Out-of-sequence skeletal growth causing oscillatory zoning in arc olivines

Abstract

Primitive olivines from the monogenetic cones Los Hornitos, Central-South Andes, preserve dendritic, skeletal, and polyhedral growth textures. Consecutive stages of textural maturation occur along compositional gradients where high Fo–Ni cores of polyhedral olivines (Fo92.5, Ni ~3500 ppm) contrast with the composition of dendritic olivines (Fo < 91.5, Ni < 3000 ppm), indicating sequential nucleation. Here we present a new growth model for oscillatory Fo–Ni olivine zoning that contrasts with the standard interpretation of continuous, sequential core-to-rim growth. Olivine grows rapidly via concentric addition of open-structured crystal frames, leaving behind compositional boundary layers that subsequently fill-in with Fo–Ni-depleted olivine, causing reversals. Elemental diffusion modeling reveals growth of individual crystal frames and eruption at the surface occurred over 3.5–40 days. Those timescales constrain magma ascent rates of 40–500 m/h (0.011 to 0.14 m/s) from the deep crust. Compared to ocean island basalts, where dendritic and skeletal olivines have been often described, magmas erupted at arc settings, experiencing storage and degassing, may lack such textures due to fundamentally different ascent histories.

Dendritic crystallization in hydrous basaltic magmas controls magma mobility within the Earth’s crust

“…However, our results illustrate that rapid growth promoted at ∆ T = 30 °C generates elongated dendritic crystal frameworks that can be progressively infilled by further crystal growth, as the growth rate decreases. The crystal growth fashion observed in the in situ 4D experiments therefore has important implications for the entrapment of melt inclusions and for constraining the growth chronology of crystals 16 , 19 , 20 , 49 , 50 .…”

Preservation of Magma Recharge Signatures in Kīlauea Olivine During Protracted Storage

“…Phosphorus enrichments in olivine record rapid growth or dissolution features that develop during magma mixing or rapid dike emplacement in cooler rocks (Welsch et al., 2014). Complex dendritic olivine growth has been shown to occur in olivine from hotspots or arc settings in the form of intricate face‐parallel elevated P and Al lamellae internal to the crystals (Salas et al., 2021; Welsch et al., 2014) or in the form of skeletal external morphologies (Mourey & Shea, 2019). In other cases (e.g., Shiveluch olivine; Gordeychik et al., 2018), the concentric nature of core‐rim Mg‐Fe‐Ni‐Ca‐Cr‐Al‐P zoning argues that “tree‐ring” like growth of olivine is the most likely scenario.…”

The effects of superheating and cooling rate on olivine growth in chondritic liquid

“…It should be possible to determine nucleation temperature, that is, the degree of undercooling, from glass inclusions lato sensu because their shape and location within the crystal depend on the degree of undercooling (Mourey & Shea, 2019), via the entrapping crystal's morphology (Colin et al., 2012; Faure & Schiano, 2005; Welsch et al., 2009). Although the specific arrangement of inclusions is eventually erased by further crystal growth in polyhedral crystals, chemical zonations (e.g., P, Al, Ni) should reflect the initial crystal growth morphology (Borisova et al., 2014; Bouvet de Maisonneuve et al., 2016; Libourel & Portail, 2018; Milman‐Barris et al., 2008; Salas et al., 2021; Shea et al., 2019; Welsch et al., 2013, 2014).…”