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At least 199 records · Page 11Linked to original sources
USGS2001

Primary centers and secondary concentrations of tectonic activity through time in the western hemisphere of Mars

Five main stages of radial and concentric structures formed around Tharsis from the Noachian through the Amazonian as determined by geologic mapping of 24,452 structures within the stratigraphic framework of Mars and by testing their radial and concentric orientations. Tectonic activity peaked in the Noachian (stage 1) around the largest center, Claritas, an elongate center extending more than 20° in latitude and defined by about half of the total grabens which are concentrated in the Syria Planum, Thaumasia, and Tempe Terra regions. During the Late Noachian and Early Hesperian (stage 2), extensional structures formed along the length of present-day Valles Marineris and in Thaumasia (with a secondary concentration near Warrego Vallis) radial to a region just to the south of the central margin of Valles Marineris. Early Hesperian (stage 3) radial grabens in Pavonis, Syria, Ulysses, and Tempe Terra and somewhat concentric wrinkle ridges in Lunae and Solis Plana and in Thaumasia, Sirenum, Memnonia, and Amazonis are centered northwest of Syria with secondary centers at Thaumasia, Tempe Terra, Ulysses Fossae, and western Valles Marineris. Late Hesperian/Early Amazonian (stage 4) structures around Alba Patera, the northeast trending alignment of Tharsis Montes, and Olympus Mons appears centered on Alba Patera. Stage 5 structures (Middle-Late Amazonian) represent the last pulse of Tharsis-related activity and are found around the large shield volcanoes and are centered near Pavonis Mons. Tectonic activity around Tharsis began in the Noachian and generally decreased through geologic time to the Amazonian. Statistically significant radial distributions of structures formed during each stage, centered at different locations within the higher elevations of Tharsis. Secondary centers of radial structures during many of the stages appear related to previously identified local magmatic centers that formed at different times and locations throughout Tharsis.

Journal of Geophysical Research E: Planets↗
USGS2004

New constraints on the active tectonic deformation of the Aegean

Site velocities from six separate Global Positioning System (GPS) networks comprising 374 stations have been referred to a single common Eurasia-fixed reference frame to map the velocity distribution over the entire Aegean. We use the GPS velocity field to identify deforming regions, rigid elements, and potential microplate boundaries, and build upon previous work by others to initially specify rigid elements in central Greece, the South Aegean, Anatolia, and the Sea of Marmara. We apply an iterative approach, tentatively defining microplate boundaries, determining best fit rigid rotations, examining misfit patterns, and revising the boundaries to achieve a better match between model and data. Short-term seismic cycle effects are minor contaminants of the data that we remove when necessary to isolate the long-term kinematics. We find that present day Aegean deformation is due to the relative motions of four microplates and straining in several isolated zones internal to them. The RMS misfit of model to data is about 2-sigma, very good when compared to the typical match between coseismic fault models and GPS data. The simplicity of the microplate description of the deformation and its good fit to the GPS data are surprising and were not anticipated by previous work, which had suggested either many rigid elements or broad deforming zones that comprise much of the Aegean region. The isolated deforming zones are also unexpected and cannot be explained by the kinematics of the microplate motions. Strain rates within internally deforming zones are extensional and range from 30 to 50 nanostrain/year (nstrain/year, 10-9/year), 1 to 2 orders of magnitude lower than rates observed across the major microplate boundaries. Lower strain rates may exist elsewhere withi the microplates but are only resolved in Anatolia, where extension of 13 ?? 4 nstrain/ year is required by the data. Our results suggest that despite the detailed complexity of active continental deformation revealed by seismicity, active faulting, fault geomorphology, and earthquake fault plane solutions, continental tectonics, at least in the Aegean, is to first order very similar to global plate tectonics and obeys the same simple kinematic rules. Although the widespread distribution of Aegean seismicity and active faulting might suggest a rather spatially homogeneous seismic hazard, the focusing of deformation near microplate boundaries implies the highest hazard is comparably localized.

Journal of Geophysical Research B: Solid Earth↗
USGS2011

Survey explores active tectonics in northeastern Caribbean

There is renewed interest in studying the active and complex northeastern Caribbean plate boundary to better understand subduction zone processes and for earthquake and tsunami hazard assessments [e.g., ten Brink and Lin , 2004; ten Brink et al ., 2004; Grindlay et al ., 2005]. To study the active tectonics of this plate boundary, the GEOPRICO-DO (Geological, Puerto Rico-Dominican) marine geophysical cruise, carried out between 28 March and 17 April 2005 (Figure 1), studied the active tectonics of this plate boundary. Initial findings from the cruise have revealed a large underwater landslide, and active faults on the seafloor (Figures 2a and 2c). These findings indicate that the islands within this region face a high risk from tsunami hazards, and that local governments should be alerted in order to develop and coordinate possible mitigation strategies.

Eos, Transactions, American Geophysical Union↗
USGS2008

Mid-Cenozoic tectonic and paleoenvironmental setting of the central Arctic Ocean

Drilling results from the Integrated Ocean Drilling Program's Arctic Coring Expedition (ACEX) to the Lomonosov Ridge (LR) document a 26 million year hiatus that separates freshwater-influenced biosilica-rich deposits of the middle Eocene from fossil-poor glaciomarine silty clays of the early Miocene. Detailed micropaleontological and sedimentological data from sediments surrounding this mid-Cenozoic hiatus describe a shallow water setting for the LR, a finding that conflicts with predrilling seismic predictions and an initial postcruise assessment of its subsidence history that assumed smooth thermally controlled subsidence following rifting. A review of Cenozoic tectonic processes affecting the geodynamic evolution of the central Arctic Ocean highlights a prolonged phase of basin-wide compression that ended in the early Miocene. The coincidence in timing between the end of compression and the start of rapid early Miocene subsidence provides a compelling link between these observations and similarly accounts for the shallow water setting that persisted more than 30 million years after rifting ended. However, for much of the late Paleogene and early Neogene, tectonic reconstructions of the Arctic Ocean describe a landlocked basin, adding additional uncertainty to reconstructions of paleodepth estimates as the magnitude of regional sea level variations remains unknown.

Paleoceanography↗
USGS2012

Laboratory triggering of stick-slip events by oscillatory loading in the presence of pore fluid with implications for physics of tectonic tremor

The physical mechanism by which the low-frequency earthquakes (LFEs) that make up portions of tectonic (also called non-volcanic) tremor are created is poorly understood. In many areas of the world, tectonic tremor and LFEs appear to be strongly tidally modulated, whereas ordinary earthquakes are not. Anomalous seismic wave speeds, interpreted as high pore fluid pressure, have been observed in regions that generate tremor. Here we build upon previous laboratory studies that investigated the response of stick-slip on artificial faults to oscillatory, tide-like loading. These previous experiments were carried out using room-dry samples of Westerly granite, at one effective stress. Here we augment these results with new experiments on Westerly granite, with the addition of varying effective stress using pore fluid at two pressures. We find that raising pore pressure, thereby lowering effective stress can significantly increase the degree of correlation of stick-slip to oscillatory loading. We also find other pore fluid effects that become important at higher frequencies, when the period of oscillation is comparable to the diffusion time of pore fluid into the fault. These results help constrain the conditions at depth that give rise to tidally modulated LFEs, providing confirmation of the effective pressure law for triggering and insights into why tremor is tidally modulated while earthquakes are at best only weakly modulated.

Journal of Geophysical Research B: Solid Earth↗
USGS2022

Interaction between climate and tectonics in the northern Lesser Antilles inferred from the last interglacial shoreline on Barbuda island

In the context of increasing evidence of plate interface coupling variability in subduction zones, there is a need to extend the short time window given by instrumental data and to gather data over multiple time and spatial scales. We hence investigated the long-term topography on Barbuda island, located in the northern part of the Lesser Antilles, west of the Caribbean subduction zone. Following pioneering work using a set of marine terraces on the eastern side of the island, we performed the first U-Th dating on 10 corals in growth position from the lowest terrace, for which the highest relative sea-level (RSL) indicator is found at 9 ± 1 m above the mean sea level. We find that this terrace corresponds to the Last Interglacial (LIG) (ages between 122.8 ± 0.3 ka and 128.1 ± 0.3 ka) and we estimate a paleo RSL of 7 ± 2 m above the current mean sea level. The present elevation of the LIG shoreline on Barbuda might imply tectonics as an additional mechanism to eustatic sea level, mantle dynamic topography and glacial isostatic adjustment. East-west morphological asymmetry of Barbuda and difference in LIG shoreline elevation between Barbuda and Antigua suggest a regional tectonic process. As with the proposed westward tilting from the forearc to the volcanic arc of the Guadeloupe archipelago, vertical deformation on Barbuda could be related to plate-scale subduction processes. Long-term uplift of Barbuda might be related to the accumulation of residual coseismic deformation not fully recovered by interseismic subsidence and the corresponding seismogenic segment would extend below the Moho.

Geochemistry, Geophysics, Geosystems↗
USGS2024

Laboratory hydrofractures as analogs to tectonic tremors

The fracture of Earth materials occurs over a wide range of time and length scales. Physical conditions, particularly the stress field and Earth material properties, may condition rupture in a specific fracture regime. In nature, fast and slow fractures occur concurrently: tectonic tremor events are fast enough to emit seismic waves and frequently accompany slow earthquakes, which are too slow to emit seismic waves and are referred to as aseismic slip events. In this study, we generate simultaneous seismic and aseismic processes in a laboratory setting by driving a penny-shaped crack in a transparent sample with pressurized fluid. We leverage synchronized high-speed imaging and high-frequency acoustic emission (AE) sensing to visualize and listen to the various sequences of propagation (breaks) and arrest (sticks) of a fracture undergoing stick-break instabilities. Slow radial crack propagation is facilitated by fast tangential fractures. Fluid viscosity and pressure regulate the fracture dynamics of slow and fast events, and control the inter-event time and the energy released during individual fast events. These AE signals share behaviors with observations of episodic tremors in Cascadia, United States; these include: (a) bursty or intermittent slow propagation, and (b) nearly linear scaling of radiated energy with area. Our laboratory experiments provide a plausible model of tectonic tremor as an indicative of hydraulic fracturing facilitating shear slip during slow earthquakes.

AGU Advances↗
USGS2026

Tectonic controls on volcanism and associated hydrothermal activity in a sediment-dominated mid-ocean ridge; Escanaba Trough

Mid-ocean ridges, the Earth's most extensive volcanic system, exhibit unique characteristics in sediment-dominant environments. Thick sediment cover insulates the crust and channels fluid along pathways that can lead to the formation of distinct crustal alteration patterns, exceptionally large mineral deposits, and specialized chemosynthetic ecosystems. This study presents an interdisciplinary investigation into the tectonics of the Escanaba Trough, a heavily sedimented axial valley at the southern Gorda Ridge in the Northeast Pacific Ocean. A primary challenge in such environments is overcoming the masking effect of thick sediments on basement structures that control magmatic and hydrothermal activity. We address this by employing three-dimensional (3D) magnetic modeling of high-resolution near-seafloor magnetic data collected by an autonomous underwater vehicle (AUV). The 2022 surveys with AUV Sentry provided data for 3D magnetic susceptibility models, refining our understanding of the geometry of sub-sediment laccoliths/saucer-shaped sills and hydrothermal alteration. In conjunction with a new 1:100,000 scale lithostratigraphic map, we outline the tectonic controls on the emplacement of Escanaba Trough's three main volcanic centers, characterize the geometry of its spreading segments, and provide volumetric data on the distribution of sub-sediment volcanism in the southern Gorda Ridge.

Escanaba Trough, Pacific Ocean↗
USGS1997

An integrated model for the tectonic development of the frontal Brooks Range and Colville Basin 250 km west of the Trans-Alaska Crustal Transect

We present a kinematic model for the sequence of deformation and sedimentation in the frontal Brooks Range and adjacent Colville Basin in the Etivluk River region, 250 km west of the Trans-Alaska Crustal Transect (TACT). The model is based on a tectonic subsidence analysis of the foreland basin, combined with structural, stratigraphic, and thermal studies of the northern edge of the Brooks Range thrust belt. We interpret six discrete tectonic events that led to the present-day configuration of the thrust belt in this area: (1) emplacement of ophiolitic allochthons over the distal continental margin rocks in Valanginian time, hundreds of kilometers south of this study, (2) Hauterivian uplift of the Barrow Arch rift margin, affecting the northern part of the Colville Basin, (3) Barremian contraction involving emplacement of distal continental margin and ophiolitic allochthons onto the Endicott Mountains allochthon and creation of a southward dipping flexural basin on the North Slope autochthon, (4) mid-Cretaceous exhumation of imbricated rocks in the Brooks Range during northward propagation of the thrust front into the foreland, (5) minor thrusting in Late Cretaceous-Paleocene in the northern foreland to the northern limit of contractional structures, and (6) regional exhumation of the orogen and the foreland in Paleocene-Eocene time. This sequence of deformation agrees well with a simple model of a forward propagating thrust system.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

b values and ω −γ seismic source models: Implications for tectonic stress variations along active crustal fault zones and the estimation of high-frequency strong ground motion

In this study the tectonic stress along active crustal fault zones is taken to be of the form , where is the average tectonic stress at depth y and Δσ p ( x, y ) is a seismologically observable, essentially random function of both fault plane coordinates; the stress differences arising in the course of crustal faulting are derived from Δσ p ( x, y ). Empirically known frequency of occurrence statistics, moment-magnitude relationships, and the constancy of earthquake stress drops may be used to infer that the number of earthquakes N of dimension ≥ r is of the form N ∼ 1/ r 2 and that the spectral composition of Δσ p ( x, y ) is of the form , where is the two-dimensional Fourier transform of Δσ p ( x, y ) expressed in radial wave number k . The γ = 2 model of the far-field shear wave displacement spectrum is consistent with the spectral composition , provided that the number of contributions to the spectral representation of the radiated field at frequency ƒ goes as ( k / k 0 ) 2 , consistent with the quasi-static frequency of occurrence relation N ∼ 1/ r 2 ; k 0 is a reference wave number associated with the reciprocal source dimension. Separately, a variety of seismologic observations suggests that the γ = 2 model is the one generally, although certainly not always, applicable to the high-frequency spectral decay of the far-field radiation of earthquakes. In this framework, then, b values near 1, the general validity of the γ = 2 model, and the constancy of earthquake stress drops independent of size are all related to the average spectral composition of . Should one of these change as a result of premonitory effects leading to failure, as has been specifically proposed for b values, it seems likely that one or all of the other characteristics will change as well from their normative values. Irrespective of these associations, the far-field, high-frequency shear radiation for the γ = 2 model in the presence of anelastic attenuation may be interpreted as band-limited, finite duration white noise in acceleration. Its rms value, a rms , is given by the expression a rms = 0.85[2 1/2 (2π) 2 /106] (Δσ/ρ R )(ƒ max /ƒ 0 ) 1/2 , where Δσ is the earthquake stress drop, ρ is density, R is hypocentral distance, ƒ 0 is the spectral corner frequency, and ƒ max is determined by R and specific attenuation 1/ Q . For several reasons, one of which is that it may be estimated in the absence of empirically defined ground motion correlations, a rms holds considerable promise as a measure of high-frequency strong ground motion for engineering purposes.

Conference Paper↗
USGS2012

Paleomagnetism of the Tertiary Clarno Formation of central Oregon and its significance for the tectonic history of the Pacific Northwest

The Clarno Formation, a mostly Eocene and partly early Oligocene sequence of andesitic lavas and volcaniclastic rocks, is the oldest Tertiary formation exposed in north central Oregon. Remanent magnetization directions at 46 sites in the lavas provide a paleomagnetic pole at 84°N, 278°E with a 95% confidence cone of 7°. Comparison of this pole with the North American reference pole for Eocene time indicates that the Clarno Formation has rotated 16° clockwise with an uncertainty of 10° but has undergone no significant latitudinal displacement. Further comparison with paleomagnetic data from the Miocene Columbia River Basalt Group and Steens Basalt shows that large‐scale block rotations in the eastern Columbia Embayment ceased sometime between 38 m.y. and 15 m.y. A paleogeographic reconstruction for 38 m.y. is offered which is consistent with the observed rotation of the Clarno and with the other paleomagnetic data from the Pacific Northwest, which are briefly reviewed. This reconstruction shows that it is possible to account for virtually all of the paleomagnetically indicated rotations in pre‐Miocene Tertiary rocks of the Pacific Northwest by an extensional tectonic model. As a consequence, only part of the rotations in the pre‐Tertiary rocks of the eastern Columbia Embayment need to be the result of accretionary tectonics. The initiation of magmatism in the eastern Columbia Embayment that is represented by the Clarno Formation itself may have been contemporaneous with the beginning of crustal extension in the Pacific Northwest.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

Paleomagnetic rotations and the Cenozoic tectonics of the Cascade Arc, Washington, Oregon, and California

Paleomagnetic results from Cenozoic (62–12 Ma) volcanic rocks of the Cascade arc and adjacent areas indicate that moderate to large clockwise rotations are an important component of the tectonic history of the arc. Two mechanisms of rotation are suggested by the regional pattern of paleomagnetic rotations. The progressive increase in rotation toward the coast in arc and forearc rocks results from distributed dextral shear, which is likely driven by oblique subduction of oceanic plates to the west. Simple shear rotation is accommodated in the upper crust by strike-slip faulting. The right-lateral Mount St. Helens seismic zone may be an active manifestation of this process. Dextral shear probably obscures a subequal contribution to arc and forearc rotation that is driven by intraarc or backarc extension. This rotation is suggested by the average southward increase in continental margin rotations into the region outboard of the Basin and Range. The southward increase in rotation parallels a change in the arc tectonic regime from largely compressional in northern Washington to extensional in Oregon. Concomitant with this change is a southward increase in the volume of eruptive rocks and the number of basaltic vents in the arc. A progressive eastward shift of the arc volcanic front with time in the rotated arc terrane is the result of the westward pivoting of the arc block in front of a zone of extension since Eocene time. Westward migration of bimodal Basin and Range volcanism since at least 16 Ma is tracking westward rotation of the frontal arc block and growth of the Basin and Range in its wake.

Journal of Geophysical Research Solid Earth↗
USGS2012

Constraints on the tectonics of the Mule Mountains thrust system, southeast California and southwest Arizona

The Mule Mountains thrust system crops out discontinuously over a 100-km-strike length in the Blythe-Quartzsite region of southeast California and southwest Arizona. Along the thrust system, middle and upper crustal metamorphic and plutonic rocks of Proterozoic and Mesozoic age are thrust north-northeastward (015° to 035°) over a lower plate metamorphic terrane that formed part of the Proterozoic North American craton, its Paleozoic sedimentary rock cover, overlying Mesozoic volcanic and sedimentary rocks, and the intruding Jurassic and Cretaceous granitic rocks. Stratigraphic, petrologic, and Pb isotopic ties for Jurassic granitoids and for Jurassic(?) and Cretaceous sedimentary rocks across the various parts of the thrust system indicate that related crustal blocks are superposed and preclude it from having large displacements. The thick-skinned thrust system is structurally symmetrical along its length with a central domain of synmetamorphic thrust faults that are flanked by western and eastern domains where lower plate synclines underlie the thrusts. Deformation occurred under low greenschist facies metamorphic conditions in the upper crust. Movement along the thrust system was probably limited to no more than a few tens of kilometers and occurred between 79±2 Ma and 70±4 Ma. The superposition of related rocks and the geometry of the thrust system preclude it from being a major tectonic boundary of post-Middle Jurassic age, as has been previously proposed. Rather, the thrust system forms the southern boundary of the narrow zone of Cretaceous intracratonic deformation, and it is one of the last tectonic events in the zone prior to regional cooling.

Journal of Geophysical Research Solid Earth↗
USGS2001

Tectonic contraction across Los Angeles after removal of groundwater pumping effects

After the 1987 Whittier Narrows and 1994 Northridge earthquakes revealed that blind thrust faults represent a significant threat to metropolitan Los Angeles , a network of 250 continuously recording global positioning system (GPS) stations was deployed to monitor displacements associated with deep slip on both blind and surface faults. Here we augment this GPS data with interferometric synthetic aperture radar imagery to take into account the deformation associated with groundwater pumping and strike-slip faulting. After removing these non-tectonic signals, we are left with 4.4 mm yr -1 of uniaxial contraction across the Los Angeles basin, oriented N 36° E (perpendicular to the major strike-slip faults in the area). This indicates that the contraction is primarily accommodated on thrust faults rather than on the northeast-trending strike–slip faults. We have found that widespread groundwater and oil pumping obscures and in some cases mimics the tectonic signals expected from the blind thrust faults. In the 40-km-long Santa Ana basin, groundwater withdrawal and re-injection produces 12 mm yr -1 of long-term subsidence, accompanied by an unprecedented seasonal oscillation of 55 mm in the vertical direction and 7 mm horizontally.

Nature↗
USGS1997

Measurement of tectonic surface uplift rate in a young collisional mountain belt

Measurement of the rate of tectonically driven surface uplift is crucial to a complete understanding of mountain building dynamics. The lack of a suitable rock record typically prevents determination of this quantity, but the unusual geology of Papua New Guinea's Finisterre mountains makes measurement of this rate possible. The tectonic surface uplift rate at the Finisterre range is 0.8-2.1 mm yr-1, approximately that expected to arise from crustal thickening.

Nature↗
USGS2019

Dome formation on Ceres by sold-state flow analogous to terrestrial salt tectonics

The dwarf planet Ceres’s outer crust is a complex, heterogeneous mixture of ice, clathrates, salts and silicates. Numerous large domes on Ceres’s surface indicate a degree of geological activity. These domes have been attributed to cryovolcanism, but that is difficult to reconcile with Ceres’s small size and lack of long-lived heat sources. Here we alternatively propose that Ceres’s domes form by solid-state flow within the compositionally heterogeneous crust, a mechanism directly analogous to salt tectonics on Earth. We use numerical simulations to illustrate that differential loading of a crust with compositional heterogeneity on a scale of tens of kilometres can produce dome-like features of scale similar to those observed. The mechanism requires the presence of low-viscosity and low-density, possibly ice-rich, material in the upper 1–10 km of the subsurface. Such substantial regional heterogeneity in Ceres’s crustal composition is consistent with observations from the National Aeronautics and Space Administration’s Dawn mission. We conclude that deformation analogous to that in terrestrial salt tectonics is a viable alternative explanation for the observed surface morphologies, and is consistent with Ceres being both cold and geologically active.

Nature Geoscience↗
USGS2002

Plumes, or plate tectonic processes?

Hotspots – large volcanic provinces – such as Iceland, Hawaii and Yellowstone, are almost universally assumed to come from plumes of hot mantle rising from deep within the Earth. At Iceland, perhaps the best-studied hotspot on Earth, this hypothesis is inconsistent with many first-order observations, such as the lack of high temperatures, a volcanic track or a seismic anomaly in the lower mantle. The great melt production there is explained better by enhanced fertility in the mantle where the mid-Atlantic spreading ridge crosses the Caledonian suture zone. The thick crust built by the excessive melt production encourages complex, unstable, leaky microplate tectonics, which provides positive feedback by enhancing volcanism further. Such a model explains Iceland as a natural consequence of relatively shallow processes related to plate tectonics, and accounts for all the first- and second-order geophysical, geological and geochemical observations at Iceland without special pleading or invoking coincidences.

Astronomy and Geophysics↗
USGS2009

Provenance and U-Pb geochronology of the Upper Cretaceous El Chanate Group, northwest Sonora, Mexico, and its tectonic significance

The Upper Cretaceous El Chanate Group, northwest Sonora, Mexico, is a 2.8km thick clastic sedimentary sequence deposited in a continental basin closely related to volcanic activity. It consists of three formations: the Pozo Duro (oldest), the Anita, and the Escalante (youngest). Petrographic study, conglomerate pebble counts, and U-Pb geochronology of detrital zircons were performed to determine the source and age of this sequence, and to interpret its tectonic setting. In the sandstones of all three formations, the most abundant grains are those of volcanic composition (Q 38 F 22 L 40 , Q 35 F 19 L 46 , and Q 31 F 22 L 47 , respectively). The Pozo Duro Formation includes well-rounded quartz-arenite clast conglomerates, whereas conglomerates of the two upper units have clasts predominantly of andesitic and rhyolitic composition. The most likely source for these sediments was the Jurassic volcanic arc exposed in northern Sonora and southern Arizona. Zircons from five sandstone samples define two main age groups, Proterozoic and Mesozoic. The first ranges mostly from 1000 to 1800Ma, which suggests the influence of a cratonic source. This zircon suite is interpreted to be recycled and derived from the same source area as the quartz-rich sandstone clasts in the basal part of the section. Mesozoic zircons range from Triassic to Late Cretaceous, which confirms the proposed Late Cretaceous age for the sequence, and also corroborates Jurassic felsic source rocks. Another possible source was the Alisitos volcanic arc, exposed along the western margin of the Baja California Peninsula. Of regional significance is the great similarity between the El Chanate Group and the McCoy Mountains Formation of southeastern California and southwestern Arizona. Both are Cretaceous, were deposited in continental environments, and have similar zircon-age patterns. Also, both exhibit intense deformation and locally display penetrative foliation. These features strongly suggest that both units underwent similar tectonic histories.

International Geology Review↗