Lithospheric and crustal reactivation of an ancient plate boundary: the assembly and disassembly of the Salmon River suture zone, Idaho, USA

Abstract

The Salmon River suture zone, western Idaho, is a fundamental lithospheric boundary between the North American craton and the accreted terranes of the Cordilleran margin. The initial juxtaposition along this north-south-oriented structure occurred during Early Cretaceous time. This zone was potentially reactivated twice by subsequent tectonism, once during Cretaceous time and once during Miocene time. The Late Cretaceous western Idaho shear zone formed along the Salmon River suture zone, as denoted by a sharp gradient in the isotopic signature of the granitoids that intruded the lithospheric boundary zone. The reconstructed Late Cretaceous orientation of the western Idaho shear zone contains subvertical fabrics (lineation, foliation). The same boundary also acted as a locus for subsequent Miocene Basin and Range extensional deformation. Domino-style normal faulting and deep (2100 m) basin formation accommodated the motion between the extending accreted terranes to the west and the unextended Idaho batholith to the east. Whereas either the mantle boundary or a crustal-scale structuring controls the regional extent of the extensionally reactivated zone, locally crustal basement faults and lithological contacts control the orientation and precise location of faults that accommodate reactivation. The multiple reactivation of the Salmon River suture zone is critical for several reasons. The Early Cretaceous suture zone apparently created a fundamental lithospheric flaw, which was reactivated after terrane accretion. Whether this zone was a fracture or a shear zone, the fabric in the mantle lithosphere was apparently not ‘healed’ during orogenesis. Thus, juxtaposition of mantle lithosphere, which is inferred to occur by faulting in the uppermost mantle, acts as a weakness during later tectonism. Second, the paucity of strike-slip plate boundaries in the geological record makes sense in the context of reactivation. The vertical, lithospheric-scale nature of these structures makes them particularly susceptible to lithospheric-scale reactivation during both transcurrent and/or extensional deformation. These reactivations both overprint the earlier deformation and modify the original geometry. Steeply dipping fabrics, rather than vertical fabrics, may be the general signature of major, ancient strike-slip faults.

Age and structure of the Crevice pluton: overlapping orogens in west-central Idaho?

“…We emphasize that steep north-south-striking zones of high shear strain are not restricted to mid-Cretaceous plutonic rocks emplaced into the arc-craton boundary, a fundamental tenet of tectonic models proposed for west-central Idaho (e.g., Tikoff et al 2001;Gray and Oldow 2005;Giorgis et al 2008;Blake et al 2009). Our structural analysis in the Riggins region shows that similarly oriented high-strain fabrics exist in arc volcanogenic and carbonate rocks 10-25 km west of the boundary.…”

“…Hammer for scale. et al 2000;Tikoff et al 2001;Giorgis et al 2005Giorgis et al , 2007Giorgis et al , 2008Blake et al 2009). This interpretation is based on the apparent transposition of L 1 -S 1 suture zone tectonites across the eastern limb of the Lake Creek antiform (e.g., Blake et al 2009).…”

“…According to McClelland et al (2000), suturing was followed by mid-Cretaceous transpressional deformation on the narrower (<10 km wide) WISZ. Although the superposition of mylonitic fabric on suture zone structures is not documented, the WISZ and SRSZ are viewed as spatially overlapping but temporally distinct tectonic elements in west-central Idaho (McClelland et al 2000;Tikoff et al 2001;Giorgis et al 2007;Blake et al 2009). This concept of "overlapping Jura-Cretaceous orogens" follows the early premise of Hamilton (1963a) and plays a fundamental role in tectonic models proposed along central portions of the North American Cordillera (e.g., Gray and Oldow 2005;Giorgis et al 2008).…”

“…Near the alpine village of McCall (Fig. 2), mid-Cretaceous calcalkaline plutons recording the arc-craton transition ( 87 Sr/ 86 Sr i ratios <0.7045 to >0.707; e.g., Manduca et al 1992) are deformed by steep mylonitic fabrics attributed to dextral transpression on the post-accretionary western Idaho shear zone (WISZ;McClelland et al 2000;Tikoff et al 2001;Giorgis et al 2005). The timing of deformation in this area (ca.…”

Two-stage cooling history of pelitic and semi-pelitic mylonite (sensu lato) from the Dongjiu–Milin shear zone, northwest flank of the eastern Himalayan syntaxis

“…Detailed reflection-and-refraction seismic surveys (e.g., Lucas et al, 1993) across the syntaxis region are required in order to confidently differentiate between them, whereby detailed 3D knowledge of the subsurface structure would allow direct testing of the validity of the crustal-scale folding (3), duplex development (4), and intersecting thrust belt (5) models. Although our new integrated petrological and geochronological data cannot readily distinguish between these tectonic models in the absence of this aforementioned seismic data, they do record the longlived nature of crustal collision zones in the sense of particular regions being fundamental zones of crustal weakness that get reworked/ overprinted as plates move and reorganize (e.g., Bailey et al, 2000;Hatcher, 2001;Tikoff et al, 2001;Müller et al, 2012). The DMSZ has been reported to include strongly deformed and weakly metamorphosed ITSZ equivalents of Tethyan Himalaya Paleozoic and Mesozoic marine sedimentary strata alongside dismembered fragments of ophiolitic and ultramafic material (Hao et al, 1999;Geng et al, 2006;Booth et al, 2009;Hébert et al, 2012).…”