West-dipping Subduction Research Articles

The evolution of the Parece Vela Basin, eastern Philippine Sea

The Parece Vela Basin is a back-arc basin. It is approximately 5000 m deep and is divided into two topographic provinces by the north-trending Parece Vela Rift. The western province is thinly sedimented and topographically rough. The eastern province is blanketed by a thick apron of volcaniclastic sediments which were derived from the West Mariana Ridge. The Parece Vela Rift is composed of a series of discrete deeps and troughs with depths commonly of 6 km and locally exceeding 7 km. Petrologic and seismic refraction data indicate that the Parece Vela Basin is of oceanic character. Low-amplitude, nort-trending, lineated magnetic anomalies are present in the basin and appear symmetric about a line near the Parece Vela Rift. In the central latitudes of the basin seafloor spreading anomalies 10 (30 m.y. B.P.) to 5E or 5D (18 or 17 m.y. B.P.) can be identified. The uncertainty in identifying the youngest anomaly may be due to ridge jumps near the end of spreading. Spreading may have started slightly later in the northern end of the basin. Anomalies in the eastern province are disrupted and are difficult to correlate. DSDP results indicate post-spreading volcanism on the eastern side of the basin and this may have degraded the anomalies. The age obtained in the western province of the basin at DSDP Site 449 (∼25m.y. B.P.) is in close agreement with that obtained from the magnetic data (∼26m.y. B.P.). It is hypothesized that subduction was occurring at a west-dipping subduction zone east of the Palau-Kyushu Ridge in the Early Oligocene. This volcanic arc split about 31 or 32 m.y. ago and interarc spreading was initiated between the Palau-Kyushu Ridge (which then became a remnant arc) and the West Mariana Ridge. The Parece Vela Basin formed between the ridges by two-limb seafloor spreading. Spreading stopped about 17 or 18 m.y. ago. Like certain other marginal basins, the Parece Vela Basin is deeper than predicted from depth vs. age curves. The average heat flow for the Parece Vela Basin is in agreement with that predicted from heat flow vs. age curves. The origin of the Parece Vela Rift is unclear. It may represent the extinct spreading center or may be a postspreading feature.

Plate Tectonic Interpretation of the Paleozoic History of the New England Fold Belt

Major middle-upper Paleozoic paleogeographic elements in both the northern and southern parts of the New England Fold Belt comprise a western volcanic chain, a fore-chain basin, and an eastern nonvolcanic arc-platform-trench complex. These elements developed above a west-dipping subduction zone. Temporary halts in subduction led to minor deformational episodes. During the Late Devonian period, the northern part of the belt was displaced eastward by movement on the west-northwest–striking Tenterfield Fault. Behind the displaced arc immediately north of the fault, an intra-arc basin developed. This was largely filled by sediment during the Carboniferous and was deformed at about the end of the Carboniferous period by reversal of movement on the fault. Subduction ceased throughout the belt in Early Permian time and was followed by major orogenesis. At a late stage in deformation, right-lateral movement on the Demon Fault displaced certain of the paleogeographic elements.