Laser-ICP-MS U–Pb zircon ages and geochemical and Sr–Nd–Pb isotopic compositions of the Niyasar plutonic complex,Iran: constraints on petrogenesis and tectonic evolution     

《International Geology Review》2012,54(1):104-132

We conducted geochemical and isotopic studies on the Oligocene–Miocene Niyasar plutonic suite in the central Urumieh–Dokhtar magmatic belt, in order better to understand the magma sources and tectonic implications. The Niyasar plutonic suite comprises early Eocene microdiorite, early Oligocene dioritic sills, and middle Miocene tonalite + quartzdiorite and minor diorite assemblages. All samples show a medium-K calc-alkaline, metaluminous affinity and have similar geochemical features, including strong enrichment of large-ion lithophile elements (LILEs, e.g. Rb, Ba, Sr), enrichment of light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs, e.g. Nb, Ta, Ti, P). The chondrite-normalized rare earth element (REE) patterns of microdiorite and dioritic sills are slightly fractionated [(La/Yb)_n = 1.1–4] and display weak Eu anomalies (Eu/Eu* = 0.72–1.1). Isotopic data for these mafic mantle-derived rocks display I_Sr = 0.70604–0.70813, ?_Nd (microdiorite: 50 Ma and dioritic sills: 35 Ma, respectively) = +1.6 and ?0.4, TDM = 1.3 Ga, and lead isotopic ratios are (²⁰⁶Pb/²⁰⁴Pb) = 18.62–18.57, (²⁰⁷Pb/²⁰⁴Pb) = 15.61–15.66, and (²⁰⁸Pb/²⁰⁴Pb) = 38.65–38.69. The middle Miocene granitoids (18 Ma) are also characterized by relatively high REE and minor Eu anomalies (Eu/Eu* = 0.77–0.98) and have uniform initial ⁸⁷Sr/⁸⁶Sr (0.7065–0.7082), a range of initial Nd isotopic ratios [?Nd(T)] varying from ?2.3 to ?3.7, and Pb isotopic composition (²⁰⁶Pb/²⁰⁴Pb) = 18.67–18.94, (²⁰⁷Pb/²⁰⁴Pb) = 15.63–15.71, and (²⁰⁸Pb/²⁰⁴Pb) = 38.73–39.01. Geochemical and isotopic evidence for these Eocene–Ologocene mafic rocks suggests that the magmas originated from lithospheric mantle with a large involvement of EMII component during subduction of the Neotethyan ocean slab beneath the Central Iranian plate, and were significantly affected by crustal contamination. Geochemical and isotopic data of the middle Miocene granitoids rule out a purely crustal-derived magma genesis, and suggest a mixed mantle–crustal [MASH (melting, assimilation, storage, and homogenization)] origin in a post-collision extensional setting. Sr–Nd isotope modelling shows that the generation of these magmas involved ～60% to 70% of a lower crustal-derived melt and ～30% to 40% of subcontinental lithospheric mantle. All Niyasar plutons exhibit transitional geochemical features, indicating that involvement of an EMII component in the subcontinental mantle and also continental crust beneath the Urumieh–Dokhtar magmatic belt increased from early Eocene to middle Miocene time.  相似文献   

Zircon ages and Hf isotopic compositions of plutonic rocks from the Central Tianshan (Xinjiang,northwest China) and their significance for early to mid-Palaeozoic crustal evolution     

《International Geology Review》2012,54(11):1413-1434

We present new zircon ages and Hf-in-zircon isotopic data for plutonic rocks and review the crustal evolution of the Chinese Central Tianshan (Xinjiang, northwest China) in the early to mid-Palaeozoic. The Early Ordovician (ca. 475–473 Ma) granitoid rocks have zircon ε_Hf(t) values either positive (+0.3 to +9.5) or negative (?6.0 to ?12.9). This suggests significant addition of juvenile material to, and coeval crustal reworking of, the pre-existing continental crust that is fingerprinted by numerous Precambrian zircon xenocrysts. The Late Ordovician–Silurian (ca. 458–425 Ma) rocks can be assigned to two sub-episodes of magmatism: zircon from rocks of an earlier event (ca. 458–442 Ma) has negative zircon ε_Hf(t) values (?6.3 to ?13.1), indicating a predominantly crustal source; zircon from later events (ca. 434–425 Ma) has positive zircon ε_Hf(t) values (+2.6 to +8.9) that reveal a predominantly juvenile magma source. The Early Devonian (ca. 410–404 Ma) rocks have near-zero zircon ε_Hf(t) values, either slightly negative or positive (?1.4 to +3.5), whereas the Mid-Devonian rocks (ca. 393 Ma) have negative values (?11.2 to ?14.8). The Late Devonian (ca. 368–361 Ma) granites are undeformed and are chemically similar to adakite but have relatively low negative whole-rock ε_Nd(t)values (?2.4 to ?5.3). We interpret the Early Ordovician to Mid-Devonian magmatic event to reflect combined juvenile crustal growth and crustal reworking processes via episodic mafic underplating and mantle–crust interaction. The Late Devonian episode may signify delamination of the over-thickened Chinese Central Tianshan crust.  相似文献   

Long-lived Neoproterozoic high-K magmatism in the Pernambuco–Alagoas Domain,Borborema Province,northeast Brazil     

《International Geology Review》2012,54(10):1280-1299

The Pernambuco–Alagoas (PE–AL) Domain contains major granitic batholiths typified by a wide range of T_DM model ages (Archaean to Neoproterozoic), reflecting the important role of quartzofeldspathic plutons attending the Brasiliano (Pan-African) Orogeny. U/Pb zircon data for eight syn- to post-collision to syn-transcurrent granitic intrusions of the PE–AL Domain allow the studied plutons to be divided into two groups: (1) granitoids with crystallization ages older than 600 Ma (Água Branca, Serra do Catú, Serra da Caiçara, and Mata Grande plutons) and (2) granitoids with ages of ca. 590 Ma (Correntes, Águas Belas, Viçosa, and Cachoeirinha plutons). The intrusions of group 1, except for the Mata Grande Pluton, all show Nd T_DM model ages ranging from 1.5 to 1.2 Ga, whereas the granitoids from group 2 and the Mata Grande Pluton have Nd T_DM model ages ranging from 2.2 to 1.7 Ga. The studied granitoids are in part high-K, calc-alkaline, shoshonitic, and in part transitional high-K calc-alkaline to alkaline in terms of their bulk chemistry. Volcanic arc signatures associated with the Palaeoproterozoic T_DM model ages are interpreted as inherited from the source rocks. The oldest ages and higher Nd T_DM model ages recorded in the granitoids intruded in the southwestern part of the PE–AL Domain suggest that these intrusions are associated with slab-tearing during convergence between the PE–AL and Sergipano domains. The investigated plutons are coeval with high-K granitoids intruded within the Transversal Zone Domain of Borborema Province and calc-alkaline granitoids of the Sergipano Domain. This suggests that these geologic realms belonged to the same crustal block during the Brasiliano Orogeny. However, such large volumes of high-K granitoids with crystallization ages older than 600 Ma are not recorded in the Sergipano and Transversal Zone domains, suggesting differences in the crustal evolution of these three areas.  相似文献   

Meso–Neoarchaean crustal evolution of the Bundelkhand Craton,Indian Shield: new data from greenstone belts     

《International Geology Review》2012,54(11):1409-1428

ABSTRACT

The Mauranipur and Babina greenstone belts of the Bundelkhand Craton are formed of the Central Bundelkhand greenstone complex (CBGC). This complex represents tectonic collage which has not been previously studied in depth. The purpose of this study is to contribute to the understanding of the main features of the Archaean crustal evolution of the Bundelkhand Craton. The CBGC consists of two assemblages: (1) the early assemblage, which is composed of basic-ultramafic, rhyolitic–dacitic, and banded iron formation units, and (2) the late assemblage, which is a felsic volcanic unit. The units and assemblages are tectonically unified with epidote–quartz–plagioclase metasomatic rocks formed locally in these tectonic zones.

The early assemblage of the Mauranipur greenstone belt is estimated at 2810 ± 13 Ma, from the U–Pb dating (SHRIMP, zircon) of the felsic volcanics. Also, there are inherited 3242 ± 65 Ma zircons in this rock. It is deduced that this assemblage is related to early felsic subduction volcanism during the Mesoarchaean that occurred in the Bundelkhand Craton.

Zircons extracted from metasomatic rocks in the early assemblage’s high-Mg basalts show a concordant age of 2687 ± 11 Ma. This age is interpreted as a time of metamorphism that occurred simultaneously with an early accretion stage in the evolution of the Mauranipur greenstone belt.

The felsic volcanism, appearing as subvolcanic bodies in the late assemblage of the Mauranipur greenstone belt, is estimated to be 2557 ± 33 Ma from the U–Pb dating (SHRIMP, zircon) of the felsic volcanic rocks. This rock also contains inherited 2864 ± 46 Ma zircons. The late assemblage of the Mauranipur greenstone belt corresponds with a geodynamic setting of active subduction along the continental margin during Neoarchaean.

The late assemblage Neoarchaean felsic volcanic rocks from the Mauranipur and Babina greenstone belts are comparable in age and geochemical characteristics. The Neoarchaean rocks are more enriched in Sr and Ba and are more depleted in Cr and Ni than the Mesoarchaean felsic volcanic rocks of the early assemblage.

Through isotopic dating and the geochemical analysis of the volcanic and metasomatic rocks of the CBGC, this study has revealed two subduction–accretion events, the Meso–Neoarchaean (2.81–2.7 Ga) and Neoarchaean (2.56–2.53 Ga), during the crustal evolution of the Bundelkhand Craton (Indian Shield).  相似文献   

卫星重力测量的应用进展     

徐海军  张永志  段虎荣  薛建华 《物探与化探》2012,(1):54-58,64

介绍了CHAMP、GRACE和GOCE三颗重力卫星,评述了卫星重力数据在恢复地球重力场模型,测定陆地水储量变化,研究大地水准面变化、弹性厚度、地壳厚度,地震前后重力场的变化、地壳运动等方面的应用,以及一系列卓有成效的研究成果,认为卫星重力探测技术相对传统的重力测量具有得天独厚的优势,将会有更大的应用空间。  相似文献   

黔南晚石炭世旋回珊瑚礁群落演化研究     

常洪伦  宋晓东  王艳敏 《吉林地质》2012,(3):23-27

发育于黔南地区的扁坪—岩板寨晚石炭世旋回珊瑚礁由3个旋回组成,每个旋回都具有较高的生物含量和生物多样性。根据生物的丰度和功能可识别出叶状藻-"不明管状物"群落、Ivanovia cf.manchurica群落、Tubiphytes群落和Fomitchevella群落。旋回珊瑚礁的演化过程可划分为6个阶段。分析表明,礁体形成过程中曾一度出现了高能的环境,第二、三旋回经历了迅速的环境变化。  相似文献   

地震预测:从芦山地震到大陆地震   总被引：5，自引：0，他引：5       下载免费PDF全文

李德威  陈桂凡  陈继乐  郝海健 《地学前缘》2013,20(3):1-10

自从1990年以来,通过对青藏高原的调查和研究,认识到下地壳流动同步形成盆地和造山带,并受控于相关洋盆地幔软流圈向大陆的顺层流动和底辟作用。下地壳不均匀流动通过韧脆性中地壳热能-应变能转换孕育地震,部分发震能量通过上地壳脆性断层释放。在地震孕育过程中通常会伴生跨年度干旱和异常降雨,构成热灾害链。近5年内青藏高原东部连续发生汶川、玉树、芦山大地震,形成于从亚东流经羊八井、安多、玉树并分支流向汶川和芦山—康定的下地壳"热河"的仰冲式和侧冲式撞击作用。从2008年9月以来连续发表5篇论文,根据地壳热构造和热灾害链的时空结构对芦山地震的三要素进行了长期和中期预测。2008年9月预测从2013年开始可能发生大地震,2012年9月将鲜水河—安宁河—小江异常热流构造带5年内将发生多个7级地震的首个大震锁定在芦山或西昌。芦山地震只释放了亚东—羊八井—安多—玉树—鲜水河—安宁河—小江"热河"剩余热能中的一小部分,在西昌—会理—昭通地区、道孚—康定地区、通海—石屏地区近5年内很可能发生4个7级左右的地震。此外,华北典型的热灾害链结构表明震情严峻,环渤海地区近3年内很可能发生大地震。从地震热流体撞击机理与地震异常之间的关联性出发,提出了动态立体监测及短临预测地震的思路和方法。  相似文献   

Basement framework and geodynamic evolution of the Palaeoproterozoic superbasins of north‐central Australia: An integrated review of geochemical,geochronological and geophysical data     

D. L. Scott  D. J. Rawlings  R. W. Page  C. Z. Tarlowski  M. Idnurm  M. J. Jackson 《Australian Journal of Earth Sciences》2013,60(3):341-380

A largely convergent setting is proposed for crustal, tectonic and basin evolution of the intracratonic regions of north‐central Australia between 1800 and 1575 Ma. The new geodynamic model contrasts with previous proposals of widespread extension during the Leichhardt, Calvert and Isa intervals. Local transtensional to extensional structures exist, but these are best explained by a combination of flexural, thermal and dynamic processes related to an active southern margin. The development of thick accumulations of sediments (superbasins) is linked geodynamically to interpreted active margin processes (subduction and magmatic arcs) in central Australia. A synthesis of geochemical data from the 1870–1575 Ma igneous units from the Arnhem, McArthur and Mt Isa regions of north‐central Australia confirms the intracratonic setting of these units and suggests that a long‐lived thermal anomaly was responsible for the generation of both mafic and felsic magmas. The geochemical characteristics suggest the igneous units are derived from the lithospheric mantle and are not typical rift‐ or plume‐related melts. A review of the U–Pb SHRIMP ages for the entire region demonstrates the minimum distribution of correlative igneous rocks was widespread. Exotic populations in the ²⁰⁷Pb/²⁰⁶Pb isotopic data provide insights into the nature and evolution of the crust throughout north‐central Australia. Archaean inheritance is found to be nearly ubiquitous. The data support the temporal subdivision of north‐central Australia into the Leichhardt (1800–1750 Ma), Calvert (1750–1690 Ma) and Isa (1690–1575 Ma) intervals which are marked by superbasins and concomitant episodes of igneous activity. A highly heterogeneous pre‐superbasin crust is interpreted from regional, newly processed geophysical data. The cratonic portion of north‐central Australia is interpreted to consist of three broad northwest‐trending belts or elements that are further distinguished into western, central and eastern geophysically distinct provinces. A map of the superbasin distribution is derived and integrated with structural and stratigraphic data to assess the evolution of the basins and the crust through time. The superbasin successions of north‐central Australia are synchronous and widespread, although not necessarily interconnected. The tectonic model incorporates dynamic tilting of the craton during episodes of subduction and transmission of compressive intraplate stresses through the craton during intervening episodes of orogeny. These processes resulted in flexure, strike‐slip deformation and a complex thermal structure. These mechanisms account for the subsidence and basin evolution that results in widespread ramp and strike‐slip basins. The model also accounts for the thermal history recorded by magmatic events. The proposed geodynamical model provides a unifying crustal evolution scenario for central and northern Australia for approximately 225 million years of the Proterozoic.  相似文献   

Progress of SinoProbe – Deep Exploration in China 2008-2012     

DONG Shuwen  LI Tingdong  GAO Rui  LU Qingtian  WEI Wenbo  YANG Jingsui  WANG Xueqiu  CHEN Qunce  SHI Yaolin  HUANG Danian  CHEN Xuanhu  ZHOU Qi 《《地质学报》英文版》2013,87(Z1):122-122

  相似文献   

Regional Isotopic Variations in Granitic Rocks of Southern Tibet and Magmatic Contributions to Crustal Thickening during the Indo-Asian Collision     

Donald J. DEPAOLO  T. Mark HARRISON  ZHU Di-Cheng  ZHAO Zhidan  MO Xuanxue 《《地质学报》英文版》2013,87(Z1):233-234

  相似文献