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UNCORRECTEDPROOF 2 Speculations on the nature and cause of mantle heterogeneity

2 Speculations on the nature and cause of mantle heterogeneity
3 Don L. Anderson
4 Seismological Laboratory 252-21, Div. of Geological and Planetary Sci., California Institute of Technology, Pasadena, CA 91125, United States
5 Received 19 August 2004; received in revised form 19 July 2005; accepted 20 July 2005
6 Abstract
7 Hotspots and hotspot tracks are on, or start on, preexisting lithospheric features such as fracture zones, transform faults,
8 continental sutures, ridges and former plate boundaries. Volcanism is often associated with these features and with regions of
9 lithospheric extension, thinning, and preexisting thin spots. The lithosphere clearly controls the location of volcanism. The nature
10 of the volcanism and the presence of `melting anomalies' or `hotspots', however, reflect the intrinsic chemical and lithologic
11 heterogeneity of the upper mantle. Melting anomalies--shallow regions of ridges, volcanic chains, flood basalts, radial dike
12 swarms--and continental breakup are frequently attributed to the impingement of deep mantle thermal plumes on the base of the
13 lithosphere. The heat required for volcanism in the plume hypothesis is from the core. Alternatively, mantle fertility and melting
14 point, ponding and focusing, and edge effects, i.e., plate tectonic and near-surface phenomena, may control the volumes and rates
15 of magmatism. The heat required is from the mantle, mainly from internal heating and conduction into recycled fragments. The
16 magnitude of magmatism appears to reflect the fertility, not the absolute temperature, of the asthenosphere. I attribute the chemical
17 heterogeneity of the upper mantle to subduction of young plates, aseismic ridges and seamount chains, and to delamination of the
18 lower continental crust. These heterogeneities eventually warm up past the melting point of eclogite and become buoyant low-
19 velocity diapirs that undergo further adiabatic decompression melting as they encounter thin or spreading regions of the


Source: Anderson, Don L. - Division of Geological and Planetary Sciences, California Institute of Technology


Collections: Geosciences