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Earth Systems and Cycles
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
Sometimes a rock may melt completely, but often only partial melting occurs, because most rocks contain more than one mineral and different minerals melt at different temperatures. So, some rocks contain relict (leftover) minerals that did not melt and veins or patches of newly produced magma. When such rocks cool, the result is a migmatite, a rock that contains two different distinguishable components. Figure 2.14 shows a migmatite from western Norway. In migmatites, the minerals that did not melt are equivalent to metamorphic minerals, and the minerals that formed from crystallization of partial melts are igneous minerals.
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
There are many instances, as in the Scottish Highlands and elsewhere, where granitic material is seen to have become intimately mingled with the country-rocks, as if it had soaked into them, and the mixed rocks are called migmatites (Greek migma, a mixture). Zones of migmatite may be formed in areas where the country-rocks are metamorphic and have been invaded by granite; the migmatites pass gradually into the metamorphic rocks and into the (paler) granitic rocks. Structures in the metamorphic rocks may be traceable through the zone of mixing as inherited, or ‘ghost’, features. Migmatites are developed on a regional scale in fold-belts, as exposed in the Precambrian of southern Sweden and Finland, and in central Sutherland in Scotland.
Investigation of shallow subsurface soil for engineering construction: A case study of Etioro Akoko, Southwestern Nigeria
Published in Cogent Engineering, 2023
Tolulope Henry Ogunribido, Temitayo Olamide Ale, Emeka Kingsley Uko, Taiwo Ayomide Ale
Etioro-Akoko is situated along the Owo–Ikare-Akoko route in the northern part of Ondo State, Nigeria. It lies between latitudes 07° 25′ 30’’ and 07° 27′ N and longitudes 005° 42′ and 005° 44′ E of the Greenwich Meridian (Figures 1). The adjoining towns are Ayegunle and Oba-Akoko to the South, East of Supare-Akoko and South of Akungba-Akoko. Etioro-Akoko is located in the tropical rainforest belt of Nigeria. The southwestern monsoon winds are responsible for the tropical wet and dry climate. The dry season is usually between October and February, while the rainy season begins in March and ends in September (Akinseye, 2010). The prevalent drainage pattern in this region is dendritic. The physical topography of this region has an average elevation of 345 m above the sea level, and it is made up of three separate landforms of hills, plains and valleys. Etioro Akoko falls within the Precambrian Basement Complex of Southwestern Nigeria under Rahaman (1988) classification. Ogunyele et al. (2019) noted that granite gneiss is the predominant rock type in Etioro Akoko with a few occurrences of migmatite rock. They further stressed that the rocks trend in WNW-ESE to ENE-WSW with moderate to steep dips to the south (Figure 2).
Mafic intrusions in southwestern Australia related to supercontinent assembly or breakup?
Published in Australian Journal of Earth Sciences, 2022
H. K. H. Olierook, F. Jourdan, C. L. Kirkland, C. Elders, N. J. Evans, N. E. Timms, J. Cunneen, B. J. McDonald, C. Mayers, R. A. Frew, Q. Jiang, L. J. Olden, K. McClay
Sample WC1 was collected from a 1.0–1.5 m-thick, sub-horizontal and north-northwest-trending (170°/23°W), ophitic basaltic sill near Whaling Cove on the northeastern end of the Vancouver Peninsula, city of Albany (Figures 1, 2 and 3; Locality 15 of Fitzsimons & Buchan, 2005). The sill crosscuts and offsets a series of steeply dipping east-northeast-trending dykes (strike ∼080°; Figure 3) that, from hand-specimen observations, has been altered and metamorphosed to at least greenschist facies; this older generation of east-northeast-trending dykes can be clearly recognised in satellite imagery along the eastern coastline of Vancouver Peninsula. Both the older dykes and the porphyritic sill intrude biotite-rich migmatite. Sample WC1 chiefly comprises partly sericitised plagioclase, clinopyroxene and Fe–Ti-oxides. Clinopyroxene has been partly replaced by actinolite, hornblende and chlorite (Figure 4; Table 2; Supplemental data, Figure A). The replacement mineralogy is indicative of greenschist (chlorite + actinolite) to amphibolite-facies (hornblende) metamorphism (Spear, 1995).
Two belts of HTLP sub-regional metamorphism in the New England Orogen, eastern Australia: occurrence and characteristics exemplified by the Wongwibinda Metamorphic Complex
Published in Australian Journal of Earth Sciences, 2020
K. Jessop, N. R. Daczko, S. Piazolo
The characteristics of the WMC that are compared in this review with other HTLP complexes in the NEO include:Metamorphism synchronous with extension (here ca 297 Ma).Orientation of the metamorphic field gradient perpendicular to a major shear zone (Wongwibinda Shear Zone), indicative of a tilted block.A high metamorphic field gradient with grade increasing towards the shear zone (west to east).Presence of low-pressure migmatite and ‘anatectic’ granite (a granite derived from partial melting of the local metasedimentary pile) (Wongwibinda Granite).Widespread occurrence of schist containing muscovite porphyroblasts, commonly poikiloblastic.Spatial and temporal association with S-type granite plutons (Hillgrove Plutonic Suite).