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Mantle plumes

Mantle 1 1450_20_15_10
Mantle 1 1450_20_15_10zoom

Mantle 2 1500_20_15_10
Mantle 2 1500_20_15_10zoom

Mantle 3 1550_20_15_10
Mantle 3 1550_20_15_10zoom

Mantle 4 1600_20_15_10
Mantle 4 1600_20_15_10zoom

This series of four models present the interaction of a mantle plume head (heat anomaly) in the upper mantle with the lithosphere.  Each model features the same step-like lithospheric architecture, to demonstrate how the plume head interacts with different depths of lithosphere.  From left to right, the depth of each lithosphere step is 200km, 150km and 100 km, respectively.  The mantle potential temperature is varied progressively between each model (values of 1450°C, 1500°C, 1550°C and 1600°C, respectively) to test how it influences model evolution.

The scenario with a low mantle potential temperature of 1450°C lacks decompression melting of the asthenosphere or asthenosphere-derived melts emplaced in the lithosphere.  Scenarios with higher mantle potential temperatures of 1500°C or greater feature adiabatic decompression melting of the asthenosphere from the beginning (prior to plume interaction) associated with emplacement of asthenosphere-derived melts into the lower and upper crust.  The greater the mantle potential temperature, the greater the volume and lateral extent of asthenosphere-derived melts produced.

In each model the plume rises, and propagates laterally to both the left and right -under the thickest and thinnest lithosphere, respectively.  Scenarios with low mantle potential temperatures (1450°C and 1500°C) produce no plume-derived melts under the thickest (200km) lithosphere, but do produce plume-derived melts under thinner (100km and 150km-thick) sections of the lithosphere.  Significantly, scenarios with hotter environments (1550°C and 1600°C mantle potential temperatures) produce low degree partial melts at deeper depths – beneath the thickest (200km) craton.  These conditions are equivalent to those in during Archean, and these plume-derived melts may correspond to Barberton-type komatiites.  Greater volumes of plume-derived melts are emplaced in the thinner sections of lithosphere under the higher temperature environments.

In the 1550°C mantle potential temperature scenario, erosion of the base of the lithosphere leads to significant lithospheric thinning – allowing the development and penetration of greater volumes of adiabatic decompression melts at the base of the lithosphere.  This in-turn drives delamination of large sections of the mantle lithosphere.

Importantly, these models demonstrate that plume interaction with the base of the lithosphere may generate 2 types of magmatism: mafic melts derived from the decompression melting of the asthenosphere, and potential komatities/basalts derived from adiabatic melting of the plume head.