Phase Relations of Peraluminous Granitic Rocks and Their Petrogenetic Implications 论文

摘要

Peraluminous granitic rocks are magmatic rocks that contain quartz, po­ tassic feldspar and/or sodic plagioclase, and one or more aluminum-rich minerals; thus these rocks contain more aluminum than could be accom­ modated by feldspar in a CIPW normative calculation and show normative corundum. Peraluminous granites are defined by their chemical nature, but their recognition is often based on petrography; this discrepancy thus may lead to inconsistency. Although granitic rocks are com­ monly true granite (Streckeisen 1973), they range from tonalite to granite. Of special interest are strongly peraluminous (as defi ned below) granite, granodiorite, or, in rare instances, trondhjemite; these rocks contain alumi­ nous minerals (almandinic garnet, cordierite, tourmaline, muscovite) that are thought to be stable in silicate magmas only if these magmas are themselves peraluminous. The origin of granite and related intrusive rocks is of much current interest. Many of these form shallow-level intrusions, and they can reach enormous sizes; examples are the batholiths in the Lachlan Fold Belt in southeastern Australia (White & Chappell 1983), the Cornub­ ian batholith in England (Exley & Stone 1966), the South Mountain batholith in Nova Scotia (McKenzie & Clarke 1975), the Manaslu batho­ lith in the Himalayas (LeFort 1981), much of the Idaho batholith