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Igneous rocks
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
Igneous rocks are formed by the solidification of magma. Magma is usually a mixture of silicate liquid (melt), crystals of minerals which are crystallising from the liquid and sometimes gas bubbles. If the liquid cools slowly at some depth in the crust the crystals will have time to grow large. Rocks which crystallized in fairly large masses at depths of a few kilometres will form bodies that are termed plutons and the rocks are termed plutonic rocks. If the magma is erupted from a volcano or from a fissure in the crust it will cool more rapidly and the resulting rock is likely to be composed of very small crystals or glass, but often also containing suspended larger crystals that formed before eruption. Such rocks are described as extrusive or volcanic rocks.
Igneous Petrology and the Nature of Magmas
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
Magmas that extrude on Earth’s surface as lava or pyroclastics (ash and/or related material) produce extrusive rocks that cool quite quickly and so have inadequate time to grow large crystals. These extrusive rocks are often associated with volcanoes (but need not be). Other magmas that crystallize at depth within Earth cool relatively slowly, producing intrusive rocks that may contain very large crystals. Intrusive rocks often form large rock bodies called plutons. So, although perhaps technically incorrect, the terms volcanic and plutonic are sometimes used to describe fine- and coarse-grained igneous rocks, respectively.
Igneous Rocks
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
The term pluton is used to denote a moderately large body of magma which is intruded essentially at one time and is contained within a single boundary. Plutons have various shapes but are commonly nearly circular in cross-section; an average area for many granitic plutons is about 150 km2 but many are larger. Those emplaced early during an episode of intrusive activity may be larger than others that come later; some reach about 1000 km2 in outcrop area and are composite.
Granite suites: a problematic concept?
Published in Australian Journal of Earth Sciences, 2020
A minor concern here is that the definition of a pluton is unspecified, and there is an assumption that the rocks in a given pluton must be comagmatic. The North American Commission on Stratigraphic Nomenclature (NACSN, 2017, p. 1572) defines a pluton as “a mappable body of plutonic rock”. Note that there is no connotation of size or structure in this definition, despite assertions to the contrary in the ISG document of Salvador (1994). The Glossary of Geology (Neuendorf, Mehl & Jackson, 2005) states that stocks and batholiths are plutons, and it defines a batholith as an igneous intrusion with an outcrop area of at least 100 km2, and a stock as a similar feature, but smaller than 100 km2. There are thus no absolute definitions, and the USGS maps batholiths that are formed by assemblages of plutons, a concept that we would accept, despite the ambiguity implied by the glossary definitions. Perhaps what we now think of as plutons would once have been called stocks. These are just semantic problems that could be solved readily if there were agreement within the community.
Sediment provenance in the Murchison and Maruia basins, Aotearoa/New Zealand: a record of Neogene strike-slip displacement, convergence, and basement exhumation along the Australian–Pacific plate boundary
Published in New Zealand Journal of Geology and Geophysics, 2022
Matthew W. Sagar, Karen E. Higgs, Dominic P. Strogen, Kyle J. Bland, Greg H. Browne
Plutons composing the batholiths are subdivided into several petrogenetic suites on the basis of whole-rock geochemistry (e.g. Tulloch 1983, 1988), and are classified according to the supracrustal–infracrustal–anorogenic–mantle-type (S–I–A–M-type) scheme (Chappell and White 1974, 1992; White 1979; Collins et al. 1982; Whalen et al. 1987). Individual suites or groups of suites also have distinctive age ranges, which are utilised to interpret the detrital zircon U–Pb age spectra of the Murchison and Maruia basin sandstone beds (summarised in Table 1).