Showing papers by "Philippe Huchon published in 1990"

Active spreading and hydrothermalism in North Fiji Basin (SW Pacific). Results of Japanese French Cruise Kaiyo 87

Abstract: The aim of the Japanese-French Kaiyo 87 cruise was the study of the spreading axis in the North Fiji Basin (SW Pacific). A Seabeam and geophysical survey allowed us to define the detailed structure of the active NS spreading axis between 16° and 22° S and its relationships with the left lateral motion of the North Fiji Fracture Zone. Between 21° S and 18°10′ S, the spreading axis trends NS. From 18°10 S to 16°40 S the orientation of the spreading axis changes from NS to 015°. North of 16°40′ S the spreading axis trends 160°. These two 015° and 160° branches converge with the left lateral North Fiji fracture zone around 16°40′ S to define an RRFZ triple junction. Water sampling, dredging and photo TV deep towing give new information concerning the hydrothermal activity along the spreading axis. The discovery of hydrothermal deposits associated with living communities confirms this activity.

The 16°40′ S triple junction in the North Fiji Basin (SW Pacific)

Abstract: During the last three years, the North Fiji Basin (SW Pacific) has been intensively studied on three oceanographic cruises carried out by French, American and Japanese ships. One of the main goals of these cruises was to study by means of precise SeaBeam, SEAMARC II, seismic and magnetic surveys, the active spreading system and its associated hydrothermal processes. The North Fiji basin, bounded by the major Pacific and Indo-Australian plates, shows a complex polyphased tectonic evolution. One of the last phases of this evolution is the functioning since 3 Ma of a NS spreading center in the axial part of the basin. The tectonic instability of the area resulted in a permanent rearrangement of the ridge axis. Among others, the 16°40′ S triple junction is one of the major manifestations of such an instability. Sinistral strike-slip motion 1 Ma ago, along the North Fiji Fracture Zone induced the change in direction of two segments of the axis from NS to N15 and N160. The first segment is characterized by a typical spreading ridge similar to various parts of the EPR, while the second shows an atypical ‘en echelon’ fan-shape opening. The N15 and N160 ridges converging with the North Fiji Fracture Zone constitute the 16°40′ S Ridge-Ridge-Fracture Zone triple junction. The detailed morphologic and kinematic study of this junction allows us to understand one of the mechanisms of the deformation in the North Fiji basin.

Subduction‐induced fragmentation of the Nazca Plate off Peru: Mendana Fracture Zone and Trujillo Trough revisited

Abstract: The Mendana Fracture Zone and the Trujillo Trough are two major intra-oceanic features on the Nazca Plate off Peru. During the SEAPERC cruise of the R/V Jean Charcot in 1986, Sea Beam bathymetric data, single-channel seismic records, geomagnetic and gravity measurements, and heat flow data have been obtained over these two areas. In this paper, we confirm that the Mendana Fracture Zone is actively opening perpendicular to its trend, resulting in the formation of new oceanic crust since about 3.5 Ma. We calculate that this new rift is propagating westward along the fracture zone at a velocity of about 10 cm yr−1 (or 2 cm yr−1 with respect to the trench). This extensional feature appears to be genetically linked with the Trujillo Trough, located 200 km to the north. This trough is bounded to the east by a left: lateral transpressive fault which became active probably at the time when the Mendana Rift started. We then discuss a possible mechanism to explain the origin of these two areas of intraoceanic deformation.

TrigonometricK riging: A New Methodf or Removingt he Diurnal Variation From Geomagnetic Data

Abstract: In order to remove the effect of the diurnal fluctuation of the magnetic field from magnetic measurements recorded at sea, we propose a new method: trigonometric kriging. This method is a particular case of the classical kriging method, but in this case we estimate locally a drift function of the form D(ti) = Ai cos (ωti) + Bi sin (ωti) or a truncated Fourier series, using a kriging neighborhood both in time and space. This method does not require any crossing point, which is a major advantage over previously published methods. After presenting the theoretical basis, we show how to put it into practice, i.e., how to choose, both in space and time, the set of points used for the estimation (kriging neighborhood) and how to determine experimentally the model for the generalized covariance which was used in the estimation. Trigonometric kriging has some interesting properties, such as to be exact at track crossings (if any), to allow an only “almost” periodic drift to be estimated, and finally to make possible filtering and gridding in one operation. Trigonometric kriging has been applied successfully to several sets of geomagnetic data recorded at sea near the equator, and we show two actual examples in Peru and in Indonesia.

The 16~ ' S Triple (SW Pacific) Junction in the North Fiji Basin

Abstract: During the last three years, the North Fiji Basin (SW Pacific) has been intensively studied on three oceanographic cruises carried out by French, American and Japanese ships. One of the main goals of these cruises was to study by means of precise SeaBeam, SEAMARC II, seismic and magnetic surveys, the active spreading system and its associated hydrothermal processes. The North Fiji basin, bounded by the major Pacific and Indo- Australian plates, shows a complex polyphased tectonic evolution. One of the last phases of this evolution is the functioning since 3 Ma of a NS spreading center in the axial part of the basin. The tectonic instability of the area resulted in a permanent rearrange- ment of the ridge axis. Among others, the 16~ triple junction is one of the major manifestations of such an instability. Sinistral strike-slip motion 1 Ma ago, along the North Fiji Fracture Zone induced the change in direction of two segments of the axis from NS to N15 and N160. The first segment is characterized by a typical spreading ridge similar to various parts of the EPR, while the second shows an atypical 'en echelon' fan-shape opening. The N15 and N160 ridges converging with the North Fiji Fracture Zone constitute the 16~ Ridge-Ridge-Fracture Zone triple junction. The detailed morphologic and kinematic study of this junction allows us to understand one of the mechanisms of the deformation in the North Fiji basin.