Sharbot Lake, and Frontenac Domains and the Adirondack Lowlands. In this belt magmatism is known to have occurred between 1.42 and 1.04 Ga depending on location. As with the Gneiss Belt, metamorphism is believed to have occurred at approximately 1.16 Ga. The Granulite Terrane is composed of meta-igneous gneisses including anorthosite massifs. Anorthosites form in plutons and are composed mostly of plagioclase. The rocks of the Grenville Province in Canada are included in this category. The oldest magmatism known in this area dates to 1.32 Ga approximately. Granulite facies metamorphism began around 1.15 Ga and continued for about 150 Ma after the onset, however the continuity of the metamorphism cannot be determined. Regional variations It is important to separate local from large-scale tectonic history of the orogenic belt in order to understand the orogeny. For this purpose, the Grenville orogen is generally broken into four localities: the southern extent in Texas and Mexico, the Appalachians, the Adirondacks and the well-studied Grenville Province of Canada. A portion of the orogen can be found in Scotland, but due to Scotland's proximity to the Grenville province prior to opening of the Iapetus Ocean (modern day Atlantic Ocean), the two share largely the same history. Texas and Mexico Texas and Mexico represent the southern margin of Laurentia, and likely collided with a different continent than that involved in the eastern collision. The Zapotecan Orogeny of Mexico is coeval with the later stages of the Grenville orogeny, and they are generally considered to be one and the same. Mesoproterozoic igneous protoliths (metamorphosed to granulite facies during the orogeny) fall into two age groups in Mexico; c. 1235–1115 Ma and c. 1035–1010 Ma. Rocks of the former group bear geochemical signatures implying island arc and back-arc basin provenance. The latter group represents AMCG magmatism. These AMCG rocks are somewhat anomalous throughout the Grenville orogen, there is no known orogenic event which immediately predates their emplacement. It is suggested that the regime of subduction under the Laurentian margin (currently in Texas, north of the accreted Mexican terrane) ended around 1230 Ma, and that subduction polarity reversed to bring the colliding continent north, since the Llano uplift, which records the history of the Grenville in Texas, bears no evidence of arc magmatism after this time. Appalachians The Appalachian Mountains contain small, isolated exposures of the Grenville orogen. The largest of these, the Long Range Inlier, comprises the Long