Procedures_Used: The linework was digitized in 1997 from a paper copy of the 1994 map at the U.S. Geological Survey's Alaska Section (Geologic Division) facilities in Anchorage, AK. The original Transverse Mercator projection of the map (Central Meridian: 100*W; Scale factor: 0.926; Reference ellipsoid:(6371204m, 63712004m)) was converted to an Albers equal-area coverage in ARC/INFO (version 7.1.2). The resulting coverage did not align exactly with an Albers equal-area coverage of the Alaskan coastline, so a rubber-sheeting operation was performed using points along the coastline and major rivers to match an Albers equal area projection. Map unit (polygon) locations and attributes were checked by the person responsible for the digitizing, and spot-checked by one reviewer, by comparing a printed copy of the coverage to the published map. Metadata were collected using document.aml v. 7.1.1, distributed by ESRI, Inc.
Revisions: None completed or planned.
Reviews_Applied_to_Data: See Procedures_Used.
Related_Spatial_and_Tabular_Data_Sets:
Other_References_Cited: Moll-Stalcup, E.J., Brew, D.A., & Vallier, T.L. 1994. Latest Cretaceous and Cenozoic Magmatic Rocks of Alaska, Plate 5 in: Volume G-1, "The Geology of Alaska", Geology of North America series (GNA-G1), Plate 5. Geological Society of America, Inc., Boulder, CO. Scale 1:2,500,000.
Notes: The completeness and quality of the geologic data in the digital coverage is that of the published 1994 map, which summarized data collected prior to that date (mainly since 1980). No recent data have been added. The geographic accuracy of the published map has been slightly degraded by the rubber-sheet operation.
MAGMATIC.PAT COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME INDEXED? 1 AREA 4 12 F 3 - 5 PERIMETER 4 12 F 3 - 9 MAGMATIC# 4 5 B - - 13 MAGMATIC-ID 4 5 B - - 17 A 2 2 B - FELDSPATHOID-BAS - 19 B 2 2 B - BASALT - 21 C 2 2 B - ANDESITE - 23 D 2 2 B - DACITE - 25 E 2 2 B - RHYOLITE-DACITE - 27 F 2 2 B - GRANITIC(INT-FEL - 29 G 2 2 B - GRANITIC(DOM-FEL - 31 H 2 2 B - GABBRO - 33 AGE-1 2 2 B - 0-5(MA) - 35 AGE-2 2 2 I - 5-30(MA) - 37 AGE-3 2 2 I - 30-45(MA) - 39 AGE-4 2 2 I - 45-55(MA) - 41 AGE-5 2 2 I - 55-65(MA) - 43 AGE-6 2 2 I - 65-76(MA) - 45 TYPE 2 2 C - - 47 FEATURE_NAME 44 44 C - -
In MAGMATIC.PAT, items A through H and AGE-1 through AGE-6, contain values of either "0" or "1". A value of "1" indicates that the polygon satisfies the criteria defined in the alternate names or in the Attribute_Definitions listed above. (For example; a value of"1" in the column named "D" indicates the presence of rocks of dacite composition; and a value "1" in the column labeled AGE-3 indicates the presence of rocks of 30-45 Ma age). A value of "0" means that the polygon does not satisfy the defined criteria. The item TYPE may contain the character "H" (indicating hypabyssal rocks) or the character "T" (indicating an area of chiefly tuff, breccia, and agglomerate).