Thermal model of MOR axial zones: formation of the magma chambersстатья

Дата последнего поиска статьи во внешних источниках: 28 октября 2016 г.

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[1] Galushkin Y. I., Dubinin E. P. Thermal model of mor axial zones: formation of the magma chambers // IZVESTIYA. Earth Sciences Section Russian Academy of Natural Sciences. Special Issue (№ 23). Presented to the 35th Session of the International Geological Congress, Cape Town, 2016. — 2016. — no. 23. — P. 90–124. The non-steady model of discrete-continuous spreading is used to analyze numerically the processes of formation and evolution of the crust and mantle magma chambers in the axial zones of the Mid - Oceanic Ridges (MOR) and refine the role of latent heat of fusion of the mantle and crust rocks in these processes. Although our model is limited by horizontal streamlines of flow of the crust and uppermost mantle rock, a more correct treatment of latent heat thermal effect during solidification or fusion of the mantle and crust rocks allows a rather satisfactory explanation of location, size and shape of the crust and mantle magma chambers and an analysis of variations in these parameters depending on the spreading rate, temperature and composition of the mantle and crust rocks. A thermal regime of the axial zones in the Mid Oceanic Ridges are computed with consideration of such factors as hydrothermal cooling of the crust, latent heat of rock fusion, change in the solidus and liquidus temperatures according to the crust and mantle rock composition. In the axial zones of the fast spreading ridges (V > 8 cm/year), the modeling confirms an occurrence of the zones with higher melt concentration (magma chambers) at two levels: at depth 1.6 km and more in the crust and just below the MOHO boundary in the mantle. Variations in the crust rock composition with depth affected a solidus temperature determine a melt degree of the rocks and a shape of the crust chamber. In the axial zones of the slow spreading ridges (V < 4 cm/year), a quasi steady-state magma cham¬ber in the crust does not exist, but it is possible here a formation of the short-living magma chambers in the crust at higher temperatures of the mantle. In all cases, the mantle zones with higher melt fraction (focused mantle upwelling zones) are formed in the axial zones in all of the ridges. Computation of temperature distribution in the MOR axial zones gives an opportunity to analyze numerically changes in the rock strength of the young oceanic lithosphere versus depth and distance from the ridge axis and refine conditions for occurrence of weak zones in the lithosphere of the ridges with different spreading rates.

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