THE ERVING FORMATION, WEST-CENTRAL MASSACHUSETTS: WHAT HAS BEEN LEARNED IN THE LAST HALF CENTURY?

The junction between “VT” and “NH” strata was described as the Monroe Thrust in the N Connecticut Valley, as the Chickenyard Line unconformity in the S. In 1988, from mapping Erving in MA, the Line was proposed as a west-directed thrust.

Emerson 1898 described amphibolite, interbedded with “whetstone” near Erving, later called Erving Hornblende Schist, with graphitic schist to E. In 1959-61 Robinson mapped these as Erving Fm., with Littleton to E. Erving consists of plagioclase-quartz granulite with non-graphitic kyanite schist and calc-silicate beds, epidote amphibolite, coticule with discrete magnetite octahedrons, and rare zoisite calc-silicate and marble. Erving in the core of the Northfield-Wendell Syncline, overlies Littleton and Clough. That Littleton touches Fitch linked to Bernardston Lochkovian conodonts, so Littleton isn’t older. Erving lies on Littleton, Clough, Partridge and Fourmile Gneiss, suggesting unconformity. If a thrust sheet, it is E-directed.

Robinson and John Rosenfeld 1960 saw similarity between Erving and Standing Pond - Gile Mtn. in “the fish hook” SE VT, so that Erving is tied to questions about “VT” and "NH" Silurian-Devonian strata. Trzcienski and Robinson 1966 studied the Whately Anticline, where amphibolites, granulites, and coticules, recognized as Erving, overlie “Partridge” rusty schist and “Clough” conglomerate, and underlie Waits R. - Gile Mtn.

Robinson et al. 1988 saw Littleton on the east limb of Whately Anticline, suggesting it was thrust W over younger Gile Mtn.-Waits R.-Erving on a Whately Thrust, also a thrust on the Chickenyard Line. Trzcienski et al. 1992 gave strong evidence that there is no Littleton at Whately, also implied that the amphibolites and associated rocks above the conglomerate belong to the Ordovician Hawley Fm., not Erving.

Geochemistry by Hepburn shows Standing Pond, Putney, and Erving amphibolites are LREE-enriched alkali basalts or LREE-depleted tholeiites likely associated with extension. Those from the “canoe” near Chester Dome are LREE-enriched; those from the Putney, the “fish-hook” of the Guilford Dome and Erving are depleted, supporting the Robinson-Rosenfeld correlation. Walsh et al. 2012 brought the Monroe Thrust S to Springfield, VT, where it points to the Chickenyard Line. So Erving and its relations stay a dilemma after >50 years.