Extrusives rocks

Basalts The igneous extrusive rocks that constitute the oceanic crust. 

Mid-oceanic ridge basalt A mafic volcanic (extrusive) rock that erupts on the ocean floor in a spreading... 

Rhyolite A felsic extrusive rock. Its intrusive equivalent is granite. 

Fig. 2.1. Location of intrusive and extrusive rocks of the Tuscany Magmatic Province. Numbers in parentheses indicate ages (in Ma).

Volcanic or extrusive rocks are those that form at or near the surface. Volcanic rocks cool quickly and tend to be fine grained or glassy in texture. From a single mass of molten rock, both plutonic and volcanic rocks may form. So for every type of volcanic rock, there is a plutonic rock with the same elemental composition (see Table 2.11). But the minerals involved will be different, as will the textures. 

In orogenic settings where multiple generations of intrusive or extrusive rocks occur, field relationships frequently provide constraints on their age relative to deformational fabrics and stmctures. By documenting that an igneous unit is post- or pre-kinematic with respect to a particular deformational feature, and by determining the... 

Rock varnish grows best on certain lithologies such as fine-grained extrusive rocks... 

Apatites associated with felsic-intermediate intrusive and extrusive rocks exhibit a relatively restricted range in composition F-Cl-OH space (Fig. 5a). Apatites from these rocks contain between 50-100% F, 0-50% OH, and < 20% Cl, with few exceptions. The dominant exchange operating is F(OH).i, due in part to the similarity in radius for F and (OH) as compared to Cl. Apatites from felsic-intermediate pegmatites display an even more restricted range of compositions, but possibly with less Cl however, this may not be due to volatile exsolution (a topic discussed later). It is interesting to note that in some meteorites, for example the achondritic Nakhlite, the Z site is filled with F (1.6 wt %) and Cl (4.0-4.3 wt %) with no detectable OH (Bunch and Reid 1975) (not on figure). 

Extrusive rock includes any igneous rock that was formed at the earth s surface. 

Caibonatite is a rare igneous carbonate rock (almost invariably intrusive), consisting of more than 50 % carbonate minerals. Worldwide, only one example of extrusive rocks is known the rocks and lavas of the (active) 01 Doinyo Lengai volcano, Tanzania. 

A knowledge of a at one known pressure and temperature will suffice for the evaluation of c ) if the liquid remains constant in composition. This evaluation is most conveniently done with extrusive rocks wherein the groundmass crystallized at pressures... 

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