内蒙古莫力达瓦旗哈达阳绿泥石白云母构造片岩LA-ICP-MS锆石U-Pb年龄及其地质意义

嫩江—黑河构造带地处松嫩地块与兴安地块的结合部位,一直以来是业内学者关注的焦点。在构造带内内蒙古莫力达瓦旗哈达阳一带野外实地调研过程中,发现一套变质变形程度与周围地质体差异很大的地层。岩石组合为绿泥石白云母构造片岩、二云母微晶片岩、黝帘白云糜棱片岩等。采用LA-ICP-MS技术获得的绿泥石白云母构造片岩中锆石U-Pb年龄为413.9Ma±2.7Ma。通过分析区域地质演化历史及不同时代地质体特征,认为沿红山梁—哈达阳—依克特一带存在一条构造混杂堆积岩带,这套强变形岩石应为构造混杂岩带的一部分,其原岩形成时代为早泥盆世,后期构造定位应与嫩江—黑河构造带最后于早石炭世末拼合作用有关。     

广西栗木泡水岭印支期岩体LA-ICP-MS锆石U-Pb年龄及其地质意义

广西栗木泡水岭花岗岩LA-ICP-MS锆石U-Pb年龄显示,泡水岭花岗岩体可能存在3期岩浆活动:210Ma、222Ma和239Ma,佐证了栗木岩体是印支期岩浆活动的产物。结合最新的研究,栗木花岗岩体形成于印支期,岩浆活动集中在210Ma±4Ma~222Ma±5Ma之间,并且在239.8Ma±4.3Ma可能存在印支早期的岩浆活动。     

大兴安岭西坡银都赋矿岩体LA-ICP-MS锆石U-Pb定年及其成因意义

银都矿床位于内蒙古大兴安岭西坡,为受断裂控制的银多金属矿床。该矿床的岩体主要为石英闪长岩。该岩体中的锆石分为岩浆锆石和热液锆石两类:岩浆锆石无色透明,自形长柱状,具有典型的振荡环带特征;而热液锆石呈浅褐色,半透明—不透明,等轴状,其暗色增生边明显切过了核部岩浆锆石结构。热液锆石相对岩浆锆石具有低Th/U和LREE,高Hf和HREE的特征。银都岩体岩浆锆石的206Pb/238 U加权平均年龄为(451.8±7.8)Ma,属加里东期,为岩体的结晶年龄;热液锆石的206 Pb/238 U加权平均年龄为(337.0±7.7)Ma,属中石炭世,代表了热液作用的年龄。热液锆石年龄表明,该区在337Ma左右经历了一次强烈的热液作用,该期热液作用可能与该区造山峰期的变质作用有关。本区的地质特征和流体包裹体特征表明,本区银矿的形成很可能与这期热液活动密切相关。     

济阳坳陷桩海地区中生界同位素年代地层学研究

济阳坳陷中生界分布广泛,具有油气成藏的基本地质条件,并取得了一定的勘探发现,但其勘探程度和研究程度相对较低,包括地层划分、沉积体系、储层特征、控藏因素等。特别是地层时代、分层与分界等基本的地质问题尚存在不同的观点和认识。根据区内14口井的10个火山岩全岩样品和79个小于2μm的泥岩自生伊利石样品,开展K-Ar法同位素年代地层学测定,分别确定了中生界的坊子组、蒙阴组、三台组和西洼组的绝对年龄值,将坊子组划归下侏罗统,蒙阴组为中侏罗统,缺失上侏罗统,并明确了各组的接触关系。     

Magmatic activity and its geological significance in Early Jurassic in Mangui area of Inner Mongolia

By investigating the U-Pb zircon isotope geochronology and petrogochemistry of the major magmatic rocks in Mangui area, the authors in this paper discussed the forming era, tectonic background and geological significance. A large amount of intrusive rocks and a small amount of medium-acid volcanic rocks in Early Jurassic were found in this area. U-Pb dating by LA-ICP-MS method shows that the ages are from (199±1)Ma to (184±1)Ma and the rock types can be divided into fine-medium-grained quartz diorite, medium-grained granodiorite, fine-medium-grained monzogranite, medium-fine-grained macrophenocryst monzogranite, rhyolite, dacite and andesite, which didn’t ouur in Neoprotezoic-Paleozoic period as previous researchers thought, revealing the tectonic and magmatic activities during the Early Mesozoic period. The geochemical results show that the rocks are Ⅰ-type magmatic rocks of subluminous-peraluminous high-K calc-alkaline series. The fractionation between light and heavy rare-erath elements((La/Yb)_N= 3.42~32.96) and the Eu depletion degree is not complied with the evaluation from basic to acidic. The large ion lithophile element Ba is relatively rich and Rb, Sr are relatively delicient. The high field strength elements Th and U are relatively rich and Nb, Ti, Y are relatively deficient. The magma origin and tectonic setting show that quartz diorite and medium-fine-grained macrophenocryst monzogranite come from crust-mantle mixed magma, while the medium-acid volcanic rocks, granodiorite and fine-medium-grained monzogranite are from the partial melting of crustal materials, whose formation is connected with the evolution of Mongol-Okhotsk Suture Zone. The geology and geochemistry of the Early Mesozoic magmatic rocks indicate that the middle part of Mongol-Okhotsk Ocean might begin subduction at the end of the middle Triassic and close the Early Jurassic. The peak collision might take place at the Early Jurassic, not in the Late Triassic as previous thought. The Mohe over-thrust nappe system might form in the remote effect of southward extrusion during the closing process of the eastem part of Mongol-Okhotsk Ocean. The middle and eastern Mongol-Okhotsk Ocean closing age is of great importance to reveal the basin-range tectonic formation during the Middle Jurassic to the Late Cretaceous in Northeast China.     

Zircon U-Pb ages and geochemistry of the monzonitic granite in Rongguo area in Middle Gangdise Belt

In order to determine the geochronology, petrogenesis and tectonic background of the monzonitic granite in Rongguo area, the authors conducted the research on petrology, LA-ICP-MS zircon U-Pb geochronology and geochemistry. The results show that the zircons from the monzonitic granite are of magmatic genesis, and the zircon ²⁰⁶Pb/²³⁸U dating is (69±1) Ma, belonging to the Late Cretaceous. Al₂O₃, Na₂O, K₂O contents and K₂O/Na₂O ratio are 13.83%~14.41%, 3.68%~3.94%, 4.28%~4.35% and 1.08~1.18 respectively. The average aluminum saturation index (A/CNK) is 1.02, belonging to the weak peraluminous series. The rocks are enriched in LILE (Rb,U,K), strongly depleted in HFSE (Nb, Ta, Ti, etc.). Combined with the study of regional tectonics, the authors insisted that magma activity had not stopped from 80 to 69 Ma. The rock mass is the magmatic product of the subduction of the Neo-Tethys Ocean, forming in the orogenic environment during the whole orogenic movement period.     

内蒙古八大关斑岩型铜钼矿床成岩成矿年代学研究

八大关斑岩铜钼矿床是中国内蒙大兴安岭地区典型的斑岩型铜钼矿床之一。对矿区Ⅱ号岩体不同位置的2件岩石样品采用高精度的LA_ICP_MS锆石U_Pb测年,获得的锆石U_Pb年龄分别为(230.6±2.8)Ma和(230.5±4.4)Ma,两者在误差范围内非常一致,由此确认花岗闪长斑岩体的形成年龄约为230 Ma;对矿区7件辉钼矿样品采用Re_Os同位素测年,获得的Re_Os等时线年龄为(228.7±3.1)Ma,指示了八大关铜钼矿床辉钼矿的沉淀时间约为228.7 Ma。结合矿区岩相学、矿物学特征,辉钼矿呈浸染状分布于花岗闪长斑岩体内,且辉钼矿与黄铜矿密切共生,以及上述2种精确方法获得的年龄在误差范围内的一致性,说明花岗闪长斑岩即为成矿岩体,成岩与成矿大致同时或成矿略晚于成岩,表明八大关铜钼矿床形成于中三叠世,属于印支期成矿。     

鄂东南鸡笼山矽卡岩型金矿床花岗闪长斑岩的成因:地球化学和锆石U-Pb年代学约束

矽卡岩型金矿床是近二十年国际上新的一类矽卡岩型矿床,鸡笼山是鄂东南地区大型矽卡岩型金床之一,成矿与花岗闪长斑岩岩体密切相关,前人对该矿床及外围花岗闪长斑岩成因的研究相对较少。文章对鸡山和白果树2个岩体进行岩石学、地球化学和年代学研究,探讨其成因和形成时代。LA-ICP-MS锆石U-Pb测年果表明鸡笼山和白果树岩体的分别形成于(151.6±0.7)Ma和(142.4±0.7)Ma,即晚侏罗世—早白垩世,与鄂东地区花岗闪长斑岩的成岩年龄在误差范围内基本一致。鸡笼山和白果树花岗闪长斑岩岩体具有中等富集硅、铝、碱的特征,类似于丰山洞铜钼矿床的含矿岩体。它们具有富集大离子亲石元素Rb、Ba、Sr,亏损高场强元素Y、N Ti,并富集轻稀土元素及无负Eu异常的特征。研究表明,鸡笼山含矿岩体为准铝质高钾钙碱性I型花岗闪长斑岩可能是富集岩石圈地幔,经历了不同程度的部分熔融,同化混染了不同比例下地壳的产物。结合区域地质和年代的资料,显示鸡笼山花岗闪长斑岩岩体的形成是在晚侏罗世—早白垩世鄂东南地区岩石圈伸展的地球动力学背下岩浆活动-成岩事件的一部分。     

内蒙古卓资县大苏计斑岩型钼矿床辉钼矿Re-Os同位素年龄及流体包裹体研究

内蒙古卓资县大苏计钼矿床位于华北克拉通北缘中段的凉城断隆内,是近年来在华北克拉通北缘发现的一个大型斑岩钼矿床,矿体主要产于印支期石英斑岩和正长花岗斑岩中。成矿过程可以划分为石英_钾长石_黄铁矿±辉钼矿±磁铁矿阶段(早阶段)、石英_绢云母_辉钼矿_黄铁矿阶段(中阶段)和石英_方解石_黄铁矿±闪锌矿±方铅矿阶段(晚阶段)。矿石中5件辉钼矿的Re_Os同位素模式年龄介于(223.6±3.1)Ma~(224.2±3.4)Ma之间,其加权平均值为(223.9±1.4)Ma(MSWD=0.017),等时线年龄为(223.5±5.5)Ma(MSWD=0.026),表明大苏计钼矿床形成于印支期。大苏计钼矿床发育富液型、富气型、H2O_CO2型、含子矿物型和纯气相包裹体。成矿早阶段主要发育富液型、富气型包裹体,另有少量H2O_CO2型包裹体,其均一温度介于342~430℃之间,盐度w(Na Cleq)介于3.4%~11.0%之间;中阶段主要发育富液型、富气型、H2O_CO2型和含子矿物型包裹体,另有少量纯气相包裹体,其均一温度为234~380℃之间,盐度w(Na Cleq)介于6.2%~34.9%之间;晚阶段仅发育富液型包裹体,其均一温度介于202~280℃之间,盐度w(Na Cleq)介于1.2%~11.7%之间,指示该阶段有大气降水的加入。成矿流体从早、中阶段的H2O_Na Cl_CO2体系演化为晚阶段的H2O_Na Cl体系。早、中阶段流体均为不混溶流体,流体沸腾是成矿物质沉淀的主要机制。集宁地区钼矿床主要为斑岩型,至少存在晚三叠世和晚侏罗世2期钼成矿事件。     

内蒙古阿拉善右旗杭嘎勒晚二叠世花岗闪长岩地球 化学特征和LA-ICP-MS锆石U-Pb定年

杭嘎勒地区晚二叠世花岗闪长岩主体与包体岩石轻重稀土分馏程度强烈,铕异常不明显,稀土配分曲线为向右倾,属轻稀土富集型。包体与主体岩石同时具有Sr、Nb、P、Ti的亏损,显示形成于增生在大陆边缘正常弧花岗岩的特征。AR—SiO2图解显示,主体与包体岩石虽同属钙碱性+拉斑玄武系列区,但却表现出不同的分布形式,反映二者应来自不同的岩浆源区。在Rb—Hf—Ta图解上,主体岩石样品全部落在弧系统岩石区,而包体岩石样品落在了弧系统岩石与板内岩石区分界处;在Nb—Y图解上,样品落在了火山弧—同碰撞花岗岩区;Rb—Y+Nb图解上,落在了火山弧花岗岩区;在R1—R2图解上,大部分样品集中在碰撞前花岗岩区。LA-ICP-MS锆石U-Pb定年表明主体岩石年龄(257.9±3.1)Ma,包体岩石年龄为(257.7±3.2)Ma。杭嘎勒地区晚二叠世花岗闪长岩为碰撞前火山弧花岗岩,研究区在晚二叠世时属于活动大陆边缘的火山弧。