describe 2 ways in which the presence of fluids can influence metamorphism?

Question

describe 2 ways in which the presence of fluids can influence metamorphism

Answer 1

Fluids in the pore spaces speed up metamorphic processes because water helps move materials around and recrystallization

Barrovian-style metamorphism is the most common type recognized in regional metamorphic terranes worldwide. This metamorphism was thought for many years to involve only the release of water and other volatiles during progressive heating and burial, but more recent research shows that it is accompanied by significant mass transfer of silica, alkali and alkaline earth metals, and heat-producing elements including uranium (Ague, 1991, 1994a, 1994b, 1997; Ague and van Haren, 1996; Ague, 2003 American Journal of Science). This mass transfer, documented quantitatively in Connecticut and the in Barrovian type locality (Scotland), can fundamentally alter rock bulk compositions, facilitating the growth of key Barrovian index minerals including garnet (Ague, 1997), staurolite, and kyanite (Ague, 1994b). New methods for quantification of mass transfer allow major fluid flow conduits (fractures) to be identified in the field. This work establishes that regional metamorphic fluid outflow involves massive time-integrated fluid fluxes of the order of 104-105 m3 fluid per m2 rock, enough to transport both mass and heat through the middle and deep crust (Ague, 2003, Treatise on Geochemistry).



2) Low-temperature, high-pressure metamorphism of accretionary prisms and oceanic crust in subduction zones is the other major metamorphic setting exposed in active and fossil mountain belts. The sources and amounts of fluid during subduction have remained controversial for decades. Based on a new type of regional mass balance analysis, Breeding and Ague (2002) concluded that fluids from downgoing, subducted oceanic crust penetrated the overlying Otago Schist accretionary prism, New Zealand, resulting in the formation of a regional quartz vein network and massive time-integrated fluid fluxes of 104-105 m3 fluid per m2 rock. These fluids ascended to shallow crustal levels where they ultimately participated in the formation of the famous Otago gold-tungsten deposits. Transfer of SiO2 from subducting slabs into accretionary prisms is a plausible mechanism for long-term bulk silica enrichment of the continents beyond that possible by magmatic differentiation alone.

Answer 2

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