The Lincoln Sill

Petrogenesis of the ultrapotassic Lincoln Syenite, Maine: Late Silurian-Early Devonian melting of a source region modified by subduction driven metasomatism

“…In discussing this whole rock chemistry, Ogilvie (1907) noted geochemical similarities with shonkinites in the Bearpaw Mountains of Montana as well as with potassic volcanic rocks in Italy. Trefethen (1937), in a paper simply titled "The Lincoln Sill," provided the first, and as it turns out, the only comprehensive study of the Lincoln syenite rocks prior to the present work. Trefethen (1937) was the first to coin the term "sill" in reference to these rocks after noting that the contacts of the intrusion were "generally concordant with the structural trend lines of the area."…”

“…Trefethen (1937), in a paper simply titled "The Lincoln Sill," provided the first, and as it turns out, the only comprehensive study of the Lincoln syenite rocks prior to the present work. Trefethen (1937) was the first to coin the term "sill" in reference to these rocks after noting that the contacts of the intrusion were "generally concordant with the structural trend lines of the area." Trefethen's studies focused on the exposures in the South Liberty -Burkettville area (area of fig.…”

“…All quoted ages are U-Pb zircon ages from Tucker and others (2001). The tip of the arrow in the inset map refers to the approximate location of the Parks Pond pluton (discussed later in the text) relative to this figure. since the work of Trefethen (1937). However, the high potassium, yet mafic to intermediate composition of these igneous rocks provides a unique fingerprint on the tectonic processes responsible for the magma generation and eventual Late SilurianEarly Devonian emplacement (418 Ϯ1 Ma: Tucker and others, 2001) along the eastern margin of the northern Appalachians.…”

“…(2) Syenites along southeastern contact of this larger body, as well as the margins of the smaller bodies to the south, while seemingly concordant with the surrounding rocks, are all strongly foliated suggesting postcrystallization modification of original intrusive relationships. Thus the apparent concordance of much of the intrusion noted by Trefethen (1937) is likely due to superimposed structural processes rather than original intrusive contact relationships. The term "Lincoln shonkinite" (Pankiwskyj, 1976;Tucker and others, 2001) has also been used frequently in reference to these rocks.…”

“…The term "Lincoln sill", first coined by Trefethen (1937) for outcrops in Lincoln County, is most commonly used in the literature to refer to these rocks. While this term is deeply engrained in the minds of many Appalachian geologists, it is not used here for the following reasons: (1) The northwestern intrusive contact of the main body of the syenite ( fig.…”