Deep crustal structure: Implications for continental evolution

Brown, L. D.; Oliver, Jack; Kaufman, S.; Brewer, J. A.; Cook, Frederick A.; Schilt, F. Steve; Albaugh, D. S.; Long, G.

doi:10.1029/gd005p0038

Cited by 7 publications

(5 citation statements)

References 42 publications

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“…It should be clearly stated that crustal lamellae, as defined in the introduction have a widespread appearance in all BIRPS and most DEKORP sections but have not yet been found in passive shield areas, where much of the COCORP data have been accumulated (Brown et al, 1981;Almendinger et al, 1987). Even in the massifs of the Variscan they are missing.…”

Section: Lower and Middle Crust; Lamellae And Crocodile4mentioning

confidence: 99%

“…They appear predominantly in young, warm, differentiated and mostly shallow crusts of Variscan Caledonian and younger extensional areas. The youngest tectonic province with huge extensional tectonics, the Basin and Range Province, shows (already) pronounced lower crustal lamellae on top of a shallow flat Moho (see Kaufman, 1988;Klemperer et al, 1986;Brown et al, 1981). Fig.…”

Section: Lower and Middle Crust; Lamellae And Crocodile4mentioning

confidence: 99%

“…Long time creep may smooth out sharp horizons in the lower-most crust. Even the Moho is generally hard to detect by near-vertical reflections (Brown et al, 1981;Wever, 1984;Almendinger et al, 1987). If it is seen at allas in the high-quality GLIMPCE sections (Behrendt et d., Fig.…”

Section: The Crust In Shield Areasmentioning

confidence: 99%

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Rupture, creep, lamellae and crocodiles: happenings in the continental crust

Meißner

1989

Terra Nova

119

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From the observation of certain seismic reflectivity patterns in Phanerozoic continental crusts a relationship is suggested between:(1) rupture and seismicity, generally restricted to the upper crust;(2) crocodile tectonics, a kind of vertical indentation, observed by diverging plane(3) creep and the formation of reflecting lamellae in the lower crust.Based on these observations and on viscosity depth estimates a conceptual model for the above-mentioned structures is presented, which is also compatible with observations in older crusts. Boundary conditions are given for rupture as well as for lamellae-forming creep.reflectors, preferably in the middle crust;

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Section: Lower and Middle Crust; Lamellae And Crocodile4mentioning

confidence: 99%

Section: Lower and Middle Crust; Lamellae And Crocodile4mentioning

confidence: 99%

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Rupture, creep, lamellae and crocodiles: happenings in the continental crust

Meißner

1989

Terra Nova

119

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“…This suggests that the entire Blue Ridge and Piedmont provinces constitute an allochthonous sheet, 6-15 km thick, thrust at least 250 km over an autochthonous Palaeozoic continental margin [Cook et al, 1979]. Thus mountain building may well be dominated by horizontal compressive forces [e.g., Rodgers, 1970;Brown et al, 1981]. Furthermore, present-day seismicity patterns I-Seeber and Armbruster, 1981] suggest that the ancient decollement surface may easily be reactivated by later plate readjustments.…”

Section: Tectonicsmentioning

confidence: 99%

Gravity anomalies and flexure of the lithosphere at mountain ranges

Karner¹,

Watts²

1983

J. Geophys. Res.

535

279

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The Bouguer gravity anomaly over the Himalayan, Alpine, and Appalachian mountains is characterized by a generally asymmetric gravity “low”, which spans the mountains and associated foreland basins. The minimum of the gravity “low” is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology. In addition, the Alps and Appalachians are associated with a generally symmetric gravity “high” that is unrelated to the topographic relief. Together the gravity low and high form a characteristic positive‐negative anomaly “couple”. The steep gravity gradient between the positive and negative couple correlates with the Insubric line and its equivalents in the Alps and the Brevard Zone in the southern Appalachians. This gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface (buried) and surface (topographic) loading. The magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography. By combining these loads the flexure of the lithosphere and the associated Bouguer gravity anomaly are calculated for different assumed values of the elastic thickness Te of continental lithosphere. The best fitting value of Te for the Himalayas is 80–100 km, for the Alps 25–50 km, and for the Appalachians 80–130 km. The model calculations suggest that the main contribution to the gravity couple in the Alps and Appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads. However, in the case of the Himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low. When subsurface loads do exist therefore, we would not expect a close correlation between mountain topographic relief and depth to the M discontinuity as required by classical models of isostasy. Rather, the M discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere. The surface and subsurface loads, inferred from the gravity anomaly, play a major role in the development of mountains and foreland basins. The emplacement of large subsurface loads represents the primary event in the Alps and Appalachians, while in the Himalayas the emplacement of the surface load is the primary event. The emplacement of the subsurface load probably marks the initiation of foreland basin development. The regional characteristics of the basin are controlled by the primary load, while local variations are controlled by the secondary, thrust sheet loads. Subsequent movement of either load will produce migration of the basin depocenter. The origin of the subsurface load is not clear, but its association with the insubric line in the Alps and the Brevard Zone in the Appalachians suggests that it may be related to the “obduction” of crustal blocks/flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of ...

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“…Murrell, 1976]. The two cases shown cover the probable case (granulites), which is of intermediate composition (e.g., see Brown et al [1981] and Berry and Fuchs [1973]). While the viscosity-depth profiles for all three stress levels in Figure 10 are based on the temperature profile for a basaltic (dolerite) lower crust [cfi Murrell, 1976], the temperature profile for granulites in the lower crust could be slightly lower.…”

Section: Plate Tectonic Stressmentioning

confidence: 99%

Upper crustal stresses and vertical stress migration in eastern Canada

Hasegawa¹,

Adams²,

Yamazaki³

1985

J. Geophys. Res.

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Diversified phenomena are contributing to our knowledge of various aspects of the stress field and the origin of the crustal stresses in eastern Canada. Both in situ stress measurements (to 2100 m) and earthquake fault plane solutions in the upper crust (• 5-20 km) indicate that the maximum horizontal stress is greater than the vertical. Absence of earthquakes in the lower crust (>20 km) implies a comparatively lower deviatoric horizontal stress in this layer. Stress directions as determined from both in situ measurements and earthquake fault plane solutions indicate an overprint confined to the ENE octant, which correlates with the direction predicted by modeling of plate tectonic stresses. Thus spreading (Mid-Atlantic) ridge stress is considered to be one of the important contributors to the stress field in eastern Canada. Viscoelastic relaxation of this stress is considered to enhance the deviatoric stress level in the upper crust, while simultaneously reducing that in the lower crust. The crust acts as a stress guide within which stresses in the upper crust that are lost through brittle failure (i.e., earthquake stress drop) can be replenished from the lower crust; moreover, the directionality predicted by modeling of spreading (Mid-Atlantic) ridge stress is maintained. Incomplete postglacial rebound also contributes to deviatoric compression. Other possible contributors to the upper crustal stress field are basal drag and membrane stress, but the relative contributions from these sources are not properly understood.

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Deep crustal structure: Implications for continental evolution

Cited by 7 publications

References 42 publications

Rupture, creep, lamellae and crocodiles: happenings in the continental crust

Rupture, creep, lamellae and crocodiles: happenings in the continental crust

Gravity anomalies and flexure of the lithosphere at mountain ranges

Upper crustal stresses and vertical stress migration in eastern Canada

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