microdiorite

plural microdiorites

1. countableuncountablegeographyA course-grained igneous rock, of volcanic origin, containing mostly plagioclase feldspar; a rock whose composition is intermediate between andesite and diorite.

   Early Miocene fossiliferous andesitic sediments are associated with some ophiolite massifs in northern Northland: Otaian volcanic grits (Hughes 1966) form a part of Maungaru Range (Fig. 3) and Waitakian–Otaian volcaniclastics are intruded by microdiorite near North Cape (Leitch 1966, 1970).

   1982 November 26, R. N. Brothers, M. Delaloye, “Obducted ophiolites of North Island, New Zealand: origin, age, emplacement and tectonic implications for Tertiary and Quaternary volcanicity”, in New Zealand Journal of Geology and Geophysics, volume 25, number 2, →ISSN, page 258

   1 more example

   It may be seen from this detailed description of localities that not only did the original character and distribution of the microdiorites vary throughout the district, but the subsequent alterations supply data from which inferences may be drawn as to the presence of concealed igneous bodies of later origin and the manner in which they have affected the microdiorites.

   1907, Joseph Barrell, Geology of the Marysville Mining District, Montana