APATITE GEOCHEMISTRY ACROSS THE NEOVOLCANIC ZONES OF ICELAND: ESTABLISHING A BASELINE AND SEARCHING FOR SPATIAL SIGNIFICANCE

Apatite is a petrologically valuable mineral due to its ability to incorporate a variety of magmatic tracers into its crystalline structure, including magmatic water, halogens, volatiles (F, Cl, H, S, C), trace elements, and the light rare earth elements (LREE). Despite its utility in investigating magmatic evolution and its ubiquity as an accessory mineral in igneous rocks, studies of Icelandic apatite are extremely recent and rare (Connors et al., in press and Bergþórsdóttir 2018). Apatite from Torfajökull, a central volcano in the Eastern Volcanic Zone, are dominantly fluorapatite (F: 1.02 to 4.03 wt. %), with low Cl (<0.4 wt.%) and variable OH (0 to 3.26 wt%). Apatites are consistently enriched in LREE (Ce 2 O 3 + La 2 O 3 +Nd 2 O 3 ). Those from warm, metaluminous, lavas have lower LREE (0.5 to 3 wt% oxides); apatite in cooler, peralkaline eruptions have significantly higher LREE (5 to 19 wt% oxides). While high REE apatites have been identified at Torfajökull, it is unclear whether this signautre is typical of Iceland or unique to Torfajökull. The goal s of this research are to (A) determine a baseline geochemical signature of apatite in Iceland; and (B) identify compositional variability, or lack thereof, in apatite from different tectonic-magmatic settings across Iceland. To this end, six volcanoes are selected to represent modern Iceland: on-rift (Krafla and Askja, Northern Volcanic Zone; Kerlingarfjöll, Western Volcanic Zone), off-rift (Oræfajökull, Oræfi Volcanic Belt), and propagating rift (Torfajökull and Hekla, Eastern Volcanic Zone). We will compare apatite compositions (measured by EMPA) from these volcanoes, and to detrital apatite separated from glacial sediments from the perimeter of Vatnajökull, which are used to represent Iceland more broadly. This study contributes a baseline of Icelandic apatite geochemistry across the neovolcanic zones for application in future geochemical studies.

*Connors L., Carley T.L., Fiege A (accepted: July 02, 2019) Apatite as a monitor of dynamic magmatic evolution at Torfajökull Volcanic Center, Iceland: for Vetere F and Fiege A (eds): Dynamic Magma Evolution (Geophysical Monograph), John Wiley & Sons.

Ingibjörg Andrea Bergþórsdóttir. 2018. “The Role of Apatite in Hekla Magmas: Trace Element Partitioning between Minerals and Melt.” University of Iceland.