Plume-induced dynamic instabilities near cratonic blocks: Implications for P–T–t paths and metallogeny

Abstract

et al.. Plume-induced dynamic instabilities near cratonic blocks: implications for P-Tt paths and metallogeny. Global and Planetary Change, Elsevier, 2012, 90-91, pp.37-50. 10.1016/j.gloplacha.2011 ÔØ Å ÒÙ× Ö ÔØ Plume-induced dynamic instabilities near cratonic blocks: Implications for P-T-t paths and metallogeny This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 AbstractPlume head -lithosphere interactions around cratonic blocks result in thermo-mechanical disturbances that lead to heating and burial phases of crustal rocks. We present results from numerical models of plume head -cratonic blocks interactions where a free upper surface condition and realistic rheologies are accounted for. These models include distinct cratonic blocks embedded within a continental lithosphere and separated by several hundreds of kilometres. Surface topography, thermal field and effective viscosity values are tracked for 20Myr of interactions. The modelled dynamic interaction of a plume head around cratonic blocks results in two main types of instabilities, each of them resulting in a distinct P-T-t path.The "slab-like" instability, focused on cratonic edges when plume head is away from the craton centre, shows a near-isothermal burial phase, while the "drip-like" instability occurring above plume head material results in a near-isobaric heating phase. Consequently, both clockwise and counterclockwise P-T-t paths can be expected around cratons, as actually observed around the Tanzanian craton and other cratonic areas. Metallogenic data from gemstone-bearing rocks in south-east Africa and data from ultrahigh temperature and ultrahigh pressure metamorphism are compatible with our model. It appears that vertical mantle dynamics around cratons may also explain thermobarometric signatures that are often attributed to horizontal tectonics.

The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U‐Th‐Sm)/He thermochronology

“…The intrinsic linkage between horizontal and vertical motions illustrated by these models suggests that the coeval changes at approximately 90 Ma and 30 Ma in the South Atlantic spreading rates (Figure ) and uplift of the southwest African continental margin are geodynamically linked to one another. The interaction between in‐plane stresses in the lithosphere and thermal convection in the mantle has been investigated by recent three‐dimensional thermomechanical models using realistic lithospheric rheologies and predict complex patterns of short‐wavelength deformation of a brittle crust overlying a ductile mantle lithosphere [ Burov , ; Guillou‐Frottier et al, ; Burov and Gerya , ; Koptev et al, ]. This work offers the interesting possibility of a regional, long‐wavelength mechanism of uplift, like mantle flow, causing quite local deformation at the surface, and would explain why we observe both regional and local signals of tectonic activity within Southern Africa during the mid‐Cretaceous.…”

The thinning of subcontinental lithosphere: The roles of plume impact and metasomatic weakening

“…Morency et al [2002] found that, depending on the width of the cratonic block, it takes 50-750 Myr to convectively remove a 250 km thick cratonic root if the lithosphere has an equilibrium thickness of about 100 km, but the chemical heterogeneity of continental lithosphere and plume events was not considered in their study. Guillou-Frottier et al [2012] argued for several different plume-induced dynamical instabilities near the cratonic root to explain the P-T-t paths recorded by the metallogenic data from South Africa. These studies do not explicitly explore the role of compositional buoyancy and strengthening on cratonic mantle dynamics for a situation in which a plume impacts on the subcontinental root.…”

“…Guillou‐Frottier et al . [] argued for several different plume‐induced dynamical instabilities near the cratonic root to explain the P‐T‐t paths recorded by the metallogenic data from South Africa. These studies do not explicitly explore the role of compositional buoyancy and strengthening on cratonic mantle dynamics for a situation in which a plume impacts on the subcontinental root.…”

Contrasting Mesozoic evolution across the boundary between on and off craton regions of the South African plateau inferred from apatite fission track and (U‐Th‐Sm)/He thermochronology

“…Insights from geodynamic models support the hypothesis that vertical stresses imposed at the base of the lithosphere by the vertical component of mantle flow will induce significant uplift (or subsidence for downwelling mantle) of the interior plateau [e.g., Gurnis et al, 2000;Moucha et al, 2008;Braun, 2010;Forte et al, 2010;Flament et al, 2014]. It is also significant that recent thermomechanical models that simulate the interaction between mantle convection and the overlying lithosphere suggest that brittle deformation of the upper crust at short-wavelength scales may also occur in tandem with longer wavelength (plume-induced) uplift of the lithosphere [e.g., Burov and Cloetingh, 2009;Guillou-Frottier et al, 2012;Cloetingh et al, 2013;Koptev et al, 2015]. In addition to deformation arising from these vertical stresses applied at the base of the lithosphere, horizontal stresses arising from plate boundary and plate kinematic changes may propagate significant distances and drive local, brittle deformation and reactivation of pre-existing structures within continental interiors [Daly et al, 1989;Janssen et al, 1995;Guiraud and Bosworth, 1997;Fairhead et al, 2013;Viola et al, 2012;Pérez-Díaz and Eagles, 2014;Salomon et al, 2014Salomon et al, , 2015.…”