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Magmatism of Phanerozoic Fold Belts
Published in O.A. Bogatikov, R.F. Fursenko, G.V. Lazareva, E.A. Miloradovskaya, A. Ya, R.E. Sorkina, Magmatism and Geodynamics Terrestrial Magmatism Throughout the Earth’s History, 2020
V.V. Yarmolyuk, V.I. Kovalenko
During the transitional stage, marked by the presence of arc complexes, the formation of igneous assemblages continued. However, most of the igneous rocks belong to the calc-alkaline series. The number of rock types and the relative volume of intermediate and acid types increase dramatically. Differentiated series of all compositions appear. The K, Sr and Ba content increases considerably, as well as the K2O/Na2O ratio in rocks similar to those formed at an early stage. The assemblages that formed as the results of a complex interaction between mantle and crustal material included: gabbro–granite, gabbro–diorite– granite (diorite–granite). Finally, a typical crustal granite–migmatite assemblage was formed, related to the regional metamorphism and anatexis of crastal sialic material. Processes of K-metasomatism that affected the earlier-formed granitoids were widespread. The transitional stage was a period during which most of the continental crust of fold belts was formed.
Rocks and rock minerals
Published in Ivan Gratchev, Rock Mechanics Through Project-Based Learning, 2019
Igneous rocks are formed from magma when it cools and solidifies (Figure 4.2a). The movement of silicate magma creates two types of igneous rocks: intrusive (or plutonic) rocks formed by slow cooling at depth and extrusive rocks formed on the surface in volcanic eruption. Intrusive rocks include granite, diorite and gabbro while common extrusive rocks are basalt, andesite and rhyolite.
Plutonic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Although some regions are dominated by volcanic rocks and some by plutonic rocks, both volcanic and plutonic rocks are found along the entire length of the Cordillera. As Figure 6.22 shows, they have similar compositions—both groups range from mafic to felsic. The vertical axis in Figure 6.22 (n) indicates the number of occurrences and, although many more volcanic rocks have been analyzed than plutonic rocks, the similarity in composition range (40%–80% SiO2) is clear. Plutonic gabbro, diorite, tonalite, granodiorite, and granite are matched by volcanic basalt, andesite, dacite, and rhyolite. Overall, though, the plutonic rocks are more felsic than the volcanic rocks.
Assessment of blast energy usage and induced rock damage in hard rock surface mines
Published in CIM Journal, 2022
M. S. Dotto, Y. Pourrahimian, T. Joseph, D. Apel
The proposed approach was implemented at Nyankanga Pit, Geita Gold Mine, Tanzania. The Nyankanga geology comprises a banded iron formation and diorite as host rocks. Mineralization is controlled by tectonic structures located within fault zones passing through the host rock. The banded iron formation is of sedimentary cyclic depositional origin and consists of iron-rich sediments and chert. The Nyankanga diorite is igneous, with variable mineral composition and grain size defining the Nyankanga Intrusive Complex. The diorite is principally plagioclase-rich and hornblende-rich diorite. Porphyry intrusions within the fault zones are the youngest Nyankanga geology. They are mainly quartz feldspar porphyry and feldspar porphyry dykes. Lithology mapping on benches 920 RL to 910 RL in Nyankanga pushback 8 identified the rock distribution shown in Figure 3. The rock quality designation was estimated using the Deere and Deere (1988) approach on core samples of sizes NQ (47.6 mm) and HQ (63.5 mm) from exploration drilling. The orientation of drill holes ranged from 52 to 79° dip and 178 to 196° azimuth. The Nyankanga rock mass quality designation is “good.” It is made up of hard rock (UCS 78–129 MPa), with slightly rough joints spaced 0.2–0.42 m and joint apertures < 5 mm. The groundwater condition is generally moist, with water dripping in a few areas.
Subduction erosion: contributions of footwall and hanging wall to serpentinite mélange; field, geochemical and radiochronological evidence from the Eocene HP-LT belt of New Caledonia
Published in Australian Journal of Earth Sciences, 2021
The Peridotite Nappe is crosscut by a wide variety of dykes and sills emplaced between 55 and 47 Ma (early Eocene; Cluzel et al., 2006, 2016), which are absent in the underlying Poya Terrane. These intrusive rocks comprise medium- to coarse-grained rocks (sills and dykes), the compositions of which vary from ultramafic (pyroxenite and hornblendite) to mafic (hornblende-gabbro, diorite) and felsic (leucogabbro, leucodiorite and granite) and minor dolerite dykes. Dolerite dykes crosscut all levels of the Peridotite Nappe, including the gabbronorite cumulates, while the other dykes and sills are restricted to the ultramafic part of the allochthon. Boudinaged dykes are present in the serpentinite sole as well. Some dykes are strongly foliated, isoclinally folded or mylonitised as a consequence of syntectonic intrusion in shear fractures. With only a few exceptions, the original composition of the dykes (geochemical and mineralogical) is surprisingly well preserved in spite of widespread serpentinisation of the host rock; however, some of them display secondary parageneses owing to post-magmatic recrystallisation. In the latter, amphibolitisation is common with hornblende or tremolite depending upon initial composition, temperature and fluid/rock ratio. A few metasomatised dykes, which display high Ca–Sr and low SiO2 contents, can be termed rodingites (Python et al., 2007, 2011) and contain secondary hydro-grossular, pink zoisite, prehnite, and clinochlore.
Character and tectonic setting of plutonic rocks in the Gällivare area, northern Norrbotten, Sweden
Published in GFF, 2019
Zmar Sarlus, Olof Martinsson, Tobias E. Bauer, Christina Wanhainen, Joel B. H. Andersson, Roger Nordin
Using normative mineral compositions (Table 2), the analyzed rocks are also classified using the QAP (quartz, alkali-feldspar, plagioclase) and ternary mineral diagrams for ultramafic and mafic rocks after Streckeisen (1976) (Fig. 6C–E). The two olivine-rich samples collected from the central part of Dundret complex (sample nos. 6 and 7 in Fig. 1) occupy the peridotite field on the boundary between lherzolite and wehrlite fields (Fig. 6C). The mafic samples from Dundret and Vassaravaara complexes show a gabbronoritic composition (Fig. 6D). Mafic-intermediate plutons and dolerite samples range from gabbro-diorite to monzonite and quartz-monzonite in composition (Fig. 6E). Felsic plutonic rocks are classified as alkali-granite and K-feldspar syenite to syenite (Fig. 6E). The classifications based on normative mineral compositions are in good agreement with results obtained from the TAS diagram and from petrographic observations.