Integrating geological and geophysical data to determine crustal architecture: application to the Fraser Zone, east Albany-Fraser Orogen

Lucy Brisbout

    Research output: ThesisMaster's Thesis

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    Structural analysis and forward modelling of the Mesoproterozoic, metagabbro-dominated Fraser Zone in the east Albany‒Fraser Orogen, has led to new interpretations of its crustal architecture. Structures that can be mapped in the southwest Fraser Zone include; 1) regional scale, northeast trending, tight to isoclinal folds (~1.6 to 4.5 km in width); 2) regional scale, north to north-northwest trending isoclinal folds (~6 km in width); and 3) eye-shaped magnetic features that can be interpreted either as doubly plunging antiforms or synforms of non-cylindrical, northeast trending folds, or as ‘magnetic porphyroclasts’ that formed during dextral shearing on northeast trending structures. These regional scale structures could be interpreted as part of a single progressive deformation event that includes the granulite facies, gneissic foliation, and formed shortly after the Fraser Zone magmatism, during Stage I of the Albany‒Fraser Orogen. Alternatively, these regional scale structures may have formed during Stage II of the Albany‒Fraser Orogen, after the Fraser Zone had been emplaced into the shallow crust.

    Two, crustal-scale 2.5 dimension, geologically and petrophysically constrained gravity and magnetic forward models were constructed traversing the east Albany‒Fraser Orogen. The Fraser Zone, modelled with the median specific gravity of the Fraser Zone samples (3 gcm-3), is interpreted to be near triangular in shape, and to extend to depths of 12.4 in profile 1, and 14.5 km in profile 2. The long wavelength gravity anomaly (~150 km) to the southeast of the Fraser Zone in profile 2, is interpreted to be a sill-like body of mafic-ultramafic material that is located in the middle crust. This body is possibly associated with the Fraser Zone, given that the intrusion of the Fraser Zone gabbros during Stage I of the Albany‒Fraser Orogen, is the only regional mafic event recognised in the Albany‒Fraser Orogen. When attributed the same density as the Fraser Zone, the interpreted mid-crustal sill has a maximum thickness of 14.5 km.

    Original languageEnglish
    Publication statusUnpublished - May 2014


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