Constraining the timing of veins, faults and fractures in crystalline rocks by in situ Rb-Sr geochronology

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Constraining the timing of veins, faults and fractures in crystalline rocks by in situ Rb-Sr geochronology

Tillberg, Mikael (författare): Linnéuniversitetet,Institutionen för biologi och miljö (BOM),Geochemistry

Drake, Henrik, Docent, 1979- (preses): Linnéuniversitetet,Institutionen för biologi och miljö (BOM)

Åström, Mats E., 1963- (preses): Linnéuniversitetet,Institutionen för biologi och miljö (BOM)

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Zack, Thomas (preses): University of Gothenburg, Department of Earth Sciences

Hogmalm, Johan (preses): University of Gothenburg, Department of Earth Sciences

Almqvist, Bjarne (opponent): Uppsala University, Department of Earth Sciences

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ISBN 9789189283022
Växjö : Linnaeus University Press, 2020
Engelska 67 s.
Serie: Linnaeus University Dissertations ; 397

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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)

Abstract Ämnesord

Stäng

Precambrian cratons are continent cores archiving the oldest crustal histories on Earth. The crystalline basement of cratons is typically characterized by complex arrays of multiple fracture and fault generations hosting minerals formed by fluids flowing through fracture networks. Disentangling absolute chronologies of the various fracturing, faulting and fluid flow events have to date been difficult given the micro-scale mineral intergrowths and zonations, inhibiting conventional dating techniques. In the general lack of age constraints, deformation and mineralization mechanisms cannot be attributed to specific tectonic regimes, hampering reconstruction of local and regional events of fluid flow and mineral precipitation, and ultimately of the geological evolution of cratons. This thesis presents diverse studies utilizing the radiogenic decay of fracture, fault and shear zone mineral assemblages sampled from the crystalline basement of the Fennoscandian Shield, aiming at detecting episodic fracturing reactivation, mineralization and microbial processes throughout the craton history.The analytical procedures involve, foremost, Rb-Sr geochronology, along with U-Pb and (U-Th)/He geochronology, stable isotope and trace element geochemistry, fluid inclusion thermometry and biomarkers. The in situ age determinations enabled 1) linking of greisen and distal veins to magmatic and post-magmatic fluid circulation, 2) slickenfibre growth to distinct faulting episodes, and 3) mineral precipitation in fractures, veins and shear zones to regionally extending deformation events across the Fennoscandian Shield. In addition, dating of mineralization related to deep fracture-hosted microbial life constrained the timing of such activity at several sites. The precipitation episodes stretch from Paleoproterozoic to Jurassic times with overgrowth generations separated in time by up to one billion years in single veins and even within individual crystals. The findings of the thesis demonstrate that the methodological protocol has potential to directly date a wide range of mineral assemblages in fractures, faults, veins and shear zones given that the isochron requirements are fulfilled. Fulfillment is ensured through detailed petrological and structural characterization followed by geochronological analysis and thorough data reduction allowing validation of isotopic data down to submicrometer level. The outcomes have implications for tectonic reconstructions at various scales, for the tracing of the deep ancient biosphere and for comprehending hydrothermal ore deposition, with direct societal relevance in the detection of ancient microbial activity and fracture reactivation at the candidate site for a spent nuclear fuel repository in Sweden.

Ämnesord

NATURVETENSKAP -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)
NATURAL SCIENCES -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

geochronology
brittle deformation
crustal fluids
mineral precipitation
ancient microbial activity
Precambrian craton
Scandinavia
Natural Science
Naturvetenskap

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Av författaren/redakt...: Tillberg, Mikael; Drake, Henrik, D ...; Åström, Mats E., ...; Zack, Thomas; Hogmalm, Johan; Almqvist, Bjarne

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NATURVETENSKAP: NATURVETENSKAP; och Geovetenskap och ...; och Geologi

Delar i serien: Linnaeus Univers ...

Av lärosätet: Linnéuniversitetet

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