Uplift and lateritization history of the ?alda? ophiolite in the context of Neo-Tethyan ophiolite obduction and uplift: Implications for the cenozoic weathering history of western anatolia

摘要

The ?alda? ophiolite, in the Bornova Flysch Zone, is a fragment of Neo-Tethys in the Aegean province, western Turkey. The Bornova Flysch Zone is probably of Cretaceous age, and is locally covered by Early Eocene sediments of the Ba?lami{dotless}? Formation that show the first evidence of exposure of ultramafic rocks. Field mapping confirms eight tectonic events correlated with the published regional history. The ? alda? ophiolite would have been exposed to weathering only from the Mid-Palaeocene to the Late Miocene and from the Mid-Pliocene until the present. This weathering has resulted in the formation of an average c. 69m thick oxide-dominated Ni-laterite. Biological, palaeoecological and isotopic records indicate favourable conditions for weathering, comparable with those of regions in which laterites form today. These data suggest that tropical to subtropical climatic conditions dominated through most of the Cenozoic; the Palaeocene- Eocene was significantly warmer than the Oligo-Miocene. Combining the exhumation history with the available climate data better constrains the periods suitable for laterite formation with implications for laterite formation regionally. The data indicate a possible total period of 50 Ma when laterite formation was possible, yet the profile measured at ? alda? is indicative of either a shorter period of actual weathering or partial erosion of the formed profile.