河南焦作云台山早前寒武纪变质基底锆石SHRIMP U-Pb年龄

应用离子探针技术,对华北太行山南缘钾长石化长英质副片麻岩和钾长石化片麻状奥长花岗岩进行了锆石年龄测定。钾长石化长英质副片麻岩的变质原岩为泥砂质碎屑沉积岩,其形成时代很可能为新太古代。碎屑锆石普遍存在强烈铅丢失,靠近上交点的5个数据点207Pb/206Pb加权平均年龄为3399Ma±8Ma,代表了物源区组成的时代。钾长石化片麻状奥长花岗岩2组锆石207Pb/206Pb加权平均年龄分别为2511Ma±13Ma(岩体形成时代)和2735Ma±16Ma(残余锆石年龄),分别代表该岩体形成时代和残余锆石年龄。新的资料支持了华北克拉通中部造山带太古宙地质体与其东部陆块存在亲缘关系的认识。     

华北克拉通新太古代板块俯冲作用:来自山西云中山地区变质高镁火成岩组合的证据

在华北克拉通中部的山西云中山地区,新太古代花岗闪长质片麻岩中存在一些超镁铁质岩-镁铁质岩块及由斜长角闪岩、角闪变粒岩、石英岩和石榴夕线黑云片岩等岩石类型构成的变质表壳岩残片,其中的超镁铁质-镁铁质岩、斜长角闪岩和角闪变粒岩构成一套高镁火成岩组合。超镁铁质岩已变质为橄榄绿泥阳起片岩等岩石类型,呈变余斑状结构,橄榄石斑晶仍有保存;岩石SiO_2含量为39.22%～44.99%,Al_2O_3为8.82%～13.47%,Mg O为19.24%～22.13%,Na_2O+K_2O=0.71%～1.11%,CaO为5.75%～8.42%;Al_2O_3/TiO_2=14.8～17.4,CaO/Al_2O_3=0.60～0.84;化学成分上与科马提岩有一定的相似性。与之紧密伴生的斜长角闪岩也具有高镁特征,Mg O含量为11.28%～15.09%,铝、硅和碱质均偏低,具正铕异常,显示堆晶辉长岩的特征。非高镁斜长角闪岩有相对高的铝、硅和碱质,其原岩应为钙碱性玄武岩。角闪变粒岩样品的SiO_2含量为54.21%～55.71%,Al_2O_3为14.24%～15.49%,Mg O为6.26%～8.28%,Fe OT/Mg O=1.11～1.58,高钠低钾,Na_2O+K_2O=3.7%～4.78%,Na_2O/K_2O=5.15%～13.13,Mg#=53.0～61.5,属于高镁安山岩。由超镁铁质质岩-斜长角闪岩-角闪变粒岩构成的变质高镁火山岩组合具有钙碱性系列趋势。超镁铁质岩稀土元素含量总量较低,具有轻稀土富集和重稀土亏损的稀土型式;斜长角闪岩与超镁铁质岩比较,除富集大离子亲石元素和Cr、Ni明显较低外,具有相似的微量元素图谱形态。三种岩石类型在微量元素蛛网图上均显示出Ta、Nb、Ti负异常和Pb正异常。野外产状和岩石地球化学特征表明超镁铁质岩和高镁斜长角闪岩属于阿拉斯加型杂岩体,角闪变粒岩属于赞岐岩质高镁安山岩。在Zr/Nb-Nb/Th和Nb/Y-Zr/Y构造环境判别图解上显示出与俯冲相关的演化趋势,在Hf-Th-Ta、Nb/La-(La/Sm)N和Th/Yb-Nb/Yb图解上也落在岛弧钙碱性岩石区域。以上特征表明高镁火成岩组合形成于与板块俯冲相关的岛弧构造背景。野外地质关系和锆石U-Pb年龄限定高镁火成岩组合形成时代在～2.5Ga。云中山地区阿拉斯加型镁铁质-超镁铁质杂岩与赞岐岩质高镁安山岩共生,表明该地区存在新太古代的板块俯冲作用,为太古宙存在板块构造机制提供了新证据。     

鲁西地区石门山—凤仙山岩体的锆石SHRIMP U-Pb定年及形成时代

鲁西地区石门山岩体主要岩性为片麻状花岗闪长岩,原划为新太古代早期侵入岩。根据新测锆石SHRIMPU-Pb年龄为（2530±8）Ma,其形成时代确定为新太古代晚期。凤仙山岩体为中粒二长花岗岩,锆石SHRIMP U-Pb年龄为（2513±12）Ma,并侵入片麻状花岗闪长岩。石门山岩体属峄山岩套,为TTG质花岗岩,是地幔岩浆侵入混入地壳物质形成的。凤仙山岩体属傲徕山岩套二长花岗岩,为上地壳物质重熔（深熔）作用形成的。峄山岩套TTG类岩石是2560~2530 Ma壳幔岩浆活动的产物,岩体普遍具有片麻状构造,表明经历变质变形作用。未受区域变质作用的傲徕山岩套大规模壳源花岗岩是2530~2500 Ma地壳物质部分熔融形成的,与华北克拉通新太古代末超大陆拼合有关,2530 Ma是鲁西地区重要的构造热事件发生时期。     

Precambrian Tectonic Affinity of the Southern Langshan Area, Northeastern Margin of the Alxa Block: Evidence from Zircon U-Pb Dating and Lu-Hf Isotopes

The Alxa Block is the westernmost part of the North China Craton (NCC), and is regarded as one of the basement components of the NCC. Its geological evolution is of great significance for the understanding of the NCC. However, the Precambrian basement of the Alxa Block is still poorly studied. In this study, we present new in situ LA-ICP-MS zircon U-Pb and Lu-Hf isotope data from the Diebusige Metamorphic Complex (DMC) which located in the eastern Alxa Block. Field and petrological studies show that the DMC consists mainly of metamorphic supracrustal rocks and minor metamorphic plutonic rocks and has experienced amphibolite-granulite facies metamorphism. Zircon U-Pb dating results suggested that the amphibolite sample yields a crystallization age of 2636 ± 14 Ma and metamorphic ages of 2517–2454 Ma and 1988–1952 Ma, proving the existence of exposed Archean rocks in the Langshan area and indicating that late Neoarchean to Paleoproterozoic metamorphic events existed in the Alxa Block. Two paragneiss samples show that the magmatic detrital zircons from the DMC yield 207Pb/206Pb ages ranging from 2.48 Ga to 2.10 Ga with two youngest peaks at 2.13 Ga and 2.16 Ga, respectively, and they were also overprinted by metamorphic events at 1.97–1.90 Ga and 1.89–1.79 Ga. Compilation of U-Pb ages of magmatic detrital and metamorphic zircons suggested that the main part of the DMC may have been formed at 2.1–2.0 Ga. Zircon Lu-Hf isotope data show that the source materials of the main part of the DMC were originated from the reworking of ancient Archean crust (3.45–2.78 Ga). The Hf isotope characteristics and the tectonothermal event records exhibit different evolution history with the Khondalite Belt and the Yinshan Block and the other basements of the Alxa Block, indicating that the Langshan was likely an independent terrain before the middle Paleoproterozoic and was subjected to the middle to late Paleoproterozoic tectonothermal events with the Khondalite Belt as a whole.     

鲁西地区新太古代地壳增生事件：来自花岗岩和二长花岗岩U-Pb年代学、Hf同位素和岩石地球化学的证据

鲁西地区是全球完整保存新太古代早期TTG（英云闪长岩-奥长花岗岩-花岗闪长岩）和绿岩带的区域,是研究太古宙岩浆演化类型和太古宙时期壳幔作用以及构造模式的典型区域。本文在野外地质调查的基础上,通过年代学、Hf同位素和岩石地球化学等手段,探讨了鲁西地区新太古代花岗岩和二长花岗岩的地球化学特征和形成背景。鲁西地区新太古代花岗岩和二长花岗岩U-Pb年龄主要为2 537和2 566 Ma。花岗岩（TA1802）εHf (t)值为-1.4～2.9,平均值为0.65,二阶段模式年龄约为2.9 Ga;二长花岗岩（TA1812）εHf (t) 值为-0.4～2.7,平均值为1.31,二阶段模式年龄为 3 073～2 886 Ma,平均值约为2.9 Ga;二长花岗岩（TA1817）εHf (t) 值为0.3～4.7,平均值为3.35,二阶段模式年龄为3 032～2 762 Ma,平均值约为2.8 Ga。在εHf (t)-t 图解上,鲁西地区新太古代花岗岩和二长花岗岩年龄演化线均落在2.9～2.8 Ga地壳演化线上,且与二阶段模式年龄大致相同,即表明鲁西地区新太古代花岗岩和二长花岗岩源于2.9～2.8 Ga的古老地壳重融。鲁西地区新太古代花岗岩和二长花岗岩均表现为高w(SiO2)、w(Al2O3)和富Na2O特征,大部分属于准铝质岩石。稀土元素球粒陨石标准化分布型式上,均表现为轻稀土元素（LREE）富集和重稀土元素（HREE）亏损,且中重稀土元素出现分馏。花岗岩样品中,有两个样品（TA1801-1与TA1824）表现出Ta富集,其余样品均表现为K、Rb、Ba和Th等大离子亲石元素富集,Nb、Ta、Ti亏损。二长花岗岩也同样表现为K、Rb、Ba和Th等大离子亲石元素富集,Nb、Ta、Ti亏损,部分熔融残余矿物存在石榴石、金红石以及少量斜长石、角闪石。根据上述地球化学特征, 并结合区域地质特征,鲁西地区新太古代花岗岩和二长花岗岩构造背景为同碰撞背景,该构造模式是大陆地壳有效增生。     

坦桑尼亚盖塔(Geita)绿岩带型金矿矿床地质特征

盖塔(Geita)金矿是坦桑尼亚重要的绿岩带型金矿之一。文章阐述了矿床地质背景、矿床地质特征,以及矿床同位素年代特征,并对矿床成矿模式进行了对比。在此基础上认为盖塔金矿以块状黄铁矿和浸染状黄铁矿的矿化为主,成矿时代约为2644~2680Ma,属于太古宙热液型金矿床,具有明显的"层控"特征,后生成矿模式可能是盖特金矿的矿床成因。     

鲁西泰山岩群变质枕状玄武岩岩相学和侵入的奥长花岗岩SHRIMP锆石U Pb年代学

鲁西泰山岩群柳杭岩组中,典型变质枕状玄武岩出露在济南章丘的团员沟村西一带。本文对变质枕状玄武岩的野外地质和岩相学特征,作了详细描述。电子探针分析表明,岩枕内部既有原生斜长石(An>30),又有绿片岩相变质形成的钠长石(An<10)。侵入柳杭岩组的片麻状奥长花岗岩中的岩浆锆石SHRIMP U-Pb年龄为2707±9Ma,它限制了泰山岩群形成时代不晚于2.71Ga。     

登封群的定年及其划分问题的探讨

对登封群人们先后采用过K—Ar、Rb-Sr、U—Pb、单颗粒锆石Pb-Pb、Sm—Nd等多种同位素定年方法。由于不同方法得到的结果差别很大,直接影响了对登封群的认识,因而对登封群出现了多种划分方案。本文综合分析后认为,登封群花岗-绿岩地体形成于新太古宙末期(2500～2600Ma),难以划分出元古代的地层单元。另外,对已有的同位素测年成果使用上要结合样品的地质、地球化学特征进行具体分析,才能得出合理的解释。     

Geochemical Characteristic of Charnockites in North Margin of North China Craton: Indicating the Significiant of the Neoarchean Tecnotic Event

The Neoarchean charnockites of North margain of North China Craton(NCC) has become a hot topic into understanding the Early Precambrian basement. Although there is a broad consensus that charnockite is usually related to granulite facies metamorphism, whether its petrogenesis and tectonics characteristics remains controversial. Inclusions within hypersthene and garnet in charnockite are used to identify the peak granulite facies mineral assemblage, with the formation of Magnesian–charnockite attributed to anatexis of the protolith associated with this granulite facies metamorphism. The distribution of major and trace elements in charnockite is very uneven, significant depleted in LILEs(eg. Cs, U, Th) and HFSEs(eg. Nb, Ta, P and Ti), riched in Sr. Raising to the coexistence of Eu–enrichment and Eu–depletion type of REE patterns that influenced by the content of plagioclase and the remnants minerals of zircon and apatite. Comparative the petrography, geochemistry and geochronology data of Magnesian–charnockite indicate that the ratios of mafic pellites and basalts involved in anatectic melting are different by the upwelling of mantle magma, also resulting in the Eu anormals characteristics. The formation of the Magnesian–charnockite is closely connected with the subduction of the NCC oceanic crust(About ～2.5 Ga). However, Ferroan–charnockite may be the formed by the crystallization differentiation of the upwelling of mantle–derived shoshonitic magma(About ～2.45 Ga), with the lower crust material addition.     

吉东南新太古代晚期片麻岩类的时代、成因及其对早期地壳形成演化的制约

吉林省东南部通化地区广泛出露早前寒武纪花岗质片麻岩类,其岩石组成、形成时代和成因对深化认识华北克拉通东北缘早期地壳形成演化历史具有重要意义。本文系统的岩石学、锆石U-Pb年代学、元素和Lu-Hf同位素地球化学等研究结果表明,这些花岗质片麻岩类按照SiO₂质量分数总体可划分为高硅和低硅两组：前者主要由二长花岗质片麻岩、奥长花岗质片麻岩及英云闪长质片麻岩组成,其原岩形成于2 549~2 557 Ma;而后者由石英二长闪长质片麻岩及花岗闪长岩质片麻岩组成,其原岩形成于2 534~2 552 Ma;并且两组岩石都含有约2 600 Ma的捕获锆石,共同遭受了约2 500 Ma变质作用的影响。地球化学分析结果显示,低硅岩组具有较高的MgO、CaO、Na₂O质量分数,属于高钾—中钾钙碱性系列,并且富集LREE、亏损HREE和HFSE;与之相比,高硅岩组则具有较低的MgO和CaO质量分数,显示更强烈的轻、重稀土元素分馏以及Nb、Ta、P、Ti等亏损的特征;但两者均具有较弱的正或负Eu异常。结合区域最新研究成果,认为研究区低硅和高硅两组岩石应具有相同的源区,其形成可能与大洋板片俯冲、岩浆底侵引起的地壳部分熔融作用有关。此外,两组岩石具有相似的ε_Hf（t）值（2.72~7.95）和模式年龄（2.86~2.55 Ga）,暗示区域主要存在新太古代晚期地壳生长事件;结合区域内变质火山岩的研究进展,认为吉林省东南部通化地区花岗质片麻岩类可能形成于活动大陆边缘的构造背景。