ABSTRACT Widespread episodes of major contractional orogenesis correlate commonly with ages of high-pressure eclogitic rocks formed during bottom-driven, induced subduction of crustal terranes. Rapid exhumation of the deeply emplaced crust has led to the development of the concept of a “tectonic dunk.” The dunk process is a hallmark component of a suite of linked tectonic, magmatic, metamorphic, and sedimentologic processes that systematically follow plate interactions, including collision, coupling, and capture resulting in plate reconfiguration and changes of movement. Plate capture, which takes place during mechanical connection of plates within a “clutch” zone, is followed generally by an abrupt transition to plate stretching in response to drag or plate spin. Plate stretch, which is accommodated during drag by a network of complementary strike-slip and normal faults or during spin by regional domains of transtension, is recorded by “postorogenic,” back-arc extension, basin formation, and magmatism, extensive domains of which comprise large igneous provinces. As a captured continental plate is dragged or rotates, ductile mantle is disrupted and displaced by protuberances, such as a slab coupled against the base of an overriding plate and/or orogenic roots extending down from a cratonic core. The mantle turbulence resembles a wave-like ship’s wake with tsunami-like movement, albeit below crust. The arrival of a moving mantle bulge or wave is inferred to be focused along continental plate margins where subduction is induced, as recorded by magmatism and eclogitic rocks that form during deep emplacement of crustal terranes. Concurrent shortening of crust in the vicinity of the plate margin is inferred from inversion and uplift of marginal rift basins, obduction, and development of fold-and-thrust belts. As the mantle wave passes beneath plate interiors, tens to hundreds of meters of uplift, recorded by oceanic atolls, continental stream incision, regional unconformities, and local transitions to evaporite within shelf settings, record epeirogeny. After passage of the wave, common development of sheet-like bodies of quartzose sandstone, especially during the early Paleozoic, suggest postwave, regional subsidence. Resumption and re-invigoration of extension are recorded by eduction of dunked crust and conspicuous, widespread, volcanic eruptions recorded by tuffaceous layers intercalated with carbonaceous black shale within broad basins developed above thickened crust.

Restoration of plate consumption recorded by Caribbean arc volcanism reveals probable plate movements that led to the emplacement of the proto–Caribbean plate into the present Caribbean region and provided the space necessary to accommodate the rotation of the Yucatán Peninsula concurrent with the opening of the Gulf of Mexico between ca. 170 Ma and 150 Ma. Fault movement of the Yucatán, caused by edge-driven processes, resulted in counterclockwise rotation, as shown by paleomagnetic studies. Restoration of Yucatán rotation necessitates the presence of a paleogeography different from the current distribution of the Greater and Lesser Antilles. During emplacement of the Caribbean plate region, four magmatic belts with distinct ages and different geochemical characteristics are recorded by exposures on islands of the Antilles. The belts distinguish the following segments of Cretaceous and Tertiary magmatic arcs: (1) an Early Cretaceous geochemically primitive island-arc tholeiite suite (PIA/IAT) typically containing distinctive dacite and rhyodacite that formed between Hauterivian and early Albian time (ca. 135–110 Ma); (2) after a hiatus at ca. 105 Ma of ∼10 m.y., a voluminous, more-extensive calc-alkaline magmatic suite, consisting mainly of basaltic andesite, andesite, and locally important dacite, developed beginning in the Cenomanian and continuing into the Campanian (ca. 95–70 Ma); (3) a second (calc-alkaline) suite, spatially restricted relative to the older belts, that consists of volcanic and intrusive rocks, which formed between the early Paleocene and the middle Eocene (ca. 60–45 Ma); and (4) a currently active calc-alkaline suite in the Lesser Antilles typically composed of a basalt-andesite-dacite series that began to develop in the Eocene (ca. 45 Ma). Plate convergence took place along northeastward- or eastward-trending axes during the formation of the Caribbean, which is outlined by the Antillean islands and Central and South America. Movements were facilitated by strike-slip faults, commonly trench-trench transforms, as subducting crust was consumed. Restoration of apparent displacements of at least several hundreds of thousands of kilometers along the inferred lateral faults of the Eocene and younger Cayman set separating Puerto Rico, Hispaniola, and the Oriente Province of southeastern Cuba brings together Eocene volcanic rocks revealing a magmatic domain along the paleo–south-southwestern margin of the Greater Antilles. The transforms along the southern margin of the Caribbean plate are mainly obscured by contractional deformation related to the northward motion of South America as it was thrust over the faulted plate margin. Restoration of the Caribbean plate also translates the Nicaragua Rise westward, thereby revealing a pathway along which Pacific oceanic lithosphere, mainly composed of a large, Late Cretaceous igneous province (Caribbean large igneous province), manifest as an oceanic plateau (Caribbean-Colombian oceanic plateau), converged toward and subducted beneath the southern flank of the Cretaceous Greater Antilles magmatic belt between 65 and 45 Ma. The Eocene arc rocks overlie or abut previously recognized Early and Late Cretaceous subduction-related units. Eocene consumption of Pacific lithosphere ceased with the arrival, collision, and accretion of buoyant lithosphere composed of Caribbean large igneous province. The Greater Antilles formed during Late Cretaceous subduction of Jurassic ocean crust beneath an Early Cretaceous arc formed at the eastern margin of the proto–Pacific plate. Formation of a volcanic edifice above Early Cretaceous arc rocks was followed by plate collision and coupling of the Greater Antilles belt against the Bahama Platform. The most straightforward path of the Greater Antilles into the Caribbean is along northeast-striking transforms, one of which coincided with the eastern margin of the Yucatán Peninsula. The transform appears to link the Motagua suture to the Pinar del Rio Province of western Cuba. To the southeast, the arc was transected by a second transform, perhaps coinciding with the present trace of the Romeral fault in northwestern South America and extending northeast to the eastern terminus of the Virgin Islands. During Late Cretaceous convergence, a segment of the extinct Early Cretaceous arc, developed at the Pacific margin, was carried northeastward.

Subsurface sandstone samples of the Upper Jurassic (Oxfordian) Norphlet Formation erg deposits and (Kimmeridgian) Haynesville Formation sabkha deposits were collected from wells in the eastern Gulf of Mexico for U-Pb detrital zircon provenance analysis. Norphlet Formation samples in southwestern Alabama are characterized by detrital zircon ages forming two dominant populations: (1) 265–480 Ma, associated with Paleozoic Taconic, Acadian, and Alleghanian orogenic events of eastern Laurentia, and (2) 950–1250 Ma, associated with the Grenville orogenies of eastern Laurentia. These detrital zircon ages indicate derivation from Laurentian and Laurentian-affinity sources, including erosion of Paleozoic strata of the remnant Alleghanian fold-and-thrust belt and Black Warrior foreland basin, as well as Laurentian cratonic rocks exposed in remnant Appalachian orogenic highlands and eastern Gulf of Mexico rift-related horst blocks. In contrast, Norphlet Formation samples from the offshore Destin Dome exhibit a major population of 540–650 Ma zircon grains, along with a small population of 1900–2200 Ma zircon grains; these ages are interpreted to indicate contribution of sediment to the Norphlet erg from peri-Gondwanan terranes sutured to eastern Laurentian, as well as from the Gondwanan Suwannee terrane, which remained attached to North America after the rifting of Pangea. Samples from south-central Alabama yield subequal proportions of four major age populations: 250–500 Ma, 520–650 Ma, 900–1400 Ma, and 1950–2250 Ma. These ages indicate sediment was sourced by both Laurentian/Laurentian-affinity and Gondwanan/Gondwanan-affinity rocks, either through a combination of these rocks in the source area, or intrabasinal mixing of Laurentian/Laurentian-affinity sediment with Gondwanan/Gondwanan-affinity sediment. Detrital zircon provenance data from the overlying Haynesville Formation clastics of the Destin Dome offshore federal lease block also show the signature of Gondwanan/Gondwanan-affinity sediment input into the eastern Gulf of Mexico, suggesting that paleotopography affecting Norphlet Formation deposition persisted throughout much of the Late Jurassic. However, samples from the Pennsylvanian Pottsville Formation synorogenic fill of the Black Warrior Basin and Middle Cretaceous Rodessa Formation marginal marine sandstone lack evidence for any significant contribution of Gondwanan or Gondwanan-affinity detritus to the basin, indicating that transport of Gondwanan/Gondwanan-affinity zircon to the eastern Gulf of Mexico was due to early Mesozoic uplift, erosion, and/or paleodrainage pattern development. These results, along with previously reported detrital zircon provenance of Triassic and Jurassic sandstone of the southern United States, suggest that early Mesozoic sediment supply in southern North America was closely associated with erosion of Gondwanan/peri-Gondwanan crust docked along the Suwannee-Wiggins suture, which likely extended westward from the Suwannee terrane to the Yucatan-Campeche terrane; much of this Gondwanan/peri-Gondwanan crust remained docked along the Suwannee-Wiggins suture after the rifting of Pangea and prior to opening of the Gulf of Mexico.

The Mojave-Sonora megashear, which bounded the Jurassic southwestern margin of the North America plate from 170 to 148 Ma, may be linked northward to Alaska via the previously recognized discontinuity between the Insular and Intermontane terranes and co-genetic regional elements such as transtensional basins, transpressional uplifts, and overlapping correlative magmatic belts. The longer, continental-scale fault thus defined, which is called the Mexico-Alaska megashear, separated the North America plate from a proto-Pacific plate (the Klamath plate) and linked the axis of ocean-floor spreading within the developing Gulf of Mexico with a restraining bend above which mafic rocks were obducted eastward onto Alaskan sialic crust that converged against the Siberian platform. The fault, about 8000 km long, lies among more than a dozen large basins (and numerous smaller ones) many of which formed abruptly at ca. 169 Ma. The basins, commonly containing Middle and Late Jurassic and Cretaceous clastic and volcanic units, distinguish a locally broad belt along the western and southwestern margin of the North America plate. The basin margins commonly coincide with easterly striking normal and northwesterly striking sinistral faults although most have been reactivated during multiple episodes of movement. The pattern of intersecting faults and the rarely preserved record of displacements along them suggest that the basins are structural pull-aparts formed at releasing steps of a sinistral continental margin transform and are therefore transtensional. The width of the zone delineated by the basins is a few hundred km and extends west-northwesterly from the Gulf of Mexico across northern Mexico to southern California where it curves northward probably coincident with the San Andreas fault. Principal basins included within the southern part of the transtensional belt are recorded by strata of the Chihuahua trough, Valle San Marcos and La Mula uplift (Coahuila, Mexico), Batamote and San Antonio basins (Sonora, Mexico), Little Hatchet and East Potrillo Mountains and Chiricahua Mountains basins (New Mexico), Baboquivari Mountains Topawa Group (Arizona), regional Bisbee basin (Arizona, New Mexico, and Sonora, Mexico), Bedford Canyon, McCoy Mountains, Inyo Mountains volcanic complex and Mount Tallac basin (California). The latter probably extend into Nevada as part of the Pine Nut assemblage. At the southern margin of the Sierra Nevada of California, the inferred fault steps west then north, roughly along the Coast Range thrust and into the Klamath Mountains. The Great Valley (California) and Josephine ophiolites (Oregon) record these two major, releasing steps along the Mexico-Alaska megashear. From the northwestern Klamath Mountains, the Mexico-Alaska megashear turns east where Jurassic contractional structures exposed in the Blue Mountains indicate a restraining bend along which transpression is manifest as the Elko orogeny. Near the border with Idaho the fault returns to a northwest strike and crosses Washington, British Columbia, and southern Alaska. Along this segment the fault mainly coincides with the eastern limit of the Alexander-Wrangellia composite terrane. West of the fault trace in Washington, the Ingalls and Fidalgo ophiolites record separate or dismembered, co-genetic, oceanic basins. Correlative sedimentary units include Nooksack, Constitution, and Lummi Formations and the Newby Group, within the Methow basin. In British Columbia, the Relay Mountain Group of the Tyaughton basin, and Cayoosh, Brew, Nechako, Eskay, and Hotnarko strata record accumulation from Bajocian through Oxfordian within a northwestward-trending zone. From southern Alaska and northwestward correlative extension is recorded in basins by sections at Gravina, Dezadeash-Nutzotin, Wrangell Mountains, Matanuska Valley (southern Talkeetna Mountains), Tuxedni (Cook Inlet), and the southern Kahiltna domain. The pull-apart basins began to form abruptly after the Siskiyou orogeny that interrupted late Early to Middle Jurassic subduction-related magmatism. Convergence had begun at least by the Toarcian as an oceanic proto-Pacific plate subducted eastward beneath the margin of western North America. As subduction waned following collision, sinistral faulting was initiated abruptly and almost synchronously within the former magmatic belt as well as in adjacent oceanic and continental crust to the west and east, respectively. Where transtension resulted in deep rifts, oceanic crust formed and/or volcanic eruptions took place. Sediment was accumulating in the larger basins, in places above newly formed crust, as early as Callovian (ca. 165 Ma). The belt of pull-apart basins roughly parallels the somewhat older magmatic mid-Jurassic belt. However, in places the principal lateral faults obliquely transect the belt of arc rocks resulting in overlap (southern British Columbia; northwestern Mexico) or offset (northern Mexico) of the arc rocks of at least several hundreds of kilometers. The trace of the principal fault corresponds with fault segments, most of which have been extensively reactivated, including the following: Mojave-Sonora megashear, Melones-Bear Mountain, Wolf Creek, Bear Wallows–South Fork, Siskiyou and Soap Creek Ridge faults, Ross Lake fault zone, as well as Harrison Lake, Bridge River suture, Lillooet Lake, and Owl Creek faults. Northward within the Coast Range shear zone, pendants of continental margin assemblages are interpreted to mark the southwest wall of the inferred fault. Where the inferred trace approaches the coast, it corresponds with the megalineament along the southwest edge of the Coast Range batholithic complex. The Kitkatla and Sumdum thrust faults, which lie within the zone between the Wrangellia-Alexander-Peninsular Ranges composite terrane and Stikinia, probably formed initially as Late Jurassic strike-slip faults. The Denali fault and more northerly extensions including Talkeetna, and Chilchitna faults, which bound the northeastern margin of Wrangellia, coincide with the inferred trace of the older left-lateral fault that regionally separates the Intermontane terrane from the Wrangellia-Alexander-Peninsular Ranges composite terrane. During the Nevadan orogeny (ca. 153 ± 2 Ma), strong contraction, independent of the sinistral fault movement, overprinted the Mexico-Alaska megashear fault zone and induced subduction leading to a pulse of magmatism.

The Early to early Late Jurassic magmatic arc of the lower Colorado River region of southern California and southwest Arizona spanned ∼30 m.y., from ca. 190 to 158 Ma. The arc-type volcanic and plutonic rocks interacted extensively with the Proterozoic Mojave Province crust and show evidence for geographic-based age and compositional changes. The region lies adjacent to an amagmatic gap in the Jurassic arc of the southwest United States, near the western terminus of proposed Late Jurassic basins formed in conjunction with the opening of the Gulf of Mexico, and near, but to the north of, the projection of the trace of the sinistral Late Jurassic Mojave-Sonora megashear where it crossed from northern Mexico into the United States. Quartz-phyric dacitic to rhyolitic pyroclastic and locally hypabyssal rocks of the Dome Rock sequence were emplaced in two broad time periods, one between 190 and 185 Ma and the second between 173 and 158 Ma. Three compositionally expanded pluton units constituting the Kitt Peak–Trigo Peaks superunit were emplaced in the mid- to upper crust between 173 and 158 Ma, broadly contemporaneous with the younger phase of explosive volcanism. The compositionally expanded plutonic rocks consist of three informally named temporally and compositionally distinct magmatic units, from oldest to youngest, the Araz Wash diorite, the Middle Camp porphyritic granodiorite, and the Gold Rock Ranch granite. Each unit was emplaced over 4–6 m.y. periods of time. Dioritic rocks dominate the older Araz Wash diorite unit (173–169 Ma), granodiorite dominates the Middle Camp porphyritic granodiorite unit (167–163 Ma), and granite dominates the Gold Rock Ranch granite unit (163–158 Ma). Shortening and regional metamorphism throughout the lower Colorado River region accompanied emplacement of the Gold Rock Ranch granite unit. A Late Jurassic(?) mafic-felsic dike swarm forms the youngest magmatic unit in the region. The Jurassic magmatic history in the lower Colorado River region ended in the early Late Jurassic at ca. 158 Ma. Termination of magmatism in the Late Jurassic in the lower Colorado River region is distinct from adjacent parts of the arc to northwest in the Mojave Desert region or to the southeast in southern Arizona, where Late Jurassic magmatism continued to at least 146 Ma. At this time in the Late Jurassic, the Mojave-Sonora megashear had cut through the arc to the south of the lower Colorado River region, where degradation of the arc is recorded in sedimentary rocks now composing the lower parts of the McCoy Mountains Formation, the Winter-haven Formation, and informally named rocks of Slumgullion.

Early Mesozoic arc magmatism of the southern Sierra Nevada region records the onset of plate convergence–driven magmatism resulting from subduction initiation near the end of Permian time along a prior transform margin. We provisionally adopt the term California-Coahuila transform for this complex boundary transform system, which bounded the southwest margin of the Cordilleran passive margin, its offshore marginal basin, and fringing island arc. In Pennsylvanian–Early Permian time, this transform cut into the arc-marginal basin and adjacent shelf system, calved off a series of strike-slip ribbons, and transported them differentially southward through ∼500–1000-km-scale sinistral displacements. These strike-slip ribbons constitute the principal Neoproterozoic–Paleozoic metamorphic framework terranes for the superposed Mesozoic batholithic belt in the Sierra Nevada and Mojave plateau regions. The southern Sierra Nevada batholith intruded along the transform truncation zone where marginal basin ribbons were juxtaposed against the truncated shelf. Strike-slip ribbons, or blocks, liberated from the truncated shelf occur today as the Caborca block in northwest Mexico, and possibly parts of the Chortis block, farther south. The oldest arc plutons in the Sierra region were emplaced between 256 and 248 Ma, which matches well with ca. 255 Ma high-pressure metamorphism recorded in the western Sierra Foothills ophiolite belt, interpreted to approximate the time of subduction initiation. The initial phases of arc plutonism were accompanied by regional transpressive fold-and-thrust deformation, kinematically marking the transition from transform to oblique convergent plate motion. Early arc volcanism is sparsely recorded owing to fold-and-thrust–driven exhumation having accompanied the early phases of arc activity. By Late Triassic time, the volcanic record became quite prolific, owing to regional subsidence of the arc into marine conditions, and the ponding of volcanics in a regional arc graben system. The arc graben system is but one mark of regional suprasubduction-zone extension that affected the early SW Cordilleran convergent margin from Late Triassic to early Middle Jurassic time. We interpret this extension to have been a dynamic consequence of the subduction of exceptionally aged Panthalassa abyssal lithosphere, which is well represented in the Foothills ophiolite belt and other ophiolitic remnants of the SW Cordillera. Middle and Late Jurassic time was characterized by important tangential displacements along the SW Cordil-leran convergent margin. In Middle Jurassic time, dextral impingement of the Insular superterrane intra-oceanic arc drove a migrating welt of transpressional deformation through the SW Cordillera while the superterrane was en route to its Pacific Northwest accretionary site. Dextral transtensional spreading in the wake of the obliquely colliding and translating arc opened the Coast Range and Josephine ophiolite basins. In Late Jurassic time, a northwestward acceleration in the absolute motion of the North American plate resulted in an ∼15 m.y. period of profound sinistral shear along the Cordilleran convergent margin. This shear is recorded in the southern Cordillera by the Mojave-Sonora megashear system. Late Jurassic intrusive units of the southern Sierra region record sinistral shear during their magmatic emplacement, but we have not observed evidence for major Late Jurassic sinistral displacements having run through the Sierran framework. Possible displacements related to the megashear in the California to Washington regions are likely to have: (1) followed preexisting transforms in the Coast Range ophiolite basin and (2) been accommodated by oblique closure of the Josephine ophiolite basin, and the northern reaches of the Coast Range ophiolite basin, proximal to the southern Insular superterrane, which in Late Jurassic–earliest Cretaceous time was obliquely accreting to the inner Cordillera terranes of the Pacific Northwest.

Late Triassic through Early Cretaceous detrital zircon separated from Lower Cretaceous sedimentary strata provides a record of arc magmatism that is not obscured by products of the mid- to Late Cretaceous surge, which dominate the exposed Sierra Nevada batholith. Matching U-Pb age-probability maxima to U-Pb dates of exposed arc plutonic rocks provides confirmation that the detrital zircon was sourced in the erupting and eroding Sierra Nevada arc. These data suggest that magmatic productivity in the southwestern arc increased steadily through the Middle Jurassic, from an Early Jurassic lull through the Late Jurassic. The detrital-zircon record documents an original footprint of the Early Cretaceous arc extending from its current exposure in the western Sierra Nevada foothills northwestward into the eastern Sacramento Valley, where its relatively mafic roots are presumably buried beneath younger sedimentary strata infilling the Great Valley. The sparse record of Late Triassic magmatism preserved in the analyzed intra-arc and forearc deposits likely reflects greater separations in both time and space between the Early Cretaceous basins and the Triassic arc. Analysis of an atypically dense sample set from the Goldstein Peak Formation intra-arc basin deposits, in conjunction with new data from the Lower Cretaceous Gravelly Flat Formation and published data from other Lower Cretaceous forearc strata of the Great Valley Group, suggests that an even greater density and broader geographic distribution of detrital-zircon samples are needed to more completely reconstruct the record of arc magmatism.

The Cuesta Ridge ophiolite is a well-preserved remnant of the Middle Jurassic Coast Range ophiolite tectonically overlying rocks of the Franciscan complex. It is a nearly complete ophiolite section, consisting of over 1 km of serpentinized harz-burgite and dunite, sills of wehrlite, pyroxenite, and lherzolite, isotropic gabbro, a sheeted complex of quartz-hornblende diorite, an ∼1200-m-thick volcanic section, late-stage mafic dikes, and 5–10 m of tuffaceous radiolarian chert. The volcanic section at Cuesta Ridge has two chemically distinct volcanic groups. The lower volcanic section is characterized by low Ti/V ratios (11–21), enriched large ion lithophile element (LILE) concentrations, and depleted high field strength elements (HFSEs). Boninitic lavas with high MgO, Cr, and Ni abundances are present in this suite, along with arc tholeiites (basaltic andesites to dacites). Basalts of the upper volcanic section, which conformably overlie the lower volcanic section, and late-stage basaltic dikes that crosscut the hornblende–quartz diorite plutonic section are characterized by higher Ti/V ratios (20–27) and HFSE abundances and lower LILE abundances than the underlying section. These late-stage volcanic rocks have mid-ocean-ridge basalt–like chemistry. The field and geochemical data indicate formation in a suprasubduction-zone setting above an east-dipping proto-Franciscan subduction zone due to the onset of subduction and subsequent slab rollback. Multiple stages of magmatism ensued, until the emplacement of the late-stage dikes and uppermost flows. These late-stage dikes, which are present in several Coast Range ophiolite remnants, signify the end of ophio-lite formation and are interpreted to represent a Late Jurassic ridge collision.

This paper is an in-depth review of the architecture and evolution of the Western Sierra Nevada metamorphic province. Firsthand field observations in a number of key areas provide new information about the province and the nature and timing of the Nevadan orogeny. Major units include the Northern Sierra terrane, Calaveras Complex, Feather River ultramafic belt, phyllite-greenschist belt, mélanges, and Foothills terrane. Important changes occur in all belts across the Placerville–Highway 50 corridor, which may separate a major culmination to the south from a structural depression to the north. North of the corridor, the Northern Sierra terrane consists of the Shoo Fly Complex and overlying Devonian to Jurassic–Cretaceous cover, and it represents a Jurassic continental margin arc. The western and lowest part of the Shoo Fly Complex contains numerous tectonic slivers, which, along with the Downieville fault, comprise a zone of west-vergent thrust imbrication. No structural evidence exists in this region for Permian–Triassic continental truncation, but the presence of slices from the Klamath Mountains province requires Triassic sinistral faulting prior to Jurassic thrusting. The Feather River ultramafic belt is an imbricate zone of slices of ultra-mafic rocks, Paleozoic amphibolite, and Triassic–Jurassic blueschist, with blueschist interleaved structurally between east-dipping serpentinite units. The Downieville fault and Feather River ultramafic belt are viewed as elements of a Triassic–Jurassic subduction complex, within which elements of the eastern Klamath subprovince were accreted to the western edge of the Northern Sierra terrane. Pre–Late Jurassic ties between the continental margin and the Foothills island arc are lacking. A Late Jurassic suture is marked by the faults between the Feather River ultramafic belt and the phyllite-greenschist belt. The phyllite-greenschist belt, an important tectonic unit along the length of the Western Sierra Nevada metamorphic province, mélanges, and the Foothills island arc terrane to the west were subducted beneath the Feather River ultramafic belt during the Late Jurassic Nevadan orogeny. South of the Placerville–Highway 50 corridor, the Northern Sierra terrane consists of the Shoo Fly Complex, which possibly contains structures related to Permian–Triassic continental truncation. The Shoo Fly was underthrust by the Calaveras Complex, a Triassic–Jurassic subduction complex. The Late Jurassic suture is marked by the Sonora fault between the Calaveras and the phyllite-greenschist belt (Don Pedro terrane). As to the north, the phyllite-greenschist belt and Foothills island arc terrane were imbricated within a subduction zone during the terminal Nevadan collision. The Don Pedro and Foothills terranes constitute a large-magnitude, west-vergent fold-and-thrust belt in which an entire primitive island-arc system was stacked, imbricated, folded, and underthrust beneath the continental margin during the Nevadan orogeny. The best age constraint on timing of Nevadan deformation is set by the 151–153 Ma Guadelupe pluton, which postdates and intruded a large-scale megafold and cleavage within the Mariposa Formation. Detailed structure throughout the Western Sierra Nevada metamorphic province shows that all Late Jurassic deformation relates to east-dipping, west-vergent thrusts and rules out Jurassic transpressive, strike-slip deformation. Early Cretaceous brittle faulting and development of gold-bearing quartz vein systems are viewed as a transpressive response to northward displacement of the entire Western Sierra Nevada metamorphic province along the Mojave–Snow Lake fault. The preferred model for Jurassic tectonic evolution presented herein is a new, detailed version of the long-debated arc-arc collision model (Molucca Sea–type) that accounts for previously enigmatic relations of various mélanges and fossiliferous blocks in the Western Sierra Nevada metamorphic province. The kinematics of west-vergent, east-dipping Jurassic thrusts, and the overwhelming structural evidence for Jurassic thrusting and shortening in the Western Sierra Nevada metamorphic province allow the depiction of key elements of Jurassic evolution via a series of two-dimensional cross sections.

Based on relationships among volcanic-plutonic arc rocks, high-pressure–low-temperature (HP-LT) metamafic rocks, westward relative migration of the Klamath Mountains salient, and locations of the Mariposa-Galice, Great Valley Group, and Franciscan depositional basins, the following geologic evolution is inferred for the northern California continental edge: (1) By ca. 175 Ma, onset of transpressive plate underflow generated an Andean-type Klamath-Sierran arc along the margin. At ca. 165 Ma and continuing to ca. 150–140 Ma, erosion supplied volcanogenic debris to proximal Mariposa-Galice ± Myrtle overlap strata. (2) Oceanic crustal rocks were metamorphosed under HP-LT conditions in an inboard, east-inclined subduction zone from ca. 165 to 150 Ma. Most such mafic rocks remained stored at depth, and HP-LT tectonic blocks only returned surfaceward during the Late Cretaceous, chiefly entrained in circulating, buoyant Franciscan mud-matrix mélange. (3) At end-of-Jurassic time, before onset of paired Franciscan and Great Valley Group + Hornbrook deposition, the Klamath salient was deformed and displaced ∼100–200 km westward relative to the Sierran arc. (4) After this ca. 140 Ma seaward step-out of the Farallon–North American convergent plate junction—stranding preexisting oceanic crust on the south as the Coast Range ophiolite—terrigenous debris began to arrive at the Franciscan trench and intervening Great Valley forearc. Voluminous sedimentation and accretion of Franciscan Eastern + Central belt and Great Valley Group coeval detritus took place during paroxysmal igneous activity and rapid, nearly orthogonal plate convergence at ca. 125–80 Ma. (5) Sierran arc volcanism-plutonism ceased by ca. 80 Ma in northern California, signaling a transition to shallow, nearly subhorizontal eastward plate underflow attending Laramide orogeny far to the east. (6) Paleogene–Lower Miocene Franciscan Coastal belt sedimentary strata were deposited in a tectonic realm nearly unaffected by HP-LT subduction. (7) Grenville-age detrital zircons apparently are absent from the post–120 Ma Franciscan section. Detritus from the Pacific Northwest is not present in the Central belt sandstones, whereas zircons from the Idaho Batholith, the Challis volcanics, and the Cascade Range appear in progressively younger Paleogene–Lower Miocene Coastal belt sediments. This trend suggests the possible gradual NW dextral offset of Franciscan trench deposits of up to ∼1600 km relative to the autochthonous Great Valley Group forearc and basement terranes of the American Southwest.

The composite Sunrise Butte pluton, in the central part of the Blue Mountains Province, northeastern Oregon, preserves a record of subduction-related magmatism, arc-arc collision, crustal thickening, and deep-crustal anatexis. The earliest phase of the pluton (Desolation Creek unit) was generated in a subduction zone environment, as the oceanic lithosphere between the Wallowa and Olds Ferry island arcs was consumed. Zircons from this unit yielded a 206 Pb/ 238 U age of 160.2 ± 2.1 Ma. A magmatic lull ensued during arc-arc collision, after which partial melting at the base of the thickened Wallowa arc crust produced siliceous magma that was emplaced into metasedimentary rocks and serpentinite of the overthrust forearc complex. This magma crystallized to form the bulk of the Sunrise Butte composite pluton (the Sunrise Butte unit; 145.8 ± 2.2 Ma). The heat necessary for crustal anatexis was supplied by coeval mantle-derived magma (the Onion Gulch unit; 147.9 ± 1.8 Ma). The lull in magmatic activity between 160 and 148 Ma encompasses the timing of arc-arc collision (159–154 Ma), and it is similar to those lulls observed in adjacent areas of the Blue Mountains Province related to the same shortening event. Previous researchers have proposed a tectonic link between the Blue Mountains Province and the Klamath Mountains and northern Sierra Nevada Provinces farther to the south; however, timing of Late Jurassic deformation in the Blue Mountains Province predates the timing of the so-called Nevadan orogeny in the Klamath Mountains. In both the Blue Mountains Province and Klamath Mountains, the onset of deep-crustal partial melting initiated at ca. 148 Ma, suggesting a possible geodynamic link. One possibility is that the Late Jurassic shortening event recorded in the Blue Mountains Province may be a northerly extension of the Nevadan orogeny. Differences in the timing of these events in the Blue Mountains Province and the Klamath–Sierra Nevada Provinces suggest that shortening and deformation were diachronous, progressing from north to south. We envision that Late Jurassic deformation may have collapsed a Gulf of California–style oceanic extensional basin that extended from the Klamath Mountains (e.g., Josephine ophiolite) to the central Blue Mountains Province, and possibly as far north as the North Cascades (i.e., the coeval Ingalls ophiolite).

The Late Jurassic (157–150 Ma) Morrison Formation of the Western Interior of the United States contains abundant altered volcanic ash. On the Colorado Plateau, this formation accumulated behind and downwind of a subduction-related volcanic arc along the western margin of North America. The ash in these distal fallout tuffs probably drifted eastward from coignimbrite ash clouds related to collapse calderas. Altered volcanic ash is particularly abundant in the Brushy Basin Member of the upper part of the Morrison Formation. In one 110-m-thick section in eastern Utah, 35 separate beds were deposited in a 2.2 m.y. period. Alteration occurred when glassy volcanic ash fell into fluvial and lacustrine environments, where it was diagenetically altered to various mineral assemblages but most commonly to smectitic clay. Periodically, ash fell into saline, alkaline lakes, and diagenetic alteration of the glassy ash produced a crudely zoned deposit on the Colorado Plateau. Altered volcanic ash beds in the outermost part of the lacustrine deposits are argillic (with smectitic clay), whereas zeolitic (clinoptilolite, analcime) and feldspathic (K-feldspar and albite) alteration dominates the interior zones. Feldspathic ash layers contain secondary silica, and consequently immobile element (e.g., Al, Ti, and high field strength elements) abundances were strongly diluted in these rocks. In contrast, the argillic ash beds experienced strong SiO 2 depletion, and, as a result, they are enriched in the relatively immobile elements. The compositions of the zeolitic ash beds are intermediate between these two extremes and experienced the least alteration. As a result of these changes, immobile element concentrations are less reliable than ratios for determining the original magmatic composition of the ash. Most of the altered ash (regardless of type) was also depleted in water-soluble elements like the alkalies, U, and V. The latter two elements were oxidized during diagenesis of the ash, became soluble, and were partially leached away by groundwater. Locally, U and V in groundwater were reduced upon contact with organic materials and formed important ore deposits. Several aspects of the mineralogy and geochemistry of the altered volcanic ash beds yield information about their original magmatic compositions. The volcanic ash beds typically have small phenoclasts of quartz, sanidine, plagioclase, biotite, zircon, apatite, and Fe-Ti oxides. Titanite is present in ∼40% of the ash beds; pyroxene and amphibole were found in less than 5%. Phenocryst assemblages, mineral compositions, inferred high f O 2 , rare earth element patterns, and immobile element ratios all suggest the parent magmas for the altered tuffs were subduction-related dacites and rhyolites. Small numbers of tuffs have Fe-rich biotite, amphibole, and/or clinopyroxene; both pyroxene and amphibole are alkali rich. These tuffs lack titanite, but some contain anorthoclase and F-rich apatite. Combined with enrichments in Nb and Y, these features show some tuffs had an A-type character and were related to some type of within-arc extension. Paleowind directions, and distribution, radiometric ages, and compositions of the volcanic ash beds and of plutons in the western United States suggest that the most likely eruption sites were in the subduction-related Jurassic magmatic arc, which extended across western Utah and central Nevada and southward into the Mojave of California and southern Arizona (present-day coordinates). Pb isotopic compositions show that at least some of the ash was erupted from magma systems (now exposed as plutons) in the Mojave Desert. We conclude that a brief ignimbrite flare-up from 157 to 150 Ma, but focused on the time period from 152 to 150 Ma, in this region may have been driven by slab steepening and conversion to a strike-slip boundary after a preceding phase of folding and thrusting. The presence of ash beds with A-type characteristics mixed with those that have more typical subduction signatures confirms that the Late Jurassic was geologically a transitional time in North America when subduction was changing to transtensional movement along the western plate boundary.

Sedimentary rocks occurred throughout much of the Late Jurassic Cordilleran margin of Laurasia. Their tectonic setting and provenance are critical to understanding the evolution of the Cordilleran margin during this time. We review published detrital zircon ages and new and published whole-rock geochemistry of the Peshastin Formation and Darrington Phyllite, Cascade Mountains, Washington State, with the goal of better understanding the tectonic development of the Cordillera and strengthening regional correlations of these sedimentary units. The Peshastin Formation conformably overlies the ca. 161 Ma Ingalls ophiolite complex. Published dating of detrital zircons from a Peshastin Formation sandstone provided a youngest U-Pb age distribution of ca. 152 Ma and a significant U-Pb age distribution of ca. 232 Ma. The Darrington Phyllite is structurally above the Shuksan Greenschist; however, this unit also occurs interbedded with the Shuksan Greenschist. The Darrington Phyllite and Shuksan Greenschist have been grouped into the Easton Metamorphic Suite. Published detrital zircons from a Darrington Phyllite metasandstone have a youngest U-Pb age distribution of ca. 155 Ma and a significant U-Pb age distribution of ca. 238 Ma. New major- and trace-element geochemistry and previously published sandstone petrography suggest that these units were derived from Late Jurassic volcanic arc sources that were predominantly transitional between mafic and intermediate compositions. Middle to Late Triassic detrital zircon ages and detrital modes suggest that some recycling of older accreted arc terranes also contributed to these sediments; however, this Middle to Late Triassic component could also be first cycle. These units consistently plot on geochemical diagrams in fields defined by modern back-arc basin turbidites. The youngest detrital zircon age distributions, detrital sandstone petrography, and geochemistry of these units suggest they formed in Late Jurassic arc-fed basins. We suggest that the Peshastin Formation and Darrington Phyllite are age correlative and formed in an arc-proximal back-arc basin that could have initiated by forearc rifting. Postulated restoration of latest Cretaceous to Cenozoic faulting places these Late Jurassic basins near the Galice Formation and underlying Josephine ophi-olite, Klamath Mountains, Oregon-California. The Galice Formation and underlying Josephine ophiolite have been correlated with the Peshastin Formation and Ingalls ophiolite complex. After postulated Late Jurassic accretion to the North American margin, the Peshastin Formation and Darrington Phyllite were dextrally displaced to the north before they were emplaced in their current position by thrust faulting during the Late Cretaceous.

The distribution and tectonic settings of structurally complex domains of generally folded and thrust-faulted, commonly allochthonous, rock assemblages, recognized in the very large (250,000 km 2 ) Koryak Upland and Chukotka regions, support the conclusion that Late Jurassic, Early Cretaceous, and Late Cretaceous shortening and, at times, accretion resulted in incorporation of the terranes into a structural collage at the northeastern Asian continental margin. The main stages of accretion and continental growth took place in the late Mesozoic during the Middle–Late Jurassic, at the Early-Late Cretaceous boundary, and in late Maastrichtian time. The Late Jurassic was the emergence time of the Oloi and Uda-Murgal volcanic belts, extending along the convergent boundaries between Siberia and the proto-Arctic and Pacific Oceans, respectively. Convergence persisted until the end of the Early Cretaceous. In Chukotka, convergence ended with collision of the Chukotka microcontinent with the active margin of Siberia that hosted the Oloi volcanic belt. During this collision, the southern passive margin of Chukotka was overthrust by tectonic nappes composed of tectono-stratigraphic units of the South Anyui terrane. Greenschists with ages of 115–119 Ma are related to accretion of oceanic- and island-arc terranes incorporated into the frontal zone of the Uda-Murgal island-arc system. The subsequent growth of the continental margin resulted from accretion of terranes of the North Koryak fold belt in the late Maastrichtian.

We present a comprehensive study of one of the key targets of the Sikhote-Alin orogen—Early Cretaceous rocks in the Kiselevka block of the Kiselevka-Manoma tectono-stratigraphic terrane. The characteristic component of natural remanent magnetization (NRM) for these rocks was isolated, and the fold test was positive (Dec = 275.8°, Inc = −33.8°, K = 33.3. α 95 = 8.0°). The paleolatitude along which rocks of the block were forming in the Early Cretaceous was defined by the direction of this component (paleolatitude 18°N ± 5°N) as well as coordinates of the paleomagnetic pole (Plat = 18.6°, Plong = 222.4°, with semi-axis of the ellipse of confidence limit dp = 5.2° and dm = 9.1° of the Kiselevka block. The geochemical composition of volcanic rocks in the block suggests that they formed in a within-plate oceanic environment like volcanic rocks of the Hawaii hotspot. Three paleoreconstructions were developed based on the newly received and published data, in accordance with which the Kiselevka block: (1) in the range of 135–105 Ma was moving on the Izanagi plate northwestward at a rate of 15–20 cm/yr up to the eastern edge of Eurasia, thus covering over 5000 km; and (2) in the range of 105–70 Ma was moving northward along the Eurasian transform margin within the accretionary complex fragment at a rate of 4–5 cm/yr to its current position (Lower Amur) as part of the Sikhote-Alin orogen.

In the Sikhote-Alin-Priamurye area of southeastern Russia, folded and faulted fragments of sedimentary and less common volcanic rocks comprise tectonostrati-graphic units (complexes) that are imbricated. Sections of coherent, correlative strata composed of chert, siliceous mudstone, mudstone, siltstone, and sandstone within the tectonic stacks distinguish subterranes that are grouped into a suite of regional terranes. Among the ubiquitously imbricated strata, the age of deformed units ranges from Middle Paleozoic up to Late Jurassic–Early Cretaceous (Tithonian–Berriasian). Chaotic units (mélange) that are represented by siltstone and sandy siltstone matrix containing different-sized and different-aged lumps, blocks, and fragments of cherts, limestone, sandstones, basalt, and gabbro are Callovian to Tithonian in age. Accretion-like processes brought together fragments of a Paleozoic oceanic plateau and abyssal plain fragments of different ages during Middle and Late Jurassic time. The transition from chert to clastic sections tracks the approach of the oceanic strata to sources of detritus presumably close to a continental margin. Paleozoic oceanic rocks began to receive clastic inputs by the Pliensbachian, and Oxfordian chert approached the margin by the Kimmmeridgian. The terrane rocks do not record high-pressure metamorphism nor are they correlative with nearby volcanic “arc” rocks. The absence of these features, commonly associated with subduction at plate margins, may indicate that the rocks have been isolated, presumably by strike-slip faulting, as suggested by mapping.

The Bureya sedimentary basin, which is located in southeastern Russia, extends north-northeasterly for 230 km. The basin, commonly ∼65 km wide, contains thick sections of Mesozoic strata that record important tectonic and eustatic changes at the edge of the East Asian continental margin. It initially developed within the passive early Mesozoic continental margin. Later, during the Late Jurassic, the basin again was strongly affected by extension. Based on up-to-date geological and geophysical data, a sequence stratigraphic model consisting of six megasequences and several sequences was constructed. Sedimentation rates, some of which are remarkably high, were calculated for each sequence. The principal evolution stages of the Bureya Basin of compound (hybrid) type are as follows: (1) During Late Triassic to Middle Jurassic, the basin formed on the passive continental margin with edge submeridional rifts. The sedimentation was influenced by erosion of an active continental margin. (2) During the Late Jurassic through Cretaceous, it was an intracontinental, NE-trending, pull-apart basin.

The Late Jurassic geologic record in Mongolia is poorly known, partly due to only sparsely preserved outcrops, but also because of the region's remoteness and limited body of published geological data compared to China and other parts of Eurasia. Considered in the broader context of Mesozoic sedimentary basin dynamics, the Late Jurassic record that has been studied is both informative and perplexing. Late Jurassic sedimentary basins are preserved in the subsurface throughout the country, and they are partially exposed (along with their igneous and metamorphic counterparts) where they have been inverted by Cretaceous–Cenozoic faulting. However, the speculated geodynamic settings for these basins are poorly reconciled: Various reconstructions place the basins between regions of contrasting tectonic styles in the late Mesozoic (contraction to the southwest and extension to the east/southeast). It is suggested that much of Mongolia represented a large-scale accommodation zone beginning in the early Mesozoic and continuing into at least Late Jurassic time. This scenario may have been expressed within an overall strike-slip framework that includes long-term reactivation structures, some of which are still active today. Although speculative, the hypothesis helps to explain evidence for differential rotation between Mongolia and surrounding blocks in the late Mesozoic, and it is testable pending additional field and analytical data. In particular, additional information is needed regarding the timing and modes of Mongol-Okhotsk Ocean closure and suturing. Current interpretations place final ocean closure and suturing in Mongolia anywhere from Permian to Cretaceous, with differing implications for collisional mechanisms and geologic expressions.