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The Wulong gold deposit (> 80 t Au) is located at the northeastern margin of the North China Craton (NCC). Gold in the most economically important quartz veins (Stages 2 and 3) is associated with a varied assemblage of Bi and Te minerals. Stage 2 is characterized by, in a temporal order, native gold-native bismuth-maldonite-hedleyite, bismuthinite-Bi-sulfotellurides, electrum-hessite-Bi-Pb-Ag sulfosalts, Bi-Pb sulfosalts, and Bi-Pb-sulfotellurides. All of these minerals except maldonite, electrum, hessite, and Bi-sulfosalts are present in Stage 3 veins, which also contain jonassonite and unnamed minerals with stoichiometry of Bi8Te3 and Bi5Te3. These complex Bi mineral assemblages resulted from changes in Pb, Ag, Te and Bi concentrations in reduced hydrothermal fluids both locally and temporally, from Stage 2 to 3. Texturally, approximately 85% of the gold grains are associated with almost all Bi minerals in each main-stage mineralization. Quartz-vein ores from Stages 2 and 3 have high Bi concentrations (up to 7332 ppm) and show a positive correlation between Bi and Au, with Bi/Au ratios > 10. These textural and geochemical associations, together with the occurrence of numerous droplet-like blebs and small inclusion trails of native bismuth and Bi-tellurides with native gold, maldonite, or jonassonite, suggest that Bi-rich melts may have formed from the hydrothermal fluids of Stages 2 and 3, and acted as an Au scavenger in a complex Bi-Au-Pb-Ag-Te system. Hence, the intimate association of Bi and Au at Wulong is the result of Au enrichment via the liquid bismuth collector mechanism. Unlike Wulong, however, other deposits in the NCC, such as Yangzhaiyu (Xiaoqinling district), Guilaizhuang (Jiaodong district) and Dongping (Jidong district), are characterized by low Bi concentrations, and are much richer in Te than Bi, so these systems could not generate low-melting point Bi-rich polymetallic melts. The low-sulfur Bi-Au-Pb-Ag-Te association at Wulong is consistent with that observed in reduced intrusion-related gold systems elsewhere and suggests that hydrothermal fluids may have been derived from the co-located Early Cretaceous diorite-granite porphyry dyke swarm. [ABSTRACT FROM AUTHOR]

Timing of the major Baiyun gold deposit (~ 70 t Au) in the northeastern North China Craton is controversial. A textural and geochronological study of high-grade gold ores identifies three generations of xenotime (Xtm-1, Xtm-2 and Xtm-3), even in single grains. The oldest Xtm-1, in grain cores, is of metamorphic origin, with very high U and U/Th ratios, and hump-shaped, HREE-enriched patterns with maximum normalized values at Yb and large negative Eu anomalies. It is dated at 1856 ± 6 Ma, consistent with its crystallization during regional metamorphism related to cratonization. In contrast, 244 ± 2 Ma Xtm-2 overgrowths are of hydrothermal origin, having low U and U/Th ratios and hump-shaped, MREE-enriched patterns with maximum normalized values at Ho and negligible Eu anomalies. Xtm-2 records a previously unrecognized Middle Triassic hydrothermal episode. Xtm-3, in equilibrium with native gold-hosting pyrite and rutile, is also hydrothermal. The Xtm-3 domains have similar U, U/Th ratios, and MREE-enriched patterns to Xtm-2, but a younger crystallization age of 231 ± 1 Ma. Associated rutile grains that show close textural associations with auriferous pyrite and native gold have an in situ SIMS U–Pb an intercept age of 229 ± 4 Ma, consistent with that of Xtm-3. Collectively, these reliable ages indicate that gold mineralization at Baiyun occurred at ca. 230 Ma, predating the emplacement of granite intrusions by more than 3 million years. Both the Middle Triassic hydrothermal event (~244 Ma) and the Late Triassic gold mineralization event (~230 Ma) lie within the temporal window of collisional tectonics in the host orogen. In combination, the new geochronology and fluid-inclusion and geological data support Bayun's classification as an orogenic gold deposit. [ABSTRACT FROM AUTHOR]

We present the results of Mesozoic sequences of the Bohai Bay basin in North China, based mainly on geochronology and interpretations of seismic profiles and logging data. Five tectono-stratigraphic sequences are defined: Lower-Middle Triassic, Lower-Middle Jurassic, Upper Jurassic, Lower Cretaceous and Upper Cretaceous. Based on an analysis of detrital zircons, the clastic rocks recorded two intervals of Jurassic magmatic activity, during 180–175 and 160–152 Ma, which can be correlated to the Nandaling and Tiaojishan Formations in the Yanshan area, respectively. However, since Jurassic volcanic rocks have not yet been found in the Bohai Bay basin, we speculate that these two stages of activity were mainly concentrated around the periphery of the North China Craton (NCC) rather than within. Based on an analysis of zircons from volcanic rocks and pyroclastics, the early Cretaceous magmatism in the Bohai Bay basin can be divided into two stages, 125–120 and 110–100 Ma, which can be correlated to magmatism in the eastern part of the NCC. The zircon ages indicate an absence of volcanic activity during the late Tuchengzi and Zhangjiakou periods which may correlate to the uplift of the Bohai Bay basin in the late Late Jurassic. Comparison of the development of Mesozoic basins and sedimentary strata in the central-eastern part of Yanshan tectonic belt and the the Bohai Bay basin indicates that the two areas are generally comparable, but with substantial differences. The central-eastern part of the Yanshan structural belt lacks Early-Middle Triassic strata, and the Bohai Bay basin lacks late Jurassic-early Cretaceous strata. Based on research results from late Mesozoic sedimentary structures in the central and eastern parts of the Yanshan tectonic belt, we infer that episode A of the Yanshanian Orogeny was weak in the Bohai Bay basin and its periphery, while episode B of the Yanshanian Orogeny had a strong influence on the Bohai Bay basin and its periphery. The available data reveal differences in the expression of these episodes: the Bohai Bay basin is characterized by vertical uplift, and the northern margin of NCC is characterized by horizontal compression uplift. [ABSTRACT FROM AUTHOR]

Evidence for the Jurassic–Cretaceous Yanshan Movement (Orogeny) was first identified in the Jingxi Basin, a part of the Yanshan fold-and-thrust belt (YFTB) along the northern margin of the North China Craton. The disconformity or angular unconformity within the Jurassic volcano-sedimentary successions in the basin was interpreted to have resulted from a period of incipient shortening during the Yanshan Movement, commonly known as event A. However, the absolute ages of both event A and associated Jurassic units remain controversial. Here, we present the results of zircon U–Pb geochronology for volcanic and clastic rocks from the Jurassic units in the Jingxi Basin. The results provide better constraints on the depositional ages of formations in the basin: (1) Early-to-early Middle Jurassic (175–167 Ma) for the Nandaling Formation; (2) middle Middle Jurassic for the Yaopo Formation; (3) late Middle Jurassic for the Longmen Formation; (4) early Late Jurassic for the Jiulongshan Formation; and (5) late Late Jurassic (157–149 Ma) for the Tiaojishan Formation. Stratigraphic and geochronological correlations indicate that the Jiulongshan Formation and the Tiaojishan Formation are of different depositional ages in different regions. The Longmen Formation in the Jingxi Basin is equivalent to the Haifanggou Formation in the eastern YFTB. Two sedimentary cycles separated by a sedimentary hiatus, shown as disconformity and local angular unconformity, have been identified in the Jurassic sequences of the YFTB. Depositional ages of the rocks above and below the disconformity, which lies between the Yaopo and Longmen formations in the Jingxi Basin, constrain the timing of event A to 167 ± 2 Ma (late Middle Jurassic). This event is the first phase of shortening deformation in eastern China induced by the paleo-Pacific plate subduction. We propose that the shortening period was relatively transient, in contrast to previous suggestions of long-duration shortening. [ABSTRACT FROM AUTHOR]

Precise time constraints of the main extrusive phase of the Emeishan large igneous province (ELIP) remain unresolved because basalts commonly do not contain suitable minerals for U-Pb dating, whereas previous 40Ar/39Ar studies on basalts yielded tectonothermal overprint ages. The timing for the ELIP was deduced from indirect dating of minor intrusions of ultramafic/mafic and felsic compositions by geochronological methods and geological correlations. The extrusive part of the ELIP consists of an older low-Ti and younger high-Ti basalt phases. We have found fresh samples of plagioclase-phyric rocks at the lower Qiaojia extrusive section (the Yunnan province of China), which belong to the ELIP unit of the high-Ti basalt series. 40Ar/39Ar dating on plagioclase from two samples conducted at two different laboratories using different age standards yielded statistically indistinguishable results with the weighted mean age of 260.1 ± 1.2 Ma for five individual measurements. This provides the direct constraints on the onset of the ELIP high-Ti basalt extrusive phase. The obtained age is within the error or slightly older than the age of the Guadalupian-Lopingian boundary and felsic ignimbrite capping the ELIP lava succession (both dated at 259.1 ± 0.5 Ma). Our new data are strengthening the short duration of the, at least, high-Ti phase of the ELIP volcanism and its temporal link with the end-Guadalupian mass extinction. Estimation of the total duration of the ELIP volcanism awaits finding of suitable for dating low-Ti basalts. [ABSTRACT FROM AUTHOR]

The North China craton (NCC) hosts numerous gold deposits and is known as the most gold-productive region of China. The gold deposits were mostly formed within a few million years in the Early Cretaceous (130-120 Ma), coeval with widespread occurrences of bimodal magmatism, rift basins and metamorphic core complexes that marked the peak of lithospheric thinning and destruction of the NCC. Stable isotope data and geological evidence indicate that ore-forming fluids and other components were largely exsolved from cooling magma and/or derived from mantle degassing during the period of lithospheric extension. Gold mineralization in the NCC contrasts strikingly with that of other cratons where gold ore-forming fluids were sourced mostly from metamorphic devolatization in compressional or transpressional regimes. In this paper, we present a summary and discussion on time-space distribution and ore genesis of gold deposits in the NCC in the context of the timing, spatial variation, and decratonic processes. Compared with orogenic gold deposits in other cratonic blocks, the Early Cretaceous gold deposits in the NCC are quite distinct in that they were deposited from magma-derived fluids under extensional settings and associated closely with destruction of cratonic lithosphere. We argue that Early Cretaceous gold deposits in the NCC cannot be classified as orogenic gold deposits as previously suggested, rather, they are a new type of gold deposits, termed as 'decratonic gold deposits' in this study. The westward subduction of the paleo-West Pacific plate (the Izanagi plate) beneath the eastern China continent gave rise to an optimal tectonic setting for large-scale gold mineralization in the Early Cretaceous. Dehydration of the subducted and stagnant slab in the mantle transition zone led to continuous hydration and considerable metasomatism of the mantle wedge beneath the NCC. As a consequence, the refractory mantle became oxidized and highly enriched in large ion lithophile elements and chalcophile elements (e.g., Cu, Au, Ag and Te). Partial melting of such a mantle would have produced voluminous hydrous, Au- and S-bearing basaltic magma, which, together with crust-derived melts induced by underplating of basaltic magma, served as an important source for ore-forming fluids. It is suggested that the Eocene Carlin-type gold deposits in Nevada, occurring geologically in the deformed western margin of the North America craton, are comparable with the Early Cretaceous gold deposits of the NCC because they share similar tectonic settings and auriferous fluids. The NCC gold deposits are characterized by gold-bearing quartz veins in the Archean amphibolite facies rocks, whereas the Nevada gold deposits are featured by fine-grained sulfide dissemination in Paleozoic marine sedimentary rocks. Their main differences in gold mineralization are the different host rocks, ore-controlling structures, and ore-forming depth. The similar tectonic setting and ore-forming fluid source, however, indicate that the Carlin-type gold deposits in Nevada are actually analogous to decratonic gold deposits in the NCC. Gold deposits in both the NCC and Nevada were formed in a relatively short time interval (<10 Myr) and become progressively younger toward the subduction zone. Younging of gold mineralization toward subduction zone might have been attributed to retreat of subduction zone and rollback of subducted slab. According to the ages of gold deposits on inland and marginal zones, the retreat rates of the Izanagi plate in the western Pacific in the Early Cretaceous and the Farallon plate of the eastern Pacific in the Eocene are estimated at 8.8 cm/yr and 3.3 cm/yr, respectively. [ABSTRACT FROM AUTHOR]

A National Science Foundation of China (NSFC) major research project, Destruction of the North China Craton (NCC), has been carried out in the past few years by Chinese scientists through an in-depth and systematic observations, experiments and theoretical analyses, with an emphasis on the spatio-temporal distribution of the NCC destruction, the structure of deep earth and shallow geological records of the craton evolution, the mechanism and dynamics of the craton destruction. From this work the following conclusions can be drawn: (1) Significant spatial heterogeneity exists in the NCC lithospheric thickness and crustal structure, which constrains the scope of the NCC destruction. (2) The nature of the Paleozoic, Mesozoic and Cenozoic sub-continental lithospheric mantle (CLM) underneath the NCC is characterized in detail. In terms of water content, the late Mesozoic CLM was rich in water, but Cenozoic CLM was highly water deficient. (3) The correlation between magmatism and surface geological response confirms that the geological and tectonic evolution is governed by cratonic destruction processes. (4) Pacific subduction is the main dynamic factor that triggered the destruction of the NCC, which highlights the role of cratonic destruction in plate tectonics. [ABSTRACT FROM AUTHOR]

Knowing when the Tibetan Plateau reached its present elevation is important for understanding the uplift history of Tibet. Recently, Rowley & Currie (2006) suggested that central Tibet exceeded 4000 m from 35 Ma to the Pliocene using the oxygen-isotope composition of calcareous minerals in Lunpola basin sediments. However, they adopted a poor age assignment for the Dingqing Formation in the Lunpola basin based on previous microfossil studies. In this study, we present SIMS U–Pb zircon dates from a bentonite layer intercalated within the middle to lower Dingqing Formation. Twenty-six measurements yield a highly reliable U–Pb age of 23.5 ± 0.2 Ma (2σ, MSWD = 1.1), suggesting that the deposition age of the Dingqing Formation is late Oligocene to early Miocene, much older than the Miocene–Pliocene age used by Rowley & Currie (2006). This age robustly constrains the age of Cenozoic sedimentary strata in central Tibet, and hence provides an important basis for estimating the palaeoelevation in the high Tibet during the geological past. [ABSTRACT FROM PUBLISHER]

Abstract: Noble gas isotopic ratios provide unique and important constraints for the evolution of the subcontinental mantle. We present one-step crushing noble gas isotope data from corundum and co-existing mantle xenoliths and megacrystals from the Changle volcanic fields in the middle part of the Tan-Lu Fault Zone, eastern North China Craton. The 3He/4He ratio is 7.6–8.3 times the atmospheric ratio (Ra) in corundum, indicating contributions of fluids from convective asthenosphere. The 3He/4He ratio in titanomagnetite megacrystals ranges from 5.8 to 6.5Ra, suggesting possible U–Th contamination in the crystal lattice, with the 3He/4He ratio of host magma being higher than 6.5Ra. The olivine and opx in lherzolite show high helium contents and homogeneous isotopic helium ratios (6.9–7.0Ra). The cpx in wehrlite show significantly higher helium contents and slightly higher helium ratio (7.6Ra) than co-existing olivine (7.0–7.5Ra). Combined with isotope correlation diagrams, the systematic difference in 4He abundance, the 3He/4He and 4He/40Ar∗ ratios of cpx, opx and olivine in pyroxenite, lherzolite and wehrlite suggest comprehensive refertilization of lithospheric mantle in the eastern North China Craton. [Copyright &y& Elsevier]

SUMMARY Widely distributed haematite-bearing red beds are an important source of palaeomagnetic field records. However, unresolved issues regarding remagnetization and inclination shallowing in red beds have questioned the reliability of the palaeomagnetic results obtained from such materials. In this study, we investigated the remagnetization mechanism in red beds from Lower Triassic sandstones in Yunnan Province, southwestern China. Our results indicate that the characteristic remanent magnetizations (ChRMs) of most samples (112/125) are dominated by only one component at temperatures 80-660 °C, with a mean direction of D/ I= 0.9/46.6° ( k= 440.2, α95= 2.1°). The corresponding geomagnetic pole is 89.1°N, 331.7°E ( k= 338.2, A95= 2.4°). This coincides with the present geomagnetic field, which is a strong indication that these ChRMs are remagnetized. Combined rock magnetic and microscope investigations reveal that the remagnetization is due to the acquisition of a chemical remanent magnetization (CRM) carried by authigenic maghemite and haematite. Despite the widespread remagnetization, about 7 per cent of the studied samples still record a magnetization that we consider to be primary that was isolated at high temperatures 610-660 °C, with a mean direction of D/ I= 213.3/18.6° ( k= 16.0, α95= 11.7°). We propose that the CRM overprinting is controlled by the overlapping degree of the unblocking temperature between the CRM carried by the authigenic haematite and the primary remanent magnetization carried by the detrital haematite. Our results further suggest that microscope investigation, rock magnetic proxies for the haematite concentration and susceptibility-temperature curves are useful methods for pre-selecting samples suitable for isolating the primary remanence at this region. The linkage among the palaeomagnetic results, rock magnetic proxies and CRM remagnetization mechanism could be extended to other studies, although the detailed proxy would be different due to specific overprint process. [ABSTRACT FROM AUTHOR]

Much attention has been paid in the last two decades to the physical and chemical processes as well as temporal-spatial variations of the lithospheric mantle beneath the North China Craton. In order to provide insights into the geodynamics of this variation, it is necessary to thoroughly study the state and structure of the lithospheric crust and mantle of the North China Craton and its adjacent regions as an integrated unit. Based on the velocity structure of the crust and upper mantle constrained from seismological studies, this paper presents various available geophysical results regarding the lithosphere thickness, the nature of crust-mantle boundary, the upper mantle structure and deformation characteristics as well as their tectonic features and evolution systematics. Combined with the obtained data from petrology and geochemistry, a mantle flow model is proposed for the tectonic evolution of the North China Craton during the Mesozoic-Cenozoic. We suggest that subduction of the Pacific plate made the mantle underneath the eastern Asian continent unstable and able to flow faster. Such a regional mantle flow system would cause an elevation of melt/fluid content in the upper mantle of the North China Craton and the lithospheric softening, which, subsequently resulted in destruction of the North China Craton in different ways of delamination and thermal erosion in Yanshan, Taihang Mountains and the Tan-Lu Fault zone. Multiple lines of evidence recorded in the crust of the North China Craton, such as the amalgamation of the Archean eastern and western blocks, the subduction of Paleo- oceanic crust and Paleo-continental residue, indicate that the Earth in the Paleoproterozoic had already evolved into the plate tectonic system similar to the present plate tectonics. [ABSTRACT FROM AUTHOR]

This paper reports the features of an as yet uncultivated magnetotactic coccus, named MYC-1, recently found from surface sediments of Lake Miyun near Beijing. Light microscope and Bacteriodrome analyses demonstrate that MYC-1 is north-seeking in the Earth's magnetic field. Transmission electron microscope (TEM) attached with energy-dispersive X-ray analyses reveal that this coccus contains a single chain of magnetosomes, containing approximately 10 large iron-oxide crystals. Morphology of these crystals is featured by prism with a mean length and width of 117 nm and 95 nm (statistics from 281 crystals), respectively; it yields an aspect factor of 1.24. A linear relationship (r2 = 0.83) clearly exists between the length and width of crystals. In agreement with previous results, we observed that the size distribution of the MYC-1 is distinctly asymmetric with cut off toward larger sizes, which is the opposite of non-biogenic crystals. Low-temperature magnetic measurements on bulk bacteria samples show a distinct Verwey transition temperature (Tv) around 115 K indicative of magnetite, thus the magnetosomes contain magnetite. For a field of 0.5 mT, we determined a swimming speed of approximately 141 μ m/s for the MYC-1. Furthermore, the magnetic moment estimated from the rotating magnetic field method is 1.8 × 10-15 Am2 per cell. Finally, this finding of freshwater magnetotactic coccus in Lake Miyun suggests that magnetite produced by the MYC-1 strain is a potentially important remanence carrier in these lake sediments. [ABSTRACT FROM AUTHOR]

Abstract: The Emeishan large igneous province has been suggested to be formed from mantle plumes; yet, the plume formation is debated. Radiometric dating showed that the main phase of the Emeishan basalts (EBs) occurred at ∼260 Ma, corresponding to the end-Guadalupian mass extinction. Recent numerical modeling suggested that the mantle-plume activity is linked closely to both the superchron and the mass extinction. Therefore, the age and duration of EBs are key issues to further understand the Emeishan mantle-plume activity, the end-Guadalupian mass extinction, and genesis of the Kiaman reverse superchron. In the present article, we summarize the recent progresses on these topics. In combination with our new paleomagnetic results, we further discussed the relationship between the EBs and the end-Guadulupian mass extinction, as well as their geodynamic significances. [Copyright &y& Elsevier]

Abstract: New palaeomagnetic and 40Ar/39Ar dating was carried out on the volcanic rocks and interbedded fossil-bearing lake sediments at the Sihetun section (northeast China) to determine the duration of deposition of the lacustrine sediments. The 40Ar/39Ar ages of the lower and upper volcanic rocks near the lava-sediment contacts are respectively 125.7±2.6Ma and 124.2±2.5Ma, which is in good agreement with a previously reported age of tuffs in the lake deposits. This is further supported by a normal palaeomagnetic polarity recorded by the whole lacustrine interval. With these palaeomagnetic investigations and new age controls, we conclude that the whole lacustrine interval at Sihetun was deposited within the normal polarity chron M3n (marine anomaly) during the Early Cretaceous. The possibly volcanic-associated ancient lake may have existed for a relatively short duration of less than 0.7myr, assuming the M3n chron age to be between 124.72–124.04Ma. [Copyright &y& Elsevier]

It has been proposed that paleoclimatic changes and tectonic events strongly affect hominoid evolution. The Zhupeng section at Yuanmou Basin, southwestern China, with the hominoid-bearing fluvial-lacustrine sediments, is an ideal natural laboratory to test this hypothesis. This study provided an integrated magnetic study, including low-frequency susceptibility, the anisotropy of magnetic susceptibility, temperature-dependent susceptibility, hysteresis loops, isothermal remanent magnetization, and anhysteretic remanent magnetization, on samples from the Baozidongqing section at Zhupeng. Results show that the dominant magnetic carrier is hematite, with minor amount of magnetite. Both the composition and concentration of magnetic minerals strongly correlate with the lithostratigraphy. At least eight short-term events defined by higher concentrations of magnetite were identified. These short events reflect that the subtropical dry-hot climate is similar to today's climate. Basing on the lithostratigraphic and rock magnetic results, we suggest that Yuanmou Basin was in a steady deposition environment from about 11 to 7 Ma, which is characterized by alternating of long-term torrid-humid climate and short-term dry-hot climate. Our study provides invaluable environment information for understanding the climate shift and the relationship between paleoenvironment and hominoid evolution in southwestern China during late Miocene. [ABSTRACT FROM AUTHOR]

Dating deposits in caves formed by rivers may yield insight into rates and processes of bedrock incision. Three cave passages at different levels have developed in the walls of the Qianyou River valley in the Qinling mountains, south of the city of Xian, China. Twelve speleothem samples near the position of palaeowater tables in three cave passages are dated by the 230Th dating method. The results show that the river cut down at the rate of 0.23 ± 0.02 mm/yr from 358,000 ± 38,000 to 247,000 ± 28,000 yr ago, 0.19 ± 0.03 mm/yr from 247,000 ± 28,000 to 118,000 ± 19,000 yr ago, and 0.51 ± 0.08 mm/yr from 118,000 ± 19,000 yr ago until today. These fall very close to the glacial–interglacial transition following marine oxygen isotope stages 10, 8, and 6, respectively. The increase in downcutting rates during the interglacial period is consistent with warm, wet weather, increasing rates of erosion. This may lead us toward an underlying mechanism for modulating incision that is not in a direct response to the presence of headwater glaciers. [Copyright &y& Elsevier]

Paleomagnetic study on the Cenozoic volcanic rocks from the Tuoyum Basin of the southwest Tien Shan indicates that most samples could isolate a stable characteristic remanent magnetization with reversed polarity. The positive fold test suggests that the characteristic component is very likely to be a primary magnetization acquired in the formation of rocks. Comparison with the reference Eurasia poles at 60 Ma indicates little or insignificant N-S convergence between the south edge of southwest Tien Shan and Siberia since the onset of the India/Asia collision at the Eocene. Furthermore, the Cretaceous and Tertiary paleomagnetic results suggest that the Tuoyun Basin was subjected to a local clockwise rotation of 20° _350 with respect to Eurasia since the Paleocene time, which is probably subsequent to the Cenozoic northward compression of the Pamir arc. [ABSTRACT FROM AUTHOR]

We report new absolute palaeointensity estimates using basalts from northeastern China (K/Ar age, 125–120 Ma) using the modified Shaw method in conjunction with the microwave technique. Samples for the palaeointensity experiments were selected mainly based on their good reversibility of thermomagnetic curves and single primary magnetization characteristics. Using the modified Shaw method, 28 out of 45 measured samples from 10 cooling units give a virtual dipole moment of , and the microwave technique using 14 acceptable determinations (out of 20 measured) give an average value of . Results using both the modified Shaw method and the microwave technique demonstrate that the geomagnetic field strength recorded by these lavas was low. This is in agreement with previous results of the same time interval obtained by the Thellier method with partial thermal remanence (p-TRM) checks. The fact that different techniques give qualitatively compatible low palaeointensity results provides greater confidence that the weak field features seen just prior to the Cretaceous normal superchron (CNS) are the result of the actual field recorded by the basalts as opposed to artefacts of the method/analysis. This study also demonstrates that the microwave technique can be used for very old basalts. [ABSTRACT FROM AUTHOR]

In order to provide the age for the ISEA (one reversed event in the CNS) a combined rock magnetic, paleomagnetic and geochronoiogic study has been conducted on two Cretaceous andesitic basalt lava flows from Sanbaoying, Liaoning Province of northeastern China. Rock magnetic investigations show that pseudo-single domain (PSD) titanomagnetite with poor-Ti content is the dominant magnetic mineral in Sanbaoying lava flows. Detailed systematic thermal demagnetization allowed us to isolate two remanence components after removing a low temperature component at 100°C/150°C; an intermediate temperature component with normal polarity at 150°C/200°C-380°C/400°C and the characteristic remanence component (ChRM) with reversed polarity above 400°C/450°C. 40Ar/39Ar dating results show that Sanbaoying rocks were erupted at 116.0±0.3 Ma. Combination of paleomagnetic results and 40Ar/39Ar dating indicates that the reversed event recorded in Sanbaoying lavas corresponds to the ISEA event in the CNS. Our age determination for ISEA reversed event provides chronological evidence to study the relevance between global geological events that occurred in the CNS and geodynamo processes. [ABSTRACT FROM AUTHOR]

We compare new anisotropy of magnetic susceptibility (AMS) data with previously-determined paleoclimatically sensitive parameters for a loess profile at Lingtai, central Loess Plateau, China, to unravel factors that control loess AMS. Magnetic lineations are clustered along NE–SW and NW–SE orientations during cold and warm periods, respectively, which probably corresponded to paleowind directions of both winter and summer monsoons. Anomalously steep magnetic foliations coincidentally occur at the paleoclimatic stage boundaries, indicating sediment disturbance. Lineation strength appears to be sensitive to millennial-scale rapid paleoclimatic fluctuations. Generally, the winter monsoon produces a lower degree of lineation than the summer monsoon. Furthermore, by studying lineation subsets for the cold and warm periods, we find that the cold-interval lineation strengths co-vary with grain size over the last ∼70 ka. During the last interglacial (about 74–128 ka), the lineation and declination of the susceptibility maximum (Dec-Kmax) are sensitive to rapid fluctuations in winter and summer monsoons. Long-term trends of magnetic foliation and anisotropy degree replicate grain size variations, with superimposed short-term peaks related to post-depositional compaction, as suggested by density. The AMS shape parameter (T) indicates oblate fabrics. These new findings will not only improve our understandings of loess AMS, but also expand the possibilities of paleoclimatic studies in the Chinese loess. [Copyright &y& Elsevier]

A combined paleomagnetic and geochronologic study has been conducted on an andesite lava sequence at Jianguo (Liaoning province, northeastern China). Thermal demagnetization and thermomagnetic analysis revealed that natural remanent magnetization is carried by both magnetite and hematite. Stepwise thermal demagnetization up to 675°C isolated well-defined reverse characteristic remanent magnetization (ChRM) in three time-independent lava flows with a mean direction of D/I=179.2°/−59.7° with α95=3.0°. It also showed that a high-temperature component (>585°C) has the same ChRM direction as that of the low- to medium-temperature (ca. 170/300–585°C) components. A modified version of the Thellier–Thellier paleointensity method [Coe, J. Geophys. Res. 72 (1967) 3247–3262] with systematic partial thermoremanent magnetization checks was used for paleointensity determinations. Twelve out of 39 samples yielded reliable results in the temperature interval of 170–550°C. Virtual dipole moment values range from 3.9 to 4.7×1022 Am2 with an average of 4.2±0.1×1022 Am2. 40Ar/39Ar age determination on one lava flow is 116.8±3.0 Myr (2σ error, relative to Fish Canyon sanidine: 28.02±0.28 Myr). The magnetic reversed polarity with well-defined age could correspond to the ‘ISEA’ within the older part of the Cretaceous normal superchron (CNS), but we cannot rule out the possibility that this reversal interval could also correspond to the M0r due to many ambiguities on previous published ages on ISEA and M0r intervals as well as the new monitor age correction we applied. It also suggests that a weak magnetic field nature already documented before the CNS extended at least into the very beginning of the CNS. [Copyright &y& Elsevier]

China is a key area for research into human occupation in the Old World after the initial expansion of early humans out of Africa. Reliable age determinations are pivotal for assessing the patterns of human evolution and dispersal in this region. This paper reviews magnetostratigraphic studies of some early Pleistocene strata bearing hominin remains and/or artifact stone tools from northern to southern China. The quality and reliability of the paleomagnetic dates are also evaluated. New magnetostratigraphic results for the Xihoudu Paleolithic site in north-central China are also presented.Among the few hominin or Paleolithic sites in China from the early Pleistocene, five have been well investigated. Three of these are in northern China at Xiaochangliang, Donggutuo and Gongwangling; the remaining two in southern China at Longgupo and Yuanmou. Considerable progress has been made during the past three decades towards paleomagnetically dating these sites. Indeed, the age estimates at Xiaochangliang and Gongwangling have been widely accepted. Magnetostratigraphic consensus about the age of the Donggutuo site has also been reached. However, the age determination for the two sites in southern China is still contested.The integration of rock-magnetic stratigraphy with magnetic polarity stratigraphy has resulted in a determined age of 1.36 Ma for a stone tool-containing layer of lacustrine sediments at the Xiaochangliang site in the Nihewan Basin. Lithostratigraphic constraints have significantly contributed to determining the age of Lantian Homo erectus at Gongwangling, which occurred in a loess–paleosol sequence of the southern Loess Plateau. Its age, paleomagnetically derived, is about 1.15 Ma. These two paleomagnetic ages suggest an expansion and flourishing of human groups from northern to north-central China during the early Pleistocene. This suggestion has been reinforced by our new magnetostratigraphic age estimate of about 1.27 Ma for the Xihoudu site as will be presented in this paper. However, more work is needed for the age determinations of the hominin-bearing strata at the Longgupo and Yuanmou sites in southern China. Finally, we stress that it is necessary to combine biostratigraphy, lithostratigraphy and rock-magnetic stratigraphy with the traditional magnetic polarity stratigraphy in order to obtain reliable age determinations for strata bearing hominin remains or stone artifacts. [Copyright &y& Elsevier]

A palaeomagnetic and geochronologic investigation has been carried out on a sequence of 19 lava flows at Sihetun in northeastern China. Age determinations by K/Ar dating indicate that the sequence spans 124–133 Ma, that is, the time just prior to Cretaceous normal superchron (CNS). Rock magnetic measurements of thermomagnetic curves and hysteresis loops show the primary carrier of remanence to be pseudo-single domain magnetite. Stepwise thermal demagnetization successfully isolated a well-defined direction of characteristic magnetization (ChRM) in all the lavas. The mean palaeodirection determined is D/I=5.4°/58.7° (α95=2.4°) and D/I=175.9°/−60.0° (α95=6.4°) for 15 normally magnetized flows and 3 reversely magnetized flows, respectively. One lava was found to possess an intermediate direction of magnetization. The inferred palaeolatitude of the sampling site is very similar to the present-day position, supporting the contention that suturing between the Mongolia and north China plates was probably completed by the Late Jurassic, and that subsequently little rotation or translation occurred in the region west of the Tanlu fault zone. Thellier–Thellier palaeointensity experiments with systematic partial thermoremanent magnetization (pTRM) checks were conducted on 66 samples from 13 lava flows. Results from the 29 samples (44%) which met strict reliability criteria indicate a range of virtual dipole moments (VDMs) from 2.83 to 4.17×1022 A m2 with an average of (3.53±0.02)×1022 A m2. This finding helps confirm that a weak geomagnetic field probably occurred just prior to the CNS. [Copyright &y& Elsevier]

The rock magnetic properties of surface sediments from the fine-grained depositional area on the outer shelf of the East China Sea, an area surrounded by sands, were investigated with a view to providing information on the sediment provenance. Multiple magnetic parameters such as magnetic susceptibility, anhysteretic remanent magnetization, saturation remanent magnetization (SIRM), coercivities of SIRM, and S ratios (relative abundance of low-coercivity magnetic minerals) were measured for all 179 surface samples, and partial representative samples were examined for their magnetic hysteresis parameters, temperature dependence of magnetic susceptibility and X-ray diffraction spectra. Our research indicates that the magnetic mineralogy is dominated by magnetite with a small amount of hematite and is primarily of a pseudo-single-domain to multidomain nature with a detrital origin. The magnetic concentration in the study area generally decreases to the east or southeast accompanied by magnetic particle fining to the east or northeast. The geographic pattern of magnetic properties is most reasonably explained by a major source of sediment jointly from the erosion of the old Huanghe River deposit and the discharge of the Changjiang River. The rock magnetic data facilitate understanding of the transport mechanism of fine-grained sediments in the outer shelf of the East China Sea. [Copyright &y& Elsevier]

Reports rock magnetic and paleomagnetic research results for Middle Silurian Gongpoquan and Middle Ordovician Huaniushan volcanic samples. Collection of the rocks from the Mazongshan and Hongliuyuan areas of Gansu Province, northwest China; Finding that the main magnetic mineral of the Gongpoquan and Huaniushan volcanic rock is magnetite; Indication its remanent magnetization was acquired at the time of formation; How the samples from site go20 differ; Finding that most of Middle Ordovician Huaniushan volcanic samples have weak remanent magnetization and erratic demagnetization behavior; Comparison of results from the Beishan area of Gansu with Paleozoic apparent polar wander paths for Tarim and Siberia; Suggestion that the Beishan tarrane, Tarim block, and Siberia plate were not connected in their present configuration by Middle Silurian time; Inference that the early Paleozoic Mingshui-Shipanjin-Xiaohuangshan oceanic basin could have opened from west to east during period from the Ordovician to Silurian, and the post-Middle Silurian closing of this basin could have resulted from a progressed eastward scissor-like rotation.

States layered cave passages have formed on the walls of the Qianyou River valley in the Qinling Mountains since the Pleistocene because of intermittent uplifts. Dating of 12 speleothem samples near the palaeowater tables in 3 cave passages; Use of the 230Th method; Geological timing of the cave uplifts; Calculation of the downcutting rates of the valley.

Presents information on a study which examined the Matuyama-Brunhes polarity transition from loess, and its association with virtual geomagnetic pole path in China. Description of the geological area; Analysis of the rock magnetic properties of the loess; Measurement of the loess' paleomagnetization.

The Lushi gold polymetallic ore-concentration area, located in the southern margin of North China Craton, is an important polymetallic ore district in the Qinling metallogenic belt. The Jianbeigou gold deposit is an important quartz vein type gold deposit in this district. In order to reveal the geological structure of the Jianbeigou gold deposit to guide deep prospecting, the EH4 conductivity image system was used in the Jianbeigou area. The sections obtained by the audio magnetotellurics method (AMT) indicate that the steeply dipping low resistivity zone in the area has a good corresponding relationship with the location of the known shallow ore bodies, and an extension in the deep. The low resistivity anomaly zone obtained by the inversion results are well correlated with the gold mineralization zone of the ore bodies, indicating good deep prospecting and exploration potential in this area. Based on geological and geophysical evidences, this paper inferred the possible occurrence location and depth range of the buried ore bodies. The AMT survey results reflect good exploration potential of the mining area and provide a geophysical basis for deep prospecting. [ABSTRACT FROM AUTHOR]

Presents proof that Chinese loess L8, which records the Matuyama/Brunhes polarity boundary, is capable of recording earth's secular variation and that the lock-in depth in Chinese loess is no more than that of marine sediments. Geomagnetic polarity transition; Paleoclimate; Matuyama/Brunhes record in marine sediments.

The Haigou lode deposit contains 40 t of gold at an average grade of 3.5 g/t, and is one of the largest deposits in the Jiapigou gold belt located along the eastern segment of the northern margin of the North China Craton. The deposit comprises 15 gold-bearing quartz veins hosted in a Carboniferous monzonite–monzogranite stock. Cretaceous dikes consisting of diorite, diabase, and granodiorite porphyries are well developed in the deposit. The diorite porphyry dikes (130.4 ± 6.3 Ma) occur together with gold-bearing quartz veins in NNE- and NE-striking faults. Gold-bearing quartz veins crosscut the diorite porphyry dikes, and the veins are in turn crosscut by E–W-striking 124.6 ± 2.2 Ma granodiorite porphyry dikes. The mineralization mainly occurs as auriferous quartz veins with minor amounts of sulfide minerals, including pyrite, galena, chalcopyrite, and molybdenite. Gold occurs as either native gold or calaverite. Common gangue minerals in the deposit include quartz, sericite, and calcite. The deposit is characterized by various types of hydrothermal alteration, including silicification, sericitization, chloritization, potassic alteration, and carbonatization. Three stages of hydrothermal activity have been recognized in the deposit: (1) a barren quartz stage; (2) a polymetallic sulfide (gold) stage; (3) a calcite stage. Fluid inclusions in hydrothermal pyrites have 3 He/ 4 He ratios of 0.3 to 3.3 Ra and 40 Ar/ 36 Ar ratios of 351 to 1353, indicating mixing of fluids of mantle and crustal origin. Hydrothermal quartz yielded δ 18 O values of −1.3‰ to +7.2‰ and δD values of fluid inclusions in the quartz vary between −80‰ and −104‰. These stable isotope data also suggest mixing of magmatic and meteoric fluids. Noble gas and stable isotopic data suggest that the ore fluids have a predominant mantle source with a significant crustal component. Based on the spatial association of gold-bearing quartz veins with early Cretaceous intrusions, and the H–O–He–Ar isotopic data from the deposit and intrusions, we propose that gold mineralization in the Haigou deposit was formed in an extensional setting and was related to the early Cretaceous, mantle-derived intrusions. [ABSTRACT FROM AUTHOR]

The Mesozoic terrestrial Jehol Biota of northern China exceeds the biomass and biodiversity of contemporaneous Lagerstätten. From 135 to 120 Ma, biotic radiation may have responded to the peak destruction of the North China Craton. However, the direct mechanistic link between geological and biological evolution is unclear. Phosphorus (P), a bio-essential nutrient, can be supplied by weathering of volcanics in terrestrial ecosystems. The middle–late Mesozoic volcanic-sedimentary sequences of northern China are amazingly rich in terrestrial organisms. Here we demonstrate episodic increases in P delivery, biological productivity, and species abundance in these strata to reveal the coevolution of volcanism and terrestrial biotas. A massive P supply from the weathering of voluminous volcanic products of craton destruction thus supported a terrestrial environment conducive to the high prosperity of the Jehol Biota. During the nascent stage of craton destruction, such volcanic-biotic coupling can also account for the preceding Yanliao Biota with relatively fewer fossils. [ABSTRACT FROM AUTHOR]

Abstract: Paleomagnetic and magnetostratigraphic investigations have been conducted on two consecutive sections of the Emeishan trap at Shuimo (SM) and Dadi (DD) in northeastern Yunnan province, southwestern China. Rock magnetic analysis indicates that the magnetic carrier of the basalts is dominantly low-Ti magnetite. Stepwise thermal demagnetization isolates a stable characteristic remanent magnetization (ChRM) at high temperatures (400–585°C). The ChRMs (301/323) at SM section are northeasterly upward of normal polarity, with a mean direction of D s/I s =11.0/−5.2° (N =12, k =53.7, α 95 =6.0°). At DD section, the ChRMs are southwesterly downward of reversed polarity, with a mean direction of 205.9/10.0° (N =5, k =78.4, α 95 =8.7°). The ChRMs from the basaltic gravels from the overlying conglomerate layer in late Permian Xuanwei Formation at DD section pass the conglomerate test, suggesting the primary nature of magnetization. Together with other magnetostratigraphic studies (e.g., N–R pattern) of the Emeishan basalts and the known radiometric ages (ca 260Ma), it suggests that the eruption period of the Emeishan large igneous province is less than 3Myr. [Copyright &y& Elsevier]

Abstract: The anisotropy of magnetic susceptibility (AMS) was investigated in three Chinese Loess Plateau sedimentary sections along a W–E transect (400km). The loess–paleosol sequences in our study represent the most recent 130kyr interval. The measured AMS was compared to expected theoretically derived magnetic fabrics occurring in strong and weak current airflow conditions. The major and minor AMS ellipsoid axis orientations were used to evaluate the paleowind direction along the transect. Previously published models assumed that cold and dry winter monsoons bringing dust from northwestern desert areas were responsible for the magnetic fabric formation of loess sequences. In our new interpretation, the stronger summer monsoons from the southeast played the major role in magnetic fabric orientation in the studied west and central parts of the Chinese Loess Plateau. Although the material was brought to the area by the winter monsoon, the AMS was generated during the rainy summer monsoon when the sedimentary particles including magnetite were rearranged, settled, and fixed. We reconstruct the summer paleomonsoon routes for the last 130kyr. These winds prevail from SE to NW but appear to be affected by regional topographic factors. In the western section, the corridor between the north and south Liupan Mountains disturbed the summer monsoon route, shifting it from SE to SEE. [ABSTRACT FROM AUTHOR]

Abstract: Timing of the early habitation and stone technologies in the Nihewan Basin, North China has provided insights into our understanding of early human adaptability to high northern latitudes in East Asia. Here we contribute to this topic with detailed magnetostratigraphic investigation, coupled with mineral magnetic measurements and palynological analyses on a lacustrine sequence in this basin, which contains the Xiantai Paleolithic site. Magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations. Magnetostratigraphic results show that the Xiantai lacustrine sequence recorded the Brunhes chron, the Jaramillo and the Olduvai subchrons, and successive reverse polarity portions of the intervening Matuyama chron. Stratigraphic correlation in terms of lithology, magnetic susceptibility and magnetic polarity sequences between the Xiantai and Xiaochangliang sections indicates that the Xiantai artefact layer is readily contemporary with the Xiaochangliang artefact layer, which has been previously estimated to be about 1.36 Ma [R.X. Zhu, K.A. Hoffman, R. Potts, C.L. Deng, Y.X. Pan, B. Guo, C.D. Shi, Z.T. Guo, B.Y. Yuan, Y.M. Hou, W.W. Huang, Earliest presence of humans in northeast Asia, Nature 413 (2001) 413–417.]. Early humans of the Xiantai Paleolithic site lived in a steppe paleoenvironment indicated from fossil pollens. Furthermore, the combined evidence of our magnetostratigraphy and previously published magnetochronology and paleoclimate data documents that early humans of North China were able to adjust to an increasing variability of paleoclimates and paleoenvironments over the Early Pleistocene. [Copyright &y& Elsevier]

• Hydrothermal rutile, co-precipitated with gold, was identified in the Wulong deposit. • Rutile SIMS U-Pb dating yields a more precise and robust age of 122.3 ± 1.1 Ma for the gold formation. • Carbon isotopes suggest mantle/magmatic sources for the ore-forming fluids. • Gold mineralization has a genetic link with the North China Craton destruction. Wulong is the largest lode gold deposit in the Liaodong Peninsula, northeastern North China Craton (NCC). Gold mineralization mainly occurs in the quartz-sulfide veins, which are hosted in Jurassic monzogranite and Early Cretaceous diorite dikes. Here, rutile grains are firstly identified in the auriferous quartz-pyrite vein. The vein-hosted rutiles have textural associations with quartz, chlorite, pyrite and Bi-sulfosalts and host fluid inclusions, indicating that they are unequivocally of hydrothermal origin and co-precipitate with gold. The rutile grains are characterized by high W and V concentrations, and U-shaped rare earth elements pattern with the greatest depletion in MREE. Due to excess Zr incorporation during fast rutile crystal growth process from the F-rich ore-forming fluids, Zr-in-rutile thermometers provide unrealistic crystallization temperatures (>550 °C), which are much higher than the previous homogenization temperatures data of fluid inclusions (Yu et al., 2018). All these geochemical signatures also support that rutiles formed from the hydrothermal fluids. The δ13C values of CO 2 gases in low-salinity, aqueous-carbonic fluid inclusions from the mineralized quartz range from –9.6‰ to –1.7‰ (average = –5.7‰), indicating mantle/magmatic sources for the ore-forming fluids. SIMS U-Pb dating yields a more precise and robust age of 122.3 ± 1.1 Ma (n = 23, MSWD = 0.82) for the gold mineralization at Wulong. This new date is roughly coeval with the ore-hosted diorite dikes and the Sanguliu granitic pluton (most in 125–120 Ma). Such close temporal association provides additional weights of evidence for a magmatic affinity to the gold formation. Regionally, the rutile U-Pb age indicates that the gold mineralization occurs in an extensional tectonic regime, caused by the thinning and destruction of the lithosphere beneath the NCC. Meanwhile, the timing of gold mineralization is the same as the peak age of NCC destruction. Therefore, we propose that the Wulong deposit has a genetic link with this craton destruction. This is similar to numerous other Early Cretaceous gold deposits across the NCC, such as those in the Xiaoqinling and Jiaodong districts. Our study indicates that rutile is a robust U-Pb chronometer for the lode gold deposit, but may be not a good geothermometer in the case of F-rich hydrothermal fluid system. [ABSTRACT FROM AUTHOR]

Abstract The characteristics of the evolution of the South Asian monsoon during the late Miocene through the Pliocene are highly debated. To obtain a better understanding, we studied the clay mineral assemblages and the clay fraction content of a high-quality sedimentary sequence (borehole core ZK1) spanning the interval of 8.8–2.62 Ma in the Zhaotong Basin, southwestern Yunnan Province, on the southeastern margin of the Tibetan Plateau. Smectite, kaolinite, illite and vermiculite were the four main clay minerals identified, and changes in their relative abundance reveal a distinct pattern of climate change during the study interval. Until the very late Miocene kaolinite and smectite, with a small amount of illite, were dominant, suggesting a relatively warm and humid climate; from ~6.2 to ~2.8 Ma smectite was dominant, with a minor amount of kaolinite and illite, indicating a relatively cool and humid climate; and from ~2.8 to 2.62 Ma vermiculite (HIV) and illite were dominant, with a minor amount of kaolinite, indicating a relatively cold and humid climate. The variation in clay mineral assemblages indicate substantial changes in the South Asian monsoon in the Zhaotong Basin that promoted a change from a warm and humid climate in the late Micoene to cool and humid climate in the very late Miocene through Pliocene, followed by a gradual trend towards a cold and humid climate in the very late Pliocene. Comparison with records from elsewhere indicates that the observed variations in the South Asian monsoon were mainly controlled by global cooling rather than by Tibetan Plateau uplift. Highlights • The climate condition at Zhaotong Basin is controlled by the South Asian monsoon. • The climate changed from late Miocene warm and humid to late Pliocene cold and dry. • The gradually weakening of South Asian monsoon was controlled by global cooling. [ABSTRACT FROM AUTHOR]

Detailed understanding to the evolution of Neogene land mammals in East Asia and its intercontinental correlation has been impeded by the absence of an integrated biochronological system of this region. The numerous and diverse records of Neogene vertebrate fossils preserved in Inner Mongolia of northern China play a key role in the establishment of an independent biochronological framework in East Asia. However, most of these faunas are poorly constrained by independent chronological controls due to the scattered distribution of fossil localities and insufficient exposure of the fossiliferous strata. Additionally, age estimates by mammalian evolution and correlation often have uncertainties greater than ~1–2 million years. Here we present new magnetostratigraphic results of the Baogeda Ula Fauna, which was generally assigned an early Baodean Age (Late Miocene), or equivalent to the European MN12 zone (middle Turolian). Hipparion remains and associated vertebrate fossils were excavated from the upper part of the fluvio-lacustrine Baogeda Ula Formation near Abaga Banner, central Inner Mongolia of northern China. At least two layers of basalt sheet flows can be observed on top of the Baogeda Ula Formation. Our magnetostratigraphy, aided by published biochronology data and K–Ar ages of the lower basalt layer suggests that the Baogeda Ula Fauna consisting of three fossiliferous horizons can be placed within chron C4n.1n with an age range of 7.642–7.528 Ma. Thus, the Baogeda Ula Fauna becomes the first and only Baodean assemblage that is constrained by both magnetostratigraphy and radiometric ages, offering an anchoring point for future biochronological correlations. [ABSTRACT FROM AUTHOR]

Geochemical analysis of the 14.4-m-thick lacustrine succession of the Lower Cretaceous Yixian Formation (Jehol Group) has yielded new insights concerning vertebrate mass mortality events in the Lake Sihetun volcanic caldera in western Liaoning Province (northeastern China) that produced the Jehol Biota fossil lagerstätten. The long-term evolution of the caldera system resulted in a shift from felsic to mafic magma chemistry, accompanied by a reduced frequency of pyroclastic eruptions, declining hydrothermal activity, and lower lacustrine productivity. The basal Tetrapod Beds exhibit strong hydrothermal influence, as indicated by enrichments of boron (B), certain alkalis (Rb, Cs), rare-earth elements (REEs), yttrium (Y), and many metals (e.g., Co, Cr, Cu, Ge, Mo, Ni, Sb, U, V, and W), and by strongly negative molybdenum isotope compositions (δ 98 Mo to –2.50‰) that may record large fractionations between molybdate and thiomolybdate species in the Sihetun caldera hydrothermal system. In contrast, the overlying Fish Beds and Non-Fossiliferous Beds have an elemental and Mo-isotopic composition similar to calc-alkaline basalts (δ 98 Mo = –0.29 ± 0.04‰) in the surrounding watershed, suggesting weathering of Yixian Formation volcanic rocks as the major source of sediment. During its < 700-kyr-long history, Lake Sihetun was affected by four environmental cycles, each commencing with a series of pyroclastic eruptions that triggered systematic changes in lakewater chemistry. Following each eruption interval, enhanced weathering of volcanic ash in the surrounding watershed caused lakewater pH to decrease and lacustrine productivity to increase. Continued weathering of bases from basement volcanic rocks subsequently produced alkaline conditions in the lake, leading to precipitation of authigenic carbonate layers and lower lacustrine productivity. Analysis of geochemical redox proxies strongly suggests that the Lake Sihetun water column was completely oxic, in contrast to earlier inferences of a stratified anoxic water column, and that ubiquitous lamination in the lacustrine succession was due to other factors such as widespread microbial mats and/or rapid sediment deposition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Extensive eruption of volcanic rocks in the Jiaodong Peninsula occurred at ca. 120 Ma. • Paleomagnetic results suggest a latitudinal motion along the Tan-Lu fault after 120 Ma. • The Paleo-Pacific subduction caused the sinistral displacement of the Tan-Lu Fault. The Jiaodong Peninsula in eastern China is separated from the main mass of the North China Craton by the Tancheng–Lujiang (Tan–Lu) Fault, the largest fault system in eastern Asia. Although accumulating lines of evidence have suggested that the Tan–Lu Fault underwent strike-slip movement in the Mesozoic, there is still debate about the timing and magnitude of the displacement. To decipher this problem, we conducted paleomagnetic and U–Pb geochronological studies of the Lower Cretaceous volcanic rocks of the Qingshan Group on the Jiaodong Peninsula, to the east of the Tan–Lu Fault on the southeastern edge of the North China Craton. LA–ICP–MS U–Pb dating of zircons from five samples yielded consistent ages of ca. 120 Ma. Stepwise thermal demagnetization conducted on 308 samples (40 sites) from two sections revealed stable characteristic remanent magnetization directions. After paleomagnetic tests and rejecting inappropriate data, the mean direction from 288 samples (31 independent units) is 200.3°/–51.4° (α 95 = 4.1°), with a corresponding pole at 215.1°/73.0° (A 95 = 4.8°). The paleolatitude calculated for the Jiaodong Peninsula is lower than that of the main block of the North China Craton, which indicates that latitudinal offset occurred between these two parts, and this offset can be ascribed to strike-slip movement along the Tan–Lu Fault. Our data provide new constraints on regional tectonic movement and Paleo-Pacific subduction processes during the late Mesozoic. [ABSTRACT FROM AUTHOR]

Evolutionary processes in hominoid primates were closely related to global and/or regional environmental changes, and therefore palaeoenvironmental reconstruction is fundamental for understanding how environmental changes shaped their evolution. Here, we present pollen data from the 16-m-thick Shuitangba (STB) section, Yunnan Province, southwestern China, bearing remains of the hominoid Lufengpithecus lufengensis of the terminal Miocene; and use principal component analysis to reconstruct the palaeovegetation and palaeoclimate during the key period when the hominoid lived. Our results show that before the STB hominoid appeared (Zone A), the vegetation was dominated by subtropical evergreen broad-leaved taxa with a few temperate deciduous taxa (e.g., Quercus , Castanea / Castanopsis , Alnus ). The development of aquatic plants commencing at the ~ 12 m depth is a prominent feature, indicating a warm and humid climate. During the time when the hominoid lived (Zone B), evergreen broad-leaved forests with evergreen Quercus were predominant, while grasses including Poaceae began to expand, and simultaneously conifers decreased, indicating a warm climate. The significant presence of aquatic pollen taxa in subzone A-2 and Zone B suggests the occurrence of lacustrine or swampy environments. In contrast, in Zone C, the vegetation changed to coniferous forest, indicating cooler and drier conditions. These results provide substantive evidence of the vegetation conditions when the hominoid lived, suggesting that the greater diversity of vegetation and the warm humid climate, compared to the present day, would have favoured its survival. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we have carried out paleointensity experiments on 918 specimens spanning the last ∼7 kyr, including pottery fragments, baked clay and slag, collected from Shandong, Liaoning, Zhejiang and Hebei Provinces in China. Approximately half of the specimens yielded results that passed strict data selection criteria and give high-fidelity paleointensities. The virtual axial dipole moments (VADMs) of our sites range from to . At ∼2250 BCE our results suggest a paleointensity low of , which increases to a high of by ∼1300 BCE. This rapid (less than 1000 yrs) six-fold change in the paleointensity may have important implications for the dynamics of core flow at this time. Our data from the last are generally in good agreement with the ARCH3k.1 model, but deviate significantly at certain time periods from the CALS3k.4 and CALS10k.1b model, which is likely due to differences in the data used to constrain these models. At ages older than , where only the CALS10k.1b model is available for comparison, our data deviate significantly from the model. Combining our new results with the published data from China and Japan, we provide greatly improved constraints for the regional model of Eastern Asia. When comparing the variations of geomagnetic field in three global representative areas of Eastern Asia, the Middle East and Southern Europe, a common general trend of sinusoidal variations since is shown, likely dominated by the dipole component. However, significant disparities are revealed as well, which we attribute to non-dipolar components caused by movement of magnetic flux patches at the core-mantle boundary. [Copyright &y& Elsevier]

Abstract: Dinosaur eggs or fragments are abundant and extensively distributed in China. They can be very informative in biostratigraphic division and correlation of continental strata where other fossils are relatively lacking. Despite remarkable discoveries of vertebrate fossils, particularly dinosaur eggs and skeletons from the middle and Late Cretaceous of both northern and southern China, there is hardly any direct evidence for the ages of the vertebrate-bearing terrestrial deposits. To constrain their depositional ages, here we have obtained SIMS U–Pb zircon ages from the tuffs interbedded with dinosaur egg-bearing sediments from the Laijia and Chichengshan formations of the terrestrial red deposits of the Late Cretaceous in the Tiantai Basin, Zhejiang Province, southeastern China. The SIMS zircon U–Pb ages from the Laijia and Chichengshan formations are about 96–99Ma (Cenomanian) and 91–94Ma (Turonian), respectively, providing direct time constraints on the vertebrate and dinosaur egg evolution in the Late Cretaceous as well as a basis for correlation with terrestrial Cretaceous deposits in other regions of southern and northern China. [Copyright &y& Elsevier]

Abstract: Metamorphic Core Complexes (MCC) constitute remarkable features within wide rifts. Based on analogue and numerical modelling, MCC dynamics and structural development are mainly controlled by first geothermal gradient, second the compositional layering, and after the strain rate and partial melting. In the Late Mesozoic, continental extension occurred in East Asia leading to the development of MCC, magmatism and extensional sedimentary basins. Based on an integrated study (i.e. structural and finite strain analysis, petrofabrics, Anisotropy of Magnetic Susceptibility (AMS) and U/Pb on zircon dating), this paper aims at constraining the tectonic evolution and deformation mechanisms in the South Liaodong Peninsula (NE China). The Gudaoling massif is identified as a “migmatitic” MCC developed from Upper Jurassic (ca. 157–154Ma) to Early Cretaceous (ca. 128–113Ma). Intrusion of the Yinmawanshan synkinematic pluton (Early Cretaceous) to the south of the dome marks out the final stages of shearing along the Gudaoling detachment zone and of exhumation of the MCC into the upper crust. The Gudaoling MCC and the Yinmawanshan pluton stay in line with the coeval South Liaodong MCC, to the south, all making a ~140×30km wide extensional band formed during a regional E–W to NW–SE crustal stretching. The area shows a bi-phased development with a “slow” and a “fast” stage which corresponds to (1) crustal necking and (2) dome amplification/exhumation stages according to published thermo-mechanical modelling results. Finally, the Gudaoling MCC lower unit almost exclusively displays migmatites and anatectic granitoids of Late Jurassic and Early Cretaceous, respectively. Occurrence of partial melting during earlier stages of extension seems controlling the initiation of MCC (as a soft anomaly within the lower crust). In East Asia, a regional-scale thermal event, during Jurassic–Cretaceous times, may have significantly reduced the bulk lithosphere strength and locally induced partial melting, emphasizing pervasive deformations and development of a wide rift system. [Copyright &y& Elsevier]

Abstract: The Nihewan Basin sedimentary sequences in northern China are rich in mammalian fossil and Paleolithic sites, thus providing insights into our understanding of Quaternary land mammal biochronology and early human settlements in East Asia. Here we present high-resolution magnetostratigraphic results that place stringent age controls on the Xiashagou (XSG) Fauna (that is, the well-known Nihewan Fauna sensu stricto) in the Nihewan Basin, northern China. Results show that the XSG sequence recorded the Brunhes normal chron, the Matuyama reverse chron and the late Gauss normal chron. The XSG Fauna resides in the Matuyama reverse chron (between the pre-Reunion Matuyama chron and the post-Olduvai Matuyama chron), yielding an estimated age of ca. 2.2–1.7Ma. The Pliocene–Pleistocene boundary (Gauss/Matuyama boundary) is located in the lower part of the XSG section. The combination of our study and previously published magnetostratigraphic data suggest that the mammalian fossil sites in the eastern Nihewan Basin can be placed between the Gauss–Matuyama geomagnetic reversal and the Matuyama–Brunhes geomagnetic reversal (2.58–0.78Ma), leading to a time range of ca. 2.6–0.8Ma for the Nihewan mammalian faunas. [Copyright &y& Elsevier]

Abstract: The fluvio-lacustrine sequence of the Shanwang Basin, eastern China, preserves a rich and important terrestrial fossil fauna and flora; the exceptional preservation of these fossils reveals the dynamics of ancient mammalian ecosystems and plant biology. However, the timing of this sedimentary sequence has been the subject of debate for decades. Here we contribute to this debate by presenting the detailed results of 40Ar/39Ar analysis of the basalts above, below, and within the Shanwang Formation. These dates place stringent constraints on the age of Shanwang Formation and associated biota. 40Ar/39Ar ages obtained from basalts of the Niushan and Yaoshan Formations, which underlie and overlie the Shanwang Formation, are 21.0±2.5Ma (2σ, full external error) and 17.3±1.5Ma (2σ, full external error), respectively. The 40Ar/39Ar age of the basalt in the Shanwang Formation is 17–18Ma. Given the age constraints of the basalts of the Yaoshan and Shanwang Formations, the age of the Shanwang biota is estimated to be ca. 17Ma, late Burdigalian of the Early Miocene, indicating that the deposition of this fauna coincided with the onset of the mid-Miocene Climatic Optimum. The results provide new age constraints on the Shanwang mammal fauna, and independently support interpretations that this fauna can be assigned to chronozone MN4, and correlated with middle Orleanian of the European Land Mammal Age, and to late Hemingfordian of the North American Land Mammal Age. Biological diversity of the Shanwang Formation could reflect the global-scale mid-Miocene Climatic Optimum. [Copyright &y& Elsevier]

Abstract: Continental extension is an important geodynamical process mostly diagnostic of a peculiar behaviour of the crust accommodated by geological structures that highlight these specific conditions in the crust. Though a Metamorphic Core Complex (MCC) reveals a much stronger crustal extension than a synkinematic pluton, the nature of those two structures implies different implications in terms of crustal extension mechanisms and geodynamic significations. In eastern Asia, a major continental extensional event occurred during Mesozoic and early Cenozoic times. The resulting various extensional events described in previous studies consist in large intracontinental basins, important volcanism, emplacement of plutons in the upper crust and exhumation of MCCs. An efficient description of MCCs and plutons in eastern Asia is essential to discriminate important differences of those two structures in terms of strain amount undergone by continental crust and geodynamic significations. In that way, an integrated structural and geophysical study has been realized to precisely discriminate the structure in the Jiaodong Peninsula (Shandong Province, eastern China), previously regarded as simple sheared plutons. A succession of three main stages have been identified all pertaining to a NW–SE extensional setting: (1) the exhumation of the Late Jurassic–Early Cretaceous Linglong MCC below the SE-dipping Linglong detachment fault, (2) the emplacement of the Guojialing syntectonic pluton below the N-dipping extensional Guojialing intracrustal shear zone (130–124Ma) and (3) a penetrative brittle normal faulting associated with gold mineralizations (∼120Ma). As a result, the maximum amount of extension in Jiaodong Peninsula, characterized by partially-melted lower to middle crust upward into the Linglong MCC should be revised to Late Jurassic–Early Cretaceous period. [ABSTRACT FROM AUTHOR]

Abstract: The fluvio-lacustrine sequences in the Nihewan Basin, northern China provide important terrestrial archives of paleoclimate and paleoenvironment as well as an important source of Paleolithic settlements and therefore early human occupation in the eastern Old World. Magnetostratigraphic dating of the sequences has permitted the precise timing of the basin infilling and associated Paleolithic and mammalian fauna sites. Here we report new magnetostratigraphic results that place stringent age controls on the Huojiadi Paleolithic site in this basin. Partially-oxidized magnetite and hematite were identified as the major carriers for the characteristic remanent magnetizations. Magnetostratigraphic results show that the Huojiadi sequence recorded the very late Matuyama reverse chron and the Jaramillo normal subchron. The stone artifact layer resides in the Jaramillo normal subchron, yielding an estimated age of around 1.0Ma for the Huojiadi Paleolithic site. Furthermore, by combining our magnetostratigraphy and previously published magnetochronology data, a magnetochronological sequence of the early Pleistocene Paleolithic sites in the Nihewan Basin has been established. The chronological sequence implies that early humans may have persistently colonized the high-latitude temperate areas in the eastern Old World, such as the Nihewan Basin, during the Early Pleistocene. [ABSTRACT FROM AUTHOR]

Abstract: The fluvio-lacustrine sequence in the Nihewan Basin is an important archive of Pleistocene climate and environmental changes in northern China, which provides excellent sources of early human settlements in high-latitude East Asia. Here a long-term environmental record from the Pleistocene fluvio-lacustrine sequence in this basin is revealed, based on selected major element pairs that are sensitive to paleoenvironmental changes. Results reveal a long-term increasing trend in aridification/cooling in the Nihewan Basin since the early Pleistocene. This provides a general setting for early human colonization in high-latitude northern China (around 40° N). The intensified aridification/cooling is envisaged to reduce tree cover and increase open savanna grass area. This, in turn, would promote prominent flourishing population and migration of savanna-adapted early humans in the Old World. Therefore, the cold/dry climate may have contributed to the evolution and expansion of early humans in the high-latitude northern China, rather than bringing hardship, as is often thought. [ABSTRACT FROM AUTHOR]

Abstract: Thick Cenozoic deposits formed from the erosion of the northern evolving edge of the Tibetan Plateau provide opportunities to study the exhumation history and climatic changes within the region. Such deposits are important because they are located in an actively deforming mountain belt as well as in a rain shadow of the Tibetan Plateau. Multi-proxy studies indicate that hyperarid climate has prevailed since 5.3Ma ago within the basin. This information, together with the geometry analysis of syntectonic deposits of the Sanju Anticline, which indicate tectonic deformation at 5.3Ma, enable us to better understand the interlay between climatic changes and tectonic uplift. Our results suggest that the tectonic uplift of the Kunlun Mountains at 5.3Ma must have been one of the significant regional tectonic events, and the uplifted elevation of the Kunlun Mountains more effectively blocks the penetration of moisture from the Indian monsoon into the Tarim Basin and thus enhances the rain shadow effect. This can account for the increasing aridity as well as the formation of the world''s second largest active sand desert (the Taklimakan Desert) in the Tarim Basin initiated at 5.3Ma ago. [Copyright &y& Elsevier]

Abstract: We applied an integrated receiver function imaging technique to the teleseismic data from 54 NCISP-III broadband seismic stations to study the fine-scale crustal structure beneath the eastern Yanshan belt (YSB) and adjacent areas at the northern margin of the North China Craton (NCC). The robustness and reliability of the resultant crustal image were noticeably improved by achieving imaging consistency between common conversion point stacking and waveform inversion of the receiver functions. Our imaging result revealed substantial lateral heterogeneities in the crust of the study region, as displayed by the undulating intra-crustal interfaces, highly varying upper-, middle-, and lower crust thicknesses, and interlayers of low and high velocities. The crustal structure of the YSB is characterized by significant structural variations together with a sharp Moho, a thin-to-normal crust and a lower crust with lower velocity and normal thickness. It differs markedly from the Bohai Bay basin and the Taihang Mountains within the interior of the NCC. The distinct features and structural complexity of the YSB might be attributed to the complex tectonic history of the region, especially the multiple phases of contraction and possible occurrence of crustal delamination, which is in large contrast to other subregions of the NCC where tectonic extension likely dominated the crustal deformation since the late Mesozoic. [Copyright &y& Elsevier]