Tracking the paleogene India-Arabia plate boundary     

《Marine and Petroleum Geology》2016

The location of the India-Arabia plate boundary prior to the formation of the Sheba ridge in the Gulf of Aden is a matter of debate. A seismic dataset crossing the Owen Fracture Zone, the Owen Basin, and the Oman Margin was acquired to track the past locations of the India-Arabia plate boundary. We highlight the composite age of the Owen Basin basement, made of Paleocene oceanic crust drilled on its eastern part, and composed of pre-Maastrichtian continental and oceanic crust overlaid by ophiolites emplaced in Early Paleocene on its western side. A major fossil transform fault system crossing the Owen Basin juxtaposed these two slivers of lithosphere of different ages, and controlled the uplift of marginal ridges along the Oman Margin. This transform system deactivated ∼40 Myrs ago, coeval with the onset of ultra-slow spreading at the Carlsberg Ridge. The transform boundary then jumped to the edge of the present-day Owen Ridge during the Late Eocene-Oligocene period, before seafloor spreading began at the Sheba Ridge. This migration of the plate boundary involved the transfer of a part of the Indian oceanic lithosphere formed at the Carlsberg Ridge to Arabia. This Late Eocene-Oligocene tectonic episode at the India-Arabia plate boundary is synchronous with a global plate reorganization event corresponding to geological events at the Zagros and Himalaya belts. The Owen Ridge uplifted later, in Late Miocene times, and is unrelated to any major migration of the India-Arabia boundary.  相似文献   

Formation,uplift and dissection of planation surfaces at passive continental margins – a new approach     

Peter Japsen  Johan M. Bonow  Paul F. Green  James A. Chalmers  Karna Lidmar‐Bergström 《地球表面变化过程与地形》2009,34(5):683-699

The usefulness of large‐scale, low‐relief, high‐level landscapes as markers of uplift events has become a subject of disagreement among geomorphologists. We argue that the formation of low‐relief surfaces over areas of large extent and cutting across bedrock of different age and resistance must have been guided by distinct base levels. In the absence of other options the most likely base level is sea level. We have analysed West Greenland landscapes in a recent study by combining the cooling history from apatite fission‐track analysis (AFTA) data with the denudation history from landscape analysis and the stratigraphic record. An important difference between our approach and that of classical geomorphology is that we now have the ability to document when thick sections of rocks have been deposited and then removed. The present‐day high‐level plateau in West Greenland is the remnant of a planation surface that was formed by denudation that lasted c. 20 million years during which up to 1 km of cover was removed after maximum burial at the Eocene–Oligocene transition. Here we present additional AFTA data to show that the planation surface is the end‐product of Cenozoic denudation even in basement areas and argue that Phanerozoic sediments – most likely of Cretaceous–Palaeogene age – must have been present prior to denudation. The planation surface was offset by reactivated faults and uplifted to present‐day altitudes of up to 2 km. The uplift occurred in two late Neogene phases that caused incision of valleys below the planation surface and their subsequent uplift. We therefore find that the elevated and deeply dissected plateau is evidence of episodic post‐rift uplift that took place millions of years after cessation of sea‐floor spreading west of Greenland. We suggest that other margins with similar morphology may also be characterized by episodic post‐rift uplift unrelated to the processes of rifting and continental separation, rather than being permanently uplifted since the time of rifting, as is commonly assumed. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Suspended sediment transport in the Gulf of Lions (NW Mediterranean): Impact of extreme storms and floods     

C. Ulses  C. Estournel  X. Durrieu de Madron  A. Palanques 《Continental Shelf Research》2008

In situ observations were combined with 3D modeling to gain understanding of and to quantify the suspended sediment transport in the Gulf of Lions (NW Mediterranean Sea). The outputs of a hydrodynamic–sediment transport coupled model were compared to near-bottom current and suspended sediment concentration measurements collected at the head of seven submarine canyons and at a shallow shelf site, over a 6-month period (November 2003–May 2004). The comparisons provide a reasonable validation of the model that reproduces the observed spatial and time variations. The study period was marked by an unusual occurrence of marine storms and high river inputs. The major water and sediment discharges were supplied by the Rhone, the largest Mediterranean river, during an exceptional flood accompanying a severe marine storm in early December 2003. A second major storm, with moderate flooding, occurred in February 2004. The estimate of river input during the studied period was 5.9 Mt. Our study reveals (i) that most of the particulate matter delivered by the Rhone was entrapped on the prodelta, and (ii) that marine storms played a crucial role on the sediment dispersal on the shelf and the off-shelf export. The marine storms occurring in early December 2003 and late February 2004 resuspended a very large amount of shelf sediment (>8 Mt). Erosion was controlled by waves on the inner shelf and by energetic currents on the outer shelf. Sediment deposition took place in the middle part of the shelf, between 50 and 100 m depth. Resuspended sediments and river-borne particles were transported to the southwestern end of the shelf by a cyclonic circulation induced by these onshore winds and exported towards the Catalan shelf and into the Cap de Creus Canyon which incises the slope close to the shore. Export taking place mostly during marine storms was estimated to reach 9.1 Mt during the study period.  相似文献   

Particle flux across the mid-European continental margin     

Avan N. Antia  Bodo von Bodungen  Rolf Peinert 《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(12):501

Results are presented from particle flux studies using sediment trap and current meter moorings along a transect at the European continental margin at 49°N within the EU-funded Ocean Margin Exchange (OMEX) project. Two moorings were placed, at the mid- and outer slope in water depths of 1500 and 3660 m, with traps at 600 and 1050 m and at 580, 1440 and 3220 m, respectively. Residual currents at the mid-slope follow the slope contour, whereas seasonal off-slope flow was registered at the outer slope. At 600 m on the slope fluxes are similar to those in the abyssal North Atlantic. The flux of all components (bulk dry weight, particulate organic and inorganic carbon, lithogenic matter and opal) increased with water depth. Highest fluxes were recorded at 1440 m at the outer slope, where off-slope residual currents mediate particle export. The injection of biogenic and lithogenic particles below the depth of winter mixing results in the export of particles from shallower waters. Calculated lateral fluxes of particulate organic carbon exceed the primary flux by over a factor of 2 at 1440 m on the outer slope. Estimated lateral fluxes of suspended particulate matter in the water column and intermediate nepheloid layers at the outer slope are potentially large compared to sinking fluxes measured by sediment traps. A comparison is made of particle flux at three continental margin sites and two sites in the adjacent open North Atlantic, from which it is seen that bulk and organic matter flux increases exponentially with proximity to the shelf break. The percentage contribution of particulate organic carbon to biogenic fluxes increases from a mean of 5.7% in the abyssal N. Atlantic to 13.9% at the continental margins.  相似文献   

Multifractal characterization of Vesuvio lava-flow margins and its implications     

G. Luongo  A. Mazzarella  G. Di Donna   《Journal of Volcanology and Geothermal Research》2000,101(3-4)

The digitized lava-flow margins of well-defined extended eruptions occurring at Vesuvio in 1760, 1794, 1861, 1906, 1929 and 1944 are found to follow fractal behaviours inside a scaling region enclosed between 50 and 400 m. Although the invariance region is well respected, the fractal dimension D varies from one lava flow to another: the more irregular the lava-flow margin, the larger the value of D. The ascertained dependence of D on the duration of premonitory activity, preceding the emission of lavas, might provide some insight into the inner volcanic processes before the eruption and into the dynamical processes operating during flow emplacement.  相似文献   

湖南龙潭煤系形成时的大地构造环境   总被引：4，自引：1，他引：3  

彭正奇 《煤田地质与勘探》1996,24(4):5-8

湖南龙潭煤系属于早二叠世末-晚二叠世初期的沉积,沉积类型复杂。江南隆起东南面,以双牌-长寿断裂为界,东西两侧分属不同的物源区。通过对龙潭煤系分布、沉积环境演化、岩相展布、岩浆活动、构造特征、砂岩矿物成分及化学成分的研究认为,早二叠世末-晚二叠世初,区内大地构造环境属于较活动的被动大陆边缘。   相似文献   

A scale-integrated exploration model for orogenic gold deposits based on a mineral system approach     

《地学前缘(英文版)》2020,11(3):719-738

Concept-based orogenic gold exploration requires a scale-integrated approach using a robust mineral system model.Most genetic hypotheses for orogenic gold deposits that involve near-surface or magmatic-hydrothermal fluids are now negated in terms of a global mineral system model.Plausible models involve metamorphic fluids,but the fluid source has been equivocal.Crustal metamorphic-fluid models are most widely-accepted but there are serious problems for Archean deposits,and numerous Chinese provinces,including Jiaodong,where the only feasible fluid source is sub-crustal.If all orogenic gold deposits define a coherent mineral system,there are only two realistic sources of fluid and gold,based on their syn-mineralization geodynamic settings.These are from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package,or release from mantle lithosphere that was metasomatized and fertilized during a subduction event,particularly adjacent to craton margins.In this model,CO_2 is generated during decarbonation and S and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 ℃.This orogenic gold mineral system can be applied to conceptual exploration by first identifying the required settings at geodynamic to deposit scales.Within these settings,it is then possible to define the critical gold mineralization processes in the system:fertility,architecture,and preservation.The geological parameters that define these processes,and the geological,geophysical and geochemical proxies and responses for these critical parameters can then be identified.At the geodynamic to province scales,critical processes include a tectonic thermal engine and deep,effective,fluid plumbing system driven by seismic swarms up lithosphere-scale faults in an oblique-slip regime during uplift late in the orogenic cycle of a convergent margin.At the district to deposit scale,the important processes are fluid focussing into regions of complex structural geometry adjacent to crustal-scale plumbing systems,with gold deposition in trap sites involving complex conjugations of competent and/or reactive rock sequences and structural or lithological fluid caps.Critical indirect responses to defined parameters change from those generated by geophysics to those generated by geochemistry with reduction in scale of the mineral system-driven conceptual exploration.  相似文献   

The Palmerville fault — a “fundamental” structure in North Queensland∗     

F. de Keyser 《Australian Journal of Earth Sciences》2013,60(2):273-278

The Palmerville Fault in North Queensland is an important structure with a probable length of at least 600 miles, extending from Princess Charlotte Bay in the north to Townsville in the south, and controlling the configuration of the coast line of eastern Cape York and at Halifax Bay. The fault forms the western boundary of both the Palaeozoic Hodgkinson Basin (Tasman Geosyncline) and of the Mesozoic Laura Basin, and has been active at least four times since the Silurian. The latest movements took place during the late Cainozoic.  相似文献   

Paleodrainage and fault development in the southern Perth Basin,Western Australia during and after the breakup of Gondwana from 3D modelling of the Bunbury Basalt     

H. K. H. Olierook  N. E. Timms  R. E. Merle  F. Jourdan  P. G. Wilkes 《Australian Journal of Earth Sciences》2013,60(3):289-305

The evolution of faults and paleodrainage patterns on the southwestern Australian passive margin during and after the breakup of Gondwana in the Early Cretaceous remains poorly understood. This contribution investigates the fault and paleodrainage evolution in the southern Perth Basin with the use of the ‘Bunbury Basalt’, the only lava flows known to be synchronous with continental breakup. New aeromagnetic data have been integrated with well intersections and outcrop constraints to establish the first 3D model of the Bunbury Basalt. The model reveals that flows are up to 100 m thick and are predominantly confined to two north–south-trending paleovalleys and their tributaries situated in the Bunbury Trough in the southern Perth Basin. The Donnybrook Paleovalley flow ponded in a paleovalley proximal to the Darling Fault and is truncated by the two later flows within the Bunbury Paleovalley, which is positioned centrally in the Bunbury Trough. Offsets of the Bunbury Basalt have been used to identify new northeast- and northwest-trending faults in the southern Perth Basin, and broad folding is interpreted as a consequence of drag into the Darling and Busselton faults. The model has been used to determine post-basalt net displacements for the Darling and Busselton faults of 370 and 210 m, respectively, and <175 m for the northeast and northwest-trending faults. The source vents for the Bunbury Basalt were probably located at extensional jogs at intersections between the Darling Fault and subordinate oblique faults. These results challenge the views on longstanding quiescence of the post-breakup western Australian passive margin.  相似文献   

Alkaline orogenic plutonism in the Karakorum batholith: the Upper Cretaceous Koz Sar complex (Karambar valley,N. Pakistan)     

François Debon  Naseer Ali Khan 《Geodinamica Acta》2013,26(4):145-160

Abstract

The Karakorum is located north of the India/Kohistan-Ladakh/Eurasia sutures. Along the Karambar valley, its axial batholith comprises four plutonic complexes. (1) The largest one represents the westerly continuation of the huge mid-Cretaceous calc-alkaline Hunza plutonic unit. This unit here displays a remarkable reverse zoning that would result from a differentiation at depth followed by multipulse intrusions. (2) A stock of subalkaline (i.e. intermediate between alkaline and calc-alkaline) granitoids (Warghut porphyritic granite). (3) A composite group of fine-grained granitoids. (4) The so-called Koz Sar alkaline complex (KSAC), a unique example of this composition of plutonism so far reported in the batholith. In addition, leucogranite dykes and rare alkaline mafic ones occur.

The KSAC is a heterogeneous and more or less deformed body, ca. 5 km wide and possibly 20 km long, comprising two coeval groups of rocks. (1) Medium- to coarse-grained rocks are the most representative members of the complex. They consist of metaluminous to slightly peralkaline monzonite, quartz monzonite, granite and leucogranite, with iron-rich mafic silicates and Fe-Ti oxide. These subsolvus granitoids define a strongly ferriferous alkaline series. Five monzonite and quartz monzonite samples yield an isochron Rb-Sr age of 88 ± 4 Ma (⁸⁷Sr/⁸⁶Sr_i = 0.70440 ± 7; MSWD = 1.7). (2) Fine-grained rocks (monzogabbro to quartz syenite) are compositionally comparable to the dark-coloured members of the preceding group.

The KSAC was emplaced into a post-collisional environment resulting from the accretion, maybe at least since Aptian times, of the Kohistan island arc to the Karakorum. Its alkaline character testifies to the development of extensional tectonics, a process compatible with an oblique collision and/or with the decrease, at the time of collision, of the convergence velocity between the two colliding terrenes. Available data suggest that this alkaline complex (1) is late-orogenic, (2) is genetically-related to the nearby subalkaline granitoids and originates from the same mantle-source with a small crustal contribution, and (3) represents the ultimate member of the mid-Cretaceous subduction-related plutonism emplaced into the Karakorum continental margin.  相似文献