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1.
西太平洋海山区蕴藏着丰富的钴结壳、磷酸盐等矿产资源,对国家的战略发展具有重要的意义。从地理位置上看,西太平洋海山区紧临菲律宾海,与我国距离较近,是未来我国最经济、最具前景的国际海底资源勘探开发合同区。因而从资源角度来说,针对西太平洋海山的科学研究异常迫切。西太平洋海山群构成了西太平洋海底  相似文献   
2.
马里亚纳弧前的橄榄岩被认为是SSZ型蛇绿岩的现代等同物,记录了弧下地幔与俯冲流体的交代反应,其中的角闪石被认为是俯冲流体交代的产物.电子探针的数据表明角闪石主要包括透闪石和镁闪石两种,其中前者具有低的钠含量,后者则具有明显高的钠、铝含量,但Mg#较低.角闪石的组成反映了俯冲流体具有高硅、钙、铝、钠等元素的特征.形成成分...  相似文献   
3.
青藏高原拉萨地块西部赛利普地区新生代火山岩依据主量元素可划分为超钾质、钾质和钙碱性系列,主要的岩石类型为粗面安山岩、粗面岩,一个超钾质岩石的40Ar-39Ar年龄为17.58Ma,指示出火山活动为中新世.超钾质、钾质和钙碱性火山岩都显示出富集LREE及LILE(Th、U)、亏损HFSE(Nb、Ta、Ti)的特征.超钾质火山岩具有较高的K2O(6.31%~8.55%)、MgO(6.75%~8.96%)、Cr(270.7×10-6~460.4×10-6)、Ni(142.3×10-6~233.9×10-6)含量,较高的(87Sr/86Sr)i(0.71883~0.72732)和较低的εNd(-14.78~-15.37),指示可能起源于一个前期亏损并经后期俯冲作用改造的富钾的方辉橄榄岩富集地幔源区.钾质火山岩具有比超钾质火山岩低的K2O、MgO、Cr、Ni含量以及高的Ba、Sr含量,初始87Sr/86Sr为0.71553~0.71628,初始143Nd/144Nd为0.51197~0.51198,在空间上与超钾质火山岩共生,可能是前者母岩浆的演化产物.钙碱性火山岩具有较高的Sr(881.7×10-6~1309.2×10-6)、Sr/Y比值(50~108)和较低的Y(12.05×10-6~18.02×10-6),明显亏损重稀土Yb(0.93×10-6~1.30×10-6),类似于典型的埃达克质岩成分特征但相对高钾,并具有相对低的(87Sr/86Sr);(0.70928~0.71374)以及高的εNd(-7.90~-10.91),指示起源于富钾增厚下地壳物质的部分熔融.区域上拉萨地块超钾质岩、钾质岩与N-S向地堑系在空间上共存、时间上相吻合,由此本文认为拉萨地块中新世钾质.超钾质岩和南北向地堑系的形成可能与中新世早期北向俯冲的印度大陆岩石圈断离有关.  相似文献   
4.
本文报道了在青藏高原东南木里地区发现的二叠纪苦橄岩和与其共生玄武岩的主微量元素地球化学特征以及Os-Sr-Nd同位素组成。苦橄岩和与其共生玄武岩受地壳混染作用影响较小。根据苦橄岩的Ti/Y比值和初始的Os同位素组成,将木里苦橄岩分为两类:高Ti/Y型苦橄岩和低Ti/Y型苦橄岩,其中高Ti/Y型苦橄岩具有高的γ_(Os)= 5.3~ 10.7和ε_(Nd)= 5.9~ 6.4,与全球典型洋岛玄武岩的Os和Nd同位素组成接近,代表了地幔柱源区的同位素特征;而低Ti/Y型苦橄岩具有低的γ_(Os)=-4.1~ 1.2和ε_(Nd)= 3.2~ 5.0,可能表明受到了SCLM(大陆岩石圈地幔)源区物质的混染。与其共生的玄武岩具有低的γ_(Os)=-3.5~-1.6和ε_(Nd)=-0.6~ 0.7,表明其来自于不同于低Ti/Y型苦橄岩也有异于高Ti/Y型苦橄岩的地幔源区,但是也可能受到了SCLM物质的混染。基于Nd-Os同位素的地幔柱与SCLM的二端元混合模型显示:低Ti/Y型苦橄岩可能是SCLM物质组分与地幔柱起源的苦橄质原始岩浆混合形成的;与苦橄岩共生的玄武岩可能是由地幔柱来源的玄武质岩浆与SCLM小比例熔融的熔体混合形成的。  相似文献   
5.
西北太平洋多金属结核铂族元素地球化学特征   总被引:1,自引:0,他引:1  
Polymetallic nodules and cobalt (Co)-rich crusts are enriched in platinum-group elements (PGEs),especially platinum (Pt) and may be important sinks of PGEs.At present,little information is available on PGEs in polymetallic nodules,and their geochemical characteristics and the causes of PGEs enrichment are unclear.Here PGEs of polymetallic nodules from abyssal basin in the Marcus-Wake Seamount area of the Northwest Pacific Ocean are reported and compared with the published PGEs data of polymetallic nodules and Co-rich crusts in the Pacific.The total PGEs (ΣPGE) content of polymetallic nodules in study area is 258×10~(–9) in average,markedly higher than that of Clarion-Clipperton Zone (CCZ) nodules (ΣPGE=127×10~(–9)) and lower than that of Co-rich crusts in the Marcus-Wake Seamount (ΣPGE=653×10~(–9)),similar to that of Co-rich crusts in the South China Sea(ΣPGE=252×10~(–9)).The CI chondrite-normalized PGEs patterns in different regions of polymetallic nodules and cobalt-rich crusts are highly consistent,with all being characterized by positive Pt and negative Pd anomalies These results,together with those of previous studies,indicate that PGEs in polymetallic nodules and Co-rich crusts are mainly derived directly from seawater.Pt contents of polymetallic nodules from the study area are negatively correlated with water depth,and Pt/ΣPGE ratios in nodules there are also lower than those of the Corich crusts in the adjacent area,indicating that sedimentary water depth and oxygen fugacity of ambient seawater are the possible important controlling factors for Pt accumulation in crusts and nodules.  相似文献   
6.
西南印度洋中脊(SWIR)增生的洋壳面积仅占印度洋的15%左右,但其具有比东南印度洋中脊和西北印度洋中脊更悠久而复杂的演化历史.基于已有的地质、地球物理和地球化学等资料,系统总结了SWIR的地质构造特征,并讨论了SWIR的演化过程、洋脊地幔的不均一性、洋脊周边海底高原成因等核心问题.SWIR地形中段高、东西两段低,空间重力异常基本与地形变化一致.按转换断层一级边界可将SWIR划分为20个一级段.SWIR的磁异常条带呈现两端渐进式分布和中段带状分布特征,对应洋脊的三期演化历史.SWIR的地幔源区极不均一,尤其是中新元古代造山带根部集中拆离的中段.源区地幔的不均一性与大陆裂解和洋脊演化过程密切相关.SWIR的东端与西北印度洋中脊和东南印度洋中脊的邻近洋脊段具有地球化学亲缘性,西端与大西洋中脊和南美洲—南极洲洋中脊的邻近洋脊段具有地球化学亲缘性,这与SWIR的渐近式扩张有关.SWIR周边海底高原普遍具有较大的地壳厚度,其成因除了陆壳基底之外,可能与热点火山作用、热点-洋脊相互作用或热点-三联点相互作用有关,目前尚未形成统一的认识.SWIR的形成演化及其作用域内的熔融异常(如海底高原)是冈瓦纳大陆裂解、残留岩石圈地幔、软流圈地幔和深部地幔热柱物质共同作用的结果.了解SWIR的演化过程对揭示冈瓦纳大陆的裂解过程和印度洋的演化具有重要意义.  相似文献   
7.
冷泉碳酸盐岩记录了甲烷渗漏活动和流体组分随时间的变化过程,对示踪冷泉系统沉积环境变化具有非常重要的意义.对南海北部获取的冷泉碳酸盐岩进行了碳、氧同位素剖面研究,并对南海北部冷泉碳酸盐岩的碳、氧同位素变化范围进行了统计分析.研究结果及已发表的δ13C和δ18O剖面数据表明,南海北部冷泉碳酸盐岩剖面的δ13C和δ18O之间普遍存在相关性,相关系数R2最高可达0.933 1.经统计,南海北部冷泉碳酸盐岩样品δ13C和δ18O均具有较大的变化范围,其最大变化分别为34.50×10-3和5.89%(Vienna Pee Dee Belemnite,V-PDB).冷泉碳酸盐岩δ13C和δ18O的相关性特征可能指示了初始流体的变化、后期矿物形成/重结晶作用、渗漏系统较为复杂或者成岩作用等环境变化信息.对不同碳酸盐岩样品来说,δ13C的变化主要由海水的参与程度决定,而δ18O的变化可能与温度和Mg元素参与方解石沉淀的程度有关.   相似文献   
8.
Hydrothermal materials in deep-sea sediments provide a robust tracer to the localized hydrothermal activity at mid-ocean ridges. Major, trace and rare earth element(REE) data for surface sediments collected from the ultraslow spreading Southwest Indian Ridge are presented to examine the existence of hydrothermal component.Biogenic carbonate oozes dominate all the sediment samples, with CaO content varying from 85.5% to 89.9% on a volatile-free basis. The leaching residue of bulk sediments by ~5% HCl is compositionally comparable to the Upper Continental Crust(UCC) in SiO_2, Al_2O_3, CaO, MgO, alkali elements(Rb, Cs) and high field strength elements(Nb, Ta, Zr, Hf, Ti). These detritus-hosted elements are inferred to be prominently derived from the Australian continent by means of eolian dust, while the contribution of local volcaniclastics is insignificant. In addition, the residual fraction shows a clear enrichment in Fe, Mn, and Ba compared with the UCC. Combining the positive Eu anomaly of residual fraction which is opposed to the UCC but the characteristic of hydrothermal fluids and associated precipitates occurred at mid-ocean ridges, the incorporation of localized hydrothermal component can be constrained. REE mixing calculations indicate that more than half REE within the residual fraction(~55%–60%) are derived from a hydrothermal component, which is inferred to be resulted from a diffuse fluid mineralization. The low-temperature diffuse flow may be widely distributed along the slow-ultraslow spreading ridges where crustal faults and fissures abound, and probably have a great mineralization potential.  相似文献   
9.
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.  相似文献   
10.
马里亚纳俯冲带弧内坡由于俯冲的太平洋板片的侵蚀而出露了相当于弧下地幔成分的橄榄岩,这些橄榄岩是研究岛弧岩浆作用及弧下地幔流体交代作用难得的样品。报道了马里亚纳南部关岛以南的弧内坡橄榄岩的矿物组成、主量元素以及微量元素地球化学特征。这些岩石具有非常难熔的矿物组成:橄榄石具有很高的Mg,斜方辉石中的Al2O3含量极低,尖晶石具有很高的Cr。滑石、蛇纹石和角闪石(透闪石为主,有少量镁角闪石和浅闪石)则指示了流体在中低温度下对橄榄岩的交代作用,并表明流体可能含有较高的SiO2、Al2O3和Na2O。全岩的主量元素中,CaO和Al2O3的质量百分比含量很低,而MgO的含量较高(干体系下多在43%左右),显示岩石经历了高度熔融。微量元素中,U和Sr的含量较高,相对富集,可能是来源较浅的板片流体化学特点的反映。  相似文献   
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