DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP I-1807 U.S. GEOLOGICAL SURVEY

GEOLOGIC MAP OF THE KETCHIKAN AND PRINCE RUPERT QUADRANGLES, SOUTHEASTERN

By Henry C. Berg, Raymond L. Elliott, and Richard D. Koch

INTRODUCTION This pamphlet and accompanying map sheet describe the geology of the Ketchikan and Prince Rupert quadrangles in southeastern Alaska (fig. 1). The report is chiefly the result of a reconnaissance investigation of the geology and mineral re­ sources of the quadrangles by the U.S. Geological Survey dur­ ing 1975-1977 (Berg, 1982; Berg and others, 1978 a, b), but it also incorporates the results of earlier work and of more re­ cent reconnaissance and topical geologic studies in the area (fig. 2). We gratefully acknowledge the dedicated pioneering photointerpretive studies by the late William H. (Hank) Con­ don, who compiled the first 1:250,000-scale reconnaissance geologic map (unpublished) of the Ketchikan quadrangle in the 1950's and who introduced the senior author to the study 130' area in 1956. 57'L__r-'-'~~~;:::::::,~~.::::r----, Classification and nomenclature in this report mainly fol­ low those of Turner (1981) for metamorphic rocks, Turner and Verhoogen (1960) for plutonic rocks, and Williams and others (1982) for sedimentary rocks and extrusive igneous rocks. Throughout this report we assign metamorphic ages to various rock units and emplacement ages to plutons largely on the basis of potassium-argon (K-Ar) and lead-uranium (Pb-U) (zircon) isotopic studies of rocks in the Ketchikan and Prince Rupert quadrangles (table 1) and in adjacent areas. Most of the isotopic studies were conducted in conjunction with recon­ naissance geologic and mineral resource investigations and re­ 0 100 200 KILOMETER sulted in the valuable preliminary data that we cite throughout our report. We recognize, however, that our age assignments may be modified in the future as the result of additional FIGURE 1-Location of Ketchikan and Prince Rupert isotopic research. quadrangles, and area of this investigation (stippled) SUMMARY OF GEOLOGY This report describes the rocks in the Ketchikan and Prince Rupert quadrangles between the United States- PRINCE OF WALES-GRAVINA-ANNETTE-MARY -DUKE border and long 132°00' W. The rocks include diverse ISLANDS AREA lithologies that range in age from Ordovician or Silurian to This area includes Prince of Wales Island east of long Quaternary. Our investigations show that the rocks are most 132°00' W. and the islands bounded by , Dixon conveniently described by dividing the quadrangles into three Entrance, , and and geographic areas (fig. 2), each of which has a distinctive as­ makes up about a sixth of the land in the study area. The area semblage of rocks that have characteristic lithologies, struc­ contains the most diverse rock types and the most complete ture, and metamorphic history. sequence of stratified rocks in the Ketchikan and Prince On the map sheet we present an interpretive g_eologic sec­ Rupert quadrangles; it also includes the least metamorphosed tion A-A', adapted from Berg and others (1978c). Our inter­ and least deformed pre-Tertiary rocks in the map area. The pretation is that many of the structural features observed east bedded rocks range in age from Ordovician or Silurian to Late of Bostwick Inlet () are manifestations of south­ Jurassic or Cretaceous; the mapped intrusive rocks range in west-vergent nappes and large-scale thrust faults that are inter­ age from Ordovician or Silurian to Oligocene or Miocene. Dis­ sected by high-angle, mainly strike-slip faults. We also suggest tinctive units include (a) a Silurian batholith of leucocratic that the thrusts served as channelways for more or less con­ trondhjemite (St) on , (b) an Upper Triassic se­ temporaneous (syntectonic) emplacement of some of the Cre­ quence of rhyolite, basalt, and sedimentary rocks ("fisv), and taceous intrusive rocks, whereas other Cretaceous or Tertiary (c) a Cretaceous zoned ultramafic intrusive complex on Duke intrusions postdate the thrusts. Island that contains spectacular zones of rhythmically layered

1 dunite and peridotite (Kum) (Irvine, 1974). Mineral occur­ in this area are basalt and andesite lava flows, breccia, and tuff rences (Berg and others, 1978a; 1981, p. 59-70, 97) include (QTv) that mainly coincide with or postdate Quaternary glacia­ (a) barite- and base- and precious-metal bearing volcanogenic tion but may in part be as old as Pliocene. sulfide deposits in the Upper Triassic rocks, (b) epithermal The oldest radiometrically dated pluton in this area is a veins carrying gold, silver, and other metals in various host­ dike of Silurian trondhjemite (too small to show on the map rocks, (c) magmatic titaniferous magnetite deposits in the sheet) that cuts metamorphosed pre-Devonian rocks near zoned ultramafic rocks, (d) a base- and precious-metal-bearing Caamano Point (Rubin and Saleeby, 1987). The oldest dated skarn deposit in marble and calcsilicate rocks intruded by pluton large enough to show is an Early Cretaceous ultramafic quartz diorite at McLean Arm on Prince of Wales Island (Mac­ complex (Kum) at Alava Bay. The largest pluton is a Kevett, 1963, p. 99-100), and (e) sparse radioactive minerals radiometrically dated middle Cretaceous quartz diorite and in pegmatite dikes near Gardner Bay on Prince of Wales Island granodiorite batholith (Kq) on northern (MacKevett, 1963, p. 93-94). and adjacent Cleveland Peninsula. Other radiometrically The area is characterized by markedly contrasting dated Cretaceous plutons include a swarm of mainly unJ. metamorphic and structural styles. These contrasting styles are metamorphosed but locally flow-foliated and deformed stocks, illustrated on Gravina Island (map sheet, section A-A'; fig. 3), diapirs(?), dikes, and sills of epidote- and garnet-bearing and where they are separated by a high-angle north-northwest­ locally plagioclase-porphyritic granodiorite and quartz diorite striking fault that divides the island nearly in half. On western (Kpg), and an epidote-bearing stock near Moth Bay (Kg). Gravina Island the rocks are only slightly regionally Other intrusive rocks, mainly of known or assumed Cretace­ metamorphosed, and the dominant regional structures include ous age, include stocks or domelike sheets of aplite or alaskite a northwest-trending open syncline and thrust and high-angle (Kig), and several other small ultramafic bodies (Kum). A faults that slightly offset rocks as young as Jurassic or Creta­ large radiometrically dated Oligocene or Miocene gabbro com­ ceous. On eastern Gravina Island, the pre-Tertiary rocks are plex (T g b) occurs near Ketchikan. penetratively deformed and regionally metamorphosed to Regional structures in the pre-Tertiary strata (map sheet, greenschist facies, and the regional structures are southwest­ section A-A'; fig. 3) include southwest-overturned to recum­ overturned isoclinal folds whose axial surfaces dip moderately bent refolded isoclines that are cut by bedding-plane thrusts northeastward. The isoclinal folds are locally refolded or and blastomylonite zones and by high-angle faults that post­ warped about steeply east(?)-plunging axes, and in places date the thrusts. Locally on southwestern Revillagigedo Island, both sets of folds are cut by kink bands associated with vertical the contact between Permian marble and structurally underly­ cleavage that strikes northeastward. The youngest mapped ing Triassic and possibly younger bedded rocks is a gently to structure in the area is a strike-slip fault along Tongass Nar­ moderately northeast-dipping fault that we interpret as a major rows that appears to dextrally offset an Oligocene or Miocene thrust zone at or near the base of the marble unit(s). In places, gabbro pluton (Tgb) by about 6.5 km. this zone appears to be intruded by Cretaceous plutons. The amount of offset on any of the faults is not known, but our in­ REVILLAGIGEDO ISLAND AND CLEVELAND terpretation of the tectonic history of the region (Berg and PENINSULA others, 1972) suggests that their cumulative displacement may The central third of the quadrangle is underlain by diverse be large. The rocks are regionally metamorphosed progres­ plutonic rocks and by multiply deformed and metamorphosed sively from greenschist facies on the southwest to amphibolite strata that include small outcrop areas of sparsely fossiliferous facies on the north and east. The map sheet and figure 3 show Permian (Pm) and Middle Triassic sedimentary and volcanic the approximate position of the gradational boundary be­ rocks ("Rs), and at least one fault-bounded outcrop area of tween the greenschist- and amphibolite-facies rocks in the schist, phyllite, and meta-igneous rocks (SOu) that are in­ Ketchikan and Prince Rupert quadrangles. The minerals and truded by Silurian trondhjemite (Rubin and Saleeby, 1987). textures resulting from this regional metamorphism, which we By far the most abundant bedded rocks, however, constitute interpret to be middle or Late Cretaceous in age, are over­ an assemblage of apparently unfossiliferous metamorphosed printed by contact metamorphism as intense as hornblende­ and deformed strata that we have subdivided into the follow­ hornfels facies near the contacts of the Cenozoic and some of ing four map units according to the lithologies of the pro­ the Mesozoic plutons. Feather schist or "garbenschiefer" toliths. (1) Locally pyritic dark-gray slate, phyllite, and meta­ (Turner and Verhoogen, 1960, p. 649), a metamorphic rock graywacke (metaflysch) intercalated with subordinate green distinguished by locally conspicuous feathery crystal aggre­ andesitic or basaltic metatuff and rusty-weathering felsic or in­ gates of actinolite in a matrix of garnet-bearing silvery musco­ termediate metatuff (MzPzms). Some of the metaflysch is simi­ vite schist, is widespread on central and southeastern Revil­ lar to Jurassic or Cretaceous sedimentary rocks on Gravina lagigedo Island; its distinctive mineralogy and texture suggest and Annette Islands. (2) Andesitic or basaltic volcanic and vol­ complex metamorphism of a bedded unit that was significantly caniclastic rocks and subordinate metaflysch (MzPzmv). Some different in original composition from that of the adjoining of the volcanic rocks consist of relict ferromagnesian-pheno­ strata. cryst porphyry similar to Jurassic or Cretaceous volcanic rocks Mineral occurrences that have been productive or exten­ on Gravina and Annette Islands. (3) Volumetrically minor but sively explored include massive lead- and zinc-sulfide deposits locally conspicuous metaconglomerate (MzPzmc). (4) A catch­ and auriferous quartz veins in the metasedimentary and all unit (MzPzu) consists of several metamorphic rock types too metavolcanic units, a stibnite (antimony) vein in marble near limited in extent to show individually on the geologic map. Caamano Point, and titaniferous magnetite in the ultramafic The assemblage of metamorphosed bedded rocks is intruded complex at Alava Bay (Berg and others, 1978a, 1981). by small bodies of metagabbro and metadiorite (MzPzmi) that may be cogenetic with some of the metavolcanic rocks. We PORTLAND PENINSULA have assigned the four units a premetamorphic age of late The east half of the Ketchikan-Prince Rupert study area is Paleozoic or Mesozoic because this assignment brackets the a peninsula, bounded by (eastern) , Revillagigedo age of the oldest (Permian) fossiliferous strata known in this Channel, and , that we informally call "Port­ area and of the oldest (Early Cretaceous) isotopically dated land peninsula". The youngest consolidated rocks known on plutonic rocks that intrude them. The youngest rocks known Portland peninsula correlate with the Tertiary or Quaternary

2 132' 130' 56'.------~------~------~r-~------~------~------.-,------.~·

.& Mt Reid

FIGURE 2-Ketchikan quadrangle and northern part of Prince Rupert quadrangle, showing areas described in selected geologic reports: 1, Brooks (1902); 2, Smith (1915); 3, Chapin (1918); 4, Buddington (1929); 5, Berg (1972); 6, Berg (1973); 7, Irvine (1974); 8, Smith (1977); 9, Berg and others (1977); 10, Koch and others (1977); 11, Elliott and others (1976) and Hudson and others (1979); 12, Gehrels and others (1984); 13, MacKevett (1963) and Gehrels and Saleeby (1987); 14, geology extrapolated from Eberlein and others (1983); 15, Koch and Elliott (1984). H, Hyder; K, Ketchikan; M, Metlakatla. Dot-dash lines outline the three geographic areas described in "Summary of Geology".

3 132' 130'

10 0 10 20 KILOMETERS

FIGURE 3--Interpretive map showing tectonostratigraphic terranes and structural framework of the Ketchikan and Prince Rupert quadrangles. Plutons not shown. Base map from the National Atlas of the United States, U.S. Geological Survey, 1970.

4 EXPLANATION FOR FIGURE 3

Tectonostratigraphic terrane-Queried where assumed Gravina-Nutzotin belt-Unpatterned, basement not exposed. Solid-line pattern shows distribution of Gravina-Nutzotin belt depositionally overlying Alexander terrane Alexander terrane Craig subterrane Annette subterrane Taku terrane-Dashed line pattern shows distribution of strata that are possibly coeval with those in Gravina-Nutzotin belt. Extent of thes€ rocks in Taku terrane is unknown ~ Tracy Arm terrane LB Stikine terrane

----- Contact-Dotted where concealed ----=~-- High-angle fault-Dotted where concealed. Arrows show relative movement. May coincide in strike with reverse or thrust fault Thrust fault-Sawteeth on upper plate; dotted where concealed. May coincide in strike with high-angle fault 20-50 • • Mapped thrust fault-Showing approximate dip 10-30 A Interred thrust fault-Showing approximate dip -?------Undefined boundary of terrane-Queried where continuation is uncertain or speculative --- -- Coast Range megalineament 50 " tf) Generalized attitude of overturned isoclinal folds-Showing direction of dip of limbs and approximate dip of axial surface, compositional layering, and foliation ---+t-- Syncline ~ Strike of vertical axial plane foliation

--"""~,---- Boundary between regional metamorphic facie~Dotted where concealed. G, greenschist facies; A, amphibolite facies (amphibolite and locally granulite facies on Portland peninsula) Bz Blastomylonite zone

basalt and andesite on Revillagigedo Island (OTv). Except for ers have applied those terms to rocks beyond the geographic small outcrop areas of these volcanic rocks, most of the penin­ limits of the plutonic-metamorphic complex as defined in our sula is underlain by a complex of Mesozoic and Cenozoic plu­ report. In our report, the complex is bounded on the west by tons that enclose metamorphic screens and roof pendants of the western contacts of three map units: foliated quartz diorite problematic premetamorphic age. This plutonic-metamorphic (TKfq) and granodiorite (TKfg), and paragneiss (MzPzyp). The complex is fringed on the west and southwest by metamorph­ southeast boundary is beyond the limits of the Ketchikan and osed upper Paleozoic or Mesozoic bedded rocks, by undivided Prince Rupert quadrangles in Alaska. The complex does not Ordovician or Silurian bedded and intrusive rocks, and by include the recrystallized lower Mesozoic and upper Paleozoic Paleozoic, Mesozoic, and Cenozoic plutons. At the northeast rocks at the northeast corner of the map area. corner of the map area the complex is bounded by recrystal­ The plutonic-metamorphic complex is a heterogeneous lized lower Mesozoic and possibly upper Paleozoic intrusive group of massive to foliated or gneissic batholiths, stocks, and and bedded rocks ('Rt, MzPzvs). Parts or all of the plutonic­ smaller plutons and regionally metamorphosed amphibolite­ metamorphic complex have been variously termed the "Coast and possibly locally granulite facies stratified rocks (MzPzp) Range batholith" (Buddington and Chapin, 1929, p. 173- that form septa, screens, roof pendants, and xenoliths within 253), "Coast plutonic complex" (Roddick and Hutchison, or between the plutons. According to our radiometric age 1974), "Central gneiss complex" (Hutchison, 1970, 1982), data, the plutons were emplaced during Early Cretaceous, "Coast plutonic-metamorphic complex" (Brew and Ford, Late Cretaceous or Paleocene, Eocene, and Oligocene or 1984), and several other variants of those terms. Some work- Miocene time. Their composition ranges from granite to gab-

5 bra; the most abundant rock type is foliated granodiorite Other mineral deposits that have been explored by private in­ (TKfg). Not shown on the map are numerous Oligocene or terests include (a) another porphyry molybdenum occurrence younger lamprophyre (Smith, 1973) and quartz porphyry on the north shore of the mouth of Borroughs Bay, (b) gold, (Hudson and others, 1979) dikes. The premetamorphic age of silver, tungsten, and base-metal veins and disseminated de­ the stratified rocks has not yet been conclusively determined posits in the Triassic or older volcanic and intrusive rocks near by isotopic methods. We assign them a Paleozoic or Mesozoic Hyder, (c) base-metal massive sulfide deposits in the age to bracket the ages of (a) probably correlative, isotopically metamorphosed bedded rocks southwest of Smeaton Bay and dated Paleozoic or older metamorphosed bedded rocks in near Humpback Lake, and (d) copper-, zinc-, and silver-bear­ neighboring (Hutchison, 1982, p. 23-24) ing sulfide veins and disseminations in paragneiss at Walker and (b) the oldest isotopically dated (Early Cretaceous) plu­ Cove (Berg and others, 1977, 1981). tons known to intrude them. The isotopically determined age of metamorphism of the foliated plutonic and bedded rocks on TECTONOSTRATIGRAPHIC TERRANES AND Portland peninsula is Eocene (Smith and Diggles, 1981, p. 2- STRUCTURAL FRAMEWORK 3). Structural trends, isograds, and lithologic units strike north­ Regional tectonic and biostratigraphic investigations (Berg west to north; foliation varies in regional dip from vertical and and others, 1972, 1978c; Monger and Berg, 1985) show that steeply westward-dipping in many places along Behm Canal to the pre-Cenozoic strata in the Ketchikan and Prince Rupert gently to moderately northeastward dipping on central Port­ quadrangles can be interpreted as constituting five, mainly land peninsula (map sheet, section A-A', fig. 3). fault-bounded assemblages (map sheet, section A-A'; fig. 3), West and southwest of the plutonic-metamorphic complex each characterized by its own distinctive stratigraphy and tec­ is a wedge-shaped outcrop belt of regionally metamorphosed tonic history. Northeastward from Prince of Wales Island these greenschist- to amphibolite-facies. Near plutons such as the tectonostratigraphic assemblages are known, respectively, as one near Point Sykes (Kgq), this metamorphism is locally the Alexander terrane, comprising the Craig and Annette sub­ overprinted by contact metamorphism that in places reaches terranes; the Gravina-Nutzotin belt; the Taku terrane; the hornblende hornfels facies. Feather schist is widespread. The Tracy Arm terrane; and the Stikine terrane. east limit of this belt is the west boundary of the plutonic­ metamorphic complex as herein defined. On the west and ALEXANDER TERRANE north the ourcrop belt is terminated by Revillagigedo Channel The Alexander terrane constitutes most of the Alexander and Behm Canal, but our mapping indicates that correlative Archipelago of southeastern Alaska and parts of neighboring rocks also occur on parts of Revillagigedo Island and on An­ British Columbia and Yukon Territory. It comprises upper Pre­ nette and neighboring islands. The outcrop belt consists of two cambrian to Triassic strata and is composed of three al­ tracts separated by a northwest-trending linear fault zone that lochthonous, originally disjunct or otherwise distinctive crustal extends from Harry Bay to beyond Kah Shakes Cove. The blocks named the Admiralty, Craig, and Annette subterranes rocks northeast of the fault are mainly phyllite and schist (Berg and others, 1978c). The Ketchikan-Prince Rupert study (MzPza, MzPzu) derived from graywacke flysch, from mafic, in­ area contains a small part of the Craig subterrane and all of termediate, and subordinate felsic volcanic and volcaniclastic the Annette subterrane. rocks, and from small amounts of limestone (m). Very sparse Craig subterrane objects, doubtfully identified as crinoid disks implying a late The Craig subterrane is distinguished by a relatively com­ Paleozoic age (Berg and Cruz, 1982) occur in marble layers plete and undeformed sequence of Ordovician to Permian (m) along Very Inlet. These objects, coupled with our map­ clastic, carbonate, and volcanic strata, by· diverse plutonic ping of lithically similar rocks on southern Revillagigedo Is­ rocks, and by a pre-Middle Ordovician metamorphic complex land, lead us to assign these marbles, and associated rocks in (Wales Group) that may be as old as Precambrian (Gehrels this tract a premetamorphic age of late Paleozoic or Mesozoic. and Saleeby, 1987, p. 126-127). Recent mapping and geo­ Mapped plutonic rocks in this tract include granodiorite (Kgq) chronologic studies (Gehrels and Saleeby, 1987; Gehrels and stocks that are isotopically dated and provisionally of Cretace­ others, 1983b, c) show that the southern part of the subter­ ous age and elongate bodies of trondhjemitic pegmatite (TKp) rane is underlain by an Ordovician or Silurian volcanoplutonic that are of inferred Late Cretaceous or Tertiary emplacement complex of diorite and trondhjemite and cogenetic volcanic age. Southwest of the fault the rocks consist mainly of a and volcaniclastic rocks and that this basement complex is in metamorphosed Silurian trondhjemite stock (Smt) that fault contact with Wales Group metabasite and metacarbonate intrudes metamorphosed bedded and intrusive rocks (SOu) rocks. In the Ketchikan and Prince Rupert quadrangles the similar to Ordovician or Silurian rocks mapped on Annette, Craig subterrane occurs west of Clarence Strait, where it is. ex­ Mary, and Duke Islands. posed only on the easternmost coastal fringes of southern About 30 km 2 of the northeasternmost corner of the Prince of Wales Island, and where it consists of Devonian(?) and Ketchikan quadrangle is underlain by recrystallized Triassic older Paleozoic bedded, intrusive, and metamorphic rocks. plutonic rocks ("Rt) and by recrystallized Triassic or older vol­ Annette subterrane canic and sedimentary rocks (MzPzvs). These rocks, which The Annette subterrane is distinguished by (a) a were locally cataclastically deformed during Mesozoic or early heterogeneous assemblage of Ordovician or Silurian, Silurian, Cenozoic time and then intruded by Eocene plutons, are nota­ and Devonian ifltrusive, extrusive, clastic, and carbonate rocks bly less deformed and metamorphosed than those of the on or near Annette and and on southwestern plutonic-metamorphic complex to the southwest. We infer that Cleveland Peninsula (Rubin and Saleeby, 1987), (b) the ab­ the boundary between these two contrasting assemblages is a sence of any known post-Middle Devonian Paleozoic strata, moderately northeast-dipping thrust zone that subsequently and (c) Upper Triassic rhyolite, basalt, clastic, and carbonate has been intruded and largely obliterated by the Eocene plu­ rocks. The youngest pre-Cenozoic stratigraphic unit assigned tons (map sheet, section A-A'; fig. 3; Berg and others, 1977, to the Annette subterrane is the Upper Triassic Chapin Peak p. 29). Formation. In 1987 the most commercially attractive mineral deposit These rocks record several episodes of magmatic-arc and on Portland peninsula is a large porphyry molybdenum lode possibly rift-related volcanism, sedimentation, and intrusion at Quartz Hill (fig. 2, area 11; Hudson and others, 1979). that began at least as long ago as early Paleozoic time. They

6 also record a history of deformation and metamorphism that, at Back Island it is intercalated with metaflysch similar to the depending on the age and location, varies from repeated pen­ flysch in the Gravina-Nutzotin belt; these relations suggest that etrative folding and polymetamorphism as intense as am­ metaconglomerate occurs in at least two stratigraphic hori­ phibolite and hornblende-hornfels facies to relatively simple zons. The trondhjemite clasts in the metaconglomerate are folding accompanied by the development of slaty cleavage compositionally similar to the Silurian trondhjemite plutons on and only slight recrystallization. Annette and Gravina Islands (St) and near Cape Fox (Smt) on Recent investigations by Gehrels and others ( 1987, Portland peninsula, which are different from any other plutons 1983b, c) show that the Annette subterrane contains an Or­ known in the Ketchikan and Prince Rupert quadrangles, and dovician or Silurian volcanoplutonic complex similar to the which may have been the source of the clasts. If the pre­ one in the Craig subterrane. These data suggest that the two metamorphic age of the trondhjemite-clast metaconglomerate subterranes may have been in related tectonic environments that may grade into upper Paleozoic marble also is late in Ordovician or Silurian time, but the marked differences in Paleozoic and if the source of the clasts is the Silurian plutons, their Devonian and later Paleozoic history supports their dis­ then the metaconglomerate may record structural juxtaposi­ tinction as separate subdivisions of the Alexander terrane. tion (amalgamation) at least of the southern Alexander and The Annette subterrane is separated from the Craig sub­ Taku terranes by late Paleozoic time. Furthermore, if the pre­ terrane by the Clarence Strait fault, and from the Taku terrane metamorphic age of the metaconglomerate that is intercalated by mapped or inferred faults, along which the rocks locally are with the metaflysch is late Mesozoic, then the metaconglomer­ metamorphosed to blastomylonite (fig. 3). Rubin and Saleeby ate may record juxtaposition of the Alexander terrane, (1987) interpret the Alexander (Annette)-Taku terrane bound­ Gravina-Nutzotin belt, and Taku terrane at that time. ary as a tectonic zone of imbricate east-dipping thrust sheets The stratigraphic base of the Taku terrane is unknown. If with a total structural thickness of over 15 km. On Annette and we assume an external provenance for the trondhjemite clasts Gravina Islands, the contact of the Annette subterrane with in the metaconglomerate, then there is no faunal, lithologic, or the Gravina-Nutzotin belt is an unconformity locally cut by stratigraphic evidence of rocks older than late Paleozoic lying normal and reverse faults. stratigraphically beneath the terrane. The west boundary of the Taku terrane is a zone of com­ GRAVINA-NUTZOTIN BELT plex faults, along which the rocks locally are metamorphosed The Gravina-Nutzotin belt (map sheet, section A-A'; fig. to blastomylonite (fig. 3). Rubin and Saleeby (1987) interpret 3) comprises Middle(?) Jurassic to Lower Cretaceous flysch, this boundary as a tectonic zone of imbricate east-dipping andesitic or basaltic volcanic rocks, and subvolcanic dioritic to thrust sheets with a total structural thickness of over 15 km. In ultramafic plutons. This assemblage is interpreted as the the study area, the northeast boundary is along the west con­ remnants of a late Mesozoic volcanic arc (Berg and others, tacts of the paragneiss (MzPzp) and foliated granodiorite 1972). On western Gravina Island, bedded rocks assigned to (TKfg) and quartz diorite (TKfq) units. Beyond the limits of the belt are only slightly folded and recrystallized; on eastern the study area, the foliated quartz diorite (tonalite) apparently Gravina Island and on Annette Island, they are regionally coalesces into a persistent zone of northwest- or north-trend­ metamorphosed to greenschist facies and folded into south­ ing sills (Brew and Ford, 1981) that probably were emplaced west-overturned, locally refolded isoclines whose axial sur­ along a now-obliterated Mesozoic suture that bounded the faces dip moderately northeast. On the southwest, the Taku and Tracy Arm terranes (map sheet, section A-A'; Berg Gravina-Nutzotin belt is in locally faulted stratigraphic contact and others, 1978c; Brew and Morrell, 1979). This boundary with the underlying Annette subterrane. On the northeast, the also is spatially related to the Coast Range megalineament (fig. extent and distribution of rocks of the Gravina-Nutzotin belt 3; Brew and Ford, 1978), an enigmatic topographic, struc­ aie not yet known. The belt is separated from the Taku terrane tural, and geophysical feature that appears to have been the by faults (Rubin and Saleeby, 1987), along which the rocks western limit of large-scale regional uplift of Portland penin­ locally are metamorphosed to blastomylonite (fig. 3). sula beginning in Early Tertiary time (Hutchison, 1970, p. 396; 1982, p. 88-90, 96-97). TAKU TERRANE rield studies in 1981 (Monger and Berg, 1985) suggest The Taku terrane is a possibly polygenetic assemblage of that the T aku terrane in southeastern Alaska comprises at least multiply deformed and metamorphosed strata that contain three distinctive stratigraphic assemblages whose northwest­ sparse fossils of Permian and Middle or Late Triassic age, as trending boundaries and internal lithologic trends obliquely in­ well as undated metaflysch and andesitic or basaltic metavol­ tersect the west and east boundaries of the terrane at angles canic rocks that may in part correlate with Jurassic or Creta­ as large as 40°. The stratigraphic differences suggest that the ceous strata in the Gravina-Nutzotin belt (fig. 3). The key Taku terrane may actually consist of structurally juxtaposed, stratigraphic sequences of the terrane include (a) a thick se­ originally disjunct crustal blocks, and the truncation of their quence of upper Paleozoic basaltic tuff and agglomerate that trends supports the interpretation that the terrane is bounded occurs in this terrane mainly north of the Ketchikan and Prince by partly obliterated regional faults. Rupert quadrangles and that is not known in any of the other terranes (Berg and others, 1978c) and (b) at least one unit of TRACY ARM TERRANE metaconglomerate (MzPzmc) that contains prominent relict The Tracy Arm terrane (map sheet, section A-A'; Berg roundstones of trondhjemite or leucocratic quartz diorite and and others, 1978c) consists of regionally metamorphosed to quartzite in the Ketchikan-Prince Rupert study area. Within amphibolite- and locally granulite-facies stratified rocks and the study area, the key basaltic volcanic sequence may be rep­ minor ultramafic bodies. These rocks form a discontinuous resented by the intermediate to mafic metavolcanic rocks belt of roof pendants, screens, and xenoliths enclosed by Cre­ (MzPzmv) on Revillagigedo Island and Clevelend Peninsula taceous or Tertiary plutons, and they lie within or east of a and by amphibolite (MzPza) on western and southwestern zone of nearly continuous sills of quartz diorite (tonalite) that Portland peninsula. has been traced for at least the length of southeastern Alaska The premetamorphic age(s) of the metaconglomerate may (Brew and Ford, 1981 ). In the Ketchikan-Prince Rupert study be the key to the tectonic history of the Taku terrane. At Gnat area, this terrane occurs on Portland peninsula and consists of Cove it may grade into upper Paleozoic crinoidal marble, and sequences of pelitic and quartzofeldspathic paragneiss and

7 schist and minor marble and amphibolite. These rocks are ____ 1982, The Alaska Mineral Resource Assessment much less abundant than the massive to gneissic plutons that Program: Guide to information about the geology and enclose them. mineral resources of the Ketchikan and Prince Rupert The premetamorphic stratigraphy of the Tracy Arm ter­ quadrangles, southeastern Alaska: U.S. Geological Sur­ rane is unknown. Preliminary strontium isotopic studies 01 vey Circular 855, 24 p. granitic rocks on Portland peninsula (J.G. Arth, written com­ Berg, H.C., and Cruz, E.L., 1982, Map showing locations of mun., 1978) suggest that Precambrian or lower Paleozoic con­ fossil collections and related samples in the Ketchikan and tinental crustal rocks are not present. On the other hand, near­ Prince Rupert quadrangles, southeastern Alaska: U.S. by in British Columbia, Pb-U (zircon) isotopic age determina­ Geological Survey Open-File Report 82-1088, 1 sheet, tions on paragneiss that is presumably correlative with that on scale 1:250,000, 27 p. Portland peninsula suggest Precambrian, older Paleozoic, and Berg, H.C., Decker, J.E., and Abramson, B.S., 1981, Metallic pre-Permian ages (Hutchison, 1982, p. 23-24). Still other in­ mineral deposits of southeastern Alaska: U.S. Geological vestigations in British Columbia (Woodsworth and others, Survey Open--File Report 81-122, scale 1:1,000,000, 1983, p. 10) suggest Late Triassic or younger Mesozoic per­ 136 p. metamorphic ages for some of the strata in the Tracy Arm ter­ Berg, H.C., Elliott, R.L., and Koch, R.D., 1978a, Map and ta­ rane. These apparently conflicting data, coupled with the wide bles describing areas of metalliferous mineral resource po­ variation in premetamorphic lithologies in the Tracy Arm ter­ tential in the Ketchikan and Prince Rupert quadrangles, rane in southeastern Alaska, suggest that the Tracy Arm ter­ Alaska: U.S. Geological Survey Open-File Report 78- rane, like the Taku terrane, may actually comprise several 73M, scale 1:250,000, 48 p. originally disjunct tectonostratigraphic assemblages. Berg, H.C., Elliott, R.L., Smith, J.G., and Kock, R.D., 1978b, In the Ketchikan-Prince Rupert study area the southwest Geologic map of the Ketchikan and Prince Rupert quad­ limit of the Tracy Arm terrane is along the west contacts of the rangles, Alaska: U.S. Geological Survey Open-File Report paragneis.;; and foliated granodiorite and quartz diorite units, 78-73A, scale 1:250,000. as discussed in the foregoing description of the Taku terrane. Berg, H.C., Elliott, R.L., Smith, J.G., Pitman, T.L., and Kim­ The northeast limit of the terrane is along a postulated zone of ball, A.L., 1977, Mineral resources of the Granite Fiords thrust faults that has been intruded by Eocene plutons (Berg Wilderness Study Area, Alaska: U.S. Geological Survey and others, 1977, p. 29). In the northeastern part of the Bulletin 1403, 151 p. Ketchikan quadrangle, this zone appears to dip north or east Berg, H.C., Jones, D.L., and Coney, P.J., 1978c, Map show­ and to thrust rocks of the Tracy Arm terrane beneath those of ing pre-Cenozoic tectonostratigraphic terranes of south­ the Stikine terrane. Thrust faults that separate rocks presuma­ eastern Alaska and adjacent areas: U.S. Geological Sur­ bly of the Tracy Arm and Stikine terranes have also been map­ vey Open-File Report 78-1085, 2 sheets, scale ped in parts of British Columbia (Woodsworth and others, 1:1,000,000. 1983, p. 10). These faults also appear to be intruded by Berg, H.C., Jones, D.L., and Richter, D.H., 1972, Gravina­ Eocene plutons, but contrary to the relations in the Ketchikan Nutzotin belt-tectonic significance of an Upper Mesozoic quadrangle, they appear to thrust rocks of the Tracy Arm ter­ sedimentary and volcanic sequence in southern and rane over those of the Stikine terrane. southeastern Alaska, in Geological Survey Research 1972: U.S. Geological Survey Professional Paper 800-D, STIKINE TERRANE p. 01-024. Rocks assigned to the Stikine terrane (map sheet, section Brew, D.A., and Ford, A.B., 1978, Megalineament in south­ A-A'; fig. 3; Berg and others, 1978c) crop out only in a 30- eastern Alaska marks southwest edge of Coast Range km2 area in the northeast corner of the study area. The rocks batholithic complex: Canadian Journal of Earth Science, consist of recrystallized, presumed upper Paleozoic and V. 15, nQ 11,p. 1763-1772. Mesozoic sedimentary and andesitic volcanic and volcaniclas­ ____ 1981, The Coast plutonic complex sill, southeast­ tic rocks that are cut by Triassic granodiorite that may be ern Alaska, in Albert, N.R.D., and Hudson, T.L., eds., cogenetic with some of the volcanic rocks. This assemblage is The United States Geological Survey in Alaska: ac­ intruded by Eocene granodiorite and quartz monzonite. The complishments during 1979; U.S. Geological Survey Cir­ pre-Eocene rocks make up the southwesternmost fringe of a cular 823-B, p. B96-B99. late Paleozoic and younger assemblage of marine and non­ ____ 1984, Tectonostratigraphic terranes in the Coast marine volcanic, intrusive, and sedimentary rocks that occur plutonic-metamorphic complex, southeastern Alaska, in mainly in British Columbia and Yukon Territory (Monger, Reed, K. L., and Bartsch-Winkler, Susan, eds., The United 1977; Monger and Price, 1979; Monger and Berg, 1985). The States Geological Survey in Alaska: accomplishments dur­ Stikine terrane probably originated as a late Paleozoic vol­ ing 1982: U.S. Geological Survey Circular 939, p. 90-93. canic arc; its key stratigraphic sequence (in British Columbia) Brew, D.A., and Morrell, R.P., 1979, Intrusive rock belts of is a thick pile of Lower and Middle Jurassic andesitic volcanic southeastern Alaska, in Johnson, K.M., and Williams, rocks that are unknown in any of the terranes to the west. In J.R., eds., The United States Geological Survey in Alaska: the Ketchikan quadrangle the southwest boundary of the accomplishments during 1978: U.S. Geological Survey Stikine terrane is a postulated thrust zone that has been mostly Circular 804-B, p. B116-B121. obliterated by the Eocene plutons. Brooks, A. H., 1902, Preliminary report on the Ketchikan min­ ing district, Alaska, with an introductory sketch of the geology of southeastern Alaska: U.S. Geological Survey Professional Paper 1, 120 p. REFERENCES CITED Buddington, A.F., 1929, Geology of Hyder and vicinity, Berg, H.C., 1972, Geologic map of Annette Island, Alaska: southeastern Alaska, with a reconnaissance of Chickamin U.S. Geological Survey Miscellaneous Geologic Investiga­ River: U.S. Geological Survey Bulletin 807, 124 p. tions Map 1-684, scale 1:63,000, 8 p. Buddington, A.F., and Chapin, Theodore, 1929, Geology and ____ 1973, Geology of Gravina Island, Alaska: U.S. mineral deposits of southeastern Alaska: U.S. Geological Geological Survey Bulletin 1373, 41 P. Survey Bulletin 800, 398 p.

8 Chapin, Theodore, 1918, The structure and stratigraphy of Geological Survey Circular 868, p. 126-128. Gravina and , Alaska, in Shorter Koch, R.D., Elliott, R.L., Smith, J.G., and Berg, H.C., 1977, contributions to general geology 1918: U.S. Geological Metamorphosed trondhjemite of the Alexander terrane in Survey Professional Paper 120-D, p. 83-100. Coast Range plutonic complex, in Blean, K.M., ed., The Eberlein, G. D., Churkin, Michael Jr., Carter, Claire, Berg, United States Geological Survey in Alaska: accomplish­ H.C., and Ovenshine, A.T., 1983, Geology of the Craig ments during 1976: U.S. Geological Survey Circular 751- quadrangle, Alaska: U.S. Geological Survey Open-File B, p. B72-B74. Report 83-91, scale 1:250,000, 53 p. MacKevett, E.M., Jr., 1963, GeoJ.ogy and ore deposits of the Elliott, R.L., Smith, J.G., and Hudson, Travis, 1976, Upper Bokan Mountain uranium-thorium area, southeastern Tertiary high-level plutons of the Smeaton Bay Area, Alaska: U.S. Geological Survey Bulletin 1154, 125 p. southeastern Alaska: U.S. Geological Survey Open-File Monger, J.W.H., 1977, Upper Paleozoic rocks of the western Report 76-507, 16 p. Canadian Cordillera and their bearing on Cordilleran Gehrels, G.E., Brew, O.A., and Saleeby, J.B., 1983a, U-Pb evolution: Canadian Journal of Earth Sciences, v. 14, p. zircon ages of major intrusive suites in the Coast plutonic­ 1832-1859. metamorphic complex near Juneau, southeastern Alaska Monger, J.W.H., and Berg, H.C., 1985, Lithotectonic terrane [abs. ]: Geological Association of Canada Program with map of western Canada and southeastern Alaska, in Sil­ Abstracts, v. 8, p. A26. berling, N.J., and Jones, D.L., eds., Lithotectonic terrane Gehrels, G.E., and Saleeby, J.B., 1987, Geology of southern maps of the North American Cordillera: U.S. Geological Prince of Wales Island, southeastern Alaska: Geological Survey Miscellaneous Field Studies Map MF-1874-B, Society of America Bulletin, v. 98, p. 123-137. scale 1:250,000. Gehrels, G.E., and Saleeby, J.B., and Berg, H.C., 1984, Monger, J.W.H., and Price, R.A., 1979, Geodynamic evolu­ Geologic framework of Paleozoic rocks on southern An­ tion of the Canadian Cordillera-progress and problems: nette and Hotspur Islands, southern Alexander terrane, in Canadian Journal of Earth Sciences, v. 16, p. 770-791. Coonrad, W.L., and Elliott, R.L., eds., The United States Roddick, J.A., and Hutchison, W.W., 1974, Setting of the Geological Survey in Alaska: accomplishments during Coast Plutonic Complex, British Columbia: Pacific Geol­ 1981: U.S. Geotogical Survey Circular 868, p. 113-115. ogy,v.8,p. 91-108. ____ 1983b, Preliminary description of the Late Silu­ Rubin, C.M., and Saleeby, J.B., 1987, The inner boundary rian-Early Devonian Klakas Orogeny in the southern zone of the Alexander terrane, southeastern Alaska-A Alexander terrane, southeastern Alaska, in Stephens, newly discovered thrust belt [abs. ]: Geological Society of C.H., ed., Pre-Jurassic rocks in western North American America Abstracts with Programs, v. 19, no. 6, p. 445. suspect terranes: Society of Economic Paleontologists and Saleeby, J.B., and Gehrels, G.E., 1985, Character of the Mineralogists, Pacific Section, Sacramento, Calif., 1983, Alexander-Taku terrane boundary, Cape Fox to Cleve­ p. 131-141. land Peninsula, southeastern Alaska [abs. ]: Geological ____ 1987, Geology of Annette, Gravina, and Duke Is­ Society of America Abstracts with Programs, v. 17, no. 6, lands, southeastern Alaska: Canadian Journal of Earth p. 406. Sciences, v. 24, p. 866-881. Saleeby, J.B., Gehrels, G.E., Eberlein, G.D., and Berg, H.C., Gehrels, G.E., and Saleeby, J.B., Berg, H.C., and Eberlein, 1984, Progress in lead/uranium zircon studies of lower G.D., 1983c, Basement continuity and variations in Paleozoic rocks of the southern Alexander terrane, in superjacent strata in the southern Alexander terrane, SE Coonrad, W.L., and Elliott, R.L., eds., The United States Alaska [abs.] 19438: Geological Society of America Geological Survey in Alaska: accomplishments during Abstracts with Programs, v. 15, no. 5, p. 385. 1981: U.S. Geological Survey Circular 868, p. 110-113. Grove, E.W., 1971, Geology and mineral deposits of the Selverstone, Jane, and Hollister, L. S., 1980, Cordierite-bear­ Stewart area, northwestern British Columbia: British Col­ ing granulites from the Coast Ranges, British Columbia; umbia Department of Mines and Petroleum Resources P-T conditions of metamorphism: Canadian Mineralogist, Bulletin 58, 219 p. v.18, pt. 1, p. 119-129. Hollister, L.S., 1975, Granulite facies metamorphism in the Silberling, N.J., Wardlaw, B.R., and Berg, H.C., 1981, New Coast Range crystalline belt: Canadian Journal of Earth paleontologic age determinations from the Taku terrane, Sciences, v. 12, p. 1953-1955. Ketchikan area, southeastern Alaska, in Coonrad, W.L., Hudson, Travis, Smith, J.G., and Elliott, R.L., 1979, Petrol­ ed., The United States Geological Survey in Alaska: ac­ ogy, composition, and age of intrusive rocks associated complishments during 1980: U.S. Geological Survey Cir­ with the Quartz Hill molybdenite deposit, southeastern cular 844, p. 117-119. Alaska: Canadian Journal of Earth Science, v. 16, p. Smith, J. G., 1973, A Tertiary lamprophyre dike province in 1805-1822. southeastern Alaska: Canadian Journal of Earth Sciences, Hutchison, W.W., 1970, Metamorphic framework and v. 10, p. 408-420. plutonic styles in the Prince Rupert region of the Central ____ 1977, Geology of the Ketchikan D-1 and Bradfield Coast Mountains, British Columbia: Canadian Journal of Canal A-1 quadrangles, southeastern Alaska: U.S. Earth Sciences, v. 7, p. 376-405. Geological Survey Bulletin 1525, 49 p. ____ 1982, Geology of the Prince Rupert-Skeena map Smith, J.G., and Diggles, M.F., 1981, Potassium-argon deter­ area, British Columbia: Geological Society of Canada minations in the Ketchikan and Prince Rupert quadrang­ Memoir 394, 116 p. les, southeastern Alaska: U.S. Geological Survey Open­ Irvine, T.N., 1974, Petrology of the Duke Island ultramafic File Report 78-73N, 1 sheet, scale 1:250,000, 16 p. complex, southeastern Alaska: Geological Society of Smith, J.G., Stern, T.W., and Arth, J.G., 1979, Isotopic ages America Memoir 138, 240 p. indicate multiple episodes of plutonism and metamorph­ Koch, R.D., and Elliott, R.L., 1984, Late Oligocene gabbro ism in the Coast mountains near Ketchikan, Alaska [abs. ]: near Ketchikan, southeastern Alaska, in Coonrad, W.L., Geological Sociey of America Abstracts with Programs, v. and Elliott, R. L., eds., The United States Geological Sur­ 11, no. 7, p. 519. vey in Alaska: accomplishments during. 1981: U.S. Smith, P.S., 1915, Notes on the geology of Gravina Island,

9 Alaska, in Shorter contributions to general geology, 1915: PRINCE OF WALES-GRA VINA-ANNEITE­ U.S. Geological Survey Professional Paper 95, p. MARY -DUKE ISLANDS AREA 97-105. Sutter, J.F., and Crawford, M.L., 1985, Timing of metamorph­ Tgb Gabbro (Tertiary)-A small intrusive body of gabbro ism and uplift in the vicinity of Prince Rupert, British Col­ crops out in tidal exposures on the northeast coast umbia and Ketchikan, Alaska [abs.] 70753L Geological of Gravina Island (Berg, 1973, p. 33-34). The Society of America Abstracts with Programs, v. 17, no. 6, gabbro, which grades into diabase, is a subophitic p. 411. to ophitic aggregate of plagioclase (An37-58), Turner, F .J., 1981, Metamorphic petrology: mineralogical, clinopyroxene, orthopyroxene, olivine, and brown field and tectonic aspects (2d ed.): New York, McGraw­ (Z) biotite, and it has subordinate to minor Hill, 524 p. amounts of green biotite, chlorite, magnetite, Turner, F.J., and Verhoogen, John, 1960, Igneous and colorless to pale-green amphibole, apatite, metamorphic petrology (2d ed.): New York, McGraw-Hill, potassium feldspar, and quartz. The olivine crystals 694p. are partly replaced by a dark, reddish-brown U.S. Geological Survey, 1977, Aeromagnetic map of Ketchi­ mineral. This undeformed and unmetamorphosed kan, Prince Rupert, and northeastern Craig quadrangles, gabbro is assigned an Oligocene or Miocene age Alaska: U.S. Geological Survey Open-File Report 77- because it is similar to isotopically dated gabbro 359, 1 sheet, scale 1:250,000. that crops out about 6 km to the southeast across Williams, Howe!, Turner, F.J., and Gilbert, C.M., 1982, Pe­ T ongass Narrows on Revillagigedo Island (see trography: an introduction to the study of rocks in thin description of unit Tgb in the Revillagigedo Island­ sections (2d ed.): San Francisco, Calif., W.H. Freeman Cleveland Peninsula area) and Co., 626 p. Kqd Quartz diorite (Cretaceous)-The only mapped Woodsworth, G.J., Crawford, M.L., and Hollister, L.S., 1983, outcrop of this unit in this area is on Spire Island Metamorphism and structure of the Coast Plutonic Com­ off the northeast coast of Annette Island. The unit plex and adjacent belts, Prince Rupert and Terrace areas, consists of sheared and hydrothermally altered British Columbia: Geological Association of Canada Vic­ brownish-gray, medium-grained quartz diorite toria Section Field Guidebook, v. 2, Field Trip 14, 62 p. containing albite and quartz and subordinate muscovite, ~hlorite, epidote-clinozoisite, calcite, apatite, sphene, and pyrite. It intrudes Jurassic or Cretaceous phyllitic graywacke that is thermally DESCRIPTION OF MAP UNITS metamorphosed to andalusite hornfels or schist near the contact with the pluton. Muscovite from Ou Glacial, glacial-marine, alluvial, and talus deposits, the pluton yielded a K-Ar age of about 89 Ma undivided (Quaternary)-Unconsolidated deposits (table 1, No. 50). Although the muscovite may of poorly sorted clay, silt, sand, gravel, and have been affected by, or is a product of, boulders locally cover bedrock, sometimes to hydrothermal alteration, we assign the pluton a depths of many meters, throughout the map area. Late Cretaceous emplacement age because it Glacial drift, till, and moraine are partly reworked. intrudes Jurassic or Cretaceous strata A glacial-marine terrace deposit, approximately 3- Kpg Plagioclase-porphyritic granodiorite and quartz m-thick but too small to show on the map occurs diorite (Cretaceous)-ln this part of the map area, at an elevation of about 25 m about 1 km this unit has been recognized in outcrop only on northwest of the head of Dall Bay on Gravina Mary Island. On western Mary· Island it consists of Island (Chapin, 1918, p. 99; Berg, 1973, p. 35). It a small stock and marginal dikes of massive, consists of stratified glacial till, gravel, and blue clay medium-grained, plagioclase-porphyritic, biotite­ and contains Quaternary marine fossils (Berg and and garnet-bearing, hornblende-epidote quartz Cruz, 1982, No. 37). The unconsolidated deposit diorite. These rocks have sharp, discordant and mapped at an elevation of about 75 m west of concordant contacts with the surrounding Blank Inlet on Gravina Island may also be a marine semischist, and show no evidence of terrace deposit that correlates with the fossiliferous metamorphism or deformation. The quartz diorite deposit northwest of Dall Bay typically is characterized by crowded centimeter­ OTv Volcanic olivine andesite, trachyandesite, and basalt size subhedral plagioclase phenocrysts separated (Quaternary and Tertiary)-This extrusive unit by a fine- to medium-grained granular aggregate of forms volcanic cones, columnar-jointed lava flows, the other minerals. Magmatic minerals include and rubbly flows containing pumice and scoria; it essential plagioclase and quartz, accessory epidote also includes patches of ash and lapilli a few em to and green hornblende, and minor amounts of a few m thick but too small to show on the map. brown biotite, garnet, potassium feldspar, apatite, Postglacial eruption is indicated by volcanic cones and opaque minerals. Some plagioclase crystals at Painted Peak on Revillagigedo Island and have multiple delicate oscillatory zones. Epidote elsewhere that still retain their constructional shape forms anhedral to subhedral grains; some are with only minor modification by stream erosion, twinned, some are concentrically zoned. Gamet and by unconsolidated pumice, lapilli, and ash and epidote occur within, but mainly are interstitial deposits that locally cover parts of glaciated ridge to, plagioclase. Minor deuteric alteration consists of tops. Evidence of preglacial eruption includes flows chlorite streaks in biotite and scattered small that locally show glacial striae and grooves. K-Ar patches of sericite. These rocks, and a small age determinations (table 1, Nos. 1-3) indicate unmapped dike of similar texture and composition volcanic activity at about 5 Ma and between about that outcrops in the intertidal zone near the 1. 0 Ma and 0.4 Ma southern tip of Mary Island, have the same

10 distinctive texture and mineralogy as rocks assigned outcrop width of 10 km on Gravina Island to unit Kpg on Revillagigedo Island. On the basis probably is due mainly to structural repetition. of this comparison, we assign the plagioclase­ On western Gravina Island these rocks are porphyritic quartz diorite on Mary Island a Late characterized by slaty cleavage and low-grade Cretaceous emplacement age metamorphism; on eastern Gravina Island and on Kum Ultramafic rocks (Cretaceous}-This unit comprises Annette Island, they are penetratively deformed dunite and peridotite, clinopyroxenite and and regionally metamorphosed to greenschist hornblendite. The dunite and peridotite locally are facies and show increasing metamorphic grade intensely serpentinized, mainly near fault zones. from southwest to northeast. On Duke Island (Irvine, 1974), a well-exposed In the Ketchikan-Prince Rupert area, the concentrically zoned ultramafic intrusive complex assemblage contains fossils of Middle or Late has a core of dunite and peridotite and a margin of Jurassic age (Berg, 1973, p. 27-30). Outside the clinopyroxenite and hornblendite. The olivine­ area, unnamed rocks that probably correspond bearing units locally show rhythmic layering, slump with undated upper parts of the assemblage on structure, and other cumulate features. On Duke Annette and Gravina Islands contain well­ and Percy Islands the ultramafic rocks intrude preserved ammonites of mid-Cretaceous (Albian) Triassic gabbro ("fig), and Ordovician or Silurian age (Berg and others, 1972, p. D11-D14). On the rocks (SOui). Near some contacts with the basis of these regional relations, the assemblage ultramafic rocks, the gabbro is metamorphosed to herein is assigned an age range of Middle(?) amphibolite and is intruded by dikes of coarse Jurassic through Early Cretaceous. On hornblende-plagioclase pegmatite. Elsewhere, northeastern Gravina Island, the assemblage is ultramafic rocks shown on the map are mainly in intruded by a small body of Oligocene or Miocene fault contact with adjacent rock units. The unit is gabbro. assigned a Cretaceous age on the basis of K-Ar Locally on northeastern Gravina Island, bedded ages ranging from 106 to 134 Ma measured on rocks of the assemblage are hydrothermally altered hornblende from four samples of hornblendite and and cut by sulfide-bearing quartz veins, some of hornblende pegmatite from southern Duke Island which were successfully worked for gold around (table 1, Nos. 57-61). the turn of the century (Berg and others, 1981, p. The dunite and peridotite in these ultramafic 63-64). Divided into: rocks contain small amounts of chromite, asbestos, KJgd Diorite and quartz diorite (Cretaceous or Jurassic)­ and platinum-group metals, and the This elongate stock on northern Annette Island is clinopyroxenite locally contains accumulations of apparently zoned from a hypidiomorphic granular titaniferous magnetite (Berg and others, 1981, n. core to a porphyritic margin. The core typically 69, 96). The ultramafic bodies on Duke and Percy contains approximately equal parts of relict Islands have been prospected for iron and chromite plagioclase and ferromagnesian crystals, up to Gravina Island Formation (Jurassic), unnamed about 10 percent quartz, and accessory sphene, (partly correlative) bedded rocks (Cretaceous apatite, and pyrite. The marginal zone contains and Jurassic)", and related dioritic intrusive rocks relict plagioclase phenocrysts as long as 1-cm, both (Cretaceous or Jurassic}-This assemblage as individual crystals and in clumps, amphibole(?) consists of flysch and other detrital sedimentary pseudomorphs of hornblende or pyroxene, and as rocks (KJgs), andesitic and basaltic volcanic and much as about 10 percent interstitial quartz, pyrite, volcaniclastic rocks (KJgv), and dioritic intrusive and undetermined metamorphic minerals. The rocks (KJgd) (Berg, 1973, p. 27-33; 1972, p. 1- pluton is massive or locally moderately foliated and 3). The dioritic rocks intrude and locally is hydrothermally altered. Plagioclase is converted metamorphose the sedimentary rocks, but locally almost entirely to very fine grained albite, epidote­ they are texturally and compositonally gradational clinozoisite, and sericite, and the ferromagnesian with the volcanic rocks. On western Gravina Island minerals to actinolite, chlorite, and epidote. The the assemblage consists solely of unnamed detrital pluton intrudes metasedimentary rocks of the sedimentary rocks; on eastern Gravina Island it Gravina Island Formation with sharp, locally consists of intertonguing sedimentary and volcanic migmatitic contacts. Its contact with the rocks assigned to the Middle or Upper Jurassic metavolcanic rocks of the Gravina Island Gravina Island Formation (Berg, 1973, p. 28); and Formation, however, apparently is compositionally on Annette Island it consists of unnamed strata and texturally gradational, suggesting that the correlative with the Gravina Island Formation and pluton and the metavolcanic rocks are cogenetic the only mapped occurrence of the diorite. On (Berg, 1972, p. 1-2). On the basis of these western Gravina Island, the sedimentary rocks relations, the pluton is assigned an age of Jurassic unconformably overlie rocks as old as Ordovician or Cretaceous or Silurian; neither the base nor top of the KJgv Andesitic to basaltic volcanic and volcaniclastic assemblage is exposed elsewhere in the map area. rocks and minor sedimentary rocks (Cretaceous The total thickness of the assemblage has not been and Jurassic}-This unit consists of locally massive measured. Limited data indicate that on western but generally foliated and schistose green Gravina Island it is at least 200 m thick (Berg, metavolcanic rocks derived from andesitic and 1973, p. 27-28); elsewhere, outcrop widths basaltic tuff and agglomerate (Berg, 1972, p. 2; suggest that it may be as much as 1,000 m thick 1973, p. 31-32). It also contains minor grayish­ (Berg, 1972, p. 2), but its original thickness green and black phyllite and phyllitic siltstone that probably varied from place to place. The maximum gradationally intertongue with the metavolcanic

11 Island Formation rocks. Chemical analyses (Berg and others, 1972, 'Rg Gabbro (Triassic)-Much of central and eastern Duke p. D15) show that the most abundant rock type is Island is underlain by a large body of pyroxene basaltic andesite. It consists of lithic and crystal­ gabbro that consists of varying proportions of lithic tuff that contains relict euhedral phenocrysts olivine, hypersthene, augite, plagioclase, of plagioclase feldspar and dark ferromagnesian hornblende, and minor opaque minerals (Irvine, minerals 1 em or less in size. The phenocrysts are 1974). The gabbro intrudes deformed and moderately to strongly saussuritized plagioclase, metamorphosed Ordovician or Silurian colorless augite, and pale-green amphibole; the sedimentary and igneous rocks (SOu, SOui), and groundmass is a fine-grained microgranular in turn is intruded by Cretaceous ultramafic rocks aggregate of relict augite and hornblende and (Kum). The gabbro is assigned a Triassic age on metamorphic actinolite, chlorite, epidote, albite, the basis of a U-Pb apparent age of 226:!: 3 Ma quartz, muscovite, prehnite, calcite, and leucoxene. (table 1, No. 61a) (Gehrels and others, 1987, Metamorphic textures and minerals (except p. 878) prehnite) indicate regional greenschist-facies 'Rc Chapin Peak Formation (Triassic)-This unit, named metamorphism that we infer to be Cretaceous in for its excellent exposures near Chapin Peak on age, on the basis of radiometrically dated Gravina Island (Berg, 1973, p. 23-26), consists Cretaceous metamorphic minerals in the chiefly of marine basaltic volcanic rocks and Revillagigedo Island-Cleveland Peninsula area ((see subordinate intertonguing sedimentary rocks that "Metamorphosed sedimentary, volcanic, and crop out mainly on western Gravina Island. We intrusive rocks (Mesozoic or Paleozoic)"). provisionally correlate outcrops of basaltic pillow On the northeastern shore of Bostwick Inlet flows and breccia north of Sylburn Harbor on (Gravina Island) the unit contains an unmapped western Annette Island (Berg, 1972, p. 3) with the intrusive(?) body of massive augite or hornblende Chapin Peak Formation on the basis of similar porphyry (H.C. Berg and J.B. Saleeby, lithology and stratigraphic position. The Chapin unpublished data, 1980). This porphyry, which we Peak Formation is characterized by basaltic pillow interpret as a subvolcanic feeder to the extrusive flows, calcareous agglomerate and volcanic breccia, rocks of the Gravina Island Formation, contains and aquagene tuff. The volcanic and volcaniclastic locally abundant xenoliths of dark-greenish-black rocks intertongue gradationally with limestone and medium- and coarse-grained pyroxene gabbro, calcareous clastic sedimentary rocks that are much whose source may be a buried ultramafic pluton less abundant and that occur mainly near the base analogous to the ultramafic gabbroic complex on of the formation. Deformation varies from slight Duke Island pillow flattening and jointing in the relatively KJgs Sedimentary rocks and minor volcanic rocks massive volcanic rocks to slaty or phyllitic fabric in (Cretaceous and Jurassic)-On western Gravina the fine-grained detrital rocks. The mineralogy and Island (Berg, 1973, p. 27-28), this unit consists of textures suggest that the volcanic rocks have basal conglomerate and grit that grade upward and undergone either widespread deuteric alteration or laterally into slaty but otherwise possibly regional metamorphism to the prehnite­ unmetamorphosed, dark-gray, thin-bedded pumpellyite facies (Berg, 1973, p. 25). Near the graywacke and minor limestone. Locally the fault zone along Bostwick Inlet, the rocks are graywacke contains a Buchia fauna indicative of a relatively strongly recrystallized and sheared. Late Jurassic age. The conglomer~te consists of Limestone beds and limestone clasts in poorly sorted angular to subrounded clasts, as conglomerate assigned to the Chapin Peak much as a meter in maximum dimension, derived Formation in Bostwick Inlet contain well-preserved from stratigraphically underlying units; the matrix is Late Triassic (late Norian) fossils (Berg, 1973, p. graywacke and grit. On Annette Island and eastern 24; Berg and Cruz, 1982). The Chapin Peak Gravina Island (Berg, 1972, p. 2-3; 1973, p. 32- Formation conformably or disconformably overlies 33), the unit consists of regionally metamorphosed older Upper Triassic sedimentary rocks. On greenschist-facies flysch and minor intertonguing Gravina Island, it is overlain by upper Mesozoic andesitic metatuff. The flysch includes phyllitic detrital rocks with apparent slight structural, but graywacke, argillite, conglomerate, grit, and minor marked erosional, discordance. The thickness of silty limestone. The conglomerate and grit typically the formation ranges from about 150 to 500 m. consist of matrix-supported angular to subrounded This variation reflects differences in original clasts, as much as a meter long, of green metatuff thickness and in postdepositional erosion. The age and dark-gray metaflysch in a metaflysch matrix. of the Chapin Peak Formation is Late Triassic Near Rock Point on northeastern Gravina Island, RSV Sedimentary and mafic volcanic rocks (Triassic)­ the conglomerate also contains prominent relict This unit includes the Upper Triassic Nehenta roundstones of quartz diorite as much as 25 em in Formation on Gravina Island (Berg, 1973, p. 19- diameter (Berg, 1973, p. 32-33). The rocks in this 23) and unnamed correlative rocks on Annette unit on Annette and eastern Gravina Islands differ Island (Berg, 1972, p. 3). It consists of three from those on western Gravina Island by greater intertonguing members: (1) carbonaceous intensity of penetrative deformation and regional limestone and siltstone that grade into limestone, metamorphism, by intertonguing andesitic and limestone breccia, and calcareous conglomerate, basaltic volcanic and volcaniclastic rocks, and by grit, and sandstone; (2) coarse, trondhjemite-clast­ poorly preserved fossil belemnoids and pectinid rich conglomerate and grit; and (3) basaltic pillow clams, possibly of Middle or Late Jurassic age. The flows, agglomerate, and aquagene tuff. The darker intertonguing volcanic rocks are lithically identical hued rocks contain abundant graphite and locally to those in the volcanic members of the Gravina are strikingly rich in well-crystallized pyrite. The

12 carbonaceous limestone and siltstone commonly angular clasts of trondhjemite. The degree of are intricately folded and complexly lineated. deformation and recrystallization varies markedly Regional deformation and metamorphism differ throughout the unit and seems to depend at least from place to place, varying from crude facture as much on the susceptibility of the original cleavage in the coarse conglomerate and grit to lithologies as on the intensity of regional phyllitic foliation in the carbonaceous member. On greenschist-facies metamorphism. Chemical Annette Island, the rocks are regionally analyses show that the composition of the unit also metamorphosed to greenschist facies and contain varies greatly, especially in alkali content (H.C. the mineral assemblage sericite, quartz, albite, Berg, unpub. data, 1966-70); the cause of this chlorite, calcite, and epidote-clinozoisite; the variation is not known. The unit occurs in a variety intensity of deformation and metamorphism of colors, most typically white, pink, or bright red. increases from west to east. On Gravina Island, The reddish hues are caused by abundant regional deformation and metamorphism generally disseminated hydrothermal hematite, especially are less intense than on Annette Island. The near the base of the unit and in some of the carbonaceous beds and the limestone locally adjacent rocks. Rhyolite near Nehenta Bay contain well-preserved Late Triassic fossils (Berg, (Gravina Island) contains bright-red veinlets of 1973, p. 20; Berg and Cruz, 1982). Buddington jasper. Locally the hematite is accompanied by and Chapin (1929, p. 170) estimated that rocks pyrite, chalcopyrite, and other sulfide minerals, assigned to this unit on Gravina Island are about partly in disseminated grains and partly in fissure 500 m thick. The unit conformably overlies or is veins with barite, calcite, and quartz. Many of these laterally gradational with Upper Triassic limestone lodes have been prospected for gold, copper, and and dolomite ("RI) and felsic volcanic rocks ("Rv), other metals since about 1900 (Berg and others, and it unconformably overlies Devonian and older 1981, p. 59-70). The unit is assigned a Late Paleozoic rocks. It is gradationally and conformably Triassic age on the basis of Late Triassic fossils overlain by Upper Triassic mafic volcanic rocks (conodonts) in dolomitic limestone that ("Rc) and unconformably overlain by upper conformably overlies rhyolite on eastern Annette Mesozoic sedimentary rocks (KJgs) The age of Island (Berg, 1982, p. 5-7), and on a U-Pb this unit is Late Triassic (zircon) apparent age of 225 ± 3 Ma on a sample "RI Limestone and dolomite (Triassic)-This unit consists of rhyolite from the mouth of Bostwick Inlet on of dark-bluish-gray, very fine grained recrystallized Gravina Island (Gehrels and others, 1987, p. 877). limestone (metacarbonate) distinguished by The unit unconformably overlies Devonian or older solution pits and valleys, caverns, and underground Paleozoic rocks and is conformably overlain by drainage. Most of the limestone is massive and Upper Triassic carbonate, detrital, and basaltic calcitic, but locally it is moderately to thicJ...Jy volcanic rocks. The estimated maximum thickness bedded and, in a few places, dolomitic. In several of the unit is about 350 m places near Crab Bay (Annette Island), this unit Dsv Sedimentary and volcanic rocks (Devonian)-On contains disseminated galena, sphalerite, and other Annette, Gravina, Harris and Hotspur Islands sulfide minerals (Berg and others, 1981). Dolomitic (Berg, 1972, p. 4-5; 1973, p. 15-16), this unit limestone near Crab and Kwain Bays on eastern consists primarily of massive and thinly bedded Annette Island contains microfossils (conodonts) of dolomitic marble and recrystallized limestone and Late Triassic age (Berg, 1982, p. 5-7). The unit of greenschist facies, locally pyritic, phyllite and conformably overlies felsic volcanic rocks; it semischist derived from graywacke flysch. It also intertongues laterally with, and is conformably contains feldspathic to arkosic calcareous siltstone overlain by, carbonaceous limestone and siltstone and sandstone, conglomerate, calcarenite and ("Rsv). The maximum thickness of the unit is about limestone breccia, and concretionary dolomite. 70 m. The age of this unit is Late Triassic Where stratigraphic relations can be determined, RV Felsic volcanic rocks (Triassic)-This unit includes the the unit unconformably overlies Silurian or older Upper Triassic Puppets Formation on Gravina Paleozoic rocks and is unconformably overlain by Island (Berg, 1973, p. 10-14) and unnamed Triassic and younger Mesozoic rocks. In this report correlative rocks on Gravina (Berg, 1973, p. 14- the unit is assigned an Early or Middle Devonian 15) and Annette (Berg, 1972, p. 4) Islands. The age because of the stratigraphic relations and the Puppets Formation is divided into two fossils in limestone and other calcareous rocks intertonguing members: massive-appearing, thinly (Berg and Cruz, 1982). The structural complexity layered recrystallized rhyolite; and recrystallized and poor exposures of this unit prevent measuring felsic tuff that varies in composition from latite to its thickness, but it probably is at least several rhyolite. The tuff member occurs in discontinuous hundred meters thick. layers and lenses, generally at or near the base of On Prince of Wales Island (Eberlein and others, the formation. At Driest Point on Annette Island, 1983, p. 16), rocks here provisionally correlated the unit includes rhythmically bedded tuffaceous with unit Dsv (their unit Dvs) consist of flyschlike limestone and calcareous tuff that probably record tuffaceous banded mudstone, graywacke, quartzo­ marine deposition of rhyolitic ash and lapilli. The feldspathic wacke, and subordinate grit. The flysch rhyolite typically consists of thin layers, interpreted section grades upward with increasing carbonate as relict flowbands, of aphanite containing minute content into (a) tuffaceous marlstone, (b) crudely relict phenocrysts of quartz and feldspar; variants graded, carbonate-cemented, broken-pillow have conspicuous fragmental and spherulitic breccia, and (c) volcanic conglomerate. These beds textures. The tuff varies from massive to schistose in turn are gradationally overlain by carbonate­ fragmental rock that locally contains conspicuous cemented lithic lapilli aquagene tuff, subordinate

13 basaltic to andesitic pillow flows, volcanic breccia, indicate that at least some of the volcanic and and conglomerate that contains rounded clasts as plutonic rocks are cogenetic (Gehrels and others, much as 1 m in diameter, of altered leucogabbro, 1984). A sample of quartz diorite from unit SOu diorite, and mafic dike material probably derived on southern Annette Island east of the mouth of from rocks in unit SOui. Fossils have not been Tam gas Harbor and a sample of quartz diorite found in this unit on Prince of Wales Island. It is from unit SOui on Duke Island have preliminary provisionally assigned a Devonian age because of Pb-U (zircon) ages in the 430-450 Ma range (table stratigraphic relations and lithologic similarities to 1, Nos. 94, 89). The unit is assigned an Ordovician faunally dated Devonian rocks elsewhere on Prince or Silurian age because it contains isotopically of Wales Island (Eberlein and others, 1983, p. 16). dated Ordovician and Silurian plutonic rocks and Its total exposed thickness is about 1, 900 m, but cogenetic volcanic rocks; and it is also intruded by the top of the unit is not exposed isotopically dated Silurian trondhjemite plutons St Trondhjemite (Silurian)-This unit consists of the (St). The thickness of the stratified rocks in this unit Annette and Central Metlakatla plutons on Annette is unknown. Island (Berg, 1972, p. 5-7) and correlative On the part of Prince of Wales Island bordering unnamed plutonic rocks on Gravina Island (Berg, the Ketchikan quadrangle, Eberlein and others 1973, p. 8-9). The plutons consist mainly of light­ (1983, p. 12) describe rocks here provisionally gray trondhjemite composed of sodic plagioclase, correlated with unit SOui (their unit Pzic) as a quartz, and minor to trace amounts of biotite, "Metaigneous complex consisting of masses of hornblende, and potassium feldspar. On Annette diorite-basite migmatite, and irregular intrusive Island, the trondhjemite grades northward into a bodies of hornblende and(or) quartz diorite ... , border zone of trondhjemite-quartz diorite leucogabbro, trondhjemite, and minor pyroxenite distinguished by increasing amounts of biotite and cut by mafic ... and felsic dike swarms". Saleeby hornblende. On Annette and southern Gravina and others (1984) report preliminary Pb-U (zircon) Islands, the trondhjemite grades locally into granite ages for various components of the complex in the by increased amounts of potassium feldspar. On 400- to 500- Ma range. On the same part of southern Gravina Island, the rocks are commonly Prince of Wales Island, rocks here provisionally pink or red because of very finely disseminated correlated with unit SOu include three units from hydrothermal hematite (Berg, 1973, p. 9). The Eberlein and others (1983, p. 17-20): unit SOs, margin of the Annette pluton characteristically is a Ordovician or Silurian marine graywacke, banded moderately to strongly foliated quartz-plagioclase­ mudstone, siltstone, argillite, and associated sericite schist that is difficult to distinguish from the basaltic flows and fragmental rocks; unit SOv, surrounding country rocks. The intermediate and Ordovician or Silurian marine andesitic to basaltic central parts of this pluton commonly are volcanic and volcaniclastic rocks; and unit Pzp£w, cataclastically deformed, and tightly healed Precambrian or Paleozoic Wales Group consisting microbreccia and protomylonite are widespread. of (a) marine andesitic, basaltic, and subordinate The unit is assigned a Silurian emplacement age on felsic flows and fragmental rocks, (b) graywacke, the basis of preliminary Pb-U (zircon) age mudstone and shale, and (c) locally interlayered determinations in the 408-424 Ma range (table 1, marble. Because the faunal ages of units SOs and Nos. 82, 84-86, 93) SOv of Eberlein and others (1983, p. 18) on SOu Extrusive, intrusive, and sedimentary rocks, Prince of Wales Island are nearly contemporaneous undivided (Silurian or Ordovician)-This with the preliminary Pb-U isotopic ages of igneous heterogeneous assemblage comprises (a) mafic, rocks in unit SOu east of Clarence Strait (table 1, intermediate, and subordinate felsic volcanic and Nos. 89, 93, and 94), we assume that these three volcaniclastic rocks, (b) clastic and carbonate units are correlative. Our provisonal correlation of sedimentary rocks, and (c) intermediate and mafic rocks in the Wales(?) Group in the Ketchikan plutonic intrusive rocks. Also, locally divided into: quadrangle near Port Johnson (Prince of Wales SOui Intermediate and mafic plutonic rocks-This Island) with those in unit SOu is inferred partly subunit is mapped separately on Prince of Wales from the mapping by Eberlein and others (1983) Island, on southwestern Annette Island (South and partly from more recent geologic mapping and Metlakatla pluton of Berg, 1972, p. 6), and on isotopic studies in that area by G.E. Gehrels (oral Duke, Mary, and southern Gravina Islands (Berg, commun., 1983) Although part of the Wales 1973, p. 16-19) Group on Prince of Wales Island may be East of Clarence Strait, most of the rocks are Precambrian in age (Gehrels and Saleeby, 1987, p. penetratively deformed to phyllite, semischist, and 127), the rocks mapped by Eberlein and others schist, and are regionally metamorphosed to (1983, p. 18-19) as the Wales Group near Port greenschist and locally amphibolite facies (Berg, Johnson are indistinguishable from those mapped 1972, p. 7-8). Premetamorphic extrusive rock as their unit SOv. On this basis, we infer that most types include basaltic tuff, agglomerate, and pillow or all of the bedded rocks near Port Johnson flows and intermediate and felsic tuff (at least partly probably are Ordovician or Silurian, not spilite and keratophyre); sedimentary rock types Precambrian, in age include argillite, graywacke-siltstone, limestone, On the part of Prince of Wales Island bordering conglomerate, and, in the matrix of some of the the Prince Rupert quadrangle south of lat 54°55' pillow flows, red chert; and intrusive rock types N., MacKevett (1963) describes a complex of include medium- and coarse-grained diorite, intrusive igneous rocks that includes pyroxenite, hornblende diorite, and quartz diorite. gabbro, quartz diorite, diorite, granodiorite, quartz Compositional, textural, and structural relations monzonite, and syenite. These plutons intrude and

14 enclose subordinate metamorphosed detrital, mapped plutons on east-central Revillagigedo calcareous, and volcanic bedded rocks. MacKevett Island. The largest body, east of Manzanita Lake, is (1963, p. 15, 40) assigned the intrusive complex a an elongate (18 km by 7 km) pluton of leucocratic provisional Cretaceous emplacement age and granodiorite that may actually comprise several provisionally assigned the bedded rocks a different plutons too small to show or Devonian premetamorphic age. Subsequent Pb-U indistinguishable at reconnaissance mapping scale. isotopic dating studies and geologic mapping, The pluton is dominantly medium- to fine-grained however, show that the emplacement age of most hypidiomorphic granular granodiorite. Locally it is of the igneous complex is Ordovician or Silurian, foliated, and has thin muscovite or biotite partings as is the premetamorphic age of most of the evenly spaced 2-10 rom apart; in places near east metamorphosed bedded rocks (Gehrels and Behm Canal it is gneissic. Color index ranges from Saleeby, 1987). We therefore provisionally 0 to 15, but it is mainly between 0 and 2. The correlate the rocks of the intrusive complex with abundance of leucocratic aplite (CI =approximately unit SOui and the metamorphosed bedded rocks 0) varies from sparse patches to more than 70 with unit SOu percent of some outcrops. Near its margins the pluton contains structurally discordant xenoliths of REVILLAGIGEDO ISLAND AND amphibolite as long as several meters. Most CLEVELAND PENINSULA outcrops are cut by albite(?)-quartz pegmatite dikes Tgp Granite and quartz monzonite porphyry (Tertiary)­ that locally contain very coarse muscovite and (or) A massive and undeformed quartz- and feldspar­ biotite. In some places, these dikes constitute most porphyritic stock 1 km in diameter and a swarm of of an outcrop. North of Manzanita Creek, outcrops quartz porphyry dikes intrude amphibolite composed almost entirely of this pegmatite were (Mzflzmv) and hornblende-biotite quartz diorite mapped with this pluton. (Kq) at the mouth of Burroughs Bay. The granite Near Mount Reid this unit forms two stocks of and quartz monzonite porphyry consists of foliated leucocratic biotite quartz monzonite potassium feldspar euhedra as much as 1.5 em containing 1-2 percent dark-red garnet. Biotite, the long and partially resorbed quartz crystals as much only mafic mineral, makes up as much as 10 as 3 rom in diameter in a fine-grained groundmass percent of the rock, and forms thin films, layers, of quartz, plagioclase, potassium feldspar, and streaks, and, locally, clots as large as 2 em in minor biotite. Pyrite is disseminated throughout the diameter. The plutonic and metamorphic rocks pluton, and molybdenite occurs locally as thin films mapped between Manzanita Lake and Mount Reid coating fracture surfaces. The dikes are mainly contain pegmatite and aplite dikes and sills too aphanite and very fine grained quartz porphyry small to show on the map. The dikes and sills containing 0.5-- to 3-mm quartz phenocrysts in an range from a few centimeters to more than 100m aphanitic groundmass. Some of the dikes contain thick, and appear to be spatially and genetically disseminated pyrite and traces of molybdenite. The related to the stocks. The dikes occur in swarms pluton is assigned an Oligocene or Miocene that locally dominate outcrops within this area. emplacement age on the basis of a K-Ar age Subhorizontal sheets of aplite cap some ridge tops determination of about 23 Ma (table 1, No. 7) on and form prominent bands across nearly vertical biotite and chlorite. The sample that was dated cliff walls. The aplite varies from massive to probably was collected from an apophysis of this moderately foliated and is characterized by sugary pluton that is too small to show on the geologic map texture, low color index (0 to 5 percent biotite), and a few small pink garnet euhedra. Locally it Tgb Gabbro (Tertiary)-A crudely zoned gabbro complex contains quartz and feldspar phenocrysts. The forms an elongate stock near Ketchikan on aplite is cut by abundant albite(?)-quartz pegmatite southwestern Revillagigedo Island (Koch and dikes that locally contain coarse biotite and (or) Elliott, 1984). An olivine-bearing two-pyroxene muscovite, and a trace of garnet. Foliation in the gabbro makes up the core of the complex; biotite­ rocks assigned to this map unit appears to hornblende two-pyroxene gabbro surrounds the generally increase northward, as does the regional core; and a discontinuous zone of quartz-bearing metamorphic grade of the enclosing sedimentary gabbro underlies two areas at the northwest and and volcanic country rocks. In many places, southeast ends of the complex. Petrographic studies indicate that the internal contacts are however, intrusive contacts of apophyses of this probably gradational. The gabbro is not deformed. unit are less penetratively deformed than the It intrudes greenschist-facies metavolcanic and enclosing metamorphic country rocks, suggesting metasedimentary rocks and quartz diorite intrusive that at least some of the unit was emplaced after, rocks. Thermal metamorphism of the stratified or during the waning stages of, the regional rocks by the gabbro has produced a zone of metamorphism of the country rocks. Rocks hornfels and spotted schist apparently as wide as 3 mapped with this unit have not been dated by km in the adjoining country rocks. This zone is isotopic methods. We assign the unit a Cretaceous shown by a stippled pattern on the map. The emplacement age because its structural gabbro complex is assigned an Oligocene or characteristics and contact relations are consistent Miocene emplacement age on the basis of K-Ar with emplacement during and after the waning age determinations on biotite and hornblende of stages of the regional metamorphism that we about 23-25 Ma (table 1, No. 5) believe is Cretaceous in age ((see "Metamorphosed Klg Leucocratic granodiorite. quartz monzonite, and sedimentary, volcanic, and intrusive rocks aplite (Cretaceous)-This unit comprises three (Mesozoic or Paleozoic)")

15 Kpg Plagioclase-porphyritic granodiorite and quartz weathering quartz-feldspar (-biotite-garnet) diorite (Cretaceous)-These plutons generally pegmatite. Garnet partially replaced by chlorite form stocks 5 km or less in outcrop diameter, and occurs in many outcrops, and all samples of the dikes and sills too small to show on the map. pluton examined in thin section contain magmatic Primary igneous textures predominate. The rocks epidote. The pluton is assigned a Late Cretaceous are locally foliated but rarely show evidence of emplacement age on the basis of Pb-U (zircon) age deformation or metamorphism except in some of determinations of approximately 90 Ma for samples the thin, unmapped sills. Typical samples contain collected from northern Revillagigedo Island and conspicuous white plagioclase phenocrysts as large Yes Bay (table 1, Nos. 42, 46) as 3 em that make up 50-60 percent of the rock. Kg Epidote-biotite-hornblende granodiorite (Creta- The groundmass consists of fine-grained quartz (8- ceous)-This pluton, which also includes minor 20 percent), potassium feldspar (<1-10 percent), amounts of quartz diorite, is characterized by nearly biotite (5-25 percent) and hornblende (0-15 ubiquitous apple-green magmatic epidote. Textures percent). Primary (magmatic) garnet and epidote and compositions vary greatly. The pluton is occur as anhedral to euhedral crystals as large as 3 relatively massive in parts of its interior, but along mm. Epidote occurs within, but mostly interstitial some margins it grades into fine-grained to, plagioclase. It commonly forms 2-5 percent, quartzofeldspathic schist (blastomylonite and but locally forms over 10 percent of the rock. mylonite schist) containing only barely recognizable Composition of the epidote varies from sample to relict porphyroclasts of granitic rock. The pluton is sample, but at least some is the iron-free variety most schistose along Revillagigedo Channel, but (clinozoisite). Some of the garnet occurs in the schistose zones occur sporadically throughout the cores of plagioclase phenocrysts, and some as unit. The pluton is assigned a Late Cretaceous age discrete crystals, but it rarely makes up more than on the basis of a hornblende plateau 40Ar/39Ar 1-2 percent of any sample. Secondary minerals cooling age determination of 96-97 Ma (Sutter and locally include clinozoisite-epidote, white mica, and Crawford, 1985, p. 411) (table 1, No. 55) chlorite. Within the outcrop areas of this map unit Kum Ultramafic rocks (Cretaceous)-This unit consists are a few small, otherwise unassigned intrusive chiefly of rusty-weathering, massive-appearing, rocks that include aplite, pegmatite, and diorite. dark-greenish-black biotite- or clinopyroxene­ Some of the mapped plutons appear to be crudely bearing hornblendite and hornblende zoned: cores are massive porphyritic garnet- and clinopyroxenite. Thin-section studies show coarse epidote-bearing quartz diorite, and margins are xenomorphic aggregates of hornblende and massive foliated equigranular granodiorite. Primary clinopyroxene and accessory sphene, apatite, and (magmatic) flow foliation, when present, is more opaque minerals; some samples also contain conspicuous near the margins, where it commonly accessory biotite. The clinopyroxene commonly is is parallel to the metamorphic foliation of the partly altered to pale-green hornblende. intruded country rocks. Field relations indicate that Hydrothermal or metamorphic minerals include most of the unmapped dikes and sills and some of biotite, chlorite or antigorite, talc(?), actinolite(?), the smaller mapped plutons are nearly parallel to epidote, and calcite. At Alava Bay (southern the compositional layering of the metamorphic Revillagigedo Island), biotite hornblendite intrudes country rocks, whereas the contacts of most of the metamorphosed bedded rocks and Early larger plutons clearly intersect the metamorphic Cretaceous granitic rocks (Kg), and it is intruded layering. Plutons that have crosscutting contacts are by undated granitic dikes too small to show on the accompanied in some places by narrow aureoles map. The contacts of ultramafic rocks mapped that show thermal metamorphism to hornblende­ elsewhere on Revillagigedo Island were not hornfels facies, that overprints the metamorphic observed during this investigation. Aeromagnetic foliation of the country rocks. These petrographic, characteristics (U.S. Geological Survey, 1977) structural, and metamorphic relations indicate that suggest that the body near Clover Passage most of the plutons assigned to this unit were (southwestern Revillagigedo Island) may be emplaced after the regional metamorphism and intrusive and that bodies east and west of Thorne deformation of the country rocks, but that at least Arm may be thin, relatively flat-lying thrust sheets some of the mapped plutons and unmapped dikes or slabs (Andrew Griscom, oral commun., 1977). and sills may have been emplaced during the The hornblendite at Alava Bay is assigned a late waning stages of metamorphism and deformation. Early Cretaceous emplacement age because a K-Ar The unit is assigned an emplacement age of Late age determination on hornblende gave an age of Cretaceous on the basis of radiometric age about 99 Ma (table 1, No. 56). Other ultramafic determinations of 82-97 Ma (table 1, Nos. 51, 52) bodies mapped on Revillagigedo Island have not Kq Quartz diorite and granodiorite (Cretaceous )-A been dated by isotopic methods. In this report they batholith of generally massive hornblende quartz are provisionally correlated with the body at Alava diorite and granodiorite crops out on northern Bay on the basis of similarities in mineralogy, Revillagigedo Island and adjacent Cleveland texture, and geologic setting Peninsula. In places, the pluton is weakly foliated ~5 Metamorphosed sedimentary rocks (Triassic)-This or contains abundant ellipsoidal dark inclusions complexly folded and regionally metamorphosed that commonly are parallel to aligned hornblende greenschist-facies unit, mapped only along the east crystals and impart a pronounced lineation. Near shore of George Inlet on southwestern east Behm Canal, the pluton is locally gneissic. Revillagigedo Island, consists chiefly of thinly Locally prominent features include zones of interbedded (average thickness less than 25 em) angular agmatite and dikes and veins of light-gray- pyrite-bearing carbonaceous (graphitic) slate,

16 phyllite, and fine-grained recrystallized limestone amphibolite-facies metamorphism there or (b) is that locally contains slightly to moderately flattened gradational with the amphibolite facies spheroidal carbonaceous and siliceous concretions metamorphic rocks. Possibly the feather schist on as much as 6 em in diameter. Three less abundant southwestern Revillagigedo Island could be but locally conspicuous lithologies are also mapped compositionally controlled by rocks that do not with this unit: silvery-gray pyritic phyllite; rusty­ occur on northern and eastern Revillagigedo Island weathering phyllite or schist (possibly derived from or it may be the result of some process that felsic or intermediate tuff) containing pyrite, quartz, affected the rocks on southwestern but not muscovite, mariposite(?), and calcite or dolomite; northern or eastern Revillagigedo Island. and outcrops of massive to laminated gray marble K-Ar age determinations have been made on similar to that in the Permian marble unit ( Pm ). several minerals from the metasedimentary and About 4.5 km south of Coon Cove, concretions metavolcanic rocks in this assemblage on from carbonaceous slate and limestone contain Revillagigedo Island (table 1, Nos. 62--69), but no fossil bivalves and ammonites of latest Middle systematic attempt has been made to distinguish or Triassic (late Ladinian) age (Silberling and others, date individual metamorphic events. Maximum 1981, p. 118-119). Other fossil remains include apparent ages of minerals in the regionally locally abundant crinoid remnants (disks) in the metamorphosed greenschist facies strata on central gray marble and southern Revillagigedo Island are about 85 Ma Metamorphosed sedimentary, volcanic, and intrusive for biotite and 87 Ma for hornblende. Maximum rocks (Mesozoic or Paleozoic)-Most of apparent ages in the regionally metamorphosed Revillagigedo Island and Cleveland Peninsula are amphibolite-facies strata on northern Revillagigedo underlain by a complexly deformed and Island are about 96 Ma for biotite, 83 Ma for metamorphosed assemblage of sedimentary rocks, hornblende, and 84 Ma for muscovite; maximum intermediate or mafic volcanic and volcaniclastic age of these rocks on the eastern part of the island rocks, and relatively sparse intermediate or mafic is about 51 Ma for biotite and 74 Ma for plutonic rocks. In most places, the rocks show hornblende. Maximum apparent ages in feather evidence of at least two stages of metamorphism: schist from the central part of the island are about an early regional metamorphism that increases in 86 Ma for biotite and 93 Ma for hornblende. The intensity northward and eastward from greenschist age determinations show an increase in to amphibolite facies; and a later metamorphism discordance and decrease in maximum apparent manifested by porphyroblastic minerals that replace ages northward and eastward on Revillagigedo the older metamorphic minerals or that randomly Island. Because virtually all ages, however, fall in overprint the earlier foliation or schistosity. Some of the mid- to Late Cretaceous age range, we suggest this later metamorphism occurs in thermal aureoles that much if not most of this regional surrounding the Cenozoic and some of the metamorphism took place in mid- to Late Cretaceous plutons. Except for the hornfels zone in Cretaceous time. The discordance and decrease in the metamorphosed sedimentary rocks adjacent to maximum apparent ages northward and eastward the Tertiary gabbro body (T g b) near Ketchikan, on Revillagigedo Island is a manifestation there of these metamorphic aureoles are too small to show a widespread regional disturbance to K-Ar systems on the map. Depending on the original during Tertiary time (Smith and Oiggles, 1981, p. composition of the country rocks, contact 3). The cause of this disturbance is unknown, but metamorphic minerals in thermal aureoles include it has been attributed either to progressive regional biotite, andalusite, muscovite, garnet, staurolite, uplift and cooling (Hutchison, 1970) or to amphibole, cordierite, sillimanite, wollastonite, and widespread heating of enigmatic origin (Smith and diopside; these minerals suggest that the intensity others, 1979). of thermal metamorphism varies from albite­ Fossils have not been identified in the epidote hornfels to pyroxene hornfels facies metasedimentary and metavolcanic rocks mapped (Turner, 1981). with this assemblage. In this report, the strata are Other evidence of complex metamorphism assigned a premetamorphic age of late Paleozoic or includes the widespread development of feathery Mesozoic for four reasons. (1) Some of the or bowtie-like porphyroblastic aggregates of metaflysch and ferromagnesian- porphyritic actinolite, commonly in a matrix of muscovite and metavolcanic rocks that crop out on Cleveland garnet, that postdates an older foliation or Peninsula and southwestern Revillagigedo Island schistosity. Herein informally called "feather schist" are similar in lithology, texture, and geologic setting or "garbenschiefer," (Turner and Verhoogen, to faunally dated Jurassic and Cretaceous flysch 1960, p. 649), this feature is widespread on (KJgs) and volcanic rocks (KJgv) that crop out on southern and southwestern Revillagigedo Island, Gravina and Annette Islands. The largest outcrop where in places it is manifested by sheaves of areas of the metaflysch and metavolcanic rocks are actinolite crystals as long as 2 m, almandine(?) on Cleveland Peninsula southwest of Helm Bay garnet euhedra as much as 2 em in diameter, and and on Revillagigedo Island from Mountain Point coarsely crystalline muscovite. The age and origin to Clover Passage. (2) On the west shore of upper of this feather schist is unknown. Because we did Thorne Arm, the metavolcanic rocks appear to be not observe the schist in the regionally interlayered with Permian marble (Pm). (3) Field metamorphosed amphibolite-facies sedimentary observations suggest that the metaconglomerate and volcanic rocks on Cleveland Peninsula and on mapped from Carroll Inlet to Thorne Arm is at least northern and eastern Revillagigedo Island, we think structurally conformable and possibly is that the feather schist (a) was destroyed by the depositionally gradational with the Permian marble

17 unit and intertonguing basaltic metavolcanic rocks. and on Cleveland Peninsula from Spacious Bay to (4) Dark-gray pyrite-rich graphitic marble the north, the unit is mainly rusty-weathering interbedded with metapelite near the abandoned crystalline gneiss and schist consisting of alternate cannery on the west shore of George Inlet is similar layers 1 em to 2 m thick of pelitic and in lithology and texture to some of the Middle quartzofeldspathic rocks. It also contains Triassic marble and recrystallized carbonaceous subordinate dark-gray gneiss, dark-green limestone (Rs) that crops out south of Coon Cove hornblende-rich schist and gneiss, and minor on the opposite shore on the inlet. A sample of the marble. Quartz veins and lenses as much as a recrystallized graphitic limestone was tested for meter thick commonly parallel the gneissic layering. microfossils (conodonts) but was barren (Berg and Thin-sections of the pelitic gneiss show strongly Cruz, 1982). The metamorphosed intrusive rocks schistose, granoblastic, and idioblastic textures. mapped with the assemblage are assigned a late Typical specimens contain (a) quartz, plagioclase, Paleozoic and Mesozoic emplacement age because biotite, garnet, and muscovite, (b) accessory their compositions, textures, and field relations clinopyroxene, calcite, sphene, apatite, and pyrite, suggest that they may be cogenetic with some of and (c) retrograde chlorite, epidote, and sericite. the metavolcanic rocks. Sillimanite occurs mainly in a narrow zone adjacent We have subdivided the assemblage into five to the quartz diorite batholith (Kq) on northern map units on the basis of their premetamorphic Revillagigedo Island. and neighboring Cleveland lithology: metamorphosed sedimentary rocks and Peninsula; kyanite and staurolite occur in a zone at minor intermediate and mafic metavolcanic and least 2 km wide beyond the sillimanite zone. The volcaniclastic rocks (MzPzms); metamorphosed quartzofeldspathic component of the gneiss is intermediate and mafic volcanic and volcaniclastic distinguished from the pelitic component by a rocks and minor sedimentary rocks (MzPzmv); stronger granoblastic fabric and by more quartz polymictic metaconglomerate (MzPzmc); and plagioclase. The dark-gray gneiss is similar in metamorphosed intrusive rocks (MzPzmi); and mineralogy and fabric to the rusty-weathering undivided metamorphosed sedimentary, volcanic, pelitic gneiss but is distinguished from it by greater and intrusive rocks (MzPzu): abundance of hornblende. The hornblende-rich MzPzms Metasedimentary rocks-This unit was derived from gneiss is distinguished by contrasting alternating pelitic and semipelitic flysch gradationally layers of dark-greenish-black hornblende-biotite­ interbedded with relatively minor amounts of quartz-plagioclase schist and light-gray quartz­ andesitic or basaltic volcanic or volcaniclastic rocks. plagioclase schist. On southwestern Revillagigedo Island and on Throughout the areal extent of this unit, the Cleveland Peninsula south of Spacious Bay, the metamorphic minerals and textures indicate prevailing lithology is dark-gray and silvery-gray regional metamorphism that grades northward and phyllite and fine-grained semischist; there are eastward from greenschist facies to amphibolite subordinate layers of green phyllite and semischist. facies. On southwestern Revillagigedo Island and The gray phyllite and semischist contain quartz, neighboring Cleveland Peninsula the regional feldspar, and varying amounts of biotite, garnet, metamorphic fabric is locally overprinted by low­ muscovite, pyrite. graphite, hornblende or pressure metamorphism to pyroxene hornfels actinolite, calcite, and chlorite. The micaceous facies that occurs in intrusive aureoles. The largest minerals commonly have two habits: as platy such aureole surrounds the Tertiary gabbro pluton crystals aligned parallel to schistosity, and as near Ketchikan and is indicated by a stipple pattern idioblasts (or chlorite pseudomorphs) as much as a on the map. Composition of the aureole changes em long that intersect the foliation at all angles. gradationally from a zone of sillimanite-, cordierite-, Thin sections of the green layers show fine-grained and staurolite-bearing hornfels near the pluton to a schist containing hornblende, subordinate quartz or periphery that is indistinguishable from the plagioclase, and minor to trace amounts of biotite, regionally metamorphosed greenschist-facies pyrite, garnet, and epidote-clinozoisite. In some metasedimentary rocks. samples, hornblende metacrysts as long as 1 em The unit is intruded by diverse mapped plutons crosscut the foliation. The unit also contains minor and by numerous unmapped dikes and sills of feather schist, fine-grained quartz-muscovite schist massive, moderately foliated, or (rarely) schistose, possibly derived from quartzite or chert, and locally garnet-bearing and feldspar-porphyritic phyllitic polymictic grit and conglomerate that in aphanite, aplite, pegmatite, and fine-grained places contain relict clasts of leucocratic plutonic granodiorite. rocks. Locally conspicuous layers of rusty­ The unit grades into metamorphosed volcanic weathering schist as thick as 2-3 m contain quartz, rocks (MzPzmv) on southwestern Revillagigedo plagioclase, calcite, biotite, muscovite, garnet, Island and neighboring Cleveland Peninsula where epidote-clinozoisite, chlorite, and pyrite. These it has more green phyllite and semischist and on layers may be relict beds of calcareous felsic or northern and eastern Revillagigedo Island and intermediate metatuff or other volcanogenic neighboring Cleveland Peninsula where it has material. Locally the unit contains auriferous quartz more hornblende-rich schist and gneiss veins and disseminated and massive sulfide MzPzmv Metavolcanic rocks-This unit was derived primarily deposits that have been prospected for gold, silver, from submarine andesitic or basaltic lava flows, copper, lead, and zinc (Berg and others, 1981, p. tuff, and agglomerate and from subordinate 59-70). gradationally intertonguing pelitic and semipelitic On northern and eastern Revillagigedo Island flysch. On Cleveland Peninsulsa southwest of Helm

18 Bay and on southwestern Revillagigedo Island from fabric is locally overprinted in contact aureoles by Mountain Point to Clover Passage, the low-pressure metamorphism to the hornblende­ metavolcanic rocks are distinguished by hornfels facies. The only such aureole shown on conspicuous relict euhedral ferromagnesian the map surrounds the Tertiary gabbro near phenocrysts (now hornblende or actinolite Ketchikan and is indicated by a stipple pattern. pseudomorphs of clinopyroxene) as long as 2 em. Contact minerals identified in this aureole are listed Outcrops of this porphyry range from thick, under unit MzPzms. massive-appearing layers or lenses of coarse, The unit is intruded by diverse mapped plutons blocky, dark-green breccia to light-green semischist and by numerous unmapped dikes and sills of and thinly laminated and lineated very fissile massive to (rarely) schistose, locally garnet-bearing phyllite. Minerals identified in thin section indicate and feldspar-porphyritic aphanite, aplite, and regional metamorphism to greenschist facies and pegmatite and fine-grained granodiorite. typically include albite, quartz, chlorite, epidote, The unit grades lithically into metamorphosed actinolite, calcite, pyrite, and sphene. sedimentary rocks (MzPzms) on southwestern Elsewhere on southwestern Revillagigedo Island Revillagigedo Island and neighboring Cleveland and on Cleveland Peninsula northeast of Helm Peninsula where it has more gray phyllite and Bay, the unit consists chiefly of dark-green, silvery­ semischist and on northern and eastern green, and greenish-gray phyllite, semischist, and Revillagigedo Island where it has more pelitic schist schist, minor marble, and some gray phyllite and and gneiss semischist. In places along the shorelines of Carroll MzPzmc Polymictic metaconglomerate-The mapped areas of Inlet, Thome Arm, and east Behm Canal, it this unit are on Revillagigedo Island between displays well-preserved pillow structures and Carroll Inlet and Thome Arm, on and near Back related volcanic-fragmental textures. Thin sections Island in Clover Passage, and near Lake Harriet show that the prevailing lithology is fine-grained Hunt; and on Cleveland Peninsula on the schist containing varying amounts of blue-green northeast shore and adjacent islets of Helm Bay. hornblende and actinolite, albite, chlorite, quartz, Between Carroll Inlet and Thome Arm, the unit is plagioclase, epidote, and pyrite. The amphibole characterized by prominent spheroidal to ellipsoidal crystals occur both parallel to the schistosity and as relict clasts of fine- to coarse-grained Jeucocratic poikiloblastic euhedra as long as 1 em that intersect plutonic rocks as much as 20 em in diameter. the foliation at all angles. The gray phyllite is Other relict clasts are more strongly deformed and lithically identical to the prevailing rock type include quartzite as well as phyllite and semischist described in unit MzPzms. The unit also contains derived from fine-grained sedimentary and possibly minor feather schist and fine-grained quartz­ volcanic rocks. Thin sections show that the matrix muscovite schist, possibly derived from quartzite or is fine-grained schist containing quartz, plagioclase, chert. Near the head of Thome Arm, quartz veins biotite, epidote-clinozoisite, garnet, calcite, and other lodes in the unit have been successfully muscovite, and pyrite. Some of the biotite and worked for gold and prospected for copper, lead, garnet crystals are partly altered to chlorite. Some zinc, and precious metals (Berg and others, 1981, chlorite pseudomorphs (of biotite?) are p. 59-70). On northern and eastern Revillagigedo perpendicular to foliation. Thin sections of Island, the unit is mainly dark green and dark gray representative plutonic clasts show fine- to amphibolitic and subordinate quartzofeldspathic medium-grained (relict) xenomorphic, granoblastic, schist and gneiss. It also contains sparse layers of and interlocking mosaics of quartz and plagioclase marble and rusty-weathering pelitic gneiss. and minor biotite, muscovite, epidote-clinozoisite, Petrographic studies of the amphibolite show calcite, chlorite, and garnet. Chemical analyses strongly schistose and idioblastic textures. Typical (Z.A. Hamlin, unpub. data, 1977), combined with specimens contain hornblende, biotite, quartz, and the petrographic data, suggest that these clasts are plagioclase and have accessory sphene, apatite, probably metamorphosed trondhjemite. The potassium feldspar, and pyrite, and retrograde metaconglomerate occurs in layers as thick as 2 m. chlorite and epidote. The quartzofeldspathic rocks It also contains thin layers of gray phyllite and are distinguished by granoblstic fabric and by more semischist containing relatively sparse pebbles of quartz and plagioclase. The mineralogy and fabric leucocratic plutonic rocks. The unit grades of this pelitic gneiss are identical to those of the structurally upward into gray phyllite that contains pelitic gneiss in unit MzPzms. The amphibolite is diminishing numbers of relict clasts and it grades characterized by ubiquitous veins and dikes as downward into intercalated green and gray phyllite much as several meters thick, of leucocratic quartz­ and semischist. At Gnat Cove on Carroll Inlet, the plagioclase-biotite-garnet pe:gmatite and aplite that structurally lowermost part of the unit contains a contrast strikingly with the dark hues of the few lenses of brown-weathering marble. enclosing amphibolite. Locally, the leucocratic At Back Island, metaconglomerate is interbedded rocks form spectacular swarms of randomly with flysch. It contains prominent relict rounded oriented dikes that make up as much as half of the clasts of recrystallized leucocratic plutonic rocks as outcrop. much as 25 em in diameter, as well as smaller, less The metamorphic minerals and textures in this prominent and more deformed relict clasts of white unit throughout its areal extent indicate regional marble, dark-hued flysch, and quartzite(?). The metamorphism that grades northeastward from matrix is pelitic phyllite and semischist similar to greenschist fades to amphibolite facies. On that in the enclosing metasedimentary rocks. southwestern Revillagigedo Island and neighboring In an outcrop of polymictic metaconglomerate Cleveland Peninsula, the regional metamorphic about 3 km southwest of Lake Harriet Hunt, about 19 10 percent of the rock consists of relict clasts in a as 2 em in diameter; the clumps are enclosed by matrix of pelitic schist containing quartz, hornblende-biotite-plagioclase-quartz schist. The plagioclase, muscovite, biotite, garnet(?), and bodies south of Neets Bay and north of Emma chlorite(?). The relict clasts average about 5 em in Lake consist mainly of massive amphibolite maximum dimension. The most prominent relict containing hornblende, plagioclase, and variable clasts are slightly flattened roundstones as much as amounts of biotite, garnet, pyrite, pyroxene, and 30 em in diameter of leucocratic plutonic rock quartz. Outcrops of relatively unmetamorphosed consisting of quartz, feldspar, and a small hornblende-plagioclase diorite and gabbro locally percentage of dark, mainly micaceous minerals. occur with the amphibolite. Field relations suggest Less prominent are ellipsoidal and lensoidal relict that the plutonic rocks grade into the amphibolite clasts, apparently originally of fine-grained felsic as the metamorphism increases. The intrusive body igneous or pelitic(?) sedimentary rocks. The most near the mouth of Carroll Creek consists of attenuated of these clasts are elongate lenses 15 relatively massive metadiorite(?) and fine-grained em long and 1 em thick parallel to the schistosity. hornblende-plagioclase schist probably derived At Helm Bay, metamorphosed conglomerate from it and grit layers as thick as 2 m are intercalated with MzPzu Metamorphosed sedimentary, volcanic, and flysch. The metaconglomerate is very fissile and intrusive rocks, undivided-This unit consists contains markedly flattened (paper-thin) to nearly chiefly of phyllite, .semischist, and schist derived perfectly spheroidal relict clasts 5-6 em in from diverse sedimentary, volcanic, and intrusive maximum dimension. Clast compositions include rocks. Because the unit is so heterogeneous, the argillite or metapelite (most flattened), principal lithologies are listed, in approximate order indeterminate fine-grained rocks, and medium- and of decreasing abundance, for each map area. fine-grained silicic igneous rocks (least deformed). Point Alava area: muscovite-calcite (or dolomite) The matrix of the metaconglomerate is metapelite. schist; phyllitic siltstone, mudstone, and graywacke; Unmapped polymictic roundstone meta- massive blastomylonitic granodiorite; phyllitic to conglomerate that contains prominent relict clasts schistose, intermediate or mafic volcanic or of leucocratic igneous rocks occurs in a small volcaniclastic rocks; feather schist; marble; and xenolith or roof pendant, accompanied by marble, clinopyroxenite. in Cretaceous granodiorite (Kg) on the east shore Coastal area from southeast of Carroll Point to of Thorne Arm about 5.8 km from Cone Point. Moth Bay: blastomylonitic granodiorite; Metaconglomerate is also associated with apparent carbonaceous metapelite (argillite); phyllitic structurally intercalated marble (Pm), siltstone, mudstone, and graywacke; phyllitic to metasedimentary (MzPzms), and metavolcanic schistose, intermediate or mafic volcanic and (MzPzmv) rocks near Ape Point on the southeast volcaniclastic rocks, including pillow flows and flow coast of Revillagigedo Island, where the breccia; feather schist; granitic-clast metaconglomerate also contains relict clasts of metaconglomerate; rusty- weathering pyrite-rich marble (M. L. Crawford, oral commun., 1982) felsic aplite; and marble. MzPzmi Metamorphosed intrusive rocks-Mainly regionally Bold and Round Islands: phyllitic siltstone, metamorphosed or otherwise recrystallized or graywacke, and grit; laminated andesitic(?) altered diorite, quartz diorite, and gabbro. The metatuff; cataclastic graywacke semischist; body at Smuggler's Cove (southeastern Cleveland cataclastic (blastomylonitic?) granodiorite; granitic­ Peninsula) consists of dark-greenish-gray clast metaconglomerate. hypidiomorphic-granular diorite and Eve Point area (Thorne Arm): rusty-weathering ferromagnesian-porphyritic diorite containing schistose calcareous metatuff or other volcanogenic magmatic plagioclase, magmatic or secondary material; phyllitic to schistose siltstone, mudstone, hornblende(?), and secondary epidote, chlorite, graywacke, and intermediate or mafic volcanic or and calcite. Rocks of the porphyritic phase closely volcaniclastic rocks; massive to schistose, locally resemble some of the enclosing metavolcanic rocks garnet-bearing and feldspar-porphyritic aphanite, (MzPzmv). West of Port Stewart (Cleveland aplite, and granodiorite sills and dikes; and Peninsula) a body of massive to foliated hornblendite and pyroxenite. hornblende-biotite diorite, quartZ diorite, and Hump Island (Clover Passage): rocks assigned to gabbro coincides with a positive aeromagnetic this unit are locally intensely iron stained and anomaly (U.S. Geological Survey, 1977). This bleached and in places contain disseminated pyrite, body may be a structurally detached fragment of a chalcopyrite, and possibly other sulfide minerals. Cretaceous zoned ultramafic intrusive complex Tentatively identified bedded(?) rocks include near Union Bay, about 6 km beyond the west hydrothermally altered felsic or intermediate boundary of Ketchikan quadrangle (Eberlein and metavolcanic, volcaniclastic, or other volcanogenic others, 1983, p. 4-5). North of Coon Cove rocks, and pelitic(?) metasedimentary rocks. (Revillagigedo Island, George Inlet), a pluton Intrusive rock types include (a) altered garnet­ mapped with this unit consists of fine-grained bearing leucocratic aplite and quartz diorite that diorite(?) that contains magmatic(?) quartz, host at least some of the disseminated sulfide plagioclase, and biotite and has metamorphic minerals and (b) hornblende porphyry, actinolite, chlorite, and epidote. Southwest of Lake hornblendite, and andesite(?) dikes that apparently Grace, another pluton consists mainly of massive­ postdate the hydrothermal alteration appearing dark-greenish-gray coarse schist Pm Marble (Permian)-Most of this unit is light-brown­ containing equant clumps of hornblende as much weathering, massive to laminated, light-gray,

20 bluish-gray, and dark gray marble. Less abundant, foliation or other evidence of significant penetrative but locally conspicuous other lithologies mapped deformation in the pegmatite indicates that it was with it include (a) dark-green, dark-gray, or rusty­ emplaced during or after the waning stages of the weathering pyritic phyllite and semischist, (b) mid- or Late Cretaceous regional metamorphism polymictic sedimentary breccia or conglomerate that apparently affected most of the rocks in the containing relict angular to subrounded clasts of Ketchikan and Prince Rupert quadrangles (see this basalt, marble, and felsic(?) metatuff as much as a report, discussion under Revillagigedo Island and meter long in a matrix of green metatuff and dark­ Cleveland Peninsula: "Metamorphosed sedi­ gray argillite, (c) schistose fragmental mentary, volcanic, and intrusive rocks (Mesozoic or (volcaniclastic?) rock comprising elongate, strongly Paleozoic)"; Smith and Diggles, 1981, p. 2). These flattened relict clasts as much as several em long of relations suggest emplacement possibly as long ago quartzite or felsic(?) metavolcanic rocks enclosed as the Late Cretaceous but before about 46 Ma by rusty-weathering, fine-grained, pyrite-quartz­ Kgq Granodiorite and quartz diorite (Cretaceous)-A muscovite-mariposite(?)-calcite or -dolomite schist, stock near Point Sykes consists of massive to and (d) greenish-black basalt dikes and sills. Thin weakly foliated, medium-grained, magmatic­ sections of the marble typically show sugary to epidote-bearing hornblende-biotite granodiorite coarsely garnoblastic aggregates of calcite or and quartz diorite. Mild deuteric(?) alteration dolomite and minor quartz, muscovite, graphite, includes feldspathized joints, disseminated pyrite, and pyrite. Near the contacts of some plutons, the sericitized plagioclase, and partial recrystallization of marble also contains wollastonite, diopside, and mafic minerals to chlorite, epidote, and iron oxides. garnet. Black crinoidal marble intercalated with The pluton intrudes the surrounding metamorphic phyllite about 0. 5 km south of Coon Cove contains rocks with a sharp contact. Dikes of granodiorite conodonts and brachiopods of late Early Permian extend into the country rock, and the pluton is (Leonardian) age (Silberling and others, 1981, p. surrounded by a contact metamorphic (hornfels) 118). Other fossil remains in the marble include aureole several hundred meters wide. The pluton is numerous occurrences of locally abundant crinoid assigned a Late Cretaceous emplacement age fragments (disks) of uncertain, but probably late because of discordant K-Ar age determinations of Paleozoic, age (Berg and Cruz, 1982) about 59 Ma for biotite and about 80 Ma for SOu Extrusive, intrusive, and sedimentary rocks, hornblende (table 1, No. 53) and because of its undivided (Silurian or Ordovician)-Rocks intrusion into, and contact metamorphism of, rocks assigned to this unit, shown on the map sheet only that were probably regionally metamorphosed in near Caamano Point on southern Cleveland late Mesozoic time (see this report, discussion Peninsula, are more highly deformed or under Revillagigedo Island and Cleveland recrystallized correlatives of those in unit SOu in Peninsula: "Metamorphosed sedimentary, volcanic, the Prince of Wales-Gravina-Annette-Mary-Duke and intrusive rocks (Mesozoic or Paleozoic)"; Smith Islands area (Saleeby and Gehrels, 1985; Rubin and Diggles, 1981, p. 2). Two stocklike plutons of and Saleeby, 1987), which are described above. A massive or slightly foliated leucocratic granodiorite single outcrop area of marble (m) is large enough about 8 km east of the mouth of Boca de Quadra to show on the map sheet. It consists of tan­ are here provisionally correlated with the pluton at weathering, sugary, white calcite and dolomite, Point Sykes on the basis of similarities in lithology, intercalated with subordinate green metavolcanic texture, and geologic setting and gray metasedimentary phyllite and schist. This Kum Ultramafic rocks (Cretaceous)-The only occurrence outcrop area is about 2 km from an occurrence of of ultramafic rocks large enough to show on the marble too small to show on the map that is host map in this area is at Humpy Point. Several small, to stibnite (antimonyl-bearing veins (Berg and unmapped ultramafic bodies crop out along the others, 1981, p. 62) east shore of Behm Canal south of Smeaton Bay. At Humpy Point, medium- to very coarse-grained PORTLAND PENINSULA biotite clinopyroxenite and subordinate Western and southwestern area hornblendite intrude undated gabbro (unmapped) TKp Trondhjemitic pegmatite (Tertiary or Cretaceous)­ and Silurian metamorphosed trondhjemite (Smt) This unit consists chiefly of pegmatite that contains with sharp contacts and no apparent thermal about 70 percent sadie plagioclase, 25 percent effects. In most outcrops, the ultramafic rocks are quartz, and accessory to minor biotite, hornblende, massive and apparently not foliated; in places, and potassium feldspar. Some of the plagioclase, however, they contain abundant secondary biotite, and quartz crystals are as long as 10 em. chlorite. On the basis of similarities in lithology, Outcrops typically show layers of coarse- and fine­ texture, and geologic setting, this ultramafic grained pegmatite that alternate with schlieren and intrusive body is correlated with the isotopically screens of amphibolite. The unit is always adjacent dated Cretaceous ultramafic pluton at Alava Bay to or enclosed by amphibolite (MzPza). MzPza Amphibolite (Mesozoic or Paleozoic)-A linear We infer a Cretaceous or Tertiary emplacement outcrop belt of distinctive dark-greenish-black age for these pegmatite bodies from their field amphibolite as much as 5 km wide crops out from occurrences and petrography and from available near the mouth of Rudyerd Bay to the boundary local and regional isotopic age data. A K-Ar age of Alaska and Canada (Berg and others, 1977, p. determination on biotite from the body on the east 13-14). The amphibolite locally is spectacularly coast of Behm Canal, about 5 km north of the streaked with strongly contrasting dikes, veins, and mouth of Smeaton Bay, gave an apparent age of lenses of white trondhjemite pegmatite (TKp) and about 46 Ma (table 1, No. 39). The absence of other leucocratic intrusive rocks. Beyond the 21 boundary, the unit continues in outcrop during emplacement of some plutons. Most of the southeastward across Sitklan Passage and into rocks in the assemblage are green or silvery-gray British Columbia, where it is mapped as the Work schists that, depending on original composition and Channel Amphibolite (Hutchison, 1982, p. 11-14). proximity to plutons, contain varying proportions of The unit commonly is strongly banded and quartz, plagioclase, chlorite, epidote-clinozoisite, consists of layers of greenish-black schist and gneiss biotite, muscovite, actinolite or hornblende, garnet, that contrast strikingly with alternating layers of kyanite, and calcite. Locally prominent rock types light-gray gneiss. The thickness of the layering also include feather schist, rusty-weathering quartz­ varies but averages about 10 em. Local variation in muscovite schist possibly derived from felsic mafic and felsic mineral content results in outcrops volcanic or volcanic-related rocks, quartzite, that vary from nearly pure hornblende schist or ultramafic rocks, marble, and sheared intrusive hornblende-biotite schist to relatively uniform dark­ rocks apparently originally granodiorite, gray gneiss containing approximately equal trondhjemite, quartz diorite, and diorite. Outcrop amounts of mafic and felsic minerals. The unit also areas of marble (m) large enough to show on the contains minor amounts of marble, pelitic gneiss, map are present locally. The marble appears and plagioclase-quartz-(biotite-garnet} aplite dikes. massive to platy, is white, gray, and bluish gray, Some of the marble layers and many of the dikes and weathers light brown. It consists of a sugary to are several meters thick coarse-grained aggregate of calcite or dolomite and Thin sections of typical samples of amphibolite has subordinate to minor amounts of muscovite, show fine-to medium-grained granoblastic and phlogopite, quartz, graphite, garnet, and pyrite. schistose textures; the composition averages about Although we were not able to subdivide this 45 percent plagioclase feldspar (oligoclase and assemblage on Portland peninsula, its lithology and andesine), 30 percent hornblende, 15 percent structural and metamorphic features apparently are biotite, 5 percent quartz, and 5 percent accessory identical with those of most of the metamorphosed minerals including apatite, clinopyroxene, garnet, bedded and intrusive rocks (MzPzu, · MzPzms, magnetite, pyrite, and sphene. Retrograde minerals MzPzmv, MzPzmi) mapped on southern include small amounts of chlorite and epidote. Revillagigedo Island. A few objects doubtfully This amphibolite is identical in lithology and identified as crinoid remnants (disks) that occur in texture to the regionally metamorphosed the marble (m} at Very Inlet (Berg and Cruz, 1982) amphibolite-facies volcanic or volcaniclastic rocks suggest possible correlation with the Permian (MzPzmv) that crop out on eastern Revillagigedo crinoidal marble on Revillagigedo Island. Island. Although the map shows thin and K-Ar determinations on metamorphic minerals in discontinuous outcrops of the amphibolite along two samples of schistose bedded rocks from this the east coast of Behm Canal north of Rudyerd unit show apparent ages ranging from about 47 to Bay, the main outcrop belt of amphibolite appears 69 Ma for biotite, and 61 to 77 Ma for hornblende to strike across Behm Canal at about the latitude of (table 1, Nos. 70-72); actinolite from a sheared Rudyerd Bay, toward the amphibolite on eastern and recrystallized mafic dike gave an apparent age Revillagigedo Island. On the basis of this assumed of about 86 Ma (No. 72). Regional geologic continuity, the amphibolite on Portland Peninsula relations suggest that at least some of the rocks is also assigned a premetamorphic age of late have undergone (a) the mid- or Late Cretaceous Paleozoic or Mesozoic. The relative proportions of regional metamorphism that apparently affected metamorphosed stratified rocks and of presumably most of the rocks in the study area (this report, younger plutonic rocks in this map unit are discussion under Revillagigedo Island and unknown. Cleveland Peninsula area: "Metamorphosed K-Ar age determinations on metamorphic sedimentary, volcanic, and intrusive rocks minerals from the amphibolite unit show apparent (Mesozoic or Paleozoic)"; Smith and Diggles, 1981, ages ranging from about 47-51 Ma for biotite and p. 2), (b) thermal metamorphism related to the about 50-58 Ma for hornblende (table 1, Nos. 73- emplacement of the Cretaceous granodiorite (Kgq) 75). These ages probably reflect the widespread stock near Point Sykes, and (c) the widespread disturbance to K-Ar systems that affected most of disturbance to K-Ar systems in rocks older than 40 the rocks on the Portland peninsula in middle Ma that affected most of Portland peninsula in Cenozoic time (Smith and Diggles, 1981, p. 3). middle Cenozoic time (Smith and Diggles, 1981, p. Field relations suggest gradational metamorphic 3}. Quartz veins and lenses in the green or gray and possibly compositional relations between the schist have been prospected for gold, and the amphibolite unit and undivided bedded and rusty-weathering schist locally contains deposits of intrusive rocks (MzPzu) on the west and between it disseminated and massive sulfides that have been and pelitic paragneiss (MzPzp), foliated quartz prospected for gold, silver, copper, and zinc (Berg diorite (TKfq), and foliated granodiorite (TKfg} on and others, 1981, p. 66) the east Smt Metamorphosed trondhjemite (Silurian}-The Cape MzPzu Metamorphosed sedimentary, volcanic, and intrusive Fox pluton (Koch and others, 1977) is an elongate rocks, undivided (Mesozoic or Paleozoic}-This (9 km x 23 km) stock of regionally map unit comprises a heterogeneous, complexly metamorphosed trondhjemite exposed at the deformed assemblage of originally diverse bedded southwest tip of Portland peninsula. The pluton and intrusive rocks that have been regionally originally crystallized as leucocratic coarse-grained metamorphosed to greenschist and possibly hypidiomorphic-granular trondhjemite. Extensive amphibolite facies and locally remetamorphosed recrystallization has reduced almost all the primary

22 biotite to chlorite. Most outcrops contain abundant Oligocene or Miocene on the basis of a K-Ar age metamorphic epidote. Pervasive fracturing and determination on biotite of 23.8 Ma (table 1, No. shearing increase outward from the core of the 4) pluton. Parts of the pluton, especially toward the Tgp Granite and granite porphyry (Tertiary)-This unit north, have been reduced to quartzofeldspa,thic (Elliott and others, 1976, p. 9-11; Hudson and semischist and schist that are difficult to distinguish others, 1979) consists of two roughly oval from the enclosing schistose country rock. At least composite felsic stocks and a suite of related some of the metamorphism probably coincided quartz- and feldspar-porphyritic felsic dikes that are with the regional metamorphism that apparently too small show on the map. The dikes occur in a affected most of the rocks in neighboring areas in belt 5 km wide that extends east-northeastward at mid- or Late Cretaceous time (this report, least 20 km from Wilson Arm to and beyond the discussion under Revillagigedo Island and stocks. The stocks contain several textural varieties Cleveland Peninsula: "Metamorphosed sedi­ of biotite granite and granite porphyry, and they mentary, volcanic, and intrusive rocks (Mesozoic or show no evidence of regional penetrative Paleozoic)"). The pluton is assigned a Silurian deformation. Typical samples of the granite consist emplacement age on the basis of a preliminary Pb­ of light-gray, fine- to medium-grained, U (zircon) age determination of about 428 Ma hypidiomorphic granular biotite granite containing (table 1, No. 83) scattered phenocrysts up to 1 em long of pinkish­ SOu Extrusive, intrusive, and sedimentary rocks, gray perthite and subhedral to euhedral gray undivided (Silurian or Ordovician)-Rocks quartz. In general, the porphyry consists of felsic assigned to this unit are here interpreted as the aplite that contains sparse to abundant euhedral more highly deformed or recrystallized correlatives phenocrysts as long as 1 em of brown biotite, sodic of those in unit SOu in the Prince of Wales­ plagioclase, perthite, and quartz. Some of the Gravina-Annette-Mary-Duke Islands area, which porphyry contains quartz-, muscovite-, and pyrite­ are described above lined miarolitic cavities as much as 2 mm in diameter. Much of the granite and porphyry in the Central and eastern area smaller stock is intensely argillized and silicified and Four stocklike plutons (Tqm, Tgb, Tgp), aligned along a cut by networks of thin quartz-molybdenite veins nearly linear eastward trend in central Portland peninsula, and molybdenite-coated fractures. This porphyry yield radiometric ages ranging from late Oligocene to middle molybdenum deposit was being developed (in Miocene. Despite their near-contemporaneity and relative 1987) by private interests. We assign this unit an proximity, the plutons differ markedly in composition and Oligocene emplacement age on the basis of K-Ar texture. The stocks intrude various metamorphic and plutonic age determinations on biotite ranging from 26.9 to rocks with minor contact· effects, and are cut by lamprophyre 30.4 Ma (table 1, Nos. 8, 9), and a Pb-U (zircon) dikes (Smith, 1973) that are too small to show on our map: age determination of 31 Ma (table 1, unnumbered Tqm Biotite quartz monzonite (Tertiary)-This pluton sample). The contacts between the stocks and the consists of massive, medium- to coarse-grained, country rocks of paragneiss (MzPzp) and gneissic hypidiomorphic granular, locally miarolitic quartz granodiorite (TKfg) are locally marked by narrow monzonite that contains sparse phenocrysts of thermal aureoles pale-pink potassium feldspar as long as 1.5 em. Three plutonic rock units (Tgq, Tdr, Tg) of up to Thin-section examination of typical samples shows batholithic dimensions have isotopically determined or inferred (a) subhedral to euhedral crystals of twinned and Eocene emplacement ages. Two of them are on eastern Portland concentrically zoned plagioclase whose cores peninsula, and continue eastward beyond Portland Canal into commonly contain minute grains of epidote, white British Columbia (Hutchison, 1982). The plutons are complexly mica, and opaque minerals, (b) interstitial quartz jointed and locally cut by faults and shear zones, but they show and discrete anhedral crystals of quartz, (c) as no evidence of penetrative deformation or regional much as 7 percent of subhedral to euhedral brown metamorphism. They range in texture from massive to foliated or biotite, (d) a percent or two of euhedral green even locally gneissic. Some of these planar and linear textures hornblende, and (e) traces of sphene. Some of the may be the result of local deformation, but we interpret them to mafic minerals are altered to chlorite. We assign be due mainly to alignment of mafic inclusions and minerals this pluton an Oligocene or Miocene emplacement during emplacement of the plutons or to partial assimilation of age on the basis of K-Ar age determinations of more foliated or gneissic country rocks. All of the plutons are 22.9 Ma for biotite and 26.8 Ma for hornblende, intruded by numerous lamprophyre dikes too small to show on and on Pb-U (zircon) age determinations of about the map: 19 Ma (table 1, No.6) Tgb Gabbro (Tertiary)-This roughly circular stock consists Tgq Granodiorite and quartz monzonite (Tertiary)-As chiefly of uniform, predominantly subophitic fine­ mapped, this unit includes the batholith composed grained gabbro containing labradorite and later of the Hyder Quartz Monzonite (Buddington, oligoclase, augite, biotite, hypersthene, green and 1929, p. 29-32; Smith, 1977, p. 32-37) and brown hornblende, magnetite, apatite, and locally correlative plutons (Berg and others, 1977, p. 22- olivine. Field and thin-section studies suggest that 23) that occur in north-central and northeastern the stock may be concentrically zoned (Berg and Portland peninsula, and a stock at Fitzgibbon Cove others, 1977, p. 24--25). Except for minor on the west coast of northernmost Portland granulation and for slight alteration of mafic peninsula. The stock at Fitzgibbon Cove is the only minerals to chlorite, prehnite(?), and bastite (inferred) Eocene pluton mapped on the western serpentine, the gabbro is undeformed and fresh. part of the peninsula. The Hyder Quartz Monzonite We assign the pluton an emplacement age of and its correlatives on northeastern Portland

23 peninsula consist mainly of massive to weakly ranging from 43.0 to 46.8 Ma, and on hornblende foliated granodiorite and quartz monzonite; the ranging from 48.9 to 55.0 Ma (table 1, Nos. 14- map unit also encompasses outcrops of paragneiss, 17) dikes, and other intrusive rocks too small to show Tg Granodiorite (Tertiary)-This pluton consists mainly of on the map. Typical specimens of the Hyder weakly foliated to massive, medium-grained Quartz Monzonite are medium grained and hornblende-biotite granodiorite, and locally of hypidiomorphic granular, and their average mineral foliated and gneissic granodiorite. Our field composition is plagioclase (45 percent), potassium examinations of this pluton suggest that its inland feldspar (23 percent), quartz (22 percent), biotite (6 outcrops are more massive appearing and less percent), and hornblende (4 percent); the most gneissic than its exposures along Portland Canal. prominent accessory mineral is sphene, which This apparent difference may be due to differences occurs as golden-yellow euhedra as large as 5 mm. in weathering and erosion or to differences in Outcrops of the Hyder Quartz Monzonite composition and texture within the pluton. commonly contain aplite and felsic pegmatite dikes. Foliation, where present, is expressed by layers that The Eocene emplacement age of the Hyder Quartz have different total mafic contents and by sparse Monzonite is based on concordant hornblende and schlieren. Mafic minerals generally make up 15 to biotite K-Ar dates of about 50 Ma (table 1, Nos. 25 percent of this pluton. Hornblende is 10-13). The contacts of the Hyder Quartz predominant in its southern part; biotite generally Monzonite with most other map units generally are equals or locally exceeds hornblende in most of its sharp and free of significant thermal or other northern part. Euhedral phenocrysts of potassium contact effects. Its contact with foliated granodiorite feldspar as large as 2 em are present in many areas of unit TKfg, however, is locally difficult to map but are rarely abundant. The pluton intrudes because of compositional and textural similiarities paragneiss (MzPzp) and is intruded by Eocene between the two units. granodiorite and quar:tz monzonite (Tgq). It also The stock at Fitzgibbon Cove consists of fine- to intrudes foliated granodiorite of unit TKfg, but this medium-grained leucocratic biotite-hornblende contact locally is difficult to map because these two granodiorite and minor quartz monzonite. It units are similar in composition and texture. The typically is hypidiomorphic granular but locally pluton is assigned an Eocene emplacement age on contains a few percent of euhedral potassium the basis of K-Ar age determinations of 43.1 and feldspar phenocrysts as long as about 1 em. 45.0 Ma for biotite and of 49.6 and 51.5 Ma for Accessory minerals include sphene, zircon, apatite, hornblende (table 1, Nos. 18-19). If this pluton magnetite, pyrite, and allanite. Outcrops generally continues in outcrop eastward across Portland appear massive and of uniform composition. Small Canal into British Columbia, it may correlate in inclusions of fine-grained mafic rock occur near part with the Ponder pluton (Hutchison, 1982) some contacts, and locally well-developed TKfq Foliated quartz diorite (Tertiary or Cretaceous)­ compositional layering and cross laminations Stocklike and elongate plutons of quartz diorite, suggest settling and flow of mafic and other crystals locally accompanied by minor amounts of other before solidification of the magma. The stock rocks, form a discontinuous belt about 10 km wide intrudes several metamorphic and plutonic rocks, along and near east Behm Canal. Scattered including Late Cretaceous or Paleocene foliated outlying bodies 15 to 25 km from the canal are quartz diorite (TKfq). We infer an Eocene aligned roughly parallel to the main belt (Berg and emplacement age because this body closely others, 1977, p. 18-19). About 60 percent of the resembles the Hyder Quartz Monzonite in unit is dark-gray-weathering, uniformly foliated to composition and texture and because it lacks any gneissic quartz diorite; the rest consists of of the distinctive features (such as miarolitic or paragneiss (21 percent), granodiorite (11 percent), strongly porphyritic textures) of the Oligocene or and subordinate migmatite, amphibolite, pegmatite, Miocene felsic plutons. Intrusive contacts of the and quartz monzonite. The quartz diorite stock with other units generally are sharp and free commonly is at least weakly foliated. Planar fabric of significant thermal or other contact effects varies from a faint alignment of mafic minerals to Tdr Davis River pluton (Tertiary)-This pluton consists of marked gneissic banding. The general trend of this porphyritic coarse-grained homogeneous biotite­ gneissic structure is shown on the map by a dashed hornblende granodiorite that locally grades into pattern. This foliation generally strikes north or quartz diorite and quartz monzonite (Smith, 1977, northwest, parallel to the regional outcrop trend p. 28-32). It typically contains about 5 percent of and to the internal structure of the adjoining euhedral phenocrysts of potassium feldspar as large metamorphosed bedded (MzPzp, MzPza) and as 5 em. The texture of the groundmass is intrusive (TKfg) rocks. Thin sections of typical hypidiomorphic granular, and the mafic minerals samples of quartz diorite show medium-grained, are interstitial to and finer grained than the felsic granular to planar aggregates of andesine (54 minerals. Approximate average composition of the percent), quartz (18 percent), hornblende (13 pluton is plagioclase (50 percent), quartz (25 percent), biotite (12 percent), and accessory percent), potassium feldspar (15 percent), and apatite, augite, garnet, magnetite, muscovite, mafic minerals (10 percent). The Davis River potassium feldspar, and sphene. Small amounts of pluton intrudes several plutonic and metamorphic epidote, chlorite, and saussurite record slight, but rocks without significant contact effects and is in widespread postemplacement alteration. Much of turn intruded by the Hyder Quartz Monzonite. The the unit also shows cataclastic textures such as Eocene emplacement age of the Davis River pluton undulatory quartz and incipient granulation along is based on K-Ar age determinations on biotite grain boundaries. The mineralogy and texture

24 indicate that the planar fabric probably resulted traces of albite(?), chlorite, epidote, and sericite. mainly from mineral alignment during Much of the granodiorite is distinguished by emplacement of the plutons, whereas the incipient euhedral crystals of potassium feldspar as long as cataclasis and generally concordant structural 2.5 em. The crystals contrast markedly in size with relations suggest that their emplacement took place the other minerals, and they weather in relief. during the waning stages of regional deformation. The contacts between the foliated granodiorite Contacts between the quartz diorite plutons and unit and adjacent units are drawn mainly on the the paragneiss (MzPzp) and foliated granodiorite basis of the regional distribution of the major rock (TKfg) units are largely inferred from the regional types. The regional map patterns and local contact distribution of the major rock types. The unit is relations show that the unit is intruded by the intruded by Oligocene or Miocene gabbro and by Eocene (Tgq, Tdr, Tg) as well as the Oligocene (inferred) Eocene quartz monzonite. (Tgp) and Oligocene or Miocene (Tgb) plutons, The unit is assigned an emplacement age of Late and that it may locally be gradational with the Cretaceous or Paleocene on the basis of Pb-U paragneiss (MzPzp), foliated quartz diorite (TKfq), (zircon) age determinations of about 55 Ma (table and foliated quartz monzonite (Kfq) units. Geologic 1, Nos. 22, 23) and 58 Ma (G.E. Gehrels, oral relations also indicate that it underlies most of the commun., 1983) for samples collected on Portland paragneiss unit on central Portland peninsula. peninsula, and of about 64-67 Ma in correlative The Cretaceous or Tertiary age assignment of rocks near Juneau (Gehrels and others, 1983a). this unit reflects our concept of it as an assemblage K-Ar radiometric studies on samples of quartz primarily of metamorphosed plutonic rocks diorite frm Portland peninsula show apparent ages possibly having more than one emplacement age. of 45.~7.5 Ma for biotite and 47.6-55.7 Ma for This assigned range of possible emplacement ages hornblende (table 1, Nos. 20, 21, 23, 24). These is based partly on a preliminary Pb-U (zircon) age data probably reflect an event that strongly determination of about 140 Ma (Early Cretaceous) disturbed K-Ar systems in rocks older than 40 Ma (table 1, No. 38) on a sample of plutonic rock in throughout much of the study area (this report, the Boca de Quadra area and partly on the discussion under Revillagigedo Island and likelihood that it contains unmapped intrusive rocks Cleveland Peninsula: "Metamorphosed sedi­ correlative with, but indistinguishable from, the mentary, volcanic, and intrusive rocks (Mesozoic or Cretaceous foliated quartz monzonite and Paleozoic)"; Smith and Diggles, 1981, p. 3). granodiorite (Kfq) and Cretaceous or Tertiary The quartz diorite pluton at the south end of foliated quartz diorite (TKfq) units. The unit may Portland peninsula continues in outcrop southward also encompass unmapped outcrops of Eocene or across Pearse Canal into British Columbia, where it younger plutonic rocks or of various metamor­ is mapped as the Quottoon pluton (Hutchison, phosed bedded rocks. 1982) Numerous samplzs of foliated plutonic rocks TKfg Foliated granodiorite (Tertiary or Cretaceous}-This from the unit yield K-Ar apparent ages ranging unit (Berg and others, 1977, p. 19-22) is an from about 43 to 50 Ma for biotite and 48 to 59 assemblage mostly of metamorphosed plutonic Ma for hornblende (table 1, Nos. 26-37). Some of rocks that we were unable to subdivide during our these ages may date the emplacement of part of largely reconnaissance-scale geologic investigations the unit, but they most probably reflect the event of Portland peninsula. More detailed mapping, for that strongly disturbed K-Ar systems in rocks older example, probably would reveal several distinct than 40 Ma in the study area (this report, plutons, possibly of different emplacement ages. As discussion under Revillagigedo Island and mapped, the unit consists mostly of foliated and Cleveland Peninsula: "Metamorphosed sedimen­ gneissic granodiorite, but it also contains a wide tary, volcanic, and intrusive rocks (Mesozoic or variety of other rock types. Based on samples Paleozoic)"; Smith and Diggles, 1981., p. 3). collected, the unit consists mainly of granodiorite Kfq Foliated quartz monzonite and granodiorite (51 percent), quartz monzonite (14 percent), and (Cretaceous}-This heterogeneous pluton consists quartz diorite (13 percent), but locally includes chiefly of foliated leucocratic quartz monzonite and such nonintrusive components as hornfels, marble, granodiorite, but it also includes significant para gneiss, and gneiss of undetermined origin (18 amounts of granodiorite and quartz monzonite percent). About 2 percent of the unit is migmatite, gneiss, and migmatite. The pluton is characterized the most prominent outcrop areas of which are by large changes in texture and composition over shown by a pattern on the map. The remaining 2 short distances. Schlieren are common throughout, percent includes aplite, diorite, granite, and layered xenoliths of amphibolite and hornblendite, lamprophyre, and one occurrence of paragneiss are present in many areas. Foliation in pyroxenite. The average of 50 modal (point count) the plutonic rocks is defined by layers of different analyses of medium-grained foliated and gneissic grain size and mafic mineral content. Mafic granodiorite typical of the unit shows 50 percent minerals generally make up less than 10 percent of plagioclase (oligocene and andesine), 20 percent the pluton: fine-grained biotite is more abundant quartz, 15 percent potassium feldspar, 8 percent than hornblende in its southern part; hornblende is hornblende, and 7 percent biotite. The rock more common in the north. The pluton intrudes commonly also contains less than one percent of paragneiss (MzPzp) and in turn is intruded by one or more of the accessory minerals apatite, Eocene plutons (Tdr, Tg). Its contact with the garnet, muscovite, pyrite, and sphene. Widespread foliated granodiorite unit (TKfg) is difficult to map incipient retrograde metamorphism has produced phyllite, and fine-grained recrystallized limestone

25 because of similarities in composition and textures environment and consisted of argillaceous clastic between these two units. The pluton is assigned a sediments and minor amounts of limestone, Cretaceous emplacement age based on preliminary chert(?), and felsic to intermediate or mafic volcanic Pb-U (zircon) age determinations of 99 and 116 or volcaniclastic rocks. The ages of these protoliths Ma (table 1, No. 54). K-Ar apparent ages of 41.2 have not been conclusively determined by isotopic Ma on biotite, and 51.2 Ma on hornblende methods. We infer the Paleozoic or Mesozoic age probably reflect an event that strongly disturbed K­ assignment for this unit from (a) studies of Ar systems in rocks older than 40 Ma throughout correlative rocks nearby in British Columbia, where much of the study area (this report, discussion geologic relations and isotopic age determinations under Revillagigedo Island and Cleveland suggest pre-Permian, older Paleozoic, and Peninsula: "Metamorphosed sedimentary, volcanic, Precambrian ages (Hutchison, 1982, p. 23-24), and intrusive rocks (Mesozoic or Paleozoic)"; Smith and (b) our assumption that some of the pelitic and Diggles, 1981, p. 3) paragneiss may correlate with the amphibolite MzPzp Paragneiss (Mesozoic or Paleozoic}-This unit (Berg facies upper Paleozoic or Mesozoic and others, 1977, p. 12-13) is characterized by metasedimentary rocks (MzPzms) on eastern rusty-brown-weathering pelitic paragneiss and Revillagigedo Island. K-Ar dating studies of several schist containing conspicuous rootbeer-brown variants of the paragneiss on Portland peninsula biotite and by subordinate quartzofeldspathic give apparent ages of 42.9-46.8 Ma for biotite and gneiss distinguished mainly by its light color and 47.0-57.0 Ma for hornblende (table 1, Nos. 76- low content of mafic minerals.. Such rocks make 80). At least one of the metamorphic events that up about 66 percent of the unit. The remainder, affected the unit probably occurred during this based on the number of samples of different rock interval, but these ages probably reflect the types collected, includes migmatite (16 percent), regional disturbance to K-Ar systems in rocks older gneissic plutonic rocks (7 percent), marble and than 40 Ma in the study area (this report, calcsilicate gneiss (4 percent), pegmatite (3 discussion under Revillagigedo Island and percent), quartzite (2 percent), amphibolite (1 Cleveland Peninsula: "Metamorphosed sedi­ percent), and aplite (1 percent). A single rock type mentary, volcanic, and intrusive rocks (Mesozoic or may underlie wide areas, or several different rock Paleozoic)"; Smith and Diggles, 1981, p. 3) types may be interlayered across a short distance; Northeastern area the latter probably represents a fragment of Texas Creek Granodiorite (Triassic}-The Texas premetamorphic stratigraphy. The unit has been "Rt Creek Granodiorite that crops out at the northeast complexly folded and was probably recrystallized corner of the Ketchikan quadrangle is the more than once. More than one set of mesoscopic southwesternmost part of a batholith that crops out structures is present at most outcrops. mainly in Alaska north of the quadrangle and in The paragneiss typically consists of alternating neighboring parts of British Columbia (Buddington, light-gray, dark-gray, or medium-brown layers, 1929, p. 22-29; Grove, 1971, p. 60--62; Smith, averaging 1-10 em in thickness and containing 1977, p. 16-24; and Berg and others, 1977, p. about percent oligoclase and andesine, 50 25 17-18). The pluton consists mainly of percent quartz, and 15 percent biotite. Up to about recrystallized, locally cataclastically deformed percent accessory minerals include potassium 10 granodiorite and minor quartz diorite. Hand feldspar, garnet, sillimanite, and muscovite. The specimens are typically greasy green with cloudy paragneiss commonly also contains traces of one or feldspars and indistinct grain boundaries. more of the following minerals: apatite, Representative thin sections show a medium­ clinopyroxene, cordierite, orthopyroxene, graphite, grained hypidiomorphic granular aggregate of (a) hornblende, magnetite, pyrite, sphene, and zircon. essential andesine or oligoclase, quartz, and This metamorphic mineral assemblage indicates potassium feldspar, (b) accessory sphene, green widespread amphibolite- and possibly locally hornblende, and green biotite, and (c) secondary granulite- facies regional metamorphism (Turner, albite, muscovite, clinozoisite-epidote, actinolite, p. Hollister, Selverstone 1981, 366-407; 1975; chlorite, calcite, and opaque minerals. In many and Hollister, Secondary minerals, the 1980). specimens, euhedral crystals of potassium feldspar results of widespread incipient retrograde and hornblende as long as 2 em impart a distinct metamorphism, include small amounts of actinolite and characteristic porphyritic texture. albite(?), chlorite, epidote, and sericite. ' In general, the Texas Creek Granodiorite is In many places, the paragneiss grades relatively massive and lacks pronounced primary or imperceptibly downward and laterally into gneissic metamorphic foliation. Instead, parts of it are granodiorite (TKfg). Elsewhere, it is in sharp characterized by cataclastic textures. The intensity contact with plutonic rocks or passes gradually into of the cataclasis generally is low, but locally the them through a zone of migmatite. The. contact granodiorite is converted to mylonite. In addition to between the paragneiss and the amphibolite unit widespread incipient cataclasis, the pluton was (MzPza) generally is a zone as wide as m of a 10 affected by low-grade regional metamorphism and transitional rock type containing approximately by thermal metamorphism to hornblende-hornfels equal amounts of biotite and hornblende. facies. The regional metamorphism partly The minerals and textures of the schist and obliterated original textures and produced mineral gneiss and the intercalated layers of marble indicate assemblages typical of the greenschist facies. The that the metasedimentary protoliths of the regional metamorphism and the cataclasis predate paragneiss sequence were deposited in a marine the intrusion of the Eocene plutons, which

26 produced thermal aureoles as wide as 2 km along actinolite, chlorite, and opaque minerals. The their contacts with the batholith. groundmass of the lapilli is mostly a recrystallized The Texas Creek Granodiorite intrudes aphanitic aggregate of albite, quartz, chlorite, recrystallized upper Paleozoic or Mesozoic bedded epidote, and opaque minerals; shapes suggestive of rocks (MzPzvs) and in turn is cut by Eocene microlites are still visible in some specimens. The granodiorite and quartz monzonite (Tgq). graywacke matrix of the tuff breccia consists of The Texas Creek Granodiorite is here assigned a sand-sized, angular mineral fragments identical to Triassic emplacement age on the basis of apparent the phenocrysts in the lapilli and a pasty K-Ar hornblende ages of 203 and 211 Ma, which (palagonite?) filling. are considered likely to be minimum ages of The sequence is characterized by low emplacement (Smith and Oiggles, 1981, p. 2) greenschist-facies mineral assemblages, but is MzPzvs Recrystallized volcanic and sedimentary rocks generally not schistose or otherwise penetratively (Mesozoic or Paleozoic)-The northeastern most deformed. Locally it also is contact corner of the Ketchikan quadrangle is underlain by metamorphosed by the intrusion of the Texas a sequence of recrystallized andesitic volcanic and Creek Granodiorite ("fit) and Eocene (Tgq) volcaniclastic rocks, flysch, and minor limestone plutons. In some places, the strata are tightly to (Smith, 1977, p. 9-14; Berg and others, 1977, p. isoclinally folded with steep axial planes; in other 15--17). The sequence extends eastward into places they are deformed into nearly recumbent British Columbia (Grove, 1971, p. 38-48) and folds with gently to moderately northeastward crops out discontinuously northwestward along the dipping axial planes. Berg and others (1977, p. 29) Alaska-Canada boundary (R.L. Elliott and R.D. postulate a zone of large-scale overthrusting, Koch, unpub. data, 1979). The dominant rocks in parallel to the semirecumbent structures, that is the sequence are interbedded andesitic tuff breccia, intruded by the Eocene plutons (map sheet, section volcanic graywacke, and siltstone and argillite; less A-A'). common rocks include coarse volcanic Neither the stratigraphic base nor the top of the conglomerate, possibly broken-pillow breccia, and sequence is exposed in the study area; its dark-blue-gray marble. minimum structural thickness, on the basis of cliff The tuff breccia is massive and commonly in exposures, is about 750 m; immediately north of beds 0.5-4.0 m thick. Representative samples the Ketchikan quadrangle, the sequence forms the contain 5-50 percent poorly sorted angular to erosional remnants of an arched roof over the subrounded, slightly vesicular lapilli, set in an Texas Creek Granodiorite (Smith, 1977, p. 10). unsorted and unstratified volcanic graywacke We found no fossils in this sequence in the matrix. Phenocrysts of euhedral, zoned plagioclase Ketchikan quadrangle. Its assigned stratigraphic age 1-10 mm long constitute 5-20 percent of the of late Paleozoic or Mesozoic is based partly on lapilli. They have largely recrystallized to albite or Permian fossils collected from limestone in a oligoclase and clinozoisite-epidote, but those that probably correlative sequence in Alaska at Mount survive recrystallization retain their original Whipple on the Alaska-Canada boundary about andesine composition. Phenocrysts of mafic 120 km northwest of the Ketchikan quadrangle minerals are much less common than those of (R.L. Elliott, unpub. data, 1979), and partly on plagioclase, and most lapilli contain no mafic geologic evidence near Hyder that indicates phenocrysts. The mafic minerals are strongly gradational, probably cogenetic relations between pleochroic, euhedral, green or brown hornblende the Texas Creek Granodiorite and some of the and subordinate colorless subcalcic augite. Most volcanic rocks in this sequence (H.C. Berg and mafic phenocrysts have recrystallized to masses of R.L. Elliott, unpub. field data, 1973)

*U.S. Government P::-inting O::fic:e 1988 - 201-985/83967

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