Paleostress Data Research Articles

Neogene block rotation inside the dextral fault zone at the Adriatic-European collision zone: Reexamination of existing results

The study focused on the post-Middle-Miocene stress analysis within the dextral strike-slip zone of the Dinaric fault system in the collision zone between the European plate, the Adria microplate and the Pannonian Domain. Block rotations were studied by re-examination of available paleostress data and their spatial distribution. The results are in agreement with the existing block model of the area, indicating CCW rotations within blocks between the main strike-slip faults in which rotation angle increases from E to W. The improved kinematic model, which is proposed in this study, will contribute to the knowledge on the kinematics within the complex collision zones and improve the seismic hazard models.

New insights on the Neogene tectonic evolution of the Aksu Basin (SE Turkey) from the Anisotropy of Magnetic Susceptibility (AMS) and paleostress data

The junction between the Aegean and Cyprus arc in the southern Turkey forms a triangular-shaped morphological structure so-called Isparta Angle (IA). In Neogene time, the inner part of the Isparta Angle became overlain by sedimentary basins including Manavgat, Köprüçay and Aksu, characterized by marine clastics and carbonates.Aksu Basin, one of these marine basins, provides geological records about the Neogene crustal deformation and stress field in the Eastern Mediterranean region. Therefore, we kinematically assess if and when tectonic stress fields affected the Aksu basin in early Miocene to recent times. For this purpose, Anisotropy of Magnetic Susceptibility (AMS) data (AMS) of cored samples and fault-slip data from the brittle mesoscopic faults were collected. The ~490 oriented samples for Anisotropy of Magnetic Susceptibility measurements were analyzed and two different maximum magnetic lineation's directions are recognized; 1) N–S magnetic lineation in Pliocene and 2) from N–S to NW-SE magnetic lineation in the Miocene. The results inferred from more than 1000 fault-slip data collected from 83 different sites combined with AMS results demonstrate that the Aksu Basin developed under four different tectonic phases; 1) ~E-W extensional phase (related to basin formation), 2) ~N–S compressional (Lycian) phase, 3) ~(N)E-(S)W compressional (Aksu) phase and 4) N–S extensional (Recent) phase.

Structural Control on the Salmas Geothermal Region, Northwest Iran, from Fractal Analysis and Paleostress Data

AbstractThe Salmas geothermal field is located in NW Iran. Subduction of Neo‐Tethys oceanic crust beneath the Iranian microcontinent caused to propagation of the magmatic‐Arc. Fractures and faults in the convergent zone have created path‐ways for the circulation of geothermal fluid. Fracture concentration in the Salmas geothermal field has been characterized using of the fractal method and creation of a fracture density map that shows the highest concentration in the central part of the study area. The permeability of fractures has been evaluated by analyzing their orientation in respect to the paleostress axes. Also, the fractal analyzing result indicates the maximum fractal dimension (1.96) is around the thermal spring outlet. Paleostress analyzing revealed that in the central part of the study area, σ1 axes orientation is S90°W/10° and the σ2 dip is near to the vertical in this stress field, where strike slip faults can be propagated. In the SE part near the recharge of the thermal springs, the σ3 plunge increases to 70° and σ1 orientation is N15°E/20°, in this local tectonic regime thrust fault developed. Fractures have an important role in the circulation of fluid and the fractal dimension increases near the thermal springs in the Salmas geothermal field. Regarding the paleostress data fracture with N‐S direction such as the F1 fault zone (parallel to the σ1 axes), a suitable pathway for deep circulation of geothermal fluid flow has been created.

Kinematics of the Havran-Balıkesir Fault Zone and its implication on geodynamic evolution of the Southern Marmara Region, NW Anatolia

ABSTRACTCenozoic convergence, collision and subsequent subduction between African and Eurasian plates are accommodating in overriding Eurasian plate both forming the Aegean extension and the North & East Anatolian fault zones. To understand the kinematic evolution of upper crust, here we provide new paleostress data from the Havran-Balıkesir Fault Zone located at the interaction area between the North Anatolian Fault Zone (NAFZ) and west Anatolian extensional structures. Paleostress reconstructions of fault-slip data reveal that three distinct deformation phases have been experienced in the region. Phase 1 is represented by left-lateral strike-slip faulting with reverse component in the pre-Pliocene period. The Phase 2 is characterized by approximately N–S trending contraction and associated E–W trending extension in Plio–Quaternary, which is spatiotemporally linked to the initiation of NAFZ through the area. The youngest deformation, Phase 3 is attributed to NE–SW trending extension and NW-SE-trending contraction commenced by the Quaternary transpressional tectonics in Southern Marmara Region. These results show that the main contraction axes have been experienced a spectacular anticlockwise rotation (from NW-SE to E-W), which is associated with; (i)the propagation geometry of the NAFZ into the region (ii)slab roll-back and retreat and tearing process on the Aegean subduction system, and (iii)the existence of inherited structures of the İzmir-Balıkesir Transfer Zone.

Neogene to Present paleostress field in Eastern Iran (Sistan belt) and implications for regional geodynamics

We conducted a stress field analysis of the northern part of the~700 km long north-south trending, seismically active Sistan orogenic belt of Eastern Iran formed as a result of the closure of a branch of the Neo-Tethys during the early Cenozoic. Fault kinematic data reveal drastic changes in the stress regime of Eastern Iran during the late Cenozoic, with three successive directions of compression (σ 1), from 90°N during the middle-late Miocene to 60°N during the late Pliocene and 25°N during the Plio-Quaternary, thereby evidencing a counterclockwise rotation of about 65°of σ 1 in less than 10 Myr. As shown by compilation of paleostress data, Plio-Quaternary direction of compression in Sistan coincides with the one recorded across the whole of Iran and with present-day Arabia-Eurasia convergence direction. This result suggests effective stress transfer from the Zagros collision and that Sistan is at present mechanically coupled and shortened along with the rest of the Iranian crust/lithosphere. By contrast, Miocene compression is markedly different in the Iranian hinterland (e.g., Sistan, Central Iran, and Kopet Dagh) and in the Zagros orogen. This could tentatively be related to the end of Sistan collision and/or to the imprint of active deformation occurring further to the east. The intermediate late Pliocene compression (i.e., 60°N) could correspond to the progressive reorientation of the stress regime, as Sistan gets mechanically coupled to the Zagros collision.

The effective stress law at a brittle‐plastic transition with a halite gouge layer

AbstractWe investigated the effect of pore pressure Pf near the brittle‐plastic transition (BPT) for a halite (NaCl) shear zone. Our series of precut friction experiments with a gas‐medium apparatus with temperature T ≤ 200°C, confining gas pressure Pc ≤ 150 MPa and Pf ≤ 140 MPa, revealed that a tanh connection between the brittle and plastic regimes works well even at elevated Pf, with a coefficient for Pf in an effective stress law α being unity. Plastic deformation around the real contacts independent of the mean stress results in α = 1 regardless of the ratio of the real contact area Ar/A. The functional dependency of the shear strength on the effective normal stress may deviate from a linear dependency with increasing Ar/A. The present findings support a smooth transition in a hypothetical steady state strength profile around a BPT, providing new insights in geologically obtained paleostress data in exhumed mylonitic shear zones.

Basin evolution in a folding lithosphere: Altai–Sayan and Tien Shan belts in Central Asia

Central Asia is a classical example for continental lithospheric folding. In particular, the Altay–Sayan belt in South-Siberia and the Kyrgyz Tien Shan display a special mode of lithospheric deformation, involving decoupled lithospheric mantle folding and upper crustal folding and faulting. Both areas have a heterogenous crust with a long history of accretion–collision, subsequently reactivated as a far-field effect of the Indian–Eurasian collision. Thanks to the youthfulness of the tectonic deformation in this region (peak deformation in late Pliocene–early Pleistocene), the surface expression of lithospheric deformation is well documented by the surface topography and superficial tectonic structures. A review of the paleostress data and tectono-stratigraphic evolution of the Kurai-Chuya basin in Siberian Altai, Zaisan basin in Kazakh South Altai and Issyk-Kul basin in Kyrgyz Tien Shan suggests that they were initiated in an extensional context and inverted by a combination of fault-controlled deformation and flexural folding. In these basins, fault-controlled deformation alone appears largely insufficient to explain their architecture. Lithospheric buckling inducing surface tilting, uplift and subsidence also played an important role. They form typical basins in a folding lithosphere (FLB). Their characteristic basin fill and symmetry, inner structure, folding wavelength and amplitude, thermal regime, time frame are examined in relation to basement structure, stress field, strain rate, timing of deformation, and compared to existing modelling results.

Active faulting and neotectonics in the Baelo Claudia area, Campo de Gibraltar (southern Spain)

The Strait of Gibraltar area is part of the western Eurasian-African convergence zone characterized by a complex pattern of deformation, including thrusting and folding and active normal faulting. Generally, the area is of low-seismicity; only some minor earthquakes have been recorded in the last hundred years. Archaeoseismological data evidences earthquake destruction occurring twice during Roman times. A better neotectonic framework and knowledge on the paleostress evolution of the Strait of Gibraltar area is necessary to find the local sources for those events and to establish an understanding of the recent deformation.Paleoseismic evidence for one moderate earthquake event around 6000-5000 BP along the normal Carrizales Fault is described in this paper. Off-shore high-resolution seismic investigations, structural and paleostress data, high-resolution GPR and geoelectrical resistivity measurements, outcrop investigations and trenching studies are discussed. The data reveal that active faulting takes place along N–S trending normal faults. Hence, N–S directed normal faults in the area are claimed as local candidates for moderate earthquake activity. Return periods of moderate earthquakes in the order of at least 2000–2500years in the study area may have to be taken into account. Structural data, such a paleostress data and joints are presented and a deformation history for the Strait of Gibraltar area in southern Spain is developed in this study.

Recurring extensional and strike-slip tectonics after the Neoproterozoic collisional events in the southern Mantiqueira province

In Eastern South America, a series of fault-bounded sedimentary basins that crop out from Southern Uruguay to Southeastern Brazil were formed after the main collisional deformation of the Brasiliano Orogeny and record the tectonic events that affected the region from the Middle Ediacaran onwards. We address the problem of discerning the basin-forming tectonics from the later deformational events through paleostress analysis of more than 600 fault-slip data, mainly from the Camaquã Basin (Southern Brazil), sorted by stratigraphic level and cross-cutting relationships of superposed striations, and integrated with available stratigraphic and geochronological data. Our results show that the Camaquã Basin was formed by at least two distinct extensional events, and that rapid paleostress changes took place in the region a few tens of million years after the major collision (c.a. 630 Ma), probably due to the interplay between local active extensional tectonics and the distal effects of the continued amalgamation of plates and terranes at the margins of the still-forming Gondwana Plate. Preliminary paleostress data from the Castro Basin and published data from the Itajaí Basin suggest that these events had a regional nature.

Recurrent Cenozoic volcanic activity in the Bohemian Massif (Czech Republic)

Cenozoic anorogenic volcanism of the Bohemian Massif is an integral part of the Central European Volcanic Province. The temporal and spatial distribution of volcanic rocks in the Bohemian Massif, their geochemistry and mineralogy as well as their tectonic setting and paleostress data are used to characterize and classify this volcanic activity. Three main volcanic periods can be distinguished based on K–Ar data and known paleostress fields: (i) pre-rift (79–49 Ma), (ii) syn-rift (42–16 Ma) and (iii) late-rift (16–0.3 Ma), with the youngest period further subdivided into three episodes. The dominant mafic rock types (> 7 wt.% MgO) of all periods are of nephelinite–basanite/tephrite composition. The exceptions are suites of melilitic ultramafic rocks of the pre-rift period in northern Bohemia and of the final episode of the late-rift period in western Bohemia. The most voluminous are volcanic rocks of the syn-rift period occurring in the Ohře Rift Graben. The initial 87Sr/ 86Sr (0.7032 to 0.7050) and 143Nd/ 144Nd (0.51264 to 0.51301) ratios of the mafic volcanic rocks of the Bohemian Massif are characteristic of magmas derived from a sub-lithospheric mantle source. The isotopic ratios resemble those of the HIMU mantle source ( 206Pb/ 204Pb ca. 19 to 20). These rocks have the most isotopically depleted compositions among the Central European Volcanic Province volcanics.

Characteristics of Magnetic Fabrics in Western Segment of the Altun Fault Belt and Its Tectonic Significance

AbstractThe parameters of magnetic fabric of deformed rocks such as Kmax,Kint,Kmin, P, T, F,L and E can be used to quantitatively display the behaviors and stages of tectonic deformation. Characteristics of magnetic fabrics in the west segment of Altun fault belt (from Guozhacuo to Kongkashankou) were analyzed in this investigation. These characteristics suggest that the segment had undergone multiple stages of mobility, and the deformation feature had experienced a successive transformation from ductile, to ductile‐brittle and to brittle deformation. Stress mechanisms are indicative of shear, stretch and compress with shear. The direction of principal stress is NNE‐SSW and approximately S‐N. The fabric characteristics of the minimum magnetic susceptibility axis (Kmin) are different between the two blocks of the strike‐slip fault, and in different areas they have different movement vectors. Sinistral strike slip is proved to be the main movement style of the Altun fault belt. Magnetic fabric data also indicate that the Altun fault belt has the character of semi‐symmetry with the most intensive deformation in the middle, and a gradual decreasing towards both sides, showing that the deformation during the early period gradually decreased from east to west along the strike‐slip fault belt. The stress, strain and the character of deformation revealed by magnetic fabrics are consistent with field features, microstructure and paleostress data.

Comparison of paleostress magnitudes from calcite twins with contemporary stress magnitudes and frictional sliding criteria in the continental crust: Mechanical implications

The evolution with depth of paleo-differential stress magnitudes (mostly derived from calcite twinning paleopiezometry) in various tectonic settings is compared to the modern differential stress/depth gradients deduced from in situ measurements. Despite dispersion, both independent sets of stress data support to a first-order that the strength of the continental crust down to the brittle-ductile transition is generally controlled by frictional sliding on well-oriented pre-existing faults with frictional coefficients of 0.6–0.9 under hydrostatic fluid pressure. Some ductile mechanisms may, however, relieve stress and keep stress level beyond the frictional yield, as for instance in the detached cover of forelands. The main conclusion is that despite inherent differences, contemporary stress and paleostress data can be combined to bring useful information on the strength and mechanical behaviour of the upper continental crust over times scales of several tens of Ma.

Kinematic and structural development of the Çankiri Basin (Central Anatolia, Turkey): a paleostress inversion study

Three different deformation phases have been recognized in the southern part of the Çankırı Basin from (1) the major structures and (2) through using paleostress inversion techniques for fault slip data. The deformation phases recognized from the paleostress data are correlated with those recognized from the major structures and dated accordingly. The first phase occurred in the Late Paleocene to pre-Burdigalian and is characterized by an oblique σ2 and NNE–SSW to NE–SW trending subhorizontal σ1 and WNW–ESE to NW–SE trending σ3 patterns which indicate transcurrent deformation associated with a combination of thrusting and strike slip faulting (transpression) possibly due to indentation of the Kırşehir Block to the Sakarya Continent. The second phase occurred from the Burdigalian to the Serravallian and is characterized by a subvertical σ1 and oblique σ2 and σ3, which indicate oblique extension associated with normal faulting possibly due to a post-orogenic collapse. The third deformation phase is characterized by a vertical σ2 while the other stresses were horizontal, which indicate regional transcurrent tectonics, which is correlated with the current transcurrent tectonics controlled by the North Anatolian Fault Zone.

Tectonic evolution of the northern African margin in Tunisia from paleostress data and sedimentary record

A reconstruction of the tectonic evolution of the northern African margin in Tunisia since the Late Permian combining paleostress, tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns. The extension lasting from the Late Permian to the Middle Triassic is contemporaneous of the rifting related to the break up of Pangea. During Liassic times, regional extensional tectonics originated the dislocation of the initial continental platform. In northern Tunisia, the evolution of the Liassic NE–SW rifting led during Dogger times to the North African passive continental margin, whereas in southern Tunisia, a N–S extension, associated with E–W trending subsiding basins, lasted from the Jurassic until the Early Cretaceous. After an Upper Aptian–Early Albian transpressional event, NE–SW to ENE–WSW trending extensions prevailed during Late Cretaceous in relationship with the general tectonic evolution of the northeastern African plate. The inversions started in the Late Maastrichtian–Paleocene in northern Tunisia, probably as a consequence of the Africa–Eurasia convergence. Two major NW–SE trending compressions occurred in the Late Eocene and in the Middle–Late Miocene alternating with extensional periods in the Eocene, Oligocene, Early–Middle Miocene and Pliocene. The latter compressional event led to the complete inversion of the basins of the northwestern African plate, originating the Maghrebide chain. Such a study, supported by a high density of paleostress data and including complementary structural and stratigraphic approaches, provides a reliable way of determining the regional tectonic evolution.

The origin of intraplate deformation in the Atlas system of western and central Algeria: from Jurassic rifting to Cenozoic–Quaternary inversion

Analysis of petroleum exploration data supplemented by paleostress data enabled discussion of the origin of the deformation in the western and central Saharan Atlas (Algeria). This intraplate area has recorded the breakup of Pangea (Late Triassic), the opening of the Maghrebian Tethys (since the Dogger) and subsequently its closure (Oligocene to Present). However, the two periods of strong coupling between Europe and Africa (late Lutetian and Pleistocene), which correspond to rapid uplifts of the Atlas system and important deformations, are not collision-related. They can be correlated to the beginning and the end of the development of the western Mediterranean Sea.

Phanerozoic tectonothermal history of the Arabian–Nubian shield in the Eastern Desert of Egypt: evidence from fission track and paleostress data

To constrain the post-Pan-African evolution of the Arabian–Nubian Shield, macro-scale tectonic studies, paleostress and fission track data were performed in the Eastern Desert of Egypt. The results provide insights into the processes driving late stage vertical motion and the timing of exhumation of a large shield area. Results of apatite, zircon and sphene fission track analyses from the Neoproterozoic basement indicate two major episodes of exhumation. Sphene and zircon fission track data range from 339 to 410 Ma and from 315 to 366 Ma, respectively. The data are interpreted to represent an intraplate thermotectonic episode during the Late Devonian–Early Carboniferous. At that time, the intraplate stresses responsible for deformation, uplift and erosion, were induced by the collision of Gondwana with Laurussia which started in Late Devonian times. Apatite fission track data indicate that the second cooling phase started in Oligocene and was related to extension, flank uplift and erosion along the actual margin of the Red Sea. Structural data collected from Neoproterozoic basement, Late Cretaceous and Tertiary sedimentary cover suggest two stages of rift formation. (1) Cretaceous strike-slip tectonics with sub-horizontal σ1 (ENE/WSW) and σ3 (NNW/SSE), and sub-vertical σ2 resulted in formation of small pull-apart basins. Basin axes are parallel to the trend of Pan-African structural elements which acted as stress guides. (2) During Oligocene to Miocene the stress field changed towards horizontal NE–SW extension (σ3), and sub-vertical σ1. Relations between structures, depositional ages of sediments and apatite fission track data indicate that the initiation of rift flank uplift, erosion and plate deformation occurred nearly simultaneously.

Recent tectonic evolution and present stress in the Northern Apennines (Italy)

The present‐day stress field and its recent tectonic evolution in the Northern Apennines are reconstructed from borehole breakout analysis and focal mechanisms of crustal earthquakes and through the comparison with paleostress data. We have considered 86 wells for breakout analysis, with depths down to 6–7 km, 125 fault plane solutions of crustal earthquakes with M<5 that occurred between 1988 and 1995 in the Northern and Central Apennines, and data of stronger earthquakes (M≤6) reported in other studies. The Tyrrhenian coastal region and the Apenninic belt are characterized by Shmin direction mainly trending NE–SW, with predominantly normal fault plane solutions. Along the outer front of the belt and the Adriatic offshore, Shmin is oriented NW–SE, and focal solutions are thrust or strike‐slip, with maximum compression around NE–SW. Conversely, south of 43°N, breakouts evidence an orthogonal direction of horizontal compression (NW–SE), following the Southern Apennine trend, where a widespread NE–SW extension was recognized by previous investigations. Comparing these results to the recent tectonic evolution inferred from structural geology, we argue that the extension‐compression pair, characteristic of the post‐Tortonian evolution of the mountain belt, has been migrating in time from late Miocene to Present only in the northern sector of the arc, whereas the southern sector underwent a generalized extension, at least since middle Pleistocene. The striking correspondence between the active compression front and the region with evidence of a remnant subducted slab suggests that the migrating extension‐compression pair has been controlled by progressive retreat of the slab.

Far‐field effects of Late Miocene subduction in the Eastern Carpathians: E‐W compression and inversion of structures in the Alpine‐Carpathian‐Pannonian region

Kinematic and paleostress data constrain a Late Miocene E‐W compressional event that affected the entire Alpine‐Carpathian‐Pannonian system after 9 Ma and prior to 5.3 Ma. The maximum horizontal compression directions obtained from 110 stations show a mean σ1 orientation of 083°. Deformation is mainly strike‐slip. E‐W directed compression followed Early to Middle Miocene upper plate extension in the Pannonian Basin which was caused by the retreating subduction boundary in the outer Carpathians. This compressional event terminated Early to Middle Miocene eastward lateral extrusion of the Eastern Alps and reverted strike‐slip faults which bounded earlier extruded wedges such as the Salzachtal‐Ennstal fault, the Periadriatic fault, the Mur‐Mürz‐Vienna Basin fault system, and strike‐slip faults in the Western Carpathians. E‐W compression caused the reorientation of the extension direction of the Alpine crustal stack. East‐directed tectonic unroofing of the metamorphic domes in the central Eastern Alps terminated between 9 and 6 Ma and Early to Middle Miocene orogen‐parallel E‐W extension switched to Late Miocene N‐S extension which parallels modern topographic slopes. In the Pannonian Basin the change from synrift extension to Late Miocene compression during the postrift phase caused the pronounced postrift subsidence by stress induced downward flexure of the loaded lithosphere.We relate Late Miocene E‐W compression to coeval late‐stage west‐ directed subduction of the European plate below the Eastern Carpathians. Slab pull of the subducted plate caused subduction roll back and upper plate extension of the Pannonian area up to the Middle Miocene. Subduction slowed down and ceased when up to 60‐km‐thick buoyant continental crust entered the subduction zone. During the short period of continued convergence E‐W ‐directed compressive stress was transmitted across the subduction boundary into the upper plate. Compressive stress was transferred through the uppermost brittle crust of the earlier extended Pannonian region into the Eastern Alps, up to 1400 km behind the subduction zone. E‐W compression terminated during the Pliocene when the Pliocene to recent NNW‐SSE compressive stress field was established in Central Europe.

Compositional changes in Trans‐Pecos Texas Magmatism Coincident with Cenozoic stress realignment

The composition and inferred sources of Cenozoic magmas in Trans‐Pecos Texas changed abruptly between 32 and 28 Ma, coincident with a fundamental change in stress regime. Magmas emplaced between 48 and 32 Ma comprise extended differentiation suites beginning with relatively evolved basaltic magmas. These rocks have low Nb and Ta compared to Zr, Hf, La, Ba, and K, characteristics typical of continental volcanic arcs. However, the Texas rocks are more alkalic, have higher concentrations of incompatible elements, and have higher ratios of Nb and Ta to Zr, Hf, La, Ba, and K than is typical of rocks from arcs near trenches. These differences reflect relative position within the Cordilleran arc. Trace element models involving partial melting in the mantle wedge combined with fractional crystallization and assimilation of upper and lower crust can account for most of the observed trace element concentrations and ratios. Trans‐Pecos magmatism may have involved smaller degrees of partial melting than is typical of arcs located closer to the subduction zone. Magmas emplaced after 31 Ma were either bimodal, alkali basalt‐rhyolite, or exclusively basaltic. They have high absolute abundances of incompatible trace elements and high ratios of Nb and Ta to Zr, Hf, La, Ba, and K. The mafic rocks are typical of continental rift or ocean island basalts. Trace element models using Nb, Ta, Y, Yb, Hf, and Zr reproduce the range of concentrations and ratios observed in these rocks and require very small degrees of partial melting, variable amounts of fractional crystallization, but little or no assimilation. The change in magma compositions and sources is best illustrated by a drop in Zr/Nb, from between 18 and 6.25 in the earlier, arc rocks to between 6.25 and 2 in the later, rift‐related rocks. Stress regime appears to play an important role in the process of magma generation and evolution. The change in trace element compositions indicative of tectonic setting supports interpretations of paleostress data that activity up to 31 Ma occurred in a continental volcanic arc, whereas later activity occurred in a setting of intraplate extension. The magmatic change may have been simultaneous with the change in stress regime or may have lagged by as much as 3–4 m.y.

Stress history during propagation of a lateral fold-tip and implications for the mechanics of fold-thrust belts

This paper evaluates the hypothesis of lateral propagation of fold-tip lines by comparing paleostress data from the lateral tip of a natural fold with a theoretical stress history at a moving screw dislocation. The fold is an asymmetric kink fold exposed in Ogden Canyon, Utah, where mapping revealed that a cylindrical anticline-syncline pair changes along strike into a noncylindrical termination. Quartz deformation lamellae data from this fold indicate that the stress history in the fold tip was relatively simple with a general pattern of layer parallel compression perpendicular to the fold axis and layer parallel extension subparallel to the fold hinge line. In contrast, data from the cylindrical part of the fold are complex, regardless of the position within the fold. The latter is significant because although the symmetry of the cylindrical fold implies a plane-strain deformation, the paleostress data indicate that the strains were actually three-dimensional; an observation that is easily explained if the fold propagated laterally (along strike) during fold growth. To test this hypothesis, we consider a simple stress model where the non-cylindrical fold-tip is treated as a moving screw dislocation. We conclude that although a broad range of models are allowable, this simple model can account for most of the complexities of the data. Thus, we conclude that the fold has propagated laterally during its growth. Recent studies of two fold-related earthquake series (the 1980 El Asnam earthquake and the 1983 Coalinga sequence) lend support to models that call on lateral propagation of fault-related folds. Thus, these active fold-thrust systems as well as our study of an ancient system are consistent with the concept that folding is a three-dimensional process rather than a simple plane-strain deformation. Clearly, further word is needed to thoroughly test the fold-propagation models. Nonetheless, the recognition of lateral propagation of folds is important because it supports Elliot's “macroscopic creep” concept for development of fold-thrust belts where propagation of fracture tip-lines is a least-work process analogous to dislocation creep in crystals.