NYSGA 2009 Trip 9 - Ratcliffe and Aleinikoff Trip 9 - Ratcliffe and Aleinikoff Pre-Ottawan (1.09 Ga) Infrastructure and Tectonics of the Hudson Highlands, New York Nicholas M. Ratcliffe1 and John N. Aleinikoff2 1U.S. Geological Survey, Reston VA 20192,
[email protected] 2U.S. Geological Survey, Denver, CO 80225,
[email protected] INTRODUCTION This trip focuses on some of the oldest Mesoproterozic rocks in the Appalachians and the nature of the pre-Ottawan (pre-1.09 Ga) infrastructure of the Hudson Highlands and Manhattan Prong. Zircon geochronology by Aleinikoff (Table 1) is revised from that given in Table 1 of Ratcliffe and Aleinikoff (2008) and is still preliminary. Ongoing geologic mapping east of the Hudson River in the Peekskill, West Point, Lake Carmel, Mohegan Lake, Brewster and Peach Lake quadrangles continues to lead to a reinterpretation and clarification of our former views (Ratcliffe and Aleinikoff, 2001, 2008) as well a new synthesis for the Hudson Highlands east of the Hudson River. After publish- ing the detailed geology of the Poughquag quadrangle (Ratcliffe and Burton, 1990) and the Oscawana Lake quad- rangle (Ratcliffe, 1992), investigations were resumed in 2000 to prepare the previously mapped but unpublished quadrangles for publication. This trip presents, in preliminary form, much of the recent, (post-2000) information, which helps clarify the age and distribution of Mesoproterozoic basement rocks of the Hudson Highlands and Manhattan Prong and is an abbrevi- ated version of our 2008 NEIGC trip. Please note that stops have been changed and that the route is different. A remarkable newly recognized aspect of Hudson Highlands geology covered in this trip is the widespread presence of orthogneisses and metavolcanic rocks belonging to the time period between 1400 Ma and 1200 Ma, or during Geochrons 14 and 13 of Rivers (1997).