Incipient Spreading within Nazca Plate: A Consequence of Subduction Along the Peru Trench

Hilde TWC,
Organization: The Australasian Institute of Mining and Metallurgy
Pages: 6
Publication Date: Jan 1, 1987
Synthesis of GLORIA side-scan sonar and other geophysical data has provided morpholo- gical and tectonic details of the interaction between the Nazca and South American plates along the Peru Trench (80S-15¦S). Our analyses suggest that a new propagating rift of the Galapagos type is evolving along the Mendana Fracture Zone (MFZ). Subduction induced rift- ing of the Nazca plate is accompanied by organized seafloor spreading for the last 3 Ma at least. GLORIA sonographs and bathymetric mapping show an 8-10¦ divergence in MFZ width towards the Peru Trench. The fracture zone comprises numerous ridges and troughs and a lack of sediment cover in the axial part. Young magnetic lineations (anomalies 1-2A) are observed within the fracture zone wni.cn are orthogonal to the older Nazca plate lineations. The central anomaly narrows west- ward and can be observed up to 400 km seaward of the trench whereas anomaly 2A is terminated about 200 km from the trench axis. Recent SeaMARC II sonar mapping in the region shows large igneous blocks in the Trench axis to the north of MFZ but absent to the south. We believe these blocks represent young seafloor of MFZ rift/spreading center broken off from the ridges as they subduct along the Peru Trench. The MFZ rift is propagating west- ward at a rate of 115 km/Ma (25 km/Ma relative to the South American plate). Given the present rates of accretion at the East Pacific Rise and of propagation along MFZ rift, the Nazca plate will be divided into two parts in about 35 Ma.
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