Remagnetization and chemical alteration of sedimentary rocks

Abstract

Chemical remagnetization is a very common phenomenon in sedimentary rocks and developing a greater understanding of the mechanisms has several benefits. Acquisition of a secondary magnetization is usually tangible evidence of a diagenetic event that can be dated by isolation of the chemical remanent magnetization and comparison of the pole position to the apparent polar wander path. This can be important because diagenetic investigations are frequently limited by the difficulty in constraining the time frames in which most past events have occurred. Remagnetization can commonly obscure a primary magnetization; developing a better understanding of remagnetization could improve our ability to uncover primary magnetizations. Many chemical remagnetization mechanisms have been proposed, including those associated with chemical alteration by a number of different fluids (orogenic, basinal and hydrocarbons), burial diagenetic processes (clay diagenesis and maturation of organic matter) or other processes. This paper summarizes our current knowledge of these chemical remagnetization mechanisms, with a focus on examples where there is a connection with chemical alteration.

Magnetomineralogical changes along the Kohistan-Karakoram collision zone inNorth Pakistan: implications for variable thermochemical activities

“…The arrow directions correspond to decrease in magnetic stability and presumed increase in thermometamorphic activity closer to the NSZ. This conforms with other studies reporting rocks along collisional margins to be more intensely remagnetized compared to their counterparts within the indenting tectonic blocks (e.g., Dekkers and Linssen, 1989;McCabe and Elmore, 1989;Katz et al, 1998;Rowan and Roberts, 2008;Meijers et al, 2011;Appel et al, 2012;Elmore et al, 2012;Van Der Voo and Torsvik, 2012).…”

An integrated paleomagnetic, rock magnetic, and geochemical study of the Marcellus shale in the Valley and Ridge province in Pennsylvania and West Virginia

“…This study reports the results of an integrated paleomagnetic, rock magnetic, and diagenetic investigation of the Marcellus Subgroup in the Appalachian Basin. Paleomagnetic data can be used to date diagenetic events, including hydrothermal fluid flow [ Elmore et al ., , ], maturation of organic matter [ Blumstein et al ., ], and clay diagenesis [ Katz et al ., ; Aubourg et al ., , ]. One or more of these diagenetic processes may have occurred in the Marcellus Subgroup, which makes the unit an ideal candidate for an integrated paleomagnetic and diagenetic study.…”

Remagnetization of lower Silurian black shale and insights into shale gas in the Sichuan Basin, south China

“…One of the reasons is that extraordinary pervasive remagnetization has occurred in these units [e.g., Kent et al , ; Dobson and Heller , ; Wang and Van Der Voo , ]. Indeed, such pervasive remagnetizations can obscure or remove the primary magnetization; however, remagnetization, especially chemical remanent magnetization (CRM), can also provide information on the processes of burial diagenesis, including the thermal maturation of organic matter and smectite‐to‐illite conversion [e.g., Lu et al , ; Woods et al , ; Zegers et al , ; Blumstein et al , ; Moreau et al , ; Manning and Elmore , ], and information on alteration events triggered by orogenic fluids, mineralizing fluids, migrated hydrocarbons, or weathering‐related fluids [e.g., Kilgore and Elmore , ; McCabe and Elmore , ; Elmore et al , , and references therein]. Presently, remagnetization data from south China, however, have rarely been applied in this way, and even the origin of the pervasive remagnetizations is still not fully understood.…”