青藏高原安多高压麻粒岩同位素年代学研究

本文报道了聂荣微陆块中新发现的高压麻粒岩锆石U-Pb定年结果及其围岩花岗片麻岩中黑云母Ar-Ar同位素年代学结果.高压麻粒岩中的锆石可分为两类,第一类具有核-边显微结构,核部残留锆石具典型岩浆结晶锆石特征,锆石U-Pb年龄541±8Ma～ 834±11Ma;第二类锆石具典型的变质锆石成因的结构特征,锆石U-Pb谐和年龄为179.0±1.7Ma.花岗片麻岩中黑云母Ar-Ar坪年龄为166.7±1.1Ma.年代学资料显示麻粒岩与其围岩均具有泛非期的年龄信息,麻粒岩的原岩经历了晚元古代-早古生代造山作用,并于早-中侏罗世发生了峰期高压变质作用改造,该变质事件可能代表着聂荣微陆块与羌南板块的碰撞拼合.伴随着早-中侏罗世的岩浆作用,麻粒岩及其围岩迅速抬升,抬升的时间跨度在13Myr左右,于166.7Ma左右抬升至地壳浅层部位或近地表.     

Ar-Ar Geochronology in a gneiss dome within the Zagros Orogénic Belt

Exhumation of the Tutak mantled gneiss dome without significant cooling has taken place in a doubly plunging anticline within the Sanandaj-Sirjan HP-LT metamorphic belt in the Zagros Thrust System of Iran. Reconstruction of structural evolution of the Tutak gneiss dome at the contact between Arabian and Iranian plates by ⁴⁰Ar/³⁹Ar geochronology exhibits history of the closure of Neo-Tethyan Ocean. There are two granites of different ages in the core of dome; the oldest corresponds to the central Iranian continental crust and was deformed at about 180 Ma. The younger granite was emplaced in the NE–SW transpression system. The timing of strain-related fabrics and exhumation history of the region illustrates the closure of Neo-Tethys and beginning of continent-continent collision at about 77 Ma, as constrained by a well defined plateau ⁴⁰Ar/³⁹Ar age obtained on biotite. Then, the biotite age corresponds to the second stage of emplacement of the Bendenow granite-gneiss which illustrating repeated orogenic events. Continuing deformation without interruption that by now has been created at about 77 Ma, was largely restricted to the transpression and high proportion of simple shear components relative to the pure shear components along the NE–SW.     

安徽庐枞盆地矾山酸性蚀变岩帽形成时代及其地质意义

酸性蚀变岩帽是岩浆热液流体和围岩在近地表相互作用的产物,是斑岩-浅成低温热液成矿系统的重要指标。发育在长江中下游成矿带庐枞盆地内的矾山酸性蚀变岩帽产出面积较大( 20km~2)。前人对该酸性蚀变岩帽中的明矾石矿床的地质和地化特征进行了相关研究,但详细的年代学研究工作尚未开展。为精确厘定矾山酸性蚀变岩帽的形成时代,本文开展了明矾石~(40)Ar-~(39)Ar法和金红石原位U-Pb法定年。矾山酸性蚀变岩帽中明矾石共有三种类型:ⅠA型明矾石主要呈交代蚀变发生在热液蚀变早阶段,与石英、粒状黄铁矿或赤铁矿、少量金红石共生;ⅠB型明矾石形成于热液蚀变晚阶段,主要呈叶片状集合体充填在开放空间中,与石英、星点状赤铁矿、粒状金红石集合体共生,少量金红石和赤铁矿沿明矾石解理裂隙分布;Ⅱ型明矾石是表生明矾石,主要呈细粒集合体沿裂隙分布,与赤铁矿、高岭石、地开石共生。三类明矾石形成于不同环境下:ⅠA和ⅠB型明矾石形成于岩浆热液环境下,是大矾山明矾石矿区的主要产物;Ⅱ型细粒明矾石分布在矾山酸性蚀变岩帽的非明矾石矿区,是表生环境下的产物。ⅠA型明矾石的~(40)Ar-~(39)Ar定年的坪年龄为131±6Ma,代表了矾山酸性蚀变岩帽的形成时代。与Ⅱ型明矾石密切共生的金红石U-Pb定年结果为32. 7±4Ma,在该期间,整个盆地内无岩浆活动发生,该年龄反映了矾山酸性蚀变岩帽经历表生氧化作用的时间。明矾石和金红石定年结果分别对应岩浆热液和表生明矾石的形成时代。在利用明矾石进行找矿工作时需先明确明矾石成因,矾山酸性蚀变岩帽中深成明矾石是下一阶段的找矿研究的基础。     

柴北缘锡铁山榴辉岩退变质成因角闪石40Ar/39Ar年代学研究

采用激光阶段加热⁴⁰Ar/³⁹Ar技术,对柴达木盆地北缘锡铁山榴辉岩退变质作用形成的榴闪岩和斜长角闪岩之角闪石进行了定年分析。09NQ44Amp来自榴闪岩,各阶段表观年龄(以现代空气氩⁴⁰Ar/³⁶Ar比值295.5扣除非放射性成因⁴⁰Ar)构成了单调下降的阶梯状年龄谱。在反等时线图解上,2~4阶段数据点和5~18阶段数据点分别构成了两条等时线,等时年龄分别为427.6±10Ma和425.1±2.6Ma,对应的初始⁴⁰Ar/³⁶Ar比值则分别为435.2±6.1和705.3±13。角闪石09NQ43Amp来自榴辉岩强烈退变质作用形成的斜长角闪岩,⁴⁰Ar/³⁹Ar阶段加热分析也获得单调下降的年龄谱,在反等时线图解上其数据点3~6阶段和7~16阶段分别构成了两条等时线,等时年龄分别为418.9±2.9Ma和418.1±2.1Ma,对应的初始⁴⁰Ar/³⁶Ar比值则分别为493.7±2.8和685.8±34.3。等时线截距值高于现代大气⁴⁰Ar/³⁶Ar比值,表明角闪石中含过剩⁴⁰Ar。同时,由低温和中-高温阶段加热数据点分别构成两条等时年龄基本一致,截距值却明显不同的等时线,表明在角闪石热力学性质不同的源区,存在两期明显不同且未混合的初始捕获Ar组分。等时年龄425~418Ma代表的是锡铁山榴辉岩角闪岩相退变质作用发生的时间。等时线图解法虽然有效的校正了角闪石中的过剩⁴⁰Ar,但仅根据表观年龄图谱和等时线图谱还无法清晰判断过剩⁴⁰Ar在角闪石中的赋存状态,有待进一步探讨。     

土耳其Pütürge变质地体晚白垩世岩浆作用与变质作用的年代学研究

Pütürge变质地体位于新特提斯构造带南部的土耳其Anatolia逆冲推覆构造带内,形成于欧亚板决与阿拉伯板块之间晚白垩纪碰撞造山事件.Pütürge变质地体主要由变质泥质片岩及片麻岩、花岗质片麻岩、石英岩、角闪岩和大理岩组成,发育类似巴罗型递增变质带的变质带序列,变质程度达高绿片岩相至低角闪岩相.此前该变质地体一直缺乏精确的年代学约束,为此我们采用了二次离子质谱锆石U-Pb测年方法和黑云母40Ar/39 Ar测年方法,对该变质地体进行了年代学研究.结果表明,区内花岗片麻岩原岩形成于84.2±1.1Ma,变质泥质片麻岩中黑云母40Ar/39 Ar年龄所代表的变质时代为83.21±0.1Ma.这说明早白垩世期间岩浆侵入事件不久,Pütürge变质地体就发生了区域变质作用.     

Pre-variscan,Variscan and Early Alpine thermo-tectonic history of the north-eastern Bohemian Massif: An 40Ar/39Ar study

The Orlica-Snieznik and Jeseník Mountains correspond to three main domes from west to east: the Snieznik, Keprnfk and Desna domes. They are composed of a basement of autochthonous gneisses, a thick series of blastomylonites and a supposed para-autochthonous or allochthonous metamorphic pre-Devonian to Devonian cover. Their broad direction is NNE-SSW. ⁴⁰Ar-³⁹Ar radiometric measurements allow three main groups of ages to be defined. (1) 300–310 Ma, represented in the Keprník and Desná domes. This age is interpretated following the constraints on the age of the metamorphism, which is linked with the extensional process occurring during the Westphalian. (2) 320–340 Ma, represented mainly in the Snieznik Dome, but not in the Keprnfk Massif. The nappe structure of Orlik-Vysoká hole, in the northern area of the Desna Dome, also exhibits this age, which is interpretated as reflecting the period of the major Variscan Barrowian metamorphism, which accompanied the compressional process. It is only represented in the zones where the extensional process was not strong enough to result in a complete overprinting. (3) 340–440 Ma, corresponding to a very strictly defined area in the eastern rim of the Desná Dome occupied by ultramylonites and mylonites. These ages, obtained on muscovites, result from an incomplete resetting of the minerals developed during the cooling of a granitic protolith and mylonitized during the extensional process. A laser probe analysis confirms the extreme inhomogeneity of the ages of the muscovites and their different resetting from one grain to another. The Late Alpine overprinting is more discrete, but can be deciphered through the low extraction temperatures with ages between 80 and 120 Ma. These ages can be compared with Alpine ages in the close Western Carpathians.     

内蒙古呼和浩特变质核杂岩韧性拆离带40Ar-39Ar定年及其构造含义

晚中生代,内蒙古大青山依次经历晚侏罗世盘羊山逆冲推覆、早白垩世呼和浩特变质核杂岩伸展、早白垩世大青山逆冲推覆断层及早白垩世以来高角度正断层复杂构造演化。其中,呼和浩特变质核杂岩韧性剪切带的冷却时间和抬升机制的制约尚不明确。本文在野外考察和显微构造分析基础上,采用逐步加热40Ar-39Ar定年法对韧性剪切带内不同单矿物的冷却年龄进行了测定。角闪石、白云母、黑云母和钾长石单矿物40Ar-39Ar冷却年龄处于120~116Ma之间。结合已有年龄数据及单矿物封闭温度,构建了韧性剪切带的冷却曲线。结果表明,韧性剪切带在122~115Ma期间存在一个明显的快速冷却过程。这一阶段快速冷却是与变质核杂岩拆离断层相关核部杂岩拆离折返作为大青山逆冲推覆断层上盘抬升的结果。     

龙门山造山带的早期活动及其对造山作用的启示

2008年汶川地震后,在映秀-北川同震地表破裂带南段虹口乡八角庙地区发现有假玄武玻璃出露于~240m宽的断裂带内,代表了断裂带以往地震和断裂活动的直接产物。这套假玄武玻璃的高温熔融成因得到了元素地球化学和熔融结构的证实。玻璃基质、蚀变矿物和碎屑斑晶的化学分析显示假玄武玻璃继承了碎裂岩/超碎裂岩围岩的主要化学成分,除石英外,主要由长石和云母两种端员组分选择性熔融形成,并呈现出了化学组分分布的不均一性。假玄武玻璃的锆石U-Pb和玻璃基质~(40)Ar/~(39)Ar定年结果证实映秀-北川断裂的古地震发生于229~216Ma的中-晚三叠世,并具有11~14km的震源深度,表明映秀-北川断裂的早期活动始于印支期的造山运动。伴随着印支造山运动的发生,龙门山断裂带形成了其初始构造框架,并对之后的构造演化产生了深远的影响。     

Geochronology of the Tore-Madeira Rise seamounts and surrounding areas: a review

We present new ⁴⁰Ar/³⁹Ar data for two of the Tore-Madeira Rise (TMR) volcanic seamounts. A sample from Tore East seamount on the northern part of the TMR yielded an ultra-precise age of 80.50 ± 0.13 Ma (2σ) that is similar within uncertainties to a published age obtained by U–Pb TIMS technique on titanites and zircons extracted from Tore NW seamount. Another sample from Isabelle seamount, located on the southern part of the TMR failed to produce a plateau age but yielded a minimum age estimate of >85 Ma. We filtered the published ages available on the TMR, the surrounding seamounts and the massifs of southwest Portugal to better understand the origin of this magmatic province. Together with this dataset, our new data suggest that: (1) a hypothetical Madeira hot-spot track spanning from Serra de Monchique on the continent to Madeira Archipelago is difficult to reconcile with the occurrence of several seamounts geographically located within or very close to this alleged hot-spot track yet being much older than the age predicted by the age trend.

(2) The geographical distribution and age pattern of the TMR and surrounding areas magmatism are still best explained by the interaction of a mantle melting anomaly emitting magma pulses and the different motion phases of the Iberia plate since 103 Ma.

     

江西冷水坑矿区构造-岩浆活动的年代学约束

江西省冷水坑矿区火成岩-构造演化一直缺少系统的年代学制约.作者运用LA-ICP-MS锆石U-Pb和40Ar/39Ar测年技术,对冷水坑矿区两套火山岩地层(打鼓顶组和鹅湖岭组)、含矿花岗斑岩和主推覆断层F2进行了年代学测试,结果表明,打鼓顶组流纹质含角砾熔结凝灰岩形成于160.8±1.9Ma,鹅湖岭组合角砾熔结凝灰岩则具有间歇性和多期喷发特点,其最初活动时间为159Ma,而主体形成于146.6±2.2Ma;矿区含矿花岗斑岩与打鼓顶组、鹅湖岭组几乎同期形成,年龄介于163.6 ±2.1Ma～154.3±3.0Ma之间;研究区构造活动起始时间不晚于加里东期,推覆断层F2中保留有40Ar/39Ar年龄为398.5±2.6Ma的构造活动痕迹,中生代重新复活,导致震旦系叠覆于鹅湖岭组之上,年龄晚于146.6Ma,可能对含矿斑岩体起破坏作用.     

Subduction and collision processes between the North China and South China blocks constrained by the geochronology and geochemistry of the Wuguan Complex in the Qinling orogen,China

ABSTRACT

The Qinling orogen is a key area for understanding the processes of subduction and collision between the South China Block (SCB) and North China Block (NCB). The Wuguan Complex, distributed along the southern margin of the Shangdan suture zone, can provide important constraints on the age of collision between NCB and SCB and the tectonic evolution of the Qinling orogen in Late Paleozoic. Detrital zircons from meta-sedimentary rocks of the Wuguan Complex in the Danfeng-Shangnan area have an age spectrum with two main peaks at ~448 Ma and ~819 Ma, and two subordinate peaks at ~938 and ~1440 Ma, respectively, and are interpreted to have been derived from the North Qinling terrane (NQT). The petrographic and geochemical characteristics of the meta-sedimentary rocks indicate that they were deposited in a fore-arc basin along the southern margin of the NQT. The youngest detrital zircons yield a weighted mean age of 378 ± 3 Ma, indicating that the fore-arc deposition was continuing at least to this time, which implies that the Paleo-Qinling Ocean between the NCB and SCB was not finally closed until at least the late Devonian. In combination with regional data, we propose that sedimentary rocks of the Wuguan Complex might once have been a sequence of late Ordovician to late Devonian strata with intercalated mafic rocks, which has been dismembered by the later tectonic activity. It was metamorphosed during northward subduction of the Paleo-Qinling Ocean at ca. 320 Ma, and slowly cooled through ca. 350°C at ca. 247 Ma (muscovite ⁴⁰Ar/³⁹Ar age). It has recorded the detailed processes of subduction and collision between the NCB and SCB.     

Amphibole Ar/Ar Geochronology from the Okcheon Metamorphic Belt, South Korea and its Tectonic Implications

An understanding of the Okcheon Metamorphic Belt (OMB) in South Korea is central to unraveling the tectono-metamorphic evolution of East Asia. Amphibole-bearing rocks in the OMB occur as calcsilicate layers and lenses in psammitic rocks, in the psammitic rocks themselves, and in the mafic volcanic layers and intrusives. Most amphiboles fail to show ⁴⁰Ar/³⁹Ar plateau ages; those that do have ages ranging from 132 to 975 Ma. The disturbed age pattern and wide variation in ⁴⁰Ar/³⁹Ar ages can be related to metamorphic grade, retrograde chemical reactions, excess Ar and amphibole composition. The oldest age (975 Ma) can be interpreted either as an old igneous or metamorphic age predating sedimentation or a false age caused by excess Ar. The youngest age of 132 Ma and the disturbed age pattern found in amphiboles from rocks located close to Jurassic granitoids are the result of retrograde thermal metamorphic effects accompanying intrusion of the granitoids. Some medium- or coarse-grained amphiboles in the calcsilicates are aggregates of fine-grained crystals. As a result, they are heterogeneous and prove to be readily affected by excess Ar. A disturbed age pattern in amphiboles from the calcsilicates occurring in the high-grade metamorphic zone may also be the product of excess Ar. On the other hand, the disturbed pattern of amphiboles present in the calcsilicates from the low-grade metamorphic zone could arise from both excess Ar and mixed ages. However, amphiboles from psammitic rocks and some calcsilicates in the high-grade metamorphic zone and in intrusive metabasites display real plateau ages of 237 to 261 Ma. The temperature conditions in the high-grade metamorphic zone were higher than the argon closing temperature for amphibole, and the amphiboles in this zone give plateau ages only when they are homogeneous in composition, lack excess Ar, and have not been thermally affected by intrusion of the granitoids. The unmodified ⁴⁰Ar/³⁹Ar ages prove rather younger than the age of the Late Paleozoic metamorphic event of 280 to 300 Ma, but they are close to muscovite K-Ar ages of 263 to 277 Ma. These ⁴⁰Ar/³⁹Ar amphibole ages are interpreted as the time of cooling that followed the main regional, intermediate-P/T metamorphic climax. The results demonstrate that interpretation of ⁴⁰Ar/³⁹Ar amphibole ages in an area subjected to several metamorphic events can be accomplished only by undertaking a thorough tectono-metamorphic study, accompanied by detailed chemical analysis of the amphiboles.     

大兴安岭南段道伦达坝铜钨锡矿床成矿作用:来自锆石和独居石U-Pb和绢云母40Ar-39Ar年龄的约束

道伦达坝中型铜钨锡矿床位于大兴安岭南段,矿体呈脉状赋存于二叠系板岩及华力西期黑云母花岗岩的断裂破碎带中。道伦达坝矿床发育铜矿体、锡矿体、钨矿体、铜钨矿体、铜锡矿体、钨锡矿体和铜钨锡矿体。矿床的成矿过程可以划分为石英-萤石-白云母-电气石-锡石-黑钨矿阶段(Ⅰ阶段)、石英-萤石-黑钨矿-黄铜矿-毒砂-磁黄铁矿阶段(Ⅱ阶段)、石英-萤石-绢云母-黄铜矿-磁黄铁矿-黄铁矿-银矿物阶段(Ⅲ阶段)和方解石-石英-萤石-黄铁矿阶段(Ⅳ阶段)。道伦达坝矿床外围的张家营子岩体中的细粒花岗岩的LA-ICP-MS锆石U-Pb年龄为136.1±0.4Ma。Ⅱ阶段Cu-W共生矿体中2件独居石的LAICP-MS U-Pb年龄分别为136.0±2.3Ma和135.1±2.2Ma。Ⅲ阶段Cu矿体中1件独居石的LA-ICP-MS U-Pb年龄为134.7±2.8Ma。Ⅲ阶段铜矿体中1件绢云母的⁴⁰Ar-³⁹Ar坪年龄为138.8±0.47Ma,等时线年龄为140.0±1.1Ma。系统的定年结果表明,道伦达坝矿床的铜钨矿体和铜矿体均形成于早白垩世,它们属于同一个成矿系统;成矿与早白垩世高分异花岗岩有密切的成因联系。     

Tectono-thermal evolution of the India-Asia collision zone based on<Superscript>40</Superscript>Ar-<Superscript>39</Superscript>Ar thermochronology in Ladakh,India

New⁴⁰Ar-³⁹Ar thermochronological results from the Ladakh region in the India-Asia collision zone provide a tectono-thermal evolutionary scenario. The characteristic granodiorite of the Ladakh batholith near Leh yielded a plateau age of 46.3 ± 0.6 Ma (2σ). Biotite from the same rock yielded a plateau age of 44.6 ± 0.3 Ma (2σ). The youngest phase of the Ladakh batholith, the leucogranite near Himya, yielded a cooling pattern with a plateau-like age of ∼ 36 Ma. The plateau age of muscovite from the same rock is 29.8 ±0.2 Ma (2σ). These ages indicate post-collision tectono-thermal activity, which may have been responsible for partial melting within the Ladakh batholith. Two basalt samples from Sumdo Nala have also recorded the post-collision tectono-thermal event, which lasted at least for 8 MY in the suture zone since the collision, whereas in the western part of the Indus Suture, pillow lava of Chiktan showed no effect of this event and yielded an age of emplacement of 128.2 ±2.6 Ma (2σ). The available data indicate that post-collision deformation led to the crustal thickening causing an increase in temperature, which may have caused partial melting at the base of the thickened crust. The high thermal regime propagated away from the suture with time.     

西藏东南部察隅地区德玛拉岩群的同位素年代学研究及其意义

青藏高原冈底斯地块东南部的德玛拉岩群为一套角闪岩相变质岩系,一直被认为是前寒武纪变质基底,但并没有可靠的年代学证据。论文对采自其中的黑云角闪片岩和黑云母石英片岩进行了锆石LA-ICP-MS U-Pb定年和黑云母³⁹Ar-⁴⁰Ar定年,测试表明,黑云角闪片岩原岩锆石U-Pb年龄为217.1Ma,由黑云母³⁹Ar-⁴⁰Ar获得的变质年龄为22.3Ma,黑云母石英片岩中碎屑锆石主要为岩浆成因,年龄范围主要集中在520~600Ma和900~1100Ma,黑云母³⁹Ar-⁴⁰Ar变质年龄为16.3Ma和22.3Ma。上述结果虽不能完全否定西藏东南部察隅地区前寒武纪基底变质岩系的存在,但至少说明现今的德玛拉岩群中还包含有遭受中生代岩浆侵入的古生代沉积岩,它们在新生代经历了变质和岩浆作用的再造,是一套变质杂岩。     

内蒙古大青山逆冲推覆体系中生代逆冲构造活动的40Ar-39Ar定年

内蒙古大青山呼和浩特段北侧发育3条走向北东东、指向北西的逆冲断层,并与被其分割的3个逆冲席体及一个原地系构成大青山逆冲推覆体系。逆冲断层上盘底部发育较深层次的糜棱岩,下盘顶部多发育低温的千糜岩。本研究在构造地质调查基础上,结合宏-微观岩石矿物学分析,采用⁴⁰Ar-³⁹Ar定年对该逆冲体系的活动时间进行约束。逆冲断层带内3个千糜岩绢云母⁴⁰Ar-³⁹Ar年龄范围为120~119Ma,另一样品给出了120Ma的概率统计峰值年龄。千糜岩为低温同变形变质产物,细粒绢云母为同变形新生矿物,其⁴⁰Ar-³⁹Ar年龄可代表变形年龄。侵位在断层内弱变形的花岗闪长岩为同构造晚期侵位,角闪石⁴⁰Ar-³⁹Ar年龄限定其冷却时间下限为121Ma,概率统计峰值年龄为119Ma。逆冲断层上盘底部发育较高温的糜棱岩,而低温千糜岩的形成时间应属于变形后期。因此,120Ma至119Ma期间,大青山逆冲推覆体系的逆冲作用应已是处于变形晚期。     

粤北良源铌钽铷钨矿床地质、成岩成矿时代与成矿模式

良源铌钽铷钨矿床位于南岭东西向构造岩浆带与武夷山北东向构造带交汇部位。良源铌钽铷钨矿床是粤北地区近年在石英型钨矿、云英岩型铌钽铷钨矿和花岗岩型铌钽铷多金属矿勘查评价取得最重要突破矿区,新发现铌钽铷钨矿体4条,共、伴生Nb2O5资源量3425.72吨,平均品位0.0108%;Ta2O5资源量1428.99吨,平均品位0.00449%;WO3资源量8205.14吨,平均品位0.25%;伴生Rb2O资源量61398.73吨,平均品位0.0987%,矿区具有大型-超大型资源潜力。良源铌钽铷钨矿床矿化特征为浅部石英脉型钨多金属矿体和云英岩型铌钽铷钨矿体+深部花岗岩型铌钽铷矿体,与以往的石英脉型钨矿"五层楼"+"地下室"成矿特征明显不同,因此对其开展成矿年代学、元素富集成矿规律和成矿模式研究具有重要意义。本文在对矿床成矿地质特征研究基础上,开展了详细的矿物学和年代学研究,应用锆石SHRIMP U-Pb法获得云英岩成岩时代为163.6~159.2Ma;黑云母花岗岩锆石206Pb/238U加权平均年龄为163.0±1.6Ma.应用白云母40Ar-39Ar等时线法获得云英岩型矿体成矿时代为166.4±1.1Ma,白云母花岗岩型矿体成矿时代为168.7±1.2Ma。研究表明,良源铌钽铷钨矿床形成于中-晚侏罗世,是华南东部中生代大规模花岗质岩浆活动与铌钽铷多金属成矿作用开始的产物,其成矿作用是花岗质岩浆高度分异形成的产物,成岩与成矿时间基本一致。浅部为石英脉型钨矿和云英岩型钨锡铌钽铷矿化,岩体接触带为云英岩型钨铌钽铷矿体,深部为高分异花岗岩型铌钽铷矿体。根据以上研究成果,本文建立了良源铌钽铷钨矿床成矿模式,对南岭地区石英脉型-云英岩型-花岗岩型稀有金属成矿理论具有一定的拓展意义,对该地区下一步勘查工作部署具有重要实践意义。     

川西木落寨稀土矿床年代学、地球化学与成矿特征

木落寨矿床位于川西冕宁-德昌稀土成矿带的北部,郑家梁子矿段是该矿床的主要成矿段。野外勘查发现,郑家梁子矿段主要的赋矿岩石是大理岩,其中发育的张性断裂充填大量矿脉,与矿带中其他矿床以正长岩为赋矿围岩的特征明显不同,而大理岩是否是成矿物质的主要来源尚不清楚。为进一步明确大理岩、正长岩和稀土物质来源之间的关系,文章对相关岩石和矿石进行地球化学特征对比分析。正长岩全岩稀土元素含量为1211×10-6～2974×10-6,稀土元素配分曲线呈轻稀土元素富集,重稀土元素亏损的特征。近矿蚀变大理岩稀土元素配分曲线整体呈右倾,稀土元素总量为1131×10-6～1935×10-6,而远矿新鲜大理岩稀土元素总量为8.20×10-6～8.69×10-6,由此可见,大理岩很可能不是稀土物质的主要来源。新鲜大理岩的δ13CV-PDB变化范围为1.3‰～1.6‰,δ18OV-SMOW介于23.2‰～23.7‰之间,显示其是海相碳酸盐岩变质的产物,蚀变大理岩的δ13CV-PDB变化范围为0.4‰～0.7‰,δ18OV-SMOW介于15.7‰～16‰之间,显示其受热液蚀变影响,并经历碳酸盐的溶解作用。新鲜大理岩与蚀变大理岩的δ13CV-PDB值变化较小(0.4‰～1.6‰),说明这2种大理岩为同源,近矿大理岩可能只是碳酸盐岩溶解蚀变的产物。矿脉中的方解石δ13CV-PDB变化范围为-4.6‰～-4.7‰,δ18OV-SMOW介于11.8‰～12.5‰之间,显示出碳酸岩岩浆经历低温蚀变的过程,证明矿脉与大理岩没有明显物质来源关系。矿石中氟碳铈矿的206Pb/204Pb、207Pb/204Pb与208Pb/204Pb分别为18.3143～18.3629、15.6243～15.6349和38.6197～38.7309,正长岩的206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.3233～18.3568,15.6298～15.6360和38.6664～38.6880。正长岩和氟碳铈矿的铅同位素特征一致,显示稀土的物质来源很可能是正长岩或隐伏的碳酸岩。本次研究选取典型矿石中与氟碳铈矿密切共生的金云母进行Ar-Ar同位素定年。鉴于矿石中的云母和氟碳铈矿并不存在多期次性,研究测得该矿段金云母的40Ar/39Ar坪年龄为(27.6±0.2)Ma,可以很好地代表成矿时代。     

大兴安岭地区德尔布干断裂带北段构造年代学研究

德尔布干断裂带是大兴安岭隆起西侧NE向的重要断裂带,处在海拉尔-拉布达林-根河盆地西缘,是著名德尔布干成矿区东南边界断裂带.为了确定德尔布干断裂带运动性质、活动时间,深入探讨该断裂带与中生代海拉尔-拉布达林-根河盆地及大兴安岭盆山格局、认识德尔布干断裂带多金属矿床成因等问题,本文应用锆石SHRIMP和云母40Ar/39Ar定年技术,分别对断裂带内的细粒黑云母花岗岩侵入体、韧性变形的花岗闪长质片麻岩、白云母石英片岩,进行了同位素年代学研究.其中花岗闪长质片麻岩岩浆型锆石SHRIMP谐和年龄300.6±9.3Ma,为花岗闪长质片麻岩海西期的侵位年龄;而花岗闪长质片麻岩中黑云母40Ar/39Ar坪年龄是130.9±1.4Ma,白云母石英片岩的白云母40Ar/39Ar坪年龄是115.6±1.6Ma,代表早白垩世伸展构造变形年龄;细粒黑云母花岗岩侵入体岩浆型锆石SHRIMP谐和年龄130.1±1.4Ma,为同伸展构造变形侵位的岩浆事件.上述地质年代说明德尔布干断裂带是早白垩世(110～130Ma)该区最年轻的重大伸展构造变形产物.控制NE向大兴安岭隆起和中生代海拉尔-拉布达林-根河等火山沉积盆地的发育格局、以及中生代以来的地壳演化与成矿类型.