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Dynamics of Plume-Triple Junction Interaction Old Dominion University ODU Digital Commons OEAS Faculty Publications Ocean, Earth & Atmospheric Sciences 2016 Dynamics of Plume-Triple Junction Interaction: Results from a Series of Three-Dimensional Numerical Models and Implications for the Formation of Oceanic Plateaus Mladen Dordevic Jennifer Georgen Old Dominion University, [email protected] Follow this and additional works at: https://digitalcommons.odu.edu/oeas_fac_pubs Part of the Geochemistry Commons, and the Geophysics and Seismology Commons Repository Citation Dordevic, Mladen and Georgen, Jennifer, "Dynamics of Plume-Triple Junction Interaction: Results from a Series of Three- Dimensional Numerical Models and Implications for the Formation of Oceanic Plateaus" (2016). OEAS Faculty Publications. 214. https://digitalcommons.odu.edu/oeas_fac_pubs/214 Original Publication Citation Dordevic, M., & Georgen, J. (2016). Dynamics of plume-triple junction interaction: Results from a series of three-dimensional numerical models and implications for the formation of oceanic plateaus. Journal of Geophysical Research: Solid Earth, 121(3), 1316-1342. doi:10.1002/2014jb011869 This Article is brought to you for free and open access by the Ocean, Earth & Atmospheric Sciences at ODU Digital Commons. It has been accepted for inclusion in OEAS Faculty Publications by an authorized administrator of ODU Digital Commons. For more information, please contact [email protected]. PUBLICATIONS Journal of Geophysical Research: Solid Earth RESEARCH ARTICLE Dynamics of plume–triple junction interaction: Results 10.1002/2014JB011869 from a series of three-dimensional numerical Key Points: models and implications for the formation • A series of dynamic models investigates mantle plume–triple junction interaction of oceanic plateaus • Variations in oceanic plateau area, bathymetry, and crustal thickness Mladen Dordevic1,2 and Jennifer Georgen3 are calculated • Models offer a framework for 1Department of Physics, Old Dominion University, Norfolk, Virginia, USA, 2Now at Incorporated Research Institutions for constraining plateau formation 3 in natural settings Seismology, Washington, District of Columbia, USA, Department of Ocean, Earth, and Atmospheric Sciences, Old Dominion University, Norfolk, Virginia, USA Correspondence to: Abstract Mantle plumes rising in the vicinity of mid-ocean ridges often generate anomalies in melt J. Georgen, production and seafloor depth. This study investigates the dynamical interactions between a mantle [email protected] plume and a ridge-ridge-ridge triple junction, using a parameter space approach and a suite of steady state, three-dimensional finite element numerical models. The top domain boundary is composed of three Citation: diverging plates, with each assigned half-spreading rates with respect to a fixed triple junction point. Dordevic, M., and J. Georgen (2016), Dynamics of plume–triple junction The bottom boundary is kept at a constant temperature of 1350°C except where a two-dimensional, interaction: Results from a series of Gaussian-shaped thermal anomaly simulating a plume is imposed. Models vary plume diameter, plume three-dimensional numerical models location, the viscosity contrast between plume and ambient mantle material, and the use of dehydration and implications for the formation of oceanic plateaus, J. Geophys. Res. Solid rheology in calculating viscosity. Importantly, the model results quantify how plume-related anomalies in Earth, 121, 1316–1342, doi:10.1002/ mantle temperature pattern, seafloor depth, and crustal thickness depend on the specific set of parameters. 2014JB011869. To provide an example, one way of assessing the effect of conduit position is to calculate normalized area, defined to be the spatial dispersion of a given plume at specific depth (here selected to be 50 km) Received 7 JAN 2015 Accepted 19 JAN 2016 divided by the area occupied by the same plume when it is located under the triple junction. For one Accepted article online 22 JAN 2016 particular case modeled where the plume is centered in an intraplate position 100 km from the triple Published online 11 MAR 2016 junction, normalized area is just 55%. Overall, these models provide a framework for better understanding plateau formation at triple junctions in the natural setting and a tool for constraining subsurface geodynamical processes and plume properties. 1. Introduction 1.1. Plume-Ridge Interactions Hot spots and mid-ocean ridges are the surface expressions of subsurface mantle upwelling and magma generation processes. At mid-ocean ridges, lithospheric plates diverge and the mantle upwells, creating the oceanic crust through decompressional melting. Hot spots are typically associated with elevated topo- graphy or shallow bathymetry and often also with linear volcanic chains showing systematic age progression of the eruptive products. It is widely believed that many hot spots are associated with mantle plumes [e.g., Morgan, 1971, 1972, 1981; Detrick et al., 2002; Ito et al., 2003; Putirka et al., 2007; Wolfe et al., 2009; Leroy et al., 2010; Barruol and Fontaine, 2013]. A mantle plume is commonly defined as a region of the mantle that is hotter than the surrounding material, originating from convective thermal boundary instabilities [Olson, 1990]. Geochemical heterogeneity has also been suggested to be important in plume dynamics and upwelling. The interaction of mantle plumes with nearby mid-ocean ridges results in physical and chemical anomalies along 15–20% of the total mid-ocean ridge system length [Ito et al., 2003]. Based upon the spatial extent of bathymetric swells and magnetic isochron data, it can be shown that plume-ridge interactions may last for several million years or longer [e.g., Cannat et al., 1999; Ito et al., 2003]. Previous authors have established scaling laws for plume-ridge dynamical interaction and tested them against experimental data obtained either in the lab using corn syrup tanks [e.g., Feighner and Richards, 1995] or using solutions from numerical models [Ribe et al., 1995; Ribe, 1996; Ito et al., 1996, 1997; Albers and ©2016. American Geophysical Union. Christensen, 2001]. For example, early studies [e.g., Feighner and Richards, 1995] found a relationship between All Rights Reserved. plume volume flux (Q), half-spreading rate (u), and waist width (W, the length of ridge axis influenced by a DORDEVIC AND GEORGEN PLUME–TRIPLE JUNCTION INTERACTION 1316 Journal of Geophysical Research: Solid Earth 10.1002/2014JB011869 dispersing mantle plume): W = c(Q/u)1/2, where c is a constant. This relatively simple relationship has been further developed and refined by subsequent modeling studies [e.g., Ito et al., 1997; Ribe and Delattre, 1998; Albers and Christensen, 2001], but it captures an essential inverse proportionality between spreading rate and waist width. That is, for a plume of a given flux, the slower a ridge’s spreading rate, the longer the ridge axis that is expected to show plume-related anomalies. 1.2. Triple Junctions A triple junction is defined as a point where three plate boundaries meet [McKenzie and Morgan, 1969]. Triple junctions represent important geological settings along the global mid-ocean ridge system where mantle dynamics are influenced by the motions of three plates. Each branch of a triple junction can be a ridge, trench, or transform fault, resulting in 16 basic possible configurations, of which only some are stable over geologic time [McKenzie and Morgan, 1969]. From the velocity vector method it can be shown that ridge-ridge-ridge (RRR) triple junctions are stable for all possible spreading rates and ridge orientations. Several previous studies [e.g., Sclater et al., 1976; Searle, 1980; Searle and Francheteau, 1986; Mitchell and Parson, 1993; Klein et al., 2005; Miranda et al., 2014] have investigated plate kinematics and the geological characteristics of the seafloor near RRR triple junctions. 1.3. Study Objectives: Plume–Triple Junction Interactions The primary objective of this investigation is to improve understanding of the dynamics of plume–triple junction interaction. A series of numerical models is used to assess the role of RRR plate divergence in gov- erning the dispersion of plume material in the upper mantle. The models vary multiple parameters, including the location of the plume with respect to the triple junction, plume flux, and mantle viscosity structure. The results from these numerical models provide insight into the generation of oceanic plateaus at RRR triple junctions. To our knowledge, this is the first numerical study that systematically investigates plume–triple junction interaction using a series of geodynamical models. As such, a major goal of this work is to explore, in the general sense, how plate boundary geometry affects plume advection and plume-related seafloor anomalies. Before the modeling is applied to any specific plume–triple junction system, it is important to develop under- standing about how various parameters interplay to affect the dynamics of the system. Therefore, this manu- script is structured to first present and discuss the results of the series of numerical models. Then examples are provided to show how the modeling methodology can be applied to specific geological settings. 1.4. Prior Geodynamic Studies: RRR Triple Junctions Previous studies [e.g., Georgen and Lin, 2002; Georgen, 2008; Georgen and Sankar, 2010; Georgen, 2011] have used numerical modeling to explore generalized properties of mantle flow and thermal patterns in the vicinity of RRR triple junctions. Georgen and Lin
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