More than 97 separate occurrences of ultramafic rocks, some of which are included in a north west-trending zone of alpine-type ultramafic rocks, have been mapped in the Eagle quadrangle, east-central Alaska. They are divided into three groups primarily on the basis of degree of serpentinization. Group I consists of lens-shaped bodies of serpentinite 1 m2 (10 ft2) to several 100 m2 (1,000 ft2) in area. Relict textures and presence of bastite indicate that the original rock was harzburgite and dunite. Group II consists of bodies composed of partially serpentinized harzburgite and dunite and includes the large Mount Sorenson and American Creek bodies. Group III is dominantly hornblendite and pyroxenite, probably intrusive and not genetically related to groups I and II. The authors believe that the ultramafic bodies of groups I and II are alpine-type peridotites and may include dismembered ophiolitc. The Tintina fault system could have provided a zone of weakness along which mantle material was tectonically emplaced or it may have been a plate boundary in late Paleozoic time. If it represents a plate boundary, the metamorphic terrane which lies between the Tintina and Denali fault systems would have to be allochthonous, perhaps originating as a northward-moving slice of continental crustal material. During the course of the movement as the two continental masses approached and perhaps collided, mantle peridotite and oceanic crustal material were squeezed up along the continental margin onto the continental slice.
","language":"English","publisher":"U.S. Geological Survey","publisherLocation":"Reston, VA","usgsCitation":"Foster, H.L., and Keith, T.E., 1974, Ultramafic rocks of the Eagle quadrangle, east-central Alaska: Journal of Research of the U.S. Geological Survey, v. 2, no. 6, p. 657-669.","productDescription":"13 p.","startPage":"657","endPage":"669","onlineOnly":"N","additionalOnlineFiles":"N","costCenters":[],"links":[{"id":307199,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"},{"id":307198,"rank":1,"type":{"id":11,"text":"Document"},"url":"https://pubs.usgs.gov/journal/1974/vol2issue6/report.pdf","text":"Report","size":"16.19 MB","linkFileType":{"id":1,"text":"pdf"},"description":"Report"}],"country":"United States","state":"Alaska","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"type\": \"Polygon\",\n \"coordinates\": [\n [\n [\n -144,\n 63\n ],\n [\n -144,\n 66\n ],\n [\n -141,\n 66\n ],\n [\n -141,\n 63\n ],\n [\n -144,\n 63\n ]\n ]\n ]\n }\n }\n ]\n}","volume":"2","issue":"6","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"568e493ae4b0e7a44bc41ad8","contributors":{"authors":[{"text":"Foster, Helen L.","contributorId":56195,"corporation":false,"usgs":true,"family":"Foster","given":"Helen","email":"","middleInitial":"L.","affiliations":[],"preferred":false,"id":569339,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Keith, Terry E.C.","contributorId":79099,"corporation":false,"usgs":true,"family":"Keith","given":"Terry","email":"","middleInitial":"E.C.","affiliations":[],"preferred":false,"id":569340,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70198184,"text":"70198184 - 1972 - Structure of Sierra Madera, Texas, as a guide to central peaks of lunar craters","interactions":[],"lastModifiedDate":"2018-07-18T15:24:14","indexId":"70198184","displayToPublicDate":"1972-12-31T00:00:00","publicationYear":"1972","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1723,"text":"GSA Bulletin","active":true,"publicationSubtype":{"id":10}},"title":"Structure of Sierra Madera, Texas, as a guide to central peaks of lunar craters","docAbstract":"Like hundreds of other lunar craters of probable impact origin, Copernicus contains central peaks presumed to expose rocks uplifted from beneath the crater floor. A possible analog of these peaks on Earth is the central uplift of the Sierra Madera cryptoexplosion structure, a probable impact scar (astrobleme) in stratified Permian and Cretaceous rocks of west Texas. The most conspicuous part of this 12-km-wide structure is its central uplift, 6 to 8 km across, in which the oldest rocks have been raised 1,200 m above their normal position. The uplift is surrounded by a structural depression, beyond which is a concentric rim containing some folds and circumferential normal faults with downthrow toward the center. The intensity of folding and faulting increases inward from the flanks of the central uplift toward a central zone about 2 km across where dips and fold plunges are near vertical or overturned. As in salt domes, the beds moved inward as well as upward to occupy their present positions, causing faulting and radial folding due to crowding in the center. Repetition by folding due to inward movement of upper beds over lower appears to have been followed by upward movement of the core of the uplift pulling away from the flanks by faulting. Minor outward-directed thrusting may have been caused by gravitational spreading of the rising dome. The structural depression surrounding the uplift resulted from tectonic thinning accompanying the inward movement of rocks in the uplift.
Analogy with experimental craters and with other cryptoexplosion structures indicates that the uplift at Sierra Madera protruded into a crater (since destroyed by erosion) that was about 12 km across. Inasmuch as the rocks forming such uplifts are derived from below the crater floors, analogous peaks in lunar craters such as Copernicus may offer samples of lunar crust uplifted from distances below the crater floor on the order of one-tenth of the crater diameter.
","language":"English","publisher":"Geological Society of America","doi":"10.1130/0016-7606(1972)83[2795:SOSMTA]2.0.CO;2","usgsCitation":"Howard, K.A., Offield, T.W., and Wilshire, H.G., 1972, Structure of Sierra Madera, Texas, as a guide to central peaks of lunar craters: GSA Bulletin, v. 83, no. 9, p. 2795-2808, https://doi.org/10.1130/0016-7606(1972)83[2795:SOSMTA]2.0.CO;2.","productDescription":"14 p.","startPage":"2795","endPage":"2808","costCenters":[{"id":312,"text":"Geology, Minerals, Energy, and Geophysics Science Center","active":true,"usgs":true}],"links":[{"id":355810,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"country":"United States","state":"Texas","otherGeospatial":"Sierra Madera crater","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"type\": \"Polygon\",\n \"coordinates\": [\n [\n [\n -103.326416015625,\n 29.878755346037977\n ],\n [\n -101.25,\n 29.878755346037977\n ],\n [\n -101.25,\n 31.662732913235317\n ],\n [\n -103.326416015625,\n 31.662732913235317\n ],\n [\n -103.326416015625,\n 29.878755346037977\n ]\n ]\n ]\n }\n }\n ]\n}","volume":"83","issue":"9","noUsgsAuthors":false,"publicationStatus":"PW","contributors":{"authors":[{"text":"Howard, Keith A. 0000-0002-6462-2947 khoward@usgs.gov","orcid":"https://orcid.org/0000-0002-6462-2947","contributorId":3439,"corporation":false,"usgs":true,"family":"Howard","given":"Keith","email":"khoward@usgs.gov","middleInitial":"A.","affiliations":[{"id":312,"text":"Geology, Minerals, Energy, and Geophysics Science Center","active":true,"usgs":true}],"preferred":true,"id":740470,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Offield, Terry W.","contributorId":15196,"corporation":false,"usgs":true,"family":"Offield","given":"Terry","email":"","middleInitial":"W.","affiliations":[],"preferred":false,"id":740471,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Wilshire, H. G.","contributorId":36125,"corporation":false,"usgs":false,"family":"Wilshire","given":"H.","middleInitial":"G.","affiliations":[],"preferred":false,"id":740472,"contributorType":{"id":1,"text":"Authors"},"rank":3}]}} ,{"id":70198177,"text":"70198177 - 1971 - Impact breccias in carbonate rocks, Sierra Madera, Texas","interactions":[],"lastModifiedDate":"2018-07-19T09:49:59","indexId":"70198177","displayToPublicDate":"1971-12-31T00:00:00","publicationYear":"1971","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1723,"text":"GSA Bulletin","active":true,"publicationSubtype":{"id":10}},"title":"Impact breccias in carbonate rocks, Sierra Madera, Texas","docAbstract":"Two main types of deformational breccia occur in the Sierra Madera cryptoexplosion structure: monolithologic breccias composed of shattered rock of a single lithology and mixed breccias composed of rocks of several lithologies. Monolithologic breccias generally show no mineralogic signs of shock deformation, but a few samples are shatter-coned in a manner suggesting simultaneous formation of breccias and shatter cones. Mixed breccias, forming irregular, cross-cutting bodies, consistently contain moderately to highly shocked material, with mineralogic evidence of shock pressures of 50 kb to more than 200 kb, which, with evidence from the structural geometry of Sierra Madera and orientation of shatter cones, indicate an impact origin of the breccias.
The mode of occurrence of the breccias, petrographic characteristics, and association with shock features are shared by breccias in many other cryptoexplosion structures in both carbonate and crystalline rock terranes, suggesting that such breccias have a common origin.
","language":"English","publisher":"Geological Society of America","doi":"10.1130/0016-7606(1971)82[1009:IBICRS]2.0.CO;2","usgsCitation":"Wilshire, H.G., Howard, K.A., and Offield, T., 1971, Impact breccias in carbonate rocks, Sierra Madera, Texas: GSA Bulletin, v. 82, no. 4, p. 1009-1018, https://doi.org/10.1130/0016-7606(1971)82[1009:IBICRS]2.0.CO;2.","productDescription":"10 p.","startPage":"1009","endPage":"1018","costCenters":[{"id":312,"text":"Geology, Minerals, Energy, and Geophysics Science Center","active":true,"usgs":true}],"links":[{"id":355802,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"country":"United States","state":"Texas","otherGeospatial":"Sierra Madera crater","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"type\": \"Polygon\",\n \"coordinates\": [\n [\n [\n -104.205322265625,\n 30.002516938570686\n ],\n [\n -102.19482421875,\n 30.002516938570686\n ],\n [\n -102.19482421875,\n 31.784216884487385\n ],\n [\n -104.205322265625,\n 31.784216884487385\n ],\n [\n -104.205322265625,\n 30.002516938570686\n ]\n ]\n ]\n }\n }\n ]\n}","volume":"82","issue":"4","noUsgsAuthors":false,"publicationStatus":"PW","contributors":{"authors":[{"text":"Wilshire, H. G.","contributorId":36125,"corporation":false,"usgs":false,"family":"Wilshire","given":"H.","middleInitial":"G.","affiliations":[],"preferred":false,"id":740433,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Howard, Keith A. 0000-0002-6462-2947 khoward@usgs.gov","orcid":"https://orcid.org/0000-0002-6462-2947","contributorId":3439,"corporation":false,"usgs":true,"family":"Howard","given":"Keith","email":"khoward@usgs.gov","middleInitial":"A.","affiliations":[{"id":312,"text":"Geology, Minerals, Energy, and Geophysics Science Center","active":true,"usgs":true}],"preferred":true,"id":740434,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Offield, Terry W.","contributorId":64217,"corporation":false,"usgs":true,"family":"Offield","given":"Terry W.","affiliations":[],"preferred":false,"id":740435,"contributorType":{"id":1,"text":"Authors"},"rank":3}]}} ,{"id":41419,"text":"ofr68103 - 1968 - Preliminary geologic map of the Eagle B-1 and C-1 quadrangles, Alaska","interactions":[],"lastModifiedDate":"2012-02-02T00:10:34","indexId":"ofr68103","displayToPublicDate":"1994-01-01T00:00:00","publicationYear":"1968","noYear":false,"publicationType":{"id":18,"text":"Report"},"publicationSubtype":{"id":5,"text":"USGS Numbered Series"},"seriesTitle":{"id":330,"text":"Open-File Report","code":"OFR","onlineIssn":"2331-1258","printIssn":"0196-1497","active":true,"publicationSubtype":{"id":5}},"seriesNumber":"68-103","title":"Preliminary geologic map of the Eagle B-1 and C-1 quadrangles, Alaska","language":"ENGLISH","doi":"10.3133/ofr68103","usgsCitation":"Foster, H.L., and Keith, T.C., 1968, Preliminary geologic map of the Eagle B-1 and C-1 quadrangles, Alaska: U.S. Geological Survey Open-File Report 68-103, 1 map, https://doi.org/10.3133/ofr68103.","productDescription":"1 map","costCenters":[],"links":[{"id":106403,"rank":700,"type":{"id":15,"text":"Index Page"},"url":"https://ngmdb.usgs.gov/Prodesc/proddesc_8243.htm","linkFileType":{"id":5,"text":"html"},"description":"8243"},{"id":172375,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/usgs_thumb.jpg"},{"id":98420,"rank":400,"type":{"id":17,"text":"Plate"},"url":"https://pubs.usgs.gov/of/1968/0103/plate-1.pdf","size":"6191","linkFileType":{"id":1,"text":"pdf"}}],"noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"4f4e4ac8e4b07f02db67b903","contributors":{"authors":[{"text":"Foster, Helen L.","contributorId":56195,"corporation":false,"usgs":true,"family":"Foster","given":"Helen","email":"","middleInitial":"L.","affiliations":[],"preferred":false,"id":224985,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Keith, Terry C.","contributorId":60304,"corporation":false,"usgs":true,"family":"Keith","given":"Terry","email":"","middleInitial":"C.","affiliations":[],"preferred":false,"id":224986,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70198168,"text":"70198168 - 1968 - Shatter cones at Sierra Madera, Texas","interactions":[],"lastModifiedDate":"2018-07-18T11:46:38","indexId":"70198168","displayToPublicDate":"1968-12-31T00:00:00","publicationYear":"1968","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":3338,"text":"Science","active":true,"publicationSubtype":{"id":10}},"title":"Shatter cones at Sierra Madera, Texas","docAbstract":"Shatter cones abound in the central uplift of Sierra Madera and they occur as far as 6.5 kilometers from the center. Apical angles average near 90 degrees. Whole cones and full cones represented by diversely oriented cone segments in any structural block show relatively uniform orientations of axes and a dominant direction of point. The cones predate faulting and folding in the central uplift, and, when beds are restored to horizontal, most cones point inward and upward, a pattern that supports the hypothesis of an impact origin.
","language":"English","publisher":"American Association for the Advancement of Science","doi":"10.1126/science.162.3850.261","usgsCitation":"Howard, K.A., and Offield, T.W., 1968, Shatter cones at Sierra Madera, Texas: Science, v. 162, no. 3850, p. 261-265, https://doi.org/10.1126/science.162.3850.261.","productDescription":"5 p.","startPage":"261","endPage":"265","costCenters":[{"id":312,"text":"Geology, Minerals, Energy, and Geophysics Science Center","active":true,"usgs":true}],"links":[{"id":355777,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"country":"United States","state":"Texas","county":"Pecos County","otherGeospatial":"Sierra Madera crater","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"type\": \"Polygon\",\n \"coordinates\": [\n [\n [\n -103.326416015625,\n 29.878755346037977\n ],\n [\n -101.25,\n 29.878755346037977\n ],\n [\n -101.25,\n 31.662732913235317\n ],\n [\n -103.326416015625,\n 31.662732913235317\n ],\n [\n -103.326416015625,\n 29.878755346037977\n ]\n ]\n ]\n }\n }\n ]\n}","volume":"162","issue":"3850","noUsgsAuthors":false,"publicationStatus":"PW","contributors":{"authors":[{"text":"Howard, Keith A. 0000-0002-6462-2947 khoward@usgs.gov","orcid":"https://orcid.org/0000-0002-6462-2947","contributorId":3439,"corporation":false,"usgs":true,"family":"Howard","given":"Keith","email":"khoward@usgs.gov","middleInitial":"A.","affiliations":[{"id":312,"text":"Geology, Minerals, Energy, and Geophysics Science Center","active":true,"usgs":true}],"preferred":true,"id":740395,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Offield, Terry W.","contributorId":15196,"corporation":false,"usgs":true,"family":"Offield","given":"Terry","email":"","middleInitial":"W.","affiliations":[],"preferred":false,"id":740396,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ]}