Synextensional magmatism leading to crustal flow in the Albion–Raft River–Grouse Creek metamorphic core complex, northeastern Basin and Range

Abstract

[1] This study addresses the origin of granitic magmas in the Albion-Raft River-Grouse Creek (ARG) metamorphic core complex and environs and how these inform us about the deep crustal processes leading to crustal flow and the formation of the ARG. SHRIMP-RG U-Pb zircon ages, whole-rock geochemical data (major and trace element data, as well as Sr and Nd isotopes), and zircon geochemistry (in situ O-isotope, Hf-isotope, and trace element compositions) from Eocene to Oligocene magmas now exposed at three structural levels of the ARG show that the 41-32 Ma Emigrant Pass and the 32-25 Ma Cassia plutonic complexes have a common origin, sharing a deep crustal "hot zone" that remained above solidus temperatures for at least 16 Myr. This magmatism is part of the protracted magmatism that swept southward across the western U.S. between ∼42 and 21 Ma, inferred to be the result of foundering of the shallow Farallon slab. Isotopic modeling of geochemical data from these magmas suggests that between 41 and 32 Ma, the influx of mantle-derived basalt into the lower crust triggered large-scale hybrid magmatism generating calc-alkaline magmas that erupted and intruded the upper crust and significantly weakened the lower and middle crust. Between 32 and 25 Ma, this "hot zone" incorporated large amounts of continental crustal melts, resulting in greater mobility of the lower and middle crust, driving middle crustal flow and the formation of granitic plutons that rose to shallower levels of the crust forming the granite-cored gneiss domes of the ARG.

Eocene and Miocene extension, meteoric fluid infiltration, and core complex formation in the Great Basin (Raft River Mountains, Utah)

“…Previous studies have proposed diverse kinematic histories including Mesozoic crustal shortening and synconvergent extension followed by multiple episodes of Cenozoic extension [Wells, 1997;Wells et al, 1998Hoisch et al, 2002;Konstantinou et al, 2012] along two oppositely directed detachment systems, which were synchronously active for at least part of their history [Malavieille, 1987;Wells et al, 2000;Sullivan and Snoke, 2007]. The top-to-the-WNW Middle Mountain shear zone located in the Albion, Grouse Creek, and western Raft River Mountains is a long-lived, amphibolite-facies extensional shear zone of middle-late Eocene to Oligocene age (Figure 1b) [Saltzer and Hodges, 1988;Wells et al, 2004;Strickland et al, 2011a] that was reactivated during the Oligo-Miocene [Sheely et al, 2001] following the intrusion of synextensional, late Eocene to Oligocene plutons [Compton et al, 1977;Egger et al, 2003;Strickland et al, 2011b;Konstantinou et al, 2012Konstantinou et al, , 2013. The top-to-the-east Miocene Raft River detachment and its underlying detachment shear zone (RRDSZ) are best exposed at the Ten Mile and Clear Creek Canyon localities in the eastern Raft River Mountains (Figure 1b) [e.g., Malavieille, 1987;Wells et al, 2000;Wells, 2001].…”

“…(a) Simplified map of the western United States showing Cenozoic extension (dark grey regions) and metamorphic core complexes (red). Modified from Foster et al [] and Sonder and Jones [], (b) simplified geological map of the Raft River‐Albion‐Grouse Creek Metamorphic Core Complex with the top‐to‐the‐east Raft River detachment shear zone (RRDSZ) in the Raft River Mountains and the top‐to‐the‐WNW Middle Mountain shear zone in the Albion and Grouse Creek Mountains (modified from Wells [], Wells et al [], and Konstantinou et al []). White dots mark Pine Creek Canyon, Clear Creek Canyon, and Ten Mile Canyon sampling localities.…”

“…One extensively studied MCC is the Raft River-Albion-Grouse Creek Metamorphic Core Complex (RAG-MCC; NW Utah, USA; Figure 1a) [Compton et al, 1977;Malavieille, 1987;Manning and Bartley, 1994;Wells, 1997Wells, , 2001Wells et al, 1998Wells et al, , 2000Wells et al, , 2004Sheely et al, 2001;Hoisch et al, 2002;Sullivan and Snoke, 2007;Gottardi et al, 2011Gottardi et al, , 2015Strickland et al, 2011aStrickland et al, , 2011bKonstantinou et al, 2012Konstantinou et al, , 2013Gottardi and Teyssier, 2013]. The RAG-MCC records a protracted tectonic history with alternating cycles of Late Cretaceous to Miocene extension and shortening [Wells, 1997;Hoisch et al, 2002;Konstantinou et al, 2012;.…”

“…One process that promotes very negative δ 2 H values (<À120‰) in formerly high grade metamorphic footwall rocks is the syntectonic interaction with meteoric water [e.g., Fricke et al, 1992;Wickham et al, 1993;Mulch et al, , 2006. Wells [1997], , and Konstantinou et al [2013]). White dots mark Pine Creek Canyon, Clear Creek Canyon, and Ten Mile Canyon sampling localities.…”

Evidence for a long‐lived accommodation/transfer zone beneath the Snake River Plain: A possible influence on Neogene magmatism?

“…In the region south of the Snake River Plain, there is a time lag between the end of arc magmatism in the Sierra Nevada (85–80 Ma) [e.g., Ducea , ] and the onset of Cenozoic calc‐alkaline magmatism at ~42 Ma (Figures ). The time of onset of volcanism migrates, becoming younger southward (Figures and ) [e.g., Armstrong and Ward , ; Christiansen and Yeats , ], and has been attributed to the progressive southward younging delamination of the shallow Farallon slab and backflow of asthenosphere to the base of the mantle lithosphere [e.g., Humphreys , ; McQuarrie and Oskin , ; Konstantinou et al ., ]. Crustal flow, melting, and magma generation continue at depth after calc‐alkaline volcanism in any given place as evidenced by the intrusion of evolved plutonic rocks that range from circa 32–24 Ma that have no surface eruptive counterparts (e.g., Ruby Mountains [ Howard et al ., ] and Albion‐Grouse Creek Mountains [ Strickland et al ., ; Konstantinou et al ., ]) (Figure ).…”