Trace element characteristics in the diopsides of peridotite xenoliths: a laser ablation-inductively coupled plasma-mass spectrometry study

Among the various xenoliths entrained by the Cenozoic Hannuoba basalts, peridotite is the most abundant one. The trace elements of the diopsides from the peridotite xenoliths were analysed by LA-ICP-MS. The overall depletion and some heterogeneity of the continental mantle beneath northern North China Craton were indicated by the characteristics of the trace elements. The ∑REE amount in diopside correlates with the Cr/(Cr+Al) ratio of diopside which is indicative of xenolith's partial melting degree. As the peridotite hosts and pyroxenite veins show similar REE distribution patterns, the composite xenoliths are probably formed by mantle deformation, rather than by the late metasomatism of mantle fluids/melts.     

Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS

A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16 32 μm.This was accomplished by introducing N 2 into ICP to increase the sensitivity.The obtained U-Pb ages for zircon standards GJ-1,TEMORA and SK10-2 are consistent with the preferred values within about 1% uncertainty (2σ) by simple external calibration against zircon standard 91500.Different data reduction softwares could yield different uncertainties for calculation of U-Pb ag...     

LA-ICP-MS锆石U-Pb测年对辽西-冀北地区晚中生代区域性角度不整合时代的约束

通过对辽西-冀北地区的凌源、承德、滦平和义县一北票地区相关层位的LA—ICP—MS的锆石U—Pb测年,结合前人的测年数据,得出了以下认识：在凌源地区,张家口组与义县组之间是角度不整合,张家口组火山岩的年龄范围在133-130Ma之间（7个样品）,义县组火山岩的年龄范围在126—120Ma之间（11个样品）;在承德的骆驼山地区,土城子组与张家口组火山岩之间是角度不整合．在该地区张家口组下部测得的年龄是124Ma（1个样品）,并结合前人的测年结果,显示了该地区张家口组的下部年龄在124—129Ma之间;在滦平盆地,中-晚中生代最大的沉积间断的底界年龄被大店子组顶部的玄武安山岩限定在130Ma左右（2个样品）;在辽西义县-北票地区,前人测得占义县组厚度约3／4厚度的义县组尖山沟层（砖城子层）及以上层位的时间范围在126—120Ma之间,义县组底部层位的年龄是132Ma．同时在辽西-冀北地区,测得土城子组的上限年龄在136Ma左右（2个样品）．综合以上数据分析,并结合辽西-冀北各个地区的地质特征,反映了在辽西-冀北地区,在土城子组形成之后（136Ma以后）到126Ma左右期间,有一次波及范围极广的构造事件,形成了区域性的角度不整合,并且该角度不整合的下限年龄在不同地区是有区别的;该角度不整合的主体形成时间在132—130Ma到126Ma之间．该角度不整合之上、之下层位中的构造特点、生物组合均有明显的区别,这暗示了该角度不整合也是该地区中生代主要的构造转换界面．     

湘西花垣铅锌矿田闪锌矿痕量元素地球化学特征

以湘西花垣铅锌矿田内不同矿床不同阶段的闪锌矿为研究对象,进行LA-ICP-MS原位点测试分析,旨在揭示闪锌矿中不同痕量元素的特征,为矿床成因提供新的约束。矿田内闪锌矿所含痕量元素种类较少且含量偏低,较富集Cd、Ga、Ge等元素,Fe、Mn、Cu、Pb、Ag、Co、Tl、Se、In等元素含量低,闪锌矿的Ga/In、Ge/In比值(大于5)、Zn/Cd比值(102)及In-Ge关系图等,均指示其形成于中低温环境。李梅、芭茅寨、土地坪及清水塘矿床主成矿阶段闪锌矿Ga/Ge原子比值估算的成矿温度主要集中在185~247℃、175~235℃、150~198℃和164~176℃,进一步证明矿床形成于中低温条件;且远离花垣-张家界断裂温度呈下降趋势,指示花垣-张家界断裂可能是导矿断裂。总体而言,闪锌矿痕量元素特征可与典型MVT型铅锌矿床类比,痕量元素特征图解中均与MVT型矿床高度吻合。结合矿床地质和闪锌矿痕量元素特征,认为花垣矿田铅锌矿属于MVT型铅锌矿床。     

Fluid mineralization of the Dajing Sn-polymetal deposit： Evidence from LA-ICP-MS analysis of individual fluid inclusions

LA-ICP-MS analyses on single fluid inclusions trapped in fluorite and quartz from the Sn-Cu orebody of the Dajing deposit and from the Sn ore-body of the Huanggangliang deposit were conducted to trace the source and evolution of Cu-rich and Sn-rich fluids in the Dajing deposit using the Rb/Sr and Sn/Cu ratios of the fluids. The results show that the Cu-rich fluids in the Dajing deposit, relatively rich in Na and probably derived from deep-seated basic magma, contain Cu several to several tens of times more than Sn, and Sr several to several tens of times more than Rb, while the Sn-rich fluids, relatively rich in K and probably derived from high level granitic magma, contain Sn several to several tens of times more than Cu, and Rb several to several tens of times more than Sr. It is suggested that the Sn-rich and the Cu-rich fluids were mixed at the stage of moderate to low temperature and low salinity, resulting in the formation of Cu-Sn orebodies at the central part of the Dajing deposit.     

～4.1 Ga xenocrystal zircon from Ordovician volcanic rocks in western part of North Qinling Orogenic Belt

High-precision U-Pb dating by in situ LA-ICP-MS yields an age of 4079±5 Ma for a xenocrystal zircon from Ordovician volcanics of the Caotangou Group in western part of the North Qinling Orogenic Belt. As a result, the North Qinling Orogenic Belt becomes one of a few localities in the world that contain Hadean age records (4276±6 Ma and 4404±8 Ma detrital zircons from Jack Hill of the Yilgarn craton, 4016 Ma Acasta gneisses of the Wopmay Orogeny and Burang quartzite with detrital zircon of 4103 Ma in Tibet). It is also the first report of the Hadean age in Phanerozoic volcanics. The finding of the 4.1 Ga xenocrystal zircon provides not only the geochronological record of the oldest crustal materials in China, but also the condition for further search for rocks forming in the region during the early time of the Earth’s evolution. Thirty-six zircon U-Pb dates from the Ordovician volcanic rocks are subgrouped into seven generations that represent different tectono-magmatic events in the North Qinling Orogenic Belt. Among them, two periods of 0.9-1.5 Ga and 0.4-0.5 Ga are consistent with Mesoproterozoic and Early Paleozoic orogenies, respectively.     

四川盆地西部上三叠统须家河组物质来源：碎屑锆石LA-ICP-MS U-Pb年龄研究

对四川盆地西部晚三叠世须三期须家河组碎屑长石石英砂岩和须四期砂岩中碎屑锆石进行了U-Pb定年。分析研究表明:1川西西部都江堰地区沉积物样品具四个主要年龄峰分别为245 Ma、460 Ma、773 Ma和1 836 Ma;川西北部广元地区样品具四个主要年龄峰分别为245 Ma、452 Ma、834 Ma和1 850 Ma;2结合碎屑锆石U-Pb测年特征,表明川西盆地北段广元地区和中段都江堰地区须家河组上部和下部年代学以及地球化学信息一致,主要显示吕梁期(峰值1 836 Ma、1 950 Ma和1 850 Ma),晋宁末期(峰值为865 Ma和834 Ma),加里东期(峰值为460 Ma和452 Ma)和海西-印支期年龄峰(峰值为245Ma),反映两个地区具有相似物源;3结合碎屑锆石U-Pb年龄与周源造山带对比分析,海西-印支期碎屑物质来源于秦岭造山带;加里东期是秦岭造山带的主要造山阶段,秦岭造山带为该阶段提供物源;晋宁末期是扬子克拉通岩浆活动最活跃时期,扬子克拉通为该阶段碎屑物质主要源区;吕梁期碎屑锆石,主要来自其北缘的华北克拉通。