Guochun Zhao 赵国春

... Young Nd model ages of 1100 Ma obtained in this study do not support earlier models that the Hulan Group was either rifted from the North China Craton to the south or from the Jiamusi Block to the north, since both these blocks have much older Nd model ages. ...

ABSTRACT The basement characteristic of the Chinese Altai is not firmly constrained, which has strictly hindered our understanding of the early crustal growth in the region. The presence of Precambrian detrital zir-cons in metasedimentary rocks and xenocrystic zircons in granitoids may be regarded as evidence for the existence of unexposed old basement rocks, but can also be explained as detritus originally derived from a nearby cratonic fragment. This paper reports detrital zircon U–Pb and Hf isotopic data for both low-and high-grade metasedimentary rocks from the Chinese Altai. Zircons from these samples have similar age patterns and Hf isotopic compositions. They are characterized by an overwhelming dom-inance of Neoproterozoic-Early Paleozoic ages, with prominent peaks around 465–542 Ma and ε Hf (t) values varying from −25 to +15. Besides, a few zircons cluster at 1.8–2.0 Ga and sparse ones yield dis-cordant ages around 2.3–2.6 Ga, and both give negative ε Hf (t) values between 0 and −28. Combined with previous results in the region, our data suggest that low-and high-grade metasedimentary rocks most likely derived from similar provenances. These data, plus some xenocrystic zircon ages from the granitoid rocks, are quite comparable with the age patterns of the micro-continents and arc terranes in western Mongolia. The zircon population of 440–580 Ma is dominant for gneissic granitoids within the Neoproterozoic–Early Paleozoic terranes in western Mongolian and the Chinese Altai. The Precambrian zircons (>540 Ma) resemble those from old rocks preserved in the Tuva-Mongolian (TM) block and its adjacent arc terranes. Therefore, we suggest that old zircons in the Chinese Altai more likely represent the detritus recycled from western Mongolia. Moreover, information from the TM-derived Precambrian zircons, combined with previous palaeomagnetic constraints, favors northern India as the potential ori-gin for the TM block, from which a small micro-continent drifted northwards and incorporated into the CAOB in a time interval from the Neoproterozoic to Early Paleozoic. Accordingly, the crustal growth of the CAOB in western Mongolia and the Chinese Altai could be outlined by a single accretionary system, and secular amalgamation of magmatic arcs around a Precambrian micro-continent can account for the accretionary history of the region in the Early Paleozoic time.

Recent lithological, metamorphic and geochronological studies show that the basement of the North China Craton (NCC) formed by collision of two discrete Archean to Paleoproterozoic blocks (Eastern and Western Blocks) along a Paleoproterozoic orogen, named the Trans-North China Orogen. However, the timing of the collision is controversial and post-collisional exhumation has not been precisely dated. This study applies the electron

Abstract The basement of the North China Craton can be divided into the Eastern and Western Blocks and the Central Zone (Trans-North China Orogen). The West Block formed by the amalgamation of the Ordos Block in the south and the Yinshan Block in the north ...

Most Neoproterozoic granitoids in the Kuluketage area, northern Tarim Craton are characterized by strongly depleted HREE abundances and high Sr/Y and (La/Yb)N ratios, showing typical geochemical features of adakitic rocks. Zircon U–Pb dating of three adakitic plutons yielded Neoproterozoic ages (754±4, 790±3 and 798±3 Ma). The adakitic granitoids exhibit low MgO and TiO2 contents. Their low Cr, Co and Ni

As part of the Xiong'er volcanic belt along the southern margin of the North China Craton, volcanic rocks in the Xiaoshan and Waifangshan areas have a compositional range from the basaltic andesite, andesite, dacite to rhyolite, which display consistent variation trends in terms of their major and trace elements and Sr–Nd isotopic compositions. The variable Yb contents with nearly constant La/Yb and Tb/Yb ratios of volcanic rocks in two areas suggest that the fractional crystallization may have played an important role in the differentiation from the basaltic andesite, through andesite and dacite, to rhyolite. The volcanic rocks in these two areas are characterized by the LILE and LREE enrichments and negative HFSE anomalies, implying hydrous melting of a mantle wedge in a subduction zone. Variable Sr/Nd ratios of the basaltic andesite and andesite are interpreted as a result of the fluid addition from a subducting slab. Non-radiogenic Nd isotopic compositions as well as high Zr/Y and Nb/Y ratios suggest that the volcanic rocks in these areas were derived from an enriched mantle source. On the other hand, the volcanic rocks of the basaltic andesite and andesite possess markedly higher Fe–Ti and HFSE concentrations than those of typical intra-oceanic arcs, implying that the mantle source from which the volcanic rocks were derived was metasomatised by siliceous melts during the Archean to Paleoproterozoic subduction/collision in the Trans-North China Orogen. These data suggest that in the Paleo-Mesoproterozoic, the southern margin of the North China Craton was most likely an Andean-type continental arc in which slab dehydration not only induced the melting of a pre-existing metasomatised mantle source, but also released LILE-enriched fluids into the mantle source, masking the inherent HFSE-enriched characteristics of the volcanic rocks along the southern margin of the craton. The results of this study indicate that the North China Craton, like many other continental components (e.g. North America, Greenland, Baltica, Amazonia, Australia, etc.) of the supercontinent Columbia (Nuna), also underwent a subduction-related outgrowth along its southern margin during the Paleo-Mesoproterozoic time.

The Paleo-Mesoproterozoic Xiong’er volcanic rocks along the southern margin of the North China Craton are lithologically and geochemically similar to those formed in subduction-related, continental margin volcanic arcs. The volcanic rocks are primarily composed of basaltic andesites and andesites, with minor dacites and dacitic rhyolites. Traditionally, the Xiong’er volcanic rocks have been divided from lower to upper into the Xushan, Jidanping and Majiahe Formations, but the ages of volcanic rocks in these formations have not been well constrained, which has hindered further understanding the tectonic significance of the Xiong’er volcanic belt at the southern margin of the North China Craton. SHRIMP and LA-ICP-MS U-Pb zircon analyses, combined with cathodeluminescence (CL) images, have enabled resolution of xenocrystic and magmatic zircons that can be directed toward determination of the ages of the Xiong’er volcanic rocks. SHRIMP and LA-ICP-MS U-Pb analyses on magmatic zircons from two basaltic andesite samples, one dacite sample and one rhyolite sample of the Xushan Formation, known as the lowest sequence of the Xiong’er volcanic rocks, indicate that the volcanic eruption of this Formation occurred at ∼1.78 Ga, but most xenocrystic/inherited zircons in these samples yielded 207Pb/206Pb ages ranging from 2.55 Ga to 1.91 Ga. Of three samples collected from the Jidanping Formation, two rhyolite samples (05XE015 and 05XE100) yielded weighted mean 207Pb/206Pb ages of 1778 ± 5.5 Ma and 1751 ± 14 Ma, respectively, similar to the ages of the volcanic rocks in the Xushan Formation, whereas one dacite sample (05XE066) gave a weighted mean 207Pb/206Pb age of 1450 ± 31 Ma, which is the youngest age obtained from the Xiong’er volcanic rocks. One andesite sample (06XS012) collected from the Majiahe Formation yielded two major age populations, with the older one at 1850 ± 5.9 Ma, interpreted as the age of the xenocrystic/inherited zircons, and the younger one at 1778 ± 6.1 Ma, interpreted as the age of the volcanic eruption to form the Majiahe andesite, coeval with the formation of most volcanic rocks from the Xushan and Jidanping Formations. These new SHRIMP and LA-ICP-MS U-Pb zircon data indicate that the traditional stratigraphic subdivision of the lower, middle and upper sequences of the Xiong’er volcanic rocks is not viable and that most of the Xiong’er volcanic rocks formed at 1.78–1.75 Ga, with minor felsic volcanic rocks erupting at ∼1.45 Ga. Similar-aged arc-related volcanic belts have also been found in the southern margin of North America, Greenland and Baltica, the western margin of the Amazonia Craton, the southern and eastern margins of the North Australia Craton, and the eastern margin of the Gawler Craton, which are considered to represent long-lived (1.8–1.3 Ga), subduction-related growth via accretion at key continental margins of the Paleo-Mesoproterzoic Columbia (Nuna) supercontinent.

The Xiong'er volcanic belt, covering an area of more than 60,000 km2 along the southern margin of the North China Craton, has long been considered an intra-continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the Paleo-Mesoproterozoic supercontinent Columbia. However, such interpretations cannot be accommodated by lithology, mineralogy, geochemistry and geochronology of the volcanic rocks in the belt. Lithologically, the Xiong'er volcanic belt is dominated by basaltic andesite and andesite, with minor dacite and rhyolite, different from rock associations related to continental rifts or mantle plumes, which are generally bimodal and dominated by mafic components. However, they are remarkably similar to those rock associations in modern continental margin arcs. In some of the basaltic andesites and andesites, amphibole is a common phenocryst phase, suggesting the involvement of H2O-rich fluids in the petrogenesis of the Xiong'er volcanic rocks. Geochemically, the Xiong'er volcanic rocks fall in the calc-alkaline series, and in most tectono-magmatic discrimination diagrams, the majority of the Xiong'er volcanic rocks show affinities to magmatic arcs. In the primitive mantle normalized trace-element diagrams, the Xiong'er volcanic rocks show enrichments in the LILE and LREE, and negative Nb–Ta–Ti anomalies, similar to arc-related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge. Nd-isotope compositions of the Xiong'er volcanic rocks suggest that 5–15% older crust has been transferred into the upper lithospheric mantle by subduction-related recycling during Archean to Paleoproterozoic time. Available SHRIMP and LA-ICP-MS U–Pb zircon age data indicate that the Xiong'er volcanic rocks erupted intermittently over a protracted interval from 1.78 Ga, through 1.76–1.75 Ga and 1.65 Ga, to 1.45 Ga, though the major phase of the volcanism occurred at 1.78–1.75 Ga. Such multiple and intermittent volcanism is inconsistent with a mantle plume-driven rifting event, but is not uncommon in ancient and existing continental margin arcs. Taken together, the Xiong'er volcanic belt was most likely a Paleo-Mesoproterozoic continental magmatic arc that formed at the southern margin of the North China Craton. Similar Paleo-Mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of Laurentia, the southern margin of Baltica, the northwestern margin of Amonzonia, and the southern and eastern margins of the North Australia Craton, which are considered to represent subduction-related episodic outbuilding on the continental margins of the Paleo-Mesoproterozoic supercontinent Columbia. Therefore, in any configuration of the supercontinent Columbia, the southern margin of the North China Craton could not have been connected to any other continental block as proposed in a recent configuration, but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the North China Craton.

... b Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong. ... The age results of Fig. ... Here, we present new zircon U–Pb crystallization age and Hf isotopic data for volcanic rocks interlayered with sedimentary rocks of the Shuangqiaoshan Group ...

The basement of the North China Craton can be divided into the eastern, central and western zones, based on lithological, structural, metamorphic and geochronological data. The western zone comprises two different petrotectonic units: Archaean tonalitic–trondhjemitic–granodioritic (TTG) grey gneisses and metamorphic mafic rocks, and Palaeoproterozoic khondalite series. The former is characterized by isobaric cooling (IBC)-type anticlockwise P–T paths in the north-northwestern

Lithological, structural, metamorphic and geochronological data for the North China Craton enable its division into the Western and Eastern Blocks of Archean to Paleoproterozoic age separated by a north–south trending Paleoproterozoic orogenic belt: the Central Zone. The Central ...

... The TTG gneisses in this region are predominantly composed of Na-rich biotite gneiss ... by several horizons of glacial deposits and volcanic rocks, separated by thick layers of ... Recent geochemical studies have also suggested that the formation of the Neoproterozoic granites and ...

... 2.5 Ga; eg Li and Qian, 1994, Tian et al., 1996, Li et al., 2000a, Li et al., 2000b and Kusky and Li, 2003). ... 2. Field relationships in the Hengshan Complex. The gneisses and migmatites of the Hengshan Complex have been described in detail by Li and Qian (1994) and Tian et al. ...

As a major lithostratigraphic unit of the Palaeoproterozoic Jiao-Liao-Ji Belt in the Eastern Block of the North China Craton, the Liaohe Group consists of an assemblage that is transitional from a lower arkose-and volcanic-rich sequence (Langzishan, Li'eryu and ...

... SHRIMP U–Pb zircon dating of the Neoproterozoic Penglai Group and Archean gneisses from the Jiaobei Terrane, North China, and their tectonic implications. ... Keywords: SHRIMP U–Pb Zircon dating; Archean; Neoproterozoic Penglai Group; North China Craton; Sulu Orogen. ...

The Wutai Complex represents the best preserved granite-greenstone terrane in the North China Craton. The complex comprises a sequence of metamorphosed ultramafic to felsic volcanic rocks, variably deformed granitoid rocks, along with lesser amounts of siliciclastic and carbonate rocks and banded iron formations. Petrological evidence from the Wutai amphibolites indicates four metamorphic evolutionary stages. The M1 assemblage is composed of

An examination of lithological, geochemical, geochronological, structural and metamorphic P–T path data suggests that the basement of the North China Craton can be divided into Eastern and Western Blocks, separated by major crustal boundaries that roughly correspond with ...

Syn- and post-orogenic Cu mineralization in the northern Xinjiang Paleozoic accretionary and collisional orogenic belt in northwestern China is of great economic interest. About 40 Cu-bearing deposits have been discovered in the area, making it one of the most important metallogenic belts in China. According to their host rocks, these deposits can be classified into four principal types: (1) volcanic-hosted

The Xiong'er volcanic rocks constitute a large Paleo-Mesoproterozoic volcanic belt along the southern margin of the North China Craton, which are composed primarily of basaltic andesites and andesites, with minor dacites and dacitic rhyolites. The basaltic andesites and andesites from the Xiong'er volcanic rocks in the Zhongtiao Mountain show consistent ɛNd(t), La/Nb and Th/Nb values irrespectively of SiO2, which preclude

The Early Cretaceous Baijuhuajian pluton is an A-type granitic intrusion, emplaced along the Jiangshan-Shaoxing (JSSX) fault zone in western Zhejiang Province, SE South China. It intruded into a Late Jurassic volcanic basin bounded by Proterozoic sandstone and siltstone. The ...

... X Ca pl < 0.17) ([Todd, 1998], [Holdaway, 2001], [Wu et al., 2004a], [Wu et al., 2004b], [Wu andZhao, 2006a] and [Wu and Zhao, 2006b]). ... Later, the intrusion of the Ruby Range Batholith led to a contact metamorphic overprint M2 producing a 5–6 km wide aureole in which the ...