RHODE ISLAND GEOLOGY: WHAT WE DON'T KNOW ABOUT THE LAST BILLION YEARS

My first encounter with Father Jim occurred before I ever met him, in the preparation of a senior project on the genesis of gneiss domes in Vermont. Subsequently I joined Jim at Weston Observatory, where I was to begin one of my most productive collaborations. He and I, and on occasion Nick Rast, were to spend many a field trip perusing Avalonian and Alleghanian terranes, and those trips were pivotal in the evolution of my skills in the observation and interpretation of tectonic environs. Here I chronicle some of those shared experiences, segue into a synopsis of our current understanding of southeastern New England tectonism, and finish with an assessment of some of the remaining problems of New England orogenesis for the region.

Although there is general agreement that the tectonic history of RI and contiguous MA and CT reflects the effects of Avalonian and Alleghanian tectonism, many unanswered questions remain, and the following will be assessed: 1) The significance of the protracted record of extensional tectonics and associated igneous activity in the region, that extend from late Precambrian through Carboniferous; 2) The apparent inconsistency between fossil and radiometric ages in the Narragansett Bay group; 3) The relation between the NNE tectonic grain of the metasedimentary rocks in the Narragansett Bay region and the E-W trend of Permian structures in eastern CT, western RI, and the New Bedford area; and 4) The extent to which gneisses, in the New Bedford area and elsewhere, that were previously considered to be Precambrian, are Permian granitoids.