皖南谭山岩体的锆石定年及地质意义

皖南地区广泛分布燕山期岩浆岩,但其年代学方面的工作较为薄弱。为厘定该地区燕山期岩浆岩年代学格架,本文利用LA-ICP-MS锆石U-Pb定年方法对皖南谭山岩体的正长花岗岩进行了锆石U-Pb年代学研究,两个样品的206Pb/238U加权平均年龄分别为128．5±1．7Ma和128．3±1．5Ma,基本一致,为早白垩世岩浆活动的产物。结合本地区高精度年代学数据,皖南地区中生代岩浆岩可划分为三个峰期：第一峰期为142～139Ma;第二峰期为133～130Ma;第三峰期为128～125Ma。     

Skarn-type tungsten mineralization associated with the Caledonian (Silurian) Niutangjie granite,northern Guangxi,China

The Niutangjie tungsten deposit is a bedded skarn-type scheelite deposit and is located at the junction between Ziyuan and Xingan counties in the north of Guangxi,China.The deposit is genetically related to a fine-grained two-mica granite within the orefield.Zircon LA-ICP-MS U-Pb dating of the granite yielded a Silurian(Caledonian)age of 421.8±2.4 Ma,which is contemporaneous with the adjacent Yuechengling batholith.Mineralization within the skarn is associated with a quartz,garnet,and diopside gangue,and scheelite is present in a number of different mineral assemblages,such as quartz-scheelite and quartz-sulfide-scheelite;these assemblages correspond to oxide and sulfide stages of mineralization.Sm-Nd isotope analysis of scheelite yielded an isochron age of 421±24 Ma.Although the uncertainty on this date is high,this age suggests that the scheelite mineralization formed during the Late Caledonian,at a similar time to the emplacement of the Niutangjie granite.Zircons within the granite have?Hf(t)values and Hf two-stage model ages of?6.5 to?11.6,and 1.79 to 2.11 Ga,respectively.These data suggest that the magma that formed the granite was derived from Mesoproterozoic crustal materials.Scheelite?Nd(t)values range from?13.06 to?13.26,also indicative of derivation from ancient crustal materials.Recent research has identified Caledonian magmatism in the western Nanling Range,indicating that this magmatism may be the source of contemporaneous tungsten mineralization.     

阿尔泰造山带南缘昆格依特岩体LA-ICP-MS锆石U-Pb年代学、岩石成因及其地质意义

昆格依特岩体出露于阿尔泰造山带南缘青河县大青格里河昆格依特一带,主要为角闪黑云英云闪长岩。LA-ICP-MS锆石U-Pb定年结果显示,锆石的²⁰⁶Pb/²³⁸U年龄加权平均值为(403.4±7.4)Ma,表明该岩体形成于早泥盆世。岩体的SiO₂含量介于52.39%~71.89%之间,里特曼指数为0.68~1.53,A/CNK 值为0.76~1.06,属中钾、钙碱性、准铝质-弱过铝质岩石。具有富集Cs、Rb、Th、U等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、Hf、Ti等高场强元素和重稀土元素,弱的负Eu异常(δEu=0.56~0.86)的岛弧岩浆岩特征。结合区域地质资料,认为阿尔泰造山带南缘早泥盆世昆格依特岩体形成于活动大陆边缘的陆缘弧构造环境,是古亚洲洋俯冲过程中幔源的基性岩浆底侵下地壳使之熔融,并发生了岩浆混合和分异作用的产物。     

东昆仑祁漫塔格地区野马泉深部的华力西期花岗闪长岩U-Pb年龄及其意义

野马泉大型矿床是近年来在东昆仑祁漫塔格地区发现的与侵入岩有关的矽卡岩型铁铜多金属矿。利用锆石LA-ICP-MS U-Pb法测得野马泉花岗闪长岩的形成年龄为(392.4±2.2) Ma,属于华力西期。前人利用辉钼矿Re-Os法,获得矽卡岩型铜钼多金属矿石和矽卡岩型钼矿石的等时线年龄分别为(225.0±4.0) Ma(n=7,MSWD=0.24)和(230.1±4.7) Ma(n=5,MSWD=0.12)、在多期热液叠加、多期成矿作用中,早期成矿的热液很可能是野马泉花岗闪长岩(392.4±2.2 Ma)提供的。由于该区有较多的中酸性岩体存在,它们可能为铁铜多金属矿的主要来源,因此确定这些侵入体的形成年龄,对于在该区寻找矽卡岩型铁铜多金属矿具有重要的理论和实践意义。     

澜沧江河流沉积物碎屑锆石U-Pb年龄、Hf同位素组成及其地质意义

为研究澜沧江沉积物的物质来源及相邻地块的地壳生长和演化规律,利用LA-MC-ICP-MS分析技术,对澜沧江河流沉积物碎屑锆石进行了U-Pb年龄和Hf同位素研究。结果表明：锆石U-Pb年龄主要有5个年龄段,分别是＜177 Ma、201~418 Ma、428~544 Ma、581~1189 Ma和1406~2533 Ma,主要峰值为260 Ma、788 Ma、1 827 Ma和2 474 Ma。其年龄分布特征与北羌塘地块的年龄分布非常一致,说明澜沧江沉积物主要来源于北羌塘地块;结合Hf同位素分析结果,能够反映源区北羌塘地块的形成与演化历史。新太古代-中元古代是北羌塘地块从亏损地幔物质增生的地壳持续生长阶段,它们构成现今北羌塘地块全部地壳物质的78%以上,此后直到0.64 Ga,北羌塘地块的地壳增生作用基本结束。     

应用氚和14C方法确定柴达木盆地诺木洪地区地下水年龄

以柴达木盆地的诺木洪为研究区,利用氚与¹⁴C方法计算了当地各水体的年龄,分析地下水年龄分布特征及其可更新能力。结果表明：山区至冲洪积扇中部地下水年龄为15~18 a,为1952年之后补给的现代水,更新能力较强;冲洪积扇前缘地下水年龄不超过2 ka,具有现代水与古水混合的特征,更新能力较差;溢出带到盆地中心地下水年龄急剧变老,变化范围为5~28 ka,据此推测研究区溢出带位置的隐伏断层具阻水性质,该位置的地下水基本无更新能力。     

阿拉善右旗地区晚石炭世埃达克岩的发现及其大地构造意义

阿拉善地块西南缘沙枣泉石英闪长岩LA-ICP-MS锆石U-Pb年龄302 ± 9.2 Ma,SiO2含量在60.66%~61.37%之间,MgO 含量在2.13%~2.51%(Mg#= 0.48~0.51)之间,具高Al(Al2O3=17.98%~ 18.44%),富Ca(CaO= 6.08%~6.59%)、富Na贫K(Na2O= 4.20%~4.46%,K2O= 0.67% ~0.92%,K2O/Na2O= 0.16~0.22), 以及高Sr(582×10 - 6~620×10 - 6), 低Y(11.4×10-6~13.7×10–6)、Yb(1.02×10- 6 ~1.51×10–6),高的Sr/Y(35.15~53.25),Y/Yb(11.00~11.23)和La/Yb(7.28~15.10)比值;岩石富集不相容元素（Rb,Th, K, U, Pb等） 及LREE,强烈亏损高场强元素Nb,Ta,Ti以及HREE,轻微的正Eu异常（δEu为0.97~1.18,平均值为 1.1）。岩体总体特征类似于环太平洋新生代埃达克岩。结合霍尔森-查干楚鲁蛇绿岩年代学及区域内其他花岗岩类地球化学 特征认为,沙枣泉埃达克岩是晚石炭世晚期霍尔森-查干楚鲁弧后盆地向南初始俯冲于阿拉善微陆块之下,玄武质洋壳 发生部分熔融且与地幔发生一定程度的交代作用、快速上升形成的,指示雅布赖-巴音诺尔公“陆缘弧”建造始于晚石 炭世-早二叠世, 古亚洲大洋最南端的南蒙古大洋闭合时限应介于275~250 Ma之间,为中-晚二叠世。     

湖南白马山龙潭超单元、瓦屋塘花岗岩锆石SHRIMP U-Pb年龄及其地质意义

运用阴极发光技术,对湖南白马山龙潭超单元2个样品和瓦屋塘花岗岩1个样品的锆石进行了内部结构分析,在此基础上利用锆石SHRIMP U-Pb定年方法进行了同位素年代学测定。其中,白马山龙潭超单元2个黑云母二长花岗岩样品分别给出了(215.9±1.9) Ma和(212.2±2.1) Ma的主体谐和年龄。同时还测得了一组较年轻的谐和年龄((201.0±2.8) Ma)和一组较老的锆石核部年龄(230.3~227.0 Ma),表明研究区印支晚期存在多期花岗质岩浆的侵入活动。瓦屋塘岩体黑云母二长花岗岩1个样品给出了(217.7±1.8) Ma的谐和年龄。这2个岩体的形成进一步佐证了华南大陆印支晚期岩浆活动于210~225 Ma,达到岩浆活动的峰期。地球化学测试结果显示,白马山和瓦屋塘岩体均为弱过铝-强过铝质花岗岩,具壳源型花岗岩的特征,形成于后碰撞期或碰撞晚期的构造环境,源于早元古代变质杂砂岩的部分熔融。结合区域大地构造背景认为,这2个岩体形成于秦岭-大别和松马2条印支期缝合带碰撞结束后的印支晚期伸展构造背景下,为热-应力松弛阶段,板内挤压加厚的地壳减压熔融作用的产物。     

Field Relationships, Geochemistry, Zircon Ages and Evolution of a Late Archaean to Palaeoproterozoic Lower Crustal Section in the Hengshan Terrain of Northern China

The Hengshan complex forms part of the central zone of the North China Craton and consists predominantly of ductilely-deformed late Archaean to Palaeoproterozoic high-grade, partly migmatitic, granitoid orthogneisses, intruded by mafic dykes of gabbroic composition. Many highly strained rocks were previously misinterpreted as supracrustal sequences and represent mylonitized granitoids and sheared dykes. Our single zircon dating documents magmatic granitoid emplacement ages between 2.52 Ga and 2.48 Ga, with rare occurrences of 2.7 Ga gneisses, possibly reflecting an older basement. A few granitic gneisses have emplacement ages between 2.35 and 2.1 Ga and show the same structural features as the older rocks, indicating that the main deformation occurred after -2.1 Ga. Intrusion of gabbroic dykes occurred at -1920 Ma, and all Hengshan rocks underwent granulite-facies metamorphism at 1.88-1.85 Ga, followed by retrogression, sheafing and uplift. We interpret the Hengshan and adjacent Fuping granitoid gneisses as the lower, plutonic, part of a late Archaean to early Palaeoproterozoic Japan-type magmatic arc, with the upper, volcanic part represented by the nearby Wutai complex. Components of this arc may have evolved at a continental margin as indicated by the 2.7 Ga zircons. Major deformation and HP metamorphism occurred in the late Palaeoproterozoic during the Luliang orogeny when the Eastern and Western blocks of the North China Craton collided to form the Trans-North China orogen. Shear zones in the Hengshan are interpreted as major lower crustal discontinuities post-dating the peak of HP metamorphism, and we suggest that they formed during orogenic collapse and uplift of the Hengshan complex in the late Palaeoproterozoic （〈1.85 Ga）.     

海南岛琼中地区琼中岩体锆石U-Pb年龄及其地质意义

琼中地区琼中岩体为钙碱性的铝弱过饱和型花岗岩,具有壳源物质来源,岩石普遍发育定向组构,生成于同碰撞期—晚造山期。其锆石U-Pb年龄为226. 5±2. 9~234. 2±2. 3Ma,为晚三叠世。通过区域分析,认为海南岛海西—印支期花岗岩从西往东,具有由老至新的演化规律,形成了略向南面突出的弧状面理构造。表明同期造山活动消减方向由西至东,呈现出剪刀式闭合的特征。