Disequilibrium crystallization and rapid crystal growth: a case study of orbicular granitoids of magmatic origin

Zhang, Julin; Lee, Cin-Ty A.

doi:10.1080/00206814.2020.1734975

Cited by 6 publications

(2 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…If these rapid crystal growth rates can be sustained, large decimeter-sized pegmatite crystals could have formed on the timescale of days. Similar rapid crystal growth rates have been inferred using independent approaches for orbicular granitoids 44 .…”

Section: Discussionsupporting

confidence: 74%

Episodes of fast crystal growth in pegmatites

2020

Self Cite

View full text Add to dashboard Cite

Pegmatites are shallow, coarse-grained magmatic intrusions with crystals occasionally approaching meters in length. Compared to their plutonic hosts, pegmatites are thought to have cooled rapidly, suggesting that these large crystals must have grown fast. Growth rates and conditions, however, remain poorly constrained. Here we investigate quartz crystals and their trace element compositions from miarolitic cavities in the Stewart pegmatite in southern California, USA, to quantify crystal growth rates. Trace element concentrations deviate considerably from equilibrium and are best explained by kinetic effects associated with rapid crystal growth. Kinetic crystal growth theory is used to show that crystals accelerated from an initial growth rate of 10−6–10−7 m s−1 to 10−5–10−4 m s−1 (10-100 mm day−1 to 1–10 m day−1), indicating meter sized crystals could have formed within days, if these rates are sustained throughout pegmatite formation. The rapid growth rates require that quartz crystals grew from thin (micron scale) chemical boundary layers at the fluid-crystal interfaces. A strong advective component is required to sustain such thin boundary layers. Turbulent conditions (high Reynolds number) in these miarolitic cavities are shown to exist during crystallization, suggesting that volatile exsolution, crystallization, and cavity generation occur together.

show abstract

Section: Discussionsupporting

confidence: 74%

Episodes of fast crystal growth in pegmatites

2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…One possibility is the Ca-rich orbicules are a conjugate liquid exsolved from an original single phase by liquid immiscibility. Comparison of the compositions of the host melt, orbicules, and orbicule dike margins and interiors to experimentally derived two-liquid solvi, however, show they fall within the one-liquid field for several systems: SiO 2 /4-CaO-Al 2 O 3 (Charlier and An alternative hypothesis is that the host melt + orbicules preserved in the dikes were two liquids unable to homogenize due to rapid crystallization and supercooling (McCarthy and Müntener 2016;Zhang and Lee 2021). In this way, the Ca-rich orbicules could represent the remnants of limestone dissolution with insufficient time for complete mixing into the recharging host melt within the dikes.…”

Section: Orbicules From Liquid Immiscibility or Incomplete Mixing?mentioning

confidence: 98%

CO2 transport at shallow depths in arc magmas: evidence from unique orbicular dikes in the Jurassic Bonanza arc, Vancouver Island, Canada

Morris

Canil

2021

Contrib Mineral Petrol

View full text Add to dashboard Cite

A growing body of evidence suggests the interaction between arc magmas and crustal carbonates may play a large role in outgassed CO 2 at arcs. We examine magma-carbonate interactions within the shallow (< 0.2 GPa) crust in the Jurassic Bonanza arc on Vancouver Island, a well-exposed island arc crustal section. Detailed mapping in the Merry Widow mountain area revealed unique, late-stage orbicular mafic dikes that only occur above the stratigraphic level of subsurface carbonates. The orbicular dikes are primitive, show physical and chemical evidence of interaction with limestone, including high CaO/ SiO 2 and low REE (~ 10-20× chondrite) that correlate with orbicule abundance, and are geochemically discordant from other rocks of the Bonanza arc. The orbicules have identical intergranular textures to the host melt but markedly higher Ca/Si. Simple binary mixing and MELTS modeling indicates the orbicular dike compositions are a mixture of a primitive hydrous arc basalt with 3-25% limestone addition. Comparisons to published experimental data on basalt-calcite reaction suggest some of the dike compositions result from > 25% calcite assimilation, producing up to 11 wt% CO 2 , orders of magnitude higher than the CO 2 solubility of the parent melt (0.11 wt% CO 2 ). We interpret the orbicules as Ca-rich hybrid melts produced from limestone assimilation that did not homogenize with the host dike magma and underwent crystallization during rapid ascent, possibly propelled by the excess CO 2 . Our results inform on the amount and mechanism of CO 2 transport at low crustal pressures (< 0.5 GPa) in island arcs built on carbonate platforms. We estimate the CO 2 flux of the Jurassic Bonanza arc to have ranged from 0.14 to > 1.16 Tg CO 2 /year during its ~ 34 Myr lifespan.

show abstract