Department or Program

Geology

Abstract

New mapping and detrital zircon geochronology in the northern part of the Jefferson 7.5’ Quadrangle has revealed a previously unknown region of Albee Formation. The region studied is near Lancaster, NH, and contains two Appalachian lithotectonic units: 1) units from the Bronson Hill Anticlinorium including the Ordovician Ammonoosuc and Cambrian Albee Formations and intrusive rocks of the Ordovician Oliverian Dome and Lost Nation Highlandcroft Pluton; and 2) Jurassic igneous cone sheets of the Pliny Caldera Complex.

Detrital zircon geochronology was conducted on a total of four samples of thinly bedded to pin-stripped quartz-rich rock. Two samples came from lower elevations near Tug Mtn with one previously mapped as Albee and the other as Ammonoosuc (Lyons et al., 1997).

The other two samples are roof pendants in a Jurassic granite from the higher peaks of Terrace Mtn and both previously mapped as Albee (Chapman, 1942). Both lower elevation samples yielded youngest zircon ages of circa 500 Ma. supporting their designation as Albee and therefore expanding the mapped region of that unit. Population density plots show similarities to other Cambrian Ganderian units (e.g. Dead River, Ellsworth, and Moretown). By contrast, the roof pendants yielded youngest zircon ages of circa 400 Ma. suggesting a Devonian age and possible correlations to the 3rd Acadian DZ cycle, outboard-derived, Tarratine Formation (Bradley and O’Sullivan, 2016).

The Albee is likely in unconformable (Penobscottian?) contact with the Ammonoosuc and is significantly more deformed showing classic pin-striping and transposition. Newly discovered quartzite units in the Ammonoosuc are interlayered and gradational with the more typical mafic Ammonoosuc amphibolites. Both the Ammonoosucs and Albee units are complexly folded by NNE plunging reclined folds of Acadian (?) age and then deformed by the Oliverian Jefferson Dome.

Lyons et al., (1997) show the Ammonoosuc Fault juxtaposing the Lost Nation and a sliver of Albee against the Ammonoosuc then continuing east through the Pliny Caldera Complex. Our mapping shows instead a chilled intrusive contact with between the complex mafic intrusive rocks of the Lost Nation Pluton and the Albee that extends south to become folded with the Ammonoosuc and no Ammonoosuc fault there or in the Pliny Complex.

Level of Access

Open Access

First Advisor

Eusden, Jr., Dykstra

Date of Graduation

5-2017

Degree Name

Bachelor of Science

Number of Pages

130

Components of Thesis

1 pdf of thesis, 1 pdf of map of the Northern part of the Jefferson 7.5’ Quadrangle, and 1 pdf of the bedrock geology of the entire Jefferson Quadrangle

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