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1.
选择盐边群底部荒田组玄武质岩石(原划为蛇绿岩),通过岩石化学和微量元素地球化学研究,认为盐边群玄武质岩石可能形成于弧后盆地环境;通过SHRIMP锆石U-Pb年代学研究,获得玄武质岩石岩浆结晶年龄为782±53Ma,其形成时代为新元古代。同时获得其中继承性变质锆石年龄为1837±14Ma。变质锆石年龄可能代表扬子地台西缘变质基底年龄,证明扬子地台西缘可能存在古元古代变质基底。  相似文献   

2.
大别山碰撞后火山岩的锆石U-Pb年龄和氧同位素组成   总被引：11，自引：0，他引：11  
利用阴极发光技术 (CL)观察了大别山碰撞后玄武岩和安山岩的锆石内部结构 ,并通过离子探针技术 (SIMS)测定了其U Pb年龄和氧同位素组成。玄武岩中锆石都是直接从玄武质岩浆中结晶的岩浆锆石 ,其年龄为 130± 2Ma(1σ) ;安山岩中有两种锆石 ,绝大多数是直接从安山质岩浆中结晶出来的岩浆锆石 ,年龄为 133± 3Ma(1σ) ,少数是残留的原岩锆石 ,其年龄有两组 :76 8～80 5Ma和 182 7～ 1873Ma。玄武岩和安山岩的岩浆锆石年龄表明 ,大别山碰撞后火山岩的主体应形成于 130Ma左右 ,属早白垩世。结合文献资料来看 ,大别山碰撞后火山岩和侵入岩无论是化学组成、微量元素配分、Sr Nd同位素比值还是年龄 ,都是基本一致的 ,说明火山岩和侵入岩的源区以及成因可能是相同的。玄武岩和安山岩的岩浆结晶年龄一致 ,暗示着它们之间的可能的成因联系。玄武岩锆石相对于正常地幔亏损18O(δ18O =(4 .1± 0 .6 )‰ ) ,说明其岩浆源区可能含有一定数量的俯冲板块断离后进入该区地幔的大别山榴辉岩原岩组分。安山岩中残留的原岩锆石既有扬子板块的年龄信息 ,又有华北板块的年龄信息 ,这表明华北和扬子的深部界线可能就在北淮阳  相似文献   

3.
铜陵狮子山地区中酸性侵入岩锆石SHRIMP U-Pb定年结果表明,白茫山辉石二长闪长岩、鸡冠山和大团山石英二长闪长岩以及胡村花岗闪长岩的年龄分别为:138.21 ±0.82Ma、139.9 ±1.1Ma、139.3 ±1.2Ma和140.9 ±1.2Ma.岩浆侵位顺序为花岗闪长岩→石英二长闪长岩→辉石二长闪长岩.根据锆石SHRIMP U-Pb年龄变化范围,推测该区岩浆活动持续的时间约为15Ma,且岩浆属脉动式多次侵位,后期岩浆侵位的热使早期岩体中已结晶的锆石发生熔解、重结晶,形成新的锆石.地下深部岩浆活动频繁,形成了多级岩浆房,使得本区的莫霍面界线不明显.  相似文献   

4.
龙江盆地是松辽盆地外围西部重要的火山断陷盆地之一,盆地内自下而上依次发育龙江组、光华组和甘河组火山岩。本文对龙江盆地火山岩进行了详细的锆石U-Pb年代学研究,结果显示：龙江组流纹岩、辉石英安岩、安山岩锆石U-Pb年龄分别为（129.7±2.4）、（129.0±2.3）和（125.6±1.3）Ma;光华组3个流纹岩锆石U-Pb年龄分别为（122.5±1.4）、（119.9±1.1）和（116.7±1.5）Ma;甘河组最年轻的锆石年龄为（114.3±2.9）Ma;显示盆地内火山岩浆活动的时限为129.7~114.3 Ma,火山岩均为早白垩世岩浆活动的产物。同时在甘河组玄武质粗面安山岩中测到多组捕获锆石年龄,反映出晚二叠世（254 Ma）、晚石炭世（302 Ma）、晚泥盆世（367 Ma）、早志留世（433 Ma）、古元古代（2 395 Ma）、新太古代（2 523 Ma）岩浆事件记录,这在一定程度上为龙江盆地存在古老结晶基底提供了证据。  相似文献   

5.
本文对巴仑台地区中天山南北边缘的变形花岗岩体进行了详细的锆石LA-ICP-MS-U-Pb年代学研究。中天山北缘花岗质片麻岩中岩浆锆石结晶年龄为630.0±5.0 Ma,代表了中天山微陆基底的新元古代岩浆事件年龄;其变质增生锆石边的年龄为440.9±3.3 Ma,精确限定了中天山北缘洋盆闭合与碰撞造山作用的时代为早志留世。中天山南缘糜棱岩化花岗闪长岩中岩浆锆石结晶年龄为389.5±3.2 Ma,指示出中天山南缘洋壳在中泥盆世向北俯冲形成陆缘岩浆弧;其变质增生锆石边的年龄为362.1±4.3 Ma,精确限定了中天山南缘洋盆闭合与碰撞造山作用的时代为晚泥盆世末期。研究结果还表明中天山微陆块具有年龄为2.5Ga和1.8Ga的古老结晶基底。  相似文献   

6.
大兴安岭地区发育大量的玄武安山岩-流纹岩双峰式火山岩。本文通过扎兰屯地区辉绿岩和斑岩脉的研究发现,它们具有明显的岩浆混合作用特征,表明它们是基本同时形成的。锆石原位U-Pb定年结果显示,其中花岗斑岩的锆石有非常一致的早白垩世U-Pb年龄(130±1Ma),而辉绿岩中虽然含有一定的捕获锆石,但岩浆结晶锆石的年龄(124±2Ma)也为早白垩世,表明早白垩世是大兴安岭中生代火山岩形成的重要时期。花岗斑岩的锆石具有正的εHf值(10.3±0.5),其亏损地幔模式年龄为349～568Ma;而辉绿岩中岩浆结晶锆石的εHf值(11.0±1.4)以及亏损地幔Hf模式年龄(…  相似文献   

7.
提要：北山地区是中国重要成矿区带之一。白山堂铜多金属矿是北山地区最重要的斑岩铜矿之一。本文采用锆石LA-ICP-MS U-Pb定年法测定了白山堂矿区I矿带两类含矿斑岩的同位素年龄。获得的花岗斑岩锆石加权平均年龄（275.0±3.0）Ma（MSWD=1.17）,代表了花岗斑岩的结晶年龄（早二叠世）。在流纹斑岩中获得两组年龄,一组系结晶较好的岩浆锆石,加权平均年龄为（371.1±2.8）Ma（MSWD=1.7）,表明流纹斑岩的结晶年龄为晚泥盆世;另一组锆石为继承锆石,晶形明显磨圆或包裹于第一组岩浆锆石中,年龄分别为（2627±35）Ma, （2598±35）Ma, （1705±44）Ma, （1722±48）Ma, （1642±51）Ma, （1213±54）Ma,大致分为26亿年、17亿年、12亿年左右的3类。结合地球化学特点,确定流纹斑岩可能与中上地壳在泥盆纪的重熔有关。  相似文献   

8.
阿尔泰造山带富蕴麻粒岩出露在富蕴县乌恰沟一带。通过四个麻粒岩样品的SHRIMP锆石U-Pb定年,本文获得四个谐和年龄,分别是268．0±5．5Ma、271．0±5．4Ma、271．0±6．0Ma、279．0±5．6Ma;同时也发现部分锆石从核部到边部存在着年龄差异,边部亮边的年龄与核部的年龄大约相差20Ma,认为这一亮边的年龄应该是代表麻粒岩变质年龄。依据锆石的发育特征,提出了该麻粒岩的原岩形成时代在268～279Ma,属于早二叠世中-晚期;而变质年龄要稍晚,约在255Ma,属于晚二叠世。结合该基性麻粒岩的演化过程和SHRIMP锆石U-Pb定年结果,认为阿尔泰造山带在早二叠世中-晚期还存在活动大陆边缘的岩浆活动,导致了麻粒岩的原岩——岛弧钙碱性玄武岩的形成;在晚二叠世时期,阿尔泰造山带曾发生过强烈的构造事件引起了岛弧钙碱性玄武岩发生麻粒岩相的变质作用,形成了富蕴乌恰沟基性麻粒岩。  相似文献   

9.
对青海省纳日贡玛斑岩钼铜矿床开展了锆石LA-ICP-MS U-Pb同位素定年研究,结果表明,纳日贡玛矿区2个黑云母花岗斑岩样品的锆石206Pb/238U同位素加权平均年龄分别为(43.4±0.4)Ma和(42.9±0.3)Ma,锆石形态、结晶振荡环带结构及元素含量均显示出岩浆成因特点;因此,锆石U-Pb年龄可代表斑岩的岩浆结晶年龄,纳日贡玛含矿斑岩岩浆的侵位年代可精确地限定于新生代喜马拉雅期,相当于中始新世。1件辉钼矿样品Re-Os同位素模式年龄为(40.8±0.4)Ma,结合前人的辉钼矿测试结果,认为在纳日贡玛岩浆活动约2.6 Ma后,岩浆热液成矿流体开始产生成矿作用。三江走滑断裂构造系统控制斑岩矿床的分布,青海三江北段斑岩钼铜矿具有很大的找矿潜力。  相似文献   

10.
北阿尔金恰什坎萨伊沟红柳泉以南早古生代蛇绿岩剖面发育两段玄武岩岩片.北段玄武岩锆石LA-ICP-MS U-Pb定年与前人对南段玄武岩定年结果(晚奥陶世)相近,表明该玄武岩形成于中—晚奥陶世;样品TR050-10-1锆石热干扰年龄为421～412 Ma、395～388 Ma和283～228Ma,TR050-13-1锆石热干扰年龄为442～434Ma、415Ma和241～221Ma.地球化学特征显示北段玄武岩和南段玄武岩的岩浆演化过程中均以单斜辉石结晶分异为主,仅表现极轻微地壳物质混染;二者均来自尖晶石二辉橄榄岩地幔源区,前者源区为原始尖晶石二辉橄榄岩相,后者源区为原始—亏损尖晶石二辉橄榄岩过渡相,前者的部分熔融程度更高.微量元素、稀土元素及构造判别图解指示其为形成于聚合背景下的E-MORB型拉斑玄武岩,具弧后盆地性质.结合区域资料,提出北阿尔金早古生代洋盆4阶段闭合模式:①早期俯冲阶段(∈2～O1),②晚期俯冲阶段(O1～O3),③俯冲-碰撞转换阶段(O3～S2),④后碰撞造山阶段(S3～D2).  相似文献   

11.
The Sittampundi Anorthosite Complex (SAC) in southern India is one of the well exposed Archean layered anorthosite-gabbro-ultramafic rock associations. Here we present high precision geochemical data for the various units of SAC, coupled with zircon U-Pb geochronology and Hf isotopic data for the anorthosite. The zircon ages define two populations, the older yield a concordia age of 2541 ± 13 Ma, which is interpreted as the best estimate of the magmatic crystallization age for the Sittampundi anorthosite. A high-grade metamorphic event at 2461 ± 15 Ma is suggested by the upper intercept age of the younger zircon population. A Neoproterozoic event at 715 ± 180 Ma resulted in Pb loss from some of the metamorphic zircons. The magmatic age of the anorthosite correlates well with the timing of crystallization of the arc-related ~ 2530 Ma magmatic charnockites in the adjacent Salem Block, while the metamorphic age is synchronous with the regional metamorphic event. The geochemical data suggest that the rocks were derived from a depleted mantle source. Sub-arc mantle metasomatism of slab derived fluids and subsequent partial melting produced hydrous, aluminous basalt magma. The magma fractionated at depth to produce a variety of high-alumina basalt compositions, from which the anorthositic complex with its chromite-rich and amphibole-rich layers formed as cumulates within the magma chamber of a supra-subduction zone arc. The coherent initial176Hf/177Hf ratios and positive εHf values (1.7 – 4.5) of the magmatic zircons in the anorthosite are consistent with derivation of a rather homogeneous juvenile parent magma from a depleted mantle source. Our study further confirms that the southern part of the Dharwar Craton was an active convergent margin during the Neoarchean with the generation and emplacement of suprasubduction zone arc magmas which played a significant role in continental growth.  相似文献   

12.
Abstract  This paper determines the crystallization ages of the Xiaotongguanshan quartz monzodiorite and Shatanjiao quartz monzonite porphyry from the Tongling area using the SHRIMP zircon U‐Pb method. The crystallization age of the former is 142.8±1.8 Ma; that of the latter is 151.8±2.6 Ma. These data indicate that they were formed during the Late Jurassic (142.8 to 151.8 Ma). Zoned magma chamber was formed because of double diffusive convection. Therefore, the intrusive sequence of magma is generally from quartz monzonite through quartz monzodiorite to pyroxene monzodiorite, i.e. an inverted sequence.  相似文献   

13.
40Ar-39Ar, Sm-Nd, U-Pb, and Lu-Hf isotope data are reported on the gabbro of the Volkovsky Massif, the only massif of the Uralian Platinum Belt wherein economic copper-iron-vanadium and high-grade gold-palladium mineralization is present. The massif is made up of gabbro blocks with concentrically zoned structure and diorite intrusions in its core. In the northeast and southwest, the gabbro is cut by syenite of the Kushva Massif. Gabbro blocks mainly consist of the olivine-anorthite gabbro, while labradorite two- pyroxene gabbro intersects both olivine-anorthite gabbro and Ti-magnetite and copper-PGE mineralization developed in them. The study of both gabbro types by Sm-Nd isochron and U-Pb (SHRIMP II) zircon methods with subsequent REE and Lu-Hf isotope analysis of zircon made it possible to date reliably (428 ± 7 Ma (SHRIMP) and 436 ± 21 Ma (Sm-Nd)) postore labradorite gabbro and, correspondingly, the upper age limit of the mineralization of the Volkovsky Massif. Ore-bearing olivine-anorthite gabbro contain four different-age zircon populations: 2682 ± 37–972 ± 18 Ma, 655 ± 15 to 565 ± 9 Ma; 450 ± 12 Ma, and 343 ± 8 Ma. Hf-Nd isotope systematics showed that zircon with an age of 450 ± 12 Ma presumably marks the formation age of the rocks, the older zircon was trapped, while zircon with an age of 343 ± 8 Ma was formed during low-temperature transformation of the rock and sometimes contains excess radiogenic Hf. Proterozoic xenogenic zircon was inherited from diverse rocks of ancient crust, while the oldest grain with an age of 2065 Ma was possibly formed in a deep mantle source. Vendian zircon was presumably also entrapped, and its morphology and geochemistry point to the crystallization from a basaltic melt. The abundance of pre-Paleozoic zircon in the olivine-anorthite gabbro suggests significant contribution of ancient material in their petrogenesis. This material could serve as source of ore components (metals and sulfur) for unique copper-sulfide gold-PGE mineralization of the Volkovsky Massif.  相似文献   

14.
The novel detailed geological and geochronological data for the tonalitie rocks and products of its structural and metamorphic overprint in the Orekhovo-Pavlogradskaya collision zone (Ukrainian Shield) are discussed. Magmatic crystallization of tonalites (3500 ± 13 Ma) followed by amphibolite (2863 ± 22 Ma) and granulite (2105 ± 40 Ma) facies metamorphic events, resulting in biotite-garnet gneisses formation. The last date also indicating the time of collision event. The earliest age of 3.64 Ga was found in the zonal zircon fragment within 3.5-Ga old magmatic zircon from tonalite.  相似文献   

15.
李楠 《地质与勘探》2020,56(4):722-731
最近，在西藏直孔地区冲尼村附近识别出一套二叠纪岛弧玄武岩.本文报道了其岩相学、全岩地球化学及锆石U-Pb年代学数据，探讨了其岩石成因和构造背景.锆石U-Pb年代学和全岩地球化学分析显示, 玄武岩浆结晶年龄为270.8±2.1 Ma，时代属中二叠世；全岩地球化学分析表明：冲尼玄武岩为钙碱性系列，轻稀土元素(LREE)富集，重稀土元素(HREE)相对亏损，无Eu异常，微量元素蛛网图显示，冲尼玄武岩亏损高场强元素(HFSE)，富集大离子亲石元素(LILE)。综合区域地质调查研究成果，中二叠世冲尼岛弧玄武岩形成于直孔-松多古特提斯洋向北俯冲消减的构造背景下，由俯冲板片之上经流体交代的地幔楔部分熔融形成。  相似文献   

16.
The Late Mesozoic geology of Southeast China is characterized by extensive Jurassic to Cretaceous magmatism consisting predominantly of granites and rhyolites and subordinate mafic rocks, forming a belt of volcanic-intrusive complexes. The Xiangshan volcanic-intrusive complex is located in the NW region of the belt and mainly contains the following lithologies: rhyodacite and rhyodacitic porphyry, porphyritic lava, granite porphyry with mafic microgranular enclaves, quartz monzonitic porphyry, and lamprophyre dyke. Major and trace-element compositions, zircon U?CPb dating, and Sr?CNd?CHf isotopic compositions have been investigated for these rocks. The precise SHRIMP and LA?CICP?CMS zircon U?CPb dating shows that the emplacement of various magmatic units at Xiangshan took place within a short time period of less than 2?Myrs. The stratigraphically oldest rhyodacite yielded a zircon U?CPb age of 135?±?1?Ma and the overlying rhyodacitic porphyry has an age of 135?±?1?Ma. Three porphyritic lava samples yielded zircon U?CPb ages of 136?±?1?Ma, 132?±?1?Ma, and 135?±?1?Ma, respectively. Two subvolcanic rocks (granite porphyry) yielded zircon U?CPb ages of 137?±?1?Ma and 137?±?1?Ma. A quartz monzonitic porphyry dyke, which represented the final stage of magmatism at Xiangshan, also yielded a zircon U?CPb age of 136?±?1?Ma. All these newly obtained precise U?CPb ages demonstrate that the entire magmatic activity at Xiangshan was rapid and possibly took place at the peak of extensional tectonics in SE China. The geochemical data indicate that all these samples from the volcanic-intrusive complex have an A-type affinity. Sr?CNd?CHf isotopic data suggest that the Xiangshan volcanic-intrusive complex derived mainly from remelting of Paleo-Mesoproterozoic crust without significant additions of mantle-derived magma. However, the quartz monzonitic porphyry, which has zircon Hf model ages older than the whole-rock Nd model ages, and which has ??Nd(T) value higher than the other rocks, may indicate involvement of a subordinate younger mantle-derived magma in its origin. Geochemical data indicate that the various rocks show variable REE patterns and negative anomalies of Ba, Nb, Sr, P, Eu and Ti in the trace element spidergrams, suggesting that these rocks may have undergone advanced fractional crystallization with separation of plagioclase, K-feldspar and accessory minerals such as allanite. We suggest that this Cretaceous volcanic-intrusive complex formed in an extensional environment, and the formation of the Xiangshan mafic microgranular enclaves can be explained by the injection of mafic magma from a deeper seated mantle magma chamber into a hypabyssal felsic magma chamber at the crustal emplacement levels.  相似文献   

17.
鱼洞子杂岩是秦岭地区最古老的复杂的地质体。前人对鱼洞子杂岩不同的地质体采用多种方法进行了年龄测定,但结果差异较大,且总体测试精度不高。依据锆石CL影像的特征,结合锆石成因分析和锆石微区的U-Pb同位素,进行了LA-ICP-MS测定,在鱼洞子杂岩糜棱岩化细粒黑云母花岗岩和强片理化黑云母花岗岩中分别获得2661Ma±17Ma和2703Ma±26Ma的岩浆结晶年龄,同时在糜棱岩化细粒黑云母花岗岩中获得2647Ma±65Ma的变质锆石年龄。其中2703Ma±26Ma是秦岭造山带目前发现的最古老的侵入岩的形成年龄,为研究秦岭造山带早前寒武纪构造岩浆事件和地球早期的形成演化提供了新的资料。  相似文献   

18.
This paper describes the results of geochronological studies (U-Pb method over micro lots and single grains of zircon) of autochtonous and allochtonous granitoids of the Barguzinskii complex of the Angara-Vitim batolite of the petrotypical area in the basin of the Dzhirga and Kovyli rivers (tributaries of the Barguzin River). The age of crystallization of gneissose granitoids is 297 ± 5 Ma, and that of intrusive leucocratic biotite granites is 291 ± 1 Ma. The estimates of the age finalize the discussion on the age of granitoids of the Barguzin complex and cannot be considered as ??rejuvenated.?? The analyses of the geochronological data that have been obtained up to the present for granitoids of the Angara-Vitim batolite with the SHRIMP and U-Pb methods for large samples of zircons show that in the majority of cases they cannot be used for precise estimation of the age of their crystallization. The geochronological data obtained with use of the U-Pb method over micro samples and single grains of zircon allow one to make a conclusion on the formation of granitoids of the described complexes of the Angara-Vitim batholite that occurred within 303 ± 7?C281 ± 1 Ma. Thus, the time length of formation of the largest in the eastern segment of the Central Asian belt of the Angara-Vitim batholite is not more than 22 Ma (minimum 6 Ma), which allows us to consider it as a large granitic province and is a boundary condition for development of the geodynamic models of its formation.  相似文献   

19.
For magmatic rocks, it is often found that zircon 206 Pb/238 U and 207 Pb/235 U ratios continuously plot on the concordia line with a relatively large age span for the same sample, which gives rise to large dating errors or even unrealistic dating results. As the trace element concentrations of zircon can reflect its equilibrated magma characteristics, they can be used to determine whether all the analytical spots on the zircons selected to calculate the weighted mean age are cogenetic and formed in a single magma chamber. This work utilizes the results of zircon trace element concentrations and U-Pb isotopic analyses to explore the screening of reasonable U-Pb ages, which can be used to determine a more accurate intrusion crystallization age. The late Mesozoic Huayuangong granitic pluton complex, which is located in the Lower Yangtze region, eastern China, was selected for a case study. The Huayuangong pluton comprises the central intrusion and the marginal intrusion. Two samples from the marginal intrusion yielded consistent zircon weighted mean 206 Pb/238 U ages of 124.6 ± 2.0 Ma and 125.9 ± 1.6 Ma. These analytical spots also exhibit Zr/Hf and Th/U ratios concordant with the evolution of a single magma, from which the dated zircons crystallized. However, for the central intrusion, the analytical spots on zircons from two samples all show a continuous distribution on the concordia line with a relatively large age span. For each sample from the central intrusion, the zircon Zr/Hf ratios do not conform to a single magma evolutionary trend, but rather can be divided into two groups. We propose that zircon Zr/Hf ratios can provide a new constraint on U-Pb zircon dating and zircon Th/U ratios can also be used as a supplementary indicator to constrain zircon dating and determine the origins of the zircons and whether magma mixing has occurred. By screening zircon analytical spots using these two indicators, the two samples from the central intrusion of the Huayuangong pluton produce results of 122.8 ± 4.3 Ma and 122.9 ± 2.2 Ma, which are consistent with the field observations that the central intrusion is slightly younger than the marginal intrusion.  相似文献   

20.
The new SHRIMP zircon U-Pb isotopic study suggests that the crystallization age of a highly fractionated magma in the NE Jiangxi ophiolite suite is 968±23 Ma. Re-calculated Sm-Nd isochron age of 955±44 Ma is within analytical errors. consistent with the zircon U-Pb age. With the exception of two anomalous Sm-Nd data, the remaining 15 analyses so far obtained for the ophiolite gaveεNd (T) values falling into a limited range from +4.3 to +6.7, indicating that the ophiolite was derived from a relatively strongly depleted mantle source. Sm-Nd isotopic systematics in some samples may have been strongly affected by post-magmatic events, such as alteration, deformation and metamorphism, resulting in anomalousεNd (T) values. Combined with published40Ar39Ar age data, it can be concluded that the collision between the Yangtze and South China Blocks occurred during 0.97-0.80 Ga. This work was financially supported by the President Grant of the Chinese Academy of Sciences.  相似文献   

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