González-Maurel Osvaldo, Deegan Frances M, le Roux Petrus, Harris Chris, Troll Valentin R, Godoy Benigno
Department of Geological Sciences, University of Cape Town, Rondebosch, 7700, South Africa.
Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile.
Sci Rep. 2020 Apr 22;10(1):6864. doi: 10.1038/s41598-020-63454-1.
The Andean continental arc is built upon the thickest crust on Earth, whose eruption products reflect varying degrees of crustal assimilation. In order to robustly model magma evolution and assimilation at subduction zones such as the Andes, the compositions of parental magmas feeding crustal magma reservoirs need to be defined. Here we present new olivine and clinopyroxene oxygen isotope data from rare mafic volcanic rocks erupted at the margins of the giant Altiplano-Puna Magma Body (APMB) of the Altiplano-Puna Volcanic Complex, Central Andes. Existing olivine and pyroxene δO values for the Central Andes are highly variable and potentially not representative of sub-arc parental compositions. However, new olivine (n = 6) and clinopyroxene (n = 12) δO values of six Central Andean volcanoes presented here display a narrow range, with averages at 6.0‰ ± 0.2 (2σ S.D.) and 6.7‰ ± 0.3 (2σ S.D.), consistent with a common history for the investigated minerals. These data allow us to estimate the δO values of sub-arc, parental melts to ca. 7.0‰ ± 0.2 (2σ S.D.). Parental melts feeding the APMB and associated volcanic centres are postulated to form in the felsic continental crust following assimilation of up to 28% high-δO basement rocks by mantle-derived magmas.
安第斯大陆弧构建于地球上最厚的地壳之上，其火山喷发产物反映了不同程度的地壳同化作用。为了有力地模拟俯冲带（如安第斯山脉）的岩浆演化和同化过程，需要确定供给地壳岩浆库的母岩浆成分。在此，我们展示了来自安第斯山脉中部阿尔蒂普拉诺-普纳火山复合体巨大的阿尔蒂普拉诺-普纳岩浆体（APMB）边缘罕见的镁铁质火山岩的新橄榄石和单斜辉石氧同位素数据。安第斯山脉中部现有的橄榄石和辉石δO值变化很大，可能无法代表弧下母岩浆成分。然而，这里展示的六个安第斯山脉中部火山的新橄榄石（n = 6）和单斜辉石（n = 12）δO值显示出较窄的范围，平均值分别为6.0‰ ± 0.2（2σ标准差）和6.7‰ ± 0.3（2σ标准差），这与所研究矿物的共同历史一致。这些数据使我们能够估计弧下母熔体的δO值约为7.0‰ ± 0.2（2σ标准差）。推测供给APMB和相关火山中心的母熔体是由地幔源岩浆同化高达28%的高δO基底岩石后在长英质地壳中形成的。
