Geotop Seminars: Dr Brice LaCroix
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 脿 12h30 - Tuesday, November 7, 2023 at 12:30 pm
Local PK-7605, 7e 茅tage, 201 ave. du Pr茅sident-Kennedy
Pour assister en vid茅oconf茅rence via Zoom:听
R茅sum茅 / abstract:
The Nacimiento block,听an exhumed assemblage of an accretionary complex formed by the subduction of the听Farallon oceanic plate under the western margin of North America,听is enigmatic as it is affected by post-metamorphic听thermal anomaly, hydrothermal activity leading to the formation of the Los Burros gold deposit, and high landslide听activity.
In order to document the important vertical uplift of the area,听we 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鈥搇ow-temperature metamorphism prior to entrainment within the present-day transform plate boundary We demonstrate that this approach, combined with regional听structural听observations, can be used to map previously unrecognized transpressive ridges and quantify the vertical听crustal movement. We propose that the Nacimiento block is affected by a localized post-metamorphic thermal anomaly听that corresponds to a localized transpressive deformation since ca. 25 Ma at an uplift rate of about 0.3 mm/yrs.