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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
Basin closure took place during the mid-late Cambrian and early Ordovician. Apparently the oceanic crust was subducted under island arcs containing calc-alkaline volcanic complexes. At that time granitoid belts were formed, which were related to the margin parts of the continental blocks surrounding the ophiolites. The granitoids could be grouped into the tonalite–plagiogranite, granodiorite and granodiorite–granite assemblages. These assemblages have a lot in common. They are characterized by an early phase of intrusion of small, gabbrodiorite, diorite and tonalite bodies. The massifs are dominated by granodiorites, plagiogranites, adamellites, tonalites and granites of the second (late) phase. The assemblage they are assigned to depends on the relative proportions of different rock types. Based on their chemical composition, they correspond with the calc-alkaline series (Table 3.2).
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
El Capitan is mostly composed of light gray granite or rocks closely related to granite. Collectively termed granitic, or sometimes granitoid, these light-colored rocks are composed chiefly of feldspars and quartz. But, if you focus in, you can see different colors of rock exposed in El Capitan’s face, suggesting that there may be significant compositional variation. In places, a much darker rock, dark gray to black, is seen in blobs and splotches. This rock becomes especially prominent as you drive farther into the Valley, around the Nose, and get a view of El Capitan’s southeast face (seen in Fig. 6.2), where a large black body of rock is exposed in the North American Wall, so named because the body of rock is shaped like the continent. On both the southwest and southeast faces, a myriad of white to light gray dikes—small veins up to several meters thick—cut across the face in near-horizontal directions.
Influence of mineralogical and chemical composition of aggregates on strength and adhesion property
Published in Maurizio Crispino, Pavement and Asset Management, 2019
H.R. Sachin, K.M. Mallesh, Mohamed Shareef
K – Feldspar and quartz were found to be predominant minerals in Granitic rocks. The granitic rock is basically coarse crystalline light colored rock with porphyritic texture. It is reasonably strong, durable with relatively fine grained varieties. But with the coarse grained types the disintegration is very rapid. The strength properties considered for the analysis have shown decreased tendency to resistance to degradation. The R2 value was more than 0.7 in all the cases. The mineral Augite is predominant in Basalt and Dolerite rocks. With increasing grain sizes from fine to medium, both rocks are found to be very much stronger and exhibits greater resistance to degradation, but there is a tendency to form more flaky materials. The R2 value was found be more than 0.70 in most of the cases.
Looking beneath the Stawell and Bendigo zones in Victoria, Australia: a view through the granite window
Published in Australian Journal of Earth Sciences, 2020
During the Devonian, the Paleozoic metasediments of the Stawell, Bendigo and Melbourne zones were intruded by numerous stocks and batholiths of essentially high-K calcalkaline, I- and S-type granitic rocks. These plutons fall into two main age groups – Early Devonian in the Stawell and Bendigo zones and Late Devonian in all three zones (e.g. VandenBerg et al., 2000). S-type rocks are more abundant in the MZ, where there are also large cauldron structures filled with subaerially deposited, intracaldera, silicic ignimbrites of similar age to the granitic plutons. Granitic magmas, of various kinds, are inferred to have been generated mainly by partial melting of deep-crustal source rocks and so afford us a valuable means of probing the lithological characteristics of a region that has little or no surface expression. The constraints derived from granite petrology are potentially useful for refining crustal models that are based on geophysical information. Naturally, however, there are complications that could invalidate the idea that each granitic magma formed from a single, distinctive source-rock package. One of the possibilities is that the granitic magmas might represent mixtures of melts formed from different sources within the crust, and possibly even in the mantle. Indeed, this idea formed the basis for one published model for the variations in silicic magma compositions throughout southeastern Australia (e.g. Collins, 1996, 1998; Keay, Collins, & McCulloch, 1997).
Crustal and thermal structure of the Thomson Orogen: constraints from the geochemistry, zircon U–Pb age, and Hf and O isotopes of subsurface granitic rocks
Published in Australian Journal of Earth Sciences, 2018
C. Siégel, S. E. Bryan, C. M. Allen, D. J. Purdy, A. J. Cross, I. T. Uysal, D. A. Gust
The studied granites can be used as probes for the deeper crust to better constrain its age and character in order to investigate the heat-producing potential of their sources. Whole-rock chemistry indicates no clear correlation between heat production and fractionation indices such as Rb/Sr and Eu/Eu*. Most intrusive rocks sampled in this study have low Rb/Sr ratios (<10) and hence no sign of significant plagioclase fractionation, and there is no relationship between heat production and Sc, Sr/Y and MREE indices that are used to assess fractionation of other phases such as clinopyroxene, amphibole and garnet, respectively. The granitic rocks are not fractionates of mantle-derived magmas, which would be clearly marked by pronounced plagioclase fractionation indicators given their high silica contents, but the granitic composition is interpreted to be controlled more by partial melting of crustal sources that must have been moderately incompatible and HPE-element-enriched and silicic to explain the presence of non-fractionated high-silica granitic rocks. This conclusion is consistent with the Thomson Orogen being floored by continental crust rather than oceanic crust.