Magmatic to solid state fabrics in syntectonic granitoids recording early Carboniferous orogenic collapse in the Bohemian Massif
41
Citation
106
Reference
10
Related Paper
Citation Trend
Keywords:
Massif
Transpression
Transpression
Strain partitioning
Cite
Citations (58)
Lineation
Batholith
Transpression
Cite
Citations (5)
Transpression
Clockwise
Cleavage (geology)
Cite
Citations (59)
The southwestern end of the Norumbega fault zone forms a 14° restraining bend in a prominent orogen-parallel dextral strike-slip system within the northern Appalachians. Late Paleozoic transpression at the Casco Bay restraining bend was controlled by the geometry of dextral strike-slip faults within an otherwise regional transtensional dextral strike-slip system. Regional shearing within this system may have begun in the Early Devonian and persisted until the latest Paleozoic with late high strain localization and syntectonic to post-tectonic granitic intrusion. Deformation related to this restraining bend involved distributed dextral shear strain and crustal shortening in a complex zone, ~30 km wide, referred to as the Casco Bay shear zone system. Regional upright F2 folds in this area are oblique to subparallel to the fault trace and developed strong hinge-parallel elongation. This is reflected in initially orthogonal boudin partings and veins within upright fold limbs. As these F2 folds were tightened and reoriented toward the fault trace, the limbs developed pervasive dextral shear fabrics and asymmetric kinematic indicators. Higher ductile shear strains were accommodated along lithologic contacts and within less-competent units. The cross-section geometry of the Casco Bay shear zones is interpreted as a positive flower structure that cored a transpressional zone of shortening, thickening, and dextral shear accompanied by strain-localized syntectonic intrusion. Oblique-slip lineations in a number of zones suggest vertical components to dextral shear including an early phase of dextral overthrusting to the northwest and a later phase of dextral oblique extension, down to the southeast, along the main Flying Point fault zone. Late structures including small normal faults, normal kink-bands to several meters in width, chevron folds, and crenulations with horizontal axial planes suggest late vertical shortening of the transpressional uplift. Swanson, M. T., 1999, Dextral transpression at the Casco Bay restraining bend, Norumbega fault zone, coastal Maine, in Ludman, A., and West, D. P., Jr., eds., Norumbega Fault System of the Northern Appalachians: Boulder, Colorado, Geological Society of America Special Paper 331.
Transpression
Cite
Citations (17)
Abstract The Heritage Range of the southern Ellsworth Mountains, West Antarctica, is composed of Cambrian to Permian sedimentary and volcanic rocks, which were deformed during the Permo-Triassic Gondwanian orogeny. The structural grain of the Heritage Range exhibits a previously unrecognized 18° swing from 333–153° in the north to 315–135° in the south. A change in structural and kinematic style accompanies this strike-swing, with a structure consistent with near-orthogonal shortening present in the south, and a structural style consistent with dextral transpression within the central and northern Heritage Range. Kinematic partitioning is present within the central Heritage Range, where strikeparallel, contemporaneous domains of dextral and reverse shear have developed simultaneously with the regional cleavage. Comparison of the structure and kinematics within both structural domains suggests that the central and northern Heritage Range experienced pure-shear dominated dextral transpression, with an approximate angle of relative shortening (α) of 65–70°. Results derived by integrating field data into a published kinematic partitioning model suggest relatively efficient kinematic partitioning has occurred. However, such efficient partitioning cannot be explained by strain partitioning models based purely on plate boundary conditions. Therefore, it is proposed that pre-existing weak structures were present within the unexposed basement facilitating the apparent high percentage of kinematic partitioning.
Transpression
Strain partitioning
Cite
Citations (25)
Granitoid plutons are a major component of pre-Carboniferous rocks in Cape Breton Island and knowledge of the time and tectonic setting of their emplacement is crucial for understanding the geological history of the island, guiding exploration for granite-related economic mineralization, and making along-orogen correlations. The distribution of these plutons and their petrological characteristics have been used in the past for recognizing both Laurentian and peri-Gondwanan components in Cape Breton Island, and for subdividing the peri-Gondwanan components into Ganderian and Avalonian terranes. However, ages of many plutons were assumed on the basis of field relations and petrological features compared to those of the relatively few reliably dated plutons. Seventeen new U–Pb (zircon) ages from igneous units reported here provide enhanced understanding of the distribution of pluton ages. Arc-related plutons in the Aspy terrane with ages of ca. 490 to 475 Ma likely record the Penobscottian tectonomagmatic event recognized in the Exploits subzone of central Newfoundland and New Brunswick but not previously recognized in Cape Breton Island. Arc-related Devonian plutonic activity in the same terrane is more widespread, continuous, and protracted (445 Ma to 395 Ma) than previously known. Late Devonian magmatism in the Ganderian Aspy terrane is similar in age to that in the Avalonian Mira terrane (380 to 360 Ma) but the tectonic settings are different. In contrast, magmatic activity in the Bras d’Or terrane is almost exclusively arc-related in the Late Ediacaran (580 to 540 Ma) and rift-related in the Late Cambrian (520 to 490 Ma). The new data support the terrane distinctions previously documented.
Devonian
Cite
Citations (18)
Abstract Synthesis of several recent structural studies in the Pyrenees points to a syntectonic emplacement of granitic plutons, more or less early during the D2 main phase of the Hercynian orogenesis. A dextral E-W component of simple shear is demonstrated for D2, which was previously considered as a pure N-S compression. This component is recorded in the granites by large shear bands and sigmoidal features, and in the country rocks by asymmetrical strain shadows of foliation trajectories in map view and by systematically dextral sense of shear in xz sections. The compressive component of D2, well known in the country rocks where it induced a strong flattening related to ubiquitous upright isoclinal tight folds, was also observed in the granites. There, we documented a reverse movement within magmatic or solid-state shear bands. The addition of all these data constrains a new interpretation for the D2 main Hercynian phase in the whole Pyrenees: this phase was a dextral transpression.
Transpression
Orogeny
Cite
Citations (45)
Rubidium and strontium concentrations and (87)Sr/(86)Sr values are documented herein for samples of plutons and associated rocks from 238 locations in the southern Sierra Nevada and vicinity. The goals of the investigation were to determine ages of rock units, to aid in the separation of plutons in poorly exposed areas, to determine the pattern of variation of initial (87)Sr/(86)Sr (hereafter called Sr(i)) for plutons, and to constrain more rigorously the boundaries of the continental Sierran and Salinian-western Mojave terranes defined on the basis of the Sr(i) of their plutons by Kistler (1978) and by Kistler and Peterman (1978). These new data expand the boundaries of the Salinian-western Mojave terrane and make it part of the Panthalassan lithosphere that lies west of the tectonic boundary, whereas the Sierran terrane is made part of the North American lithosphere that lies east of the tectonic boundary.
Cite
Citations (20)