Abstract The location of the Meso-Tethyan suture in SE Asia is ambiguous due to the strong overprint by the later India–Asia collisional tectonics. For the SE Asian extension of the Meso-Tethyan Bangong–Nujiang Suture (BNS) in Tibet, the two main candidates are the Longling–Ruili Suture (between the Tengchong and Baoshan blocks) and the Myitkyina ophiolite belt. Here, we present new detrital zircon U–Pb ages from high-grade metasedimentary rocks of the Gaoligong Group, which is considered to be the basement of the Tengchong Block located between the Longling–Ruili Suture and Myitkyina ophiolite belt. Our data suggest that the Gaoligong Group contains Cambrian, Triassic and Cretaceous zircons and is not a Precambrian basement, with a diagnostic age population peak at c. 1110 Ma. This peak is comparable to the c. 1170 Ma peak reported in the Australia-derived blocks (e.g. Lhasa and West Australia). Such similarities, as well as the similarities in the stratigraphy, palaeobiogeography and magmatic history of the Tengchong Block, suggest that the Tengchong Block was located adjacent to the northern Australia margin in Gondwana, and was most likely to have been linked with the Lhasa Block (southern Tibet) since the Early Paleozoic. Thus, the Longling–Ruili Suture is likely to represent a continuation of the Meso-Tethyan BNS in SE Asia.

ABSTRACT Avalonia and Ganderia are composite microcontinental fragments in the northern Appalachian orogen likely derived from Gondwanan sources. Avalonia includes numerous Neoproterozoic magmatic arc sequences that represent protracted and episodic subduction-related magmatism before deposition of an Ediacaran–Ordovician cover sequence of mainly siliciclastic rocks. We characterized the nature of the basement on which these arcs were constructed using zircon grains from arc-related magmatic rocks in Atlantic Canada that were analyzed for their Lu-Hf isotope composition. The majority of zircon grains from Avalonia are characterized by initial 176 Hf/ 177 Hf values that are more radiogenic than chondritic uniform reservoir, and calculated crust formation Hf T DM (i.e., depleted mantle) model ages range from 1.2 to 0.8 Ga. These data contrast with those from Ganderia, which show typically positive initial εHf values and Hf T DM model ages that imply magmatism was derived by melting of crustal sources with diverse ages ranging from ca. 1.8 to 1.0 Ga. The positive distribution of initial εHf values along with the pattern of Hf T DM model ages provide a clear record of two distinct subduction systems. Cryogenian–Ediacaran magmatism is interpreted to have resulted from reworking of an evolved Mesoproterozoic crustal component in a long-lived, subduction-dominated accretionary margin along the margin of northern Amazonia. A change in Hf isotope trajectory during the Ediacaran implies a greater contribution of isotopically evolved material consistent with an arc-arc–style collision of Ganderia with Avalonia. The shallow-sloping Hf isotopic pattern for Paleozoic Ganderian magmatism remains continuous for ~200 m.y., consistent with tectonic models of subduction in the Iapetus and Rheic Oceans and episodic accretion of juvenile crustal terranes to Laurentia.

Abstract The Elan Bank microcontinent was separated from East India during the Early Cretaceous break-up. The crustal architecture and rifting geometry of East India and the Elan Bank margins document that the early break-up between India and Antarctica was initiated in the eastern portions of the Cauvery and Krishna–Godavari rift zones, and in the southern portion of Elan Bank. However, the westwards break-up propagation along the Krishna–Godavari Rift Zone continued even after the break-up in the overstepping portion of the Cauvery Rift Zone. Eventually, the western propagating end of the Krishna–Godavari Rift Zone became hard-linked with the failed western portion of the Cauvery Rift Zone by the dextral Coromandel transfer fault zone. Consequently, the break-up location between India and Antarctica shifted from its initial to its final location along the northern portion of the Elan Bank formed by the western Krishna–Godavari Rift Zone. The competition between the two rift zones to capture continental break-up and asymmetric ridge propagation resulted in a ridge jump and the Elan Bank microcontinent release.

Abstract The study focuses on the role of wrenching-involved continental break-up in microcontinent release, drawing from a review of examples. It indicates that the main groups of release mechanisms in this setting are associated with ‘competing wrench faults’, ‘competing horsetail structure elements’, ‘competing rift zones’ and ‘multiple consecutive tectonic events’ controlled by different stress regimes capable of release. Competing-wrench-fault-related blocks are small, up to a maximum 220 km in length. They are more-or-less parallel to oceanic transforms. The competing horsetail-structure-element-related blocks are larger (up to 610 km in length) and are located at an acute angle to the transform. Competing-rift-zone-related blocks are large (up to 815 km) and are either parallel or perpendicular to the transform. The multiple-consecutive-tectonic-event-related blocks have variable size and are generally very elongate, ranging up to 1100 km in length. The role of strike-slip faults in release of continental blocks resides in: linking the extensional zones, where the blocks are already isolated, by their propagation through the remaining continental bridges and subsequent displacement; facilitating rapid crustal thinning across a narrow zone of strike-slip-dominated faults; and slicing the margin into potentially detachable fault blocks.