Geologic Map of the Latir Volcanic Field and adjacent areas, Northern New Mexico by Peter W. Lipman and John C. Reed, Jr. Digital Edition by Theodore R. Brandt, released 2011 Miscellaneous Investigations Series Map I-1907, version 1.1 ABSTRACT This is the digital edition of a map originally published in 1989. The geologic data have now been captured digitally are presented here along with images of the printed map sheets as PDF files. This map encompasses all or parts of ten 7.5 minute quadrangles in the Taos Range of the Sangre de Cristo Mountains in northern New Mexico between latitudes 36 degrees 30 minutes and 37 degrees 00 minutes north latitude and 105 degrees 00 minutes and longitude 105 degrees 37 minutes 30 seconds west. Geologic mapping was initiated in this area by the U.S. Geological Survey in response to its mandate under the Wilderness Act of 1964 to evaluate the mineral resource potential of the Latir and Wheeler Peak Wildernesses and the Columbine–Hondo Wilderness Study Area in the Carson National Forest. The mapping was later extended to adjacent areas in order to better understand the regional geology and geologic history of the range. The present map focuses on the early Tertiary (largely Oligocene) Latir Volcanic Field and plutonic rocks associated with it. The basement rocks in the map area are Paleoproterozic amphibolite-facies metasedimentary and metavolcanic rocks intruded by large bodies of quartz monzonite, granodiorite and gabbro dated at between 1750 and 1690 Ma. The basement rocks are locally overlain by Mississippian limestone or by Pennsylvanian and Permian redbeds. The basement rocks were thrust eastward across a thick section of similar late Paleozoic rocks along low-angle faults during the Laramide Orogeny. Post-Laramide erosion largely removed the sedimentary cover from the basement rocks and reduced the topography to a low-relief surface locally overlain by scattered lenses Eocene of Oligocene shale, sandstone, and conglomerate. It was on this surface that the earliest rocks of the Latir Volcanic Field were deposited, beginning in the Oligocene, about 30 Ma. The early volcanic rocks comprise a thick sequence of andesite, dacite, and minor rhyolite, deposited as flows, breccia, and volcaniclastic sediments from numerous local volcanic centers; thin layers of rhyolite tuff are from distant eruptions, some probably in the San Juan Mountains. These volcanic rocks probably record early growth of an upper-crustal batholith. At 25 Ma enormous eruptions of peralkaline rhyolite ash-flow tuff were accompanied by collapse of the roof of the growing batholith to form the Questa Caldera, a volcanic depression at least 14 km across. The ash flows traveled for tens of kilometers from the caldera rims to form a widespread sheet of densely welded tuff; ash also fell back to fill the subsiding caldera depression. Concurrent extension along northwest- trending faults segmented the volcanic edifice and rotated the originally sub-horizontal layers, so that some are nearly vertical. Formation of the caldera was accompanied by further batholith growth, involving intrusion of large plutons of granite, granodiorite, and related rocks into both caldera fill and the adjacent rocks, including both the earlier volcanic rocks and the basement rocks. The large molybdenum deposit along the Red River east of Questa is related to the emplacement of one of these late granitic plutons. Intrusive activity continued into the Miocene. Development of the Rio Grande Rift beginning at about 15 Ma was accompanied by development of the north-south trending normal faults along the western foot of the Taos Range. The rift is filled with thousands of meters of clastic sediments interleaved with basalt flows, some as young as 3.6 Ma. The bounding faults of the rift cut the Questa Caldera so that the western part of the original structure is now deeply buried beneath the rift fill. DISCLAIMERS This database, identified as I-1907, has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty, expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. Although this information product, for the most part, is in the public domain, it also contains copyrighted material as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured from the copyright owner. DATA FILES The database can be downloaded via the Web from http://pubs.usgs.gov/imap/i-1907/. ArcInfo export files, ArcView shapefiles, and an ArcGIS geodatabase may be extracted from a zip-compressed file (I-1907_GIS.zip). In addition, an Adobe Portable Document Format (PDF) file (I-1907_map.pdf) can be downloaded, from which paper copies may be printed. The database contact is: Theodore R. Brandt 303-236-1901 tbrandt@usgs.gov U.S. Geological Survey Box 25046, Mail Stop 980 Denver, CO 80225 This geospatial database consists of ArcInfo export files (.e00), ArcView shapefiles, and ArcGIS geodatabase files contained in a zip archive See the list below. Please refer to the file I-1907.met for detailed metadata documentation for this geospatial database. List of files: 00ReadMe.txt I-1907_map.pdf I-1907_xsec.pdf I-1907.met I-1907textonly.doc datafiles.zip: I-1907.mxd I-1907.mxt I-1907.pmf I-1907-WebGraphic40.jpg (3D shaded relief graphic) e00 directory: latgeo.e00 latpts.e00 latpta.e00 latage.e00 latxs.e00 lathlsd.e00 wpgcmykg.shd.e00 geol_sfo.lin.e00 geoscamp2.mrk.e00 import.aml shapefiles directory: latgeo.shp (contains polygon attributes for latgeo database) latgeo.shx/dbf/prj latgeol.shp (contains line attributes for latgeol database) latgeol.shx/dbf/prj latxs.shp (contains line attributes for latxs database) latxs.shx/dbf/prj latage.shp (contains point attributes for latage database) latage.shx/dbf/prj latpts.shp (contains point attributes for latpts database) latpts.shx/dbf/prj latpta.shp (contains point attributes for latpta database) latpta.shx/dbf/prj I-1907_GIS.gdb directory (contains GIS data as geodatabase feature classes) HOW TO OBTAIN THE DIGITAL FILES The digital files constituting the geologic map database of this report can be obtained via the Internet from the U.S.Geological Survey publications website. Go to the web page at http://pubs.usgs.gov/imap/i-1907/downloads/I-1907_map.pdf and follow the directions to download the files. The main product is a Portable Document Format (.pdf) map, which requires Adobe Acrobat for viewing. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com.