Middle-Late Triassic sedimentation in the Helanshan tectonic belt: Constrain on the tectono-sedimentary evolution of the Ordos Basin, North China

The Helanshan tectonic belt is located to the west of the Ordos Basin, and separates the Alxa(or Yinshan)Massif to the west from the Ordos block to the east. Triassic sedimentation in the Helanshan tectonic belt records important information about tectono-sedimentary process between the Alxa Massif and the Ordos block. Detailed geological mapping and investigation on the lithological package, sedimentary facies and paleocurrent orientation have been conducted on the Middle to Upper Triassic clastic rocks in the Helanshan tectonic belt. The succession is characterized by upward-fining sequence and comprises coarse grained alluvial-fluvial facies in the lower part as well as deltaic-lacustrine facies in the upper part. Based on detailed study and comparisons on the sedimentary sequence along various sections, the Middle to Upper Triassic strata have been revealed that show clear southeastward-deepening sedimentary differentiation and transgression from southwest to northeast, which are consistent with the southeastward flowing paleocurrent. These features indicate a southeastward-dipping paleogeography in the Helanshan tectonic belt, which was original western part of southeastward orientated fluviallacustrine system in the northwestern proto-Ordos Basin. Further to the east, the Triassic succession in the Ordos Basin displays gradually thickening and alluvial-fluvial system flowed from southeast to northwest, showing a huge thick sedimentary wedge in the western basin margin. Together with the Late Permiane Early Triassic closure of the Paleo-Asian Ocean to the north, the Late Triassic extensional structures and diabase dykes in the Helanshan tectonic belt, all the above sedimentary features could be mostly interpreted as records of an extensional basin correlated to post-collisional collapse of the Central Asian Orogenic Belt.

Geochemistry of Permian Mafic Igneous Rocks from the Napo-Qinzhou Tectonic Belt in Southwest Guangxi, Southwest China: Implications for Arc-Back Arc Basin Magmatic Evolution

The Napo-Qinzhou Tectonic Belt （NQTB） lies at the junction of the Yangtze, Cathaysia and Indochina （North Vietnam） Blocks, which is composed of five major lithotectonic subunits： the Qinzhou-Fangcheng Suture Zone （QFSZ）, the Shiwandashan Basin （SB）, the Pingxiang-Nanning Suture Zone （PNSZ）, the Damingshan Block （DB） and the Babu-Lingma Suture Zone （BLSZ）. On the basis of geochemical compositions, the Permian mafic igneous rocks can be divided into three distinct groups： （1） mafic igneous rocks （Group 1） from the Longjing region in the PNSZ and Hurun region in the BLSZ, which are characterized by intermediate Ti, P and Zr with low Ni and Cr contents; （2） mafic igneous rocks （Group 2） from the Naxiao and Chongzuo region in the DB, characterized by low-intermediate Ti, P and Zr with high Ni and Cr concentrations; and （3） mafic igneous rocks （Group 3） from the Siming region in the Jingxi carbonate platform of the northwestern margin of the NQTB, with intermediate-high Ti, P and Zr and low Ni and Cr contents. The Group 1 rocks yield a weighted mean 206 Pb/ 238 U age of 250.5±2.8 Ma and are geochemically similar to basalts occurring in back-arc basin settings. The Group 2 rocks exhibit geochemical features to those basalts in island arcs, whereas the Group 3 rocks show geochemical similarity to that of ocean island basalts. All three groups are characterized by relatively low ε Nd （t） values （-2.61 to ＋1.10） and high initial 87 Sr/ 86 Sr isotopic ratios （0.705309-0.707434）, indicating that they were derived from a subduction-modified lithospheric mantle and experienced assimilation, fractional crystallization, and crustal contamination or mixing during magmatic evolution. Accordingly, we propose the existence of an arc-back arc basin system that developed along the NQTB at the border of SW Guangxi Province （SW China） and northern Vietnam, and it was formed by continued northwestward subduction of the Cathaysian （or Yunkai） Block under the Yangtze Block, and northeastward subduction of the Indochina Block beneath the Yangtze Block during Permian time.

Revised Chronostratigraphic Framework of the Metamorphic Strata in the Jiangnan Orogenic Belt,South China and its Tectonic Implications

In a re-study of regional geology by the China Geological Survey （CGS）, the key problem is in the stratigraphical division and correlation. According to the new isotopic dating of the Mesoand Neoproterozoic in China, there have been great changes in the strata correlation and tectonic explanation. The authors obtained four zircon sensitive high resolution ion micro-probe （SHRIMP） U- Pb datings from the bentonite of the Lengjiaxi Group （822±10 Ma, 823±12 Ma and 834±11 Ma） and Banxi Group （802.6±7.6 Ma） in north Hunan Province, which is considered to be the middle part of the Jiangnan Orogenic Belt. On the basis of the zircon dating mentioned above, the end of the Wuling orogen is first limited in the period from 822 Ma to 802 Ma in one continued outcrop （Lucheng section） in Linxiang city, Hunan Province. Combining a series of new zircon U-Pb datings in the Yangtze and Cathaysia blocks, several Neoproterozoic volcanic events and distribution of the metamorphic rocks in the Jiangnan Orogenic Belt have been distinguished. In the context of the global geodynamics, it is useful to set up a practical and high precision chronological framework and basic and unified late Precambrian section in South China.

Metallogenesis of Precambrian gold deposits in the Wutai greenstone belt:Constrains on the tectonic evolution of the North China Craton

The Wutai greenstone belt in central North China Craton(NCC) hosts a number of Precambrian gold deposits and ore occurrences. Based on the host rock association, these can be divided into Banded Iron Formation(BIF), meta-volcano-sedimentary and meta-conglomerate types. The two former types formed during ~2.5-2.3 Ga and the third one at ~1.85 Ga. The characteristics of these Precambrian gold deposits are broadly similar with those of the orogenic gold deposits. Based on available geochronological data, here we reconstruct the major tectonic events and their relationship with gold mineralization in the Wutai-Hengshan-Fuping region during Neoarchean to Paleoproterozoic as follows.(1)~2.6-2.5 Ga: widespread intrusion of tonalite-trondhjemite-granodiorite(TTG) magmas in the Hengshan terrane and Fuping continental arc, formation of the Wutai volcanic arc in the southern margin of Hengshan terrane with granitoids emplacement, and the Hengshan-Wutai intra-oceanic arc accretion to the Fuping arc at the end of Neoarchean.(2) ~ 2.5-2.3 Ga: the subduction of Hengshan arc from north leading to persistent magmatism and orogenic gold mineralization.(3)~2.2-2.1 Ga:extension leading to the formation of graben structure in the Wutai and Fuping region, deposition of the Hutuo and Wanzi Group sediments, formation of placer gold through erosion of the orogenic gold deposits.(4)~2.2-2.0 Ga: widespread magmatism in the Wutai-Hengshan-Fuping region.(5)~1.95-1.8 Ga: regional metamorphism associated with collision of the Western and Eastern Blocks of the NCC and associated orogenic gold deposits. The multiple subduction-accretion-collision history and subsequent deep erosion has significantly affected most of the Precambrian gold deposits in the Wutai greenstone belt.

Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt in NE China

The eastern Central Asian Orogenic Belt(CAOB)in NE China is a key area for investigating continental growth.However,the complexity of its Paleozoic geological history has meant that the tectonic development of this belt is not fully understood.NE China is composed of the Erguna and Jiamusi blocks in the northern and eastern parts and the Xing’an and Songliao-Xilinhot accretionary terranes in the central and southern parts.The Erguna and Jiamusi blocks have Precambrian basements with Siberia and Gondwana affinities,respectively.In contrast,the Xing’an and Songliao-Xilinhot accretionary terranes were formed via subduction and collision processes.These blocks and terranes were separated by the Xinlin-Xiguitu,Heilongjiang,Nenjiang,and Solonker oceans from north to south,and these oceans closed during the Cambrian(ca.500 Ma),Late Silurian(ca.420 Ma),early Late Carboniferous(ca.320 Ma),and Late Permian to Middle Triassic(260-240 Ma),respectively,forming the Xinlin-Xiguitu,Mudanjiang-Yilan,Hegenshan-Heihe,Solonker-Linxi,and Changchun-Yanji suture zones.Two oceanic tectonic cycles took place in the eastern Paleo-Asian Ocean(PAO),namely,the Early Paleozoic cycle involving the Xinlin-Xiguitu and Heilongjiang oceans and the late Paleozoic cycle involving the Nenjiang-Solonker oceans.The Paleozoic tectonic pattern of the eastern CAOB generally shows structural features that trend east-west.The timing of accretion and collision events of the eastern CAOB during the Paleozoic youngs progressively from north to south.The branch ocean basins of the eastern PAO closed from west to east in a scissor-like manner.A bi-directional subduction regime dominated during the narrowing and closure process of the eastern PAO,which led to“soft collision”of tectonic units on each side,forming huge accretionary orogenic belts in central Asia.

ON GOLD-BEARING CHARACTERISTICS OF GEOSYNCLINAL TECTONIC LAYER IN XUEFENG MOUNTAIN TECTONIC BELT,HUNAN,CHINA

1. Material composition of the geosynclinal tectonic LayerThe geosynclinal tectonic layer is mainly composed of the following two parts: sandyslate rocks of Precambrin and volcanic rocks inbeded within the sand-slate rocks.The sandy-slate rocks embrace the chemical compositional characteristics of light metamorphic rocks: SiO2=54.5681.63（Wt%）, with average of 63.96（wt%）（n=58, the same as following）; Al2O3=9.4717.75（wt%）, with average of 15.36（wt%）, and Al2O3】K2O+Na2O+CaO; the content of （FeO+Fe2O3） varies greatly with FeO】Fe2O3; （CaO+MgO）=0.789.22 （wt%）with average of 23 （wt%）, and MgO】CaO; the ratios of K2O/Na2O rang from 2 to 4（】1）. By comparing all this chemical data with that of the other kind rocks, We can know that the sand y-slate rocks were the eunic and /or bathyal sediments which formed under the strongly active eugeosynclinal tectonic setting.

Geochronology and geochemistry of mafic dykes in the Helanshan complex: Implications for Mesozoic tectonics in the North China Craton

The Helanshan tectonic belt(HTB) is a major tectonic divide between the Alxa and Ordos blocks in the North China Craton. The geochronology and petrogenesis of the mafic dykes in the northern HTB are keys to understanding the tectonic evolution of this belt. The mafic dykes, intruded into the Neoarchean-Paleoproterozoic metamorphic basement, are mainly composed of diabase with a mineral assemblage of plagioclase(45%-60%), pyroxene(25%-35%), minor quartz and Fe-Ti oxides. The LA-ICPMS U-Pb analysis of zircon grains from representative dykes yield a weighted mean age of 206 ± 1.9 Ma, which represents the crystallization age of the dyke. The diabases show high contents of Fe_2 O_3~T(11.88-17.55 wt.%), low contents of SiO_2(45.65-50.95 wt.%) and MgO(3.31-5.50 wt.%) with low Mg#(=100×MgO/(MgO + FeO) atomic ration) of 33-44. They are characterized by enrichment of light rare earth elements(LREEs) and large ion lithophile elements(LILEs)(e.g., Rb, Ba and Pb), and slight depletion of high field strength elements(HFSEs). These features suggest that the magma has undergone extensive fractionation of olivine and pyroxene but only minor crustal contamination during its evolution. Their high Sm contents and La/Sm ratios, and low Sm/Yb ratios indicate that magma from which the dykes formed was derived from low degree(about 5%) partial melting of an enriched garnet + spinel lherzolite mantle source. Together with regional geology, these geochemical and geochronological data suggest that the mafic dykes in the HTB were formed in an intracontinental extensional setting during the late Triassic.

Attribution of the Langshan Tectonic Belt: Evidence from zircon U-Pb ages and Hf isotope compositions

This study describes a previously unidentified Neoproterozoic mafic dyke emplaced in the northern flank of the Langshan Tectonic Belt. This dyke intruded into the micaquartz schist of the Zhaertaishan Group, and yielded an age of 908 ± 8 Ma. The youngest U-Pb ages of micaquartz schist from the Zhaertaishan Group in the Langshan area were 1118 ± 33 Ma,1187 ± 3 Ma and 1189 ± 39 Ma,suggesting that the depositional age of the protolith of the schist was between 908 ± 8 Ma and 1118 ± 33 Ma. In addition, 436 U-Pb age data and 155 Lu-Hf isotopic data from six samples in the Langshan Tectonic Belt and one Permian greywacke from the Wuhai area show distinct differences between the northern and southern flanks of the Main Langshan area. The U-Pb ages of the northern flank are primarily Meso-Neoproterozoic; similar ages have not been identified in the southern flank to date.Moreover, two-stage Hf model ages of the northern flank feature three age peaks at ～900 Ma,～1700 Ma and ～2600 Ma; this differs from Hf model ages of the southern flank, which feature one strong age peak at ～2700 Ma. These results suggest that the northern and southern flanks of the Main Langshan area have different geochronologic characteristics and should be divided further. Based on the U-Pb ages and Hf model ages, the northern and southern flanks of the Main Langshan area are named the North and South Langshan Tectonic Belts. Comparison of the U-Pb age and two-stage Hf model age distributions from the North Langshan Tectonic Belt, South Langshan Tectonic Belt, Alxa Block and the North China Craton(NCC) reveal that the North Langshan Tectonic Belt is similar to the Alxa Block and that the South Langshan Tectonic Belt is similar to the NCC. In addition, the zircon U-Pb age of 860 ±7 Ma commonly observed in the Alxa Block was detected in the Permian greywacke from the Wuhai area of the NCC, which suggests that the amalgamation of the North and South Langshan Tectonic belts(i.e.,the amalgamation of the Alxa Block and the NCC), occurred between Devonian and late Permian.

Earthquake-induced Soft-sediment Deformation Structures in the Dengfeng Area,Henan Province,China:Constraints on Qinling Tectonic Evolution during the Early Cambrian

Soft-sediment deformation structures are abundant in the Cambrian Zhushadong and Mantou formations of the Dengfeng area, Henan Province, China. Soft-sediment deformation structures of the Zhushadong Formation consist of fluidized deformation, synsedimentary faults, seismo-folds and plastic deformation; the Mantou Formation is dominated by small-scale horst faults, intruded dikes, fluidized veins, and seismo-cracks. These structures are demonstrated to be earthquake-related by analysis of trigger mechanisms, and may indicate the activity of the Qinling tectonic belt during the early Cambrian. Furthermore, the assemblages of soft-sediment deformation structures altered with time： large-scale, intense deformation in the Zhushadong Formation alters to small-scale, weak deformation in the Mantou Formation. This striking feature may have been caused by changes in hypocentral depth from deep-focus to shallow-focus earthquakes, indicating that the Qinling tectonic belt developed from the subduction of the Shangdan Ocean to the extension of the Erlangping back-arc basin. This study suggests that soft-sediment deformation structures can be used to reveal the activity of a tectonic belt, and, more importantly, changes in deformation assemblages can track the evolution of a tectonic belt.

Research on the Terrane Tectonics in China

This paper summarizes the lalest advances in research on the terrane tectonics of China. The terranes of China distributed around various plates may be divided into four terrane belts of different ages and sizes, i. e., the East China, Northwest China, Southwest China and Qinling-Dabie terrane belts. Among them, the East China belt may be subdivided into three composite terrane groups; each terrane group is composed of several terranes that were formed roughly at the same time and have distinct geologic histories. The accretion of China’s terranes involves three types: the collision type, the flake-thrusting type, and the docking type. The results of the latest study in the five widening fields and some advances in the metheds of research on the terrane tectonics in China are presented in the present paper.

Palinspastic Reconstruction for Tectonics of Northeast China and Its Vicinity

Collision and amalgamation of continent and microcontinent block were recognized as one of the major processes for building up a continent. The pre Jurassic structure of Northeast China and its adjacent region (including south of Russia Far East, north of North Korea and inner part of southwest Japan) is characterized by collision and amalgamation of microcontinent blocks, such as the North China block (NCB), Northeast China block (NECB), Khanka block and Hida block.The central Jilin belt and Yanbian Grodekovsk belt that juxtapose and amalgamate these blocks in between in Northeast China and its vicinity were formed by a series of rock assemblages that are typical for Paleozoic active continental margin island arcs. The dominant Permian marine sequences in Yanbian (Yanbian Grodekovsk) belt, which are known for bearing transitional marine fauna, include turbidite olistostrome sediments of a slope facies, and limestones, sandstones as well as siltstones of a neritic littoral facies sediments along with predominant acidic to intermediate volcanic materials. The Maizuru belt in southwest Japan is supposed to be the equivalent of Yanbian Grodekovsk belt. The central Jilin belt consists of a well developed sedimentary sequence and volcanics of Paleozoic. The Bamiantong Gudonghe Fuerhe Chongjin suture complex in Northeast China and the equivalent Sangun Akiyoshi belt in southwest Japan serve as a major suture zone among these microcontinental blocks and belts.

Neoarchean granite-greenstone belts and related ore mineralization in the North China Craton:An overview

Tectonic processes involving amalgamations of microblocks along zones of ocean closure represented by granite-greenstone belts(GGB) were fundamental in building the Earth's early continents. The crustal growth and cratonization of the North China Craton(NCC) are correlated to the amalgamation of microblocks welded by 2.75-2.6 Ga and ~2.5 Ga GGBs. The lithological assemblages in the GGBs are broadly represented by volcano-sedimentary sequences, subduction-collision related granitoids and bimodal volcanic rocks(basalt and dacite) interlayered with minor komatiites and calc-alkalic volcanic rocks(basalt, andesite and felsic rock). The geochemical features of meta-basalts in the major GGBs of the NCC display affinity with N-MORB, E-MORB, OIB and calc-alkaline basalt, suggesting that the microblocks were separated by oceanic realm. The granitoid rocks display arc signature with enrichment of LILE(K,Rb, Sr, Ba) and LREE, and depletion of HFSE(Nb, Ta, Th, U, Ti) and HREE, and fall in the VAG field. The major mineralization includes Neoarchean BIF-type iron and VMS-type Cu-Zb deposits and these,together with the associated supracrustal rocks possibly formed in back-arc basins or arc-related oceanic slab subduction setting with or without input from mantle plumes. The 2.75-2.60 Ga TTG rocks,komatiites, meta-basalts and metasedimentary rocks in the Yanlingguan GGB are correlated to the upwelling mantle plume with eruption close to the continental margin within an ocean basin. The volcanosedimentary rocks and granitoid rocks in the late Neoarchean GGBs display formation ages of 2.60-2.48 Ga, followed by metamorphism at 2.52-2.47 Ga, corresponding to a typical modern-style subduction-collision system operating at the dawn of Proterozoic. The late Neoarchean komatiite(Dongwufenzi GGB), sanukitoid(Dongwufenzi GGB and Western Shandong GGB), BIF(Zunhua GGB) and VMS deposit(Hongtoushan-Qingyuan-Helong GGB) have closer connection to a combined process of oceanic slab subduction and mantle plume. The Neoarchean cratonization of the NCC appears to have involved two stages of tectonic process along the 2.75-2.6 Ga GGB and ~2.5 Ga GGBs, the former involve plume-arc interaction process, and the latter involving oceanic lithospheric subduction, with or without arcplume interaction.

Discovery and Genetic Mechanism of Basic Granulite in the Altay Orogenic Belt, Xinjiang, NW China

Altay granulite (AG), which represents the product of high-grade metamorphism in the lower crust, was newly found in the Wuqiagou area, Fuyun County in the Altay orogenic belt, Northwest China. It is composed mainly of hypersthene, augite, basic plagioclase, amphibole and brown biotite. Its mineral compositions of amphibole and biotite are rich in Mg/(Mg+Fe2+) and Ti. Geochemically, the AG is enriched in Mg/(Mg+Fe2+) and A12O3, and poor in CaO, with depletion of U, Th, K and Rb contents. Furthermore, geochemical data reflect that the protolith of the AG is igneous-genetic calc-alkaline basalt formed under an island arc environment. The AG has ZREE of 92.38-96.58 ppm and enriched LREE model with weak positive Eu anomaly of 1.09-1.15. In the MORB normalized spider diagram, the AG shows tri-doming pattern with a strong negative Nb anomaly and medium negative P and Ti anomalies, reflecting that the AG has tectonic relation with subduction or subduction-related materials. The P-T conditions of peak metamorphism of the AG are 750-780℃ and >0.6-0.7 GPa. Retrograde metamorphism implies that the protolith of the Altay granulite might undergo a metamorphic process along a clockwise P-T trajectory. Therefore, the formation and evolution of the AG may have a genetic association with continental collision/orogeny and the AG was taken into the Late Paleozoic meta-strata by way of tectonic emplacement.

Archaean Greenstone Belts in China

Chinese Achaean greenstone belts are mainly distributed along the northern and southwestern margins of the North China platform. In terms of their geological characteristics, the greenstone belts in China are comparable to those in other countries but at the same time have unique features of their own. In view of their geochemistry, the Chinese greenstone belts may be grouped into three types: the Jiapigou type, Qingyuan type and Xiaoqinling type. The greenstone belts were formed possibly in a rift-type palaeo-tectonic setting, similar to that of the modern island are-continental margin mobile belts.

Devonian alkaline magmatism in the northern North China Craton:Geochemistry,SHRIMP zircon U-Pb geochronology and Sr-Nd-Hf isotopes

The Wulanhada pluton is among the rare suite of Devonian alkaline plutons occurring along the northern margin of the North China Craton（NCC）.The intrusion is mainly composed of quartz-monzonite.Here we report zircon SHRIMP U-Pb data from this intrusion which shows emplacement age of ca.381.5 Ma.The rock is metaluminous with high（Na2O ＋ K2O） values ranging from 8.46 to 9.66 wt.%.The REE patterns of the rocks do not show any Eu anomaly whereas the primitive-mantle-normalized spider diagram shows strong positive Sr and Ba anomalies.The Wulanhada rocks exhibit high initial values of（87Sr/86Sr）t = 0.70762-0.70809,low εNd（t） =-12.76 to-12.15 values and negative values of εHf（t） =-23.49 to-17.02 with small variations in（176Hf/177Hf）,（0.281873-0.282049）.These geochemical features and quantitative isotopic modeling results suggest that the rocks might have been formed through the partial melting of Neoarchean basic rocks in the lower crust of the NCC.The Wulanhada rocks,together with the Devonian alkaline rocks and mafic-ultramafic complex from neighboring regions,constitute a post-collisional magmatic belt along the northern NCC.

Early Devonian Ultrapotassic Magmatism in the North China Craton: Geochemical and Isotopic Evidence for Subcontinental Lithospheric Mantle Metasomatism by Subducted Sediment–Derived Fluid

The North China Craton(NCC) represents one of the oldest and largest cratons in the earth with a nearly complete record of Precambrian history. In the northern part of the NCC, the earliest phase of alkaline magmatism occurred in discrete pulses in the Early and Middle Devonian;whereas the next episode of alkaline magmatism took place in the early Mesozoic. The Gucheng pluton is exposed in the northern part of the NCC and forms a composite intrusion, consisting of K-feldspar–bearing clinopyroxenite, clinopyroxene–bearing syenite and alkali-feldspar syenite. Mineral phases in these lithologies include clinopyroxene(Wo43-48En19-35Fs18-38), sanidine(An0 Ab3-11Or89-97), and subordinate titanite, andradite and Na-feldspar. These rocks show homogeneous Sr but variable Nd isotopic compositions, and have relatively high zircon in-situ oxygen isotopes(δ18O=5.2–6.7). The Gucheng plutonic rocks formed through fractional crystallization and accumulation from ultrapotassic magmas, which were originated from partial melting of metasomatic vein systems in the subcontinental lithospheric mantle of the NCC. These vein networks developed as a result of the reactions of fluids derived from subducted pelitic sediments on the downgoing Palaeo-Asian ocean floor with the enriched, subcontinental lithospheric mantle peridotites. SHRIMP U-Pb zircon dating has revealed a crystallization age of 415 Ma for the timing of the emplacement of the Gucheng pluton that marks the early stages of alkaline magmatism associated with the Andean-type continental margin evolution along the northern edge of the NCC facing the Palaeo-Asian Ocean.

Relationship between Crustal Structure and Tin Mineralization in South China

A close relationship between tin metallogenic and crustal structure in South China is demonstrated, which is based on a careful study on crustal structure and a detailed comparison between typical deposits in different tectonic units. Types, locations, emplacement of ore bodies and ore genesis of tin deposits are relative to crustal structure. Tin mineralization zones of South China can be divided into three tin metallogenic units including the west part corresponding to Youjiang fold belt, middle part corresponding to fold belt of Hunan Guangdong Jiangxi provinces and the east part corresponding to Southeast China coastal volcanic faulting depression. From the above, it is concluded that crustal compositions and structures are the main facts of Sn concentration in South China.

中国东部中生代上叠造山系

印支运动和燕山运动是中国东部中生代时期两次十分重要的造山运动。由这两次造山运动形成的构造带,既不是陈国达所说的地壳演化第三阶段的产物,也不是一些学者所谓的由板块内部动力产生的陆内(或板内)造山带。它们是在古太平洋动力体系作用下,在中国东部先成大陆地壳之上形成的上叠造山系,过去我们曾称其为中国东部滨太平洋大陆边缘活动(活化)带。中生代时期,在古太平洋动力体系作用下,于俄罗斯东北部—锡霍特阿林—日本—琉球—中国台湾—巴拉望一带形成亚洲东缘造山系,在邻接亚洲东部陆缘的中国东部大陆地壳之上形成中国东部上叠造山系。二者在同一动力体系作用下,同步发展,共同组成亚洲东部太平洋构造域规模宏大的巨型中生代造山系,彻底改变了亚洲东部印支造山前的构造面貌。

华北板块北缘东段库伦杂岩的发现及其构造意义

在华北板块北缘东段辽宁与内蒙古交界的库伦旗地区新发现了以晚古生代变质火山岩为主体的库伦杂岩.通过剖面测制,确定库伦杂岩岩石组合包括凝灰岩、安山岩及变沉积岩.凝灰岩锆石LA-ICP-MS U-Pb同位素测试结果为391.0±3.7 Ma,确定库伦杂岩形成时代为中泥盆世.地球化学特征显示库伦杂岩形成于晚期岛弧环境.通过对新发现的中泥盆世库伦杂岩及相关古生代的沉积事件、岩浆事件及变形的研究,结合本区古生代杂岩、岩浆岩及火山沉积地层研究成果,建立了华北板块北缘东段古生代增生型造山带的构造演化过程,其经历了志留纪活动大陆边缘阶段、泥盆纪弧-陆碰撞阶段、石炭纪-中二叠世活动大陆边缘阶段和晚二叠世碰撞造山阶段.志留系方家屯岩组、西别河岩组形成于弧后盆地环境,反映了奥陶纪-志留纪研究区处于活动大陆边缘环境;泥盆纪库伦杂岩火山-沉积为弧-陆碰撞结果,伴随伸展背景下的岩浆活动.石炭纪-中二叠世研究区在碰撞后伸展背景下重新拉张,接受了白家店岩组、酒局子岩组沉积并导致了佟家屯岩组火山岛弧的形成.晚二叠世古亚洲洋闭合,发生陆-陆碰撞,后造山作用延续到三叠纪.