Rb-Sr whole-rock isochrons for four main representatives of the syntectonic to post-tectonic New Hampshire Plutonic Suite (name revised) yields the following ages: Concord Granite, 359 +/-11 m.y. (or 330 +/-3 m.y.); Spaulding Quartz Diorite, 402 +/-5 m.y.; Bethlehem Gneiss, 405 +/-78 m.y.; and Kinsman Quartz Monzonite, 411 +/-19 m.y. [GNC records contain this note regarding this report: There is enough doubt concerning the absolute time scale for the Devonian so that the above ages cannot yet be assigned with certainty to either the Early, Middle, or Late Devonian, even if it is agreed, as most evidence now suggests, that the Silurian-Devonian break lies within the range of 413-430 m.y. The age of the Spaulding Quartz Diorite should be considered to be Devonian (egh).]

Source: GNU records (USGS DDS-6; Reston GNULEX).

Used as Early Devonian Spaulding Tonalite of New Hampshire Plutonic Suite. Previously called Spaulding Quartz Diorite of Fowler-Billings (1949). Lithologic term changed from Quartz Diorite to Tonalite in accordance with rock classification scheme of Streckeisen (1973). Consists of weakly foliated to nonfoliated, spotted biotite quartz diorite, tonalite, granodiorite, and granite, with or without garnet or muscovite. Report includes geologic map and correlation chart, and 1:500,000-scale map showing plutons.

Source: GNU records (USGS DDS-6; Reston GNULEX).