Field relations, crystallization, and petrology of reversely zoned granitic plutons in the Bottle Lake Complex, Maine

Abstract

The Bottle Lake Complex is a composite batholith of Middle Devonian age that intrudes the core of the Merrimack synclinorium in eastcentral Maine. The batholith consists of the Whitney Cove and Passadumkeag River plutons. Both are granites and are petrographically and geochemically reversely zoned, having more mafic cores than rims. Primary sphene, magnetite, and abundant mafic xenoliths are characteristic of these plutons. The abundance and composition of amphibole, biotite, and plagioclase indicate that the most mafic rocks are concentrated in the core fades. The bulk composition of granites in the Bottle Lake Complex is also reversely zoned, from high SiO2 in the rim facies (71-77 weight percent) to low SiO2 in the core facies (67-72 percent). Higher contents of A1A (14-16.5), Fe2O3 (2.5-5.4), MgO (0.6-1.3), and TiO2 (0.3-0.8) are characteristic of the core facies, compared to the abundance of A12O3 (12.0-14.5), Fe2O3 (1.4-3.0), MgO (0-0.8), and TiO2 (0.1-0.5) in the rim facies. Reverse zonation is also evident in the generally higher strontium, niobium, yttrium, and zirconium of the more mafic granites in the interior. Mafic xenoliths show more dispersed major and trace element variations compared to the host granites. Calculated biotite stabilities coupled with the granite minimum melting curve suggest that emplacement conditions were as follows: P= 1-1.8 kbar, t=720-780°C, and fo slightly higher than the Ni-NiO but lower than hematite-magnetite buffer equilibrium curve. Reversely zoned plutons in the Bottle Lake Complex result from remobilization (resurgence) of the more mafic lower layers and of the accumulated and scavenged crystal mush into the upper, more felsic parts of the plutons modified by fractional crystallization (plagioclase, biotite, amphibole, apatite, zircon, magnetite-ilmenite). In the initial stages of evolution, each pluton was a convecting and chemically stratified system with more mafic granitic magma at the base. Periodic influxes of more mafic granitic magma resulted in mixing of liquids and redistribution of minerals. Surges of more mafic granitic magmas or venting of the magma chamber may have triggered the remobilization of the lower layers into the upper, more felsic layers. Mafic xenoliths and their host granites are not related by fractionation and probably represent foreign blocks obtained at depth. Granite magmas in the Bottle Lake Complex were emplaced consecutively and were obtained from a compositionally variable source. The trend in isotopic composition becomes more radiogenic for strontium, lead, and oxygen from the Passadumkeag River to the Whitney Cove pluton. A volcaniclastic source (graywacke) that progressively became more continental in character accounts for the range of isotopic compositions in the Bottle Lake Complex. Although multiple injection of granite magmas occurred in the batholith, each pluton represents a closed geochemical system. Significant input of lead from reservoirs similar to the oceanic mantle, lower continental crust (granulite), or upper conti...

Pluton emplacement in arcs: a crustal-scale exchange process

“…Ayuso 1984;Nabelek et al 1986;Allen 1992) bodies that we believe to be nested diapirs; and (2) horizontally layered systems in which lateral zoning is at best only weakly developed (e.g. Guadalupe Igneous Complex).…”

Geochemical and metallogenic contrasts in Paleozoic granitic rocks of the northern New England Appalachians

“…1A) in the Central Maine terrane includes intensely fractured and, altered granitic rocks (Ayuso, 1984). Anomalously high abundances of U, Th, As, Mo, Sb, Bi, and W are found in stream sediments (Otton and Nowlan, 1980;Nowlan and Hessin, 1972;Post et al, 1967) derived from the biotite-bearing Topsfield facies in the complex.…”

“…A wide range of granitic rocks is found in the Central Maine terrane, from quartz gabbro and diorite to leucogranites (e.g., Scambos et al, 1986;Ayuso, 1984;Moench et al, 1995;Hon, 1980). Middle to Late Ordovician (Taconian) granitic rocks belonging to the calc-alkaline granite to tonalite Oliverian plutonic suite and Highlandcroft plutonic suite (Billings, 1956;Leo, 1991;Moench et al, 1995) are present along the western flank of the Central Maine terrane (Wones and Sinha, 1988).…”

Multistage shearing of the Deblois granite in the Kellyland fault zone, eastern Maine

“…Miarolitic cavities in plutons that intrude the Fredericton suite and metamorphic assemblages in their contact aureoles show more precisely that the Bottle Lake, Deblois, and Pocomoonshine plutons (see Fig. 2) were emplaced at pressures ≤1.5-2.5 kbar (Ayuso, 1984;Ludman et al, 1989). Similar epizonal levels are reported for other Late Silurian and Early Devonian batholiths in eastern Maine and western New Brunswick, including the Lucerne (Wones and Ayuso, 1993) and Pokiok (Rast and Lutes, 1979) plutons.…”

“…Most of their interpretations have been revised substantially, but they correctly identified northeast-and northwesttrending faults in the plutons and their host rocks. Ayuso (1984) described the evolution of the Bottle Lake complex, more accurately defined its limits in the Wabassus Mountain area, and recognized a fault contact (now viewed as part of the Waite fault Osberg et al (1985). Main map shows variation in regional metamorphic grade along the NFS in Maine (after Guidotti, 1985).…”