Showing papers in "Science China-earth Sciences in 2013"

Tectonics of South China continent and its implications

Abstract: This paper aims at exploring the tectonic characteristics of the South China Continent (SCC) and extracting the universal tectonic rules from these characteristics,to help enrich the plate tectonic theory and better understand the continental dynamic system. For this purpose, here we conduct a multi-disciplinary investigation and combine it with the previous studies to reassess the tectonics and evolution of SCC and propose that the tectonic framework of the continent comprises two blocks, three types of tectonic units, four deformation systems, and four evolutionary stages with distinctive mechanism and tectonic characteristics since the Neoproterozoic. The four evolutionary stages are: (1) The amalgamation and break-up of the Neoproterozoic plates, typically the intracontinental rifting. (2) The early Paleozoic and Mesozoic intracontinental orogeny confined by plate tectonics, forming two composite tectonic domains. (3) The parallel operation of the Yangtze cratonization and intracontinental orogeny, and multi-phase reactivation of the Yangtze craton. (4) The association and differentiation evolution of plate tectonics and intracontinental tectonics, and the dynamic characteristics under the Meso-Cenozoic modern global plate tectonic regime.

Multiple-aged granitoids and related tungsten-tin mineralization in the Nanling Range, South China

Abstract: The Nanling metallogenic belt in South China is characterized by well-developed tungsten-tin mineralization related to multiple-aged granitoids. This belt is one of the 5 key prospecting and exploration areas among the 19 important metallogenic targets in China. Important progress has been made in recent years in understanding the Nanling granitoids and associated mineralization, and this paper introduces the latest major findings as follows: (1) there exists a series of Caledonian, Indosinian, and Yanshanian W-Sn-bearing granites; (2) the Sn-bearing Yanshanian granites in the Nanling Range form an NE-SW trending aluminous A-type granite belt that stretches over 350 km. The granites typically belong to the magnetite series, and dioritic micro-granular enclaves with mingling features are very common; (3) the Early Yanshanian Sn- and W-bearing granites possess different petrological and geochemical features to each other: most Sn-bearing granites are metaluminous to weakly peraluminous biotite (hornblende) granites, with zircon ɛHf(t) values of ca. −2 to −8, whereas most W-bearing granites are peraluminous two-mica granites or muscovite granites with ɛHf(t) values of ca. −8 to −12; (4) based on the petrology and geochemistry of the W-Sn-bearing granites, mineralogical studies have shown that common minerals such as titanite, magnetite, and biotite may be used as indicators for discriminating the mineralizing potential of the Sn-bearing granites. Similarly, W-bearing minerals such as wolframite may indicate the mineralizing potential of the W-bearing granites. Future studies should be focused on examining the internal relationships between the multiple-aged granites in composite bodies, the metallogenic peculiarities of multiple-aged W-Sn-bearing granites, the links between melt evolution and highly evolved ore-bearing felsic dykes, and the connections between granite domes and mineralization.

Holocene vegetational and climatic variation in westerly-dominated areas of Central Asia inferred from the Sayram Lake in northern Xinjiang, China

Abstract: Changes in the vegetation and climate of the westerly-dominated areas in Central Asia during the Holocene were interpreted using pollen-assemblages and charcoal data from a 300-cm-long sediment core of the Sayram Lake, northern Xinjiang. Accele-rator Mass Spectrometry (AMS) radiocarbon dating methods were applied to bulk organic matter of the samples. Artemisia spp./Chenopodiaceae ratios and results from principal component analysis were used to infer that the lake basin was dominated by desert vegetation before ca. 9.6 cal. ka BP, which suggests a warm and dry climate in the early Holocene. Desert steppe/steppe expanded during 9.6-5.5 cal. ka BP, indicating a remarkable increase both in the precipitation and temperature during the mid-Holocene. Desert vegetation dominated between 6.5 and 5.5 cal. ka BP, marking an extreme warmer and drier interval. The steppe/meadow steppe recovered, and temperatures decreased from 5.5 cal. ka BP in the late Holocene, as indicated by the increased abundance of Artemisia and the development of meadows. Holocene temperatures and moisture variations in the Sayram Lake areas were similar to those of adjacent areas. This consistency implies that solar radiation was the main driving factor for regional temperature changes, and that the effect of temperature variations was significant on regional changes in humidity. The evolution of climate and environment in the Sayram Lake areas, which were characterized as dry in the early Holocene and relatively humid in the middle-late Holocene, are clearly different from those in monsoonal areas. Dry conditions in the early Holocene in the Sayram Lake areas were closely related to decreased water vapor advection. These conditions were a result of reduced westerly wind speeds and less evaporation upstream, which in turn were caused by seasonal changes in solar radiation superimposed by strong evaporation following warming and drying local climate.

Contributions of climate and human activities to changes in runoff of the Yellow and Yangtze rivers from 1950 to 2008

Abstract: Runoffs in the Yellow River and Yangtze River basins, China, have been changing constantly during the last half century. In this paper, data from eight river gauging stations and 529 meteorological stations, inside and adjacent to the study basins, were analyzed and compared to quantify the hydrological processes involved, and to evaluate the role of human activities in changing river discharges. The Inverse Distance Weighted (IDW) interpolation method was used to obtain climatic data coverage from station observations. According to the runoff coefficient equation, the effect of human activities and climate can be expressed by changes in runoff coefficients and changes in precipitation, respectively. Annual runoff coefficients were calculated for the period 1950–2008, according to the correlation between respective hydrological series and regional precipitation. Annual precipitation showed no obvious trend in the upper reaches of the Yellow River but a marked downward trend in the middle and downstream reaches, with declines of 8.8 and 9.8 mm/10 a, respectively. All annual runoff series for the Yellow River basin showed a significant downward trend. Runoff declined by about 7.8 mm/10 a at Sanmenxia and 10.8 mm/10 a at Lijin. The series results indicated that an abrupt change occurred in the late 1980s to early 1990s. The trend of correlations between annual runoff and precipitation decreased significantly at the Yellow River stations, with rates ranging from 0.013/10 a to 0.019/10 a. For the hydrologic series, all precipitation series showed a downward trend in the Yangtze River basin with declines ranging from about 24.7 mm/10 a at Cuntan to 18.2 mm/10 a at Datong. Annual runoff series for the upper reaches of the Yangtze River decreased significantly, at rates ranging from 9.9 to 7.2 mm/10 a. In the middle and lower reaches, the runoff series showed no significant trend, with rates of change ranging from 2.1 to 2.9 mm/10 a. Human activities had the greatest influence on changes in the hydrological series of runoff, regardless of whether the effect was negative or positive. During 1970–2008, human activities contributed to 83% of the reduction in runoff in the Yellow River basin, and to 71% of the increase in runoff in the Yangtze River basin. Moreover, the impacts of human activities across the entire basin increased over time. In the 2000s, the impact of human activities exceeded that of climate change and was responsible for 84% of the decrease and 73% of the increase in runoff in the Yellow River and Yangtze River basins, respectively. The average annual runoff from 1980 to 2008 fell by about 97%, 83%, 83%, and 91%, compared with 1951–1969, at the Yellow River stations Lanzhou, Sanmenxia, Huayuankou and Lijin, respectively. Most of the reduction in runoff was caused by human activities. Changes in precipitation also caused reductions in runoff of about 3%, 17%, 17%, and 9% at these four stations, respectively. Falling precipitation rates were the main explanation for runoff changes at the Yangtze River stations Cuntan, Yichang, Hankou, and Datong, causing reductions in runoff of 89%, 74%, 43%, and 35%, respectively. Underlying surface changes caused decreases in runoff in the Yellow River basin and increases in runoff in the Yangtze River basin. Runoff decreased in arid areas as a result of increased water usage, but increased in humid and sub-humid areas as a result of land reclamation and mass urbanization leading to decreases in evaporation and infiltration.

SHRIMP zircon U-Pb dating of late Paleoproterozoic kondalites in the Daqing Mountains area on the North China Craton

Abstract: The Daqing Mountains area comprises a typical occurrence of the Khondalite Belt in the Western Block of the North China Craton (NCC). In this area, both early and late Paleoproterozoic metasedimentary rocks have been identified in what was originally called the Upper Wula Mountains “Subgroup”. Six metasedimentary rock samples yielded SHRIMP U-Pb zircon ages of 2.56–2.04 Ga for detrital and 1.96–1.83 Ga for metamorphic zircons. Based on these data and previously published results, the following conclusions can be drawn: 1) The source region for the late Paleoproterozoic detrital sedimentary rocks is mainly 2.55–2.4 and 2.2–2.04 Ga in age, consistent with the early Precambrian geological history identified widely in the basement of the NCC. 2) The majority of sedimentary rocks of the khondalite series were deposited between 2.04 and 1.95 Ga, and then in a protracted period (1.96 and 1.83 Ga) underwent a complex history of amphibolite to granulite-facies metamorphism.

Stress changes on major faults caused by 2013 Lushan earthquake and its relationship with 2008 Wenchuan earthquake

Abstract: On April 20, 2013, an M s7.0 earthquake occurred in Ya’an-Lushan region, Sichuan Province, China, killing and injuring more than one thousand people. Therefore, it is critical to outline the areas with potential aftershocks before reconstruction and re-settlement as to avoid future disasters. Based on the elastic dislocation theory and multi-layered lithospheric model, we calculate the co- and post-seismic stress changes caused by the Wenchuan and Lushan earthquakes to discuss the relationship between M w7.9 Wenchuan earthquake and M s7.0 Lushan earthquake, the influences on the distribution of aftershock caused by the Lushan earthquake, and the stress changes on major faults in this region. It is shown that the Coulomb failure stress increment on the hypocenter of Lushan earthquake caused by the Wenchuan earthquake is about 0.0037–0.0113 MPa. And the possible maximum value (0.0113 MPa) is larger than the threshold of stress triggering. Therefore, the occurrence of Lushan earthquake is probably effectively promoted by the Wenchuan earthquake. The aftershock distribution is well explained by the co-seismic stress changes of Lushan earthquake. By the two ends of the rupture of Lushan earthquake with increased Coulomb failure stress, a lack of aftershock recordings indicates the high seismic hazard. The stress accumulation and corresponding seismic hazard on the Kangding-Dafu segment of the Xinshuihe fault, the Beichuan-Yingxiu fault, the Pengxian-Guanxian fault, and the Ya’an fault are further increased by the Lushan earthquake and post-seismic process of Wenchuan earthquake.

Early Permian Tarim Large Igneous Province in northwest China

Abstract: Tarim Large Igneous Province (TLIP) is the second Late Paleozoic LIPs in China after the recognition of Emeishan LIP, and is a hot research topic in geosciences. On the basis of the analysis of research history about TLIP, this paper summarizes the research result during last twenty years and suggests the key research area in the future. The residual distribution range of TLIP is up to 250000 km2, and the largest residual thickness is 780 m. The eruption of basalt happened during 290–288 Ma and belongs to LIPs magmatic event with fast eruption of magma. The lithological units of the TLIP include basalt, diabase, layered intrusive rock, breccia pipe mica-olivine pyroxenite, olivine pyroxenite, gabbro, ultramafic dyke, quartz syenite, quartz syenite porphyry and bimodal dyke. The basalt and diabase of TLIP exhibit OIB-like trace element patterns and enrichment of LILE and HFSE, and mainly belong to high TiO2 series. There is an obvious difference in isotope among the basalt from Keping and the basalt and dibase from the northern Tarim Basin. The basalt from Keping with negative ɛ Nd and high REE value derives from enriched mantle, and the diabase and basalt from the northern Tarim Basin with positive ɛ Nd and low REE value are related to depleted mantle. The crust uplifting in the Early Permian and the development of picrite and large scale dyke and formation of large scale V-Ti-Magnetite deposit in Wajilitag area support the view that the TLIP is related to mantle plume. The TLIP has a temporal-spatial relationship with Permian basic to ultra-basic igneous rock, which is distributed widely in Central Asia, and they represent a tectono-magmatic event with very important geodynamic setting. This paper also suggests that the deep geological process, the relation with mantle plume, mineralization, the relation with environmental change and biological evolution, and the geodynamics of the TLIP will be the key research topics in the future.

General characteristics of climate changes during the past 2000 years in China

Abstract: The general characteristics of climate changes over the past 2000 years in China, regional differences and uncertainties were analyzed based on the recently peer-reviewed high time-resolution climatic reconstructions. The results showed that there exists four warm periods of the temperature variation in China since the Qin Dynasty, including the western and eastern Han Dynasties (200 BC-AD 180), the Sui and Tang dynasties (541–810), the Song and Yuan dynasties (931–1320), and the 20th century, and three cold phases involving the Wei, Jin, and North-South Dynasties (181–540), the late Tang Dynasty (811–930), and the Ming and Qing dynasties (1321–1920). The Song and Yuan warm period is consistent with the Medieval Warm Period over the Northern Hemisphere, and the cold phases of the North-South Dynasties and the Ming and Qing dynasties are paralleled to the Dark Ages Cold Period and the Little Ice Age, respectively. The 13th-15th century could be a shift to the wet condition of the climate, and the low precipitation variability is exhibited in western China prior to 1500. In the context of the climate warming, the pattern of the drought in north and flood in south is prevalent over the eastern China. In addition, the published reconstructions have a high level of confidence for the past 500 years, but large uncertainties exist prior to the 16th century.

U-Pb zircon age and Hf isotope compositions of Mesoproterozoic sedimentary strata on the western margin of the Yangtze massif

Abstract: The Mesoproterozoic sedimentary strata on the western margin of the Yangtze massif are a clastic-carbonate rock association intercalated with a small amount of tuff and basalt and deposited in a relatively stable environment. They are termed as the Kunyang Group, the Huili Group, and the Dongchuan Group respectively in different regions. We performed zircon U-Pb dating of the tuff from the groups. The results, coupled with the detrital zircon U-Pb ages of clastic rocks from the Kunyang Group and the Dongchuan Group, indicate that the sedimentation ages of the Kunyang Group and the Huili Group range from 1050 to 1000 Ma and that the Kunyang Group and the Huili Group belong to a sedimentary association with contemporaneous heterotopic facies. The detrital zircon ages and Hf isotope compositions reveal that the clastic materials in the Kunyang Group and the Huili Group are derived primarily from the Cathaysia massif. Zircons of the tuff in the Dongchuan Group yields an age of ca.1.5 Ga and all the zircon ages of clastics in the Dongchuan Group are older than 1.5 Ga, indicating that the sedimentation of the Dongchuan Group occurred during the late Mesoproterozoic Changcheng Period. Age spectra of the detrital zircons indicate that the clastic materials of the Dongchuan Group are derived primarily from the ancient basement of the Yangtze massif. A systematic Hf isotope determination of various types of zircons in the above three stratigraphic units shows that there is a rapid elevation in the initial Hf value of zircon at ∼1.5 and ∼1.0 Ga. Previous studies on the sedimentary characteristics of the Kunyang Group and the Huili Group show that both were deposited in a foreland basin. Combining our data with previous studies, we suggest that the Kunyang Group and the Huili Group are foreland basin sedimentary successions formed along the southern side of the Yangtze massif after an amalgamation between the Yangtze massif and the Cathaysia massif during the Grenvillian. The assembly of the Yangtze massif and the Cathaysia massif developed gradually from the west to the east and was finally completed in the eastern segment of the Yangtze massif at 0.9 Ga, representing the last stage of the Rodinia supercontinent assembly. Hf isotope compositions in zircon indicate that the supercontinent cycle has an intimate relation with crustal growth.

Rupture process of the M s 7.0 Lushan earthquake, 2013

Abstract: On April 20, 2013 at 8:02 am, a magnitude 7.0 earthquake occurred in Lushan County, Sichuan Province, China, which induces massive landslides, causes great losses to life and property. Based on the locations of aftershocks provided by the China Earthquake Network Center and the characteristic of Longmenshan active faults system, combined with the current preliminary focal mechanism solution, the fault rupture direction is determined. With the finite fault inversion method, we invert the rupture process of the Lushan M s7.0 earthquake by teleseismic waveforms data. The inversion results indicate that the main shock is dominated by thrust fault component and the rupture initiated at depth of 15 km, and most of slip ruptured around the hypocenter with the peak slip of about 1.5 m. Most of rupture slips released at the first 20 s and the main rupture occurred at the first 10 s after the onsets of the mainshock. Most of seismic energy released near the hypocenter with a length of 28 km, especially on both sides of the hypocenter with the range of 20 km, and the seismic energy released relatively smaller in other areas. There is a large area with weak slip between the main rupture and another two asperities on both sides of the hypocenter; it may imply that the accumulated strain on the rupture fault has not been completely released. Therefore, there is a significant possibility of having strong aftershocks in the areas where energy is not fully released. This is also the main reason why there are a lot of moderate to strong aftershocks in the Lushan aftershock sequence. In addition, there is an earthquake vacant zone with a length of about 50 km between the Wenchuan M w7.9 earthquake and this event, which is of high earthquake risk and is deserved to be paid close attention to.

The main old lands in China and assembly of Chinese unified continent

Abstract: The main old lands in China include the North China Block (NCB), South China Block (SCB) and Tarim Block (TRB), all of which have individual tectonic evolving histories. The NCB experienced complex geological evolution since the early Precambrian onwards, and carries important records from the old continental nuclei, giant crustal growth episode and cratonization (stabilitization), then to the Paleoproterozoic rifting-subduction-accretion-collision with imprints of the Great Oxygen Event (GOE), and to the Late Paleoproterozoic-Neoproterozoic multi-stage rifting representing North China platform tectonic features. The TRB has two-layer basement of the Early Precambrian metamorphic complexes and Neoproterozoic sedimentary sequences. Three till sheets have been reported. The SCB consists of the Yangtze Block (YZB) and Cathaysia Block (CTB) that were cohered in the Neoproterozoic. The YZB recorded tectonic processes of the Early Precambrian crustal growth, 1.0-0.9 Ga and 0.8-0.6 Ga metamorphic-magmatic events, and two Neoproterozoic glaciations. The CTB consists of ca. 1.8 Ga, 1.0 to 0.9 Ga and ca. 0.8 Ga granitic gneisses and metamorphic rocks, indicating there was a vast Precambrian basement. The Neoproterozoic sedimentary rocks overlie partly on the basement. That the YZB and CTB have a Neoproterozoic uniform cover layer illustrates the SCB should form, at least, during 1.0-0.9 Ga, corresponding to the Rodinia Supercontinent. The Central Chinese Orogenic System with high-ultra-high-pressure metamorphic rocks supports a suggestion that the above-mentioned three old lands were collided to assemble a unified Chinese Continent during the Pangea orogenic period.

Time constraints for the closing of the Paleo-Asian Ocean in the Northern Alxa Region: Evidence from Wuliji granites

Abstract: The Wuliji pluton in the Northern Alxa Region, Inner Mongolia, is the principal part of Shalazhashan Mountain. It belongs to the Zongnaishan-Shalazhashan Arc Zone, northwestern North China Plate, whose north is Engger Us Ophiolite Belt and south is Qagan Qulu Ophiolite Belt. The pluton was emplaced into Upper Carboniferous-Lower Permian Amushan Formation. According to the research about the original Carboniferous Amushan Formation, the lower and middle sections of the Carboniferous Amushan Formation consist of volcanic, clastic, and carbonate rocks, interpreted to represent the sedimentary association of a volcanic arc and back-arc basin; the upper section of the Amushan Formation is a molasse composed of silty shale, sandstone, gravel-bearing sandstone, and conglomerate. The Wuliji pluton consists mainly of biotite monzonitic granite, amphibole-bearing biotite monzonitic granite, and monzonitic granite. Geochemical analyses show that the pluton has both metaluminous and peraluminous characteristics, and on average has SiO2 > 70 wt%, Al2O3 > 14 wt%, and high contents of Na2O+K2O (8.5 wt%), which define a calc-alkaline series. In addition, REE patterns show enrichment of LREE and weak negative Eu anomalies (δEu = 0.3–1). Altogether, the samples are depleted in Nb, Ta, Ti, P, Sr, and Ba, and enriched in Rb, Th, and K. These geochemical traits are interpreted to reflect an arc component. A secondary ion mass spectrometry (SIMS) U-Pb zircon age of the biotite monzonitic Wuliji pluton in the Northern Alxa Region, Inner Mongolia, is 250.8 ± 2.0 Ma (1σ). Samples have ɛNd(t) values between −0.1 and 1.3, which suggests that the granites were derived from mixing between the crust and mantle. Based on the SIMS age and geochemical characteristics, Wuliji granite is interpreted to be a post-collisional granite, the result of mantle-derived melt and assimilated juvenile arc crust. However, according to the newest international stratigraphic classification standard, the upper section of the Amushan Formation is Lower Permian in age, indicating that the back-arc basin had already closed in Early Permian. We conclude that the Paleo-Asian Ocean represented by the Engger Us Ophiolite Belt subducted southward in Late Carboniferous, at the same time that the trench-arc-basin system formed in the Northern Alxa Region. The Paleo-Asian Ocean was closed in Early Permian and the Northern Alxa Region entered a post-collisional period in the Late Permian, as indicated by the Wuliji granites. This suggests that the genesis of the Wuliji granites is consistent with the pluton emplacement at the upper crust, which occurred widely in the northern margin of the North China Plate in Late Carboniferous to Triassic.

Development of a 50-year daily surface solar radiation dataset over China

Abstract: Although solar radiation is a crucial parameter in designing solar power devices and studying land surface processes, long-term and densely distributed observations of surface solar radiation are usually not available. This paper describes the development of a 50-year dataset of daily surface solar radiation at 716 China Meteorological Administration (CMA) stations. First, a physical model, without any local calibration, is applied to estimate the daily radiation at all 716 CMA routine stations. Then, an ANN-based (Artificial Neural Network) model is applied to extend radiation estimates to earlier periods at each of all 96 CMA radiation stations. The ANN-based model is trained with recent reliable radiation data and thus its estimate is more reliable than the physical model. Therefore, the ANN-based model is used to correct the physical model dynamically at a monthly scale. The correction generally improves the accuracy of the radiation dataset estimated by the physical model: the mean bias error (MBE) averaged over all the 96 radiation stations during 1994–2002 is reduced from 0.68 to −0.11 MJ m−2 and the root mean square error (RMSE) from 2.01 to 1.80 MJ m−2. The new radiation dataset shows superior performance over previous estimates by locally calibrated Angstrom-Prescott models. Based on the new radiation dataset, the annual mean daily solar radiation over China is 14.3 MJ m−2. The maximal seasonal mean daily solar radiation occurs in the Tibetan Plateau during summer with a value of 27.1 MJ m−2, whereas the minimal seasonal mean daily solar radiation occurs in the Sichuan Basin during winter with a value of 4.7 MJ m−2.

Crustal and upper mantle structure and the deep seismogenic environment in the source regions of the Lushan earthquake and the Wenchuan earthquake

Abstract: Following the Mw7.9 Wenchuan earthquake, the Mw6.6 Lushan earthquake is another devastating earthquake that struck the Longmenshan Fault Zone (LFZ) and caused severe damages. In this study, we collected continuous broadband ambient noise seismic data and earthquake event data from Chinese provincial digital seismic network, and then utilized ambient noise tomography method and receiver function method to obtain high resolution shear wave velocity structure, crustal thickness, and Poisson ratio in the earthquake source region and its surroundings. Based on the tomography images and the receiver function results, we further analyzed the deep seismogenic environment of the LFZ and its neighborhood. We reveal three main findings: (1) There is big contrast of the shear wave velocities across the LFZ. (2) Both the Lushan earthquake and the Wenchuan earthquake occurred in the regions where crustal shear wave velocity and crustal thickness change dramatically. The rupture faults and the aftershock zones are also concentrated in the areas where the lateral gradients of crustal seismic wave speed and crustal thickness change significantly, and the focal depths of the earthquakes are concentrated in the transitional depths where shear wave velocities change dramatically from laterally uniform to laterally non-uniform. (3) The Wenchuan earthquake and its aftershocks occurred in low Poisson ratio region, while the Lushan earthquake sequences are located in high Poisson ratio zone. We proposed that the effect of the dramatic lateral variation of shear wave velocity, and the gravity potential energy differences caused by the big contrast in the topography and the crustal thickness across the LFZ may constitute the seismogenic environment for the strong earthquakes in the LFZ, and the Poisson ratio difference between the rocks in the south and north segments of the Longmenshan Fault zone may explain the 5 years delay of the occurrence of the Lushan earthquake than the Wenchuan earthquake.

Primary dolostone related to the Cretaceous lacustrine hydrothermal sedimentation in Qingxi sag, Jiuquan Basin on the northern Tibetan Plateau

Abstract: Based on comprehensive studies in petrography, petrofabric analysis and geochemistry, this paper describes a unique and rare laminated micritic ferruginous primary dolostone crystallized and precipitated from the alkaline hot brine under the conditions of the Mesozoic faulted lake basin. The main rock-forming mineral of this dolostone is ferruginous dolomite with a micritic structure. This dolomite mostly exhibits laminae of 0.1–1 mm thick and is often discovered with other minerals, such as albite, analcite, barite and dickite, which have at least two types of interbedded laminae. Petrogeochemistry reveals that this dolostone contains a large number of typomorphic elements of hydrothermal sedimentation, including Sb, Ba, Sr, Mn, and V. In addition, the LREE is in relatively high concentrations and possesses the typical REE distribution pattern with negative Eu anomaly. Oxygen isotope values (δ18OPDB) range from 5.89‰ to 14.15‰ with an average of 9.69‰. The ratio of 87Sr/86Sr is between 0.711648 and 0.719546, with an average of 0.714718. These data indicate that the depositional environment is a stable, blocked, anoxic low-lying hot brine pool in the bottom of deep lake controlled by basement faults. The hydrothermal fluid is the alkaline hot brine formed by the combination of the infiltration lake water and mantle-derived magmatic water, consisting of many ions, including Ca2+, Mg2+ and Fe2+. Under the driving flow power of magmatic heat, gravity and compaction, the hydrothermal fluid overcame the overburden pressure and hydrostatic pressure of the lake water body, and boiled to explosion, and then the explosion shattered the original laminated micritic ferruginous primary dolostone near the vent and then formed a new type of dolostone called shattered “hydroexplosion breccias”. In the low-lying, unperturbed hot brine pool, far from the vent, the laminated micritic ferruginous primary dolostone was quickly crystallized and chemicals precipitated from the hydrotherm. This study of special rocks contributes to research into the causes of the formation of lacustrine carbonate rocks and dolostone. In particular, it provides new examples and research insights for future studies of the lacustrine dolomite from the similar Mesozoic and Cenozoic basins in China.

Mass extinction and Pangea integration during the Paleozoic-Mesozoic transition

Abstract: The greatest Phanerozoic mass extinction happened at the end-Permian to earliest Triassic. About 95% species, 82% genera, and more than half families became extinct, constituting the sole macro-mass extinction in geological history. This event not only caused the great extinction but also destroyed the 200 Myr-long Paleozoic marine ecosystem, prompted its transition to Mesozoic ecosystem, and induced coal gap on land as well as reef gap and chert gap in ocean. The biotic crisis during the Paleozoic-Mesozoic transition was a long process of co-evolution between geospheres and biosphere. The event sequence at the Permian-Triassic boundary (PTB) reveals two-episodic pattern of rapidly deteriorating global changes and biotic mass extinction and the intimate relationship between them. The severe global changes coupling multiple geospheres may have affected the Pangea integration on the Earth’s surface spheres, which include: the Pangea integration→enhanced mountain height and basin depth, changes of wind and ocean current systems; enhanced ocean basin depth→the greatest Phanerozoic regression at PTB, disappearance of epeiric seas and subsequent rapid transgression; the Pangea integration→thermal isolation effect of continental lithosphere and decrease of mid-ocean ridges→development of continental volcanism; two-episode volcanism causing LIPs of the Emeishan Basalt and the Siberian Trap (259–251 Ma)→global warming and mass extinction; continental aridification and replacement of monsoon system by latitudinal wind system→destruction of vegetation; enhanced weathering and CH4 emission→negative excursion of δ 13 C; mantle plume→crust doming→regression; possible relation between the Illawarra magnetic reversal and the PTB extinction, and so on. Mantle plume produced the Late Permian LIPs and mantle convection may have caused the process of the Pangea integration. Subduction, delamination, and accumulation of the earth’s cool lithospheric material at the “D” layer of CMB started mantle plume by heat compensation and disturbed the outer core thermo-convection, and the latter in turn would generate the mid-Permian geomagnetic reversal. These core and mantle perturbations may have caused the Pangea integration and two successive LIPs in the Permian, and probably finally the mass extinction at the PTB. Permian-Triassic boundary, mass extinction, Pangea integration, multi-sphere coupling mantle plume

Seasonal characterization of components and size distributions for submicron aerosols in Beijing

Abstract: Submicron aerosols (PM1) in Beijing were studied using an Aerodyne aerosol mass spectrometer (AMS) from January to October 2008. This paper presents seasonal variations of different chemical components (sulfate, nitrate, ammonium, chloride and organics) and size distributions of PM1. Results show that mass concentration of PM1 was highest in summer, and lowest in autumn. Organics represented the dominant species in all seasons, accounting for 36%–58% of PM1, and their concentrations were highest in winter. Concentrations of inorganic components, sulfate, nitrate, and ammonium were highest in summer. Based on principal component analysis, organics were deconvolved and quantified as hydrocarbon-like and oxygenated organic aerosol (HOA and OOA, respectively). HOA was highest in winter, accounting for about 70% of organics. However, OOA was highest in summer, and had lower values in autumn and winter. A similar diurnal pattern of various components was observed, which is higher at nighttime and lower during daytime. HOA increased more dramatically than other species between 17:00 and 21:00 and peaked at noon, which could be related to cooking emissions. OOA, sulfate, nitrate, ammonium and chloride varied with the same trend. Their concentrations increased with solar radiation from 9:00 to 13:00, and declined with weakening solar radiation. Size distributions of all species showed apparent peaks in the range 500–600 nm. Size distributions of organics were much broader than other species, particularly in autumn and winter. Distributions of sulfate, nitrate and ammonium had similar patterns, broadening in winter. Contributions of different species were size-dependent; the finer the particle, the greater the contribution of organics. Organics represented more than 60% of particles smaller than 200 nm, contributing 50% to PM1 in winter. In spring and summer, HOA was the dominant organic fraction for particles smaller than 200 nm, while OOA contributed more to particles larger than 300 nm. In winter, HOA contributed more than OOA to all PM1 particles.

Source parameters inversion of the 2013 Lushan earthquake by combining teleseismic waveforms and local seismograms

Abstract: On April 20, 2013, a magnitude Ms7.0 earthquake occurred in Lushan, Sichuan Province, China, and caused heavy casualties and economic losses. Based on the local broadband waveforms in Sichuan and adjacent provinces regional networks and teleseismic broadband records from IRIS stations, the focal mechanism and the focal depth are determined by the CAP (Cut And Paste) and its upgraded methods, CAPtele and CAPjoint, respectively. The results show that the focal mechanisms and depth from different methods are steady, and the best double couple solution derived from the joint inversion is 210°, 44°, and 91° for strike, dip, and rake angles respectively for one nodal plane and 29°, 46°, and 89° for another with 16 km focal depth and Mw6.66 moment magnitude. In order to verify the reliability of the results, a number of tests are performed based on local seismograms with different velocity models. They indicate that there is about 10 degree’s fluctuation in focal mechanisms and about 2 km variation in focal depth with a complex velocity structure. Furthermore, inverted by re-sampling the teleseismic waveforms on the basis of epicentral distance, the solutions are consistent with each other, which manifests that the teleseismic records are effective for constraining source parameters of the Lushan earthquake. Lushan earthquake, focal mechanism, focal depth, CAP method

Long-term changes in the fishery ecosystem structure of Laizhou Bay, China

Abstract: Laizhou Bay provides a critical spawning and nursery habitat for many fishery species, including commercially important species, such as Fenneropenaeus chinensis and Larimichthys polyactis. The bay is severely stressed due to high fishing pressure and environmental changes. Based on the long-term ecosystem surveys in Laizhou Bay during the main spawning period (May) of most fishery species from 1959 to 2008, the responses of the Laizhou Bay fishery ecosystem were analyzed here, including regime shifts in species composition, biomass, species diversity, zooplankton, phytoplankton, and environmental variables. The dominant species of large-size and high economic value (e.g. Trichiurus haumela, L. polyactis) have been replaced by the short-lived, low-trophic-level planktivorous pelagic species (e.g. Setipinna taty, Engraulis japonicus) since the 1980s, and it is probable that the small-sized pelagic fishes have been recently replaced by invertebrates (e.g. Oratosquilla oratoria, Crangon affinis). The biomass of fishery resources declined continuously from 423.6 kg haul−1 h−1 in 1959 to 164.6 kg haul−1 h−1 in 1982, 37.7 kg haul−1 h−1 in 1993, and less than 8 kg haul−1 h−1 in 1998–2008. Moreover, the biomass of zooplankton showed an increasing trend during 1959–2006, but showed a slight decline in 2008. The abundance of phytoplankton increased from 1959 through 1982, decreased substantially in 1993, and increased again until 2004. More recently, however, the phytoplankton abundance was very low. The sea surface temperature (SST) and sea bottom temperature (SBT) in May increased by 0.23°C a−1 and 0.16°C a−1, respectively, during 1982–2008. The salinity in May showed large fluctuations and reached its lowest values in 2004 and 2006. The ratio of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphate (DIP) increased. However, the dissolved silicon (DSi):DIP and DSi:DIN ratios decreased to a low level during 1959–2008. These changes seriously impacted primary production, and cascade effects then changed the structure and function of the fishery ecosystem. Further analysis indicated that multiple stresses caused the alterations in the structure of the Laizhou Bay fishery ecosystem. The top-down effect was identified as the main influence on the fishery species (at the top of the food chain) over the past five decades due to the increasing fishing pressure, whereas the bottom-up effect increased over the past three decades due to the strong variations in the environment.

Variations of pore water sulfate gradients in sediments as indicator for underlying gas hydrate in Shenhu Area, the South China Sea

Abstract: Shenhu Area is one of the most promising areas for gas hydrate exploration in the northern South China Sea (SCS). Pore water sulfate gradient, sulfate-methane interface (SMI) depth, and sulfate flux were analyzed at 53 sites in this area. SO4 −2 gradient ranges between 0.33 and 4.43 mmol L−1 m−1. SMI depths are from 7.7 to 87.9 mbsf. Sulfate flux varies between 2.0 and 26.9 mmol m−2 yr−1, with a mean of 11.7 mmol m−2 yr−1. Correlation coefficient between SMI depth and methane flux for the 53 sites is −0.80, implying that methane flux regulates the rate of anaerobic methane oxidation (AMO), SMI depth, and sulfate flux. Twelve anomalous fields with high methane flux and steep sulfate gradients were recognized. Bottom simulating reflector (BSR) is distributed mainly in areas where SMI depth is less than 50 mbsf or places with sulfate flux larger than 3.5 mmol m−2 yr−1. It is suggested that the Baiyun Sag and the Southern Uplift are potential areas for gas hydrate exploration.

Methods, current status, and prospect of targeted observation

Abstract: Targeted observation is an observation strategy by which the concerned phenomenon is observed. In geoscience, targeted observation is mainly related to the forecasts of weather events or predictions of climate events. This paper will first review the history of targeted observation, and then introduce the main methods used in targeted observation. The discussion on the theoretical basis of targeted observation includes its advantages and limitations. After presenting the current situation of domestic and international targeted observations in atmospheric and oceanic sciences, the methods used for targeted observation, and their effect evaluation and testing are mainly discussed here. Finally, the author presents his suggestion about the prospect of further development in the field, and how to extend the method of targeted observation to deal with numerical model errors.

Regional distribution and diurnal variation of deep convective systems over the Asian monsoon region

Abstract: Using 12 years of data from the Tropical Rainfall Measuring Mission (TRMM)-based Precipitation Radar (PR), spatial and diurnal variations of deep convective systems (DCSs) over the Asian monsoon region are analyzed. The DCSs are defined by a 20 dBZ echo top extending 14 km. The spatial distribution of DCSs genesis is also discussed, with reference to the National Centers for Environmental Prediction (NCEP) reanalysis data. The results show that DCSs occur mainly over land. They concentrate in south of 20°N during the pre-monsoon season, and then move distinctly to mid-latitude regions, with the most active region on the south slope of the Himalayas during monsoon season. DCSs over the Tibetan Plateau are more frequent than those in central-eastern China, but smaller in horizontal scale and weaker in convective intensity. DCSs in central-eastern China have more robust updrafts and generate more lightning flashes than in other Asian monsoon regions. The horizontal scale of DCSs over the ocean is larger than that over the other regions, and the corresponding minimum infrared (IR) brightness temperature is lower, whereas the convective intensity is weaker. Continental DCSs are more common from noon through midnight, and DCSs over the Tibetan Plateau are more frequently from noon through evening. Oceanic DCSs frequency has a weaker diurnal cycle with dawn maximum, and diurnal variation of DCSs over the tropical maritime continent is consistent with that over the continent.

Petrogenesis of early Yanshanian highly evolved granites in the Longyuanba area, southern Jiangxi Province: Evidence from zircon U-Pb dating, Hf-O isotope and whole-rock geochemistry

Abstract: Early Yanshanian (Jurassic) granitoids are widespread in the Nanling Range, South China. Whereas large granitic batholiths commonly crop out in the center of the Nanling Range (corresponding geographically to the central and northern parts of Guangdong Province), many small stocks occur in the southern part of Jiangxi Province. Most of the small stocks are associated closely with economically significant rare-metal deposits (W, Sn, Nb, Ta). Here we report the results for biotite granites and two-mica granites from three Yanshanian stocks of the Longyuanba complex. LA-ICPMS U-Pb dating of zircon yields an age of 156.1±2.1 Ma for Xiaomubei biotite granite, and U-Pb zircon dating using SIMS yields an age of 156.7±1.2 Ma for Longyuanba-Chengjiang biotite granite and 156.4±1.3 Ma for Jiangtoudong two-mica granite. Biotite granites are silica-rich (SiO2=70%–79%), potassic (K2O/Na2O>1.9), and peraluminous (ASI=1.05–1.33). Associated samples are invariably enriched in Rb, Th, Pb and LREE, yet depleted in Ba, Nb, Sr, P and Ti, and their REE pattern shows a large fractionation between LREE and HREE ((La/Yb)N=10.7–13.5) and a pronounced Eu negative anomaly (δEu=0.28–0.41). Two-mica granite samples are also silica-rich (SiO2=75%–79%), potassic (K2O/Na2O>1.2), and peraluminous (ASI=1.09–1.17). However, in contrast to the biotite granites, they are more enriched in Rb, Th, Pb and extremely depleted in Ba, Nb, Sr, P and Ti, and exhibit nearly flat ((La/Yb)N=0.75–1.08) chondrite-normalized REE patterns characterized by strong Eu depletion (δEu=0.02–0.04) and clear tetrad effect (TE1.3=1.10–1.14). Biotite granites and two-mica granties have comparable Nd isotopic signatures, and their ɛNd(t) are concentrated in the −13.0 to −9.6 and −11.5 to −7.7 respectively. Their zircon Hf-O isotopes of both also show similarity (biotite granites: ɛHf(t)=−10.8–−7.9, δ 18O=7.98‰–8.89‰ and ɛHf(t)= −13.8 to −9.1, δ 18O=8.31‰–10.08‰; two-mica granites: ɛHf(t)=−11.3 to −8.0, δ 18O=7.91‰–9.77‰). The results show that both biotite and two-mica granites were derived mainly from sedimentary source rocks with a minor contribution from mantle-derived materials. In spite of some S-type characteristics, the biotite granites were formed by fractional crystallization of I-type magma and assimilation of peraluminous sedimentary rocks during their ascent to the surface. Therefore, they belong to highly fractionated I-type granites. Two-mica granites exhibit a tetrad effect in their REE patterns, but share the same isotopic features with the biotite granites, suggesting that they are highly fractionated I-type granites as well. Their Lanthanide tetrad effects may be attributed to the hydrothermal alteration by magmatic fluids that have suffered degassing at late stages. Granitic magmas undergoing fractional crystallization and wall-rock assilimation can generate highly evolved granites with no REE tetrad effect in the uni-phase system. However, in the late-stage of magmatic evolution in the multi-phase system (i.e., magmatic-hydrothermal system), these magmas also can lead to the highly evolved granites exhibiting mew-shaped REE pattern characterized by tetrad effect as the consequence of melt-fluid and fluid-vapor fractionation, and the resultant autometasomatism. We thus suggest that the REE pattern exhibiting tetrad effect feature is an important indicator of rare metal mineralization in the early Yanshanian time in southern China, implying the metamorphism of the ore fluid.

Zircon SHRIMP U-Pb age, geochemical, Sr-Nd isotopic, and in-situ Hf isotopic data of the Late Carboniferous-Early Permian plutons in the northern margin of the North China Craton

Abstract: The main rock types of the Boluonuo and Daguangding plutons are diorite, quartz diorite, tonalite, granodiorite, and subordinate plagioclase-bearing hornblendite and hornblende gabbro. Zircon SHRIMP U-Pb dating for a quartz diorite of the Boluonuo pluton suggests that the pluton was emplaced at about 296 ± 4 Ma. Plagioclase-bearing hornblendites show typical cumulative textures, which, in combination with their convex-upward REE patterns and the large variation of compatible elements such as Co, V and Sc, suggests that these hornblendites formed through accumulation of hornblende during magma evolution. Microgranular mafic enclaves (MMEs) are common in the Boluonuo and Daguangding intermediate to felsic plutons. Many plagioclase grains show compositional and textural disequilibrium, with calcium-rich cores (An46–50) mantled abruptly by sodium-rich plagioclase (An26–33). Whole-rock samples of the plutons are characterized by quite negative ɛNd(t) values (−16.5 to −11.8) and ɛHf(t) values (−22.5 to −16.8), and the ɛNd(t) values are negatively correlated with silica contents. All these features suggest that the intermediate to felsic plutons formed through magma mixing of enriched mantle-derived, evolved basaltic magma with granitic, crustal melts, followed by fractional crystallization of mainly hornblende and small amounts of pyroxene, apatite and zircon. The hornblende-dominated fractionation contributed significantly to the adakite-like features of the intermediate to felsic plutons, like the high Sr and Sr/Y ratios and low Yb abundance. In addition, the Boluonuo and Daguangding plutons are highly enriched in LILEs (e.g., Ba and Sr), but depleted in HFSEs (e.g., Nb, Zr and Ti), which is typical of arc magmas. Therefore, the formation of Boluonuo and Daguangding plutons was probably related to the subduction of the Paleo-Asian oceanic slab beneath the North China Craton in the Paleozoic.

Characteristics of Cd isotopic compositions and their genetic significance in the lead-zinc deposits of SW China

Abstract: National Basic Research Program of China [2009CB421005]; Chinese Academy of Sciences for Key Topics in Innovation Engineering [KZCX2-YW-Q04-01]

Lower limits of evaluation parameters for the lower Paleozoic Longmaxi shale gas in southern Sichuan Province

Abstract: Here we present six key parameters that have been applied to evaluate the Silurian Longmaxi shale gas accumulations of southern Sichuan Province. These parameters include richness of organic matter, single layer shale thickness, burial depth of the shale, maturity, shale properties, and brittle mineral content. In combination with drilling data, the lower limits of these six parameters for marine shale gas have been evaluated and the following conclusions are drawn: (1) Organic carbon recovery, gas content inversion, and production tests have been applied for the first time to measure the lower limit of TOC, which is determined to be 1.0%. (2) Based on the hydrocarbon generation and expulsion theory for source rocks and the characteristics of Longmaxi shale, the lower limit of the single-layer thickness is estimated to be 30 m, of which a thickness of at least 15 m should contain high-quality shale. (3) Based on the correlation of TOC and porosity, the lower limit of gas-filled porosity is 1.2%. (4) Other parameters, such as maturity, burial depth, and brittle mineral content have also been studied with regard to the geologic conditions of southern Sichuan. Based on the study results, an evaluation index system has been established for highly evolved marine shale gas, and the system has been applied successfully to geologically screened shale gas occurrences in southern Sichuan Province.

North Indian Ocean tropical cyclone activities influenced by the Indian Ocean Dipole mode

Abstract: Using Joint Typhoon Warning Center tropical cyclone (TC) track data over the North Indian Ocean (NIO), National Centers for Environmental Prediction monthly reanalysis wind and outgoing long-wave radiation data, and National Oceanic and Atmospheric Administration sea surface temperature data from 1981 to 2010, spatiotemporal distributions of NIO TC activity and relationships with local sea surface temperature (SST) were studied with statistical diagnosis methods. Results of empirical orthogonal function (EOF) analysis of NIO TC occurrence frequency show that the EOF1 mode, which accounts for 16% of total variance, consistently represents variations of TC occurrence frequency over the whole NIO basin. However, spatial distributions of EOF1 mode are not uniform, mainly indicating variations of westward-moving TCs in the Bay of Bengal. The prevailing TC activity variation mode oscillates significantly on a quasi-5 year interannual time scale. NIO TC activity is notably influenced by the Indian Ocean dipole (IOD) mode. When the Indian Ocean is in a positive (negative) phase of the IOD, NIO SST anomalies are warm in the west (east) and cold in the east (west), which can weaken (strengthen) convection over the Bay of Bengal and eastern Arabian Sea, and cause anticyclonic (cyclonic) atmospheric circulation anomalies at low levels. This results in less (more) TC genesis and reduced (increased) opportunities for TC occurrence in the NIO. In addition, positive (negative) IOD events may strengthen (weaken) westerly steering flow over the Bay of Bengal, which further leads to fewer (more) westward-moving TCs which appear in regions west of 90°E in that bay.

Social impacts of the climatic shift around the turn of the 19th century on the North China Plain

Abstract: Historical case studies of climate change impacts and the resulting social responses can provide analogies for better understanding the impacts of current and future climate changes. Around the turn of the 19th century, the climate of the North China Plain experienced a shift from a relatively warm stage in the 18th century to a colder stage in the 19th century, which was characterised by a much colder climate and more frequent and severe floods and droughts. Historical information about refugees, social disorder, grain transportation, and disaster relief on the North China Plain in 1780–1819 is collected from the Veritable Records of the Qing Dynasty (a collection of official records). The mechanism of climate change affecting the food security of the society, as indicated by the development of a refugee problem around the turn of the 19th century, is analyzed by examining the social vulnerability. There are four basic findings: (1) In the 40 years from 1780–1819, the society on the North China Plain was unstable and characterised by a significant deterioration of the refugee situation. The number of refugees increased markedly, and their behaviour became increasingly violent. In the 1780s, most of the disaster victims chose to stay at their residences waiting for relief. From 1790 to 1800, hundreds of thousands of refugees migrated to northeast China. In the 1810s, the frequency of farmer rebellions increased sharply. (2) The increase in instability corresponded to the climatic cooling over the same time period. The increased instability was a result of the negative impacts of climate change accumulating and transmitting to the social level. (3) For food security, a precondition for the negative impacts of climate change on human society was the vulnerability of the regional socioeconomic system, which had a high sensitivity and low capacity to respond. This vulnerability could be described by the following three observations: ① The regional balance of supply and demand for food was in a critical state, which led to a high sensitivity and dramatic reduction in yield that was caused by climate change; ② the capacity for disaster relief efforts by the government was too low to meet the needs of crisis management; ③ the capacity for refugees’ resettlement in eastern Inner Mongolia and northeast China, which both border the North China Plain, was severely restricted by climatic conditions or the quarantine policy. (4) It is estimated that climate change caused the social vulnerability to reach a critical level approximately 20 years earlier on the North China Plain.

A comparison of two kinds of eastward-moving mesoscale vortices during the mei-yu period of 2010

Abstract: During the mei-yu period, the east edge of the Tibetan Plateau and the Dabie Mountain are two main sources of eastward-moving mesoscale vortices along the mei-yu front (MYF). In this study, an eastward-moving southwest vortex (SWV) and an eastward-moving Dabie vortex (DBV) during the mei-yu period of 2010 have been investigated to clarify the main similarities and differences between them. The synoptic analyses reveal that the SWV and DBV were both located at the lower troposphere; however, the SWV developed in a “from top down” trend, whereas the DBV developed in an opposite way. There were obvious surface closed low centers corresponding to the DBV during its life span, whereas for the SWV, the closed low center only appeared at the mature stage. Cold and warm air intersected intensely after the formation of both the vortices, and the cold advection in the SWV case was stronger than that in the DBV case, whereas the warm advection in the DBV case was more intense than that in the SWV case. The Bay of Bengal and the South China Sea were main moisture sources for the SWV, whereas for the DBV, in addition to the above two moisture sources, the East China Sea was also an important moisture source. The vorticity budget indicates that the convergence was the most important common factor conducive to the formation, development, and maintenance of the SWV and DBV, whereas the conversion from the vertical vorticity to the horizontal one (tilting) was the most important common factor caused the dissipation of both of the vortices. The kinetic energy (KE) budget reveals that the KE generation by the rotational wind was the dominant factor for the enhancement of KE associated with the SWV, whereas for the DBV, the KE transport by the rotational wind was more important than the KE generation. The KE associated with the SWV and the DBV weakened with different mechanisms during the decaying stage. Furthermore, the characteristics of baroclinic and barotropic energy conversions during the life spans of both vortices indicate that the SWV and DBV both belong to the kind of subtropical mesoscale vortices.

Middle Triassic post-orogenic extension on Hainan Island: Chronology and geochemistry constraints of bimodal intrusive rocks

Abstract: This work studies new petrological and geochemical data and zircon U-Pb ages for bimodal intrusive rocks from Xinglong region, Hainan Island. Zircon U-Pb dating yields mean 238U/206Pb ages of 238 ± 2 Ma and 234 ± 2 Ma for diabasic and granitic phases, respectively, representing the Middle Triassic emplacement. The diabase and granite bodies were formed from discrete mafic and acidic magma sources that experienced local mechanical mixing at their mutual contacts. Although SiO2 content of intrusions is bimodal, trace element ratios indicate that both were formed in a post-orogenic extensional setting. Sr-Nd isotopic composition reflects a shared EMII type enriched mantle source component, possibly influenced by subduction-fluid metasomatism.