Geology of the Delarof and Westernmost Andreanof Islands Aleutian Islands, Alaska By GEORGE D. F'RMER end H. FRANK BARNETT INVESTIGATIONS OF ALASKAN VOLCANOES Prepared in coofirration with the Departments of the Army, Nawy, and Air Force UN1TE.D STATES GOVERNMENT PRINTENG OFFICE, WASHINGTON 1 1959 UNITED STATES DEPARTMENT OF TffE INTERIOR FRED A, SEATON, Smrettny GEOLOGICAL SURVEY Thomen B. Nolan, Mrectw Rawer, George Mitt, 1926 GBolom of the Delnrof and Westernmost Andreanof Is- lands, Aleutian Islands, Alaska, by Gear D. Fraser and H. Frank Barnett. JF7ashington, U.S. &vt. Print. Off., 1959. v, 211-248 p. Ww, maw (4 fold. cal. in pocket) profile, tablea, 25 cm. (U.8. QmIoglcal Survey. Bulletin 1028-1. Investigations of Alaekan volcanws) "Prepared in mperatlon with the Dements d the Army, Navy, and Air Force?' Blbliograpag : p. 2444H. 1. (feology-Aleutian Island& 2. Rocks, Igneous. I. Barnett, Henry Frttnk, 1921- joint author. u TltIe: I3ela.d and western- mmt Andreanof Idmds, Aleutian Man&, Alaska. (SerIea: C.8. Qeologlcal Bumey. Bulletin 10-I. Scrim : V.& ~eologlcal Sur- vey. Investigattona of Alnskan volcanoes) 557.984 The U. S. Geological Smy,in response to the October 1945. request of the War Department (now Department of the Army), made rr reconnsriassxrce during 1946-64 of volcanic activity in the Aleutian Islands-Alaska Penimula area. Rwdi% of the first year's research, fieId, and laboratory work were hastily wembled as mo administrative reports to the War Department. Some of the early findings, as recorded by Robert R, Coats, were published in Bulletin 974-B (1950), "Volcanic Activity in the Aleutian Arc," and in Bulletin 989-A (1961), "Geology of Euldir Island, Ahutian IsIands, Alaska!' Unpublished results of the early work and all data gathered in later studies are being published u %parate cpterrt of Bulletin 1028. The investigations of 1946 were financed principally by the Military Intelligence Division of the Office, Chief of Engineers, U. S. Army. From 1947 until 1955 the Departments of the Army, Navy, and Air Force jointly furnished financial and logistie wistrtnce. m CONTENTS Lo~ation,,,------------------------,-.--,----~-------------~- Climate and ~WtEon,,,----------- --,- ,- -- ,- - --------------*, k10~y,.,,,---- * ----- * ---------..,-----****-* ..------------------. hydrncks-------,,,,,.***-------------*-----------*-*---* Amatfgnak laland,, ,- - - - - - - - + - - - - - -I- - -II - - - - - - - -- - - - - - - Ulak Idand,,,----,,,,--------------------~--------------- Central Delamf Islands and southern parts of Tanaga and Ramp Xwlands-- ---,,-- ,- --- - - - - - - ------ - - - - - - - - - - - --- --- ---- Early eMeld wlcanw-,-- -,,, , , , - - - - - - - ,- --I - - - - - - - - - - - -- - - - Recent volcanic cones,,- ---,.,,, ,------ --,-,----- - --,,----- Surficial deposits-----------,,,,,---,-----,---------,,,---- megrained intmive rocks-. .-,-,,-,,.,,,-,----,---,----- -- ----- Coamgmined intrusive rocks,,- - -,,, , , . , - - - _,- -- - - - - * - - ,,- - - - - - - - - - References ~ikd--------~-----.--------------+---------------,----,- ILLUSTRATIONS PLATE27. Gmneralhd geoldc map of Delamf and weeternmost Andreanof Islands. 28. Geolouie map of westeft) peninmls of Kanaga Ialand. 29. Geologic map of Kavdga Island. 80. Geologic map of Ogliuga and Skagul Idands. 31. Garetoi Volcano from Skagul Island - - ,, - --- ---- ----- , Facing 212 a2. Kavalga Idaad, looking west-- ---,--.,----,,,,,,,,--Facing 213 Ram 41. Index map of Aleutian Islands -----,--.,,,---------------213 46. Detsiledaubmarine topography of central Delamf Islands atea 236 46. Surfaces of planation and drainage map, central Ranaga I~land---------,..----~------------~,~~-239 47. Seleckd bpographic proAIea showing orientations of planar aurfam of five islends of Delarof groap,, .-. ,,, - ,,, ----,242 TABLES Tm1. Fosrdls from Kansga and Tanaga Ialands- - - - - - - - - - ,, , . -, - 218 2. Chemical composition of roeka from Deldand areshrnmoirt Andreanof Ialande----------,..-.---+---------,..,,,,- 222 w fn~~&~-.-~---~---*-----------~,-------------*--------.--~--. ~praphy-,--,---rr--------------c--------------It------.--.-c--- hcation,,,----------------------------------------------.--- Climate and v~htion,,--. ------,,,-.---- ---------- --------------- Layared rocks ------------------.------------*------- ---------- Amatdgnak Idand,, -------- --,,- ------------------- ------- Ulak Idand ---------------------------------~------------- Cenh.aI Debf Ialanh and muthem parts of Tamp and Xanaga Islands-,,- -,, - - - ,- - - -,,, , , - - - - - - - - - - - - - - I - - - - - - - - - - - - Early shield volcam-,--------- --,- -.-- - ------ -,---------,- Recent volcanic cones--- - - - - - - ,, - - - - - - - - r-- - - - - - - - - - - - - - - - - Surficid deposits- - - -- -- - - - - - - ,, - - -,,, - ,. - ., - - - + - - --a - - - - a nne-grained intrusive rucks-. .-- - - - ,- -,,- - ., , - ,,- - - - - - - - - --- +- - - Coam+graid intrusive rocks-----, - -----. ---- ,-- --+-+------- Submarine topography,- ---- ---- ------------- -------------- ph@ogr~phy--.-~.-.~------------,---------,---,-------------~--- -logic history,. ,-, ,,- ,, .- - -- - - - - - - -- - - - - - - .- -- - Referencescited---,----------+------------------------------------ - ILLUSTRATIONS mrn 27. Generalized geologic map of Delarof and weaternmat Andreanot Islands. 28. Geologic map of western peninmula of Hmga Ialand. 29. Geologic map of Kavalga Inland. SO. Geologic map of Ogliuga and Skagul Idanda 31. Gareloi VoIcano from Sbgul Idand - - ,,----,----- .,-, Facing 212 32. Kavalga bland, looking west-, - ,------,-------,,-.,.Facing 213 44, Index map of Aleutian Islands ,-,,-,-------- ---- -- - ,, - -,, 213 45. DebiIedaubmarine topography oZ central Delamt hLands area- 236 45. Surfacea of planation and drainage map, central Kanaga Island--------------,--..,.--.---,-2----------------.- 239 47. Selected topographic profiles ehowing orientations of planar surfaces of five islanch of Delarof group- ----------,,--,,242 TABLES 1- 1. Fodm from lhnaga and Tanaga Islands,, ,-, ,, - - - - - - - - - - - 218 R Chemical composition of mka from Delmf and w&enrrnost Andreanof Islands -,--,,---,.---,.-,,,--,,,-----------222 v INVESnGATEONS OF AMUN VOLCANOES GEOLOGY OF TWE DELAROF AND WESTERNMOST ANDREANOF ISLANDS, ALEUTIAN ISLANDS, ALASKA By GEORGE D. FRAsER and H. FRANK BmmTT Th8 layered mks of the Delarof and westernmoat Andreanof Ihdn are divisible Into dve unlta, generaIlp younger from south to north. Unit 1, the rockn of Amatignak IsIand, ia composed of sltered, well-bedded Macmua mka including thick, finely banded, pen6~~13Ibempa~a~~tr~l~de formed argillib. These rocks apparently grade northward into unit 2, the altered pillow lava3 and pyroclastic depwita of Ulak Island which are in- terpreted as a near-~oamfacies of unit 1. The age of these twa dta is unknown but preamablp 31 Tertiary. Unit 3 is a composite sequence of almost unaltered ahallow marine and mbaerial wleanic r& cmpoeed of tuf-breccia, lava, pillow lava, and mrbrdinate sedimentary r& Thin units extends in a belt acrasa the central Delarof Idands and the sonthem part^ of Tanage and Kanaga Islands. Upper Tertiary fwfla are found in the roc3ts on Tanaga and Kanaga; the rocks of the central Dehofs are comlsted with these because of lithologic ~imilarities. The rocks in unit 3 may be partly qaivalent, extreme faciea of the Amstignak OF they may be younger. The mtact is not exposed. Unit 4 is composed of Pleistmene precaldere lam that fonna fragments of old sbidd volcamw near the presently active cones. This lava, younger than most of unit 3, Etpp~terI* intertongum in places with the upper part of the older sequence. Unit 6 comprises the composite cones of presently active Gareloi, Tanaga, and &ma@ Volcanoes. All five bedrock units are andesitic to basaltic in composition. Unita 1, 2, and 3 are cut by many dlkea, dike mrrns, and sills of andeb ikic of basaltic cornpodtion. One limburgite Intrusive mass and one Eight rhpdacite dike represent divergent compodtiona. The older nnib are alao cut by coaree-grained tlills, dikes, and plnhna, mostly of granodioritic cornpo~ition, 31ak Island is part of a granodiorlte pluton cut by aplite and andedte diben; none of the invaded rock b mposed and the age is unknown. None of the r& have been m'onally mhmorphoeed: mem lowee foliated meks, auch as slate and phyllite, are absent. Submarine contour8 reveal a major trench and ridge abuctare for tho Alsutian arc Islands are actnally peah of a great arcuata mountain r- In this area the range rises 25,000 feet from a foxdeep on the Pacific ~Ide and 13,000 feet from a deep on the north. The main ridge in apparently an arch botlnded on the uouth bp; a norkhaipping thrust soae and cnr the nwth by a high-angle fault mne, downthrown to the north. Volcanoes are located dong the inferred fault an the north. A grmp of transverse mb- marine and rmbaerial linear elements nuggesh further that the area bas been segmented by high-angle faulting. An Aldan island arc wan probably formed in this general area as early as Miocene time, but the pment voleanoss end the ieland loeationa and Plhapas were formed much labr, probably In Pleiwne time. Several stage8 of Iate Tertiary or Quaternary wave planation nnd mb- aequmE differential tilting eba~the late hiatory of the era; sporadic central-type volcanism at ita north edge began in early Pleiistocene and has continued to the present time. Widespread deposition d Recent ash, and hi~torjeernptiana from Gamloi, Tanaga, and Kanaga Volmnoes,