Structure and evolution of the East Sierran thrust system, east central California

Abstract

A belt of arc‐parallel, northeast vergent contractional deformation, the East Sierran thrust system (ESTS), crops out for ∼150 km along the east side of the Sierran continental margin arc. The ESTS is nowhere wider than ∼20 km, and it accommodated an estimated minimum of ∼9.3 km of horizontal shortening. Remarkably, it experienced repeated episodes of broadly coaxial and coaxial‐planar contractional deformation beginning prior to 188 Ma and continuing past 140 Ma. We postulate that the ESTS resulted primarily from episodic underthrusting of the back arc lithosphere beneath the east edge of the Sierran arc, facilitated by a buttressing effect of the arc. As a result of this process, rocks along the east flank of the batholith, including the ESTS, were episodically shortened against the arc buttress. The ESTS experienced significant deformation during the Nevadan orogeny, indicating that contractional to transpressive deformation affiliated with this event affected the eastern wall rocks of the arc as well as its western wall rocks.

Regional and temporal variability of melts during a Cordilleran magma pulse: Age and chemical evolution of the Jurassic arc, eastern Mojave Desert, California

“…This deformation age bracket is consistent with the >148 Ma age for deformation suggested by Schermer et al (2001) and in a broader regional sense is consistent with the 169 to 154 Ma timing for deformation correlated with regional intra-arc thrusting in the East Sierran thrust system (Walker et al, 1990;Dunne and Walker, 2004).…”

“…Zircon ages for ignimbrites interlayered with or capping the eolian sandstones (Fackler-Adams et al, 1997;Schermer et al, 2002;Busby et al, 2002;Fohey-Breting et al, 2010;Stone et al, 2013) indicate these eolian sands are correlative with the Early Jurassic Navajo/Aztec and/or Middle Jurassic Carmel cratoninterior sandstones (Kowallis et al, 2001;, suggesting that the low-standing arc persisted until early Middle Jurassic time, as late as 167 Ma. In contrast, Dunne et al (1998) Shortening occurred by about 176 Ma in the Clipper Mountains area (Howard et al, 1995), and shortening is bracketed between 172 and 162 Ma in the Fort Irwin region (Schermer et al, 2001, and this study), 169 and 154 Ma in the Cronese Hills (Walker et al, 1990) and 165 to 151 Ma at Iron Mountain (Boettcher and Walker, 1993), the later three comprising the regional early to middle interval of the East Sierran thrust system of Dunne and Walker (2004). Taken together, the geochronologic and structural data permit an interpretation with minimal overlap in time between an Early to Middle Jurassic low-standing arc and Middle to Late Jurassic shortening within the arc basement as the magma pulse reached its maximum and waned.…”

“…Contractile structures developed locally in concert with magmatism and may record a regional arc-fringing to intra-arc thrust belt reflecting arc-parallel contraction at relatively deeper structural levels (Walker et al, 1990;Dunne et al, 1998;Walker et al, 2002;Dunne and Walker, 2004).…”

“…In the specific case of the Jurassic arc, the timing of magmatism relative to intra-arc shortening and/or extension remains uncertain, as is the relationship between the arc and continental interior stratigraphic records, especially eolian sand sheets (Busby-Spera, 1988;Walker et al, 1990;Dunne et al, 1998;Dunne and Walker, 2004;Haxel and Miller, 2007). The exposed parts of the Jurassic arc in the Mojave Desert (Figure 1) record evidence of both extensional and contractile deformation that was broadly synchronous with magmatism, but it is unclear if this evidence indicates alternation of deformational style with time or with position in the arc infrastructure (Walker et al, 2002;Busby et al, 2002).…”

Jurassic Barrovian metamorphism in a western U.S. Cordilleran metamorphic core complex, Funeral Mountains, California

“…1), is commonly attributed to strong coupling between the eastwardunderfl owing Farallon plate and the westwardmoving North America plate (e.g., Burchfi el et al, 1992;Coney and Evenchick, 1994). In contrast, Early to Middle Jurassic retroarc shortening (e.g., Wyld, 2002;Dunne and Walker, 2004) may have been driven by arc collision and/or accretion (e.g., Dorsey and LaMaskin, 2007). Through combined Lu-Hf garnet geochronology, pressure-temperature (P-T) paths, and 40 Ar/ 39 Ar thermochronology of metamorphic rocks from the central Funeral Mountains, California, we present the fi rst conclusive evidence for Late Jurassic (ca.…”