Late Cretaceous Shortening Research Articles

Geology and geochronology of the Jurassic magmatic arc in the Magdalena quadrangle, north-central Sonora, Mexico

This work reports on the geology and U–Pb LA-ICPMS zircon geochronology of a crustal section that is part of the Jurassic magmatic arc in the Magdalena quadrangle of north-central Sonora, Mexico. This rock succession is variably metamorphosed and strained as it was affected by Late Cretaceous shortening, intruded by early Tertiary granitoids, and further exhumed in the lower plate of the early Miocene Magdalena metamorphic core complex. The older and more extensively exposed Jurassic unit is the >3.5 km thick Sierra Guacomea rhyolite that is composed of massive to poorly bedded rhyolite, bedded quartz-phyric rhyolitic ignimbrite and interbedded ash-fall tuffs and quartz-rich sandstone beds. Three rhyolite samples collected at different localities of its outcrops yielded concordia ages of 175.2 ± 0.9, 171.7 ± 0.6, and 171.4 ± 0.7 Ma. The quartz-phyric Rancho La Víbora, Los Vallecitos, and the Agua Caliente rhyolitic domes that are associated with the Sierra Guacomea rhyolite yield concordia ages of 176 ± 0.8, 174.4 ± 0.9 and 173.1 ± 0.8 Ma, respectively. The Rancho Los Pozos unit composed of interbedded rhyolitic ash-fall tuff and flows, sandstone, siltstone and subordinate limestone beds has an estimated thickness of 600 m and yielded a crystallization concordia age of 170.7 ± 0.6 Ma from a rhyolite bed. The porphyritic El Rincón granite that intrudes into the Sierra Guacomea rhyolite yields crystallization ages of 167.43 ± 0.42 and 164.4 ± 0.7 in samples from different localities. The La Jojoba metasandstone that consists of foliated, quartz-rich to arkosic strata of fluvial origin is at least 900 m thick; detrital zircon grains dated from three sandstone samples yielded dominantly Jurassic ages with peaks at 172, 170, and 163.7 Ma, and a combined maximum depositional age of ca. 163 Ma.The younger plutons are the porphyritic El Nopalito granite that has an interpreted crystallization age of 160.8 ± 0.6 Ma, and the leucocratic, two-mica, garnet-bearing La Cebolla granite that yielded a concordia age of 158.1 ± 1 Ma. These granitic intrusions record the waning magmatic pulses of the arc, in the study quadrangle, but their volcanic equivalents were not identified. Inherited zircon grains in the reported volcanic and plutonic units are only of Jurassic age, except by two Proterozoic zircon grains yielded by the El Nopalito granite. The El Salto granite augen gneiss is a xenolith dated at 1071.9 ± 5 Ma that indicates the presence of Grenvillian basement in the study area.Major- and trace-element geochemical data indicate that the volcanic and plutonic units are silica-rich, mostly high K calc-alkaline to shoshonitic rocks associated with a continental margin arc setting. The plutons are mostly peraluminous, and in conjunction with trace element geochemistry data, they suggest crustal assimilation of magmas emplaced in a probably thickened continental crust. Chondrite-normalized REE patterns and primitive mantle-normalized trace element diagrams also suggest partial melting and fractional crystallization processes.The ages obtained indicate that the arc in the study area developed from ca. 176 to 158 Ma, encompassing a 17 m.y. interval of magmatism and associated sedimentation. Regional correlation and geochronologic published data indicate that the arc crustal section of the Magdalena quadrangle is part of the Jurassic magmatic arc that regionally lasted from ca. 190 to 158 Ma.

Geological control of the eastern Great Wall: Mountain-basin relationships in the eastern North China Craton

The E–W trending Yanshan belt, an intraplate fold-thrust belt located in the northern North China Craton, has experienced several episodes of Mesozoic deformation, which resulted in the widely distributed magmatism and mountain-basin tectonics that completely re-shaped the topography of the eastern North China Craton. The eastern part of the famous Chinese Great Wall was built on the high range of the southeastern Yanshan mountain belt juxta-posed to the plain, which directly relates to the Bohai Bay basin. Our study focuses on which tectonic processes created such mountain-basin couple in Mid-Late Mesozoic times. The U-Pb LA-ICP-MS dating of zircons yield ages of 114 to 201 Ma for various granites and 115 to 116 Ma for volcanic rocks from Yixian and Jiufotang Fms. The detrital zircons from the Lower Cretaceous sandstones yield four age groups of 2587 to 2460 Ma, 2222 to 1828 Ma, 297 to 190 Ma and 187 to 100 Ma, which are all sourced from the Qinglong and surrounding areas and indicating that the Qinglong area started to uplift after the Middle Jurassic. The Qinglong area underwent multiple deformation by NE–SW compression in the Middle-Late Jurassic times, WNW–ESE compression in the Late Jurassic to Early Cretaceous, ENE–WSW extension in the Early Cretaceous and NNW–SSE compression in the Late Cretaceous during the final stage of the Yanshanian orogeny. Meanwhile, widely distributed granite intrusions and emplacement of the Upper Jurassic-Lower Cretaceous volcanic rocks indicate a large amount of magma input into the area. The Qinglong area with the Great Wall along its southern margin close to adjacent plain to the south was uplifted to form the Qinglong highland and surrounding related basins by combination of the following three processes: the multiple tectonic Late Jurassic and Late Cretaceous shortening processes related to Yanshanian orogeny, Early Cretaceous regional extension triggered by slab-retreat of the Paleo-Pacific ocean and inflation of large amount magma at depth during Jurassic and Early Cretaceous.

Paleomagnetic and magnetic fabric data from Lower Triassic redbeds of the Central Western Carpathians: new constraints on the paleogeographic and tectonic evolution of the Carpathian region

In the Central Western Carpathians (CWC), most published paleomagnetic results from Permo-Mesozoic rocks document extensive remagnetizations and come from thin-skinned thrust units that have undergone multistage deformation. We present results from lower Triassic redbeds from the autochthonous cover overlying the basement that carry a primary magnetization. Petromagnetic results indicate that the dominant ferromagnetic carrier is hematite, while magnetic susceptibility and its anisotropy are controlled by both ferromagnetic and paramagnetic minerals. Magnetic fabrics document weak deformation related to Late Cretaceous shortening. The directions of the high unblocking temperature remanence components pass both reversal and fold tests, attesting to their primary nature. Paleomagnetic inclinations are flatter than expected from reference datasets, suggesting small latitudinal separation between the CWC and stable Europe. Paleomagnetic declinations are mostly clustered within individual mountain massifs, implying their tectonic coherence. They show only minor differences between the massifs, indicating a lack of significant vertical-axis tectonic rotations within the studied central parts of the CWC. The paleomagnetic declinations are therefore representative of the whole of the CWC in terms of regional paleogeographic interpretations, and imply moderate counterclockwise rotations ( c . 26°) of the region with respect to stable Europe since the Early Triassic.

Timing of Late Cretaceous shortening and basin development, Little Hatchet Mountains, southwestern New Mexico, USA – implications for regional Laramide tectonics

AbstractLaser ablation‐multi collector‐inductively coupled mass spectrometry U‐Pb geochronology, detailed field mapping and stratigraphic data offer improved insights into the timing and style of Laramide deformation and basin development in the Little Hatchet Mountains, southwestern New Mexico, USA, a key locality in the ‘southern Laramide province.’ The Laramide synorogenic section in the northern Little Hatchet Mountains comprises upper Campanian to Maastrichtian strata consisting of the Ringbone and Skunk Ranch formations, with a preserved maximum thickness of >2400 m, and the correlative Hidalgo Formation with a total thickness >1700 m. The Ringbone Formation and superjacent Skunk Ranch Formation are each generally composed of (1) a basal conglomerate member; (2) a middle member consisting of lacustrine shale, limestone, sandstone, and interbedded ash‐fall tuffs; and (3) an upper sandstone and conglomerate member. Basaltic andesite flows are intercalated with the upper member of the Ringbone Formation and the middle member of the Skunk Ranch Formation. The Hidalgo Formation, which crops out in the northern part of the range, is dominantly composed of basaltic andesite breccias and flows equivalent to those of the Ringbone and Skunk Ranch formations. The Laramide section was deposited in an intermontane basin partitioned across intrabasinal thrust structures, which controlled growth‐stratal development. U‐Pb zircon ages from five tuffs indicate that the age range of the Laramide sedimentary succession is ca. 75–70 Ma. U‐Pb detrital‐zircon age data (n = 356 analyses) from the Ringbone Formation and a Lower Cretaceous unit indicate sediment contribution from uplifted Lower and Upper Cretaceous rocks adjacent to the basin and the contemporary Tarahumara magmatic arc in nearby northern Sonora, Mexico. The new ages, combined with published data, indicate that uplift, basin development, and magmatism in the region proceeded diachronously northeastwards as the subducting Farallon slab flattened under northern Mexico and southern New Mexico from Campanian to Palaeogene time.

Style and chronology of the Late Cretaceous shortening in the Zihuatanejo area (southwestern Mexico): Implications for the timing of the Mexican Laramide deformation

Terrane accretion, variations of the convergence rate, and interaction with the Caribbean plate have been proposed as the causes of the Mexican Laramide orogeny. However, the mechanism that triggered this regional deformation event remains unknown. Based on available data, some authors supported the notion that the Laramide shortening migrated from the present-day Pacifi c coast to the Mexican mainland. However, such migration has been inferred based on paleon tologic and isotopic data from the central and eastern parts of the fold-and-thrust belt, without considering the western part of the orogen. The identifi cation of a chronologic pattern of the deformation is crucial to understand the cause of the Laramide orogeny, because it is a direct consequence of the tectonic process that triggered this regional shortening. Here we present the fi rst structural study of the Zihuatanejo area, which is located in southwestern Mexico, within the interior of the Guerrero composite terrane. Our data document that this region underwent progressive shortening during the Late Cretaceous, which resulted in regional uplift and unconformable deposition of continental red beds over a Lower Cretaceous marine arc succession. We interpret the continental rocks as the infi ll of a piggyback basin related to the early evolution of the Laramide orogeny. According to this scenario, the ~94 Ma age obtained for the oldest continental strata constrains the beginning of the Laramide shortening in the Zihuatanejo area, which was thus the fi rst area of the Laramide belt to be deformed. Considering that during terrane accretion the deformation propagates from the suture zone to the continent and terrane interiors, the timing of the Laramide deformation in southern Mexico cannot be explained as a direct consequence of the accretion of the Guerrero terrane. In fact, we document that the Laramide shortening started at the Cenomanian‐Turonian boundary within the interior of the terrane, and migrated progressively eastward involving the suture belt and the continental mainland. Based on the chronologic pattern documented for the Late Cretaceous‐Paleogene shortening in southern Mexico, the Laramide deformation front can be envisioned as a tectonic wave that propagates from the presentday Pacifi c coast to the continental mainland, probably as the result of the increasing subduction rate or collision of a Caribbean terrane along the Mexican Pacifi c trench.

Analogue model of inversion tectonics explaining the structural diversity of Late Cretaceous shortening in southwestern Mexico

The Laramide fold-and-thrust belt in southern Mexico is characterized by N-S–trending structures in its central and eastern part and by NW-SE–trending structures in its western part. Here, we investigate, experimentally, the possibility that the Laramide structures of southern Mexico may be the result of inversion of previously thinned lithosphere zones under oblique compression. A revision of the geology of this region shows that the presence of two extensional basins, representing relatively weak blocks within more rigid lithosphere, strongly controlled the subsequent deformation pattern. For modeling purposes, we divided the southern Mexico lithosphere into blocks with different strength profiles: (1) a stable craton; (2) a weak block composed of the Guerrero Morelos Platform; (3) a relatively strong block exposing the pre-Cretaceous Tejupilco schist and the Early Cretaceous Teloloapan volcanic arc (Tejupilco anticlinorium); and (4) a weak block represented by the Arcelia–Palmar Chico basin. A series of physical experiments simulating the mechanical response of an analogue lithosphere composed of five simplified strength profiles was constructed. The model lithosphere was thinned orthogonally and shortened obliquely. Shortening was accommodated mainly by reactivation of preexisting extensional structures. The resulting orogenic deformation in the models is not entirely sequential and foreland-progressive. Inversion tectonics of extensional basins is thus proposed as an explanation for the structural diversity observed in Late Cretaceous shortening of southwestern Mexico. The predictions of our lithospheric model may be tested when more geophysical information about the structure of the southern Mexico lithosphere becomes available.

Late Cretaceous shortening and early Tertiary shearing in the central Sierra Madre del Sur, southern Mexico: Insights into the evolution of the Caribbean–North American plate interaction

A wide region in the central part of the Sierra Madre del Sur (SMS), southern Mexico, records two deformational phases between the Late Cretaceous and early Tertiary. The first is a progressive approximately E‐W shortening phase that spans from the Coniacian to earliest Paleocene and involves deformation of Cretaceous marine sedimentary units. The second phase corresponds to Paleocene to early Eocene deformation that also affects continental sediments and is characterized by gentle folding and counterclockwise rotation of previous shortening structures associated with strike‐slip faulting. Here we present geologic, geochronologic, and structural data of two key areas of the Sierra Madre del Sur, the Guerrero‐Morelos Platform (GMP), and the Huajuapan‐Tamazulapan area in western Oaxaca to describe the geometry, kinematics, and timing of the Late Cretaceous and early Tertiary deformation. Two regional magmatic episodes constrain the deformational history: (1) the first between the Maastrichtian and the Paleocene (68–57 Ma) documents the end of Late Cretaceous shortening in the GMP; and (2) the second between the late Eocene and early Oligocene (37–29 Ma) has a more regional distribution. The time and space analysis of deformation and magmatism in southern Mexico led us to exclude flat subduction or collision of the Guerrero terrane to the west as the cause for Late Cretaceous shortening in the GMP. Considering the similarity in the time and style of deformation with that of the northern Chortis block, we favor an interpretation in which the tectonic evolution of the central and eastern SMS is the result of progressive interaction of the Caribbean plate with the southernmost edge of North America since the Late Cretaceous.

Missing Idaho arc: Transpressional modification of the 87Sr/86Sr transition on the western edge of the Idaho batholith

The North American Cordillera is characterized by subduction-related Mesozoic batholiths with voluminous middle Cretaceous plutonism. In the Cordillera, the Idaho batholith is anomalous, containing only a narrow (<10 km) band of middle Cretaceous plutons on its extreme western margin. These plutons are spatially coincident with the Late Cretaceous, crustal-scale, dextral transpressional western Idaho shear zone. Finite strain analysis indicates that there is significant east-west shortening in the western Idaho shear zone. A reconstruction using isotopic variations as strain markers, and comparing them to the undeformed middle Cretaceous Sierra Nevada batholith, results in a middle Cretaceous magmatic arc in western Idaho similar in width (∼85– 100 km) to other sections of the Cordilleran magmatic arc. The tectonic implications include: (1) a full magmatic arc existed in Idaho in the middle Cretaceous prior to Late Cretaceous deformation; (2) the currently sharp 87Sr/86Sr transition in western Idaho represents structural modification of the batholith after emplacement (i.e., the steep isotopic gradient results from deformation); and (3) as a result of Late Cretaceous shortening in the western Idaho shear zone, the main part of the Idaho batholith (i.e., post–ca. 90 Ma) intruded farther eastward into thick North American lithosphere. Consequently, the main part of the Idaho batholith has a stronger continental signature than the other coastal batholiths.

The role of crustal heterogeneity in controlling vertical coupling during Laramide shortening and the development of the Caribbean-North America transform boundary in southern Mexico: insights from analogue models

Abstract Analogue models of polyphase deformation involving crustal differences in strength, thickness and density give insights into lateral and vertical strain propagation during Late Cretaceous shortening and Early Tertiary left-lateral shearing related to the early development of the North America-Caribbean plate boundary in southern Mexico. Analogue models reproduce a two-phase deformation characterized by a first stage of compression orthogonal to the plate boundary, simulating deformation induced by the Laramide orogeny, followed by a later stage of left-lateral transpression associated with the transfer of the Chortis block from the North American to the Caribbean plate during the early stage of development of the new plate boundary in Early Tertiary times. Based on detailed structural observations in the Guerrero-Morelos platform and the western part of the Mixteco terrane of southern Mexico, we document that a transpressive regime affected continental red bed sequences of Early Paleocene to Late Eocene, and rotated and refolded Laramide structures during this second phase. Our model ends before the transtensional regime that affected the region, which is marked by a volcanic episode of Late Eocene-Oligocene. This change in the deformation regime records the passage of the NW tip of the Chortis block (North America-Cocos-Caribbean triple junction), when subduction replaced transform faulting along the southern Mexico margin. The models focus on the structures formed around the flanks of a thicker/more rigid crustal block that simulates the rock assemblages of the Palaeozoic orogens of southern Mexico (Mixteco-Oaxaca-Juarez block, MOJB). The comparison of the mechanism of deformation of three different analogue models with the natural prototype explains most of the structures observed around the MOJB. Counterclockwise vertical-axis rotations of pre-existing structures in the western flank of the MOJB observed in the Guerrero-Morelos platform are consistent with the modelled structures. Vertical movements of the modelled MOJB induced by the transpressive regime can explain the Papalutla thrust and the basement upheaval and gravitational sliding of the cover in the Tentzo Ranges observed at the western and northern margins of the MOJB, respectively. The growth and propagation of thrusting controlled by the geometry of the block along the eastern margin also correlates with the Vista Hermosa fault. The propagation of strain to the north increases with higher contrast in strength of the thick block with respect to the adjacent modelled crust. Analogue modelling failed to reproduce all the structural details of southern Mexico and, specifically, the structures observed inside the MOJB. The latter, however, are controlled by pre-existing discontinuities, which are not simulated in the model. As a whole, the results demonstrate that crustal heterogeneity in a developing left-lateral plate boundary zone produces a stronger vertical coupling between ductile and brittle crust and a widening of the deformation zone along the margin of the North America plate in southern Mexico.

Post-Permian evolution of the Central North Sea: a numerical model

A dynamic thermomechanical model is presented for the post-Permian evolution of the Central North Sea including the Central Graben. Permo-Carboniferous and Jurassic thermal events, as well as Triassic and Jurassic extensional phases and Late Cretaceous shortening, are considered. The equations of force balance for a continuum and the transient heat equation are solved using the finite element method. The lithosphere responds to applied forces by elastic deformation at low deviatoric stress levels, fracture at low temperature and pressure conditions and nonlinear viscous flow at high temperature and pressure. A first-order rheological strain softening is incorporated to simulate a transition from strong to soft material behaviour, such as a change from dislocation creep to diffusion creep. Seismic refraction and reflection data indicate crustal thinning below the Central Graben by a factor of ∼2. While the Triassic rifting appears to have been associated with a more distributed deformation pattern, the Upper Jurassic rifting is more localised. Pure shear extensional models have been advocated to explain this. However, dipping seismic reflectors in the upper mantle indicate that simple shear could be important. The strain softening of the present model allows for modelling of strain localisation during the Upper Jurassic rifting phase and detailed modelling of Moho structures. The present model accounts for the main structural and stratigraphic observations in the Central North Sea. Furthermore, the results indicate that in the part of the Central North Sea investigated in this paper, a pure shear regime in Triassic changed into a simple shear-dominated regime with mantle shear zones developing during Late Jurassic extension.

Thrust-top basin formation along a suture zone, Cantwell basin, Alaska Range: Implications for development of the Denali fault system

The Cantwell Formation consists of a lower sedimentary sequence as much as 4000 m thick and an upper volcanic sequence with a maximum thickness of 3750 m that was deposited in the Cantwell basin, south-central Alaska. Previous to this study, the Cantwell basin was interpreted as a Paleogene, nonmarine (mainly fluvial), pull-apart basin that formed in response to dextral, strike-slip displacement on the Denali fault system. This study proposes that the Cantwell basin formed as part of the Mesozoic accretionary phase of deformation, prior to the development of the Cenozoic postaccretionary Denali fault system. Our reinterpretation is based on several new lines of data. (1) Age . New data based on palynologic analyses of 135 fine-grained samples indicate that the lower Cantwell Formation was deposited during the late Campanian and early Maastrichtian. On the basis of previous regional tectonic studies and this new age constraint, the formation of the Cantwell basin was coeval with regional Late Cretaceous shortening associated with accretionary tectonics in southern Alaska. (2) Depositional systems . Our analysis of the Cantwell Formation demonstrates that sedimentation occurred mainly in stream-dominated alluvial fan, axial braided stream, and lacustrine settings. These depositional systems were strongly influenced by a southward dipping, asymmetric basin floor. The presence of abundant terrestrially derived organic material, together with palynological assemblages that include marine dinoflagellates and the associated presence of oncolites, may be suggestive of a time of marginal marine influence during the deposition of the upper part of the lower Cantwell Formation. The late Campanian to early Maastrichtian timing of this possible marine influence is within the range of the Bearpaw transgressive event of the Cordilleran foreland basin and allows for regional stratigraphic correlation of the Cantwell basin with other sedimentary basins in northwestern North America. (3) Structural controls on basin formation . Mapping of intraformational angular unconformities and progressively tilted strata along the southern margin of the Cantwell basin provides direct evidence that thrust fault deformation and lower Cantwell Formation sedimentation were synchronous. Distinctive Cantwell Formation conglomerate clasts derived from the uplifted hanging walls of nearby thrust sheets adjacent to the southern basin margin also support a syndepositional thrusting interpretation. Provenance data and the concentration of proximal alluvial fan deposits along the northwestern basin margin adjacent to the Hines Creek fault indicate that it, too, was active during deposition of the Cantwell Formation. On the basis of the new data, the Cantwell basin is interpreted to have formed as a thrust-top basin (i.e., piggyback basin) along the Late Cretaceous suture zone between the accreting Wrangellia composite terrane and the North American continental margin. In contrast to previous studies, this reinterpretation of the formation of the Cantwell basin implies that the lower Cantwell Formation is not a synorogenic deposit directly associated with strike-slip displacement along the Denali fault system. Therefore, the Cantwell basin cannot be used to constrain the timing for the early development of the Denali fault system.

Early to mid Tertiary crustal extension in the Central Alps: The Turba Mylonite Zone (Eastern Switzerland)

In the Penninic‐Austroalpine boundary zone of Eastern Switzerland a clear distinction can be made between upper and lower stacks of nappes with contrasting tectonic evolution that are separated by the Turba mylonite zone (TMZ). The Austroalpine nappes, Platta ophiolites, and Malenco‐Forno‐Lizun ophiolites belong to the upper stack. These nappes were formed by predominantly west directed, late Cretaceous shortening and imbrication. The lower stack, comprising the Suretta nappe, Schams nappes, Avers schists, and Oberhalbstein flysch units, includes Tertiary sediments and was deformed and metamorphosed in early Tertiary time. Kinematic indicators in the mylonites of the TMZ, representing the boundary between the two stacks, show a top‐to‐the‐east directed movement, which is clearly distinct from the regionally prevalent top‐to‐the‐north direction of thrusting in the Tertiary. The main foliation in the shear zone is discordant with respect to the structures of the hanging wall, and concordant to the footwall. Vitrinite reflectance in shaly sediments above and below the TMZ in the northern part indicates that the TMZ coincides with a drop in peak metamorphic temperature from about 350°C in the top of the footwall to about 280°C at the base of the hanging wall. Therefore the TMZ is interpreted as an east dipping, low‐angle normal fault. The age of its activity is bracketed between about 45 and 30 Ma, based on overprinting relations with radiometrically dated features (45–30 Ma: main foliation in the footwall, older than TMZ activity; 30 Ma: Bergell granodiorite intrusion, younger than TMZ activity). Extension along the TMZ was followed by further north‐south shortening, as indicated by postmylonitic folding of the TMZ. Normal faulting along the TMZ accommodated relative uplift of the Lepontine structural dome, a large metamorphic complex in the Central Alps. Unroofing of this dome started before 30 Ma and continued in the Miocene with activity of further normal faults situated at deeper structural levels.

Correction [to “The Coast Belt Thrust System: Evidence of Late Cretaceous shortening in southwest British Columbia” by J.M. Journeay and R.M. Friedman

Correction [to “The Coast Belt Thrust System: Evidence of Late Cretaceous shortening in southwest British Columbia” by J.M. Journeay and R.M. Friedman

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.