The tectonic regime along the Andes: Present settings as a key for the Mesozoic regimes

VICTOR A. RAMOS

GEOLOGICAL JOURNAL (CHICHESTER)

Whiley

Lugar: Chichester; Año: 2010 vol. 45 p. 2 - 25

0072-1050

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The analyses of the main parameters controlling the present tectonic settings developed along the eastern Pacific region show four end members regarding their tectonic regime: a nearly neutral Oregon-type; major extensional regimes as the Nicaragua-type developed in continental crust and the Sandwich-type with ocean floored back-arc basin, and the dominant Chile-type under compression. The magmatic, structural and sedimentary behavior of these four settings is discussed to characterize them. Based on these geological characteristics past tectonic regimes in the Mesozoic Andes are recognized and categorized. The evaluation of the different parameters that governed the past and present tectonic regimes indicates that absolute motion of the upper plate and the consequent trench roll-back velocity are the first order parameters that control the deformation. Locally, the influence of the trench fill, linked to the dominant climate in the forearc, and the age of the subducted oceanic crust, has secondary roles. Eastward mantle flow, either globally or regionally, has a subordinate effect in comparison with absolute motion of the upper plate. Ridge collisions of aseismic and seismic oceanic ridges have also a local outcome, and may produce an increase of coupling that reinforce compressional deformation. Local strain variations in the past and present Andes are not related with changes in the relative convergence rate, which is less important than absolute motion, or changes in the thermal state of the upper plate. Changes in the slab dip, mainly those linked to steepening subduction zones, produce significant variations in the thermal state, that are important to generate extreme deformation in the foreland.