Lower Yangtze River Region Research Articles

Formation of the Jinshandian Fe skarn ore field in the Edong district, Eastern China: Constraints from U–Pb and 40Ar/39Ar geochronology

The Jinshandian ore field represents one of the largest concentrations of Fe skarn deposits in the Edong district of Eastern China. Orebodies of these deposits occur in skarn along the contacts between quartz diorite or quartz monzonite and Triassic sedimentary country rocks. In this paper, we present new U–Pb geochronological data for magmatic zircon and hydrothermal titanite, as well as 40Ar/39Ar ages on hydrothermal phlogopite, to determine whether multiple magmatic-hydrothermal events associated with formation of the Fe skarn deposits in the Jinshandian ore field. The robust U–Pb zircon ages demonstrate that the quartz monzonite and quartz diorite were emplaced at 130Ma and 127Ma, receptively. The U–Pb and 40Ar/39Ar ages of hydrothermal titanite and phlogopite form the skarn indicate that Fe mineralization also formed at ca. 131–128Ma, but with an additional 118Ma hydrothermal event recorded by phlogopite. This geochronology confirms a causative linkage between granitic intrusion and skarn mineralization. The data also indicate that at least two hydrothermal events took place in the Jinshandian ore field, one at 131–128Ma and the other at ∼118Ma. Integrating these ages from the ore field with previous geochronological data from the broader Edong district, two regional magmatic-hydrothermal events are recognized in the Edong district after 135Ma, with the older one at 131–127Ma in excellent agreement with the ∼131Ma formation age of magnetite-apatite deposits in the eastern part of Middle–Lower Yangtze River region, and the younger one at 122–118Ma post-dating emplacement of the ca. 126Ma A-type granite and syenite in the eastern part of Middle–Lower Yangtze River region. A detailed comparison between the Fe skarn deposits and magnetite-apatite deposits in the Middle–Lower Yangtze River region suggests that these two deposit types not only share similar alteration assemblages and association with the evaporites within the ore-forming systems, but also may have formed during the same Early Cretaceous magmatic-hydrothermal event.

Rice bulliform phytoliths reveal the process of rice domestication in the Neolithic Lower Yangtze River region

Abstract Recent studies have shown that the proportion of rice bulliform phytoliths with ≥9 fish-scale decorations can be used as a criterion to differentiate wild rice from its domesticated counterpart. The analysis of rice bulliform phytoliths recovered from 38 samples collected from eight archaeological sites dated to around 10,000–2200 BP suggests that the process of rice domestication in the Lower Yangtze River region lasted for around 6000 years and can be divided into three stages. Stage I was from around 10,000 to 6500 BP. The process of domestication was very slow, and even went backwards. Stage II was between 6500 and 5600 BP, when the process was accelerated. During stage III, from 4500 to 2200 BP, the domestication process eventually resulted in the breed of the modern rice.

Geochronology and petrogenesis of shoshonitic igneous rocks, Luzong volcanic basin, middle and lower Yangtze River reaches, China

The Luzong volcanic basin has a unique tectonic background, being located at the northeastern margin of the Yangtze craton and the foreland of the Dabie–Sulu orogen, near the intersection of the renowned Tanlu and Yangtze River faults. The volcanic and subvolcanic rocks in the basin are characterized by high potassium contents and are rich in alkali elements, and belong to a typical shoshonite series. Geochemically, these rocks are depleted in high field strength elements such as Nb and Ta, and enriched in highly incompatible elements such as Rb, Th, U, K, and light rare earth elements. Nd and Sr isotope compositions, combined with elemental geochemical characteristics, indicate that the parental magmas were formed mainly by partial melting of enriched subcontinental lithospheric mantle. The magmas underwent minor or negligible contamination by upper crustal rocks or fractional crystallization at low pressures (i.e., <1.5GPa). Nevertheless, variation trends for major and trace elements indicate that these shoshonitic mantle-derived magmas experienced fractional crystallization at high pressures (i.e., above the stability field of plagioclase, >1.5GPa), dominated by the removal of clinopyroxene and Fe–Ti oxides. The volcanic rocks of the Luzong Basin can be divided into four formations, which, from early to late, are the Longmenyuan, Zhuanqiao, Shuangmiao, and Fushan Formations, each separated by clear gaps in eruptive activity. In this study, we obtained zircon U–Pb SHRIMP ages from two subvolcanic samples from the Longmenyuan and Zhuanqiao Formations, which yield emplacement ages of 132±1Ma and 131±1Ma. These data, combined with ages reported by other workers, show that the duration of volcanism in the Luzong Basin (and the whole middle and lower Yangtze River reaches) was very short (⩽8Ma). We consider that in the Early Cretaceous the foreland area of the Dabie orogenic belt was under extension, influenced by the relative motion of the Pacific and Eurasian plates, and by sinistral displacement along the Tanlu Fault. At this time, rapid mechanical delamination of thickened lithosphere caused lithospheric thinning and resultant asthenospheric upwelling in the middle and lower Yangtze River region and the Dabie orogenic belt. These deep geological and tectonic events in turn produced the shoshonite volcanic rocks in the Luzong Basin.

Crustal and uppermost mantle velocity structure and its relationship with the formation of ore districts in the Middle–Lower Yangtze River region

In this study, we conduct ambient noise tomography and teleseismic two-plane-wave tomography to probe the crustal and uppermost mantle structures in the Middle–Lower Yangtze River region. The data used include 14 months (from July 2012 to August 2013) of continuous vertical component ambient noise data and 219 teleseismic earthquakes recorded at 138 broadband seismic stations from Chinese provincial networks and 19 temporary seismic stations deployed by China University of Geosciences (Beijing). First, we apply ambient noise tomography to the collected ambient noise data to generate Rayleigh wave group and phase velocity maps at 5–42 s periods and two-plane-wave tomography method to earthquake data to generate intermediate-to-long period phase velocity maps at 20–143 s periods. We then combine the short-to-intermediate period velocity maps from ambient noise and the intermediate-to-long period phase velocity maps from earthquake data to generate broadband phase velocity maps at periods from 5 to 143 s. By inverting these 5–143 s Rayleigh wave velocity maps, we construct a 3-D shear wave velocity model from the surface to ∼250 km depth in the Middle–Lower Yangtze River region. The 3-D model shows that in the upper crust, the basin regions, including the JiangHan, HeHuai, SuBei, HeFei and NanYang basins, are all featured with low velocities, and the mountain regions with high velocities. In the uppermost mantle, a low-velocity zone at ∼100–200 km depth is observed beneath the Middle–Lower Yangtze River Metallogenic Belt. Moreover, our tomographic results show that the NingWu and NingZhen ore districts are clearly characterized by the strongest low velocity anomaly in the uppermost mantle at ∼70–200 km depth. The depth extent of the low-velocity zone becomes shallower and the amplitude of low velocity anomaly becomes larger from the southwest JiuRui ore district to northeast NingWu ore districts. The change pattern of the low-velocity zone in the depth extent and the amplitude is consistent with the fact that peak ages of magmatic events along the Middle–Lower Yangtze River Metallogenic Belt progressively become younger and younger from 148 Ma in the southwest to 125 Ma in the northeast. The observed low-velocity zone may represent the cooling hot upper mantle which was partially molten in the past resulting from partial melting of the paleo-Pacific plate or of an enriched mantle source induced by the westward subduction of the paleo-Pacific plate. The upwelling of the mantle-derived magmas may result in the formation of these granitic rocks and coeval ores deposits along the Middle–Lower Yangtze River Metallogenic Belt.

Establishing and Applying a Schistosomiasis Early Warning Index (SEWI) in the Lower Yangtze River Region of Jiangsu Province, China

BackgroundChina has made remarkable progress in schistosomiasis control over the past decades. Transmission control has replaced morbidity control as the country moves towards the goal of elimination and the current challenge is to find a sensitive measure capable of gauging transmission risk in low-prevalence areas. The study aims to develop a Schistosomiasis Early Warning Index (SEWI) and demonstrate its use in Jiangsu Province along the lower Yangtze River.Methodology/Principal FindingsThe Delphi approach, a structured communication technique, was used to develop the SEWI. Two rounds of interviews with 30 public health experts specialized in schistosomiasis control were conducted using 40 indicators that reflected different aspects of schistosomiasis transmission and control. The necessity, feasibility, and sensitivity of each indicator were assessed and the weight value of each indicator determined based on these experts' judgment. The system included 3 first-order indicators, 7 second-order indicators, and 30 third-order indicators. The 3 first-order indicators were endemic status, control measures, social and environmental factors, with the weight values 0.366, 0.343 and 0.291, respectively. For the 7 second-order indicators, the highest weight value was for control measures for snails (0.175) and the lowest for transmission route (0.110). We estimated and mapped the SEWI for endemic areas at the county scale in Jiangsu Province finding that the majority of the endemic areas were characterized as medium transmission risk (SEWI risk values between 0.3 and 0.6), while areas where transmission interruption had been officially declared showed SEWI values <0.30. A few isolated areas (e.g. endemic islands in the Yangtze River) produced SEWI values >0.60. These estimates are largely in agreement with the endemicity levels based on recent epidemiological surveys.Conclusions/SignificanceThe SEWI should be useful for estimation of schistosomiasis transmission surveillance, particularly with reference to the elimination of the disease in China.

U-Pb ages of zircon grains reveal a proximal dust source of the Xiashu loess, Lower Yangtze River region, China

Deciphering the eolian sources is critical to understand the paleo-significance of the Quaternary eolian deposits (the Xiashu loess) in the lower reaches of the Yangtze River. Both a local source from the fluvial sediments of the Yangtze River and a distal source from the northern deserts similar to that of the loess on the Chinese Loess Plateau (CLP) have been proposed. Recent researches show great advantages of detrital zircon ages as a source tracer for Asian dust based on the laser ablation U-Pb isotopic dating technique. This work presents the U-Pb ages of zircon grains extracted from the Xiashu loess. The results indicate that the Xiashu loess has a very different age distribution of zircon grains from that of the loess on the CLP as well as the materials in the arid lands of the Asian Interior. Instead, the zircon ages of the Xiashu loess are indistinguishable from the fluvial sediments of the Yangtze River, indicating the dominance of proximal dust source. Proximal source of the Xiashu loess implies that extensive eolian processes might have existed in the currently wet South China, possibly in response to the full glacial conditions after the middle Pleistocene transition of global climate.

Eskimo Art Prototypes in the Chinese Neolithic: A Comparison of Okvik/Old Bering Sea and Liangzhu Ritual Art

One of the central decorative features of the Okvik/Old Bering Sea (OBS) Eskimo art is a theriomorphic design with an eyelike circle-dot motif. Seventy-five years ago, Henry B. Collins proposed the resemblance between OBS animal motifs and the Taotie (or t'ao t'ieh) faces on Chinese Shang and Zhou bronze wares. However, today his conclusion is based on outdated archaeological data. New evidence in recent decades indicates that the Chinese Bronze Age Taotie originated from mask-like imagery on jade objects of the Liangzhu Neolithic culture, third millennium BC in the Lower Yangtze River region. Comparative studies suggest more similarities in artistic designs between Okvik/OBS and Liangzhu jade than between Okvik/OBS culture and the Shang/Zhou Bronze Age cultures. The prototype theriomorphic design in Okvik/OBS Eskimo art, therefore, may originate from Liangzhu rather than from Shang and Zhou.

Application of a triangular fuzzy AHP approach for flood risk evaluation and response measures analysis

Flood risk evaluation and prediction represents an essential analytic step to coherently link flood control and disaster mitigation. The paper established a hybrid evaluation model based on fuzzy analytic hierarchy process (AHP) and triangular fuzzy number. It comprises flood risk evaluation and prediction to obtain risk factors ranking and comprehensive flood risk prediction, and then analyzed flood risk response measures. A case study is proposed entailing a flood risk evaluation and prediction in the Lower Yangtze River region. The evaluation results showed that the proposed evaluation and prediction model was capable of adequately representing the actual setting. In addition, a comparison with the previously described AHP and trapezoidal fuzzy AHP, and experimental results are encouraging, which fully demonstrates the effectiveness and superiority of the proposed model.

Geochemistry, and zircon U-Pb and molybdenite Re-Os geochronology of Jilongshan Cu-Au deposit, southeastern Hubei Province, China

The Jilongshan skarn Cu–Au deposit is located at the Jiurui ore cluster region in the southwestern part of the Middle–Lower Yangtze River valley metallogenic belt. The region is characterized by NW-, NNW- and EW-trending faults and the mineralization occurs at the contact of lower Triassic carbonate rocks and Jurassic granodiorite porphyry intrusions. The intrusives are characterized by SiO2, K2O, and Na2O concentrations ranging from 61.66 to 67.8 wt.%, 3.29 to 5.65 wt.%, and 2.83 to 3.9 wt.%, respectively. Their A/CNK (A/CNK = n(Al2O3)/[n(CaO) + n(Na2O) + n(K2O)]) ratio, δEu, and δCe vary from 0.77 to 1.17, 0.86 to 1, and 0.88 to 0.96, respectively. The rocks show enrichment in light rare earth elements ((La/Yb)N = 7.61–12.94) and large ion lithophile elements (LILE), and depletion in high field strength elements (HFSE), such as Zr, Ti. They also display a peraluminous, high-K calc-alkaline signature typical of intrusives associated with skarn and porphyry Cu–Au–Mo polymetallic deposits. Laser ablation inductively coupled plasma spectrometry (LA-ICP-MS) zircon U–Pb age indicates that the granodiorite porphyry formed at 151.75 ± 0.70 Ma. A few inherited zircons with older ages (677 ± 10 Ma, 848 ± 11 Ma, 2645 ± 38 Ma, and 3411 ± 36 Ma) suggest the existence of an Archaean basement beneath the Middle–Lower Yangtze River region. The temperature of crystallization of the porphyry estimated from zircon thermometer ranges from 744.3 °C to 751.5 °C, and 634.04 °C to 823.8 °C. Molybdenite Re–Os dating shows that the Jilongshan deposit formed at 150.79 ± 0.82 Ma. The metallogeny and magmatism are correlated to mantle–crust interaction, associated with the subduction of the Pacific Plate from the east. Copyright © 2013 John Wiley & Sons, Ltd.

Statistical tests for a correlation between decadal variation in June precipitation in China and sunspot number

Six different statistical methods (i.e., correlation, difference, prominent period, variance contribution, scale‐averaged spectrum, and cross spectrum) are used to test for regional differences in the relationship between the 11 year sunspot cycle and June precipitation in China during the 20th century. In the Huaihe River basin (HRB) of central China, located at the marginal region of the East Asian summer monsoon (EASM), there exists a reliable positive‐correlation relationship between the 11 year sunspot cycle and June precipitation; whereas, possible negative and very weak positive correlations in the south of the middle–lower Yangtze River Region and the HeTao Basin (HTB), located in the interior of the EASM and the westerlies, respectively. The reasons for these regional differences are investigated, revealing that the marginal region of EASM may be more sensitive to solar forcing than is its interior, which results in the HRB becoming the most susceptible (strongest correlation) region. That is to say, in June during the high sunspot number (SSN) years, the influence of the EASM is significantly greater and more to the north than that in June during the low SSN years, causing the HRB to be mainly influenced by the EASM (westerlies) in June during the high (low) SSN years. The northward expansion of the June EASM probably resulted from enhancement of the low‐level southwesterly monsoon flow over the northern tropical Indian Ocean, combined with an expansion of the western Pacific subtropical high at times of high SSN.

A tectono-genetic model for porphyry–skarn–stratabound Cu–Au–Mo–Fe and magnetite–apatite deposits along the Middle–Lower Yangtze River Valley, Eastern China

The Middle–Lower Yangtze River Valley metallogenic belt (YRB), situated along the northern margin of the Yangtze craton, is characterized by porphyry–skarn–stratabound Cu–Au–Mo–Fe deposits in the areas of uplift and magnetite–apatite deposits in Cretaceous fault basins. Following detailed field investigations and a review of published data, we recognize two episodes of magmatism and mineralization in the YRB: 1) 156–137 Ma high-K calc-alkaline granitoids associated with 148–135 Ma porphyry–skarn–stratabound Cu–Au–Mo–Fe deposits and 2) 135–123 Ma shoshonitic series, associated with 134.9–122.9 Ma magnetite–apatite deposits. A-type granitoids and associated alkaline volcanic have a small age range from 126.5 to 124.8 Ma and are temporally, spatially and genetically associated with the second episode. The geodynamic history of the YRB did not experience the Paleozoic to Mesozoic lithospheric thickening that took place in the North China craton. This process is inferred to be linked to partial melting of the delaminated lower crust at high pressures, resulting in the development of C-type adakitic rocks. The petrochemical and Sr/Nd isotopic data show that both the shoshonitic series and A-type granitoids are quite different from adakites, with only some of the K-calc-alkaline granitoids having adakitic signatures. Previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono-thermal evolution from 150 to 100 Ma. All data obtained for the Middle–Lower Yangtze River region consistently show that the Tan–Lu regional strike-slip fault zone, initiated at 233 ± 6 to 225 ± 6 Ma from the collision between the North China and Yangtze cratons and was reactivated at ca. 160 Ma. The Tan–Lu fault was caused by the oblique subduction of the Izanagi plate, which along the YRB the low-angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks. The high-K calc-alkaline granitoids magmas were derived from melting of the subducted slab, with some input of crustal material. These magmas were emplaced at the intersections between NE- and EW-trending faults and formed porphyry–skarn–stratabound Cu–Au–Mo–Fe deposits between 156 and 137 Ma. After 135 Ma the subducted plate changed its direction of motion to northeast, now running parallel to the Eurasian continental margin, and leading to large-scale continental extension. The shoshonitic series and subsequent A-type granitoids magmatism and the development of magnetite–apatite ores in the YRB, took place in both fault basins and NE-trending rifts between 135 and 124 Ma.

Neoproterozoic subducted materials in the generation of Mesozoic Luzong volcanic rocks: Evidence from apatite geochemistry and Hf–Nd isotopic decoupling

A combined study including apatite geochemistry, zircon U–Pb, Lu–Hf isotopes and whole-rock geochemistry including Nd isotopes was carried out for the late Mesozoic volcanic rocks from the Luzong Basin, in the lower Yangtze River region, South China. Whole-rock geochemistry indicates the enrichments of large ion lithophile elements (LILE) and light rare earth elements (LREE) as well as depletions of Nb, Ta and Ti. The extremely low Cl contents in apatites strongly contrast with the rather high-K contents in whole rocks. Potential loss of Cl during syn- and post-magmatic processes having been ruled out, Cl–K decoupling is attributed to be a feature inherited from the primary magma, which indicates the involvement of highly dehydrated sediments and altered oceanic crust in the mantle source. A calculation based on apatite and whole-rock geochemistry further illustrates that the source was composed of four end-members in the perspective of Cl/K, Cl/Nb and F/K ratios. The Hf–Nd isotopes are decoupled for the basaltic trachytes from the lower volcanic sequences in the Luzong Basin, with rather low ε Hf (t) values (mean = − 10.3) and inconsistent Hf–Nd model ages (Hf ~ 1.8 Ga, Nd ~ 1.3 Ga), which indicate the “zircon effect” that in turn requires the incorporation of continental detritus in the source via subduction. However, Hf and Nd isotopes are nearly coupled for the rocks from the upper volcanic sequences in the Luzong Basin. Late-Mesoproterozoic two-stage Hf and Nd model ages (ca. 1.2 Ga) of rocks from the upper volcanic sequences in the Luzong Basin are similar to those of the Neoproterozoic igneous rocks from the Jiangnan orogen, suggesting their relationship with the same subduction event. Based on the combined apatite geochemistry and Hf–Nd isotopes, this work suggests that the source of Luzong volcanic rocks might incorporate Neoproterozoic subducted slab fragments and detrital sediments that had been blocked in the deep lithospheric mantle below the Luzong area since the Neoproterozoic assembly between the Yangtze and Cathaysia blocks. The partial melting may be triggered by the back-arc lithospheric extension related to the subduction of Paleo-Pacific plate in the late Mesozoic.

Changes of Grain Quality During Evolution of Mid-season Indica Rice Cultivars in Jiangsu Province

Mid-season rice ( Oryza sativar L. subsp. indica) is the dominant type of cultivated rice in the Middle and Lower Yangtze River Region of China. This study aimed at studying the characteristics of evolution on grain quality in the mid-season rice cultivars commercially grown in Jiangsu Province, China since the 1950s. Thirteen cultivars or hybrids were selected to represent the types of early-tall, dwarf, semidwarf, semidwarf hybrid, and super rice according to their application times, plant types, and genotypes. The milling quality indicators, including brown rice rate, milled rice rate, and head milled rice rate, were different within the same type of cultivars, but showed no significant differences between types. Compared with the early-tall and dwarf cultivars that were released in earlier years, modern cultivars in semidwarf hybrid and super rice types had lower levels of chalkiness, setback value, and prolamin content in grains and significant higher breakdown value and contents of albumin, glutelin, lysine, glycine, and arginine. The continuously increasing grain yield with the evolution of cultivars was mainly attributed by the augment of spikelet number and grain number per panicle, which resulted from the large panicle trait. These results suggest that both quality and yield are improved during the evolution of mid-season indica rice cultivars.