Paleomagnetic dating of fluid-flow events in dolomitized Caledonian basement rocks, central Scotland

Palaeomagnetic and geochemical studies of Cambrian-Ordovician serpentinite in the Highland Border Complex (HBC), a tectonic terrane along the Highland Boundary Fault (HBF) in Scotland, indicate that the HBF was a conduit for fluids in the Carboniferous-Permian. The fluids caused dolomitization, silicification, and haematite authigenesis. Both red dolomitized serpentinite and relatively unaltered serpentinite were sampled at multiple localities. The unaltered serpentinite contains a poorly defined magnetization with westerly declinations that resides in magnetite and has a pole which plots well off the apparent polar wander path. Most specimens of the red dolomitized serpentinite contain a magnetization with southerly declinations and negative inclinations that resides in haematite. A regional fold test suggests that this magnetization post-dates tilting and the pole positions for the different locations fall on the Carboniferous to Permian part of the apparent polar wander path. In some specimens of red dolomitized serpentinite, alternating field (AF) demagnetization prior to thermal treatment removes a component with a similar direction. Dolomitized basement rocks along the fault contain a similar although apparently slightly older magnetization. Fluid inclusion and geochemical studies indicate that the fluids were hydrothermal in origin (110-2408C) and had a range of sources. The Carboniferous-Permian magnetization in haematite is interpreted as a chemical remanent magnetization that formed when warm fluids moved along the fault zone and caused haematite authigenesis. The component removed by AF treatment is interpreted as a thermal resetting of primary magnetite by the fluids. The variability of the palaeomagnetic, fluid inclusion, and stable isotope results suggests that there were probably multiple flow events that caused the alteration. The origin of the fluids could be related to the intrusion of late Carboniferous dikes in central Scotland and/or to reactivation of the HBF in the Carboniferous-Permian.

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“…Altered serpentinite in the HBC at Toward also contains a complex multicomponent magnetization (Elmore et al . 2000).…”

Section: Results and Interpretationsmentioning

confidence: 99%

Palaeomagnetic dating of fluid‐flow events in dolomitized rocks along the Highland Boundary Fault, central Scotland

et al. 2002

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“…Several mechanisms have been proposed for the origin of chemical remanent magnetizations (CRM). They can be broadly divided into two categories: the first one corresponds to remagnetization related to internal processes alone, like in situ alteration of clays (Katz et al 1998, 2000) and maturation of organic material (Elmore et al 1993) related to burial or weathering; the second one requires fluid migrations leading sometimes to dolomitization (Lewchuk et al 1998, 2000; Elmore et al 2000), hydrocarbon pooling (Oliver 1986) or base metal mineralization (Lewchuk & Symons 1995). Warm fluids could also act similarly as burial on internal processes, simply by thermal effect.…”

Section: Discussionmentioning

confidence: 99%

Chemical remagnetizations in the Illizi basin (Saharan craton, Algeria) and their acquisition process

Henry

Merabet

Derder

et al. 2004

Geophysical Journal International

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S U M M A R YDuring remagnetization, chemical changes limited to moderate grain growth from pre-existing single domain (SD) grains do not modify the palaeomagnetic direction carried by these grains. Palaeomagnetic direction from new SD grains, on the contrary, is that of the magnetic field during remagnetization. The resulting direction becomes intermediate between the directions carried by previous and new SD grains, as it appears often in case of a partial magnetic overprint. If the growth of pre-existing grains is more important, these grains become large multidomain (MD) and loose the primary magnetization. Stable magnetization is then only related to the new SD grains, which carry the total remagnetization. In the Illizi basin (Saharan platform), these different cases of partial or total magnetic overprint have been observed, resulting from palaeomagnetic studies of different Palaeozoic and Mesozoic formations.

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“…For the past several years we have investigated the role of faults as fluid conduits in Scotland (e.g., Elmore et al, 2002). Faults can act as barriers to flow or they can be conduits for flow, thereby controlling the distribution of diagenetic alteration, mineralization, and remagnetization (e.g., Knipe, 1993).…”

Section: Remagnetization and Fluid Migration Along Faults In The Calementioning

confidence: 99%

Development and Application of a Paleomagnetic/Geochemical Method for Constraining the Timing of Burial Diagenetic Events

Elmore¹,

Engel²

2006

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1 PROJECT SUMMARYStudies of diagenesis caused by fluid migration or other events are commonly hindered by a lack of temporal control. Our results to date demonstrate that a paleomagnetic/geochemical approach can be used to date fluid migration as well as burial diagenetic events. Our principal working hypothesis is that burial diagenetic processes (e.g., maturation of organic-rich sediments and clay diagenesis) and the migration of fluids can trigger the authigenesis of magnetic mineral phases. The ages of these events can be constrained by comparing chemical remanent magnetizations (CRMs) to independently established Apparent Polar Wander Paths. Whilst geochemical (e.g. stable isotope and organic analyses) and petrographic studies provide important clues for establishing these relationships, the ultimate test of this hypothesis requires the application of independent dating methods to verify the paleomagnetic ages. Towards this end, we have used KAr dating of illitization as an alternative method for constraining the ages of magnetic mineral phases in our field areas.We have made significant progress toward understanding the origin and timing of chemical remagnetization related to burial diagenetic processes. For example, a recently completed field study documents a relationship between remagnetization and the maturation of organic matter . We have tested the hypothesized connection between clay diagenesis and remagnetization by conducting K-Ar dating of authigenic illites in units in Scotland and Montana with CRMs (e.g., Elliott et al., 2006a;Elliott et al., 2006b). We have also developed a fluid related model for alteration and remagnetization of Appalachian red beds that involves reduction and mobilization of iron phases by hydrocarbons and precipitation of authigenic hematite as a result of the introduction of meteoric fluid recharge . In addition, our recent studies of fluid-related CRMs along faults in Scotland provide information on the timing and origin of fluid flow events along the Moine and Great Glen faults Blumstein et al., 2005;.

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Paleomagnetic dating of fluid-flow events in dolomitized Caledonian basement rocks, central Scotland

Cited by 4 publications

References 11 publications

Palaeomagnetic dating of fluid‐flow events in dolomitized rocks along the Highland Boundary Fault, central Scotland

Palaeomagnetic dating of fluid‐flow events in dolomitized rocks along the Highland Boundary Fault, central Scotland

Chemical remagnetizations in the Illizi basin (Saharan craton, Algeria) and their acquisition process

Development and Application of a Paleomagnetic/Geochemical Method for Constraining the Timing of Burial Diagenetic Events

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