THE MAPPING SAID NO, THE GEOCHEMISTRY INDICATES YES, THE INTERPRETATION IMPLIES MAYBE. WHAT WAS THE PROTOLITH TO THE MASSABESIC GNEISS COMPLEX MIGMATITES. THE MYSTERY UNFOLDS

The Massabesic Gneiss Complex (MGC) is a northeast trending belt of rocks in southern New Hampshire that has been folded into recumbent nappes, migmatized, faulted and eroded to expose a complicated pattern of bedrock. Bedrock mapping over a six-year period covering almost 250 square miles of the MGC led to the conclusion that there were three melt events that began during the Acadian Orogeny and continued long after (Kerwin, 2000; Kerwin 2007). The first melt event produced the Barrington Granite of the New Hampshire Plutonic Suite. The second was an anatexic event that began by dehydration of muscovite that produced stromatic migmatites during burial and culminated as non-modal batch melt diatexis when biotite underwent decompression melting as the complex was unroofed. The third melt event produced Permian granites (Milford granite of NH) that intruded and surrounded the MGC. Melt modeling using bulk rock analyses of rocks from within the MGC indicates the early granites, the migmatites and the late granites did not contribute melt material to any other melt producing event but their own. Mapping also led to the conclusion that the metasedimentary rocks of the MGC were melted to create the various migmatite textures found, but the question of what the protolith might have been, remained. Three hypothetical solutions are as follows: the metasediments were from, and were part of an unknown crustal block and have no relationship to the bounding formations, they were part of the Merrimack Group (MG) (Silurian Berwick Formation (Sob)) or they were part of the Central Maine Terrane (CMT) rocks (Silurian Rangeley Formation (Sr)). Based on lithology, it was felt that the Sr rocks (rusty weathering metawacke and pelite layers) were a better match than the predominately massive, purplish weathering, metawacke granofels of the SOb. Preliminary comparison of bulk rock analyses from this work and Dorais et al., 2009, of major, minor, trace and Rare Earth Elements of rocks from the MGC, CMT and MG indicate that the protolith may be the SOb rocks, assuming the MGC metasedimentary rocks are not restitic. However, the closeness of Sr, MGC and SOb compositions allows for a fourth solution, that Sr and SOb (in proximity to the MGC) are conformable, which has been and continues to be, a topic of discussion on the outcrops, in the field.