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Orogenic disseminated gold in Phanerozoic fold belts: some examples
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
F.P. Bierlein, A.B. Christie, P.K. Smith, S. Maher, N.G. Corner
The formation of sediment-hosted disseminated gold deposits is still the subject of some debate, but recent investigations suggest that mineralisation in most of these occurrences is epigenetic and forms at depths in excess of 2 km (e.g., Arehart 1996). Although the tectonic framework varies from collisional settings through passive margins to extensional tectonics, the deposits are almost invariably associated with broad thermal anomalies and long-lived deep crustal structures. Therefore, the extent of structural control on sediment-hosted disseminated gold deposits must be considered important, in particular within collisional settings, where deep-seated shear zones and reverse faults provide conduits for the ascending hydrothermal fluid.
A possible Jurassic age for the New Caledonia Trough and implications for Zealandia’s history
Published in New Zealand Journal of Geology and Geophysics, 2023
It is generally accepted that Zealandia separated from Australia and Antarctica around 83 Ma (end Piriauan – end Santonian; Gaina et al. 1998; Sutherland et al. 2001; Campbell and Mortimer 2014) and began to drift, accompanied by formation of the Tasman Sea and Southern Ocean crust (Figure 3B, C). As it drifted, Zealandia cooled and subsided gradually until, in the Oligocene, very little, if any, land was emergent (Landis et al. 2008). The cause of extensional tectonics that continued until near the end of the Paleocene, is unclear. It would be expected that as plate separation occurred, the driver for rifting 7would be removed and rifting would cease. It cannot be coincidence that rifting continued while the Tasman Sea and the Southern Ocean spreading ridges were both active and that rifting ceased when the Tasman Sea stopped opening. The current orientation of the Late Cretaceous and Paleocene rift faults is approximately north–south to northeast-southwest, strongly oblique to the dominant northwesterly structural trends of Northwest Zealandia (Figure 4).
Three-dimensional simulations of rockfalls in Ischia, Southern Italy, and preliminary susceptibility zonation
Published in Geomatics, Natural Hazards and Risk, 2022
Massimiliano Alvioli, Ada De Matteo, Raffaele Castaldo, Pietro Tizzani, Paola Reichenbach
The regional extensional tectonics is supposed to be related to the opening of back-arc basins caused by an East-retreating subduction of the Apulo-Adriatic lithosphere (Doglioni et al. 1996). The resurgent dome generated an uplifted block, the Mount Epomeo horst, located in the central and western sector of the island; it is marked by a system of subvertical faults striking NW-SE and NE-SW, on the edges of the dome and away from it, and and N-S and W-E mainly located at the borders of the dome (Acocella and Funiciello 1999). The southeastern part of the island is characterized by highly dipping ENE-WSW normal faults. Volcanism at Ischia started over 150 ka B.P. (Cassignol and Gillot 1982) and continued, with very long period (centuries to millennia) of quiescence, until the last eruption occurred in 1302 A.D. (de Vita et al. 2006). The oldest exposed rocks belong to a partially eroded volcanic complex, which crops out in the south-eastern part of the island, covered by more recent deposits, composed of volcanic effusive and explosive rocks, mostly trachytes and phonolites (de Vita et al. 2006). The large Mount Epomeo Green Tuff caldera formed during the eruption that took place 55 ka ago. In addition to volcanic soils, debris flow deposits cover the southern slope of Mount Epomeo and in the northern and western sectors of the island (de Vita et al. 2006). Southern sector collapses of Ischia, probably occurred between between 8.6 and 5.7 ka ago as a consequence of the resurgence, generated three major debris flow deposit units (Tibaldi and Vezzoli 2004).
Early Devonian volcanic facies, central Lachlan Orogen, New South Wales: implications for tectonic and metallogenic models
Published in Australian Journal of Earth Sciences, 2022
In the northern volcanic belt, the Cobar Basin and its broadly north–south-oriented volcanic sub-basins, such as the Rast and Mount Hope troughs, opened coeval to volcanic activity in the volcanic belt owing to sinistral transtension. These troughs have controlled and confined the eruptive products. We suggest the Gurragong and Culcairn groups' subaerial pyroclastic deposits were similarly controlled by extensional tectonics. The subaerial depositional environment of the southern volcanic successions suggests the basins experienced less subsidence than their northern siblings, and the proximity of exposed Siluro-Devonian granites, and the contact metamorphic overprint by younger intrusions, imply shallow intrusion depths accompanied by uplift and erosion of the intrusions prior to and during rift development.