Metamorphic consequences of thrust emplacement, Fall Mountain, New Hampshire

Research Article| October 01, 1990 Metamorphic consequences of thrust emplacement, Fall Mountain, New Hampshire FRANK S. SPEAR; FRANK S. SPEAR 1Department of Geology, Rensselaer Polytechnic Institute, Troy, New York 12180 Search for other works by this author on: GSW Google Scholar DONALD D. HICKMOTT; DONALD D. HICKMOTT 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Search for other works by this author on: GSW Google Scholar JANE SELVERSTONE JANE SELVERSTONE 3Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138 Search for other works by this author on: GSW Google Scholar Author and Article Information FRANK S. SPEAR 1Department of Geology, Rensselaer Polytechnic Institute, Troy, New York 12180 DONALD D. HICKMOTT 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 JANE SELVERSTONE 3Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1990) 102 (10): 1344–1360. https://doi.org/10.1130/0016-7606(1990)102<1344:MCOTEF>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation FRANK S. SPEAR, DONALD D. HICKMOTT, JANE SELVERSTONE; Metamorphic consequences of thrust emplacement, Fall Mountain, New Hampshire. GSA Bulletin 1990;; 102 (10): 1344–1360. doi: https://doi.org/10.1130/0016-7606(1990)102<1344:MCOTEF>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Metamorphic pressure-temperature (P-T) paths from the upper and lower plates of the Fall Mountain nappe, southwest New Hampshire, reveal different thermal histories in the two structural levels. Upper-plate rocks experienced early low-P, high-T (contact?) metamorphism to peak P-T conditions of 700-750 °C, 3-4.5 kbar. These P-T conditions were followed by loading to approximately 5-6 kbar, and then by nearly isobaric cooling to approximately 500 °C, 4.5 kbar. Upper-plate rocks then experienced minor heating with unloading and finally cooling. The lower-plate rocks also experienced early low-P, high-T (contact?) metamorphism but only to P-T conditions of 480-510 °C, 2-3.5 kbar. Nappe emplacement resulted in nearly isothermal loading to 500 °C, 5-6 kbar, which was followed by either heating or cooling, depending on the proximity of the sample to the upper plate.The early pressures recorded in both the upper- and lower-plate rocks suggest a depth of approximately 10 km for origination of the nappe; the post-nappe pressures (5-6 kbar) imply a total tectonic thickness of approximately 20 km or a doubling of the overburden thickness. Diffusion calculations suggest that the emplacement of the nappe took less than approximately 10 m.y., and U/Pb chronology on zircon suggests that it occurred between 400 and 410 Ma. 4OAr/39Ar cooling ages on micas indicate that the terrane was cooled to approximately 300 °C by 340 Ma. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.