CENOZOIC VOLCANIC ROCK SERIES IN SOUTHEASTERN CHINA (Ⅱ)——TRACE ELEMENT GEOCHEMISTRY

On the premise of the sister paper, the trace element geochemistry of Cenozoic volcanic rocks of southeastern China is discussed in detail in this paper. The data presented in this paper indicate that the upper mantle beneath the area studied is enriched in the strongly HYG elements as compared with the chondritic mantle, and that the depth of Cenozoic basaltic magma sources progressively increases from the coast to the inland. The Cenozoic basaltic volcanism has occurred in a geotectonic setting of rifting continental margin; on the contrary, the Mesozoic volcanic rocks are predominated by the felsic volcanics erupting in a geotectonic setting of active continental margin. It can be inferred from the studies of ultramafic inclusion-derived geotherm that the Cenozoic rifting of eastern China continent has been mainly controlled by the thermal mantle diapirism.     

Source Rocks of the Caledonian-Age Granitoid Rocks in Wanyanshan-Zhuguangshan, Southeast China (Ⅱ)——Topological Analysis in Isotopic Multispace

Topological analysis in Sr-Nd-O-Pb_3 six-dimensional isotopic space suggests that the source rocks of the Caledonian-age granitoid rocks in Wanyangshan-Zhuguangshan, southeast China, comprise three end-member components. Isotopic mixing model discrimination indicates that the granitoid rocks were produced through mixing of the three componentsin varying proportions. Comprehensive study of multiple isotopic systems and geochemistry of the granitoid rocks suggests that the three end-member components were crustal rocks which are continent-derived sediments, geosycline sediments and altered basic volcanic rocks.     

REE AND Sr, Nd, Pb ISOTOPIC GEOCHEMISTRY OF HUANGYISHAN BASALT, KUANDIAN, LIAONING, NORTHEAST CHINA

In the light of major element geochemistry, mineral chemistry and REE and isotopic data, the small but apparent isotopic differences between the Cenozoic volcanic rocks east and west of the Tancheng-Lujiang fault are believed to be caused by the mixing and metasomatism of crustal and mantle material in tho mantle source region in response to Pacific plate subduction. The presence of phlogopite and pargasite in mantle xenoliths lends strong support to mantle metasomatism.     

THREE-COMPONENT MIXING AND FOUR-SYSTEM RECYCLING MODELS FOR EXPLAINING Nd-Sr-Pb ISOTOPIC CORRELATIONS OF SUBOCEANIC AND SUBCONTINENTAL MANTLES

The Pb-Sr-Nd isotopic data of Cenozoic volcanic rocks from the continent of China show that there exist three main end members of the mantle, which are the enriched mantle of Wudalianchi in Northeast China, the depleted mantle in South China and the recycling mantle of Yunnan in southwestern China. A11 the data can well fit a curved surface of three-component mixing in Pb-Sr-Nd isotopic space. Seven major end members in the global mantle can be identified. Based on the intersection line between two curved surfaces of three-component mixing in the continent of China and the ocean, the Pb-Sr-Nd isotopic ratios in the primatire mantle can be calculated. In order to explain the genesis of seven end members of the mantle, four-and three-system recycling models were used. The theoretical results are well comparative with the isotopic distribution observed in global Cenozoic volcahics, and can provide useful constraints on the process of the geochemical evolution in the crust-mantle system.     

SUBVOLCANIC GRANITOIDS IN SOUTHEASTERN CHINA AND THEIR METALLOGENESIS

Mesozoic volcanic rocks are widely distributed in southeastern China. There exist various kinds of subvolcanic granitoids associated with the volcanic rocks. This paper deals with the geological setting, the characteristics and the metallogenesis of these subvolcanic granitoids.     

SOME PROBLEMS CONCERNING PETROLEUM GEOLOGY OF THE TARIM BASIN

This paper gives mainly an explanation that the Tarim Basin is a unified piedmont basin formed in the Cenozoic by shear stress and superimposed on a dissected fault depression basin of the Middle Cenozoic. According to our analysis of the insoluble residues of Carboniferous rocks, trace elements, oxygen and carbon isotopes and clay minerals, the basin was then a dustpan-like one with the southern part deeper than the northern part.From the viewpoint of oil generation, the most favorable should be the Jurassic source rock (though limited in distribution), the less——the Carboniferous-Permian rocks which feature wide distribution and ample potentialities of oil generation, and the least——the Cretaceous-Eogene rocks which are found in a certain area.     

GEOCHEMISTRY OF SEDIMENTS AND ENVIRONMENT IN XIHU LAKE OF GREAT WALL STATION OF CHINA, ANTARCTICA

The determined results in this paper, which were obtained by the multielement analysis of the 260 cm-deep core sediments under the water of Xihu Lake in the Great Wall Station area, are as follows: The Cenozoic volcanic rocks around Xihu Lake are the main source of sediments in the lake. The chemical differentiation in very fine particles is still detectable. From the variation of ratios of the Cs/Rb, Br/CI and La/Yb in the clay fraction with depth and from the variation or CaCO_3 contained in the sediments, cation replacing amount in the clay grains and the sediment grain sizes in time, it can be seen that since 3600 a. B. P., there has existed the climatic variation of warm-cold-warm, which embodies the advance and retreat history of the ice sheet in this area.     

A STUDY ON THE ORDERING PATH OF ALKALINE FELDSPAR IN VOLCANIC ROCKS

In this paper, the study on the ordering path of alkaline feldspar from some volcanic areas by X-ray powder method is presented. The published data by mathematical statistics is treated, a series of formulas and figures to determine chemical composition and degree of Al site occupancy of alkaline feldspar are reset-up, and the simulated function Y=Z~(?) with Thompson's coefficients Y, Z and κ as the indexes of ordering path is suggested. Based on the difference between ordering paths distinguished by κ of alkaline feldspar from volcanic basins, the petrological characters of volcanic basins and the petrological characters of volcanic rocks, some preliminary conclusions of the origin are also summarized.     

MELT AND FLUID INCLUSIONS IN IGNEOUS ROCKS IN CENTRAL XIZANG (TIBET)

Through a study of the characteristics and composition of melt and fluid inclusions in volcanic rocks and their associated granites in the subduction zone of the Tibetan plate, it has been found that the characteristics of the inclusions in quite a few minerals of various rock types are closely related to the nature of molten magmas, thickness of strata and cooling speed. Therefore, their characteristics may be used to discriminate different lithofacies types. In this paper the evolution and crystallization of magmas are discussed on the basis of the glass composition of the inclusions measured using the electron probe, and the gas composition and its parameters are used in elucidating the physico-chemical conditions of rock and ore formation.     

New evidence from stable isotope for the uplift of mountains in northern edge of the Qinghai-Tibetan Plateau

New data of oxygen and carbonate isotope in calcite cements from Cenozoic rocks inthe Jianggelesayi area to reconstruct the uplift history of mountains in northern edge of the Qing-hai-Tibetan Plateau are presented. Analyses results show that rapid changes of δ~(18)O and δ~(13)C inthe calcite cement occurred in both the Early Oligocene and Early Miocene. Studies on sedimen-tary features indicate that a rapid up-coarsing of the sediments size occurred in the Early Miocene,and sedimentary velocity increased rapidly during the Pliocene and Early Quaternary. Thus, it issuggested that the uplift of mountains in the northern edge of the Qinghai-Tibetan Plateau initiatedfrom the Early Oligocene, and a rapid uplift occurred in the early stage of the Miocene, while thesharp difference in topography between the northern plateau and the Tarim Basin predominatelyformed later than the Miocene.     

CRETACEOUS AND PALAEOGENE PALYNOFLORAS AND DISTRIBUTION OF ORGANIC ROCKS IN CHINA

This paper illustrates the Cretaceous and Palaeogene palynofloras and climatic belts and deals with distribution of dinoflagellates and acritarchs. In view of the relationship between organic rocks and climatic environments and that between petroleum and phytoplanktons, the probably advantageous areas to the formation of organic rocks are drawn.     

TRACE ELEMENTS GEOCHEMISTRY OF GRANITOID IN PANXI AREA

A lot of granitoid rocks occur in Panxi area, SW China, which were formed during Jinningnian-Chengjiangnian, Hercynian-Indosinian and Yenshanian. According to their trace elements geochemical and petrochemical characteristics, they can be divided into calc-alkaline and alkaline granites. The petrogenesis and magma sources of these granitoid rocks are different. The Jinningnian-Chengjiangnian granitoid rocks include Mopanshan granite body, Moshaying granite body and Lugu granite body. The Mopanshan body might be formed by partial melting of the lower crust and due to refusion of basic volcanic rocks. The magma source of the Moshaying and the Lugu bodies might be formed by partial melting of the upper crust. The Hongge-Ailanghe granites belonging to the Hercynian-Indosinian may be products of complex melting from the crust-mantle materials caused by the increase of temperature during rifting stage in the area. The Cida and Taihe alkaline granites belonging to the Hercynian-Indosinian might be derived from     

EVOLUTION OF OCEANIC CRUST OF MESOZOIC TETHYS IN THE LIGHT OF TWO SUITES OF VOLCANIC ROCKS IN THE YARLUNG ZANGBO OPHIOLITE BELT

The Yarlung Zangbo ophiolite represents the ocean crustal residue of the Mesozoic Tethys. In this ophiolite belt, there are two suites of volcanic sequences. One is Late Jurassic-Early Cretaceous metabasalts, and the other is Early Cretaceous pillow basalts. These two suites of volcanic rocks are significantly different in time and space patterns and geochemistry. Based on an investigation on their geochemical characteristics, the authors would have a discussion on the two stages of the ocean crustal evolution of the Mesozoic Tethys.The evolution of the Mesozoic Tethys went through three stages, namely the early rift valley, the intermediate ocean crustal development and the last closing stage. The development of oceanic crust experienced the early discontinuous spreading stage which formed the metabasalt and the late continuous spreading stage which produced the Early Cretaceous oceanic crust.     

THE ALTITUDE AND LATITUDE EFFECTS OF H-O ISOTOPIC SYSTEM IN GRANITOID ROCKS

A lot of Mesozoic and Cenozoic granitoid rocks are widely distributed along the east coastalregion and in the southern part of Xizang, China. In order to study the altitude and latitude effect ofH-O isotopic system in these granitoid rocks, we have first studied the altitude and latitude effects ofδ~(18)O, δD values of recent meteoric water. The altitude and latitude effect equations of recent meteoricteoric water were established. The altitude effects of δD vaues for hydroxyl minerals from granitoid rocks inLhasa-Yadong region of Xizang were found. The average elevated rate of Xizang Plateau is 0.1 mm/yr.The δ~(18)O and δD values of whole rock samples for late Yanshanian miarolitic granite in the east coastalregion wete progressively lower as a function of latitude. The negative correlation between δ~(18)O and δDvalues in each miarolitic pluton represents the relationship between δ~(18)O, δD values of rocks or mineralsand temperatures in the condition with the same ω/r ratio in the interactiv     

STUDY ON ERAS OF DATONG VOLCANIC ACTIVITIES BY THERMOLUMINESCENCE DATING

This paper reports that the ages determined on the baked strata of 8 typical seciionsin the Datong volcanic cluster are within (0.98±0.02)×10~5yr. and (2.9±0.2)×10~5yr B. P.by using quartz thermoluminescence dating technique. The age values and stratigraphical position of the volcanic lava flow reveal that 4 typi-cal sections may be taken for the study of thc eras of Datong volcanic activities, i. e. the Yu-jiazhai section, 300,000 yr B. P.; the Yuangou section, 200,000 yr B. P.; the South Canyonsection of Heishan, 150,000 yr B. P.; the Huangjiawa section, 100,000 yr B. P.     

Geochemical Characteristics of Gases From Hot Springs in Seismic Region

Chemical and isotopic compositions of He, Ar, CH4(δ13C) of hot spring gas in Lancang and Batang earthquake regions show that the concentrations of He , H2 , non-atmospheric sourced N2 and 3He/4He value are closely related to seismic activity. During earthquake activity, gas release is related to the dilation that rocks take on under stress action. Earthquake magnitude (energy) between the two seismic regions suggests that the amount of released gas from rocks increases significantly with the increase of magnitude and energy. As indicators of earthquake prediction, the following parameters of gases from hot spring are effective: He, 3He/4He, H2 and N2B/N2total.     

Silicon Isotopic Compositions of Archean Banded Si-Fe Formation (BIF)in the Gongchangling Ore Deposit, Liaoning Province, China

The results of silicon isotope analyses of Precambrian BIF are reported for the first time. The δ~(30)Si values of magnetite-quartzite in the Gongchangling ore deposit are between —0.9 and —2.2‰, which are obviously different from those in host rocks (0.2——0.6‰). It is suggested that the BIF may be a product of chemical precipitation in Archean submarine hydrothermal environment. There is a possibility of using silicon isotopes to distinguish the protolith of metamorphic rocks and trace the origin of silicon of altered minerals.     

STUDIES ON THE MESOZOIC MARGINAL ARC SYSTEM OF THE SOUTHEAST COAST AND TAIWAN IN CHINA

The southeast coastal Zhejiang, Fujian, Guangdong provinces and Taiwan in China comprised an important area in ancient Asia where the Yenshanian continental margin magmatic arc well developed in the late Mesozoic time. It is believed that the oceanic trench and subduction zone are situated on the east side of the Central Range in Taiwan. It seems unlikely that the so-called Hercynian-Indosinian ancient island arc folded system would have occurred in this region.     

HSIANGHUAGITE——A NEW TYPE OF MAGMATIC ROCK

There is a vein (431 vein) in Hsianghualing district, Linwu County, Hunan Province, and it has been investigated and named "aplite" or "altered aplite" by many geologists and petrologists. On the basis of thorough study in the field work and in laboratory, and according to its occurrence, structure, texture, petrochemistry and mineral assemblages, the authors of this paper have an objection to this name and are of the opinion that it is a new type of ultrahypabyssal rock, and name it hsianghuagite.In this paper, the authors recommend briefly the characteristics of hsianghuagite, make a comparison between hsianghuagite and the relative rocks such as ougonite, topazite, etc., and discuss the origin of hsianghuagite.     

JIANGSHAO FRACTURE BELT, E. CHINA: MAGMA MINGLING AND RELATED PRECAMBRIAN GEOLOGY

In this paper, the authors have confirmed the mingling of magma which occurred along the Jiangshan-Shaoxin fracture belt (simplified name: Jiangshan fracture belt) in the late Proterozoic and discussed spectacular problems of Precambrian igneous rocks and geology on either side of the belt. It is believed that the most important events of Precambrian orogeny in the border area of Zhejiang, Jiangxiand Anhui provinces happened before 900Ma. In this period, collision between Cathaysia and Jiangnan Ancient Island Arc (JAIA), which began developing ca 1100 Ma ago, took place and ended. Also, the activities and mingling of basaltic and acidic magmas accompanying the orogeny were widely generated and lasted up to the early Sinian period (about 800 Ma ago).