Froude supercritical flow bedforms in deepwater slope channels? Field examples in conglomerates,sandstones and fine‐grained deposits     

《Sedimentology》2018,65(3):639-669

Active margin continental slope outcrops from the Eocene Juncal Formation, the Eocene La Jolla Group and the Miocene Capistrano Formation display sedimentary structures and depositional geometries that suggest deposition from Froude supercritical flow, based on comparison to strata produced by flume experiments. These deposits range from boulder‐size soft clasts and cobble‐size hard clasts to silt and mud, and display long‐wavelength and low‐amplitude convex‐up and concave‐up geometries that range from centimetre to hundreds of metres scale, low‐angle foresets and backsets, and common internal and bounding erosion surfaces from centimetres to tens of metres in depth. In places, planar laminations, structureless beds and normally graded beds are laterally or vertically associated with such structures. In other places, consistent backsets or deep and steep‐sided scours occur. This study aimed to discuss the origin of the observed bedforms, contributed to recognition of supercritical flow deposits on continental slopes and expanded the outcrop examples of supercritical flow deposits to silt and mud. This work implies that the erosive and powerful Froude supercritical flow turbidity currents may have a substantial impact on erosional and depositional dynamics on deepwater slopes, especially on active margins due to the steep gradients and high sediment supply.  相似文献   

Tectonic environments of sapphire and ruby revealed by a global oxygen isotope compilation     

Jacqueline Wong  Charles Verdel 《International Geology Review》2018,60(2):188-195

Many sapphire and ruby occurrences are spatially linked with orogenic belts such as the Pan-African Orogen, the Himalayas, and regions of active or former subduction along the western margin of the Pacific Ocean. These gemstones have oxygen isotope compositions (δ¹⁸O) that span >45‰, reflecting the wide range of environments and conditions involved in corundum (Al₂O₃) formation. We compiled a global data base of sapphire and ruby δ¹⁸O, from which the following major groups of gemstones emerge: a dominant population of sapphires with δ¹⁸O centred around 5.5‰ (the mantle value) that is spatially related to regions of former subduction; a lesser population of sapphires and rubies with slightly higher δ¹⁸O that are associated with skarn and pegmatite; rubies with relatively low δ¹⁸O of 0‰–7‰ that occur in hydrothermally altered ultramafic metamorphic rocks in collision zones; and rubies with high δ¹⁸O of 14‰–25‰ that are found, almost exclusively, in Himalayan marble. The spatial distribution of the δ¹⁸O groups relative to plate boundaries provides insight into the two major periods of continental collision involved in sapphire and ruby formation: the Ediacaran collision of East and West Gondwana (the East African Orogeny) and the Cenozoic collision of India and Asia.  相似文献   

松辽盆地大陆深部科学钻探地球科学研究进展   总被引：10，自引：8，他引：2       下载免费PDF全文

侯贺晟  王成善  张交东  马峰  符伟  王璞珺  黄永建  邹长春  高有峰  高远  张来明  杨瑨  国瑞 《中国地质》2018,45(4):641-657

松辽盆地大陆深部科学钻探工程"两井四孔"之一的松科二井东孔(简称松科二井),位于黑龙江省安达市境内,于2018年5月26日正式完井。松科二井的科学目标涵盖古气候研究、资源能源探索、基础地质研究和发展深部探测技术四个方面。自2014年正式开钻以来,松科二井科学钻探工程组织实施了钻井取芯、原位测井、岩芯元素化学分析以及井周边深部结构探测等工作,目前已取得初步科研进展:获取长4134.81 m原位岩芯资料,完成了对白垩纪最完整最连续陆相地层厘米级高分辨率的精细刻画,初步建立起陆相地层标准剖面;发现了松辽盆地深部非常规天然气资源与盆地型干热岩良好的勘探开发前景;首次重建了白垩纪陆相百万年至十万年尺度气候演化历史,并发现白垩纪气候波动重大事件;揭示了古大洋板块俯冲、聚合的深部证据,为松辽盆地成因再认识及深层油气勘探提供了理论依据。松辽盆地大陆深部科学钻探工程的实施,对探索地球奥秘、解决深部能源环境等重大问题,具有重要意义,是"向地球深部进军"道路上迈出的坚实一步。  相似文献   

阿尔泰造山带喀纳斯群变质碎屑岩地球化学特征及年代学研究          下载免费PDF全文

李晓光  弓小平  裴国栋  韩琼  赵同阳  郑加行 《中国地质》2018,45(2):319-333

喀纳斯群为一套巨厚的中低压型浅变质碎屑岩系,主要由片岩、片麻岩、变质砂岩等组成,其形成时代未有统一的认识,致使阿尔泰构造带的构造演化过程争议较大。对喀纳斯群变质岩进行原岩恢复,认为该套变质岩为副变质岩,考虑到变质碎屑岩的成岩物质继承母岩特征和变质程度的影响,利用碎屑岩研究方法对元素地球化学特征进行探讨,显示出喀纳斯群变质碎屑岩原岩形成环境以大陆岛弧为主,兼有活动大陆边缘的特征,CIA、ICV指数反应出原岩经历了相对温暖、湿润的风化作用,成熟度较低。锆石U-Pb定年结果表明,最年轻的锆石年龄集中在(500±3.0)Ma,代表喀纳斯群的上限年龄,认为该套地层形成于晚寒武世晚期之前,为一套形成于大陆岛弧或活动大陆边缘的复理石建造。新元古代青白口纪初期基底裂解事件,暗示着阿尔泰构造带存在前寒武纪大陆地壳基底。  相似文献   

祁连造山带东段中寒武世深沟组中-基性火山岩锆石U-Pb年龄、地球化学特征及构造环境     

李瑞保  裴先治  王兴  陈有炘  李佐臣  刘成军  王盟  裴磊  张玉  颜全治  彭思钟  胡晨光 《地质通报》2018,37(4):589-603

拉脊山构造带南东端磨沟地区出露一套变安山岩夹片理化变玄武岩组合,其原岩分别为亚碱性拉斑系列安山岩和玄武岩。研究表明,变安山岩锆石U-Pb年龄为503.1±6.6Ma,形成于中寒武世。玄武岩稀土元素总量为93.40×10~(-6)～135.39×10~(-6),(La/Yb)_N值为2.76～3.64,δEu为0.87～1.00,微量元素蛛网图具有不相容元素富集特征,没有明显的Nb、Ta负异常,与板内火山岩特征相似。安山岩稀土元素总量低于玄武岩,而微量元素蛛网图具有富集大离子亲石元素Cs、Rb、Ba等,亏损高场强元素Nb、Ta、Ti等特征。岩石成因研究表明,玄武岩没有经历显著的地壳混染,为软流圈地幔石榴子石+尖晶石二辉橄榄岩低程度部分熔融的产物,而安山岩为地壳部分熔融的产物。构造环境判别表明,深沟组火山岩形成于大陆裂谷环境,表明祁连地块中部的拉脊山构造带南东端可能没有发育成熟的洋盆系统,随后在南祁连洋早古生代俯冲消减过程中以裂谷型岩石圈碎片的方式构造侵位于中祁连地块南缘。  相似文献   

Extension and magmatism in the Cerocahui basin,northern Sierra Madre Occidental,western Chihuahua,Mexico     

Bryan P. Murray  Cathy J. Busby  María de los Angeles Verde Ramírez 《International Geology Review》2015,57(5-8):893-918

The Sierra Madre Occidental of northwestern Mexico is the biggest silicic large igneous province of the Cenozoic, yet very little is known about its geology due to difficulties of access to much of this region. This study presents geologic maps and two new U-Pb zircon laser ablation inductively coupled plasma mass spectrometry ages from the Cerocahui basin, a previously unmapped and undated ~25 km-long by ~12 km-wide half-graben along the western edge of the relatively unextended core of the northern Sierra Madre Occidental silicic large igneous province. Five stratigraphic units are defined in the study area: (1) undated welded to non-welded silicic ignimbrites that underlie the rocks of the Cerocahui basin, likely correlative to Oligocene-age ignimbrites to the east and west; (2) the ca. 27.5–26 Ma Bahuichivo volcanics, comprising mafic-intermediate lavas and subvolcanic intrusions in the Cerocahui basin; (3) alluvial fan deposits and interbedded distal non-welded silicic ignimbrites of the Cerocahui clastic unit; (4) basalt lavas erupted into the Cerocahui basin following alluvial deposition; and (5) silicic hypabyssal intrusions emplaced along the eastern margin of the basin and to a lesser degree within the basin deposits.

The main geologic structures in the Cerocahui basin and surrounding region are NNW-trending normal faults, with the basin bounded on the east by the syndepositional W-dipping Bahuichivo–Bachamichi and Pañales faults. Evidence of syndepositional extension in the half-graben (e.g. fanning dips, unconformities, coarsening of clastic deposits toward basin-bounding faults) indicates that normal faulting was active during deposition in the Cerocahui basin (Bahuichivo volcanics, Cerocahui clastic unit, and basalt lavas), and may have been active earlier based on regional correlations.

The rocks in the Cerocahui basin and adjacent areas record: (1) the eruption of silicic outflow ignimbrite sheets, likely erupted from caldera sources to the east during the early Oligocene pulse of the mid-Cenozoic ignimbrite flare-up, mostly prior to synextensional deposition in the Cerocahui basin (pre-27.5 Ma); (2) synextensional late Oligocene mafic-intermediate composition magmatism and alluvial fan sedimentation (ca. 27.5–24.5 Ma), which occurred during the lull between the Early Oligocene and early Miocene pulses of the ignimbrite flare-up; and (3) post-extensional emplacement of silicic hypabyssal intrusions along pre-existing normal faults, likely during the early Miocene pulse of the ignimbrite flare-up (younger than ca. 24.5 Ma). The timing of extensional faulting and magmatism in the Cerocahui basin and surrounding area generally coincides with previous models of regional-scale middle Eocene to early Miocene southwestward migration of active volcanism and crustal extension in the northern Sierra Madre Occidental controlled by post-late Eocene (ca. 40 Ma) rollback/fallback of the subducted Farallon slab.  相似文献   

Middle Jurassic continental to marine transition in an extensional tectonics context: the Genna Selole Fm depositional system in the Tacchi area (central Sardinia,Italy)     

Luca Giacomo Costamagna 《Geological Journal》2016,51(5):722-736

In Eastern Sardinia during the early Middle Jurassic, Alpine Tethys opening triggered the rise of a temporary tectonic high. The high collapsed rapidly, was fragmented into separate blocks, and subsequently covered by continental, transitional, and finally shallow marine deposits forming a narrow depositional system comprising the Genna Selole Fm. Present‐day exposures in the southern part of the palaeo‐high allow the sedimentological evolution of the transgressive cover sequence to be ascertained. Initial terrestrial deposits comprise alluvial fan deposits located at the mouths of palaeovalleys. These pass into braid‐deltas and in the coastal areas located between adjacent valleys mouths, palustrine and coastal plain tidally‐influenced environments developed. These environments interfingered laterally and passed seaward into a transitional, siliciclastic to carbonate tidal environment. With the collapse of the tectonic high, the continental to transitional environments were transgressed with deposition of marine carbonates. A comparison with similar coeval deposits of the W‐Mediterranean domain has been undertaken. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

东昆仑南缘哥日卓托地区马尔争组砂岩碎屑组成、地球化学特征与物源构造环境分析   总被引：2，自引：0，他引：2  

裴先治  胡楠  刘成军  李瑞保  李佐臣  陈有炘  裴磊  刘战庆  陈国超  杨杰 《地质论评》2015,61(2):307-323

出露于东昆仑南缘布青山构造混杂岩带内的马尔争组沉积地层,其主体为一套沉积于被动大陆边缘构造环境的大陆斜坡相深海-半深海浊积岩。利用砂岩碎屑组分统计分析及岩石地球化学特征研究,探讨物源区源岩类型及其构造环境。砂岩骨架成分统计表明马尔争组砂岩主要类型为长石岩屑砂岩且成熟度较低,砂岩碎屑骨架成分为石英、长石、岩屑,含量平均值分别为44%、21%、35%,Dickinson三角图解显示其物源类型为再旋回造山带物源区和岩浆弧物源区的混合物源。砂岩岩石地球化学特征结果显示,马尔争组砂岩样品SiO,=58.12%~72.98%,均值67.77%,REE配分曲线总体表现为右倾,∑LREE/∑HREE=6.5~12.1,δEu=0.63~0.75,Eu具弱负异常,CIA值为56说明源岩遭受初级强度风化作用,具近源沉积特征。研究结果指示马尔争组砂岩物源区构造环境为大陆岛弧,源岩性质为长英质火山岩和花岗岩类源岩且主要来源于北侧东昆仑造山带加里东期岩浆弧与变质基底,沉积盆地类型为深海半深海盆地。它是古特提斯洋北支布青山阿尼玛卿洋演化历史过程中一次重要的沉积响应。  相似文献   

Microstratigraphy of a Miocene layered phosphatic pebble from the western margin of South Africa     

John S. Compton 《Sedimentology》2013,60(3):666-678

Detailed microstratigraphy and geochemistry of a single‐layered phosphatic pebble from the Southern Rocky Plateau at the Head of the Cape Canyon on the western margin of South Africa are utilized to reveal a complex interplay between deposition, erosion and authigenesis in the Miocene. The phosphatic pebble has three micrite and carbonate fluorapatite cemented layers separated by Fe‐rich hardground surfaces. The layers contain a diverse grain assemblage of reworked glauconite, phosphorite, detrital quartz and biogenic carbonate. Overlapping Sr‐isotope derived ages of point‐drilled samples from the three layers range from 19·1 to 17·6 Ma, although a single point near the outer edge of the uppermost layer has a Sr age of 12·8 to 10·4 Ma, and a reworked bivalve shell fragment from the middle layer has a Sr age of 26·3 to 24·6 Ma. The microstratigraphy of the phosphatic pebble provides evidence of multiple Baturin cycles, where periods of deposition and carbonate fluorapatite authigenesis are followed by reworking, erosion and precipitation of iron oxide hardground surfaces. The condensed microstratigraphy of the pebble is consistent with the regional depositional history of the area and indicates significant fluctuations in the depositional environment related to changes in sea‐level, sediment supply and upwelling along the western margin of southern Africa during the early to middle Miocene.  相似文献   

In situ zircon U–Pb and Hf–O isotopic results for ca. 73 Ma granite in Hainan Island: Implications for the termination of an Andean-type active continental margin in southeast China     

《Journal of Asian Earth Sciences》2014

We report in the paper integrated analyses of in situ zircon U–Pb ages, Hf–O isotopes, whole-rock geochemistry and Sr–Nd isotopes for the Longlou granite in northern Hainan Island, southeast China. SIMS zircon U–Pb dating results yield a crystallization age of ∼73 Ma for the Longlou granite, which is the youngest granite recognized in southeast China. The granite rocks are characterized by high SiO₂ and K₂O, weakly peraluminous (A/CNK = 1.04–1.10), depletion in Sr, Ba and high field strength elements (HFSE) and enrichment in LREE and large ion lithophile elements (LILE). Chemical variations of the granite are dominated by fractional crystallization of feldspar, biotite, Ti–Fe oxides and apatite. Their whole-rock initial ⁸⁷Sr/⁸⁶Sr ratios (0.7073–0.7107) and ε_Nd(t) (−4.6 to −6.6) and zircon ε_Hf(t) (−5.0 to 0.8) values are broadly consistent with those of the Late Mesozoic granites in southeast China coast. Zircon δ¹⁸O values of 6.9–8.3‰ suggest insignificant involvement of supracrustal materials in the granites. These granites are likely generated by partial melting of medium- to high-K basaltic rocks in an active continental margin related to subduction of the Pacific plate. The ca. 73 Ma Longlou granite is broadly coeval with the Campanian (ca. 80–70 Ma) granitoid rocks in southwest Japan and South Korea, indicating that they might be formed along a common Andean-type active continental margin of east–southeast Asia. Tectonic transition from the Andean-type to the West Pacific-type continental margin of southeast China likely took place at ca.70 Ma, rather than ca. 90–85 Ma as previously thought.  相似文献