Progressive alkali ion exchange with stratigraphic position in a pyroclastic cooling-unit; Mt. Torro, Sabatini, Central Italy

被引：0

作者：

Jorgensen, JO ^{[1
]}

Holm, PM ^{[1
]}

机构：

[1] Univ Copenhagen, Inst Geol, DK-1350 Copenhagen, Denmark

来源：

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH | 1998年 / 86卷 / 1-4期

关键词：

cooling-unit; alteration; alkali-ion exchange; glass;

D O I：

10.1016/S0377-0273(98)00041-9

中图分类号：

P [天文学、地球科学];

学科分类号：

07 ;

摘要：

Significant variation of K2O/Na2O ratios and total alkali contents, elevated Loss on Ignition (12-16 wt.%) values and elevated Fe3+/Fe2+ are shown in new data from a road cut profile of pyroclastic rocks in an area of young ultra-potassic rocks. Decreasing K2O/Na2O ratios and total alkali contents are systematically related to stratigraphic position, being most pronounced at the centre of the deposit, probably because of the slower cooling rate. Pumice bombs are less altered than ash but show the same variation pattern. Except for the alkalis, hydration and the oxidation state of iron, the geochemical compositions of the rocks are unchanged. (C) 1998 Elsevier Science B.V. All rights reserved.

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页码：179 / 185

页数：7