Detrital-zircon record of major Middle Triassic-Early Cretaceous provenance shift, central Mexico: demise of Gondwanan continental fluvial systems and onset of back-arc volcanism and sedimentation

摘要

New stratigraphic and petrographic data and zircon U-Pb geochronology from sandstones and volcanic rocks in the states of Queretaro and Guanajuato in central Mexico indicate an important provenance change between Late Triassic and latest Jurassic-Early Cretaceous time. The Upper Triassic El Chilar Complex consists of pervasively deformed, deep-marine olistostromes, and debris-flow deposits of arkosic and subarkosic composition. Detrital-zircon populations range from latest Palaeoproterozoic (1.65 Ga) to Middle Triassic (240 Ma), all predating the depositional age of the strata. The detrital-zircon populations are similar to those previously reported from turbidites of the Potosi fan complex of north-central Mexico and interpreted as derived from Grenville and Pan-African (Maya block) basement and Permo-Triassic arc of continental Mexico directly to the east of the basin. A single sample with a dominant Proterozoic population at ~ 1.65-1.30 Ga was likely derived either from the Rio Negro-Juruena province of the Amazonian craton or from a local source in the Huiznopala Gneiss, and indicates that El Chilar strata were likely deposited in the proximal part of a submarine-fan system separate from the Potosi fan.