南秦岭武当山群变质酸性火山岩锆石U-Pb年代学

对武当山群3个变质酸性火山岩样品的锆石U-Pb定年结果表明,武当山群变质酸性火山岩形成年龄为675.2±3.1 Ma,说明武当山群存在新元古代南华纪的地层组成.武当山群变质变形复杂,具多期岩浆活动,可能由不同时代火山岩和少量沉积岩组成,部分变质火山岩具有与耀岭河群火山岩和侵入到武当山群中的基性侵入岩相似的形成年龄,指示了武当山群变质酸性火山岩可能与基性侵入岩群和耀岭河群火山岩存在成因联系.基于现有同位素定年数据,武当山群火山岩数据具有年龄跨度大(太古宙至中生代)的显著特征,但总的趋势是新近取得的年龄数据多数比早期获得的数据要年轻.     

火山-侵入杂岩带的成岩-成矿专属性

成岩成矿关系问题,特别是成矿作用与岩浆活动的专属性问题,一直是矿床学研究中的重要课题。粤东地区热液脉状锡、钨（多金属）矿床产于中生代花岗质火山岩、次火山岩和侵入岩组成的火山侵入杂岩带中,成岩年龄与成矿年龄一致,但矿床地质、矿床矿物流体包裹体和同位素地球化学没有相对标准来区分这些来源于岩浆作用不同阶段、不同产出状态岩浆岩的成矿物质特征,使得人们对于区内矿床成因的认识不一。文中运用稀土元素地球化学方法,着重探讨和对比了矿床矿石、蚀变岩石及与成矿有关的岩浆岩的稀土元素特征和配分型式,并进一步根据在不同压力条件下Ｃｌ－在熔体和热液间的分配系数实验数据和不同压力条件下热液与相应熔体平衡时的稀土元素分配系数实验结果,分别计算了厚婆坳锡矿床和莲花山钨矿床与矿区有关岩浆岩熔体平衡的热液中的稀土元素浓度并制出配分型式,再与矿床矿石及矿石矿物稀土元素配分型式比较,从而确定成矿与侵入阶段的花岗岩岩浆活动关系密切。区内矿床为岩浆热液矿床。研究结果表明,稀土元素作为热液流体来源的示踪剂能有效地确定火山侵入杂岩带的成岩成矿专属性。     

鲁东中生代青山群火山岩锆石U-Pb年代学

青山群火山岩是山东境内最具代表性的中生代火山岩,研究其形成时代及其成因对了解华北克拉通东部的地质演化历史具有重要意义.对鲁东万第地区中生代青山群中基性火山岩和中酸性火山岩样品进行LA-ICP-MS锆石U-Pb定年,结果分别为117±2 Ma和116±4 Ma,表明万第地区中生代青山群火山岩的形成年龄为早白垩世中晚期.结合前人研究结果,可得鲁东青山群火山岩岩浆开始和结束的时间均略晚于鲁西;万第中基性和中酸性火山岩形成过程中均受到过华北克拉通古老地壳物质的影响,且万第中基性火山岩还受到了扬子陆壳深俯冲的影响.      

藏北羌塘戈木错北部新生代钾质火山岩40Ar/39Ar定年

1∶25万玛依岗日幅区域地质调查期间,在藏北戈木错北部发现了一套新生代钾质火山岩。对保存较好的3处火山岩的样品进行40Ar/39Ar年代学研究,获得了30.6Ma±0.4Ma、30.0Ma±0.2Ma和29.8Ma±0.3Ma三个坪年龄,代表该地区火山岩的喷溢时代。戈木错北部火山岩的地球化学特征与钾质火山岩的类似,它与鱼鳞山、走构由茶错、多格错仁等地区的新生代火山岩共同构成了羌塘地区钾质—超钾质火山岩带,它们的形成与印度大陆同亚洲大陆的碰撞和青藏高原的隆升密不可分。     

内蒙古月牙山一带基性火山岩的地质特征、形成时代及归属

内蒙古月牙山一带出露一条基性火山岩带,呈北西西向带状展布,由层状玄武岩、枕状玄武岩和蚀变玄武岩组成,前人对该套火山岩的归属意见不同。该套火山岩分布于月牙山蛇绿质构造混杂岩带中部,空间上与月牙山蛇绿岩套紧密共生,枕状构造较发育,显示海底火山喷发的特征;岩石化学、地球化学研究表明,该套火山岩具有典型的正常洋中脊玄武岩(NMORB)特征。因此,月牙山基性火山岩属于月牙山蛇绿岩套的组成部分。在侵入该套火山岩的辉长闪长岩中获得了530Ma左右的同位素年龄,在辉长岩、斜长花岗岩中获得了527~530Ma的同位素年龄,相当于早寒武世,说明该套基性火山岩的形成时代为早寒武世。     

鲁东胶莱盆地青山组火山岩的^40Ar—^39Ar定年——以五莲分岭山火山机构为例

以五莲分岭山火山机构为例，运用高精度的^40Ar－^39Ar定年技术，对胶莱盆地青山组火山岩的形成年龄进行了精确测定。结果表明。青山组第一旋回中偏碱性富钾火山岩的形成年龄为109．9±0．6Ma，第二旋回酸性流纹质火山岩形成年龄为108．2±0．6Ma，据此确定胶莱盆地青山组火山岩应为早白垩世岩浆活动的产物。根据该组火山岩在空间上具有自西向东年龄渐新的演变趋势，表明中生代伊泽奈崎板块向欧亚板块碰撞俯冲应是制约区内火山活动的主要动力因素。     

北淮阳早白垩世金刚台组火山岩LA-ICP-MS锆石U-Pb年龄及其地质意义

金刚台组火山岩是大别造山带北缘北淮阳晚中生代火山岩带的重要组成部分,选取金刚台组的粗面安山岩、熔结凝灰岩以及紧邻火山岩的正长斑岩,用LA-ICP-MS锆石U-Pb法进行了年龄测定,结果显示:两个火山岩样品的年龄分别为128.8±0.7 Ma和127.6±0.5 Ma,紧邻火山岩的正长斑岩的年龄为129.8±0.7 Ma,这3组年龄值在误差范围内近于一致,说明金刚台组火山岩和紧邻火山岩的正长斑岩是在很短的时间内形成的。这些年龄与整个苏鲁-大别造山带内早白垩岩世岩浆活动年龄的峰值区间一致,可能意味着它们形成于相同的动力学条件下。     

Geochronological framework of Mesozoic volcanic rocks in the Great Xing’an Range,NE China,and their geodynamic implications

Mesozoic volcanic rocks are widespread throughout the Great Xing’an Range, NE China. However, precise data constraining the exact eruption ages are limited, especially for those from the southern Great Xing’an Range, which severely hampers our understanding of the petrogenesis and geodynamics of these rocks. In this paper, we report precise in situ LA-ICPMS zircon U–Pb age measurements for these volcanic rocks. Volcanic rocks in the southern Great Xing’an Range were divided into four units from bottom to top, namely, the Manketouebo, Manitu, Baiyingaolao and Meiletu formations. The previous studies suggested that these volcanic rocks were mainly formed in the Late Jurassic. Our data demonstrate that the Manketouebo formation erupted during Late Jurassic to Early Cretaceous time, whereas the other formations are all of Cretaceous age. The southern Great Xing’an Range age dataset, along with recently obtained precise ages for volcanic rocks from the northern Great Xing’an Range indicate that Mesozoic volcanism throughout the Great Xing’an Range commenced in Late Jurassic, but peaked during the Cretaceous. They formed under an extensional tectonic setting which resulted from closure of the Mongol–Okhotsk Ocean and subsequent orogenic collapse. The globally elevated mantle temperature in Cretaceous may provided thermal contributions to the generation of the volcanisms.     

甘肃白银矿田基性火山岩的LA—ICP—MS同位素年代学

对白银矿田基性火山岩进行LA—ICP—MS法单颗粒锆石U—Pb年代学研究,查明白银矿田基性火山岩的成岩时代为465．0Ma±3．7Ma．相当于中奥陶世。结合前人的矿田酸性火山岩精确的同位素定年资料（467．3±2．9Ma和467．1±2．2Ma）,认为白银矿田成矿时代为中奥陶世。舍矿火山岩系形成于奥陶纪的岛弧-裂谷环境。这些成果对进一步深入研究白银矿田的构造演化和指导北祁连山白银式块状硫化物矿床的找寻具有重要意义。     

冈底斯西段第四纪钾质火山岩的发现及赛利普组的建立

冈底斯西段赛利普一带分布有大面积的钾质火山岩,以前曾被划归上新世一早更新世赛利普群。作者对这套火山岩地层进行了详细野外调查并重新测制了火山岩地层剖面,在该套火山岩下伏及层间湖相碎屑沉积层中获得ESR年龄0．268Ma与0．349Ma。岩石学、岩石化学研究表明,这套火山岩是以安粗质熔岩为主的钾玄岩系列一钾质碱性玄武岩系列火山岩,岩石类型及岩石组合稳定,岩层产状平缓,岩石新鲜,层位相对清楚,故将其命名为赛利普组,属第四纪早一中更新世。这一发现对研究冈底斯构造带新生代以来岩浆活动、构造演化,进而探讨青藏高原隆升机制有着重要的地质意义。     

阿尔泰造山带康布铁堡组变质火山岩锆石特征和铀—铅年龄

康布铁堡组的变质程度为绿片岩—低角闪岩相 ,已报道的同位素年龄均为变质年龄。根据锆石颜色、晶形、U Pb同位素组成 ,将该组酸性火山岩中的锆石分为继承性锆石、岩浆锆石、混合锆石 (含继承锆石核 )和变生锆石 4类。通过单颗粒锆石U Pb法年龄测定 ,获得了康布铁堡组火山岩的年龄 (4 0 7.3± 9.2 )Ma ,属早泥盆世 ,同时得出两期变质年龄和火山岩源区的参考年龄。     

大兴安岭北部±130Ma火山岩的地质意义

大兴安岭地区北部广泛发育一套早白垩世中酸性火山岩组合,这套组合下部以粗面岩-粗安岩为主,上部以流纹岩为主,二者的形成时代完全一致,锆石年龄均为130Ma,对应的地质时代为早白垩世欧特里夫期。岩石地球化学资料表明,火山岩以富硅、碱及贫镁为特征,且轻重稀土分馏明显,都具有明显的Eu负异常,反映其同源演化的特点。火山岩时代与相邻正常沉积地层中化石组合时代的对比结果表明,这套火山岩与其上下正常沉积地层的沉积时代是连续演化的。火山岩之下南屯组的化石组合时代为早白垩世凡兰吟期,对应的数值年龄为139~132 Ma,之上大磨拐河组—伊敏组的化石组合时代为早白垩世欧特里夫期晚期—芭蕾姆期,对应的数值年龄为129~125 Ma。这一证据揭示,大兴安岭北部在139~125Ma的早白垩世期间经历了连续的沉积—火山—沉积作用演化过程,反映了该区当时伸展盆地的演化特点。其中,约130 Ma的火山岩是该区一次重要的区域性火山岩喷发事件。     

Isotopic geochronology of mesozoic acid volcanic rocks in Zhejiang Province,China

Volcano-sedimentary series of the Upper Jurassic to the Lower Cretaceous are extensively developed in Zhejiang Province. But ages and stratigraphic correlation concerning these rocks have long been a controversial problem. Systematic sampling was made of volcanic rocks of the Laocun, Huangjian, Shouchang and Moshishan Formations in western Zhejiang considered thus far as the Late Jurassic. Isotopic age determinations show that U-Th-Pb zircon ages are approximately concordant with Rb-Sr isochron ages, whereas K-Ar biotite ages and K-Ar isochron ages are all slightly lower. It can therefore be established that the ages of volcanic rocks mentioned above range from 134±6 to 122±2 m.y., corresponding to the “transitional period” from Jurassic to Cretaceous. It can also be concluded that the rocks have not undergone apparent epigenetic metamorphism. The initial⁸⁷Sr/⁸⁶Sr ratio is about 0.7089–0.7121, on the basis of which it may be postulated that the volcanic magma seems to have originated from the upper mantle with contamination by sialic materials subsequent to differentiation. For age determinations of such acid volcanic rocks Rb-Sr isochron method is considered more suitable in view of its following advantages: the high reliability of results; wide applicability to different samples; smaller sample requirement and the possibility for further studies involving petrogenesis by use of initial⁸⁷Sr/⁸⁶Sr ratio.     

Cretaceous Volcanic Events in Southeastern Jilin Province, China: Evidence from Single Zircon U-Pb Ages

Mesozoic volcanic rocks in southeastern Jilin Province are an important component of the huge Mesozoic volcanic belt in the northeastern area.Study of the age of their formation is of great significance to recognize Mesozoic volcanic rule in northeastern China.Along with the research of rare Mesozoic biota and extensive Mesozoic mineralization in western Liaoning,a number of researchers have focused on Mesozoic volcanic events.The authors studied the ages of the Cretaceous volcanic rocks in southeastern Jilin Province using single Zircon U-Pb.The result shows that the Sankeyushu Formation volcanic rocks in the Tonghua area are 119.2 Ma in age,the Yingcheng Formation in the Jiutai area 113.4±3.1 Ma,the Jinjiatun Formation in Pinggang Town of Liaoyuan City and the Wufeng volcanic rocks in the Yanji area 103.2±4.7 Ma and 103.6±1 Ma,respectively. Combined with the data of recent publication on volcanic rocks ages;the Cretaceous volcanic events in southeastern Jilin Province can be tentatively subdivided into three eruption periods:119 Ma,113 Ma and 103 Ma.The result not only provides important chronology data for subdividing Mesozoic strata in southeastern Jilin Province,establishing Mesozoic volcanic event sequence,discussing geological tectonic background,and surveying the relation between noble metals to the Cretaceous volcanic rocks,but also offers important information of Mesozoic volcanism in northeastern China.     

江西冷水坑矿田火山-岩浆活动时限:SHRIMP锆石U-Pb年龄证据

冷水坑铅锌银矿是武夷山北缘中生代火山岩带中独具特色的斑岩型矿床,含矿花岗斑岩侵位于打鼓顶组和鹅湖岭组火山岩地层中.笔者采用SHRIMP锆石U-Pb测年技术,对冷水坑矿田含矿花岗斑岩与鹅湖岭组晶屑凝灰岩进行了年代学研究.3个晶屑凝灰岩的锆石U Pb年龄分别为(157.8±1.6) Ma、(157.2±1.5)Ma和(158.2±1.8) Ma,花岗斑岩形成于(157.6±1.3) Ma.含矿斑岩与其赋存的火山岩活动时间高度一致,是同一构造岩浆活动的产物.与区域上其他火山盆地不同,冷水坑矿田鹅湖岭组与打鼓顶组火山岩属于侏罗系.广泛发育于武夷山北坡中生代火山岩盆地的打鼓顶组与鹅湖岭组火山岩,其活动时间在不同火山盆地也各不相同,不能简单地统一划归为侏罗纪或白垩纪,这套地层的时代应予以重新厘定.区域上该套火山岩活动时间的差异,指示武夷山北缘火山岩浆活动具有阶段性或间隙性的演化过程,且构造背景也有很大不同.玲水坑矿田火山岩与含矿斑岩形成于中国东部陆内挤压构造环境.     

西天山查岗诺尔和智博铁矿区火山岩地球化学特征、锆石U-Pb年龄及地质意义

西天山东段的查岗诺尔铁矿和智博铁矿赋存于以玄武岩、玄武安山岩、粗面岩以及安山质凝灰岩为主的晚石炭世火山岩中, 对火山岩的形成时代以及构造地质背景的研究是重建成矿过程的关键。本文通过对两个矿区的火山岩进行岩石地球化学和LA-ICP-MS锆石U-Pb测年分析来探讨火山岩形成的构造环境与时代。地球化学分析表明大多数火山岩化学成分从钙碱性、高钾钙碱性变化到钾玄岩系列,富集轻稀土元素(LREE)和大离子亲石元素(LILE; 如Rb、Th、K),重稀土元素(HREE)配分平坦,同时具有Nb、Ta、Ti的强烈亏损,类似于岛弧火山岩的地球化学特征。大多数玄武质火山岩在构造环境判别图中位于火山弧环境。LA-ICP-MS锆石U-Pb测年显示流纹岩和英安岩的²⁰⁶Pb/²³⁸U加权平均年龄分别为301.8±0.9Ma和300.3±1.1Ma。此外,对两件闪长岩样品测年获得²⁰⁶Pb/²³⁸U加权平均年龄介于303.8～305Ma之间。火山岩与闪长岩样品具有类似的地球化学特征以及形成时代,表明它们可能来源于同一母岩浆,形成于相同的构造背景下。结合区域地质资料,本文认为矿区内出露的高钾钙碱性到钾玄岩系列火山岩可能属于俯冲过程末期阶段大陆岛弧岩浆作用的产物。     

松辽盆地北部火山岩锆石SHRIMP测年与营城组时代探讨

前人对松辽盆地营城组的时代存在不同认识。利用松辽盆地北部徐家围子断陷区营城组广泛发育的中—酸性火山岩取芯资料,开展了详细的火山岩锆石SHRIMP U-Pb年代学研究,结果表明营城组火山岩年龄集中在113—111Ma之间,属于早白垩世晚期的Aptian与Albian界线附近,从而明确该套火山岩应发育在营城组中上部的新认识,并由此说明营城组的顶界已跨入Albian。因此,认为松辽盆地营城组的时代为Hauterivian到Albian。     

应用SHRIMP铀-铅定年法研究腾冲地区中更新世英安岩的形成时代

腾冲火山岩群是我国著名的年轻火山岩群,前人主要采用K-Ar法、不平衡铀系等同位素定年方法研究该区火山岩的年龄并划分其喷发期次,采用K-Ar法获得腾冲火山岩0.013~17.84 Ma的年龄以及0.13~2.9 Ma的等时线年龄,不平衡铀系法主要用于该地区0.23 Ma以来的样品年龄研究。传统的同位素定年体系的精确度和定年范围对于研究该区火山岩的年龄存有很大局限性。近年来,微区原位离子探针U-Pb定年在年轻地质体年代学研究中表现出巨大潜力,在国际上已经应用于中更新世晚期地质体的年龄测定。本文报道了应用锆石SHRIMP U-Pb定年方法对腾冲曲石地区中更新世英安岩的3次测定结果,3次实验的年龄值在误差范围内一致。在对一次离子流选择及其强度、二次离子积分时间等实验条件探讨的基础上,综合分析3次实验中的二次离子计数表明第3次实验结果具有更高的精确度,年龄值为0.41±0.01 Ma,属中更新世,代表该英安岩的形成时代,该年龄结果是目前我国获得的最年轻的高精度锆石SHRIMP U-Pb年龄。本研究获得的中更新世锆石U-Pb年龄为年轻地质体的年代学研究提供了新的思路。     

冈底斯中段格达地区典中组火山岩锆石U-Pb年龄和地球化学特征

青藏高原南部广泛发育的林子宗火山岩蕴涵着新特提斯洋俯冲与印度—亚洲大陆碰撞过程的地质信息。为探讨冈底斯中段格达地区典中组火山岩的形成时代、岩浆源区及构造环境等特征,对其开展了LA-ICP-MS锆石U-Pb同位素测年和地球化学特征研究。研究结果表明: 该地区典中组火山岩锆石U-Pb年龄为(61.6±1.0) Ma; 典中组火山岩相对富集LILE和LREE、亏损HFSE,具典型岛弧火山岩的特征; 岩浆源区主要来源于地壳物质部分熔融,是俯冲岛弧构造环境下新特提斯洋北向俯冲消减过程的产物。     

Cretaceous Volcanic Events in Southeastern Jilin Province, China: Evidence from Single Zircon U-Pb Ages

Mesozoic volcanic rocks in southeastern Jilin Province are an important component of the huge Mesozoic volcanic belt in the northeastern area. Study of the age of their formation is of great significance to recognize Mesozoic volcanic rule in northeastern China. Along with the research of rare Mesozoic biota and extensive Mesozoic mineralization in western Liaoning, a number of researchers have focused on Mesozoic volcanic events. The authors studied the ages of the Cretaceous volcanic rocks in southeastern Jilin Province using single Zircon U-Pb. The result shows that the Sankeyushu Formation volcanic rocks in the Tonghua area are 119.2 Ma in age, the Yingcheng Formation in the Jiutai area 113.4±3.1 Ma, the Jinjiatun Formation in Pinggang Town of Liaoyuan City and the Wufeng volcanic rocks in the Yanji area 103.2±4.7 Ma and 103.6±1 Ma, respectively. Combined with the data of recent publication on volcanic rocks ages; the Cretaceous volcanic events in southeastern Jilin Province can be tentatively subdivided into three eruption periods： 119 Ma, 113 Ma and 103 Ma. The result not only provides important chronology data for subdividing Mesozoic strata in southeastern Jilin Province, establishing Mesozoic volcanic event sequence, discussing geological tectonic background, and surveying the relation between noble metals to the Cretaceous volcanic rocks, but also offers important information of Mesozoic volcanism in northeastern China.