首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 78 毫秒
1.
The mud volcano and sandstone intrusions complex occurring in the Boyadag anticline, western Turkmenistan, is the only well‐documented example of co‐existing, but not synchronous, mud volcanism and sand intrusion. Integrated field and laboratory evaluation investigates the spatial and genetic relations between the mud extrusion and the later sand intrusion. A sandstone dike and a pillar pierce mud volcano deposits on the crest of Boyadag anticline. Two more dikes occur near the escarpment caused by a crestal normal fault. The rising of mud and hydrocarbons from the Oligocene Maykop Fm. fed the mud volcano after the exposure of the Lower Pleistocene units at the core of the anticline. The main physical process that later led to sand fluidisation is identified as the progressive increase in pore fluid pressure, during a stage of reduced or null activity of the mud volcano, caused by the up‐dip migration of hydrocarbons from the deep basin into the Pliocene sandstone reservoir within the Boyadag anticline. The hydrocarbons generated in the source rock levels of the Maykop Fm., whereas the saline water involved in the sand fluidisation is identified as the connate water of the Pliocene Red Beds Fm. The pressure rise was responsible for the fracturing of the sealing units, already weakened by the crestal normal fault and the mud volcano feeding system. The sand intruded into sealing units and mud breccia deposits, also using the mud volcano conduit and the crestal normal fault as preferential pathways. During the present‐day background activity, the outcropping sandstone intrusions provide high permeability pathways for continuous fluid leakage, precluding the re‐establishment of high pressures in the reservoir.  相似文献   

2.
Mud volcanoes are geomorphological phenomena and there is a limited volume of knowledge about them. Output of a composition of water, mud, and gas forms the mud volcano phenomenon. Geographical distribution of mud volcanoes indicates their relationship with pressured, rapid and thick sedimentation, which is seen in both tectonically active and inactive zones. Naftlige mud volcano is located in the southwest of the Caspian Sea and west of Gomishan Wetland in Golestan Province, Iran. Since no study has ever been conducted with a specific focus on mud volcanoes, field and laboratory studies were carried out for the first time to overcome the shortage of library resources. The objective was to determine the composition of emerging mud and study its morphometric and geomorphic features so that there would be a method for identifying and introducing some unknown aspects of this mud volcano. Therefore, three samples of this mud volcano which were taken on 27 Apr., 2012 were tested and analyzed using X‐ray diffraction and X‐ray fluorescence techniques to determine the mineral and chemical composition. The results of this analysis showed that, in these three samples, silicon oxide with the chemical formula SiO2 had 40.88% volatile materials, 19.15% H2O Loss on Ignition (LOI) and 13.97% calcium oxide. Quartz, calcite and albite formed the three main phases of minerals.  相似文献   

3.
Pre-volcanic structure of the basement influences volcanism distribution and avalanche generation in volcanic edifices. Therefore, systematic studies of basement structure below volcanic chains are necessary to understand the deformation effects observed in the surface and vice versa. Based on a compilation of pre-existing data, interpretation of aerial photographs and satellite images, and a collection of structural data we analyzed morphological and structural features of the Cofre de Perote–Pico de Orizaba (CP–PO) volcanic chain and its basement. We have identified three sets of regional lineaments that are related to basement trends. (1) NW 55° SE fractures are parallel to anticline folds observed in Cretaceous rocks that originated during Laramide shortening. These folds present an abrupt morphology observed only in the eastern flank but that is likely to continue below the volcanic chain. (2) NE 55° SW fractures are parallel to normal faults at the basement. We infer that these basement faults confine the CP–PO chain within a stepped graben with a total normal displacement of about 400 m. These faults have been active through time since they have affected volcanic deposits and induced the emplacement of monogenetic vents. Notably, lineaments of monogenetic vents concentrate where the basement is relatively shallow. (3) Another set of faults, oriented N–S, has been observed affecting the scarce basement outcrops at the western flank of the chain covered by lacustrine deposits. Lineaments measured in the volcanic edifice of Pico de Orizaba correlate with the regional trends.In particular, the NE 55° SW alignment of monogenetic vents and fractures at Pico de Orizaba suggest that the same dike trend exists within the volcanic edifice. A normal fault with similar orientation was documented at the NE continuation of an alignment crossing the volcanic edifice along the Jamapa canyon. In the absence of magmatic activity related to collapses, the displacement of NE 55° SW faults represents a potential triggering mechanism for generating avalanches at Pico de Orizaba volcano. Instability is enhanced by the presence of N–S trending fractures crossing the entire volcanic edifice and E–W fractures affecting only the present day cone. We conclude that mechanical instability of the volcanic chain is influenced by the basement structure heterogeneity, but further detailed studies are necessary at individual volcanoes to evaluate their effects on volcano deformation.  相似文献   

4.
《Basin Research》2018,30(2):217-236
This study documents the seismic expression of the conduits underlying over 350 mud volcanoes that were erupted in an area of the western Nile Cone in the past 5.3 Myr. The study is based on a c. 4300 km2 3D seismic survey. The conduits are interpreted to transect the >1000‐m‐thick Messinian Evaporite succession, demonstrating that the eruptive process is sufficiently dynamic to breach the formidable seal represented by the evaporites. The mud volcano conduits are remarkably similar in geometry and seismic characteristics to many previously described examples of fluid escape pipes. They are vertical to subvertical structures with a crudely cylindrical geometry, but that can either widen or narrow upwards towards their upper terminations in the mud volcano edifices. Imaging at depth within the Messinian Evaporites and pre‐evaporite successions is more uncertain, but direct sampling of mud from surface volcanoes suggests a pre‐Messinian source, confirming the seismic interpretation that they root within presalt stratigraphy. A conceptual model for the genesis of these mud volcano conduits through salt is proposed, for which hydraulic fracturing is driven by high overpressures that developed in the presalt source stratigraphy as a response to the Messinian Salinity Crisis. Dissolution and removal of evaporites resulting in fracturing and collapse via a stoping mechanism is a slow process by comparison to hydraulic fracturing but is argued to potentially contribute to conduit formation. The analysis presented here demonstrates the potential for bypassing a >1‐km‐thick unit of sealing evaporites via focused fluid and sediment mobilisation from deeper overpressured cells in other salt basins worldwide, and has significant implications for hydrocarbon exploration, CO2 sequestration and nuclear waste disposal.  相似文献   

5.
Interacting river discharge, tidal oscillation, and tropical rainfall across the 22,000 km2 Orinoco delta plain support diverse fresh and brackish water ecosystems. To develop environmental baseline information for this largely unpopulated region, we evaluate major coastal plain, shallow marine, and river systems of northeastern South America, which serves to identify principal sources and controls of water and sediment flow into, through, and out of the Orinoco Delta.The regional analysis includes a summary of the geology, hydrodynamics, sediment dynamics, and geomorphic characteristics of the Orinoco drainage basin, river, and delta system. Because the Amazon River is a major source of sediment deposited along the Orinoco coast, we summarize Amazon water and sediment input to the northeastern South American littoral zone. We investigate sediment dynamics and geomorphology of the Guiana coast, where marine processes and Holocene history are similar to the Orinoco coast.Major factors controlling Orinoco Delta water and sediment dynamics include the pronounced annual flood discharge; the uneven distribution of water and sediment discharge across the delta plain; discharge of large volumes of water with low sediment concentrations through the Río Grande and Araguao distributaries; water and sediment dynamics associated with the Guayana littoral current along the northeastern South American coast; inflow of large volumes of Amazon sediment to the Orinoco coast; development of a fresh water plume seaward of Boca Grande; disruption of the Guayana Current by Trinidad, Boca de Serpientes, and Gulf of Paria; and the constriction at Boca de Serpientes.  相似文献   

6.
《Basin Research》2018,30(Z1):437-451
Many prospective sedimentary basins contain a variety of extrusive volcanic products that are ultimately sourced from volcanoes. However, seismic reflection‐based studies of magmatic rift basins have tended to focus on the underlying magma plumbing system, meaning that the seismic characteristics of volcanoes are not well understood. Additionally, volcanoes have similar morphologies to hydrothermal vents, which are also linked to underlying magmatic intrusions. In this study, we use high resolution 3D seismic and well data from the Bass Basin, offshore southern Australia, to document 34 cone‐ and crater‐type vents of Miocene age. The vents overlie magmatic intrusions and have seismic properties indicative of a volcanic origin: their moderate–high amplitude upper reflections and zones of “wash‐out” and velocity pull‐up beneath. The internal reflections of the vents are similar to those found in lava deltas, suggesting they are composed of volcaniclastic material. This interpretation is corroborated by data from exploration wells which penetrated the flanks of several vents. We infer that the vents we describe are composed of hyaloclastite and pyroclasts produced during submarine volcanic eruptions. The morphology of the vents is typical of monogenetic volcanoes, consistent with the onshore record of volcanism on the southern Australian margin. Based on temporal, spatial and volumetric relationships, we propose that submarine volcanoes can evolve from maars to tuff cones as a result of varying magma‐water interaction efficiency. The morphologies of the volcanoes and their links to the underlying feeder systems are superficially similar to hydrothermal vents. This highlights the need for careful seismic interpretation and characterization of vent structures linked to magmatic intrusions within sedimentary basins.  相似文献   

7.
A succession of depositional sequences, recording middle-late Pleistocene and Holocene glacial–interglacial cycles, documents the impact of short-term tectonic deformation on the western Adriatic margin. The western Adriatic margin is part of the Apennine foreland which was intensely, though variably, deformed during the Meso-Cenozoic evolution of the Adriatic region from a passive margin to a foreland basin. The study area extends offshore Gargano Promontory, an uplifted sector of the Adriatic foreland, and includes three major deformation belts located along or cross-strike to the margin: (1) the NW-SE Gallignani-Pelagosa ridge, (2) the WSW-ENE Tremiti-Pianosa high (both located north of Gargano) and (3) the W-E to NW-SE Gondola fault deformation belt (in the south Adriatic). Long-term deformation along these tectonic lineaments is documented on conventional low-frequency seismic profiles by regional folds and faults affecting Eocene–Miocene units overlain by dominantly draping Plio-Quaternary deposits. At this scale of observation, only north of Gargano Promontory there is some evidence of Plio-Quaternary units thinning against structural highs, thus suggesting that tectonic deformation was protracted through this interval. Based on new high-resolution seismic data, we show that deformation along these pre-existing tectonic structures continued during the Quaternary, affecting middle-late Pleistocene and even Holocene units on the shelf and upper slope north and south of Gargano Promontory. These recent deformations consist of gentle folds and high-angle faults, locally producing topographic relief that affects the stratigraphy and thickness of syn-tectonic deposits. We interpret the small-scale, shallow faults and gentle folds affecting middle-late Pleistocene and Holocene deposits, north and south Gargano Promontory, as the evidence of ongoing foreland deformation along inherited regional fold and fault systems.  相似文献   

8.
In this article, we document a large number of focused fluid escape structures using high quality 2D seismic reflection data and multibeam bathymetry data from a poorly known area at the intersection of the northern South China Sea (SCS) and the western SCS. Three types of focused fluid escape systems are identified and described: mud volcanoes, pipes and associated pockmarks. The mud volcanoes occur singly or as clustered groups. The overpressure driving the mud volcanism is argued herein to be related to the generation of thermogenic hydrocarbons. The clustered distributions are related to localized tectonic uplift in the basin. Pipes mainly occur within the Guangle Uplift or accompany the mud volcano clusters. The pipes located within the Guangle Uplift are attributed to carbonate dissolution caused by hydrothermal fluids. Fluids ascended through these structures and were expelled at the palaeo‐seabed or present seabed forming palaeo‐pockmarks and present‐day pockmarks. Some ‘mega‐pockmarks’ show evidence of enlargement due to bottom currents. The marginal basins of the SCS are petroliferous, with attention gradually shifting to the deep‐water area. Our results show that fluid migration must be taken into account when assessing seabed stability. This analysis also improves our understanding the petroleum geology in the study area, and is also useful for predicating where chemosynthetic ecosystems may be located.  相似文献   

9.
Relationships between tectonic framework and gravity-driven phenomena have been investigated in an area of the Central Apennines (Italy) characterised by high relief. The north–south, half-dome shaped Maiella anticline lies in the easternmost part of the Apennine fold-and-thrust belt. Its backlimb is bordered by the Caramanico Fault, a normal fault with a maximum downthrown of about 3.5 km that separates the western slope of the Maiella Massif from the Caramanico Valley. The southwestern Maiella area is affected by deep-seated gravitational slope deformation indicated by major double crest lines, down-hill and up-hill facing scarps, a pattern of crossing trenches, bulging at the base of slopes and the presence of different types of landslide and talus slope deposits.The onset and development of deep-seated gravitational slope deformations and the location of Quaternary, massive rockslope failures have been strongly influenced by the structural framework and tectonic pattern of the anticline. Deep-seated gravitational slope deformation at Mt. Macellaro–Mt. Amaro ridge has developed along the Maiella western, reverse slope in correspondence with the anticline axial culmination; it is bordered at the rear by a NNW–SSE oriented, dextral, strike-slip fault zone and has an E–W direction of rock mass deformation. Closer to the southern plunging area of the anticline, gravity-driven phenomena show instead a N–S and NW–SE direction, influenced by bedding attitude.3D topographic models illustrate the relationship between deep-seated gravitational slope deformation and massive rockslope failures. The Campo di Giove rock avalanche, a huge Quaternary failure event, was the result of an instantaneous collapse on a mountaine slope affected by a long-term gravity-driven deformation.  相似文献   

10.
We describe the internal structure of a multi‐kilometre scale mud volcano edifice from the South Caspian Sea using three‐dimensional (3D) seismic reflection data leading to a reconstruction of the volcano system's eruptive history. By adapting elements of classic seismic stratigraphy to the study of this volcano, we have found its edifice to consist of a series of stacked mud cones. This internal architecture is most likely to have formed as a result of repeated episodes of expulsion of a fluid‐mud mix. Underlying the stack of cones is an asymmetric fault‐bounded caldera measuring approximately 2 km in diameter. This caldera shows close structural similarity to the trapdoor type of magmatic caldera. Based on the geometrical relationships of individual mud cones to this caldera, we conclude that caldera‐like collapse of the edifice floor initiated following the deposition of the first mud cone (the pioneer cone). Growth of the caldera continued until the later stages of edifice evolution when it eventually abated. This eruptive history shows strong similarities to recent models for magmatic caldera eruption cycles. The study therefore highlights the potential analogue value of mud volcano systems to the study of igneous volcanism. Furthermore, it identifies 3D seismic data as a potentially useful tool in reconstructing the history of mud volcanic eruption and fluid and sediment expulsion from sedimentary basins.  相似文献   

11.
黄镇国  张伟强 《地理科学》1995,15(2):109-117
  相似文献   

12.
The Pakuashan anticline is uniquely suited for study of the forward and lateral growth of fault-related folds. The Pakuashan ridge development arises from the late Quaternary uplift of the most external thrust zone of the western foothills of Taiwan. From Kaoshiung to Taichung, recent and active westward thrusting occurs at the front of the foothills. The Pakuashan anticline, trending N 150°E in the northern part to N 000° in the southern part, has been active throughout the Quaternary period. This activity is marked by geological structures, tectonic geomorphology and seismicity. A multisource and multiscale approach to study of the continental collision setting has been undertaken to combine tectonics, sedimentology and geomorphology. Studies of fracture patterns allow identification of two main features of stress orientations: a WNW/ESE compression direction, and E–W and N–S extension directions. Quantitative geomorphic parameters have been used to define the morphotectonic evolution and to infer tectonic style along the mountain front. Geomorphic evidence provides significant information on the processes that govern lateral propagation of an active anticline. Quaternary terraces are uplifted, tilted and folded over the Pakuashan ridge. Drainage systems in areas of active compression give information on the thrust zone structures and their development. Steep drainage and high local relief indicate that the Pakuashan anticline forms a well-defined zone of high uplift, especially in the southern part. The two main controls on drainage in that area are rock strength in the hanging wall and propagation of the deformation towards the south.  相似文献   

13.
Three successive zones of fault‐related folds disrupt the proximal part of the northern Tian Shan foreland in NW China. A new magnetostratigraphy of the Taxi He section on the north limb of the Tugulu anticline in the middle deformed zone clarifies the chronology of both tectonic deformation and depositional evolution of this collisional mountain belt. Our ～1200‐m‐thick section encompasses the upper Cenozoic terrigenous sequence within which ～300 sampling horizons yield an age span of ～8–2 Ma. Although the basal age in the Taxi He section of the Xiyu conglomerate (often cited as an indicator of initial deformation) is ～2.1 Ma, much earlier growth of the Tugulu anticline is inferred from growth strata dated at ～6.0 Ma. Folding of Neogene strata and angular unconformities in anticlines in the more proximal and distal deformed zones indicate deformation during Miocene and Early Pleistocene times, respectively. In the Taxi He area, sediment‐accumulation rates significantly accelerate at ～4 Ma, apparently in response to encroaching thrust loads. Together, growth strata, angular unconformities, and sediment‐accumulation rates document the northward migration of tectonic deformation into the northern Tian Shan foreland basin during the late Cenozoic. A progradational alluvial–lacustrine system associated with this northward progression is subdivided into two facies associations at Tugulu: a shallow lacustrine environment before ～5.9 Ma and an alluvial fan environment subsequently. The lithofacies progradation encompasses the time‐transgressive Xiyu conglomerate deposits, which should only be recognized as a lithostratigraphic unit. Along the length of the foreland, the locus of maximum shortening shifts between the medial and proximal zones of folding, whereas the total shortening across the foreland remains quite homogeneous along strike, suggesting spatially steady tectonic forcing since late Miocene times.  相似文献   

14.
New classification system for mass transport complexes in offshore Trinidad   总被引：3，自引：1，他引：2  
This paper delineates our use of 10 708 km2 of three‐dimensional (3D) seismic data from the continental margin of Trinidad and Tobago West Indies to describe a series of mass transport complexes (MTCs) that were deposited during the Plio‐Pleistocene. This area, situated along the obliquely converging boundary of the Caribbean/South American plates and proximal to the Orinoco Delta, is characterized by catastrophic shelf‐margin processes, intrusive/extrusive mobile shales and active tectonism. Extensive mapping of different stratigraphic intervals of the 3D seismic survey reveals several MTCs that range in area from 11.3 to 2017 km2. Three types of MTCs are identified: (1) shelf‐attached systems that were fed by shelf‐edge deltas whose sediment input is controlled by sea‐level fluctuations and sedimentation rates; (2) slope‐attached systems, which occur when upper‐slope sediments catastrophically fail owing to gas‐hydrate disruptions and/or earthquakes and (3) locally detached systems, formed when local instabilities in the seafloor trigger relatively small collapses. Such classification of the relationship between slope mass failures and sourcing regions enables a better understanding of the nature of initiation, length of development history and petrography of such MTCs. 3D seismic enables more accurate calculation of deposit volumes, improves deposit imaging, and, thus, increases the accuracy of physical and computer simulations of mass failure processes.  相似文献   

15.
F. Gutirrez 《Geomorphology》2004,57(3-4):423-435
The salt valleys over the axis of the salt-cored anticlines in the Paradox fold and fault belt (Canyonlands, Utah and Colorado) are created by subsidence of the anticline crests. Traditionally, the collapse of the anticlinal crests was attributed to dissolution of the salt walls (diapirs) forming the anticline cores. Recent studies based on scaled physical models and field observations propose that the salt valleys are a result of regional extension and that salt dissolution had only a minor influence in the development of the axial depressions. This paper presents several arguments and lines of evidence that refute the tectonic model and support the salt dissolution subsidence interpretation.The development of contractional structures in salt dissolution experiments led the advocates of the tectonic interpretation to reject the dissolution-induced subsidence explanation. However, these salt dissolution models do not reproduce the karstification of salt walls in a realistic way, since their analog involves removal of salt from the base of the diapirs during the experiments. Additionally, numerous field examples and laboratory models conducted by other authors indicate that brittle subsidence in karst settings is commonly controlled by subvertical gravity faults.Field evidence against the regional extension model includes (1) a thick cap rock at the top of the salt walls, (2) the concentration of subsidence deformation structures along the crest of the anticlines (salt walls), (3) deformational structures not consistent with the proposed NNE extension, like crestal synforms and NE–SW grabens, (4) dissolution-induced subsidence structures controlled by ring faulting, revealing deep-seated dissolution, (5) large blocks foundered several hundred meters into the salt wall, (6) evidence of recent and active dissolution subsidence, and (7) the aseismic nature of the recently active collapse faults. Although underground salt dissolution seems to be the main cause for the generation of the salt valleys, this phenomenon may have been favored by regional extension tectonics that enhance the circulation of groundwater and salt dissolution.  相似文献   

16.
The Miocene Waitemata Basin was deposited on a moving base provided by the Northland Allochthon, which was emplaced in the Late Oligocene, as a new convergent plate boundary was established in northern New Zealand. The basin experienced complex interaction between tectonic and gravity‐driven shallow deformation. Spectacular examples of the resulting structures exposed on eastern Whangaparaoa Peninsula 50 km north of Auckland provide a world‐class example of weak rock deformation, the neglected domain between soft‐sediment and hard rock deformation. Quartz‐poor turbidite sequences display a protracted sequence of deformations: D1, synsedimentary slumping; D2, large scale deeper‐seated sliding and extensional low‐angle shearing, associated with generation of boudinage and broken formation; D3, thrusting and folding, indicating transport mostly to the SE; D4, thrusting and folding in the opposite direction; D5, further folding, including sinistral shear; D6, steep faults. The deformation sequence suggests continuous or intermittent southeastward transport of units with increasing sedimentary and structural burial. By phase D3, the rocks had passed from the soft‐sediment state to low levels of consolidation. However, with a compressive strength of ～5 MPa they are weak rocks even today. Such weak‐rock deformation must be important in other sedimentary basins, especially those associated with active convergent plate boundaries and with immature source areas for their sediments.  相似文献   

17.
Deep‐marine deposits provide a valuable archive of process interactions between sediment gravity flows, pelagic sedimentation and thermohaline bottom‐currents. Stratigraphic successions can also record plate‐scale tectonic processes (e.g. continental breakup and shortening) that impact long‐term ocean circulation patterns, including changes in climate and biodiversity. One such setting is the Exmouth Plateau, offshore NW Australia, which has been a relatively stable, fine‐grained carbonate‐dominated continental margin from the Late Cretaceous to Present. We combine extensive 2D (~40,000 km) and 3D (3,627 km2) seismic reflection data with lithologic and biostratigraphic information from wells to reconstruct the tectonic and oceanographic evolution of this margin. We identified three large‐scale seismic units (SUs): (a) SU‐1 (Late Cretaceous)—500 m‐thick, and characterised by NE‐SW‐trending, slope‐normal elongate depocentres (c. 200 km long and 70 km wide), with erosional surfaces at their bases and tops, which are interpreted as the result of contour‐parallel bottom‐currents, coeval with the onset of opening of the Southern Ocean; (b) SU‐2 (Palaeocene—Late Miocene)—800 m‐thick and characterised by: (a) very large (amplitude, c. 40 m and wavelength, c. 3 km), SW‐migrating, NW‐SE‐trending sediment waves, (b) large (4 km‐wide, 100 m‐deep), NE‐trending scours that flank the sediment waves and (c) NW‐trending, 4 km‐wide and 80 m‐deep turbidite channel, infilled by NE‐dipping reflectors, which together may reflect an intensification of NE‐flowing bottom currents during a relative sea‐level fall following the establishment of circumpolar‐ocean current around Antarctica; and (c) SU‐3 (Late Miocene—Present)—1,000 m‐thick and is dominated by large (up to 100 km3) mass‐transport complexes (MTCs) derived from the continental margin (to the east) and the Exmouth Plateau Arch (to the west), and accumulated mainly in the adjacent Kangaroo Syncline. This change in depositional style may be linked to tectonically‐induced seabed tilting and folding caused by collision and subduction along the northern margin of the Australian plate. Hence, the stratigraphic record of the Exmouth Plateau provides a rich archive of plate‐scale regional geological events occurring along the distant southern (2,000 km away) and northern (1,500 km away) margins of the Australian plate.  相似文献   

18.
The Colombian accretionary complex forms the active convergent margin of the North Andes block of South America beneath which the east Panama Basin of the Nazca plate is subducted at a rate of 50–64 km Myr?1. Multichannel seismic reflection data, collected as part of RRS Charles Darwin cruise CD40, image a series of well-developed forearc basins along the length of the margin, bounded on their oceanward side by an active accretionary complex and on their landward side by oceanward-dipping continental basement. Sedimentary sequences within the forearc basins indicate successive landward migration of the basin depocentre as the structural high bounding its oceanward edge is forced upward and landward by continued growth of the accretionary complex. Uplift beneath the oceanward side of the basins has resulted in progressive landward rotation of the older sedimentary sequences. Prominent seismic reflectors across the basins show a complex onlap–offlap relationship between successive sequences that reflects the interplay between tectonic uplift, sediment supply, differential sediment compaction and basement subsidence due to loading. A numerical model has been devised to investigate how Miocene to Recent forearc basin stratigraphy is controlled by progressive growth of the accretionary complex resulting in elevation of the outer-arc high and landward motion of the rear of the complex up the seaward-dipping backstop formed by the leading edge of the continental lithosphere. The effects of sediment accretion are modelled by treating the accretionary complex as a doubly vergent, noncohesive Coulomb wedge, where forces exerted by the proto- and retro-wedges must be balanced for the system to be in equilibrium. The model generates synthetic basin-fill architecture over a series of steps, each of which represents the deposition of individual sedimentary sequences and their subsequent deformation due to wedge growth. The model accounts for differential sediment compaction and the flexural response of the underlying lithosphere to changes in load distribution over time. Forearc basin evolution is simulated for various rates of sediment supply to the forearc and accretionary complex growth until the synthetic basin-fill geometry matches the observed geometry. The model enables either the rate of accretionary wedge growth or the rate of sediment supply to the forearc basin to be established. The technique is generally applicable to those convergent margins with forearc basins that have developed between an actively accreting wedge and a seaward-dipping backstop. Other examples include Peru, S. Chile, Sumatra and Barbados.  相似文献   

19.
Pliocene–Quaternary basins of the Ionian islands evolved in a complex tectonic setting that evolved from a mid to late Cenozoic compressional zone of the northern external Hellenides to the rapidly extending Pliocene–Quaternary basins of the Peloponnese. The northern limit of the Hellenic Trench marks the junction of these two tectonic regimes. A foreland-propagating fold and thrust system in the northern external Hellenides segmented the former Miocene continental margin basin in Zakynthos and permitted diapiric intrusion of Triassic gypsum along thrust ramps. Further inboard, coeval extensional basins developed, with increasing rates of subsidence from the Pliocene to Quaternary, resulting in four principal types of sedimentation: (1) condensed shelf-sedimentation on the flanks of rising anticlines; (2) coarse-grained sedimentation in restricted basins adjacent to evaporitic diapirs rising along thrust ramps; (3) larger basins between fold zones were filled by extrabasinal, prodeltaic mud and sand from the proto-Acheloos river; (4) margins of subsiding Quaternary basins were supplied at sea-level highstands by distal deltaic muds and at lowstands by locally derived coarse clastic sediment.  相似文献   

20.
On the basis of the major metal grades from the super-large Bainiuchang Ag-rich polymetallic ore deposit, enrichment evolution processes were divided into three populations by using a new multiple time-series model. Population 1 shows the highest temporal/spatial autocorrelation with the ore-forming processes. Population 3 is considered to be a white noise process. The lithologies of populations 1 and 2 are closely related to submarine exhalative hydrothermal sedimentation. By using a semi-Markov process and a dynamic lithologic ratio parameter model, the paleogeographic environment of the bathyal basin in which the Bainiuchang Agrich polymetallic ore deposit formed was simulated. The result of the simulation suggests that four major submarine exhalation cycles occurred during basin evolution. Hydrothermal sedimentary metallization took place in the middle stage of each cycle. Hydrothermal sedimentation in each of the four cycles suggests an evolution from weak to strong to stronger to weak. Debris and turbidity currents related to syndepositional faulting along the northwestern margin of the basin and submarine hydrothermal exhalation originated from vents and flowed from northwest to southeast. A three-dimensional, finite-element method was used to simulate quantitatively the dynamic evolution of the temperature field of heat fluid circulation. A model is proposed that allows for the submarine heat fluid circulation from seawater that percolates downward, the upflow along a syndepositional falut to exhalation on the seafloor, and the formation of lenticular ore bodies in a single tectonic pulse. Comparison of the simulated temperature field and the mixing population of thermometric data of fluid inclusions suggests that the major submarine exhalation took about 35,000 years and that after 15,000 years from the initial establishment of the temperature field, the temperature of heat fluid circulation at the vents reached a maximum of 280°C.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号