Submarine slope–fan sedimentation in an ancient forearc related to contemporaneous magmatism: The Upper Cretaceous Izumi Group,southwestern Japan          下载免费PDF全文

Atsushi Noda  Daisuke Sato 《Island Arc》2018,27(2)

The Izumi Group in southwestern Japan is considered to represent deposits in a forearc basin along an active volcanic arc during the late Late Cretaceous. The group consists mainly of felsic volcanic and plutonic detritus, and overlies a Lower to Upper Cretaceous plutono‐metamorphic complex (the Ryoke complex). In order to reconstruct the depositional environments and constrain the age of deposition, sedimentary facies and U–Pb dating of zircon grains in tuff were studied for a drilled core obtained from the basal part of the Izumi Group. On the basis of the lithofacies associations, the core was subdivided into six units from base to top, as follows: mudstone‐dominated unit nonconformably deposited on the Ryoke granodiorite; tuffaceous mudstone‐dominated unit; tuff unit; tuffaceous sandstone–mudstone unit; sandstone–mudstone unit; and sandstone‐dominated unit. This succession suggests that the depositional system changed from non‐volcanic muddy slope or basin floor, to volcaniclastic sandy submarine fan. Based on a review of published radiometric age data of the surrounding region of the Ryoke complex and the Sanyo Belt which was an active volcanic front during deposition of the Izumi Group, the U–Pb age (82.7 ±0.5 Ma) of zircon grains in the tuff unit corresponds to those of felsic volcanic and pyroclastic rocks in the Sanyo Belt.  相似文献   

东昆仑二叠系格曲组火山岩年代学、地球化学特征及其构造意义     

张耀玲  倪晋宇  胡道功  韩建恩  高万里  王超群 《地球学报》2024,45(2):152-164

东昆仑古特提斯造山带经历了从洋壳俯冲到陆-陆碰撞及后碰撞伸展的造山过程,但对古特提斯洋闭合时间一直存在争议,争论的焦点集中在晚二叠世格曲组沉积盆地原型及中上二叠统之间不整合关系代表的构造事件。本文对东昆仑红石山地区格曲组火山岩开展了锆石U-Pb年代学与岩石地球化学研究,结果表明,岩石富集Rb、Th、Ba等大离子亲石元素(LILE)而亏损Nb、Ta、Ti、P等高场强元素(HFSE),具有大陆岩浆弧的地球化学特征。火山岩具有高Ba/Th比值(53.6)、Th/Ce比值(0.23)、Nb/Ta比值(18.35)及低Dy/Yb比值(1.42),表明晚二叠世火山岩由枕状玄武岩和洋底沉积物等洋壳物质俯冲至60 km左右深度时熔融所形成。锆石U-Pb定年表明,格曲组下部碎屑岩段流纹质凝灰岩和英安质沉凝灰岩206Pb/238U加权平均年龄分别为(257.5±2.5)Ma和(256.2±4.8)Ma,上部灰岩段粗安质晶屑凝灰岩206Pb/238U加权平均年龄为(251.8±2.3) Ma。结合区域上已报道的格曲组及花岗岩研究成果,认为古特提斯洋在晚二叠世开始向北俯冲消减,沉积于弧前盆地的格曲组为古特提斯...  相似文献   

Temporal variations in channel patterns and facies architecture in a gravelly fluvial system: The Paleogene Iwaki Formation on the Joban Coalfield,a forearc basin in Northeast Japan     

Kenichiro Shibata  Makoto Ito  Nagayuki Nemoto  Sakae O'Hara 《Island Arc》2010,19(3):489-505

This paper examined sequence‐stratigraphic features of a gravelly fluvial system of the Iwaki Formation, which developed in a forearc‐basin setting in Northeast Japan during the Eocene through Oligocene. On the basis of three‐dimensional architectural element analysis, we discriminated three major cycles of channel complexes, which contain ten component channel deposits in total in the fluvial succession. Component channel deposits in the uppermost part of each cycle are sandier and associated with overbank muddy deposits and coal beds as compared with those in the lower part of the cycle. Mean clast‐size also decreases upsection in the entire gravelly fluvial deposits. The fluvial succession is interpreted to have been deposited in response to an overall rise in relative sea level that was superimposed by three short‐term relative sea‐level rises on the basis of vertical stacking patterns and component lithofacies features of channel deposits, and of correlation of the fluvial succession with an age‐equivalent marine succession in an area about 50 km offshore. However, geometry and stacking patterns of the channel complexes do not exhibit any distinct temporal variation and amalgamated channel and bar deposits are dominant throughout the transgressive fluvial succession. On the other hand, an overall fining‐upward pattern of the entire Iwaki Formation fluvial deposits in association with three component fining‐upward patterns is distinct, and is interpreted to be consistent with the tenet of the standard fluvial sequence‐stratigraphic models. This indicates that the present example represents one type of variation in the standard fluvial sequence‐stratigraphic models, possibly reflecting the forearc‐basin setting, which is generally represented by higher valley slope, higher shedding of coarse‐grained sediments, and shorter longitudinal profiles to the coastal area as compared with a passive‐continental‐margin setting.  相似文献   

Geodynamic evolution of a forearc rift in the southernmost Mariana Arc     

Julia M. Ribeiro  Robert J. Stern  Fernando Martinez  Osamu Ishizuka  Susan G. Merle  Katherine Kelley  Elizabeth Y. Anthony  Minghua Ren  Yasuhiko Ohara  Mark Reagan  Guillaume Girard  Sherman Bloomer 《Island Arc》2013,22(4):453-476

The southernmost Mariana forearc stretched to accommodate opening of the Mariana Trough backarc basin in late Neogene time, erupting basalts at 3.7–2.7 Ma that are now exposed in the Southeast Mariana Forearc Rift (SEMFR). Today, SEMFR is a broad zone of extension that formed on hydrated, forearc lithosphere and overlies the shallow subducting slab (slab depth ≤ 30–50 km). It comprises NW–SE trending subparallel deeps, 3–16 km wide, that can be traced ≥ ∼30 km from the trench almost to the backarc spreading center, the Malaguana‐Gadao Ridge (MGR). While forearcs are usually underlain by serpentinized harzburgites too cold to melt, SEMFR crust is mostly composed of Pliocene, low‐K basaltic to basaltic andesite lavas that are compositionally similar to arc lavas and backarc basin (BAB) lavas, and thus defines a forearc region that recently witnessed abundant igneous activity in the form of seafloor spreading. SEMFR igneous rocks have low Na₈, Ti₈, and Fe₈, consistent with extensive melting, at ∼23 ± 6.6 km depth and 1239 ± 40°C, by adiabatic decompression of depleted asthenospheric mantle metasomatized by slab‐derived fluids. Stretching of pre‐existing forearc lithosphere allowed BAB‐like mantle to flow along the SEMFR and melt, forming new oceanic crust. Melts interacted with pre‐existing forearc lithosphere during ascent. The SEMFR is no longer magmatically active and post‐magmatic tectonic activity dominates the rift.  相似文献   

Structural style and tectono-stratigraphic evolution of the Neogene–Quaternary Siderno Basin,southern Calabrian Arc,Italy     

《International Geology Review》2012,54(4):468-481

The Neogene–Quaternary Siderno Basin is located in the southern Calabrian Arc, along an E–W transect including the Ionian side and part of the Tyrrhenian margin. The orogenic belt was generated by ongoing northward subduction of Ionian oceanic lithosphere beginning in the Early Cretaceous. Since the Oligocene, the area has experienced complex tectonics, including NW–SE-oriented pull-apart basins. The forearc region contains >2000 m of Oligocene-to-Quaternary strata that cover pre-Tertiary rocks. The succession forms an E-dipping monocline, with tectonic growth structures increasing upward. Erosional truncations and thickness variations suggest a different evolution for the Siderno Basin, which in comparison with northern and southern parts of the Ionian accretionary wedge, evolved differently during the Serravallian–Tortonian stages. NW–SE and NE–SW fault systems are dominant, the first exhibiting strike–slip and normal kinematics in the Nicotera–Gioiosa and Molochio–Antonimina fault zones. These structures were active during infilling of the Neogene basin, and represent a complex transfer zone.

The NE–SW system shows two types of tectonic kinematics: (1) a compressive stage, with NW–SE-orientated shortening, responsible for inversion tectonics documented by east-verging folds, thrusts, and back-thrusts, and (2) emplacement of the variegated clay during the Langhian, which is related to back-thrust propagation. The strike–slip accommodated stress generated in the accretionary prism in response to subduction of Ionian lithosphere and progradation of the accretionary front of the Calabrian forearc.  相似文献   

广西凭祥中三叠世盆地沉积特征与构造属性分析   总被引：2，自引：0，他引：2  

宋博  闫全人  向忠金  陈辉明  马铁球  杨广元 《地质学报》2013,87(4):453-473

凭祥中三叠世盆地位于印支地块与华南地块碰撞拼合的缝合带内,记录了沿华南地块南缘展布的古特提斯分支洋盆俯冲闭合、印支地块与华南地块碰撞拼合的过程。本文通过大比例尺实测地质剖面,详细测量了凭祥盆地沉积相序及其组合变化,分析了不同相序的沉积环境及其物源,并探讨了盆地构造属性。结果表明,凭祥盆地主要充填有深水盆地相、浊积扇相和三角洲相等不同环境的沉积物。中三叠世期间盆地呈现为一系列因碰撞拼合作用形成的构造高地间夹深谷的岩相古地理面貌。深水盆地相以发育大套深灰色泥页岩和裹夹碎屑流沉积为特征,碎屑流沉积发育于构造高地陡坡一侧。浊积扇相以发育槽模、正粒序、爬升波纹层理、包卷层理、双向交错层理、透镜状层理、平行层理为特征。三角洲相以发育大型板状交错层理、潮沟、厚层透镜状砂体和砖红色泥岩为特征,类似发育于俯冲汇聚环境下的牙买加型扇三角洲,可能发育于构造高地缓坡一侧。沉积作用分析表明,主要存在碎屑流、浊流等重力流作用,并识别出底流作用。古水流分析表明存在向南和向北两个方向的物质搬运。岩相学特征表明盆地砂岩成分成熟度和结构成熟度均较低,物源为再旋回造山带或碰撞造山带。本文研究结果认为：凭祥盆地是一个伴随古特提斯分支洋盆俯冲闭合而被强烈改造的残余弧前盆地,时空上与之相配套是北泗组岛弧型流纹斑岩。该弧盆系统可能于晚二叠世末开始发育,中三叠世末结束沉积充填,暗示印支地块和华南地块最终于中三叠世碰撞拼合。  相似文献   

2009年3月19日M_w7.6级汤加大地震的“震前扰动”现象          下载免费PDF全文

胡小刚  郝晓光 《地球物理学进展》2009,24(3):866-870

汶川大地震爆发后,作者在武汉大地测量国家野外科学观测站的重力仪资料中发现了震前约48小时的“重力扰动”现象、并在随后对全国数十个台站宽带地震仪资料的分析中得到了证实.2009年3月19日,太平洋岛国汤加海域爆发了M_w7.6级（里氏7.9级）大地震,宽带地震仪资料中再次出现了显著的、信号周期为4~8秒的“震前扰动”现象：从大地震前约16天的3月4日开始一直持续到地震发生.  相似文献   

Cenozoic geodynamic evolution of the Andaman–Sumatra subduction margin: Current understanding     

Partha P.  Chakraborty  Prosanta K.  Khan 《Island Arc》2009,18(1):184-200

The Andaman–Sumatra margin displays a unique set‐up of extensional subduction–accretion complexes, which are the Java Trench, a tectonic (outer arc) prism, a sliver plate, a forearc, oceanic rises, inner‐arc volcanoes, and an extensional back‐arc with active spreading. Existing knowledge is reviewed in this paper, and some new data on the surface and subsurface signatures for operative geotectonics of this margin is analyzed. Subduction‐related deformation along the trench has been operating either continuously or intermittently since the Cretaceous. The oblique subduction has initiated strike–slip motion in the northern Sumatra–Andaman sector, and has formed a sliver plate between the subduction zone and a complex, right‐lateral fault system. The sliver fault, initiated in the Eocene, extended through the outer‐arc ridge offshore from Sumatra, and continued through the Andaman Sea connecting the Sagaing Fault in the north. Dominance of regional plate dynamics over simple subduction‐related accretionary processes led to the development and evolution of sedimentary basins of widely varied tectonic character along this margin. A number of north–south‐trending dismembered ophiolite slices of Cretaceous age, occurring at different structural levels with Eocene trench‐slope sediments, were uplifted and emplaced by a series of east‐dipping thrusts to shape the outer‐arc prism. North–south and east–west strike–slip faults controlled the subsidence, resulting in the development of a forearc basins and record Oligocene to Miocene–Pliocene sedimentation within mixed siliciclastic–carbonate systems. The opening of the Andaman Sea back‐arc occurred in two phases: an early (～11 Ma) stretching and rifting, followed by spreading since 4–5 Ma. The history of inner‐arc volcanic activity in the Andaman region extends to the early Miocene, and since the Miocene arc volcanism has been associated with an evolution from felsic to basaltic composition.  相似文献   

CHRONOSTRATIGRAPHY,SEDIMENTATION AND EVOLUTION OF THE XIGAZE FOREARC BASIN: IMPLICATIONS FOR DYNAMIC EVOLUTION OF THE YARLUNG ZANGBO SUTURE ZONE     

Wang Chengshan  Liu Zhifei    Li Xianghui WT  ”BX 《地学前缘》2000,(Z1)

CHRONOSTRATIGRAPHY,SEDIMENTATION AND EVOLUTION OF THE XIGAZE FOREARC BASIN: IMPLICATIONS FOR DYNAMIC EVOLUTION OF THE YARLUNG ZANGBO SUTURE ZONE1　All埁ｇｒｅＣＪ,CourtillotV ,TapponnierP ,etal.StructureandevolutionoftheHimalaya Tibetorogenicbelt[J] .Nature,1984 ,30 7:17～ 2 2 . 2　CoulonC ,MaluskiH ,BollingerC ,etal.MesozoicandCenozoicvolcanicrocksfromcentralandsouthernTibet:3 9Ar 40 Ardating ,petrotogicalcharacteristicsandgeodyn…  相似文献   

大别山低级变质岩的构造背景     

徐树桐  吴维平  陆益群 《地质通报》2010,29(5):795-810

大别山南北两侧的浅变质岩是碰撞造山以前洋壳俯冲造山阶段的重要组成部分。木兰山片岩或张八岭群是俯冲的洋壳;苏家河群、信阳群和佛子岭群是由洋壳俯冲形成的海沟沉积,并因俯冲过程中的前进变形而形成增生楔;杨山煤系和梅山群是石炭纪弧前盆地沉积,并因俯冲过程中的前进变形而被增生楔逆掩。宿松群是扬子大陆被动边缘沉积,不是俯冲造山带的成员。因洋壳俯冲形成的弧和弧后盆地可能已被新生界沉积物掩盖。高压—超高压变质带是碰撞造山后期从深部折返的外来体。高压—超高压变质带正好处于洋壳和增生楔之间,破坏了早期洋壳俯冲造山带的完整性,使得洋壳俯冲造山阶段的特征被破坏,因而不易辨别。俯冲造山阶段应为奥陶纪到泥盆纪,碰撞造山阶段应从二叠纪开始。  相似文献