Detailed patrems of near surface tectonics and heat flow were investigated at two locations at the toe of the Barbados Ridge accretionary prism. At the two locations, in the thickly sedimented southern portion of the prism near 12ø202q and in the northern area drilled during Ocean Drilling Program (ODP) leg 110 near 15ø322q, relative highs of heat flow were associated with zones of thrusting. We attribute them to upward advection of water rising from the d6collement along faults through the sediments. In the ODP area, a significant heating plate effect from warm fluids flowing along the d6collement and thrusts is required to account for the high regional heat flow. This effect implies high rates of fluid flow at the d6collement, which can only be non-steady state or would require massive lateral transport of fluids along strike. Paper number 90IB00828.0148-0227/90/90JB00828505.00 decrease in heat flow to the background value over a lateral distance of 300 m. Although the heat flow profile does not extend all the way across the second thrust-outcrop wedge farther upslope, the two westernmost measurements suggest that a similar heat flow anomaly is associated with this upper wedge.The only reasonable explanation that we find for this anomaly, in particular because of its short wavelength, is upward fluid 8859 J.P. Foucher, D6partement de G6osciences Marines
There has been a considerable amount of studies of the lands bordering the Eastern Mediterranean basin but the basin itself is stip relatively poorly known . The tectonic analysis of this basin is difficult to do because a great part of it has disappeared within a double system of subduction zones, the Hellenis one that is stip active and the Calabrian one that stopeed being active less than one minion years ago . To discus the tectonic evolution of the Eastern Mediterranean basin, it is first necessary to evaluate the effect of the present kinematics and then to reconstruct the geometry of the basin prior to subduction . We now are able to precisely evaluate using geodetic methods these present kinematics that are dominated by the lateral extrusion of Anatolia and the N/S extension of Aegea. We have the possibility to reconstruct rather confidently the middle Miocene shape of the basin that was then about twice larger than today . It is much more difficult to reconstruct the geometry of the basin prior to Miocene . Important guides for such reconstructions are the present strostores of the basins, of the accretionary wedges that cover half of them and of their margins . Based in great part on work that has been obtained by oor own laboratory, we summarize oor present state of knowledge about these three topics : 1)The crustal strostore of the basins . There are significant differences between the western (Ionian) and eastern (Levantine) basins . The strostore of the Ionian basin is better known . It is clearly oceanic . The sedimentary cover is well stratified and the main layers may be followed over the whole basin . The Ionian basin was affected by active shortening prior to Messinian, and most probably during late middle Miocene . The strostore of the Levantine basin is more difficult to characterize doe to the much ihicker sedimentary cover. It is compatible either with an oceanic crost or with a thinned continental crost . 2} The strostore and development of the Mediterranean and Calabrian wedges . TheMediterranean ridge is the accretionary complex formed since Middle Miocene time by the Hellenis subduction . We have proposed that the backstop against which this accretionary complex is formed consists of Hellenis napees that same from the Aegea during lower Miocene . The strostore of the Calabrian wedge is less well knawn bot appears to be riaostly related to the post-middle Miocene Calabrian subduction that now appears to be inactive . We have identified a major stip active transform fault that limits the Calabrian wedge on its western side and that appears to be linked to the formatian of the Etna . We relate its activity to the progressive verticalization of the Calabrian (Tyrrhenian) slab .2) The altes and developments of the southern (African) African and northern (European ) raargins. We argue that the age ofthe African margin of the Levantine basin is Triassic whereas it is midfile Cretaceous for the Ionian basin . A phase of subsidence af this age is well known over several plateaus, seamounts an...
Birch [1967] has called attention to an elegant analytical model of sea floor topography which, he feels, can account for the relatively large number of low heat flow values measured in the ocean. In this model, the sea floor surface is given by the implicit equation • z --ae cos rx z being the vertical coordinate positive downward and x the horizontal coordinate. The temperature .gradient at the surface of the model is given by ( d T/ dz) r. ro = a(1 q-rz) a being the value of gradient reached at z infinite. Birch obtains the proportion of vertical gradients less than x/• of the mean that would result from measurements randomly spaced over his model, and he compares it with the proportion of heat values less than x/• of their mean obtained over the entire oceans. Such a comparison is misleading for it implies that the same histogram governs the distribution of heat flow values in all provinces of the oceans. This is not the case. For the Atlantic Ocean Langseth et al. [1966] have shown that there is little variation in heat flow measurements within the ocean basins. In fact, there are no heat flow measurements smaller than x/• the mean, using the definition of the basins of Langseth et al. [1966]. Published and unpublished measurements in the northwestern Pacific basins gives values that are more uniform than values in the Atlantic basins. By contrast, the variation is extremely large over the ridges and low values are frequently found, particularly over the flanks. Thus, a valid comparison of Birch's theoretical distribution with the measured distribution of heat flow values requires a distinction between • Lamont Geological Observatory Contribution 1121. ridges and basins. Even over the ridges two distinct distributions correspond to the crest and the flank regions. Table 1 summarizes separately ocean data for ridges and basins, using the statistics of Lee and" Uyeda [1965], which were the basis of the Birch comparison. The values for Bireh's theoretical model were computed by a development in series of e-". The table illustrates that the distribution of values for his model does not fit the ocean basins but agrees better with the ridges. Even over the ridges, however, the scatter of measurements is much larger than that predicted by Birch as shown in Figure 1, which compares the Atlantic ridges and basins histogram of Lee and Uyeda [1965] with Bireh's model.
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