Geologic map of the Lucerne granite, Hancock and Penobscot counties, Maine
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IMAP↗
Geology topics
D. R. Wones
Publications and source records attributed to D. R. Wones.
The Center Pond pluton: The restite of the story (phase separation and melt evolution in granitoid genesis)
The Center Pond pluton is a calc-alkaline post-tectonic Acadian body intruding chlorite grade Silurian metasediments of E-central Maine. Mapping and petrographic work reveal that the pluton contains 5 igneous rock types; quartz diorite, hornblende-biotite granodiorite, biotite granite, porphyritic granite, and aplitic granite. The linearity of major and trace element trends and Rb-Sr isotope systematics indicate that partial melting and unmixing of a single mafic or intermediate metaigneous rock to restite (residual phases in equilibrium with the melting event at depth) and near-eutectic minimum melt may account for much of the observed geochemical variation within the Center Pond pluton. Major and trace element trends rule out fractional crystallization as a model for Center Pond. -from Authors
Maine↗
Table of major constituents, in percent, determined by point-count of stained slabs of intrusive rocks of the Milford-Dedham zone, eastern Massachusetts, and locality map of samples
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Open-File Report↗
Comparative geochronology in the reversely zoned plutons of the Bottle Lake Complex, Maine: U-Pb on zircons and Rb-Sr on whole rocks
The Bottle Lake Complex is a composite granitic batholith emplaced into Cambrian to Lower Devonian metasedimentary rocks. Both plutons (Whitney Cove and Passadumkeag River) are very coarse grained hornblende and biotite-bearing granites showing petrographic and geochemical reverse zonation. Two linear whole rock Rb/Sr isochrons on xenolith-free Whitney Cove and Passadumkeag River samples indicate ages of 379??5 m.y. and 381??4 m.y., respectively, in close agreement with published K-Ar ages for biotite from Whitney Cove of 377 m.y. and 379 m.y., and for hornblende 40Ar/39Ar determinations from Passadumkeag River which indicate an age of 378??4 m.y. The initial Sr isotopic ratio for Whitney Cove is 0.70553 and for Passadumkeag River is 0.70414. A whole-rock isochron on a suite of xenoliths from the Passadumkeag River granite indicates a whole rock Rb-Sr age of 496??14 m.y., with an initial Sr isotopic ratio of 0.70262. Two types of zircon exhibiting wide petrographic diversity are evident in variable proportions throughout the batholith. One of these types is preferentially found in a mafic xenolith and it is widely dispersed in the host granites forming discrete grains and probably as inclusions in the other type of zircon. U-Pb analyses of zircons give concordia intercept ages of 399??8 m.y. for Whitney Cove, 388??6 m.y. for Passadumkeag River, 415 m.y. for a mafic xenolith in Passadumkeag River, and 396??32 for combined Whitney Cove and Passadumkeag River granite. The zircons show a spread of up to 20 m.y. in the 207Pb/206Pb ages. Omitting the finest zircon fraction in the Passadumkeag River results in a concordia intercept age of 381??3 m.y., in better agreement with the whole-rock Rb-Sr and mineral K-Ar ages. For the Whitney Cove pluton, exclusion of the finest fraction does not bring the zircon age into agreement with the Rb-Sr data. Age estimates by the whole rock Rb-Sr, mineral K-Ar and Ar-Ar methods suggest that the crystallization age of the plutons is about 380 m.y., slightly younger than the U-Pb zircon intercept ages. A possible reason for this discrepancy is that the zircons contain inherited lead. Thus, zircon U-Pb ages might represent a mixture of newly developed zircon and older inherited zircon, whereas the Rb-Sr whole rock age (380 m.y.) reflects the time of crystallization, and the argon ages result from rapid cooling after emplacement. ?? 1984 Springer-Verlag.
Contributions to Mineralogy and Petrology↗
A tale of two plutons: petrographic and mineralogic constraints on the petrogenesis of the Red Lake and Eagle Peak plutons, central Sierra Nevada, California
The two plutons are similar in age (K/Ar, 87-89 m.y.) and range in composition from granodiorite to granite. The Red Lake pluton is equigranular, has a locally greisened marginal zone, and shows only minor mineralogical and chemical zoning, whereas the Eagle Peak pluton is mineralogically, compositionally and texturally zoned, with an equigranular margin and a porphyritic core. Modal and normative trends within each pluton are consistent with separation of plagioclase and mafic minerals leading to a residual liquid enriched in quartz and alkali feldspar. The presence of homogeneous cores in the plagioclase, early titanite crystallization in the Red Lake magma and irregular hornblende compositions suggest that refractory material was present when the magmas were intruded. Inferred source regions for the two plutons are amphibolite for the Red Lake magma and a more biotite-rich amphibolite for the Eagle Peak magma.
California↗
The Pikes Peak batholith, Colorado front range, and a model for the origin of the gabbro-anorthosite-syenite-potassic granite suite
This study of the Pikes Peak batholith includes the mineralogy and petrology of quartz syenite at West Creek and of fayalite-bearing and fayalite-free biotite granite near Mount Rosa; major element chemistry of the batholith; comparisons with similar postorogenic, intracratonic, sodic to potassic intrusives; and genesis of the batholith. The batholith is elongate in plan, 50 by 100 km, composite, and generally subalkalic. It was emplaced at shallow depth 1,040 m. y. ago, sharply transects its walls and may have breached its roof. Biotite granite and biotite—hornblende granite are predominant; quartz syenite, fayalite granite and riebeckite granite are present in minor amounts. Fayalite-bearing and fayalite-free quartz syenite, fayalite-biotite granite and riebeckite granite show a well-defined sodic differentiation trend; the less sodic fayalite-free granites exhibit a broader compositional range and no sharp trends. Crystallization was largely at P H2O < P total ; P H2O approached P total only at late stages. Aplite residual to fayalite-free biotite granite in the north formed at about 1,500 bars, or 5 km depth. Feldspar assemblages indicate late stages of crystallization at about 720°C. In the south ilmenite and manganian fayalite indicate f O2 of 10 −17 or 10 −18 bars. Biotite and fayalite compositions and the ‘granite minimum’ imply completion of crystallization at about 700°C and 1,500 bars. Nearby fayalite-free biotite granite crystallized at higher water fugacity. All types of syenite and granite contain 5–6% K 2 O through a range of SiO 2 of 63–76%. Average Na 2 O percentages in quartz syenite are 6.2, fayalite granite 4.2, and fayalite-free granite 3.3 MgO contents are low, 0.03–0.4%; FeO averages 1.9–2.5%. FeO/Fe 2 O 3 ratios are high. Fluorine ranges from 0.3 to 0.6%. The Pikes Peak intrusives are similar in mode of emplacement, composition, and probably genesis to rapakivi intrusives of Finland, the Younger Granites of Nigeria, Cape Ann Granite and Beverly Syenite, Mass., and syenite of Kungnat, Greenland, among others — allowing for different levels of erosion. A suite that includes gabbro or basalt, anorthosite, quartz syenite, fayalite granite, riebeckite granite, and biotite and/or hornblende granites is of worldwide occurrence. A model is proposed in which mantle-derived, convecting alkali olivine basaltic magma first reacts with K 2 O-poor lower crust of granulite facies to produce magma of quartz syenitic composition. The syenitic liquid in turn reacts with granodioritic to granitic intermediate crust of amphibolite facies to produce the predominant fayalite-free biotite and biotite-hornblende granites of the batholith. This reaction of magma and roof involves both partial melting and the reconstitution and precipitation of refractory phases, as Bowen proposed. Intermediate liquids include MgO-depleted and Na 2 O-enriched gabbro, which precipitated anorthosite, and alkali diorite. The heat source is the basaltic magma; the heat required for partial melting of the roof is supplied largely by heats of crystallization of phases that settle out of the liquid — mostly olivine, clinopyroxene and plagioclase.
Colorado↗
Huntington Lake Quadrangle, central Sierra Nevada, California; analytic data
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Professional Paper↗
A low pressure investigation of the stability of phlogopite
Phlogopite reacts to form orthorhombic kalsilite, leucite, forsterite and fluid (H 2 O) at 1012 ± 7° C , 400 bars pressure, and 905 ± 5° C at 100 bars pressure. The heat of reaction is 39 ± 4 kcal compared to 44 ± 6kcal for the reaction of annite to form orthorhombic kalsilite, leueite, fayalite and fluid (H 2 O). The results are consistent with earlier experiments, but not with the interpretations of those experiments.
Geochimica et Cosmochimica Acta↗
Mica polytypes: Systematic description and identification
X-ray studies of mica specimens from a variety of geological localities show that biotite and certain lithium-rich mica samples are composed of a mixture of different polytypes. Many of the biotite structures are new complex polytypes not before reported. A new method of designating mica polytypes is proposed. Techniques are described for the systematic generation of all the possible layer-stacking sequences of mica polytypes and for the verification of the stacking sequences in newly discovered forms.
Science↗
Stability relations of the ferruginous biotite, annite
Annite , KFe 3 AISi 3 O 10 (OH) 2 a member of the iron biotites and the ferrous analogue of phlogopite, has been synthesized and its phase relations have been determined as functions of temperature, fugacity of oxygen (fo 2 ), and total pressure (P total ≈PH 2 O+PH 2 ). A method for controlling fo 2 at high total pressures is described, and data for the 'oxygen buffers' used are given. Buffers range from quartz+iron+fayalite assemblages (low fo 2 ) to magnetite-hematite assemblages (high fo 2 ). Optical properties and unit-cell dimensions of synthetic annites depend on the conditions of synthesis.By recalculating published analyses of natural iron-rich biotites it can be shown that one cannot assume a constant hydrogen content for such biotites. Oxidation may have occurred by drying at 115°C. Octahedral occupancy therefore cannot be calculated from such data.Phase relations of annite are presented in 2,070 and 1,035 bar sections. Depending on fo 2 -T values annite was found to decompose to one of the following assemblages: hematite+ sanidine, magnetite+sanidine, fayalite+leucite+kalsilite, iron+sanidine. All decompositions are dehydration and redox reactions and are sensitive to changes in fH 2 0 and fo 2 (or fH 2 0 and fH 2 ). At 2, 070 bars total pressure annite +magnetite+sanidine can coexist between 425°C and 825° C, depending upon the magnitude of fo 2 .In the presence of quartz the stability field of annite is more restricted. Phase equilibria in the system KAlSiO 4 -SiO 2 -Fe-O 2 -H 2 have been summarized schematically.Wherever possible, thermodynamic extrapolations are made to test the internal consistency of the data. Enthalpies of formation are calculated for both annite and phlogopite. Ranges of fo 2 values in nature as well as mechanisms for changes in fo 2 are investigated. It is useful to distinguish between assemblages which are internally buffered with respect to fo 2 changes and those which are not buffered. The applications of individual reactions involving annite to specific geologic problems are discussed with respect to igneous, metamorphic, and sedimentary rocks.
Journal of Petrology↗