Geochronology, Geochemistry and Tectonic Setting of the Bairiqiete Granodiorite Intrusion (Rock Mass) from the Buqingshan Tectonic Mélange Belt in the Southern Margin of East Kunlun   总被引：1，自引：0，他引：1  

LI Zuochen  PEI Xianzhi  LI Ruibao  PEI Lei  LIU Chengjun  CHEN Youxin  LIU Zhanqing  CHEN Guochao  XU Tong  YANG Jie  WEI Bo 《《地质学报》英文版》2014,88(2):584-597

This study focuses on the zircon U–Pb geochronology and geochemistry of the Bairiqiete granodiorite intrusion(rock mass) from the Buqingshan tectonic mélange belt in the southern margin of East Kunlun. The results show that the zircons are characterized by internal oscillatory zoning and high Th/U(0.14–0.80), indicative of an igneous origin. LA–ICP–MS U–Pb dating of zircons from the Bairiqiete granodiorite yielded an age of 439.0 ± 1.9 Ma(MSWD = 0.34), implying that the Bairiqiete granodiorite formed in the early Silurian. Geochemical analyses show that the rocks are medium-K calc-alkaline, relatively high in Al2O3(14.57–18.34 wt%) and metaluminous to weakly peraluminous. Rare-earth elements have low concentrations(45.49–168.31 ppm) and incline rightward with weak negative to weak positive Eu anomalies(δEu = 0.64–1.34). Trace-element geochemistry is characterized by negative anomalies of Nb, Ta, Zr, Hf and Ti and positive anomalies of Rb, Th and Ba. Moreover, the rocks have similar geochemical features with adakites. The Bairiqiete granodiorite appears to have a continental crust source and formed in a subduction-related island-arc setting. The Bairiqiete granodiorite was formed due to partial melting of the lower crust and suggests subduction in the Buqingshan area of the Proto-Tethys Ocean.  相似文献   

Geochemistry and Zircon U–Pb–Hf Isotopic Systematics of the Sanchahe Quartz Monzonite Intrusion in the North Qinling Tectonic Zone,Central China： Implications for its Petrogenesis and Tectonic Setting     

YAN Ming  LIU Shuwen  LI Qiugen  ZHANG Wanyi  YANG Pengtao  YAN Zhen  WANG Ruiting  WANG Wei  GUO Rongrong 《《地质学报》英文版》2014,88(1):154-175

The Sanchahe quartz monzonite intrusion is situated in the middle segment of the North Qinling tectonic belt, Central China mainland, and consists chiefly of sanukitoid–like and granodioritic-monzogranitic rocks. The sanukitoid–like rocks are characterized by quartz monzonites, which display higher Mg#（55.0–59.0）, and enrichments in Na2 O＋K2 O（7.28–8.94 %）, Ni（21-2312 ppm）, Cr（56-4167 ppm）, Sr（553-923 ppm）, Ba（912-1355 ppm） and LREE（（La/Yb）N =9.47–15.3）, from negative to slightly positive Eu anomalies（δEu=＋0.61 to ＋1.10）, but also depletion in Nb, Ta and Ti. The granodioritic-monzogranitic rocks diaplay various Mg#of 6.00-53.0, high Na2 O＋K2 O（7.20– 8.30%）, Sr（455–1081 ppm） and（La/Yb）N（27.6–47.8）, with positive Eu anomalies（δEu=1.03–1.57） and depleted Nb, Ta and Ti. Laser ablation inductively coupled plasma mass spectrometry（LA-ICPMS） zircon U-Pb isotopic dating reveals that the sanukitoid-like rocks were emplaced at two episodes of magmatism at 457±3 Ma and 431±2 Ma, respectively. The monzogranites were emplaced at 445±7Ma. Sanukitoid–like rocks have their εHf（t） values ranging from ＋0.3 to ＋15.1 with Hf–depleted mantle model ages of 445 to 1056 Ma, and the monzogranite shows its εHf（t） values ranging from 21.6 to ＋10.8 with Hf–depleted mantle model ages of 635 to 3183 Ma. Petrological, geochemical and zircon Lu –Hf isotopic features indicate that the magmatic precursor of sanukitoid–like rocks was derived from partial melting of the depleted mantle wedge materials that were metasomatized by fluids and melts related to subduction of oceanic slab, subsequently the sanukitoid magma ascended to crust level. This emplaced mantle magma caused partial melting of crustally metamorphosed sedimentary rocks, and mixing with the crustal magma, and suffered fractional crystallization, which lead to formations of quartz monzonites. However, the magmatic precursor of the granodioritic-monzogranitic rocks were derived from partial melting of subducted oceanic slab basalts. Integrated previous investigation for the adackitic rocks in the south of the intrusion, the Sanchahe intrusion signed that the North Qinling tectonic zone was developed in an early Paleozoic transitionally tectonic background from an island arc to back–arc.  相似文献   

Dating of zircon from high-grade rocks： Which is the most reliable method？     

Alfred Kroner  ;Yusheng Wan  ;Xiaoming Liu  ;Dunyi Liu 《地学前缘(英文版)》2014,5(4):515-523

Magmatic zircon in high-grade metamorphic rocks is often characterized by complex textures as revealed by cathodoluminenscence （CL） that result from multiple episodes of recrystallization, over- growth, Pb-loss and modifications through fluid-induced disturbances of the crystal structure and the original U-Th-Pb isotopic systematics. Many of these features can be recognized in 2-dimensional CL images, and isotopic analysis of such domains using a high resolution ion-microprobe with only shallow penetration of the zircon surface may be able to reconstruct much of the magmatic and complex post- magmatic history of such grains. In particular it is generally possible to find original magmatic domains yielding concordant ages. In contrast, destructive techniques such as LA-ICP-MS consume a large volume, leave a deep crater in the target grain, and often sample heterogeneous domains that are not visible and thus often yield discordant results which are difficult to interpret. We provide examples of complex magmatic zircon from a southern Indian granulite terrane where SHRIMP lI and LA-ICP-MS analyses are compared. The SHRIMP data are shown to be more precise and reliable, and we caution against the use of LA-ICP-MS in deciphering the chronology of complex zircons from high-grade terranes.  相似文献   

An Andean tectonic cycle:From crustal thickening to extension in a thin crust(34°-37°SL)     

VictorA.Ramos  VanesaD.Litvak  AndresFolguera MauroSpagnuolo 《地学前缘(英文版)》2014,5(3):351-367

Several orogenic cycles of mountain building and subsequent collapse associated with periods of shallowing and steepening of subduction zones have been recognized in recent years in the Andes.Most of them are characterized by widespread crustal delamination expressed by large calderas and rhyolitic flare-up produced by the injection of hot asthenosphere in the subduction wedge.These processes are related to the increase of the subduction angle during trench roll-back.The Payenia paleoflat-slab,in the southern Central Andes of Argentina and Chile(34°—37°S) recorded a complete cycle from crustal thickening and mountain uplift to extensional collapse and normal faulting,which are related to changes in the subduction geometry.The early stages are associated with magmatic expansion and migration,subsequent deformation and broken foreland.New ages and geochemical data show the middle to late Miocene expansion and migration of arc volcanism towards the foreland region was associated with important deformation in the Andean foothills.However,the main difference of this orogenic cycle with the previously described cycles is that the steepening of the oceanic subducted slab is linked to basaltic flooding of large areas in the retroarc under an extensional setting.Crustal delamination is concentrated only in a narrow central belt along the cordilleran axis.The striking differences between the two types of cycles are interpreted to be related to the crustal thickness when steepening the subducting slab.The crustal thickness of the Altiplano is over 60-80 km,whereas Payenia is less than 42 km in the axial part,and near 30 km in the retroarc foothills.The final extensional regime associated with the slab steepening favors the basaltic flooding of more than 8400 km~3 in an area larger than 40,000 km2,through 800 central vents and large fissures.These characteristics are unique in the entire present-day Andes.  相似文献   

Pe trology and SHRIMP zircon geochronology of granulites from Vesleknausen,Lützow-Holm Complex,East Antarctica: Neoarchean magmatism and Neoproterozoic high-grade metamorphism     

Toshiaki Tsunogae  Daniel J. Dunkley  Kenji Horie  Takahiro Endo  Tomoharu Miyamoto  Mutsumi Kato 《地学前缘(英文版)》2014,5(2):167-182

We report new petrological data and geochronological measurements of granulites from Vesleknausen in the highest-grade section of the L＆#252;tzow-Holm Complex, part of the Gondwana-assembling collisional orogen in East Antarctica. The locality is dominated by felsic to intermediate orthogneiss （charnockite and minor biotite gneiss）, mafic orthogneiss, and hornblende-pyroxene granulite, with deformed and undeformed dykes of metagranite and felsic pegmatite. Pseudosection analysis of charnockite in the system NCKFMASHTO, supported by geothermometry of mafic orthogneiss, was used to infer peak metamorphic temperatures of 750e850 ？C, approximately 150 ？C lower than those estimated for met-asedimentary gneisses from Rundv？gshetta, 6 km to the northeast. SHRIMP U-Pb analysis of zircons from feldspar-pyroxene gneiss, which corresponds to a partially molten patch around mafic orthogneiss, yielded a Concordia upper intercept ages of 2507.9 ？ 7.4 Ma, corresponding to the time of formation of the magmatic protolith to the orthogneiss. Partial melting during peak metamorphism probably took place between 591 and 548 Ma, as recorded in rims overgrew around magmatic zircon. Our results suggest that Rundv？gshetta-Vesleknausen-Strandnibba region in southwestern L＆#252;tzow-Holm Bay, where orthogneisses are dominant, consists of a single crustal block, possibly formed by ca. 2.5 Ga arc mag-matism. The Neoarchean magmatic terrane was tectonically mingled with other fragments （such as metasedimentary units in northern L＆#252;tzow-Holm Bay） by subduction/collision events during the as-sembly of Gondwana supercontinent, and subsequently underwent w850 ？C granulite-facies meta-morphosed during Neoproterozoic to Cambrian final collisional event.  相似文献   

北黄海冷水团季节变化特征分析     

LI Xi-bin  SUN Xiao-yan  ZHANG Qiu-feng  NIU Fu-xin  YAO Zhi-gang 《海洋通报(英文版)》2013,(2):15-25

基于2006至2007年“908”项目执行期间春夏秋冬共四个航次的CTD温盐数据,针对四个季节底层大面及大连一成山头断面温度和盐度的分布特征,分析了北黄海冷水团的季节变化,初步探讨了其消长过程,并与历史资料相比较,发现了关于北黄海冷水团的新问题。研究表明：夏季,北黄海冷水团温度和盐度与历史资料相比,低温中心位置存在东偏,但低温中心温度和盐度变化不大。春季,32．8psu高盐水舌主轴位置较冬季偏西约75km,123．5°E以东的原冬季盐度高值区的范围向北延伸的势力大减,退化为较弱的小高盐水舌冬。冬季,北黄海冷水团已经消失,黄海暖流呈舌状向北延伸。秋季,减弱的北黄海冷水团存在两个中心温度约9℃的低温中心。  相似文献   

第五届<地震学报>编委会在北京召开          下载免费PDF全文

<地震学报>编辑部 《地震学报》2000,22(1):107

1999年12月29日,在庆祝中国地震学会成立20周年纪念活动的专业委员会分会场,由主编陈运泰院士主持召开了<地震学报>编委会会议.出席庆祝活动的30余位编委及编辑部全体成员参加了会议.首先,副主编张以勤编审就<地震学报>创刊20年来的工作向编委们作了汇报,主要谈及20年来<地震学报>概况、 <地震学报>刊登文章的重点领域、 <地震学报>在国内科技期刊中的地位,以及学报文章所反映的我国地震科学工作正在面向世界、不断扩大对世界的影响,并对<地震学报>的未来作了展望…….  相似文献   

北京地区风沙活动及其整治的初步研究   总被引：8，自引：2，他引：6  

中国科学院兰州沙漠所北京风沙课题组 《中国沙漠》1987,7(3):1-15

根据两年来北京地区的野外风沙考察,半定位风沙(尘)观测,室内风洞实验以及有关区域资料的分析研究得出:风沙问题是北京区域环境存在的严重问题之一,区域风沙活动由来已久,在频繁程度上不亚于半干旱区的河北坝上和乌盟后山地区。区内各地风沙活动均以春季为主,冬春两季风沙活动约占全年的80%以上。风沙天气的年际变化较大,五十年代最为频繁,六十年代最少,七十年代初期又有回升,中期以后至八十年代中期又逐渐趋于减少。风沙活动的形成及其盛衰变化,除与自然因素有关外,还与地表植被和土壤结构等因人类活动所造成的变化息息相关。风沙活动不仅使大气遭受污染,而且使土地资源遭受破坏。全区风沙危害严重的区域(风沙区)面积达342万亩,约占平原区总面积的35.6%,其中沙质地表因长期遭受风力作用所形成的风沙化土地面积约为136万余亩,占平原区面积的14.2%,以永定河冲积平原分布面积最大。研究证明,北京地区风沙主要来源于本地,系就地起沙。因此,风沙防治要立足于本地,特别是风沙土地的治理,对根治本区风沙危害、改善首都环境具有根本性意义。  相似文献   

叶连俊教授从事地学研究五十年          下载免费PDF全文

中国科学院地质研究所 《地质科学》1987,(4):301-305

正当秋高气爽,喜庆丰收的金色季节到来之际,我们高兴地迎来了著名地质学家叶连俊教授从事地学研究五十周年。叶教授的科学业绩正象这金秋的果树硕果累累,这是他在崎岖的科学道路上五十年如一日地艰苦奋斗、不畏艰难险阻、努力攀登的结果。这五十年,是他充满理想、奋斗、成功、挫折、再成功、再前进、不断向科学高峰迈进的五十年,是他富有科学创造力的五十年,也是他热爱祖国、与人民同呼吸共命运、全心全意为人民服务的五十年。  相似文献   

2005’水产科技论坛暨第13届基因、基因族、同工酶国际研讨会     

《海洋与湖沼》编辑部 《海洋与湖沼》2005,36(3):247-247

主办单位:中国水产科学研究院协办单位:中国科学院遗传与发育生物研究所、上海水产大学支持单位:国家自然科学基金委员会、中国生物技术发展中心、世界渔业中心、国际生物科学联合会中国委员会、韩国国立水产科学院时间地点:2005年9月17日—21日,上海市2005’水产科技论坛暨第13届基因、基因族、同工酶国际研讨会将于2005年9月17日至21日在中国上海召开。基因、基因族、同工酶国际研讨会是具有较高影响力的国际系列性会议,每两年举办一次。第13届研讨会的主题是基因组研究进展及其对21世纪生物学的意义,主要讨论近年来基因分子生物学领域和…  相似文献