TY - JOUR

T1 - Implications of pore space characteristics on diffusive transport in basalts and granites

AU - Dultz, Stefan

AU - Simonyan, Anna V.

AU - Pastrana, Julio

AU - Behrens, Harald

AU - Plötze, Michael

AU - Rath, Thomas

N1 - Funding information: Acknowledgments This research used samples provided by the Ocean Drilling Program (ODP). X-ray-tomographic microscopy was performed at the TOMCAT beamline at the synchrotron facility of the Paul Scherrer Institute, Villigen, Switzerland. Skillful help by Federica Marone is gratefully acknowledged. This research was funded by the Deutsche Forschungsgemeinschaft (DFG, projects Du 271/3-1, 2 and Be 1720/17-1, 2).

PY - 2013/6

Y1 - 2013/6

N2 - A detailed characterization of the pore space is crucial for understanding of transport and element transfer in rocks. Here, the effect of differences in texture and content of secondary minerals on transport in pore systems was determined for two rocks of widespread occurrence, mid-ocean ridge basalts (MORB) and granites. Pore space characteristics were analyzed by Hg-porosimetry, intrusion of a molten alloy, and synchrotron-based X-ray tomographic microscopy. For evaluating the role of pore space characteristics for the prediction of diffusive transport, data on porosity, and the effective diffusion coefficient (Deff) were compared. Extended connective pore systems due to cracks and mineral dissolution are present in samples of both rocks, indicating high internal specific surface area. Uneven pore size distributions in altered MORB samples can be assigned to secondary minerals. Pore spaces determined by X-ray tomography, used to determine main direction of pores in the 3-D orthogonal system, suggest a slight anisotropy. In log-log plots, both rocks show roughly a linear dependence of Deff for H2O and compounds with comparable diffusivities (D2O, monovalent cations, and anions) on porosity, but at same porosity Deff is clearly higher in granitic than in basaltic samples. This difference is increasing with decreasing porosity, indicating that at low porosities the efficiency of element transport in basaltic samples is diminished, mainly inherited by the presence of small pores slowing down diffusion. The fact that diffusive transport in basaltic rocks is stronger dependent on porosity than in granitic rocks shows that also other rock characteristics such as pore size distribution and tortuosity of the pore network, highly affected by the alteration degree, can markedly affect transport and reactivity of pore solution.

AB - A detailed characterization of the pore space is crucial for understanding of transport and element transfer in rocks. Here, the effect of differences in texture and content of secondary minerals on transport in pore systems was determined for two rocks of widespread occurrence, mid-ocean ridge basalts (MORB) and granites. Pore space characteristics were analyzed by Hg-porosimetry, intrusion of a molten alloy, and synchrotron-based X-ray tomographic microscopy. For evaluating the role of pore space characteristics for the prediction of diffusive transport, data on porosity, and the effective diffusion coefficient (Deff) were compared. Extended connective pore systems due to cracks and mineral dissolution are present in samples of both rocks, indicating high internal specific surface area. Uneven pore size distributions in altered MORB samples can be assigned to secondary minerals. Pore spaces determined by X-ray tomography, used to determine main direction of pores in the 3-D orthogonal system, suggest a slight anisotropy. In log-log plots, both rocks show roughly a linear dependence of Deff for H2O and compounds with comparable diffusivities (D2O, monovalent cations, and anions) on porosity, but at same porosity Deff is clearly higher in granitic than in basaltic samples. This difference is increasing with decreasing porosity, indicating that at low porosities the efficiency of element transport in basaltic samples is diminished, mainly inherited by the presence of small pores slowing down diffusion. The fact that diffusive transport in basaltic rocks is stronger dependent on porosity than in granitic rocks shows that also other rock characteristics such as pore size distribution and tortuosity of the pore network, highly affected by the alteration degree, can markedly affect transport and reactivity of pore solution.

KW - Diffusive transport

KW - Granite

KW - Hg-porosimetry

KW - Mid-ocean ridge basalt

KW - Pore space characteristics

KW - Wood's metal intrusion

KW - X-ray-tomographic microscopy

UR - http://www.scopus.com/inward/record.url?scp=84877670443&partnerID=8YFLogxK

U2 - 10.1007/s12665-012-1981-8

DO - 10.1007/s12665-012-1981-8

M3 - Article

AN - SCOPUS:84877670443

VL - 69

SP - 969

EP - 985

JO - Environmental earth sciences

JF - Environmental earth sciences

SN - 1866-6280

IS - 3

ER -