Chains of basement uplifts within cratons marginal to orogenic belts

Rodgers, J.

doi:10.2475/ajs.287.7.661

Cited by 79 publications

(39 citation statements)

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“…Such thickening of the midcrustal layers presumably reflects the crustal thickening processes that are commonly associated with mountain building. These same processes are responsible for a contrast in [Rodgers, 1987].…”

Section: Discussionmentioning

confidence: 89%

Three‐dimensional velocity structure and earthquake locations beneath the northern Tien Shan of Kyrgyzstan, central Asia

Ghose¹,

Hamburger²,

Virieux³

1998

J. Geophys. Res.

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Abstract. We used the arrival times of local earthquakes and quarry blasts recorded by the Kyrgyzstan Broadband Network (KNET) to obtain three-dimensional (3-D) P and $ wave velocity models of the upper crust beneath an actively deforming mountain front and its associated foreland in the Kyrgyz Tien Shan. The continuous velocity models, described by cubic B spline interpolation of the squared slowness over a regular 3-D grid, were computed by simultaneous inversion of hypocenter and medium parameters. Exact ray tracing was done in the smooth 3-D medium by shooting rays from the sources to the stations by an analytical perturbation method based on the paraxial ray theory. The deduced large, sparse, linear system was solved using the damped, iterative, least squares algorithm LSQR. The stability and resolution of the result was qualitatively tested by two synthetic tests: the spike test and the checkerboard resolution test. We found that the models are well resolved up to a depth of -•27 km for most parts of our image domain. The P and $ wave velocity models are consistent with each other and provide evidence for marked heterogeneity in the upper crustal structure beneath the northern Tien Sham At shallower depths (< 7 km) the sediment-filled foreland is imaged as a relatively lower velocity feature compared to the mountains, which are cored by crystalline basement rocks. In contrast, at midcrustal depths the mountains are underlain by relatively lower velocity materials compared to the foreland. A distinct contrast in velocity structure is also observed between the eastern and western parts of the Kyrgyz Range at midcrustal depths, with the presence of relatively higher velocities toward the east. The seismicity is concentrated near the traces of major active faults and extends deeper beneath the foreland compared to the mountains. The regional compression in the Tien Shan is accommodated along a series of high-angle reverse faults distributed throughout the orogenic system that extend from the surface down to midcrustal depths. The range-bounding fault zone can be identified by a sharp lateral gradient in seismic velocities with a pronounced southward dip combined with a zone of seismicity that also deepens to the south and reverse fault source mechanisms from moderate-sized events. A pronounced low-velocity zone (LVZ) is imaged in the P wave field, at midcrustal depths, beneath the western part of the Kyrgyz Range. This LVZ is presumably correlatable with reported high-conductivity zones in this region that have been proposed to mark active fault zones along which fluid migration occurs. The location of the LVZ, which is closely coincident with the depth of maximum earthquake generation, might imply that it is a crustal decoupling zone at the brittle-ductile transition.

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Section: Discussionmentioning

confidence: 89%

Three‐dimensional velocity structure and earthquake locations beneath the northern Tien Shan of Kyrgyzstan, central Asia

Ghose¹,

Hamburger²,

Virieux³

1998

J. Geophys. Res.

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“…Intracontinental mountains such as the Atlas, the Palmyride Mountains of Syria, and the Tien Shan in central Asia are located at considerable distances inboard of their respective plate boundaries and commonly involve reactivated basement structures (e.g., Rodgers 1987;Letouzey 1990). They are further characterized by the absence of several diagnostic features present in typical interplate mountains, including nappe structures, ophiolites, regional metamorphism, and granitoid intrusions.…”

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confidence: 99%

Active tectonism in the intracontinental Middle Atlas Mountains of Morocco: synchronous crustal shortening and extension

Gomez

Barazangi

Bensaid

1996

JGS

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Geological field observations are integrated with digital topography, LANDSAT imagery, and earthquake focal mechanisms to investigate the Middle and Late Quaternary tectonism in the intracontinental Middle Atlas mountain belt in northern Morocco. The NE-SW-trending Middle Atlas Mountains, approximately 80 km in width and about 200 km long, are part of the Atlas system of northwestern Africa and represent an inverted rift that developed into an intracratonic mountain system in the foreland of the Alpine collisional zone. The Middle Atlas is composed of two provinces, the Folded and Tabular Middle Atlas, representing the palaeo-rift and a flank of the palaeo-rift, respectively. Evidence for Late Quaternary tectonism is provided by the analysis of stream morphology in addition to geological relations. Kinematic analysis of fault-slip data and earthquake focal mechanisms demonstrate the coexistence of both extensional and compressional deformation in different areas of the Middle Atlas with a common sinistral component of slip along NE-SW-striking fault zones. Compressional features dominate the Folded Middle Atlas, whereas extension predominates in the Tabular Middle Atlas. Extension is also manifested by widespread Middle to Late Quaternary alkali volcanism. The observed kinematic variations appear to correlate with the Mesozoic palaeogeography; one possible model may involve tectonic escape. This suggests that differences in the structures inherited from the Mesozoic and Palaeozoic may influence the responses of the different regions to the Cenozoic Alpine collision between Europe and northwest Africa.

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“…5A-C) [5]. Balancing and rheology considerations make such a gentle folding interpretation improbable [67], however, and we infer that the AntiAtlas basement uplifts must be associated with a series of major crustal scale reverse faults, supposedly in a Windriver-style well known in the foreland of the Rocky Mountains [67,76,94]. This uncommon proposal is illustrated in a section across the western tip of the Adrar Zouggar anticlinorium (Fig.…”

Section: The Anti-atlas Chain -What Kind Of Fold Belt?mentioning

confidence: 97%

“…On closer inspection, however, and in stark contrast to the frontal Appalachian chain, the AntiAtlas fold belt does not easily conform with the standard anatomy of foreland fold-and-thrust belts worldwide [77]. The most striking difference is the existence of major basement domes at a very short distance behind the deformation front [76]. Similarities exist with Wind River-style basement uplifts of the frontal Rocky Mountains, but in the Anti-Atlas, the basement uplifts occur amidst a tightly folded thick Palaeozoic cover series.…”

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confidence: 91%

Tectonics of the Anti-Atlas of Morocco

Burkhard

Caritg

Helg

et al. 2006

Comptes Rendus. Géoscience

142

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The Anti-Atlas is reviewed and examined in the light of its geodynamic significance as a Palaeozoic basin and fold belt. Shortening is accommodated by polyharmonic buckle folding of the cover in a thick-skinned fashion without the development of any significant thrust/duplex systems. The Anti-Atlas is heavily inverted deep intracratonic basin, rather than a former passive margin of the Palaeo-Tethys Ocean. Inversion took place in Late Carboniferous to Early Permian times. Main shortening directions changed from NW-SE to north-south and maybe NE-SW through time, leading to the development of dome and basin patterns on scales from 100 m to 10 km.

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Chains of basement uplifts within cratons marginal to orogenic belts

Cited by 79 publications

References 0 publications

Three‐dimensional velocity structure and earthquake locations beneath the northern Tien Shan of Kyrgyzstan, central Asia

Three‐dimensional velocity structure and earthquake locations beneath the northern Tien Shan of Kyrgyzstan, central Asia

Active tectonism in the intracontinental Middle Atlas Mountains of Morocco: synchronous crustal shortening and extension

Tectonics of the Anti-Atlas of Morocco

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