Detrital Zircon Geochemistry in the Morita Formation, Northern Sonora, Mexico: Implications for Origin and Source Rock Type

We present trace and rare earth element concentrations for 384 detrital zircon grains from four sandstone samples of the Aptian age Morita Formation in the localities of Sierra Anibacachi and Rancho Bufalo in northeastern Sonora to infer origin and source rocks type of their sediments. Zircon grains show large variations in P, Ti, Y, U, Th and Hf concentrations, while ΣREE concentrations in zircons vary significant from sample to sample. Zircon composition from the Sierra Anibacachi and Rancho Bufalo stratigraphic sections shows wide variations in Th/U ratios (0.12- 2.1; 0.12-1.91; respectively) although they have ratios that are well within the range of igneous zircons. U versus Yb and U/Yb ratio versus Hf as well as U/Yb versus Yb plots suggest that most of the zircon grains from the studied samples were contributed by a continental arc. In chondrite-normalized REE plot, most of the zircons show depleted LREE and very strongly enriched HREE patterns with positive Ce and negative Eu anomalies. The presence of significant negative Eu anomalies in these zircons suggest also that they were largely contributed by granitoids sources. Some zircons have relatively flat LREE and very strongly enriched HREE with positive or absence of Ce anomaly and negative or absence of Eu anomaly. On Y versus U and Y versus Yb/Sm plots, the majority of the zircons fall in the leucogranites and granites fields suggesting a felsic nature of the source rocks.