包裹体测温在海底火山喷发矿物中的试验与讨论     

陈建林 《海洋学研究》1993,11(3):17-21

国内对海底火山喷发矿物中的包裹体测温实例并不多见。本文首次对火山活动较为活跃的冲绳海槽底质沉积物中的紫苏辉石进行了淬火法包裹体测温。根据包裹体特征及类型确定该矿物属海底火山喷发成因,均匀化温度南北存在明显差异,并认为它们是属于不同时代的海底基性岩浆喷发产物。  相似文献   

Namibia volcanic margin     

Gladczenko  Tadeusz P.  Skogseid  Jakob  Eldhom  Olav 《Marine Geophysical Researches》1998,20(4):313-341

Two end members of passive margin types are present on the Namibia margin: volcanic and non-volcanic. The central and southern parts of the Namibia margin feature characteristic volcanic margin elements such as thickened initial oceanic crust, seaward dipping reflectors, and high-velocity/density lower crust that extends beneath the rift zone that was formed during initial seafloor spreading in Early Cretaceous. The margin north of the Walvis FZ is non-volcanic in character and probably formed as a result of a ridge jump that occurred after cessation of the initial magmatic activity. The Walvis Ridge forms the boundary between the two margin types and resulted from the persistent magmatism associated with the Tristan plume. MCS data in conjunction with gravity modeling reveal a Paleozoic rift zone beneath the Namibia margin south of the Walvis FZ. The Paleozoic rift zone partly overlaps the Jurassic/Early Cretaceous rift zone which produced the breakup between Africa and South America. We calculate an average stretching value of =1.4 for the Paleozoic rift, based on subsidence modeling. The rift is partly bounded by low-angle faults, related to the orogenic collapse of the Pan-African fold belt, which provided a major Paleozoic sediment source. The offshore continuity of onshore ophiolitic complexes is suggested by the coast parallel high-amplitude magnetic anomaly G, and low-angle detachment faults along the southern part of the margin. The average stretching value for the Jurassic/Early Cretaceous rift is =1.7, which implies a syn-rift displacement on this margin of 70 km. The minimum igneous volume of the South Atlantic LIP was found to be in excess of 3.62×106 km³.  相似文献   

Thermal rejuvenation of the Yermak Plateau     

Nilgün Okay  Kathleen Crane 《Marine Geophysical Researches》1993,15(4):243-263

The Yermak Plateau, bordering the Arctic Ocean and the Norwegian-Greenland Sea, and adjacent to the continental Svalbard Archipelago, is characterized by high heat flow relative to its surrounding region. South of and parallel to the trend of the plateau lies the formerly active-Spitsbergen Shear Zone (De Geer Zone), which is now occupied by the slowly spreading Knipovich and Molloy Ridges. An analysis of these heat flow data suggest that asymmetric spreading within the Norwegian-Greenland Sea propagated northwards along one of the faults associated with the Spitsbergen Shear Zone. The broad zone of faults, once associated with this paleo-shear zone, extends throughout Svalbard as well as on and to the west of the Knipovich Ridge. This network of faults may comprise a complex system of detachment surfaces along which magma may rise from a deep-seated source and across which simple shear extension may develop. Dike injection into the Yermak Plateau, north of the propagating ridge may have been initiated by the thermal response of the highly fractured lithosphere to this propagating asthenospheric front. We suggest that one of these faults, acting as a secondary detachment to the main fault underlying the Knipovich Ridge, may be dissecting the Yermak Plateau. Based on an analysis of the thermal data, simple shear extension may have been taking place along a broad zone of intrusion. This region has undergone and is probably still undergoing thermal rejuvenation. Multiple zones of intrusion may be a common phenomena along newly rifted continental margins especially when they have been substantially faulted prior to rifting.  相似文献   

论火山喷发危险的监测研究中的CT技术的应用前景     

郭履灿  曲韵笙 《CT理论与应用研究》1997,6(3):43-45

在“九五”科技重点项目“中国若干近代火山潜在喷发危险及其监测研究”项目起动之际,作者对于火山喷发危险的监测研究中的ＣＴ技术者进行调研,本文总结了这方面的研究３方法和思路,并介绍了中国在这方面的部分成果,展望今后的研究动向。  相似文献   

CMIP6火山强迫的气候响应模拟比较计划（VolMIP）概况与评述     

满文敏  左萌 《气候变化研究进展》2019,15(5):526-532

为揭示造成火山强迫气候响应模拟不确定性的原因,第六次国际耦合模式比较计划（CMIP6）设立了火山强迫的气候响应模拟比较计划（VolMIP)。该计划由基于历史火山爆发的理想火山扰动试验组成,包括三组主要的试验：第一组关注短期（季节至年际）大气动力响应;第二组关注海气耦合系统的长期（年际至年代际）响应;第三组关注气候系统对火山群的响应。VolMIP旨在通过给定相同的辐射强迫并进行多成员集合模拟,揭示模式对外强迫响应的不确定性,通过设定不同的背景气候态,阐明内部变率和外强迫对气候响应的相对贡献。  相似文献   

Extreme source heterogeneity and complex contamination patterns along the Cameroon Volcanic Line: New geochemical data from the Bamoun plateau     

《Comptes Rendus Geoscience》2018,350(3):100-109

We investigated mafic and felsic volcanic rocks from the Bamoun plateau, a magmatic province located north of Mount Cameroon, in the continental part of the Cameroon Volcanic Line (CVL). Basalts and dacites were probably emplaced more than 40 Ma ago, while basanites represent very young volcanic eruptions. Among the basalts, some of them have suffered crustal contamination during their uprise through the continental crust, and their primary trace element and isotopic compositions have been slightly modified. The formation of the dacites was also accompanied by some crustal contamination. Non-contaminated rocks show that the oldest magmas are transitional basalts formed by relatively high degrees of partial melting of a moderately enriched mantle source, probably containing pyroxenites. Recent basanites were produced by very low partial melting degrees of an enriched mantle source with HIMU composition, but different from the source of the nearby Mount Cameroon lavas. The mantle beneath the CVL is thus very heterogeneous, and the tendency towards more alkaline mafic-ultramafic compositions in the youngest volcanic manifestations along the CVL seems to be a general feature of all CVL.  相似文献   

Evolution of Mafic Alkaline Melts Crystallized in the Uppermost Lithospheric Mantle: a Melt Inclusion Study of Olivine-Clinopyroxenite Xenoliths, Northern Hungary   总被引：1，自引：0，他引：1  

Zajacz  Zoltan; Kovacs  Istvan; Szabo  Csaba; Halter  Werner; Pettke  Thomas 《Journal of Petrology》2007,48(5):853-883

Olivine-clinopyroxenite xenoliths exhumed in alkali basalts(sensu lato) in the Nógrád–GömörVolcanic Field (NGVF), northern Hungary, contain abundant silicatemelt inclusions. Geothermobarometric calculations indicate thatthese xenoliths crystallized as cumulates in the upper mantlenear the Moho. These cumulate xenoliths are considered to representa period of Moho underplating by mafic alkaline magmas priorto the onset of Late Tertiary alkaline volcanism in the Carpathian–Pannonianregion. The major and trace element compositions of silicatemelt inclusions in olivine display an evolutionary trend characterizedby a strong decrease in CaO/Al₂O₃. The parental melt of thecumulates was a basanite formed by low-degree ( 2%) partialmelting of a garnet peridotite source. The compositional trendof the silicate melt inclusions, textural features, and modellingwith pMELTS show that the parental melt evolved by major clinopyroxeneand minor olivine crystallization followed by the appearanceof amphibole simultaneously with significant resorption of theearlier clinopyroxene and olivine. The resulting residual meltwas highly enriched in Al₂O₃, alkalis and most incompatibletrace elements. This type of melt is likely to infiltrate andreact with surrounding mantle peridotite as a metasomatic agent.It might also form high-pressure pegmatite-like bodies in themantle that might be the source of the amphibole and sanidinemegacrysts also found in the alkali basalts of the NGVF. Preferentialremelting of the later-formed (i.e. lower temperature) mineralassemblage (amphibole, sanidine, residual glass) might havesignificantly contaminated the host alkaline mafic lavas, increasingtheir Al₂O₃ and total alkali contents and, therefore, reducingtheir MgO, FeO and CaO content. KEY WORDS: silicate melt inclusions; geochemistry; petrogenesis; Nógrád–Gömör Volcanic Field; Pannonian Basin  相似文献   

The genesis of pyroclasts and the mechanism of submarine eruption of Naozhou Island in Guangdong,South ChinaSCIEI北大核心CSCD     

王丽竹  赵勇伟  李霓  陈正全 《岩石学报》2023,(3):907-920

水下火山喷发作用机制不同于陆地环境喷发,随着水参与程度的变化,喷发机制趋向复杂。本文以雷琼火山群的湛江硇洲岛作为研究对象,聚焦浅海火山产物的判断依据和水下火山喷发机制。硇洲岛是我国最大的第四纪火山岛,其上的那晏湾剖面保留了完整的火山喷发堆积序列。在那晏湾剖面的凝灰岩中,主要有三类火山成因的大粒径原生碎屑(2-5mm):塑变熔岩碎屑、碎玄玻璃及玄武玻璃,推断为不同程度水-岩浆相互作用的产物,根据水的参与程度大致排序为:碎玄玻璃>玄武玻璃>塑变熔岩碎屑。通过对硇洲岛水-火山作用机制研究,发现水-岩浆混合质量比(Mwater/Mmelt)是控制爆炸强度和火山碎屑粒度的关键因素。火山喷发序列分析表明,硇洲岛的喷发过程总体可分为三期,早期是冰岛苏特塞式喷发的浅水环境蒸汽爆炸与“火喷泉”喷发;中期过渡转为“火喷泉”喷发,伴随陆上的射汽岩浆喷发;最终以岩浆溢流式喷发结束。  相似文献   

Nature and evolution of the lower crust under central Spain: Inferences from granulite xenoliths (Calatrava Volcanic Field-Spanish central system)     

《地学前缘(英文版)》2023,14(3):101525

So far, the nature and evolution of the lower crust under central Spain have been constrained mainly on the basis of a heterogeneous suite of granulite xenoliths from the Spanish Central System (SCS). In recent years, ultramafic volcanics from the Calatrava Volcanic Field (CVF) have also provided deep-seated crustal xenoliths which have not been studied in detail. Our data, combining mineral, whole-rock and isotopic geochemistry with U–Pb–Hf isotope ratios in zircons from the CVF and SCS xenoliths, highlight the felsic composition of the lower crust under central Iberia. A number of the Calatrava xenoliths represents Variscan igneous protoliths, which are a minor population in the SCS, and were likely formed by crystallisation of intermediate and felsic melts in the lower crust during the Variscan orogeny (leucodiorite protolith age of 314 ± 3 Ma and leucogranite protolith age of 308 ± 2.5 Ma). U–Pb data of metamorphic zircons show that granulite-facies metamorphism mainly occurred from 299 to 285 Ma in both areas. These ages are slightly younger than those of granitic intrusions that could be genetically related to the granulitic residue, which points to a main role of U–Pb isotope resetting in lower crustal zircons during HT or UHT conditions. The zircon U–Pb–Hf isotopic ratios support the idea that the lower crust in central Iberia consists mainly of Ordovician–Neoproterozoic metaigneous and metasedimentary rocks associated with the Cadomian continental arc of northern Gondwana. These rocks provide evidence of mixing between juvenile magmas and an enriched crustal component, ultimately extracted from an Eburnean crust. Other more evolved components present in detrital zircons are likely related to recycling of Archean crust derived from North Africa cratonic terranes.  相似文献   

Geochemical composition of dykes along the Cameroon Line (CL): Petrogenesis and similarities with the Central Atlantic Magmatic Province     

Asobo Nkengmatia Elvis Asaah  Tetsuya Yokoyama  Hikaru Iwamori  Festus Tongwa Aka  Jules Tamen  Takeshi Kuritani  Tomohiro Usui  Takeshi Hasegawa  Eric Martial Fozing 《Chemie der Erde / Geochemistry》2022,82(2):125865

We report whole-rock geochemistry and Sr–Nd–Pb isotopic compositions of mafic dykes intruded in the Precambrian granito-gneissic basement complex, exposed at Nyos, Batibo, Dschang and Foumban on the Cameroon Line. The dykes are alkaline (Batibo), transitional (Foumban), and subalkaline (Nyos, Batibo and Dschang) with SiO₂ of 45–54 wt% and MgO of 2–9 wt%, similar to dykes reported in other areas of the Cameroon Line (CL) and the Central Atlantic Magmatic Province (CAMP). The abundances of rare earth elements (REE) and the Primitive Mantle normalised patterns for the Nyos, Batibo and Dschang dykes are similar to those of MORB, indicating that the dykes formed at shallower depths by a higher degree of partial melting relative to the Foumban dykes and the alkaline lavas of the CL. The transitional basaltic dykes with steeper REE patterns have their sources at deeper levels in the lithospheric mantle, possibly the garnet-spinel transition zone and were generated by a lower degree partial melting of the lithospheric and plume components. The Nyos and Batibo subalkaline dykes show similar isotopic compositions with a spectrum extending from depleted (DMM-like) to enriched (EM1-like) mantle, indicating the similarity in their source components. The Dschang dykes show distinct isotopic characteristics with relatively unradiogenic Nd-Pb isotope compositions compared to the Batibo and Nyos dykes. The Foumban transitional dykes with characteristic wide ranges in Sr-Nd-Pb isotopic compositions reveal varying contributions from enriched mantle components (EM1 and EM2) in addition to its plume signature similar to those of CL lavas. The Nyos and Batibo dykes alongside other dykes on the CL have low TiO₂ abundances (<2 wt%), negative PM-normalised Nb-anomalies, and moderately to strongly enriched REE patterns, and isotopic composition that overlaps with those of CAMP, suggesting a similar lithospheric origin.  相似文献