Record of the ∼540 My collision-stage of Gondwana in NW Angola

• Main Authors: Nsungani, Pedro, Bosch, Delphine, Monié, Patrick
• Other Authors: Géosciences Montpellier, Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Agostinho Neto University, Agostinho Neto Universit, Geochemical Society & European Association of Geochemistry, Cambridge Publications
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2009
• Subjects: [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Boa; Antarc*; Antarctica
• Online Access: https://hal.science/hal-03945156

The temporal evolution of the main geological units from Angola remains poorly known until now and, in particular, no clear relationships can be established within the regional context of the Neoproterozoic-Cambrian Pan-African orogenic system from this part of Africa nor on its role during the amalgamation of the western part of Gondwana. Thus, the main aim of this study was to shed lights on the geological evolution of the Caxito-Pedra Boa area (NW Angola). In this zone, outcrops of various lithologies (granulites, amphibolites, granitoids.) can be found. LA-ICPMS U-Pb analyses have been conducted on zircons from three different samples: aleucocratic vein in an amphibolite, a gneiss and a pegmatite. Moreover, laser Ar-Ar datings on amphiboles and biotites have been also performed. Zircons from the leucocratic vein in the amphibolite define a 206Pb/238U weighted mean age of 539±7 My. Zircons from the gneiss show a complex distribution with a first group of analyses defining a precise age at 538±6 My and ten spots showing older ages ranging from 589 to 678 My. At last zircons from the pegmatite define two groups. The younger analyses yield an age of 544±13 My (n=6) whereas inherited grains have ages ranging from 603 to 2213 My (n=13). Amphiboles Ar-Ar analyses yield ages from 493 to 498 My whereas biotite ages range from 466 to 479 My. These ages are interpreted as cooling ages. Reconstruction of western Gondwana indicates a major high grade event at ∼545-535 My which has been registered in the western part of Antarctica and in the Kalahari craton. This event has been attributed to the younger collisionnal phase of the three main stages registered during the amalgamation history, i.e. at ∼650-620 My, ∼590-560 My, ∼545-510 My. At a glocal scale, distribution of suture ages suggests a Southward younging of collisional events from the Nigeria/Borborema Province to Namibia. The identification of the c. 540 My event in the Northern part of Western Angola allows to reconsider the global evolution of the suture through ...