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Experimental constraints on the origin and evolution of mildly alkalic basalts from the Kerguelen Archipelago, Southeast Indian Ocean.

Авторы: Scoates J., Cascio M., Weis D.

2006 г.

Contrib.Miner.Petrol.

      This experimental study examines the role of clinopyroxene fractionation on major element trends and alkalinity variations in mildly alkalic basalts from the Kerguelen Archipelago, Southeast Indian Ocean. Equilibrium crystallization experiments were carried out on a natural basalt (MgO=5 wt.%, alkalinity index= 0.10) over a range of pressures (0–1.43 GPa) and water contents (nominally dry to hydrous, 1.2 wt.% H2O) under relatively oxidizing conditions (Dlog FMQ=+1 to +2) at 0 GPa and relatively reducing conditions (Dlog FMQ=0 to –2) at all higher pressures. The hydrous experiments at 0.93 GPa closely reproduce most of the compositional variations in the 24–25 Ma mildly alkalic lavas from the archipelago, which supports a major role for high-Al clinopyroxene fractionation (5–9 wt.% Al2O3) at pressures corresponding to the base of the Northern Kerguelen Plateau (15–20 km). However, clinopyroxene fractionation at depth fails to produce important changes in the alkalinity of the residual melts. The transition from tholeiitic to mildly alkalic basalts on the Kerguelen Archipelago thus reflects primarily changes in melting conditions (lower extents of partial melting at higher pressures), which is related to crustal and lithospheric thickening as distance from the Southeast Indian Ridge increased over time from 43 to 24 Ma.

Файл: 646.pdf


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железо и магнитные свойства почв
тяжелые металлы в почвах
исследования с применением синхротронного излучения
TRM
вязкая намагниченность
морские базальты
изверженные породы
осадки
коэрцитивные свойства
химическая намагниченность
самообращение TRM
метод Телье
термомагнитные измерения
осадочная намагниченность
геохимия
синтезированные образцы
анизотропия магнитной восприимчивости
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