Fluid infiltration, heat transport, and healing of microcracks in the damage zone of magmatic veins: Numerical modeling

Abstract

[1] Alteration halos with sharp boundaries are flanking pegmatitic veins in high-grade metamorphic and magmatic rocks of Dronning Maud Land, Antarctica. These halos are interpreted to represent the damage zone, formed as the wake of the process zone at the tip of the propagating magma-filled fracture and infiltrated by the fluid phase liberated from the crystallizing hydrous melt. On the basis of a set of assumptions, our numerical model explores the time scales of the infiltration processes, taking into account the combined effects of fluid flow, heat transfer, and temperature-dependent decay of interconnected porosity due to microcrack healing. Assuming an initial magma temperature of 700°C, a far field temperature in the host rock of 300°C, an initial porosity range of 0.5-2% in the damage zone, a permeability of 10 À16 m 2 , and a pressure difference of 300 MPa, we find that the fluid infiltration into the damage zone proceeds within seconds to minutes and that the fluid flow contributes significantly to the heat transfer into the host rock. Assuming an initial microcrack aperture of 1 mm, the model predicts that the crack healing time scale is significantly longer than that of fluid infiltration in the case of thin veins with narrow damage zones; in this case, crack healing does not hinder fluid infiltration. Only for thick veins with high heat content and prolonged crystallization history does permeability become reduced by crack healing during progressive fluid infiltration. The results indicate that the formation of the alteration halos flanking pegmatitic veins may be a quasi-instantaneous process on geological time scales.Citation: Engvik, L., B. Stöckhert, and A. K. Engvik (2009), Fluid infiltration, heat transport, and healing of microcracks in the damage zone of magmatic veins: Numerical modeling,

Prolonged high-grade metamorphism of supracrustal gneisses from Mühlig-Hofmannfjella, central Dronning Maud Land (East Antarctica)

“…Spectacular examples of fluid-rock interaction phenomena are widespread in central DML (Markl and Piazolo, 1998;Ohta, 1999;Engvik et al, 2005). The fluid-rock interactions form discordant light bands with a central pegmatite or aplite vein (Engvik et al, 2005(Engvik et al, , 2009Bucher and Frost, 2005;Engvik and Stöckhert, 2007), and were formed by infiltrating of H2O-CO2 volatiles into the characteristic brownish high-grade granitoids. The late pegmatites, fluid infiltration and associated alteration in a quartz-syenite in Filchnerfjella was dated to around 486 Ma by U-Pb ID-TIMS dating of titanite (Paulsson, 2003).…”

Effect of Permeability Evolution in Fault Damage Zones on Earthquake Recurrence

“…Nevertheless, the system will eventually reach a stable state where the pore pressure will stay fixed or oscillate in a narrow range. Furthermore, the temperatures in the fault zones are often controlled by a variety of factors, such as shear heating during coseismic ruptures (Rice, 2006), heat transferred by fluid infiltration (Engvik et al., 2009; Yehya & Rice, 2020), etc. While some may have a long‐term effect on the healing rate of off‐fault cracks and should be incorporated into the simulation framework, some just have a short‐term effect (such as shear heating) which has a limited influence on the permeability evolution during long‐term earthquake cycles, and may be considered when focusing on assessing the short‐term permeability changes.…”

“…10.1029/2021JB021787 3 of 17 Engvik et al (2009) obtained a dimensionless crack lifetime healing parameter for a temporally varying temperature, which is defined as:…”

“…Since Equation 6 is derived for constant temperature, Engvik et al. (2009) obtained a dimensionless crack lifetime healing parameter for a temporally varying temperature, which is defined as: where represents the time when the crack has been created and represents the current time. If temperature does not change with time, the calculation of could be simplified to …”

Influence of Fluid‐Assisted Healing on Fault Permeability Structure

“…The range of the activation energy, based on the Brantley et al ( 1990) experiments, is between Q = 50 and 110 kJ/mol. Then, the distance r from the center of the crack to the healing front at the elapsed time t is (Engvik et al, 2009)…”