China
Africa
Explore chapters and articles related to this topic
Geology
Published in Ronald C. Chaney, Marine Geology and Geotechnology of the South China Sea and Taiwan Strait, 2020
The Spratly Islands consists of 14 islands ranging in area from 0.4 to 46 ha with an additional 600 coral reefs. A list of the various individual islands is presented in Table 2.4. The largest island is Taiping Island, which is occupied by the Republic of China (ROC). These islands consist of a combination of reefs, banks, and shoals that are built of biogenic carbonate on the higher crests of major submarine horsts. A horst is an uplifted fault block. These horsts are part of a series of parallel and en echelon half-grabens and rotated fault blocks. Their long axis defines linear trends that are parallel to magnetic anomalies exhibited by the oceanic crust. The rotational block faulting is a result of tectonic plates stretching apart. The horsts, grabens, rotated fault blocks, and the rock forming the base consist of stretched and subsided continental crust. This rock is composed of Triassic (220 Ma), Jurassic (192 Ma), and Cretaceous (135 Ma) strata. These rocks include calc-alkalic extrusive igneous rocks, intermediate to acid intrusive igneous rocks, sandstorms, siltstones, dark green claystones, and metamorphic rock. That includes both biotite-muscovite-feldspar-quartz highly complex rock and garnet-mica schists (Wikipedia, 2020).
Geological Structures
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Several normal faults throwing down in the same direction are spoken of as ‘step faults’ (Fig. 8.20c); two normal faults dipping towards one another produce ‘trough faulting,’ and dipping apart form a pair of ‘ridge faults.’ Where a stratum approaches a fault it is often bent backwards a little, away from the direction of movement along the fault plane, as shown in the figure. A sunken block, bounded on all sides by faults, is called a graben; the Rhine Valley and the Midland Valley of Scotland are examples of this structure on a large scale. A horst is a fault-bounded ridge-block, the converse of graben; e.g. the Black Forest and Harz Mountains, Germany, and on a smaller scale the ridge of the Malvern Hills, Hereford. The North Sea contains many horst and graben structures, some of which have provided important traps for oil and gas.
Introduction
Published in Sukumar Laik, Offshore Petroleum Drilling and Production, 2018
In the case of compaction, the overburden load plays a major role. Owing to the high overburden pressure, compaction in porous medium takes place and thus vertical subsidence of beds form folded structures. In the case of tensional folds, the rock layers are pulled away from each other by tensional forces. When this tensional force exceeds the threshold values, the gradual crustal thinning and finally faulting takes place in the form of horst and graben. Horsts are the elevated faulted blocks whereas graben are the subsided faulted blocks. Then continuous sedimentation on horst and graben gradually give birth to the folded strata as described in Figure 1.11.
Evaluation of the potential corrosivity of groundwater using an Analytic Hierarchy Process-based index
Published in Urban Water Journal, 2023
Aksaray city is located between North Latitudes 38°20″ and 38°23″ and East Longitudes 33°59″ and 34°3″ in the Central Anatolian Region of Turkey (Figure 1). The population of the city center is 239,523 according to 2022 population data. Aksaray province is in the middle climate zone and has a cold, continental climate type. The average temperature, precipitation rate and average annual evaporation rate in the study area, between 1927 and 2022 period, are 12.0 ◦C, 392 mm and 210 mm, respectively. Over the course of the year, the temperature typically varies from −6°C to 31°C and is rarely below −13°C or above 36°C. The study area has a flat topography in terms of geomorphology and is surrounded by high-elevation hills in the east due to tectonism. The most significant structural element of the region is the Lake Tuz Fault Zone (LTFZ), which lies in a 25–60° NW direction with a length of approximately 190–200 km (Kürçer and Gökten 2014). This fault zone consists of parallel faults showing a step-shaped half-graben or horst graben morphology.
Cenozoic volcanism, tectonics and mineralisation of Woodlark Island (Muyuw), eastern Papua
Published in Australian Journal of Earth Sciences, 2021
A major phase of extensional tectonics along the Kulumadau Horst and Graben Zone commenced post-middle Miocene and has persisted to the Holocene. The sedimentary record preserved in the extensive gravels of the Na’ku’iel Conglomerate provides an insight into the tectonics of the horst and graben zone. Energetic post-middle Miocene tectonic activity resulted in the uplift of metamorphosed basement (Loluai Formation and Utavai Basalt Member) and juxtaposition with middle Miocene volcanic rocks of the Watou Mountain Eruptive Centre. Uplift accompanied rapid erosion and deposition of the poorly to chaotically sorted Na’ku’iel Conglomerate. Proximal deposits are dominated by mass wasting and sediment gravity flows, including landslide deposits, debris flow deposits and alluvial fan deposits. The presence of auriferous gravels of the Na’ku’iel Conglomerate on Taneigas Ridge at Great Northern and Waiakum, containing a high percentage of clasts sourced from the Loluai Formation and the Busai Hill Ignimbrite, suggests the Na’ku’iel paleo-stream passed through the Busai–Bomagai area and transported coarse, auriferous gravels for distances up to 10 km from headwaters in either or both the Okiduse Range and Suloga Range.
Production key figures for planning the mining of manganese nodules
Published in Marine Georesources & Geotechnology, 2018
Sebastian Ernst Volkmann, Felix Lehnen
Preliminary results of this paper give already an impression on how the seafloor may look like after mining took place (Figure 8). Mining would leave patchy areas scattered on the ocean seafloor (Kuhn, Rühlemann, and Wiedicke-Hombach 2012). Potential mining fields are embedded in horst and graben structures and are predefined by geology (Rühlemann et al. 2009). Considering that horizontal structures visible in the processed (filter-) images are artifacts as assumed by Rahn (2016), there may be fewer but longer fields. This cannot be clarified with the underlying data. Moreover, only about 3% of E1 was analyzed, which may not be representative for other regions inside or outside the license area. The factsheet on polymetallic nodules published by the ISA, referring to results of J. P. Lenoble for the French pioneer area, states: “In the best areas, they would be 1 to 5 km wide and 10 to 18 km long, with a north-south orientation. They might cover 35% of the bottom with a nodule abundance of 15 kg/m2.” (International Seabed Authority 2003) These dimensions are comparable to those determined in the scope of this study.