The Nianzi granite unit,which includes the Nianzi,Xiaolianghou and Xiawopu granitic intrusions,is a significant component of the northern part of the North China Craton(NCC)and is situated in the Yanshan fold and thru...The Nianzi granite unit,which includes the Nianzi,Xiaolianghou and Xiawopu granitic intrusions,is a significant component of the northern part of the North China Craton(NCC)and is situated in the Yanshan fold and thrust belt(YFTB).However,there is still debate regarding the tectonic evolutionary history of the YFTB during the late Permian to Triassic period,specifically regarding the timing of subduction and collision between the NCC and the Paleo-Asian Ocean.The Nianzi granite unit exhibits unique petrological,geochronological and geochemical signatures that shed light on the tectonic evolutionary history of the YFTB.This study presents detailed petrology,whole-rock geochemistry,together with Sr-Nd isotopic,zircon U-Pb dating and Lu-Hf isotopic data of the granites within the Nianzi granite unit.Our findings demonstrate that the granites primarily consist of subhedral K-feldspar,plagioclase,quartz,minor biotite and hornblende,with accessory titanite,apatite,magnetite and zircon.Zircon U-Pb dating indicates that the Xiaolianghou granite was emplaced at 247.5±0.62 Ma.Additionally,the adakitic characteristics of the Nianzi,Xiawopu and Xiaolianghou granitic intrusions,such as high Sr and Ba contents and high ratios of Sr/Y and(La/Yb)N,combined with negative Sr-Nd and Lu-Hf isotopes(87Sr/86Sr)i=0.705681–0.7057433,εNd(t)=−21.98 to−20.97,zirconεHf(t)=−20.26 to−9.92,as well as the I-type granite features of high SiO_(2),Na_(2)O and K_(2)O/Na_(2)O ratios,enriched Rb,K,Sr and Ba,along with depleted Th,U,Nb,Ta,P and Ti,suggest that the Nianzi granitic unit was mainly derived from the partial melting of a thickened lower crust containing hydrous,calc-alkaline to high-K calc-alkaline,mafic to intermediate metamorphic rocks.In light of these parameters,we further integrate our data with previous studies and conclude that the Nianzi granitic unit was generated in a post-collisional extensional environment during the Early Triassic.展开更多
The eastern Qiulitagh fold and thrust belt （EQFTB） is part of the active Kuqa fold and thrust belts of the northern Tarim Basin. Seismic reflection profiles have been integrated with surface geologic and drill data ...The eastern Qiulitagh fold and thrust belt （EQFTB） is part of the active Kuqa fold and thrust belts of the northern Tarim Basin. Seismic reflection profiles have been integrated with surface geologic and drill data to examine the deformation and structure style of the EQFTB, particularly the deformational history of the Dina 2 gas field. Seismic interpretations suggest that Dongqiu 8 is overall a duplex structure developed beneath a passive roof thrust, which generated from a tipline in the Miocene Jidike Formation, and the sole thrust was initiated from the same Jidike Formation evaporite zone that extends westward beneath the Kuqatawu anticline. Dongqiu 5 is a pop-up structure at the western part of the EQFTB, also developed beneath the Jidike Formation evaporite. Very gentle basement dip and steep dipping topographic slope in the EQFTB suggest that the Jidike Formation salt provides effective decoupling. The strong deformation in the EQFTB appears to have developed further south, in an area where evaporite may be lacking. Since the Pliocene, the EQFTB has moved farther south over the evaporite and reached the Yaken area. Restoring a balanced cross-section suggests that the minimum shortening across the EQFTB is more than 7800 m. Assuming that this shortening occurred during the 5.3 Ma timespan, the shortening rate is approximately 1.47 mm/year.展开更多
Geochemical and geochronological studies have been carry out on the leucosomes of Yaoundé series with the aims to identify the magma sources and to indicate their production periods and emplacement within the for...Geochemical and geochronological studies have been carry out on the leucosomes of Yaoundé series with the aims to identify the magma sources and to indicate their production periods and emplacement within the formations of the Pan-African North-Equatorial Fold Belt (PANEFB) in Cameroon. The Yaoundé series belongs to the Southern domain of the PANEFB and it is composed of migmatites in which two types of granitic leucosomes (in situ leucosomes and injected leucosomes) have been distinguished. These rocks display characteristic of calc-alkaline (in situ leucosomes) and high-K calc-alkaline to shoshonitic series (injected leucosomes). All the rocks are peraluminous with in situ leucosomes conform to S-type and injected leucosomes conform to I- and S-type granitoids. Major and trace elements composition reveal that in situ leucosomes derived from the partial melting of the host metapelite whereas injected leucosomes derived from the melting of metagreywacke. These sources are similar to those of granitoids from central and northern domains of the PANEFB. Th-U-Pb dating by electron microprobe (EMP) and LA-ICP-MS U-Pb dating on zircon have been used to constraints the melting event and emplacement of leucosomes in Yaoundé series. Th-U-Pb monazite dating, undertaken in two samples of leucosomes, gives two groups of monazite ages. The older group gives an age of 658 Ma whereas the age of younger group is 592 Ma. U-Pb dating of zircons from the leucosomes reveals a Pan-African age ranging from 626 to 654 Ma whereas zircons from metapelitic host rock reveal the overprinting of an early Pan-African event 911 - 1127 Ma on Palaeoproterozoic (2127 Ma) inheritance. These data clearly indicate that the host rocks of leucosomes of Yaoundé series have been firstly metamorphosed during Tonien-Stenien period (911 - 1127 Ma) and reveal the existence of extended unique melting event (592 and 658 Ma) in the Yaoundé series which is contemporaneous with the magmatism responsible for the emplacement of granitoids in the other domains of the PANEFB.展开更多
Upper Cretaceous Kawagarh Formation is well exposed in the Attock Hazara Fold and Thrust Belt (AHFTB) and shows significant lateral and vertical variations in lithology. The present work deals with the sedimentologica...Upper Cretaceous Kawagarh Formation is well exposed in the Attock Hazara Fold and Thrust Belt (AHFTB) and shows significant lateral and vertical variations in lithology. The present work deals with the sedimentological studies of marl and marly limestone sequence of Kawagarh Formation exposed at the Bagh Neelab, Ghariala north and Sojhanda villages in Northern Kalachitta Range. Detailed petrographic studies of marly limestone and hard marl substrate show that planktons and oysters are the main skeletal constituents of studied samples and clay and detrital quartz mainly composed the non skeletal fraction. X-Ray diffraction analyses of selected marl samples confirm the petrographic data. On the basis of skeletal and non skeletal content, two microfacies—marl microfacies and Planktonic microfacies are constructed. The faunal content, their paleoecology and detrital content of microfacies suggest that marl and marly limestone sequence of Kawagarh Formation was deposited over the mid and outer ramp settings.展开更多
Triangle zones, generally found in foreland fold-and-thrust belts, serve as favorable objects of petroleum exploration. Taking the Dabashan foreland belt as an example, we studied the formation and development of tria...Triangle zones, generally found in foreland fold-and-thrust belts, serve as favorable objects of petroleum exploration. Taking the Dabashan foreland belt as an example, we studied the formation and development of triangle zones, and investigated the effect of d^collements and the mechanical contrast of lithology by employing the method of physical modeling. Four experimental models were conducted in the work. The results showed that ＇sand wedges＇ grew episodically, recorded by deformational length, height and slope angle. The height versus shortening rate presented an S-shape curve, and uplifting occurred successively in the direction of the foreland belt. During the formation of the triangle zone, layer-parallel shortening took place at the outset; deformation decoupling then occurred between the upper and lower brittle layers, divided by a middle-embedded silicone polymers layer. The upper brittle layers deformed mainly by folding, while the lower sand layers by thrusting. As shortening continued, the geometry of a triangle zone was altered. We consider that the triangle zone in the Dabashan foreland belt was modified from an early one based on available seismic profiles and the experimental results. In addition, dccollements and mechanical contrast impose significant influence on structural development, which can directly give rise to structural discrepancies. More d^collements and obvious mechanical contrast between brittle layers can promote the coupling between the upper and lower brittle layers. Basal d^collement controls the whole deformation and decreases the slope angle of the wedge, while roof d^collement determines whether a triangle zone can be formed.展开更多
The tectono-stratigraphic sequences of the Kuqa foreland fold-thrust belt in the northern Tarim basin, northwest China, can be divided into the Mesozoic sub-salt sequence, the Paleocene-Eocene salt sequence and the Ol...The tectono-stratigraphic sequences of the Kuqa foreland fold-thrust belt in the northern Tarim basin, northwest China, can be divided into the Mesozoic sub-salt sequence, the Paleocene-Eocene salt sequence and the Oligocene-Quaternary supra-salt sequence. The salt sequence is composed mainly of light grey halite, gypsum, marl and brown elastics. A variety of salt-related structures have developed in the Kuqa foreland fold belt, in which the most fascinating structures are salt nappe complex. Based on field observation, seismic interpretation and drilling data, a large-scale salt nappe complex has been identified. It trends approximately east-west for over 200 km and occurs along the west Qiulitag Mountains. Its thrusting displacement is over 30 km. The salt nappe complex appears as an arcuate zone projecting southwestwards along the leading edge of the Kuqa foreland fold belt. The major thrust fault is developed along the Paleocene-Eocene salt beds. The allochthonous nappes comprise large north-dipping faulting monoclines which are made up of Paleocene-Pliocene sediments. Geological analysis and cross-section restoration revealed that the salt nappes were mainly formed at the late Himalayan stage (c.a. 1.64 Ma BP) and have been active until the present day. Because of inhomogeneous thrusting, a great difference may exist in thrust displacement, thrust occurrence, superimposition of allochthonous and autochthonous sequences and the development of the salt-related structures, which indicates the segmentation along the salt nappes. Regional compression, gravitational gliding and spreading controlled the formation and evolution of the salt nappe complex in the Kuqa foreland fold belt.展开更多
Recent discoveries of ophiolites indicate that there must be a Palaeotethyan geosuture zone bordering China and Vietnam, which separates the Vietbac block from the South China subcontinent. The Indosinian foreland fol...Recent discoveries of ophiolites indicate that there must be a Palaeotethyan geosuture zone bordering China and Vietnam, which separates the Vietbac block from the South China subcontinent. The Indosinian foreland fold-and-thrust belt bordering Yunnan and Guangxi provided further evidence for the palaeotethysides. The oceanic crust was subducted southwestwards while the magmatic arc migrated northeastwards, and the continent-arc collision occurred in the Late Triassic with the thrusting being extended towards the north or northeast. The features of thrust-nappe structure are discussed, which proved the continental margin of the Palaeotethyan ocean there to be a complicated one. A face-to-face collision occurred first along the NW-striking segment and then along the ENE-striking segment accompanied by transpression or oblique thrusting occurring along the NW-striking one.展开更多
The Central Africa Fold Belt(CAFB)is a collision belt endowed with gold deposits in Eastern Cameroon area mined for about 50 years.However,favorable areas for gold exploration are poorly known.This paper presents(1)th...The Central Africa Fold Belt(CAFB)is a collision belt endowed with gold deposits in Eastern Cameroon area mined for about 50 years.However,favorable areas for gold exploration are poorly known.This paper presents(1)the kinematics of the brittle deformation in the Kékem area in the SW portion of the Central Cameroon Shear Zone and(2)constraints gold mineralization events with respect to the collisional evolution of the CAFB.The authors interpret that the conjugate ENE to E and NNW to NW trending lineament corresponds to the synthetic(R)and the antithetic(R’)shears,which accompanied the dextral slip along the NE to ENE striking shear.The latter coincides with the last 570-552 Ma D3 dextral simple shear-dominated transpression,which is parallel to the BétaréOya shear zone hosting gold deposits.Gold mineralizations,which mainly occurred during the last dextral shearing,are disseminated within quartz veins associated to Riedel’s previous structures reactivated due to late collisional activities of the CAFB as brittle deformation.Gold mineralizations occurred mainly during the 570-552 Ma D3 event.The reactivation,which might be due to dextral simple shear during mylonitzation,plausibly remobilized the early gold deposits hosted in syn-compressional rocks and/or possibly focused deep-sourced fluid mixed with those released by dehydration.Therefore,the Central Cameroon Shear Zone where Kékem is located,and which shows similar petrographical and structural features to those controling Batouri gold district,is a target area for gold exploration in Cameroon.展开更多
The evolution of the Tarim southwest depression lying at the piedmont of the West Kunlun orogen differs completely from the evolution of the main part of Tarim basin after Later Palaeozoic because the former strongly ...The evolution of the Tarim southwest depression lying at the piedmont of the West Kunlun orogen differs completely from the evolution of the main part of Tarim basin after Later Palaeozoic because the former strongly subsides many times.. Subsidence is related closely to the West Kunlun fold thrust\|belt, thus the evolution of the Depression and the fold\|thrust\|belt reflects clearly the formation and evolution of the West Kunlun and even the Tibet.1 Evolution of the West Kunlun fold\|thrust\|belt\;Thrusting of the fold\|thrust\|belt can be classified into three stages:(1) Devonian thrusting:This is the oldest thrusting distinguished in the northern margin of the West Kunlun while the Silurian—Devonian thrusting was discriminated a few years ago by seismic data in the northern part of the East Kunlun. The Devonian thrusting is proved by the Upper Devonian dynamometamorphic rocks outcropping at the core of the anticline in the Sangzhu lying at the fold\|thrust\|belt. The rocks consist of slightly metamorphic clastic rock and have always been regarded as the Mid\|Proterozoic strata. But they are actually Upper Devonian strata according to the amount of perfect plant fossils that we found recently in the metamorphic rock, and they are overburdened `with an angular unconformity by another reliable Upper\|Devonian conglomerate in the core of the Aqike anticline. A possible explanation for this and its limited lined distribution parallel to the West Kunlun orogen is that they are subjected to metamorphism during the Later Devonian thrusting.展开更多
The Ordovician volcanic rocks in the Mayaxueshan area have been pervasivelyaltered or metamorphosed and contain abundant secondary minerals such as albite, chlorite, epidote,prehnite, pumpellyite, actinolite, titanite...The Ordovician volcanic rocks in the Mayaxueshan area have been pervasivelyaltered or metamorphosed and contain abundant secondary minerals such as albite, chlorite, epidote,prehnite, pumpellyite, actinolite, titanite, quartz, and/or calcite. They were denoted as spilitesor spilitic rocks in terms of their petrographic features and mineral assemblages. The metamorphicgrades of the volcanic rocks are equivalent to that of the intercalated metaclastic rocks. Thisindicates that both the spilitic volcanic rocks and metaclastic rocks in the Mayaxueshan area haveformed as a result of Caledonian regional metamorphism. We suggest that the previously denotedspilitic rocks or altered volcanic rocks should be re-denoted as metabasalts or metabasaltic rocks.The metamorphic grade of the volcanic rocks increases with their age: prehnite-pumpellyite faciesfor the upper part of the Middle Ordovician volcanic rocks, prehnite-pumpellyite to lowergreenschist facies for the lower part of the Middle Ordovician volcanic rocks, and lower greenschistfacies for the Lower Ordovician volcanic rocks. The P-T conditions are estimated as T = 240 - 290deg C and P = 1.5-4.5 kbar for the lower part of the Middle Ordovician rocks, and T = approx 300 degC for the Lower Ordovician rocks. The variations of mineral assemblages occurring at differentdomains of the volcanic rocks were controlled by the variations of the effective bulk composition inthose domains during metamorphism. The geochemical characteristics of Mg-Al chromite in theMayaxueshan volcanic rocks are consistent with an origin of island arc environment.展开更多
The Songpan Garzê Fold Belt records Triassic shortening of a relict Palaeo\|Tethyan basin during assembly and accretion of the Cimmerian continental chain to Laurasia’s southern margin. Enclosed by palaeo\|Laura...The Songpan Garzê Fold Belt records Triassic shortening of a relict Palaeo\|Tethyan basin during assembly and accretion of the Cimmerian continental chain to Laurasia’s southern margin. Enclosed by palaeo\|Laurasia and the Cimmerian fragments of Qiangtang (North Tibet) and Yangtze (South China), the Songpan Garzê Fold Belt was shortened by more than 50% during the Indosinian Orogeny c.200Ma. [BW(D(S,,)G2*7][BHDWG2*7,WK*2,WK5,WK15*2,WK17*2,WK*2W] 2000,7(增刊) 地 学 前 缘 [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau [BW(S(S,,)G2*7][BHDWG2*7,WK*2,WK17*2,WK15*2,WK5,WK*2W] [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau 地 学 前 缘 2000,7(增刊)South\|directed Indosinian compression decolléd onlapping basin sediments from the Yangtze Block’s passive margin—reactivating the margin’s tiered geometry and partitioning strain into margin\|normal and margin\|parallel structures on a large scale. Margin\|normal transport of the allochthonous sedimentary pile was accommodated by southeast\|directed nappe propagation in the Longmen Mountains Thrust—Nappe Belt, whilst conjugate, margin\|parallel (southwest\|directed) transport was accommodated by a flat\|lying detachment at the base of the sedimentary pile.The later is characteristic of deformation of the greater Songpan Garzê Fold Belt.展开更多
The Fomopea granitic pluton is emplaced in gnessic and amphibolitic basement. These gneissic and amphibolitic basement rocks are represented in the pluton＇s body as sub-rounded, elongated or stretched xenoliths. Amph...The Fomopea granitic pluton is emplaced in gnessic and amphibolitic basement. These gneissic and amphibolitic basement rocks are represented in the pluton＇s body as sub-rounded, elongated or stretched xenoliths. Amphibolitic xenoliths display testimonies of two main tectonic events namely： （i） El flattening deformation event characterized by a NW-SE to E-W foliation with a best pole at 246/57 and a mineral stretched lineation with a best line at 293/47; and （ii） E2 compressive event typified by （1） N-S to NNE-SSW steeply dipping foliation; （2） S-type flexion-fold indicating a sinistral shear movement. These amphibolite rocks indicate a magnetic susceptibility magnitude （Km） range from 418 ~SI to 90092 IISI for 87% of the stations showing a ferromagnetic behavior. K-T curves reveal the presence of Ti-poor magnetite as susceptibility mineral carrier. Magnetic foliation and lineation suggest that the N-S strike direction observed in the Bamendou amphibolite is, as pointed out elsewhere in the Central African Fold Belt, of paramount importance in the tectonic evaluation of the Fomopea area, since it has most likely acted as major deformation phase in the second tectonic event in the belt.展开更多
Whether there existed the Songpan-Garze massif is a controversial problem. This paper expounds and proves that the old basement of the massif is represented by the pre-Sinian granitic rock series. This massif and the ...Whether there existed the Songpan-Garze massif is a controversial problem. This paper expounds and proves that the old basement of the massif is represented by the pre-Sinian granitic rock series. This massif and the South Qinling fold belt might both be a part of the old Yangtze platform. Rifting generated by the Caledonian orogeny in the terminal Early Palaeozoic caused the massif to be disintegrated from the northwestern part of the Yangtze platform. This disintegration, however, was not thorough, and the rift troughs were later gradually closed and filled up. The Emei taphrogeny that was initiated in the Early Permian Maokou' an Stage involved a second disintegration of this massif from the Yangtze platform. The rift line largely goes along the Muli-Pingwu line. This rifting belongs to synchronous extensional rifting at peripheries of the Yangtze platform and in its interior, showing that the posterior, lateral and interior extension resulting from rapid northward shift of the Yangtze platform led to isolation of this massif together with South Qinling from their adjacent areas. During the Ladinian Stage, the Songpan-Garze massif and southern Qinling sank strongly en masse. This subsidence continued till the end of the Late Triassic when the late Indosinian movement caused the sea trough to be closed and Songpan-Garze1 and southern Qinling to be folded and uplifted and become mountains.展开更多
Bafia Group is part of the southernmost portion of the Central African Fold Belt (CAFB) in Cameroon. The geological feature of the group is characterized by the presence of metamorphic rocks in which tourmaline had be...Bafia Group is part of the southernmost portion of the Central African Fold Belt (CAFB) in Cameroon. The geological feature of the group is characterized by the presence of metamorphic rocks in which tourmaline had been recognized among accessory minerals. In the present study, attention is focus on the tourmaline bearing quartzite to the southeast of Kombé II. Structure refinement shows that tourmaline is a Fe-dravite with the formula X(Na<sub>0.95</sub>[]<sub>0.05</sub>)Y(Mg<sub>2.39</sub>Fe<sub>0.61</sub>)Z(Al<sub>5.10</sub>Mg<sub>0.90</sub>)(BO<sub>3</sub>)<sub>3</sub>T[Si<sub>6</sub>O<sub>18</sub>](OH)<sub>3</sub>[(O,OH)<sub>0.88</sub>F<sub>0.12</sub>]. The Fe-dravite is hosted in a Ca-poor quartzite, which is made up, in addition to quartz and tourmaline, of biotite and muscovite. The structure of the dravites shows a low vacancy at the X site, which militates for a crystallization of the tourmaline at a high temperature > 750℃. This is in agreement with previous work which shows that the metamorphic peak in the associated biotite gneiss reaches 825℃. The R1 value of 1.24% means that the crystal structure of the tourmalines is of high quality. The genetical link between gold mineralization and tourmaline should stimulate exploration interest in the study area.展开更多
Mesoproterozoic North Delhi fold belt of NW Indian shield comprises three volcano-sedimentary basins viz. Bayana, Alwar and Khetri aligned parallel to each other from east to west. Each basin contains excellent exposu...Mesoproterozoic North Delhi fold belt of NW Indian shield comprises three volcano-sedimentary basins viz. Bayana, Alwar and Khetri aligned parallel to each other from east to west. Each basin contains excellent exposures of mafic volcanic rocks. Major, trace and rare earth element abundances of volcanic rocks of the three basins are significantly diverse. Bayana and Alwar volcanics are tholeiites bearing close similarity with low Ticontinental flood basalts. However, Bayana volcanics are characteristically enriched in incompatible trace elements and REEs while Alwar volcanics display least enriched incompatible trace element abundances and flat REE patterns. The Khetri volcanics exhibit a transitional composition between tholeiite and calc-alkaline basalts. REE based source modeling suggests that Bayana suite was formed from the melts derived from 1 % to 10 %(avg.4 %) of the partial melting of a spinel lherzolite source giving a residual mineralogy of 56 % Olv, 25 % Opx and19 % Cpx. Whereas Alwar suite evolved through 12 %–20 %(avg. 15 %) partial melting of the same source with a residual mineralogy 61 % Olv, 25 % Opx and 14 % Cpx.Khetri volcanics are exposed at two localities Kolihan and Madhan–Kudhan. The Kolihan volcanics were derived from 1 % to 6 %(avg. 4 %) partial melting with residualmineralogy 56 % Olv, 25 % Opx and 19 % Cpx whereas the magma of Madhan Kudhan volcanic suite was generated by 15%–30 % partial melting of the same source leaving behind 64 % Olv, 25 % Opx and 11 % Cpx as residual mineralogy. This source modeling proves that melts of Bayana and Alwar tholeiites were generated by partial melting of a common source within the spinel stability field under the influence of mantle plume. During the course of ascent, Bayana melts were crustally contaminated but Alwar melts remained unaffected. There was two tier magma production in Khetri region, one from the partial melting of the mantle wedge overlying the subducted oceanic plate which formed Kolihan suite and two the melting of the subducted plate itself generating Madhan–Kudhan volcanics. It is interpreted that during Mesoproterozoic(1,800 Ma), the continental lithosphere of NW Indian shield suffered stretching, attenuation and fracturing in response to a rising plume. Consequently, differential crustal extension coupled with variable attenuation brought the asthenosphere to shallower setting which led to the production of tholeiitic melts. These melts enroute to the surface suffered variable lithospheric contamination depending upon the thickness of traversed crust. The Khetri basin attained maturity which resulted in the generation of true oceanic crust and its subsequent destruction through subduction. The spatial existence of three suites of mafic volcanics of diverse chemical signatures is best example of subduction–plume interaction. It is therefore, proposed that the Mesoproterozoic crust of NW Indian shield has evolved through the operation of a complete Wilson cycle at about1,832 Ma, the age of mafic volcanics of Khetri basin.展开更多
The map expression of ＂abrupt＂ changes in lateral stratigraphic level of a thrust fault has been traditionally interpreted to be a result of the presence of （1） a lateral （or oblique） thrust-ramp, or （2） a fro...The map expression of ＂abrupt＂ changes in lateral stratigraphic level of a thrust fault has been traditionally interpreted to be a result of the presence of （1） a lateral （or oblique） thrust-ramp, or （2） a frontal ramp with displacement gradient, and/or （3） a combination of these geometries. These geometries have been used to interpret the structures near transverse zones in fold-thrust belts （FTB）. This contribution outlines an alternative explanation that can result in the same map pattern by lateral variations in stratigraphy along the strike of a low angle thrust fault. We describe the natural example of the Leamington transverse zone, which marks the southern margin of the Pennsylvanian-Permian Oquirrh basin with genetically related lateral stratigraphic variations in the North American Sevier FTB. Thus, the observed map pattern at this zone is closely related to lateral stratigraphic variations along the strike of a horizontal fault. Even though the present-day erosional level shows the map pattern that could be interpreted as a lateral ramp, the observed structures along the Leamington zone most likely share the effects of the presence of a lateral （or oblique） ramp, lateral stratigraphic variations along the fault trace, and the displacement gradient.展开更多
基金funded by the National Natural Science Foundation of China(41872232)the Beijing Geological Survey Project(PXM 2016-158203-000008,PXM 2018-158203-000014)the Beijing Innovation Studio(Urban Geology,Active Structure,and Monitoring).
文摘The Nianzi granite unit,which includes the Nianzi,Xiaolianghou and Xiawopu granitic intrusions,is a significant component of the northern part of the North China Craton(NCC)and is situated in the Yanshan fold and thrust belt(YFTB).However,there is still debate regarding the tectonic evolutionary history of the YFTB during the late Permian to Triassic period,specifically regarding the timing of subduction and collision between the NCC and the Paleo-Asian Ocean.The Nianzi granite unit exhibits unique petrological,geochronological and geochemical signatures that shed light on the tectonic evolutionary history of the YFTB.This study presents detailed petrology,whole-rock geochemistry,together with Sr-Nd isotopic,zircon U-Pb dating and Lu-Hf isotopic data of the granites within the Nianzi granite unit.Our findings demonstrate that the granites primarily consist of subhedral K-feldspar,plagioclase,quartz,minor biotite and hornblende,with accessory titanite,apatite,magnetite and zircon.Zircon U-Pb dating indicates that the Xiaolianghou granite was emplaced at 247.5±0.62 Ma.Additionally,the adakitic characteristics of the Nianzi,Xiawopu and Xiaolianghou granitic intrusions,such as high Sr and Ba contents and high ratios of Sr/Y and(La/Yb)N,combined with negative Sr-Nd and Lu-Hf isotopes(87Sr/86Sr)i=0.705681–0.7057433,εNd(t)=−21.98 to−20.97,zirconεHf(t)=−20.26 to−9.92,as well as the I-type granite features of high SiO_(2),Na_(2)O and K_(2)O/Na_(2)O ratios,enriched Rb,K,Sr and Ba,along with depleted Th,U,Nb,Ta,P and Ti,suggest that the Nianzi granitic unit was mainly derived from the partial melting of a thickened lower crust containing hydrous,calc-alkaline to high-K calc-alkaline,mafic to intermediate metamorphic rocks.In light of these parameters,we further integrate our data with previous studies and conclude that the Nianzi granitic unit was generated in a post-collisional extensional environment during the Early Triassic.
基金supported by the National Major Fundamental Research and Development Project of China(no.:19990433).
文摘The eastern Qiulitagh fold and thrust belt （EQFTB） is part of the active Kuqa fold and thrust belts of the northern Tarim Basin. Seismic reflection profiles have been integrated with surface geologic and drill data to examine the deformation and structure style of the EQFTB, particularly the deformational history of the Dina 2 gas field. Seismic interpretations suggest that Dongqiu 8 is overall a duplex structure developed beneath a passive roof thrust, which generated from a tipline in the Miocene Jidike Formation, and the sole thrust was initiated from the same Jidike Formation evaporite zone that extends westward beneath the Kuqatawu anticline. Dongqiu 5 is a pop-up structure at the western part of the EQFTB, also developed beneath the Jidike Formation evaporite. Very gentle basement dip and steep dipping topographic slope in the EQFTB suggest that the Jidike Formation salt provides effective decoupling. The strong deformation in the EQFTB appears to have developed further south, in an area where evaporite may be lacking. Since the Pliocene, the EQFTB has moved farther south over the evaporite and reached the Yaken area. Restoring a balanced cross-section suggests that the minimum shortening across the EQFTB is more than 7800 m. Assuming that this shortening occurred during the 5.3 Ma timespan, the shortening rate is approximately 1.47 mm/year.
文摘Geochemical and geochronological studies have been carry out on the leucosomes of Yaoundé series with the aims to identify the magma sources and to indicate their production periods and emplacement within the formations of the Pan-African North-Equatorial Fold Belt (PANEFB) in Cameroon. The Yaoundé series belongs to the Southern domain of the PANEFB and it is composed of migmatites in which two types of granitic leucosomes (in situ leucosomes and injected leucosomes) have been distinguished. These rocks display characteristic of calc-alkaline (in situ leucosomes) and high-K calc-alkaline to shoshonitic series (injected leucosomes). All the rocks are peraluminous with in situ leucosomes conform to S-type and injected leucosomes conform to I- and S-type granitoids. Major and trace elements composition reveal that in situ leucosomes derived from the partial melting of the host metapelite whereas injected leucosomes derived from the melting of metagreywacke. These sources are similar to those of granitoids from central and northern domains of the PANEFB. Th-U-Pb dating by electron microprobe (EMP) and LA-ICP-MS U-Pb dating on zircon have been used to constraints the melting event and emplacement of leucosomes in Yaoundé series. Th-U-Pb monazite dating, undertaken in two samples of leucosomes, gives two groups of monazite ages. The older group gives an age of 658 Ma whereas the age of younger group is 592 Ma. U-Pb dating of zircons from the leucosomes reveals a Pan-African age ranging from 626 to 654 Ma whereas zircons from metapelitic host rock reveal the overprinting of an early Pan-African event 911 - 1127 Ma on Palaeoproterozoic (2127 Ma) inheritance. These data clearly indicate that the host rocks of leucosomes of Yaoundé series have been firstly metamorphosed during Tonien-Stenien period (911 - 1127 Ma) and reveal the existence of extended unique melting event (592 and 658 Ma) in the Yaoundé series which is contemporaneous with the magmatism responsible for the emplacement of granitoids in the other domains of the PANEFB.
文摘Upper Cretaceous Kawagarh Formation is well exposed in the Attock Hazara Fold and Thrust Belt (AHFTB) and shows significant lateral and vertical variations in lithology. The present work deals with the sedimentological studies of marl and marly limestone sequence of Kawagarh Formation exposed at the Bagh Neelab, Ghariala north and Sojhanda villages in Northern Kalachitta Range. Detailed petrographic studies of marly limestone and hard marl substrate show that planktons and oysters are the main skeletal constituents of studied samples and clay and detrital quartz mainly composed the non skeletal fraction. X-Ray diffraction analyses of selected marl samples confirm the petrographic data. On the basis of skeletal and non skeletal content, two microfacies—marl microfacies and Planktonic microfacies are constructed. The faunal content, their paleoecology and detrital content of microfacies suggest that marl and marly limestone sequence of Kawagarh Formation was deposited over the mid and outer ramp settings.
文摘Triangle zones, generally found in foreland fold-and-thrust belts, serve as favorable objects of petroleum exploration. Taking the Dabashan foreland belt as an example, we studied the formation and development of triangle zones, and investigated the effect of d^collements and the mechanical contrast of lithology by employing the method of physical modeling. Four experimental models were conducted in the work. The results showed that ＇sand wedges＇ grew episodically, recorded by deformational length, height and slope angle. The height versus shortening rate presented an S-shape curve, and uplifting occurred successively in the direction of the foreland belt. During the formation of the triangle zone, layer-parallel shortening took place at the outset; deformation decoupling then occurred between the upper and lower brittle layers, divided by a middle-embedded silicone polymers layer. The upper brittle layers deformed mainly by folding, while the lower sand layers by thrusting. As shortening continued, the geometry of a triangle zone was altered. We consider that the triangle zone in the Dabashan foreland belt was modified from an early one based on available seismic profiles and the experimental results. In addition, dccollements and mechanical contrast impose significant influence on structural development, which can directly give rise to structural discrepancies. More d^collements and obvious mechanical contrast between brittle layers can promote the coupling between the upper and lower brittle layers. Basal d^collement controls the whole deformation and decreases the slope angle of the wedge, while roof d^collement determines whether a triangle zone can be formed.
基金This research received financial supports from the National Natural Science Foundation of China(grant 40172076)the National Major Fundamental Research and Development Project(grant G1999043305)the National Key Project of the Ninth Five—Year Plan(grant 99—1111)
文摘The tectono-stratigraphic sequences of the Kuqa foreland fold-thrust belt in the northern Tarim basin, northwest China, can be divided into the Mesozoic sub-salt sequence, the Paleocene-Eocene salt sequence and the Oligocene-Quaternary supra-salt sequence. The salt sequence is composed mainly of light grey halite, gypsum, marl and brown elastics. A variety of salt-related structures have developed in the Kuqa foreland fold belt, in which the most fascinating structures are salt nappe complex. Based on field observation, seismic interpretation and drilling data, a large-scale salt nappe complex has been identified. It trends approximately east-west for over 200 km and occurs along the west Qiulitag Mountains. Its thrusting displacement is over 30 km. The salt nappe complex appears as an arcuate zone projecting southwestwards along the leading edge of the Kuqa foreland fold belt. The major thrust fault is developed along the Paleocene-Eocene salt beds. The allochthonous nappes comprise large north-dipping faulting monoclines which are made up of Paleocene-Pliocene sediments. Geological analysis and cross-section restoration revealed that the salt nappes were mainly formed at the late Himalayan stage (c.a. 1.64 Ma BP) and have been active until the present day. Because of inhomogeneous thrusting, a great difference may exist in thrust displacement, thrust occurrence, superimposition of allochthonous and autochthonous sequences and the development of the salt-related structures, which indicates the segmentation along the salt nappes. Regional compression, gravitational gliding and spreading controlled the formation and evolution of the salt nappe complex in the Kuqa foreland fold belt.
文摘Recent discoveries of ophiolites indicate that there must be a Palaeotethyan geosuture zone bordering China and Vietnam, which separates the Vietbac block from the South China subcontinent. The Indosinian foreland fold-and-thrust belt bordering Yunnan and Guangxi provided further evidence for the palaeotethysides. The oceanic crust was subducted southwestwards while the magmatic arc migrated northeastwards, and the continent-arc collision occurred in the Late Triassic with the thrusting being extended towards the north or northeast. The features of thrust-nappe structure are discussed, which proved the continental margin of the Palaeotethyan ocean there to be a complicated one. A face-to-face collision occurred first along the NW-striking segment and then along the ENE-striking segment accompanied by transpression or oblique thrusting occurring along the NW-striking one.
文摘The Central Africa Fold Belt(CAFB)is a collision belt endowed with gold deposits in Eastern Cameroon area mined for about 50 years.However,favorable areas for gold exploration are poorly known.This paper presents(1)the kinematics of the brittle deformation in the Kékem area in the SW portion of the Central Cameroon Shear Zone and(2)constraints gold mineralization events with respect to the collisional evolution of the CAFB.The authors interpret that the conjugate ENE to E and NNW to NW trending lineament corresponds to the synthetic(R)and the antithetic(R’)shears,which accompanied the dextral slip along the NE to ENE striking shear.The latter coincides with the last 570-552 Ma D3 dextral simple shear-dominated transpression,which is parallel to the BétaréOya shear zone hosting gold deposits.Gold mineralizations,which mainly occurred during the last dextral shearing,are disseminated within quartz veins associated to Riedel’s previous structures reactivated due to late collisional activities of the CAFB as brittle deformation.Gold mineralizations occurred mainly during the 570-552 Ma D3 event.The reactivation,which might be due to dextral simple shear during mylonitzation,plausibly remobilized the early gold deposits hosted in syn-compressional rocks and/or possibly focused deep-sourced fluid mixed with those released by dehydration.Therefore,the Central Cameroon Shear Zone where Kékem is located,and which shows similar petrographical and structural features to those controling Batouri gold district,is a target area for gold exploration in Cameroon.
文摘The evolution of the Tarim southwest depression lying at the piedmont of the West Kunlun orogen differs completely from the evolution of the main part of Tarim basin after Later Palaeozoic because the former strongly subsides many times.. Subsidence is related closely to the West Kunlun fold thrust\|belt, thus the evolution of the Depression and the fold\|thrust\|belt reflects clearly the formation and evolution of the West Kunlun and even the Tibet.1 Evolution of the West Kunlun fold\|thrust\|belt\;Thrusting of the fold\|thrust\|belt can be classified into three stages:(1) Devonian thrusting:This is the oldest thrusting distinguished in the northern margin of the West Kunlun while the Silurian—Devonian thrusting was discriminated a few years ago by seismic data in the northern part of the East Kunlun. The Devonian thrusting is proved by the Upper Devonian dynamometamorphic rocks outcropping at the core of the anticline in the Sangzhu lying at the fold\|thrust\|belt. The rocks consist of slightly metamorphic clastic rock and have always been regarded as the Mid\|Proterozoic strata. But they are actually Upper Devonian strata according to the amount of perfect plant fossils that we found recently in the metamorphic rock, and they are overburdened `with an angular unconformity by another reliable Upper\|Devonian conglomerate in the core of the Aqike anticline. A possible explanation for this and its limited lined distribution parallel to the West Kunlun orogen is that they are subjected to metamorphism during the Later Devonian thrusting.
文摘The Ordovician volcanic rocks in the Mayaxueshan area have been pervasivelyaltered or metamorphosed and contain abundant secondary minerals such as albite, chlorite, epidote,prehnite, pumpellyite, actinolite, titanite, quartz, and/or calcite. They were denoted as spilitesor spilitic rocks in terms of their petrographic features and mineral assemblages. The metamorphicgrades of the volcanic rocks are equivalent to that of the intercalated metaclastic rocks. Thisindicates that both the spilitic volcanic rocks and metaclastic rocks in the Mayaxueshan area haveformed as a result of Caledonian regional metamorphism. We suggest that the previously denotedspilitic rocks or altered volcanic rocks should be re-denoted as metabasalts or metabasaltic rocks.The metamorphic grade of the volcanic rocks increases with their age: prehnite-pumpellyite faciesfor the upper part of the Middle Ordovician volcanic rocks, prehnite-pumpellyite to lowergreenschist facies for the lower part of the Middle Ordovician volcanic rocks, and lower greenschistfacies for the Lower Ordovician volcanic rocks. The P-T conditions are estimated as T = 240 - 290deg C and P = 1.5-4.5 kbar for the lower part of the Middle Ordovician rocks, and T = approx 300 degC for the Lower Ordovician rocks. The variations of mineral assemblages occurring at differentdomains of the volcanic rocks were controlled by the variations of the effective bulk composition inthose domains during metamorphism. The geochemical characteristics of Mg-Al chromite in theMayaxueshan volcanic rocks are consistent with an origin of island arc environment.
文摘The Songpan Garzê Fold Belt records Triassic shortening of a relict Palaeo\|Tethyan basin during assembly and accretion of the Cimmerian continental chain to Laurasia’s southern margin. Enclosed by palaeo\|Laurasia and the Cimmerian fragments of Qiangtang (North Tibet) and Yangtze (South China), the Songpan Garzê Fold Belt was shortened by more than 50% during the Indosinian Orogeny c.200Ma. [BW(D(S,,)G2*7][BHDWG2*7,WK*2,WK5,WK15*2,WK17*2,WK*2W] 2000,7(增刊) 地 学 前 缘 [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau [BW(S(S,,)G2*7][BHDWG2*7,WK*2,WK17*2,WK15*2,WK5,WK*2W] [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau 地 学 前 缘 2000,7(增刊)South\|directed Indosinian compression decolléd onlapping basin sediments from the Yangtze Block’s passive margin—reactivating the margin’s tiered geometry and partitioning strain into margin\|normal and margin\|parallel structures on a large scale. Margin\|normal transport of the allochthonous sedimentary pile was accommodated by southeast\|directed nappe propagation in the Longmen Mountains Thrust—Nappe Belt, whilst conjugate, margin\|parallel (southwest\|directed) transport was accommodated by a flat\|lying detachment at the base of the sedimentary pile.The later is characteristic of deformation of the greater Songpan Garzê Fold Belt.
基金support from the IRD-CORUS project "Concentrations minérales en Afrique" of M. Jessell and J.L. Bouchez for LMTG(Toulouse)
文摘The Fomopea granitic pluton is emplaced in gnessic and amphibolitic basement. These gneissic and amphibolitic basement rocks are represented in the pluton＇s body as sub-rounded, elongated or stretched xenoliths. Amphibolitic xenoliths display testimonies of two main tectonic events namely： （i） El flattening deformation event characterized by a NW-SE to E-W foliation with a best pole at 246/57 and a mineral stretched lineation with a best line at 293/47; and （ii） E2 compressive event typified by （1） N-S to NNE-SSW steeply dipping foliation; （2） S-type flexion-fold indicating a sinistral shear movement. These amphibolite rocks indicate a magnetic susceptibility magnitude （Km） range from 418 ~SI to 90092 IISI for 87% of the stations showing a ferromagnetic behavior. K-T curves reveal the presence of Ti-poor magnetite as susceptibility mineral carrier. Magnetic foliation and lineation suggest that the N-S strike direction observed in the Bamendou amphibolite is, as pointed out elsewhere in the Central African Fold Belt, of paramount importance in the tectonic evaluation of the Fomopea area, since it has most likely acted as major deformation phase in the second tectonic event in the belt.
基金This paper is one of the research results of the subject "The Ecostratigraphy of the Indosinian Continental Margins on the Sichuan-Gansu-Qinghai Border"(No.48970080)supported by the National Natural Science Foundation of China
文摘Whether there existed the Songpan-Garze massif is a controversial problem. This paper expounds and proves that the old basement of the massif is represented by the pre-Sinian granitic rock series. This massif and the South Qinling fold belt might both be a part of the old Yangtze platform. Rifting generated by the Caledonian orogeny in the terminal Early Palaeozoic caused the massif to be disintegrated from the northwestern part of the Yangtze platform. This disintegration, however, was not thorough, and the rift troughs were later gradually closed and filled up. The Emei taphrogeny that was initiated in the Early Permian Maokou' an Stage involved a second disintegration of this massif from the Yangtze platform. The rift line largely goes along the Muli-Pingwu line. This rifting belongs to synchronous extensional rifting at peripheries of the Yangtze platform and in its interior, showing that the posterior, lateral and interior extension resulting from rapid northward shift of the Yangtze platform led to isolation of this massif together with South Qinling from their adjacent areas. During the Ladinian Stage, the Songpan-Garze massif and southern Qinling sank strongly en masse. This subsidence continued till the end of the Late Triassic when the late Indosinian movement caused the sea trough to be closed and Songpan-Garze1 and southern Qinling to be folded and uplifted and become mountains.
文摘Bafia Group is part of the southernmost portion of the Central African Fold Belt (CAFB) in Cameroon. The geological feature of the group is characterized by the presence of metamorphic rocks in which tourmaline had been recognized among accessory minerals. In the present study, attention is focus on the tourmaline bearing quartzite to the southeast of Kombé II. Structure refinement shows that tourmaline is a Fe-dravite with the formula X(Na<sub>0.95</sub>[]<sub>0.05</sub>)Y(Mg<sub>2.39</sub>Fe<sub>0.61</sub>)Z(Al<sub>5.10</sub>Mg<sub>0.90</sub>)(BO<sub>3</sub>)<sub>3</sub>T[Si<sub>6</sub>O<sub>18</sub>](OH)<sub>3</sub>[(O,OH)<sub>0.88</sub>F<sub>0.12</sub>]. The Fe-dravite is hosted in a Ca-poor quartzite, which is made up, in addition to quartz and tourmaline, of biotite and muscovite. The structure of the dravites shows a low vacancy at the X site, which militates for a crystallization of the tourmaline at a high temperature > 750℃. This is in agreement with previous work which shows that the metamorphic peak in the associated biotite gneiss reaches 825℃. The R1 value of 1.24% means that the crystal structure of the tourmalines is of high quality. The genetical link between gold mineralization and tourmaline should stimulate exploration interest in the study area.
文摘Mesoproterozoic North Delhi fold belt of NW Indian shield comprises three volcano-sedimentary basins viz. Bayana, Alwar and Khetri aligned parallel to each other from east to west. Each basin contains excellent exposures of mafic volcanic rocks. Major, trace and rare earth element abundances of volcanic rocks of the three basins are significantly diverse. Bayana and Alwar volcanics are tholeiites bearing close similarity with low Ticontinental flood basalts. However, Bayana volcanics are characteristically enriched in incompatible trace elements and REEs while Alwar volcanics display least enriched incompatible trace element abundances and flat REE patterns. The Khetri volcanics exhibit a transitional composition between tholeiite and calc-alkaline basalts. REE based source modeling suggests that Bayana suite was formed from the melts derived from 1 % to 10 %(avg.4 %) of the partial melting of a spinel lherzolite source giving a residual mineralogy of 56 % Olv, 25 % Opx and19 % Cpx. Whereas Alwar suite evolved through 12 %–20 %(avg. 15 %) partial melting of the same source with a residual mineralogy 61 % Olv, 25 % Opx and 14 % Cpx.Khetri volcanics are exposed at two localities Kolihan and Madhan–Kudhan. The Kolihan volcanics were derived from 1 % to 6 %(avg. 4 %) partial melting with residualmineralogy 56 % Olv, 25 % Opx and 19 % Cpx whereas the magma of Madhan Kudhan volcanic suite was generated by 15%–30 % partial melting of the same source leaving behind 64 % Olv, 25 % Opx and 11 % Cpx as residual mineralogy. This source modeling proves that melts of Bayana and Alwar tholeiites were generated by partial melting of a common source within the spinel stability field under the influence of mantle plume. During the course of ascent, Bayana melts were crustally contaminated but Alwar melts remained unaffected. There was two tier magma production in Khetri region, one from the partial melting of the mantle wedge overlying the subducted oceanic plate which formed Kolihan suite and two the melting of the subducted plate itself generating Madhan–Kudhan volcanics. It is interpreted that during Mesoproterozoic(1,800 Ma), the continental lithosphere of NW Indian shield suffered stretching, attenuation and fracturing in response to a rising plume. Consequently, differential crustal extension coupled with variable attenuation brought the asthenosphere to shallower setting which led to the production of tholeiitic melts. These melts enroute to the surface suffered variable lithospheric contamination depending upon the thickness of traversed crust. The Khetri basin attained maturity which resulted in the generation of true oceanic crust and its subsequent destruction through subduction. The spatial existence of three suites of mafic volcanics of diverse chemical signatures is best example of subduction–plume interaction. It is therefore, proposed that the Mesoproterozoic crust of NW Indian shield has evolved through the operation of a complete Wilson cycle at about1,832 Ma, the age of mafic volcanics of Khetri basin.
基金supported by MLTM of Korean Government Program 20052004 to S.Kwon
文摘The map expression of ＂abrupt＂ changes in lateral stratigraphic level of a thrust fault has been traditionally interpreted to be a result of the presence of （1） a lateral （or oblique） thrust-ramp, or （2） a frontal ramp with displacement gradient, and/or （3） a combination of these geometries. These geometries have been used to interpret the structures near transverse zones in fold-thrust belts （FTB）. This contribution outlines an alternative explanation that can result in the same map pattern by lateral variations in stratigraphy along the strike of a low angle thrust fault. We describe the natural example of the Leamington transverse zone, which marks the southern margin of the Pennsylvanian-Permian Oquirrh basin with genetically related lateral stratigraphic variations in the North American Sevier FTB. Thus, the observed map pattern at this zone is closely related to lateral stratigraphic variations along the strike of a horizontal fault. Even though the present-day erosional level shows the map pattern that could be interpreted as a lateral ramp, the observed structures along the Leamington zone most likely share the effects of the presence of a lateral （or oblique） ramp, lateral stratigraphic variations along the fault trace, and the displacement gradient.
