Tracking paleodeformation fields in the Mesozoic central Sierra Nevada arc: Implications for intra-arc cyclic deformation and arc tempos

Abstract

In this study, structures in plutons and host rocks are coupled with geochronology to track paleodeformation fields from the late Paleozoic to Late Cretaceous in the central Sierra Nevada. Regional NW-striking host-rock foliation, NE-or SW-vergent thrust faults, and associated folds developed from the early Mesozoic to Early Cretaceous. Dextral transpressional shear zones developed in the Late Cretaceous. Strikes of steep-dipping magmatic foliations in Mesozoic plutons temporally vary from approximately NW (Triassic-Jurassic) to WNW (Late Cretaceous), displaying a progressive counterclockwise rotation. Joint interpretation based on combining host-rock and magmatic structures suggests that intra-arc paleodeformation fields were dominated by coaxial and arc-perpendicular contraction from the early Mesozoic to Early Cretaceous, becoming increasingly dextral transpressive in the Late Cretaceous. The switch from contraction to transpression was likely caused by oblique convergence between the Farallon and North American plates. Based on observations in the study area and other host-rock pendants in the central Sierra Nevada, we propose that the intensity of intra-arc deformation is cyclic. To some extent, it mimics the episodic pattern of arc magmatism: Stronger deformation coincides with magmatic flare-ups. Magmatism promotes intra-arc deformation, which in turn causes crustal thickening during transfer of materials downward to the magma source regions, potentially fertilizing source regions with supracrustal materials and resulting in increased magma generation. Thus, models addressing continental arc tempos should include intra-arc processes. Evolution of continental arcs may be influenced by linked cyclic processes within the arcs accompanied by noncyclic processes driven by events external to the arcs.

The rise and fall of continental arcs: Interplays between magmatism, uplift, weathering, and climate

“…We can compare our model outputs to paleo-altimetry constraints. Elevations prior to the Cretaceous magmatic flare-up were likely low or close to sea-level based on the fact that Cretaceous plutons intruded into 150-190 Ma old marine sediments throughout the Sierras, such as the Mariposa Formation (Cao et al, 2015;. Oxygen isotopic constraints suggest elevations reached ∼3 km by ∼85 Ma, indicating that magmatism was accompanied by surface uplift (Poage and Chamberlain, 2002).…”

“…U-Th/He thermochronology and coupled studies of pluton barometry and U-Pb geochronology provide some constraints on the paleo-depths of plutons as a function of time (Ague and Brimhall, 1988;Cecil et al, 2006;House et al, 1998House et al, , 1997Wakabayashi and Sawyer, 2001) as can be seen in Fig. 5.…”

“…In fact, continued thickening of a pyroxenite layer due to progressive magmatic addition causes elevations and erosion rates to decrease. However, once magmatism ends, erosion will thin the crust, and in so doing, the thickness of the pyroxenite layer H px also decreases because the top of the (Cao et al, 2015;Paterson et al, , 2011. B.…”

“…Red curve includes mafic cumulates (down to 70 km) and is thus more representative of the total magmatic input. C. Paleo-depth estimates in the batholith versus time based on Al-in-hornblende barometry and U-Th/He and apatite fission track thermochronology (Ague and Brimhall, 1988;Cecil et al, 2006;House et al, 1997;Wakabayashi and Sawyer, 2001). D. Paleo-elevation of surface markers .…”

Spatial and Depth‐Dependent Variations in Magma Volume Addition and Addition Rates to Continental Arcs: Application to Global CO2 Fluxes since 750 Ma

“…Moreover, the amount of magma added at different crustal levels (volcanics to deep crust) can vary dramatically, typically showing an increase in magmatism toward deeper levels of the crust (e.g., DeBari & Greene, 2011). And lastly, the magnitude of deformation of the crust can vary during the lifespan of individual arc segments and with crustal depth (e.g., Cao et al, 2015) contributing to variable arc widths and thicknesses, which affect magma addition calculations. This complex behavior of continental arc magmatism must be accounted for when calculating magma VAs to the arc crust.…”