The development of talus slopes around Lord Howe island and implications for the history of island planation     

M. E. Dickson 《The Australian geographer》2004,35(2):223-238

Lord Howe Island is a small eroded remnant of a Late Miocene shield volcano. A fringing coral reef dissipates wave energy along a portion of the shoreline, but the remainder of the coast is rugged with spectacular high basaltic sea cliffs. This paper investigates the evolution of talus slopes that occur beneath the loftiest cliffs, and places this analysis within the context of a longer history of island planation that has resulted in a wide truncated shelf around the island. During the Last Glacial, when the sea level was lower than at present, talus slopes accumulated around the extent of the island's cliffed coast because material eroded from cliffs by subaerial processes could not be removed by marine processes. The survival of these slopes during the Holocene has depended on a balance achieved between rates of subaerial and marine erosion. This balance is fundamentally influenced by cliff height, as cliffs higher than 200 m are plunging or veneered by talus slopes, whereas lower cliffs have erosional shore platforms. On comparison with published erosion rates from inland basalt scarps it appears that marine processes may account for over 90 per cent of the total cliff retreat that has occurred at Lord Howe Island, yet contemporary coastal morphology attests to the significance of subaerial processes in recent times. It is likely that marine cliffing was very rapid soon after volcanism ceased, but rates of erosion decreased through time as wave energy became increasingly attenuated across a widening planation surface, and as increasing cliff heights yielded greater quantities of talus that provided protection from rapid marine erosion.  相似文献   

Geometry of extensional faults developed at slow-spreading centres from pre-stack depth migration of seismic reflection data in the Central Atlantic (Canary Basin)     

T. J. Reston  C. R. Ranero  O. Ruoff  M. Perez-Gussinye  J. J. Dañobeitia 《Geophysical Journal International》2004,159(2):591-606

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Onset of small-scale instabilities at the base of the lithosphere: scaling laws and role of pre-existing lithospheric structures     

Caroline Dumoulin  Marie-Pierre Doin  Diane Arcay  Luce Fleitout 《Geophysical Journal International》2005,160(1):345-357

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Temporal and spatial cyclicity of accretion at slow-spreading ridges—evidence from the Reykjanes Ridge     

Christine Peirce  Alex Gardiner  Martin Sinha 《Geophysical Journal International》2005,163(1):56-78

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The Stonyford Volcanic Complex: a Forearc Seamount in the Northern California Coast Ranges   总被引：2，自引：0，他引：2  

SHERVAIS  JOHN W.; SCHUMAN  MARCHELL M. ZOGLMAN; HANAN  BARRY B. 《Journal of Petrology》2005,46(10):2091-2128

Jurassic age volcanic rocks of the Stonyford volcanic complex(SFVC) comprise three distinct petrological groups based ontheir whole-rock geochemistry: (1) oceanic tholeiites; (2) transitionalalkali basalts and glasses; (3) high-Al, low-Ti tholeiites.Major and trace element, and Sr–Nd–Pb isotopic dataindicate that the oceanic tholeiites formed as low-degree partialmelts of normal mid-ocean ridge basalt (N-MORB)-source asthenospheresimilar in isotope composition to the East Pacific Rise today;the alkalic lavas were derived from an enriched source similarto that of E-MORB. The high-Al, low-Ti lavas resemble second-stagemelts of a depleted MORB-source asthenosphere that formed bymelting spinel lherzolite at low pressures. Trace element systematicsof the high-Al, low-Ti basalts show the influence of an enrichedcomponent, which overprints generally depleted trace elementcharacteristics. Tectonic discrimination diagrams show thatthe oceanic tholeiite and alkali suites are similar to present-daybasalts generated at mid-oceanic ridges. The high-Al, low-Tisuite resembles primitive arc basalts with an enriched, alkalibasalt-like overprint. Isotopic data show the influence of recycledcomponents in all three suites. The SFVC was constructed ona substrate of normal Coast Range ophiolite in an extensionalforearc setting. The close juxtaposition of the MORB-like olivinetholeiites with alkali and high-Al, low-Ti basalts suggestsderivation from a hybrid mantle source region that includedMORB-source asthenosphere, enriched oceanic asthenosphere, andthe depleted supra-subduction zone mantle wedge. We proposethat the SFVC formed in response to collision of a mid-oceanridge spreading center with the Coast Range ophiolite subductionzone. Formation of a slab window beneath the forearc duringcollision allowed the influx of ridge-derived magmas or themantle source of these magmas. Continued melting of the previouslydepleted mantle wedge above the now defunct subduction zoneproduced strongly depleted high-Al, low-Ti basalts that werepartially fertilized with enriched, alkali basalt-type meltsand slab-derived fluids. KEY WORDS: CRO; oceanic basalts; California  相似文献   

黑龙江饶河枕状玄武岩地质、地球化学特征及其构造属性   总被引：1，自引：0，他引：1  

何松  孙晓猛  张旭庆  万阔  郑涵  李多姿 《世界地质》2016,35(4):942-954

为了确定饶河玄武岩的构造属性,在野外地质观察的基础上,对玄武岩进行岩石学研究和地球化学分析。玄武岩具有典型的枕状构造、淬冷边、中空骸晶和鬣刺结构等特征,反映其形成于海底喷发环境。化学分析样品具有高TiO_2、MgO和低Al_2O_3、CaO、P_2O_5、K_2O等特征,富集大离子亲石元素(Rb、Sr和Ba),微量元素蛛网图呈向上隆起形态,稀土元素配分曲线为右倾型(∑LREE/∑HREE为5.8~6.5),无δEu异常(0.92~0.97),表明样品具有洋岛玄武岩特征。主量和微量元素构造环境判别图指示了样品形成于洋岛或板内环境。样品与亚速尔型和夏威夷型洋岛玄武岩地球化学特征对比,表现出明显的夏威夷型洋岛玄武岩特征。岩石源区分析揭示出岩浆具有地幔热柱起源,并有先期交代地幔熔体的混入,岩浆源区还受壳幔循环的影响。研究表明,饶河枕状玄武岩为夏威夷型洋岛玄武岩,形成于洋壳消减阶段的洋中脊轴外板内喷发环境,为饶河地区存在成熟的洋盆提供直接证据。结合区域研究成果,认为饶河地区经历了古太平洋板块的扩张、洋中脊轴外板内地幔柱上涌、洋壳俯冲消减以及向佳木斯地块仰冲增生的构造演化过程。  相似文献   

内蒙古巴林右旗晚二叠世埃达克质火山岩特征及其地质意义     

杨文鹏  张生旭  姜海洋  刘洪大  隋成禹  孙江军  张俭峰  吕石佳  李新鹏 《地质通报》2018,37(9):1710-1721

内蒙古东南部巴林右旗地区发育晚二叠世埃达克质火山岩,岩石组合为安山岩、粗安岩、英安岩及辉石安山岩,其LA-ICP-MS锆石U-Pb测年结果为256.7±2.7Ma,指示其形成于晚二叠世。地球化学特征显示,该套火山岩属准铝质-弱铝质中钾钙碱性岩石系列,具富Si(SiO_256%)、高Al(Al_2O_315%)、富Na、贫K、高Sr、低Yb和Y等特征,Na_2O/K_2O值为2.33~3.90,Mg~#值为35.3~60.8;稀土元素总量为96.69×10~(-6)~192.4×10~(-6)、轻重稀土元素分馏较明显((La/Yb)_N值为6.27~13.82),具正的Eu(δEu=1~1.67)异常,在原始地幔标准化蛛网图中,富集大离子亲石元素Rb、Ba、U,亏损高场强元素Nb、Ta,为O型(大洋型)埃达克质火山岩地球化学特征。综合区域资料,巴林右旗埃达克质火山岩是残留在地幔中的古亚洲洋残余洋壳部分熔融并受到地幔橄榄岩混染形成的,暗示晚二叠世存在古亚洲洋向华北板块俯冲消亡事件。  相似文献   

Depositional setting,provenance, and tectonic-volcanic setting of Eocene–Recent deep-sea sediments of the oceanic Izu–Bonin forearc,northwest Pacific (IODP Expedition 352)     

Alastair H. F. Robertson  Steffen Kutterolf  Aaron Avery  Alan T. Baxter  Katerina Petronotis  Gary D. Acton 《International Geology Review》2018,60(15):1816-1854

New biostratigraphical, geochemical, and magnetic evidence is synthesized with IODP Expedition 352 shipboard results to understand the sedimentary and tectono-magmatic development of the Izu–Bonin outer forearc region. The oceanic basement of the Izu–Bonin forearc was created by supra-subduction zone seafloor spreading during early Eocene (c. 50–51 Ma). Seafloor spreading created an irregular seafloor topography on which talus locally accumulated. Oxide-rich sediments accumulated above the igneous basement by mixing of hydrothermal and pelagic sediment. Basaltic volcanism was followed by a hiatus of up to 15 million years as a result of topographic isolation or sediment bypassing. Variably tuffaceous deep-sea sediments were deposited during Oligocene to early Miocene and from mid-Miocene to Pleistocene. The sediments ponded into extensional fault-controlled basins, whereas condensed sediments accumulated on a local basement high. Oligocene nannofossil ooze accumulated together with felsic tuff that was mainly derived from the nearby Izu–Bonin arc. Accumulation of radiolarian-bearing mud, silty clay, and hydrogenous metal oxides beneath the carbonate compensation depth (CCD) characterized the early Miocene, followed by middle Miocene–Pleistocene increased carbonate preservation, deepened CCD and tephra input from both the oceanic Izu–Bonin arc and the continental margin Honshu arc. The Izu–Bonin forearc basement formed in a near-equatorial setting, with late Mesozoic arc remnants to the west. Subduction-initiation magmatism is likely to have taken place near a pre-existing continent–oceanic crust boundary. The Izu–Bonin arc migrated northward and clockwise to collide with Honshu by early Miocene, strongly influencing regional sedimentation.  相似文献   

甘孜—理塘蛇绿混杂岩带中段理塘地区混杂岩物质组成及其洋盆演化史          下载免费PDF全文

严松涛  吴青松  李虎  秦蒙  毛世东  李余生  张勇 《中国地质》2021,48(6):1875-1895

理塘混杂岩位于甘孜-理塘蛇绿混杂岩带中段新龙县-理塘县一带,其内部保存有完整的混杂岩系,包括蛇绿岩残片、洋岛残块、洋内弧残块、复理石建造、裂谷残片、高压变质岩等,是恢复和反演甘孜-理塘洋盆演化的理想地区。在总结前人研究的基础上,结合笔者近年来的研究成果,详细阐述了理塘混杂岩的物质组成、构造环境及形成时代,进一步约束了甘孜-理塘洋盆的时空、性质以及演化历程。LA-ICP-MS锆石U-Pb测年结果表明,甘孜-理塘混杂岩带内蛇绿岩年龄为（346±17）Ma、（286.2±5.1）Ma、（219.5±2.2）Ma、（216.1±2.3）Ma,洋岛年龄为（271±10）Ma、（245.1±1.5）Ma、（211.8±1.8）Ma,在侏罗纪瑞环山组粉砂岩夹层中测得碎屑锆石最新年龄为（196±3）Ma,结合大量的古生物化石鉴定结果,分析认为理塘混杂岩最早的年龄记录可追溯至中泥盆世,最晚可延至早白垩世,是甘孜-理塘洋盆中泥盆世-早白垩世连续演化的记录。综合以上研究成果,笔者还大致建立了甘孜-理塘洋盆晚古生代-中生代的演化过程模式。  相似文献   

鱼粪化石特征对早侏罗世托阿尔期湖泊生态系统的启示:以川东大安寨段为例^*          下载免费PDF全文

周小梅  金鑫  吴强旺  葛禹  时志强 《古地理学报》2021,23(3):600-609

早侏罗世托阿尔期早期大洋缺氧事件(Toarcian Oceanic Anoxic Event,~183.8 Ma)是一次全球性的多幕式生物—环境事件,其在四川盆地下侏罗统自流井组大安寨段亦有显示。对采集自川东北地区大安寨段的鱼粪化石进行形态学描述和内含物分析,发现鱼粪化石中含有大量的磷质成分,多为未经消化的鱼骨化石,另有大量介壳类化石与有机质混杂在一起。据露头岩性和显微薄片特征认为: (1)粪化石呈螺旋状,生产该粪化石的鱼类为大型肉食性鱼类,其喜食小型鱼类和软体动物等,推测可能是肺鱼类(角齿鱼);(2)鱼粪化石形成于开放型淡水湖泊中的半深湖—深湖区,其中湖泊表层含氧量丰富,主要由生产者、消费者构成了研究区早侏罗世托阿尔期大型湖泊生态系统,食物链较为复杂,而湖底为水动力条件较弱的还原环境。该研究成果可为早侏罗世托阿尔期大洋缺氧事件在湖泊中的沉积响应及生态影响研究提供依据。  相似文献