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High Ba-Sr granites are geochemically distinct from the more familiar I-, S- and A-types (of igneous, sedimentary or anorogenic/anhydrous/alkaline parentage), in particular by their lack of depletion in Ba and Sr relative to other large-ion lithophile elements (LILE). These differences are sufficient enough to indicate different petrogenetic processes which are still the subject of considerable debate. High Ba-Sr plutons from the classic Caledonian type location in NW Scotland show a range of elemental and isotopic enrichment, ideal for novel petrogenetic investigations such as the application of "non-traditional" stable isotope systems. Two directly comparable plutons have been analysed for Ba and Mg isotopes, from either end of the range of enrichment. Barium isotopes (δ 138/134Ba values of −0.05 to +0.23 ‰ in the relatively "depleted" Strontian pluton and −0.19 to +0.03 ‰ in the enriched Rogart comparator) overlap normal mantle values but extend to lighter compositions, consistent with addition of up to 5 % pelagic sediment that has incorporated variable amounts of biogenic barite. Magnesium isotopes (δ26Mg values of −0.30 to −0.25 ‰ versus −0.42 to −0.23 ‰ in Strontian and Rogart, respectively) lie largely within the normal mantle range, with two light outliers possibly indicative of carbonate involvement but for which fractional crystallization cannot be excluded. Associated relationships between fluid-mobile and melt-mobile elements suggest that sediment melting transfers the crustal isotope signature to a dominantly mantle source, itself variable between isotopically depleted mantle wedge and previously enriched lithospheric mantle. The combined Ba, Mg, O, Sr, and Nd isotope and elemental data are all consistent with a small percentage of pelagic sediment in a mantle source for high Ba-Sr granites, and this is sufficient to disguise these essentially mantle-derived rocks as reworked continental crust. First-order estimates suggest that some 10 % of granites worldwide may have high Ba-Sr character, although the proportion of these that represent largely juvenile origin is currently unknown. Nevertheless, as compositional equivalents of Archean sanukitoids, they may represent unrecognized mantle contributions to crustal growth over some 3 billion years of Earth history. [ABSTRACT FROM AUTHOR]

Understanding the composition, formation and evolution of the oldest continental crust is crucial for comprehending the mechanism and timing of crustal growth and differentiation on early Earth. However, the preservation of the ancient continental crust is limited due to extensive reworking by later tectonothermal events. In the Lulong area of eastern Hebei, abundant ca. 3.8–3.4 Ga detrital zircons of the fuchsite quartzite have been previously identified. Nonetheless, the provenance and Hf isotopic compositions of the fuchsite quartzite remain unclear. In this study, we present new detrital zircon ages and Hf isotopic for the fuchsite quartzite in the Lulong area to establish the timing of deposition, the provenance and the regional stratigraphic relationship. Zircon U-Pb dating indicates that the fuchsite quartzite was deposited between 3.3–3.1 Ga and most grains were sourced from the 3.8 Ga TTG gneisses and Paleoarchean magmas. Field investigations and regional correlations reveal that the fuchsite quartzite from the Lulong area is equivalent to that of the Caozhuang area. Zircon Hf isotopic data from eastern Hebei Province (Lulong and Caozhuang areas) and Anshan and Xinyang areas indicate that the oldest crustal growth event of North China Craton occurred in the Hadean. [ABSTRACT FROM AUTHOR]

• Minimal reworking of ancient crust in NAC during the Archean. • Long-lived, near-chondritic Hf isotope signatures from an isolated mantle source. • Primary melting leaves an infertile harzburgitic restite. • Fertile mantle is continuously sourced from an undepleted mantle reservoir. Generation of continental crust during early Earth was a vital step towards stabilizing the cratonic lithosphere. How and when this happened is, however, still poorly understood. Radiogenic isotope data from the oldest crust, and minerals therein, provide a unique insight into the timing and processes that operated during Earth's earliest evolution. Using combined zircon U-Pb, O and Lu-Hf isotope data from a glacial stream-sediment within the Isukasia (Isua) terrane of southern West Greenland, we argue for an isolated mantle source for the ca. 1.3 Ga of initial stages of crustal growth in the North Atlantic Craton. Zircon Hf isotope data between 3939 and 2950 Ma yield strikingly homogeneous, near chondritic signatures, with the few analyses that deviate slightly being indicative of ancient Pb-loss. Combined with published data from carefully selected and well-characterized ca. 3.9–2.6 Ga magmatic rocks of the NAC, almost no indications of reworking of older crust can be detected, but all strongly sub-chondritic data rather fall on Pb-loss trends tracing back to chondritic sources. This long-lived and near-chondritic signature with negligible influence from a strongly depleted mantle, or from un-radiogenic sources, argues for protracted crust separation from an isolated mantle source. We suggest a scenario whereby primary melting to produce basaltic and komatiitic crust leaves an infertile harzburgitic residue, unlikely to re-melt, that becomes sequestered as mantle lithosphere. Hence, domains of primordial fertile mantle are continuously sourced from an undepleted mantle reservoir. Combined with small wavelength mantle convection, a near-chondritic to mildly depleted regional mantle is retained into at least the Mesoarchean. [ABSTRACT FROM AUTHOR]

The Jiao-Liao-Ji belt (JLJB), in the Eastern Block of the North China Craton, is a major Paleoproterozoic orogen and underwent a complicated tectonic evolution during 2.2–1.8 Ga. The Liaohe Group, an important stratigraphic unit in the JLJB, is key to understanding the complex evolution of this belt. In this paper, we present new detrital zircon U–Pb ages and Hf isotope data for meta-sedimentary rocks from the Gaixian Formation in different areas of the JLJB, in addition to compiled data for other formations of the Liaohe Group, to establish the depositional age and source of detrital materials of the group. U–Pb age results show that the age ranges of zircons from the different samples are broadly similar. The youngest zircon group is ca. 2.06 Ga, and the youngest single-grain age is ca. 2.0 Ga, constraining the depositional age of the Gaixian Formation to between 2.0 Ga and the metamorphic age of ca. 1.9 Ga. The zircon age data indicate that the provenance was primarily Archaean basement of the Nangrim Block and Paleoproterozoic volcanic rocks of the Li'eryu Formation. On the basis of the new geochronological data and results from previous studies, it is inferred that the JLJB underwent a successive process of rifting–subduction–collision, with the different formations of the Liaohe Group being deposited in different stages from rift to passive continental margin and then to active continental margin. Zircon Hf isotope data from the JLJB and adjoining Longgang and Nangrim blocks indicate that a major crustal growth event occurred at 2.9–2.5 Ga, followed by crustal growth and intense recycling of ancient crust at ca. 2.2 Ga. [ABSTRACT FROM AUTHOR]

The Late Precambrian Wufoshan Group from the southern North China Craton (NCC) is significant for its contribution to our understanding of the Precambrian evolution of the NCC, which consists of the Lower Ma'anshan, Upper Ma'anshan, Puyu, Luotuopan, and Hejiazhai formations. Detrital zircon U–Pb ages and Lu–Hf isotopes from the Puyu, Luotuopan, and Hejiazhai formations are used in this study to constrain the depositional age and provenance of the Wufoshan Group and crustal evolution of the NCC. The Puyu Formation is characterized by detrital zircon U–Pb age populations of ~2.13 Ga and ~2.50 Ga, similar to the Lower–Upper Ma'anshan formations from the literature. The Luotuopan Formation exhibits age populations of 1.85–2.18 Ga and 2.28–2.98 Ga, with mainly negative εHf(t) values and scattered positive εHf(t) values clustering at two groups of 2.48–2.52 Ga and 2.64–2.97 Ga. The Hejiazhai Formation displays age populations of 0.98–2.00 Ga and 2.51–2.79 Ga with mainly positive εHf(t) values, whose depositional age is constrained as Neoproterozoic era by the youngest graphical detrital zircon age of 976 ± 20 Ma. Provenance studies indicate that the Mesoproterozoic Lower–Upper Ma'anshan and Puyu formations were sourced from the middle Trans‐North China Orogen (TNCO), while the Neoproterozoic Luotuopan and Hejiazhai formations were derived from the southern TNCO and the North Qinling Terrane, respectively. The clastic rock series in the southern NCC is divided into Luotuopan type and Hejiazhai type by detrital zircon U–Pb age pattern and Hf isotopic characteristics, suggesting Late Mesoarchean to Early Palaeoproterozoic (2.47–2.97 Ga) crustal growth in the interior NCC, and Late Palaeoproterozoic to Early Neoproterozoic (0.98–2.08 Ga) crustal growth in the marginal NCC. The crustal evolution of the NCC can be classified into three stages, namely >3.0 Ga continental nuclei generation, the Meso‐Neoarchean massive growth, and the Palaeo‐Mesoproterozoic interior reworking and marginal growth. [ABSTRACT FROM AUTHOR]

This paper presents new zircon U-Pb geochronological, Hf isotopic and whole-rock geochemical data for the granitic plutons in the Xing'an Massif, Northeast China, to constrain the Late Mesozoic tectonic evolution of the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean. The zircon U-Pb ages indicate that the granitoids emplaced during the Late Jurassic-Early Cretaceous. The granodiorites show an adakitic affinity with high Sr/Y ratios and low Yb (< 1.30 μg/g) contents. The monzogranites exhibit high SiO2, low MgO contents, enrichment in LILEs (Rb, K, and Th), and depletion in HSFEs (Ta, Nb, Zr, P, and Ti). Petrological and geochemical features of these monzogranites suggest that they are highly fractionated I-type granitoids. In addition, the zircon εHf(t) values and two-stage model ages (TDM2) are in the range of +2.6 to +8.1 and 669-1011 Ma, respectively, indicating that primary magma was generated by partial melting of juvenile lower-crustal materials, and there was a significant crustal growth in the Phanerozoic in the Northeast China. Combined with the coeval granitoids widely exposed in the Xing'an Massif, we conclude that the Late Jurassic magma in Northeast China was generated in an extensional setting related to the closure of the Mongol-Okhotsk Ocean, but the Early Cretaceous magma was related to the subduction of the Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The Central Tianshan microcontinent (CTM) in the southern Central Asian Orogenic Belt is characterized by Precambrian crustal basements and widespread Palaeozoic granitic rocks. However, the Palaeozoic tectonic process and associated crustal evolution of the CTM have not been well constrained. In this paper, we report whole‐rock geochemistry, zircon U–Pb ages, Hf isotopes, and trace elements for the Late Carboniferous granodiorite and monzogranite from the Hongliujingbei area of the eastern CTM. These data were further integrated with previously published whole‐rock geochemistry and zircon Hf isotopic data of the intensive Late Carboniferous (327–300 Ma) magmatic rocks in the CTM in order to gain more insights into the crustal and tectonic evolution of the CTM during the Late Carboniferous. LA‐ICP‐MS zircon U–Pb dating results indicate that the granodiorite and monzogranite from the Hongliujingbei area were emplaced at ~320 Ma. Their highly variable zircon εHf(t) values (−0.1 to +12.9) suggest that the magmas of these rocks were formed by the mixing of mantle‐ and crustal‐derived magmas. The Late Carboniferous magmatic rocks from the CTM, as a whole, show a wide range of zircon εHf(t) values (−3.7 to +13.4) and geochemical characteristics typical for magma evolution in an active continental margin setting. Therefore, we suggest that the Late Carboniferous magmatic rocks in the CTM were probably generated in a continental arc formed by the southward subduction of the North Tianshan Ocean Plate beneath the CTM, and their mostly depleted zircon Hf isotopic compositions indicate that juvenile crustal growth was a dominant process in the CTM during the Late Carboniferous. [ABSTRACT FROM AUTHOR]

This paper presents whole-rock Hf isotopic data for a suite of eclogite and garnet clinopyroxenite xenoliths hosted in the Early Cretaceous dioritic intrusions from the Xuzhou-Suzhou area along the southeastern margin of the Eastern Block of the North China Craton (NCC). Six of the eight studied xenolith samples plot significantly above the terrestrial Hf-Nd isotopic array and have εHf(0) value up to +60. All the samples define a well correlated 147Sm/144Nd-143Nd/144Nd age of 2 081 Ma, which is considered to record the granulite-facies metamorphism. In contrast, the Lu-Hf isotope system faithfully records the protolith information. The mineralogical assemblage, especially garnet and/or zircon (rutile to some extent) mainly controlled the decoupling of Hf-Nd isotope. The metamorphic modification on protolith characteristics and the differences in element mobility during metamorphism may also reinforce the observed decoupling between the Sm-Nd and Lu-Hf isotope systems; i.e., the absence of the correlations in εNd-εHf and also 87Sr/86Sr-143Nd/144Nd diagram. The Lu/Hf isochron age of 2 424 Ma is similar to the zircon age peak of the studied xenoliths and the dominant age of NCC basement, indicating that the igneous protolith has an affinity to the Archean basement of the NCC. Furthermore, the positive εHf(t) values at 2 500 Ma indicate a crustal growth event of 2 500 Ma in the NCC. [ABSTRACT FROM AUTHOR]

Detailed studies on U‐Pb ages and Hf isotope have been carried out in zircons from a carbonatite dyke associated with the Bayan Obo giant REE‐Nb‐Fe deposit, northern margin of the North China Craton (NCC), which provide insights into the plate tectonic in Paleoproterozoic. Analyses of small amounts of zircons extracted from a large sample of the Wu carbonatite dyke have yielded two ages of late Archaean and late Paleoproterozoic (with mean 207Pb/206Pb ages of 2521±25 Ma and 1921±14 Ma, respectively). Mineral inclusions in the zircon identified by Raman spectroscopy are all silicate minerals, and none of the zircon grains has the extremely high Th/U characteristic of carbonatite, which are consistent with crystallization of the zircon from silicate, and the zircon is suggested to be derived from trapped basement complex. Hf isotopes in the zircon from the studied carbonatite are different from grain to grain, suggesting the zircons were not all formed in one single process. Majority of ∊Hf(t) values are compatible with ancient crustal sources with limited juvenile component. The Hf data and their TDM2 values also suggest a juvenile continental growth in Paleoproterozoic during the period of 1940–1957 Ma. Our data demonstrate the major crustal growth during the Paleoproterozoic in the northern margin of the NCC, coeval with the assembly of the supercontinent Columbia, and provide insights into the plate tectonic of the NCC in Paleoproterozoic. [ABSTRACT FROM AUTHOR]

The Wuma magmatic suite is a group of large granite plutons and small diorite stocks in the Erguna Block, northeast China. These intrusions were emplaced along the Mongol–Okhotsk Suture Zone during the late Permian–early Triassic (253–248 Ma). Significant chemical and isotopic diversity within the granites and diorites suggests variable formation conditions and the involvement of multiple magmatic sources. The granitic intrusions are dominantly characterized by moderate to large, uniform light rare earth element enrichments and variable heavy rare earth element depletions. Zircons from the Wuma granites have εHf(t) values of −6.0 to 0.5 and TDM2 ages of 1.6–1.2 Ga, suggesting that these granitic magmas were generated by partial melting of Mesoproterozoic continental crust. The diorites are compositionally similar to Andean plutonic rocks with moderate light rare earth element and heavy rare earth element fractionations and likely formed by partial melting of a sediment‐metasomatized mantle. The Wuma intrusions belong to the high‐K calc‐alkaline series and are characterized by a significant enrichment in large‐ion lithophile elements (e.g., Rb, Ba, K, and U) and depletion of high‐field strength elements (e.g., Nb, Ta, and Ti). These geochemical characteristics are typical of subduction‐related magmatism, which can be linked to the southward subduction of the Mongol–Okhotsk oceanic plate. Combined with data from published studies, our Hf isotopic analyses indicate 4 main periods of crustal growth beneath the Erguna Block: Mesoarchean (3.0–2.8 Ga), Neoarchean–Paleoproterozoic (2.6–1.8 Ga), Meso‐ to Neoproterozoic (1.6–0.7 Ga), and Phanerozoic (mainly Ordovician and Late Triassic–Early Cretaceous). [ABSTRACT FROM AUTHOR]

This study reports the Sr-Nd isotopic composition of Indian shale samples of Archean to Recent age from different litho-units of Archean cratons and Proterozoic basins. Combining our measured Sr-Nd isotopic ratios with literature data, we calculated the Nd model ages of these shales and estimated the growth rate of the Indian continental crust, assuming that the Nd model age of clastic sediments represents an average of existing continental crustal sources. Unlike the widely variable 87Sr/86Sr ratio (0.76 ± 0.12, 1 S.d) and 87Rb/86Sr (2.53 ± 1.09) in the Indian shales, the average present-day 143Nd/144Nd (0.51170 ± 0.00028; ε Nd(0) = −18.8 ± 5.4) and 147Sm/144Nd (0.111 ± 0.009) isotopic ratios of Indian shales (n = 54) estimated in this study are comparable to that of the average global clastic sediments (mostly shales), North American shales, and Ganga River sediments. However, the Nd isotopic compositions of these shales (ε Nd(0) ≈ −19) are slightly different from those of the Upper Continental Crust (UCC), loess, and average river/aeolian particulates (ε Nd(0) ≈ −10), despite having similar Sm/Nd ratios (0.17−0.19). The striking uniformity of Sm/Nd ratios and 143Nd/144Nd in contemporary UCC-derived erosional products like the Ganga River sediments suggests that the isotopic compositions of average Indian shale might be representative of Indian UCC. Using a dimensionless erosional parameter K , the growth of the Indian shield was modeled considering the effect of preferential erosion, which leads to less contribution from older shield areas. We thus develop a two-stage crustal growth model that assumes K = 1 for the Archean (no erosion) and K = 6 for the post-Archean to Recent. Our results suggest that ∼80% of the continental crust was formed by the end of Archean with the mean age of the continent of 2.42 Ga, which is different from the Australian shield. This study represents a first-ever estimate of the growth rate of the Indian shield that manifests a rapid growth in the Archean and a long-term, slow and progressive growth in the post-Archean comprising short periods of rapid crustal growth, which could be correlated with the supercontinent cycle and mantle plume activities forming large igneous provinces (LIPs). • Average 143Nd/144Nd and Sm/Nd ratios of shales are representative of Indian crust. • Depleted mantle Nd model ages of shales constrain the growth of the Indian shield. • ∼80% of the crust formed by the end of Archean, with mean age of continent ∼2.4 Ga. • Growth of continental crust correlates with supercontinent cycles and plume activity. [ABSTRACT FROM AUTHOR]

There is a long-standing controversy regarding the tectonic division, composition and structure of the continental crust in the Da Hinggan Mountains and adjacent areas, which are mainly part of the southeastern Central Asian Orogenic Belt (CAOB). This paper approaches these issues via neodymium isotopic mapping of Paleozoic–Mesozoic (480 to 100 Ma) granitoids. On the basis of 943 published and 8 new whole-rock Nd isotopic data, the study area can be divided into four Nd isotopic provinces (I, II, III and IV). Province I (the youngest crust, Nd model ages (T DM ) = 0.8–0.2 Ga) is a remarkable region of Phanerozoic crustal growth, which may reflect a major zone for closures of the Paleo-Asian Ocean. Province II (slightly juvenile crust, T DM = 1.0–0.8 Ga), the largest Nd isotopic province in the southeastern CAOB, is considered to reflect the recycling of the initial crustal material produced during the early stage (Early Neoproterozoic) evolution of the Paleo-Asian Ocean. Province III (slightly old crust, T DM = 1.6–1.1 Ga) is characterized by ancient crustal blocks, such as the central Mongolian, Erguna, Dariganga and Hutag Uul–Xilinhot blocks, which represent micro-continents and Precambrian basements in the southeastern CAOB. Several parts of Province III are located along the northern margin of the North China Craton (NCC), which is interpreted as a destroyed cratonic margin during the Paleozoic and Mesozoic. Province IV (the oldest crust, T DM = 2.9–1.6 Ga) mainly occurs within the NCC and reflects its typical Precambrian nature. These mapping results indicate that the boundary between Provinces II and III (the northern margin of the NCC) along the Solonker–Xar Moron Fault can be regarded as the lithospheric boundary between the CAOB and NCC. Provinces I and II account for 20% and 44% of the area of the southeastern CAOB, respectively, and therefore the ratio of continental growth is 64% from the Neoproterozoic to the Mesozoic, which is typical for this part of the CAOB and distinguishes the CAOB from other Phanerozoic orogens in the world. [ABSTRACT FROM AUTHOR]

The combination of U Pb zircon ages with Hf-Sr-Pb isotopes of different intrusive and extrusive felsic and sedimentary rocks provides constraints on the petrogenetic evolution of the continental crust in the western Dharwar Craton, India. The oldest detrital zircon preserved formed at ∼3.6 Ga and represents a relic of the oldest felsic crustal material in the region. The dominant granitoid units of the western Dharwar Craton contain zircon grains with magmatic ages between 3.4 Ga and 3.0 Ga that indicate the formation of major felsic continental crust during this interval. Trace element abundances of the granitoids indicate that the oldest members of the intermediate to felsic suite derived by partial melting of mafic material at ∼3.6–3.4 Ga. The initial bulk rock Hf isotope compositions of these granitoids are consistent with their formation by melting of even older mafic material that was slightly enriched relative to the depleted mantle composition. This mafic and slightly enriched material formed by mantle melting at ∼ < 3.8 Ga. The Hf isotope compositions of individual zircon grains, obtained by two different analytical techniques (in-situ and complete dissolution followed by chromatographic separation) give evidence for the presence of such older mafic material (<3.8 Ga) that formed the immediate precursor of their granitoid host rocks. Such a mafic source for the granitoids is consistent with Pb Sr isotope systematics of these that shows no indication of Eoarchean enriched/evolved material in the western Dharwar Craton. The mafic source material of the granitoids thus represents an intermediate stage of crust formation that started after 3.8 Ga with the formation of mafic crust by mantle melting. The combined geochronological and isotopic constraints suggest that the Mesoarchean felsic crust of the Dharwar Craton formed by differentiation of melts derived from an amphibolite/eclogite source rock and included increasing contributions of reprocessed crustal material with time from ∼3.6 to 3.0 Ga. The major interval of growth of felsic continental crust was from 3.4 to 3.0 Ga. The younger generation of granitoids formed mostly by reworking of older intermediate to felsic crust. These different felsic magmatic bodies with distinct petrogeneses and sources, that include the depleted mantle, older mafic crust and the evolved continental crust, became essential elements of the stable continental crust of the western Dharwar Craton, the majority of which was generated from 3.4 to 3.0 Ga. • Major crust formation, stabilization in the western Dharwar Craton at 3.4–3.0 Ga • Pb Sr isotopes show no indication of evolved continental crust before 3.6 Ga. • Old mafic source material represents an intermediate stage of crust formation. • Younger granitoids formed dominantly by reworking of older felsic crust. • ɛHf i measured in-situ (zircon) and by isotope dilution (whole rock and zircon). [ABSTRACT FROM AUTHOR]

Abstract: We synthesize more than 2600 Hf isotope data on the Archean-Paleoproterozoic zircons from the North China Craton (NCC). Recalculation of the data based on single stage and two-stage Hf model ages of the Eastern Block of the NCC shows peak ages of 3902±13Ma and 3978±18Ma, respectively, and also small peaks at 3.5–4.0Ga. The majority of zircon ε Hf(t) values are positive, suggesting the possibility of the crust and the mantle differentiation at ca. 3.9–4.0Ga in the Eastern Block of the NCC. Most magmatic zircons from the whole of NCC have their Hf model age range of 2.4–2.9Ga, and the single stage model ages is cluster at 2698±4Ma, whereas the two-stage model ages concentrate at 2714±5Ma, implying that the protoliths were juvenile crustal rocks. The most prominent peak at 2.7Ga indicates that this period marks the most important stage of the crust-mantle differentiation and crust formation of the NCC. The widespread 2.5Ga rocks in the NCC and the absence of the 2.5Ga peaks in Hf model ages are consistent with the partial melting and reworking of the juvenile rocks at 2.5Ga. Furthermore, the 2.5–1.7Ga zircon Hf isotope features are also related to the reworking of the crustal rocks. Our results from the integration of a large database suggest that the Eastern Block and the Trans-North China Orogen have undergone similar crust-mantle differentiation and magmatism, leading to the conclusion that the essential cratonization of the North China took place at the end of Neoarchean. [Copyright &y& Elsevier]

Abstract: We report isotopic (Sm–Nd, Rb–Sr and zircon Hf and U–Pb SIMS SHRIMP) data on rocks collected from various localities throughout the southern Prince Charles Mountains known as the Ruker Province. The area is made up of a high-grade metamorphic basement, overlain by variably deformed and metamorphosed supracrustal associations of Proterozoic age. The area comprises two distinct tectonic terranes, experienced major tectonothermal processes in the Archaean (ca. 3400–2800Ma: the Ruker Terrane) or in the Palaeoproterozoic (ca. 2500–2100Ma: the Lambert Terrane). New zircon U–Pb ages of ca. 3180–3150Ma, ca. 2800, and ca. 2500Ma were obtained for various orthometamorphic rocks from the Ruker Terrane and ca. 2200Ma, ca. 1740Ma, and ca. 920Ma for syn-tectonic granitic veins and leucosomes from the Lambert Terrane. The Sm–Nd data provide evidence for the initial separation of the continental crust of the Ruker Terrane from the mantle mainly between ca. 3.2 and 3.4Ga, but up to 3.8Ga, and indicate the presence of two mantle reservoirs which correspond to (1) depleted to slightly enriched, and (2) ultra-depleted mantle. Some material was also derived from the mantle at ca. 2.7–3.0Ga; the crust of this age apparently underlies the central part of the Ruker Terrane (the CumpstonMassif–Mt Newton block), which is also distinguished by younger (ca. 2.5–2.1Ga) zircon ages. The Lambert Terrane contains subordinate ca. 3.6–3.8Ga protoliths, and the bulk of the crust seems to have originated between 2.6–2.9Ga from various mantle sources and it may represent an accretional complex onto the Archaean Ruker Terrane. We also summarize published isotopic data and propose an integrated geological evolution for both terranes of the Ruker Province, discuss its relationships with the bordering Rayner Province, and compare its isotopic features with other Precambrian cratons of Gondwana. The key geological features of the Ruker Terrane suggest a similarity to the Yilgarn Craton, which would imply considerable mineral resource potential of the Prince Charles Mountains. [Copyright &y& Elsevier]

The available geological, geochronological and isotopic data on the felsic magmatic and related rocks from South Siberia, Transbaikalia and Mongolia are summarized to improve our understanding of the mechanisms and processes of the Phanerozoic crustal growth in the Central Asian mobile belt (CAMB). The following isotope provinces have been recognised: ‘Precambrian’ (TDM=3.3–2.9 and 2.5–0.9 Ga) at the microcontinental blocks, ‘Caledonian’ (TDM=1.1–0.55 Ga), ‘Hercynian’ (TDM=0.8–0.5 Ma) and ‘Indosinian’ (TDM=0.3 Ga) that coincide with coeval tectonic zones and formed at 570–475, 420–320 and 310–220 Ma. Continental crust of the microcontinents is underlain by, or intermixed with, ‘juvenile’ crust as evidenced by its isotopic heterogeneity. The continental crust of the Caledonian, Hercynian and Indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments. The crustal growth in the CAMB had episodic character and important crust-forming events took place in the Phanerozoic. Formation of the CAMB was connected with break up of the Rodinia supercontinent in consequence of creation of the South-Pacific hot superplume. Intraplate magmatism preceding and accompanying permanently other magmatic activity in the CAMB was caused by influence of the long-term South-Pacific plume or the Asian plume damping since the Devonian. [Copyright &y& Elsevier]

We investigated the Sm–Nd isotopic characteristics of the Gyeonggi massif, Korea, in order to delineate its crustal growth history. Nd isotopic depleted-mantle model ages (TDM), obtained from 32 new measurements of basement and supracrustal samples and from the literature, suggest that the Gyeonggi massif is as old as Middle Archean (>3.0 Ga) and was primarily extracted from the mantle during the Late Archean (2.9–2.5 Ga). In addition, minor crustal formation occurred during the Early Proterozoic (ca. 1.9–1.8 Ga). Late Archean–Early Proterozoic crustal growth of the Gyeonggi massif is comparable with that of the Sino-Korean or Yangtze craton. The TDM distribution pattern alone is not sufficient to determine the crustal affinity of the Gyeonggi massif with either of the Chinese cratons. However, Late Proterozoic crustal evolution of the Gyeonggi massif appears to favor its tectonic correlation with the Yangtze craton. [Copyright &y& Elsevier]

Because the Hercynian overprint was extremely weak, the Sierra de Co´rdoba (southeastern Ossa-Morena Zone, OMZ) provides an excellent opportunity to study the tectonic evolution of sequences deposited close to the Late Neoproterozoic–Early Palaeozoic boundary. In order to put constraints on the sources and geodynamic significance of the Late Proterozoic magmatism, a representative set of 18 igneous rocks, and 3 interbedded sedimentary rocks from the San Jero´nimo Formation have been studied for major and trace element geochemistry and for the Sm–Nd isotopic systematics. The igneous rocks are generally porphyritic to microporphyritic andesites, with abundant plagioclase (±amphibole) phenocrysts. With the exception of two intrusive rocks, possibly not related to the Late Proterozoic episode, all the samples display positive &epsiv;Nd550 Ma values, ranging from +2.9 to +7.6. Most of them, with +4<&epsiv;Nd550 Ma<+6, exhibit LREE enrichment, high La/Nb ratios, and elevated Zr/Nb ratios ranging from 21 to 32. There is no obvious correlation between the shape of REE patterns, La/Nb ratios and &epsiv;Nd550 Ma values, precluding simple models of late-stage interaction with typical crustal components having low &epsiv;Nd and high LREE/HREE and La/Nb ratios. Based on their major element composition and enriched, continental crust-like trace element characteristics, combined with distinctly positive &epsiv;Nd initial values, the Co´rdoba andesites document an episode of crustal growth through the addition of calc-alkaline magmas, extracted from a mantle reservoir which was strongly depleted in LREE on a time-integrated basis. The occurrence of interlayered sediments of continental provenance (negative &epsiv;Nd values) does not favour a purely ensimatic arc setting, remote from continental land masses, for this subduction-related magmatism, but the geochemical data suggest an active margin environment located on relatively juvenile crust. In any case, the Co´rdoba andesites document the addition of materials chemically similar to the bulk continental crust which were extracted from mantle sources with strong time-integrated LREE depletion. Therefore, they provide evidence for crustal growth related to Cadomian orogenic events during Late Proterozoic times. [Copyright &y& Elsevier]

Determining the origin and related mantle dynamics responsible for the generation of giant granitic batholiths in convergent margins is critical to unravel the formation mechanism of the silica–rich continental crust. This paper reports the whole–rock major element, trace element, Sr-Nd isotopic, and zircon U-Pb age and Hf isotope data of samples from the Menglian Batholith in the eastern Tengchong Terrane of southwest Yunnan. These samples consist of two groups, including the Group I rocks that are mostly granitic with zircon U-Pb ages of 132–122 Ma and the Group II rocks that display varying compositions from gabbroic to granitic with zircon U-Pb ages of 122–112 Ma. The Group I samples have zircon ε Hf (t) of −11.7 to −4.2 and whole–rock ε Nd (t) of −10.1 to −8.9, whereas the Group II samples show elevated zircon ε Hf (t) of −7.8 to +7.1 and whole–rock ε Nd (t) of −9.0 to −6.9 and ε Hf (t) of −3.1 to −1.0. The Nd-Hf isotopic compositions of the Group I rocks are coupled, likely resulting from the partial melting of an ancient lower crust. However, the Nd-Hf isotopic compositions of the Group II rocks are decoupled, likely inheriting from the mantle–derived material with decoupled Nd-Hf isotopic compositions. Regional geological correlation and compositional transition documented by the Group I and Group II samples collectively indicate that the slab rollback and subsequent breakoff of the subducting Bangong–Nujiang ocean lithosphere during the Tengchong–Baoshan collision can be invoked to explain the generation of the Menglian Batholith. The similarity of average compositions between the Group II samples and the bulk continental crust suggests that the addition of mantle–derived material to the ancient crust–derived melts seems to be an efficient process for crustal growth during continental collisions. • Menglian Batholith was emplaced at 132–122 Ma (Group I) and 122–112 Ma (Group II). • Group I and II samples are coupled and decoupled in Nd-Hf isotopes, respectively. • Decoupling Nd-Hf isotopic compositions are inherited from mantle–derived material. • Group I and II samples are associated with slab rollback and breakoff. • Addition of mantle–derived material contributes to crustal growth efficiently. [ABSTRACT FROM AUTHOR]

Potassic feldspar-bearing augen granitoids are a fundamental component of the architecture of the Yukon-Tanana terrane and the ancient Pacific margin of the northern Cordillera. These augen granitoids form a belt that extends from Alaska to southeast Yukon Territory, vary in age, and provide probes of the crustal evolution and tectonic history of the Yukon-Tanana terrane and ancient Pacific margin of North America in the Paleozoic. We present results of an integrated field mapping, geochemical, Sm-Nd tracer isotopic, and U-Pb zircon geochronologic study of the augen granitoids in the Stewart River area in an attempt to understand their role in the crustal evolution and tectonic history of the Yukon-Tanana terrane and ancient Pacific margin of North America. Augen granitoids of the Stewart River area are of three distinct ages: Late Devonian, early Mississippian, and Permian. U-Pb zircon geochronology of these augen granitoids has yielded ages of 362.1 ± 2.7 Ma (Stewart River augen granite), 347.5 ± 0.7 Ma (Mount Burnham augen granite), and 264.8 ± 3.7 Ma (Wounded Moose augen granite). All of the augen granitoids, regardless of age, have negative Ndt values (-2.0 to -15.3) and Proterozoic-Archean depleted-mantle model ages (TDM = 1.37-2.56 Ga). These geochemical and isotopic attributes, coupled with the presence of inherited zircon with Precambrian ages, suggestthatthesegranitoidsaretheproductof crustal melting and crust-mantle mixing during three different cycles of arc magmatism in the Paleozoic. Furthermore, these granitoids represent net crustal recycling along the ancient Pacific margin of North America in the Paleozoic. Importantly, however, there are minor secular variations in crustal recycling, and the younger Permian augen granitoids exhibit higher Ndt, Nb/Ta, V/Yb, and Sc/Yb, consistent with a greater juvenile component in their genesis. This juvenile component is probably due to assimilation of underplated mafic material derived from older early Mississippian Yukon-Tanana terrane arc magmatism and/or a greater mantle component due to enhanced infiltration of underplated mafic material into augen granitoid magma chambers through rheologically weak crust associated with Permian subduction. The older Late Devonian and early Mississippian augen granitoid suites represent two pulses of Yukon-Tanana terrane arc magmatic activity that developed in response to east-dipping subduction along the western edge of the North America craton in the mid-Paleozoic. This east-dipping Yukon-Tanana terrane arc system continued to evolve throughout the Mississippian to Early Permian and was coincident with the development of the Slide Mountain backarc basin that formed between the Yukon-Tanana terrane arc system and the North American craton; this east-dipping arc-backarc system continued until ca. 275 Ma. After ca. 275 Ma, the east-dipping arc and backarc magmatism ceased and was replaced by ca. 270-269 Ma high-pressure metamorphism and the establishment of a new subduction zone that formed in response to the closure of the Slide Mountain backarc basin. The Permian augen granitoids from the Stewart River are the magmatic record of this new west-dipping subduction zone. Although there are subtle variations, the petrogenetic and tectonic histories of the three suites of augen granitoids in the Stewart River area are remarkably similar and attest to the constancy of magmatic and tectonic processes that occurred along the ancient Pacific margin of North America in the Paleozoic. [ABSTRACT FROM AUTHOR]