Contractional Belt Research Articles

Crustal-scale balanced cross-section and restorations of the Central Pyrenean belt (Nestes-Cinca transect): Highlighting the structural control of Variscan belt and Permian-Mesozoic rift systems on mountain building

In this paper, we combined new field geological, structural, paleo-temperature and subsurface data together with deep geophysical data to build a new 210 km-long crustal-scale balanced and sequentially restored cross-section in the Central Pyrenean belt (Nestes-Cinca transect). The present-day surficial thrust system geometry of the belt consists of bi-vergent basement-cover thrust sheets with inverted extensional basins and halokinetic structures. Its crustal geometry consists of a thrust wedge geometry of the European lithosphere between the Axial Zone imbricate system of the Iberian upper crust and the north-directed subduction of the Iberian lower crust. Along the study transect, the contractional belt corresponds to the inversion of the Mesozoic Pyrenean Rift system, which consisted in a hyper-extended relay zone of two metamorphic zones with exhumation of lithospheric mantle, the Montillet and Baronnies zones, separated by the Barousse upper crustal boudin. Surface and subsurface data show that the European and Iberian crusts include major inherited structures of the Variscan belt and Permian Rift. These old crustal features controlled the location and geometry of the Mesozoic Pyrenean Rift system. During the upper Cretaceous-lower Miocene contraction, both Paleozoic and Mesozoic inherited features controlled the thrust kinematics and the structural architecture of the Pyrenean orogen. Palinspastic restorations show that the orogenic shortening recorded in the Central Pyrenean belt reaches 127 km (39%) including the closure of the hyper-extended Pyrenean Rift system that initially archived 56 km of extension. This study emphasizes the long-term influence of Paleozoic-Mesozoic structural and thermal inheritances for the evolution of orogenic belts.

Structure and kinematic evolution of the Southern Sivas Fold-Thrust Belt, Sivas Basin, Central Anatolia, Turkey

The architecture, kinematics, and timing of fold-and-thrust belt development provide essential first-order constraints on the structural evolution of continental collision zones. The southern Sivas fold-thrust belt (SSFTB) is a ~300 × 50-km-long, ENEtrending contractional belt located in the Sivas Basin at the western end of the Arabia-Eurasia collision zone, and along the Izmir- Ankara-Erzincan and Inner Tauride suture zones. We present new geologic mapping and the first detailed structural characterization and seismotectonic evidence of active deformation along the western and central segments of the SSFTB that provide new insights into the timing and kinematics of deformation associated with collision and escape in Central Anatolia. The SSFTB is a dominantly north-vergent contractional belt that initiated during the late Eocene and experienced several punctuated episodes of shortening and exhumation, primarily during the late Oligocene and late Miocene. Structural mapping and balanced cross-sections reveal that minimum cumulative shortening increases from west (29%) to east (34%) along the belt, along with a gradual eastward increase in fold asymmetry and a progressive transition from fold-related to overturned fold-and-thrust-related shortening. The kinematics of the central and eastern SSFTB changed from north-vergent thrusting during the late Eocene and Oligocene to predominantly south-vergent during the Miocene. Contraction in the SSFTB ended by ~7-6 Ma and was followed by a switch to distributed and kinematically linked sinistral strike-slip and normal faulting along the northeastern segment of the Central Anatolian fault zone. Offset strain markers suggest a total of at least 1.7-2.4 km of left-lateral slip on the Deliler fault and ~940 m of normal slip on the Hinzir fault. The latest Miocene to Pliocene switch to intraplate strike-slip deformation marks a regional transition to westward tectonic escape of the Anatolian microplate.

A Robust Estimation of the 3‐D Intraplate Deformation of the North American Plate From GPS

AbstractGlacial isostatic adjustment (GIA) is the main cause of deformation in intraplate North America. Here we use up to 3,271 Global Positioning System station velocities to image this 3‐D deformation across the entire plate. We apply a new robust strain rate estimation algorithm (median estimation of local deformation), which does not require the assumption that part of the plate is unaffected by GIA, an assumption we show to be false. Our results show extension in the area underneath the Laurentide ice sheet, contrasted with a semiannular belt of horizontal contraction of up to ~4 × 10−9 yr−1 around the former ice sheet. This contractional belt is kinematically linked to an ~1–2 mm yr−1 far‐field horizontal motion directed toward the ice sheet. Our results, together with a new robustly imaged vertical velocity field, are consistent with GIA as the main cause of deformation, although the contractional strain rates around the former ice sheet and the far‐field horizontal velocities are significantly higher than those predicted by the ICE6G_C(VM5a) model. This finding suggests that our results, including the location of reversal in sign of horizontal motion relative to the ice sheet, will be useful to reevaluate the mantle viscosity structure used by GIA models. Besides the GIA‐attributed deformation, we find almost no other region with significant strain accumulation. A plate‐scale spatial correlation between strain rate and seismicity is absent, suggesting that GIA is a limited driver of contemporary seismogenesis and that intraplate seismicity must be attributable to factors other than secular strain accumulation.

An active oblique-contractional belt at the transition between the Southern Apennines and Calabrian Arc: The Amendolara Ridge, Ionian Sea, Italy

High-resolution, single-channel seismic and multibeam bathymetry data collected at the Amendolara Ridge, a key submarine area marking the junction between the Apennine collision belt and the Calabrian subduction forearc, reveal active deformation in a supposedly stable crustal sector. New data, integrated with existing multichannel seismic profiles calibrated with oil-exploratory wells, show that middle to late Pleistocene sediments are deformed in growth folds above blind oblique-reverse faults that bound a regional pop-up. Data analysis indicates that ~10 to 20 km long banks that top the ~80 km long, NW-SE trending ridge are structural culminations above en echelon fault segments. Numeric modeling of bathymetry and stratigraphic markers suggests that three 45° dipping upper crustal (2–10 km) fault segments underlie the ridge, with slip rates up to ~0.5 mm/yr. Segments may be capable with M ~ 6.1–6.3 earthquakes, although an unknown fraction of aseismic slip undoubtedly contributes to deformation. The fault array that bounds the southern flank of the ridge (Amendolara Fault System) parallels a belt of Mw < 4.7 strike-slip and thrust earthquakes, which suggest current left-oblique reverse motion on the array. The eastern segment of the array shows apparent morphologic evidence of deformation and might be responsible for Mw ≤ 5.2 historic events. Late Pliocene-Quaternary growth of the oblique contractional belt is related to the combined effects of stalling of Adriatic slab retreat underneath the Apennines and subduction retreat of the Ionian slab underneath Calabria. Deformation localization was controlled by an inherited mechanical interface between the thick Apulian (Adriatic) platform crust and the attenuated Ionian Basin crust.

Link between thrust tectonics and sedimentation processes of stratigraphic sequences from the southern Apennines foreland basin system, Italy

We discuss here tectonics and sedimentation processes occurring during continent-continent collision and relationships between accretionary processes on overplate, flexural lithosphere on underplate and related controls on clastic sedimentation in developing foreland basin systems. This paper focuses on and clastic sedimentation developed during the sequential history of the southern Italy orogenic system. These clastic trends, covering a large time span from pre-collisional Early Mesozoic to the present, may contribute: (1) to the paleogeographic and paleotectonic reconstructions of the southern Italy portions of the western Mediterranean orogen, and (2) to the general models of complex relationships between clastic sedimentation and paleotectonic history of other major orogens. The evolutionary record of Earth’s processes preserved in the form of sedimentary rocks has been pivotal in paleogeographical and paleotectonic reconstructions of source/basin systems. Compositional trends of clastic strata through space and time are used to infer the structural history of adjacent mountain belts and to monitor the key geodynamic changes during orogenic processes (e.g. Dickinson, 1985, 1988; Critelli & Ingersoll, 1994; Critelli, 1999). The controls on the composition and dispersal pathways of clastic strata along the convergent plate margins have long been debated (e.g. Dickinson, 1988; Ingersoll et alii, 1995). Clastic infilling of sedimentary basins in orogenic systems have been used as important indicators of tectonic activity and climatic changes. In the orogenic systems, clastic sedimentation may record the accretionary processes, the accomodation of the thrust units, and the flexural features of the foreland plate. The development of an orogenic wedge during continental collision results in thickening of the crust. The excess mass of this thickened crust acts as a load on the underthrust plate, causing it to be flexed downwards close to the load, so developing a foreland basin (e.g. Beaumont, 1981; Sinclair and Allen, 1992). During plate convergence, the vertically acting load of the mountain belt migrates over the foreland plate, thus resulting in the migration of the associated foreland basin. The foreland is the region between the front of a thrust belt and the adjacent craton (e.g. Dickinson, 1974; Bally and Snelson, 1980; Allen et alii, 1986; Miall, 1995). Large volumes of clastic sediment are derived from erosion of the thrust belt and deposited in the foreland basin. The foreland basin generally is defined as an elongate trough that forms between a linear contractional orogenic belt and the stable craton, mainly in response to flexural subsidence caused by thrust-sheet loading in the orogen.Foreland basin stratigraphy records tectonic, eustatic, and climatic changes at convergent plate margins (e.g. Miall, 1995). The formation of unconformities is the results of the interplay of temporal variations in the erosion and lateral progradation rates of the orogenic wedge, as well as tectonic and eustatic sea-level changes (e.g. Beaumont, 1981; Jordan, 1981; Schedl & Wiltsc hko, 1984; Peper et alii, 1995).

Constraining neotectonic orogenesis using an isostatically compensated model of transpression

Current models of transpression allow upward flow of material to compensate for shortening in the horizontal plane. We present an isostatically compensated model of transpression, where material is allowed to flow both upwards to create topographic relief and downwards to form a crustal root. Our model also incorporates the effects of erosion to more accurately examine the developing topography in orogenic systems. The modeling results suggest that topographic relief and crustal root thickness developed in transpressional orogens are most dependent on the magnitude of shortening, the initial thickness of the crust, and the density contrast between the crust and mantle. In contrast, the rate of convergence and final width of the deformed zone are relatively unimportant parameters in this model. Application to the Alpine fault system in New Zealand, a well-constrained active transpressional plate boundary, shows good agreement between topography-based model estimates of shortening and those derived from plate reconstructions. Application of our model to the Central Range fault zone in Trinidad suggests 2 ± 1 km of neotectonic shortening. The strain analysis approach presented here may be useful for isolating the effects of modern deformation in a region that has reactivated an ancient contractional belt.

Extensional detachment faulting on the Tyrrhenian margin of the southern Apennines contractional belt (Italy)

The tectonic evolution of the Campania margin during the late Pliocene–Pleistocene is characterized by extensional deformation coeval with the opening of the Marsili oceanic basin. The initial stages of stretching are represented in the analysed area by the development of low-angle normal faults that extended the belt in the same direction as the direction of spreading recognized for the oceanic basin. Detachment faulting was accompanied by the onset of magmatic activity and by major uplifts that resulted in the accumulation of thick conglomerate successions in the half-grabens that developed in the upper plate of the extensional detachment. Deformation continued during the Mid-Pleistocene with the formation of strike-slip and normal faults trending almost parallel to the spreading direction of the Marsili basin. These faults dissected the extensional detachment and promoted counter-clockwise block rotations about vertical axes, which accommodated the ESE-directed stretching of the Marsili basin and the consequent sinistral shear imposed on the southern Apennine chain. The development of a regional detachment fault along the Tyrrhenian margin of Campania explains the complex patterns of subsidence and uplift that characterize this area during the Pleistocene and fits well within the regional geodynamic framework of the southern Tyrrhenian Sea.

Structural development of the Peregrina–Huizachal anticlinorium, Mexico

The Sierra Madre Oriental fold belt is a NW–SE-trending contractional belt that spans nearly the entire length of Mexico. This area underwent Triassic–Middle Jurassic rifting and Late Cretaceous–Early Cenozoic shortening. Our structural investigation of the Peregrina–Huizachal anticlinorium in east central Mexico shows that its development is characterized by two phases of deformation: an early thin-skinned phase and a late thick-skinned phase. A detachment developed at the contact between the rift sedimentary rock and overlying limestone. During the thin-skinned phase, deformation of the Upper Jurassic–Cretaceous strata is accommodated by a series of detachment folds and faults. The rift boundary faults are sub-perpendicular to the late stage compression in east central Mexico. This makes rift-related faults prone to be inverted as reverse faults. During the thick-skinned phase, the basement in the rift is uplifted along two opposing reverse faults and experience internal deformation. Its uplift contributed to the growth of the Peregrina–Huizachal anticlinorium.

Crustal deformation along the Altyn Tagh fault system, western China, from GPS

We collected GPS data from the southern Tarim basin, the Qaidam basin, and the western Kunlun Shan region between 1993 and 1998 to determine crustal deformation along the Altyn Tagh fault system at the northern margin of the Tibetan plateau. We conclude from these data that the Altyn Tagh is a left‐lateral strike slip fault with a current slip rate of ∼9 mm/yr, in sharp contrast with geological estimates of 20–30 mm/yr. This contrast poses an enigma: because the GPS data cover a wider region than the geologic data, they might be expected to reveal somewhat more slip. We also find that the Tarim and Qaidam basins behave as rigid blocks within the uncertainty of our measurements, rotating clockwise at a rate of ∼11 and ∼4.5 nrad/yr, respectively, with respect to the Eurasia plate. The rotation of the Tarim basin causes convergence across the Tian Shan, increasing progressively westward from ∼6 mm/yr at 87°E to ∼18 mm/yr at 77°E. Our data and other GPS data suggest that the Indo‐Asia collision is mainly accommodated by crustal shortening along the main Himalayan thrust system (∼53%) and the Tian Shan contractional belt (∼19%). Eastward extrusion of the Tibetan plateau along the Altyn Tagh and Kunlun faults accommodates only ∼23% of the Indo‐Asia convergence.

Contractional and extensional tectonics in Flysch and Penibetic units (Gibraltar Arc, SW Spain): new constraints on emplacement mechanisms

Abstract The Aljibe Unit (Flysch Trough Complex), which can be described as a thin-skinned contractional belt, represents a major element of the Gibraltar Arc accretionary prism. It is shown that this unit underwent WNW–ESE shortening during the Miocene, as did the underlying Penibetic units. The organization of the Aljibe unit suggests a push-from-behind emplacement mechanism during this first contractional event. By contrast, the current boundary between the Penibetic and Aljibe units is found to be a normal, low-to-moderate angle fault that was later folded. This extensional faulting occurred between two compressional pulses (Lower-to-Middle and Upper Miocene in age) with similar shortening directions.

The Gargano Promontory: a Neogene contractional belt within the Adriatic plate

The Gargano Promontory lies on the Adriatic plate between the Dinaride and Apennine fold‐and‐thrust belts and associated foredeeps. Neogene sediments and structures in the Gargano Promontory demonstrate the existence of significant contrac‐tional structures which have not been reported previously. Beginning in early Miocene times, the future Gargano Promontory experienced shortening along NW‐trending, mainly SW‐vergent folds and thrusts. Deformation persisted until the Tortonian, and, most likely, until the Messinian. Limited NW‐directed contraction affected the Promontory probably during Pliocene times. Morphological relief was minimal until the Messinian but from the middle Pliocene onwards, it was substantially similar to the present‐day one partly as a consequence of extension along NE–SW‐trending normal faults. The along‐strike projection of kinematic relationships and quantities observed in the Gargano might call for a re‐interpretation of previously underestimated structures NW and SE of the Promontory.

Large-scale longitudinal extension in the southern Apennines contractional belt, Italy: Comment and Reply

Research Article| September 01, 1994 Large-scale longitudinal extension in the southern Apennines contractional belt, Italy: Comment and Reply Francesca Ghisetti; Francesca Ghisetti 1Istituto di Geologia e Geofisica, Corso Italia 55, 95129 Catania, Italy Search for other works by this author on: GSW Google Scholar Livio Vezzani; Livio Vezzani 2Dipartimento di Scienze della Terra, Via Accademia delle Scienze 5, 10123 Torino, Italy Search for other works by this author on: GSW Google Scholar J. S. Oldow; J. S. Oldow 3Department of Geology and Geophysics, Rice University, Houston, Texas 77005 Search for other works by this author on: GSW Google Scholar B. D'Argenio; B. D'Argenio 4Dipartimento di Scienze delta Terra, Università di Napoli, Federico II, Naples, Italy Search for other works by this author on: GSW Google Scholar L. Ferranti; L. Ferranti 4Dipartimento di Scienze delta Terra, Università di Napoli, Federico II, Naples, Italy Search for other works by this author on: GSW Google Scholar G. Pappone; G. Pappone 4Dipartimento di Scienze delta Terra, Università di Napoli, Federico II, Naples, Italy Search for other works by this author on: GSW Google Scholar E. Marsella; E. Marsella 5Geomare Sud, Istituto di Geologia Marina, Consiglio Nazionale dell Ricerche, Naples, Italy Search for other works by this author on: GSW Google Scholar M. Sacchi M. Sacchi 5Geomare Sud, Istituto di Geologia Marina, Consiglio Nazionale dell Ricerche, Naples, Italy Search for other works by this author on: GSW Google Scholar Author and Article Information Francesca Ghisetti 1Istituto di Geologia e Geofisica, Corso Italia 55, 95129 Catania, Italy Livio Vezzani 2Dipartimento di Scienze della Terra, Via Accademia delle Scienze 5, 10123 Torino, Italy J. S. Oldow 3Department of Geology and Geophysics, Rice University, Houston, Texas 77005 B. D'Argenio 4Dipartimento di Scienze delta Terra, Università di Napoli, Federico II, Naples, Italy L. Ferranti 4Dipartimento di Scienze delta Terra, Università di Napoli, Federico II, Naples, Italy G. Pappone 4Dipartimento di Scienze delta Terra, Università di Napoli, Federico II, Naples, Italy E. Marsella 5Geomare Sud, Istituto di Geologia Marina, Consiglio Nazionale dell Ricerche, Naples, Italy M. Sacchi 5Geomare Sud, Istituto di Geologia Marina, Consiglio Nazionale dell Ricerche, Naples, Italy Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1994) 22 (9): 860. https://doi.org/10.1130/0091-7613(1994)022<0860:LSLEIT>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Francesca Ghisetti, Livio Vezzani, J. S. Oldow, B. D'Argenio, L. Ferranti, G. Pappone, E. Marsella, M. Sacchi; Large-scale longitudinal extension in the southern Apennines contractional belt, Italy: Comment and Reply. Geology 1994;; 22 (9): 860. doi: https://doi.org/10.1130/0091-7613(1994)022<0860:LSLEIT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract No abstract available This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Coast Belt Thrust System: Evidence of Late Cretaceous shortening in southwest British Columbia

The Coast Belt Thrust System (CBTS) is the leading edge of a west vergent contractional belt that formed along the inboard margin of the Insular superterrane in late Cretaceous time. The foreland of this contractional belt comprises a system of east dipping frontal thrusts that imbricate Jurassic and Early Cretaceous supracrustal arc sequences and related plutonic suites of the Western Coast Belt (WCB). These faults root eastward into an imbricate zone of folded thrusts and out‐of‐sequence reverse faults across which the metamorphic gradient has been structurally inverted. To the east and structurally above the imbricate zone is a folded stack of high‐pressure thrust sheets comprising metamorphosed island arc and oceanic rocks of the Central Coast Belt (CCB). These rocks represent the exhumed crustal root of the CBTS. Metamorphosed volcanic and volcaniclastic rocks that occur in thrust sheets of the imbricate zone yield U‐Pb zircon dates which support a correlation with lower‐plate Jurassic and Early Cretaceous arc sequences of the WCB. Structural and geochronologic data indicate a two‐stage history of Late Cretaceous shortening. During the early stage of shortening, supracrustal arc and related basin sequences along the inboard margin of the Insular superterrane were structurally imbricated and accreted to the toe (footwall) of a westward prograding accretionary complex made up of previously assembled terranes of the CCB. These early‐stage structures are represented by folded thrusts in the imbricate and hinterland zones of the CBTS. The timing of this early‐stage thrusting is bracketed by the emplacement of synorogenic plutonic suites, which yield U‐Pb zircon dates of 97 ± 1 Ma and 96 +6/−3 Ma. Late‐stage shortening involved both thin‐skinned thrusting and folding of Jura‐Cretaceous arc sequences in the WCB foreland and out‐of‐sequence thrusting of higher‐grade thrust sheets in the imbricate and hinterland zones of the CBTS. In the foreland this episode of deformation is bracketed by late‐and postkinematic plutons, which yield U‐Pb zircon dates of 94 ± 2 Ma and 91 +4/−3 Ma, respectively. In the imbricate zone, this episode of deformation is bracketed by the emplacement of synkinematic and postkinematic plutons, which yield U‐Pb zircon dates of 96 +6/−3 Ma and 94 +6/−5 Ma, respectively. The development of thick‐skinned out‐of‐sequence thrusts in the imbricate and hinterland zones of the CBTS signals a northeastward migration of the deformation front in Late Cretaceous time. This shift in the locus of thrusting resulted in southwestward telescoping and structural inversion of the metamorphic hinterland and may account for the complex stacking order and thermal history of the Southern Coast Belt.

Large-scale longitudinal extension in the southern Apennines contractional belt, Italy

During late Cenozoic thrusting, the interior of the peri-Tyrrhenian orogenic belt in the southern Apennines underwent two episodes of nearly orthogonal extension. Early extension was oriented subparallel to the axis of the tectonic belt and formed in response to progressive thrust-belt arcuation. The length of the tectonic belt increased by ∼50%, and the longitudinal strain was accommodated by low-angle normal faults concentrated in tectonic domains recording up to 150%-200% extension. Younger extension, oriented at a high angle to the orogen, was accompanied by Pliocene-Pleistocene uplift and by southeasterly migration of Tyrrhenian Sea rifting.

Tectonic implications of syn- and post-emplacement deformation of the Mount Stuart batholith for mid-Cretaceous orogenesis in the North Cascades

The 93–96 Ma Mount Stuart batholith intruded across the boundary between the Northwest Cascades thrust system and the crystalline core of the North Cascades. Although previously considered posttectonic, the northeast margin of the Mount Stuart batholith and its wall rocks have been involved in syn- to post-emplacement, southwest-directed thrusting and folding, and west-northwest stretching. Contraction ended shortly after emplacement, as indicated by high-temperature recrystallization in thrust-related mylonites of the pluton and by geochronological data, whereas west-northwest stretching continued for an unknown period of time. This is the best documented mid-Cretaceous contractional belt in the main part of the crystalline core. The shortening direction and timing are identical to that of southwest-vergent thrusts in the offset continuation of the core in British Columbia. The contractional belt provides a link between thrusting in the Northwest Cascades thrust system and deformation in the crystalline core.

Speculative reconstruction of the Mojave‐Snow Lake Fault: IMPLICATIONS FOR Paleozoic and Mesozoic orogenesis in the western United States

Available evidence suggests that the Mojave‐Snow Lake fault, a major Early Cretaceous dextral fault with up to 400 km displacement, formerly existed in what is now the axial part of the Sierra Nevada batholith. Regional relations suggest that the fault formerly continued in western Nevada, the Mojave Desert, and in rocks now exposed in the Salinian block. Restoration of 400 km of Early Cretaceous dextral displacement on the Mojave‐Snow Lake fault leads to speculative but testable reconstructions of Mesozoic and Paleozoic tectonic features of California and Nevada. Insights derived from these reconstructions include the following: (1) Two regionally extensive Jurassic thrust belts of opposed vergence appear to have intersected in the northern Sierra Nevada. The eastern, east‐vergent thrust belt, which includes the Fencemaker and Liming thrusts in western Nevada and several east‐vergent thrusts in the northern Sierra, may be a contractional belt along which an Early Jurassic interarc or marginal basin was closed in Middle to Late Jurassic time. The western, west‐vergent thrust belt is part of the classic Nevadan orogen of the western Klamath Mountains and the western Sierra metamorphic belt, in which collisions and/or thrusting of various island arc terranes occurred during Middle and Late Jurassic time. (2) The early Mesozoic continental arc included paired belts of Triassic‐Jurassic blueschist and melange, and igneous rocks including Late Triassic and younger plutons and volcanic rocks. This conclusion is not new, but the reconstruction provides a slightly different geometry than previously thought. (3) Sonomia, the late Paleozoic island‐arc terrane of the western U. S., may have formed a relatively narrow belt extending from northwestern Nevada to the latitude of the western Mojave Desert. The geologic development of the Paleozoic basement complex of Sonomia was very different from that of the Cordilleran miogeocline in Death Valley and the Mojave Desert, requiring that a continuation of the Sonoma suture belt (or Golconda thrust) must have extended southward through the Sierra Nevada batholith to the Mojave region. (4) A heterogeneous belt of Permian to Triassic or Triassic deformation in the Mojave and eastern Sierra Nevada, together with the Golconda allochthon in Nevada, may represent the protracted response to the collision of Sonomia with the western margin of North America. The contractional deformation continued during the evolution of the early Mesozoic continental arc. (5) Several predictions can be made about the nature of concealed basement within the Sierra Nevada batholith and within western Nevada. The reconstruction suggests that elements of the Antler and Sonoma orogenic belts should underlie areas of the batholith and western Nevada, as a result of northward displacement along the Mojave‐Snow Lake fault from the western Mojave and southern Sierra Nevada.