Deep Structures in China and Its Adjacent Areas: Plate Tectonics and Its Metallogenic Significance

This paper proposes a new tectonic pattern of the deep-seated structures in China and its adjacent areas (including the T - A - B system of the Ryukyu Islands). This is based on studies of the gravity field and gravity inversion coupled with the summation of the most recent achievements in geophysical studies. From a plate-tectonic point of view, the metallogenic characteristics and their indications at depth, as well as relevant geophysical-geological characteristics of four tectonic environments of the Chinese continent are analysed, and a classification of composite metallogenic provinces and belts and prediction of metallogenic prospects are made. The author extends the Kunlun-Qilian-Qinling tectonic belt to the T-A-B system of the Ryukyu Islands through the NW deep boundary of the Hangzhou Bay, and also proposes the following basic views' the migration and superposition of tectonic environments led to the formation of a composite metallogenic system; the change in the tectonic environment resulted in the superposition of various types of mineral deposits; seismic activities and metallogeny are mutually inducing factors. These views will be helpful to a discussion on the tectonic environments and metallogenic regularities.

Geochemistry,Geochronology,Sr-Nd Isotopic Compositions of Jiang Tso Ophiolite in the Middle Segment of the Bangong- Nujiang Suture Zone and Their Geological Significance

The Jiang Tso ophiolite, situated in the middle segment of the Bangong- Nujiang Suture Zone, is a part of the easternmost Qieli Lake ophiolite subzone and is close to the south of Pung Lake ophiolite. The rock association of Jiang Tso ophiolite is relatively complete and is mainly composed of metamorphic peridotite, gabbro and diabase. Comparing with N-MORB, the ophiolite is high in Mg and low in Ti, K, Na, P, and is depleted in Nb, Ta, Hf, Th and enriched in Rb, Sr and Ba. Geochemical characteristics of the Jiang Tso ophiolite indicate it is of a supra-subduction zone type formed in the spreading ridge of back arc basin. The SHRIMP U-Pb dating of zircons from the gabbro yielded a weighted average age of 188.1±4.1 Ma （MSWD=1.4）, indicating the Jiang Tso ophiolite was formed in the late stage of early Jurassic. The Sr, Nd isotopic compositions show that the Tethyan mantle domain is the depleted mantle （DM）, with enriched mantle domain II （EMII）. They have the same Sr, Nd isotopic composition with the India Ocean MORB type.

Petrochemistry ,Chronology and Tectonic Setting of Strong Peraluminous Anatectic Granitoids in Yunkai Orogenic Belt , Western Guangdong Province ,China

Arguments persist on the genesis and ages for the banded-augen （rapakivi） anatectic granitoids （charnockite） extensively outcropped in the Yunkai （云开） region, western Guangdong （广东） Province. Their petrochemistry, SHRIMP dating, deformational and metamorphic structure were studled. The results show that most granitoids are A/CNK〉1. 1, CaO/Na2O= 0. 62-1. 61 （average 0.94〉0.3）, Al2O3/TiO2 =16.6-60.6 （average 23.68）, depleted high field strong elements Ta, Nb, Zr, strong peraluminous high-K calcalkaline and calcalkaline granitoids in the post-collisional tectonic environment of a subduction-collision orogenic belt in an active-continental margin. The temperatures of charnockite and gneissic garnet-bearing biotite monzonitic granite are obviously higher than those of banded-augen （rapakivi） biotite monzonitic granite, and charnockite and gneissic garnet-bearing biotite monzonitic granite with the evolutional characteristics of A-type granites. The forming ages from banded-augen （rapakivi） biotite monzonitic granite to charnockite and gneissic garnet-bearing biotite monzonitic granite, whose crystallizing zircon SHRIMP ages are （465±10） Ma, （467±10 ） Ma, （435±11 ） Ma and （413±8） Ma, respectively, become younger. This shows that there was an oceaniccontinental subduction-collision and post-collisional extension-delamination-underplating between the Yangtze and Cathaysia plates during the Caledonian, and the granitoids experienced compressional uplift and extensional exhumation during the lndosinian. This provides important evidence of subduction collision of the Yangtze plate to the Cathaysia plate during the Caledonian in South China.

Magnetite-Fluorite Rock:A New Rock Type of Hot Water Sedimentation

The new type hot water sedimentary rock -- magnetite-fluorite rock occurs as quasi-layers in flat parts of contact zones between rock body and strata in Bamianshan of Changshan County, Zhejiang Province, China. The main mineral assemblage is fluorite＋magnetite＋cassiterite. The rock shows typical laminated structure and obvious mosaic texture. Its formation temperature is between 123℃-160℃, averaging at 142℃. The major chemical composition of the rock includes CaF2, SiO2, Al2O3, FeO, and Fe2O3; the high-content microelement association includes W, Sn, Be, Rb, Sr, S, and CI; and the total content of REE is low （∑REE between 35.34×10^-6-38.35×10^-6）, showing LREE enrichment type of distribution pattern. Diagenesis： driven by the tectonic stress, the formation water heated in the deep strata had moved along the fissures or fractures in strata and had extracted components from the strata on the way, and finally stagnated in the flat parts of contact zones between rock body and strata. With drop in temperature, magnetite and fluorite were separated from the hot water and precipitated alternately, forming this hot water sedimentary rock with new type mineralogical composition, typical laminated structure, obvious mosaic texture and sub-horizontal occurrence. The characteristics of the new type mineralogical composition, sedimentary tectonic environment and chemical composition are different from that of the well-known traditional hydrothermai sedimentary rocks.

Huanggang Intrusive Complexin Northern Tongbai Area:Island-Arc Tectonic Environment and Its Geological Significance

The Huanggang intrusive complex in northern Tongbai area was formed in Early Paleozoic. It mainly consists of ultra basic, basic, intermediate and acid rocks, dominated by intermediate and basic rocks. The complex belongs to calc alkaline series. Geochemical characteristics of major and trace elements show that the complex was derived from the fractional crystallization of co source magma. It is suggested that the complex was formed in island arc tectonic environment and was closely related to the northward subduction of the Erlangping back arc basin. Thus, the subduction of the back arc basin can induce the island arc type magmatism similar to the one formed in the setting of ocean plate subduction.

Sequence Stratigraphy and Tectonic Environment of the Chartai Group,Inner Mongolia

The Middle Proterozoic Chartai Group separated by two unconformities consists of three depositional se-quences: the Shujigou Formation-Zenglongchang Formation (DS Ⅰ), the Agulugou Formation (DS Ⅱ), andthe Liuhongwan Formation (DS Ⅲ). The carbonate platform and back-platform basin are the basic environ-ment model of the Chartai Group. The syndepositional faults on the oceanward side of the carbonate platformand large-scale slumping in the soft sediments are important marks of facies tracts. The newly establishedZenglongchan uplifting, an epeirogenetic uplifting, plays an important role in the formation of thepalaeogeographic framework of the Chartai Group. The stratigraphic correlation between the Chartai Groupand the Bayan Obo Group is made for the first time by using sequence stratigraphic principle and model estab-lished by P.R. Vail. The Chartai Group, which was deposited on the northern passive continental margin of theNorth China platfom, represents the platform cover.

A Preliminary Review on the Metallogeny of Pb-Zn Deposits in China

Lead and zinc resources are abundant in China, with the reserves of 100 million tons ranking only second in the world. There are more than 3000 lead-zinc mine areas nationwide. The classification of lead-zinc （Pb-Zn） deposits has been a highly controversial issue. From the standpoint of evaluating the potential of mineral resources, we construct a Pb-Zn deposit predictive type of classification scheme, and propose a Pb-Zn deposit comprehensive classification scheme （including 5 classes and 13 sub-types） that regards mineralization as the primary factor and the ore rock as secondary. According to the temporal and spatial distribution of Pb-Zn deposits, we conclude that a multi-period, multi-cycle orogenic environment is the most favorable for lead-zinc deposit growth, that the Proterozoic is the major eon for the growth of igneous-type deposits, the Paleozoic is an important development era for sedimentary Pb-Zn deposits, and the Mesozoic and Cenozoic are the heyday eras of magmatic type lead-zinc deposits. On this basis, we analyse the relationship between tectonic evolution and Pb-Zn metallogenic, and propose that the key factors determining geological mineralization are the metallogenic epoch of mineralization and tectonic environment, which determine the temporal and spatial distribution.

Correlation between Tectonic Environment and Chracteristics of Mass Movement （Landslides）： A Case Study from Java, Indonesia

In Central Java and Yogyakarta Special Region, there are several zones, which potential of landslide disaster. The zones are in general located at uplitted and or folded mountains, such as North Serayu Mountains, South Serayu Mountains, Menoreh Mountains, Southern Mountains and slopes of young volcanic area, including Ungaran-Merbabu-Merapi area, and Slamet-Sundoro-Sumbing area. Besides morphology, another main factor influencing vulnerability of the terrain is physical properties of the composing lithology. The geologic formations in the study area are predominantly composed of clayey and volcanic rocks. The cohesion force of clayey rock ranges 0.4-0.7 kg/cm^2, the internal friction angle ranges 20°-35°, while the cohesion force of volcanic rock （weathered） ranges 0.25-0.27 kg/cm^2, and the friction angle ranges 20°-35°. In general, rocks occupying the area are collectively dissected by joints and active faults, with soil of more than 5 m thick. Local rainfall belongs to high category （〉 2,500 mm/y）. However, landslides that occur in each physiographic zone mentioned above show different characterizations.

Geological division of gas in the Pingdingshan mine area based on its tectonic dynamics characteristics

In this paper,we used tectonic dynamics theories to study the tectonic evolution characteristics of the Pingdingshan mine area,and analyzed the impact of tectonic progressive control on gas occurrence.The study results are as follows:the Pingdingshan mine area has been mainly controlled by multiple squeezing and shearing actions of the Qinling orogenic belt since early and middle Yanshan,forming the tectonic control characteristics of master control in two directions,namely NWW trending and NNE trending;the NWW trending structure is dominated by squeezing and shearing,while the NNE trending structure is dominated by tension.Progressively controlled by the structure,the gas occurrence presents partition and zonation,i.e.compared with the western structure,the eastern NWW-NW trending structure of the mine area is more highly developed,resulting in the mine area gas occurrence distribution characteristics are distinct in the east while indistinct in the west.Based on this,the mine area can be divided into the following two geological dynamic areas:the western half of mine area,namely the Guodishan fault control area,where the NW-SE trending synchronous tension action suffered by the northeast side(footwall) is relatively strong,and compared with the southwest side(hanging wall),its coal and gas outburst seriousness is weak;and the eastern half of mine area,namely the NWW-NW thrust nappe fracture fold control area,which is a serious area of coal and gas outburst,in particular the axial area of the Likou syncline is the intersection compound and combination position of the NW and NE trending structures,a tectonic concentrated area,and the gas pressure and content here are the largest.

Tectonic environment and cause of earthquakes in the Three Gorges reservoir area

Seismotectonics in the Three Gorges reservoir area is investigated by using the P-wave tomography with earthquakes that occurred before the impoundment of the reservoir. The result indicates that most of these events occurred in or around the velocity-gradient belts between high-velocity and low-velocity anomalies. These belts have similar characteristics to buried-fauh zones. Stresses generated by movement of partially molten upper-mantle materials and thermal stress may have jointly contributed to the seismic activities along the faults and such buried faults, and possibly activated new earthquake ruptures.

Gravity variation before the Akto Ms6.7 earthquake, Xinjiang

The relationship between gravity variation and the Akto Ms6.7 earthquake on November 11, 2016, was studied by use of mobile gravity observation data from the China continental structural environmental monitoring network. The result revealed that before the Akto earthquake, a high positive gravity variation was observed in the Pamir tectonic knots region （within a maximum magnitude of approximately ＋80 microgal）, which was consistent with the existing knowledge of gravity abnormality and the locations of strong earthquakes. In view of the recent strong seismic activities in the Pamir tectonic knots region, as well as the strong upward crust movement and compressive strain, it is believed that gravity change in the Pamir tectonic knots region reflects the recent strong seismic activities and crust movement.

Activity of the Lenglongling fault system and seismotectonics of the 2016 MS6.4 Menyuan earthquake

The MS6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault(LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-Damaying and Huangcheng-Shuangta faults, eastern of the Northern Qilian Shan fault zone. A near northwest-striking rupture plane intersects the two faults at a certain angle. The focal mechanism solution shows that this was a thrust-type earthquake, slightly different from the strike-slip movement with a thrust component of the LLLF. Field geological mapping, tectonic geomorphology analysis, trench excavation and 14 C dating reveal that(1) the LLLF has been obviously active since the Holocene, and may behave with characteristic slip behavior and produce M_W7.3–7.5 earthquakes;(2) the LLLF appears as a flower structure in terms of structure style, and dips NNE at a steep angle; and(3) the most recent earthquake event occurred after 1815–1065 a BP. An associated fault, the Northern Lenglongling fault(NLLLF), is located at the northwestern end of the LLLF. Consequently, the NLLLF was continually subject to tectonic pushing effects from the left-lateral shear at the end of the LLLF, and, accordingly, it bent and rotated outward tectonically.Subsequently, the fault deviated from the dominant rupture azimuth and activity weakened. In the late Quaternary, it behaved as a thrust fault with no obvious deformation at the surface. This is indicated by the arc shape, with a micro-protrusion northeastward,and no geologic or geomorphic signs of surface rupturing since the late Quaternary. However, such faults could still rupture at depth, producing moderate-strong earthquakes. The geometric and kinematic properties of the NLLLF are in good agreement with the occurrence and kinematic properties of nodal plane 2, and with the distribution characteristics of the aftershocks and seismic intensity. Therefore, the NLLLF is a more suitable seismogenic structure for the MS 6.4 Menyuan earthquake. In addition, the thrust movement of the NLLLF accommodates subsequent movement of the LLLF. During the historical evolution of the NLLLF,the LLLF and the NLLLF have affected the local topography through tectonic uplift.

A study on geological structure prediction based on random forest method

The Xingmeng orogenic belt is located in the eastern section of the Central Asian orogenic belt,which is one of the key areas to study the formation and evolution of the Central Asian orogenic belt.At present,there is a huge controversy over the closure time of the Paleo-Asian Ocean in the Xingmeng orogenic belt.One of the reasons is that the genetic tectonic setting of the Carboniferous volcanic rocks is not clear.Due to the diversity of volcanic rock geochemical characteristics and its related interpretations,there are two different views on the tectonic setting of Carboniferous volcanic rocks in the Xingmeng orogenic belt:island arc and continental rift.In recent years,it is one of the important development directions in the application of geological big data technology to analyze geochemical data based on machine learning methods and further infer the tectonic background of basalt.This paper systematically collects Carboniferous basic rock data from Dongwuqi area of Inner Mongolia,Keyouzhongqi area of Inner Mongolia and Beishan area in the southern section of the Central Asian Orogenic Belt.Random forest algorithm is used for training sets of major elements and trace elements in global island arc basalt and rift basalt,and then the trained model is used to predict the tectonic setting of the Carboniferous magmatic rock samples in the Xingmeng orogenic belt.The prediction results shows that the island arc probability of most of the research samples is between 0.65 and 1,which indicates that the island arc tectonic setting is more credible.In this paper,it is concluded that magmatism in the Beishan area of the southern part of the Central Asian Orogenic belt in the Early Carboniferous may have formed in the heyday of subduction,while the Xingmeng orogenic belt in the Late Carboniferous may have been in the late subduction stage to the collision or even the early rifting stage.This temporal and spatial evolution shows that the subduction of the Paleo-Asian Ocean is different from west to east.Therefore,the research results of this paper show that the subduction of the Xingmeng orogenic belt in the Carboniferous has not ended yet.