Plume head–lithosphere interactions near intra-continental plate boundaries

Abstract

Plume-lithosphere interactions (PLI) have important consequences both for tectonic and mineralogical evolution of the lithosphere: for example, Archean metallogenic crises at the boundaries of the West African and Australian cratons coincide with postulated plume events. In continents, PLI are often located near boundaries between younger plates (e.g., orogenic) and older stable plates (e.g., cratons), which represent important geometrical, thermal and rheological barriers that interact with the emplacement of the plume head (e.g., Archean West Africa, East Africa, Pannonian-Carpathian system). The observable PLI signatures are conditioned by plume dynamics but also by lithosphere rheology and structure. We address the latter problem by considering a free-surface numerical model of PLI with two stratified elastoviscous-plastic (EVP) lithospheric plates, one of which is older and thicker than another. The results show that: (1) plume head flattening is asymmetric, it is blocked from one side by the cold vertical boundary of the older plate, which leads to the mechanical decoupling of the crust from the mantle lithosphere, and to localized faulting at the cratonic margin; (2) the return flow from the plume head results in sub-vertical downthrusting (delamination) of the lithosphere at the margin, producing sharp vertical cold boundary down to the 400 km depth; (3) plume head flattening and migration towards the younger plate results in concurrent surface extension above the centre of the plume and in compression (pushing), down-thrusting and magmatic events at the cratonic margin (down-thrusting is also produced at the opposite border of the younger plate); these processes may result in continental growth at the "craton side"; (4) topographic signatures of PLI show basin-scale uplifts and subsidences preferentially located at cratonic margins. Negative Rayleigh-Taylor instabilities in the lithosphere above the plume head provide a mechanism for crustal delamination. Inferred consequences of PLI near intra-continental plate boundaries, such as faulting at cratonic edges and enhanced magmatic activity, could explain plume-related metallogenic crises, as suggested for West Africa and Australia.

Origin, Distribution and Evolution of Plume Magmatism in East Antarctica

“…Similar isotopic ratios are characteristic of the tholeiites of the Afanasy Nikitin Rise (Borisova et al, 2001;Sushchevskaya et al, 1996), which were formed 90 Ma near the proto-Southeast Indian Ridge, and of the 115 Ma tholeiites of the central part of the Kerguelen Island . The problem of the deep origin of hotspots (and low-velocity zones) in the Earth's shells has acquired special significance, because it has a direct influence on the possible spatial movement (both vertical and horizontal) of convective mantle flows (Burov et al, 2007). For instance, Pushcharovskii (Pushcharovskii & Pushcharovskii, 1999) emphasized that the Earth's shells, including the upper, middle, and lower mantle, with boundaries at depths of 670-900 km, 1700-2000 km, and 2900 km, have heterogeneities of various scales, which reflect possible lateral movement of materials.…”

The earth dynamic system: the earth rotation vs mantle convection

“…In the models like Figure 7 and Figure 8, if the Coriolis force and some other force relating to the earth rotation are accounted, the mantle movement situation will be more complex. For example, when a mantle plume, which has considerable impact on tectonic evolution of plates [25], moves from the deep to shallow, it will deflect westward because line speed in shallow layer is greater than that in deep layer.…”

“…The former mainly occurs in lithosphere and the latter in mantle [24]. The heat convection of the earth interior have two methods which are plate means and mantle plume means [23,25] (Figure 4). As reckoned, the Rayleigh number of the mantle is at least 3 × 10 6 , which exceeds 2000, the critical value of convection far away.…”

Coupled thermo-mechanical 3D subsidence analysis along the SW African passive continental margin

“…Additional work has been focused towards a quantification of the surface expression of mantle dynamics (e.g. Burov and Guillou-Frottier 2005;Burov et al 2007;Burov and Cloething 2007;Burov and Gerya 2014;Moucha and Forte 2011;Faccena and Becker 2010;Flament et al 2013). Although these investigations provided useful insights into the dynamics of the deep mantle and its interactions with surface deformation processes, they usually relied on first order geodynamic principles thus hampering to link modelling results to available observations on the present-day margin configuration.…”