Fast strain rates during pluton emplacement: Magmatically folded leucocratic dikes in aureoles of the Mount Stuart Batholith, Washington, and the Tuolumne Intrusive Suite, California

Abstract

Finite strain analysis and thermal modeling of magmatically folded leucocratic dikes in the Mount Stuart Batholith, Washington and the Tuolumne Intrusive Suite, California, yield strain rates in the range of 10 −2 to 10 −13 s -1 . Compared to published regional strain rates (10 −13 to 10 −15 s -1 ), wallrock strain rates associated with dike-fed expansion (10 −7 s -1 ), and rates resulting from numerical modeling of crystal-plastic creep in aureoles (10 −11 s -1 ), our fast rates are several orders of magnitude higher.Field and microstructural observations suggest that multiple material transfer processes, including rigid rotation, ductile fl ow, cracking, and potentially melt-assisted granular fl ow operated in the aureoles to accommodate emplacement of these two plutons. Calculated durations of pluton construction and bulk shortening in the aureoles indicate that aureole deformation requires only slow, long-term strain rates of 10 −14 s -1 . Thus our local fast strain rates indicate that aureoles may be characterized by pulsating high strain rate surges. We suggest that magmatically folded dikes in these and other pluton aureoles around the world may be used as evidence for fast host rock strain rates during pluton emplacement.

On the conditions of magma mixing and its bearing on andesite production in the crust

“…Our results therefore reveal that, at shear rates expected to occur at depth 25,26 (o10 À 3 s À 1 ) mixing through enclave disaggregation is unlikely to occur if the mafic blob has a viscosity higher by 40.3 log unit relative to that of its host. Therefore, the fate of an enclave, that is, whether it disaggregates via lateral shearing or remains intact 42 , will be controlled by the viscosity contrast.…”

“…We report here viscosity measurements performed during high-pressure felsic-mafic mixing experiments at moderate-tolow strain rates and P-T-fluid conditions relevant to crustal reservoirs [25][26][27] . These results are then combined with recent phase equilibria of magmas to evaluate the optimum conditions, leading to efficient mixing, that is, hybrids, when mafic and felsic magmas come into contact during single-intrusive events.…”

The spatial and temporal patterning of the deep crust and implications for the process of melt extraction

“…In the absence of overprinting, various characteristic microstructures have been used to infer the former presence of melt at the grain scale in residual migmatites and granulites (e.g. Sawyer 1999Sawyer , 2001Brown 2001a,b;Albertz et al 2005;Holness & Sawyer 2008).…”

Magmatic stoping as an important emplacement mechanism of Variscan plutons: evidence from roof pendants in the Central Bohemian Plutonic Complex (Bohemian Massif)

“…Instead, additional mechanisms, such as brittle cracking and stoping, which are several-orders-of-magnitude faster, are necessary (Albertz et al 2005). Our study thus may provide an excellent field example for predictions made by these numerical models, since large calc-alkaline and high-K calc-alkaline plutons of the Central Bohemian Plutonic Complex (e.g., $346 Ma Blatna´pluton) were emplaced into the upper crust over a relatively short-time span and therefore fast strain rates in the host rocks were required to accommodate emplacement of the Central Bohemian Plutonic Complex.…”

“…Indeed, recent numerical models of fault-assisted emplacement and strain rates in pluton aureoles (Albertz et al 2005;Gerbi et al 2004;Johnson et al 2001;Paterson and Schmidt 1999;Yoshinobu et al 1998) point out that neither fault-slip rates nor ductile flow on their own could accommodate fast strain rates during emplacement of large magma batches. Instead, additional mechanisms, such as brittle cracking and stoping, which are several-orders-of-magnitude faster, are necessary (Albertz et al 2005).…”