The geologic development of the Bay d'Espoir area, southeastern Newfoundland

Bay d'Espoir on the south coast of Newfoundland exposes a section across the southeastern marginal metamorphic belt of the Newfoundland Appalachians. Two major tectonostratigraphic divisions are recognized; in the south the Little Passage Gneisses of the older division (probably Precambrian), consisting of amphibolitic and psammitic gneisses intruded by tonalite, are overlain by metavolcanic and metasedimentary cover rocks of the younger division, the Baie d'Espoir Group (possibly Ordovician). The Little Passage Gneisses have been intruded post-tectonically by a megacrystic potash feldspar granite. Both this granite and the enclosing gneisses are extensively mylonitised and reconstituted close to the contact with the cover rocks and the gneissic foliations have been largely destroyed. -- The Baie d'Espoir Group has undergone two, regionally penetrative deformations, the second of which has produced a major recumbent south-east facing anticline, the Bay d'Espoir Nappe. These deformations are the cause of the mylonitised and reconstituted zone along the contact with the Little Passage Gneisses. Garnetiferous leucocratic granite and associated aplites and pegmatites have intruded the Little Passage Gneisses, the megacrystic granite, and the Baie d'Espoir Group after its first deformation but before its second; the intrusion coincided with the metamorphic climax of the Baie d'Espoir Group. Sheets of this garnetiferous granite have been tightly folded with the reconstituted gneisses near the contact with the cover. -- It is concluded that the gneisses form the basement to the Baie d'Espoir Group and that the contact is now tectonic. Deposition of the Baie d'Espoir Group was along a continental margin which was initially of Atlantic-type but later changed to Andean-type. Deformation was probably caused by continental collision along the line of the Cape Ray Fault and the Lower Palaeozoic outcrop of central Newfoundland. Correlations with similar rocks in the Gander region, central Newfoundland, on the southwest coast of Newfoundland, and in Nova Scotia are proposed

The role of multiple weak lithologies in the deformation of cover units in the northwestern segment of the zagros fold-and-thrust belt

The geometry, kinematics and dynamics of fold-and-thrust belts are strongly influenced by the mechanical behaviour of the basal decollement. However, many fold-and-thrust belts also include mechanically weak lithologies such as evaporites and marls or mudstones at different levels within the shortened stratigraphy. The kinematics and dynamic evolution of these thrust belts are controlled by the mechanical behaviour both of the basal decollement and of the weak units embedded within the overlying stratigraphic succession. In the Zagros fold-and-thrust belt (ZFTB), the shortened sedimentary cover is between 7 and 12 km thick and mechanically weak lithologies compartmentalize the stratigraphic column at shallow and intermediate levels. In this paper, satellite, field and seismic data from the Kurdistan Region of Iraq are used to identify structures of different sizes and surface traces. The observations are used to underline the role of mechanically weak horizons within the Zagros stratigraphy and the decoupling of deformation both laterally and with depth in the belt. The decoupling between shallow and deeper structures observed in seismic profiles from the Kurdistan Region of Iraq is also reported from field observations from the Iranian part of the Zagros fold-and-thrust belt, where folds with different surface traces occur. Decoupling between shallow and deep layers by incompetent lithologies at intermediate depths (e.g. marls, mudstones and evaporites) results in the formation of disharmonic folds. The geometry, size and location of such folds may differ between outcropping and subsurface structures. Decoupling may have a significant impact on hydrocarbon exploration in different parts of the Zagros fold-and-thrust belt due to potential offsets between outcropping and subsurface structures and their associated traps

Rates and Processes of Active Folding Evidenced by Pleistocene Terraces at the Central Zagros Front (Iran)

http://www.springerlink.com/content/mr0420359248741x/The Zagros fold belt results from active collision of the Arabian plate with central Iran, and is characterized by the development of a spectacular >200 km-wide fold-train in its sedimentary cover. Although the architecture of this accretionary prism has been extensively studied because of its important implications for hydrocarbon exploration, aspects such as the kinematics of individual folds and the sequence of fold development remain to be investigated in detail. It is commonly believed that the ongoing deformation through the Zagros belt has led to the south-westward migration of the front of the fold belt. In the south-western Fars province (central Zagros), the most frontal structure is delineated by the Mand anticline, a well-exposed detachment fold on the shore of the Persian Gulf. This near-symmetrical anticline involves relatively competent Phanerozoic sedimentary rocks above a regional décollement in Hormuz salt. In order to document the geometry and kinematics of this fold, we have constructed several balanced cross-sections on the basis of a recently published section constrained by seismic data (Letouzey and Sherkati, 2004). Several solutions to the length versus area restoration problem common to detachment folds are then proposed: fault-related folding, detachment folding with internal deformation, and detachment folding accompanied by the flexure of the flanking synclines below the regional stratigraphic level. On the western limb of the anticline, fluvio-marine terraces, tilted by 1.7 to 4.5°, provide an additional constraint on fold kinematics and suggest that surface deformation is most compatible with a detachment fold, probably associated with synclinal flexure. Applying such a model, as well as new 14C ages for the marine terrace deposits, we calculate tilting rates of 0.04 to 0.05°/kyr, which would be produced by a Late Pleistocene shortening rate (perpendicular to the structure) of 3 to 4 mm/yr. Although this preliminary estimate suffers from relatively large uncertainties, mostly due to the absence of independent dating of the terraces and independent constraints on the folding model, we conclude that shortening across the Mand anticline could absorb 20 to 35% of the 8 mm/yr convergence across the entire Zagros. This result is consistent with a normal forward-propagating deformation sequence in a thin-skinned tectonic regime. It also implies that the sedimentary cover of the frontal Zagros is fully decoupled from the basement, most probably at the level of the Hormuz salt, in contrast to recent models that suggested active deformation of the sedimentary cover to be controlled by thrust faults in the basement