New Chronological Evidence for Indosinian Diagenetic Mineralization in Eastern Xinjiang, NW China

There have been conflicting ideas about the Indosinian mineralization in E. Xinjiang, a subject that has attracted many geologists' attention over a long period. Isotopic dating shows that the Shiyingtan gold deposit located on the southern margin of the Turpan-Hami basin has a quartz fluid inclusion Rb-Sr isochron age of 237±9 Ma (95% conf.); the Shuangfengshan gold deposit on the southern margin of the Junggar orogenic belt has a quartz fluid inclusion Rb-Sr isochron age of 226 ±21 Ma (95% conf.); the Weiya vanadium-titanium magnetite in the E. Tianshan mountains has a mineral-whole rock Sm-Nd isochron age of 220 ±30 Ma (95% conf.); the Jinwozi and Jinwozi 210 gold deposits in the E. Tianshan mountains have quartz fluid inclusion Rb-Sr isochron ages of 228±22 Ma (95% conf.) and 230±6 Ma (95% conf.), respectively; and the Xiaobaishitouquan scheelite deposit in the E. Tianshan mountains has a quartz fluid inclusion Rb-Sr isochron age of 248±7 Ma (95% conf.). The metallogenetic ages mentioned above prove the existence of Indosinian mineralization in E. Xinjiang, and the metallogenetic event might have been related to Triassic intraplate magmatic evolution, intra-continent subduction, strike-slip shoving and ductile shearing in the studied area, representing another mineralization peak after the Late Paleozoic.

LA-ICPMS Zircon U-Pb Dating for Three Indosinian Granitic Plutons from Central Hunan and Western Guangdong Provinces and Its Petrogenetic Implications

The LA-ICPMS zircon U-Pb geochronology of three typically Indosinian granitic plutons yielded weighted mean ^206pb/^238U ages of 214.1±5.9 Ma and 210.3±4.7 Ma for the biotite monzonitic granites from the Xiema and Xiangzikou plutons in Hunan Province, and 205.3±1.6 Ma for biotite granite from the Napeng pluton, western Guandong Province, respectively, showing a similar late Indosinian age of crystallization. In combination with other geochronological data from Indosinian granites within the South China Block （SCB）, it is proposed that those late Indosinian granites with an age of -210 Ma and the early Indosinian granites （230-245 Ma） have the similar petrogenesis in identical tectonic setting. The Indosinian granites within the SCB might be the products of anatexis of the thickening crust in a compressive regime. These data provide a further understanding for the temporal and spatial distribution of the Indosinian granites and the dynamic evolution of the SCB.

Indosinian Orogenesis in the Lhasa Terrane, Tibet: New Muscovite ^(40)Ar-^(39)Ar Geochronology and Evolutionary Process

Muscovite 40 Ar-39 Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220-240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan ocean basin and the following collision of the northern Lhasa terrane and southern Gondwana land. This Indosinian orogenesis is further confirmed by the regional sedimentary characteristics, magmatic activity and ophiolite mélange. This evidence suggests that the Indosinian orogenic belt in the Lhasa terrane is widely distributed from the Coqen county in the west, and then extends eastward through the Ningzhong and Sumdo area, finally turning around the eastern Himalayan syntaxis into the Bomi county. Based on the evolutionary process, the geological development of Lhasa terrane from early Paleozoic to early Mesozoic can be divided into seven stages. All of the seven stages make up a whole Wilson circle and reveal a perfect evolutionary process of the Paleo-Tethys ocean between the northern Lhasa terrane and southern Gondwana land. The Indosinian orogenisis is a significant event for the evolution of the Lhasa terrane as well as the Tibetan Plateau.

Structural characteristics and evolution of the South Yellow Sea Basin since Indosinian

Based on the seismic data gathered in past years and the correlation between the sea and land areas of the Lower Yangtze Platform,the structural characteristics of the South Yellow Sea Basin since the Indosinian tectonic movement is studied in this paper.Three stages of structural deformation can be distinguished in the South Yellow Sea Basin since the Indosinian.The first stage,Late Indosinian to Early Yanshanian, was dominated by foreland deformation including both the uplifting and subsidence stages under an intensively compressional environment.The second stage,which is called the Huangqiao Event in the middle Yanshanian,was a change for stress fields from compression to extension.While in the third stage (the Sanduo Event)in the Late Himalayan,the basin developed a depression in the Neogene-Quatemary after rifting in the Late Cretaceous-Paleogene.The long-time evolution controlled 3 basin formation stages from a foreland basin,then a fault basin to a final depression basin.In conclusion,since the Indosinian,the South Yellow Sea Basin has experienced compressional fold and thrust,collisional orogen,compressional and tensional pulsation,strike-slip,extensional fault block and inversion structures,compression and convergence.The NE,NEE,nearly EW and NW trending structures developed in the basin.From west to east,the structural trend changed from NEE to near EW to NW.While from north to south,they changed from NEE to near EW with a strong-weak-strong zoning sequence.Vertically,the marine and terrestrial facies basins show a "seesaw"pattern with fold and thrust in the early stages,which is strong in the north and weak in the south and an extensional fault in later stages,which is strong in the north and weak in the south.In the marine facies'basin,thrust deformation is more prevailing in the upper structural layer than that in the lower layer.The tectonic mechanism in the South Yellow Sea Basin is mainly affected by the collision between the Yangtze and North China Block,while the stress environment of large-scale strike- slip faults was owing to subduction of the Paleo-Pacific plate.The southern part of the Laoshan uplift is a weak deformation zone as well as a stress release zone,and the Meso-Paleozoic had been weakly reformed in later stages.The southern part of the Laoshan uplift is believed,therefore,to be a promising area for oil and gas exploration.

Hercynian-Indosinian Sedimento-Tectonic Evolution of the Nanpanjiang Basin

Following the orogeny in the Early Palaeozoic, the tectonic evolution of the Nanpanjiang basin in the Hercynian-Indosinian stage constituted a complete Wilson Cycle, made up of the stages of early rifting (D-P1), late rifting and passive margin developement (P2-T1), and peripheral foreland basin developement (T2-T3). The REE data of the initial Early Triassic basalts from the southern part of the basin has verified the existence of the oceanic crust once in the basinal evolution. The basin developed into a foreland one in the Middle-Late Triassic, indicating that the Yangtze plate once collided with the Indo-Sinian plate along the Black River fracture zone.

A New Potential Caledonian–Indosinian Ore Concentration Area:Evidence from Diagenesis and Mineralization Ages of the Miao'ershan–Yuechengling Region

Objective The Miao＇ershan-Yuechengling composite granite, located in northern Guangxi at the western section of the Nanling Range, is a multi-period and multi-stage composite pluton with an exposed area of more than 3000 km2 （Fig. 1）. Paleozoic and Proterozoic strata are exposed around it, and magmatic activities mainly occurred during the Caledonian and Indosinian periods. Till now, more than one hundred W-Sn-Mo-Pb-Zn-Cu （U） deposits and ore occurrences have been discovered along the inner and outer contact zones of this granite. Through recent years＇ research, we infer that this area is not only a preferred area for studying granite and mineralization in Caledonian and lndosinian periods, but also a potential Caledonian- lndosinian ore-concentrated area.

Post-ore Modification and Preservation of the Indosinian Porphyry Copper Deposit in Geza Arc, Yunnan, SW China

Objective The post-ore modification and preservation of porphyry copper deposits is controlled and influenced by various geological processes, and the regional uplift and denudation is the most important factors. This study used biotite mineral geobarometer and Apatite Fission Track （AFT） to restore the uplift evolution of the granitic porphyries in the Geza arc and to obtain quantitative data of rock erosion degree and denudation rate.

The Characteristics of the Indosinian Pacific-Type Ancient Continental Margin in the Qinghai-Xizang(Tibet)-Sichuan-Yunnan Region

The Qinghai-Xizang (Tibet) Plateau and the 'Sanjiang' area②, where are extensively developed theTethys-type marine Triassic sequences with Indosinian tectonic disturbance and magmatism, provide an impor-tant region for the study of the tectonic evolution and the Indosinian movement of China as well as for thestudy of the boundary between Gondwana and Laurasia and the characteristics of the time-space distributionof the Tethys oceanic crust within the territory of China. Over a long period of time in the past, quite a numberof scholars made substantial studies and discussious from various viewpoints on the geotectonie and regionalgeological evolution of this region. Based on some new data obtained recently and the field observations by theauthor, and by using the plate tectonic theory, the author considers that there developed a Pacific-type (activetype) ancient continental margin bordering the Palaeo-Tethys ocean (or North Tethys ocean) in the south inLate Permian to Triassic times in the region of south-central Qinghai, northeastern Xizang (Tibet), western andsouthwestern Sichuan, and western Yunnan. Its characteristics basically represent the Indosinian tectonic evo-lution of this region.

Provenance Variability of the Triassic Strata in the TurpanHami Basin: Detrital Zircon Record of Indosinian Tectonic Reactivation in the Eastern Tianshan

The Triassic strata in the Turpan-Hami Basin potentially chronicled the missing sedimentary record of Indosinian tectonic evolution in the Eastern Tianshan.In this study,we conducted detrital zircon U-Pb geochronological analyses on subsurface Triassic samples collected from the Turpan-Hami Basin to unravel sedimentary response of Indosinian tectonic reactivation and its geodynamics.The detrital zircon age spectra of the Triassic samples are quite different,reflecting significant provenance variability.The zircon grains in the Lower Triassic sample were mainly from the Central Tianshan,while the Jueluotag acted as a minor provenance.By contrast,the Late Paleozoic rocks in Jueluotag act as the main provenance for the Middle-Upper Triassic samples,while the Central Tianshan acted as a minor provenance.Furthermore,zircon grains in the Middle Triassic sample were mainly from the Permian rocks in Jueluotag,while Indosinian strike-slipdriven rapid exhumation brought deeper Carboniferous rocks of Jueluotag as an important age population for the Upper Triassic sample.The inter-sample variability of age spectra of the Triassic samples provides sedimentary evidence for Indosinian tectonic reactivation in the Eastern Tianshan and its periphery,which could be attributed to differential exhumation of different sources driven by coeval strike-slip tectonics along deep faults.The Indosinian tectonic behavior in the Eastern Tianshan,which is characterized by partial melting of the pre-thickened crust and strike-slip deformation,acted as a far-field respond to the coeval continental accretion occurring along the southern Eurasian margin.Additionally,our new detrital zircon data,together with previously published data in the Turpan-Hami Basin,demonstrate that there are significant changes in source-to-sink system from the Permian to the Triassic,suggesting that the Permian-Triassic unconformity in the Eastern Tianshan and its periphery was generated by Late Permian-Early Triassic tectonic contraction and inversion rather than an increasingly arid climate.

The Metamorphism and Its Tectonic Implications of Indosinian High Pressure Granulites from the Badu Complex of the Cathaysia Block, Southwestern Zhejiang Province, South China

The Badu Complex is the oldest metamorphic rock in Cathaysia Block which experienced several episodes of metamorphism Especially indosinian metamorphic reworking in the southwestern Zhejiang Province, South China. The degree of indosinian metamorphism reaches granulite facies. However, there is still insufficient understanding of the characteristics of the Indosinian granulite metamorphism in the Cathaysia and many interpretations of its tectonic significance. Therefore, we present detailed petrology, mineral chemistry and LA-ICP-MS zircon U-Pb age in this paper from pelitic granulites of the Badu Complex, which is composed of "sillimanite + garnet + cordierite + spinel + biotite + k-feldspar" assemblage and garnet pyroxenite with garnet amphibolite which is consists of "garnet + clinopyroxene + orthopyroxene + amphibole + plagioclase". By comprehensive study we get following new findings: Pelitic granulites record four stages of metamorphic mineral assemblages, including prograde(M1), pressure peak(M2), Peak(M3) and post-peak decompressional and then cooling(M4) stages. The prograde M1 assemblage consists of garnet1(core) + staurolite + kyanite + biotite + quartz ± rutile ± chlorite;The pressure peak M2 assemblage consists of garnet1(mantle) + sudoite + rutile + kyanite + corundum + biotite + quartz;The peak M3 have garnet2(rim-mantle) + biotite + sillimanite + quartz ± K-feldspar ± plagioclase ± ilmenite assemblag;the M4 stage is consist of garnet + cordierite + biotite + sillimanite + quartz + ilmenite ± spine ± K-feldspar. The garnet pyroxenite and garnet amphibolites have experienced three stages of metamorphic evolution. Peak high-pressure granulite facies stage M2 consists of garnet + sahlite ± ilmenite ± quartz;Post-peak near isothermal decompression medium granulite facies stage M3 is characterized by typical decompression reaction textures and assemblage of orthopyroxene + plagioclase(An=90–92);amphibolites facies retrograde metamorphic stage M4 is characterized by amphibole + plagioclase(An=33–35) + ilmenite ± sahlite ± quartz mineral assemblage. By means of phase equilibrium simulation and traditional thermobarometer, P-T conditions of 785–820 ℃ and 8.9–9.9 kbar for M3 stage, 780–860 ℃ and 5.7–6.2 kbar for decompressional M4 stage, 705–720 ℃ and 4.5–4.7 kbar for cooling M4 stage in pelitic granulites were obtained. And also 11.6–12.5 kbar and 780–840 ℃ for M2 stage, 7.4–8.2 kbar and 800–880 ℃ for M3 stage, 6.6–7.5 kbar and 500–560 ℃ for M4 stage were obtained in garnet pyroxenite and garnet amphibolite. A clockwise P-T path is confirmed in the two type rocks of the Badu Complex which reflected a near-isothermal decompressional metamorphic process. The peak metamorphism can reach highpressure granulite facies. In addition, the mineral assemblage of garnet + rutile + kyanite + corundum in the peak metamorphic stage of pelitic granulite indicates that it may underwent ultra-high-pressure metamorphism, and the acidic plagioclase exsolution of clinopyroxene in garnet pyroxenite also suggests that it may be retrograded eclogites, which indicates that the deeper Cathaysian block may have eclogite metamorphism. Analyses of LA-ICP-MS zircon U-Pb dating indicate that the metamorphic age of pelitic granulite is 233.5 Ma–subduction/collision followed by rapid exhumation and cooling events. The events may relate with the amalgamation of the Indochina BlockSouth China Block North China Block in the paleo-Tethyan domain.

Characteristics of soure region and tectonic implications of Early Indosinian Weiya gabbroic rock,eastern Tianshan mountains

Based on the detailed petrographic study,the characteristics of source region of the Weiya gabbro and tectonic implications were studied.The results show that the gabbroic rock consists mainly of gabbro,with less amount of ultra-mafic rocks.The ultra-mafic rocks show cumulate texture and are gradually transitional contact with gabbro,indicating that they are cumulate products of parental magma.The ultra-mafic rocks consist mainly of spinel periodite and spinel clinopyroxenite.The former is mainly composed of olivine(65%-70%),spinel(10%-15%),hornblende(5%-10%) and phlogopite(5%-10%);the latter consists mainly of clinopyroxene(70%-80%),spinel(15%-20%) and phlogopite(0-10%),with minor amounts of carbonate(0-2%).No olivine or orthopyroxene is found.The gabbro is composed mainly of clinopyroxene(35%-40%),plagioclase(An 55-65,40%-45%),hornblende(5%-15%),with variable amounts of carbonate(0-5%).Petrographic observations show that the source region of the Weiya gabbroic rock is water-rich due to intensive intra-continental A-type subduction occurring in this region during late Permian to early Triassic.

右江盆地卡林型金矿成矿年代学研究进展

右江盆地是全球仅次于美国内华达地区的第二大卡林型金矿床集中分布区。由于成矿时代的不确定性,盆地内卡林型金矿床的成矿动力学背景一直不清。为准确确定这些金矿床的成矿时代,近四十年来国内外矿床学家进行了孜孜不倦的探索,从早期以石英裂变径迹和流体包裹体Rb-Sr等时线法为代表的定年,到中期以硫化物Re-Os等时线法为代表的单矿物溶样法定年,再到最新以热液金红石、独居石和磷灰石U-Th-Pb法为代表的微区原位定年,其定年对象和方法见证了同位素地质年代学的发展历程。现已基本明确,右江盆地主要发育两期卡林型金矿成矿作用,分别为215~200 Ma和155~140 Ma,相当于印支期和燕山期,其动力学背景分别对应于印支-华南-华北地块碰撞后的印支期陆内造山过程以及燕山期软流圈上涌诱发的岩石圈伸展作用。

印支造山带:Song Chay构造带

印支运动是二十世纪初法国地质学家根据越南北部晚三叠世大规模角度不整合所提出。越南北部的Song Chay构造带作为印支造山带概念的提出地,记录了大量经典的印支造山相关的信息,是理解印支造山带构造演化的关键地区。本文在课题组对Song Chay地区十多年研究基础上,结合前人研究成果,系统厘定了Song Chay构造带的几何空间格架、运动学特征及其演化过程。详细的野外地质考察表明,Song Chay构造带从SW向NE依次可以划分成:新生代的大象山单元、代表缝合带的Song Chay蛇绿混杂岩单元,以及越南东北部褶皱冲断系统。其中蛇绿混杂岩单元和褶皱冲断系统中发育NE-SW向矿物拉伸线理,并具有顶部向NE方向的剪切变形特征,指示了Song Chay洋壳向SW的俯冲以及向NE的逆冲过程。精确的年代学工作表明,Song Chay蛇绿混杂岩中斜长花岗岩的结晶年龄为356.4±2.9Ma,表明至少在早石炭世Song Chay洋就已经形成了成熟的大洋地壳。褶皱冲断带内部的低温年代学数据约束了顶部向NE的剪切变形年龄在250~245Ma之间,表明为华南和印支板块碰撞时间。另外,Song Chay蛇绿混杂岩基质中碎屑锆石物源研究表明,Song Chay蛇绿混杂岩基质中碎屑锆石主要是来自于俯冲的华南板块,只有很少一部分来自印支板块,因此推测Song Chay洋可能为一个十分有限的小洋盆。构造几何学、运动学以及碎屑锆石物源研究表明,在Song Chay构造带内的“滇-琼缝合带”两侧构造特征可对比,并未因“滇琼洋”的闭合而造成差异。因此,我们认为“滇-琼缝合带”并不能代表一个大洋。根据我们及前人的构造学、岩石学、年代学工作,建立了一个初步的Song Chay洋从晚石炭世至中三叠世的构造演化模型:(1)310~270Ma,Song Chay洋开始向SW俯冲到印支板块之下,此时岩浆弧并不发育,蛇绿混杂岩物源主要为华南板块;(2)270~250Ma,Song Chay洋继续俯冲,此时弧岩浆岩大量发育,蛇绿混杂岩同时接受弧岩浆岩及华南板块碎屑物质;(3)250~245Ma,Song Chay洋闭合,华南板块与印支板块碰撞;(4)245~230Ma,印支造山带进入碰撞后伸展阶段。

中晚三叠世鄂尔多斯盆地两期沉降及其形成机制

基于近年来新补充的大量深井资料,深入开展中晚三叠世鄂尔多斯盆地沉降作用研究,提出该沉积期鄂尔多斯盆地经历了两期重要沉降事件,并对两期沉降作用下的地层发育特征、岩性组合、汇水区分布、沉积演化等进行系统对比分析。认为两期沉降作用均是印支期秦岭构造活动在其北侧克拉通边缘的响应;延长组10段沉降幅度大,碎屑供给多,沉积速率快,以较粗碎屑充填为主,快速沉降伴随快速堆积,地层自东北向西南呈楔形增厚,沉降中心位于盆地西南环县—镇原—庆阳—正宁一带,地层厚800~1 300 m,沉降中心与沉积中心偏离,发育多个汇水区,此时尚未形成统一湖盆;延长组7段沉积期,在构造沉降与卡尼期暴雨事件共同作用下,形成了大面积深水坳陷,沉积速率慢,沉降中心与沉积中心基本重合,均位于麻黄山—华池—黄陵一带,沉降中心深水沉积厚120~320 m,以细粒沉积为主;两期沉降机制存在差异,早期沉降与秦岭地区中三叠世勉略洋向北俯冲相关,在挤压背景下强烈拗陷,晚期沉降为晚三叠世后碰撞弱伸展动力环境下的结果。

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。

U-Pb zircon geochronology and Hf isotope study of metamorphosed basic-ultrabasic rocks from metamorphic basement in southwestern Zhejiang:The response of the Cathaysia Block to Indosinian orogenic event

A combined study using LA-ICP-MS U-Pb dating, Hf isotopes, trace elements and the Ti-in-zircon geo-thermometer was carried out on zircons from the metamorphosed basic-ultrabasic rocks in the meta-morphic basement of the Cathaysia Block, southwestern Zhejiang Province. The formation and meta-morphic ages of the rocks from the metamorphic basement of the Cathaysia Block were determined based on zircon U-Pb geochronology. The age for the magmatic crystalline zircons from the protolith is about 1.85 Ga. The εHf(t) values of the older zircons were from ?7 to ?3, with two-stage model Hf ages (TDM2LC) of about 2.9 to 3.4 Ga, indicating that the source material was derived from anatexis and recy-cling of the Archean crust. The newly formed metamorphic zircons yielded U-Pb ages of 260―230 Ma. The metamorphic temperature calculated using the Ti-in-zircon geothermometer ranged from 610 to 720℃, consistent with the results from petrographic observations, indicating that the Cathaysia Block experienced an amphibolite facies metamorphism during the Indosinian. Results from this study pro-vided an important timeframe for the tectonic evolution in South China and the Southeast Asia during the Late Permian and Early Triassic times.

Geochronological evidence of Indosinian(high-pressure) metamorphic event and its tectonic significance in Taxkorgan area of the Western Kunlun Mountains,NW China

The CL images,LA-ICP-MS in situ trace elements analysis,and U-Pb dating for zircons indicate that the metamorphic ages of the sillimanite-garnet-biotite gneiss and the garnet-amphibole gneiss from eastern Taxkorgan of the Western Kunlun Mountains are 220±2 and 220±3 Ma respectively,and their protolith ages are younger than 253±2 and 480±8 Ma respectively.Two samples were collected at the same outcrops with HP mafic granulite and HP pelitic granulite.Mineral assemblage of the sillimanite-garnet-biotite gneiss(Grt+Sill+Per+Q) is consistent with that of HP pelitic granulite at early high amphibolite-granulite facies stage.Mineral assemblage of the garnet-amphibole gneiss(Grt+Amp+Pl+Q) is consistent with retro-metamorphic assemblage of HP mafic granulite at amphibolite facies stage.The dating results suggest that these HP granulites underwent peak metamorphism at 220±2 to 253±2 Ma.Thus,the Kangxiwar tectonic zone was probably formed by subduction and collision of the Paleo-Tethys Ocean during Indosinian.Protolith ages of the two samples,together with previously published U-Pb zircon dating age,suggest that the sillimanite-garnet schist-quartzite unit is a late Paleozoic unit,not a part of the Paleoproterozoic Bulunkuole Group.

海南岛印支-燕山期花岗岩年代学格架与成因

海南岛分布着大面积的印支-燕山期岩浆岩,是华南岩浆活动的重要组成部分。近年来,对这些花岗岩已开展了一系列工作,但其年代学格架仍需完善,成因类型及源区性质仍需限定,区域构造机制仍存在争议。本文详细梳理了已发表的海南岛晚古生代-中生代花岗岩地球化学和年代学数据,结合作者近年来的相关工作,对海南岛花岗岩的年代学格架和岩石地球化学特征进行总结,并对源岩、岩浆演化过程和地球动力学背景进行讨论。海南岛印支期(二叠纪-三叠纪)花岗岩(部分具有片麻状构造)整体以NE走向展布,形成于278~225Ma,峰期为240Ma。岩相学和地球化学研究表明,此期岩浆活动形成了具有不同地球化学特征的S型、I型和A型花岗岩。其中,S型花岗岩(278~241Ma)与I型花岗岩(272~233Ma)均为高钾钙碱性花岗岩,具有较低的全岩锆饱和温度(平均<750℃),低于大规模角闪石分解引起的脱水熔融所需的温度,可能是由底侵玄武质岩浆释放的水加入到下地壳诱发部分熔融的产物;A型花岗岩(257~225Ma)的全岩锆饱和温度较高(>800℃),表明源区无流体加入或为已有花岗岩生成的去水源岩在高温条件下脱水熔融形成。此外,本区还存在少量燕山期花岗岩,包括燕山早期(侏罗纪)岩浆活动(如本研究识别出的161Ma高钾钙碱性I型花岗岩)以及集中在白垩纪的三期侏罗纪-白垩纪岩浆活动(按年龄可分为:ca.120Ma、ca.110~90Ma和ca.70Ma,峰期为ca.100Ma)。地球化学数据表明燕山期花岗岩具有高钾钙碱性I型特征,源区中有幔源年轻组分的加入。据此,本文作者认为:(1)印支-燕山期大规模的花岗岩浆作用与古太平洋板块向华南大陆俯冲有关;(2)古太平洋板块向华南大陆的俯冲可能起始于早-中二叠世(ca.280Ma),结束于晚白垩世末期(ca.70Ma);(3)自二叠纪起至白垩纪末期安第斯型活动大陆边缘结束,海南岛保存了古太平洋俯冲相关的岩浆活动记录。

渤海海域印支期构造变形分带性及其特征的数值模拟研究

印支运动为现今渤海海域构造格局的形成奠定了基础,导致渤海海域内部发育3个主要逆冲带。渤海基底内部的先存断层与滑脱层在此过程中可能起到了极为重要的作用,但其如何影响渤海海域印支期的构造变形与分带特征的机制尚不清楚。为了解决上述问题,本文基于地震剖面数据,结合二维热力学数值模拟代码LaMEM对渤海海域印支期的构造变形展开了详细研究。模拟结果揭示,在先存断层存在的条件下,当基底内部无滑脱层或未呈阶梯式在渤海海域分布时,渤海海域内部不会形成相应的逆冲中心;而当基底内部的滑脱层呈阶梯状分布在渤海海域西南部、渤中坳陷以及辽东坳陷3个区域时,应力通过滑脱层在基底内部进行传导,使海域形成了3个逆冲中心,并导致渤海内部大规模的逆冲断层与褶皱变形的发育,与地震剖面具有较好的一致性。数值模拟实验结果证实,基底内部的先存断层与滑脱层是控制渤海海域构造分带性及构造变形特征的重要因素。同时,多逆冲中心演化模式也为解释现今龙门山和四川盆地的形成与演化过程提供了重要的借鉴。