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Event

Geotop Seminars: Dr Brice LaCroix

Tuesday, November 7, 2023 12:30to13:30

Dr Brice LaCroix, Kansas State University

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The Enigma of the Nacimiento Block of Central California: Where Is the Slabless Window?

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Mardi 7 novembre 2023 à 12h30 - Tuesday, November 7, 2023 at 12:30 pm

Local PK-7605, 7e étage, 201 ave. du Président-Kennedy

Pour assister en vidéoconférence via Zoom:Ìý

Résumé / abstract:

The Nacimiento block,Ìýan exhumed assemblage of an accretionary complex formed by the subduction of theÌýFarallon oceanic plate under the western margin of North America,Ìýis enigmatic as it is affected by post-metamorphicÌýthermal anomaly, hydrothermal activity leading to the formation of the Los Burros gold deposit, and high landslideÌýactivity.

In order to document the important vertical uplift of the area,Ìýwe present a novel approach for mapping vertical uplifts in exhumed metasedimentary rocks by coupling Raman spectroscopy of carbonaceous material with (U-Th)/He thermochronometry on apatite and zircon. We apply this approach to carbonaceous metasedimentary rocks of the Franciscan subduction complex, exposed in the Nacimiento block of central California, USA, an area that records high-pressure–low-temperature metamorphism prior to entrainment within the present-day transform plate boundary We demonstrate that this approach, combined with regionalÌýstructuralÌýobservations, can be used to map previously unrecognized transpressive ridges and quantify the verticalÌýcrustal movement. We propose that the Nacimiento block is affected by a localized post-metamorphic thermal anomalyÌýthat corresponds to a localized transpressive deformation since ca. 25 Ma at an uplift rate of about 0.3 mm/yrs.

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