东太平洋海盆地山玄武岩特征

东太平洋海山玄下央属于大洋岛屿拉斑玄武岩，主要由橄榄拉斑玄武岩，石英拉斑玄武岩和橄榄玄武岩组成，具有拉斑玄武岩系列和过渡玄武央系列，岩石具有基质为斑拉玄武结构或间隐结构的斑状结构和气孔构造，斑晶主要由拉长石和普通辉石组成，基质除拉长石和玻璃质外，还有少量普通辉石和磁铁矿等，岩石化学成分中Ａｌ２Ｏ３Ｎａ２Ｏ，Ｋ２Ｏ含量偏高，玄武岩中稀土元素分配型式基本相同，曲线较平坦，稀土分馏不明显，具Ｃｅ，Ｅｕ异     

麦哲伦海山区MA、MC海山玄武岩基岩的岩石学特征

麦哲伦海山区MA、MC海山玄武岩基岩的岩石学特征研究表明,岩性为蚀变玄武岩、橄榄玄武岩等;结构为基质具间隐、间往结构及拉斑玄武结构的斑状结构;矿物组成为斜长石、橄榄石、辉石及脱玻化玻璃等。按岩石化学成分分类属碱性玄武岩,而稀土分配模式属洋岛碱性玄武岩类型。     

冲绳海槽碱性玄武岩浆的起源及演化

利用电子探针对冲绳海槽133站位玄武岩的斑晶矿物、基质以及斑晶矿物中关晶石包体和岩浆包裹体作了化学主成分分析,结果表明,该站位玄武岩属橄榄玄武岩,岩石中斑晶矿物由培长石、普通辉石、贵橄榄石和磁铁矿组成,尚见有少量外来的脉石英碎块,基质成分由拉长石微晶和玻璃组成。培长石和贵橄榄石中含有玻璃质岩浆包裹体和铬镁尖晶石或铬镁铁尖晶石包体。尖晶石的化学成分证明它是地幔部分熔融成因的。岩浆包裹体代表了一种原生的碱性橄榄玄武岩浆,其化学成分相当于橄榄辉长岩。该站位的玄武岩浆起源于上地幔尖晶二辉橄榄岩的部分熔融,并沿着“碱性橄榄玄武岩浆-粗面玄武岩浆-玄武质粗面岩浆-粗面岩浆”方向演化,每一阶段的岩浆在上升过程中都不同程度地受到地壳物质的同化和混染作用。     

南马里亚纳海槽岩石学特征

南马里亚纳海槽岩性比较复杂：有玄武岩，根据准矿物组合，进一步划分为碱性玄武岩，橄榄拉斑玄武岩和石英拉斑玄武岩；火山碎屑岩，包括凝灰岩和角砾凝灰岩，以及方辉橄榄岩，大部分玄武岩样品是距今五百万年以后形成的，个别岩石样品的形成年龄为八百万年左右，不同类型的玄武岩是含Ｈ２Ｏ的地幔岩块在底辟上升过程中，避部熔融，分离的产物；火山碎屑岩是火山喷发的火山灰，火山被水化学分解的物质胶结而成；方辉橄榄岩是地幔岩浆     

冲绳海槽海底热液活动区玄武岩的矿物学和岩石化学特征及其地质意义

１９９２年５月－１９９２６月对绳海槽热液活动区进行调查采样，对拖网采到的新鲜的玄武岩样品做了斑晶矿物学及岩石化学研究。结果表明，冲绳海槽玄武岩的斑晶矿物主要由橄榄石、单斜辉石、斜方辉石和斜长石组成，副矿物有铬铁尖晶石和磁铁矿，因而将样品定为橄榄玄武岩。     

胡安·德·富卡洋中脊(Juan de Fuca Ridge)上拉斑玄武岩的研究

该岩样系太平洋东北部胡安·德·富卡洋中脊上底拖所取得的岩石样品,其表面具有黑色玻璃质,由表面向下逐渐过渡为晶质。 对该岩样的化学成分做了较全面的(化学、X光、红外光谱、电镜等)分析。其化学成分虽与大洋拉斑玄武岩的平均值相近似,但Ca、Mg略高于大洋拉斑玄武岩的平均值;而Si,K含量又稍低于大洋拉斑玄武岩。表明该岩石系地幔岩浆分异早期溢出而成的。其主要矿物成分是拉长石和普通辉石,其中拉长石占斑晶的70—80％左右。 镜下研究表明该岩石从顶面到底部可被划分成若干层次,并具有气孔的存在,表明该岩石系水下溢出而生成的。 电子探针分析发现Cu、Co、Ni三元素在冷却玻璃质部份的含量较结晶主体部份的含量为高,而Rb、Sr、Cs三元素在岩石冷却边部份与结晶主体中的含量上没有什么显著的差别。 根据扫描电镜和电子探针的微区元素分析研究,结晶表明铁镁硅酸盐先结晶,随后结晶的为基性斜长石。     

麦哲伦海山区MA、MC、MD、ME、MF海山结壳基岩的岩石学

麦哲伦海山区MA、MC、MD、ME、MF海山的结壳基岩类型主要有玄武岩、火山碎屑岩，其次为灰岩和磷块岩。玄武岩为蚀变玄武岩、橄榄玄武岩等，造岩矿物斜长石的成份多为拉长石和中长石，辉石多为普通辉石，橄榄石多已伊西石化。玄武岩的硅酸盐全分析表明，其P2O5含量普遍偏高，超出了玄武岩正常值范围；玄武岩的稀土分配模式与洋岛碱性玄武岩类型基本相似，但出现一定程度的Ce负异常，这是由于玄武岩中混有磷酸盐矿矿物的结果，经过成分校正后，化学成分分类上属碱性系列的碱性玄武岩。火山碎屑主要为玄武质火山碎屑岩，其中玄武质碎屑的矿成分及结构特征与玄武岩相似，玄武质火山碎屑岩的稀土分配模式与玄武岩的稀土分布模式基本相似，推测其与玄武岩为同一期火山喷发的产物。灰岩包括生物屑微晶灰岩、微晶生物屑灰岩等，多数灰岩具有不均匀的磷酸盐化现象，成为磷块岩。另一种类型的磷块岩，是由磷酸盐矿物交火山碎屑岩形成。磷块岩的稀土元素特征表现为稀土总量较高，Ce呈明显负异常。灰岩和火山碎屑岩的磷酸盐化作用对稀土元素的富集及Ce的亏损起了重要作用。     

冲绳海槽南部橄揽拉斑玄武岩研究

1995年夏季航次冲绳海槽地质、地球物理调查对海底岩石实施拖网取样，在与那国海底洼地西南边线采集到新鲜玄武岩样品。对岩石样品进行了薄片鉴定、岩石化学分析、稀土和微量元素分析以及银同位素分析等。结果表明，岩石为橄榄拉斑玄武岩，岩石微量元素和稀土元素分布具有地慢柱洋中脊玄武岩的特点；成岩熔浆来自上地慢，分异程度较低，混合作用较弱，结晶液线温度为1150－1200℃。     

东海陆架边缘北部玄武岩的矿物及化学特征

对东海陆架边缘北部一个站位的玄武岩进行了镜下观测、XRD定量分析和电子探针分析。结果表明东海陆架边缘北部玄武岩斑晶主要由拉长石、贵橄榄石和普通辉石组成，其中，单斜辉石的结晶温度为1108．49℃，岩浆起源深度在42．9km以深。与冲绳海槽和琉球岛弧玄武岩相比，在斜长石An值、辉石Ca-Mg-Fe比例与橄榄石Fo值上均有明显的不同，表明三地玄武岩在成因上有一定的差异。     

南马里亚纳海槽岩石学特征

南马里亚纳海槽岩性比较复杂：有玄武岩，根据标准矿物组合，进一步划分为碱性玄武岩，橄揽拉斑玄武岩和石英拉斑玄武岩；火山碎屑岩，包括凝灰岩和角砾凝灰岩；以及方辉橄榄岩．大部分玄武岩样品是距今五百万年以后形成的，个别岩石样品的形成年龄为八百万年左右．不同类型的玄武岩是含Ｈ２Ｏ的地幔岩块在底辟上升过程中，局部熔融、分离的产物；火山碎屑岩是火山喷发的火山灰、火山砾被水化学分解的物质胶结而成；方辉橄榄岩是地幔岩浆底辟上升直接侵入结晶的产物．     

冲绳海槽玄武岩玻璃主量、微量元素地球化学特征

The Okinawa Trough(OT) is a back-arc basin at an initial spreading stage that is under the influence of subduction of the Philippine Sea Plate. In this study, we analyzed the geochemical compositions of basaltic glass in the OT and discussed the effects of different magmatic sources, evolution, and subducted components in basalts. Our results showed that the middle and southern regions of the OT exhibit characteristics consistent with an iron-rich tholeiite series. Trace element proportions conform to the typical spider diagram pattern characteristic of back-arc basin basalts, rich in large ion lithophile elements(LILEs) including Rb, Ba, Pb, U, and Th, while depleted in high field-strength elements(HFSEs) including Nb, Ta, Zr, Hf, and Ti. The distribution of rare earth elements(REEs) is also consistent with enrichment by right-leaning light rare earth elements(LREEs).The addition of enriched mantle type I(EMI) materials as well as mantle heterogeneity may have led to variable degrees of enrichment in different regions. The magma source of the middle trough has undergone crystallization towards pyroxene, while development of plagioclase was restricted partly, and the crystallization of spinel and olivine ceased altogether. At the same time, crystallization of the southern OT magma source was dominated by olivine and including the formation of plagioclase, pyroxene, and magnetite(or titanomagnetite). Finally, the results of this study showed that 90% Th, 95% Ba in the southern basalt, 50%–70% Th and 70%–90% Ba in the middle basalt originated from subducted component. Different subducted component influence may be due to different subduction zone structural feature.     

Age,volume, compositional and spatial relations of small isolated oceanic central volcanoes

The volumes and ages of small isolated seamounts from both fracture zone and normal crust settings are related to the chemical composition of their lavas. Small volcanoes on or near ridge crests are composed of LIL-depleted ocean ridge tholeiite and are later capped successively by alkalic basalt and alkalic differentiated lavas as they drift away from the ridge. In addition, it appears that contemporaneous seamount volcanism is tholeiitic near the ridge crest and alkalic on the ridge flanks. No significant differences are found between the chemical compositions of lavas from small seamounts located on fracture zones and those on normal oceanic crust.     

Basalts from the Solomon and Bismarck Seas

Volcanic rocks collected from the Solomon Sea Basin are mostly ferrobasalt lavas similar to evolved MORB; an exception is a single sample of basaltic crystal tuff invaded by later basalt. The rocks contain labradorite, aluminous diopsidic augite, and titanomagnetite, with olivine and pigconite in the more vitrophyric samples, and segregation vesicles in some. Cobbles dredged from Gudaraba Canyon, south of the Solomon Sea Basin, include both MORB-like glassy lava and K-metasomatised basalt and andesite(?). Two small pieces of volcanic glass from the southern Bismarck Sea are more primitive MOR-type basalts.     

马里亚纳海槽热液区岩石矿物学和岩石化学特征研究

马里亚纳海槽中央轴裂谷中的小扩张脊部位 ,广布火山喷发的玄武岩体 ,海底热液硫化物就是从这些岩体的裂隙中喷溢堆积起来的。利用我国“大洋一号”船拖网所获岩样进行了矿物学和岩石化学特征研究 ,认定为高铝低钾的大洋底玄武岩或拉斑玄武岩系列和钙 -碱玄武岩。为进一步弄清马里亚纳海槽区热液活动岩石学条件和探讨海槽区热液物质来源提供科学证据     

西太平洋海山年龄及地球化学:地幔过程及岩石成因

Research on seamounts provides some of the best constraints for understanding intraplate volcanism, and samples from seamounts reveal crucial evidence about the geochemical makeup of the oceanic mantle. There are still many seamounts in the West Pacific Seamount Province(WPSP) that have not been studied, meaning their ages and geochemistry remain unknown. A better understanding of these seamount trails and their evolutionary history, investigated with age and geochemistry data, will enable better understanding of the geological processes operating underneath the Pacific Ocean Plate. Here, new ~(40)Ar/~(39) Ar ages and trace element and Sr-Nd-Pb isotopic data for seven basalt rocks from four seamounts in the WPSP are provided. Chemically, these rocks are all Oceanic Island Alkali basalt(OIA type); analysis of olivine phenocrysts shows that the magmas experienced strong olivine fractionation and changed from olivine + plagioclase to olivine + plagioclase + clinopyroxene cotectic during their evolution. Rare earth element(REE) patterns and a spider diagram of the samples in this study show OIB(Ocean Island Basalt) like behavior. The range of ~(87)Sr/~(86) Sr values is from 0.704 60 to 0.706 24, the range of ~(206)Pb/~(204) Pb values is from 18.241 to 18.599, and the range of ~(143)Nd/~(144) Nd values is from 0.512 646 to 0.512 826; together, these values indicate magma sources ranging from EMI to EMII. Finally, new ~(40)Ar/~(39) Ar age data show that these seamounts formed at ～97 and ～106 Ma, indicating that some may have undergone the same formation processes as seamounts in the eastern part of the Magellan Seamount Trail, but other seamounts likely have different origins.     

印度洋Carlsberg洋脊玄武岩岩石地球化学特征及其地质意义

本文对采自印度洋Carlsberg脊14个站位的新鲜玄武岩样品进行了常量和微量元素组成分析,旨在研究岩浆源区地幔的性质以及岩浆作用过程。研究结果表明:该区玄武岩为典型的源于亏损型地幔的大洋中脊玄武岩,不同样品经历了不同程度的结晶分异作用,演化过程主要受控于橄榄石的结晶分异作用,部分样品中有单斜辉石结晶分异作用的影响,斜长石的结晶分异作用不显著;玄武岩岩浆来源于亏损型尖晶石二辉橄榄岩地幔的熔融,主微量元素组成中尚未见到富集型组分混入的证据;源区地幔不同比例的熔融作用及其后岩浆演化过程的差异是造成不同样品间地球化学性质差异的主要原因,彼此独立的局部岩浆作用过程是岩浆作用差异的主控制因素。Carlsberg脊玄武岩整体与全球标准大洋中脊玄武岩(N-MORB)平均组分相近,不同脊段间岩浆源区地幔的组成、熔融程度(比例)和熔融深度等无明显差异,这种特征向南直到CIR的北段。     

Tasman Sea guyots

Tasman Sea guyots are former volcanic islands that have subsided an average of 166 fathoms since the Middle or Late Tertiary. These guyots have heights up to 2333 fathoms above the surrounding sea floor; their flat-topped platforms are at depths ranging from 50 to 500 fathoms below present sea level. Reef formations are found along the edges and on the tops of the guyots. Volcanic rocks dredged from these truncated undersea mountains are alkaline olivine basalts with large augite, olivine and plagioclase phenocrysts in a glassy matrix. Limestones dredged from the guyots are either hard, light brown, massive foraminiferal limestones or grey, porous limestones composed mainly of skeletal material. Using foraminiferal evidence we assign an age for the limestone accumulation of Late Pliocene or Early Pleistocene. Phosphorite is also present and is thought to be formed from the replacement of carbonate ions in calcareous material by phosphate ions. There is some evidence of direct precipitation of phosphatic material as coatings on many of the basalt samples.     

西南印度洋中脊玄武岩地球化学特征及其对岩浆过程的指示意义

对采自西南印度洋中脊(SWIR)50°E附近5个站位的玄武岩样品进行了岩石学和元素地球化学研究.样品主量元素、TAS分类图解和AFM图解显示,SWIR研究区样品类型主要为低钾拉斑玄武岩.相对原始地幔SWIR区玄武岩具有Ba、Nb、Sr负异常,K表现为正异常.稀土元素分配模式均为左倾型,具有轻微的Eu、Ce正异常;SWI...     

中太平洋海山玄武岩的岩石学特征与年代

玄武岩在中太平洋海山分布广泛, 且普遍存在风化蚀变现象.对测区内玄武岩样品的岩石学特征研究表明, 玄武岩具斑状结构, 基质以间粒结构为主.斑晶矿物为基性斜长石、单斜辉石和伊丁石化橄榄石.基质矿物为斜长石、辉石、橄榄石、铁矿物、磷灰石、玻璃及次生矿物等. 各海山玄武岩同属碱性玄武岩系列, 并为钾质类型玄武岩, 它们的形成基本上处于同一地质构造环境中.稀土元素分析结果为轻稀土富集型, 轻重稀土在岩石形成过程中发生了不同程度的分异作用.CM5海山玄武岩比其他海山年代相对较老（60 Ma）.