Ophiolitic Magma Chamber Processes, a Perspective from the Canadian Appalachians

Magma‐Mush Interactions in the Lower Oceanic Crust: Insights From Atlantis Bank Layered Series (Southwest Indian Ridge)

“…Ross and Elthon (1997) described similar anomalous TiO 2 Cpx contents in oceanic olivine gabbro samples from the Mid‐Atlantic Ridge, and argued for the occurrence of “postcumulus crystal growth from, or interaction with evolving intercumulus melts” to explain such Ti over‐enrichments. The favored model of Ross and Elthon (1997) is the occurrence of trapped melt crystallization and late magmatic reequilibration, which is classically considered for the evolution of igneous cumulates (e.g., Bédard, 2015; Borghini & Rampone, 2007; Coogan et al., 2000). Beyond trapped melts, a RPF process can alternatively explain Cpx Ti over‐enrichments.…”

“…Layering can originate from internal processes to magma reservoirs such as crystal settling and related gravitational sorting, variations in nucleation and growth rates, and compaction (Namur et al., 2015 and references therein; Mock et al., 2020). Layering formation can also be linked to intrusive events (Holness et al., 2007; Tegner et al., 1993), or to tectonic deformation of magma bodies in domains like mid‐ocean ridges (Bédard, 2015; Higgie & Tommasi, 2012; Jousselin et al., 2012; Quick & Denlinger, 1993). Alternatively, crystal‐plastic deformation can overprint initial magmatic layering that potentially acted as a planar anisotropy to favor deformation (MacLeod et al., 2017a), thus altering the record of magmatic layering.…”

Consequences of a crystal mush-dominated magma plumbing system: a mid-ocean ridge perspective

“…deformation operated when the system was a crystal mush. If deformation occurs in a crystal mush, this will lead to expulsion and focusing of interstitial melts into melt-rich zones, thus facilitating melt segregation from the compacting crystal framework [47][48][49]. Hence, although the degree to which compaction occurs in relatively small continental magma chambers remains an open question [35], the observations of the mid-ocean ridge crystal mush suggest that compaction is an important process in this setting.…”

Weak B‐Type Olivine Fabric Induced by Fast Compaction of Crystal Mush in a Crustal Magma Reservoir

“…Possible formation mechanisms of adcumulates include primocryst growth with effective chemical communication with the overlying bulk magma at the top of a mushy layer (Campbell, , ; Morse, ), strong compositional convection in crystal mush (Tait & Jaupart, ), melt segregation induced by penetrative shearing (Bédard, ), or gravitationally driven compaction (Schmidt et al, ; Sparks et al, ; Tegner et al, ). The weak fabric strength of olivine and clinopyroxene in the Poyi peridotites excludes the existence of magmatic currents or shearing of unconsolidated cumulates as observed in the Oman ophiolites (Boudier & Nicolas, ; Nicolas et al, ).…”