Comment on “segmentation and disruption of the East Pacific Rise in the mouth of the Gulf of California” by Peter Lonsdale (Marine Geophysical Researches 17, pp. 323–359, 1995)

Abstract

The Pacific-Rivera Rise and Rivera transform fault which recorded the Pacific-Rivera motions are complex features and the evolution of the Rivera plate boundaries is still a matter of controversy (Ness and Lyle, 1991; Lonsdale, 1991; Stock and Lee, 1994). Different locations for the Pacific-Rivera Euler pole have been recently published (DeMets and Stein, 1990; Bandy and Pardo, 1994) and point out the difficulties to describe the Rivera-Pacific relative motions. On the basis of available and new multibeam bathymetry and magnetic data, Lonsdale (1995) proposes a new location for the Pacific-Rivera Euler pole and a new model for the evolution of the Rivera plate boundaries. This new compilation shows that the Pacific-Rivera Rise is segmented in several "en echelon" spreading segments. Lonsdale (1995) claims that the Pacific-Rivera Rise is made of two main segments belonging, respectively, to the Pacific-North America and to the Pacific-Rivera plate boundaries. Strike measurements of tectonic features outlining the plate boundaries are part of the data that constrains Lonsdale's model. Lonsdale (1995) notes a misalignment of 3 ~ between the Tamayo transform (N305 ~ E) and the western segment of the Rivera transform (N302 ~ E) strikes. Spreading segments on either side of the Tamayo transform strike N35 ~ E. South of 22.6~ the Rivera-Pacific Rise segments strike N39 ~ E, N38~ and N36~ from North to South, respectively. Although no multibeam data are presented at appropriate scale, we do not raise doubt about the strike values proposed by Lonsdale (1995) since DeMets and Stein (1990, Figure 2) have shown a misalignment of about 5 ~ between the southern and the northern part of the Rivera-Pacific Rise. Lonsdale (1995) concludes that: 1)the spreading segments on either side of the Tamayo transform belongs to the Pacific-North America boundary; and 2)further to