Melt inclusions in plutonic rocks / Расплавленные (газовожидкие) включения в плутонических породах

Melt inclusions (MI) are small droplets of melt now containing some combination of crystals, glass and vapor that are trapped in crystals formed in magmas. Over the past few decades, the study of MI has matured to become an accepted technique to investigate melt evolution in volcanic systems (Clocchiatti 1975, Roedder 1979, Lowenstern 1995, 2003, Sobolev 1996, Frezzotti 2001, Hauri et al. 2001, Anderson 2003, Schiano 2003). MI in volcanic rocks are commonly large (>50 µm), glassy and contained in fresh and transparent minerals, and are generally easy to identify. MI in volcanic rocks generally provide consistent and reasonable results concerning the chemistry of melts at depth and provide the best tool available for assessing the volatiles in magmas (Anderson 1973, 1974, Lowenstern 1994, 1995, 2003). The best MI are often found in the most rapidly cooled parts of pyroclastic deposits and glassy rinds of lavas, which are not so easy to find (A.T. Anderson, Jr., personal communication, 2006).
Compared to studies of MI in extrusive rocks, there are many fewer studies of MI from plutonic rocks, and there is still some uncertainty concerning the interpretation of data obtained from these samples. Roedder (1984) noted, “The lack of evident silicate melt inclusions in many igneous intrusive rocks, particularly those formed at greater depths, is puzzling.” Roedder further stated, “One of the major problems in the study of melt inclusions in intrusive rocks is the difficulty in recognizing the inclusions.” MI in intrusive rocks are usually small (5–20 µm) compared to those in extrusive rocks. Thomas et al. (1996) noted that about 80% of the MI in granitic rocks from the Erzgebirge, Germany, were smaller than 20 µm, with a mean diameter of about 10 µm. R. Thomas (personal communication, 2006) also noted a correlation between inclusion size and volatile content, with more volatile-rich inclusions reaching 200 µm in diameter. Thomas also suggested that MI in Precambrian rocks are generally smaller than those in younger rocks. MI in plutonic rocks are commonly completely crystalline and contain a distorted bubble that is not always recognizable, and are much more likely to have reequilibrated following entrapment, owing to slow cooling and contact with subsolidus hydrothermal fluids. This chapter summarizes progress in the development of techniques to study MI from plutonic/intrusive rocks and focuses on MI from more silicic (granitic) environments (Table 1-1). Veksler (2006) discusses crystallized MI from gabbroic rocks, and Veksler & Lentz (2006) consider MI in carbonatites and related rocks. The application of MI in understanding pegmatite formation is discussed by Thomas et al. (2006). In a more general sense, this chapter focuses on MI that have experienced significant devitrification or crystallization following entrapment, or subsolidus aqueous alteration. This discussion thus applies to MI from the plutonic environment, as well as inclusions from the volcanic or extrusive environment that have undergone slow cooling and/or hydrothermal alteration <...>