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c1 oc50C10001500_j_///.///II:I? 0:3502000,rniIFigure 3.Vertical distributions of plankton biomass (wet weight in mg) inthe North Pacific Ocean (NPO), in the Mediterranean (MS) and inthe Red Sea (RS) (from WEIKERT, 1982).306
THE CRUST BENEATH THE RED SEA - GULF OF ADEN RIFTSYSTEM:A REVIEW1HOW KIN WONG AND EGON T. DEGENSGeologisch-Palaontologisches Institut und Museum der Universitat HamburgBundestraae 55, D-2000 Hamburg 13, FRGABSTRACTThe Red Sea - Gulf of Aden - East African Rift System is one of the key areas to studyrift-drift processes. Within this single system, geodynamic processes ranging from uplift,block-faulting, volcanism, and seismic activity, to hydrothermal circulation and seafloor spreading arerepresented. In this paper we review the geological, geophysical, sedimentological and geochemicalcharacteristics of the Red Sea-Gulf of Aden, with special emphasis on the structure and evolution ofthe crust, as well as on their implications to continental rifting and plate accretion.INTRODUCTIONNorthern and northeastern Africa has always attracted the attention of geoscientists,particularly from the hydrogeological, tectonic and geomorphological points of view. With the recentpopularity of plate tectonics, this area together with its neighbours to the east and south has gainedeven greater significance. While the East African Rift is generally believed to be characterized bycontinental rifting, the Gulf of Aden and the Red Sea already have undergone active seafloorspreading. These three tectonic features meet at the Afar Depression, a triple junction with activevolcanism and earthquake activity attesting to ongoing tectonism.Rifting is a process generally believed to precede seafloor spreading. Studies of continentalrifts in Europe, North America and Africa (ILLIES and FUCHS, 1974; ILLIES and MUELLER,1970; MAGUIRE and KHAN, 1980; NOLET and MUELLER, 1982; PRODEHL, 1979; RAMBERGand NEUMANN, 1978) suggest that rifting may start with the diapiric intrusion of sub-lithosphericmaterial from a depth of several hundred kilometers into the lithosphere. A zone of tension isproduced along which partition of the continental crust eventually occurs. OXBURGH andTURCOTTE (1974), on the other hand, argued that the tensional failure at the earth's surface maysimply be a response to membrane stresses set up as the plate moves over a non-spherical earth. Otherunresolved questions include the spatial distribution of hypocenters in a rift system, the seismicvelocity structure of the crust and upper mantle within the graben and over its flanks, and the detailedstructure of the crust/mantle transition.The process of crustal formation at oceanic ridges is still not well-understood. It is generallyagreed that under the ridge crest, a mixture of mantle material and basaltic melt is being injected into thecrust. The basaltic melt, being lighter, migrates upwards and accumulates near the top of the injectiondiapir as magma chambers (BALLARD and VAN ANDEL, 1977; BRYAN and MOORE, 1977;LEWIS, 1983). These magma chambers are very limited in lateral extent (at most a few km), and it isunlikely that they represent a steady state phenomenon, certainly not in the Atlantic. The extrusion ofpillow basalts and lava flows from such magma chambers onto the seafloor is episodic, both in spaceand in time. Under the ridge axis, plate-driving forces produce an extensional strain which facilitateshydrothermal circulation, since crack propagation as a result of convective cooling is enhanced.Eventually, hydrothermal alteration of the crust and infilling of cracks by precipitation take place.Whether the Moho represents a petrologic boundary or is determined by the depth to whichhydrothermal penetration extends is still not resolved.Modified from a paper that appeared in Mitt.Geo1.-Palbnt. Inst., Univ. Hamburg, Georg Knetsch Heft 56, p. 53-94.307
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Intergovernmental Oceanographic Com
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of the IOC Marine Pollution Monitor
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PageMARGINAL SEASSTORM SURGES IN TH
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Marine PollutionAt present, marine
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THE INDIAN OCEAN --- AN ENVIRONMENT
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The subtropical anticyclonic gyre i
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GEOLOGICALBecause of its asymmetric
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RADIOACTIVE AND THERMAL WASTESIn co
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RESEARCH AND MONITORING ACTIVITIESM
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2-5, Mn 3-7, Zn 8-31, Fe 35-94, Pb
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Localized problems, both short-term
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HOLEMAN, J.N. (1968). The sediment
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UNEP/UNIDO (1982a). Industrial sour
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0-5-24 -I I I I I I I I I 11--25- A
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I*in '0( U N '0- '0 '0 N , p d'0I I
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C'EO IIFigure 6. Observations of oi
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Table 2.Ranges of Dissolved heavy m
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d.2 W2n2 n z0U.IzIO N m mENmIYEE*Ed
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Table 6. Population and related dat
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PROBLEMS IN THE PHYSICAL OCEANOGRAP
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B2: How does the Agulhas Current in
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0Q0mbWbvx(U49
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Figure 6 Average wind stress curl f
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THE DESTRUCTION OF THE TETHYS AND P
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part of the Seychelles-Mascarene bl
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Much of the old Tethys seafloor has
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when there was little or no movemen
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scouring of the sediments by cold b
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CANDE, S.C. and MUTTER, J.C. (1982)
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SHACKLETON, N.J. and KENNETT, J.P.
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0EYNz 10c2XaYWeKB20LuUz a5 cl300 10
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CALCAREOUS FORAMINIFERANANNOFOSSIL
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GEOLOGICAL-GEOPHYSICAL MAPPING OF T
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The latest tectonic generalization
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LE PICHON, X. and HEIRTZLER, J.R. (
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AN EXAMINATION OF THE FACTORS THAT
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is the specific volume anomaly. Po
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circulation. At Nagappattinam, Madr
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Table 1.MarmagaoCochin1969-781958-7
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tFigure 2. An idealized coastal cur
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STATION : BOMBAY~ J , F I M .- , A
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STATION : COCHIN, J , F , M , A , M
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3007STATION : MADRASI J I F , M I A
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STATION : CALCUTTA, J l F , M , A ,
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RED TIDE§ IN THE INDO-WEST PACIFIC
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were observed as early as 1770 duri
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diarrhetic shellfish poisoning (DSP
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GACUTAN, R.Q., TABBU, M.Y., AUJERO,
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Table 1.Clinical symptoms of variou
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Table 3. Fish species implicated in
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FIGURE CAPTIONSFigure la. Trichodes
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(*14aEE15aHH15c120
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MINERAL RESOURCES OF THE INDIAN OCE
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tonnes of monazite. Similar deposit
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Madagascar and the Red Sea. Within
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South Australian Basin: (Figs. 10-1
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Offshore placers are likely to occu
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MILLIMAN, J.D. (1974). Marine Carbo
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Thailand Tin 5560 (1980) NA 4.2 (19
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Table 2. The range (in percent) of
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Table 4. Chemical composition of po
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141FIGURE - 1
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~IT 73qw p' le' IS IFigure 4. Map s
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@A5 3 9 93 3 s 3 m4P 8O C ' . .' ,
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Figure 10. Map showng the abundance
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Figure 14. Map showing the distribu
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IFigure 17. Marine mineral explorat
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central are corals to the integrity
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Very little information is availabl
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leaving little trace of their exist
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REFERENCESAGASSIZ, A. (1903). The c
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PILLAI, C.S.G. (1969b). Studies on
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Table 1.Extent of damage to coral r
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STATUS OF CRITICAL MARINE HABITATS
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OCCURRENCEThe distribution of reefs
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Mining of Reef RockMining of reef r
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-resource. Their significance deriv
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Coating of Aerial Roots by Fine Sed
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associated with the roots (e.g. GOE
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Temperature and SalinityThe effects
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significant numbers in the Red Sea,
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mersas are known to serve as nurser
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BURCHARD, J.E. (1979). Coral fauna
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HIRTH, H.F., KLIKOFF, L.G. and HARP
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MacNAE, W. (1974). Mangrove forests
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RINKEVITCH, B. and LOYA, Y. (1977).
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WALKER, D.I. and ORMOND, R.F.G. (19
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DAMMING AND DIVERSION OF RIVERSIn d
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FUTURE STUDIESWhat can marine scien
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!0OD9 -8 Nc80,a,u-3(dcab(Dbrr)8brr)
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0 0-0 00 O0O 0% LD d- m cu 0 0202
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STORM SURGES IN THE BAY OF BENGAL*T
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low pressure centres over the Bay i
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ACKNOWLEDGEMENTSThe writers wish to
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Table 1.Latitude and longitude of p
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214
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0Poa9nU0m0Yan-I2li7mYUVQk?401mc0mYm
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0In218
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221
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Table 3. Nomenclature used by India
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ANDHRAB A Y OFB E N G A L ,.16'LO 4
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INDIABAY OF-Point CalirnereLanka L-
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pressure in the South Pacific and l
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SWALLOW, J.C. (1983). Arabian Sea c
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234
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236
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scale wind phenomenon that occurs w
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Several two-dimensional models of t
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HARTMANN, M., LANGE, H., SEIBOLD, E
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Y-Model Domaint=6hrs.b-250 0 59 Xw-
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UELEVATIONS (m) ai 18 HOURS L2:-+EL
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HARMONIC CONSTITUENT K,Figure 8. Ob
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Age of Semi-Diurnal Tide (hrs)28".+
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! 5"BOTTOMFigure 13. Predicted mode
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Page 260 and 261: in 6 months when spawning occurs. T
Page 262 and 263: REFERENCES3BANSE, K. (1968). Hydrog
Page 264 and 265: GILSON, H.C., (1937). The nitrogen
Page 266 and 267: ROYAL SOCIETY (1963). International
Page 268 and 269: APPENDIX:REGIONAL COOPERATIVE INVES
Page 270 and 271: 20 015 20 25FEBOC015 20 25 30 35M A
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Page 278 and 279: ...... :'I. .. ,... .. 8.*.. ... ._
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Page 294 and 295: 50010001 scoOxygen (rnl/l)0I1I2I3I4
Page 298 and 299: THE RED SEAPHYSIOGRAPHYThe Red Sea
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Page 310 and 311: EYAL, M., EYAL, Y., BARTOV, Y. and
Page 312 and 313: LEWIS, B.T.R. (1983). The process o
Page 314 and 315: TARLING, D.H. and MITCHELL, J.G. (1
Page 316 and 317: mC- 1000- 2000- 3000E0Figure 2.Sche
Page 318 and 319: -20b-0,20wFigure 4. Seismicity and
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Page 330 and 331: SUPERFICIAL SEDIMENTS OF NORTHERN R
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Page 334 and 335: EL-SAYED (1983) used the trace meta
Page 336 and 337: BEHAIRY, AKA. (1983). Marine transg
Page 338 and 339: SHUKRI, N.M. (1953). Bottom deposit
Page 340 and 341: Table 2 Heavy metal concentrations
Page 342 and 343: EGYPTEl-Morgan 1Bargan IBargan 2Yub
Page 344 and 345: Figure 4. Distribution of minerals
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ARAGONITEHIGH HG-CALCITEFigure 6. T
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MARINE LIVING RESOURCES OF THE RED
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This elevated productivity may resu
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REVELLE (1981) mentioned that the p
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FISHELSON, L. (1964). Observation o
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