3-D inversion of deep tow magnetic data on the Atlantis II Deep (Red Sea): hydrothermal and geodynamic interpretation

Abstract

Abstract To study the magnetic signature of hydrothermal oceanic crust areas, data were collected, using a magnetometer towed a few hundred meters above the sea floor, within an acoustic transponder net. The experiment was performed in the Red Sea over the Atlantic II Deep (near 21°20′N 38°05′E). This deep, created during the Brunnes Epoch, is well known for its intense hydrothermal activity and the presence of hot brines overlying metalliferous sediments. The magnetic field was inverted to obtain the distribution pattern of crustal magnetization, including the effects of topography and irregular depth of the magnetic sensor. The procedure, however, does not produce any unique solution. It is approximated, using probabilistic linear methods (Tarantola and Valette, 1982), which require the introduction of constraints, in the form of gaussian probability density functions. The resultant magnetization pattern then follows a gaussian law; the mean and standard deviation are then computed. The results show, contrary to what has been suggested formerly (Rona, 1978a, b), that the strongest magnetization, as well as the most frequent hydrothermal and magmatic occurrences are found in the Southwest Basin. The high magnetic intensities are thus associated with a recent magmatism, which initiates the hydrothermal circulation. Two hypotheses explain this: 1. (1)The freshness of the basalts and the low-temperature alteration are the principal causes of magnetization contrasts and represent, respectively, the discharge and recharge zones of the hydrothermal plumbing. 2. (2)In the general framework of the Red Sea opening by progressive tearing, the formation of the Atlantis II was extremely fast, according to the elastic rebound theory (Reid, 1911). This hypothesis is applicable to some other deeps.