汉诺坝长英质麻粒岩包体同位素年代学及其地球动力学意义   总被引：10，自引：0，他引：10  

刘勇胜  高山  周炼  张利  金淑燕 《地球化学》2001,30(1):51-56

汉诺坝地区周坝长英质麻粒岩包体的岩石学、地球化学特征指示它们部分为变沉积岩。从周坝麻粒岩相变沉积岩包体的 Sm- Nd同位素分析结果获得了 (424± 10) Ma的全岩-单矿物 Sm- Nd同位素等时线年龄。全岩 Sm- Nd同位素组成指示这些包体可能与地表出露的太古宙麻粒岩有亲缘关系，但二者的 Pb- Pb与 U- Pb锆石年龄又反映二者成因不同。周坝长英质麻粒岩包体可能为残留于大陆下地壳的古老物质。 424 Ma的 Sm- Nd年龄可能反映了与加里东运动时期蒙古板块向华北地台俯冲而发生的变质与再就位抬升作用。  相似文献   

颗粒接触概率在划分矿物共生组合中的应用—以冀东太平寨紫苏花岗岩为例     

赵国春  贺同兴 《岩石矿物学杂志》1992,11(2):184-188

颗粒接触概率研究的基本方法是在一个岩石薄片切面上，沿着某一条线统计一个 晶体或矿物种与另一个晶体或矿物种的接触顺序，然后把每一类型的接触数目用“接触概率矩 阵”表示，并与“随机接触概率矩阵”加以比较，从而验证一个矿物的位置是否或在多大程度上 依赖于另一个矿物的位置。一般说来，同种矿物或同世代矿物有相互接触的趋势，因而颗粒接 触概率的研究能够用来划分矿物共生组合。冀东太平寨地区紫苏花岗岩的颗粒接触概率研究结 果表明，其主要矿物相是由两个不同世代矿物所组成。该研究结果与镜下岩相研究结论一致。  相似文献   

颗粒接触概率在划分矿物共生组合中的应用——以冀东太平寨紫苏花岗岩为例     

赵国春  贺同兴 《岩石矿物学杂志》1992,(2)

颗粒接触概率研究的基本方法是在一个岩石薄片切面上,沿着某一条线统计一个晶体或矿物种与另一个晶体或矿物种的接触顺序,然后把每一类型的接触数目用“接触概率矩阵”表示,并与“随机接触概率矩阵”加以比较,从而验证一个矿物的位置是否或在多大程度上依赖于另一个矿物的位置。一般说来,同种矿物或同世代矿物有相互接触的趋势,因而颗粒接触概率的研究能够用来划分矿物共生组合。冀东太平寨地区紫苏花岗岩的颗粒接触概率研究结果表明,其主要矿物相是由两个不同世代矿物所组成。该研究结果与镜下岩相研究结论一致。  相似文献   

Relationship between shear zones and igneous activity: The Closepet Granite of Southern India     

M. Jayananda  B. Mahabaleswar 《Journal of Earth System Science》1991,100(1):31-36

The late Archaean Closepet granite of southern India is bounded by N-S trending shear zone. At the southern end of the granite both charnockite and granite veins are spatially associated with ductile shears. These shears continue further north and are confined to the contact zones in the central part of the granite outcrop. The main component of the shear zone are highly deformed granite sheets, augen gneisses and mylonites. Field observations and microstructural fabric of mylonites indicate a dextral sense of shear movement. Field evidence suggests that shear deformation was active throughout the evolution of the Closepet granite  相似文献   

Late Sveconorwegian (Grenville) high-pressure granulite facies metamorphism in southwest Sweden   总被引：3，自引：0，他引：3  

L. JOHANSSON  A. LINDH  C. MÖLLER 《Journal of Metamorphic Geology》1991,9(3):283-292

Mafic granulite, garnet amphibolite and charnockite occur in the southwest Swedish part of the Baltic Shield. This part is generally considered to be the continuation of the Grenville collisional belt in Canada. The area with granulite facies rocks, the Southwest Swedish Granulite Region (SGR), is considerably larger than previously thought. The SGR is bounded to the east and west by two major tectonic zones. The first quantitative age data and P–T determinations for the high-grade metamorphism in the SGR are presented.
Conventional geothermobarometry was applied to mafic granulites from five localities. The estimated P–T conditions for the peak of metamorphism range from 705°C and 8.1 kbar at Hallandsås in the south, to 770°C and 10.5 kbar at Ullared in the north (medium- to high- P granulite facies conditions). Sm–Nd geochronology on minerals from the mafic granulites at Hallandsås and Ullared give late Sveconorwegian (Grenville) ages of 907 ± 12 and 916 ± 11 Ma for the high-grade metamorphism, which is considerably younger than previously thought.
Our results stress the hitherto underestimated importance of the late Sveconorwegian high-grade metamorphism in the southwestern part of the Baltic Shield.  相似文献   

山东诸城榴辉岩相长英质岩石变质特征   总被引：1，自引：0，他引：1  

赖兴运  苏尚国  陈珍珍 《地质论评》1996,42(3)

通过变质矿物及岩石学的特征确定出山东诸城地区含有榴辉岩块体的片麻岩经历了榴辉岩相到绿帘角闪岩相、绿片岩相的退变质过程。证据有:(1)在榴辉岩块体的边缘片麻岩与榴辉岩呈1-2cm宽的条带状相间排列;(2)硅质片岩中出现Ky-Zo-Q的高压矿物组合;(3)钠长石的矿物晶体内出现硬玉质辉石的残留体;(4)出现高度富Si的多硅白云母(Si=3.55);(5)镁钠闪石及与其共生的暗硬玉(Jd=21)的出现。  相似文献   

Bimodal back-arc alkaline magmatism after ridge subduction: Pliocene felsic rocks from Central Patagonia (47°S)     

Felipe Espinoza  Diego Morata  Mireille Polv  Yves Lagabrielle  Ren C. Maury  Christle Guivel  Joseph Cotten  Herv Bellon  Manuel Surez 《Lithos》2008,101(3-4):191-217

Volumetrically minor microsyenites, alkali microgranite and related trachytic dykes intrude early Pliocene OIB-like alkali basaltic and basanitic flows of the Meseta del Lago Buenos Aires in Central Patagonia (47°S–71°30′W), and occur together with scarce trachytic lava flows. Whole-rock K–Ar ages between 3.98 and 3.08 Ma indicate that the emplacement of these felsic rocks occurred more or less synchronously with that of the post-plateau basaltic sequence that they intrude, during a bimodal mafic–felsic magmatic episode devoid of intermediate compositions. Chemically, these rocks have A₁-type granitoid affinities and are characterized by high silica and alkali contents (60–68 wt.% SiO₂; 8.7–10.8 wt.% Na₂O + K₂O), major and trace elements patterns evidencing evolution by low-pressure fractional crystallization, and Sr and Nd isotopic signatures similar to those of coeval basalts ((⁸⁷Sr/⁸⁶Sr)_o = 0.70488–0.70571; (¹⁴³Nd/¹⁴⁴Nd)_o = 0.512603–0.512645). Nevertheless, some of them have the most radiogenic Sr values ever reported for a magmatic rock in the Meseta and even in the whole Neogene Patagonian Plateau Lavas province ((⁸⁷Sr/⁸⁶Sr)_o = 0.70556–0.70571; (¹⁴³Nd/¹⁴⁴Nd)_o = 0.512603–0.512608). In addition, very high contents of strongly incompatible elements in the most evolved rocks, together with Sr isotopic ratios higher than those of coeval basalts, suggest the occurrence of open-system magmatic processes. Continuous fractional crystallization from a primitive basaltic source, similar to post-plateau coeval basalts, towards alkali granites combined with small rates of assimilation of host Jurassic tuffs (AFC) in a shallow magmatic reservoir, best explains the geochemical and petrographic features of the felsic rocks. Therefore, A₁-type magmatic rocks can be generated by open-system crystallization of deep asthenospheric melts in back-arc tectonic settings.

In Central Patagonia, these  3–4 Ma old alkaline intrusions occur aligned along a  N160–170 trending lineament, the Zeballos Fault Zone, stacking the morphotectonic front of one segment of the Patagonian Cordillera. Intrusion along this fault zone occurred during the onset of a new transtensional or extensional event in the area, related to major regional tectonics occurring in possible relation with the collision of one segment of the Chile Spreading Ridge with the trench.  相似文献   

Early Cretaceous Magma Mingling in Xiaocuo, Southeastern China Continental Margin: Implications for Subduction of Paleo-Pacific Plate     

ZHOU Liyun  WANG Yu  HEI Huixin  ZHOU Xiaohui 《《地质学报》英文版》2016,90(5):1713-1742

Magma mingling has been identified within the continental margin of southeastern China.This study focuses on the relationship between mafic and felsic igneous rocks in composite dikes and plutons in this area,and uses this relationship to examine the tectonic and geodynamic implications of the mingling of mafic and felsic magmas.Mafic magmatic enclaves(MMEs) show complex relationships with the hosting Xiaocuo granite in Fujian area,including lenticular to rounded porphyritic microgranular enclaves containing abundant felsic/mafic phenocrysts,elongate mafic enclaves,and back-veining of the felsic host granite into mafic enclaves.LA-ICP-MS zircon U-Pb analyses show crystallization of the granite and dioritic mafic magmatic enclave during ca.132 and 116 Ma.The host granite and MMEs both show zircon growth during repeated thermal events at-210 Ma and 160-180 Ma.Samples from the magma mingling zone generally contain felsic-derived zircons with well-developed growth zoning and aspect ratios of 2-3,and maficderived zircons with no obvious oscillatory zoning and with higher aspect ratios of 5-10.However,these two groups of zircons show no obvious trace element or age differences.The Hf-isotope compositions show that the host granite and MMEs have similar ε_(Hf)(t) values from negative to positive which suggest a mixed source from partial melting of the Meso-Neoproterozoic with involvement of enriched mantlederived magmas or juvenile components.The lithologies,mineral associations,and geochemical characteristics of the mafic and felsic rocks in this study area indicate that both were intruded together,suggesting Early Cretaceous mantle—crustal interactions along the southeastern China continental margin.The Early Cretaceous magma mingling is correlated to subduction of Paleo-Pacific plate.  相似文献   

赣闽长英质隐爆角砾岩和基底围岩水-岩作用的实验研究及其地质意义     

章邦桐  陈培荣  倪琦生 《华东地质学院学报》1998,(3)

对闽北５７０铀矿床,赣南６７２２铀矿床,赣东北银山多金属矿床的长英质隐爆角砾岩及其基底岩石,用ｐＨ＝１．９,含ΣＳ＝３．２×１０－４,Σｄ＝３．５×１０－４,ΣＦ＝３×１０－５的水溶液,在９０℃条件下进行水－岩作用实验,研究岩石中活动性Ｕ,Ｔｈ,Ｐｂ,Ｚｎ等元素的地球化学行为。实验结果证实：岩石中铀、锌、铅具有较强的活化迁移能力;交代蚀变作用对铀活化和成矿富集有特殊重要意义;长英质隐爆角砾岩不是所研究矿床矿物质的主要来源;基底围岩对成矿有重要贡献。  相似文献   

Melting experiments on hydrous low-K tholeiite: Implications for the genesis of tonalitic crust in the Izu–Bonin – Mariana arc     

KATSUJI  NAKAJIMA & MAKOTO  ARIMA 《Island Arc》1998,7(3):359-373

A series of water-deficient partial melting experiments on a low-K tholeiite were carried out under lower crustal P–T–H₂O conditions (900–1200 °C, 0.7–1.5 GPa, 2 and 5 wt% H₂O added) using a piston-cylinder apparatus. With increasing temperature at 1.0 GPa, supersolidus mineral assemblages vary from amphibolitic to pyroxenitic. Garnet crystallizes in the higher pressure runs (> 1.2 GPa). Melt compositions show low-K calc-alkalic trends, and are classified as metaluminous or peraluminous tonalite. These features are similar to the felsic rocks in the Izu–Bonin – Mariana (IBM) arc, for example Tanzawa plutonic rocks. The anatectic origin of Tanzawa tonalites is consistent with geochemical modeling, which demonstrates that the rare earth element (REE) characteristics of Tanzawa plutonic rocks (which represent the middle crust of the IBM arc) can be generated by partial melting of amphibolite in the lower crust (∼ 50% melting at 1050 °C and below 1.2 GPa). Estimated densities of pyroxenitic restites (∼ 3.9 g/cm³) after extraction of andesitic melts are higher than that of mantle peridotite beneath the island arc (3.3 g/cm³). The high density of the restite could cause delamination of the IBM arc lower crust. Rhyolitic magmas in the IBM arc (e.g. Niijima) could be formed by low degrees of partial melting of the amphibolitic crust at a temperature just above the solidus (10% melting at or below 900 °C).  相似文献