scholarly journals Supplemental Material: Quantifying shortening across the central Appalachian fold-thrust belt, Virginia and West Virginia, USA: Reconciling grain-, outcrop-, and map-scale shortening

2020 ◽  
Author(s):  
D. Lammie ◽  
et al.
Keyword(s):  
West Virginia ◽  
Finite Strain ◽  
Bedding Plane ◽  
Thrust Belt ◽  
Data Table ◽  
Strain Ellipsoid ◽  
Map Scale ◽  
Best Fit ◽  
Supplemental Data Table

Supplemental Data Table S1 contains axial ratios for the best-fit vacancy field (with statistics) of grain-scale bulk finite strain from the three mutually perpendicular cuts. Supplemental Data Table S2 contains orientations of the best-fit strain ellipsoid (with statistics) and ellipticity ratios and orientations on the bedding plane.

scholarly journals Supplemental Material: Quantifying shortening across the central Appalachian fold-thrust belt, Virginia and West Virginia, USA: Reconciling grain-, outcrop-, and map-scale shortening

2020 ◽  
Author(s):  
D. Lammie ◽  
et al.
Keyword(s):  
West Virginia ◽  
Finite Strain ◽  
Bedding Plane ◽  
Thrust Belt ◽  
Data Table ◽  
Strain Ellipsoid ◽  
Map Scale ◽  
Best Fit ◽  
Supplemental Data Table

Supplemental Data Table S1 contains axial ratios for the best-fit vacancy field (with statistics) of grain-scale bulk finite strain from the three mutually perpendicular cuts. Supplemental Data Table S2 contains orientations of the best-fit strain ellipsoid (with statistics) and ellipticity ratios and orientations on the bedding plane.

scholarly journals Quantifying shortening across the central Appalachian fold-thrust belt, Virginia and West Virginia, USA: Reconciling grain-, outcrop-, and map-scale shortening

Geosphere ◽  
2020 ◽  
Vol 16 (5) ◽  
pp. 1276-1292
Author(s):  
Daniel Lammie ◽  
Nadine McQuarrie ◽  
Peter B. Sak
Keyword(s):  
West Virginia ◽  
Cross Section ◽  
Middle Devonian ◽  
Finite Strain ◽  
Thrust Belt ◽  
Upper Ordovician ◽  
Appalachian Plateau ◽  
Central Appalachians ◽  
Oriented Samples ◽  
Valley And Ridge Province

Abstract We present a kinematic model for the evolution of the central Appalachian fold-thrust belt (eastern United States) along a transect through the western flank of the Pennsylvania salient. New map and strain data are used to construct a balanced geologic cross section spanning 274 km from the western Great Valley of Virginia northwest across the Burning Spring anticline to the undeformed foreland of the Appalachian Plateau of West Virginia. Forty (40) oriented samples and measurements of >300 joint orientations were collected from the Appalachian Plateau and Valley and Ridge province for grain-scale bulk finite strain analysis and paleo-stress reconstruction, respectively. The central Appalachian fold-thrust belt is characterized by a passive-roof duplex, and as such, the total shortening accommodated by the sequence above the roof thrust must equal the shortening accommodated within duplexes. Earlier attempts at balancing geologic cross sections through the central Appalachians have relied upon unquantified layer-parallel shortening (LPS) to reconcile the discrepancy in restored line lengths of the imbricated carbonate sequence and mainly folded cover strata. Independent measurement of grain-scale bulk finite strain on 40 oriented samples obtained along the transect yield a transect-wide average of 10% LPS with province-wide mean values of 12% and 9% LPS for the Appalachian Plateau and Valley and Ridge, respectively. These values are used to evaluate a balanced cross section, which shows a total shortening of 56 km (18%). Measured magnitudes of LPS are highly variable, as high as 17% in the Valley and Ridge and 23% on the Appalachian Plateau. In the Valley and Ridge province, the structures that accommodate shortening vary through the stratigraphic package. In the lower Paleozoic carbonate sequences, shortening is accommodated by fault repetition (duplexing) of stratigraphic layers. In the interval between the duplex (which repeats Cambrian through Upper Ordovician strata) and Middle Devonian and younger (Permian) strata that shortened through folding and LPS, there is a zone that is both folded and faulted. Across the Appalachian Plateau, slip is transferred from the Valley and Ridge passive-roof duplex to the Appalachian Plateau along the Wills Mountain thrust. This shortening is accommodated through faulting of Upper Ordovician to Lower Devonian strata and LPS and folding within the overlying Middle Devonian through Permian rocks. The significant difference between LPS strain (10%–12%) and cross section shortening estimates (18% shortening) highlights that shortening from major subsurface faults within the central Appalachians of West Virginia is not easily linked to shortening in surface folds. Depending on length scale over which the variability in LPS can be applied, LPS can accommodate 50% to 90% of the observed shortening; other mechanisms, such as outcrop-scale shortening, are required to balance the proposed model.

QUANTIFYING SHORTENING ACROSS THE CENTRAL APPALACHIAN FOLD-AND-THRUST BELT OF WEST VIRGINIA

2016 ◽  
Author(s):  
Daniel Benjamin Lammie ◽  
◽  
Peter B. Sak ◽  
Nadine McQuarrie
Keyword(s):  
West Virginia ◽  
Thrust Belt ◽  
Fold And Thrust Belt

QUANTIFICATION OF SHORTENING FOR BALANCED CROSS SECTIONS ACROSS THE CENTRAL APPALACHIAN FOLD-THRUST BELT OF PENNSYLVANIA AND WEST VIRGINIA

2017 ◽  
Author(s):  
James A. Fisher ◽  
◽  
Daniel Benjamin Lammie ◽  
Joshua Wagner ◽  
Peter B. Sak ◽  
...  
Keyword(s):  
West Virginia ◽  
Cross Sections ◽  
Thrust Belt

Analogue and numerical modelling of shape fabrics: application to strain and flow determination in magmas

2000 ◽  
Vol 91 (1-2) ◽  
pp. 97-109 ◽  
Author(s):  
Laurent Arbaret ◽  
Angel Fernandez ◽  
Josef Ježek ◽  
Benoît Ildefonse ◽  
Patrick Launeau ◽  
...  
Keyword(s):  
Finite Strain ◽  
Numerical Solutions ◽  
Flow Direction ◽  
Theoretical Models ◽  
Large Strains ◽  
Strain History ◽  
Shape Distribution ◽  
Strain Ellipsoid ◽  
Fluid Systems ◽  
The Matrix

We summarise numerical and analogue models of shape fabrics, and discuss their applicability to the shape preferred orientation of crystals in magmas. Analyses of flow direction and finite strain recorded during the emplacement of partially crystallised magmas often employ the analytical and numerical solutions of the Jeffery's model, which describe the movement of noninteracting ellipsoidal particles immersed in a Newtonian fluid. Crystallising magmas, however, are considered as dynamic fluid systems in which particles nucleate and grow. Crystallisation during magma deformation leads to mechanical interactions between crystals whose shape distribution is not necessarily homogeneous and constant during emplacement deformation. Experiments carried out in both monoparticle and multiparticle systems show that shape fabrics begin to develop early in the deformation history and evolve according to the theoretical models for low-strain regimes. At large strains and increasing crystal content, the heterogeneous size distribution of natural crystals and contact interactions tend to generate steady-state fabrics with a lineation closely parallel to the direction of the magmatic flow. This effect has been observed in all threedimensional experiments with particles of similar size and for strain regimes of high vorticity. On the other hand, studies of feldspar megacryst sub-fabrics in porphyritic granites suggest that these record a significant part of the strain history. Thus, the fabric ellipsoid for megacrysts evolves closer to the strain ellipsoid than for smaller markers. This behaviour results from the fact that the matrix forms of the melt and smaller crystals behave like a continuous medium relative to the megacrysts. Consequently, in the absence of these markers, and because the fabric intensities of smaller particles such as biotite are stable and lower than predicted by the theory, finite strain remains indeterminate. In that case, strain quantification and geometry of the flow requires the addition of external constraints based on other structural approaches.

Strain variation in shear belts

1970 ◽  
Vol 7 (3) ◽  
pp. 786-813 ◽  
Author(s):  
J. G. Ramsay ◽  
R. H. Graham
Keyword(s):  
Shear Zone ◽  
Strain State ◽  
Finite Strain ◽  
High Strain ◽  
Shear Zones ◽  
Finite Strains ◽  
Strain Variation ◽  
Strain Ellipsoid ◽  
Intensity Of Development ◽  
Variable Displacement

In rocks deformed by natural orogenic processes it is usual to find that the finite strain state varies from locality to locality. In some deformed rocks high strain states are localized within approximately planar zones commonly known as "shear belts".The general relationships that exist between variable displacement and variable strain state are established, and these general equations are solved for particular types of strain within shear zones. Only a limited number of types of solution are possible. Using these solutions the geometric forms of the structures found in shear zones in several regions are analyzed. Methods for computing the finite strain through these zones are described, and these finite strains are integrated to determine the total displacements across these zones. Schistosity is developed in some of the shear zones described. It is not parallel to the walls of the shear zone and is therefore not parallel to the dominant displacement (shear) directions. The schistosity appears to be formed perpendicular to the principal finite shortening (i.e. perpendicular to the shortest axis of the finite strain ellipsoid). Variations of the schistosity planes represent variations in the finite strain trajectories of XY planes in the strain states ([Formula: see text] ellipsoid axes). The intensity of development of the schistosity is correlated with the values of the principal finite strains.

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