Geochemistry of sands from the Huatabampo and Altata beaches, Gulf of California, Mexico

Abstract

Grain size, heavy minerals, mineralogical, and geochemical analyses were undertaken on the sand samples from Huatabampo (HB) and Altata (AA) beaches to infer palaeoweathering conditions and source rock characteristics. The mean grain size of HB and AA sands is fine‐grained and fine‐ to medium‐grained, respectively. Magnetite and hypersthene are the common heavy minerals identified in HB sands, whereas magnetite and ilmenite are the dominant heavy minerals in AA sands. HB sands have a high proportion of quartz and plagioclase followed by K‐feldspar and zeolite. Quartz is the dominant mineral in the AA sands, followed by plagioclase and K‐feldspar. Geochemically, the sand samples from HB are classified as wacke, whereas AA sands are classified as wacke and arkose. In chondrite‐normalised REE plot, HB and AA sands show LREE enriched and HREE depleted pattern with negative Eu anomaly. Chemical index of alteration (CIA), plagioclase index of alteration (PIA) values and Th/U ratios of HB and AA sands suggest a low intensity of chemical weathering in the source area. The tectonic discriminant function diagram suggestsan arc setting for HB sands, whereas a rift setting for AA sands. The chondrite‐normalised REE patterns, Eu anomaly, Al2O3/TiO2 ratio, trace elemental ratios, discriminant function, and ternary diagrams suggest that the HB and AA sands were dominantly derived from felsic source rocks. The comparison of REE patterns of HB and AA sands with the source rocks exposed near to the study area suggest that the central granites of Laramide plutonic rocks exposed in Sonora were contributing sediments to the HB beach, whereas AA sands received sediments mainly from the felsic Francisco gneiss in the western Sonobari Complex of Sinaloa.