排序方式： 共有56条查询结果，搜索用时 15 毫秒
31.
内蒙古固阳东部碱性侵入岩:年代学、成因与地质意义 总被引：10，自引：7，他引：3
在内蒙古固阳县东部出露了两个碱性岩体,最近的年代学研究显示这两个碱性侵入体分别形成于中元古代早期和晚古生代早期,瓦窑石英正长岩的锆石SHRIMP U-Pb年龄为1702±32Ma,高家村角闪正长岩的SHRIMP年龄为399±7Ma,TIMS法锆石U-Pb为389.9±4.7Ma。瓦窑石英正长岩相对贫Ca、贫Sr、高TiO2/MgO和FeOT/MgO、高Ga/Al,Eu负异常;岩石高87Sr/86Sr比值、低143Nd/144Nd比值、εNd(t)为-6.2～-6.5,地球化学特点显示铝质"A"型花岗岩性质,岩浆源区为大陆上部地壳,是拉张低压背景下部分熔融的产物。高家村角闪正长岩高碱(K2O+Na2O为10.92%～11.67%),Sr正异常,弱正铕异常,具有较低的87Sr/86Sr比值、适中的143Nd/144Nd比值,εNd(t)为-14.4～-14.9,具有高压型正长岩的特征,岩石应形成于大陆下部地壳,属后造山崩塌早期阶段的产物。这两个岩体的形成时代分别与冀北地区的中元古代非造山岩浆岩组合(斜长岩-正长岩-环斑花岗岩组合)和晚古生代的水泉沟正长岩相对应,有可能构成华北克拉通北缘两条延伸数百千米的碱性侵入岩带。中元古代早期的碱性侵入岩带代表着华北克拉通在古元古代末汇聚造山后的裂解事件;而早(-中)泥盆世的碱性侵入岩带则代表着华北克拉通北缘早古生代末弧-陆拼合造山后的伸展事件。 相似文献
32.
Charles Cartannaz Patrick Rolin Joël Le Métour Olivier Fabbri 《Comptes Rendus Geoscience》2006,338(3):214-221
The South Armorican Shear Zone consists of a set of faults that runs across the southern Armorican Massif and extends eastwards to the Massif Central. One of its branches, the Cholet Shear Zone of South Brittany, can be correlated with the North-Millevaches–La Courtine Shear Zone in the Massif Central. It was active immediately after the regional Frasnian anatexis (372–368 Ma) as a right-lateral strike-slip fault. The horizontal offset, which can be estimated between 110 and 170 km, was achieved before the emplacement of non-deformed Late Tournaisian calc-alkaline and peraluminous granites (355–350 Ma). This newly established age of activity (Fammenian–Tournaisian) of the Cholet–La Courtine Shear Zone (CCSZ) has to be taken into account in geodynamical reconstructions of the Variscan belt of western Europe. To cite this article: C. Cartannaz et al., C. R. Geoscience 338 (2006). 相似文献
33.
Emplacement age for the mafic-ultramafic plutons in the northern Dabie Mts. (Hubei): Zircon U-Pb, Sm-Nd and 40Ar/39Ar dating 总被引：2，自引：0，他引：2
The protoliths of mafic-ultramafic plutons in the northern Dabie Mts. (NDM) (Hubei) include pyroxenite and gabbro. The zircon U-Pb dating for a gabbro suggests that emplacement of mafic magma took place in the post-collisional setting at the age of 122.9(0.6 Ma. It is difficult to obtain a reliable Sm-Nd isochron age, due to disequilibrium of the Sm-Nd isotopic system. Two hornblende 40Ar/39Ar ages of 116.1(1.1 Ma and 106.6(0.8 Ma may record cooling of metamorphism in the mafic-ultramafic plutons in Hubei below 500(C. The hornblende 40Ar/39Ar ages for the mafic-ultramafic rocks in Hubei are evidently 15-25 Ma younger than those for the same rocks in Anhui, indicating that there is a diversity of the cooling rates for the mafic-ultramafic rocks in Hubei and Anhui. The difference in their cooling rates may be controlled by the north-dipping normal faults in the NDM. The intense metamorphism occurring in the mafic-ultramafic rocks in Hubei may result from the Yanshanian magmatic reheating and thermal fluid action induced by the Cretaceous migmatization. The geochemical similarity of these mafic-ultramafic rocks wherever in Hubei and Anhui may be attributed to the same tectonic setting via an identical genetic mechanism. 相似文献
34.
James H. Bourne 《Mathematical Geology》1993,25(3):357-375
Magnetic susceptibility, density, modal mineral, and whole rock geochemical data have been collected from two granitic plutons in Quebec. Each of the first three variables is correlated with SiO2 to some degree. Multiple regression using all three variables simultaneously as independent variables and SiO2 as a dependent variable yielded pluton dependent equations which were then used to calculate SiO2 values for each analysis. Calculated values of SiO2 typically differ from the analysed values by 1.5% for the first pluton and 1.0% for the second. The polynomials thus can be used to estimate the SiO2 value of unanalyzed samples with some confidence. Plots of calculated SiO2 reveal details of chemical variation with the pluton which were not observed when using chemical data alone due to the small number of analyzed rocks. The method also provides an independent evaluation of possible analytical errors. 相似文献
35.
冀北闪长质岩石的锆石SHRIMP U-Pb年龄：晚古生代岩浆弧的地质记录 总被引：6，自引：6，他引：6
华北克拉通北缘的丰宁-承德地区分布着许多被认为是古元古代的片麻状闪长质-石英闪长质-花岗闪长质侵入体,新的年代学资料揭示这些侵入体中许多是晚古生代的产物。本次工作从京北喇叭沟门闪长岩体和丰宁天桥含石英闪长岩体中分别获得了(288.0±4.8)Ma和(279.5±5.6)Ma的锆石SHRIMP U-Pb年龄。这些钙碱性岩石的存在表明华北克拉通北缘在早二叠世是一条安第斯型的活动大陆边缘。综合分析冀北地区晚古生代侵入岩的侵位时代和变形特点,结合该地区晚古生代发生变形变质作用的年龄信息,推测华北克拉通北侧的古亚洲洋在晚二叠世末封闭,随后进入了主造山期之后的构造松弛阶段。 相似文献
36.
Veridiana T. de S. Martins Wilson Teixeira Carlos M. Noce Antonio C. Pedrosa-Soares 《Gondwana Research》2004,7(1):75-89
Nd and Sr isotope data were obtained for three plutonic suites (595–505 Ma) and distinct young granitoid intrusions (503 Ma), from the southern part of the Neoproterozoic Araçuaí Orogen. The Sr and Nd isotopes (87Sr/86Sr, eNd) and TDM values from the plutons and distinct basement rocks are used to constrain the magma genesis of the granitoid plutons. These isotopic parameters, with eNd values ranging from −4 to −24 and TDM ages from 1.3 to 2.8 Ga, for the granitoid suites, and −5 to −40 and 3.5 to 1.5 Ga, for the distinct Archean and Proterozoic basement complexes, suggest that the Jequitinhonha Complex metasediments are the main crustal source for most of these plutons, except for the youngest granitoid intrusions, which may have a protolith similar to the Mantiqueira and Guanhães complexes. Furthermore, the isotope data indicate a minor, but important, participation of Neoproterozoic oceanic lithosphere in the granite genesis, which corroborates with a confined orogenic model and a narrow oceanic consumption (B-subduction) for the Araçuaí Orogen. 相似文献
37.
藏北阿翁错复式岩体及其暗色微粒包体年龄、地球化学与地球动力学意义 总被引：1，自引：0，他引：1
对班公湖-怒江缝合带西段阿翁错复式岩体及其暗色微粒包体开展了岩石学、全岩地球化学及同位素年龄研究。结果表明,阿翁错复式岩体中出露大量闪长质暗色微粒包体,包体具典型的火成结构,发育针状磷灰石。寄主岩与包体均为准铝质、高钾钙碱性-钾玄岩系列过渡岩石,主要氧化物含量在Harker图解上具有良好的线性关系,稀土元素配分曲线和微量元素原始地幔标准化蛛网图具有高度的一致性,表明二者具有强烈的地球化学亲源关系,且经历了相似的岩浆演化过程;主量、微量元素同分母协变图中包体和寄主岩表现为良好的线性关系,表明二者之间的演化与岩浆混合作用关系密切;包体的原始岩浆可能来源于受俯冲带流体交代的地幔楔,寄主岩为幔源岩浆与熔融下地壳岩浆混合的产物,以熔融下地壳岩浆为主。寄主岩和暗色微粒包体的成岩年龄分别为109.1±1.0Ma和107.4±0.7Ma,显示岩浆混合作用发生在早白垩世。结合班公湖-怒江缝合带的演化及构造判别,认为阿翁错复式岩体形成于班公湖-怒江特提斯洋软碰撞阶段,为受俯冲带流体交代的地幔楔上升与其诱发的下地壳花岗质岩浆混合作用的产物。 相似文献
38.
班公湖-怒江缝合带西段阿翁错复式岩体的岩浆混合成因:地球化学、年代学和暗色微粒包体证据 总被引：1，自引：1，他引：0
阿翁错复式岩体位于班公湖-怒江缝合带西段,是班公湖-怒江特提斯洋俯冲消减,造山过程中岩浆响应的重要组成部分,以广泛发育暗色微粒包体和岩浆混合、不协调现象为特征。本文以阿翁错复式岩体为研究对象,对寄主岩和暗色微粒包体开展了系统的地质学、地球化学和锆石U-Pb年代学研究,探讨了阿翁错复式岩体的岩浆混合成因。暗色微粒包体塑性变形特征明显,与寄主岩呈截然或渐变接触,偶见反向脉发育,包体具细-中粗粒结构,含斜长石、钾长石、角闪石、暗色镶边石英等斑晶,偶见角闪石斑晶横跨包体和寄主岩,在包体及包体周围寄主岩中见长柱状斜长石、角闪石和针状磷灰石等结构特征,表明暗色微粒包体为岩浆混合作用的产物。寄主岩与包体均为准铝质、钙碱性-高钾钙碱性系列岩石,主要氧化物含量在Harker图解上具有良好的线性关系,稀土元素配分曲线图和微量元素蛛网图具有高度一致性,表明二者具有强烈的地球化学亲源关系,且经历了相似的岩浆演化过程。寄主岩和暗色微粒包体的成岩年龄分别为109. 1±1. 0Ma和107. 4±0. 7Ma,岩浆混合作用发生在早白垩世晚期,处于班公湖-怒江特提斯洋由弧-陆碰撞向陆陆碰撞的转换阶段即软碰撞阶段。研究表明,在班公湖-怒江特提斯洋向北向羌塘地块之下俯冲的背景下,洋壳脱水,引起上覆地幔楔发生部分熔融,形成镁铁质岩浆,镁铁质岩浆向上运移,并底侵于壳-幔边界,引发下地壳物质发生部分熔融,形成长英质岩浆,当镁铁质岩浆从底部注入长英质岩浆房时,镁铁质岩浆快速冷凝,形成部分色率高、粒度细,具冷凝边的包体,与寄主岩呈截然型接触,随着端元岩浆之间的温差逐渐降低,包体色率降低,粒度变大,与寄主岩呈渐变过渡。 相似文献
39.
Giovanni Guglielmo 《Geological Journal》1993,28(2):149-157
Contacts within nested plutons are crucial for constraining the relative timing of pluton emplacement and the internal geometry of composite plutons. Exposures in orogenic belts are commonly discontinuous, however, disguising these contacts. In this paper, the Merrimac plutons in the northern Sierra Nevada of California are used as an example of how composition and foliation patterns can allow the definition of unexposed contacts and identify nested plutons. Image analysis techniques were used to determine modal compositions of a total of 52 samples from the Merrimac plutons. The integrated analysis of compositional data and foliations patterns reveals a critical contact within the plutons, and suggests that the Merrimac plutons indicate way-up towards the north-east at the time of emplacement 142 ± 3 Ma ago. This paper provides guidelines for recognizing nested plutons in poorly exposed areas and shows that consistent structural and compositional assymmetries within nested plutons can be used as regional top-direction indicators. 相似文献
40.