An application of the response function technique to profiles of bathymetry and gravity in the Gulf of Aden

Abstract

Summary. The relationship between bathymetry and gravity in the eastern, and the western Gulf of Aden, is analysed by computing response functions. The form of the response functions indicates that the short‐wavelength topography is isostatically compensated. The most appropriate mechanism of compensation is one in which the topography is not locally compensated, but regionally compensated by flexure of the lithosphere. Though the sets of profiles from the eastern and the western Gulf of Aden are separated by only 500–750 km, the observed response functions are very different. The lithosphere in the eastern Gulf of Aden can be modelled by an elastic plate 15 ± 3 km thick, whereas an elastic plate 3 ± 2km thick is probably an appropriate model for the lithosphere in the western Gulf of Aden. A different mechanism of isostasy (the Pratt) operates in the compensation of the long‐wavelength topography of the mid‐ocean ridge in the Gulf of Aden. A larger negative broad Bouguer gravity anomaly across the western Gulf of Aden than across the east, indicates that upper mantle temperatures increase from east to west. The long‐wavelength shallowing of the Gulf of Aden and increasing elevation of the adjacent continents from east to west are therefore probably mainly the result of thermal uplift. The subdued nature of the median valley and (consequently) other short‐wave‐length topography in the west, can be explained by hot, low viscosity, asthenosphere, and the inferred thin lithosphere in the west also suggests high temperature mantle. Finally, a magnetic anomaly superimposed on the axial anomaly, which is probably related to the depth of the Curie temperature, is more common in the western Gulf of Aden than in the east, and this is also consistent with upper mantle temperatures increasing to the west. There are a number of similarities between the mid‐ocean ridge in the western Gulf of Aden and the Reykjanes ridge. It is suggested that the western Gulf of Aden is anomalous because of its proximity to the Afar ‘hot spot’ in the same way that the Reykjanes ridge is often considered to be anomalous because of its proximity to the Iceland ‘hot spot'.

Isostatic response of the Laccadive Ridge from admittance analysis of gravity and bathymetry data

“…The two most commonly used models in admittance analysis are the Airy and flexure models (McKenzie and Bowin, 1976;Watts, 1978;Louden, 1981;Karner and Watts, 1982;Tamsett, 1984;Young and Hill, 1986). In this study, the observed admittance values are analyzed and interpreted in terms of the Airy and flexure models of isostasy.…”

Lithospheric structure of a nascent spreading ridge inferred from gravity data: The western Gulf of Aden

“…As chron 5 is identified along almost the entire Gulf of Aden, the propagation of the opening was probably either instantaneous [Cochran, 1981;Le Pichon and Gaulier, 1988] or very rapid (at least 10 cm yr-•) with possible slowing down at fracture zones [Manighetti et al, 1997]. Among noteworthy geophysical studies in the western Gulf of Aden, the analysis of gravity and bathymetry profiles with spectral methods has inferred the westward decrease of the equivalent elastic thickness from 15 to 3 km between 52øE and 44øE [Tamsett, 1984]. It has been interpreted as resulting from a hotter mantle temperature in the westernmost area, in agreement with the vicinity of a hot spot beneath Afar.…”

Carlsberg Ridge, northern Indian Ocean: gravity and isostasy

“…The Sheba Ridge (Gulf of Aden) is an extension of the Carlsberg Ridge across the Owen fracture zone. It is interesting to note from Table 3 that the elastic thickness of 5-10 km is intermediate between the values of 15 f 3 km for the Eastern Gulf of Aden and 3 f 2 k m for the Western Gulf of Aden (Tamsett 1984). The low values obtained for the Western Gulf of Aden are believed to be due to its proximity to the Afar hotspot.…”