TY - JOUR
T1 - Petrogenesis of silicic magmas in iceland through space and time
T2 - The isotopic record preserved in zircon and whole rocks
AU - Carley, Tamara L.
AU - Miller, Calvin F.
AU - Fisher, Christopher M.
AU - Hanchar, John M.
AU - Vervoort, Jeffery D.
AU - Schmitt, Axel K.
AU - Economos, Rita C.
AU - Jordan, Brennan T.
AU - Padilla, Abraham J.
AU - Banik, Tenley J.
N1 - Funding Information:
We are extremely grateful to David Peate and Ilya Bindeman for their thoughtful reviews and to David Rowley for his editorial management, which greatly improved this study. This work was supported by funding from National Science Foundation (NSF) graduate research fellowship DGE 0909667 (Carley), NSF research grant EAR 1220523 (Miller), National Geographic Society grant 9030-12 (Miller), an Natural Sciences and Engineering Research Council Canada Discovery Grant (Hanchar), and support from the Keck Geology Consortium (Jordan). The ion microprobe facility at the University of California Los Angeles is partly supported by a grant from the Instrumentation and Facilities Program of the NSF Division of Earth Sciences. We thank Olgeir Sig-marsson for sharing his Icelandic expertise in the field and in subsequent discussions. Joe Wooden and Matthew Coble of the sensitive high-resolution ion microprobe with reverse geometry (SHRIMP-RG) laboratory provided invaluable guidance in acquiring, reducing, and interpreting zircon age data. We greatly appreciate the analytical assistance provided by Aaron Covey (Vanderbilt University), Brad Ito (SHRIMP-RG), Rebecca Lam (Memorial University of Newfoundland), and Diane Wilford and Charles Knaack (Washington State University).
Publisher Copyright:
© 2019 by The University of Chicago. All rights reserved.
PY - 2020/1
Y1 - 2020/1
N2 - Iceland exemplifies the potential for generation of abundant silicic magma in the absence of mature island arc or preexisting continental crust. Zircon ages (U-Th and U-Pb) and isotope compositions (Hf and O), combined with whole-rock isotope data (Nd, Hf, Pb), provide insight into the petrogenesis and mantle heritage of these silicic magmas. Zircon and whole-rock samples represent the past 15 Ma of Iceland’s geologic evolution, geographic extent (marginal fjordlands to neovolcanic zones), and modern tectonic settings (on-rift, propagating-rift, off-rift). The generation of Icelandic silicic magma has been influenced by hydrothermally altered crust, via assimilation and/or anatexis, throughout Iceland’s history. This is shown by consistently depleted O isotopes in zircon (median d18 O 13.1‰; 198% below 15.3‰), and silicic rocks. Zircon d18 O values appear to have become lower and more diverse since ca. 0.7 Ma (median 11.9‰). This decrease may reflect lower d18 O of meteoric waters involved in hydrothermal alteration during the Pleistocene and/or more volumetrically significant contributions from low d18 O altered crust. Zircon O compositions from historically active volcanoes confirm that the role of altered crust is greater in on-rift than in off-rift settings; diversity in d18 O at volcanoes in propagating rift settings suggests highly variable contributions from altered crust. The silicic record (whole-rock and zircon) exhibits a correlation between geographic position and isotope composition that seems to be independent of local tectonic setting. Silicic samples of all ages collected above 657 N have more radiogenic whole-rock Hf and Nd isotopic compositions, and less radiogenic Pb, than samples collected in southern Iceland; published isotopic data for basalts suggest a similar time-independent latitudinal trend. The persistence of this trend through time suggests that northern Iceland has been underlain by a more depleted mantle source than southern Iceland throughout the island’s history.
AB - Iceland exemplifies the potential for generation of abundant silicic magma in the absence of mature island arc or preexisting continental crust. Zircon ages (U-Th and U-Pb) and isotope compositions (Hf and O), combined with whole-rock isotope data (Nd, Hf, Pb), provide insight into the petrogenesis and mantle heritage of these silicic magmas. Zircon and whole-rock samples represent the past 15 Ma of Iceland’s geologic evolution, geographic extent (marginal fjordlands to neovolcanic zones), and modern tectonic settings (on-rift, propagating-rift, off-rift). The generation of Icelandic silicic magma has been influenced by hydrothermally altered crust, via assimilation and/or anatexis, throughout Iceland’s history. This is shown by consistently depleted O isotopes in zircon (median d18 O 13.1‰; 198% below 15.3‰), and silicic rocks. Zircon d18 O values appear to have become lower and more diverse since ca. 0.7 Ma (median 11.9‰). This decrease may reflect lower d18 O of meteoric waters involved in hydrothermal alteration during the Pleistocene and/or more volumetrically significant contributions from low d18 O altered crust. Zircon O compositions from historically active volcanoes confirm that the role of altered crust is greater in on-rift than in off-rift settings; diversity in d18 O at volcanoes in propagating rift settings suggests highly variable contributions from altered crust. The silicic record (whole-rock and zircon) exhibits a correlation between geographic position and isotope composition that seems to be independent of local tectonic setting. Silicic samples of all ages collected above 657 N have more radiogenic whole-rock Hf and Nd isotopic compositions, and less radiogenic Pb, than samples collected in southern Iceland; published isotopic data for basalts suggest a similar time-independent latitudinal trend. The persistence of this trend through time suggests that northern Iceland has been underlain by a more depleted mantle source than southern Iceland throughout the island’s history.
UR - https://www.scopus.com/pages/publications/85088942166
U2 - 10.1086/706261
DO - 10.1086/706261
M3 - Article
AN - SCOPUS:85088942166
SN - 0022-1376
VL - 128
SP - 1
EP - 28
JO - Journal of Geology
JF - Journal of Geology
IS - 1
ER -