The stable isotope composition (O,H) of whole-rock and mineral separates of Cambrian-Ordovician gabbros, diorites, granodiorites and granites forming the Mt. Abbott composite intrusions (Northern Victoria Land, Antarctica) was measured to constrain the origin and evolution of the magmas postdating the Ross Orogen. The delta(18)O values of olivine gabbros plot in the field of slightly evolved mantle-derived melts (delta(18)O(WR) = 6.8-7.4parts per thousand). The O-isotope character of the mantle source inferred from the 6180 values of cumulous olivine in gabbros (5.7-6.8parts per thousand) is enriched in O-18 compared to modem arc-related magmas. Geochemical data and concurrent high 6180 values, and initial strontium (Sr-87/Sr-86=0.7060) and neodymium (Nd-143/Nd-144=0.5122) isotope ratios indicate that the olivine gabbros formed by crustal contamination of a primary calc-alkaline basaltic melt. The diorites have high 6180 values, among the highest ever measured for dioritic rocks (8.7-10.3parts per thousand), and Sr-isotope ratios that partially overlap with the adjacent and mingled felsic lithologies (0.708-0.710). The diorites have pyroxene with high, nearly constant (delta(18)O values (8.2-8.6parts per thousand) that are independent from the silica content of the rocks; thus, they did not increase in response of the chemical evolution of the rocks. The diorites originated from the same primary calc-alkaline basalt experiencing different amounts of crustal contamination, and underwent different degrees of mixing with the adjacent granites, producing granodioritic facies and quartz/feldspar xenocrystic diorites. The delta(18)O, Sr-87/Sr-86 and Nd-143/Nd-144 compositions of the granites and granodiorites overlap (10.8-12.1parts per thousand, 0.7096-0.7108, 0.5119-0.5120). They are distinct from the values of the mafic rocks and indicate that gabbros and granites were not cogenetic. The granites are a separate melt component likely derived from nonmodal partial melting of fertile meta-igneous protoliths. (C) 2002 Elsevier Science B.V. All rights reserved.

Oxygen isotope evidence for crustal assimilation and magma mixing in the Granite Harbour Intrusives, Northern Victoria Land, Antarctica / Dallai, L; Ghezzo, C; Sharp, Zd. - In: LITHOS. - ISSN 0024-4937. - 67:1-2(2003), pp. 135-151. [10.1016/S0024-4937(02)00267-0]

Oxygen isotope evidence for crustal assimilation and magma mixing in the Granite Harbour Intrusives, Northern Victoria Land, Antarctica

Dallai L;
2003

Abstract

The stable isotope composition (O,H) of whole-rock and mineral separates of Cambrian-Ordovician gabbros, diorites, granodiorites and granites forming the Mt. Abbott composite intrusions (Northern Victoria Land, Antarctica) was measured to constrain the origin and evolution of the magmas postdating the Ross Orogen. The delta(18)O values of olivine gabbros plot in the field of slightly evolved mantle-derived melts (delta(18)O(WR) = 6.8-7.4parts per thousand). The O-isotope character of the mantle source inferred from the 6180 values of cumulous olivine in gabbros (5.7-6.8parts per thousand) is enriched in O-18 compared to modem arc-related magmas. Geochemical data and concurrent high 6180 values, and initial strontium (Sr-87/Sr-86=0.7060) and neodymium (Nd-143/Nd-144=0.5122) isotope ratios indicate that the olivine gabbros formed by crustal contamination of a primary calc-alkaline basaltic melt. The diorites have high 6180 values, among the highest ever measured for dioritic rocks (8.7-10.3parts per thousand), and Sr-isotope ratios that partially overlap with the adjacent and mingled felsic lithologies (0.708-0.710). The diorites have pyroxene with high, nearly constant (delta(18)O values (8.2-8.6parts per thousand) that are independent from the silica content of the rocks; thus, they did not increase in response of the chemical evolution of the rocks. The diorites originated from the same primary calc-alkaline basalt experiencing different amounts of crustal contamination, and underwent different degrees of mixing with the adjacent granites, producing granodioritic facies and quartz/feldspar xenocrystic diorites. The delta(18)O, Sr-87/Sr-86 and Nd-143/Nd-144 compositions of the granites and granodiorites overlap (10.8-12.1parts per thousand, 0.7096-0.7108, 0.5119-0.5120). They are distinct from the values of the mafic rocks and indicate that gabbros and granites were not cogenetic. The granites are a separate melt component likely derived from nonmodal partial melting of fertile meta-igneous protoliths. (C) 2002 Elsevier Science B.V. All rights reserved.
2003
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Oxygen isotope evidence for crustal assimilation and magma mixing in the Granite Harbour Intrusives, Northern Victoria Land, Antarctica / Dallai, L; Ghezzo, C; Sharp, Zd. - In: LITHOS. - ISSN 0024-4937. - 67:1-2(2003), pp. 135-151. [10.1016/S0024-4937(02)00267-0]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1528731
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