Structural controls of kimberlite and lamproite emplacement

Abstract

This paper presents the first results of the geostructural and tectonophysical studies of the crustal stress state in the Catoca kimberlite pipe area at the southwestern flank of the Kasai Shield in the northeastern Angola. In the evolution of the crustal stress state, six main stages are distinguished by analyzing the displacements of markers, fold hinges, long axes of boudins, granite dikes of various intrusion phases and kimberlites, as well as fractures with striations. For each of these stages, a dominating horizontal tectonic stress and its orientation is identified. During stage 1 (NW extension and shearing) and at the beginning of stage 2 (NW compression), structures formed in the host rocks in brittle-plastic conditions. The replacement of plastic deformation by faulting could occur about 530-510 Ma ago, when the continental crust of Africa had completely formed. Stage 3 (radial, mainly NW extension) and stage 4 (shearing, NW extension, and NE compression) were the most important for kimberlite occurrence: in the Early Cretaceous, radial extension was replaced by shearing. Both stages are related to opening of the central segment of the South Atlantic. The main kimberlite magmas occurred during the break-up of the Angola-Brazilian segment of Gondwana. In the course of all the four stages, stress was mainly released by the NE-and E-NE-striking faults and, to a lesser extent, by the NW-striking and latitudinal faults. The initial stage of kimberlite magmatism is associated with the NE-and E-NE-striking faults due to the presence of the Precambrian zones of flow and schistosity, which facilitated the NW-trending subhorizontal extension. Stage 5 (NE compression) began in the second half of the Cretaceous and possibly lasted until the end of the Paleogene, and compression occurred mainly along the NW-striking faults. Regionally, it corresponds to two stages of inversion movements in the southern regions of Africa, during which the Angola dome-shaped uplift emerged and the shoulders of the East African rifts began to take shape. Stage 6 (horizontal extension, mainly in the N-NE direction) is related to the processes that took place in the southern segment of the Tanganyika rift and the eastern coast of the Atlantic. Based on the results of our studies, it became for the first time possible to get an idea of the main stages in the evolution of the studied region. Further geostructural measurements and dating of the host rocks will provide for a more precise definition of the proposed stages.

Segmentation and differential post-rift uplift at the Angola margin as recorded by the transform-rifted Benguela and oblique-to-orthogonal-rifted Kwanza basins

“…The 50-90 km-wide Lucapa tectonic corridor concentrates kimberlite and carbonatite pipes and dykes at the intersection between NE-SW and NW-SE structural trends disrupting the Angolan shield (Fig. 5;White et al, 1995). Considering the brittle upper crustal structures of Lower Cretaceous age, we suggest a close link between the Benguela sinistral transform rift and a deep-seated hot-spot magmatism in the continental interior as illustrated by the emplacement of the Angolan kimberlites along the Lucapa corridor (Fig.…”

“…6, White et al, 1995;Jelsma et al, 2004) and can be traced for over 1600 km across the Angolan shield (Reis, 1972). Most kimberlites in Africa and Brazil are of Early to Late Cretaceous age (124-83 Ma; e.g.…”

Re–Os isotopic composition of peridotitic sulphide inclusions in diamonds from Ellendale, Australia: Age constraints on Kimberley cratonic lithosphere

“…The main fields that comprise the West Kimberley province are, from North to South, the Ellendale, Calwynyardah and Noonkabah lamproites. These lamproite fields are emplaced in the hanging wall of the Oscar Shear system, which forms the contact between the King Leopold Orogen and the Lennard Shelf (White et al, 1995), and has been traced into the upper mantle by deep seismics (Drummond et al, 1989). There are 48 intrusions in the Ellendale lamproite field that are Miocene in age (24-19 Ma;Wellman, 1973;Pidgeon et al, 1989), of which 34 are diamond-bearing .…”

Major- and Trace-Element Compositions of Indicator Minerals that Occur as Macro- and Megacrysts, and of Xenoliths, from Kimberlites in Northeastern Angola

“…The trans-lithosphere discontinuity of the Lucapa structure played a very important role by favoring a thermal perturbation, melt production, and mantle upwelling [28,29], and in the evolution of the host rocks. The integration of petrography, geochemistry, and geothermobarometric studies of the less altered samples from six kimberlites in the northeastern Angola suggests that these kimberlites originated from different sources in spite of the fact that they are all located in the same tectonic corridor.…”