کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4716465 1638701 2012 8 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Nephelinite–melilitite–carbonatite relationships: Evidence from Pleistocene–recent volcanism in northern Tanzania
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
Nephelinite–melilitite–carbonatite relationships: Evidence from Pleistocene–recent volcanism in northern Tanzania
چکیده انگلیسی

The younger (< 1.2 Ma) nephelinite–melilitite–carbonatite-volcanoes in the Gregory Rift Valley of northern Tanzania (termed the Younger Extrusives) comprise one of the most concentrated areas of carbonatite magmatism on Earth. The larger strato-volcanoes, characterised by strongly evolved magmatism, are surrounded by volumetrically much-smaller features (scoria and tuff-cones, explosion craters, lava flows) of carbonate-rich olivine-bearing nephelinites or melilitites that, in their relative primitiveness, are potential parents to the much-largerstrato-volcanoes. The bimodal size distribution is mirrored in bulk magma chemistry, and in their Sr, Nd and Pb isotopes, with the more primitive magmas lying close to a HIMU source; the isotope data for the larger strato-volcanoes cover a wider, linear array interpreted as due to variable degrees of interaction between HIMU magmas and enriched lithosphere, evidence for which is found in Tanzanian mantle xenoliths.An integrated model involves carbonated olivine–nephelinite magma generated in the asthenosphere by melting of carbonate-bearing peridotite. Small amounts of the melt migrate rapidly and are extruded as the olivine–nephelinites and –melilitites. Larger amounts of magma pond in the lithosphere with which they react and, during variable periods of stagnation, varying degrees of olivine–pyroxene–spinel fractionation take place before upward migration of now-differing magma batches. Variable residence time within, and reaction with, variably enriched lithosphere accounts for the array between the HIMU and enriched mantle end-members in the isotope mixing model.


► The young (1 Ma) N. Tanzania volcanic province is the most concentrated area of carbonatite volcanism on Earth.
► Small volcanic features are of parental primitive ultrabasic composition.
► Larger volcanoes are of well-differentiated nephelinites, phonolites and carbonatites.
► Volume and isotopic differences are due to different rates of ascent through, and residence time in, ancient lithosphere.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Lithos - Volume 152, 1 November 2012, Pages 3–10
نویسندگان
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