内蒙古苏尼特左旗早古生代乌华敖包弧前盆地的识别及其古地理意义

通过野外观察和剖面测量、锆石年代学分析及沉积相分析等方法, 对新发现的苏尼特左旗乌华敖包地区浅变质岩系进行研究, 并探讨其古地理意义。结果表明, 该套浅变质岩系以变质火山岩、变质砂岩与大理岩互层为特征, 构成 3 个沉积旋回, 代表弧前盆地中?晚期向上变浅的海相火山喷发?沉积环境; 多层火山岩的出现揭示持续的岩浆活动; 火山岩锆石U-Pb定年结果为454.4±4.1 Ma, 与北部早古生代宝力道岛弧带的岩浆岩年龄相近, 表明该套浅变质岩系与早古生代岛弧岩浆活动有关。由于该岩系位于北部宝力道岛弧岩浆岩带与南部混杂岩带之间, 因此其古地理位置应属早古生代弧前盆地。乌华敖包浅变质岩系的层序、成分、时代和位置特征揭示研究区曾存在弧前盆地。根据早古生代地层、岩浆岩和变质特征, 认为弧前盆地经历了俯冲及碰撞两个阶段。     

西藏措勤—赛利普地区新生代火山岩地球化学特征

青藏高原拉萨地块是印度板块与欧亚板块碰撞的重要地区之一,其中广泛发育的碰撞—后碰撞岩浆岩记录了新生代以来印度大陆岩石圈向北俯冲的全过程以及拉萨地块在碰撞-后碰撞之后的岩浆作用类型.基于对措勘—赛利普地区新生代火山岩地球化学及Sr、Nd同位素资料的分析,表明火山岩中以明显富碱和高钾为特征;Sr同位素呈递增而Nd同位素呈递...     

Detrital zircon U-Pb ages of Late Cenozoic sediments from the Yangtze delta: Implication for the evolution of the Yangtze River

Detrital zircon grains of Late Cenozoic sediments dated back to ca.3.6 Ma from core DY03 in the Yangtze delta were dated by LA-ICP-MS,in order to investigate the sedimentary provenance and to find some clue for the evolution of the Yangtze River.Most of the detrital zircon U-Pb ages are distributed at 100 300 Ma,350 550 Ma,600 1000 Ma,1400 2000 Ma and 2200 2800 Ma,which correspond well with the main tectonic and magmatic events in the Yangtze drainage.The detrital zircon age patterns show distinct differenc...     

早泥盆世古亚洲洋构造作用:来自可可托海和额济纳旗花岗岩年代学研究

古亚洲构造域内发育有大量的古生代酸性侵入岩。对阿尔泰造山带可可托海近3号脉的酸性侵入岩体进行LA-ICP-MS锆石U-Pb定年分析,以确定其岩浆作用时代及其岩浆活动的构造意义。研究区内的花岗岩包含的锆石大部分为自形-半自形晶,显示为典型的岩浆成因;测年结果发现,该岩体形成于404.4±3.2 Ma,为早泥盆世岩浆活动的产物。通过对额济纳辉森乌拉西糜棱岩化二长花岗岩中白云母⁴⁰Ar/³⁹Ar同位素年代学分析,获得白云母的坪年龄和等时线年龄分别为407.69±3.09 Ma和407.65±3.99 Ma,这暗示了拐子湖-呼和音乌苏弧形挤压带在早泥盆世活动的冷却年龄。以上事件与早泥盆世古亚洲洋的俯冲、碰撞的构造环境关系密切。     

苏北盆地与周围地区的新生代玄武岩及其形成的大地构造环境

本文首先计算了苏北盆地及周围地区30多个地点的150多个玄武岩的岩石化学分析数据的标准矿物值,并进行化学分类,进而探讨了各时期岩浆活动性质。利用地质温度计和压力计对照计算了部分地点玄武岩的形成条件,并综合各种岩石化学特征指数、岩浆来源深度以及微量元素含量等分析结果,着重讨论了岩浆活动的规律及其所反映的大地构造环境问题。     

扬子板块西缘盐边群及周边岩体地质年代学新格局

扬子板块西缘的盐边群及其周边岩体,作为前寒武纪构造岩浆活动带的核心,是观察和研究新元古代大陆壳生长的重要窗口.查明这一构造岩浆活动带内地质体的产出时代及构造岩浆活动的轨迹,是揭示新元古代大陆壳产生、发展地球动力学过程的重点环节.对盐边群及周边岩体的地质年代学研究表明:(1)区内大规模的岩浆事件集中在中元古代晚期至新元古...     

珠江口盆地阳江东凹新生代岩浆活动特征与期次

根据阳江东凹邻区的录井及岩矿等资料,通过对阳江东凹的地震反射、地层关系及地层厚度等特征的分析,系统划分阳江东凹新生代的岩浆岩体类型及期次,并探讨其岩浆活动与南海区域构造运动的耦合关系。研究表明,阳江东凹新生代岩浆岩体分为侵入岩体与火山岩体两种类型,前者主要分布在东部洼陷内,后者主要发育于南部洼陷边部及周缘隆起区;岩浆活动可划分为文昌期、恩平期及珠江-粤海期,并受区域构造运动制约。珠琼运动两幕裂陷控制文昌期、恩平期的岩浆侵入活动,而裂陷后期的白云运动和东沙运动则控制盆地NWW向的断裂活动,从而影响珠江-粤海期的火山喷发活动。     

Timing of hydrothermal activity associated with the Douzhashan uranium-bearing granite and its significance for uranium mineralization in northeastern Guangxi, China

The Miaoershan uranium(U)ore field in northeastern Guangxi is one of the important granite-related U deposits in south China and is closely related to the Douzhashan U-bearing granite.The Douzhashan granite contains primary U-rich accessory minerals,including monazite(UO2=0.98-1.75 wt%)and xenotime(UO2=1.48-6.14 wt%).Primary monazite and xenotime yield chemical ages of 231±28 Ma and 230±38 Ma by electron microprobe analysis and U-Pb isotopic ages of 220±6 Ma and 211±7 Ma by laser ablation-inductively coupled-mass spectrometry respectively.These ages demonstrate that the Douzhashan granite formed during the period of Indosinian magmatic activity.Back scattered electron imaging shows that monazite and xenotime are commonly altered to assemblages of low-U synchisite and apatite,which was associated with loss of U to hydrothermal fluids.U-Th-Pb analyses of secondary apatite yielded a chemical age of 136±17 Ma,which corresponds to the timing of Cretaceous-Tertiary crustal extension in south China.We suggest that the heat and CO2required for mineralization was the result of Yanshanian crustal extension,and that this triggered the breakdown of U-rich accessory minerals in the Douzhashan U-bearing granite.Uranium remobilization from the Douzhashan granite provided materials for mineralization within the granite and/or surrounding country rocks.Therefore,a combination of Indosinian compression and Yanshanian extensional overprint produced the hydrothermal U deposits associated with the Douzhashan granite.     

SHRIMP U-Pb zircon dating for the dacite of the Sangxiu Formation in the central segment of Tethyan Himalaya and its implications

The Tethyan Himalaya is located between the In-dus-Yarlung Zangbo suture zone to the north and HigherHimalayan crystallines to the south, paleogeographicallybelonging to the northern margin of “Greater India”. TheSangxiu Formation is used to define a series of specialstrata with rich volcanic interbeds, and is only distributedto the southeast of Yangzuoyong Co within 200 km×50 km along the eastern part of central Tethyan Hima-laya[1]. Based on overlapped relationships of strata andfos…     

埕岛地区中生代和新生代断层发育特征及其对沉积的控制作用

对穿过埕岛地区中生代和新生代主要断层的地震测线进行了详细的解释和分析，以了解该地区断层的发育演化特征及其对沉积的控制作用。结果表明，埕岛地区中生代以埕北断层、埕北20断层、埕北30北断层及其派生断层活动为主，主断层的发育演化普遍经历了由逆到正的构造负反转过程；新生代主断层中埕北20断层停止活动，其余两条断层均继承性活动，并开始发育以走滑性质为主的埕北30南断层以及其他次级北东向正断层。断层活动是埕岛地区中、新生代地层沉积的主要控制因素。埕岛地区中、新生代断层发育演化特征与济阳坳陷其他构造单元相似，但其平面组合特征具有一定的差异性，这与距离郯庐断裂带较近，受到更强烈的走滑作用有关。     

4.1 Ga old detrital zircon in western Tibet of China

4.1 Ga old detrital zircon was found by SHRIMP U-Pb dating for quartz schist from Buring County in western Tibet, Southwest China. This is the oldest zircon U-Pb age found in China so far. The detrital zircon is a zircon of magmatic origin because its Th/ U ratios are 0.76 to 0.86. Two dates older than 4.0 Ga were measured only in one grain. U-Pb ages of 35 measured spots in 24 zircons can be subdivided into 6 groups, corresponding to at least 6 episodes of magmatic activity in the target area. The present results provide an important geochronological constraint on the geological evolution of Qinghai-Tibet Plateau.     

Geochronolosic constraints on masmatic intrusions and mineralization of the Zhunuo porphyry copper deposit in Gansdese, Tibet

In situ zircon U-Pb ages for the recently discovered Zhunuo porphyry copper deposit in the western part of the Gangdese metallogenic belt in Tibet were determined by sensitive high-resolution ion microprobe （SHRIMP）. The ages can be divided into two separate groups, reflecting more than four major tectono-magmatic events in the area. The 62.5±2.5 Ma age of inherited zircons may be related to the volcanic eruption of the Linzizong Group formed shortly after the India-Asia continental collision. The 50.1±3.6 Ma age most likely corresponds to the time of underplating of mantle-derived mafic magma in Gangdese. The 15.6±0.6 Ma age obtained from magmatic zircons is interpreted as the age of crystallization of the Zhunuo ore-forming porphyry. Finally, a molybdenite Re-Os isochron age of 13.72±0.62 Ma is consistent with another zircon U-Pb age of 13.3±0.2 Ma, representing the time of copper mineralization. These ages, in combination with available literature data, indicate that magmatic crystallization and copper mineralization in the Gangdese metallogenic belt became gradually younger westward, and further suggest that the Zhunuo porphyry copper deposit was formed in the same tectonic stage as other porphyry copper deposits in the eastern and central Gangdese belt. This conclusion provides critical information for future exploration of porphyry copper deposits in western Gangdese.     

SHRIMP U-Pb zircon dating of the Ordos Basin basement and its tectonic significance

SHRIMP U-Pb zircon 207 Pb/206 Pb ages were obtained from two drill cores from the basement of the Ordos Basin.A garnet-sillimanite-biotite-plagioclase gneiss(QI1-1) from the western Ordos Basin basement yielded an average age of 2031 10 Ma.Based on the mineral assemblages,the source material of the gneiss is speculated to be pelitic-felsic system.A gneissic two-mica granite(Long1-1) from the eastern Ordos Basin basement yielded an average age of 2035 10 Ma.The zircons from both samples exhibit magmatic growth pattern.The shapes of the zircons suggest that the zircons should crystallize from a granitic of felsic volcanic terrain.The ages and the characters of zircons are consisitent with the other researches in the Ordos Basin and indicate that the basement of the Ordos Basin had experienced an intensive magmatic epsode during the late Paleoproterozoic period.The date from this study suggest the possible existences of a Paleoproterozoic mobile tectonic belt in the region.The reconstruction of such a belt is critical for understanding the tectonomagmatic evolution of the western block of the North China Craton.     

A ∼2.5 Ga magmatic event at the northern margin of the Yangtze craton: Evidence from U-Pb dating and Hf isotope analysis of zircons from the Douling Complex in the South Qinling orogen

The poorly studied Douling Complex is a crystalline basement that developed in the Neoproterozoic-Paleozoic weakly metamorphosed to non-metamorphosed strata at the South Qinling tectonic belt. Five banded dioritic-granitic gneiss samples from the Douling Complex were chosen for LA-MC-ICPMS U-Pb zircon dating, which yielded protolith emplacement ages of 2469 ± 22 Ma, 2479 ± 12 Ma, 2497 ± 21 Ma, 2501 ± 17 Ma and 2509 ± 14 Ma, respectively. An important peak age of ～2.48 Ga was also obtained for a metasedimentary rock in the same region. These discoveries suggest the occurrence of magmatic activity of 2.51–2.47 Ga at the northern margin of the Yangtze craton. The age-corrected ? _Hf(t) values obtained from in situ zircon Hf isotopic analysis are mainly between ?5.5 and +0.3, and the two-stage zircon Hf model ages range from 3.30 to 2.95 Ga. Considering two important periods of ～3.3–3.2 Ga and ～2.95–2.90 Ga for the continental crustal growth in the Yangtze craton, we infer that the dioritic-granitic gneisses from the Douling Complex are the products of reworking of Paleo- to Mesoarchean crust at the northern margin of the Yangtze craton at ～2.5 Ga. In addition, metamorphic ages of 837 ± 8 Ma and 818 ± 10 Ma were obtained for zircon overgrowth rims from a dioritic gneiss and a metasedimentary rock, indicating that the main phase amphibolite facies metamorphism of the Doulng Complex occurred during the Neoproterozoic, although its geological meaning remains ambiguous.     

黑龙江金厂金矿花岗斑岩锆石地球化学、U-Pb年代学及地质意义

为确定与金厂金矿成矿有关的岩浆类型、活动时限和构造背景,采用LA-ICP-MS技术对研究区花岗斑岩开展了锆石U-Pb年龄及原位微区微量元素测定。结果表明:锆石环带发育,wTh/wU值>0.4,具有岩浆锆石特征;锆石年龄分布于220Ma和103～123Ma 2个区间,代表了2期岩浆事件;对2种锆石分别命名为捕获岩浆锆石和新生岩浆锆石;锆石的地球化学和年龄信息显示捕获岩浆锆石的原岩为早三叠世花岗岩;锆石微量元素信息暗示花岗斑岩是早三叠世花岗岩高度熔融结晶分异、侵位于浅部氧化环境而形成,这一过程导致新生岩浆锆石负Eu异常程度降低。新生锆石加权平均年龄为(113.5±3.8)Ma,与成矿年龄一致,据此认为早白垩世的岩浆事件是金厂金矿成矿事件的直接原因,成矿背景为太平洋板块俯冲后的岩石圈伸展。     

渤海湾盆地中、新生代构造演化研究

根据中生界上侏罗统和下白垩统地层和控盆断裂分布分析,中生代晚期晚侏罗—早白垩世郯庐断裂带的左旋走滑平移导致郯庐断裂带以西自北向南发育了3个北西向断堑系,即北部的渤海断堑系、中部的济阳断堑系和南部的鲁西南断堑系。从区域资料综合分析,渤海湾盆地的基本格局是早第三纪以来的新生代盆地格局。渤海湾盆地的形态、构造和沉积特征及热流值分布表明该盆地在新生代为拉分盆地。根据渤海湾盆地的各个坳陷内新生代各时期的地层分布、沉积厚度和控盆边界断裂在各时期的空间位置以及活动性质综合分析,恢复了盆地新生代以来的构造演化格局。中、新生代盆地构造和沉积分布特征表明渤海湾盆地是一个中、新生代叠合盆地。     

Formation age and tectonic environment of the Gantaohe Group, North China Craton: Geology, geochemistry, SHRIMP zircon geochronology and Hf-Nd isotopic systematics

The Gantaohe Group is an important early Precambrian unit in the Trans-North China Orogen,North China Craton,and is mainly composed of greenschist-facies metabasalt,meta-sandstone and dolomitic marble.We report whole-rock geochemical compositions and SHRIMP zircon ages as well as LA-ICP-MS Hf-in-zircon isotopeic analyses for metabasalts from the Gantaohe Group.SHRIMP dating yielded a weighted mean 207Pb/206Pb age of 2087±16 Ma(MSWD=1.3) for magmatic zircons,but there are also abundant ca.2.5 Ga inherited zircon xenocrysts.The magmatic zircons shows a large Hf(t) variation in Hf(t) from 7.17 to +0.45,suggesting an isotopically highly heterogeneous source for the metabasalt.Chemically all samples show no distinct Zr or Hf anomalies,and some samples show no Nd or Ta anomalies in a primitive mantle-normalized trace element variation diagram,and their whole-rock Nd(t) values range from 4.0 to 0.8.We suggest that the basalt is formed by partial melting of a depleted mantle source,followed by significant crustal contamination.Field observations,the presence of abundant inherited zircon,as well as isotope and trace elements geochemistry support formation of the Gantaohe Group on top of a continental basement.These data and the regional geology lead us to conclude that the Trans-North China Orogen constituted an intracontinental rift during the Paleoproterozoic that was connected to the Eastern Block since the end of the Archean.     

Zircon U-Pb and Hf isotopes of volcanic rocks from the Batamayineishan Formation in the eastern Junggar Basin

An internal structural study was conducted to investigate U-Pb age, trace elements and Hf isotopes of basaltic zircons from the Batamayineishan Formation. The basalt was obtained from drill well San-Can 1 on the eastern Luliang uplift within the Junggar Basin. Trace element data of zircons show that all samples are magmatic, with similar REE patterns, including positive Ce (δCe=5.06–134), but negative Eu (δEu=0.06⦒0.55) anomalies and enrichment in heavy rare earth elements. Among 25 grains, the concordant ages were subdivided into three groups; ages of 300.4±1.3 Ma (n=11), 339.2±2.7 Ma (n=3) and 392.0±1.7 Ma (n=8). Three remaining grains were nearly concordant, with ²⁰⁶Pb/²³⁸U ages of 510±7, 488±6 and 453±6 Ma, respectively. The youngest concordant age (i.e., 300.4±1.3 Ma) could be interpreted as the formation age of the studied basaltic rock; this is consistent with the sampling position at the upper part of the Batamayineishan Formation. On the other hand, ages such as Ordovician and early Devonian are consistent with the ages of island-arc volcanic rocks (enrichment in Pb) or ophiolites around the basin. Moreover, the positive ɛ _Hf(t) values of the early and middle Paleozoic zircons (+3.6–+10.5) may suggest that the basement traversed by the studied volcanic rocks may be Paleozoic in age, formed from the residual oceanic crust and island-arc complex. The ɛ _Hf(t) values (+4.2–+17.1) of the late Paleozoic (∼300.4 Ma) zircons suggest that the basaltic magmas were derived from partial melting of the asthenospheric mantle or depleted lithospheric mantle. These magmas were slightly contaminated by the existence of early-middle Paleozoic materials. The late Carboniferous basalts represent direct eruption of mantle-derived magmas at the upper crustal level during a post-collisional tectonic setting. We therefore consider that extensive vertical growth of the continental crust to have occurred before the late Carboniferous.     

Subduction age of Neo-Tethys oceanic crust in southwest Yunnan, China: Laser micro-area40Ar-39Ar dating

The basic granulite, which is considered to be the MORE based on geochemistry and isotopic characteristics[1], has been discovered recently as the enclaves in the Yingjiang island-arc magmatic suite on the border of Burma and west Yunnan, east of Myitkyina suture in the eastern Burma. The laser micro-area 40Ar-39Ar technique is used to date the age of garnet and cliopyroxene that is the result of the early metamorphic event. The isochron outcome is -74.4 Ma which is induced to be the age of the suduction event of the Myitkyina oceanic crust on the basis of the Cenozoic lithosphere tectonic evolution, tectonic thermal events and the age of deformation and metamorphism. The discovery of the high-grade or high-pressure metamophic rocks in the island-arc magmatic suite by the way of studying its P-T-t paths can provide a good way to study the age and process of oceanic crust subduction, slab break-off, metamorphic terrain exhumation and the evolution of paleoocean basin.     

Palaeoproterozoic Khondalite Belt in the western North China Craton： New evidence from SHRIMP datin8 and Hf isotope composition of zircons from metamorphic rocks in the Bayan Ui-Helan Mountains area

Zircom U-Pb age and Hf isotope analyses were made on gneissic granite and garnet-mica two-feldspar gneiss from the Helanshan Group in the Bayan Ul-Helan Mountains area, the western block of the North China Craton (NCC). Zircons from the gneissic granite commonly show core-mantle-rim structures, with magmatic core, metamorphic mantle and rim having ages of 2323±20 Ma, 1923±28 Ma and 1856±12 Ma, respectively. The core, mantle and rim show similar Hf isotope compositions, with single-stage depleted mantle model ages (TDM1) of 2455 to 2655 Ma (19 analyses). Most of the detrital zircons from the garnet-mica two-feldspar paragneiss have a concentrated U-Pb age distribution, with a weighted mean 207Pb/206Pb age of 1978±17 Ma. A few detrital zircons are older (2871 to 2469 Ma). The age for metamorphic overgrown rim was not determined because of strong Pb loss due to their high U content. The zircons show large variation in Hf isotope composition, with TDM1 ages of 1999 to 3047 Ma. In com- bination with previous studies, the main conclusions are as follows: (1) protolith of the khondalite se- ries in the Helanshan Group formed during Palaeoproterozoic rather than the Archaean as previously considered; (2) The results lend support to the contention that there is a huge Palaeoproterozoic Khondalite (metasedimentary) Belt between the Yinshan Mountains Block and the Ordos Block in the Western Block of NCC; (3) The widely-distributed bodies of early Palaeoproterozoic orthogneisses in the Khondalite Belt might be one of the important sources for detritus material in the khondalite series; (4) Collision between the Yinshan Block, the Ordos Block and the Eastern Block occurred in the same tectonothermal event of late Palaeoproterozoic, resulting in the final assembly of the NCC.