Sr isotope zoning in plagioclase from andesites at Cabo De Gata, Spain: evidence for shallow and deep contamination
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Sr isotope zoning in plagioclase from andesites at Cabo De Gata, Spain : evidence for shallow and deep contamination. / Waight, Tod Earle; Tørnqvist, Jakob .
I: Lithos, Bind 308-309, 2018, s. 159-167.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
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TY - JOUR
T1 - Sr isotope zoning in plagioclase from andesites at Cabo De Gata, Spain
T2 - evidence for shallow and deep contamination
AU - Waight, Tod Earle
AU - Tørnqvist, Jakob
PY - 2018
Y1 - 2018
N2 - Plagioclase crystals in andesites from the Cabo De Gata region show generally radiogenic Sr isotope compositions and consistent core to rim increases in 87Sr/86Sr that are indicative of open system processes in the lithosphere and crustal contamination during crystallization. High-grade metamorphic rocks of the Alpujárride and Nevado-Filábride complexes represent the most likely crustal contaminants. The plagioclases are characterized by subtly zoned and resorbed calcic cores (An73-86). These cores also have radiogenic 87Sr/86Sr (0.7127-0.7129), although less radiogenic than plagioclase rims, groundmass plagioclase and whole rock compositions (up to 87Sr/86Sr = 0.7135). These cores are interpreted to represent early crystallization of plagioclase from hydrous melts emplaced into the lower crust. The parental melts to these andesites must therefore have already inherited their radiogenic Sr isotope compositions prior to entering the lower crust and before the onset of crystallization of plagioclase, which is inconsistent with previous models suggesting that the generally radiogenic nature of Sr in these volcanics reflects large amounts of crustal contamination. Instead, the isotope systematics are consistent with previous models invoked significant addition of a subducted sediment component to the mantle source. The high-An% plagioclase cores are characterized by resorption textures, which are consistent with dissolution during rapid decompression and/or devolatisation during magma migration from the lower crust into upper crustal magma chambers.
AB - Plagioclase crystals in andesites from the Cabo De Gata region show generally radiogenic Sr isotope compositions and consistent core to rim increases in 87Sr/86Sr that are indicative of open system processes in the lithosphere and crustal contamination during crystallization. High-grade metamorphic rocks of the Alpujárride and Nevado-Filábride complexes represent the most likely crustal contaminants. The plagioclases are characterized by subtly zoned and resorbed calcic cores (An73-86). These cores also have radiogenic 87Sr/86Sr (0.7127-0.7129), although less radiogenic than plagioclase rims, groundmass plagioclase and whole rock compositions (up to 87Sr/86Sr = 0.7135). These cores are interpreted to represent early crystallization of plagioclase from hydrous melts emplaced into the lower crust. The parental melts to these andesites must therefore have already inherited their radiogenic Sr isotope compositions prior to entering the lower crust and before the onset of crystallization of plagioclase, which is inconsistent with previous models suggesting that the generally radiogenic nature of Sr in these volcanics reflects large amounts of crustal contamination. Instead, the isotope systematics are consistent with previous models invoked significant addition of a subducted sediment component to the mantle source. The high-An% plagioclase cores are characterized by resorption textures, which are consistent with dissolution during rapid decompression and/or devolatisation during magma migration from the lower crust into upper crustal magma chambers.
U2 - 10.1016/j.lithos.2018.03.007
DO - 10.1016/j.lithos.2018.03.007
M3 - Journal article
VL - 308-309
SP - 159
EP - 167
JO - Lithos
JF - Lithos
SN - 0024-4937
ER -
ID: 192380234