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At least 19 recordsLinked to original sources
USGS2003

Lithospheric structure, composition, and thermal regime of the East European Craton: Implications for the subsidence of the Russian platform

A new mechanism for Paleozoic subsidence of the Russian, or East European, platform is suggested, since a model of lithosphere tilting during the Uralian subduction does not explain the post-Uralian sedimentation record. Alternatively, I propose that the Proterozoic and Paleozoic rifting (when a platform-scale Central Russia rift system and a set of Paleozoic rifts were formed) modified the structure and composition of cratonic lithosphere, and these tectono-magmatic events are responsible for the post-Uralian subsidence of the Russian platform. To support this hypothesis, (a) the thermal regime and the thickness of the lithosphere are analyzed, and (b) lithospheric density variations of non-thermal origin are calculated from free-board constraints. The results indicate that Proterozoic and Paleozoic rifting had different effects on the lithospheric structure and composition. (1) Proterozoic rifting is not reflected in the present thermal regime and did not cause significant lithosphere thinning (most of the Russian platform has lithospheric thickness of 150-180 km and the lithosphere of the NE Baltic Shield is 250-300 km thick). Paleozoic rifting resulted in pronounced lithospheric thinning (to 120-140 km) in the southern parts of the Russian platform. (2) Lithospheric density anomalies suggest that Proterozoic-Paleozoic rifting played an important role in the platform subsidence. The lithospheric mantle of the Archean-early Proterozoic part of the Baltic Shield is ??? 1.4 ?? 0.2% less dense than the typical Phanerozoic upper mantle. However, the density deficit in the subcrustal lithosphere of most of the Russian platform is only about (0.4-0.8) ?? 0.2% and decreases southwards to ???0%. Increased densities (likely associated with low depletion values) in the Russian platform suggest strong metasomatism of the cratonic lithosphere during rifting events, which led to its subsidence. It is proposed that only the lower part of the cratonic lithosphere was metasomatized as a result of Proterozoic rifting; the boundary between a depleted upper and more fertile lower layers can be at ca. 90-150 km depth and can produce a seismic pattern similar to the top of a seismic low-velocity zone. Paleozoic rifting has modified the entire lithospheric column and the regions affected are still subsiding. Published by Elsevier B.V.

Earth and Planetary Science Letters↗
USGS2002

On the relations between cratonic lithosphere thickness, plate motions, and basal drag

An overview of seismic, thermal, and petrological evidence on the structure of Precambrian lithosphere suggests that its local maximum thickness is highly variable (140-350 km), with a bimodal distribution for Archean cratons (200-220 km and 300-350 km). We discuss the origin of such large differences in lithospheric thickness, and propose that the lithospheric base can have large depth variations over short distances. The topography of Bryce Canyon (western USA) is proposed as an inverted analog of the base of the lithosphere. The horizontal and vertical dimensions of Archean cratons are strongly correlated: larger cratons have thicker lithosphere. Analysis of the bimodal distribution of lithospheric thickness in Archean cratons shows that the "critical" surface area for cratons to have thick (>300 km) keels is >6-8 ?? 106 km2 . Extrapolation of the linear trend between Archean lithospheric thickness and cratonic area to zero area yields a thickness of 180 km. This implies that the reworking of Archean crust should be accompanied by thinning and reworking of the entire lithospheric column to a thickness of 180 km in accord with thickness estimates for Proterozoic lithosphere. Likewise, extrapolation of the same trend to the size equal to the total area of all Archean cratons implies that the lithospheric thickness of a hypothesized early Archean supercontinent could have been 350-450 km decreasing to 280-400 km for Gondwanaland. We evaluate the basal drag model as a possible mechanism that may thin the cratonic lithosphere. Inverse correlations are found between lithospheric thickness and (a) fractional subduction length and (b) the effective ridge length. In agreement with theoretical predictions, lithospheric thickness of Archean keels is proportional to the square root of the ratio of the craton length (along the direction of plate motion) to the plate velocity. Large cratons with thick keels and low plate velocities are less eroded by basal drag than small fast-moving cratons. Basal drag may have varied in magnitude over the past 4 Ga. Higher mantle temperatures in the Archean would have resulted in lower mantle viscosity. This in turn would have reduced basal drag and basal erosion, and promoted the preservation of thick (>300 km) Archean keels, even if plate velocities were high during the Archean.

Tectonophysics↗
USGS2024

Mantle melting in regions of thick continental lithosphere: Examples from Late Cretaceous and younger volcanic rocks, Southern Rocky Mountains, Colorado (USA)

Major- and trace-element data together with Nd and Sr isotopic compositions and 40 Ar/ 39 Ar age determinations were obtained for Late Cretaceous and younger volcanic rocks from north-central Colorado, USA, in the Southern Rocky Mountains to assess the sources of mantle-derived melts in a region underlain by thick (≥150 km) continental lithosphere. Trachybasalt to trachyandesite lava flows and volcanic cobbles of the Upper Cretaceous Windy Gap Volcanic Member of the Middle Park Formation have low εNd(t) values from −3.4 to −13, 87 Sr/ 86 Sr(t) from ~0.705 to ~0.707, high large ion lithophile element/high field strength element ratios, and low Ta/Th (≤0.2) values. These characteristics are consistent with the production of mafic melts during the Late Cretaceous to early Cenozoic Laramide orogeny through flux melting of asthenosphere above shallowly subducting and dehydrating oceanic lithosphere of the Farallon plate, followed by the interaction of these melts with preexisting, low εNd(t), continental lithospheric mantle during ascent. This scenario requires that asthenospheric melting occurred beneath continental lithosphere as thick as 200 km, in accordance with mantle xenoliths entrained in localized Devonian-age kimberlites. Such depths are consistent with the abundances of heavy rare earth elements (Yb, Sc) in the Laramide volcanic rocks, which require parental melts derived from garnet-bearing mantle source rocks. New 40 Ar/ 39 Ar ages from the Rabbit Ears and Elkhead Mountains volcanic fields confirm that mafic magmatism was reestablished in this region ca. 28 Ma after a hiatus of over 30 m.y. and that the locus of volcanism migrated to the west through time. These rocks have εNd(t) and 87 Sr/ 86 Sr(t) values equivalent to their older counterparts (−3.5 to −13 and 0.7038–0.7060, respectively), but they have higher average chondrite-normalized La/Yb values (~22 vs. ~10), and, for the Rabbit Ears volcanic field, higher and more variable Ta/Th values (0.29–0.43). The latter are general characteristics of all other post– 40 Ma volcanic rocks in north-central Colorado for which literature data are available. Transitions from low to intermediate Ta/Th mafic volcanism occurred diachronously across southwest North America and are interpreted to have been a consequence of melting of continental lithospheric mantle previously metasomatized by aqueous fluids derived from the underthrusted Farallon plate. Melting occurred as remnants of the Farallon plate were removed and the continental lithospheric mantle was conductively heated by upwelling asthenosphere. A similar model can be applied to post–40 Ma magmatism in north-central Colorado, with periodic, east to west, removal of stranded remnants of the Farallon plate from the base of the continental lithospheric mantle accounting for the production, and western migration, of volcanism. The estimated depth of the lithosphere-asthenosphere boundary in north-central Colorado (~150 km) indicates that the lithosphere remains too thick to allow widespread melting of upwelling asthenosphere even after lithospheric thinning in the Cenozoic. The preservation of thick continental lithospheric mantle may account for the absence of oceanic-island basalt–like basaltic volcanism (high Ta/Th values of ~1 and εNd[t] > 0), in contrast to areas of southwest North America that experienced larger-magnitude extension and lithosphere thinning, where oceanic-island basalt–like late Cenozoic basalts are common.

Geosphere↗
USGS2012

Crustal seismicity and the earthquake catalog maximum moment magnitudes (Mcmax) in stable continental regions (SCRs): Correlation with the seismic velocity of the lithosphere

A joint analysis of global seismicity and seismic tomography indicates that the seismic potential of continental intraplate regions is correlated with the seismic properties of the lithosphere. Archean and Early Proterozoic cratons with cold, stable continental lithospheric roots have fewer crustal earthquakes and a lower maximum earthquake catalog moment magnitude ( M cmax ). The geographic distribution of thick lithospheric roots is inferred from the global seismic model S40RTS that displays shear-velocity perturbations (δ V S ) relative to the Preliminary Reference Earth Model (PREM). We compare δ V S at a depth of 175 km with the locations and moment magnitudes ( M w ) of intraplate earthquakes in the crust ( Schulte and Mooney, 2005 ). Many intraplate earthquakes concentrate around the pronounced lateral gradients in lithospheric thickness that surround the cratons and few earthquakes occur within cratonic interiors. Globally, 27% of stable continental lithosphere is underlain by δ V S ≥3.0%, yet only 6.5% of crustal earthquakes with M w >4.5 occur above these regions with thick lithosphere. No earthquakes in our catalog with M w >6 have occurred above mantle lithosphere with δ V S >3.5%, although such lithosphere comprises 19% of stable continental regions. Thus, for cratonic interiors with seismically determined thick lithosphere (1) there is a significant decrease in the number of crustal earthquakes, and (2) the maximum moment magnitude found in the earthquake catalog is M cmax =6.0. We attribute these observations to higher lithospheric strength beneath cratonic interiors due to lower temperatures and dehydration in both the lower crust and the highly depleted lithospheric root.

Earth and Planetary Science Letters↗
USGS1990

Chapter 15: Two different lithosphere types in the Sierra Nevada, California

Chemical and isotopic characteristics of plutons in the western United States reflect compositions and protoliths of subjacent source materials. A discontinuously exposed shear zone that extends along the length of the Sierra Nevada in California marks a boundary between two areas manifested geologically by wall-rock and roof-pendant lithologies of different ages, depositional environments, and structural histories. In addition, plutons on either side of the boundary have different chemical and isotopic compositions, which indicate that their source regions are of two fundamentally different lithosphere types. The western lithosphere type is called Panthalassan, whereas the eastern type is called North American. Isotopic investigations of plutons have defined an initial 87 Sr/ 86 Sr (Sr i ) = 0.706 line in each lithosphere type. However, δ 18 O more than +9 per mil in plutons with Sr i greater than 0.706 in the Panthalassan lithosphere indicates a significantly greater sedimentary component in the source materials for these plutons than for those plutons with similar Sr i but δ 18 O less than +9 per mil intruded into North American lithosphere. In contrast to the North American lithosphere, there is no evidence that a Proterozoic crystalline sialic basement exists where plutons have Sr i greater than 0.706 in the Panthalassan lithosphere. Instead, the plutons with Sr i greater than 0.706 intruded into Panthalassan lithosphere probably acquired that characteristic by assimilation of sediments derived from a Proterozoic sialic crust. Plutons with Sr i less than 0.706 have chemical and Nd isotopic characteristics that indicate time-integrated depletion in large ion lithophile elements in their source regions in the Panthalassan lithosphere relative to their sources in the North American lithosphere. The tectonic contact between the two lithosphere types may be the extension of the Sonora-Mojave megashear into northern California.

California↗
USGS2001

Thermal thickness and evolution of Precambrian lithosphere: A global study

The thermal thickness of Precambrian lithosphere is modeled and compared with estimates from seismic tomography and xenolith data. We use the steady state thermal conductivity equation with the same geothermal constraints for all of the Precambrian cratons (except Antarctica) to calculate the temperature distribution in the stable continental lithosphere. The modeling is based on the global compilation of heat flow data by Pollack et al. [1993] and more recent data. The depth distribution of heat‐producing elements is estimated using regional models for ∼300 blocks with sizes varying from 1°×1° to about 5°×5° in latitude and longitude and is constrained by laboratory, seismic and petrologic data and, where applicable, empirical heat flow/heat production relationships. Maps of the lateral temperature distribution at depths 50, 100, and 150 km are presented for all continents except Antarctica. The thermal thickness of the lithosphere is calculated assuming a conductive layer overlying the mantle with an adiabat of 1300°C. The Archean and early Proterozoic lithosphere is found to have two typical thicknesses, 200–220 km and 300–350 km. In general, thin (∼220 km) roots are found for Archean and early Proterozoic cratons in the Southern Hemisphere (South Africa, Western Australia, South America, and India) and thicker (>300 km) roots are found in the Northern Hemisphere (Baltic Shield, Siberian Platform, West Africa, and possibly the Canadian Shield). We find that the thickness of continental lithosphere generally decreases with age from >200 km beneath Archean cratons to intermediate values of 200±50 km in early Proterozoic lithosphere, to about 140±50 km in middle and late Proterozoic cratons. Using known crustal thickness, our calculated geotherms, and assuming that isostatic balance is achieved at the base of the lithosphere, we find that Archean and early Proterozoic mantle lithosphere is 1.5% less dense (chemically depleted) than the underlying asthenosphere, while middle and late Proterozoic subcrustal lithosphere should be depleted by ∼0.6–0.7%. Our results suggest three contrasting stages of lithosphere formation at the following ages: >2.5 Ga, 2.5–1.8 Ga, and <1.8 Ga. Ages of komatiites, greenstone belts, and giant dike swarms broadly define similar stages and apparently reflect secular changes in mantle temperature and, possibly, convection patterns.

Journal of Geophysical Research B: Solid Earth↗
USGS1991

A comparison of Sr-Nd-Pb isotopes in young and old continental lithospheric mantle: Patagonia and eastern China

It is commonly accepted that beneath the continental crust lies a keel of lithospheric mantle, which extends 50–200 kilometres downward to a transition zone into the asthenosphere. The chemical and physical properties of this reservoir are best known through studies of the basalts and xenoliths that provide samples of the subcrustal mantle. Although sharing many characteristics with oceanic island basalts, some continental basalts become increasingly distinct isotopically as crustal age increases, strongly supporting a permanent association between crust and mantle. Consequently, the distinctive trace element and isotope composition of the lithospheric mantle is able to give important clues to its origin and evolution. The mantle under newly‐created crust is typified by a radiogenic isotope variability that emphasizes the materials from which the continental lithosphere is assembled. Old lithospheric mantle, on the other hand, exhibits more evolved isotopic patterns that attest to the existence of long‐lived, chemically complex systems. A comparison of the Pb, Sr and Nd isotopes in alkalic to sub‐alkalic basalt derived from Phanerozoic (Patagonia) and Middle Archaean to Early Proterozoic (eastern China) subcrustal mantle is useful for identifying ‘end‐member’ components of the lithosphere. One component, having an isotopic composition close to PREMA, either continues to evolve virtually unchanged after incorporation into the lithosphere or is, itself, a relatively new addition even to old lithosphere. Another component, beginning with the isotopic composition of BSE, undergoes significant reduction in U/Pb and Sm/Nd (but not Rb/Sr) upon incorporation into the lithosphere and, with time, shows an increasingly retarded evolution of 206 Pb/ 204 Pb and negative ε Nd‐values approaching the isotopic composition of EMI. Five models are discussed that relate the isotopic composition of the continental lithospheric mantle to that of other parts of the terrestrial system, which may be involved in its origin and evolution. The potential locations of the contributing components and the mechanisms and timing of their assembly into lithosphere are considered. Current knowledge, however, does not allow us to distinguish unequivocally among the various scenarios for the creation and evolution of this reservoir.

Australian Journal of Earth Sciences↗
USGS2010

Lithospheric buoyancy and continental intraplate stresses

Lithospheric buoyancy, the product of lithospheric density and thickness, is an important physical property that influences both the long-term stability of continents and their state of stress. We have determined lithospheric buoyancy by applying the simple isostatic model of Lachenbruch and Morgan (1990). We determine the crustal portion of lithospheric buoyancy using the USGS global database of more than 1700 crustal structure determinations (Mooney et al., 2002), which demonstrates that a simple relationship between crustal thickness and surface elevation does not exist. In fact, major regions of the crust at or near sea level (0-200 m elevation) have crustal thicknesses that vary between 25 and 55 km. Predicted elevations due to the crustal component of buoyancy in the model exceed observed elevations in nearly all cases (97% of the data), consistent with the existence of a cool lithospheric mantle lid that is denser than the asthenosphere on which it floats. The difference between the observed and predicted crustal elevation is assumed to be equal to the decrease in elevation produced by the negative buoyancy of the mantle lid. Mantle lid thickness was first estimated from the mantle buoyancy and a mean lid density computed using a basal crust temperature determined from extrapolation of surface heat flow, assuming a linear thermal gradient in the mantle lid. The resulting values of total lithosphere thickness are in good agreement with thicknesses estimated from seismic data, except beneath cratonic regions where they are only 40-60% of the typical estimates (200-350 km) derived from seismic data. This inconsistency is compatible with petrologic data and tomography and geoid analyses that have suggested that cratonic mantle lids are ??? 1% less dense than mantle lids elsewhere. By lowering the thermally determined mean mantle lid density in cratons by 1%, our model reproduces the observed 200-350+ km cratonic lithospheric thickness. We then computed gravitational potential energy by taking a vertical integral over the computed lithosphere density. Our computed values suggest that the thick roots beneath cratons lead to strong negative potential energy differences relative to surrounding regions, and hence exert compressive stresses superimposed on the intraplate stresses derived from plate boundary forces. Forces related to this lithosphere structure thus may explain the dominance of reverse-faulting earthquakes in cratons. Areas of high elevation and a thin mantle lid (e.g., western U.S. Basin and Range, East African rift, and Baikal rift) are predicted to be in extension, consistent with the observed stress regime in these areas.

International Geology Review↗
USGS2012

Evolution of the Precambrian lithosphere: Seismological and geochemical constraints

Several recent models of crustal evolution are based on the belief that the thickness of the continental crust is proportional to its age, with ancient crust being the thickest. A worldwide review of seismic structure contradicts this belief and falsifies these models, at least for the Archean. Proterozoic crust has a thickness of 40–55 km and a substantial high‐velocity (>7 km/s) layer at its base, while Archean crust is only 27–40 km thick (except at the site of younger rifts and collisional boundaries) and lacks the basal high‐velocity layer. Seismology also provides evidence that the lithosphere is thickest beneath Archean cratons, while diamond ages show that this lithospheric keel must have already existed in the Archean. Geochemical data also indicate significant differences between Archean and Proterozoic lithosphere. Major and trace element studies of sediments show a change in upper crustal composition between the Archean and Proterozoic. Archean rocks are depleted in Si and K and enriched in Na, Ca, and Mg. There is also a marked change in the Eu/Eu * ratio. Mantle xenoliths and continental flood basalts show that the mantle lithosphere beneath Archean crust is ultradepleted in FeO compared to that beneath post‐Archean crust. The secular change in the crust‐forming process is attributed to a decline in mantle temperature, leading to a change in the composition of the lithospheric mantle. The higher temperature of the Archean mantle led to the eruption of komatiitic lavas, producing a refractory lithospheric mantle which is ultradepleted in FeO and volatiles. The resultant lithospheric keel is intrinsically less dense than the surrounding mantle and thus not susceptible to delamination. It was sufficiently thick and cool for diamonds to form during the Archean. In contrast, Proterozoic crust developed above fertile mantle. The eruption of continental flood basalts and underplating of basaltic sills is attributed to subsequent heating and partial melting of the lithospheric mantle. Consequently, Proterozoic crust is thickened and has a high‐velocity basal layer.

Journal of Geophysical Research B: Solid Earth↗
USGS1996

Uplift of the Colorado Plateau due to lithosphere attenuation during Laramide low-angle subduction

The Colorado Plateau is blanketed by Phanerozoic marine and nonmarine strata as young as Cretaceous that are now exposed at elevations of about 2 km. Crustal thickening due to magmatism and horizontal crustal shortening was far less than necessary to cause this uplift, which is commonly attributed to the consequences of mantle lithosphere thinning and heating. The Colorado Plateau and the midcontinent region around Iowa consist of Precambrian bedrock overlain by a similar amount of Paleozoic platformal strata, and thus both regions once had similar lithospheric buoyancy. Mesozoic sedimentation increased the crustal thickness and lithospheric buoyancy of the Colorado Plateau relative to the midcontinent region. Backstripping calculations yield elevation without these sediments and lead to a calculated elevation difference between the two areas of about 1200 m, which represents unexplained plateau uplift. Review of constraints on uplift timing finds little support for a late Cenozoic uplift age and allows early to middle Cenozoic uplift, which is consistent with uplift mechanisms related to low-angle subduction that ended in the middle Cenozoic. Finite element heat flow calculations of low-angle subduction and lithosphere attenuation, using a range of initial lithosphere thicknesses and degree of attenuation, indicate that required uplift can result from tectonic removal of about 120 km of mantle lithosphere from an initially 200-km-thick lithosphere. This allows for partial preservation of North American mantle lithosphere with its distinctive isotopic signature in some late Cenozoic volcanic rocks and is consistent with normal Pn velocities in the uppermost mantle beneath the plateau.

Journal of Geophysical Research B: Solid Earth↗
USGS2006

Lithospheric controls on the formation of provinces hosting giant orogenic gold deposits

Ages of giant gold systems (>500 t gold) cluster within well-defined periods of lithospheric growth at continental margins, and it is the orogen-scale processes during these mainly Late Archaean, Palaeoproterozoic and Phanerozoic times that ultimately determine gold endowment of a province in an orogen. A critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle (SCLM) beneath a province at the time of gold mineralisation, as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere. A proxy for the latter is a short pre-mineralisation crustal history such that thick SCLM was not developed before gold deposition. In constrast, orogens with protracted pre-mineralisation crustal histories are more likely to be characterised by a thick SCLM that is difficult to delaminate, and hence, such provinces will normally be poorly endowed. The nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks, with back-arc basalts, transitional basalts and basanites enriched in gold relative to other rock sequences. Thus, segments of orogens with thin lithosphere may enjoy the conjunction of giant-scale fluid flux through gold-enriched sequences. Although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits, the precise siting of those giants depends on the critical conjunction of a number of province-scale factors. Such features control plumbing systems, traps and seals in tectonically and lithospherically suitable terranes within orogens. ?? Springer-Verlag 2006.

Mineralium Deposita↗
USGS2007

Lithosphere stress and deformation

After several decades of investigation, a surprisingly simple view of the lithospheric state of stress has emerged. Broad regions of the lithosphere (scales up to thousands of kilometers) are characterized by remarkably uniform stress fields, both in terms of orientations and relative magnitudes. There is a strong correlation between observed intraplate stress orientations and orientations predicted by models of the plate-driving forces acting on the plate geometry, suggesting that the same forces that drive the plates also stress their interiors. Lateral variations in density and thickness of the crust and lithosphere give rise to gravitational potential energy differences that locally induce forces comparable in magnitude to plate-driving forces. In addition, mantle density inhomogeneities may also influence lithospheric stresses through the linkage of mantle flow. Direct measurements of stress magnitudes at depth indicate that the brittle crust is in a state of ‘frictional faulting equilibrium’, that is, the stress differences are close to, and limited by, the stress levels required to induce slip on the most well-oriented pre-exising planes. This characteristic of ‘critically stressed crust’ stress applies equally well to active plate boundary regions as well as ‘stable’ intraplate regions, indicating that stress differences at depth are comparable in these very distinct tectonic provinces. The difference in deformation between the two provinces is simply the rate of deformation, primarily controlled by the integrated strength of the lithosphere. Warmer, weaker lithosphere (such as along plate boundaries) will deform about eight orders of magnitude more rapidly than old, cold lithosphere in the interior of plates.

Book chapter↗
USGS1996

Inelastic models of lithospheric stress - I. Theory and application to outer-rise plate deformation

Outer-rise stress distributions determined in the manner that mechanical engineers evaluate inelastic stress distributions within conventional materials are contrasted with those predicted using simple elastic-plate models that are frequently encountered in studies of outer-rise seismicity. This comparison indicates that the latter are inherently inappropriate for studies of intraplate earthquakes, which are a direct manifestation of lithospheric inelasticity. We demonstrate that the common practice of truncating elastically superimposed stress profiles so that they are not permitted to exceed laboratory-based estimates of lithospheric yield strength will result in an accurate characterization of lithospheric stress only under relatively restrictive circumstances. In contrast to elastic-plate models, which predict that lithospheric stress distributions depend exclusively upon the current load, inelastic plate models predict that stress distributions are also significantly influenced by the plate-loading history, and, in many cases, this influence is the dominant factor in determining the style of potential seismicity (e.g. thrust versus normal faulting). Numerous ‘intuitive’ interpretations of outer-rise earthquakes have been founded upon the implicit assumption that a unique relationship exists between a specified combination of plate curvature and in-plane force, and the resulting lithospheric stress distribution. We demonstrate that the profound influence of deformation history often invalidates such interpretations. Finally, we examine the reliability of ‘yield envelope’ representations of lithospheric strength that are constructed on the basis of empirically determined frictional sliding relationships and silicate plastic-flow laws. Although representations of this nature underestimate the strength of some major interplate faults, such as the San Andreas, they appear to represent a reliable characterization of the strength of intraplate oceanic lithosphere.

Geophysical Journal International↗
USGS2008

Temporal evolution of continental lithospheric strength in actively deforming regions

It has been agreed for nearly a century that a strong, load-bearing outer layer of earth is required to support mountain ranges, transmit stresses to deform active regions and store elastic strain to generate earthquakes. However the dept and extent of this strong layer remain controversial. Here we use a variety of observations to infer the distribution of lithospheric strength in the active western United States from seismic to steady-state time scales. We use evidence from post-seismic transient and earthquake cycle deformation reservoir loading glacio-isostatic adjustment, and lithosphere isostatic adjustment to large surface and subsurface loads. The nearly perfectly elastic behavior of Earth's crust and mantle at the time scale of seismic wave propagation evolves to that of a strong, elastic crust and weak, ductile upper mantle lithosphere at both earthquake cycle (EC, ???10?? to 103 yr) and glacio-isostatic adjustment (GIA, ???103 to 104 yr) time scales. Topography and gravity field correlations indicate that lithosphere isostatic adjustment (LIA) on ???106-107 yr time scales occurs with most lithospheric stress supported by an upper crust overlying a much weaker ductile subtrate. These comparisons suggest that the upper mantle lithosphere is weaker than the crust at all time scales longer than seismic. In contrast, the lower crust has a chameleon-like behavior, strong at EC and GIA time scales and weak for LIA and steady-state deformation processes. The lower crust might even take on a third identity in regions of rapid crustal extension or continental collision, where anomalously high temperatures may lead to large-scale ductile flow in a lower crustal layer that is locally weaker than the upper mantle. Modeling of lithospheric processes in active regions thus cannot use a one-size-fits-all prescription of rheological layering (relation between applied stress and deformation as a function of depth) but must be tailored to the time scale and tectonic setting of the process being investigated.

GSA Today↗
USGS2006

Deep Europe today: Geophysical synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga

We present a summary of geophysical models of the subcrustal lithosphere of Europe. This includes the results from seismic (reflection and refraction profiles, P- and S-wave tomography, mantle anisotropy), gravity, thermal, electromagnetic, elastic and petrological studies of the lithospheric mantle. We discuss major tectonic processes as reflected in the lithospheric structure of Europe, from Precambrian terrane accretion and subduction to Phanerozoic rifting, volcanism, subduction and continent-continent collision. The differences in the lithospheric structure of Precambrian and Phanerozoic Europe, as illustrated by a comparative analysis of different geophysical data, are shown to have both a compositional and a thermal origin. We propose an integrated model of physical properties of the European subcrustal lithosphere, with emphasis on the depth intervals around 150 and 250 km. At these depths, seismic velocity models, constrained by body-and surface-wave continent-scale tomography, are compared with mantle temperatures and mantle gravity anomalies. This comparison provides a framework for discussion of the physical or chemical origin of the major lithospheric anomalies and their relation to large-scale tectonic processes, which have formed the present lithosphere of Europe. ?? The Geological Society of London 2006.

Geological Society Memoir↗
USGS2002

34 - State of stress in the Earth's lithosphere

The state of stress in the lithosphere is the result of the forces acting upon and within it. Knowledge of the magnitude and distribution of these forces can be combined with mechanical, thermal and rheological constraints to examine a broad range of lithospheric deformational processes. For example, such knowledge contributes to a better understanding of the processes that both drive and inhibit lithospheric plate motions as well as the forces responsible for the occurrence of crustal earthquakes − both along plate boundaries and in intraplate regions. Although the topic of this chapter is the state of stress in the Earth's lithosphere, the comments below come primarily from the perspective of the state of stress in the brittle upper crust. As defined by the depth of shallow earthquakes, the brittle crust extends to ˜15–20 km depth at most continental locations around the world. This perspective is adopted here because nearly all the data available on lithospheric stress come from the upper crust of continents. Furthermore, in the sections that follow, we argue that, to first order, the state of stress in the brittle crust results from relatively large-scale lithospheric processes so that knowledge of crustal stress can be used to constrain the forces involved in these processes.

International Geophysics↗
USGS2022

Quantifying permanent uplift due to lithosphere-hotspot interaction

Vertical motions that accompany the passage of the lithosphere over a mantle hotspot can shed light on the nature of the hotspot and its effect on the lithosphere. However, quantifying the temporal vertical and spatial extent, is challenging due to the paucity of evidence in the geological record. Here, we utilize dense seismic and well data covering the intersection of the Great Meteor Hotspot (GMH) track with the U.S. Atlantic continental margin to constrain the surface expression of the hotspot passage under the lithosphere. The continuous sedimentary record of the eastern North American margin during its passage over the hotspot allows determination of the timing, magnitude, width and rate of denudation. We find that a ∼300 km wide region was denuded by up to 850 m between ∼97 and 86 Ma, ∼10 m.y. after the passage of the GMH. Stratigraphic relationships suggest a decaying rock uplift rate with time and no subsequent sagging. The broad, long-lasting, and delayed uplift was modeled as a surface manifestation of either sub-lithospheric mantle depletion, permanently eroded base of the continental lithosphere, or intrusions of depleted magma. We consider sub-lithospheric depletion to be the most likely cause, based on seismic imaging results.

Tectonics↗
USGS2012

Tectonic stresses in the lithosphere: constraints provided by the experimental deformation of rocks.

The strengths of rocks clearly place an upper limit on the stress that can be sustained by the upper half of the lithosphere. Laboratory data on rock rheology are generally lacking at intermediate temperatures and pressures on the important rock types expected in the lithosphere, so a definitive accounting of the strength distribution with depth in the upper lithosphere is presently unattainable. Analogies are drawn between the fragmentary strength data on silicates at intermediate temperature and the more extensive experimental data on marble and limestone, and several tentative conclusions are drawn: First, brittle processes, such as faulting and cataclasis, are expected to control rock strength at low pressures and temperatures. The strengths associated with these brittle mechanisms increase rapidly with increasing effective pressure and are relatively insensitive to temperature and strain rate. Second, the transitions between brittle and ductile processes occur at critical values of the least principal stress σ 3 . I suggest that the concept of the deformation mechanism map of Ashby (1972) be extended to brittle-ductile transitions by normalizing the applied differential stress σ by σ 3 , i.e., the transitions occur at critical values of σ/σ 3 . Third, the high temperature flow law of olivine, widely applied to problems involving flow in the asthenosphere, is inappropriate to the conditions of temperature found in the lithosphere, because different dislocation flow mechanisms dominate at low to intermediate temperatures. The fragmentary rheological data suggest the following rheological structure of the lithosphere where it is inelastically deforming: A rapid pressure-driven increase in rock strength with depth culminates with a shear strength maximum of up to 8 kbar at depths that depend on the state of stress and on the temperature distribution. A review of the mechanisms of weakening associated with water suggests that water weakening effects are probably not important in the oceanic lithosphere but are likely to be controlling in the continental crust.

Journal of Geophysical Research Solid Earth↗