کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
8911604 | 1638619 | 2018 | 58 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
The magmatic evolution and genesis of the Quaternary basanite-trachyphonolite suite of Itasy (Madagascar) as inferred by geochemistry, Sr-Nd-Pb isotopes and trace element distribution in coexisting phases
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موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
The Itasy is a Pleistocene-Holocene volcanic field in central Madagascar, located to the west of the Ankaratra volcanic complex. It comprises scoria cones and lava domes (>120), with associated pyroclastic fall and mafic lava flows, covering an area of ab. 400â¯km2. The last volcanic episodes probably dated ca. 6000-7100â¯y BP; warm springs and geysers are active. The juvenile samples comprise a peculiar, almost bimodal, rock suite ranging from potassic leucite-kaersutite-bearing basanites, tephrites and phonotephrites, to benmoreites and titanite-haüyne-bearing trachyphonolites (MgO from 9-10â¯wt% to 0.1â¯wt%). These rocks show continuous and overlapping variations in the bulk-rock and phase composition (olivine, clinopyroxene, amphibole, feldspar, leucite, haüyne, nepheline, oxides, apatite, titanite, glass and other accessories). The basanites have homogeneous isotopic composition (87Sr/86Srâ¯=â¯0.70366-0.70378, 143Nd/144Ndâ¯=â¯0.51274-0.51277, 206Pb/204Pbâ¯=â¯18.7-18.9, 207Pb/204Pbâ¯=â¯15.53-15.56; 208Pb/204Pbâ¯=â¯38.89-39.01), and a marked enrichment in the most incompatible elements (LILE and HFSE reach 100-215 times primitive mantle). These features are consistent with low degrees of partial melting of a volatile-, LILE- and HFSE-rich, amphibole-bearing peridotitic mantle induced by uplift during an E-W-directed extensional regime, as is found in central Madagascar. The marked changes in the geochemical composition, and small variations of the Sr-Nd-Pb isotopes in the trachyphonolites (87Sr/86Srâ¯=â¯0.70425-0.70446, 143Nd/144Ndâ¯=â¯0.51266-0.51269, 206Pb/204Pbâ¯=â¯18.18-18.39, 207Pb/204Pbâ¯=â¯15.49-15.51; 208Pb/204Pbâ¯=â¯38.38-39.57) with respect to basanites and tephrites point to a limited amount of crustal contamination by the relatively low-206Pb/204Pb, low-143Nd/144Nd, high-87Sr/86Sr Precambrian basement rocks (of Middle Archean to Late Proterozoic age), and highlight the geochemical effects of titanite and anorthoclase removal on the trace element fractionation trends, a feature also shown in the trace element composition of the phenocrysts in trachyphonolites.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Lithos - Volumes 310â311, June 2018, Pages 50-64
Journal: Lithos - Volumes 310â311, June 2018, Pages 50-64
نویسندگان
L. Melluso, R.D. Tucker, C. Cucciniello, A.P. le Roex, V. Morra, A. Zanetti, R.L. Rakotoson,