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1.
This article outlines geomorphological and tectonic elements of the Afar Depression, and discusses its evolution. A combination of far-field stress, due to the convergence of the Eurasian and Arabian plates along the Zagros Orogenic Front, and uplift of the Afar Dome due to a rising mantle plume reinforced each other to break the lithosphere of the Arabian–Nubian Shield. Thermal anomalies beneath the Arabian–Nubian Shield in the range of 150 °C–200 °C, induced by a rising plume that mechanically and thermally eroded the base of the mantle lithosphere and generated pulses of prodigious flood basalt since ∼30 Ma. Subsequent to the stretching and thinning the Afar Dome subsided to form the Afar Depression. The fragmentation of the Arabian–Nubian Shield led to the separation of the Nubian, Arabian and Somalian Plates along the Gulf of Aden, the Red Sea and the Main Ethiopian Rift. The rotation of the intervening Danakil, East-Central, and Ali-Sabieh Blocks defined major structural trends in the Afar Depression. The Danakil Block severed from the Nubian plate at ∼20 Ma, rotated anti-clockwise, translated from lower latitude and successively moved north, left-laterally with respect to Nubia. The westward propagating Gulf of Aden rift breached the Danakil Block from the Ali-Sabieh Block at ∼2 Ma and proceeded along the Gulf of Tajura into the Afar Depression. The propagation and overlap of the Red Sea and the Gulf of Aden along the Manda Hararo–Gobaad and Asal–Manda Inakir rifts caused clockwise rotation of the East-Central Block. Faulting and rifting in the southern Red Sea, western Gulf of Aden and northern Main Ethiopian Rift superimposed on Afar. The Afar Depression initiated as diffused extension due to far-field stress and area increase over a dome elevated by a rising plume. With time, the lithospheric extension intensified, nucleated in weak zones, and developed into incipient spreading centers.  相似文献   

2.
A combination of palaeomagnetic, seismological, gravitational, aeromagnetic and geochemical observations, as well as geological and regional considerations are strongly indicative of anticlockwise rotational movements of the Danakil Alps and formation of new oceanic crust in the Northern Afar Triangle. The decreasing amount of spreading in the Southern Red Sea is compensated by en chelon crustal spreading (formation of oceanic crust in a continental environment) in the Danakil-Afar Depression. Here, the geophysical properties are generally intermediate between the more typical continental (Ethiopia) and oceanic (Red Sea, Gulf of Aden) data. Such intermediate type crust is proposed to be caused by “oceanization” of formerly continental crust, i. e. fragmentation and basification through massive dyke injections (mantle diapirism). The structure and evolution of the wider Afar Triangle, East-African Rift System, Red Sea and Gulf of Aden are used to derive a model for possible stages during initial continental break-up and compared with selected, similarly structured parts of the n-Atlantik. The continental break-up probably develops in the following stages: 1. general uplift associated with surface fracturing above an asthenospheric diapir (uplift), 2. development of linear “Scheitel”-Grabensystems along the crest of the uplift or uplift chains (rupture), 3. graben with (contaminated) volcanism stage (volcanism), 4. “oceanization” of the developing depression through fragmentation and basification by massive oceanic and/or contaminated dyke-injections of the former continental crust along several sporadically active lineaments, 5. “crustal spreading” on land or concentration of mantle derived, oceanic crust-injections along one major lineament in a dry, continental environment, 6. “evaporit-stage of sea-floor spreading” with sporadic seawater connections to an open marine basin and 7. “ocean-floor spreading” in the deep-sea environment of advanced oceanic troughs. The derivation of these stages basically involves the addition of “sea-floor spreading” processes (oceanization, crustal-, sea- and ocean-floor spreading) to the well known sequence: Hebung — Spaltung — Vulkanismus (Cloos, 1939) and relate it to mantle-diapirism processes. All the above stages are recognizable along the Afro-Arabian Rifts and seem to have morphological equivalents in the Atlantic.  相似文献   

3.
The western part of Yemen is largely covered by Tertiary volcanics and is bounded by volcanic margins to the west (Red Sea) and the south (Gulf of Aden). The Oligo–Miocene evolution of Yemen results from the interaction between the emplacement of the Afar plume, the opening of the Red Sea, and the westward propagation of the Gulf of Aden. Structural and microtectonic analyses of fault slip data collected in the field reveal that the volcanic margins of Yemen are affected by three main extensional tectonic events. The chronological order of these events is as follows: first E–W extension was associated with the emplacement of volcanic traps of Yemen, then NE–SW extension was related to the Red Sea rifting, and finally, the volcanic margin was submitted to N160°E extension, perpendicular to the overall trend of the Gulf of Aden, which we interpret as induced by the westward propagation of the oceanic ridge of the Gulf of Aden.  相似文献   

4.
J.D. Fairhead 《Tectonophysics》1973,20(1-4):261-267
Seismic refraction profiles now number 9 in the Gulf of Aden and 15 in the Red Sea with a further intensive study by the Cambridge University group between latitudes 22 and 23°N. The results of these surveys indicate that the main trough of the Gulf of Aden is underlain by oceanic crust while only the deep axial zone and a questionable amount of the main trough of the Red Sea are underlain by oceanic crust.

Seismic reflexion profiles reveal the nature of Layer 1 and the upper surface of Layer 2. A strong subbottom reflector is found beneath the main trough of the Red Sea at 0.5 km but is found to be absent in the axial zone. This survey together with the refraction work and geological evidence suggests a complex history for the main trough of the Red Sea. Reflexion profiles and dredging in the Gulf of Aden indicate that the thickness of sediments increases away from the central rough zone and that the sediment is underlain by volcanic material.  相似文献   


5.
The history of sea level within the Red Sea basin impinges on several areas of research. For archaeology and prehistory, past sea levels of the southern sector define possible pathways of human dispersal out of Africa. For tectonics, the interglacial sea levels provide estimates of rates for vertical tectonics. For global sea level studies, the Red Sea sediments contain a significant record of changing water chemistry with implications on the mass exchange between oceans and ice sheets during glacial cycles. And, because of its geometry and location, the Red Sea provides a test laboratory for models of glacio-hydro-isostasy. The Red Sea margins contain incomplete records of sea level for the Late Holocene, for the Last Glacial Maximum, for the Last Interglacial and for earlier interglacials. These are usually interpreted in terms of tectonics and ocean volume changes but it is shown here that the glacio-hydro-isostatic process is an additional important component with characteristic spatial variability. Through an iterative analysis of the Holocene and interglacial evidence a separation of the tectonic, isostatic and eustatic contributions is possible and we present a predictive model for palaeo-shorelines and water depths for a time interval encompassing the period proposed for migrations of modern humans out of Africa. Principal conclusions include the following. (i) Late Holocene sea level signals evolve along the length of the Red Sea, with characteristic mid-Holocene highstands not developing in the central part. (ii) Last Interglacial sea level signals are also location dependent and, in the absence of tectonics, are not predicted to occur more than 1–2 m above present sea level. (iii) For both periods, Red Sea levels at ‘expected far-field’ elevations are not necessarily indicative of tectonic stability and the evidence points to a long-wavelength tectonic uplift component along both the African and Arabian northern and central sides of the Red Sea. (iv) The observational evidence is consistent with tectonic and isostatic processes both operating over the past 300,000 years without requiring changes in the time averaged (over a few thousand years) tectonic rates. (v) Recent bathymetric data for the Bab al Mandab region have been compiled to confirm the location and depth of the sill controlling flow in and out of the Red Sea. Throughout the last 400,000 years the Red Sea has remained open to the Gulf of Aden with cross sectional areas at times of glacial maxima about 2% of that today. (vi) The minimum channel widths connecting the Red Sea to the Gulf of Aden at times of lowstand occur south of the Hanish Sill. The channels are less than 4 km wide and remain narrow for as long as local sea levels are below ?50 m. This occurs for a number of sustained periods during the last two glacial cycles and earlier. (vii) Periods suitable for crossing between Africa and Arabia without requiring seaworthy boats or seafaring skills occurred periodically throughout the Pleistocene, particularly at times of favourable environmental climatic conditions that occurred during times of sea level lowstand.  相似文献   

6.
The seasonal cycle of temperature—salinity variations in the Bab el Mandab region (southern Red Sea) is described using CTD data collected during four cruises spread over the period May 1995—August 1997. A two layer system exists during early summer, winter and spring while a three layer system exists during summer. During summer, a large amount of the Gulf of Aden water intrudes into the Bab el Mandab region; up to the northern limit (14.5‡N). The quantity of Red Sea water that flows into the Gulf of Aden is maximum during the winter and minimum during the summer  相似文献   

7.
A number of basins are observed to extend inland from the coasts on both sides of the Gulf of Aden. The basins are orientated at approximately right angles to the spreading direction and intersect the coasts at the meeting of sheared and rifted continental margins. They appear to be grabens, one wall of which is continuous with the half graben of the neighbouring rifted margin. It is suggested that these were once parts of a number of discrete rifts arranged en-echelon along a zone of lithospheric weakness during the early opening of the Gulf of Aden, which became redundant when transform faults formed. The proposed development of rifts and transform faults is similar to that of a spreading centre, transform fault, spreading centre pattern developed in the freezing wax model of Oldenburg and Brune (1975). The Gulf of Suez at the northern end of the Red Sea is interpreted in a similar way since it has a number of features in common with the basins in the continents adjacent to the Gulf of Aden.  相似文献   

8.
Newly discovered outcrops of the middle Pleistocene Benot Ya'aqov Formation are strongly disturbed due to recent tectonic activity along the Dead Sea Rift. The lacustrine-fluviatile sediments of this formation comprise the littoral facies of a paleo-lake that occupied the adjacent Hula Basin. Acheulian artifacts, found embedded in the formation, have typical African characteristics. The geographical position of the site (the northern extension of the East African Red Sea Rift System) is important for understanding hominid diffusion from Africa to Eurasia.  相似文献   

9.
The Arabian Plate is important and unique in many ways. The worker wants to highlight the important features characterizing the Arabian Plate. It is a unique fit of the earth's surface jig saw puzzle, different than all other lithospheric plates. It has the three known main tectonic plate boundaries, divergent, convergent and conservative ones. These boundaries are the Red Sea and Gulf of Aden, Zagros-Taurus and Dead Sea, respectively. It has three main well-defined and sharp plate boundaries, and it is surrounded by three major plates, African, Eurasian and Indian plates. The Red Sea and Gulf of Aden form the divergent boundary and spreading center. The Dead Sea Transform Fault (the Gulf of Aqaba Transform Fault) represents the conservative boundary and transform fault system. The Zagros-Taurus Thrust (Zagros-Taurus-Bitlis Thrust and Fold Belt) represents the convergent boundary and collision zone. The Arabian Plate incorporates a wide range and variety and subvariety of all three rock types, igneous, metamorphic and sedimentary rocks, this in addition to all kinds of structures. Among these are folding with major fold belts, faulting, foliation, lineation and diapirism. Transform, transcurrent, normal, graben, reverse, thrust faults are all represented one way or another. The tectonics of the Arabian shield, which forms a major part of the Arabian Plate, has long tectonic history prior to the formation of the Red Sea. After the opening and formation of the latter, the tectonics of the Arabian shield became affected and controlled by its tectonics. The Arabian Plate includes the Arabian Platform which has a relatively different setting of tectonics represented by the Central Arabian Graben. The Arabian Plate contains one of the best representative outcropped ophiolite sequences in the world. The Arabian Plate most importantly incorporates most of world oil reserve. Seismic and volcanic activities are also manifested and affected many areas in the Arabian Plate.  相似文献   

10.
The tectonic position of Egypt in the northeastern corner of the African continent suggests that it may possess significant geothermal resources, especially along its eastern margin. The most of the thermal springs in Egypt are located along the shores of Gulf of Suez and Red Sea. These springs are probably tectonic or nonvolcanic origin associated with the opening of the Red Sea—Gulf of Suez rifts, where the eastern shore of the Gulf of Suez is characterized by superficial thermal manifestations including a cluster of hot springs with varied temperatures. Hammam Faraun area consists of the hottest spring in Egypt where the water temperature is 70°C. Conceptual as well as numerical models were made on the Hammam Faraun hot spring based on geological, geochemical, and geophysical data. The models show that the heat source of the hot spring is probably derived from high heat flow and deep water circulation controlled by faults associated with the opening of the Red Sea and Gulf of Suez rifts.  相似文献   

11.
The volcanic and sedimentary successive paleogeographic reconstructions, as well the volcanic emissions as the fluvial, lacustrine and marine deposits, are compared to the tectonic mechanisms, and show that the geologic history is controlled:
  1. During Pliocene and lower Pleistocene times, by a collapse tectonics in the Red Sea - Aden Gulf area with a correlative uplift of the Tadjoura - Ali Sabîh hörst (a southern prolongation of the Danakil horst), and by a tectonic shear according to a NE-SW trend, which gives rise to NW-SE trending uplifts and basins (Nazaret phase of the Ethiopian rift).
  2. From the middle Pleistocene time, by the progressive opening, according to an EW direction, of the Gulf of Tadjoura, as a western prolongation of the Aden rift. A correlative epiglyptic arching, according to an EW direction, is located westwards. It appears as a superimposed structure with respect to the previous building.
The successive coastal uplifts since the lower Pleistocene are correlated to the successive alluvial deposits, which fit one-another, until the Holocene time included.  相似文献   

12.
Large areas of north-east Africa were dominated by regional extension in the Late Phanerozoic. Widespread rifting occurred in the Late Jurassic, with regional extension culminating in the Cretaceous and resulting in the greatest areal extent and degree of interconnection of the west, central and north African rift systems. Basin reactivation continued in the Paleocene and Eocene and new rifts probably formed in the Red Sea and western Kenya. In the Oligocene and Early Miocene, rifts in Kenya, Ethiopia and the Red Sea linked and expanded to form the new east African rift system.This complex history of rifting resulted in failed rift basins with low to high strain geometries, a range of associated volcanism and varying degrees of interaction with older structures. One system, the Red Sea rift, has partially attained active seafloor spreading. From a comparison of these basins, a general model of three-dimensional rift evolution is proposed. Asymmetrical crustal geometries dominated the early phases of these basins, accompanied by low angle normal faulting that has been observed at least locally in outcrop. As rifting progressed, the original fault and basin forms were modified to produce larger, more through-going structures. Some basins were abandoned, others experienced reversals in regional dip and, in general, extension and subsidence became focused along narrower zones near the rift axes. The final transition to oceanic spreading was accomplished in the Red Sea by a change to high angle, planar normal faulting and diffuse dike injection, followed by the organization of an axial magma chamber.  相似文献   

13.
The Tertiary granitic intrusive body(～21 Ma) of the Jabal Sabir area was emplaced during the early stages of the Red Sea opening.This intrusive body occupies the southern sector of Taiz City.It is triangular in shape,affected by two major faults,one of which is in parallel to the Gulf of Aden,and the other is in parallel to the eastern margin of the Red Sea coast.The petrogenesis of such a type of intrusion provides additional information on the origin of the Oligo-Miocene magmatic activity in relation to the rifting tectonics and evolution of this part of the Arabian Shield.The granitic body of Jabal Sabir belongs to the alkaline or peralkaline suite of A-type granites.It is enriched in the REE.The tight bundle plot of its REE pattern reflects neither tectonism nor metamorphism.This granite body is characterized by high alkali(8.7%-10.13%),high-field strength elements(HFSE),but low Sr and Ba and high Zn contents.The abundance of xenoliths from the neighboring country rocks and prophyritic texture of the Jabal Sabir granite body indicate shallow depths of intrusion.The major and trace elements data revealed a fractional crystallization origin,probably with small amounts of crustal contamination.It is interpreted that the Jabal Sabir intrusion represents an anorogenic granite pertaining to the A-type,formed in a within-plate environment under an extensional tectonic setting pertaining to rift-related granites.  相似文献   

14.
This study of the Afro-Arabian gräben, which concentrates on the region between Kenya and the Levant reviews their evolution that begun not earlier than in the latest Oligocene or in the lower Miocene. The gräben continue to sink in several major downfaulting phases, especially during the transitional times of Miocene to Pliocene, of Pliocene to Pleistocene and in the Mid-Pleistocene. We have no proof of erstwhile major graben structures in the crystalline Precambrian basement or in the pre-Oligocene sedimentary cover revived during the young Cenozoics that could have redeemed the formation of the Afro-Arabian megagräben. Significant faults in the pre-Oligocene sedimentary cover are seldom observed. Where they occur, their tectonic direction scarcely runs parallel to the principal trend of the Cenozoic graben. At best these ancient faults may have had an impact on the development of cross — and diagonal faulting which played also a role in the disposition of the subgräben, grabensplays and other offshoots of the main gräben. Equally rarely has parallelism of trend between the basement metamorphics as well as their intrusive dykes and that of the main graben lineations been established. The Afro-Arabian gräben originated in a lower Tertiary peneplain of regional dimension which had expanded over large part of Gondwana. The graben dissection thus took place regardless of former tectonic highs and lows such as swells and basins — a phenomenon that negates the theory of key-stone dropping as a result of preceding upwarping. The occasional impression of vaulting with the graben as its axis is purely of morphological significance; it is due to “isostatic” uplifting and tilting of the main horsts attached to the main graben. Besides, most megahorsts are not “halfhorsts” but huge blocks mountains (Levant, Etbai, Ethiopia, Danakil, Yemen) bordered on both flanks by major tensional faults with throws of thousands of meters. These major uplifts, which are especially noticed in the Plio-Pleistocene, caused, moreover, the removal of the sedimentary cover by erosion and denudation in the elevated parts of the graben shoulders and its hinterland. The few known outcrops of Cretaceous-Eocene in the coastal area of the Red Sea, believed to be indications of ancient marine gulfs and thus forerunners of the Rift valley are in all likelihood the relics of such coverbeds that were saved from erosion in the down dropped blocks of the graben. The surveyed marginal faults are normal dip-slips of average 70° dip. These remained in the ensuing taphrogenic episodes the “localized” fixed graben frames. In the interior of the graben they are followed by a Vorberge zone consisting of tilted blocks that implicate also subsidiary horsts and gräben. In the superdimensional rifts of Afar and Red Sea, the subsidiary gräben and horsts of the Vorberge zone may approach a width comparable to that of the East Levant rift valleys. In the axial part of the Afar, Red Sea and Gregory Rift valley appears as youngest, that is, Pleistocene structural element a distinct graben-in-graben or rift-in-rift. This young structure is much less developed in the graben of the Gulf of Aden. The Aden graben differs also in other aspects from the pattern of the Red Sea, particularly in its submarine axial topography and in the peculiar transversal fault offsets, both morphotectonic features reminiscent of the Indian mid-oceanic ridges. A comparison of geophysical, especially of gravity measurements, carried out in the various main gräben reveals very conflicting results. While higher positive Bouguer values led to the conjecture of heavy magmatic material in the bottom of the rift-in-rift of the Red Sea, in most of the Afar fault-funnel and in the entire Gregory Rift valley there prevails an unusual large gravity deficiency that would point to an extremely thick crust. This is all the more remarkable as both rift valleys and horsts of Ethiopia and of Kenya are dominated by huge basaltic trap lavas and by other basic volcanic material. The hypothesis of anticlockwise rotation and drifting of the Arabian peninsula (including its supposed impact on the orogenic origin of the Zagros fold belt) has many pitfalls.
  1. As the taphrogenic destruction is not restricted to the intercontinental Afro-Arabian gräben, but extended far into the Mediterranen and into the Indian Ocean, any anticlockwise rotation of Arabia must exceed the 7° postulated movement.
  2. Yemen and Ethiopia, that is Arabia and Africa, were in the Miocene still a continuous continent. When they became separated in the Pliocene by the Bab el Mandeb splay, northern Sinai and northernmost Egypt had been transformed into a landlocked isthmus that has remained a continental bridge to this day. In fact at the end of the Miocene the Red Sea graben had already been turned — though for a short period — into an enclosed evaporitic basin.
  3. As regards the axial graben-in-graben of the Red Sea that especially prompted the assumption of a drift between Africa and Arabia, its Pleistocene age would demand a drifting rate of half a meter per year. There are, however, at the coastal area of the Red Sea no prehistoric, historic or recent witnesses of lateral stretching at the Red Sea and certainly not of such excess. The deduced annual drift of half a meter there, exceed even the most optimistic calculations and images hitherto made by the adherents of such large drifting as has been postulated to have taken place between Africa and South America.
  4. Finally, in the studies on drifts — and this also applies to the question of horizontal fault displacement — there is wanting a proper discussion on the mechanical deformations to which the rigid crustal parts must have been subjected in the course of such intensive tearing apart motions.
  相似文献   

15.
The Red Sea represents an extreme marine environment, with high salinity, high temperature and low level of nutrients, complicating the application of standard geochemical palaeotemperature proxies. In order to investigate the applicability of the TEX86 (TetraEther indeX of GDGTs with 86 carbons) proxy for sea surface temperature (SST) in the Red Sea, the distribution of glycerol dialkyl glycerol tetraether membrane lipids (GDGTs) in sediments from the Red Sea and the Gulf of Aden were examined. Against expectations, TEX86 values for the Red Sea do not show a simple linear relationship with SST and deviate from the global core top calibration. In the northern Red Sea, at temperatures between 25 and 28 °C, the values increase linearly with SST, whereas in the southern Red Sea, at temperatures above 28 °C, TEX86 decreases with increasing temperature. Factors like seasonality and depth of production, salinity and nutrient availability, as well as diagenetic overprint or influence of allochtonous terrestrial lipids, cannot explain this pattern. However, the observed TEX86 relationship with SST could be explained by the presence of a hypothetical endemic Crenarchaeota population in the Red Sea with a specific TEX86 vs. SST relationship. In the Southern Red Sea, a two-component mixing model implies an exponential decrease in the endemic population towards the Gulf of Aden. Thus, the application of the TEX86 as a palaeotemperature proxy in the Red Sea is likely only possible for the northern Red Sea area with the specific SST vs. TEX86 relationship determined in this study and potentially for the whole Red Sea basin during glacials, when water exchange with the Indian Ocean was more restricted than today and the endemic archaeal lipid distribution was not affected by transport from the Indian Ocean. Our results suggest that distinct populations of Crenarchaeota in extreme environments such as evaporitic basins may have different membrane composition, necessitating application of another calibration than the global core top calibration for TEX86 palaeothermometry.  相似文献   

16.
This paper describes the updated stratigraphy, structural framework and evolution, and hydrocarbon prospectivity of the Paleozoic, Mesozoic and Cenozoic basins of Yemen, depicted also on regional stratigraphic charts. The Paleozoic basins include (1) the Rub’ Al-Khali basin (southern flanks), bounded to the south by the Hadramawt arch (oriented approximately W–E) towards which the Paleozoic and Mesozoic sediments pinch out; (2) the San’a basin, encompassing Paleozoic through Upper Jurassic sediments; and (3) the southern offshore Suqatra (island) basin filled with Permo-Triassic sediments correlatable with that of the Karoo rift in Africa. The Mesozoic rift basins formed due to the breakup of Gondwana and separation of India/Madagascar from Africa–Arabia during the Late Jurassic/Early Cretaceous. The five Mesozoic sedimentary rift basins reflect in their orientation an inheritance from deep-seated, reactivated NW–SE trending Infracambrian Najd fault system. These basins formed sequentially from west to east–southeast, sub-parallel with rift orientations—NNW–SSE for the Siham-Ad-Dali’ basin in the west, NW–SE for the Sab’atayn and Balhaf basins and WNW–ESE for the Say’un-Masilah basin in the centre, and almost E–W for the Jiza’–Qamar basin located in the east of Yemen. The Sab’atayn and Say’un–Masilah basins are the only ones producing oil and gas so far. Petroleum reservoirs in both basins have been charged from Upper Jurassic Madbi shale. The main reservoirs in the Sab’atayn basin include sandstone units in the Sab’atayn Formation (Tithonian), the turbiditic sandstones of the Lam Member (Tithonian) and the Proterozoic fractured basement (upthrown fault block), while the main reservoirs in the Say’un–Masilah basin are sandstones of the Qishn Clastics Member (Hauterivian/Barremian) and the Ghayl Member (Berriasian/Valanginian), and Proterozoic fractured basement. The Cenozoic rift basins are related to the separation of Arabia from Africa by the opening of the Red Sea to the west and the Gulf of Aden to the south of Yemen during the Oligocene-Recent. These basins are filled with up to 3,000 m of sediments showing both lateral and vertical facies changes. The Cenozoic rift basins along the Gulf of Aden include the Mukalla–Sayhut, the Hawrah–Ahwar and the Aden–Abyan basins (all trending ENE–WSW), and have both offshore and onshore sectors as extensional faulting and regional subsidence affected the southern margin of Yemen episodically. Seafloor spreading in the Gulf of Aden dates back to the Early Miocene. Many of the offshore wells drilled in the Mukalla–Sayhut basin have encountered oil shows in the Cretaceous through Neogene layers. Sub-commercial discovery was identified in Sharmah-1 well in the fractured Middle Eocene limestone of the Habshiyah Formation. The Tihamah basin along the NNW–SSE trending Red Sea commenced in Late Oligocene, with oceanic crust formation in the earliest Pliocene. The Late Miocene stratigraphy of the Red Sea offshore Yemen is dominated by salt deformation. Oil and gas seeps are found in the Tihamah basin including the As-Salif peninsula and the onshore Tihamah plain; and oil and gas shows encountered in several onshore and offshore wells indicate the presence of proven source rocks in this basin.  相似文献   

17.
The Cenozoic volcanic activity in northeastern Nigeria began with the intrusion into the Benue trough of a trachyte-phonolite suite of plugs 22-11 m.y. ago. Later activity, which was more widespread and dominantly basaltic in character, began some 7 m.y. ago and has continued until very recent times. It resulted in basaltic plugs and lava plateaux within the Benue trough, and cinder cones and lavas on the Jos Plateau.The initial 87Sr/86Sr ratios of nine of the fifteen analyzed basic and alkalic rocks lie in the range 0.7025–0.7032, and the highest ratio measured is 0.7129.The main group of trachytes and phonolites are considered to be fractional melts derived from the upper mantle, modified in small part by potassium feldspar crystal fractionation. Two Sr-rich phonolite plugs may have a separate origin from the main group of trachytes and phonolites.The Cenozoic volcanic activity in northeastern Nigeria is probably related to the nearby Cameroun volcanic line. The concentration of plugs within the Benue trough may reflect internal adjustments along old lines of weakness within the African lithosphere plate, in response to synchronous changes affecting the plate's external dimensions and internal structure, such as the growth of the Red Sea and the Gulf of Aden, and the volcanism of the east African rift valley.  相似文献   

18.
《Precambrian Research》2001,105(2-4):357-369
The Precambrian basement of Yemen occupies a key location in the Pan-African orogen of Gondwana. This paper reviews geological, isotopic and geochronological data and presents new Pb- and Nd-isotope data which help define distinct gneiss terranes within this basement, constraining correlations of these terranes with neighbouring regions of Saudi Arabia and Somalia. Existing whole-rock Pb- and Nd-isotopic data are also summarised. These data should facilitate a more objective assessment of the contribution of the Yemen Precambrian to Cenozoic magmatism associated with the opening of the Red Sea and the Gulf of Aden.  相似文献   

19.
The Red Sea is part of the Afro-Arabian rift system, the world’s largest active continental rift system. The early opening phases of the Red Sea Rift were accompanied by continental flood magmatism. Large volumes of flood basalts emplaced in the Oligocene through to the present time at discrete eruptive centres along the western margin of the Arabian plate. Some of these rocks, in Southern Yemen, were investigated by geochemistry and K/Ar whole rock (WR) geochronology. In addition, the Jabal At-Tair (JAT) volcano, in the Red Sea trough, was investigated by geochemistry, with particular concern to the lavas of the last eruption of September 2007. The magmatism of Yemen is divided in: Oligocene–Early Miocene trap series (YOM), Tertiary intrusive rocks, and Late Miocene–recent volcanic series (YMR). YOM and Tertiary intrusions yielded K/Ar WR ages mostly in the range 31.6–16.6 Ma. Three older ages of 34.6, 35.4 and 49.0 Ma, if confirmed by further investigation, could suggest an Eocenic pre-trap phase of magmatic activity. YMR samples yielded K/Ar WR ages between 2.52 and 8.14 Ma. Both YOM and YMR basalts are alkaline, but YMR tend to be richer in alkalis than YOM. JAT basalts have subalkaline tholeiitic character, are geochemically homogeneous, and in the hygromagmaphile element spidergrams display increasing normalised concentrations from Cs to Ta, then decreasing up to Lu, with negative spikes of Nb, K and Pb. YOM have patterns almost identical to those of JAT, whereas YMR have higher normalized concentrations of all trace elements, but REE. The geochemical characteristics of JAT, YOM and YMR, framed in the broader context of the Red Sea Rift, are mostly consistent with a model of continental uplift and magmatism occurring across a linear, north–south axis of mantle upwelling, which intersects the Red Sea axis at the initiation site of axial seafloor spreading. The symmetrical propagation of the rift system to opposite sides of the N–S lineament, along the Red Sea axis, resulted in the observed symmetrical distribution of geochemical signatures of the Red Sea basalts and Yemen continental magmas.  相似文献   

20.
During mid-Oligocene to early-Miocene times the northeastern Afro-Arabian plate underwent changes, from continental breakup along the Red Sea in the south, to continental collision with Eurasia in the north and formation of the N–S trending Dead Sea fault plate boundary. Concurrent uplift and erosion of the entire Levant area led to an incomplete sedimentary record, obscuring reconstructions of the transition between the two tectonic regimes. New well data, obtained on the continental shelf of the central Levant margin (Qishon Yam 1), revealed a uniquely undisturbed sedimentary sequence which covers this time period. Evaporitic facies found in this well have only one comparable location in the entire eastern Mediterranean area (onland and offshore) over the same time frame — the Red Sea–Suez rift system. Analysis of 4150 km of multi and single-channel seismic profiles, offshore central Levant, shows that the sequence was deposited in a narrow basin, restricted to the continental shelf. This basin (the Haifa Basin) evolved as a half graben along the NW trending Carmel fault, which at present is one of the main branches of the Dead Sea fault. Re-evaluation of geological data onland, in view of the new findings offshore, indicates that the Haifa basin is the northwestern-most of a larger series of basins, comprising a failed rift along the Qishon–Sirhan NW–SE trend. This failed rift evolved spatially parallel to the Red Sea–Suez rift system, and at the same time frame. The Carmel fault would therefore seem to be related to processes occurring several million years earlier than previously thought, before the formation of the Dead Sea fault. The development of a series of basins in conjunction with a young spreading center is a known phenomenon in other regions worldwide; however this is the only known example from across the Arabian plate.  相似文献   

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