Dredge petrology of the boninite‐ and adakite‐bearing Hahajima Seamount of the Ogasawara (Bonin) forearc: An ophiolite or a serpentinite seamount?§     

Akira Ishiwatari  Yuki Yanagida  Yi‐Bing Li  Teruaki Ishii  Satoru Haraguchi  Kazuto Koizumi  Yuji Ichiyama  Masaru Umeka 《Island Arc》2006,15(1):102-118

Abstract During the Hakuho‐Maru KH03‐3 cruise and the Tansei‐Maru KT04‐28 cruise, more than 1000 rock samples were dredged from several localities over the Hahajima Seamount, a northwest–southeast elongated, rectangular massif, 60 km × 30 km in size, with a flat top approximately 1100 m deep. The rocks included almost every lithology commonly observed among the on‐land ophiolite outcrops. Volcanic rocks included mid‐oceanic ridge basalt (MORB)‐like tholeiitic basalt and dolerite, calc‐alkaline basalt and andesite, boninite, high‐Mg adakitic andesite, dacite, and minor rhyolite. Gabbroic rocks included troctolite, olivine gabbro, olivine gabbronorite (with inverted pigeonite), gabbro, gabbronorite, norite, and hornblende gabbro, and showed both MORB‐type and island arc‐type mineralogies. Ultramafic rocks were mainly depleted mantle harzburgite (spinel Cr? 50–80) and its serpentinized varieties, with some cumulate dunite, wehrlite and pyroxenites. This rock assemblage suggests a supra‐subduction zone origin for the Hahajima Seamount. Compilation of the available dredge data indicated that the ultramafic rocks occur in the two northeast–southwest‐oriented belts on the seamount, where serpentinite breccia and gabbro breccia have also developed, but the other areas are free from ultramafic rocks. Although many conical serpentinite seamounts 10 km in size are aligned along the Izu–Ogasawara (Bonin)–Mariana forearc, the Hahajima Seamount may be better interpreted as a fault‐bounded, uplifted massif composed of ophiolitic thrust sheets, resembling the Izki block of the Oman ophiolite in its shape and size. The ubiquitous roundness of the dredged rocks and their thin Mn coating (<2 mm) suggest that the Hahajima Seamount was uplifted above sealevel and wave‐eroded, like the present Macquarie Is., a rare example of ophiolite exposure in an oceanic setting. The Ogasawara Plateau on the Pacific Plate is adjacent to the east of the Hahajima Seamount, and collision and subduction of the plateau may have caused uplift of the forearc ophiolite body.  相似文献   

The angular velocity of Nubia relative to Somalia and the location of the Nubia–Somalia–Antarctica triple junction     

Benjamin C. Horner-Johnson  Richard G. Gordon  Sara M. Cowles  Donald F. Argus 《Geophysical Journal International》2005,162(1):221-238

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Kurosegawa Terrane as a Transform Fault Zone in Southwest Japan     

Kiyoshi Kato  Yukiyasu Saka 《Gondwana Research》2003,6(4):669-686

The Kurosegawa Terrane intervening in the Jurassic-Early Cretaceous accretionary complexes along the Pacific side of the SW Japanese Islands is a serpentinite mélange zone. It contains various kinds of exotic rocks, for example, granitoids, metamorphic rocks, Siluro-Devonian deposits and is intimately associated with Cretaceous forearc basin deposits. The terrane is regarded as a key to clarify the Mesozoic geotectonic history of the western circum-Pacific orogenic belts. The current model, in which the formation of the Kurosegawa Terrane is attributed to nappe-movement or sinistral strike-slip faulting, can explain neither the mode of occurrence of the Kurosegawa Terrane we observed in eastern Kii Peninsula nor the array of evidence obtained from the Ryoke Terrane southward to the Shimanto Terrane. We suggest a new hypothesis in which the Kurosegawa Terrane was a transform fault zone that originated because of oceanic ridge subduction along the southern margin of the coeval accretionary prism (Butsuzo T.L.) in the late Early Cretaceous. Our model is mainly based on new geological evidence from the Kurosegawa Terrane in eastern Kii Peninsula where the deepest erosion level is exposed due to neotectonic uplift.  相似文献   

The RAMESSES experiment—II. Evidence for accumulated melt beneath a slow spreading ridge from wide-angle refraction and multichannel reflection seismic profiles     

D. A. Navin  C. Peirce  & M. C. Sinha 《Geophysical Journal International》1998,135(3):746-772

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m个相依回归方程系统回归参数的预检验岭估计     

归庆明 《测绘学院学报》1998,(2)

对于由 m个相依线性回归方程组成的线性回归系统 ,本文作者基于岭回归估计和预检验估计 ,提出了回归参数的一种新型估计 ,即预检验岭回归估计。并讨论了它的统计性质。  相似文献   

滇中大红山岩群变质火山岩类的原岩性质和构造属性   总被引：6，自引：0，他引：6  

徐启东 《地球化学》1998,27(5):422-431

大红山岩群中的变质火山岩类经在了区域性的海水蚀变和区域变质的改造,其岩石学特征和化学成分都发生了较大的变化,不活动组分的研究显示,其原岩主查拉斑玄武岩类,且具有形成于洋中脊环境的地球化学特征,可能属于Ｔ型地幔源区的洋中脊玄武岩（ＭＯＲＢ）大红山式Ｃｕ－Ｆｅ矿床具有富洋壳成矿元素特性,与所识别的变质火山岩类的原岩和形成的大地构造背景是一致的。  相似文献   

Oxygen isotope evidence for the origin of enriched mantle beneath the mid-Atlantic ridge   总被引：1，自引：0，他引：1  

Kari M. Cooper  John M. Eiler  Paul D. Asimow  Charles H. Langmuir 《Earth and Planetary Science Letters》2004,220(3-4):297-316

Geochemical variations in mid-ocean ridge basalts have been attributed to differing proportions of compositionally distinct mantle components in their sources, some of which may be recycled crust. Oxygen isotopes are strongly fractionated by near-surface interactions of rocks with the hydrosphere, and thus provide a tracer of near-surface materials that have been recycled into the mantle. We present here oxygen isotope analyses of basaltic glasses from the mid-Atlantic ridge south of and across the Azores platform. Variations in δ¹⁸O in these samples are subtle (range of 0.47‰) and may partly reflect shallow fractional crystallization; we present a method to correct for these effects. Relatively high fractionation-corrected δ¹⁸O in these samples is associated with geochemical indices of enrichment, including high La/Sm, Ce/Pb, and ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd. Our results suggest two first-order conclusions about these enriched materials: (1) they are derived (directly or indirectly) from recycled upper oceanic crustal rocks and/or sediments; and (2) these materials are present in the north Atlantic MORB sources in abundances of less than 10% (average 2–5%). Modeling of variations of δ¹⁸O with other geochemical variables further indicates that the enriched component is not derived from incorporation of sediment or bulk altered oceanic crust, from metasomatism of the mantle by hydrous or carbonate-rich fluids, or from partial melting of subducted sediment. Instead, the data appear to require a model in which the enriched component is depleted mantle that has been metasomatized by small-degree partial melts of subducted, dehydrated, altered oceanic crust. The age of this partial melting is broadly constrained to 250 Ma. Reconstructed plate motions suggest that the enriched component in the north Atlantic mantle may have originated by subduction along the western margin of Pangea.  相似文献   

夏季西太平洋副高脊线的活动特征及其可能的机制   总被引：14，自引：1，他引：14  

温敏  何金海 《南京气象学院学报》2002,25(3):289-297

通过对多年平均的逐日资料的分析表明 ,夏季不同区域副热带高压脊轴的垂直结构和活动特征存在明显不同 ,这与空间非均匀加热的分布密切相关。西太平洋地区副高脊轴随高度向北倾斜 ,而 1 60°E～ 1 80°地区向南倾斜 ;北太平洋中、西部副高在北进期的脊线活动均存在显著的 1 0～ 2 0 d周期低频振荡 ,东亚季风区还具有明显的准 40 d振荡周期。分析表明 :副高的季节性南北移动主要受太阳辐射的影响 ,而空间非均匀加热起着调节副高移动速率以及改变副高强度的作用 ,特别是对副高的异常活动起重要作用  相似文献   

基本地貌形态数学定义的研究   总被引：17，自引：4，他引：17  

钟业勋  魏文展  李占元 《测绘科学》2002,27(3):16-18

根据拓扑学中覆盖和同胚的定义 ,论证等高线图形保持着覆盖它的三维曲面的拓扑性质 ,据此我们可以在平面上定义和描述三维曲面的空间特性。继而给出了如斜坡、山、山脊、凹地、谷地、鞍部等基本地貌形态的数学定义。这些数学定义使局限于定性描述的基本地貌概念获得了精密的数学形式和定量的刻划 ,并揭示了事物从量变到质变的变化规律和内在联系  相似文献   

A 3-D dynamic model for the anomalous topography and geoid over the south-east Indian Ridge     

Ban-Yuan Kuo  Shu-Huei Hung  Ling-Yun Chiao 《Geophysical Journal International》1995,121(1):1-20

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