Post-collisional transition from calc-alkaline to alkaline volcanism during the Neogene in Oranie (Algeria): magmatic expression of a slab breakoff   总被引：2，自引：0，他引：2  

Christian Coulon  M'hamed Megartsi  Serge Fourcade  Ren C. Maury  Herv Bellon  Amina Louni-Hacini  Joseph Cotten  Alain Coutelle  Daniel Hermitte 《Lithos》2002,62(3-4):87-110

During the Neogene, a magmatic change from calc-alkaline to alkaline types occurred in all the regions surrounding the western Mediterranean. This change has been studied in Oranie (western Algeria). In this area, potassic to shoshonitic calc-alkaline andesites (with La/Nb ratios in the range 4–6) were mainly erupted between 12 and 9 Ma. They were followed (between 10 and 7 Ma) by basalts displaying geochemical features which are transitional between calc-alkaline and alkaline lavas (La/Nb=1–1.7). After a ca. 3-Ma quiescence period, volcanic activity resumed, with the eruption of OIB-type alkaline basalts (La/Nb=0.5–0.6), from 4 to 0.8 Ma. A combined geochemical approach, using incompatible elements and Sr, Nd and O isotopes, allows us to conclude that the transitional basalts derived from the melting of a heterogeneous mantle source, at the boundary between lithosphere and asthenosphere. We propose that melting of a previously subduction-modified lithospheric mantle occurred between 12 and 10 Ma, in response to the upwelling of hot asthenosphere flowing up into an opening gap above a detached sinking slab. As a result, calc-alkaline magmas were formed. From 10 to 7 Ma, the transitional basalts were generated through melting of the boundary mantle zone between the lithosphere and the upwelling asthenosphere. During that stage, the contribution of the lithospheric source was still predominant. Then, as sinking of the oceanic slab progressed, the increasing uprise of the asthenosphere led to the formation and emplacement (from 4 to 0.8 Ma) of typical within-plate alkaline basalts derived from a plume-modified asthenospheric mantle.  相似文献   

伊豆-小笠原下方660km间断面的区域性差异     

周元泽  蒋志勇  臧绍先 《地震学报》2002,24(3):317-324

利用南、北加州地震台网、华盛顿州西北太平洋地震台网单分量短周期地震仪和德国、瑞士地震台网／台阵的三分量宽频带地震仪记录的1981～2000年伊豆——小笠原地区下方地震的波形资料，使用N次根倾斜叠加方法提取近源一侧来自间断面SdP转换震相，以研究660km间断面区域性差异．研究发现，自35Ｎ 到26Ｎ 的各剖面依次体现了和达 本尼奥夫带（Wadati-Benioff zone）倾角逐渐加大，且地震分布的最大深度也逐步增大，俯冲板块对660km间断面存在的影响也因此产生了差异性:没有俯冲板块影响的情况下，该间断面出现在CM）660km深度处，而受到俯冲板块明显作用的地区，则该间断面普遍出现下陷．转换点分布的一定程度分散性可能是间断面本身复杂结构、震相误判或一维球对称地球模型假定等因素造成的．这一转换点分布的分散性是一个亟需解决的问题．   相似文献   

日本列岛下太平洋俯冲板块的精细结构   总被引：1，自引：0，他引：1  

江国明  赵大鹏  张贵宾 《地学前缘》2008,15(1):222-231

尽管许多学者对日本列岛下的太平洋俯冲板块做了大量的研究,但板块内部的结构(比如板块厚度,板块内地震波速度随深度的变化以及洋壳的俯冲情况等)仍然不太清楚。利用日本地区密集台网收集到的中深和深发地震到时数据来探讨上述问题。采用三维射线追踪正演模拟法,首先利用333个远震计算得到了日本地区太平洋板块的厚度为85km;然后利用3283个地震(震源深度大于40km)的130227条P波到时进一步研究板块内部的精细结构。结果显示,沿深度方向6个地层段(间隔100km)内的速度扰动值分别为5.5%,4.0%,3.5%,2.5%,2.0%和6.0%,在40～500km范围内速度扰动随深度的增加而减小,这与温度随深度的变化情况相一致。当深度大于500km时,速度扰动突然增大到6.0%,分析认为该异常可能由发生在东亚大陆边缘下方的深发地震无法精确定位导致的。最后利用40～500km深度范围内的近震测试得到日本东北和北海道地区下方洋壳俯冲的深度均为110km,平均厚度分别为7.5km和5km,相对于一维模型的速度扰动分别为1%和-3%。这说明洋壳在俯冲到110km以深时,由于受温度和压力的影响,逐渐脱水、变质,直至与板块融合。通过分析震源与洋壳的位置关系,本研究认为北海道地区比东北地区下方的俯冲洋壳可能含有更多的流体(比如水),导致两地区洋壳内的速度相差如此之大。此外,因为日本南部与洋壳对应的区域多为海洋,观测台站较少,所以本研究无法测试得到该区域内的洋壳俯冲情况。  相似文献   

甘肃北山柳园地区花岗岩类的年代学、地球化学特征及构造意义   总被引：8，自引：10，他引：8  

赵泽辉  郭召杰王毅 《岩石学报》2007,23(8):1847-1860

北山柳园地区分布大量的花岗岩类岩石,岩石类型有花岗闪长岩、二长花岗岩、钾长花岗岩和斑状花岗岩。锆石SHRIMP U—Pb 定年分析结果为:花岗闪长岩的侵位年代为423±8Ma 辉铜山以东(HT-)钾长花岗岩和二长花岗岩的侵位分别为436±9Ma 和397±7Ma。该区花岗质岩石都具有大离子亲石元素和轻稀土元素相对富集,K、Ni、Ta、P 和 Ti 负异常的特征,属于准铝质到过铝质的高 K 花岗岩。花岗闪长岩无 Sr 和 Eu负异常的特征,ε_(Nd)(t)=-2.5～-0.8,其岩浆源于岩石圈地幔或是软流圈与岩石圈地幔相混合的岩浆熔融,并受到了含有火山弧组分的年轻地壳的混染。钾长花岗岩和二长花岗岩具有 Sr 和 Eu 负异常的特征,ε_(Nd)(t)值分别为 1.4、-4.0～-2.0和-2.7～-0.3。HT-钾长花岗岩岩浆主要源于由于岩石圈地幔岩浆作用而导致上覆年轻地壳物质的部分熔融;花牛山附近(HN-)钾长花岗岩岩浆主要源于软流圈地幔部分熔融,可能受到了部分年轻地壳物质的混染;二长花岗岩岩浆主要源于年轻地壳的部分熔融。柳园地区4类花岗岩类岩石都是后碰撞构造背景下的岩浆产物,岩浆形成可能与俯冲板片断离有关。  相似文献   

滇西高黎贡带～40Ma OIB型基性岩浆活动：消减特提斯洋片与印度板块断离的产物？     

蓝江波徐义刚  杨启军黄小龙 《岩石学报》2007,23(6):1334-1346

滇西高黎贡带基性岩脉形成于40～42Ma,以高 FeO、TiO_2,低 K_2O 含量为特征。虽然多数样品经历了不同程度的地壳混染,少量样品的 Nb/La 大于1,La/Yb 比值较小和 Mg~#值较高,显示了似洋岛玄武岩(OIB)的地球化学特征,从而为研究区提供了软流圈上涌的岩石学证据。模拟计算进一步暗示高黎贡基性岩脉的源区在尖晶石相橄榄岩中(<70km),说明软流圈地幔上涌到很浅的部位,这与目前青藏高原巨厚的岩石圈(>150km)形成鲜明对比。因此,～40Ma 高黎贡基性岩浆活动记录了研究区陆-陆碰撞后特殊的构造演化阶段。高黎贡带基性岩脉与达孜-甲马基性次火山岩在形成时间和地球化学性质上一致,两者均代表了碰撞后消减特提斯洋片与印度板块断离过程中软流圈上涌熔融的产物。  相似文献   

The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle   总被引：1，自引：0，他引：1  

W.P. Schellart   《Tectonophysics》2007,445(3-4):363-372

A geodynamic model exists, the westward lithospheric drift model, in which the variety of overriding plate deformation, trench migration and slab dip angles is explained by the polarity of subduction zones. The model predicts overriding plate extension, a fixed trench and a steep slab dip for westward-dipping subduction zones (e.g. Mariana) and predicts overriding plate shortening, oceanward trench retreat and a gentle slab dip for east to northeastward-dipping subduction zones (e.g. Chile). This paper investigates these predictions quantitatively with a global subduction zone analysis. The results show overriding plate extension for all dip directions (azimuth α = − 180° to 180°) and overriding plate shortening for dip directions with α = − 90° to 110°. The wide scatter in data negate any obvious trend and only local mean values in overriding plate deformation rate indicate that overriding plate extension is somewhat more prevalent for west-dipping slabs. West-dipping subduction zones are never fixed, irrespective of the choice of reference frame, while east to northeast-dipping subduction zones are both retreating and advancing in five out of seven global reference frames. In addition, westward-dipping subduction zones have a range in trench-migration velocities that is twice the magnitude of that for east to northeastward-dipping slabs. Finally, there is no recognizable correlation between slab dip direction and slab dip angle. East to northeast-dipping slabs (α = 30° to 120°) have shallow (0–125 km) slab dip angles in the range 10–60° and deep (125–670 km) slab dip angles in the range 40–82°, while west-dipping slabs (α = − 60° to − 120°) have shallow slab dip angles in the range 19–50° and deep slab dip angles in the range 25–86°. Local mean deep slab dip angles are nearly identical for east and west-dipping slabs, while local mean shallow slab dip angles are lower by only 4.7–8.1° for east to northeast-dipping slabs. It is thus concluded that overall, there is no observational basis to support the three predictions made by the westward drift model, and for some sub-predictions the observational basis is very weak at most. Alternative models, which incorporate and underline the importance of slab buoyancy-driven trench migration, slab width and overriding plate motion, are better candidates to explain the complexity of subduction zones, including the variety in trench-migration velocities, overriding plate deformation and slab dip angles.  相似文献   

Discussion and Applications of Slab Models of the Convective Boundary Layer based on Turbulent Kinetic Energy Budget Parameterisations     

M. G. Villani  A. Maurizi  F. Tampieri 《Boundary-Layer Meteorology》2005,114(3):539-556

Some of the most widely used slab model formulations for applications in the convective boundary layer are analysed and discussed. Three main classes are identified based on different approximations of the turbulent kinetic energy equation. The models appear to be quite insensitive to the initial values for boundary-layer height, and temperature discontinuity at the boundary-layer top. The slab models are applied to a case of sea-land transition from the literature, and a case of convective boundary layer time evolution over a homogeneous terrain at San Pietro Capofiume (Bologna, Italy). The different parameterisations turn out to be almost equivalent for the cases studied. The models generally underpredict the value for the height, while all give very good estimates for the mean mixed-layer temperature.  相似文献   

新疆西天山那拉提构造带变质核部杂岩地质构造特征     

高鹏  王宏运  倪新元  李兵  胡志军  王耀武 《陕西地质》2005,23(2):61-69

新疆西天山那拉提构造带变质核部杂岩分布于新疆巩留县那拉提山山脊北侧，整体沿那位提南缘构造带北侧呈近东西向展布，为一套由高级变质表壳岩、灰色片麻岩组成的早前寒武系高级片麻岩系，历经多期不同构造体制变形变质改造与再造，形成多相片麻岩系，并呈长垣状变质核部杂岩隆升，构成那拉提造山带的核部构造物质组成。  相似文献   

黄岩海山链俯冲与吕宋岛斑岩铜金成矿     

詹美珍  孙卫东  凌明星  李贺 《岩石学报》2015,31(7):2101-2114

菲律宾吕宋岛上约5Ma以来的斑岩铜金矿床主要集中在北部的Baguio和Mankayan地区,它们在时空上与黄岩海山链密切相关。1907~2013年间的地震数据表明,在吕宋岛中部(16°N)附近存在地震稀疏带。吕宋岛上的斑岩铜金矿床分布在该地震稀疏带的两侧。收集到的相应时期埃达克岩的Sr/Y-(La/Yb)N、Sr/Y-Y和La/Yb-Yb图解表明,这些埃达克岩几乎都是洋壳部分熔融形成的。与吕宋岛北部侵入型埃达克岩相比,位于16°N附近的埃达克岩具有更高的Sr含量,这可能与南海古扩张脊俯冲撕裂形成的板片窗有关。斜长石是辉长岩的主要矿物之一,因此,撕裂的洋壳边缘的辉长岩层部分熔融,形成具有更高Sr含量的埃达克质岩浆。而位于吕宋岛南部Bataan弧中的埃达克质火山岩,可能是在南海古扩张脊俯冲之前形成的。根据已发表的斑岩铜金矿床数据,Mankayan地区的成矿年龄在约3.5~1.4Ma,Baguio地区的成矿年龄在约3.1~0.5Ma之间,有从北向南变年轻的趋势,这与黄岩海山链沿马尼拉海沟向南迁移一致。此外,吕宋岛北部Mt.Cagua到Baguio之间存在一个延伸了220km的第四纪火山活动的空隙,该区域大部分火山已经在中新世停止活动。这可能是黄岩海山链的俯冲使得俯冲倾角逐渐变缓、挤压加强而导致的。同时期的斑岩铜矿床正好分布在这一火山空隙中,是俯冲洋壳部分熔融的产物。  相似文献   

The basins of Sundaland (SE Asia): Evolution and boundary conditions     

《Marine and Petroleum Geology》2014

Most of the basins developed in the continental core of SE Asia (Sundaland) evolved since the Late Cretaceous in a manner that may be correlated to the conditions of the subduction in the Sunda Trench. By the end of Mesozoic times Sundaland was an elevated area composed of granite and metamorphic basement on the rims; which suffered collapse and incipient extension, whereas the central part was stable. This promontory was surrounded by a large subduction zone, except in the north and was a free boundary in the Early Cenozoic. Starting from the Palaeogene and following fractures initiated during the India Eurasia collision, rifting began along large faults (mostly N–S and NNW–SSE strike-slip), which crosscut the whole region. The basins remained in a continental fluvio-lacustrine or shallow marine environment for a long time and some are marked by extremely stretched crust (Phu Khanh, Natuna, N. Makassar) or even reached the ocean floor spreading stage (Celebes, Flores). Western Sundaland was a combination of basin opening and strike-slip transpressional deformation. The configuration suggests a free boundary particularly to the east (trench pull associated with the Proto-South China Sea subduction; Java–Sulawesi trench subduction rollback). In the Early Miocene, Australian blocks reached the Sunda subduction zone and imposed local shortening in the south and southeast, whereas the western part was free from compression after the Indian continent had moved away to the north. This suggests an important coupling of the Sunda Plate with the Indo-Australian Plate both to SE and NW, possibly further west rollback had ceased in the Java–Sumatra subduction zone, and compressional stress was being transferred northwards across the plate boundary. The internal compression is expressed to the south by shortening which is transmitted as far as the Malay basin. In the Late Miocene, most of the Sunda Plate was under compression, except the tectonically isolated Andaman Sea and the Damar basins. In the Pliocene, collision north of Australia propagated toward the north and west causing subduction reversal and compression in the short-lived Damar Basin. Docking of the Philippine Plate confined the eastern side of Sundaland and created local compression and uplift such as in NW Borneo, Palawan and Taiwan. Transpressional deformation created extensive folding, strike-slip faulting and uplift of the Central Basin and Arakan Yoma in Myanmar. Minor inversion affected many Thailand rift basins. All the other basins record subsidence. The uplift is responsible for gravity tectonics where thick sediments were accumulated (Sarawak, NE Luconia, Bangladesh wedge).  相似文献