Crustal Evolution History Research Articles

Early Paleoproterozoic magmatism in the Yangtze Block: Evidence from zircon U-Pb ages, Sr-Nd-Hf isotopes and geochemistry of ca. 2.3 Ga and 2.1 Ga granitic rocks in the Phan Si Pan Complex, north Vietnam

Our understanding of the early evolution of the Yangtze Block is limited by the sparsely dispersed nature of pre-Neoproterozoic exposures. New, integrated petrographic, zircon U-Pb age and Hf-Nd isotope analyses, and whole-rock geochemical data for early Paleoproterozoic granites in the Phan Si Pan Complex provides new insights into the evolution of the Yangtze Block as well as its role in the Pre-Nuna supercontinent. LA-ICP-MS zircon U-Pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207Pb/206Pb ages of 2306 ± 12 Ma and 2096 ± 15 Ma, respectively. Zircons from the quartz monzonite have εHf(t) values ranging from −4.1 to −2.1, corresponding to TDM2 model ages of 3002–2890 Ma, whereas zircons in the gneissic granite have εHf(t) values between −0.95 and +1.72 and corresponding TDM2 model ages of 2660–2516 Ma, which are consistent with their whole-rock Nd isotope values. Geochemically, the quartz monzonites are I-type granites. Combined with their relatively high Sr/Y ratios and low Y concentrations, as well as fractionated REE patterns with relatively high LREE but low HREE concentrations, they were probably generated by partial melting of the thickened middle-lower crust under elevated temperature. Geochemical and isotopic signatures suggest that the ca. 2.1 Ga gneissic granites are high-K calc-alkaline, ferroan A-type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material. The Phan Si Pan complex has a distinct early Paleoproterozoic crustal evolution history compared with the other crustal provinces of the Yangtze Block, suggesting independent histories that were not unified until the late Paleoproterozoic during the assembly of Nuna. Moreover, the magmatism and tectonic evolution of the north Vietnam region is broadly similar to that of the Arrowsmith Orogen of the Rae craton in Laurentia suggesting a potential spatial linkage. The geologic record of the Yangtze Block does not support an early Paleoproterozoic shutdown of plate tectonics.

Identification of ca. 2.65 Ga TTGs in the Yudongzi complex and its implications for the early evolution of the Yangtze Block

In this contribution, we carry out an integrated study of petrology, whole-rock geochemistry, as well as zircon morphology, trace element, U–Pb and Lu–Hf isotopes for granitic gneisses and leucogranites from the Yudongzi complex, a poorly studied Archean outcrop in the northwestern Yangtze Block. The granitic gneisses have the TTG affinity characterized by relatively high Na2O/K2O and Sr/Y ratios, and fractionated REE pattern with relatively high LREE but low HREE concentrations. Zircon grains in the granitic gneisses show magmatic cores and metamorphic rims. U–Pb dating on zircon core of four granitic gneiss samples yielded their formation ages as 2660–2632 Ma with a weighted average of 2650 ± 21 Ma (MSWD = 1.6; n = 4). Their average εHf (t) values range from −0.6 to 0.5 and two-stage model ages from 3.20 to 3.10 Ga, suggesting that the granitic gneisses were likely generated by remelting of thickened Mesoarchean proto-mafic crust. The metamorphic zircon rims have relatively high Th/U ratios and identical Hf isotope compositions to their corresponding cores, indicating that the rims were formed via solid-state recrystallization process. The metamorphic zircons recorded a metamorphic event at ca. 2.5 Ga. U-Pb dating and Lu-Hf isotopes on magmatic zircons from a leucogranite sample revealed a magmatic event at 2477 ± 18 Ma. The recognization of the 2.65 Ga TTG magmatism and the 2.48 Ga intercrustal remelting event in the Yudongzi complex demonstrates the widespread Neoarchean magmatism in the Yangtze Block. Combined with the age spectra of previous detrital zircons, we show that the Yangtze Block has experienced a major tectonothermal event in the late Archean. The Yudongzi complex has a distinct crustal evolution history compare with the Paleoarchean continent nucleus in the eastern part of the Yangtze Block, suggesting that the continent nucleus might have subjected to lateral growth by accretion processes.

Gold mineralization in Bubin area, Gilgit-Baltistan, Northern Areas, Pakistan

The complex history of crustal evolution and the diverse geological history of Northern areas of Pakistan (i.e., Indian Plate, Kohistan-Ladakh Island arc, and Eurasian Plate) made the area most favorable for economic mineral deposits such as gold and copper. Sulfide-bearing mineralized rock samples from Ladakh terrane are analyzed for gold, silver, and base metals. Bulk samples analyses for gold, silver, and base metal concentrations demonstrate that almost all samples have variable amounts of gold, silver, and base metals. In these samples, gold concentration up to 95 ppm was found in chalcopyrite, galena-rich mineralized quartz veins, and their alteration products. The mineralized veins are few meters to 10 m wide and are associated with dioritic rocks. Dominant minerals in the mineralized zone include galena, chalcopyrite, limonite, pyrite, and malachite. The enrichment and depletion of different types of minerals suggest that the magmatic hydrothermal fluids played a key role in copper and lead mineralization with gold concentration. Study of ore minerals in these samples shows association with sulfide-bearing alterations in shear zones.

Paleozoic intrusive rocks from the Dunhuang tectonic belt, NW China: Constraints on the tectonic evolution of the southernmost Central Asian Orogenic Belt

The Dunhuang tectonic belt (DTB) is of great importance for understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt (CAOB). In this study, the temporal-spatial distribution, petrogenesis and tectonic setting of the Paleozoic representative intrusive rocks from the DTB were systematically investigated to discuss crustal evolution history and tectonic regime of the DTB during Paleozoic.Our results reveal that the Paleozoic magmatism within the DTB can be broadly divided into two distinct episodes of early Paleozoic and late Paleozoic. The early Paleozoic intrusive rocks, represented by a suite metaluminous-slight peraluminous and medium- to high-K calc-alkaline I-type granitoids crystallized at Silurian (ca. 430–410Ma), are predominantly distributed along the northern part of the DTB. They were probably produced with mineral assemblage of eclogite or garnet+amphibole+rutile in the residue, and were derived from magma mixing source of depleted mantle materials with various proportions of Archean-Mesoproterozoic continental crust. The late Paleozoic intrusive rocks can be further subdivided into two stages of late Devonian stage (ca. 370–360Ma) and middle Carboniferous stage (ca. 335–315Ma). The former stage is predominated by metaluminous to slight peraluminous and low-K tholeiite to high-K calc-alkaline I-type granitic rocks distributed in the central part of the DTB. They were also generated with mineral assemblage of amphibolite- to eclogite-facies in the residue, and originated from magma source of depleted mantle materials mixed with different degrees of old continental crust. The later stage is represented by adakite and alkali-rich granite exposed in the southern part of the DTB. The alkali-rich granites studied in this paper were possibly produced with mineral assemblage of granulite-facies in the residue and were generated by partial melting of thickened lower continental crust. Zircon Hf isotopes and field distribution of those Paleozoic intrusive rocks reveal that both the Silurian and the late Devonian magmatic activities predominantly represent crustal growth processes in the DTB, accompanied by different degrees of reworking of pre-existing continental crust. However, the middle Carboniferous (ca. 335–315Ma) magmatic activity reflects a crustal reworking process. The Silurian and late Devonian intrusive rocks were most likely formed in the arc-related subduction zones, whereas, the middle Carboniferous intrusive rocks were possibly formed in a transitional tectonic setting from compression to extension, representing the final stage of Paleozoic orogeny in the DTB.These Paleozoic magmatic rocks further suggest that the DTB has reactivated from a stable block to an orogen and undergone two episodes (the early Paleozoic and the late Paleozoic) of orogeny during Paleozoic. It represents a Paleozoic accretionary orogen of the southernmost margin of the CAOB between the Tarim Craton and North China Craton, and tectonically extends northward to the Beishan orogen and westward to the eastern South Tianshan Belt.

Tracing crustal evolution by U-Th-Pb, Sm-Nd, and Lu-Hf isotopes in detrital monazite and zircon from modern rivers

Abstract Detrital zircon U-Pb age and Hf isotope studies are useful for identifying the chemical evolution of the continental crust. Zircon, however, is typically a magmatic mineral and thus often fails to document the timing of low-grade metamorphism, and its survival through multiple sedimentary cycles potentially biases the crustal evolution record toward older events. In contrast, monazite typically records metamorphic events and is less likely to survive sedimentary recycling processes, thus providing information not available by zircon. Here, we demonstrate that monazite apparently faithfully records the Sm-Nd isotope composition of the bulk rock and can therefore track the record of crustal evolution and growth, similar to Hf isotopes in zircon. We examine the utility of detrital zircon and monazite for studies of crustal evolution through a comparison of age and tracer isotope information using sediments from two large rivers draining the South China block (SCB). Monazite and zircon grains yield mostly Mesozoic and Paleozoic U-Pb ages and depleted mantle model age peaks at ca. 1900–1300 Ma, indicating that both minerals preserve similar, yet critical, information on the crustal evolution of the catchment area. In contrast, zircon yields abundant Neoproterozoic and older U-Pb ages with a very large spread of model ages, preserving a history strongly skewed to older ages. Based on the lack of known rocks of this age in the catchments, ancient zircon was likely sourced from sedimentary rocks within the catchment area. This combined data set presents a more complete history of crustal evolution and growth in the SCB and demonstrates the advantages of an integrated approach that includes both detrital monazite and zircon.

Late Mesoarchean crust growth event: evidence from the ca. 2.8 Ga granodioritic gneisses of the Xiaoqinling area, southern North China Craton

Recently, more attention has been paid to Precambrian magma events and crustal growth of the North China Craton (NCC), accompanying with controversy in activity stages and dynamic mechanism. In this study, we report the Archean (2802 ± 13Ma) granodioritic gneisses in the Taihua Complex from the Xiaoqinling area, located in the southern margin of the NCC. The zircon Lu–Hf isotope analysis of the rocks showed 176Hf/177Hf ratios of 0.280977–0.281228, corresponding to εHf(t) values ranging from −3.5 to +6.6, and two–stage Hf model ages varying from 2836 to 3409Ma. It was confirmed that late Mesoarchean (2.9–2.8Ga) juvenile crust made contribution to the source material of these ca. 2.8Ga granodioritic gneisses in the Xiaoqinling area. The whole rock geochemical data indicate that the granodioritic gneisses are high-K calc-alkaline series, probably generated at relatively high pressure and temperature, and formed under the continental arc setting. Statistically, we conclude that the magmatic activities during 2.9–2.7Ga may represent the most intense crustal growth events in the NCC and these Archean rocks at different locations in southern NCC underwent a similar crustal evolution history.

Detrital zircon U–Pb, Lu–Hf, and O isotopes of the Wufoshan Group: Implications for episodic crustal growth and reworking of the southern North China craton

The Paleoproterozoic orogens of the North China Craton (NCC) provide important windows to evaluate the crustal evolution history during early Precambrian. Here we report results from SIMS zircon geochronology and oxygen isotopes, as well as LA-ICPMS zircon Hf isotopic analyses on detrital zircons from Mesoproterozoic-Neoproterozoic sandstones of the Wufoshan Group from the southern NCC to probe the Paleoarchean-Paleoproterozoic crustal evolution. Our data show episodic magmatism during the Paleoarchean-Neoarchean and Paleoproterozoic as inferred from the 207Pb/206Pb age range of 3514–2751Ma and the well-defined 207Pb/206Pb weighted mean ages of 2669±15Ma, 2510±8Ma, 2402±39Ma, 2298±36Ma, 2179±10Ma, 2058±16Ma, 1940±6Ma, 1874±7Ma and 1819±5Ma. The similarity in U–Pb geochronology and Hf isotopes of the Archean detrital zircons from the Wufoshan Group to those from the Paleoproterozoic Songshan Group reveal that the 2669Ma zircons record a major phase of Neoarchean crustal growth, and that 2510Ma zircons correspond to the latest Neoarchean crustal reworking. The 18O-depleted isotopic features displayed by some detrital zircons are absent in those from Songshan Group, and together with the rarity of core-rim textures which were widespread in Archean zircons from the Songshan Group, we suggest that the source materials for the Mesoproterozoic-Neoproterozoic Wufoshan Group are different from the Archean cratonic source for the Paleoproterozoic Songshan Group. We propose that the zircons were probably sourced from the newly-formed Trans-North China Orogen (TNCO). Our Paleoproterozoic zircon data provide robust evidence for continuous and complex reworking of the Mesoarchean to early Neoarchean crust in the southern NCC during Early Paleoproterozoic at ca. 2402Ma, 2298Ma, and 2179Ma. The Middle Paleoproterozoic ages (2058Ma, 1940Ma, and 1874Ma) mark a partial cycle of oceanic crust subduction to continental collision during the formation of the TNCO. The extreme oxygen isotopic variation with the fairly restricted range in Hf isotopes demonstrates that the components from both high-temperature and the low-temperature rock–water interaction induced by the release of hydrothermal fluids from the subducted altered oceanic crust must have played a significant role during the growth of the zircons. The Paleoproterozoic thermal event at 1819Ma records post-collisional uplifting, as evidenced by an apparent negative correlation in the ɛHf(t) vs. δ18O plot, possibly inherited from the mixing of the ancient crust and the juvenile input during the oceanic subduction and continental collision. Integrated with the information from granulite facies metamorphic rocks in the orogenic root of the TNCO, our data suggest that the episodic Paleoproterozoic magmatism was mainly induced by the tectonics of plate subduction and subsequent continental collision, leading to the final cratonization of the NCC. Following the Mesoproterozoic-Neoproterozoic sedimentation of the Paleoproterozoic zircons, except for the Pb loss during the subsequent thermal events, there was no major alteration in the Hf and oxygen isotopic compositions. Thus, the remarkably large variation of oxygen isotopes from the lower than normal mantle to the supracrustal value (δ18O=2.28–10.09‰) in the Paleoproterozoic detrital zircons further demonstrates that these zircons came from the uplifted and exposed upper part of the TNCO. Our detrital zircon data provide convincing evidence for the repeated crustal reworking in Early Paleoproterozoic and the onset of modern-style plate tectonics in the NCC in Middle Paleoproterozoic.

Zircon U–Pb ages of Paleoproterozoic mafic granulites from the Huai’an terrane, North China Craton (NCC): Implications for timing of cratonization and crustal evolution history

The North China Craton (NCC) is considered to have been incorporated into the Columbia supercontinent during late Paleoproterozoic. The Huai’an terrane located in north-central part of the NCC is an important tectonic window to investigate the Paleoproterozoic crustal evolution history of this craton, particularly due to the wide occurrence of high-grade metamorphic rocks including retrograded eclogites and high-pressure granulites. Available data show two controversial peak metamorphic ages of these rocks as 1.95–1.90 or ∼1.85–1.80Ga. Thus, determining the precise timing of metamorphism of the high-pressure granulites is important in reconstructing the collisional history. In this study, we present zircon U–Pb ages, bulk chemistry, and mineral inclusions in zircons and matrix mineral assemblages from the high-pressure granulites to evaluate the timing of metamorphism. Our results reveal ca. 2.05–2.0Ga ages from magmatic zircons in these rocks representing the timing of emplacement of mafic magmas. The metamorphic zircons yield two groups of ages at 1.95–1.90 and ∼1.85∼1.80Ga. Clinopyroxene, plagioclase, titanite, and apatite occur as common mineral inclusions within the ∼1.85–1.80Ga metamorphic zircons. The chemical compositions of clinopyroxene and plagioclase occurring as inclusions are very similar to those of the rim compositions of those minerals in the matrix, suggesting their formation during retrograde granulite metamorphism, and are distinctly different from those of the core domains of the minerals in the matrix which represent high-pressure granulite metamorphism. These results indicate that the metamorphic zircons formed during retrograde granulite metamorphism dated as ∼1.85–1.80Ga and the age range of ∼1.95–1.90Ga corresponds to high-pressure granulite metamorphism. The dual nature of the geological and geochronological features suggest that the Archean gray gneisses in the Huai’an terrane represent the basement rocks detached from the Khondalite Belt of the NCC after collision. Integrating with published data, a double-side collision with scissor-like suturing model is proposed for the Paleoproterozoic cratonization of the NCC.

Age and evolution of the deep continental root beneath the central Rae craton, northern Canada

Canada is host to at least six separate cratons that comprise a significant proportion of its crustal extent. Of these cratons, we possess knowledge of the cratonic lithospheric roots beneath only the Slave craton and, to a lesser extent, the Superior craton, despite the discovery of many new diamond-bearing kimberlites in Canada's North. Here we present the first age, composition and geothermal information for kimberlite-borne peridotite xenoliths from two localities within the central Rae craton: Pelly Bay and Repulse Bay. Our aim is to investigate the nature and evolution of the deep lithosphere in these regions and to examine how events recorded in the mantle may or may not correlate with the complex history of crustal evolution across the craton.Peridotite xenoliths are commonly altered by secondary processes including serpentinization, silicification and carbonation, which have variably affected the major element compositions. These secondary processes, as well as mantle metasomatism recorded in pristine silicate minerals, however, did not significantly modify the relative compositions of platinum-group elements (PGE) and Os isotope ratios in the majority of our samples from Pelly Bay and Repulse Bay, as indicated by the generally high absolute PGE concentrations and mantle-like melt-depleted PGE patterns. The observed PGE signatures are consistent with the low bulk Al2O3 contents (mostly lower than 2.5%) of the peridotites, as well as the compositions of the silicate and oxide minerals. Based on PGE patterns and Os model ages, the peridotites from both localities can be categorized into three age groups: Archean (3.0–2.6Ga overall; 2.8–2.6Ga for Pelly Bay and 3.0–2.7Ga for Repulse Bay), Paleoproterozoic (2.1–1.7Ga), and “Recent” (<1Ga, with model ages similar to the ca. 546Ma kimberlite eruption age). The Archean group provides the first direct evidence of depleted Archean lithospheric mantle forming coevally with the overlying Archean crustal basement, indicating cratonization of the Rae during the Archean. The subtle difference in Os model ages between Pelly Bay and Repulse Bay coincides with the age difference between crustal basement rocks beneath these two areas, supporting the suggestion that the Rae craton was assembled by collision of separate two Archean blocks at 2.7–2.6Ga. The Paleoproterozoic peridotites are interpreted to represent newly formed lithospheric mantle, most likely associated with regional-scale underplating during the 1.77–1.70Ga Kivalliq-Nueltin event via removal of the lower portion of Archean lithospheric mantle followed by replacement with juvenile Paleoproterozoic lithospheric mantle. The existence of multiple age clusters in the lithosphere at each locality is consistent with the observation of present-day seismic lithospheric discontinuities (Snyder et al., 2013, 2015) that indicate two or more layers of fossil lithospheric mantle fabric beneath this region. Our data define a shallow mantle lithosphere layer dominated by Archean depletion ages underlain by a layer of mixed Archean and Paleoproterozoic ages. This lithospheric mantle structure is probably a response to complex tectonic displacement of portions of the lithospheric mantle during Paleoproterozoic orogeny/underplating. The best equilibrated Archean and Paleoproterozoic peridotites at both Pelly Bay and Repulse Bay define a typical cratonic geotherm at the time of kimberlite eruption, with a ∼200km thick lithospheric root extending well into the diamond stability field, in keeping with the diamondiferous nature of the kimberlites. Such thick lithosphere remains in place to the present day as suggested by seismic and magnetotelluric studies (Snyder et al., 2013, 2015; Spratt et al., 2014). The metasomatically disturbed peridotites in the Rae lithospheric mantle, yielding model ages indistinguishable from kimberlite eruption, may represent parts of the Rae craton mantle root that show anomalous magnetotelluric signatures.

The Precambrian tectonic evolution of the western Jiangnan Orogen and western Cathaysia Block: Evidence from detrital zircon age spectra and geochemistry of clastic rocks

The Jiangnan Orogen and Cathaysia Block constitute integral components in the geological framework of the South China Craton. However, the tectonic attributes of these two regions remain controversial. In this study we present LA–ICP–MS zircon U–Pb ages, Lu–Hf isotopes, and major and trace elements data from a suite of clastic rocks. Two hundred and forty seven zircon U–Pb ages obtained from the Neoproterozoic meta-sandstones in western Jiangnan Orogen define three major age populations: 2564–2395Ma, 2068–1849Ma and 963–730Ma, corresponding to the early Paleoproterozoic crustal growth, amalgamation of the supercontinent Columbia and tectonics associated with Rodinia. Two hundred and forty three zircon U–Pb age data from Cambrian and Ordovician sandstones in the western Cathaysia yield five age populations: 2626–2392Ma, 2050–1518Ma, 1173–904Ma, 857–708Ma and 630–502Ma, which can be correlated to the Neoarchean–early Paleoproterozoic continental growth, the tectono-thermal events associated with the Columbia supercontinent, the assembly and breakup of Rodinia, as well as the Pan-African event. The 630–502Ma population correlates with the assembly of Gondwana supercontinent during late Neoproterozoic to early Paleozoic, although direct geological evidence for this event has not yet been reported from this region. These results suggest that the western Jiangnan belt and western Cathaysia Block have distinct crustal evolution histories albeit with close affinities. The REE geochemisty and Lu–Hf isotope data also indicate that the provenances of the Neoproterozoic and early Paleozoic detritus in western Jiangnan belt and western Cathaysia are mostly composed of reworked crustal materials. The metamorphic rims of zircon grains with core–rim structures yield ages of 912–891Ma and 853–835Ma, suggesting two phases of metamorphic events during Neoproterozoic in the source areas. These two events are likely associated with the tectonics related to the collision of Yangtze and Cathaysia blocks in the western and eastern segments, respectively.

A Preliminary Review of Metallogenic Regularity of Molybdenum Deposits in China

Molybdenum is one of the dominant minerals in China because of its rich reserves. In recent years, outstanding breakthroughs have been made in molybdenum prospecting in China, and the distribution of molybdenum deposits in China is found to have a “planar pattern”. In general, the molybdenum deposits are concentrated in eastern China, including the largest molybdenum reserves of Henan Province. In terms of the scale of molybdenum deposits, the identified resources of the superlarge deposits are the most important, which account for about 53% of the whole country, and those of the large deposits account for about 30%, those of the medium‐sized deposits account for about 14%, those of the small‐sized deposits, mine spots and mineralization account for about 3%. The molybdenum deposits are mainly classified as porphyry type, skarn type, hydrothermal (vein) type and sedimentary (metamorphic) type in genesis, and the identified resources of these types account for 85.75%, 8.83%, 2.79% and 2.63% of the total resources respectively. Based on the statistics of precise chronology data of molybdenites Re‐Os, Mo‐mineralization can be divided into 6 periods in Chinese geological history, which are Precambrian (&gt;800 Ma), Cambrian‐Silurian (540–415 Ma, Caledonian), Devonian‐Permian (400–290 Ma, Hecynian), Triassic (260–200 Ma, Indosinian), Jurassic‐Cretaceous (195–70 Ma, Yanshanian) and Paleogene‐Neogene (65–10 Ma, Himalayan). Mo mineralization during the Yanshanian period is the strongest one, in which about 76.69% of the Chinese total identified resources was formed. The second is the Himalayan period. According to spatial‐temporal distribution characteristics of molybdenum deposits, the metallogenic regularity of molybdenum deposits was preliminarily summarized, and 41 level‐III molybdenum‐forming belts, 13 level‐II molybdenum‐forming provinces and 4 level‐I molybdenum‐forming domains were ascertained in the mainland of China. There are 39 metallogenic series of and 60 sub‐series of molybdenum deposits with molybdenum as the dominant metal and corresponding representative molybdenum deposits proposed. Metallogenic lineages of molybdenum deposits were also established. Spatial‐temporal evolution of different types of molybdenum deposits, and the relationship between Mo‐mineralization and tectonic evolution have been discussed in this paper. On this basis, the authors think that element Mo is an effective tracer for recording the crustal evolution history of China. At present, there are some problems in the exploration of Mo deposits in China, such as uneven exploration degrees in eastern and western China, shallow exploration depth, low and uneven grade, complex associated components, difficulty of mineral development and utilization, increasing costs of prospecting, and so on. According to successful experience of superficial and deep prospecting and considering also the discussion above, some suggestions are proposed for the prospecting of molybdenum deposits in the future.

Origin and formational history of some Pb-Zn deposits from Alborz and Central Iran: Pb isotope constraints

Several Pb-Zn deposits and occurrences within Iran are hosted by Mesozoic–Tertiary-aged sedimentary and igneous rocks. This study reports new Pb isotope analyses for galena from 14 Pb-Zn deposits in the Alborz and Central Iran structural zones. In general, Pb isotope ratios are extremely variable with data plotting between the upper crustal and orogenic curves in a plumbotectonic diagram. The latter may be attributed to Pb inputs from crustal and mantle end-members. Most of the galena samples are characterized by high 207Pb/204Pb ratios, suggesting significant input of Pb from old continental crust or pelagic sediment. Pb isotope data also indicate that some of the deposits, which are hosted by sedimentary rocks in Central Iran and Alborz, have similar Pb isotopic compositions and hence suggest similar source regions. Most of the galenas yield Pb model ‘ages’ that vary between ~140 and ~250 Ma, indicating that mineralization resulted from the extraction of ore-bearing fluids from Upper Triassic–Lower Jurassic sequences. The similarity in Pb isotope ratios for the Pb-Zn deposits located within these zones suggests analogous crustal evolution histories. Our preferred interpretation is that Pb-Zn mineralization within the sedimentary and igneous rocks of the Central Iran and Alborz tectonic regions occurred following a Late Cretaceous–Tertiary accretionary stage of crustal thickening in Iran.

Zircon U–Pb ages, geochemistry, and Nd–Hf isotopes of the TTG gneisses from the Jiaobei terrane: Implications for Neoarchean crustal evolution in the North China Craton

The Precambrian basement in the Jiaobei terrane is largely composed of Tonalite–Trondhjemite–Granodiorite (TTG) suite of rocks and offers important insights into the crustal evolution history of the North China Craton (NCC). The LA-ICP-MS zircon U–Pb age data presented in this study show that the magmatic protoliths of the TTG gneisses formed during 2508–2547Ma and recorded the Paleoproterozoic metamorphism (∼1905Ma). The rocks are enriched in LILE (Rb, Ba and Sr) and depleted in HFSE (Nb, Ta, Zr and Hf). They are characterized by high Sr contents (406–2906ppm), Sr/Y ratios (31.3–355) and subchondritic Nb/Ta ratios (18.5–68.9). The TTGs show relatively high ΣREE contents (72.0–266ppm) with strongly enriched LREE ((La/Yb)N=11.5–121) and positive or negligible negative Eu anomalies (Eu/Eu∗=0.84–1.89). These geochemical features suggest that the magma source might have been rutile-bearing amphibole eclogite. Their high Mg# numbers (42–56) and high Cr (153–285ppm) and Ni contents (22.2–74.5ppm) indicate interaction with the mantle wedge during magma ascent. The whole rock εNd (t) values (+2.6 to +3.8) and most of the magmatic zircon εHf (t) values (+1.3 to +7.6) suggest juvenile to evolved isotopic signatures. All these lines of evidence suggest that the TTG rocks in this study formed through partial melting of subducted oceanic slab in a continental arc environment. The drill holes in the Jiaobei terrane are dominated by ∼2.5Ga TTG gneisses, suggesting that the TTG magma at ∼2.5Ga is more widely distributed deep underground than that of ∼2.7–2.9Ga, at least within the approachable depth range of our research. Some zircon grains from Jiaobei TTGs give high εHf (t) values plotting above the curve of 0.75∗εHf of DM, and their TCDM ages are very close to the time of the zircon crystallization. However, the majority of the εHf (t) values fall below the curve of 0.75∗εHf of DM and their TCDM ages are concentrated between ∼2.7–2.9Ga. Therefore, combining with other related studies, we propose that the ∼2.5–2.6Ga magmatism in the NCC probably represents a coherent event of crustal growth and major reworking (remelting).

Anatomy of zircon growth in high pressure granulites: SIMS U–Pb geochronology and Lu–Hf isotopes from the Jiaobei Terrane, eastern North China Craton

Granulite facies rocks that witnessed high pressure and high temperature metamorphism preserve important records of the growth and recrystallizaton of zircons during the multiple stages of tectonic evolution of orogenic belts developed in complex subduction–collision settings. Here we investigate zircons in the Paleoproterozoic high pressure (HP) granulites from Jiaobei Terrane in the eastern North China Craton that experienced a multi-stage metamorphic evolution. We present SIMS zircon U–Pb ages for zircons from garnet amphibolites, mafic granulites and pelitic granulites. Our data show four age peaks at 2.5Ga, 1.92Ga, 1.87–1.85Ga and 1.83Ga. Zircons belonging to the latter three age groups show similar characteristics of low Th and U contents, low Th/U ratios (<0.1), sector zoning or unzoned internal structures, corresponding to the features of zircon growth during metamorphism. Using zircon Lu–Hf isotopic compositions combined with a careful analysis of the morphology of the zircons, we evaluate the processes of solid-state recrystallization, intergranular melt growth, coupled dissolution–reprecipitation and subsolidus growth. Zircons formed through solid-state recrystallization during peak metamorphic stage inherited the relatively high 176Lu/177Hf ratios and low 176Hf/177Hf ratios of zircons from the protoliths. The youngest U–Pb age of ca. 1899Ma is interpreted as the maximum estimate of the time of peak metamorphism. Zircons formed through intergranular melt growth during low- to medium-pressure retrogression display homogeneous Lu–Hf isotope compositions, low 176Lu/177Hf and high 176Hf/177Hf ratios. The U–Pb age of 1870–1850Ma yielded by zircons crystallized from intergranular melt is interpreted to represent the time of low- to medium-pressure granulite facies retrogression. Some zircon grains with prismatic morphology and low 176Lu/177Hf and 176Hf/177Hf ratios display heterogeneous Lu–Hf isotopic compositions, possibly related to coupled dissolution–reprecipitation. The U–Pb ages of these zircons are identical to those formed from intergranular melt and these two groups of zircons formed during the same metamorphic stage. Zircons formed through subsolidus growth show large variations in Lu–Hf isotopic compositions and their ca.1833Ma age represents the timing of amphibolite facies retrogression. The HP granulite facies metamorphism in Jiaobei is thus constrained between 1870 and 1899Ma, with low- to medium-pressure granulite facies retrogression at ca. 1850–1870Ma followed by amphibolite facies retrogression at ca. 1833Ma.Our data show that several zircon cores and recrystallized grains were entrained from basement rocks during the emplacement of the mafic magmatic protoliths in the case of mafic granulites. For the pelitic granulites, the older zircons are detrital grains of magmatic origin. The Hf crustal model ages of these zircons that show peaks at ca. 2.7Ga and 2.9Ga are consistent with the timing of mafic magmatism in the region as identified in previous studies. The Lu–Hf isotopes of newly grown metamorphic zircons which have equilibrated chemical compositions trace the nature of the protolith. The zircon Hf crustal model age of ca. 2.5–2.7Ga from the pelitic granulites is consistent with that of the basement rocks in the Jiaobei Terrane and the zircon Hf model ages (TDM) of ca.2.0Ga and 2.2–2.3Ga from the mafic granulites might represent the time of magma generation from the mantle with crustal contamination. The geochronology of the basement rocks as revealed by the old zircon cores and the metamorphic evolution of the Jiaobei Terrane are comparable with the tectonic history of the central and western North China Craton and provide insights into the complex tectonothermal events associated with the Neoarchean–Paleoproterozoic crustal evolution history of the craton. Also, the pervasive ~2.5Ga zircons in a variety of rocks seem to suggest that the Jiaobei Terrane was already part of a coherent tectonic unit at such time.

한국 현생 화강암류의 Nd 동위원소 조성 특성과 성인적 의미

Nd isotopic compositions analyzed from the Phanerozoic granitoids of Korea are integrated and discussed. Variations in Nd isotopic compositions can be explained either by temporal trend or by regional differences. Among the three active periods, first two periods during the Permian-Triassic and Jurassic seem to show variations from rather high values at the beginning to lower values during the later stages. Such trends probably reflect melting of the subducting oceanic crust and producing magma with higher proportion of depleted mantle derived materials during the early stage of subduction process, and subsequent magmas with greater proportion of old continental crust with progress of subduction. However, the Cretaceous-Paleogene period of active magmatism displays higher values during the advanced stage of the igneous activities, which is opposite to the previous active periods. The other explanation is that such differences in reflect regional differences, based on the observations that such high- granitoids distribute in the northeastern Gyeongbuk Province and Gyeongsang Basin. If this is the case, the regions with highr values may have distinct crustal evolution histories, e.g. younger average age. The choice between the two hypothesis could be made through further studies.

Hadean to Neoarchean episodic crustal growth: Detrital zircon records in Paleoproterozoic quartzites from the southern North China Craton

The Archean terranes exposed in several regions of the North China Craton (NCC) provide important windows to evaluate the Hadean-Archean continental crustal evolution history. Here we report results from SIMS zircon geochronology and oxygen isotopes, as well as LA-ICPMS zircon Hf isotopic analyses on detrital zircons from Paleoproterozoic quartzites to probe the early crustal evolution in the southern NCC. Our data show episodic magmatism during the Eoarchean, Paleoarchean, Mesoarchean, Neoarchean and Paleoproterozoic as inferred from the concordant ages of 3.6Ga and 2.2Ga and the well-defined upper intercept ages of 3404±30Ma, 2919±31Ma, 2772±9.5Ma, 2698±4.7Ma, 2652±6.7Ma, and 2532±5.2Ma. The Hf and oxygen isotopic compositions of Eoarchean–Paleoarchean zircons demonstrate that the cratonic nucleus of the NCC was built in the Hadean (∼4.0Ga), similar to the timing of formation of the nuclei of old cratons elsewhere on the globe such as the Yilgarn Craton, Western Australia, and the Slave Craton, Canada, with the Eoarchean–Paleoarchean (3.8Ga, 3.6Ga and 3.4Ga) marking the first phase of crustal reworking of the Hadean crust. The salient aspect of our data is that the Meoarchean to early Neoarchean (3.0–2.6Ga with a peak at 2.7Ga) was a significant period for crustal growth from the mantle throughout the NCC, comparable with the event of major Archean crustal growth worldwide. The latest Neoarchean (∼2.5Ga) marks a period of significant crustal reworking that led to remelting of the newly-formed juvenile mafic crust (∼2.7Ga). Integration with the data obtained from the TTG (tonalite–trondhjemite–granodiorite) and granitoid rocks of the Archean terranes and the lower crustal granulite xenoliths from various parts of the NCC suggests that the episodic Eoarchean via Paleoarchean and Mesoarchean to Neoarchean crustal growth as well as crustal reworking intensely destroyed the ancient cratonic nucleus, resulting in the scarce preservation of the Hadean and Eoarchean remnants in both the upper and lower crust of the NCC. Following the Paleoproterozoic sedimentation of the Archean zircons, apart from Pb loss during the subsequent thermal events, there was no major alteration in the Hf and oxygen isotopic compositions. Thus, our detrital zircon data provide convincing evidence for the repeated crustal growth and reworking of the NCC in the Archean.

Precambrian tectonic attribution and evolution of the Songliao terrane revealed by zircon xenocrysts from Cenozoic alkali basalts, Xilinhot region, NE China

U–Pb dating and Hf isotopic analyses were carried out on xenocrystic zircons from the Cenozoic alkali basalts in the Xilinhot region, NE China, to constrain the nature and evolution of the underlying Songliao terrane, and its role in the assembly of the Central Asian Orogenic Belt. Our data show a wide range of U–Pb age distributions, with Precambrian clusters of ca. 2500Ma, 2400–2200Ma, 2000–1700Ma, 1500Ma, 1000–800Ma, 700–500Ma, and Phanerozoic peaks at 494Ma, 411Ma, 312Ma, 263Ma, 214Ma, 140Ma and 44Ma. The Phanerozoic age peaks are well-recognized in supracrustal rocks in the Songliao terrane or near the sample location. Although most Phanerozoic zircons have positive ɛHf(t) values, which is consistent with many locations throughout the Central Asian Orogenic Belt, some Phanerozoic ones have negative ɛHf(t) values and Tcrust up to ca. 2.5Ga, indicating the involvement of old crustal components during the Phanerozoic thermal events. More importantly, zircons with 207Pb/206Pb ages between ca. 2500Ma and 1700Ma have Tcrust of 2.5–3.5Ga, revealing the possible occurrence of unexposed Archean crustal remnants beneath the Songliao terrane, where no known supracrustal rocks are older than Neoproterozoic. Integrating the U–Pb and Hf isotopic results, we interpret the Songliao terrane as ancient in nature and with a complex crustal evolution history, including the addition of juvenile materials at ∼2.5Ga, reworking of pre-existing crustal components at 2.4–2.2Ga, 2.0–1.8Ga, 1.8–1.7Ga, 1.0Ga, 0.7–0.6Ga, and massive crustal growth during the Phanerozoic. Comparing these data with the Precambrian zircon age distributions of other cratons or micro-continents, we suggest the Songliao terrane shows an affinity to both Monglia and NE Gondwana.

The Pre-Mesozoic crustal evolution of the Cathaysia Block, South China: Insights from geological investigation, zircon U–Pb geochronology, Hf isotope and REE geochemistry from the Wugongshan complex

The multiphase emplacements of granitoids and well-developed depositional sequences from Neoproterozoic to Mesozoic are exposed widely in the Wugongshan domain of South China provide important keys for the reconstruction of the pre-Mesozoic tectonic evolution of the Cathaysia Block. Here we present the results from geological investigations, detrital zircon U–Pb geochronology, in situ Hf-isotope and REE composition of the Ordovician meta-sandstones, together with the U–Pb age data on a Mesozoic pluton with an attempt to evaluate the petrogenesis and crustal evolution history. A group of 276 detrital zircon U–Pb ages are reported from four meta-sandstones which show five major age populations: 2630–2350Ma with a peak of 2440Ma, 1890–1540Ma (peak of 1680Ma), 1120–870Ma (peak of 980Ma), 810–700Ma (peak of 760Ma) and 660–510Ma (peak of 550Ma). Among these, the most prominent age at 980Ma fits well with the collisional event of Yangtze and Cathaysia Blocks. The second prominent age at 760Ma correlates with a breakup of Rodinia, and the third one at 1680Ma corresponds to the initial breakup of Columbia. For the fourth (peak of 2440Ma) and fifth (peak of 550Ma) ages, no corresponding magmatic rocks are exposed in the study area or in the adjacent regions, although the age populations broadly correspond to the global continental growth in the early Paleoproterozoic and the latest Neoproterozoic ‘Pan-African’ orogeny. We obtained 132 in situ Hf isotope compositions, among which 98 show negative εHf(t) values (−36.88 to −0.3) with two-stage model ages (TDM2) of 3.5–1.7Ga (peak of 2.2Ga), and 34 display positive εHf(t) values (+0.3 to +9.89) with crystallization ages of 1.5–1.1Ga (peak of 1.4Ga).Zircons from two Mesozoic granitic samples yield rather similar late Jurassic ages of 158.1±2.1Ma and 154.0±3.9Ma. All the corresponding εHf(t) values of zircons are negative (−24.2 to −4.2) and the Hf two-stage model ages range from 1.5 to 3.0Ga with a peak of 1.68Ga. Combined with previous age data on 120Ma massive granitoids and 230Ma on ductile sheared plutons, we consider that the magmatism in the Wugong complex started from the late Triassic, and reached a peak in the late Jurassic, but was gradually weakened since the early Cretaceous (130Ma) and culminated at 120Ma. Almost all the Wugongshan granitic plutons were derived from the partial melting of Mesoproterozoic crustal material, with little mantle components. We also discuss the provenance of the metasedimentary rocks and pre-Mesozoic crustal evolution of Cathaysia.

The formation and rejuvenation of continental crust in the central North China Craton: Evidence from zircon U–Pb geochronology and Hf isotope

The Trans-North China Orogen (TNCO) along the central part of the North China Craton (NCC) is considered as a Paleoproterozoic suture along which the Eastern and Western Blocks of the NCC were amalgamated. Here we investigate the Precambrian crustal evolution history in the Fuping segment of the TNCO and the subsequent reactivation associated with extensive craton destruction during Mesozoic. We present zircon LA-ICP-MS U–Pb and Lu–Hf data on TTG (tonalite–trondhjemite–granodiorite) gneiss, felsic orthogneiss, amphibolite and granite from the Paleoproterozoic suite which show magmatic ages in the range of 2450–1900Ma suggesting a long-lived convergent margin. The εHf(t) values of these zircons range from −11.9 to 12 and their model ages suggest magma derivation from both juvenile components and reworked Archean crust. The Mesozoic magmatic units in the Fuping area includes granite, diorite and mafic microgranular enclaves, the zircons from which define a tight range of 120–130Ma ages suggesting a prominent Early Cretaceous magmatic event. However, the εHf(t) values of these zircons show wide a range from −30.3 to 0.2, indicating that the magmatic activity involved extensive rejuvenation of the older continental crust.

Zircon Hf isotopes and geochemistry of the early paleoproterozoic high-Sr low-y quartz-diorite in the Quanji massif, NW China: Crustal growth and tectonic implications

The metamorphosed Early Paleoproterozoic granitoids in the Quanji massif, Northwestern China provide constraints for relationship between the Tarim Craton and North China Craton. Among granitoids batholiths, rocks of the Mohe quartz-diorite show typically adakitic geochemical characteristics, with medium K2O/Na2O ratios (0.56–1.17) and high Sr (519–619 ppm) low Y (9.37–20.40 ppm) and Yb (0.97–1.77 ppm) concentrations. The rocks have ɛ Nd(t) values between +2.4 and +4.4 and depleted mantle Nd model ages of 2.43–2.59 Ga. The magmatic zircons have positive ɛ Hf(t) values ranging from +0.40 to +7.60 and depleted mantle Hf model ages of 2.43–2.70 Ga, with major peaks at ∼2.54 and ∼2.65 Ga. The geochemical and Nd-Hf isotopic characteristics indicate that the Mohe quartz-dioritic rocks might be formed by partial melting of high-pressure metamorphosed juvenile crustal rocks in post-orogenic extensional regime in the Early Paleoproterozoic. It suggests that important crustal growth occurred in the Quanji massif and the Tarim Craton at ∼2.4 and 2.5–2.7 Ga. The Quanji massif and Tarim Craton might share a similar crustal evolution history with the North China Craton in the Neoarchean.