Heterogenous zircons from Mesozoic igneous rocks in the North China Craton and their tectonic implications

Based on a synthesis of zircon inheritance from Mesozoic igneous rocks in the eastern portion of the North China Craton (NCC) , it is proposed that inherited zircons with Neoproterozoic ages identified from these rocks are of a heterogenous derivation from the Yangtze /South China block, rather than from the NCC itself. The mechanism that introduces these zircons incorporated into the NCC is likely by tectonic underplating during the Triassic continental subduction of the Yangtze block beneath the NCC. Tectonic addition of abundant crustal materials represented by the heterogenous zircons into the NCC, probably along Moho or weak interfaces within the NCC's crust, led to the crustal thickening in the NCC. These heterogenous materials, either as ( partial) source rocks or as contaminants of the magmas generated during an extension environment following the crustal thickening, were reworked and therefore have significant contribution to petrogenesis of the Mesozoic igneous rocks. The crustal thickening resulted from the tectonic underplating, as indicated by the distribution extent of the heterogenous zircons, is spatially similar to that of the lithospheric thinning, with both mainly occurring in the eastern segment of the NCC. This is probably suggestive of an intrinsic relation between the thickening and thinning events during the Mesozoic evolution of the NCC.     

桐柏—大别山碰撞造山带的大地构造演化

桐柏—大别山碰撞造山带是华北板块南部大陆边缘和扬子板块北部大陆边缘长期演化和碰撞的结果。造山带主要由北淮阳加里东构造带、桐柏—大别山古老断块隆起带和随广加里东构造带组成。根据现今查明的三条蛇绿混杂岩带和不同时代岩系的原岩建造及区域构造特征,重建了其碰撞期前的古地理-古构造格局。在加里东末期,华北板块与扬子板块发生碰撞,形成了桐柏—大别山造山带。在碰撞期及碰撞期后曾发生了大规模的滑脱-推覆构造。     

中条山涑水杂岩的同位素年代学研究及其地质意义

中条山是中国重要的铜多金属成矿带,拥有著名的晚太古代"变斑岩型"铜矿峪大型铜矿床和元古代"层控型"胡家峪—篦子沟铜矿床,近年来又在中条山西南段的涑水杂岩中发现以变基性火山岩(斜长角闪岩)为容矿岩石的桃花洞铜矿。为了弄清楚该铜矿的形成时代及其成矿地质背景,利用电感耦合等离子质谱(LA-MC-ICP-MS)方法对桃花洞铜矿容矿围岩—涑水杂岩中的寨子—西姚灰色片麻岩、斜长角闪岩及二长花岗岩进行了同位素年代学研究。结果表明:寨子—西姚灰色片麻岩、斜长角闪岩脉和二长花岗岩中锆石的岩浆结晶年龄分别为(2 625±11)、(2 592±16)、(2 548±15)Ma;岩石中古老继承性锆石的年龄分别为(2 790±15)、(2 773±24)、(2 782±34)Ma;三种不同成生顺序的岩石中均有大于2 700Ma的锆石存在,且年龄相当接近;中条山地区涑水杂岩可能最初形成于太古代。涑水杂岩作为与成矿关系密切的容矿围岩,其成岩时代可以间接指示成矿时代,由此得出赋存在变基性火山岩层中的古火山含矿原岩建造型铜矿有可能是中国最古老的铜矿之一。     

华机构造单元划分及其特征

华南（研究区）由杨子地块东南部和华夏地块组成。前者划分为三个次级构造单元;江南构造城,怀玉山—浙西北构造域,彭庐构造域;后者划分为二个次级构造单元;闽北—浙东南构造域,桂粤湘赣闽构造域。华夏地块相对于扬子地块是比较活动的构造单元。     

黔西赫章2.5 Ga石英二长闪长岩的发现及其地质意义

黔西位于扬子板块西南缘,有关扬子板块内约2.5 Ga的岩浆事件记录极少。最近,对黔西赫章发现的石英二长闪长岩的研究表明,其成岩年龄为（2 542±9）Ma,为该区首次发现的新太古代晚期岩石。该岩石主要由斜长石、碱性长石、石英、角闪石、黑云母等矿物组成,具有较高的SiO₂（59.2%~60.6%）、Na₂O（4.70%~4.85%）质量分数和Na₂O/K₂O（3.02%~3.19%）比值,以及较低的Al₂O₃（17.0%~17.7%）、MgO（2.42%~2.61%）质量分数。样品稀土元素总质量分数为120×10-6~221×10-6,（La/Yb）_N=8.32~17.98,轻、重稀土元素分异不明显,表现为弱的右倾稀土元素配分模式,并具有弱的Eu负异常。在微量元素蛛网图上,样品富集大离子亲石元素（Ba、Sr）、亏损高场强元素（Nb、Ta、Ti）,具有弱负到正的ε_Hf（t）值（-0.51~+6.93）和正的ε_Nd（t）值（+0.22~+0.88）,与太古宙低铝型高重稀土元素TTG的地球化学性质基本一致。综合研究显示,该岩石可能是在角闪岩相下,下地壳基性岩部分熔融形成的,源区残留相主要为金红石以及斜长石。黔西约2.5 Ga岩石的发现证实了扬子板块西南缘具有新太古代基底的存在,这为扬子周缘新太古代岩浆成因的碎屑锆石研究提供了依据,为扬子板块新太古代地壳演化提供了新的信息。      

青藏高原东南缘碰撞造山结构与物质组成:来自岩石地球化学和地球物理的联合约束

青藏高原东南缘位于印度板块与欧亚板块侧向汇聚部位,是检验碰撞造山动力学模型的理想场所。尽可能全面收集该区已有地球物理和新生代岩浆岩数据,探讨这些资料对碰撞造山带结构和物质组成的指示。结果表明:青藏高原东南缘不同部位的壳幔结构和组成存在较大差异。兰坪—思茅地块、保山地块和腾冲地块等的中地壳(15~30 km深度)普遍发育低速层,表明富水层或者部分熔融物质的存在,为青藏高原物质向东南流动提供了可能。部分熔融产物以大型剪切带内具有高Sr、低Nd同位素特征的淡色花岗岩脉为代表。但是,扬子板块同等深度下却发育高速层,其组成很可能是峨眉山玄武岩,它的存在阻隔了碰撞带物质向东流动。扬子板块和兰坪—思茅地块下地壳底部均出现呈条带状展布的高速体。根据新生代具有高Sr、低Y的岩石显示的下地壳源区特征,结合该区地质演化历史,将上述两套呈条带状展布的高速体分别解释为新元古代铁镁质弧岩浆岩和二叠纪—三叠纪铁镁质弧岩浆岩。青藏高原东南缘地幔各向异性存在明显南、北分区特征,在26°N以北表现为SN向,在26°N以南表现为近EW向。这一差异跟俯冲的印度板片撕裂有密切关系。该撕裂在综合地球物理剖面上显示为突变的印度板片俯冲角度,在地表表现为苦橄岩、煌斑岩、埃达克岩以及淡色花岗岩等的集中出露。这一新模型明显区别于前人的岩石圈拆沉和对流减薄等作用。     

Discovery of Late Permian Jianshanzi volcanic rocks in Qinghe valley of northern Liaoning and its geologic significance

Jianshanzi volcanic rocks at Qinghe valley in the northern Liaoning were considered belonging to Early Proterozoie Gaojiayu Formation of Liaohe Group, or to Early Cambrian Beidagou Formation of Qinghezhen Group, or Middle-Late Proterozoic Shenjiapu Formation-Complex of Kaiyuan Group-complex. Dating the zircons from the dacite with schistosity is 2 506 Ma in method of U-Pb （SHRIMP）. This evidence indicates the rocks may be referred to Late Permian in age. Discovery of the rocks is significant to re-recognize stratigraphic property of ＂Liaohe Group＂, regional geoteetonie location and revolution of orogenic zone in Qinghe valley of the northern Liaoning.     

苏鲁造山带北缘五莲地区五莲群变质地层特征及形成时代——锆石MCICPMS UPb测年的证据

五莲群下部为海眼口组,一段以斜长角闪岩为主,二段以云母变粒岩、片岩为主;上部为坤山组,主要为白云石大理岩、方解石大理岩,下部夹石英岩、云母片岩。五莲群下部地层海眼口组电气石石英岩与黑云变粒岩最年轻的碎屑锆石MC-ICPMS U-Pb年龄数据为1685～1727Ma,这限定了五莲群原岩沉积时代属中元古代。而侵入海眼口组黑云变粒岩的花岗岩脉岩浆锆石206Pb/238 U表面年龄加权平均值为(777.5±1.8)Ma。表明花岗岩脉所代表的热事件与扬子北缘Rodinia超大陆裂解事件有关;说明南华纪时期,五莲群位于扬子地台的北缘,而不是华北地台的东南缘。所以将五莲群再从粉子山群中重新划出,恢复为原五莲群及海眼口组、坤山组。     

青藏高原东南缘构造应力场重构

采用有限元方法，针对青藏高原东南缘建立更细致、更精确的三维有限元弹性模型。选取9种不同的应力边界条件，分别进行优化分析后处理，将对应台站形变模拟值与GPS实测值进行误差分析，最终选取最佳方案作为古构造应力场。结果表明，青藏高原东南缘4 Ma BP的古应力场主要起源于中国大陆周围板块的相互作用，特别是印度板块NNE向强烈碰撞作用，成为中国大陆尤其是西南部青藏高原地区构造应力场最主要的动力来源，控制各个块体相互作用的方式和运动格局。青藏高原东南缘古应力场主要包括几个力源：西北部青藏高原侧向挤压造成的WE向应力约105 MPa；西南部直接来自于印度板块的NE-WS向应力约70 MPa；南部NS向作用力33 MPa；东南部扬子块体侧向NW-SE阻挡力56 MPa；北东部受扬子块体强烈EW向阻挡力90 MPa。这些力源共同作用于青藏高原东南缘，形成现今复杂应力场。
     

内蒙古柴胡栏子金矿区闪长玢岩锆石U——Pb定年及其地质意义

内蒙古柴胡栏子金矿区断裂构造发育,岩浆岩类型复杂。本文在野外地质工作的基础上,通过锆石LA-ICP-MSU-Pb同位素年代学研究,得到了矿区岩浆岩的形成时代,并对海西期的岩浆活动进行了讨论。闪长玢岩样品中存在(2447±13)Ma(MSWD=0.0108)的继承性岩浆锆石和(296.6±3.5)Ma(MSWD=0.58)的结晶岩浆锆石。认为结晶锆石的年龄代表了闪长玢岩的形成年龄;(2447±13)Ma的继承性岩浆锆石的存在说明了闪长玢岩在侵位过程中存在壳源物质的重熔和加入。     

Discovery of Late Permian Jianshanzi volcanic rocks in Qinghe valley of northern Liaoning and its geologic significance

Jianshanzi volcanic rocks at Qinghe valley in the northern Liaoning were considered belonging to Early Proterozoic Gaojiayu Formation of Liaohe Group, or to Early Cambrian Beidagou Formation of Qinghezhen Group, or Middle-Late Proterozoic Shenjiapu Formation-Complex of Kaiyuan Group-complex. Dating the zircons from the dacite with schistosity is 2 506 Ma in method of U-Pb (SHRIMP). This evidence indicates the rocks may be referred to Late Permian in age. Discovery of the rocks is significant to re-recognize stratigraphic property of "Liaohe Group", regional geotectonic location and revolution of orogenic zone in Qinghe valley of the northern Liaoning.     

安徽南陵—宣城地区岩浆岩锆石U-Pb年龄及元素地球化学特征

安徽南陵-宣城地区是一个中-新生代火山-沉积盆地,位于长江中下游构造-岩浆-成矿带东北段的东南翼。对该区发育的岩浆岩开展了较为系统的LA-ICP-MS锆石U-Pb定年及岩石主量、微量和稀土元素分析,并与长江中下游构造-岩浆-成矿带其他地区岩浆岩进行对比,旨在确定岩浆岩的成岩时代、探讨岩浆岩成因及其与成矿的关系。南陵-宣城地区岩浆岩一部分侵入于盆地基底中,另一部分喷发形成盆地盖层,还有一部分产于盆地之上的推覆构造(体)中。侵入岩的岩性主要为花岗岩、花岗闪长岩、石英闪长岩、辉石闪长岩等,火山岩主要为英安质火山碎屑岩和熔岩。获得的侵入岩锆石U-Pb年龄主要为138~135 Ma,火山岩年龄均小于134 Ma,表明岩浆作用发生于晚中生代(燕山晚期)早白垩世。岩浆岩主量元素显示高Si、K的特征,为亚碱性高钾钙碱性系列岩石;微量元素组成显示岩浆岩富集Rb、Th、U、K等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素,火山岩比侵入岩较为亏损Sr和P;球粒陨石标准化稀土元素配分模式均表现为富集轻稀土元素的右倾模式和较弱的Eu负异常。元素地球化学特征指示区内岩浆岩具有壳幔混源且以幔源为主的特征。南陵-宣城地区既发育与长江中下游构造-岩浆-成矿带隆起区(如铜陵地区)同位素地质年龄和地球化学特征基本一致的侵入岩,又发育与凹陷区(如庐枞、宁芜等盆地)同位素地质年龄和地球化学特征基本一致的火山-次火山岩,显示该区晚中生代岩浆作用具有长江中下游构造-岩浆-成矿带隆起区和凹陷区的双重特征。岩浆作用的双重特征暗示与其有关的成矿作用也可能具有双重性,即既可能发育与隆起区侵入岩浆作用有关的斑岩型、矽卡岩型和脉型铜金等多金属矿床,也可能发育与凹陷区火山-次火山岩有关的玢岩型铁(硫)矿床。     

Provenance and Tectonic Implications of Paleozoic Strata in the South Yellow Sea Basin,China–Revealed from the Borehole CSDP-2

Well CSDP-2 is a fully coring deep drilling hole, penetrating the thick Paleozoic marine strata in the South Yellow Sea Basin(SYSB) in the lower Yangtze Block(LYB). Based on the petrological and geochemical analysis of 40 sandstone samples from the core CSDP-2, the provenance and tectonic features of Paleozoic detrital rocks from SYSB are analyzed and systematically delineated in this article. The results show that the Silurian – Carboniferous sandstones are mature sublitharenite, while the Permian sandstones are unstable feldspathic litharenite. The average CIA(chemical index of alteration) is 74.61, which reflects these sediments were derived from source rocks with moderate chemical weathering. The REE(rare earth element) patterns are characterized by LREE enrichment, flat HREE and obviously negative Eu anomaly, which are similar to that of the upper continental crust. Dickinson QFL discrimination results indicate the recycled orogeny provenance. Various diagrams for the discrimination of sedimentary provenance based on major and trace element data show all the sediments were derived predominantly from quartz sedimentary rocks, of which the Permian strata contain more felsic sedimentary rocks. Geochemical data for these detrital rocks suggest they occur at the passive continental margin and island arc settings, and the Permian sandstone presents active continental margin setting.     

金川铜镍硫化物矿床Hf同位素地球化学特征与岩浆源区

金川铜镍硫化物矿床是中国最大镍资源基地,形成于新元古界超镁铁质小岩体中,围岩是古元古界白家嘴子组一套角闪岩相变质岩,矿床的成矿关键因素一直受到广泛关注。详细的地质填图发现岩体与围岩为侵入接触,呈岩席状产出,西南部为岩体顶部,东北部为岩体底部。通过SHRIMP锆石U-Pb年代学及Hf同位素研究,获得矿床中锆石年龄平均为(840±10)Ma,与前人获得的年龄(831.8±0.6)Ma在误差范围内一致,代表成岩年龄的锆石εHf(t)值主要集中在-8.52~-4.85;Hf模式年龄大于锆石U-Pb年龄,表明其岩浆源区受到过地壳物质的混染或来自于富集地幔。Hf-Sr-Nd-Pb-Os同位素研究发现,形成金川铜镍硫化物矿床的岩浆源区属于Ⅰ型富集地幔(EMⅠ),成岩成矿地质背景与陆内裂谷有关,这种特殊的构造环境与地幔源区可能对形成金川超大型铜镍硫化物矿床发挥了重要贡献。     

Zircon U-Pb geochronology and geochemistry of diorite dikes from Nancha ore deposit in Tonghua area of Jilin and its geological significance

The authors presented geochronology and geochemical data of diorites from Nancha gold deposit in Tonghua region,with the aim to constraining its formation age,magma source and tectonic setting.LA-ICP-MS U-Pb dating results of zircons from the diorites indicate that the rocks were formed in the Middle Jurassic( 171± 2 Ma,MSWD = 1.19).Geochemically,these rocks have Si O_2 concentrations of 52.52%--54.90%,K_2 O of2.14%--3.84%,Na_2 O of 3.17%--3.35%,Mg O of 7.43%--9.34% and high Mg~# of 68.57-72.57.These rocks are characterized by enrichment in large ion lithophile elements( LILE,such as K,Ba,Rb and Sr) and light rare earth elements( LREE),relatively depletion in high field strength elements( HFSE,such as Ta,Nb,Ti and Zr),and heavy rare earth elements( HREE).These characteristics suggest that primary magma of the rocks were derived from the partial melting of mantle with miner crustal contamination,which may related to partial melting of mantle wedge by addition of sediment melt from subducting oceanic crust.Based on former and present studies,the authors consider that the Nancha ore deposit high-Mg diorites were formed in compressional structural setting which is similar to volcanic arc.It could be related to the subduction of the Paleo-Pacific plate beneath the Eurasian continent.     

华北地区重力和地形及其对克拉通破坏深部过程的约束

以重力和地形数据研究现今华北克拉通区域岩石圈热化学结构,探讨华北克拉通破坏过程。首先计算自由空气重力异常、布格重力异常、Airy均衡重力异常;再利用地震学莫霍面观测从地形和布格异常中扣除对应部分,计算残余重力异常及残余地形;最后对残余重力异常进行剩余密度反演。结果表明：1）华北克拉通中、东部存在浮力;2）克拉通东部由温度效应引起的密度负扰动效应略强于化学组分差异引起的密度正扰动;3）现今华北克拉通东部是古老克拉通型地幔和新生正常地幔的混合物,约保留50%~60%古老克拉通地幔成分;4）由重力和密度约束得到的混合地幔结果支持前人提出的多期幕式拆沉的华北克拉通深部破坏过程。     

贺兰山群变质杂岩主变质期的时代探讨

分布在贺兰山脉北端的贺兰山群变质杂岩是一套变质程度已达角闪麻粒岩相的孔兹岩系。以往的研究者均认为它的主期变质作用发生在中太古代。本文利用变质岩中矿物的Rb/Sr等时线年龄,同变质花岗岩全岩Rb/Sr等时线年龄及变质岩和花岗岩中锆石~(207)Pb/~(206)Pb年龄值结合地质事实,证明这套变质岩的主期变质作用发生在早元古代。     

南秦岭碧口群岩石组合特征及其构造意义

碧口群是扬子板块西北缘中晚元古代古海沟—岛弧体系的重要组成部分。岩石组合、岩石化学及稀土元素特征研究表明,其下部为蛇绿岩组合,以大洋E型拉斑玄武岩为特征,代表古俯冲杂岩;上部为重力流沉积组合,以火山质碎屑浊积岩及陆源碎屑浊积岩为特征,类似于海沟型复理石组合,代表古海沟堆积。同时构造变形及变质作用特征表明,在蛇绿岩分布区发育有大型韧性剪切带和高压低温变质的蓝闪片岩。由此可见碧口群属于中晚元古代扬子板块西北缘的古海沟—俯冲地体。     

西昆仑库孜——带长城纪火山岩地球化学特征及地质意义

西昆仑库孜一带长城纪赛图拉岩群为一套火山熔岩-火山碎屑岩-沉积岩组合,火山岩主体为中酸性岩。通过对该地区长城纪火山岩分布特征、岩石学特征及地球化学特征进行分析研究,划分了2个火山喷发旋回。2个喷发旋回岩性无明显区别,均为一套中酸性火山熔岩、火山碎屑岩、沉积岩建造。第一喷发旋回自下而上见7个喷发韵律,爆发指数为41.70%,喷溢指数24.51%,该旋回岩相总体表现为爆发—喷溢—沉积—爆发—沉积—爆发的特点;第二喷发旋回自下而上见4个喷发韵律,爆发指数为46.67%,喷溢指数为18.15%,该旋回岩相总体表现为爆发—沉积—爆发—沉积—爆发的特点,揭示了西昆仑库孜一带古塔里木陆块裂解古洋盆的演化特征,对研究该地区古陆块裂解具有一定的借鉴意义。     

Geochronology,geochemistry and geological significance of Early Cretaceous volcanic rocks from Niangniangshan Formation,Ningwu Basin,middle and lower reaches of the Yangtze River

Ningwu Basin is one of the Mesozoic continental volcanic basins in the middle and lower reaches of the Yangtze River.The volcanic rocks of the Longwangshan,dawangshan,Gushan and Niangniangshan formations,as well as the homologous subvolcanic rocks or small intrusions,are developed from old to new in the Ningwu Basin.Zircon U-Pb dating results show the latialite phonolite of Niangniangshan Formation was erupted at 128±1 Ma(i.e.,Early Cretaceous).The latialite phonolite contains moderate SiO2 contents(57.28%-60.96%)with high Na 2O+K 2O contents,belonging to shoshonite series.The samples have high REE contents,and display right-inclined REE distribution pattern.They are characterized by enrichment in some large ion lithophile elements(e.g.,LILEs,Rb,K),and depletion in some high field strength elements(e.g.,HFSEs,Nb,Ta,Ti).All volcanic samples have relatively depleted Nd isotopic compositions(ISr=0.707197--0.707878;εNd(t)=-0.5--0.9),indicating no genetic relationship with the lower crust of Yangtze plate,but a drift trend towards the EMII.The geochemical data suggest that the Early Cretaceous latialite phonolite was derived from the partial melting of an enriched lithospheric mantle metasomatized by subduction-related fluids in an arc-related setting.Based on the temporal and spatial distribution and geochemical variation characteristics of the regional volcanic rocks,it is suggested that the tectonic system within the study area changed from a subduction-related compression to an extensional environment in the early Early Cretaceous,which was caused by the ridge subduction of the Paleo-Pacific Ocean.