China
Africa
Explore chapters and articles related to this topic
Elatsite porphyry Cu deposit, Bulgaria: mineralisation, alteration, and structures
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
L. Fanger, T. Driesner, C.A. Heinrich, A. Von Quadt, Irena Peycheva
Field evidence clearly shows at least four distinguishable types of dikes. In terms of mass, a polyphase plagioclase dominated porphyry (see figures: 1 & 2, units 4 & 5) is the most important. It probably belongs to the first dike generation followed by multiple phases of amphibole dominated porphyry (7, 8), which intruded into the host rock as well as into the plagioclase-porphyry. Simultaneously, dikes consisting almost exclusively of potassium feldspar (9, 10) intruded. Some of them cut amphibole-porphyries and in turn some are cut by amphibole-porphyries. From some outcrops we can assume that they are probably aplitic apophyses of the amphibole-porphyries. The fourth type is a dark, fine-crystalline dike with few small amphibole phenocrysts (6), for which no direct cross-cutting relationships with other types could be observed. Since it is mineralized and shows some potassic alteration similar to the other dike types, we can assume that it intruded at approximately the same time. The mineralisation started with magnetite veining accompanied by with a potassic alteration. The magnetite stage is largely absent in the dikes but abundant in the paleozoic granodiorite. The potassic alteration accompanies also the subsequent chalcopyrite+magnetite+bornite paragenesis, which is the carrier of the platinoids and partly of the gold. Connected to this mineralisation we can also observe an propylitic mineral assemblage with mainly epidote. This is the only occurence of propylitic alteration within the whole pit area. At this stage some dikes were already intruded because they show this paragenesis. While the typical stockwork porphyry veining took place, the intensity of potassic alteration decreased and chalcopyrite, pyrite and molybdenite were precipitated. The last dikes intruded during this stage as evidenced by a reduced degree of potassic alteration and quartz vein density. Subsequently, veins of massive chalcopyrite+pyrite were formed and later the deposit is overprinted by a feldspar destructive alteration (mainly sericite and quartz), which is also seen along late, thick (1-30 cm) massive quartz-pyrite veins (11). Late subvertical, WNW-ESE striking brittle faults (12) cut and displaced all the lithologies and caused remobilisation of ore at least along the two major faults and some smaller ones. First structural evaluation of these faults and the massive quartz+pyrite veins measurements show subparallel pattern of these features in comparison to the large WNW-ESE striking subvertical faults.
Variability of syn-rift geometry in Pearl River Mouth Basin, China: implications for faulting patterns in two-phase rift basins
Published in Australian Journal of Earth Sciences, 2023
G. R. Peng, P. Liu, B. S. Ma, J. W. Ge
Numerous rift basins have been shown to undergo two or more distinct phases of extension (Deng, Fossen, et al., 2017; Deng, Gawthorpe, et al., 2017; Duffy et al., 2015; Frankowicz & McClay, 2010; Henstra et al., 2019; Whipp et al., 2014). Multiphase rifts that experience a change in extension direction between rift phases will commonly develop faults with multiple trends and various interaction styles, as observed in many natural examples (Duffy et al., 2015; Frankowicz & McClay, 2010; Morley et al., 2004; Whipp et al., 2014). However, the natural examples display the final geometry of multiphase rifting. Therefore, much of our understanding of fault evolution and controlling factors in multiphase rifts is based on the observations from physical models (Bellahsen & Daniel, 2005; Bonini et al., 1997; Chattopadhyay & Chakra, 2013; Henza et al., 2010, 2011; Keep & McClay, 1997). Physical experiments that simulate two-phase non-coaxial extension indicate that the development of second-phase faults is controlled by factors such as the geometry (e.g. orientation and dip) of first-phase faults and the orientation of the first-phase faults relative to the second-phase extension direction (Henza et al., 2010, 2011). Fault interaction and linkage result in the zigzag geometry, abutting and cross-cutting relationships (Henza et al., 2010, 2011).
Evaluating 9 m of near-surface transpressional displacement during the Mw 7.8 2016 Kaikōura earthquake: re-excavation of a pre-earthquake paleoseismic trench, Kekerengu Fault, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2023
Philippa Morris, Timothy Little, Russ Van Dissen, Matthew Hill, Mark Hemphill-Haley, Jesse Kearse, Kevin Norton
Finally, the post-earthquake trench logs also illustrate that fault-perpendicular cross-cutting relationships can be the result of a progression of structures developing (possibly over just seconds) during a single earthquake, rather than evidence for multiple earthquakes. This is exemplified in Figure 9, where fault 1 is inferred to have initially ruptured in 2016 as an open fault fissure on the ground surface (probably a Riedel fault), which then infilled with surface topsoil (unit bp yielding a modern 14C age). Subsequently, the raft of material bounded by this structure probably rotated coseismically about a vertical axis, during which the rafts were forced to shorten (Figure 12a), activating oblique thrust faults (faults 1A and 1B). These thrusts overrode and sealed the previously formed fissure, and displaced older stratigraphic units overtop it (units ml, o and ts). The several fault strands involved are locally cross-cutting, yet they probably moved at intervals only seconds apart.
Features of seafloor hydrothermal alteration in metabasalts of mid-ocean ridge origin from the Chrystalls Beach Complex
Published in New Zealand Journal of Geology and Geophysics, 2021
Caroline Hung, Lisa A. Gilbert, Damon A. H. Teagle, Dave Craw, Reinhard A. Wobus
A concentrated zone of vertically dipping veins (Figure 3A,B) at the headland outcrop fills a main normal fault structure with no offset. Cross-cutting relationships of fracture veins (Figure 3C, 4C) and microfaults show sequences of genesis and structural changes. An example of a sequence is outlined in Figure 3C, where at least three distinct events are present. Stage 1 records the sub-vertical vein and the network of veinlets surrounding it. Stage 2 records the low angle normal microfault that offsets and fractures the Stage 1 vein. Stage 3 shows sub-vertical epidote-quartz-chlorite vein that cross-cuts the main features of Stage 1 and 2. Although the duration and exact timing between events are not addressed here, the relative sequence of fracturing is well-preserved: fracture genesis, sub-horizontal normal faulting, compression, and modern erosion after emplacement. In the lava flow zone of the headland, slickensides on the underside of overhanging rock of a minor thrust fault (Figure 3A) with an estimated throw of 1 m suggest the direction of the fault slip motion is 212° while the dip is 20°NE relative to the modern tilt of the lava flow.