The Somuncura Large Igneous Province in Patagonia: Interaction of a Transient Mantle Thermal Anomaly with a Subducting Slab     

Kay  S. Mahlburg; Ardolino  A. A.; Gorring  M. L.; Ramos  V. A. 《Journal of Petrology》2007,48(1):43-77

The Oligo-Miocene Somuncura province is the largest (55 000km²) back-arc mafic volcanic field in Patagonia, and one ofEarth's largest with no clear link to a hotspot or major extension.Major and trace element and Sr–Nd–Pb isotopic datasuggest involvement of a plume-like component in the mantlemagma source mixed with hydrous, but not high field strengthelement (HFSE)-depleted components, from a disintegrating subductingplate. Magmatism is attributed to mantle upwelling related todisturbances during plate reorganization, possibly at a timewhen the South America plate was nearly stationary over theunderlying mantle. Melting was enhanced by hydration of themantle during Paleogene subduction. Crustal contamination wasminimal in a refractory crust that had been extensively meltedin the Jurassic. Eruption began with low-volume intraplate alkalinemafic flows with depleted Nd–Sr isotopic signatures. Thesewere followed by voluminous 29–25 Ma tholeiitic maficflows with flat light and steep heavy rare earth element (REE)patterns, intraplate-like La/Ta ratios, arc-like Ba/La ratiosand enriched Sr–Nd isotopic signatures. Their source canbe explained by mixing EM1–Tristan da Cunha-like and depletedmantle components with subduction-related components. Post-plateau24–17 Ma alkaline flows with steep REE patterns, highincompatible element abundances, and depleted Sr–Nd isotopicsignatures mark the ebbing of the mantle upwelling. KEY WORDS: Somuncura plateau; slab interaction; Patagonia; large igneous province (LIP); plume-like upwelling  相似文献   

Eocene magmatism(Maden Complex) in the Southeast Anatolian Orogenic Belt: Magma genesis and tectonic implications     

《地学前缘(英文版)》2018,9(6):1829-1847

The origin and geodynamic setting of the Maden Complex, which is situated in the Bitlis-Zagros Suture Zone in the Southeast Anatolian Orogenic Belt, is still controversial due to lack of systematic geological and geochemical data. Here we present new whole rock major-trace-rare earth element and Sre Nd isotope data from the Middle Eocene volcanic rocks exposed in Maden Complex and discuss their origin in the light of new and old data. The volcanic lithologies are represented mainly by basalt and andesite, and minor dacite that vary from low-K tholeiitic, calc-alkaline, high-K calc-alkaline, and shoshonitic in composition. They exhibit enrichments in large ion lithophile and light rare earth elements, with depletions in high field strength elements. Basaltic rocks have uniform Sr and Nd isotope ratios with high εNd(t) values varying from t5.5 to t6.7, in contrast to, andesitic rocks are characterized by low εNd(t) values ranging from à1.6 to à10. These geochemical and isotopic characteristics indicate that two end-members, a subduction-related mantle source and a continental crust, were involved in the magma genesis. Considering all geological and geochemical data, we suggest that the Eocene Maden magmatism occurred as a post-collisional product by asthenospheric upwelling owing to convective removal of the lithosphere during an extensional collapse of the Southeast Anatolian ranges.  相似文献   

Complex slab structure and arc magmatism beneath the Japanese Islands     

《Journal of Asian Earth Sciences》2013

A dense nationwide seismic network recently constructed in Japan has resulted in the production of a large amount of high-quality data that have enabled the high-resolution imaging of deep seismic structures in the Japanese subduction zone. Seismic tomography, precise locations of earthquakes, and focal mechanism research have allowed the identification of the complex structure of subducting slabs beneath Japan, revealing that the subducting Philippine Sea slab underneath southwestern Japan has an undulatory configuration down to a depth of 60–200 km, and is continuous from Kanto to Kyushu without disruption or splitting, even within areas north of the Izu Peninsula. Analysis of the geometry of the Pacific and Philippine Sea slabs identified a broad contact zone beneath the Kanto Plain that causes anomalously deep interplate and intraslab earthquake activity. Seismic tomographic inversions using both teleseismic and local events provide a clear image of the deep aseismic portion of the Philippine Sea slab beneath the Japan Sea north of Chugoku and Kyushu, and beneath the East China Sea west of Kyushu down to a depth of ∼450 km. Seismic tomography also allowed the identification of an inclined sheet-like seismic low-velocity zone in the mantle wedge beneath Tohoku. A recent seismic tomography work further revealed clear images of similar inclined low-velocity zones in the mantle wedge for almost all other areas of Japan. The presence of the inclined low-velocity zones in the mantle wedge across the entirety of Japan suggests that it is a common feature to all subduction zones. These low-velocity zones may correspond to the upwelling flow portion of subduction-induced convection systems. These upwelling flows reach the Moho directly beneath active volcanic areas, suggesting a link between volcanism and upwelling.  相似文献   

A 300-kyr record of aridity and wind strength in southwestern Africa: inferences from grain-size distributions of sediments on Walvis Ridge, SE Atlantic   总被引：13，自引：0，他引：13  

Jan-Berend W. Stuut  Maarten A. Prins  Ralph R. Schneider  Gert Jan Weltje  J. H. Fred Jansen  George Postma 《Marine Geology》2002,180(1-4):221-233

The terrigenous fraction of sediments recovered from Walvis Ridge, SE Atlantic Ocean, reveals a history of southwestern African climate of the last 300 kyr. End-member modelling of a data set of grain-size distributions (n=428) results in three end members. The two coarsest end members are interpreted as eolian dust, the third end member as hemipelagic mud. The ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the SE trade winds. Trade winds were intensified during glacials compared to interglacials. Changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern African aridity. Late Quaternary southwestern African climate was relatively arid during the interglacial stages and relatively humid during the glacial stages, owing to meridional shifts in the atmospheric circulation system. During glacials the polar front shifted equatorward, resulting in a northward displacement of the zone of westerlies, causing increased rainfall in southwestern Africa. The equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient, leading to enhanced atmospheric circulation and increased trade-wind intensity.  相似文献   

Geochemical modelling of early Eocene adakitic magmatism in the Eastern Pontides,NE Anatolia: continental crust or subducted oceanic slab origin?     

《International Geology Review》2012,54(16):2083-2095

Early Eocene adakitic volcanic and granitoid rocks are widespread in the Eastern Pontides of NE Turkey, providing significant constraints for the early Cenozoic tectonomagmatic evolution of the region. These adakitic rock units exhibit relatively high Sr/Y and La/Yb ratios, but low Y and Yb values, similar to modern adakites generated by partial fusion of a subducted oceanic slab. They also have high K₂O and low MgO contents, and show moderately enriched I_Sr and low ?_Nd(t) isotopic signatures. Our trace element modelling suggests that these adakitic magmas were generated from partial melting at low pressures of a garnet-bearing amphibolitic source in the continental lower crust. This lower crustal melting resulted from slab break off-induced asthenospheric upwelling and related magmatic underplating beneath the Eastern Pontides. We interpret this melting event and the adakitic magmatic activity as a syn- to post-collisional process involving early Cenozoic collision of the Pontide and Anatolide–Tauride continental blocks. The geochemical and tectonic constraints presented here indicate that early Eocene adakitic magmatism in the Eastern Pontides did not result from partial fusion of a subducted oceanic slab, but instead represent continental-type adakite formation.  相似文献   

Decadal variation of thermocline-sea surface temperature feedback in the tropical Indian Ocean and the underlying mechanisms     

Meiqi Zhang  Shuangwen Sun  Lin Liu  Yongcan Zu  Lin Feng 《海洋学报(英文版)》2021,40(11):31-38

The thermocline-sea surface temperature (SST) feedback is the most important component of the Bjerknes feedback, which plays an important role in the development of the air-sea coupling modes of the Indian Ocean. The thermocline-SST feedback in the Indian Ocean has experienced significant decadal variations over the last 40 a. The feedback intensified in the late twentieth century and then weakened during the hiatus in global warming at the early twenty-first century. The thermocline-SST feedback is most prominent in the southeastern and southwestern Indian Ocean. Although the decadal variations of feedback are similar in these two regions, there are still differences in the underlying mechanisms. The decadal variations of feedback in the southeastern Indian Ocean are dominated by variations in the depth of the thermocline, which are modulated by equatorial zonal wind anomalies. Whereas the decadal variation of feedback in the southwestern Indian Ocean is mainly controlled by the intensity of upwelling and thermocline depth in winter and spring, respectively. The upwelling and thermocline depth are both affected by wind stress curl anomalies over the southeastern Indian Ocean, which excite anomalous Ekman pumping and influence the southwestern Indian Ocean through westward propagating Rossby waves.  相似文献   

2011年夏季台湾海峡上升流的变化特征及其与风场的关系     

林培根  陈照章  胡建宇  朱佳  孙振宇 《台湾海峡》2012,31(3):307-316

根据2011年6月27日至7月4日台湾海峡航次的调查资料,结合6月1日至8月31日海表温度和风场的卫星遥感数据,分析了平潭附近海域、澎湖北部海域、东山附近海域、台湾浅滩东南部海域上升流的变化特征及其与风场的关系.以海表温度差值(SSTd)来反映上升流强度,该值负值越大,上升流强度越强,分析可知:在2011年夏季,平潭附近海域上升流的强度除了7月中、下旬和8月底外,其余时段较为稳定.SSTd值与局地沿岸风速存在滞后3 d左右的相关关系,特别是稳定持续的西南风对其强度有较大的影响.澎湖北部海域上升流的SSTd值在-1℃左右,强度相对较小,且6、7月比8月时强盛,局地风场对澎湖北部海域上升流有一定的影响,但不是主要影响因素,而是由地形和风共同作用.东山附近海域上升流的强度并不稳定,在6、7月变化较剧烈,到8月SSTd值稳定在-3℃左右,SSTd值的变化对于局地沿岸风的响应同样存在一个3 d左右的滞后时间,除此之外还与上升流中心的水平变动有关.而台湾浅滩东南部海域上升流虽有波动,但持续存在,且6、7月比8月时强盛,其变化与局地风场的关系不大,主要受海流和地形等其他因素的影响.  相似文献   

Numerical simulation of the structure and variation of upwelling off the east coast of Hainan Island using QuikSCAT winds   总被引：3，自引：0，他引：3  

李毅能  彭世球  杨威  王东晓 《中国海洋湖沼学报》2012,30(6):1068-1081

The spatial structure and variation of the upwelling in the waters east and northeast of Hainan Island, China during 2000-2007 were investigated using a nested high-resolution Princeton Ocean Model (POM) forced by QuikSCAT winds. The model produced good simulations of the summer upwelling and the seasonal and annual variability. Strong upwelling occurs from mid-July to mid-August with a peak east of Hainan Island associated with the southwesterly monsoon in the South China Sea. Sensitivity experiments indicated that when the local wind stress controls the variability of the upwelling, the large-scale circulation significantly enhances the upwelling northeast of Hainan Island by inducing a local upwelling and transporting cold water northeast-ward along the island’s east coast. The joint effects of the local wind stress and large-scale circulation result in stronger upwelling northeast of Hainan Island. This implies that the annual variation of the upwelling northeast of Hainan Island is controlled not only by the local alongshore wind stress but also by the large-scale circulation. This result will help us investigate the decadal variation of the upwelling in this region in the future.  相似文献   

Estimates of potential new production in the Java-Sumatra upwelling system     

韦惺  廖晓眉  詹海刚  刘海龙 《中国海洋湖沼学报》2012,30(6):1063-1067

The Java-Sumatra upwelling is one of the most important upwelling systems in the Indian Ocean, with maximum upwelling intensity in July through August. To estimate the nitrate supplied by upwelling, we developed a three-dimensional hydrodynamic model to calculate the mean vertical speed and determine the depth of upwelling. We used in-situ vertical nitrate profiles to assess nitrate concentration in the upwelled waters, and calculated the nitrate supply as the product of nitrate concentration and vertical transport obtained from the numerical model. The calculated result represents potential new production generated in the upwelling region. We found that on the event time scale (monthly) of Java-Sumatra upwelling, water brought to the surface originated from locations 100-m deep, giving a nitrate supply of 93.77×10 3mol/s and potential new production of 1.02×10 14gC/a.  相似文献   

伊通地堑深部软流圈的上涌及其对盆地发育演化的控制和影响   总被引：1，自引：0，他引：1  

余芳  孙家振  张玉芬 《地质科技情报》2009,28(3)

对广泛分布于伊通地堑边界断裂的新生代玄武岩稀土元素组成进行了岩石圈厚度反演,得到了新生代岩石圈厚度变化情况,并结合该区构造演化特征综合分析得出晚白垩世至更新世发生两期深部熔岩上涌：第一期发生于晚白垩世至古新世,软流圈上涌强度大,上涌至约50km,直接导致伊通盆地的断陷和沉降;第二期发生于中新世11．5～11．0Ma,持续时间短,软流圈上涌强度较弱,表现为隆起构造,对盆地断陷后期起改造作用,控制着莫里青地区尖山构造带的形成以及该地区沉降中心的迁移。  相似文献