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The Eastern Lesser Himalayan fold-thrust belt is punctuated by a row of orogen-transverse domal tectonic windows. To evaluate their origin, a variety of thrust-stack models have been proposed, assuming that the crustal shortening occurred dominantly by brittle deformations. However, the Rangit Window (RW) in the Darjeeling-Sikkim Himalaya (DSH) shows unequivocal structural imprints of ductile deformations of multiple episodes. Based on new structural maps, coupled with outcrop-scale field observations, we recognize at least four major episodes of folding in the litho-tectonic units of DSH. The last episode has produced regionally orogen-transverse upright folds (F4), the interference of which with the third-generation (F3) orogen-parallel folds has shaped the large-scale structural patterns in DSH. We propose a new genetic model for the RW, invoking the mechanics of superposed buckling in the mechanically stratified litho-tectonic systems. We substantiate this superposed buckling model with results obtained from analogue experiments. The model explains contrasting F3-F4 interferences in the Lesser Himalayan Sequence (LHS). The lower-order (terrain-scale) folds have undergone superposed buckling in Mode 1, producing large-scale domes and basins, whereas the RW occurs as a relatively higher-order dome nested in the first-order Tista Dome. The Gondwana and the Proterozoic rocks within the RW underwent superposed buckling in Modes 3 and 4, leading to Type 2 fold interferences, as evident from their structural patterns. [ABSTRACT FROM AUTHOR]

Abstract: The deformation history of sedimentary units incorporated in the North Cuban fold and thrust belt in the Paleocene to middle–late Eocene was associated with major shortening between the Caribbean and North American plates. This led to the formation of an intensely deformed tectonic pile comprising from top to bottom of a volcanic arc nappe, a deformed mafic–ultramafic complex with Mesozoic ophiolite components and a serpentinitic mélange with blocks of sedimentary (the Placetas belt) and metamorphic rocks; and the structurally lower unit composed of folded and thrusted sediments of the southern promontory of the Bahamas platform. In this paper we study the deformation history of sedimentary units incorporated in the North Cuban fold and thrust belt associated with this shortening history. We find that the occurrences of the Placetas sedimentary rocks within the foliated serpentinite mélange show varying styles and intensity of deformation, and varying number of deformation phases. They form isolated blocks within the serpentinite mélange and do not represent a coherent nappe underlying the allochtonous mafic–ultramafic complex. The deformation of the Remedios belt, part of the Bahamas platform, underwent a single phase of folding and thrusting, with shortening perpendicular to the plate contact. This folding occurred in the middle to late Eocene and marks the arrest of subduction and arc–continent collision. We find no evidence for a component of strike-slip during collision. The volcanic arc is thrusted upon the mafic–ultramafic complex, and the original forearc ophiolite appears to be shortened. This shortening may attest to a period of subduction erosion. Thrusting of the volcanic arc led to deposition of the Paleocene-lower Eocene Taguasco olistostrome which may date this event. We show that careful analysis of the complexly deformed Cuban fold and thrust belt may allow identification of subduction erosion and subduction accretion episodes. Expanding the analysis carried out in this paper to the scale of the northern Caribbean fold and thrust belt may provide a new and independent geological tool to constrain the geodynamic processes associated with subduction and arc–continent collision along the northern Caribbean margin. [Copyright &y& Elsevier]

Abstract: Modern orogenic belts may be rifted and reworked during later tectonic cycles. In ancient collision zones, such as the Eastern Ghats Belt (EGB), India, identification of such processes is complicated by the multiply folded nature of the exposed deep crustal section. Along the northern EGB margin, (M1) granulite facies metamorphism (∼7–8kbar, >760°C) at ∼960–930Ma outlasted D1 fabric formation, and D2 isoclinal folding and shearing. N-S trending mafic dykes and N-S trending, west-dipping shear zones accompanied D3 extension. Syn-D3 cooling and decompression caused garnet breakdown in mafic granulites. Granite and pegmatite emplacement at c. 850Ma accompanied uplift on E-W trending, subvertical D4 shear planes. Top-to-the-south thrusting on WNW-ESE trending, north-dipping D5 shears resulted in regional-scale fabric reorientation. During M2 amphibolite facies metamorphism (∼5.5kbar, 630°C) at c. 700Ma following D5, garnet reformed in mafic granulites, and stabilized within syn-D3 mafic dykes and syn-D4 granites. Thus, the terrane margin experienced heating, loading and uplift during a first tectonic cycle, followed by renewed burial during a later orogeny. Since the mesoscopic-scale folds correspond to shears that interfere in low strain zones, the structural pattern represents heterogeneous, rather than homogeneous strain accommodation during mid-crustal deformation. [Copyright &y& Elsevier]