The active thermogene travertine deposits along the Cameroon volcanic line (CVL), central africa: Petrology and insights for neotectonics and paleoenvironmental approach

Abstract

Two main active thermogene travertine deposits along the continental part of the Cameroon Volcanic Line have been investigated petrologically and paleontologically. The Bongongo travertine in a swampy environment, near Mount Cameroon has a thickness of less than 8 m, meanwhile that of Ngol which is located near Mount Manengouba has a cascade morphology and is less than 4 m thick. Volcanic activities that made up the Cameroon Volcanic Line are related to reactivation of the Precambrian fault at the time of the evolution of the South Atlantic Ocean during the Cenozoic. The mineralogical composition in the Ngol deposit is dominated by calcite (98.5%–99.5%) associated with detrital quartz and feldspar (0.5%–1.5%) and small amount of aragonite while the Bongongo deposit is made up of calcite (99.2%–99.8%) associated with detrital quartz (0.2%–0.8%) and small quantities of aragonite. The process of precipitation of these travertines is physico-chemical essentially. The heavy minerals concentrate are made up of varied types (epidote, chlorite, tourmaline, zircon, sillimanite, etc.) suggesting that the deep water has crossed granite-gneissic basement. The abundance of Li (Lithium) in the springs is linked to lepidolite present in the Bongongo deposit, while Sr (Strontium) and Ba (Barium) are found in the hydrothermal minerals as celestite (SrSO4) and Barite (BaSO4) associated to epidote/chlorite abundant in the deposits. The evidence of the deep origin (volcanic and crustal metamorphism origin) of CO2 (500–1050 mg/L) and the temperatures (29–49 °C) of the hot springs suggest a possible mixture of endogenic and epigenic waters in the subsurface. There is abundant fossil leafs belonging to Angiosperm. The gastropod fossils (Archachatina and Helix genus) are similar to extant species. These paleontological data are indicative of tropical climatic conditions, hot and humid episodes similar to present day's but without any link to the travertine deposits. Active thermogene travertines, a product of plate tectonic activities and volcanism, are also known in Europe (France, Turkey, Greece and Italy).