Neoproterozoic subduction-related metavolcanic and metasedimentary rocks from the Rey Bouba Greenstone Belt of north-central Cameroon in the Central African Fold Belt: New insights into a continental arc geodynamic setting

摘要

This paper presents new geochemical and geochronological data for the low to medium grade Rey Bouba Greenstone Belt (RBGB), located in northern Cameroon at the northern margin of the Central African Fold Belt (CAFB), and discusses the maximum age of volcanic activity, the maximum depositional age of metasedimentary rocks and geotectonic implications. Geochemical data on volcanic rocks highlight the predominance of transitional to calc-alkaline magma compositions (Zr/Y= 3.62-26.38) with mostly andesite to basaltic andesite with an unusually high Mg concentration (>5 wt.%, high-Mg andesite), but also basalt and trachy-andesite protoliths. Moreover, chondrite-normalized REE patterns and primitive mantle-normalized spidergrams show enrichment of LREE relative to HREE with flat to depleted elements, and moderate to slight negative Nb-Ta, Ti and Eu anomalies respectively; which are consistent with a continental arc setting related to a subduction zone. U-Pb zircon LA-ICP-MS geochronology on felsic metavolcanic or metatuff fix the maximum age for the volcanic activity in the RBGB at ca 670 Ma. Detrital zircon grains indicate that Neoproterozoic zircon (Ediacaran to Cryogenian) are the main source for the detritus that fed the basin, combined with minor Paleoproterozoic and Mesoproterozoic inputs. The maximum depositional age, corresponding to the youngest graphical age peak controlled by multiple grain ages is consistently constrained between 645 and 630 Ma, whereas the age of low grade metamorphism weakly recorded by overgrowths on detrital zircon in the RBGB basin is around 600 Ma. These results provide new insights into the geodynamic processes during the Neoproterozoic along the northern margin of the CAFB of northern Cameroon, suggesting that the RBGB, where high-Mg andesite magmatism has taken place is consistent with a continental arc-related basin. (C) 2015 Elsevier B.V. All rights reserved.