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Late Cretaceous Gravitational Collapse of the Southern Sierra Nevada Batholith, California

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Late Cretaceous Gravitational Collapse of the Southern Sierra Nevada Batholith, California Origin and Evolution of the Sierra Nevada and Walker Lane themed issue Late Cretaceous gravitational collapse of the southern Sierra Nevada batholith, California Alan D. Chapman1,2,*, Jason B. Saleeby1, David J. Wood1,†, Alison Piasecki1, Steven Kidder1, Mihai N. Ducea2, and Kenneth A. Farley1 1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA ABSTRACT between the shallow and deep crust during age. Furthermore, this effort focuses on specifi c extension, and (2) that the development of and elusive issues pertaining to Late Cretaceous The Sierra Nevada batholith is an modern landscape in southern California disruption and dispersion of the southern Sierra ~600-km-long, NNW-trending composite was greatly preconditioned by Late Creta- Nevada batholith and vicinity, including: (1) the arc assemblage consisting of a myriad of ceous tectonics. magnitude and timing of tectonic transport of plutons exhibiting a distinct transverse zona- upper crustal fragments along a regional detach- tion in structural, petrologic, geochrono- INTRODUCTION ment system; (2) the degree of strain coupling logic, and isotopic patterns. This zonation between differentially exhuming levels of the is most clearly expressed by a west-to-east In zones of convergence, regional gradients crust; (3) the importance of strike-slip faulting variation from mafi c to felsic plutonic assem- in gravitational potential energy can be relaxed during collapse; and (4) the extent to which blages. South of 35.5°N, the depth of expo- through lateral spreading and vertical thinning the development of the southern Sierra Nevada sure increases markedly, and fragments of of orogenic crust (e.g., Dewey, 1988; Rey et al., landscape was infl uenced by Late Cretaceous shallow-level eastern Sierra Nevada batho- 2001). Deep-crustal exposures of the southern tectonism. lith affi nity rocks overlie deeper-level west- Sierra Nevada batholith, subjacent subduction Major plutonic units and metamorphic pen- ern zone rocks and subjacent subduction accretion assemblages, and fl anking shallow- dants of the southern Sierra Nevada batholith are accretion assemblages along a major Late level assemblages of the Mojave Desert and fairly well characterized in terms of geologic, δ18 87 86 Cretaceous detachment system. The mag- Salinian block represent a multi-tiered regional U-Pb zircon, O zircon, Sr/ Sr (Sri), thermo- nitude of displacement along this detach- core complex that formed in response to crustal barometric, paleontologic, and bulk composi- ment system is assessed here by palinspastic thickening and subsequent extensional collapse tional data (Kistler and Peterman, 1973, 1978; reconstruction of vertical piercing points (Glazner et al., 1989; Malin et al., 1995; Wood Chen and Moore, 1979, 1982; Saleeby et al., provided by batholithic and metamorphic and Saleeby, 1997; Kidder et al., 2003; Saleeby, 1987, 2007, 2008; Ross, 1989; Kistler and Ross, pendant structure and stratigraphy. Integra- 2003; Chapman et al., 2010, 2011). The col- 1990; Pickett and Saleeby, 1993, 1994; Saleeby tion of new and published U-Pb zircon geo- lapse phase is marked by the structural ascent and Busby, 1993; Lackey et al., 2005, 2008; chronologic, thermobarometric, (U-Th)/He of presently exposed high-pressure (7–11 kbar) Nadin and Saleeby, 2008; Memeti et al., 2010). thermochronometric, and geochemical data rocks of the southern Sierra Nevada batholith These data sets reveal a regional primary zona- from plutonic and metamorphic framework and vicinity (Ague and Brimhall, 1988; Pickett tion pattern to the batholith and distinct longitu- assemblages in the southern Sierra Nevada and Saleeby, 1993; Fletcher et al., 2002; Grove dinal belts of Neoproterozoic to lower Mesozoic batholith reveal seven potential correlations et al., 2003; Kidder et al., 2003; Saleeby et al., metamorphic pendant sequences. In aggregate between dispersed crustal fragments and 2007; Nadin and Saleeby, 2008; Chapman et al., the pendants and plutons of the southern Sierra the Sierra Nevada batholith autochthon. 2010, 2011) and the dispersal of lower pressure Nevada batholith are characterized well enough Each correlation suggests at least 50 km of (2–4 kbar), southeastern Sierra Nevada batho- to recognize allochthonous equivalents. south- to southwest-directed transport and lith affi nity assemblages across the entire width In this study, we present new: (1) fi eld and tectonic excision of ~5–10 km of crust along of the batholith (May 1989; Malin et al., 1995; structural relations to provide the basis for the Late Cretaceous detachment system. The Wood and Saleeby, 1997; Saleeby, 2003; Chap- recognizing potential correlations; (2) U-Pb timing and pattern of regional dispersion man et al., 2010). geochronology of plutonic and detrital zircon of crustal fragments in the southern Sierra Dokka and Ross (1995) speculate that exten- populations to identify the age and provenance Nevada batholith is most consistent with Late sion in the southern Sierra-Salinia core complex of displaced plutonic and metamorphic assem- Cretaceous collapse above the underplated is Neogene in age. Glazner et al. (1996) refute blages; (3) thermo barometric work to assess accretionary complex. We infer, from data this model, arguing that late Cenozoic structures pressure differentials between native and dis- presented herein (1) a high degree of coupling and structural relief in the core complex resulted placed assemblages; (4) major and trace ele- instead from crustal shortening. We contribute ment geochemistry and Sr and Nd isotopic *Email: [email protected]. to this debate by showing that major extension ratios to determine the sources of allochthonous †Present address: 3423 Broadmead Drive, Houston, and basement rotations in the southern Sierra- metavolcanic rocks; and (5) zircon (U-Th)/He Texas 77025, USA. Salinia core complex are Late Cretaceous in thermochronometry to constrain the timing of Geosphere; April 2012; v. 8; no. 2; p. 314–341; doi:10.1130/GES00740.1; 15 fi gures; 5 tables; 3 plates; 1 supplemental fi le. 314 For permission to copy, contact [email protected] © 2012 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/8/2/314/3342599/314.pdf by guest on 28 September 2021 Collapse of the Sierra Nevada batholith extension. These results are integrated with pre- from ~0.703 to ~0.709. The boundary between of the Sierra Nevada batholith (Saleeby, 1978, vious geologic studies and thermobarometric, tonalitic and granodioritic zones is generally 1987; Walker, 1988; Saleeby and Busby, 1993; geochronologic, and geochemical databases in defi ned by the Sri = 0.706 isopleth (Nadin and Manuszak et al., 2000; Memeti et al., 2010). order to recognize allochthon-autochthon pairs Saleeby, 2008). and to estimate the magnitude of transport that Tectonostratigraphy of the Southern they imply. Pre-Cretaceous Plutons and Sierra Nevada Region Metamorphic Framework GEOLOGIC BACKGROUND South of 35.5° N, the depth of exposure Cretaceous plutons of the Sierra Nevada increases markedly and the transverse structure “Autochthonous” Sierra Nevada Batholith batholith intruded a framework of Neoprotero- of the “autochthonous” Sierra Nevada batho- zoic to Mesozoic continental shelf, slope, and lith is disrupted by two major Late Cretaceous The Sierra Nevada block is a NNW-trending rise strata, a belt of accreted abyssal lithosphere, systems of parallel low-angle normal faults composite batholith with juvenile batholithic and Triassic to Jurassic plutons, now all exposed that juxtapose: (1) subduction accretion assem- crust extending to ≥35 km depth (Ruppert et al., as metamorphic pendants (Saleeby et al., 2008; blages and deep-level exposures of the Sierra 1998; Saleeby et al., 2003, 2007). Gradients Figs. 1–3). Covariation of pendant stratigraphy, Nevada batholith (the Rand fault and Salinas in pluton ages, integrated bulk compositions, age, and provenance track with plutonic zona- shear zone; Postlethwaite and Jacobson, 1987; amounts of recycled crustal components, and tion patterns discussed above (Figs. 2 and 3). Nourse, 1989; Kidder and Ducea, 2006; Chap- the paleogeographic affi nities of metamorphic West to east longitudinal zones include: (1) the man et al., 2010, 2011) and (2) eastern and west- pendants defi ne a distinct west to east zonation Paleozoic Foothills ophiolite belt with overlying ern Sierra Nevada batholith assemblages (the (Figs. 1 and 2). These zones may be used to rec- Permian to Triassic (?) Calaveras complex hemi- southern Sierra detachment; Wood and Saleeby, ognize and reconstruct superimposed tectonic pelagic deposits, and unconformable infolds of 1997; Fig. 1). The resulting generalized tec- disruptions. suprasubduction mafi c volcanic rocks and silici- tonostratigraphy of the southern Sierra Nevada For convenience, we refer to the pre-Late Cre- clastic turbidites (Saleeby, 2011; Fig. 2). (2) A batholith, from top to bottom, is that of a multi- taceous architecture of the Sierra Nevada batho- belt, spanning western to eastern Sierra Nevada tiered core complex consisting of three pack- lith and adjacent southern California batholith of batholith zones, of Cambrian to Ordovician ages: allochthonous shallow-level mafi c rocks the Mojave Desert and Salinia as autoch thonous, eugeoclinal (i.e., deep marine sediments of the and eastern Sierra Nevada batholith affi nity
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