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Here new evidence of the isotope geochronology and the geochemistry from the Yuanmou-Miyi complexes reveal the Precambrian tectono-magmatism geodynamic process in the study area. The Yangtze Block basement with 1.81- ~1.77 Ga and negative εHf(t) values of −7.8 to −0.7 corresponded to the assembly of the Columbia-supercontinent. However, the rifting magmatic event of ~ 1.70 Ga, which caused the continental crust extension-thinning in the study area, may exert influence on the subduction-magmatism in the Grenvillian period. The Yuanmou-Miyi complexes of 1.19- ~1.00 Ga are characterized by (La/Sm)N＞1, depletion in HFSEs, negative anomalies of Nb-Ta, and enrichment of LILEs, which show a genetic link with the subduction-magmatism. The temporal tendency that the magmatism from Yuanmou to Miyi gradually became younger, may be responsible for the subducting direction. The subduction caused the reactivation of the Anninghe-Lvzhijiag fault zone, and created the rupture windows of the subduction slab, leading to upwelling of the deep magma. These granitoids were derived from the partial melting of the mantle wedge, while the small-scale gabbro dikes intruded into the granitoids were likely spillover products from the asthenosphere mantle melts through the rupture windows. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt (CAOB) contains many microblocks, and their Precambrian basement origin and crustal evolution are disputed. This study focuses on the geochronology of metamorphic complexes from the Shuangsheng area, southeastern Inner Mongolia. Combined with regional geological data, we discuss the tectonic attribution of the metamorphic complexes and provide geochronological evidence for regional crustal evolution and tectonic affinity. From the Shuangsheng area, the Pingandi metamorphic complex and Baolige metamorphic complex are composed of greenschist–amphibolite facies metamorphic intrusive rocks and metamorphic supracrustal rocks, mainly including tremolite rock, chlorite rock, actinolitite (gneissic) plagioamphibolite, actinolitite schist, marble, and feldspar quartzite. Zircon U-Pb geochronology analysis of actinolitite and plagioamphibolite suggests that there were two intermediate-acid magmatic events (2500–2400 Ma and 2050–1980 Ma), one basic magmatic event (1860 Ma), and three metamorphic events (1930–1890 Ma, 1815–1785 Ma and 1740–1730 Ma). Based on comparisons with the regional Precambrian chronological spectrum, geotectonically, Precambrian geological records from the Shuangsheng area should belong to the basement of the Bainaimiao Arc Terrane (BAT). Each segment of the BAT shows consistent Precambrian chronological frameworks, which indicates that the BAT has a unitive Precambrian basement. The basement underwent crustal growth during 3.0–2.4 Ga and 2.1–1.4 Ga and multistage crustal reconstruction between 2.75 and 0.55 Ga, which is different from the crustal evolution of the North China Craton, northeast Gondwana continent, and Tarim Craton. In the early Palaeozoic, the Precambrian material provided varying source contributions to the arc crust of the BAT through crust–mantle interaction. [ABSTRACT FROM AUTHOR]

The tectonic setting of the Jiamusi–Khanka Massif in the eastern sector of the Central Asian Orogenic Belt (CAOB) in NE China is still highly controversial. This review considers all existing data to evaluate the origin of the Jiamusi–Khanka Massif. The Precambrian basement in the Jiamusi–Khanka Massif is dominated by the Neoproterozoic orthogneisses (898–891 and 757–751 Ma), the Mashan Complex (peak metamorphism at 530–500 Ma), and syntectonically deformed early Palaeozoic granitoids (530–484 Ma) related to the metamorphism of the Mashan Complex. The Mashan Complex reveals a clockwise orogen-style P–T path with peak conditions of 850–870°C/8–9 kbar followed by isothermal decompression. It was intruded by syn- (530–500 Ma) and post-tectonic (490–476 Ma) granitic rocks. The Jiamusi–Khanka Massif cannot be directly derived from the North China, South China, or Tarim cratons. Instead, it may have originated in the Siberian Craton and formed once part of the Altai-Sayan and Baikal orogens at ~500 Ma. For the Jiamusi Massif, we developed a plate tectonic model, and relate the final granulite facies metamorphism to slab break-off after consumption of a branch of the Palaeo-Asian Ocean. [ABSTRACT FROM AUTHOR]

The Tarim Craton (or Tarim Block) is geographically located in the Northwest of China and tectonically between the Central Asian Orogenic Belt (CAOB) to the north and the Tethys to the south, which underwent a secular Precambrian evolution history from Ecoarchaean to Ediacaran. Owing to its marginal positions both in the Columbia (or Nuna) and Rodinia supercontinent configurations, it could play a key role in understanding the geodynamics of the assembly and break-up of the Precambrian supercontinents. This paper aims to present a critical review on the comprehensive synthesis of the Tarim Craton, detailing the Precambrian evolution processes and discussing its coupling with the Precambrian supercontinents. The Tarim Craton shows a typical plateform-like and double-layered structure, comprising the pre-middle Cryogenian basement with the middle Cryogenian-Ediacaran cover sequence. During its protracted basement evolution, diverse types and multiple stages of pre-Ediacaran intrusions were emplaced in the basement. Since Pleoproterozoic to early Cryogenian, crust reworking, rather than juvenile crust addition, played a key role in the final cratonization of its basement. Despite the final cratonization of the Tarim completed in the middle Cryogenian, both the bulk-rock Sm-Nd and zircon Lu-Hf isotope compositions demonstrated that its crust mainly formed in Archaean. Its characteristics of sedimentary features, metamorphic temporal-spatial architecture, the multiple phases and diverse types of intrusions reveal that the Tarim Craton is possibly composed of two main terranes with distinct features, i.e. the Northern Tarim Terrane (NTT) and the Southern Tarim Terrane (STT). It has been suggested that the STT could be a continental fragment that has drifted from West Africa, while the NTT shows a significant affinity with the India–North China Craton before Calymmian. Both were involved in the assembly and break-up of the Columbia supercontinent, and amalgamated during the assembly of the Rodinia. At the same time, it docked at the northern margin of Australia in the middle Cryogenian. Nevertheless, the subduction along the northern margin of the NTT continued at least until ca. 760 Ma. The voluminous 820–760 Ma diverse-type intrusions in the NTT have been ascribed to a genetic relation in the interaction between the circum-Rodinia subduction and the Rodinian superplume. The upwelling of the Rodinian superplume terminated the long-lasting subduction along the northern margin of the Tarim Craton. Since 740 Ma, being consistent with the break-up of the Rodinia, the Tarim Craton started drifting from the Rodinia supercontinent. The transition from signature to the passive continental margin of the middle Cryogenian-Ediacaran (for its cover sequences) rules out the possibility of the circum subduction along its northern margin lasting to early Palaeozoic. Additionally, with the Rodinia breaking up into the assembly of the Gondwana, the Tarim Craton, together with other continents in Eastern Asia, had docked at the margin of the Eastern Gondwana in early Palaeozoic. [ABSTRACT FROM AUTHOR]

The Eocene Challis-Kamloops volcanic belt, which runs through the interior of British Columbia and northwest United States for >2, 000 km, developed within a short time interval from ~55 to ~45 Ma. Volcanic rocks of the belt are discontinuously distributed in a series of grabens, half-grabens and calderas. Although predominantly composed of high- to medium-K calc-alkaline rocks that are typical of continental arcs, they were extruded during a time of regional transtensional tectonics in the Cordilleran orogen, which also led to the contemporaneous emplacement of Precambrian metamorphic core complexes near the belt. Their relative contents in Y, Nb, La, Sm, Gd, Yb and Ta suggest that the magmas were formed in relation to slab-failure (slab break-off). Initial Sr and Nd isotopic ratios and neodymium depleted mantle model ages indicate that the northern and southern parts of the belt had isotopically distinct lithospheric mantle sources with, respectively, Palaeozoic to Mesozoic and Precambrian model ages. As all rocks of the belt share common tectonic and petrogenetic settings, greater contents in incompatible trace elements in rocks from the southern part of the belt suggest that the Precambrian sources were more metasomatically enriched in these elements than the Phanerozoic sources. [ABSTRACT FROM AUTHOR]

Episodic Neoproterozoic magmatic suites in the Altyn Tagh, NW China, are thought to be related break-up of the Rodinia supercontinent. These suites resulted from long-term extension of the lithosphere during orogenic collapse and subsequent rifting. New geochemical and U-Pb-Hf zircon data indicate that the 825 Ma Hongliugou granite displays the characteristics of A-type granites derived from a juvenile source. Gneissic granites (780–760 Ma) are characterized by high Rb (>200 × 10−6), low Zr/Hf (23.28–29.28) and low Nb/Ta (4.20–12.99) typical of highly fractionated granites. A diabase exhibits trace element patterns between OIB and E-MORB which we infer as derivation from an enriched asthenosphere mantle. Combined with previous reported ca. 850 Ma and 620 Ma extension-related magmatism in this region, we interpreted the Altyn Tagh sequences as part of a lengthy supercontinental break-up process. Neoproterozoic magmatism in the Altyn Tagh is broadly correlative with magmatism in East Kunlun and North Qaidam orogenic belts around the Qaidam basin. Collectively, the Qaidam block, exposed mainly in the Altyn Tagh, East Kunlun and North Qaidam, represents a succession of accretionary orogenic, postorogenic, and within plate magmatism between 1200 and 620 Ma. The similarity in age of magmatism and metamorphism in the Altyn Tagh-North Qaidam-East Kunlun regions indicate that these Precambrian sequences collectively represent the basement of Qaidam block. [ABSTRACT FROM AUTHOR]

The growth mechanisms of the southeastern Tibetan Plateau are debated between models of Oligocene shortening and lateral extrusion of coherent crustal blocks versus Late Miocene flow of low-viscosity lower crust. To test these models, we examine brittle deformation of the north-striking Anninghe fault, which has been acting as a left-lateral strike-slip fault since Late Miocene time, using structural and bedrock low-temperature thermochronologic methods. Different from previous interpretations of Late Miocene strike-slip motion, our structural observations indicate westward contractional dip-slip along the southern segment of the fault. New zircon and apatite (U-Th)/He thermochronologic data along a vertical profile of Precambrian volcanoclastic cover both sides of the Anninghe fault. The age-elevation relationships and inverse thermal modelling suggest a phase of Oligocene-Early Miocene (~24-18 Ma) differential rock exhumation and cooling across the fault, with a mean erosion rate of ~0.30 ± 0.12 km/m.y. and ~0.007 ± 0.007 km/m.y. in the hanging wall and footwall, respectively. Consistent with the structural observations, the higher rate of rock exhumation in the hanging wall indicates an Oligocene-Early Miocene phase of west-verging reverse faulting. Combined with previously published data from adjacent sites, we suggest that the Anninghe fault has experienced a tectonic transition from Oligocene-Early Miocene east-west contraction to Late Miocene strike-slip motion. The early to Mid-Cenozoic crustal shortening contributed to the uplift of the southeastern Tibetan Plateau, supporting the crustal shortening and extrusion model. [ABSTRACT FROM AUTHOR]

The Meseta Goaïda magmatism, which occurs as gabbro, dolerite and rhyolitic intrusions in the Neoproterozoic basement and Cambrian platform sedimentary series of the Moroccan Hercynian orogen, has been ascribed to the Variscan orogenesis in the late Palaeozoic. Here, we provide new LA–ICP-MS U-Pb zircon ages – ranging from c. 519 Ma to c. 479 Ma – of this magmatism that reveal, for the first time in the Moroccan Central Meseta, the existence of early Cambrian to early Ordovician bimodal magmatism. Inherited zircons in these magmatic rocks yield dates that range from c. 1.2 to 1.0 Ga and c. 0.63 to 0.50 Ga. This inheritance suggests provenance from Precambrian crustal sources in the Cadomian‒Pan-African of the NW margin of the West African Craton, which is buried beneath the currently exposed Paleozoic Moroccan Meseta. The affinity of this early Palaeozoic magmatism is mainly tholeiite to transitional for the mafic rocks and high-K calc-alkaline for the silicic rocks. The Cambrian–Ordovician age and varying parental magma signature – as shown by trace element and Sr-Nd-Pb isotopic data from this magmatism and its Neoproterozoic granitoid basement rocks – indicate that the Moroccan Meseta early-Paleozoic magmatism might be associated with the weakening of the continental lithosphere during the early stages of rifting during the Cambrian–Ordovician along the NW Gondwana margin. This is supported by the presence of inherited zircons derived from reworking of the Precambrian crust in the early-Palaeozoic magmas. [ABSTRACT FROM AUTHOR]

The study of Precambrian tectonics is an intricate task, demanding a holistic approach to take an accurate view of geologic history. Here we attempt to set up the overview of an Orosirian-Statherian continental arc in the northwestern Amazon Craton, the Cauaburi Belt. Field relations, petrological, geochemical, and geochronological data of calc-alkaline metagranitoids, high-grade metasedimentary rocks, and peraluminous metasyenogranites yielded new interpretations about its tectonic evolution. The record of intense and episodic calc-alkaline magmatism between ca. 1805 and 1759 Ma, assign to the Cauaburi Complex, with field evidence of magma mixing and lodgement in a compressional tectonic regime, suggest a continental arc as the tectonic setting. During the magmatic lulls, deformation and metamorphism increase, culminating with the partial fusion of the high-grade metasedimentary rocks of the Taiuaçu-Cauera Complex. This succession composes the precursor paleobasin, presenting maximum and minimum depositional ages of 1819 and 1794 Ma, and was a relevant source for the calc-alkaline magmatism. The geochronological record of a low-volume production of peraluminous crustal rocks (Igarapé Tocandira Granite), with crystallization age at ca. 1791 Ma and metamorphic age at ca. 1771 Ma, also highlights the time and effect of the magmatic lulls. The Cauaburi Belt structural framework follows a general E-W to ENE-WSW trend, expressed in the Paleoproterozoic rocks as syn-magmatic and solid-state deformation fabrics. Assuming that Columbia Supercontinent nucleus assembled in the late Orosirian, we interpret that this coeval continental arc developed at its border and followed a north-south shortening direction, at current orientation. [ABSTRACT FROM AUTHOR]

Early Precambrian geological events in the Zhongtiao Mountain of China provide important clues for understanding Neoarchean to Paleoproterozoic crustal evolution in the southern segment of North China Craton (NCC). Based on analysis and compare of the component features, spatial and temporal distribution and geochemical features of the crystalline basements in the Zhongtiao Mountain with its surroundings, we identify five distinct episodes of the early Precambrian geological events in the Zhongtiao Mountain as: ca. 2.72–2.61 Ga, ca. 2.56–2.44 Ga, ca. 2.35–2.20 Ga, ca. 2.20–2.0 Ga and ca. 1.97–1.85 Ga. The ca. 2.72–2.61 Ga magmatism mainly involved a significant period of crustal growth with some crustal reworking. These ca. 2.72–2.70 Ga TTG gneisses were produced by partial melting of a subducted oceanic slab, and the ca. 2.62–2.61 Ga granitic rocks were originated from the partial melting of a protolith of juvenile origin (such as the pre-existing ca. 2.72–2.70 Ga TTG suite) together with its intermixing with mantle material. Together with other ca. 2.90–2.61 Ga old rocks in the southern segment of NCC, they made up the 'Southern Ancient Terrane'. The ca. 2.56–2.44 Ga magmatism represented a major crustal reworking (melting) event with some juvenile addition in the Zhongtiao Mountain, and the formation of TTGs and K-rich granitic rocks during ca. 2.56–2.44 Ga marked a tectono-magmatic event resulting in stabilization of the NCC. The ca. 2.35–2.20 Ga magmatic activities reflected another stage of crustal extension and reworking of the basement rocks. The ca. 2.20–2.0 Ga volcanic-sedimentary rocks, A-type granites, and metamorphic basic volcanic rocks indicated that the stabilized blocks in the NCC still experienced the stage of extension. The ca. 1.97–1.85 Ga magmatic and metamorphic events formed in a phase of compressional deformation and led to the reworking of pre-existed old rocks. [ABSTRACT FROM AUTHOR]

Evolving atmospheric oxygen levels during the early Earth history had a profound impact on Earth's surface processes, especially on the mineralization of redox-sensitive elements such as iron (Fe) and Uranium (U). Here we present a review of the effect of the Great Oxidation Event (GOE) that started at ~2.44 Ga on the style of Uranium mineralization with reference to Indian uranium occurrences. GOE was responsible for the initiation of intense chemical oxidative weathering of the Neoarchean U-rich K-granites mobilizing U from the source rocks in the U6+ soluble state. By 2.32 Ga, anoxic/euxinic conditions in the oceans developed on a global scale mainly due to the bacterial sulphate reduction that was triggered by enhanced sulphate concentrations in the ocean caused by the GOE. Such a development of anoxic/euxinic conditions acted as a sink for the hexavalent U by reducing it to tetravalent state and its deposition on a large scale in the strata of post-2.0 Ga age. Majority of Uranium deposits of India are hosted in the Proterozoic rock formations unlike the global pattern, where the Phanerozoic strata are more prominent. Among the uranium reserves that occur in the Precambrian sequences of India, the mineralization during the 1.9 to 1.6 Ga time window constitute ~75% of the total. In India, the Archaean U occurrence is exemplified by the Bababudan quartz pebble conglomerates (~2.72 Ga) hosting detrital uraninite, while the Proterozoic period witnessed a marked change with most of the U deposits being of redox-controlled-type in sedimentary formations. A model is proposed to explain such an enrichment in Uranium reserves among the Proterozoic strata of India. It appears that the emplacement of large ion lithophile element (LILE)-enriched granites, the onset of GOE and ensuing oceanic anoxic conditions played a major role in controlling the Uranium mineralization of the late Paleoproterozoic in the Indian scenario. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Palaeokarsts are rarely preserved and recognized from Precambrian strata. However, a Mesoproterozoic palaeokarst was recently discovered on the top of the Tuanshanzi Formation in Xingcheng, Liaoning Province, China. This palaeokarst recorded karstification fissures, three types of breccias and unique vadose filling. Four factors: no bedding fillings, vadose cements, restricted palaeokarst development, and the overlying beds without involved any karstification, supported this palaeokarst occurred before the deposition of the Dahongyu Formation. Relative sea-level changes and tectonic movement provided the essential external cause for this palaeokarst, which revealed the hiatus between the Dahongyu Formation and the Tuanshanzi Formation in the Yan-Liao Aulacogen of the North China Craton. This finding was significant and valuable for discussing the 'Xingcheng Movement' and unconformity contact relationships between the two formations observed around the basin. As the palaeokarst did not extend to the interior of the basin and the unconformity occurred mainly in the margins of basin, the significance of them is always underestimated. Nevertheless, this palaeokarst and other sedimentary features could represent an apparent transition of Yan-Liao Aulacogen basin evolved from rift to depression under the background of Supercontinent Columbia breakup. [ABSTRACT FROM AUTHOR]

The Nanling range (Nanling) is characterized by intense and widespread Mesozoic magmatism related large-scale W-Sn mineralization. A summary of geochemistry, geochronology, and petrogenesis for the W-Sn-bearing granites has been carried out in this study. A series of rock- and ore-forming ages in Nanling indicate that the W-Sn mineralization is closely related to the Early Yanshanian granitic magmatism both in temporal and spatial dimensions (165-150 Ma). Geochemical features show that both of the W- and Sn-bearing granites, which mainly belong to highly fractionated I-type granites with a few A-type granites, are characterized by high contents of SiO2, Al2O3, Na2O, and K2O; enrichment in Rb, Th, U, Zr, Hf, and REE; depletion in Sr, Ba, P, and Ti; and high ratios of A/CNK. Furthermore, the different Sr-Nd-Hf isotopic compositions indicate that they are mainly originated from the partial melting of the Precambrian basement rocks of the Cathaysia Block at low oxygen fugacity, and the estimated temperatures for the tungsten-bearing and tin-bearing granites are ca. 700°C and ca. 800°C, respectively. The model of the mantle-crust interaction exhibits that different percentages of mantle-derived magma were likely involved in the generation of the tin-bearing granites and tungsten-bearing granites. In combination with previous studies, we propose that these granites in Nanling were emplaced in an extensional setting, as a response to the break-off and roll-back of the subducted Palaeo-Pacific Plate during 175-150 Ma. [ABSTRACT FROM AUTHOR]

The Sawtooth Metamorphic Complex (SMC) of central Idaho contains exposures of metasupracrustal rocks, in a crucial location between the Archaean Wyoming craton to the east and the adjacent Mesozoic terranes to the west, that provide constraints on Precambrian crustal evolution in the northwestern United States. Mineral textures, whole-rock geochemistry, and thermobarometry of calc-silicate gneisses record multiple stages of crustal evolution, including protolith deposition, burial and multiple metamorphic and deformational overprints. Whole-rock signatures are consistent with derivation from post-Archaean, continental sources that have undergone sedimentary maturation and recycling typical of clastic sedimentation in passive-margin environments and with a metamorphosed sequence of calcareous sandstones and marls, containing varying proportions of clay and quartzo-feldspathic detritus. The sandstone-to-marl continuum may reflect a shallow-to-deep water transition in the depositional environment of the calc-silicate protoliths. Two metamorphic events and three deformational events are preserved. The assemblage clinopyroxene + quartz + plagioclase + K-feldspar + rutile represents peak metamorphic conditions (M1), estimated at 750–775°C with relatively oxidized metamorphic fluids, during development of D1a foliation. Deformation twinning in clinopyroxene records a widespread, high strain D1b event at high temperature. A second static thermal event (M2), associated with randomly oriented amphiboles overprinting M1 and D1b features, records conditions of ~550–725°C and H2O-rich fluids. Late-stage, brittle–ductile D2 deformation is characterized by mylonitic lenses of quartz, fractures within M1 clinopyroxenes that crosscut D1b deformation twins, and localized fracturing of M2 amphiboles. Geochemical and mineral chemical signatures of SMC calc-silicates preserve fingerprints of the original protolith through burial to mid-crustal conditions and high-grade metamorphism and suggest crustal thickening to about 20 km. The SMC may reflect rocks at depth beneath the Idaho batholith. These data, indicative of newly recognized post-Archaean terrain with passive-margin, continental sediments suggest that a continuous Cordilleran passive margin sequence may have extended along the western edge of Laurentia. [ABSTRACT FROM AUTHOR]

Late Jurassic to Early Cretaceous extensional structures are widespread in Northeast China and the eastern part of the Asian continent. The Yiwulüshan ductile detachment shear zone, the master ductile detachment zone of the Yiwulüshan metamorphic core complex (MCC), occurs in the northern North China Craton. This shear zone dips to the northwest on the western flank and to the southeast on the eastern flank of the MCC and consists of brittle faults, breccia, chloritized microbreccia, and ductile (mylonite) zones. The well-developed mylonitic foliation and stretching lineation are characterized by oriented minerals (quartz and feldspar) that exhibit ductile deformation, including undulose extinction, deformation bands, subgrain formations, and recrystallized grains. The shear indicators, such as asymmetric porphyroclasts, S-C fabrics, and shear bands, suggest consistent top-to-the-NW shear on both the western and eastern flanks of the MCC. Strain measurements using feldspar porphyroclasts show that the strain intensity (Es), Lode’s parameter (υ), and Flinn parameter (k) range from 0.46 to 1.03, −0.23 to 0.62, and 0.23 to 1.6, respectively. Kinematic vorticity (Wk) values, estimated by the Polar Mohr diagram and the C′ methods, range from 0.61 to 0.96, with an average of 0.80, for the mylonitic deformation, and from 0.24 to 0.53, with an average of 0.37, for extensional crenulation cleavage (ecc) domains. The kinematic vorticity values, together with the regional structural background, suggest the Yiwulüshan ductile detachment zone experienced simple-shear-dominated general shearing that formed the mylonitic fabric in the early stages of extension. Later in the deformation history, pure-shear-dominated general shearing dominated when ecc developed. Strain measurements and kinematic vorticity estimates indicate that the Yiwulüshan ductile detachment zone is a lengthening-thinning shear zone. It is proposed that simple-shear-dominated general shear developed during crustal extension and that pure-shear-dominated general shear is related to the upward flow of Precambrian basement and Jurassic plutons. [ABSTRACT FROM PUBLISHER]

In many Precambrian provinces, the understanding about the tectonic history is restrained by the limited exposure of rocks so that aerogeophysical data can provide information below the surface cover of sediments, soil, and water to build a tectonic model of the region. However, the tectonic evolution of cratons and shear zones is very complex due to scarce aerogeophysical and geological data. The integrated observation of geology, aerogammaspectrometry, and aeromagnetometry of the Brazilian Shield, states of Santa Catarina, Paraná, and southern São Paulo, is enhanced by a 2011 high-resolution aerogeophysical survey. The Ponta Grossa and Florianópolis dike swarms show two sets of linear high magnetic signal. Peralkaline–carbonatitic complexes are observed in all images, e.g. Jacupiranga, Tunas, and Anitápolis. Three main geotectonic provinces are apparent in the shield. The Dom Feliciano Belt has two domains in terms of radioelements K, Th, and U. This belt includes granitic rocks of the Florianópolis Batholith, Brusque Group schists, and Itajaí Basin of sedimentary and volcanic rocks. The Luís Alves Craton has mostly the Santa Catarina Granulitic Complex and other gneisses. The craton has patches of high emission rates and extends to the northeastern extreme of the studied area with a high-contrast magnetic signal in most of the unit. The Ribeira Belt also has high in gammaspectrometric images, although less homogeneous than the Dom Feliciano Belt. This belt contains granitic complexes, gneisses, and schists and has a low magnetic signal with patches of high analytical signal amplitude. Shear zones delimit different geotectonic units, but are also significant in the Ribeira Belt. The Luís Alves Craton is the most complex unit, as seen in ternary K + eTh + eU images, requiring the future discrimination of small features. This novel study of the Brazilian Shield based on new geophysical data supports the classification of the proposed main geotectonic units. [ABSTRACT FROM AUTHOR]

Mid-Neoproterozoic rift-related Tadong amphibolites (TDA) are situated in the junction of the East Kunlun Orogen (EKO) and the West Qinling Orogen (WQO) in western China, and have important significance in the break-up of the Supercontinent Rodinia. The mineral assemblage of the TDA exhibits amphibolite facies metamorphism, and the protolith is basic volcanic rocks. Here, we present a detailed laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U–Pb age and geochemical data of TDA. LA-ICP-MS U–Pb zircon age determination indicates that the basic volcanics formed at ca. 743–711 Ma. Geochemically, TDAs are characterized by low SiO2(46.06–50.18%), K2O (0.66–1.86%), and Mg#(40–45) and high TiO2(1.9–3.5%), and are attributed to tholeiite basalts. Their chondrite-normalized REE patterns are characterized by moderate enrichments in LREEs (LREE/HREE = 4.98–5.51) with insignificant Eu anomalies (δEu = 0.99–1.12). The primitive mantle-normalized trace element diagrams are characterized by pronounced enrichment of high-field-strength elements (HFSEs, e.g. REE, Nb, Ta, Zr, Hf) with slightly positive anomalies of Ti, which is different from the subduction zone basalts and normal mid-ocean ridge basalts (NMORBs), but similar to the ocean-island basalts (OIBs) and Emeishan continental flood basalts (ECFBs), resembling the features of an OIB-like mantle source. Most samples exhibit high Nb/Ta (16.6–17.4), Nb/La (0.70–0.94), and positive ΔNb (ΔNb = 1.74 + log (Nb/Y) − 1.92*log (Zr/Y)) values. These geochemical features suggest that the Tadong basaltic rocks were most likely derived from an OIB-like mantle source and were the products of a lower degree partial melting of garnet lherzolite. Along with the tectonic discrimination diagrams, it is further inferred that these rocks were formed in a continental rifting setting. These results from our research confirm the existence of continental rifting in the junction of the EKO and the WQO in the mid-late Neoproterozoic, implying that the rifting is a response to the break-up of the Supercontinent Rodinia. [ABSTRACT FROM AUTHOR]

An Archaean continent ‘SIWA’, an acronym for South India–Western Australia, comprising the Bastar–Dharwar craton, the Yilgarn craton, the Napier Complex, and the Vestfold Hills has been identified from palaeomagnetic and spatio-temporal data. This assembly was dispersed in three phases with the development of the proto-Indian ocean. The first and second events ~2350 and ~2000 Ma were related to the separation of the Yilgarn craton and the Napier Complex, respectively, to form a proto-Indo-Antarctic ocean and the Cuddapah basin. The proto-ocean was closed ~1650 Ma by the collision of the Lambert Terrane of East Antarctica and the Bastar–Dharwar craton. This collision, associated with ultra-high temperature (UHT) granulite facies metamorphism, is identified in the southern domain of the Eastern Ghats and the Oygardens domain of East Antarctica. The third extensional event between 1500 and 1200 Ma was associated with the separation of the Vestfold Hills block and a second phase of opening of the proto-Indian ocean, and the development of a series of basins on the western side of the Eastern Ghats (the Chhatisgarh, Khariar, Ampani, Indravati, and Sabari basins). The closing of this ocean basin during the Eastern Ghats–Rayner orogeny at ~950 Ma was related to the amalgamation of India and East Antarctica to form the supercontinent Rodinia. During the Neoproterozoic, this part of Rodinia was involved in orogenic collapse/extension and deposition of the Sodruzhesvo Group. The Pan-African Prydz Bay orogeny at ~550 Ma caused the closing of the basin to form East Gondwanaland. [ABSTRACT FROM AUTHOR]

Recrystallization of zircons under the influence of fluids was studied using examples from Precambrian rocks (microcline granites, metasedimentary, and mafic rocks) of the Kola Peninsula. All zircon crystals showed complex internal textures visible by cathodoluminescence and backscattered electron (BSE) imaging. Detailed mineralogical and geochemical studies with subsequent secondary ion mass spectrometer U–Pb dating of different zircon domains show that secondary texture formation can be interpreted in terms of metasomatic replacement of zircon crystals on the base of crystallogenetic experimental models. Mechanisms of zircon replacement and interpretation of U–Pb ages for secondary zircon domains are dependent on the degree of damage of the zircon structure and the fluid composition. The recrystallization of metamict zircon without additional supply of new zircon substance (Zr, SiO2) goes with the dissolution of amorphous domains and precipitation of new polycrystalline zircon, which preserves the U–Pb initial age, but loses radiogenic lead, and the lower intercept of Discordia lines with the Concordia curve determines the time of fluid influence. The recrystallization of metamict zircon or crystalline zircon with high contents of impurities with additional supply of Si and Zr forms monocrystalline replacements. Dissolution of primary zircon is accompanied by growth of new zircon domains differing in the composition of isomorphic impurities and zones of transitional composition, whose ages have no geological sense. The study is of particular importance for zircons from Precambrian rocks with long and complex histories. [ABSTRACT FROM AUTHOR]

The depositional age of the Wadi Zaghra metasediments (Zaghra Formation) of the Sa’al-Zaghra metamorphic complex (Sinai) in the Arabian–Nubian Shield (ANS) has been constrained by LA-ICP-MS dating of zircons from (1) metaconglomerate granitoid clasts, (2) the metaconglomerate matrix, (3) biotite-schist, and (4) diorites and granites intruding the metasediments. Three granitoid boulders from a metadiamictite of the Zaghra Formation give crystallization ages of 651 ± 3, 647 ± 3, and 640 ± 4 Ma respectively. Detrital zircon age populations from laminated siltsones and conglomerate matrix vary somewhat with stratigraphic position, a variation best explained by changes in depositional environment and source area with time. Three distinct zircon age populations are identified in the matrix; at ca. 1000, 750, and 630 Ma, with less pronounced peaks at ~780 and ~800 Ma. The youngest detrital zircons indicate deposition after 630–625 Ma. The emplacement age of the post-depositional intrusives is enigmatic due to a large population of xenocrystic zircons, but is interpreted to be as old as ca. 615 Ma. This implies deposition and deformation of the Zaghra Formation in the time interval 625–615 Ma, thus older than the inferred depositional age of the Hammamat deposits in the Eastern Desert of Egypt, which is commonly correlated. The inferred depositional age is similar to the deposits in nearby Rutig Basin, where conglomerates were deposited in two pulses; at ca. 620–610 and 600–590 Ma. The appearance of late Mesoproterozoic (ca. 1.1 to –1.0 Ga) detrital zircons in the fine-grained laminated matrix facies of the Zaghra Formation demonstrates that ~1.0 Ga basement rocks (Sa’al terrane?) were exposed when Zaghra basin sediments were being deposited. [ABSTRACT FROM AUTHOR]

Northwestern Fujian contains abundant well-studied Precambrian basement, and was a composite terrane in Cathaysia during the Neoproterozoic; however, its magmatic activity, petrogenesis, and tectonic evolution remain controversial. This article focuses on the geochronology and geochemistry of the Neoproterozoic Group in order to resolve the above problems. We provide new SHRIMP U-Pb zircon dating for the Mamianshan Group: 851.9 ± 9.2 to 825.5 ± 9.8 Ma for the Longbeixi Formation, 796.5 ± 9.3 Ma for the Dongyan Formation, and 756.2 ± 7.2 Ma for the Daling Formation. These ages document the existence of Neoproterozoic magmatism in the northwestern Cathaysia Block. Dongyan Nd-Sr isotopic data show that mafic amphibolite schists, mafic greenschists, and quartzofeldspathic schists were derived from a more depleted mantle (initial εNd˜ +5.5 and87Sr/86Sr ratio 0.703409643), a mixture of depleted mantle and crustal components (initial εNd˜ −1 and87Sr/86Sr ratio 0.702045282–0.704147714), and late Palaeoproterozoic continental crustal materials (initial εNd< −1 and87Sr/86Sr ratio 0.71083603), respectively. These new data, together with previous studies, suggest a bi-subduction-collision orogenic model for the Neoproterozoic evolution of the Yangtze and Cathaysia blocks. Our plate tectonic scenario involves earlier NW-dipping subduction during 1.0 Ga–860 Ma along the southeastern margin of the Yangtze Block and later NW-dipping subduction near the northwestern margin of the Cathaysia Block starting at ca. 850 Ma. The 796.5 ± 9.3 Ma age of the volcanic Dongyan Formation suggests that the final assembly of the Yangtze and Cathaysia blocks probably occurred after ca. 800 Ma. The 756.2 ± 7.2 Ma age of the Daling Formation indicates that post-orogenic extensional magmatism took place after 800 Ma along the northwestern margin of Cathaysia. [ABSTRACT FROM AUTHOR]

The location of the suture zone between the South China and Indochina blocks in northwest Vietnam has been under debate for decades. Generally, the boundary between these blocks has been placed along (1) the Ailaoshan–Red River zone or (2) the Song Ma zone. The Sin Quyen Formation, lying between these zones, was previously regarded as a Palaeo- and Mesoproterozoic sequence. It comprises its provenance and tectonic affinity. We analysed detrital zircons from two paragneisses and one migmatite of the Sin Quyen Formation employing laser ablation inductively coupled plasma mass spectrometry U–Pb dating techniques. U–Pb ages of these zircons show three main periods of zircon formation: ∼2.7–3.0, ∼2.2–2.5, and ∼1.8 Ga, suggesting that Sin Quyen rocks were mainly derived from Palaeoproterozoic and Archaean basement units. Inasmuch as the South China basement comprises rocks of similar ages, we conclude that the Sin Quyen Formation belongs to that block. Our new data strengthen the view that the suture between the South China and Indochina blocks is located within the Song Ma zone. In addition, zircons with U–Pb ages >3.0 thousand million years represent the oldest minerals reported in northwest Vietnam so far, indicating the existence of Mesoarchaean crustal remnants in this region. [ABSTRACT FROM AUTHOR]