A Triassic large igneous province in the Pontides, northern Turkey: geochemical data for its tectonic setting     

. Can Gen 《Journal of Asian Earth Sciences》2004,22(5):503

A strongly deformed and metamorphosed Triassic oceanic seamount(s) and plateau succession extends as an east–west belt for 1100 km along the Pontides of northern Turkey. This succession, known widely as the Nilüfer unit, consists mainly of metabasic lava and tuff–marble–phyllite association including tectonic slices of ultramafic rock and gabbro. According to the conodont findings the unit formed during the Early to Mid-Triassic, and the isotopic age data indicate that it underwent high-pressure greenschist facies metamorphism during the latest Triassic period. The metavolcanic rocks form over 80% of the sequence. The Nilüfer unit covers an area of 120,000 km², with the volume of mafic lava estimated as 2×10⁵ km³. Such a huge volcanic pile has erupted rapidly in a relatively short period during the Early to Mid-Triassic (approx. 10 Ma). Hypotheses for the origin of the Nilüfer unit include a ‘seamount’, ‘intra-arc and/or fore-arc basin’, ‘oceanic plateau’, and ‘Early Triassic rift’. The geochemistry of metabasites and that of relict magmatic clinopyroxenes indicate that there are two main mafic rock groups in the Nilüfer unit displaying tholeiitic and alkaline affinities. No metabasite and clinopyroxene sample display typical orogenic basalt affinity or a subduction signature. Geochemical data obtained in this study are consistent with the derivation of the metabasites from the topmost extrusive layers of an oceanic plateau (LIP) together with the volcanic rocks of seamount(s).  相似文献   

The upper ocean circulation at Great Meteor Seamount     

Aike Beckmann  Christian Mohn 《Ocean Dynamics》2002,52(4):179-193

 The circulation patterns at Meteor Seamount are investigated for implications for the marine ecosystem, using a numerical ocean circulation model. The importance of tidal amplification and rectification as well as internal tide generation has been documented in Part I of this study. Passive tracers confirm the idea that there is an area above the seamount which is largely isolated from the surroundings. Lagrangian particle trajectories are used to test and quantify the potential for retention. We find that passively advected organisms are more likely to remain in the near-surface layers above Meteor Seamount than actively migrating organisms, which might escape from the area. Finally, the importance of strong wind events on the distribution of particles is illustrated. Received: 10 January 2002 / Accepted: 2 September 2002 Acknowledgements The authors gratefully acknowledge helpful discussions with Catriona Clemmesen, Rabea Diekmann, Frank Hartmann, Inga Hense, Manfred Kaufmann and Bettina Martin. This work was funded by the DFG under contracts Me 487/38-2 and Be 1851/1-1 as part of the Great Meteor Seamount project. Responsible Editor: Jean-Marie Beckers  相似文献   

Hahajima Seamount: An enigmatic tectonic block at the junction between the Izu–Bonin and Mariana Trenches     

Kantaro  Fujioka  Wataru  Tokunaga  Hisayoshi  Yokose  Junzo  Kasahara  Toshinori  Sato  Ryo  Miura  Teruaki  Ishii 《Island Arc》2005,14(4):616-622

Abstract   The Hahajima Seamount, located at the junction between the Izu–Bonin and Mariana forearc slopes, is a notable rectangular shape and consists of various kinds of rocks. An elaborated bathymetric swath mapping with geophysical measurements and dredge hauls showed the Hahajima Seamount is cut by two predominating lineaments, northeast–southwest and northwest–southeast. These lineaments are of faults based on the topographic cross-sections and a 3-D view (whale's eye view). The former lineament is parallel to the transform faults of the Parece Vela Basin, whereas the latter is parallel to the nearby transform fault on the subducting Pacific Plate. The rocks constituting the seamount are ultramafic rocks (mostly harzburgite), boninite, basalt, andesite, gabbro, breccia and sedimentary rocks, which characterize an island arc and an ocean basin. Gravity measurement and seismic reflection survey offer neither a definite gravity anomaly at the seamount nor definite internal structures beneath the seamount. A northwest–southeast-trending fault and small-scale serpentine flows were observed during submersible dives at the Hahajima Seamount. The rectangular shape, size of the seamount, various kinds of rocks and geophysical measurements strongly suggest that the Hahajima Seamount is not a simple serpentine seamount controlled by various tectonic movements, as previously believed, but a tectonic block.  相似文献   

Geology, geochemistry and earthquake history of L?ihi Seamount, Hawaìi's youngest volcano     

Michael O. Garcia  Jackie Caplan-Auerbach  M.D. Kurz 《Chemie der Erde / Geochemistry》2006,66(2):81-108

A half-century of investigations are summarized here on the youngest Hawaiian volcano, L?ihi Seamount. It was discovered in 1952 following an earthquake swarm. Surveying in 1954 determined it has an elongate shape, which is the meaning of its Hawaiian name. L?ihi was mostly forgotten until two earthquake swarms in the 1970s led to a dredging expedition in 1978, which recovered young lavas. The recovery of young lavas motivated numerous expeditions to investigate the geology, geophysics, and geochemistry of this active volcano. Geophysical monitoring, including a real-time submarine observatory that continuously monitored L?ihi's seismic activity for 3 months, captured some of the volcano's earthquake swarms. The 1996 swarm, the largest recorded in Hawaìi, was preceded earlier in the year by at least one eruption and accompanied by the formation of a ∼300-m deep pit crater, Pele's Pit. Seismic and petrologic data indicate that magma was stored in a ∼8-9 km deep reservoir prior to the 1996 eruption.Studies on L?ihi have altered conceptual models for the growth of Hawaiian and other oceanic island volcanoes, and refined our understanding of mantle plumes. Petrologic and geochemical studies of L?ihi lavas showed that the volcano taps a relatively primitive part of the Hawaiian plume, producing a wide range of magma compositions. These compositions have become progressively more silica-saturated with time, reflecting higher degrees of partial melting as the volcano drifts toward the center of the hotspot. Helium and neon isotopes in L?ihi glasses are among the least radiogenic found at ocean islands, and may indicate a relatively deep and undegassed mantle source for the volcano. The north-south orientation of L?ihi rift zones indicates that they may have formed beyond the gravitational influence of the adjacent older volcanoes. A new growth model indicates that L?ihi is older, taller and more voluminous than previously thought. Seismic and bathymetric data have clarified the importance of landsliding in the early formation of ocean island volcanoes. However, a fuller understanding of L?ihi's internal structure and eruptive behavior awaits installation of monitoring equipment on the volcano.The presence of hydrothermal activity at L?ihi was initially proposed based on nontronite deposits on dredged samples that indicated elevated temperatures (31 °C), water temperature, methane and ³He anomalies, and clumps of benthic micro-organisms in the water column above the volcano in 1982. Submersible observations in 1987 confirmed a low temperature geothermal system (15-30 °C) prior to the 1996 formation of Pele's Pit. The sulfide mineral assemblage (wurtzite, pyrrhotite, and chalcopyrite) deposited after the pit crater collapsed are consistent with hydrothermal fluids with temperatures >250 °C, although the highest measured temperature was ∼200 °C. Vent temperatures decreased to ∼60 °C during the 2004 dive season indicating a waning of the current phase of hydrothermal activity.  相似文献   

Petrogenesis and tectonic implications of early Carboniferous alkaline volcanic rocks in Karamay region of West Junggar,Northwest China     

《International Geology Review》2012,54(10):1278-1293

ABSTRACT

Zircon U–Pb geochronological and geochemical analyses are reported for a suite of the early Carboniferous volcanic rocks from West Junggar (Northwest China), southern Central Asian Orogenic Belt (CAOB), with the aim to investigate the sources, petrogenesis, and tectonic implications. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb analysis from an andesite yielded concordant weighted mean ²⁰⁶Pb/²³⁸U age of 345 ± 3 Ma, indicating the presence of early Carboniferous volcanic rocks in West Junggar. The early Carboniferous volcanic rocks consist of basalt, basaltic andesite, and andesite. Geochemically, all the samples bear the signature of ocean island basalt (OIB), and are characterized by alkaline affinity with minor variations in SiO₂ compositions (45.13–53.05 wt.%), high concentrations of Na₂O + K₂O (5.08–8.89 wt.%) and TiO₂ (1.71–3.35 wt.%), and LREE enrichment and HREE depletion ((La/Yb)_N = 7.1–12.4), with weak Eu anomalies (Eu/Eu* = 0.9–1.1) and no obvious Nb, Ta, and Ti negative anomalies. These features suggest that the early Carboniferous volcanic rocks were derived from an OIB-related source that consists of oceanic lithosphere with ~1–3% degree partial melting of garnet lherzolite. From these observations, in combination with previous work, we conclude that the early Carboniferous alkaline volcanic rocks in Karamay region formed by upwelling of asthenospheric mantle through a slab window in a forearc setting during consumption of the West Junggar Ocean. Meanwhile, seamounts, which formed in the Late Devonian and were accreted and subducted in Karamay arc, also brought geological effects in the subduction zone.  相似文献   

Role of Hydrology in the Formation of Co-rich Mn Crusts from the Equatorial N Pacific,Equatorial S Indian Ocean and the NE Atlantic Ocean     

Geoffrey P. Glasby  Bruce Mountain  Theckethottathil C. Vineesh  Virupaxa Banakar  Ramesh Rajani  Xiangwen Ren 《Resource Geology》2010,60(2):165-177

Co-rich Mn crusts from four different locations of the world ocean have been studied to understand the role of dissolved oxygen of the ambient seawater in the formation of Co-rich Mn crusts. WOCE (World Ocean Circulation Experiment) oxygen profiles of modern seawater in the Equatorial North Pacific Ocean, Equatorial South Indian Ocean and the North East Atlantic Ocean have been evaluated with respect to the occurrence of Co-rich Mn crusts at depths ranging from 1500 to 3200 m. The oxygen content at these depths varied from ∼90–240 µmol/kg. The oxygen minimum zone (OMZ), with oxygen contents in the range ∼45–100 µmol/kg, is located in the depth range 800–900 m in these regions. The age of the ocean crust on which seamounts formed is in the range 80.3–180 Ma. Profiles of the oxygen contents of seawater with depth in the oceans are shown to be extremely useful in establishing the optimum conditions for the formation of Co-rich Mn crusts. The use of WOCE oxygen profiles to study geochemical processes in the oceans is highly recommended.  相似文献   

Incorporation of Transition and Platinum Group Elements (PGE) in Co-rich Mn Crusts at Afanasiy-Nikitin Seamount (AFS) in the Equatorial S Indian Ocean     

Geoffrey P. Glasby 《Resource Geology》2010,60(2):212-215

Of the 12 elements enriched in Co-rich Mn crusts from the Afanasiy-Nikitin Seamount in the Equatorial S Indian Ocean, Mn, Fe and Co are enriched by a factor of ~10⁹ compared to their concentrations in seawater whereas Ni and Cu are enriched by a factor of ~10⁷ and the PGE and Au by a factor of ~10⁵ to 10⁷ compared to their concentrations in seawater. The relatively high concentration of Pt in the crusts reflects its occurrence as fine-grained particles in the crusts rather than adsorption of the elements from seawater.  相似文献   

晚中新世南海珍贝-黄岩海山岩浆活动及其演化:岩石地球化学和年代学证据   总被引：10，自引：0，他引：10       下载免费PDF全文

王叶剑  韩喜球  罗照华  邱中炎  丁巍伟  李家彪  高水土  陈荣华 《海洋学报》2009,31(4):93-102

南海海盆15°N附近呈东西向展布的珍贝-黄岩海山被认为是32~17Ma前南海海盆的残留扩张中心.对采自黄岩海山的两个火山岩样品(9DG,9DG-2)进行了岩石学、地球化学和年代学研究.两个样品的SiO₂含量分别为60.3%和63.6%,Al₂O₃含量分别为17.56%和17.55%,TiO₂含量分别为0.48%和0.31%,碱度率分别为3.88和3.62.根据岩石学和岩石化学分类,样品属碱性系列的粗面岩.对稀土元素和微量元素分析表明岩石具有洋岛玄武岩(OIB)型配分型式,轻重稀土总量比(∑c(LREE)/∑c(HREE))和球粒陨石标准化镧镱比((La/Yb)N)分别高达17.22和27.23,并具有铕负异常和锶、磷、钛亏损的特点.样品9DG的锶-钕-铅同位素分析结果为锶-87的含量与锶-86的含量之比值为0.704183,钕-143的含量与钕-144的含量之比值为0.512827,铅-206的含量与铅-207的含量之比值为18.68668,铅-207的含量与铅-204的含量之值为15.67962,铅-208的含量与铅-204的含量之比值为39.00261,表明初始岩浆来自软流圈地幔,具有与珍贝海山玄武岩相似的同位素组成.经钾-氩法测年,粗面岩的年龄为(7.77±0.49)Ma,略晚于珍贝海山玄武岩的年龄[(9.1±1.29)~10.0±1.80Ma],属于南海扩张期后晚中新世火山活动的产物.对比珍贝海山玄武岩的地球化学和同位素特征,认为两者有相同的岩浆源区,但是它们经历了不同程度的结晶分异过程,在晚中新世期间珍贝-黄岩海山可能有地幔柱活动.  相似文献