The age of the Tunas formation in the Sauce Grande basin-Ventana foldbelt (Argentina): Implications for the Permian evolution of the southwestern margin of Gondwana     

《Journal of South American Earth Sciences》2013

New SHRIMP radiogenic isotope dating on zircons in tuffs (280.8 ± 1.9 Ma) confirms the Early Permian (Artinskian) age of the uppermost section of the Tunas Formation. Tuff-rich levels in the Tunas Formation are exposed in the Ventana foldbelt of central Argentina; they are part of a deltaic to fluvial section corresponding to the late overfilled stage of the Late Paleozoic Sauce Grande foreland basin. Recent SHRIMP dating of zircons from the basal Choiyoi volcanics exposed in western Argentina yielded an age of 281.4 ± 2.5 Ma (Rocha-Campos et al., 2011). The new data for the Tunas tuffs suggest that the volcanism present in the Sauce Grande basin can be considered as the distal equivalent of the earliest episodes of the Choiyoi volcanism of western Argentina. From the palaeoclimatic viewpoint the new Tunas SHRIMP age confirms that by early Artinskian glacial conditions ceased in the Sauce Grande basin and, probably, in adajacent basins in western Gondwana.  相似文献   

缅甸钦敦-睡宝盆地火山岛弧带沉积环境分析   总被引：1，自引：0，他引：1       下载免费PDF全文

李运振  吕明  白海强  刘子玉 《沉积与特提斯地质》2013,(3):48-55

缅甸钦敦-睡宝盆地在上新世之前的沉积相主体由东北部的海岸平原向西南逐渐过渡到滨浅海,三角洲相对不发育,火山岩呈南北向断续分布在盆地的中部。构造运动、火山活动和海平面升降决定了火山岛弧带的沉积环境。宽缓的构造背景是形成海岸平原．滨浅海沉积环境的决定因素;岛弧带的火山活动自白垩纪至中新世整体表现出较持续的喷发,形成的火山碎屑不仅参与了正常的地层沉积,还对古生物的繁殖和化石的保存起到破坏作用。海平面升降也是控制沉积体系展布的重要因素。  相似文献   

Geochemistry of Pliocene/Pleistocene basalts along the Central Anatolian Fault Zone (CAFZ), Turkey     

Osman Parlak  Michel Delaloye  Cavit Demirkol  Ulvi Can Ünlügenç 《Geodinamica Acta》2013,26(1-3):159-167

Abstract

Pliocene-Pleistocene volcanism accompanied strike-slip-related transtensional deformation along the K?z?l?rmak fault segment of the Central Anatolian fault zone (CAFZ) in the west of ?ark??la (Sivas-central Turkey). These volcanic rocks are represented by alkali olivine basalts. They can be divided into four different sub-groups on the basis of their Zr, Nb, TiO₂ contents. A primitive mantle-normalized incompatible trace element diagram for four subgroups shows close similarity to typical OIB pattern. Some of the incompatible trace element ratios (Ce/Y, Zr/Nb, La/Ba, La/Nb) are also akin to OIB values. Highly fractionated REE patterns (La/Yb_N=24.7–9.2) with no Eu anomaly are the main features of the alkali basalts and are comparable to alkaline volcanism in continental rift zones. On the basis of Al₂O₃/TiO₂, Nb/Y, Zr/Y Zr/Nb ratios, the geochemical differences among four sub-groups can be explained by variable degrees of partial melting of compositionally similar mantle source. Th/Nb, Th/Y, Nb/Y ratios and the primitive mantle-normalized trace element diagram suggests significant amount of crustal involvement for most of the alkali olivine basalts erupted along the CAFZ. Rupture of the continental lithosphere by strike-slip-related transtensional deformation might have caused decompressional partial melting of the asthenospheric mantle and generating alkali olivine basalts in this region. © 2001 Éditions scientifiques et médicales Elsevier SAS.  相似文献   

Neotectonic and volcanic characteristics of the Karasu fault zone (Anatolia,Turkey): The transition zone between the Dead Sea transform and the East Anatolian fault zone     

Bora Rojay  Ariel Heimann  Vedat Toprak 《Geodinamica Acta》2013,26(1-3):197-212

Abstract

The Karasu Rift (Antakya province, SE Turkey) has developed between east-dipping, NNE-striking faults of the Karasu fault zone, which define the western margin of the rift and westdipping, N-S to N20°-30°E-striking faults of Dead Sea Transform fault zone (DST) in the central part and eastern margin of the rift. The strand of the Karasu fault zone that bounds the basin from west forms a linkage zone between the DST and the East Anatolian fault zone (EAFZ). The greater vertical offset on the western margin faults relative to the eastern ones indicates asymmetrical evolution of the rift as implied by the higher escarpments and accumulation of extensive, thick alluvial fans on the western margins of the rift. The thickness of the Quaternary sedimentary fill is more than 465 m, with clastic sediments intercalated with basaltic lavas. The Quaternary alkali basaltic volcanism accompanied fluvial to lacustrine sedimentation between 1.57 ± 0.08 and 0.05 ± 0.03 Ma. The faults are left-lateral oblique-slip faults as indicated by left-stepping faulting patterns, slip-lineation data and left-laterally offset lava flows and stream channels along the Karasu fault zone. At Hacilar village, an offset lava flow, dated to 0.08 ± 0.06 Ma, indicates a rate of leftlateral oblique slip of approximately 4.1 mm?year^?1. Overall, the Karasu Rift is an asymmetrical transtensional basin, which has developed between seismically active splays of the left-lateral DST and the left-lateral oblique-slip Karasu fault zone during the neotectonic period. © 2001 Éditions scientifiques et médicales Elsevier SAS  相似文献   

闽西武夷山建宁—泰宁地区白垩纪火山-沉积序列:对华南东部晚中生代构造演化的制约     

任俊  张岳桥 《地质学报》2021,95(8):2411-2435

闽西武夷山建宁—泰宁地区发育2套白垩纪火山-沉积序列,构成2个火山-沉积旋回,每套序列由下部火山岩和上部沉积岩地层组成.锆石U-Pb年代学和地球化学分析显示,早期中酸性火山岩喷发时代为早白垩世141～135 Ma,具有陆缘火山弧的地球化学亲缘性,并富集Hf同位素(-20.2～1.9);而晚期火山岩活动集中在早、晚白垩世之交(105～97 Ma),呈现弧后伸展特征并相对亏损Hf同位素(-16.1～10.2).通过这两套白垩纪火山-沉积序列区域对比,发现早、晚两套火山活动之间的岩浆活动宁静期呈现自南西向北东逐渐消减的趋势,于120 Ma前后基本结束,这个时期在华南东部陆缘加积了一套河湖相沉积地层,并遭受不同程度的挤压变形.晚期火山-沉积序列受到伸展断陷盆地的控制,其中加积了一套含膏盐红层沉积.研究认为,华南东部陆缘白垩纪2套火山-沉积序列记录了该陆缘2个显著不同的构造演化阶段,从早期陆缘火山弧及其挤压变形到晚期的弧后伸展和断陷湖盆的发展历程.  相似文献   

Multistage Deformation in the Northeastern Segment of the Jiangshao Fault (Suture) Belt: Constraints for the Relationship between the Yangtze Plate and the Cathaysia Old Land     

ZHANG Jin  LI Jinyi  XIAO Wenxi  FENG Qianwen  MA Zongjin 《《地质学报》英文版》2013,87(4):948-978

Multistage deformation events have occurred in the northeastern Jiangshao Fault (Suture) Belt. The earliest two are ductile deformation events. The first is the ca. 820 Ma top-to-the-northwest ductile thrusting, which directly resulted from the collision between the Cathaysia Old Land and the Chencai Arc (?) during the Late Neoproterozoic, and the Jiangnan Orogenic Belt that formed as the ocean closed between the Yangtze Plate and the jointed Cathaysia Old Land and the Chencai Arc due to continuous compression. The second is the ductile left-lateral strike-slipping that occurred in the latest Early Paleozoic. Since the Jinning period, all deformation events represent the reactivation or inversion of intraplate structures due to the collisions between the North China and Yangtze plates during the Triassic and between the Philippine Sea and Eurasian plates during the Cenozoic. In the Triassic, brittle right-lateral strike-slipping and subsequent top-to-the south thrusting occurred along the whole northeastern Jiangshao Fault Zone because of the collision between the North China and Yangtze plates. In the Late Mesozoic, regional extension took place across southeastern China. In the Cenozoic, the collision between the Philippine Sea and Eurasian plates resulted in brittle thrusts along the whole Jiangnan Old land in the Miocene. The Jiangshao Fault Belt is a weak zone in the crust with long history, and its reactivation is one of important characteristics of the deformation in South China; however, late-stage deformation events did not occur beyond the Jiangnan Old Land and most of them are parallel to the strike of the Old Land, which is similar to the Cenozoic deformation in Central Asia. In addition, the Jiangnan old Land is not a collisional boundary between the Yangtze Plate and Cathaysia Old Land in the Triassic.  相似文献   

Opaque Mineralogy as a Tracer of Magmatic History of Volcanic Rocks:an Example from the Neogene-Quaternary Harrat Rahat Intercontinental Volcanic Field, North Western Saudi Arabia     

A.A. SUROUR  A.M.B. MOUFTI 《《地质学报》英文版》2013,87(5):1281-1305

The Neogene-Quaternary Harrat Rahat volcanic field is part of the major intercontinental Harrat fields in western Saudi Arabia.It comprises lava flows of olivine basalt and hawaiite,in addition to mugearite,benmorite,and trachyte that occur mainly as domes,tuff cones and lava flows.Based on opaque mineralogy and mineral chemistry,the Harrat Rahat volcanic varieties are distinguished into Group I(olivine basalt and hawaiite) and Group II(mugearite,benmorite and trachyte).The maximum forsterite content(~85) is encountered in zoned forsteritic olivine of Group I,whereas olivine of Group II is characterized by intermediate(Fo=50),fayalitic(Fo=25) and pure fayalite in the mugearite,benmorite and trachyte,respectively.The more evolved varieties of Group II contain minerals that show enrichment of Fe2+,Mn2+and Na+that indicates normal fractional crystallization.The common occurrence of coarse apatite with titanomagnetite in the benmorite indicates that P5+becomes saturated in this rock variety and drops again in trachyte.Cr-spinel is recorded in Group I varieties only and the Cr#(0.5) suggests lherzolite as a possible restite of the Harrat Rahat volcanics.The plots of Cr# vs.the forsterite content(Fo) suggest two distinct trends,which are typical of mixing of two basaltic magmas of different sources and different degrees of partial melting.The bimodality of Harrat Rahat Cr-spinel suggests possible derivation from recycled MORB slab in the mantle as indicated by the presence of high-Al spinel.It is believed that the subcontinental lithospheric mantle was modified by pervious subduction process and played the leading role in the genesis of the Harrat Rahat intraplate volcanics.The trachytes of the Harrat Rahat volcanic field were formed most probably by melting of a lower crust at the mantle-crust boundary.The increase in fO2 causes a decrease in Cr2 O3,and Al2 O3,and a strong increase in the proportion of Fe3+and Mg# of spinel crystallizing from the basaltic melt at T ~1200°C.The olivine-pyroxene and olivine-spinel geothermometers yielded equilibrium temperature in the range of 935-1025°C,whereas the range of <500-850°C from single-pyroxene thermometry indicates either post crystallization reequilibrium of the clinopyroxene,or the mineral is xenocrystic and re-equilibrated in a cooling basaltic magma.  相似文献   

大兴安岭南段晚中生代双峰式火山作用   总被引：52，自引：24，他引：52  

郭锋  范蔚茗等 《岩石学报》2001,17(1):161-168

大兴安岭南段晚中生代克头鄂博组山岩表现出双峰式特征，主要由玄武质安山岩、英安岩和流纹岩组成。基性火山岩属于代钾拉斑系列，轻微富集LREE，Eu异常不明显（Eu/Eu=0.99-1.04)和HREE无明显分馏的特征（Dy/YbcN=1.030-1.089);富集大离子亲石元素（LILE）而亏损高场强元素（HFSE），尤其是强烈亏损Nb,Ta。英安岩和流纹岩为钙碱性系列，在REE配分模式上为LREE富集型，其中英安岩为Eu弱负异常（Eu/Eu=0.81-1.01)，流纹岩的Eu负异常明显（Eu^*/Eu=0.65-0.76)；在微量元素蛛网图上，英安岩类似于基性火山岩，流纹岩除了具LILE富集和HFSE亏损特征外，还显示出Sr,P,Ti等元素的强烈亏损，可能与岩浆演化过程中斜长石、磷灰石的分离结晶作用相关。晚中生代双峰式火山岩分离结晶的结果。流纹岩表现出较高的La/Sm比值和很高的K／P、K／Ti比值，其成因可能与地壳混染作用或与大陆中、下地壳重熔作用有关。结合区域晚中生代盆岭构造格局特征、大兴安岭南段晚中生代双峰式火山岩形成于造山后阶段，是岩石圈快速伸展体制下导致受早期流体交代的岩石圈地幔发生减压部分熔融作用的产物。  相似文献   

Hydrothermal activity on the southern Mid-Atlantic Ridge: Tectonically- and volcanically-controlled venting at 4–5°S     

C.R. German  S.A. Bennett  D.P. Connelly  A.J. Evans  B.J. Murton  L.M. Parson  R.D. Prien  E. Ramirez-Llodra  M. Jakuba  T.M. Shank  D.R. Yoerger  E.T. Baker  S.L. Walker  K. Nakamura 《Earth and Planetary Science Letters》2008,273(3-4):332-344

We report results from an investigation of the geologic processes controlling hydrothermal activity along the previously-unstudied southern Mid-Atlantic Ridge (3–7°S). Our study employed the NOC (UK) deep-tow sidescan sonar instrument, TOBI, in concert with the WHOI (USA) autonomous underwater vehicle, ABE, to collect information concerning hydrothermal plume distributions in the water column co-registered with geologic investigations of the underlying seafloor. Two areas of high-temperature hydrothermal venting were identified. The first was situated in a non-transform discontinuity (NTD) between two adjacent second-order ridge-segments near 4°02′S, distant from any neovolcanic activity. This geologic setting is very similar to that of the ultramafic-hosted and tectonically-controlled Rainbow vent-site on the northern Mid-Atlantic Ridge. The second site was located at 4°48′S at the axial-summit centre of a second-order ridge-segment. There, high-temperature venting is hosted in an  18 km² area of young lava flows which in some cases are observed to have flowed over and engulfed pre-existing chemosynthetic vent-fauna. In both appearance and extent, these lava flows are directly reminiscent of those emplaced in Winter 2005−06 at the East Pacific Rise, 9°50′N and reference to global seismic catalogues reveals that a swarm of large (M 4.6−5.6) seismic events was centred on the 5°S segment over a  24 h period in late June 2002, perhaps indicating the precise timing of this volcanic eruptive episode. Temperature measurements at one of the vents found directly adjacent to the fresh lava flows at 5°S MAR (Turtle Pits) have subsequently revealed vent-fluids that are actively phase separating under conditions very close to the Critical Point for seawater, at  3000 m depth and 407 °C: the hottest vent-fluids yet reported from anywhere along the global ridge crest.  相似文献   

Assessing the potential for future explosive activity from Teide–Pico Viejo stratovolcanoes (Tenerife,Canary Islands)     

J. Martí  A. Geyer  J. AndujarF. Teixidó  F. Costa 《Journal of Volcanology and Geothermal Research》2008

Since the onset of their eruptive activity within the Cañadas caldera, about 180 ka ago, Teide–Pico Viejo stratovolcanoes have mainly produced lava flow eruptions of basaltic to phonoltic magmas. The products from these eruptions partially fill the caldera, and the adjacent Icod and La Orotava valleys, to the north. Although less frequent, explosive eruptions have also occurred at these composite volcanoes. In order to assess the possible evolution Teide–Pico Viejo stratovolcanoes and their potential for future explosive activity, we have analysed their recent volcanic history, assuming that similar episodes have the highest probability of occurrence in the near future. Explosive activity during the last 35000 years has been associated with the eruption of both, mafic (basalts, tephro–phonolites) and felsic (phono–tephrites and phonolites) magmas and has included strombolian, violent strombolian and sub-plinian magmatic eruptions, as well as phreatomagmatic eruptions of mafic magmas. Explosive eruptions have occurred both from central and flank vents, ranging in size from 0.001 to 0.1 km³ for the mafic eruptions and from 0.01 to < 1 km³ for the phonolitic ones. Comparison of the Teide–Pico Viejo stratovolcanoes with the previous cycles of activity from the central complex reveals that all them follow a similar pattern in the petrological evolution but that there is a significant difference in the eruptive behaviour of these different periods of central volcanism on Tenerife. Pre-Teide central activity is mostly characterised by large-volume (1–> 20 km³, DRE) eruptions of phonolitic magmas while Teide–Pico Viejo is dominated by effusive eruptions. These differences can be explained in terms of the different degree of evolution of Teide–Pico Viejo compared to the preceding cycles and, consequently, in the different pre-eruptive conditions of the corresponding phonolitic magmas. A clear interaction between the basaltic and phonolitic systems is observed from the products of phonolitic eruptions, indicating that basaltic magmatism is the driving force of the phonolitic eruptive activity. The magmatic evolution of Teide–Pico Viejo stratovolcanoes will continue in the future with a probably tendency to produce a major volume of phonolitic magmas, with an increasing explosive potential. Therefore, the explosive potential of Teide–Pico Viejo cannot be neglected and should be considered in hazard assessment on Tenerife.  相似文献