Fluid migration on early-accreting planetesimals

Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online's data policy on reuse of materials please consult the policies page. Introduction: The parent bodies of primitive meteorites and asteroids of the outer main belt accreted with a significant complement of volatiles such as H 2 O, CO 2 , and Cl [1]. The potential migration of these volatiles strongly influences the subsequent chemical and physical evolution of the body. Upon progressive interior heating due to the presence of short-lived ra-dioisotopes such as 26 Al, water ice melts and reacts with surrounding anhydrous silicate and metal phases. Migration of aqueous fluids during these reactions potentially leads to unique signatures in the elemental and isotopic composition of chondritic material [2, 3]. The efficiency of fluid transport also strongly impacts the thermal evolution of volatile-rich bodies such as the asteroid Ceres, imminent target of the NASA Dawn mission [4, 5]. If the interior temperature reaches the silicate solidus, the concentration of retained volatiles is a critical factor in the buoyancy of the resulting silicate melts and the likelihood of their upward migration [6]. The ascent of silicate melts strongly affects the thermal evolution of the planetesimal and its surface composition. Magmas with a high volatile content may also lead to pyroclastic volcanism [7]. Despite the important implications of aqueous fluid migration in early-accreting planetesimals, broad uncertainty exists as to the extant of fluid mobility. Early studies argued that fractures would enhance the perme-ability of chondritic material and permit the flow of water in parent bodies with diameter greater than 120 km [4, 8]. However, theoretical calculations based on the estimated characteristic grain size of chondritic matrices suggest that such planetesimals were essentially impermeable and that fluid flow did not occur on scales of greater than 100 µm [9]. Here we consider the likelihood of aqueous fluid migration in the parent bodies of several chondrite groups. We evaluate the likely permeability of bulk, fractured chondrite material and examine vaporization of interior fluids as a driver of fracturing on early-accreting parent bodies. Global permeability of chondritic parent bodies: The capacity for aqueous fluids to migrate through their parent bodies depends on a balance between driving forces, predominantly gravity, and the permeability of the host material. In the case of single pass ascent via density-driven Darcy flow [6], …