Paleoproductivity records for the past 30 ka in the southern Nansha area, the South China Sea

This note presents productivity variations for the past 30 ka in the southern Nansha area, the South China Sea, from the gravity core 17962 (7°11′N, 112° 5′E, core length: 8 m, water depth: 1 968 m). Estimated surface productivity demonstrates that at the last glacial maximum the productivity was about 1.6 times as much as that in the Holocene, and the change may be ascribed to an increase of terrestrial nutrients as sea level lowered in the glacial time.     

Changes in South Asian monsoon: New high-resolution paleoclimatic records from Tibet, China

High-resolution pollen records from 6 small lakes in the Tibetan Plateau provided the details of evolution of South Asian monsoon since the Last Glacial Maximum. Prior to 16 kaBP, the region was a desert-steppe characterized by cold and dry climates, the January temperature was 7 -10℃lower than that of present and the annual precipitation only accounted for 40% of the present. The temperature and precipitation increased gradually and trees began to live in the region after 12 kaBP, but during the interval from 9.2 to 6.3 kaBP, forest and forest-meadow appeared occasionally. From 8 to 5 kaBP, both January and July temperature was 2-3℃ higher and annual precipitation was also about 200 mm higher than that of the present. After 5 kaBP, temperature and precipitation decreased linearly and steppe vegetation began to degenerate.     

十万大山地区下-中泥盆统白云岩成岩层序地层学研究

以广西十万大山地区下-中泥盆统白云岩为研究对象,在白云岩层序地层划分、白云岩或白云石成因类型认识的基础上,探索了白云岩成因类型发育与层序地层的关系,建立了区内下-中泥盆统层序地层框架内的白云石化作用模式,即高水位体系域晚期发育蒸发泵和渗透回流白云石化作用模式,Ⅰ型层序不整合界面期间发育大气水-海水混合白云石化作用模式;进一步探索了此种背景下,受层序和白云石化作用的控制,白云岩储层的发育分布特征,对于指导油气勘探有重要意义.     

Crustal activities recorded in coral reefs in the northwestern South China Sea

Coral reefs in the northwest of South China Sea have recorded the information from not only the environmental variation but also the crustal activities there during their development. The main crustal activities correlated with the coral reef development include fault, seismic, and volcano activities, etc. The high-resolution spark seismic profiles in the northwestern South China Sea show that the fault activities in the coral reef region have been clearly recorded, and appear as neonatal faults incising reefs. Earthquakes in the coral reef region are rather intense, especially the two occurring on December, 31, 1994, and January, 10, 1995, around the southwest of Leizhou Peninsula, with the magnitude of 6.1 and 6.2, respectively. They have great influence on the growth of the local coral reefs. Quaternary volcanos are active in the northwestern South China Sea, especially around the southwest of Leizhou Peninsula, and they have obvious control of the coral reef development. Some submarine volcanoes form the substrates of coral reef, while a few emerge above the sea surface and form coral islands.     

Thirty million year deep-sea records in the South China Sea

In the spring of 1999 the Ocean Drilling Program (ODP) Leg 184 Shipboard Party cored 17 holes at 6 deep water sites in the northern and southern parts of the South China Sea (SCS). Chinese scientists actively participated in the entire process of this first deep-sea drilling leg off China, from proposal to post-cruise studies. More than 30 categories of analyses have been conducted post-cruise in various Chinese laboratories on a large number of core samples, and the total number of analyses exceeded 60 thousand.The major scientific achievements of the Leg 184 studies are briefly reported in three successive papers, with the first one presented here dealing with deep-sea stratigraphy and evolution of climate cycles. This ODP leg has established the best deep-sea stratigraphic sequences in the Western Pacific: the 23-Ma isotope sequence from the Dong-Sha area is unique worldwide because of its continuity; the last 5-Ma sequence from the Nansha area represents one of the best 4 ODP sites worldwide with the highest time-resolution for that time interval, and the sequences of physical properties enable a decadal-scale time resolution. All these together have provided for the first time high-quality marine records for paleoenvi-ronmental studies in the Asian-Pacific region. This new set of stratigraphic records has revealed changes in climate cyclicity over the last 20 Ma with the fluctuating power of the 100 ka, 400 ka, 2000 ka eccentricity cycles, indicating the evolving response of the climate system to orbital forcing along with the growth of the Antarctic and Northern Hemisphere ice sheets.     

Petrology, geochemistry and geodynamics of basic granulite from the Altay area, North Xinjiang, China

The basic granulite of the Altay orogenic belt occurs as tectonic lens in the Devonian medium- to lower-grade metamorphic beds through fault contact. The Altay granulite (AG) is an amphibole plagioclase two-pyroxene granulite and is mainly composed of two pyroxenes, plagioclase, amphibole and biotite. Its melano-minerals are rich in Mg/(Mg Fe^2 ),and its amphibole and biotite are rich in TiO2. The AG is rich in Mg/(Mg Fe^2 ), Al2O3 and depletion of U, Th and Rbcontents. The AG has moderate ∑REE and LREE-enriched with weak positive Eu anomaly. The AG shows island-arc pattern with negative Nb, P and Ti anomalies, reflecting that formation of the AG may be associated with subduction. Geochemical and mineral composition data reflect that the protolith of the AG is calc-alkaline basalt and formed by granulite facies metamorphism having peak P-T conditions of 750℃-780℃ and 0.6-0.7 Gpa. The AG formation underwent two stages was suggested. In the early stage of oceanic crustal subduction, calc-alkaline basalt with island-arc environment underwent granulite facies metamorphism to form the AG in deep crust, and in the late stage, the AG was thrust into the upper crust.     

Hf isotopic composition of zircons from the Huashan-Guposhan intrusive complex and their mafic enclaves in northeastern Guangxi: Implication for petrogenesis

High precision zircon U-Pb dating indicates that main intrusive bodies (Tong'an,Niumiao,Huashan,Lisong),and a mafic microgranular enclave in the Huashan-Guposhan complex were formed at 160-163 Ma.The εHf(t) values of zircons from the Huashan granite vary from -2.8 to +0.3 and those from the Lisong granite vary from -2.3 to +0.3,which are obviously different with those values (+2.6 to +7.4) of the mafic enclaves from the Lisong granite.These Hf isotopic data indicate that the mafic enclaves and host granites...     

Nd isotopic variations and its implications in the recent sediments from the northern South China Sea

The chondrite-normalized REE distribution patterns in recent sediments from the northern South China Sea and surrounding areas are similar, with the HREE values being almost equal to or slightly higher, and the La_N/Lu_N ratio being lower, than PAAS standards. However, samples from the Xijiang River, a major branch of the Pearl River system, show opposite trends, i.e., with slightly lower HREE values and higher La_N/Lu_N ratio than PAAS. The distribution of Nd isotopes in sediments from the northern South China Sea was controlled by the Pearl River and the inshore area of South China, respectively. The volume of ε_Nd(0) from inshore areas of southern China is apparently higher than that from the Pearl River, and ε_Nd(0) values in offshore sediments and Taiwan Island are between these values. The results clearly show that ε_Nd(0) volume in the northeastern South China Sea is higher than in the southwest part of the northern South China Sea, indicating different source rock types. The main source rock of the Pearl River sediment is carbonate types and affects sediment deposition in the southwest of the northern South China Sea, while the source rock in the inshore area of southern China, mainly Mesozoic and Cenozoic granites, contributes to sediments in the northeastern area of the northern South China Sea. Due to different source rock types, the HREE values and the volume of ε_Nd(0) in recent sediments supplied by the inshore area of southern China are higher than those from the Pearl River. Over 80% of the rapidly accumulated sediments on the northern slope of the South China Sea in the southeast of Dongsha Islands area were derived from Taiwan Island and from inshore areas of South China, with only less than 20% from the Pearl River. Supported by National Natural Science Foundation of China (Grant Nos. 40276019, 40238060 and 40621063), and National Basic Research Program of China (Grant No. 2007CB819501)     

Carbon isotopic record of foraminifers in surface sediments from the South China Sea and its significance

Since the 1990s, the papers and data involved withthe South China Sea (SCS) have been emerging in largenumbers in the world as people pay more attention to thepaleoceanography of the SCS. There have been more than100 cores mentioned in papers containing p…     

The P2O5 content of feldspars from the Yashan granites, Jiangxi Province, South China

The P₂O₅ contents of feldspars in the Yashan F-rich and P-rich granite yield a maximum value of 0.93% (In albite) and a maximum average value of 0.65% (hereinafter weight percent) (in K-feldspar), and is generally between 0.10% and 0.35%. Most of the distribution coefficient D_p[Ab/Kt] values are greater than 1(1.13–28.9). The study shows that phosphorus could preferably enter the albite structure mainly by PAISi₂ substitution relative to K-feldspar.     

Turbidite deposition in the southern South China Sea during the last glacial: Evidence from grain-size and major elements records

High-resolution grain size and major element geochemical measurements were performed on the marine sediments of Core MD05-2895 to help understand the formation of turbidite sequences. Grain-size results show that these turbidite sediments contain more coarse sediment grains than normal marls. The coarse sediment grains are mostly derived from relict sediments on the Sunda Shelf. Relict sediments are composed mainly of quartz, feldspar, tephra and a few titaniferous or ferruginous heavy minerals. Corresponding to the concentration of these minerals, increases in Si/Al, K/Al, Ti/Al and Fe/Al ratios are observed in the turbidite layers. As all the observed turbidite sequences were deposited during the last glacial, the occurrence of these turbidity events is implied to be closely related to instabilities in sea-level-induced sediment supply. We suggest that deposition of sediment particles from a single turbidity current is usually controlled by a counterbalance between gravity and buoyancy, with the interaction of individual grains being of minor importance.     

Discovery of granulite from the Fuping area in southern Qinling Mountains and its geological significance

Two-pyroxene-bearing granulites were discovered for the first time in the Hercynian-Indosinian metamorphic belt of the southern Qinling Mountains. The granulites occur in the lower part of the Fuping complex and are dominated by intermediate-acidic rocks intercalated with a small amount of bands and lenses of basic granulites. The main metamorphic minerals include orthopyroxene, clinopyroxene, biotite, plagioclase and quartz, and orthopyroxenes are often retrogressively transformed into amphiboles. The metamorphic conditions have been estimated to be %T%=720-780℃ and %P%=0.6 GPa. The granulite-bearing Fuping complex probably belongs to early Proterozoic in age. Whether it occurs as the crystalline basement of the southern Qinling Hercynian-Indosinian orogenic belt or as a thrusted slice in the collisional process needs further study.     

Carbon isotopic records in paleosols over the Pliocene in Northern China: Implication on vegetation development and Tibetan uplift

Carbon isotopic composition of pedogenic carbonate can be used to estimate the proportion of C₄ and C₃ plants. Here we present carbon isotopic data of carbonate in a red earth section at Xifeng, central Loess Plateau. Results show that C₄ vegetation increased in ∼4.4 Ma B.P., stabilized between 4.0 and 3.0 Ma B.P. The character and timing of C₄ expansion on the Loess Plateau are similar, but different with other localities, e.g. Pakistan and Africa, implying that regional climate changes were main factors driving the expansion of C₄ plants. This event is comparable in timing with increased aridity evidenced by Xifeng grain size and North Pacific eolian dust records. Therefore we argue that the Pliocene expansion of C₄ plants in northern China might have been caused by the increased aridity, which in turn might be related to rapid uplift of the Tibetan Plateau.     

Evolution of the South China Sea and monsoon history revealed in deep-sea records

As the third summary report of ODP Leg 184 to the South China Sea (SCS), this paper discusses the evolution of the East Asian monsoon and the SCS basin. A multi-proxy approach, involving geochemistry, micropale-ontology, pollen and other analyses, was adopted for reconstructing the evolutionary history of the East Asian monsoon, which was characterized by a series of paleo-climate events especially at 8, 3.2, 2.2 and 0.4 Ma. The new record indicates similar stages in the development of the East and South Asian monsoons, with an enhanced winter monsoon over East Asia being the major difference. The rich spectrums of monsoon variability from the southern SCS also reveal other characteristic features of the low latitude ocean. Evidence for the evolution of the SCS includes the hemipelagic Oligocene sediments, implying the existence of deep water environments during the early seafloor spreading stage of the SCS basin. The four major unconformities and some remarkabl ediagenetic features in upper Oligocene deposits indicate the strongest tectonic events in the region. From a careful comparison of lithologies and sedimentation rates, we conclude that the prominent differences in sedimentary environments between the southern and northern SCS were established only by ～3 Ma.     

Formation and evolution of Precambrian continental crust in South China

The occurrence of zircons with U-Pb ages of ~3.8 Ga and Hf model ages of ~4.0 Ga in South China suggests the existence of the Hadean crustal remnants in South China. Furthermore, a detrital zircon with a U-Pb age as old as 4.1 Ga has been found in Tibet. This is the oldest zircon so far reported in China. These results imply that continental crust was more widespread than previously thought in the late Hadean, but its majority was efficiently reworked into Archean continental crust. On the basis of available zircon U-Pb age and Hf isotope data, it appears that the growth of continental crust in South China started since the early Archean, but a stable cratonic block through reworking did not occur until the Paleoproterozoic. Thus the operation of some form of plate tectonics may occur in China conti- nents since Eoarchean. The initial destruction of the South China craton was caused by intensive magmatic activity in association with the assembly and breakup of the supercontinent Rodinia during the Neoproterozoic. However, most of the Archean and Paleoproterozoic crustal materials in South China do not occur as surface rocks, but exist as sporadic crustal remnants. Nevertheless, the occur- rence of Neoproterozoic magmatism is still a signature to distinguish South China from North China.     

An in situ zircon Hf isotopic,U-Pb age and trace element study of banded granulite xenolith from Hannuoba basalt： Tracking the early evolution of the lower crust in the North China craton

Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied. The results show that the banded granulite is a sample derived from the early lower crust of the North China craton. It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes, however, is contained in the granulite. These processes in-clude the addition of mantle material, crustal remelting, metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842 ±40 Ma, except few ages of 3097-2824 Ma and 2489-2447 Ma. The zircons with ages older than 2447 Ma have high εHf (up to +18.3) and high Hf model age (2.5-2.6 Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εhf of the zircons with early Proterozoic U-Pb age vary around zero, but two have     

Nd isotopic characteristics of post-Archean sediments from the Eastern Nanling Range： Evidence for crustal evolution

A systematic Sm-Nd isotopic study was carried out for sediments and metasediments of different ages from Mesoproterozoic to early Mesozoic era in southwestern Fujian, Eastern Nanling Range. The results show that Nd model age (tDM) and εNd(t) value of most sediments are closely similar to those of Paleoproterozoic Mayuan Group, indicating that they may mainly be the recycling product of Paleoproterozoic crustal materials. However, the Nd model age significantly decreases with a corresponding increase in the εNd(t) value at Neoproterozoic (ca. 0.8-0.7 Ga) and Late Paleozoic (ca. 0.25 Ga), respectively. This is manifested by prominent vales and apexes on the diagrams of tDM VS. tStr. (stratum age) and εNd(t) VS. tstr. The decrease in tDM and the increase in εNd(t) are explained as a result of the significant incorporation of juvenile crustal materials that originated from depleted mantle due to strong lithospheric extension during both periods. It appears that tectonic magmatism in the Neoproterozoic and the Late Paleozoic is of prominent importance in affecting the geochemical nature of sediments in South China.     

Precipitation of rutile needles in garnet from sillimanite-bearing pelitic granulite from the Khondalite Belt,North China Craton

Pelitic granulite from the Khondalite Belt, North China Craton, is composed of garnet, sillimanite, perthite, biotite and quartz. Oriented rutile needles in gar- net are reported for the first time from the granulite. The rutile needles have been identified by optical microscopy and confirmed by in situ Raman spectroscopy, where they show the characteristic bands at 446-448 and 610 cm-1. Because of their very strong shape preferred orientation in 3-4 easily observable directions, these futile needles are interpreted to have formed by precipitation during exhu- mation and cooling following peak metamorphism. The ternary feldspar geothermometer gives a peak metamorphic temperature of ,- 980 ℃ at 10 kbar. The presence of oriented rutile needles in garnet is suggested to be a valuable indicator of ultrahigh-temperature （UHT） metamorphism in the Khondalite Belt and therefore likely in other UHT terrains.     

High-resolution sedimentary records of heavy metals in Guangzhou section of the Pearl River, South China

The sedimentary feature and variation of heavy metals in ca. 100 years, especially in the last three decades, in the riverbed of Guangzhou section of the Pearl River were revealed by the sedimentary heavy metal fluxes and total organic carbon (TOC) in a 210Pb-dated sedimentary core. It is suggested that the historical changes of heavy metal contamination can be recorded by pollutant sedimentary fluxes rather than by their concentrations. The heavy metal contamination in the river section was divided into 6 sedimentary historical stages of 3 groups, which correspond to the economic development and regional urbanization process.