Microtexture and U-Pb geochronology of detrital zircon grains in the Chachalacas beach, Veracruz State, Gulf of Mexico

摘要

Microtextures, trace element concentrations, and U-Pb geochronology of detrital zircon grains recovered from the Chachalacas beach in the western Gulf of Mexico were investigated to infer palaeoenvironmental conditions. The mineralogy of bulk sediments revealed the presence of both chemically stable (titano-magnetite, zircon, and quartz) and unstable (amphibole and K-feldspar) minerals. The zircon grain microtextures or surface features were grouped as two types: (a) mechanical origin and (b) mechanical and chemical origin. The mechanical surface features such as V-marks, arc shaped, and meandering steps indicate a high-energy littoral and sub-aqueous marine environment. The chemical surface features like solution pits, precipitation, solution crevasses, adhered particles, and silica pellicle revealed a silica saturated marine environment. The well-rounded zircon grains with bulbous edges are characterized by long transport and aeolian origin. The Th/U ratio, a negative Eu (Eu/Eu* = similar to 0.08-0.72) and positive Ce (Ce/Ce* = >1) anomalies in the chondrite-normalized REE patterns of all zircon grains suggested that they primarily formed from magmatic processes. The detrital zircon grain U-Pb ages showed a wide variation from Cenozoic to Proterozoic with an abundance of Cenozoic ages (similar to 1.59-64.3 Ma;n= 44), interpreted as mixing of beach sediments by a longshore current. The comparison of zircon grain ages of this study with ages reported from the source terranes revealed that the likely source for Cenozoic zircon grains was the Eastern Alkaline Province of Mexico. Similarly, the Mesozoic (similar to 68.5-241.9 Ma) and Palaeozoic (similar to 253.2-284.8 Ma) zircon grains in the Chachalacas beach were possibly derived from the Valle de Huizachal and Mesa Central provinces. Proterozoic ages from similar to 574 to 1846 Ma indicated a probable contribution from the Oaxacan and Chiapas Massif complexes, which are dominated by Grenvillian basement rocks.