Geochemical Characteristics and Tectonic Significance of Triassic Granite from Taer Region, the Northern Margin of West Kunlun

Late Hercynian-early Indosinian （Triassic） granite is widely distributed around the Taer region of the northern margin of West Kunlun. The rock mass is mainly composed of calc-alkaline porphyroid biotite adamellite and characterized by SiO2-rich, high-Ca, moderate-alkaline, and strongly peraluminous attributes, and relatively low ~REE with LREE enrichment and a moderate Eu anomaly. As shown in the trace element spider web diagram, distinct peaks appear for Th, La, Nd, and Zr and clearly low values appear for Ba, Nb, Sr, P, and Ti. Further, compared with the primitive mantle, Rb/Sr and Rb/Ba are considerably higher and Nd/Th and Nb/Ta are relative low, all falling into the scope of the crust-origin rocks, indicating the characteristics of the crust-origin S-type granite. The rock mass＇s zircon U-Pb isotopic age is determined to be 235.7 -~ 3.9 Ma. On the basis of the age data, spatio-temporal location, lithology, and geochemistry of the rock mass, we conclude that the formation of the rock mass is closely related to the strong compressional orogenic movement （240 Ma） of the Tianshuihai terrane and the South Kunlun terrane. The rock mass is the product of the collision orogenic movement. However, distinct differences are observed between the studied rock mass and the synorogenic Bulunkou rock mass, which may be caused by the different collision strength and different positions with respect to the collision zone.

Petrogenesis and Tectonic Significance of the Three-Period Porphyries from the Daruoluolong Cu(Au) Deposit, Tibet, China

Objective The Daruoluolong deposit is the first high-grade Cu(Au)deposit discovered in the middle section of the Bangonghu-Nujiang(herein after referred to as Ban-Nu)metallogenic belt,which has not been documented about previously.This deposit is located in Shuanghu County of northern Tibet,and its geotectonic position belongs to the

Felsic Igneous Rocks in the Hua'aobaote Pb-Zn-Ag Polymetallic Orefield,Southern Great Xing'an Range:Genesis,Metallogenetic and Tectonic Significance

The Hua’aobaote Pb-Zn-Ag Polymetallic orefield is situated in the southern section of the Great Xing’an Range(GXAR),which has experienced extensive magmatism.Since the Paleozoic,there are two stages of magmatism in Hua’aobaote orefield occurred in the Paleozoic and Mesozoic.The Mesozoic magmatism is of great significance for the PbZn-Ag Polymetallic mineralization in Hua’aobaote orefield.In this study,new geochemical data was obtained to discuss the timing and petrogenesis of the magmatic rocks and its geodynamic and metallogenic significance.Zircon U-Pb ages reveal that the felsic igneous rocks from the Hua’aobaote orefield were formed in the Early Permian(294.8±3.2 Ma)and Early Cretaceous(132.6±1.4 Ma).Geochemically,the Early Permian granodiorite porphyrite is characterized by high Sr/Y(42-63)ratios and Mg^(#)(62.24-70.74)values and low heavy rare earth element(HREE)(5.09-6.79 ppm)contents.The granodiorite porphyrite is also characterized by depleted Sr-Nd initial isotopic signatures[ε_(Nd)(t)=5.91-7.59,(^(87)Sr/^(86)Sr)i=0.7029-0.7030],exhibiting adakitic characteristics.The Early Cretaceous granite porphyry and rhyolite are A-type felsic igneous rocks,and demonstrate high SiO_(2),Na_(2)O+K_(2)O and rare earth element(REE)contents,low CaO and MgO contents,low(^(87)Sr/^(86)Sr)i ratios(0.7044-0.7058),and positive ε_(Nd)(t)values(2.57-4.65).Whole-rock Pb isotopic compositions in granodiorite porphyrite are:206Pb/204Pb=17.631-18.149,^(207)Pb/^(204)Pb=15.422-15.450,and ^(208)Pb/^(204)Pb=37.325-37.729.The granite porphyry and rhyolite have initial ^(206)Pb/^(204)Pb,^(207)Pb/^(204)Pb,and ^(208)Pb/^(204)Pb ratios of 18.106-19.309,15.489-15.539,and 37.821-38.05,respectively.Sr-Nd-Pb isotopic evidence suggests that the Early Permian granodiorite porphyrite is likely to derive from slab melts and modified by peridotitic mantle wedge in the subduction tectonic setting of the Paleo-Asian Ocean.The Early Cretaceous A-type felsic igneous rocks were derived from juvenile lower crust,accompanied by limited crustal contamination and various degree of fractional crystallisation during magma emplacement.The Early Cretaceous magmatism and related mineralization were formed in a post-orogenic tectonic setting that attributed to the closure of the Mongol-Okhotsk Ocean.Pb isotopic data for the various rock units in the study area indicate that the Mesozoic magma source contributed substantial Pb,Zn,and Ag to the Hua’aobaote deposit.

Petrogenesis and Tectonic Significance of the Xiuwacu Two-Period Magmatism in Geza Arc of Yunnan Province： Constraints from Lithogeochemistry, Zircon U-Pb Geochronology and Hf isotopic Compositions

Objective The Late Cretaceous Xiuwacu ore-bearing porphyry is located in the Geza area of southern Yidun arc, SW China. In this area, the rock mass is mainly composed of three lithofacies： biotite granite porphyry, monzonitic granite and light alkali feldspar granite. As a part of the Yidun arc, the Geza arc has common structure and temporal- spatial evolution with the ~idun arc, which has experienced three stages of oceanic crust subduction, collision orogeny and intracontinent convergence stages. The molybdenite ores in the area are mainly hosted in monzonitic granite-porphyry and structural fracture zone, and the ore bodies are strictly controlled by faults. In recent years, great geological prospecting results have been achieved in Xiuwacu, and the deposit has reached a medium scale. However, there are few researches on the metallogenic porphyry. Based on the previous research, we determined the rock-forming and ore-forming age of the porphyry, and found that there were two stages of magmatism intrusion in Xiuwacu： Indosinian and Yanshanian. We also discussed the geochemical characteristics and source area of the rocks in the area.

Landslides triggered by the 1970 Ms 7.7 Tonghai earthquake in Yunnan,China: an inventory, distribution characteristics, and tectonic significance

The 1970 Tonghai earthquake, which occurred on January 5, 1970, in Tonghai County, Yunnan Province, China, triggered a large number of landslides. Since the occurrence of the earthquake, there have been a huge number of research reports on the seismogenic structure and earthquake mechanism, but rare reports on the seismic landslides. As the largest earthquake recorded in the Qujiang fault zone, the study on the coseismic landslides triggered by this earthquake are of great significance to the prevention and mitigation of earthquake-induced landslides in this region. In this study, we established a coseismic landslide inventory for the VⅢ–X seismic intensity areas of the Ms 7.7 Tonghai earthquake, and conducted spatial analysis on the coseismic landslides, mainly having analyzed the effect of the topographic factors, geological factors, and seismic factors on the development of the coseismic landslides. To enhance the understanding of this earthquake, we converted the earthquake epicenter and magnitude with empirical formulas based on the distributions and areas of the coseismic landslides. Comparing with coseismic landslides in other earthquake-hit areas, we found the capability that this earthquake could induce landslides is low. This study provides a useful supplement to the global coseismic landslide inventories and could be the basic data for seismic landslide assessment in this earthquake-prone region.

Geochronology, Geochemistry and Tectonic Significance of Dike Swarms in Beishan, Gansu

Study area is located at Beishan,Gansu province.Beishan area located at conjunction site among Tarim plate,Sino-Korean plate and Kazakhstan plate,this special tectonic position has a very complex geological tectonic.

The Spatial-Temporal Distribution Patterns of Dyke Swarms in Central Asia and their Tectonic Significance: Case Studies in Eastern Tianshan and Western Junggar

Dykes are a special kind of intrusive rocks which were formed by deep magma intruded into the existing brittle fractures in the crust.Dykes swarms in different tectonic environments are very significant to re-construct the

Discovery of the Early Devonian Sinistral Shear in the Jiangshan-Shaoxing Fault Zone and its Tectonic Significance

The Jiangshan-Shaoxing fault zone （JSFZ） was formed by the amalgamation of the Yangtze and Cathaysia blocks in the Neoproterozoic.Since the Paleozoic,the JSFZ has experienced three episodes of tectonic activities：the Early Paleozoic ductile strike-slip shear,Early Mesozoic thrust,and the Late Mesozoic extension.

MAIN CENTRAL THRUST ZONE IN THE KATHMANDU AREA, CENTRAL NEPAL, AND ITS TECTONIC SIGNIFICANCE

The Himalaya, a fold\|and\|thrust belt in the northern margin of the Indian continent, is characterized by thrust tectoncis (Schelling and Arita, 1991). It consists mainly of three thrust\|bounded lithotectonic units: from south to north the Sub\|Himalayan imbricate zone, the Lesser Himalayan thrust package (LH) and the Higher Himalayan thrust sheet (HH) with the overlying Tethys Himalayan sequence. These units are separated by a series of propagated thrusts, i.e. from south to north the Himalayan Frontal Fault (HFF), Main Boundary Thrust (MBT) and Main Central Thrust (MCT). These thrusts are splays off of an underlying mid\|crustal subhorizontal d$B;D(Jollement (Main Detachmen Trust or Main Himalayan Thrust), and were propagated southward with time. Among these thrusts the MCT is most important intracrustal thrust in considering the geological evolution of the Himalaya, and is controversial regarding its location and nature. In western and eastern Nepal the Higher Himalayan Crystalline sheet is thrust over the Lesser Himalayan rocks along the MCT. In the Kathmandu area of central Nepal also the high\|grade rocks of the HH with the overlying Tethyan sediments covers southward the Lesser Himalayan rocks, and form the Kathmandu nappe. In the north of the Kathmandu nappe the Higher Himalayan crystallines are skirted by the Main Central Thrust zone (MCT zone) which consists of green and black phyllites with sporadic garnet snow\|ball garnet and calcareous schist associated with characteristic mylonitic augen gneiss. The southern margin of the nappe is bounded by the Mahabharat Thrust (MT: Stoecklin, 1990) with a narrow zone of the LH which is cut by the MBT. But the relationship of the MCT in the north and the MT in the south is disputable and important (Arita et al., 1997: Rai et al., 1998: Upreti and Le Fort, 1999), and in the margin of the Kathmandu nappe the MCT zone has not been confirmed.

Feldspar Lead Isotopic Composition of Granitoids from the Eastern Qinling Orogenic Belt and Their Tectonic Significance

This paper reports 48 feldspar lead isotope analyses from 27 granitic intrusions,which formed from the Late Proterozic to Mesozoic within the Eastern Qinling oregenic belt. Itis found that the granitic rocks of South Qinling are characterized by a strong block-effect anddepletion in U-Pb and Th-Pb, showing that these rocks came from the same lead isotopetectono-geochemical province, while those of North Qinling are characterized by higher U-Pband Th-Pb for Late Proterozoic to Early Paleozoic ones and lower U-Pb and Th-Pb forLate-Palaeozoic and younger ones in their feldspar lead isotopic composition. In the NorthQinling block, lead isotopic signatures reflect that the source of granitic magma had changedsince the Late Palaeozoic. Comparison of feldspar lead isotopic composition between SouthQinling and North Qinling shows that there is marked difference in lead isotopic compositionfor pre-Palaeozoic granitoids, indicating that the South Qinling and the North Qinling blocksbelong to different tectonic units, but the similarities in lead isotopic composition are quiteclear, which indicates that the South Qinling block had been welded with the North Qinlingblock and that the magma sources of both blocks were identical. The analysis provides directevidence for underplating of the continental crust of South Qinling beneath the North Qinlingblock in the continent-continent interaction stage of the Eastern Qinling oregenic belt.

Tectonic analysis and petroleum significance of Cenozoic faults in Dongping-Niuzhong area in Altyn slope

The evolution process and petroleum significance of two groups of fault structures,the NW-SE trending and near EW trending ones in the Cenozoic of Dongping-Niuzhong area of the Altyn slope,Qaidam Basin,were investigated using high precision 3-D seismic data.The NW-SE faults were generated in Oligocene,causing the formation of a series of folds related to transpression faults in the Niuzhong and Dongping area.After the Miocene,with the continuous extension of the Altyn Tagh strike-slip fault zone,the EW trending faults began to develop massively in Altyn slope.The activity of near EW trending faults and large-scale uplift of the bedrock in the northern Niuzhong area shared most of the compression torsion in Niuzhong and Dongping area,consequently,the activity of NW-SE trending faults weakened significantly after the Miocene.Then good hydrocarbon source rocks developed in the inherited Jurassic sags.The faults were effective pathways for oil and gas migration in Dongping and Niuzhong areas,and the oil and gas charging time matched well with the formation period of the NW-SE trending faults and their related structures,making the fault-related anticlines favorable targets for oil and gas accumulation.The Niuzhong area has been less affected by the Cenozoic movement after the Miocene,and thus has better conditions for gas reservoir preservation.

Precambrian Dykes in the Sao Francisco Craton Revisited:Geochemical-isotopic Signatures and Tectonic Significance

Several generations of mafic dyke swarms(2.7 to 0.8Ga),highlighted by aeromagnetic data,petrography,geochemistry,isotope geology and mostly U-Pb baddeleyite ages,crosscut the Archean and

The Metamorphic Evolution and Tectonic Significance of the Sumdo High and Ultrahigh Pressure Metamorphic Terrane, Central-South Lhasa Block, Tibet

Asthemaintectoniccomponentofthe Himalayan–Tibetan orogen,the Lhasa terrane has received much attention as it records the entire history of the orogeny.The occurrence of high pressure eclogite in the Sumdo complex in central Lhasa terrane has a significant importance on the understanding of the Paleo-Tethys subduction and plate itineration processes in this area.The petrological,geochemical and geochronological data of eclogite and associated blueschist and garnet-bearing mica schist from Sumdo,Jilang and Bailang area have been briefly reviewed to explore the origin and metamorphic evolution of this suture.Eclogites from the Sumdo complex have experienced low temperature,high pressure to ultrahigh pressure metamorphism,revealing a fastsubduction and exhumation process in a typical oceanic subduction zone.The large P-T range between different eclogites in the literature may be affected by the big error of unappropriated using geothermobarometry and may also because of slices of subducted blocks derived from different depths juxtapose together during exhumation.By summarizing the U-Pb,Lu-Hf and Sm-Nd ages of eclogites,the eclogite facies metamorphism is likely to occur in early Triassic during 245-225 Ma,but not the previously accepted late Permian at ca.260 Ma by the reinterpretation of the former geochronological data from literature.The opening of Paleo-Tethys Ocean between the Lhasa terrane initiate prior to ca.280 Ma and ultimate closure to integrate the Lhasa terrane was no earlier than225 Ma and may triggered by the initial subduction of Bangong-Nujiang Tethys Ocean in the north.

Petrogenesis and Tectonic Significance of An Early Paleoproterozoic High-Mg Boninite-Norite-Diorite Suite of Rocks from the Bastar Craton, Central India

Mafic/ultramafic rocks derived from high siliceous(high-Si)high magnesium(high-Mg)mantle melts are an important feature observed during early Precambrian.They provide much important geological and petrological

CHARACTERISTICS OF CRUST-MANTLE TRANSITION ZONE AND ITS TECTONIC SIGNIFICANCE IN THE CONTINENT OF CHINA

The crust-mantle transition zone (CMTZ) is an important site for mass and energy exchange between the lower crust and upper mantle. Several kinds of CMTZ exist beneath the continent of China, which show different seismic reflection characteristics and are composed of different rock associations. In this paper, we identify three types of CMTZ in the continent of China. (a) The CMTZ beneath the Tibet Plateau exhibits a grid-shaped seismic reflection characterized by random and reticular high and low seismic velocity lamellae. It is about 30 km thick, comprising both mafic granulites of lower crust and ultramafic rocks of upper mantle. Such lithological association and seismic velocity structure were inherited from the crustal overthrust and overlapping during the Cenozoic collision between the Indian and Euro-Asian continents; The corresponding crust movement is still very intense in this region. (b) The CMTZ underneath North China Block is usually composed of a thinner strong positive velocity gradient layer with dual properties in the rock associations. This suggests that the crust is still active in the North China Block after significant lithospheric thinning and thermal accretion. (c) The CMTZ in the remaining platform basins of China is characterized by a relatively sharp seismic discontinuity and a clear lithological boundary between the low crust and upper mantle. Such features of the CMTZ beneath Ordos basin correspond to weak crustal movement after a long period of isolation from thermo-tectonic overprinting.

Geochemistry and tectonic significance of volcanic rocks from Qushenla Formation in Gerze area of northern Tibetan Plateau

By using petrological,isotope chronological,and geochemical methods,the authors studied the volcanic rocks in the studied area,mainly including dacites and trachytes. The results show that they formed during the late Early Cretaceous. Geochemically,the volcanic rocks are relatively enriched in large-ion lithophile elements( Rb,K,and Th) and depleted in high field strength elements( Nb,Ta,and Ti),and rich in light rare earth elements,and depleted in heavy rare earth elements. The fact indicates that the main body of the volcanic rocks in the Qushenla Formation was derived from the partial melting of lower crust. The lithological assemblages are characterized by continental high-K calc-alkaline and shoshonitic series,suggesting that the southward-subducting oceanic slab in southern Bangong Lake had break off and that the Bangong Lake-Nujiang Ocean had closed before 107 Ma. The main dynamic mechanisms for the genesis of this set of intermediate-acidic volcanic rocks were upwelling of the asthenosphere and partial melting of the lower crust caused by slab break-off.

Characteristics of strike-slip inversion structures of the Karatau fault and their petroleum geological significances in the South Turgay Basin,Kazakhstan

The Karatau fault is one of the important strike-slip faults in central Asia,and the South Turgay Basin is located towards its northern end.Detailed seismic interpretation indicated that the strikeslip tectonism of the Karatau fault weakened gradually from west to east in the South Turgay Basin.Typical flower structures developed on the section,and strike-slip faults showed an echelon pattern on planar view.The Karatau strike-slip fault affected the South Turgay Basin in two periods：（1） The South Turgay strike-slip pull-apart rift basin formed as a result of regional extensive stress in the Early-Middle Jurassic,characterized by the juxtaposition of horsts and grabens.The formation of horsts provided favorable reservoir spaces for later hydrocarbon accumulation,and different filling stages of grabens controlled different reservoir-forming factors in grabens.（2） Two stages of tectonic inversion occurred in the Late Jurassic and Late Cretaceous and played a crucial role in the final shape of the structure in the South Turgay Basin.The oil and gas migrated to form reservoirs and mainly concentrated in the horsts,graben slopes and in both sides of the strike-slip fault zone.In the case of the degree of accumulation of petroleum,the factor explaining why horsts are better than grabens is the strike-slip pull-apart of the South Turgay Basin,and the structure inversion of the South Turgay Basin explains why the west graben is better than the east one.Overall,the Karatau strike-slip fault played a very important role in the formation of the South Turgay Basin and its hydrocarbon accumulations.

华北克拉通栖霞地区~2.9Ga变质基性火山岩锆石SHRIMP U-Pb定年、Hf-O同位素特征及构造意义

胶东地区是华北克拉通重要的早前寒武纪研究区之一。中太古代唐家庄岩群在形成时代、岩石成因及构造环境等方面一直少有研究。作者在栖霞地区对出露的唐家庄岩群变质表壳岩进行系统地质调查研究基础上,开展了变质基性火山岩全岩地球化学、锆石SHRIMP U-Pb和Hf-O同位素等分析研究。结果显示,变质基性火山岩岩浆锆石年龄为2907.9±6.3Ma,代表了中太古代唐家庄岩群的形成时间,并遭受新太古代早、晚期变质作用。这是~2.9Ga唐家庄岩群变质基性火山岩在胶东地区首次报道。岩石地球化学特征表现为相对富集大离子亲石元素K、Rb、Sr等,Th、Nb、Zr、Hf等高场强元素相对亏损,具有中等分异的REE配分模式。岩石中岩浆锆石具有相似的Hf、O同位素组成,εHf(t)值介于-0.68~+4.21,δ18 O值介于1.38‰~6.73‰。结合前人的工作,我们得出的主要结论如下:(1)胶东地区经历~2.9Ga岩浆事件,局部地段仍保留下了同时期的变质表壳岩;(2)唐家庄岩群是中太古代初始的洋盆环境中所形成的一套火山-沉积建造;(3)华北克拉通中太古代晚期是亏损地幔新生地壳加积的主要时期,局部地壳再循环了较老的陆源物质;(4)华北克拉通新太古代晚期经历了伸展构造背景,岩浆底侵作用使岩石发生强烈变质作用。

内蒙古武川地区早白垩世火山岩的年代学及其构造意义

以华北克拉通北缘西部内蒙古武川地区早白垩世火山岩为研究对象,对其进行了LA-ICP-MS锆石U-Pb定年。定年结果显示玄武粗安岩的形成年龄为(123±3)Ma(MSWD=2.63,n=16),时代为早白垩世;流纹岩的形成年龄为(121±3)Ma(MSWD=0.02,n=13),时代为早白垩世。早白垩世玄武粗安岩和流纹岩形成了典型的双峰式火山岩组合,应形成于大陆板内裂谷环境,该构造环境主要是由于华北克拉通北缘薄弱地带受到早白垩世蒙古—鄂霍茨克造山带造山后重力垮塌事件的远程作用而拉张,与古太平洋板块的俯冲作用并未有直接关系。

东天山印支期闪长质岩墙岩石成因及构造意义

东天山地区发育大量的印支期岩浆岩,其岩石成因及其动力学背景对于理解中亚造山带晚期构造演化过程具有重要意义。本文对东天山尾亚和天湖地区新发现的闪长质岩墙开展了岩石学、地球化学及锆石U-Pb年代学和Hf同位素综合研究。锆石U-Pb测年结果表明,天湖地区闪长质岩墙形成时代为246.6±1.9Ma和248.4±3.8Ma,为早三叠世岩浆活动的产物;尾亚地区闪长质岩墙形成时代为237.7±1.3Ma、234.4±2.1Ma、238.3±1.6Ma和233.9±1.6Ma,为中三叠世岩浆活动的产物。岩石地球化学特征显示研究区闪长质岩墙总体呈现出较高硅(SiO_(2)为60.51%~67.56%)、富碱(K_(2)O+Na_(2)O为6.39%~8.23%)和准铝质(A/CNK为0.91~0.98)特征,属于高钾钙碱性系列。岩石相对富集K、Rb、Ba等大离子亲石元素(LILE),亏损Nb、Ti、Ta等高场强元素(HFSE),具有微弱Eu负异常(δEu=0.83~1.03)。锆石Hf同位素分析显示样品具有正的ε_(Hf)(t)值(+1.26~+6.32)和较年轻的亏损地幔模式年龄(tDM1=638~828Ma)。结合岩石地球化学特征,表明闪长质岩墙可能为交代地幔楔部分熔融形成的幔源岩浆底侵诱发新生下地壳熔融,随后由底侵的玄武质岩浆与壳源长英质岩浆混合形成。结合区域地质和相关构造环境分析,指示闪长质岩墙形成于板内伸展环境。结合前人研究,本文认为东天山发育的闪长质岩墙群可作为区域伸展作用的重要标志,表明东天山在印支期为陆内伸展的构造环境。