U.S. Department of the Interior U.S. Geological Survey AEROMAGNETIC MAPS, GRAVITY ANOMALY MAPS, AND DERIVATIVE MAPS OF THE CRAIG AND DIXON ENTRANCE 1-DEGREE BY 3-DEGREE QUADRANGLES AND THE WESTERN EDGES OF THE KETCHIKAN AND PRINCE RUPERT QUADRANGLES, SOUTHEAST ALASKA, ALONG WITH AN INTERPRETATION OF WHAT THEY REPRESENT. By J.C. Wynn, R.P. Kucks, and D. J. Grybeck U.S. Geological Survey Digital Data Series 56 This CD-ROM contains digital data files and images of gravity and aeromagnetic data acquired by the US Geological Survey in the Craig and Dixon Entrance (CDE) 1-degree x 3-degree quadrangles through August 1991. The CDE 1:250,000 quadrangles occupy the southern tip of Alaska's Panhandle and are located west of Ketchikan, Alaska. This CD-ROM also includes a new simplified geologic map by Don Grybeck (USGS - Anchorage Office) and topographic grids. The raw geophysical data, the grids, and the images are combined in several different kinds of overlays to aid interpretation. The interpretive report and the images are included here in several different document formats for ease of viewing by the widest possible audience. DISCLAIMERS This Compact Disc-Read Only Memory (CD-ROM) publication was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Although all data and software published on this CD-ROM have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and (or) the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data, software, or related materials. DESCRIPTION OF CONTENTS: A report (DDS56.PDF) describing the data acquisition and processing, with a brief interpretation of the magnetic and gravity data as they relate to the geology and mineral resources (including modeling of selected features), is included here in Adobe Portable Document Format. An extensive CDE general bibliography (more extensive than the report's references), is included in the directory "\Bibl_Ndx". To begin, read the file "DDS56.PDF" in the "Root" directory. To view this report, you must have Adobe Reader. Images of the geophysical grids overlaid as either colored grids on shaded-relief topography, or contoured grids on color-shaded topography, or contoured grids overlaid on the simplified geologic map are found in the directory "\Imagery". All these images can be viewed with any number of different graphics packages, both commercial and shareware. They can also be viewed using Web browsers, but these latter do not generally permit zoom and pan, restricting the usefulness of the data. The magnetic data were acquired by contract surveys during the 1980's and were originally processed by Robert Kucks (USGS-Denver) to a residual magnetic field (by removing the IGRF field), and then reduced to the magnetic pole. Both residual magnetic and reduced-to-the-pole grids are contained in the directory "\Grids", while the data files in several different binary and ASCII formats are found (and explained) in the directory "\Data". Images of these data, in a number of different combinations with the geology map and the topography, are found in the directory "\Images". The gravity data were acquired beginning in 1968 by Dave Barnes (USGS-Retired) and Jeff Wynn (USGS-Reston, from 1984 through 1991) and processed with help from Robert Morin (USGS - Menlo Park, CA) to the Complete Bouguer Anomaly (CBA) to remove elevation and terrain effects using USGS digital terrain files, and then further reduced to the Isostatic Anomaly (ISO) using terrain and bathymetry data. This isostatic correction was done because the quadrangles sit astride a continental margin transition zone and could reasonably be expected to show a substantial isostatic gradient. This correction has been done mainly to improve the correlation between the gravity data and the geology. The ASCII data file for all gravity stations is contained in the directory "\Data". Both CBA and ISO gravity grids are contained in the directory "\Grids", while images of these data are found in "\Images". USGS digital topographic data (USGS digital elevation models - DEMs) for the two quadrangles have also been acquired and stitched together, and the combined grid is included in several forms in this CD-ROM. CDE-DEM includes the northern part of the Queen Charlotte Islands of Canada; CDE-DEM-USA includes only the CDE quadrangles. These grids are in a UTM projection in order to overlay with existing topographic maps. USGS DRG images of the CDE quadrangles are also included. These are Zip-compressed raster images of the 1:250,000-scale topographic maps. When uncompressed to about 20 megabytes, they can be printed directly to a large plotter using most commercial graphics software. All these products are contained in directory "\Grids". A simplified geologic map compiled by Don Grybeck (USGS - Anchorage) was digitized by Kelly Brunt under the supervision of Nora Shew (both working with the USGS-Anchorage office) and is included as several ARC/INFO files, a geo-referenced Geosoft-format grid, and as several different resolution- versions of TIFF images in the directory "\Geology". Contours of isostatic gravity and reduced-to-the-pole magnetic data superimposed on a geo-referenced grid version of this geology map are also included in the directory "\Images". Following is a listing with descriptions of all files on this CD-ROM: FILE DESCRIPTIONS FILE NAME FORMAT TYPE DESCRIPTION ----ROOT directory readme.txt ASCII text (this file) DDS56.pdf PDF (CDE report in PDF format) ----BIBL_NDX directory, containing the CDE bibliography and several map indices---- Bibliography.txt ASCII Selected bibliography of geoscientific work done in the CDE quadrangles. It is more extensive than the references within CDE-report. Bibliography.wpd WordPerfect The bibliography in WordPerfect 6/7/8 format. Bibliography.doc MS Word The bibliography in MS Word 97 format. Bibliography.pdf Portable document The bibliography in Adobe Acrobat format. Alaska_index75DPI.jpg JPEG image A low-resolution index file for the CDE area. Alaska_index150DPI.jpg JPEG image A moderate-resolution index file for the CDE area. Craig-Charlotte_Topo.jpg JPEG image Topographic image of the CDE quadrangles, showing the main towns and also location with respect to the Dixon Entrance and the Queen Charlotte Islands of Canada. Craig-Charlotte_Topo.gif GIF image Topographic image of the CDE quadrangles, showing the main towns and also location with respect to the Dixon Entrance and the Queen Charlotte Islands of Canada. ----DATA directory, containing original processed and edited magnetic and gravity data---- Mag_ASEG-GDF.dat ASEG-GDF Residual magnetic grid-data in xyz form, ASEG-GDF data standard. Mag_ASEG-GDF.dfn ASEG-GDF ASEG-GDF definition file, explaining columns (Society of Exploration Geophysicists "A-Format"). Mag_ASCII.dat CSV data Residual magnetic grid-data in xyz form, CSV data standard (ASCII) Mag_Geosoft_XYZ.dat Geosoft ASCII Residual magnetic grid-data in xyz form, Geosoft xyz data standard. Gravity_May92.dat ASCII CDE gravity data in ASCII columns: Station ID, Decimal Long, Decimal Lat, Free Air Anomaly, Complete Bouguer Anomaly, Elevation in feet, Inner Terrain Correction, Outer Terrain Correction, Observed Gravity Minus 980000, Isostatic Anomaly USGS_gravity_format.txt ASCII Explanation of the USGS gravity data format Craig_DRG_250k.gz ZIP-tif The 1:250,000 scale topographic map of the Craig 1-degree by 3-degree quadrangle, ZIP-compressed TIFF format (uncompressed *.tif file is ~20 Mbytes). Dixon_DRG_250k.gz ZIP-tif The 1:250,000 scale topographic map of the Dixon Entrance 1-degree by 3-degree quadrangle, ZIP-compressed TIFF format (uncompressed *.tif file is ~20 Mbytes). Rock_Densities.txt Comma-delim ASCII A list of rock densities acquired by Dave Barnes in the early 1970's, listed by lat, long, and the associated gravity station where the samples were acquired. ----GEOLOGY directory, containing several versions of the simplified geology map---- Geology.e00 ARC/INFO Simplified geologic map of the CDE quadrangles by Don Grybeck, standard ARC/INFO Export file. Geology.lin ARC/INFO *.lin is an ARC/INFO lineset (like a font set) Geology.shd ARC/INFO *.shd is ARC/INFO shadeset (like a color palette) Geology.ps Postscript Simplified geologic map in PostScript format Geology.tif TIFF Simplified geologic map as a TIF image Geology.jpg JPEG Simplified geologic map as a JPEG image Geology.CDR CorelDraw8 Simplified geologic map in CorelDraw8 format GEOLOGIC_Units ASCII A description of the map units in the simplified CDE geologic map Geology_Map.META ASCII Metadata file describing the simplified CDE geology map. NOTE: Geology.grd, a geo-registered Geosoft1 Color Grid of the simplified geologic map is located in the directory "\Grids". ---GRIDS directory, containing digital magnetic and gravity grids in two formats each---- CBA_Grav.grd Geosoft GRD CDE Complete Bouguer Anomaly grid, unprojected (lat-long grid) CBA_Grav_UTM.grd Geosoft GRD CDE Complete Bouguer Anomaly grid, UTM projection Iso_Grav.GRD Geosoft GRD CDE Isostatic-correction gravity grid, unprojected (lat-long grid) Iso_Grav_UTM.grd Geosoft GRD CDE Isostatic-correction gravity grid, UTM projection RedPole_Mag.grd Geosoft GRD CDE Reduced-to-the-pole magnetic grid, unprojected (lat-long grid) RedPoleMag_UTM.grd Geosoft GRD CDE Reduced-to-the-pole magnetic grid, UTM projection Resid_Mag.grd Geosoft GRD CDE Residual magnetic grid, unprojected (lat-long grid) Resid_Mag_UTM.grd Geosoft GRD CDE Residual magnetic grid, UTM projection Topo.grd Geosoft GRD CDE Digital Elevation Model, unpro- jected (lat-long grid) Topo_UTM.grd Geosoft GRD CDE Digital Elevation Model, UTM projection Cra-Dix-Topo ER Mapper CDE Digital elevation data, unprojected (lat-long grid), ER Mapper format. Cra-Dix-Topo.ers ER Mapper CDE Digital elevation ER file, unpro- jected (lat-long grid) ER Mapper control file. Cra-Dix-Topo_UTM ER Mapper CDE Digital elevation data, UTM pro- jection, ER Mapper format. Cra-Dix-Topo_UTM.ers ER Mapper CDE Digital elevation ers file, UTM projection, ER Mapper control file. Geology.grd Geosoft CDE simplified geology map as a geo-referenced Geosoft color grid, generated for overlay purposes... This file is 75 Mbytes in size, requiring a computer with at least 100 Mbytes of RAM. NOTE: Magnetic and gravity grids, both unprojected lat-long and UTM projection, have also been converted to the general Grid eXchange Format (*.GXF) and are also included in this same "\Grids" directory with the same file names but with *.gxf extensions.. ----IMAGES directory, containing images of the gravity and mag data superimposed over the shaded-relief topography and the geology. NOTE: all images are in UTM projection ONLY---- AnnotatedMagAnomalyES.cpt An editable Corel PhotoPaint image of the magnetic anomaly map superimposed on shaded topography, with annotations showing place names and the modeling profiles described in files CDE-Report.* AnnotatedMagAnomalyMap.jpg The annotated magnetic map as a JPG (Colored RTP mag over shaded topo) image. CBAGravColorShadTopo.tif The Complete Bouguer Anomaly gravity data plotted in color and superimposed over a gray-shaded-relief image of the topography. IsoGravColorONShadTopo.tif The Isostatic gravity data plotted in color and superimposed over a gray-shaded- relief image of the topography. RedPoleMagONColoShadTopo.tif The RedPole mag data plotted in color and superimposed over a gray-shaded- relief image of the topography. ResidualMagONColoShadTopo.tif The residual mag data plotted in color and superimposed over the gray-shaded- relief image of the topography. ***Several additional experimental products are also included in this directory: ContIsoGravColorShadTopo.tif The isostatic gravity data as contours on a color-shaded-relief image of the topography. ContRedPoleMagColorTopo.tif The RedPole mag data as contours on a color-shaded-relief image of the topography. Euler-SI1-OnShadedTopo.jpg The Euler deconvolution (depth-to-source) of the magentic data from the CDE area; this is a depth-to-source and 3-D structure representation, using a Structural Index of 1 (see CDE-Report.* for an explanation) -- JPEG format. Euler-SI2-OnShadedTopo.jpg The Euler deconvolution (depth-to-source) of the magentic data from the CDE area; this is a depth-to-source and 3-D structure representation, using a Structural Index of 2 (see CDE-Report.* for an explanation). ContRedPoleOnGeology.jpg The contoured reduced-to-pole magnetic field superimposed on the simplified color CDE geologic map - JPEG format. ContIsoGravOnGeology.jpg The contoured isostatic gravity super- imposed on the simplified color CDE geologic map. *.META Metadata files describing in detail the generation and corner coordinates of the preceding images. Dall_Island_Model.jpg A JPEG image of the results of the magnetic model of a profile over northern Dall Island. Twin_Mountain_Model.jpg A JPEG image of the results of a combined magnetic and gravity model over the Twin Mountain anomaly, north-central Prince of Wales Island. ----ACROBAT directory, containing installation programs for Adobe Acrobat Reader version 4.0 for Macintosh and Windows 9x & NT PC's; see system requirements---- To contact the first author: Jeff Wynn US Geological Survey Vancouver, WA Phone: (360) 993-8919 email: jwynn@usgs.gov