Accretionary Mesozoic–Cenozoic expansion of the Cordilleran continental margin in California and adjacent Oregon William R. Dickinson Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA ABSTRACT Franciscan subduction was largely coeval motion of the Pacifi c plate along the evolving with intrusion of the dominantly Cretaceous San Andreas transform. My method is to pre sent The Mesozoic–Cenozoic Cordilleran oro- Sierra Nevada batholith into the roots of the summary geologic maps showing the accretion- gen of California includes multiple accre- Cordilleran magmatic arc, but Franciscan ary belts in plan view and accompanying chro- tionary belts incorporated sequentially into accretion was just a late phase of continuing nostratigraphic diagrams that display transverse the continental margin since Middle Trias- tectonic expansion that spanned more than age relationships of rocks both within the accre- sic time. Accreted tectonic elements include 200 m.y. along the California continental tionary belts and superimposed upon them. The subduction complexes assembled along the margin. coordinated maps and diagrams spanning the Cordilleran margin, intraoceanic island full width of California Mesozoic–Cenozoic arcs attached to the continental margin by Keywords: accretion, California, Klamath accretionary tracts were compiled from mul- Jurassic arc-continent collision, and subduc- Mountains, Sierra Nevada, tectonics. tiple sources cited in fi gure captions, and have tion complexes associated with the fl anks of no counterparts of equivalent scope in the litera- the exotic island arcs. Systematic analysis INTRODUCTION ture. The ages of the rock assemblages within of areal relations and geochronological data the accretionary belts, and of the stitching plu- displayed on subregional geologic maps and Ever since the seminal papers of Hamilton tons and sedimentary cover sequences that tie summary chronostratigraphic diagrams (1969) on “underfl ow” (subduction) of Pacifi c the belts together, set constraints on the times allows the punctuated but quasi-continuous mantle beneath California, and of Moores (1970) of amalgamation of the successive belts into the pattern of tectonic accretion to be discerned. on the accretion of intraoceanic arc structures to edge of the continent. Systematic interpretations Stitching plutons and sedimentary overlap the continental margin, geoscientists have been of the maps and diagrams also call attention to successions constrain the times that succes- trying to comprehend the scope and geometry of shortcomings in the currently available database, sive accretionary belts were juxtaposed and tectonic accretion at ancient subduction zones in and thereby indicate the kinds of information amalgamated into the edge of the continental California (e.g., Ernst, 1983, 1984). This paper needed to resolve uncertainties in the tectonic block. In the Klamath Mountains and Sierra is an appraisal of the Mesozoic–Cenozoic accre- history of the region. Nevada, a continental-margin magmatic arc tionary expansion of the California continental The northwest-trending Mesozoic–Cenozoic of Triassic–Jurassic age includes volcanic and margin based on a fresh synthesis of incremen- lithotectonic belts of California are separated plutonic components built upon and intruded tal geologic mapping and geochronological from the interior of the Laurentian craton by the into deformed Paleozoic assemblages that studies by many geoscientists during the past deformed Cordilleran miogeocline overthrust were accreted to the Laurentian margin several decades. Traverses along key transects by Paleozoic terranes accreted before Middle before Middle Triassic time. The native arc across all the accretionary belts during the inter- Triassic time and discussed in detail elsewhere assemblage is separated from intraoceanic val 1998–2004 gave me personal impressions of (Dickinson, 2000, 2006). Westward toward the Triassic–Jurassic arc assemblages exposed each as a context for understanding descriptions coast, multiple subparallel tectonic assemblages farther west by a compound suture belt of by others in the literature. This overview does of diverse origin were thereafter added to the mélange and broken formation derived from not extend southward into the California Trans- fl ank of Laurentia during Mesozoic–Cenozoic the remnant ocean basin that separated the verse Ranges, where onshore transrotation and subduction (Fig. 1): (1) a native Mesozoic arc east-facing intraoceanic arc system from the offshore rifting have transposed and disrupted succession built on pre-Mesozoic rocks of the Cordilleran margin. Polarity reversal after key tectonic elements, but does extend north- evolving continental margin; (2) a suture zone Middle to Late Jurassic arc-continent colli- ward to include the Oregon extension of the of tectonic mélange and broken formation sion was followed by accretion of a disrupted Klamath Mountains. immediately seaward; (3) accreted Mesozoic arc ophiolitic belt forming mafi c basement in My aim is to outline the pattern of punctu- structures seaward from the mélange belts; and the subsurface of the Great Valley forearc ated but quasi-continuous accretion of diverse (4) both Mesozoic and Cenozoic components of basin. Subsequent forearc sedimentation oceanic elements to the California continen- the Franciscan subduction complex farther west accompanied the assembly of multiple belts tal margin from mid-Triassic to mid-Tertiary near the coast. of mélange and broken formation that form time. Subsequently, tectonic accretion ended as Following introductory passages addressing the Mesozoic–Cenozoic Franciscan subduc- subduction of the Farallon and derivative oce- key topical issues, my areal treatment begins tion complex of the California Coast Ranges. anic plates was gradually supplanted by lateral with a discussion of the Klamath Mountains Geosphere; April 2008; v. 4; no. 2; p. 329–353; doi: 10.1130/GES00105.1; 9 fi gures. For permission to copy, contact [email protected] 329 © 2008 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/4/2/329/3336520/i1553-040X-4-2-329.pdf by guest on 29 September 2021 Dickinson 115° 120° WA ID e n W o A 45° Z OR B LUE MTNS. marginal C offset n o i t E 45° c M u IDb d N ID T b u S O Z s O e d I C E R sca C O V a C OR OR ID CA NV ID NV MTJ NV UT t s u r h st t e ru th lin s e 40° n i n a i G t l n c r u e a o 40° o backarc d e a n M basin g t lco o e o i g n V G s m rt hi a e ll b o SB n N e R a a f y r e l h l tc i a f d s o r h r SNb rc e Wa a ar Co UT N AZ l c V ta SB C n A e p R b in a if a t l NV n e S s o o H i c s f AZ s u S n n b A a d f 35° u c ti ictr o N f o 35° n a z f Ga o le a P z B o rotated isb n ee e Transverse PRb SI ri Ranges f ft ba sin 0 100 200 US M A EXI scale in km CO 120° 115° ABCDEFG T-Fran K-Fran is arcs sut belt acc Pz nat arc batho Figure 1. Position of California continental margin (west of Great Valley forearc basin) in tectonic framework of southwest Laurentia (adapted after Reed et al., 2005). Regional tectonic relations after Dickinson (2000, 2004, 2006), Dickinson et al. (2005), and this paper, with Jurassic–Cretaceous Bisbee rift basin after Dickinson and Lawton (2001b) and Triassic–Jurassic backarc basin in Nevada adapted after Wyld (2002). Barbed lines are principal thrusts (solid barbs where active). Heavy lines are strike-slip faults (Gaf—Garlock; Naf— Nacimiento; Rif—Rinconada; SAf—San Andreas; SHf—San Gregorio–Hosgri; SIf—San Isidro) with associated Mendocino triple junction (MTJ) and Salinian block (SB). Symbols: A (T-Fran)—Tertiary–uppermost Cretaceous Franciscan subduction complex and Paleogene Siletz-Umpqua assemblage; B (K-Fran)—Cretaceous–latest Jurassic Franciscan subduction complex; C (is arcs)—accreted intraoceanic Triassic–Jurassic island arcs; D (sut belt)—mid-Mesozoic suture belt (pre-Franciscan mélanges); E (acc Pz)—accreted Paleozoic crustal elements (oceanic allochthons and island arcs); F (nat arc)—native Triassic–Jurassic continental-margin arc assemblage (not shown to southeast where crosses miogeocline and southwestern prong of craton); G (batho)—major batholiths of largely Cretaceous age (IDb— Idaho; PRb—Peninsular Ranges; SNb—Sierra Nevada). 330 Geosphere, April 2008 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/4/2/329/3336520/i1553-040X-4-2-329.pdf by guest on 29 September 2021 Accretionary expansion of California and adjacent California-Oregon coastal ranges Golconda thrust of Nevada, to the subduction transport estimated from paleofaunal interpre- where the various accretionary belts are most zone associated with a Permian–Triassic (284– tations as thousands of kilometers of longitude completely exposed, and then proceeds south- 232 Ma) magmatic arc in eastern Mexico to was required to bring the Tethyan limestones to ward along the Sierra Nevada and the Califor- the southeast (Dickinson and Lawton, 2001a). the Cordilleran continental margin (Stevens et nia Coast Range. Original relationships of the Major strike slip postdated terminal juxtaposi- al., 1990, 1991; Belasky and Stevens, 2006). accretionary belts are progressively obscured tion of Gondwana against Laurentia along the southward by intrusion of the Mesozoic Sierra diachronous Ouachita-Marathon suture belt that Lateral Translation Nevada batholith, deposition of overlying Meso- closed in earliest Permian time in west Texas zoic or Cenozoic sedimentary cover, and post- (Ross, 1986). Interpretations of the California segment of accretion deformation including disruption by The line of truncation was oriented northwest- the Cordilleran orogen developed for the Geo- multiple strands of the Neogene San Andreas southeast at a high angle to the northeast-south- logical Society of America Decade of North transform fault system near the coast.