TY - JOUR

T1 - The migration history of the Nazca Ridge along the Peruvian active margin: A re-evaluation

AU - Hampel, Andrea

N1 - Funding information: Helpful comments and discussions with Nina Kukowski, Onno Oncken, Ulrich Riller and David Hindle are gratefully acknowledged. Udo Barckhausen and Garrett Ito are thanked for their help with the magnetic anomaly data and useful comments. Many thanks to Edmundo Norabuena for his helpful comments on the plate motion data. The GMT [70] software was used to create Figs. 2–5 . I thank the reviewers Emile Okal, Tim Dixon and Steven Cande for constructive comments that helped to improve the manuscript. Funding was provided by the German Ministry of Education, Science and Technology (BMBF) within the GEOPECO project (Grant no. 03G0146A). [AC]

PY - 2002/10/30

Y1 - 2002/10/30

N2 - The collision zone of the 200 km wide and 1.5 km high Nazca Ridge and the Peruvian segment of the convergent South American margin between 14°S and 17°S is characterized by deformation of the upper plate and several hundred meters of uplift of the forearc. This is evident by a narrowing of the shelf, a westward shift of the coastline and the presence of marine terraces. As the Nazca Ridge is oblique with respect to both trench and convergence direction of the Nazca Plate, it migrates southward along the active plate boundary. For reconstructing the migration history of the Nazca Ridge, this study uses updated plate motion data, resulting from a revision of the geomagnetic time scale. The new model suggests that the ridge crest moved laterally parallel to the margin at a decreasing velocity of ~75 mm/a (before 10.8 Ma), ~61 mm/a (10.-4.9 Ma), and ~43 mm/a (4.9 Ma to present). Intra-plate deformation associated with mountain building in the Peruvian Andes since the Miocene reduces the relative convergence rate between Nazca Plate and Peruvian forearc. Taking an intra-plate deformation at a rate of ~10 mm/a, estimated from space-geode tic and geological data, into account, does not significantly reduce these lateral migration velocities. Constraining the length of the original Nazca Ridge by its conjugate feature on the Pacific Plate yields a length of 900 km for the subducted portion of the ridge. Using this constraint, ridge subduction began ~ 11.2 Ma ago at 11°S. Therefore, the Nazca Ridge did not affect the northern sites of Ocean Drilling Program (ODP) Leg 112 located at 9°S. This is supported by benthic foraminiferal assemblages in ODP Leg 112 cores, indicating more than 1000 m of subsidence since at least Middle Miocene time, and by continuous shale deposition on the shelf from 18 to 7 Ma, recorded in the Ballena industrial well. At 11.5°S, the model predicts the passage of the ridge crest ~9.5 Ma ago. This agrees with the sedimentary facies and benthic foraminiferal stratigraphy of ODP Leg 112 cores, which argue for deposition on the shelf in the Middle and Late Miocene with subsequent subsidence of a minimum of several hundred meters. Onshore at 12°S, the sedimentary record shows at least 500 m uplift prior to the end of the Miocene, also in agreement with the model.

AB - The collision zone of the 200 km wide and 1.5 km high Nazca Ridge and the Peruvian segment of the convergent South American margin between 14°S and 17°S is characterized by deformation of the upper plate and several hundred meters of uplift of the forearc. This is evident by a narrowing of the shelf, a westward shift of the coastline and the presence of marine terraces. As the Nazca Ridge is oblique with respect to both trench and convergence direction of the Nazca Plate, it migrates southward along the active plate boundary. For reconstructing the migration history of the Nazca Ridge, this study uses updated plate motion data, resulting from a revision of the geomagnetic time scale. The new model suggests that the ridge crest moved laterally parallel to the margin at a decreasing velocity of ~75 mm/a (before 10.8 Ma), ~61 mm/a (10.-4.9 Ma), and ~43 mm/a (4.9 Ma to present). Intra-plate deformation associated with mountain building in the Peruvian Andes since the Miocene reduces the relative convergence rate between Nazca Plate and Peruvian forearc. Taking an intra-plate deformation at a rate of ~10 mm/a, estimated from space-geode tic and geological data, into account, does not significantly reduce these lateral migration velocities. Constraining the length of the original Nazca Ridge by its conjugate feature on the Pacific Plate yields a length of 900 km for the subducted portion of the ridge. Using this constraint, ridge subduction began ~ 11.2 Ma ago at 11°S. Therefore, the Nazca Ridge did not affect the northern sites of Ocean Drilling Program (ODP) Leg 112 located at 9°S. This is supported by benthic foraminiferal assemblages in ODP Leg 112 cores, indicating more than 1000 m of subsidence since at least Middle Miocene time, and by continuous shale deposition on the shelf from 18 to 7 Ma, recorded in the Ballena industrial well. At 11.5°S, the model predicts the passage of the ridge crest ~9.5 Ma ago. This agrees with the sedimentary facies and benthic foraminiferal stratigraphy of ODP Leg 112 cores, which argue for deposition on the shelf in the Middle and Late Miocene with subsequent subsidence of a minimum of several hundred meters. Onshore at 12°S, the sedimentary record shows at least 500 m uplift prior to the end of the Miocene, also in agreement with the model.

KW - Forearc

KW - Nazca Ridge

KW - Oblique subduction

KW - Peru

KW - Plate reconstruction

UR - http://www.scopus.com/inward/record.url?scp=0037202095&partnerID=8YFLogxK

U2 - 10.1016/S0012-821X(02)00859-2

DO - 10.1016/S0012-821X(02)00859-2

M3 - Article

AN - SCOPUS:0037202095

VL - 203

SP - 665

EP - 679

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

SN - 0012-821X

IS - 2

ER -