean, late Neoarchean, middle Paleoproterozoic, and late Paleoproterozoic times.  相似文献   

3.
Although Yangtze Craton have no～1.8 Ga collision orogens that occurred in North China named Trans-North China Orogen, both 2.0-1.8 Ga Metamorphic and Quanqitang granite in the Kongling terrain in the northern part of the Yangtze Craton, together with detrital zircons, recorded its amalgamation to and separation from Columbia Supercontinent.  相似文献   

4.
The detrital zircon population in quartzitic conglomerates from the northern Tanzania Craton yield ages between 2640 Ma and 2790 Ma which includes most of the igneous history from this part of the craton. The igneous evolution is characterised by mafic volcanism with an oceanic plateau‐like geochemical signature at ~2800 Ma followed by diorite and tonalite–trondhjemite–granodiorite dominated magmatism between 2790 and 2700 Ma, which transitioned into more evolved high‐K magmatism between 2700 and 2620 Ma. The εHf values of the detrital zircons range from +2.4 to ?1.4 and change with time from radiogenic Hf pre‐2700 Ma (98% positive εHf) to unradiogenic Hf post‐2700 Ma (41% positive εHf). The petrological progression from mafic to felsic crust is reflected in the detrital age distribution and Hf isotopes and is consistent with juvenile mafic crust slowly maturing into more evolved felsic crust through a series of successive partial melting events in an oceanic‐plateau‐like environment.  相似文献   

5.
We present results of study of the trace-element and Lu–Hf isotope compositions of zircons from Paleoproterozoic high-grade metasedimentary rocks (paragneisses) of the southwestern margin of the Siberian craton (Irkut terrane of the Sharyzhalgai uplift). Metamorphic zircons are represented by rims and multifaceted crystals dated at ~ 1.85 Ga. They are depleted in either LREE or HREE as a result of subsolidus recrystallization and/or synchronous formation with REE-concentrating garnet or monazite. In contrast to the metamorphic zircons, the detrital cores are enriched in HREE and have high (Lu/Gd)n ratios, which is typical of igneous zircon. The weak positive correlation between 176Lu/177Hf and 176Hf/177Hf in the zircon cores evidences that their Hf isotope composition evolved through radioactive decay in Hf = the closed system. Therefore, the isotope parameters of these zircons can give an insight into the provenance of metasedimentary rocks. The Paleoproterozoic detrital zircon cores from paragneisses, dated at ~ 2.3–2.4 and 2.0–1.95 Ga, are characterized by a wide range of εHf values (from + 9.8 to –3.3) and model age T C 2.8–2.0 Ga. The provenance of these detrital zircons included both rocks with juvenile isotope Hf parameters and rocks resulted from the recycling of the Archean crust with a varying contribution of juvenile material. Zircons with high positive εHf values were derived from the juvenile Paleoproterozoic crustal sources, whereas the lower εHf and higher T C values for zircons suggest the contribution of the Archean crustal source to the formation of their magmatic precursors. Thus, at the Paleoproterozoic stage of evolution of the southwestern margin of the Siberian craton, both crustal recycling and crustal growth through the contribution of juvenile material took place. On the southwestern margin of the Siberian craton, detrital zircons with ages of ~ 2.3–2.4 and 1.95–2.0 Ga are widespread in Paleoproterozoic paragneisses of the Irkut and Angara–Kan terranes and in terrigenous rocks of the Urik–Iya graben, which argues for their common and, most likely, proximal provenances. In the time of metamorphism (1.88–1.85 Ga), the age of Paleoproterozoic detrital zircons (2.4–2.0 Ga), and their Lu–Hf isotope composition (εHf values ranging from positive to negative values) the paragneisses of the southwestern margin of the Siberian craton are similar to the metasedimentary rocks of the Paleoproterozoic orogenic belts of the North China Craton. In the above two regions, the sources of detrital zircons formed by both the reworking of the Archean crust and the contribution of juvenile material, which is evidence for the crustal growth in the period 2.4–2.0 Ga.  相似文献   

6.
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   

7.
Field observations integrated with new petrographic and sensitive high-resolution ion microprobe (SHRIMP) U–Pb age data for detrital zircons from the Paleoproterozoic Speewah Group of northern Western Australia provide evidence of depositional conditions, source of detritus, timing and evolution of the sedimentary rocks in the Speewah Basin. The Speewah Group is a 1.5 km-thick succession of poorly outcropping, predominantly siliciclastic rocks that preserve a fluviatile to marine, transgressive and regressive event. The Speewah Group unconformably overlies crystalline rocks of the Lamboo Province that were stabilised by the 1870–1850 Ma Hooper Orogeny, then accreted as the Kimberley region onto the North Australian Craton during the 1835–1810 Ma Halls Creek Orogeny. Unconformably overlying the Speewah Group is about 4 km of predominantly siliciclastic marine sedimentary rocks of the Kimberley Group in the Kimberley Basin. This study has detected a detrital zircon component within the Speewah Basin at 1814 ± 10 Ma, with a youngest zircon at 1803 ± 12 Ma (1σ) in fluviatile sandstones located beneath a volcaniclastic rock with magmatic zircons that have been dated at ca 1835 Ma. Previous studies proposed that the Speewah Basin developed as a retro-arc foreland basin during accretion of the North Australian Craton. We interpret the ca 1835 Ma zircons in the volcaniclastic rocks to be xenocrystic in origin. This new 20 million years younger maximum depositional age indicates that the Speewah Group in the Speewah Basin, similarly to the overlying Kimberley Group in the Kimberley Basin, developed in a post-orogenic setting on the North Australian Craton rather than in a syn-orogenic setting associated with the 1835–1810 Ma Halls Creek Orogeny.  相似文献   

8.
The Yili Block is one of the major Precambrian microcontinents of the Central Asian Orogenic Belt (CAOB). Detrital zircon U-Pb ages and Hf isotopic data of the Meso-Neoproterozoic (meta)-sedimentary units within the Yili Block constrain the tectonic affinity and early history of the block. Detrital zircon U-Pb ages, in combination with related magmatic age data, indicate that the Tekesi and Kusitai groups were deposited during the latest Mesoproterozoic-earliest Neoproterozoic (1040–960 Ma) and early Neoproterozoic (<926 Ma), respectively. Zircons from the Kusitai Group yield major age groups at 941–910 Ma and 1887–1122 Ma, whereas the Tekesi Group have a dominant age group at ca. 2.0–1.1 Ga with age peaks at ca. 1.9 Ga, 1.8 Ga, 1.75–1.70 Ga, 1.58 Ga, 1.5 Ga, 1.47–1.43 Ga and 1.27–1.20 Ga. A minor age peak of ca. 2.5 Ga is also recognized in the middle part of the Tekesi Group. Early Neoproterozoic detrital zircons with relatively uniform εHf(t) values (+0.7 to +3.2) were mainly derived from contemporaneous magmatic rocks in the Yili Block. The Central Tianshan Block provides a likely source for detritus with ages of ca. 1.7–1.4 and 2.5 Ga. The predominant late Paleoproterozoic to latest Mesoproterozoic detrital zircons with positive εHf(t) values (+0.5 to +12.0) in the Yili Block were probably derived primarily from regions exhumed during collisional assembly of Rodinia. These populations are consistent with those from the late Mesoproterozoic-early Neoproterozoic (meta)-sedimentary successions in the Central Tianshan, Kokchetav-North Tianshan and Erementau-Niyaz blocks, and Southeast Siberia and northeastern Laurentia cratons. The Yili Block, together with the Precambrian microcontinents in the southwestern Central Asian Orogenic Belt, was likely located at the margin of Rodinia supercontinent, between the southeast Siberia and northeast Laurentia during the early Neoproterozoic.  相似文献   

9.
Records of Precambrian glaciation have been reported from southeastern Brazil for over a century. We present sedimentological, stratigraphic and isotopic (U-Pb and Lu-Hf on detrital zircons, C and O on carbonates) studies on diamictite-rich to diamictite-free successions of the Araçuaí Orogen, the Brazilian counterpart of the Araçuaí – West Congo Orogenic System (AWCO). From base to top, the Chapada Acauã Formation (Macaúbas Group) includes a diamictite-rich unit, with lenses of graded sandstone and clast-supported conglomerate, that gradually passes to graded sandstone, pelite with sparse oversized clasts and rare carbonate lenses on top, representing mass flow and turbidity current deposits of submarine fan, followed by finer-grained turbiditic sedimentation with iceberg discharges along fan fringes, from glaciomarine to post-glacial scenarios. The Salinas Formation comprises a deep-sea sand-mud sequence composed of pelites and pelitic wackes. The Chapada Acauã Formation was deposited in-between 750 and 667 Ma. It shows wide spectra of zircon ages (typical of continental rift to passive margin settings) that start around 3.2 Ga and display main age peaks indicating sediment provenance from the Rhyacian-Orosirian basement (εHf(t) = +14.6 to −18.5) and Early Tonian anorogenic rocks (950–880 Ma; εHf(t) = −3.2 to −23.2) for the diamictite-rich lower unit and, for the upper unit, also in Early Cryogenian anorogenic rocks (ca. 715 Ma, εHf(t) = −9.6). In contrast, the Salinas Formation shows most ages in-between 676 and 620 Ma and a maximum sedimentation age around 551 Ma, with εHf(t) from +6.9 to −18.2, unravelling an important shifting of sediment provenance to sources located in magmatic arcs and collisional granites of the Araçuaí and Ribeira orogens. The Early Cryogenian age and negative Hf signature for the glaciomarine Chapada Acauã Formation point to sediment sources in the 720–670 Ma anorogenic igneous rocks found in AWCO and adjacent Congo – São Francisco Craton, and suggest correlation with the Sturtian global glaciation.  相似文献   

10.
《Precambrian Research》2001,105(2-4):331-356
The Paleoproterozoic Lower Aillik Group is a deformed metasedimentary–metavolcanic succession located in the Makkovik Province of Labrador, eastern Canada. The group is situated near the boundary between reworked Archaean gneiss of the Nain (North Atlantic) craton and juvenile Paleoproterozoic crust that was both tectonically accreted and formed on or adjacent to this craton during the ca. 1.9–1.78 Ma Makkovikian orogeny. The Lower Aillik Group is structurally underlain by Archaean gneiss and structurally overlain by ca. 1860–1807 Ma bimodal, dominantly felsic volcanic and volcaniclastic rocks of the Upper Aillik Group. We present geochemical data from metavolcanic rocks and U–Pb geochronological data from several units of the Lower Aillik Group in order to address the depositional and tectonic history of this group. U–Pb data were obtained using both thermal ionization mass spectrometry (TIMS) and laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS). Two quartzite units near the structural base of the Lower Aillik Group contain detrital zircons only of Archaean age, and are interpreted to have been deposited on the Nain craton during post-2235 Ma rifting and initiation of a passive continental margin. Overlying mafic metavolcanic rocks contain thin horizons of intermediate tuff, one of which is dated at 2178±4 Ma. This relatively old age, and an inferred stratigraphic relationship with underlying sedimentary units, suggest that the volcanic rocks represent transitional oceanic crust, consistent with their geochemical similarity to tholeiitic rifted margin sequences of Mesozoic age in eastern North America. A package of interlayered psammitic and semipelitic metasedimentary rocks that appears to stratigraphically overlie the mafic volcanic unit is dominated by Paleoproterozoic detrital zircons but also contains Archaean grains. This package was deposited after 2013 Ma, the age of the youngest concordant zircon. The U–Pb data imply a minimum 165 m.y. time gap between mafic volcanism and sedimentation, and are consistent with deposition of the psammite–semipelite unit in an evolving foredeep that heralded the approach of a Paleoproterozoic arc terrane. Accretion of this terrane to the Nain cratonic margin at ca. 1.9 Ga initiated the Makkovikian orogeny. Although the Lower Aillik Group is highly deformed and may contain internal tectonic boundaries or be incomplete, the U–Pb and geochemical data allow quantitative assessment of a prolonged rift-drift-basin closure cycle that characterized the Early Paleoproterozoic evolution of the southern Nain cratonic margin.  相似文献   

11.
刘超辉  刘福来 《岩石学报》2015,31(10):3107-3128
华北克拉通存在三个主要的中元古代裂谷带,从南到北分别为熊耳裂谷带、燕辽裂谷带以及渣尔泰-白云鄂博-化德裂谷带。其中熊耳群中火山岩的峰期年龄为1780~1750Ma,其上还有形成于被动大陆边缘的五佛山群、汝阳群以及官道口群。中北部的燕辽裂谷带包括长城系、蓟县系和青白口系,其中长城系团山子组和大红峪组火山岩的年龄分别为~1640Ma和1626~1622Ma,蓟县系高于庄组、雾迷山组和铁岭组凝灰岩的年龄分别为1560Ma、1485Ma和1437Ma,而下马岭组凝灰岩年龄为1366~1380Ma。北缘渣尔泰-白云鄂博-化德裂谷带中渣尔泰群书记沟组玄武岩年龄为1743Ma,阿古鲁沟组酸性火山岩年龄为~810Ma,白云鄂博群尖山组中基性火山岩年龄为1728Ma,化德群比鲁特组火山碎屑岩年龄为1515Ma。中元古代岩浆事件除了裂谷带中的火山作用外,还包括三期基性岩墙群(~1780Ma太行-吕梁岩墙群、~1730Ma密云岩墙群和~1620Ma泰山岩墙群)以及1.76Ga到1.65Ga非造山岩浆组合(斜长岩-环斑花岗岩体-A型花岗岩)。中元古代中期,华北克拉通北缘发育了基性岩席(墙)、A型花岗岩以及碳酸岩脉,双峰式岩浆作用说明华北北缘在中元古代中期经历了裂谷作用,与哥伦比亚超大陆的最终裂解有关,并且与白云鄂博巨型REE-Nb-Fe矿床的形成具有成因上的联系。华北克拉通北部两个裂谷带中的地层具有可以对比的层序以及时代,而中元古代中期辉绿岩墙、A型花岗岩以及碳酸岩脉可以与其它克拉通同时期的非造山岩浆作用对比,证明华北克拉通经历了哥伦比亚超大陆的最终裂解。古地磁数据已经证明在哥伦比亚超大陆时期Siberia、Laurentia、Baltica、Amazion以及华北克拉通是连接在一起的,而北缘中元古代中期大陆裂谷相关岩浆岩的发现也说明它是与另一个古大陆相连的。华北克拉通南缘熊耳火山岩的构造背景到底是大陆裂谷还是大陆边缘弧则关系着其是与另一个克拉通相连还是面向大海,这需要我们进一步深入研究。  相似文献   

12.
Detrital zircon U-Pb geochronology combined with Hf isotopic and trace element data from metasedimentary rocks of the Aracuai Belt in southeastern Brazil provide evidence for break-up of the Congo-Sao Francisco Craton. The U-Pb age spectra of detrital zircons from metasediments of the Rio Doce Group(RDG) range from 900-650 Ma and define a maximum depositional age of ca. 650 Ma. Zircon trace element and whole rock data constrain an oceanic island arc as source for the deposition setting of the protoliths to the metasediments. Zircon ε_(Hf)(t) values from these rocks are positive between +1 and +15, supporting previous evidence of a Neoproterozoic extensional phase and oceanic crust formation in a precursor basin to the Aracuai Belt. Recrystallization of detrital zircon at ca. 630 Ma is compatible with a regional metamorphic event associated with terrane accretion to the Paleoproterozoic basement after transition from an extensional to a convergent regime. The juvenile nature, age spectra and trace element composition recorded in detrital zircons of metasediments from the Aracuai Belt correspond with zircons from metasedimentary rocks and oceanic crust remnants of other orogenic belts to its south. This suggests that rifting and oceanic crust formation of the entire orogenic system, the so-called Mantiqueira Province, was contemporaneous, most likely related to the opening of a large ocean. It further indicates that the cratonic blocks involved in the orogenic evolution of the Mantiqueira Province were spatially connected as early as 900 Ma.  相似文献   

13.
《Gondwana Research》2013,23(3-4):843-854
The Western Dharwar Craton in peninsular India comprises a typical Meso- to Neo-Archean granite-greenstone terrain. Detrital zircons from two metagreywackes in a late basin from the Gadag Greenstone Belt preserve at least eight age populations ranging in age from ca 3.34 to 2.55 Ga, and grains as old as ca 3.54 Ga. The zircon provenances for the two samples appear to be the same up to ca 3.25 Ga, with relatively juvenile εHf values largely between zero and depleted mantle values. After 3.25 Ga, one sample has similar εHf values whereas the other has only negative values indicative of Hf-evolution in a crustal environment. After ca 3.25 Ga the source regions for the two samples were distinctly different.The detrital zircons reflect the age and evolution of the upper crust of the Western Dharwar Craton. Modeling of Hf isotopic evolution of the detrital zircons suggests two major crust-forming events at ca. 3.6 and 3.36 Ga, and some indication of juvenile addition to the crust at ca 2.6 Ga. The maximum sedimentation age of the greywackes is constrained by the youngest detrital zircon population at 2547 ± 5 Ma. Gold mineralization in the belt is dated at 2522 ± 6 Ma and constrains greywacke sedimentation, deformation and metamorphism to a ca 25 my interval.  相似文献   

14.
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   

15.
The North China Craton (NCC) has been considered to be part of the supercontinent Columbia. The nature of the NCC western boundary, however, remains strongly disputed. A key question in this regard is whether or not the Alxa Block is a part of the NCC. It is located in the vicinity of the inferred boundary, and therefore could potentially resolve the issue of the NCC's relationship to the Columbia supercontinent. Some previous studies based on the Alxa Block's geological evolution and detrital zircon ages suggested that it is likely not a part of the NCC. The lack of evidence from key igneous rock units, however, requires further constraints on the tectonic affinity of the western NCC and Alxa Block and on the timing of their amalgamation.In this study, new zircon U–Pb age and Hf–O isotopes and whole-rock geochemical and Sr–Nd–Pb isotopic data for the Paleozoic granitoids in or near the eastern Alxa Block were used to constrain the petrogenesis of these rocks and the relationship between the Alxa Block and NCC. Secondary ion mass spectrometry (SIMS) U–Pb zircon dating indicates that the Bayanbulage, Hetun, Diebusige and South Diebusige granitoids were formed at ca. 423 Ma, 345 Ma, 345 Ma and 337 Ma, respectively. The Late Silurian (Bayanbulage) quartz diorites have variable SiO2 (58.0–67.9 wt.%), and low Sr/Y (20–24) values, while the Early Carboniferous (Hetun, Diebusige and South Diebusige) monzogranites have high SiO2 (71.5–76.7 wt.%) and Sr/Y (40–94) values. The Late Silurian quartz diorites display relatively homogeneous and high zircon δ18O (8.5–9.1‰) and εHf(t) (− 8.6 to − 5.3) values, high whole-rock εNd(t) values (− 9.2 to − 7.6) and highly radiogenic Pb isotopes (206Pb/204Pb = 18.13–18.25), whereas the Early Carboniferous monzogranites exhibit relatively low and variable zircon δ18O (5.7–7.2‰) and εHf(t) (− 23.1 to − 7.4) values, low whole-rock initial 87Sr/86Sr (0.7043–0.7070) and εNd(t) (− 19.1 to − 13.5) values and variable Pb isotopes (206Pb/204Pb = 16.06–18.22). The differences in whole rock Nd model ages and Pb isotope compositions of the Paleoproterozoic–Permian rocks in either side of the west fault of the Bayanwulashan–Diebusige complexes suggest that the Alxa Block is not a part of the NCC, and that the western boundary of the NCC is probably located on this fault. Furthermore, the linear distribution of the Early Paleozoic–Early Carboniferous granitoids, the high zircon δ18O values of the Late Silurian quartz diorites, the Early Devonian metamorphism and the foreland basin system formed during the collision between the Alxa Block and the NCC indicate that a Paleozoic cryptic suture zone likely existed in this area and records the amalgamation of the Alxa Block and North China Craton. Together with detrital zircon data, the initial collision was considered to have possibly occurred in Late Ordovician.  相似文献   

16.
班韦乌卢变质克拉通活动时间和地壳增长问题一直是地质学家关注的焦点。本文通过对班韦乌卢地块中卡帕图地区姆波罗科索群姆巴拉组石英砂岩进行了碎屑锆石U-Pb年代学和Hf同位素研究,结合变质克拉通已有成果获得认识如下：(1)姆巴拉组的形成时间可能介于(1833±22 Ma)～(1712±22 Ma)之间,属于古元古代。(2)姆巴拉组具有丰富的物质来源,其中2728～2602 Ma(峰值为2650 Ma)的物质可能来源于坦桑尼亚克拉通中的花岗岩类、粗面安山岩及流纹岩等岩石。2246～1833 Ma(峰值为1880 Ma)的物质主要来源于班韦乌卢地块中花岗岩类、石英闪长岩及火山岩类等岩石。(3)班韦乌卢变质克拉通的活动时间包括中太古代、新太古代、古元古代和中元古代四个时期,其中古元古代(1870 Ma)为活动的高峰期,涉及范围广泛,可能与哥伦比亚超大陆的演化密切相关。(4)班韦乌卢变质克拉通沉积岩的源区地壳增生除来自古老地壳的再循环物质外,还存在新生地壳的物质。同时,地壳在古太古代-古元古代均实现了增长,其中凯诺兰超大陆聚合时期(2550 Ma)增长最快。在古元古代之前的地壳主增长期与坦桑尼亚克拉通及全球大陆地壳主增长期基本一致。  相似文献   

17.
The Miyun area of Beijing is located in the northern part of the North China Craton(NCC)and includes a variety of Archean granitoids and metamorphic rocks.Magmatic domains in zircon from a tonalite reveal Early Neoarchean(2752±7 Ma) ages show a small range in ε_(Hf)(t) from 3.1 to 7.4and t_(DM1)(Hf) from 2742 to 2823 Ma,similar to their U-Pb ages,indicating derivation from a depleted mantle source only a short time prior to crystallization.SHRIMP zircon ages of granite,gneiss,amphibolite and hornblendite in the Miyun area reveal restricted emplacement ages from 2594 to2496 Ma.They also record metamorphic events at ca.2.50 Ga,2.44 Ga and 1.82 Ga,showing a similar evolutionary history to the widely distributed Late Neoarchean rocks in the NCC.Positive ε_(Hf)(t) values of 1.5 to 5.9,with model ages younger than 3.0 Ga for magmatic zircon domains from these Late Neoarchean intrusive rocks indicate that they are predominantly derived from juvenile crustal sources and suggest that significant crustal growth occurred in the northern NCC during the Neoarchean.Late Paleoproterozoic metamorphism developed widely in the NCC,not only in the Trans-North China Orogen,but also in areas of Eastern and Western Blocks,which suggest that the late Paleoproterozoic was the assembly of different micro-continents,which resulted in the final consolidation to form the NCC,and related to the development of the Paleo-Mesoproterozoic Columbia or Nuna supercontinent.  相似文献   

18.
In order to constrain the detrital provenance of the siliciclastic rocks, palaeogeographic variations, and crustal growth history of central China, we carried out simultaneously in situ U–Pb dating and trace element and Hf isotope analyses on 368 detrital zircons obtained from upper Permian–Triassic sandstones of the Songpan terrane, eastern Tibetan Plateau. Two groups of detrital zircons, i.e. magmatic and metamorphic in origin, have been identified based on cathodoluminescence images, zircon Ti-temperatures, and Th/U ratios. Our data suggest that the derivation of siliciclastic rocks in the Songpan terrane was mainly from the Qinling, Qilian, and Kunlun orogens, whereas the Yangtze and North China Cratons served as minor source areas during late Permian–Triassic times. The detrital zircons from Middle–Late Triassic siliciclastic rocks exhibit wide age spectra with two dominant populations of 230–600 Ma and >1600 Ma, peaking at ~1.8–1.9 Ga and ~2.4–2.5 Ga, suggestive of a derivation from the Qinling, Qilian, and Kunlun orogens and the Yangtze Craton being the minor source area. The proportions of detrital zircon populations from the northern Qinling, Qilian, and Kunlun orogens distinctly decreased during Middle–Late Triassic time, demonstrating that the initial uplift of the western Qinling occurred then and it could have blocked most of the detritus from the Qilian–northern Qinling orogens and North China Cratons into the main Songpan–Ganzi depositional basin. The relatively detrital zircon proportions of the Yangtze Craton source decreased during Early-Middle Late Triassic time, indicating that the Longmenshan orogen was probably being elevated, since the early Late Triassic and gradually formed a barrier between the Yangtze Craton and the Songpan terrane. In addition, our Lu–Hf isotopic results also reveal that the Phanerozoic magmatic rocks in central China had been the primary products of crustal reworking with insignificant formation of a juvenile crust.  相似文献   

19.
Collision can be subdivided into “soft” and “hard” types, with the “soft” collision occurring after double-sided oceanic subduction and the “hard” collision after single-sided oceanic subduction. Although two types of collision involve different geodynamics and generate distinct petrological assemblages, whether they can preserve distinct records of detrital zircons remains unclear. This study confirms “soft” collision between the north Western Kunlun terrane (NKT) and the south Western Kunlun terrane (SKT) after the closure of the Proto-Tethys Ocean. We further compare detrital zircon Hf isotope compositions of the “soft” collision with those of the “hard” collision related to the amalgamation of Rodinia in southern Tarim. Our results show that the NKT is characterized by dominant ca. 800 Ma zircons, whereas the SKT is featured by ca. 244 Ma, ca. 440 Ma, and ca. 620 Ma zircons. As such, sample 17WP53 deposited at 431 Ma in the NKT displays a dominant peak at ca. 500 Ma, indicating minor material exchange between the NKT and the SKT at ca. 431 Ma. Given the 420–405 Ma North Kudi granites displaying geochemical features of within-plate granites formed at a post-orogenic stage, we infer that the final closure of the Proto-Tethys Ocean occurred at 431–420 Ma along Western Kunlun. Moreover, zircon εHf(t) data indicate that the “soft” collision between the NKT and the SKT during the amalgamation of Gondwana produced ca. 40% of juvenile crustal materials, whereas the “hard” collision related to the formation of Rodinia generated ca. 12% of juvenile crustal materials. More juvenile materials generated in the “soft” collision may be attributed to complete detachment and sinking of a oceanic slab.  相似文献   

20.
为了探讨华北板块北缘晚古生代的隆升历史和古亚洲洋的闭合过程,利用碎屑岩的锆石U-Pb年代学、Hf同位素和锆石微量元素组成对北京周口店太平山南坡晚石炭世-早二叠世地层进行物源分析,并判定源区的大地构造背景.5件样品的碎屑锆石U-Pb年龄主要分布在3个时代:显生宙（285~425 Ma）、古元古代（1 700~2 450 Ma）和新太古代（2 500~2 747 Ma）.前寒武纪的锆石年龄主要集中在2.5 Ga和1.8 Ga,与华北克拉通的前寒武纪基底岩石相似.显生宙的锆石年龄主要集中在308~297 Ma,最年轻的峰值年龄在299~291 Ma,在误差范围内与地层沉积年龄相似,因此这些最年轻的碎屑锆石属于早二叠世同沉积锆石.29颗同沉积锆石的Hf同位素结果显示,原始176Hf/177Hf比值介于0.282 021~0.282 318,εHf（t）值介于-20.1~-9.6.显生宙锆石的年龄谱特征以及Hf同位素组成与内蒙古隆起同期的岩浆锆石特征十分相似,因此显生宙碎屑锆石可能来源于内蒙古隆起,并伴随有少量来自北侧兴蒙造山带南部的早古生代岛弧碎屑的输入.二叠纪同沉积锆石的微量元素特征表明锆石结晶的岩浆源区具有大陆岛弧的构造属性.上述数据表明:（1）华北板块北缘在晚石炭世-早二叠世为活动大陆边缘;（2）晚古生代古亚洲洋向华北北缘的持续俯冲消减导致了内蒙古隆起的快速隆升;（3）古亚洲洋闭合的时间应晚于早二叠世.   相似文献   

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