西秦岭关子镇蛇绿混杂岩的地球化学和锆石SHRIMP U-Pb年龄

西秦岭沿天水武山断裂带产出的关子镇蛇绿混杂岩由变玄武岩、变中-基性深成岩浆岩以及少量蛇纹岩组成。变玄武岩具有平坦或轻稀土略亏损的稀土配分型式((La/Yb)_N=0.63～1.24),且不存在Nb、Ta和Ti的负异常,表明它们形成于洋中脊环境。变中-基性深成岩浆岩包含两种类型:类型Ⅰ显示轻稀土富集((La/Yb)_N>2.2)、具有显著Nb负异常((La/Nb)_N>2.4)的特征,类似于岛弧火山岩;类型Ⅱ显示轻稀土亏损到略富集((La/Yb)_N=0.44～1.38)、无显著Nb负异常((La/Nb)_N<1.5),这些特征与上述变玄武岩类似,表明它们也是关子镇蛇绿岩的组成部分。蛇绿岩中辉长岩和闪长岩(该闪长岩属"大洋斜长花岗岩类")样品的锆石SHRIMP U-Pb年龄分别为534±9Ma和517±8Ma,这反映关子镇蛇绿岩可能为早-中寒武世古洋壳残片。由于西秦岭的天水武山断裂带是东秦岭商丹断裂带的西延并共同被认为是华北和华南陆块之间的主缝合线,上述年龄对理解该带及古秦岭洋的演化提供了重要制约。     

漠河盆地东南部中生代火山岩年代学与地球化学研究

漠河盆地东南部中生代火山岩地层主要由光华组和甘河组组成,锆石U--Pb定年结果确定两组火山岩分别形成于128~125 Ma和126~120 Ma。光华组流纹岩高硅富碱、贫钙铁镁;轻重稀土分馏较明显[w(La/Yb)N=13.01~17.99],铕异常中等(δEu=0.49~0.67);富集大离子亲石元素Rb、K、Th、U,亏损高场强元素Nb、Ta、P、Ti;锆石εHf(t)值为-2.5~3.0,两阶段Hf模式年龄为989~1 130 Ma;岩浆源区为中元古代末期的地壳物质。甘河组粗安岩和玄武粗安岩富碱高钾,镁指数较大(Mg#≈48);稀土元素配分曲线为轻稀土富集的右倾型[w(La/Yb)N=12.67~23.21],铕异常不明显(δEu=0.77~0.91);富集Rb、Ba、K、Th、U等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素;锆石εHf(t)值为-1.2~4.1;岩浆源区为俯冲流体交代过的岩石圈地幔,岩浆经历了一定程度分离结晶作用。     

华北克拉通对Rodinia超大陆裂解的响应——来自贺兰山北段小松山地区辉长岩地球化学、年代学及Hf同位素的新证据

华北克拉通西缘贺兰山北段小松山地区辉长岩锆石U-Pb年代学、岩石地球化学和锆石Hf同位素的研究结果表明,辉长岩的侵位结晶年龄为835.5±5.3Ma,即形成于新元古代早期,属于板内拉斑玄武岩系列岩石,总体上略富集轻稀土元素、大离子亲石元素Rb、Ba、La,略亏损高场强元素Th、Nb、Zr、Hf等;具有较高的εHf(t)值(5.83~7.87),其单阶段模式年龄tDM1为1075~1155Ma,两阶段模式年龄tDM2为1176~1289Ma。综合研究发现,辉长岩的原始岩浆起源于中元古代富集型地幔,形成于华北陆块西缘的板内伸展环境,说明华北陆块响应了Rodinia超大陆裂解,也是Rodinia超大陆的一部分。     

华北克拉通怀安杂岩中～2.03 Ga变质石榴花岗岩的成因其对古元古代裂谷事件的制约

本文报道了怀安杂岩中的董家沟变质石榴花岗岩岩体的地球化学、锆石U-Pb年龄和Hf同位素数据。变质石榴花岗岩高SiO_2、富K_2O+Na_2O,低CaO、MgO和TiO_2;富集轻稀土元素,亏损重稀土元素,具有明显的负铕异常;同时亏损Nb、Ta、Ti等高场强元素,高Zr+Nb+Ce+Y含量和10 000*Ga/Al比值,具有A型花岗岩特征。通过锆石LAMC-ICPMS U-Pb定年,获得岩石形成年龄为2 031±21 Ma,并遭受1 837±12 Ma变质作用改造。变质石榴花岗岩的锆石Hf同位素分析表明,核部岩浆锆石ε_(Hf)(t)值为-0.47～+5.51,绝大部分为正值,且二阶段模式年龄T_(DM2)主要介于2 505～2 658 Ma,与围岩TTG片麻岩年龄相近,表明其来源于新太古代TTG岩石的部分熔融。华北克拉通中部造山带广泛分布古元古代中期(2.2～2.0 Ga)A型花岗岩,且同时期存在大量幔源基性岩墙侵位,指示该期岩浆活动形成于伸展的构造体制下,可能与华北克拉通内部(晋冀地块)裂谷活动有关。古元古代俯冲造山启动时限应小于2.0 Ga。     

西藏松多地区早侏罗世变质辉长岩的成因及其构造意义

冈底斯岩浆岩带中东部松多地区新发现的变质辉长岩对于讨论松多古特提斯洋演化历史具有重要约束意义。在详细野外地质调查基础上,本文报道了松多变质辉长岩的LA-ICP-MS锆石U-Pb年龄、锆石Hf同位素成分分析和全岩地球化学组成,并探讨了岩石的成因及其对松多古特提斯洋构造演化的启示。结果表明,松多变质辉长岩原岩形成于195±6Ma～202±2Ma之间; Si O2含量为45. 56%～53. 69%,MgO含量较高为6. 04%～11. 75%,Mg#为66～77;高Cr(209×10-6～746×10-6)和Ni(80×10-6～234×10-6)含量。该岩石富集轻稀土元素,平滑右倾的稀土配分模式介于E-MORB和OIB之间;富集大离子亲石元素和Nb、Ta等高场强元素;具有较低的(La/Yb)N=2. 06～4. 81、(La/Sm)N=1. 50～2. 48、(Gd/Yb)N=1. 21～1. 67和(Ce/Y)N2。锆石εHf(t)值为-1. 9～3. 9,具相对古老Hf模式年龄(988～1361Ma)。综合对区域地质、年代学、岩石地球化学以及锆石Hf同位素等资料的全面分析,认为松多早侏罗世变质辉长岩原岩的岩浆可能起源于下地壳改造的亏损岩石圈地幔的部分熔融,形成于松多古特提斯洋壳板片断离事件所引发岩石圈减薄的伸展构造背景。     

塔里木克拉通北部沙雅隆起古元古代A型花岗岩的发现及其构造意义

本文对塔里木克拉通北部沙雅隆起桥古2井(QG2)基底碱长花岗岩进行了岩石学、锆石U-Pb年代学和元素地球化学分析。LA-ICP-MS锆石U-Pb定年结果显示其形成时代为1847±19Ma,为古元古代晚期。岩石SiO_2=66.32%~76.39%,Na_2O+K_2O=7.13%~8.93%,Al2O3=11.21%~13.46%,FeO~T/Mg O=12.1~19.2,TiO_2=0.29%~0.57%,A/CNK=0.89~0.99,为高硅、富碱、富铁、低钙镁、贫钛的准铝质花岗岩。稀土元素总量相对较低(∑REE=64.4×10~(-6)~212.7×10~(-6)),轻稀土元素富集,(La/Yb)_N=10.2~13.8,轻重稀土元素分馏较明显,δEu值为0.67~1.03,富集Rb、Ba、Th、U等大离子亲石元素和Zr、Hf等高场强元素,亏损Sr、P、Ti、Ta、Nb等元素。锆石饱和温度介于856~959℃之间,Ga/Al比值高,显示A型花岗岩特征。岩石具有低Y、Yb、∑HREE、(La/Yb)N和Mg~#值及较高的Nb/Ta、Zr/Sm比值,推测岩浆源区为含有石榴石、斜长石、金红石、辉石等的麻粒岩相,岩浆的形成可能与加厚地壳的部分熔融有关。QG2井A型花岗岩可能代表了塔里木克拉通北部古元古代晚期(约1850Ma)造山期地壳增厚事件的结束,指示了区域构造环境从挤压体制开始转为造山后陆内伸展体制。     

太岳山17.9亿年英安斑岩的发现及其对华北克拉通南部裂谷系成因的约束

熊耳群火山岩系主要分布于华北克拉通南部地区,主体喷发时限是1.75～1.80Ga。作为华北克拉通早期板块构造调整阶段的首次大规模岩浆活动,该火山-侵入岩系的形成时限、时空分布规律和地球动力学背景尚有争议,制约了对华北克拉通中元古代构造演化的进一步认识。本次研究在华北中部太岳山地区识别出中元古代英安斑岩,与古元古代花岗质片麻岩围岩呈侵入关系,无明显变质变形。锆石U-Pb年龄分析结果表明,该英安斑岩形成于1.79Ga,属于熊耳期岩浆活动的产物。样品中约90%的锆石显示出～1.92Ga和～2.16Ga两期年龄峰值,推测其为围岩的捕获锆石。英安斑岩SiO₂含量为65.12%～66.11%,A/CNK=0.91～1.05,全碱(K₂O+Na₂O)含量为6.85%～7.28%,Na₂O/K₂O=0.48～0.54,属于钾玄岩系列。样品稀土元素含量较高,亏损Nb、Ta、Zr、Hf等高场强元素,富集Rb、Ba、La等大离子亲石元素,与华北克拉通南部地区熊耳期英安-流纹斑岩的地球化学特征完全一致...     

华北克拉通南缘小秦岭地区新太古代晚期-古元古代晚期岩浆构造热事件:锆石U-Pb-Hf同位素和地球化学证据

为了探讨华北克拉通南缘早前寒武纪形成演化,对华北克拉通南缘小秦岭地区早前寒武纪变质基底花岗质片麻岩开展了SHRIMP U-Pb锆石定年、Hf同位素组成及地球化学组成研究,获得了2个TTG片麻岩样品~2.50 Ga的岩浆锆石年龄和时代相近的变质锆石年龄,岩浆锆石ε_Hf（t）值为0.71~4.37;1个花岗质片麻岩样品的岩浆锆石年龄为~2.30 Ga,ε_Hf（t）值为－1.21~0.11.它们也记录了古元古代晚期变质锆石年龄或显示古元古代晚期构造热事件影响的存在.岩石以轻重稀土强烈分异为特征,大离子亲石元素相对富集,Nb、P、Ti相对亏损.在小秦岭地区首次发现新太古代晚期TTG岩石,并识别出新太古代晚期构造热事件.现有资料支持华北克拉通南缘与华北克拉通其他地区具有类似的早前寒武纪形成演化历史的认识.但是,华北克拉通南缘以2.3 Ga左右岩浆作用十分发育而显示出独特性.      

大别造山带古元古代黑云紫苏斜长片麻岩年代学、 地球化学特征及其地质意义

为探讨大别造山带早期结晶基底物质组成及其演化特征,对大别造山带蕙兰山地区出露的黑云紫苏斜长片麻岩的岩石学、地球化学、锆石U-Pb年代学及Lu-Hf同位素组成进行研究,显示其原岩应为石英闪长岩,成岩时代为古元古代早期(2463±22 Ma),且经历了古元古代麻粒岩相变质作用,锆石Ti地质温度计显示其变质温度为767～827℃(平均799℃),变质时间为2002±11 Ma(MSWD=0.46)。岩石地球化学成分显示其SiO₂含量为55.16%～57.10%,MgO为4.74%～5.89%,Mg^#值为47.5～50.4,钙碱性系列,富Mg贫Si,稀土配分曲线呈现轻稀土相对富集的右倾分布特征((La/Yb)_N=19.3～34.1),无明显Eu异常((Eu/Eu^*)=0.9～1.2),且具较高的Sr、Ni、Cr含量,以及较低的Yb_N值及Y含量,与镁质闪长岩具相似特征;明显富集Rb、Ba、K等大离子亲石元素,相对亏损Nb、Ta、Zr、Hf等高场强元素;锆石Lu-Hf同位素显示具有较为均一...     

阿尔金北缘古元古代壳源火成碳酸岩的发现

报道了阿尔金东段北缘的古元古代晚期壳源火成碳酸岩全岩地球化学和锆石SHRIMP定年结果.它们明显切割围岩, 以岩株状、岩脉状产出, 包裹不同类型围岩包体.岩石主要由方解石、透辉石组成, 含石英、长石等长英质矿物.岩石高CaO(20.56%~39.80%), SiO₂含量变化较大(23.33%~54.06%), 稀土总量低(TREE=28.36×10-6~63.01×10-6)、弱负铕异常(Eu/Eu*=0.69~0.83)、轻重稀土分离不强((La/Yb)_N=9.20~16.85), 相对富集大离子亲石元素Sr、Rb、Ba、Th, 亏损高场强元素Nb、Ti、P.锆石具核-边结构, 边部锆石普遍存在不明显的环带, 具变质深熔锆石的结构特征, 其207Pb/206Pb加权平均年龄为1 931±18 Ma.它们是高级变质作用条件下米兰岩群不纯大理岩深熔作用的产物.      

华北克拉通古元古代晚期地壳演化和荆山群形成时代制约——胶东地区变质中-基性侵入岩锆石SHRIMP U-Pb定年

胶东地区的荆山群呈近东西向环绕太古宙TTG花岗质片麻岩展布,主要由成熟度高的含石墨变泥砂质岩石、钙硅酸岩和大理岩组成,变质程度达高角闪岩相-麻粒岩相,具孔兹岩系性质。变质中-基性岩侵入到荆山群。它们的侵位时代对于探讨华北克拉通东部元古宙构造演化以及对荆山群沉积时代的制约,都有重要意义。锆石SHRIMP U-Pb定年结果表明,遭受低级变质的闪长岩(S0835)岩浆锆石年龄为1852±9Ma (MSWD=2.1),遭受中高级变质的辉长岩(S0816)变质锆石年龄为1865±11Ma (MSWD=0.76)。结合区域资料,可得出如下结论:(1)荆山群孔兹岩系形成于古元古代晚期(2.2~1.9Ga);(2)古元古代期间,胶东地区从挤压体制转入伸展体制的时间在1.87Ga之前。在华北克拉通中西部的恒山、大青山地区,存在1.97~1.92Ga辉长岩,在1.92~1.83Ga期间发生变质,与本文研究结果类似。这表明华北克拉通中-西部和东部具有类似的古元古代演化历史。     

U‐Pb Ages and Hf Isotope of Zircons from a Carbonatite Dyke in the Bayan Obo Fe‐REE Deposit in Inner Mongolia: its Geological Significance

Detailed studies on U-Pb ages and Hf isotope have been carried out in zircons from a carbonatite dyke associated with the Bayan Obo giant REE-Nb-Fe deposit, northern margin of the North China Craton(NCC), which provide insights into the plate tectonic in Paleoproterozoic. Analyses of small amounts of zircons extracted from a large sample of the Wu carbonatite dyke have yielded two ages of late Archaean and late Paleoproterozoic(with mean 207 Pb/206 Pb ages of 2521±25 Ma and 1921±14 Ma, respectively). Mineral inclusions in the zircon identified by Raman spectroscopy are all silicate minerals, and none of the zircon grains has the extremely high Th/U characteristic of carbonatite, which are consistent with crystallization of the zircon from silicate, and the zircon is suggested to be derived from trapped basement complex. Hf isotopes in the zircon from the studied carbonatite are different from grain to grain, suggesting the zircons were not all formed in one single process. Majority of εHf(t) values are compatible with ancient crustal sources with limited juvenile component. The Hf data and their TDM2 values also suggest a juvenile continental growth in Paleoproterozoic during the period of 1940–1957 Ma. Our data demonstrate the major crustal growth during the Paleoproterozoic in the northern margin of the NCC, coeval with the assembly of the supercontinent Columbia, and provide insights into the plate tectonic of the NCC in Paleoproterozoic.     

U–Pb zircon,zircon Hf and whole-rock Sm–Nd isotopic constraints on the evolution of Paleoproterozoic rocks in the northern Gawler Craton

U–Pb zircon analyses from a series of orthogneisses sampled in drill core in the northern Gawler Craton provide crystallisation ages at ca 1775–1750 Ma, which is an uncommon age in the Gawler Craton. Metamorphic zircon and monazite give ages of ca 1730–1710 Ma indicating that the igneous protoliths underwent metamorphism during the craton-wide Kimban Orogeny. Isotopic Hf zircon data show that 1780–1750 Ma zircons are somewhat evolved with initial ε_Hf values –4 to +0.9, and model ages of ca 2.3 to 2.2 Ga. Isotopic whole rock Sm–Nd values from most samples have relatively evolved initial ε_Nd values of –3.7 to –1.4. In contrast, a mafic unit from drill hole Middle Bore 1 has a juvenile isotopic signature with initial ε_Hf zircon values of ca +5.2 to +8.2, and initial ε_Nd values of ～+3.5 to +3.8. The presence of 1775–1750 Ma zircon forming magmatic rocks in the northern Gawler Craton provides a possible source for similarly aged detrital zircons in Paleoproterozoic basin systems of the Gawler Craton and adjacent Curnamona Province. Previous provenance studies on these Paleoproterozoic basins have appealed to the Arunta Region of the North Australian Craton to provide 1780–1750 Ma detrital zircons, and isotopically and geochemically similar basin fill. The orthogneisses in the northern Gawler Craton also match the source criteria and display geochemical similarities between coeval magmatism in the Arunta Region of the North Australian Craton, providing further support for paleogeographic reconstructions that link the Gawler Craton and North Australian Craton during the Paleoproterozoic.     

Geochronology and geochemistry of the late Neoproterozoic A-type granitic clasts in the southwestern Tarim Craton: petrogenesis and tectonic implications

ABSTRACT

Due to sparse data for deciphering the late Neoproterozoic tectonic history, there is still considerable debate on whether long-lasting superplume-related or long-duration subduction-related dynamics dominated the Tarim Craton. In this contribution, our field investigations detail the late Neoproterozoic siliciclastic successions, and we report the first granitic conglomerates with zircon U–Pb ages of 753.9 ± 3.7 Ma in the SW Tarim Craton. Importantly, detrital zircons from the thick Cryogenian sedimentary basin also contain a major zircon population at ca. 750 Ma. Together with seismic data, this suggests a large ca. 750 Ma magmatic event in the SW Tarim Craton. Geochemically, the granitic clasts exhibit A-type granite features with high SiO₂, high alkali but extremely low K, high FeO^T/MgO and Ga/Al, and high high-field strength elements (HFSEs) (i.e. Nb, Hf, and Ta) with significant depletion in Rb, K, Sr, P, Eu, and Ti, and significant negative Eu anomalies (Eu* = 0.13–0.36), showing ferroan granite affinities. Including the detrital zircons, the ca. 750 Ma zircons have a large range of negative εHf(t) values (?19.46 to ?1.16). Elemental and zircon Hf isotope data suggest that the granites were derived from Palaeoproterozoic reworked continental crust and are probably related to crustal thinning and extension. By comparison with previous studies, we conclude that Rodinia breakup was diachronous in the outer parts of the supercontinent.     

辽宁本溪歪头山条带状铁矿的成因类型、形成时代及构造背景

辽宁鞍本地区位于华北克拉通东北缘,分布有诸多大型-特大型条带状铁矿床。本文对该区歪头山铁矿进行了岩石学、矿物学及年代学研究。歪头山铁建造以条带状铁矿石为主,兼含有少量的块状矿石,其顶底板围岩及矿体夹层主要为太古界鞍山群斜长角闪岩。元素地球化学分析表明,铁矿石富集重稀土[(La/Yb)_PAAS=0.24~0.33],具La正异常(La/La^*=1.43~1.61)、Eu正异常(Eu/Eu^*=2.40~4.54)及Y正异常(Y/Y^*=1.10~1.30),Y/Ho值平均30.59,Sr/Ba值平均17.62,Ti/V值平均19.45,反映成矿物质可能来源于由海底火山活动带来的高温热液与海水的混合溶液。铁矿石无明显Ce负异常(Ce/Ce^*=0.92~1.06),暗示BIF沉积时海水处于缺氧环境。除Fe₂O₃^T与SiO₂外,铁矿石中其它氧化物含量均非常低,且贫Th、U、Zr等具有陆源性质的元素,表明大陆碎屑物质对BIF贡献极少。斜长角闪岩稀土元素配分型式近于平坦[(La/Yb)_N=0.80~1.10],无明显Ce异常(Ce/Ce^*=0.95~0.99)与Eu异常(Eu/Eu^*=0.88~1.16);其大离子亲石元素富集,高场强元素无明显亏损。地球化学分析表明,斜长角闪岩原岩可能为产于弧后盆地的玄武质火山岩。锆石形态与微量元素分析显示,斜长角闪岩中的锆石均属岩浆成因。SIMS锆石U-Pb定年显示斜长角闪岩原岩形成于2533±11Ma,代表了歪头山BIF的成矿年龄;在玄武质岩浆喷发过程中,还捕获了一组年龄为2610±5Ma的锆石。电子探针分析显示磁铁矿成分纯净(FeO^T=92.04%~93.05%),其标型组分特征暗示歪头山BIF属沉积变质型铁矿。综合分析认为,歪头山铁矿属Algoma型BIF,成矿与弧后盆地岩浆活动密切相关,指示了新太古代末华北克拉通普遍发育的一期BIF成矿事件。     

Timing of late Neoarchean to late Paleoproterozoic events in the North China Craton: SHRIMP U–Pb dating and LA-ICP-MS Hf isotope analysis of zircons from magmatic and metamorphic rocks in the Santunying area,eastern Hebei

Santunying is an important area for revealing nature of the late Neoarchean tectono-magmato-thermal events in the eastern Hebei part of the North China Craton. It is mainly composed of meta-intrusive rocks. Supracrustal rocks sporadically occur in the meta-intrusive rocks. The meta-intrusive rocks are subdivided into the Santunying tonalitic gneiss, Qiuhuayu tonalitic-trondhjemitic gneiss, Xiaoguanzhuang dioritic gneiss and Qingyangshu meta-gabbro. Respectively, SHRIMP U–Pb zircon dating on fourteen samples yielded weighted mean ²⁰⁷Pb/²⁰⁶Pb ages of 2525–2537, 2532–2546, 2530–2544 and ∼2531 Ma for magmatic zircons from them. Dioritic gneiss of the Xiaoguanzhuang gneiss contain abundant 2544–3487 Ma xenocrystic zircons. SHRIMP U–Pb dating on a garnet-biotite gneiss sample yielded a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 2537 Ma for detrital zircons. All rocks underwent strong metamorphism, deformation and anatexis, resulting in formation of leucosomes and residues, with some leucosomes concentrating to form large veins. They record a strong late Neoarchean event by metamorphic zircon ages of 2489–2519 Ma. Some rocks also record metamorphic zircon ages of 1772–1843 Ma. Magmatic zircons from the magmatic rocks show large variations in ε_Hf(t) values ranging from −1.7 to +8.7. Combined with early studies, conclusions are: 1) Intrusive rocks with the involvement of mantle-derived materials have a narrow range of magmatic zircon ages from 2525 to 2546 Ma, and supracrustal rocks were formed during the same period. 2) Ancient crustal remnants (>2600 Ma) are present, consistent with the late Neoarchean arc magmatism involving older continental crust, similar to Phanerozoic Andean margins. 3) The Archean basement underwent a strong tectonothermal event at the end of the Neoarchean, with the metamorphic zircon ages being 10–30 million years younger than the timing of magmatism, a common feature of the North China Craton. 4) A late Paleoproterozoic tectonothermal event widely occurred in the western part of eastern Hebei, which is linked with regional ductile deformation.     

内蒙古沙麦钨矿花岗岩岩石地球化学、锆石U-Pb年代学及其地质意义

沙麦钨矿床位于内蒙古东乌旗地区,是该区目前已探明的中型岩浆热液型钨矿床。矿体主要赋存在黑云母二长花岗岩和黑云母二长花岗斑岩中,对这两种花岗质岩石的岩相学、岩石地球化学和LA-ICP-MS锆石U-Pb年代学进行了研究。结果表明,黑云母二长花岗岩锆石U-Pb年龄为135.6±1.6 Ma和136.3±1.8 Ma,黑云母二长花岗斑岩锆石U-Pb年龄为138.6±1.1 Ma,二者侵位时间均为早白垩世。两种花岗质岩体具有富SiO₂(73.73%～78.23%)、高钾钠(Na₂O+K₂O)(7.56%～8.89%)、贫MgO(0.09%～0.20%)、贫CaO(0.51%～0.89%)、贫TiO₂(0.03%～0.12%)的特征,属于过铝质-高钾钙碱性系列;微量元素富集Rb、K、Th和U,相对亏损Sr、Ba、Nb、P和Ti元素,具有强烈的Eu负异常,具有较高的FeO^T含量,较高的FeO^T/MgO和FeO^T/(FeO^T+M...     

http://www.sciencedirect.com/science/article/pii/S1674987114000322

The Central Hebei Basin （CHB） is one of the largest sedimentary basins in the North China Craton, extending in a northeast-southwest direction with an area of 〉350 km2. We carried out SHRIMP zircon dating, Hf-in-zircon isotopic analysis and a whole-rock geochemical study on igneous and metasedi- mentary rocks recovered from drill holes that penetrated into the basement of the CHB, Two samples of gneissic granodiorite （XG1-1） and gneissic quartz diorite 048-1） have magmatic ages of 2500 and 2496 Ma, respectively. Their zircons also record metamorphic ages of 2.41-2.51 and ～2.5 Ga, respec- tively. Compared with the gneissic granodiorite, the gneissic quartz diorite has higher REE contents and lower Eu/Eu＊ and （La/Yb）n values. Two metasedimentary samples （MG1, H5） mainly contain ～2,5 Ga detrital zircons as well as late Paleoproterozoic metamorphic grains. The zircons of different origins have eHf （2.5 Ga） values and Hf crustal model ages ranging from 0 to 5 and 2.7 to 2,9 Ga, respectively, Therefore, ～2.5 Ga magmatic and Paleoproterozoic metasedimentary rocks and late Neoarchean to early Paleoproterozoic and late Paleoproterozoic tectono-thermal events have been identified in the basement beneath the CHB. Based on regional comparisons, we conclude that the early Precambrian basement beneath the CHB is part of the North China Craton.     

内蒙古苏右旗毕力赫金矿区安山岩LA-ICP-MS锆石 U-Pb年龄、元素地球化学特征及其形成的构造环境

毕力赫大型斑岩型金矿位于华北克拉通北缘早古生代增生造山带。矿区出露一套岩性为安山岩-英安岩-流纹岩的火山岩组合,安山岩属于亚碱性、高钾钙碱性系列,具有较高的MgO含量(2.05%~10.29%), 低的FeO^T/MgO比值和TiO₂含量(0.21%~0.85%);Cr (44×10^-6~473×10^-6)、Ni (19.3×10^-6~249.4×10^-6)含量高,亏损Nb、Ta、Ti、P,无或弱的Eu/Eu^*异常,具有安底斯型活动大陆边缘火山岩特征。LA-ICP-MS锆石U-Pb测年获得安山岩和安山质凝灰岩成岩年龄分别为281±4.3Ma和281±12Ma,为早二叠世,这与毕力赫金矿成矿年代以及与成矿有关的花岗闪长斑岩结晶年龄一致,表明了矿区成岩-成矿作用与晚古生代华北板块与西伯利亚板块之间俯冲-造山作用有关,指示华北克拉通北缘寻找晚古生代浅成低温-斑岩型金(铜)矿具有巨大潜力。火山岩以及与成矿相关侵入岩出现U-Pb年龄为1.8Ga、2.0Ga和2.4Ga的古老继承性锆石,暗示矿区存在华北克拉通基底,古老变质基底岩石可能是制约本区金矿成矿主要因素之一。     

河南鲁山地区太华杂岩LA-ICP-MS锆石U-Pb年代学及其地质意义

华北克拉通是我国最大且最古老的克拉通,是研究太古宙岩浆活动和构造演化的理想区域,一直备受地质学家的关注。太华杂岩是华北克拉通的重要组成部分,主要分布在其南缘,总体呈近北西西-南东东向分布。在详细野外地质调查的基础上,对鲁山地区太华杂岩中的斜长角闪岩样品进行了LA-ICP-MS锆石U-Pb定年,以揭示其成岩及变质事件时代。样品的锆石U-Pb加权平均207Pb/206Pb年龄为2 788±16、2 714±12和1 920±18 Ma,分别代表斜长角闪岩成岩年龄、早期变质事件年龄及晚期变质事件年龄。综合梳理前人的锆石U-Pb年代学及Hf同位素研究数据,分析并讨论了3次地质事件的地质意义:2 850~2 700 Ma为一期重要的岩浆事件,代表了太古宙新生地壳的形成;2 800~2 600和~1 900 Ma为两期变质事件,期间太华杂岩分别遭受新太古代和古元古代两次变质变形改造。本次研究不仅可以解释太华杂岩的形成、变质时代及其地质意义,而且为进一步研究华北克拉通南缘乃至整个华北克拉通的形成与演化过程提供了新的数据资料。