Lu-Hf geochronology of Mississippian high-pressure metamorphism in the Acatlán Complex, southern México

Abstract

Since the first discovery of eclogite in the Acatlán Complex in southern México, the age of the high-pressure metamorphism has been a matter of debate. Several attempts to date high-pressure metamorphic rocks of the Acatlán Complex have been made using the U-Pb and 40Ar-39Ar methods. The resulting dates, however do not correspond unambiguously to the time of eclogite facies metamorphism. In this study, the age of high-pressure metamorphism in the Acatlán Complex has been determined by Lu-Hf garnet-whole rock geochronology. This paper presents four high precision, 4- to 7-point garnet-whole rock isochrons of amphibolitized eclogite from the Piaxtla Suite and the Asís Lithodeme, in the Acatlán Complex. The four dates agree within uncertainties, yielding a weighted mean of 352.5±1.6Ma, which we interpret to be the age of eclogite facies metamorphism in the Piaxtla Suite and the Asís Lithodeme, marking active subduction in the Acatlán Complex in the Carboniferous. Mississippian high-pressure metamorphism in turn, might be related to the closure of the Rheic Ocean and the assembly of Pangea.