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1.
新疆要拉套山花岗岩类的K—Ar和^40Ar—^39Ar同位素定年 总被引：3，自引：1，他引：3
新疆西北部阿拉套山南坡的花岗岩体的＾４０Ａｒ－＾３９Ａｒ和Ｋ－Ａ定年结果表明它们都是海西期侵入体，侵入活动可分为三个阶段：最早的东部的岩基，岩性为花岗闪长岩和钾长花岗岩，年齿约３０５Ｍａ；而后是西部的二长花岗岩和钾长花岗岩，与钨锡成矿有关，年龄约２９０Ｍａ；最晚的是最西部的二长花岗岩，年龄约２８０－２７０Ｍａ。岩浆活动中心有自动东或北东向西或南西迁移的趋势。 相似文献
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浙江省陈蔡群的^40Ar—^39Ar年龄与变质年代 总被引：2，自引：0，他引：2
本文对陈蔡群变质岩进行了４０Ａｒ－３９Ａｒ年龄测定。其中在诸暨陈蔡测得的４１５．１Ｍａ的坪年龄代表了主变质晚期的冷却年代。采自义乌尚阳的样品受燕山期火山活动影响有明显的氩丢失，与主变质有关的年龄亦明显降低，仅３１５．３Ｍａ。在龙泉东书获得的年龄谱和当地广泛发育的混合岩化作用有关，２７６．９Ｍａ的坪年龄为这次热事件的冷却年代。根据对现有年代资料的讨论，可以认为不同衰变体系记录了陈蔡群主变质事件的演化。Ｒｂ－Ｓｒ体系在变质早中期实现均匀化，年龄值为５５２．４～６６０．６Ｍａ。锆石、磷灰石在变质高峰期形成的铅丢失年龄为５０８，４～５７８Ｍａ。上述资料表明陈蔡群主变质年代属加里东期。 相似文献
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激光质谱测定南极乔治王岛北海岸A635玄武岩微区~(40)Ar-~(39)Ar的等时年龄 总被引：1，自引：0，他引：1
采用连续激光直接对岩石光片样品微区熔样，以高灵敏度、高精确度的质谱计测试，对南极乔治王岛玄武岩样品进行（４０）Ａｒ－（３９）Ａｒ法定年，取得了成功。样品置反应堆中心Ｅ－５孔道，以１．８×１０（１８）ｎ／ｃｍ２的快中子总通量照射，时间为５０ｈ，放射性冷却后进行测定。样品的加热源为自行设计的Ｎｄ：ＹＡＧ固体激光器，以Ｈｅ－Ｎｅ准激光器导光。测定中对４个２５０μｍ直径的微区分别在１５００℃高温熔融，经Ｚｒ－Ａｌ泵纯化的气体用ＭＭ１２００质谱计测量氩同位素各峰值。经计算得到该样品的等时年龄为５２．４±１．１Ｍａ，远远低于江个点的视年龄值，而（（４０）Ａｒ／（３６）Ａｒ）＞＞２９５．５。这不仅证明该样品含有过剩氩，同时也证明了由Ｋ－Ａｒ稀释法得到的偏高年龄值亦是样品中存在过剩氩造成的。激光微区等时年龄的获得进一步厘定了南极乔治王岛北海岸火山岩时代为第三纪，同时证明了我们建立的激光质谱微区、微粒熔样和测定技术是可行的和成功的。 相似文献
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秦岭地区花岗岩的K-Ar等时年龄和~(39)Ar-~(40)Ar年龄及其地质意义 总被引：3，自引：0，他引：3
本文在总结大量的公开发表的Ｋ－Ａｒ表面年龄的基础上，提出了３６Ａｒ对定年的影响，揭示了３６Ａｒ对秦岭地区花岗岩Ｋ－Ａｒ定年系统的意义，较好地显示出该区岩浆活动的冷却时间主要集中在４７０～５７０、３０９～３６０、２１４～１９０、９５～１０５Ｍａ年前四个时期，为扬子板块与华北板块在古生代以后动力地质的过程提供了明确的时间轨迹的上限。 相似文献
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青藏高原西部的抬升速率：叶城—狮泉河花岗岩^40Ar—^39Ar年龄的地质解释 总被引：19，自引：2，他引：17
通过对叶城－狮泉河剖面花岗岩中黑云母４０Ａｒ－３９Ａｒ法年龄研究,获得西昆仑北岩带库地岩体海拔高度２９５０ｍ和２８５０ｍ黑云母的封闭年龄分别为３９６．９Ｍａ和３８８．９Ｍａ,西昆仑南岩带塔西土路克、三十里营房和奇台大坂岩体黑云母的封闭年龄为１９５．８～１８３．９Ｍａ,班公湖－喀喇昆仑北岩带日土岩体黑云母封闭年龄为８０．３～７９．６Ｍａ,其时代分别为加里东期、印支期和燕山晚期。年龄结果表明,同一岩体海拔高的黑云母封闭年龄大于海拔低的黑云母封闭年龄,根据海拔高程差和坪年龄差计算出岩体的抬升速率,表明青藏高原西部从加里东期到燕山晚期,隆起速度有增大的趋势,而且具脉动性。 相似文献
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对采自河北省迁西县太平寨ＨＢＴ１麻粒岩中的辉石、角门石、斜长石进行了４０Ａｒ－３９Ａｒ年龄测定，并对上述三种矿物做了４０Ｋ－４０Ａｒ同位素封闭温度计算，进而根据封闭温度与年龄的关系，研究了该区麻粒岩体的冷却抬升历史。分别得到辉石坪年龄为２．１６Ｇａ，封闭温度为６２０℃；角闪石坪年龄为１．９７Ｇａ，封闭温度为５１７℃；斜长石坪年龄为１．６６Ｇａ，封闭温度为２６５℃。从２．５Ｇａ（麻粒岩相变质年龄）到２．１６Ｇａ，岩体抬升速率为１４．１ｍ／Ｍａ，冷却速率为０．３９℃／Ｍａ；从２．１６Ｇａ到１．９７Ｇａ岩体抬升速率为１８．５ｍ／Ｍａ，冷却速率为０．５５℃／Ｍａ，从１．９７Ｇａ至１．６６Ｇａ岩体抬升速率为２９．１ｍ／Ｍａ，冷却速率为０．８１℃／Ｍａ。Ａｒ－Ａｒ法给出的这些同位素证据，反映了冀东太古代麻粒岩体变质作用晚期多阶段冷却抬升的漫长历史。 相似文献
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本次研究从华北克拉通五台地区基底中识别出一套-25亿年的基性侵入体(主要为岩株)。其中,龙王堂岩株出露面积约5km2,侵入新太古界五台群台怀亚群,岩石类型主要为粗粒辉长岩。一条北东向基性岩墙侵入该岩株,岩墙边部发育明显的冷凝边,岩性为中粒辉长岩。LA-ICP-MS锆石U-Pb同位素年代学分析显示龙王堂粗粒辉长岩岩株形成时代为新太古代晚期(-2520Ma),中粒辉长岩岩墙形成时代为晚三叠世(-230Ma)。锆石原位Lu-Hf同位素分析显示龙王堂岩株具有正的εHf(t)值(4.75-7.95,峰值为6.3),其亏损地幔Hf模式年龄与岩浆年龄接近(tDM=2.64-2.53Ga),指示龙王堂粗粒辉长岩的原始岩浆来自于亏损地幔端元。全岩主微量元素地球化学分析显示龙王堂粗粒辉长岩表现出与洋岛玄武岩(OIB)相似的地球化学特征,并经历了橄榄石和单斜辉石等的结晶分异。结合前人研究成果,本文认为龙王堂新太古代晚期辉长岩岩株与区域上绿岩带(五台群)及同时期花岗侵入体形成时代接近,可能共同指示早期地幔直接分异形成陆壳物质的过程。这可能与俯冲构造体制不同,而与地幔柱作用产生的岩浆特征更为相似。 相似文献
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M. Qasim Jan Amanullah Laghari M. Asif Khan M. Hassan Agheem Tahseenullah Khan 《Arabian Journal of Geosciences》2018,11(2):25
The Nagar Parkar area contains three distinct groups of rocks, from oldest to youngest, (1) basement rocks ranging in composition from mafic to (quartz)diorite, tonalite, granite, and younger granodiorite, (2) granite plutons similar in general features to those of the Malani Igneous Suite of Rajasthan, and (3) abundant mafic, felsic and rhyolitic dykes. The basement rocks show strong brittle and local plastic deformation, and epidote amphibolite/upper greenschist facies metamorphic overprint. The chemistry of the basement rocks contrasts the commonly agreed within plate A-type character of the Neoproterozoic granites (group 2) that are emplaced into them. The basement rock association is calc-alkaline; the granodiorite displays the compositional characteristics of adakites, whereas the tonalite has intermediate composition between typical adakite and classical island arc rocks. This paper presents detailed petrography of the basement rocks and compares their geochemistry with those of the group 2 granites as well as with rocks from other tectonic environments. It is proposed that the Nagar Parkar basement is part of a 900–840 Ma magmatic arc that was deformed before it was intruded 800–700 Ma ago by the A-type continental granitic rocks followed by mafic to felsic dykes. 相似文献
13.
Large volumes of Devonian-Carboniferous granites were emplaced across Tasmania in southeast Australia, which was along the easternmost boundary of mid-Palaeozoic Gondwana. Some of these granites are associated with world class Sn–W deposits. Previous studies have focused mainly on relationships between granite petrogenesis and source rocks, and rarely on geochemical controls on Sn mineralisation. New zircon U-Pb ages of 405 to 396 Ma reveal that the George River Granodiorite, Grant Point Granite and Mt. Pearson Granite from eastern Tasmania intruded prior to the Tabberabberan Orogeny. The Coles Bay Granite has a U-Pb age of 388 ± 7 Ma, implying that it was emplaced simultaneously with the Tabberabberan Orogeny in Tasmania. The western Tasmanian granites mostly intruded from 374 to 360 Ma, after the Tabberabberan Orogeny. Granites associated with Sn–W deposits are moderately to strongly fractionated, including the Housetop, Meredith, Pine Hill and Heemskirk granites. Lead isotopic compositions of K-feldspars from the analysed granites, combined with isotopic evidence from other studies, suggest that differentiated granites in Tasmania had been highly contaminated by a crustal (sedimentary) component, and that western Tasmanian granites had a crustal source with substantially different isotopic characteristics to that of eastern Tasmania, which has a character similar to the Lachlan Orogen in southeast Australia. Tin-mineralised granites in Tasmania formed in a post-collisional extensional margin, a favourable environment for the production of Sn-rich melts from the lower crust. Prolonged fractional crystallisation, low oxygen fugacity and enrichments of volatiles are crucial factors to promote Sn enrichment in magmatic-hydrothermal fluids exsolved from crystallised felsic magmas. 相似文献
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激光ICP-MS锆石年龄测定结果显示,出露于辽东半岛南部金州地区的太古宙花岗岩形成年龄为2440～2500Ma左右,比辽宁北部—吉林南部大致同时的太古宙花岗岩形成略晚,或基本相当。结合其它地质证据,上述两者在太古宙可能是相互独立的两个块体(分别称辽南地块和辽北—吉南地块),它们在古元古代晚期因造山作用而拼合在一起。古元古代花岗岩形成于两个时期,早期形成的条痕状花岗岩侵位年龄为2160Ma,为辽河群沉积的基底岩石;晚期形成的斑状二长花岗岩和角闪辉石正长岩形成于距今约1850Ma,标志着辽吉古元古代造山作用的结束。据此,可确定辽河群沉积—变质的时限为距今2160～1850Ma,其演化时间不超过300Ma。 相似文献
15.
Mahmoud I. Sherif Mohamed F. Ghoneim Mohamed Th. S. Heikal Bothina T. El Dosuky 《Mineralogy and Petrology》2013,107(5):765-783
Precambrian granites of the Sharm El-Sheikh area in south Sinai, Egypt belong to collisional and post-collisional Magmatism (610–580 Ma). The granites are widely distributed in the northern part of the Neoproterozoic Arabian-Nubian Shield. South Sinai includes important components of successive multiple stages of upper crust granitic rocks. The earliest stages include monzogranite and syenogranites while the later stages produced alkali feldspar granites and riebeckite-bearing granites. Numerous felsic, mafic dikes and quartz veins traverse the study granites. Petrographically, the granitic rocks consist mainly of perthite, plagioclase, quartz, biotite and riebeckite. Analysis results portray monzogranites displaying calc-alkaline characteristics and emplaced in island-arc tectonic settings, whereas the syenogranites, alkali-feldspar granites and the riebeckite bearing-granites exhibit an alkaline nature and are enriched in HFSEs similar to granites within an extensional regime. Multi-element variation diagrams and geochemical characteristics reinforce a post-collision tectonic setting. REEs geochemical modeling reveals that the rocks were generated as a result of partial melting and fractionation of lower crust basaltic magma giving rise to A1 and A2 subtype granites. They were subsequently emplaced within an intraplate environment at the end of the Pan-African Orogeny. 相似文献
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浙江省内发育着众多中-大型萤石矿,但是对成矿岩体的研究相对较弱,制约着对区域成矿过程的认识.本文首次对安吉统里地区萤石成矿花岗岩体进行了系统的锆石U-Pb年代学和地球化学研究.锆石U-Pb测年结果显示小圩坞花岗闪长岩形成于146～140 Ma,而五房里细粒二长花岗岩形成于135 Ma,二者均形成于早白垩世早期,与华南地区大规模爆发的晚中生代岩浆作用时代相一致.全岩主微量元素地球化学表明统里地区花岗岩体可以划分为钙碱性Ⅰ型花岗岩和高分异Ⅰ型花岗岩两类,二者均显示高硅、富铝、贫铁和镁等特征,在地球化学上属于准铝质-过铝质岩石系列.其中小圩坞花岗闪长岩相对富集轻稀土元素和大离子亲石元素,亏损重稀土元素和高场强元素,而五房里细粒二长花岗岩则显示明显的中稀土元素亏损.研究认为小圩坞Ⅰ型花岗岩是变火成岩中下地壳熔融的产物,而五房里高分异Ⅰ型花岗岩是花岗质岩浆在浅层岩浆房内经历广泛结晶分异作用的产物.结合华南地区晚中生代岩浆作用由陆向海迁移的趋势,本文研究认为古太平洋板块俯冲过程中的板片回转过程是统里地区花岗岩侵入最为合理的深部动力学机制. 相似文献
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《International Geology Review》2012,54(12):1134-1142
The Rio Maria area (southeastern Carajás metallogenic province, Brazil) consists of a typical Archean Au-bearing granite-greenstone association intruded by Paleoproterozoic anorogenic granites. U-Pb analyses were performed on single zircon grains from the main Archean units of this area in order to elucidate the history of formation and evolution of the continental crust in this part of the southeastern Amazonian Craton. The Arco Verde metatonalite yielded one of the oldest U-Pb zircon ages from the Amazonian Craton (2957 +25/?21 Ma). Zircons from a meta-rhyodacite from the greenstone belt of the Lagoa Seca Group (Andorinhas Supergroup) are dated at 2904 +29/?21 Ma. This sequence is crosscut by Archean granitoids, such as the Rio Maria granodiorite, emplaced at 2874 +9/?10 Ma. These results suggest a short time interval (～100 Ma) for crustal evolution of the Rio Maria area. 相似文献
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North Yemen (Y.A.R.) was affected, from 30 to 20 Ma ago, by intense magmatic activity (Trap Series), contemporary with the main tensional tectonic phases of the Afro-Arabian Plate. In the Trap activity, two main phases have been recognized; the former, mainly basaltic, between 30 and 26 Ma; and the second, mainly acidic, between 23 and 20 Ma. During the latter period of activity, a basaltic dyke swarm and stock-like bodies and dykes (granophyres) were emplaced along the escarpment and coastal plain. Some granitic bodies intruded the Trap Series towards the end of the first phase and during the second one.
On the basis of geochemical and petrological data, the Tertiary granites of Yemen belong to alkaline or peralkaline associations of A-type. The textural characteristics indicate that the granites are either hypersolvus or subsolvus. The mafic mineral assemblages allow three main types of granites to be distinguished by their different environments of crystallization.
As regards the origin of these kinds of granites, several hypotheses account for the peculiarities observed. The lack of crustal xenoliths, the preliminary data on the Sr isotopic ratio, the data on major and trace elements point to a direct origin by fractional crystallization, without substantial crustal interaction. This agrees well with the strong tensile tectonics, linked with the uplift of the Afro-Arabian dome and with the lithosphere thinning, which provide a minimal opportunity for interaction of the magmas with the crust. 相似文献
19.
朝鲜半岛平南盆地中元古代岩浆事件 总被引：4，自引：2，他引：2
朝鲜平南盆地翁津地区发育中元古代黄海群和同时期(称之为瓮津期)花岗岩,花岗岩体侵入于黄海群。本文采用锆石原位微区U-Pb定年技术,对黄海群中的酸性火山岩及花岗岩进行了年龄测试。获得的数据表明,黄海群中下部层位及上部层位的酸性火山岩分别在1235±5Ma和1203±7Ma喷发,由此说明黄海群的沉积时代应为中元古代,而不是传统上认为的古元古代;两个翁津期花岗岩体(翁津和黄衣山岩体)的侵位年龄分别为1251±22Ma和1248±13Ma,为中元古代花岗质岩浆活动的产物。上述1251~1203Ma年龄的获得,表明朝鲜半岛发育中元古代岩浆作用,从而明确朝鲜黄海裂谷与华北东缘裂谷在时间上具有同期性,同时也表明中国华北与朝鲜在中元古代具有类似的发展历史。 相似文献
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西昆仑布隆二长花岗岩出露于西昆仑库地蛇绿混杂岩两侧。地球化学特征显示,布隆二长花岗岩主要为高钾钙碱-钾玄岩系列、过铝质花岗岩(A/CNK=1.1)。岩石具有低的Rb/Sr(0.67～0.88)、Sr/Y比值(13.2～16.6),弱的负Eu异常(Eu/Eu*=0.68～0.84)和中等Sr(214×10-6～247×10-6)、Rb含量(165×10-6～191×10-6),指示布隆二长花岗岩主要为黑云母和角闪石脱水熔融源区,其原岩可能来自于杂砂岩或壳源中性岩类。LA-ICP-MS锆石U-Pb定年结果显示该花岗岩的结晶年龄为441±2 Ma(MSWD=0.33)。锆石的εHf(t)值(平均值为-3.0)和Hf两阶段模式年龄值(1 493～1 116 Ma)反映该花岗岩来自于中新元古代地壳的熔融。新获得的资料显示,西昆仑早古生代花岗岩均发育于库地蛇绿混杂岩两侧,且具有多个期次: 507～500 Ma、471～468 Ma、447～430 Ma和408～404 Ma,推测西昆仑早古生代花岗岩为古特提斯洋在该地区长期俯冲的背景下形成的产物。 相似文献