Petrogenesis of the Fe-Ti intrusive complexes in the Sierra Leone region, Central Atlantic |
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Authors: | V A Simonov E V Sharkov S V Kovyazin |
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Institution: | (1) Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA;(2) Present address: University of Malaya, 50603 Kuala Lumpur, Malaysia |
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Abstract: | The study of melt inclusions in Cr-spinels from melanocratic troctolites provided the first direct information on the physicochemical
parameters of enriched magmatic systems that produced high-Fe and high-Ti intrusive complexes in the Sierra-Leone region (Central
Atlantic, 6°N). These complexes are made up of predominating hornblende Fe-Ti oxide gabbronorites and gabbrodiorites with
subordinate amount of ultramafics, diorites, quartz diorites, and trondhjemites. The study of melt inclusions and rocks showed
that the majority of gabbroids of the Central Atlantic (Sierra Leone area and 15°20′ Fracture Zone) were derived from N-MORB-type
melts, whereas differentiated Fe-Ti-oxide rocks were crystallized from other melts, which were preserved as inclusions in
the Cr-spinels from the melanocratic troctolites of the Sierra Leone region. The ion-microprobe study of these inclusions
yield direct evidence on the elevated water content (up to 1.24–1.77 wt %) in the parental melts of Fe-Ti oxide rocks. Data
on trace and rare-earth element distribution together with high (La/Sm)N and (Ce/Yb)N ratios in the inclusions indicate the possible influence of deep plume source on the generation of these magmas. Simulation
based on melt inclusion data testifies that high-Fe intrusions of the Sierra Leone area were crystallized from the water-saturated
magmas at relatively low temperatures (1020–1240°C). It was shown that the geochemically enriched Fe-Ti melts were presumably
formed regardless of N-MORB-type magmatism predominant in Central Atlantic, under the influence of new mantle plume that caused
melting of hydrated oceanic lithosphere. |
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