Tectonic Subsidence Analyses of Miogeoclinal Strata from Mesozoic Marginal Basin of Peru

William J. Devlin

The Western Peruvian trough is composed of an eastern miogeoclinal facies of carbonate and clastic strata, and a western eugeoclinal facies consisting of a succession of volcanic and sedimentary rocks. In northern and central Peru, the miogeocline is located between a tectonic hinge adjacent to platformal facies of the Maranon geanticline on the east, and an outer marginal high bounded by the Cordillera Blanca fault and Tapacocha axis on the west. Miogeoclinal and platformal strata in southern Peru occur in a broad belt between Arequipa and Lago Titicaca.

A marginal basin setting has been proposed for the Western Peruvian trough and the several kilometers of subsidence in the basin has been attributed to back-arc extension and crustal thinning. As a test of this model, quantitative tectonic subsidence curves were constructed from representative sections within miogeoclinal strata from four localities. Preliminary results indicate that the calculated curves have the same overall form as the age-depth curve for ocean floor, suggesting that subsidence was controlled by cooling and thermal contraction of heated lithosphere. The slopes of the curves are less than those for subsidence of oceanic lithosphere. However, they are in agreement with geologic evidence that the miogeocline accumulated on continental crust. Significant variations in he timing of onset, duration, and magnitude of subsidence are observed between sections from northern and southern Peru.

In a broader context, the data from the Western Peru trough imply that the subsidence mechanism associated with rifting processes behind a marginal volcanic arc is similar to that of modern and ancient passive margins that were formed as a result of extension during continental separation.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.