Magmatism of Kunashir island (Kuril island arc) from aerogeophysical evidence     

T. V. Volodkova 《Russian Journal of Pacific Geology》2007,1(6):515-536

The existence of a lateral volcanic zoning in the Kuril island arc (KIA) was confirmed by the analysis of the 1: 50 000 scale maps of the abundances of natural radioactive elements (NRE). Trends of the NRE ratios were calculated for the magmatic complexes of the KIA, and their relation to fluidization processes was proved. Based on aerogeophysical data (maps of NRE ratios and the magnetic field), the main cyclic sequence of the formation of active volcanoes and magmatism was distinguished. Multicyclic volcanoes related to mantle sources usually show the predominance of calc-alkaline volcanic complexes, the occurrence of magnetite precipitation processes, and weak development of metasomatic aureoles. Other volcanoes connected to crustal sources are characterized by the development of calcic complexes and extensive hydrothermal-metasomatic systems.  相似文献   

长白山天池火山双岩浆房岩浆作用与互动式喷发   总被引：6，自引：0，他引：6  

樊祺诚  隋建立  李霓  孙谦  徐义刚 《矿物岩石地球化学通报》2007,26(4):315-318

广义的长白山火山在我国境内包括天池火山、望天鹅火山、图们江火山和龙岗火山,是我国最大的第四纪火山岩分布区。长白山各个火山区的火山活动具有此起彼伏的穿时性特征,天池火山之下地壳和地幔两个岩浆房具有上下呼应、互动式喷发之特点。一方面来自地幔的钾质粗面玄武岩浆直接喷出地表,在天池火山锥体内外形成诸多小火山渣锥;另一方面钾质粗面玄武岩浆持续补给地壳岩浆房,发生岩浆分离结晶作用和混合作用,形成双峰式火山岩特征并触发千年大喷发。西太平洋板块俯冲-东北亚大陆弧后引张是长白山天池火山喷发的动力学机制。  相似文献   

Neo-Proterozoic rift-related syenites (Northern Damara Belt, Namibia): Geochemical and Nd–Sr–Pb–O isotope constraints for mantle sources and petrogenesis     

S. Jung  E. Hoffer  S. Hoernes 《Lithos》2007,96(3-4):415-435

Major element, trace element and Nd–Sr–Pb–O isotope data for a suite of Neo-Proterozic, pre-orogenic, rift-related syenites from the Northern Damara orogen (Namibia) constrain their sources and petrogenesis. New U–Pb ages obtained on euhdreal titanite of inferred magmatic origin constrain the age of intrusion of the Lofdal and Oas syenites to ca. 750 Ma compatible with previous high-precision zircon analyses from the Oas complex. Major rock types from Lofdal and Oas are mildly sodic nepheline-normative and quartz-normative syenites and were primarily generated by fractional crystallization from a mantle-derived alkaline magma. Primitive samples from Lofdal and Oas show depletion of Rb, K and Th relative to Ba and Nb together with variable negative anomalies of P and Ti on a primitive mantle-normalized diagram. Evolved samples from Oas develop significant negative Ba, Sr, P and Ti anomalies and positive U and Th anomalies mainly as a function of crystal fractionation processes. The lack of a pronounced negative Nb anomaly in samples from Lofdal suggests that involvement of a crustal component is negligible. For the nepheline-normative samples from Lofdal, the unradiogenic Sr and radiogenic Nd isotope composition and low δ¹⁸O values suggest derivation of these samples from a moderately depleted lithospheric upper mantle with crustal-like U/Pb ratios (⁸⁷Sr/⁸⁶Sr: 0.7031–0.7035, ε Nd: ca. + 1, δ¹⁸O: 7‰, ²⁰⁶Pb/²⁰⁴Pb: ca.18.00, ²⁰⁷Pb/²⁰⁴Pb: 15.58–15.60). Primitive samples of the Oas quartz-normative syenites have identical isotope characteristics (⁸⁷Sr/⁸⁶Sr: 0.7034, ε Nd: ca. + 1, δ¹⁸O: 6.5‰, ²⁰⁶Pb/²⁰⁴Pb: ca.18.00, ²⁰⁷Pb/²⁰⁴Pb: 15.59) whereas more differentiated samples have higher ⁸⁷Sr/⁸⁶Sr ratios (0.709–0.714), slightly higher δ¹⁸O values (7.0–7.1‰), less radiogenic ε Nd values (− 1.1 to − 1.4) and more radiogenic ²⁰⁶Pb/²⁰⁴Pb ratios up to 18.27. These features together with model calculations using Sr–Nd–Pb isotopes suggest modification of a primary syenite magma by combined AFC processes involving ancient continental crust. In this case, high Nb abundances of the parental syenite liquid prevent the development of significant negative Nb anomalies that may be expected due to interaction with continental crust.  相似文献   

太行山北段中生代岩基及其包体锆石U-Pb年代学和Hf同位素性质及其地质意义   总被引：2，自引：1，他引：2  

陈智超  陈斌田伟 《岩石学报》2007,23(2):295-306

太行山北段出露大规模中生代岩浆岩带,以中酸性岩为主,普遍含有基性微粒包体。锆石的SHRIMP U-Pb年代学研究表明,包体形成于126Ma左右,与寄主岩石大致同时形成。锆石的LA-MC-ICPMS Lu-Hf同位素原位测量研究表明,基性岩来自富集地幔的部分熔融,并遭受了一定程度的地壳混染;主要的中酸性岩基形成于壳幔岩浆混和过程,而岩基中微粒基性包体是经历分离结晶的基性岩浆注入酸性岩浆房中形成。  相似文献   

Early J_2 basalts in SE China:Incipience of large-scale late Mesozoic magmatism   总被引：9，自引：0，他引：9  

XIE Xin  XU Xisheng  ZOU Haibo  JIANG Shaoyong  ZHANG Ming  QIU Jiansheng 《中国科学D辑(英文版)》2006,49(8)

The voluminous late Mesozoic igneous rocks in SE China were formed by the multi-stage magmatism. Between 204 Ma (the Ar-39Ar age of limburgite sam- 40 pled at Daoxian in Hunan Province[1]) and 180 Ma, magmatism was dormant for a period of about 25 Ma. Then the magmatism started to become active in the study region during 180―170 Ma (early J2), and con-tinued until the end of the Cretaceous[2]. Therefore, the magmatism in 180―170 Ma is the incipience of large-scale late Mesozoic magmat…  相似文献   

Late Cenozoic volcanic activity in the Chugoku area, southwest Japan arc during back-arc basin opening and reinitiation of subduction   总被引：3，自引：0，他引：3  

Jun-Ichi Kimura  Tomoyuki Kunikiyo  Isaku Osaka  Takashi Nagao  Seiki Yamauchi  Susumu Kakubuchi  Shomei Okada  Norie Fujibayashi  Ryuhei Okada  Hisashi Murakami  Takashi Kusano  Koji Umeda  Shintaro Hayashi  Tsuneari Ishimaru  Atusi Ninomiya  Atsushi Tanase 《Island Arc》2003,12(1):22-45

Abstract Temporal–spatial variations in Late Cenozoic volcanic activity in the Chugoku area, southwest Japan, have been examined based on 108 newly obtained K–Ar ages. Lava samples were collected from eight Quaternary volcanic provinces (Daisen, Hiruzen, Yokota, Daikonjima, Sambe, Ooe–Takayama, Abu and Oki) and a Tertiary volcanic cluster (Kibi Province) to cover almost all geological units in the province. Including published age data, a total of 442 Cenozoic radiometric ages are now available. Across‐arc volcanic activity in an area approximately 500 km long and 150 km wide can be examined over 26 million years. The period corresponds to syn‐ and post‐back‐arc basin opening stages of the island arc. Volcanic activity began in the central part of the rear‐arc ca 26 Ma. This was followed by arc‐wide expansion at 20 Ma by eruption at two rear‐arc centers located at the eastern and western ends. Expansion to the fore‐arc occurred between 20 and 12 Ma. This Tertiary volcanic arc was maintained until 4 Ma with predominant alkali basalt centers. The foremost‐arc zone activity ceased at 4 Ma, followed by quiescence over the whole arc between 4 and 3 Ma. Volcanic activity resumed at 3 Ma, covering the entire rear‐arc area, and continued until the present to form a Quaternary volcanic arc. Adakitic dacite first occurred at 1.7 Ma in the middle of the arc, and spread out in the center part of the Quaternary volcanic arc. Alkali basalt activities ceased in the area where adakite volcanism occurred. Fore‐arc expansion of the volcanic arc could be related to the upwelling and expansion of the asthenosphere, which caused opening of the Japan Sea. Narrowing of the volcanic zone could have been caused by progressive Philippine Sea Plate subduction. Deeper penetration could have caused melting of the slab and resulted in adakites. Volcanic history in the Late Cenozoic was probably controlled by the history of evolution of the upper mantle structure, coinciding with back‐arc basin opening and subsequent reinitiation of subduction.  相似文献   

华南东部中生代岩浆作用的动力学背景及其与铀成矿关系   总被引：31，自引：1，他引：31  

陈培荣 《铀矿地质》2004,20(5):266-270

中国东南大陆在中生代岩浆作用十分强烈 ,形成了大批稀有和有色金属矿床。发生在早中生代 (T)的印支运动和晚中生代 (J K)的燕山运动是发动该区岩浆作用和成矿作用的动力条件。印支运动在区域挤压框架下导致华南大陆发生板内伸展作用 ,形成印支期花岗岩。燕山运动是相对于印支运动的后造山地质事件 ,以岩石圈发生强烈裂解为特征 ,诱发了大规模岩浆活动 ,并形成了丰富的矿产资源。受燕山期构造 岩浆热事件叠加的印支期花岗岩与铀成矿关系密切 ,可能是铀源体。因此 ,在华南的铀矿找矿工作应加强对印支期花岗岩分布格局和成矿因素的研究  相似文献   

东坪金矿床上水泉花岗岩单颗粒锆石U—Pb年龄及其地质意义   总被引：1，自引：1，他引：0  

莫测辉  王秀璋  梁华英  程景平 《矿物学报》1998,18(3):298-302

本文对与东坪金矿有密切空间关系的上水泉花岗岩进行了单颗粒锆石U－Pb同位素定年,结果为135．5±0．4Ma,与东坪金矿的成矿年龄有几千万年的时差,表明该岩体与东坪金矿无成因联系,两者分别是不同地质作用的产物。研究结果对目前流行的把金矿与花岗岩密切的空间关系等同于成因联系的传统认识提出异议。  相似文献   

地幔柱构造与地幔动力学--兼论其在中国大陆地质历史中的表现   总被引：5，自引：0，他引：5  

肖龙 《矿物岩石地球化学通报》2004,23(3):239-245

地幔柱构造是基于全地慢对流模式、主要依据热点火山活动提出的新的全球构造理论。它的主要表现形式和产物是地幔柱头上部地壳抬升、岩浆活动形成大火成岩省、大型放射状岩墙群，并导致大陆裂解、板块运动和大规模成矿，是生物灭绝、磁极倒转的诱因。中国大陆的地质演化历史中保存了多期地幔柱活动印记，它们主要是华南新元古代Rodinia地幔柱、古生代古特提斯和峨眉山地幔柱和中一新生代中国东部地慢柱构造事件。上述地幔柱活动产生了地壳抬升、强烈岩浆活动、大陆伸展与裂解、岩石圈剧烈减薄和大规模成矿等重要地质事件。  相似文献   

On the Origin of Crystal-poor Rhyolites: Extracted from Batholithic Crystal Mushes   总被引：22，自引：3，他引：22  

BACHMANN  OLIVIER; BERGANTZ  GEORGE W. 《Journal of Petrology》2004,45(8):1565-1582

The largest accumulations of rhyolitic melt in the upper crustoccur in voluminous silicic crystal mushes, which sometimeserupt as unzoned, crystal-rich ignimbrites, but are most frequentlypreserved as granodioritic batholiths. After approximately 40–50%crystallization, magmas of intermediate composition (andesite–dacite)typically contain high-SiO₂ interstitial melt, similar to crystal-poorrhyolites commonly erupted in mature arc and continental settings.This paper analyzes the feasibility of system-wide extractionof this melt from the mush, a mechanism that can rationalizea number of observations in both the plutonic and volcanic record,such as: (1) abrupt compositional gaps in ignimbrites; (2) thepresence of chemically highly evolved bodies at the roof ofsubvolcanic batholiths; (3) the observed range of ages (up to200–300 ka) recorded by zircons in silicic magmas; (4)extensive zones of low P-wave velocity in the shallow crustunder active silicic calderas. We argue that crystal–meltsegregation occurs by a combination of several processes (hinderedsettling, micro-settling, compaction) once convection is hamperedas the rheological locking point of the crystal–melt mixture(  相似文献