Geologic Strip Map Along the Hines Creek Fault Showing 

Evidence for Cenozoic Displacement in the Western 

Mount Hayes and Northeastern Healy Quadrangles, 

Eastern Alaska Range, Alaska

By Warren J. Nokleberg, John N. Aleinikoff, Thomas K. Bundtzen, and Maiana N. Hanshaw 

Pamphlet to accompany

Scientific Investigations Map 3238

2013

U.S. Department of the Interior 

U.S. Geological Survey 
ii
iii

Contents

Introduction.......................................................................................................................................................................................1

General Information......................................................................................................................................................................1

Major Geologic Units ....................................................................................................................................................................1

Summary of Hines Creek and Adjacent Faults.............................................................................................................................2

Topographic Setting of Eastern Alaska Range and Sources of Geologic Mapping .....................................................................2

Acknowledgments ........................................................................................................................................................................3

Evidence for Cenozoic Displacement on Hines Creek and Associated Faults.................................................................................3

Cenozoic Displacement Along the Hines Creek Fault..................................................................................................................3

Evidence for Cenozoic Displacement Along the Trident Glacier Fault .........................................................................................4

Evidence for Cenozoic Displacement Along the McGinnis Glacier Fault .....................................................................................5

SHRIMP U-Pb Geochronology of Zircon ..........................................................................................................................................5

Methods........................................................................................................................................................................................5

Samples........................................................................................................................................................................................6

Results..........................................................................................................................................................................................6

Description of Map Units ..................................................................................................................................................................6

Surficial Units................................................................................................................................................................................6

Sedimentary Units ........................................................................................................................................................................8

Mélange....................................................................................................................................................................................9

Post-Accretionary Plutonic Rocks ................................................................................................................................................9

Terranes (North to South)...........................................................................................................................................................11

Yukon-Tanana Terrane ..........................................................................................................................................................11

Jarvis Creek Glacier Subterrane ........................................................................................................................................11

Pingston Terrane—South of Hines Creek Fault and North of Nenana Glacier and Denali Faults .........................................15

Aurora Peak Terrane—South of Nenana Glacier Fault and North of Denali Fault .................................................................18

Windy Terrane—Within Splays of Denali Fault ......................................................................................................................21

Maclaren Terrane—South of Denali Fault and North of Broxson Gulch Thrust .....................................................................23

Wrangellia Terrane .................................................................................................................................................................25

References Cited............................................................................................................................................................................26

Figure

Figure 1. Representative images and SHRIMP U-Pb data from zircon from plutonic rocks. 

A, CL images of zircon from 10ANK001 (leucodiorite). 

B, Tera-Wasserburg plot of SHRIMP data from 10ANK001. 

C, CL images of zircon from 10ANK004 CL images of zircon from 10ANK004 (porphyritic granodiorite). 

D, Tera-Wasserburg plot of SHRIMP data from 10ANK004 (porphyritic granodiorite). ............................................ 30

Table

Table 1. SHRIMP U-Th-Pb data for zircon from two granitic plutons near the Hines Creek Fault, Alaska. ............................... 31
iv
1

Geologic Strip Map Along the Hines Creek Fault Showing 

Evidence for Cenozoic Displacement in the Western 

Mount Hayes and Northeastern Healy Quadrangles, 

Eastern Alaska Range, Alaska

By Warren J. Nokleberg John N. Aleinikoff, Thomas K. Bundtzen, and Maiana N. Hanshaw 

Introduction 

General Information

This pamphlet augments the companion geologic map by providing an interpretative text 

describing Cenozoic faulting in the region and by providing a detailed description of map units. The 

companion geologic map is a strip geologic map along the Hines Creek Fault from the central and 

northwestern Mount Hayes quadrangle into the northeastern Healy quadrangle. The strip geologic map 

is provided in ArcMap GIS and Adobe PDF formats. For a listing of files and directories for the 

map, read the file titled 1_Hines_Creek_Fault_Map_readme.txt.

Major Geologic Units

Nine major groups of surficial units and bedrock units are present in the map area: (1) upper 

Pliocene, Pleistocene, and Holocene surficial units—mainly various types of alluvium, colluvium, and 

glacial deposits; (2) Oligocene through Pliocene sedimentary units—mainly the Nenana Gravel and an 

older unit of sandstone, siltstone, and lesser conglomerate; (3) an extensive suite of plutonic units—

mainly Cretaceous granodiorite and quartz monzonite; (4) Devonian and possibly older Jarvis Creek 

Glacier subterrane that comprises the southern part of the Yukon-Tanana terrane; (5) Silurian through 

Triassic metasedimentary and metavolcanic rock structural mélange (that is, a structural breccia formed 

of highly sheared rock fragments) of the Pingston terrane; (6) Aurora Peak terrane with Paleozoic 

metasedimentary rock and Cretaceous and lower Tertiary metagranitic rock; (7) sedimentary and 

volcanic rock structural mélange of the mainly Cretaceous Windy terrane; (8) Maclaren terrane with 

metamorphosed Upper Jurassic and Lower Cretaceous flysch and Cretaceous and lower Tertiary 

metagranitic rock; and (9) upper Paleozoic sedimentary and volcanoclastic rock, ultramafic plutonic 

rock, gabbro, and metagabbro of the Wrangellia terrane. 

North of the Denali Fault, the bedrock geology is dominated by the Devonian and older YukonTanana terrane, a complex of multiply deformed and metamorphosed sedimentary, volcanic, and 

plutonic rocks (Jones and others, 1987; Aleinikoff, 1984a,b; Aleinikoff and Nokleberg, 1985a,b; 

Nokleberg and Aleinikoff, 1985). To the south of the fault, the bedrock geology is dominated by the 

Mesozoic Maclaren and Paleozoic and Mesozoic Wrangellia terranes (Jones and others, 1987; 
2

Nokleberg and others, 1982, 1985, 1989). A number of granitic to gabbroic plutons, chiefly of Mesozoic 

age, intrude the terranes both north and south of the Denali Fault. Major faults or sutures separate 

terranes, and many younger Cenozoic faults occur along the margins of, and within, terranes. 

Summary of Hines Creek and Adjacent Faults

Geologic mapping of the Hines Creek Fault and the adjacent Trident Glacier and McGinnis 

Glacier Faults to the north in the eastern Alaska Range, Alaska, reveals that these faults were active 

during the Cenozoic. Previously, the Hines Creek Fault, which is considered to be part of the strike-slip 

Denali Fault system (Ridgway and others, 2002; Nokleberg and Richter, 2007), was interpreted to have 

been welded shut during the intrusion of the Upper Cretaceous Buchanan Creek pluton (Wahrhaftig and 

others, 1975; Gilbert, 1977; Sherwood and Craddock, 1979; Csejtey and others, 1992). Our geologic 

mapping along the west- to west-northwest-striking Hines Creek Fault in the northeastern Healy 

quadrangle and central to northwestern Mount Hayes quadrangle reveals that (1) the Buchanan Creek 

pluton is truncated by the Hines Creek Fault and (2) a tectonic collage of fault-bounded slices of various 

granitic plutons, metagabbro, metabasalt, and sedimentary rock of the Pingston terrane occurs south of 

the Hines Creek Fault. 

Our geologic mapping also identified the less extensive Trident Glacier and McGinnis Glacier 

Faults located 1 to 5 km north of the Hines Creek Fault that extend for about 60 km in the northwest 

Mount Hayes quadrangle. The mapping along these faults reveals that the older bedrock of the middle 

to late Paleozoic Yukon-Tanana terrane is (1) juxtaposed against upper Pliocene to lower Pleistocene 

glacial moraines along thrust or strike-slip faults and (2) juxtaposed against Oligocene to Pliocene 

sedimentary rocks along thrust or strike-slip faults. To the southeast, the Trident Glacier and McGinnis 

Glacier Faults merge with the Hines Creek Fault that, in turn, merges with the main strand of the strikeslip Denali Fault in the area of the Delta River and Canwell Glacier. 

Field relations for the Hines Creek and adjacent faults to the north indicate the following: (1) the 

faults have been active throughout most of the Cenozoic, (2) the faults exhibit young (Pleistocene) 

movement; (3) the three faults have potential for future movement; and (4) the faults are major parts of 

the Alaska Range suture zone. In addition, a recent geophysical transect study, east of the Parks 

Highway in the central Healy quadrangle, also revealed that the Moho is offset across the Hines Creek 

Fault and that the fault may be a major crustal boundary in eastern Alaska (Veenstra and others, 2006). 

For additional information about the entire Mount Hayes quadrangle, including previous studies and 

more detailed descriptions of map units, refer to Nokleberg and others (1992a,b). 

Topographic Setting of Eastern Alaska Range and Sources of Geologic Mapping

The area underlain by the strip map, the central and northwestern Mount Hayes and northeastern 

Healy quadrangles, form a major part of the eastern Alaska Range. The range is a great glacially 

sculptured arcuate mountain range extending approximately 1,000 km from near the Canadian border in 

the east to the Aleutian Range to the west and southwest. The eastern Alaska Range features rugged 

peaks ranging to over 13,800 ft in elevation and spectacular alpine glaciers as long as 66 km. The range 

is bisected by the Denali Fault, which is a major geologic and geographic boundary between the Yukon 

River Basin in interior Alaska to the north and the Copper River Basin of southern Alaska to the south. 

From the 1950s to the 1990s, geologic maps of parts of the central Mount Hayes quadrangle and 

northeastern Healy quadrangles, the area underlying this strip map, were published by Bond (1976), 

Gilbert (1977), Sherwood and Craddock (1979), Brewer (1982), Csejtey and others (1992), and 

Nokleberg and others (1992b). Surficial geologic maps of the central part of the Mount Hayes 

quadrangle, mostly along the Delta River and adjacent Richardson Highway, were published by Holmes 

and Benninghoff (1957), the U.S. Army Corps of Engineers (1960), Weber (1971), and Carter and 
3

Galloway (1978). The geologic map described herein is based partly on these published geologic maps 

but to a much greater degree on the 1:63,360-scale geologic mapping completed for the geologic map of 

the Mount Hayes quadrangle that was published at a scale of 1:250,000 (Nokleberg and others, 1992b) 

and on new geologic mapping by the authors for the northeast Healy quadrangle. 

This geologic map is based on mapping of 1:63,360-scale quadrangles from the central and 

northwestern Mount Hayes to the northeastern Healy quadrangles, including parts of the Mount Hayes 

B4, B5, C4, C5, C6 and D6 quadrangles and the Healy C6 and D6 quadrangles. The geologic mapping 

was supported by the Alaskan Mineral Resource Assessment Program (AMRAP) of the U.S. Geological 

Survey during the summers of 1978–1982, 1985, and 1986 as part of the Trans-Alaskan Transect 

Program (TACT) (Fuis and others, 2008). 

Acknowledgments

We are greatly indebted to the hard work and excellent science published by present and past 

geologists in the Mount Hayes quadrangle and adjacent areas as described above. Our work is, in part, 

based on their fine efforts and accomplishments. We are grateful to H.C. Berg, Donald Grybeck, E.M. 

MacKevett, Jr., A.T. Ovenshine, T.P. Miller, and G.R. Winkler, who greatly encouraged and supported 

the geologic mapping. We thank D.L. Jones and N.J. Silberling for their stimulating geological 

discussions of bedrock geology and tectonics. We thank D.L. Campbell, P.L. Herzon, the late Carl Huie, 

I.M. Lange, J.S. Lull, R.T. Miyaoka, George Plafker, S.R. Silva, and R.E. Zehner for assisting in part of 

the bedrock geologic mapping, and L.D.Carter, T.D. Hamilton, and Warren Yeend for assisting in 

mapping of surficial deposits and older Quaternary and Holocene faults. We also thank the late G.C. 

Bond and J.H. Stout for contributing unpublished geologic mapping of parts of the quadrangle. We 

thank C.L. Burhmaster, R.C. Roback, and C.E. Schwab for extensive petrologic studies of bedrock in 

the quadrangle. We also thank helicopter pilots Michael Arline, Richard Rossiter, and Barry Roberts for 

their superb flying in an extremely difficult and remote area. We thank N.B. Shew for assisting in 

providing digital topographic base maps. We thank P.J. Haeussler and T.E. Moore for their constructive 

scientific reviews. 

Evidence for Cenozoic Displacement on Hines Creek and Associated Faults

This geologic map reveals that the Hines Creek Fault and associated faults to the north have been 

active in the Cenozoic. The data supporting this revelation are revealed by examination of the 

juxtaposition of various units along the faults. 

Cenozoic Displacement Along the Hines Creek Fault

The Hines Creek Fault extends from an area of acute convergence with the Denali Fault in the 

center of the Mount Hayes B-4 quadrangle to the western edge of the strip map in the Healy D-6 

quadrangle, a distance of about 96.5 km. Farther west, the fault continues across the northern part of the 

Healy quadrangle and westward into the central part of the Mount McKinley quadrangle, where it 

merges with the Denali Fault. The total length of the Hines Creek Fault is about 275 km. 

In the area of the strip map, the fault is the locus of thrusting of Silurian to Triassic Pingston 

terrane, located to the south and southwest, over the Jarvis Creek Glacier subterrane, located to the north 

and northeast. 

The following observations are the major data indicating Cenozoic displacement. The letters 

(A, B, C, D) correspond with the Cenozoic faulting observation sites labeled on the map. 

A. Along the east-southeast part of the Hines Creek Fault in the Mount Hayes B-4 quadrangle, 

where the metasedimentary rocks of the Jarvis Creek Glacier subterrane are juxtaposed 

against the high-grade metasedimentary rocks of the Aurora Peak terrane, the glacial valley 
4

of the Black Rapids Glacier displays a minor dextral deflection along the fault. Also in this 

area, both bedrock units contain abundant brittle shears (microfaults). 

B. To the northwest in the Mount Hayes C-6 quadrangle, the Hayes Glacier valley displays 

dextral deflection across the fault. 

C. Farther west-northwest in the Healy C-6 quadrangle, the Gillam Glacier valley displays 

dextral deflection across the fault. 

D. To the west-northwest of the Gillam Glacier in the Healy C-6 and D-6 quadrangles, a collage 

of fault-bounded wedges of various granitic plutons trend parallel to the fault. The wedges of 

granitic plutons possess unique compositions, are internally homogenous, do not have finegrained margins and do not contain stoped inclusions of wall rock. The wedges of the 

granitic plutons are (1) leucodiorite and granodiorite of Buchanan Creek (unit Kbc); (2) the 

herein informally named porphyritic granodiorite of Vertical Angle Bench Mark (VABM) 

Marganne (unit Km) with K-Ar biotite and hornblende ages ranging from 101.8 to 92.6 Ma 

(Sherwood and Craddock, 1979; Csejtey and others, 1992); (3) an unnamed granodiorite 

(unit Kgd); and (4) an unnamed gabbro (unit mgb) that may be part of the Yukon-Tanana 

terrane. The wedges of granitic plutons are juxtaposed along the fault or against 

metasedimentary rock of the Jarvis Creek Glacier subterrane. 

The evidence for fault juxtaposition includes (1) planar surfaces with abundant brittle shears 

(microfaults) along the faults; (2) no diking or stoping of one granite pluton by the other, indicating that 

the contacts are not intrusive; (3) no contact metamorphism of adjacent rock along contacts; and 

(4) occurrence of a structural mélange (unit m) of highly deformed (with abundant brittle shears 

(microfaults)) marble, chert, metavolcanic, and metasedimentary rock, diorite, and porphyritic 

granodiorite rock (unit m) along the Hines Creek Fault. 

The occurrence of four wedges of distinct, fault-bounded granite plutons along the Hines Creek 

Fault poses some major and unsolved questions. From which plutons along strike did each of the four 

wedges originate? What are the timings of displacements? 

Evidence for Cenozoic Displacement Along the Trident Glacier Fault

The Trident Glacier Fault extends from an area of acute convergence with the Hines Creek Fault 

in the toe of the Nenana Glacier in the Mount Hayes C-5 quadrangle along a northwest strike to the 

northern edge of the Mount Hayes C-6 quadrangle for a distance of about 39 km. The fault is defined as 

the locus of thrusting of bedrock units to the southwest over surficial units to the northeast and the locus 

of dextral slip. 

The following observations are the major data indicating Cenozoic displacement. The letters 

(E, F, G, H) correspond with the Cenozoic faulting observation sites labeled on the map. 

E. Near the intersection with the Hines Creek Fault, the glacial valley of the northern branch of 

the Nenana Glacier displays dextral deflection. 

F. Farther northwest, on the ridge to the northwest of the Nenana Glacier, a unit of colluvium 

(unit Qc) and the metavolcanic rock of the Jarvis Creek Glacier subterrane (unit jcv) to the 

southwest are thrust over the upper Pliocene or lower Pleistocene (Illinoian or Wisconsin 

stages) moraine (unit Qom) to the northeast. Local brittle shears (microfaults) occur in the 

bedrock units adjacent to this part of the fault. 

G. Farther northwest on the ridge to the northwest of the Trident Glacier along the fault for about 

16 km, the Jarvis Creek Glacier subterrane is thrust northeastward over a high, wide, and 

long upper Pliocene or lower Pleistocene (Illinoian or Wisconsin stages) moraine (unit Qom) 

and over the unit of Oligocene and Pliocene sandstone and siltstone (unit Ts). 
5

H. Farther northwest, in the southern Mount Hayes D-6 quadrangle, the metavolcanic and 

metasedimentary rocks of the Jarvis Creek Glacier subterrane (unit jcv) is thrust 

northeastward over the unit of Oligocene and Pliocene sandstone and siltstone (unit Ts). 

Evidence for Cenozoic Displacement Along the McGinnis Glacier Fault

The McGinnis Glacier Fault extends from an area of acute convergence with the Hines Creek 

Fault on the ridge northwest of the terminus of the Black Rapids Glacier in the Mount Hayes C-4 

quadrangle to the northern edge of the map along a northwest strike for a distance of about 22.5 km. The 

fault is the locus of both northeastward thrusting and dextral strike-slip displacement. 

The following observations are the major data indicating Cenozoic displacement. The letters 

(I, J, K) correspond with the Cenozoic faulting observation sites labeled on the map. 

I. Near the intersection with the Hines Creek Fault, brittle shears (microfaults) that crosscut a 

penetrative schistosity occur within the bedrock of the Jarvis Creek Glacier subterrane and 

schistosity is opposed along the fault. 

J. Farther northwest on the ridge north of the toe of the Nenana Glacier, the unit of Tertiary 

sedimentary rock (unit Ts) is thrust northeastward over the metavolcanic unit of the Jarvis 

Creek Glacier subterrane (unit jcv) along a fault contact containing abundant brittle shears. 

K. Farther northwest, north of the toe of the McGinnis Glacier, fluviolacustrine deposits (unit 

Qfl) contain abundant shears (microfaults) along the fault. About 6.4 km northwest, brittle 

shears (microfaults) occur within the bedrock of the Jarvis Creek Glacier subterrane (unit 

jcs) and within an adjacent alluvial fan (unit Qaf), an observation also describe by 

Woodward-Lundgren and Associates (1974). Based on subtle topographic ridges that are 

interpreted as Holocene mole track pressure ridges, the fault extends northwest to the edge of 

the strip map. 

SHRIMP U-Pb Geochronology of Zircon

Controversy has existed about whether the Buchanan Creek pluton intruded across the Hines 

Creek Fault in the Late Cretaceous and thereby welded the fault. Supporting the intrusion of the 

Buchanan Creek pluton across the fault is one set of data that shows similar K-Ar biotite and hornblende 

ages for samples of granite on opposite sides of the fault. However, as described below, this map reveals 

a tectonic collage of various granite plutons that are structurally juxtaposed along the various strands of 

the Hines Creek Fault. In order to resolve the isotopic age dilemma of similar ages for these plutons, 

new samples of the highly different granite plutons on opposite sides of the Hines Creek Fault were 

collected for SHRIMP U-Pb zircon isotopic analysis. As described below, this analysis reveals 

significantly different ages and zircon morphologies for the leucodiorite and granodiorite of Buchanan 

Creek as compared to the porphyritic granodiorite of VABM Marganne. 

Methods

U-Pb geochronology of zircon was performed using the U.S. Geological Survey/Stanford 

University sensitive high resolution ion microprobe-reverse geometry (SHRIMP-RG). About 2 kg of 

rock were collected from outcrops for each dated sample. Zircon was extracted using standard mineral 

separation techniques, including crushing, pulverizing, Wilfley table, magnetic separator, and heavy 

liquids. Individual grains were hand picked, mounted in epoxy, ground to half-thickness to expose 

internal zones, and polished sequentially using 6 μm and 1 μm diamond suspension. All grains were 

digitally imaged in transmitted and reflected light using a petrographic microscope and in 

cathodoluminescence (CL) using a scanning electron microscope. 
6

Following the methods of Williams (1998), SHRIMP analysis consisted of excavating a pit about 

25–35 μm in diameter to a depth of 0.5–1 μm, using a primary oxygen beam at a current of about 

5-6 nA. The magnet cycled through the mass stations five times per analysis. Raw data were reduced 

using Squid 2 (Ludwig, 2009) and plotted using Isoplot 3 (Ludwig, 2003). Instrument fractionation for 

206Pb/238U ages was corrected using zircon standard R33 (419±1 Ma; Black and others, 2004). Uranium 

concentrations are believed to be accurate to ±20%. U-Pb data are plotted on Tera-Wasserburg 

concordia plots to visually identify coherent age groups. Weighted averages of selected individual 

206Pb/238U ages were calculated to obtain an age for each sample. 

Samples

As shown by representative CL images, zircon from the two dated plutonic rocks have distinctly 

different morphologies. Zircon from sample 10ANK001 (leucodiorite of Buchanan Creek that occurs 

north of the Hines Creek Fault) is colorless and slightly deformed and has pitted crystal faces and 

numerous small inclusions. All grains contain fine, concentric CL zoning (fig. 1A). Zircon from sample 

10ANK004 (porphyritic granodiorite of VABM Marganne that occurs south of the Hines Creek Fault) is 

colorless, and relatively pristine, and has mirror-like crystal faces and a few large inclusions. All grains 

contain fine to medium CL zoning (fig. 1C). The outermost parts of many grains are composed of dark, 

unzoned material that resembles a homogeneous igneous component. Alternatively, despite the 

undeformed character of the grains, we considered the possibility that the dark rims might be 

metamorphic in origin. These outermost areas were targeted for SHRIMP analysis to determine their 

origin. 

Results

Sixteen (of 17) analyses of cores of zircon from 10ANK001 (table 1) yield a weighted average 

age of 94.7±1.4 Ma (fig. 1B). This age is interpreted as the time of emplacement of the leucodiorite of 

Buchanan Creek. One slightly younger analysis was excluded from the age calculation. Five dark (in 

CL), unzoned, homogeneous tips have ages that are similar to the core ages, indicating that these zones 

formed as part of the magmatic process; they do not represent a later metamorphic event. 

Fourteen (of 18) analyses of cores of zircon from 10ANK004 (table 1) yield a weighted average 

age of 98.0±1.4 Ma (fig. 1D). This age is interpreted as the time of emplacement of the porphyritic 

granodiorite of VABM Marganne. Four slightly younger ages were excluded from the age calculation. 

Although both samples listed in table 1 have early Late Cretaceous ages, the different SHRIMP 

ages support the interpretation, based on compositional differences, that these are two distinctly different 

plutons. Furthermore, zircon from the younger rock (leucodiorite of Buchanan Creek; 94.7±1.4 Ma) is 

slightly damaged, suggesting a complicated post-emplacement history, whereas zircon from the older 

rock (porphyritic granodiorite of VABM Marganne; 98.0±1.4 Ma) is pristine. This morphologic 

variability is additional evidence for the interpretation that these rocks evolved separately and were 

tectonically juxtaposed well after crystallization. 

DESCRIPTION OF MAP UNITS

SURFICIAL UNITS 

Qi Icefield, glacier, and lesser unconsolidated deposits of Alaska glaciation 

(Holocene)—Chiefly icefield, small glacier, and lesser unconsolidated sand 

and gravel on flood-plains, fans, and cones. Only large, well-defined cones 

differentiated from colluvium. Oldest deposits may be outwash from a late 
7

advance of the Wisconsin stage glaciation. Includes unconsolidated rocks in 

stream beds and river beds 

Qa Alluvial deposits (Holocene)—Chiefly unconsolidated sand and gravel in 

floodplains and minor, gentle-gradient fans. Only large, well-defined fans 

differentiated from colluvium. Oldest deposits may be outwash from a late 

advance of the Wisconsin stage glaciation 

Qc Colluvial deposits and minor lateral moraine (Holocene)—Chiefly talus and other 

slope debris deposits. Also includes alluvium of minor streams and, locally, 

glacial, rock glacier, and mass-wasting deposits. In areas of gentle slopes, 

consists chiefly of mixed colluvium and alluvium with local bedrock rubble 

but may include older glacial drift deposits. Locally grades into deposits of 

Alaskan, Wisconsin, and older glaciations. Chiefly rubble, gravel, sand, silt, 

and clay 

Qaf Alluvial fan (Holocene)—Chiefly fans and cones. Only large, well-defined cones 

differentiated from colluvium. Oldest deposits may be outwash from a late 

advance of the Wisconsin stage glaciation. Chiefly unconsolidated sand and 

gravel 

Qam Alaskan neoglaciation lateral and terminal moraine and glacial debris from 

Alaskan glaciation (Holocene)—Chiefly rubble and diamicton left after 

recession of existing glaciers 

Qrg Rock glacier (Holocene)—Chiefly unconsolidated boulder, gravel, and sand that 

occur downslope from a glacier cirque. Contains ice core 

Qfl Fluviolacustrine deposits (Holocene)—Chiefly sand, silt, and clay in lakes, ponds, 

and low-gradient streams 

Qoa Older, uplifted alluvium and minor lateral moraine (Holocene and 

Pleistocene)—Chiefly unconsolidated sand and gravel in uplifted terraces 

along Denali Fault 

Qwm Wisconsin stage glaciation lateral moraine (Holocene and Pleistocene)—Chiefly 

poorly sorted and unstratified till of unconsolidated sand and gravel. Mainly 

consists of rubble and diamicton of local sand and gravel. May locally include 

deposits of neoglaciation (Qam). At higher elevations, deposits grade 

vertically with and are covered by colluvium (Qc) 

Qwf Wisconsin stage glaciation glaciofluvial deposits (Holocene and Pleistocene)—

Chiefly moderately well stratified layers and lenses of well-rounded gravel 

with matrix of silt and sand. Contains poorly to moderately well sorted gravel 

and sand with local lenses of well-sorted sand. Includes minor lateral and 

ground moraines and some deposits of Alaskan neoglaciation (Qam). May 

include postglacial alluvium and pond deposits. Generally occurs downslope 

from end moraines of Wisconsin stage glaciation (Qwm) 

Qom Illinoian stage or early Wisconsin stage lateral moraine (lower Pleistocene or 

upper Pliocene)—Chiefly poorly sorted and unstratified till of unconsolidated 

sand and gravel. Occurs in a large lateral moraine about 16 km wide (in an 

east-west direction) and 30 km long (in a north-south direction) in the Mount 

Hayes C-5 and D-5 quadrangles. Occurs between paired Wisconsin stage 

glaciation lateral moraines (Qwm) in the Mount Hayes C-5 and C-6 

quadrangles 
8

Qog Drift of older glaciations (lower Pleistocene or upper Pliocene)—Chiefly small 

areas on canyon walls consisting of poorly sorted and unstratified till of 

unconsolidated sand and gravel. Unit occurs above and adjacent to Wisconsin 

stage glacial moraines along west side of Delta River canyon 

SEDIMENTARY UNITS 

Scattered exposures of Tertiary continental sedimentary rocks occur north of the Denali Fault 

and consist of, from youngest to oldest, the Nenana Gravel and a sandstone unit. The Nenana Gravel 

occurs mainly in the northwestern corner of the Mount Hayes quadrangle. The sandstone unit occurs 

mainly in fault-bounded prisms along the northern edge of the Alaska Range along the Hines Creek and 

associated faults. 

Tn Nenana Gravel (lower Pliocene to upper Miocene)—Consists chiefly of poorly 

cemented conglomerate but includes some sandstone and siltstone. Clast 

composition within the Mount Hayes D-6 quadrangle (in decreasing order of 

abundance) is schist, quartzite, granitic rocks, gabbro, and metagabbro. At one 

locality in the Mount Hayes C-3 quadrangle, clasts consist of approximately 

80% schist, 10% quartzite, and 10% felsic volcanic rocks, mafic volcanic 

rocks, and diabase. Bedding strikes northeast and dips gently south in the 

Mount Hayes D-6 quadrangle. Eroded at top. Maximum exposed stratigraphic 

thickness of a few hundred meters 

Unit is mainly exposed along northern Mount Hayes D-6 quadrangle 

boundary and northeastern C-4 quadrangle. Unconformably overlies finegrained metasedimentary rocks (jcs) of Jarvis Creek Glacier subterrane; 

locally in fault contact with Jarvis Creek Glacier terrane (unit jcs). 

Unconformably overlain by Pleistocene glacial deposits, and locally 

unconformably overlies the sandstone unit of Oligocene to Pliocene age (unit 

Ts). Inferred to be of upper Tertiary (Pliocene) age. Lithologically similar to 

rocks assigned to Nenana Gravel. Gravel unit, which occurs to west in the 

Healy quadrangle, is assigned a Miocene(?) and Pliocene age by Csejtey and 

others (1992) 

Ts Sandstone, siltstone, and lesser conglomerate (Pliocene to Oligocene)—Chiefly 

brown graywacke sandstone but includes some interbedded conglomerate and 

dark argillite. Generally fault bounded. Maximum exposed stratigraphic 

thickness of a few hundred meters 

Unit consists mainly of fine- to medium-grained, poorly sorted, 

angular quartz-rich sandstone that grades into graywacke. Composition varies 

from quartz grains in a clay-rich matrix to quartz, plagioclase, K-feldspar, 

pyroxene, hornblende, and biotite in a clay-rich matrix. Conglomerate pebbles 

locally composed of granitic rocks and schist; locally imbricated. Argillite 

composed of tiny quartz grains and opaque minerals in a yellow-brown, clayrich matrix 

Unit occurs in scattered exposures as much as 3.5 km across in the 

Mount Hayes C-5, C-6, D-5, and D-6 quadrangles. Strikes northeast and dips 

moderately west in the C-5 quadrangle. Overlies and locally faulted against 

rocks of the Jarvis Creek Glacier subterrane. Sparse plant fossils indicate 

Oligocene, Miocene, and Pliocene age (Nokleberg and others, 1992a, table 1, 

localities 1, 2, 3, 4, 6) 
9

MÉLANGE

m Structural mélange along Hines Creek Fault (Holocene to Paleocene)—Consists 

of structurally imbricated lenses of low-grade metasedimentary rock, 

metavolcanic schist, and granite, with local abundant brittle shears 

(microfaults) that occur in a narrow zone adjacent to the Hines Creek Fault in 

the Mount Hayes D-6 and Healy D-1 quadrangles. Zone is as wide as 300 m 

and extends for about 7 km. Mélange mainly occurs along northern edge of 

porphyritic granodiorite of VABM Marganne (Km). Units adjacent to the 

structural mélange also contain abundant brittle shears (microfaults) 

POST-ACCRETIONARY PLUTONIC ROCKS 

Extensive areas of granitic plutonic rocks occur in terranes north of the Denali Fault as small 

dikes, stocks, and a few large plutons. Some occurrences are too small to depict on the geologic map. 

The larger plutons are at Buchanan Creek and Molybdenum Ridge in the northwest Mount Hayes 

quadrangle. The granitic rocks are generally equigranular to porphyritic and medium grained and usually 

contain both hornblende and biotite. 

Kbc Leucodiorite and granodiorite of Buchanan Creek (lower Tertiary to Upper 

Cretaceous)—Chiefly fine- to medium-grained biotite-hornblende 

leucodiorite with lesser granodiorite. Fine- to medium-grained, 

hypidiomorphic granular texture. Major igneous minerals are quartz, 

K-feldspar, plagioclase, hornblende, and biotite. Locally altered, fractured, 

and coarse grained, and contains a local weak schistosity. Plagioclase is 

partially recrystallized to sericite; hornblende and biotite to chlorite. Intrudes 

Jarvis Creek Glacier subterrane (unit jcv). Southern margin locally terminated 

along the Hines Creek Fault. As illustrated on the thin section 

microphotograph on the map, the leucodiorite of Buchanan Creek is fine to 

medium grained with a low color index, contains abundant plagioclase and 

little to no K-feldspar, and is quartz poor 

Unit occurs in an area approximately 15 km across in the southern 

Healy D-1 quadrangle and extends eastward into the Mount Hayes D-6 

quadrangles. Intrudes and contains inclusions of fine-grained, schistose 

metavolcanic rocks and metasedimentary rocks (jcv) of the Jarvis Creek 

Glacier subterrane. Locally intruded by andesite and granite dikes as wide as 

1 m 

A Late Cretaceous or early Tertiary age is inferred from intrusion into 

rocks of the Jarvis Creek Glacier subterrane, subsequent to the main phase of 

the Lower to middle Cretaceous metamorphism. Slight schistosity and sericite 

and chlorite alteration of the unit most likely occurred during the waning 

stages of metamorphism 

Km Porphyritic granodiorite of VABM Marganne (lower Tertiary to Upper 

Cretaceous)—Chiefly medium- to coarse-grained, biotite-hornblende 

porphyritic granodiorite with pink K-feldspar phenocrysts to 2 cm diameter. 

Seven K-Ar hornblende ages range from 101.8 to 93.2 Ma (Sherwood and 

Craddock, 1979; Csejtey and others, 1992). Unit occurs in southern Healy D-1 

and northern Healy C-1 quadrangles in fault-bounded wedge south of 

metavolcanic rocks of Jarvis Creek Glacier subterrane (unit jcv) and north of 

unnamed granodiorite (unit Kgd). Local brittle shears (microfaults) along 
10

margins. Wedge is about 20 km long and as wide as 3.2 km. As illustrated on 

the thin-section microphotograph on the map, the porphyritic granodiorite of 

VABM Marganne is coarse to medium grained with a moderate color index, 

contains pink K-feldspar phenocrysts ranging to 2 cm diameter, and is quartz 

rich 

Kmo Granodiorite of Molybdenum Ridge (lower Tertiary to Upper Cretaceous)—

Chiefly biotite-hornblende granodiorite with lesser granite and quartz diorite. 

Contains local inclusions of fine-grained metasedimentary rocks (jcs) of 

Jarvis Creek Glacier subterrane. Unit is medium grained with 

ahypidiomorphic granular texture and local phenocrysts of plagioclase to 

4 mm. Major minerals are plagioclase, K-feldspar, quartz, hornblende, and 

biotite. Hornblende is locally replaced by biotite. Displays a weak local 

schistosity near contact with unit jcs. Locally fractured and granulated. 

Contains local hydrothermal alteration with hornblende and biotite partially 

replaced by chlorite and plagioclase by white mica. Unit exposed in an 

irregular body approximately 9 km across. Intrudes and locally faulted against 

fine-grained metasedimentary rocks (jcs) of the Jarvis Creek Glacier 

subterrane; intruded by granite, rhyolite, dacite, and andesite dikes 

approximately 1 m wide. An Upper Cretaceous age of intrusion indicated 

from K-Ar biotite and hornblende dates, and U-Pb zircon ages range from 84 

to 93 Ma (Nokleberg and others, 1992a, table 2, locality 13). Distinguished 

from other nearby granitic plutons by above features 

Kgd Unnamed granodiorite (Upper Cretaceous)—Chiefly biotite-hornblende 

granodiorite. Medium grained. Occurs in southern Healy D-1 and northern 

Healy C-1 quadrangles in a fault-bounded wedge south of porphyritic 

granodiorite of VABM Marganne and north of metavolcanic and lesser 

metasedimentary rocks of Pingston terrane. Local brittle shears (microfaults) 

along edges. Fault-bounded wedge is about 18 km long and 1.5 km wide. Unit 

differs from leucodiorite of Buchanan Creek in having a smaller grain size and 

higher color index 

Kqm Unnamed granite (Upper Cretaceous)—Chiefly an elongate fault-bounded wedge 

of granite exposed in a thin, fault-bounded wedge approximately 1 km wide 

and 12 km long in fault contact with Aurora Peak terrane to the northeast and 

Windy terrane to the southwest in the northwest Mount Hayes B-4 

quadrangle. Fine to coarse grained. hypidiomorphic granular and locally 

porphyritic with phenocrysts of plagioclase to 5 mm. Major minerals are 

quartz, plagioclase, K-feldspar, biotite, and hornblende. Unit displays a local 

weak to intense hydrothermal alteration and is locally schistose. Plagioclase is 

partially recrystallized to sericite; biotite to chlorite plus epidote-clinozoisite. 

Contains local quartz and calcite veins 

Unit occurs in an area between the Windy and Aurora Peak terranes in 

Mount Hayes B-4 quadrangle. Unit exhibits K-Ar biotite and hornblende ages 

of 85.2, 85.9, 89.6, and 94.7 Ma (Nokleberg and others, 1992a, table 2, 

localities 39, 40, 41). These K-Ar values may be minimum ages for the pluton 

because of low-grade hydrothermal alteration and (or) low-grade static 

metamorphism 
11

Unit also includes a small pluton intruding metasedimentary rock of 

pingston terrane (unit pis) in central Mount Hayes C-6 quadrangle. Also 

includes locally numerous dikes and sills rarely more than 1 m across 

mgb Metamorphosed gabbro and diabase (Upper Triassic)—Chiefly hornblende 

metagabbro and metadiabase and minor amphibolite. Unit is generally fine to 

medium grained with hypautomorphic granular to diabasic texture; locally 

porphyritic texture. Major minerals are plagioclase, hornblende, local biotite, 

and minor clinopyroxene, orthopyroxene, quartz, sphene, and opaque 

minerals. Hornblende and biotite are partially replaced by chlorite and 

epidote, and plagioclase by sericite, calcite, and epidote. Unit is variably 

metamorphosed to greenschist facies and locally schistose. Occurs in 

(1) southeastern Healy D-1 quadrangle (western part of map) in a narrow 

fault-bounded wedge south of leucodiorite of Buchanan Creek (unit Kbc) and 

north of unnamed granodiorite (unit Kgd) in a wedge about 5 km long and 1 

km wide and (2) northern Mount Hayes B-4 and southern Mount Hayes C-4 

quadrangles (eastern part of map) as scattered dikes and small bodies 

intruding Jarvis Creek Glacier subterrane. An Upper Triassic crystallization 

age of 225.8±0.7 Ma (by U-Pb zircon analysis) was obtained for a suite of 

gabbro sills intruding the metasedimentary and metavolcanic rocks of the 

Jarvis Creek Glacier subterrane in the Bonnifield mining district in the 

northern Healy D-1 quadrangle (Dashevsky and others, 2003; Dusel-Bacon 

and others, 2006) 

TERRANES (NORTH TO SOUTH) 

YUKON-TANANA TERRANE 

Adjacent to and north of the Hines Creek Fault, the southern part of the Yukon-Tanana terrane 

consists of unnamed metagabbro and metadiabase and the Jarvis Creek Glacier subterrane (Nokleberg 

and others, 1992b) that contains two major units: (1) metavolcanic rock with lesser metasedimentary 

rock (Upper Devonian) and (2) metasedimentary schist (Devonian and older). The Yukon-Tanana 

terrane is interpreted as a highly metamorphosed and deformed Devonian submarine continental-margin 

igneous arc (Aleinikoff, 1984a,b; Dusel-Bacon and Aleinikoff, 1985; Nokleberg and Aleinikoff, 1985; 

Aleinikoff and others, 1986, 1987; Nokleberg and others, 1989, 1992b; Nokleberg and Richter, 2007). 

Jarvis Creek Glacier Subterrane 

The Jarvis Creek Glacier subterrane (Aleinikoff and Nokleberg, 1985a; Nokleberg and 

Aleinikoff, 1985) occurs across the northern part of the Mount Hayes quadrangle and northwestern part 

of the Healy quadrangle. The subterrane consists of fine-grained, polydeformed schists derived from 

Devonian and Mississippian sedimentary rocks and Devonian metavolcanic and metagranitic rocks. 

This subterrane is subdivided into two units: (1) a metasedimentary rock unit (jcs) composed 

chiefly of fine-grained metasedimentary rocks and very minor metavolcanic rocks and (2) a 

metavolcanic rocks unit (jcv) composed chiefly of fine-grained metavolcanic rocks and moderate 

amounts of fine-grained metasedimentary rocks. 

The metasedimentary and metavolcanic rocks are almost totally recrystallized and are composed 

of varying proportions of pelitic schist, quartzite, calc-schist, quartz-feldspar schist, and marble. 

Protoliths are shale, quartz sandstone, marl, sandstone, volcanic graywacke, and limestone. The 

metavolcanic rocks consist of varying proportions of abundant metaandesite and metamorphosed quartz 

keratophyre, less abundant metadacite and metabasalt, and very minor metarhyodacite. 
12

The metasedimentary and metavolcanic rock units were ductily deformed and regionally 

metamorphosed at greenschist facies into mylonitic schist or local phyllonite (Nokleberg and others, 

1986). 

jcs Fine-grained metasedimentary rocks (Devonian and older)—Chiefly fine-grained, 

mylonitic metasedimentary rocks. Unit comprised of approximately 65% 

quartz-mica schist; 15% quartzite; and 5% each of chlorite-white mica schist, 

quartz-biotite schist, calc-schist, and marble. Protoliths of the unit are mainly 

pelite, quartz sandstone, graywacke, marl, and limestone. Intense deformation 

and recrystallization has obliterated most relict minerals and textures. The unit 

has an estimated structural thickness of a few thousand meters 

Quartz-mica schists are fine grained and consist of (in descending 

order of abundance) quartz-white mica schist; quartz-white mica-chlorite 

schist; quartz-white mica calcite schist; quartz-white mica calcite-chlorite 

schist; quartz-white mica-garnet-chlorite schist; and garnet-white mica quartz 

schist. Common minor minerals are epidote, garnet, K-feldspar, graphite, 

sphene, and rarely tourmaline and cordierite. Porphyroblasts are chiefly 

quartz, plagioclase, garnet, and K-feldspar and average 1 mm across, rarely 

exceeding 3 mm across. Rare relict clastic quartz and plagioclase grains are 

present. Compositional layering is generally parallel to schistosity, defined 

principally by alternating bands and lenses of schistose micas and granular 

quartz and feldspar. Variably distorted, fractured, and granulated quartz and 

plagioclase form augen or augen-shaped aggregates that accompany bent mica 

and local helicitic garnet. Unit contains local blastomylonite. Plagioclase and 

andalusite are locally replaced by white mica, and biotite by chlorite 

Quartzite grain size averages approximately 1 mm with scattered 

porphyroclasts to 2 mm. No relict sedimentary textures are present. Common 

major minerals are quartz, biotite, white mica, calcite, and minor plagioclase, 

K-feldspar, chlorite, opaque minerals, and epidote. Common minor minerals 

are opaque minerals, K-feldspar, calcite, white mica, and rarely hornblende. 

Orientation of elongate quartz grains, lenses of calcite and (or) opaque 

minerals, and local crystallographic orientation of quartz parallels schistosity. 

Variable fracturing and granulation of mineral grains are common. Plagioclase 

is partially recrystallized to white mica and calcite 

Chlorite-white mica schists are very fine to fine grained. Local 

plagioclase porphyroblasts range to 1 mm. Major minerals are quartz, epidoteclinozoisite, plagioclase, and K-feldspar, with lesser calcite and opaque 

minerals. Minor minerals are biotite and garnet. Local compositional layering 

parallels schistosity and is defined by bands of quartz alternating with white 

mica and chlorite 

Quartz-biotite schists are mainly fine grained. Plagioclase 

porphyroblasts range to 1.5 mm. Local major minerals are plagioclase, 

chlorite, K-feldspar, and epidote, with minor white mica, garnet, calcite, 

sphene, and garnet. Compositional layering parallels schistosity and is defined 

by alternating bands of biotite and chlorite or white mica with bands of quartz 

and plagioclase. Helicitic garnet occurs locally. Biotite is partially 

recrystallized to chlorite; garnet to biotite and chlorite 

Calc-schists and marbles are fine grained and consist of calcitechlorite schist, plagioclase-quartz-epidote schist, marble, and quartz-rich 
13

marble. Minor minerals are white mica, graphite, opaque minerals, and garnet. 

Porphyroblasts are principally of quartz, plagioclase, and garnet to 5 mm and 

average approximately 1 mm. Rare relict clastic quartz grains are present. In 

calc-schists, compositional layering parallels schistosity and is generally 

defined by alternations of quartz and (or) chlorite with variable combinations 

of plagioclase, calcite, or epidote. Compositional layering in marbles defined 

by calcite alternating with quartz-rich and (or) chlorite-rich layers. Fracturing 

and granulation of mineral grains is common. Plagioclase is locally replaced 

by white mica and calcite; garnet by chlorite 

Unit is intensely deformed and exhibits strong schistosity. Schistosity 

and parallel compositional layering dip gently to moderately north or south, 

locally defining broad antiforms and synforms. A broad, major antiform 

occurs in Mount Hayes B-4 quadrangle, subparallel to the Denali Fault. 

Towards the south, near the Hines Creek and Denali Faults, schistosity and 

compositional layering dip moderately to steeply south and strike westnorthwest parallel to the faults. In outcrop and thin section, compositional 

layering and schistosity are generally folded into moderately appressed to 

tight isoclinal folds with axial planes parallel to the schistosity. Folds deform 

an older schistosity and compositional layering. Minor folds are generally 

asymmetrical with south or southwest vergence. Unit was metamorphosed at 

greenschist facies. Diagnostic lower to middle greenschist facies metamorphic 

minerals are actinolite, chlorite, white mica, epidote-clinozoisite, and calcite 

Unit is faulted against Aurora Peak terrane along the Hines Creek 

Fault in B-4 and B-5 quadrangles and against Wrangellia terrane along the 

Denali Fault in B-4 quadrangle. Unit is intruded, from west to east, by granite 

and granodiorite plutons and by numerous granitic to gabbroic dikes and sills 

On strike to the west in the Healy quadrangle, metasedimentary rocks 

correlated with the fine-grained metasedimentary rocks (jcs) of the Jarvis 

Creek Glacier subterrane contain Devonian to Mississippian age conodonts 

(Sherwood and Craddock, 1979; Csejtey and others, 1992). U-Pb isotope 

analysis of clastic zircons in quartzites (in unit jcs) indicates the protolith was 

derived, in part, from a lower Proterozoic source rock with radiometric sample 

ages of 2.0 to 2.3 Ga (Nokleberg and others, 1992a, table 2, localities 22, 23; 

Aleinikoff and Nokleberg, 1985a,b; Aleinikoff and others, 1987) 

Isotopic analyses of the schistose minerals in units jcs and jcv indicate 

that regional metamorphism and associated penetrative deformation occurred 

in the Lower to middle Cretaceous. K-Ar isotopic analysis of white mica 

yields isotopic ages of 106, 107, 115, and 118 Ma (Nokleberg and others, 

1992a, table 2, localities 14, 16, 18, 20). These isotopic ages are interpreted as 

the age of metamorphism, rather than as the age of later cooling, because 

higher-temperature isotopic systems for higher-grade rocks, in the deepest 

structural levels of the Yukon-Tanana terrane to the north, yield the same 

Lower to middle Cretaceous ages (Nokleberg and others, 1989) 

jcv Fine-grained schistose metavolcanic rocks and metasedimentary rocks (Upper 

Devonian)—Chiefly fine-grained, schistose, metavolcanic rocks interlayered 

with lesser metasedimentary rocks. Metavolcanic rocks consist chiefly of 

metamorphosed quartz keratophyre, metadacite, and metaandesite with lesser 

metarhyodacite and metabasalt derived from fine-grained tuffs and flows. 
14

Metasedimentary rocks chiefly quartz-mica schists and some calc-schists, 

marble, skarn, and quartzite. Protoliths for metasedimentary rocks are mainly 

pelite, quartz sandstone, siltstone, marl, and limestone. Metavolcanic rocks 

occur in layers from about 0.5 m to a few meters thick and are interlayered 

with thin to thick layers of metasedimentary rocks. Unit has an estimated 

structural thickness of a few thousand meters 

Metavolcanic rocks generally are characterized by relict 

microporphyritic texture containing euhedral to subhedral, twinned, and often 

zoned plagioclase phenocrysts to 4 mm long in a fine-grained groundmass of 

quartz, plagioclase, and schistose mica. Poikilitic and clean, relict plagioclase 

phenocrysts are common. Relict quartz and K-feldspar phenocrysts occur 

locally. Local resorbed outlines of quartz and feldspar phenocrysts occur. 

Common metamorphic minerals are quartz, plagioclase, white mica, chlorite, 

epidote-clinozoisite, and calcite; opaque minerals are present. Sparse 

metabasalts are composed mainly of actinolite and, locally, epidote and 

calcite. Minor metamorphic minerals are sericite, chlorite, sphene, biotite, 

garnet, hornblende, and opaque minerals. Compositional layering parallels 

schistosity and is defined by bands and lenses of granoblastic quartz and 

feldspar that alternate with schistose mica. Fracturing and granulation of relict 

phenocrysts are common with development of augen and augen-shaped 

aggregates of quartz and feldspar in finer-grained recrystallized matrix. 

Plagioclase and K-feldspar are partially replaced by sericite, biotite, and 

actinolite; and hornblende by chlorite 

Quartz-mica schists consist of generally fine grained quartz-white 

mica schist, graphite-quartz-white mica schist, quartz-plagioclase-white micachlorite schist, quartz-white mica-chlorite-plagioclase schist, and calcitechlorite-quartz schist. Minor minerals are calcite, plagioclase, chlorite, 

graphite, and other opaque minerals, with sparse garnet, hornblende, apatite, 

sphene, cordierite, zircon, and tourmaline. Sparse porphyroclasts of quartz and 

feldspar to 2 mm. Relict clastic grains of quartz and feldspar occur locally. 

Compositional layering parallels schistosity and is generally defined by layers 

of granoblastic quartz and feldspar that alternate with micaceous layers. 

Variably distorted, fractured, and granulated quartz and feldspar form augen 

or augen-shaped aggregates that accompany bent mica. Plagioclase is partially 

replaced by white mica and calcite; biotite by chlorite 

Calc-schists and marbles consist of generally fine grained quartz-white 

mica-calcite schist, quartz-calcite schist, quartz-plagioclase-white mica-calcite 

schist, quartz-epidote-clinozoisite schist, quartz-white mica-epidote schist, 

epidote-plagioclase-actinolite schist, hornblende-biotite-calcite schist, 

hornblende-plagioclase-calcite schist, marble, and biotite marble. Minor 

minerals are K-feldspar, biotite, graphite, and opaque minerals. Skarns 

composed of variable proportions of epidote, garnet, chlorite, calcite, and, 

locally, clinopyroxene, actinolite, and wollastonite. Porphyroclasts of quartz 

and plagioclase to 6 mm long occur locally. Compositional layering generally 

defined by granoblastic layers of quartz and (or) plagioclase alternating with 

calcite and combinations of schistose mica, epidote-clinozoisite, amphibole, 

and opaque minerals. Quartz and calcite grains are locally elongate parallel to 

schistosity and compositional layering. Plagioclase is partially replaced by 
15

sericite and calcite; whereas hornblende, actinolite, and biotite are replaced by 

chlorite 

Quartzites are generally composed of sparse flakes to stringers and 

bands of schistose white mica and (or) biotite and chlorite in fine-grained 

granoblastic quartz. Weak to strong alignment of elongate quartz grains 

parallel to schistosity is common. Calcite occurs locally as porphyroclasts and 

in bands and patches. Local fracturing and granulation is common. Minor 

minerals are graphite, plagioclase, K-feldspar, and opaque minerals 

Unit is intensely deformed and exhibits strong schistosity. Schistosity 

and parallel compositional layering dips gently to moderately north or south, 

locally defining broad antiforms and synforms. In outcrop and thin section, 

compositional layering and schistosity are generally folded into moderately 

appressed to tight isoclinal folds with axial planes parallel to the schistosity. 

Unit occurs mainly structurally above fine-grained metasedimentary rocks 

(jcs). Folds are formed in an older schistosity and are subparallel to 

compositional layering. Ductile deformation adjacent to major faults has 

formed locally abundant phyllonites and blastomylonites 

Unit metamorphosed at lower greenschist facies. Upper greenschist to 

lower amphibolite facies minerals are biotite, garnet, cordierite, and 

hornblende. Lower to middle greenschist facies metamorphic minerals are 

actinolite, chlorite, graphite, white mica, epidote-clinozoisite, and calcite 

Unit occurs in elongate northwest-trending wedge, approximately 50 

km long and as much as 5 km wide, located principally between the Trident 

Glacier Fault to the northeast and the Hines Creek Fault to the southwest in 

the western part of the Mount Hayes quadrangle. Unit is in fault contact with 

the fine-grained metasedimentary rocks (jcs) of the Jarvis Creek Glacier 

subterrane to the north and with the Pingston terrane to the south. Unit is 

intruded by the granodiorite of Molybdenum Ridge (unit Kmo) 

U-Pb zircon isotopic analysis of samples of metavolcanic rocks (jcv), 

locally interlayered with metasedimentary rocks, yield ages of 364, 372, and 

about 375 Ma (Nokleberg and others, 1992a, table 2, localities 12, 15, 28), 

and are interpreted to indicate eruption in Devonian time 

PINGSTON TERRANE—SOUTH OF HINES CREEK FAULT AND NORTH OF NENANA 

GLACIER AND DENALI FAULTS

The Pingston terrane (former Hayes Glacier subterrane of Nokleberg and others, 1992b) occurs 

across the west-central part of the Mount Hayes quadrangle and extends westward into the northwestern 

and north-central part of the Healy quadrangle. In the Mount Hayes quadrangle, the terrane is bounded 

to the north by the Jarvis Creek Glacier subterrane along the Hines Creek Fault and to the south by 

Aurora Peak terrane along the Nenana Glacier Fault. Because of post-1992 analysis, this unit is now 

identified as a unique, fault-bounded terrane with a stratigraphy and structure that is highly distinct from 

the structurally adjacent Jarvis Creek Glacier subterrane of the Yukon-Tanana terrane to the north and 

the Aurora Peak terrane to the south (Nokleberg and others, 1983, 1992b). 

The Pingston terrane consists chiefly of highly deformed and structurally interleaved lenses and 

blocks of metasedimentary and metavolcanic rocks. Large portions of units form a structural mélange 

with local blastomylonite and mylonite that occur in structurally interleaved lenses and blocks that also 
16

contain abundant brittle shears (microfaults). Stratigraphic relations are mostly obscured by intense 

deformation with local random interleaving of stratigraphic units. 

Because of the intense deformation, the terrane can only be divided into the following five major 

units: (1) metagabbro with lesser diabase (Cretaceous?); (2) limestone, calcareous sandstone, and 

phyllite (Triassic); (3) metabasalt (Paleozoic or Mesozoic?); (4) metasedimentary rock, chiefly phyllite 

and phyllonite with lesser chert, and intermediate to siliceous metavolcanic rock (Silurian to Devonian); 

and (5) mafic to siliceous metavolcanic rock with lesser phyllite, metasiltstone, and chert (Devonian, 

Pennsylvanian, and Triassic). The terrane differs from the Jarvis Creek Glacier subterrane of the YukonTanana terrane to the north in possessing (1) no Devonian metagranitic rocks; (2) a greater abundance of 

graphitic-rich metasedimentary rocks and fewer metavolcanic rocks; (3) a lower metamorphic grade; 

(4) a finer metamorphic grain size; and (5) a locally intensely developed, low-grade metamorphic fabric 

with abundant mylonitic textures. 

The protolith of the terrane is interpreted as chiefly continental rise or slope sedimentary rock 

and associated submarine continental-margin arc rock that were intruded by metagabbro (Nokleberg and 

others, 1983; Nokleberg and Richter, 2007). 

pimg Gabbro and lesser diabase of Mount Moffit (Cretaceous?)—Fine- to mediumgrained, hypidiomorphic granular texture. Two dominant lithologies occur: 

(1) plagioclase, clinopyroxene, and minor biotite and (2) plagioclase, biotite, 

local hornblende and minor quartz and K-feldspar. Opaque minerals are 

locally abundant. Strongly zoned and twinned plagioclase phenocrysts to 1.8 

mm occur locally. Clinopyroxene partially replaced by igneous biotite locally. 

Unit displays light, local alteration of biotite to chlorite and plagioclase to 

sericite. Unit underlies McGinnis Peak and Mount Moffit in the southwestern 

Mount Hayes C-5 quadrangle, an area approximately 6 km across 

pil Limestone, calcareous sandstone, and phyllite (Triassic)—Chiefly medium to 

thick beds of dark- to light-gray, medium- to coarse-grained limestone and 

local marble; medium-gray, medium-grained calcite-quartz sandstone; and 

dark-gray phyllite and phyllonite. Lithologies occur in highly deformed and 

structurally interleaved lenses and blocks in a random order. Local mylonite 

with extensive brittle shears (microfaults). West of the map area, in the central 

Healy quadrangle, this unit has yielded Triassic age megafossils and 

conodonts (Sherwood and Craddock, 1979) 

pimb Metabasalt (Triassic to Silurian)—Chiefly fine grained, amygdaloidal, and 

porphyritic. Unit is medium- to dark-greenish-gray and massive. Contains 

relict plagioclase phenocrysts to 3 mm long in a very fine grained, 

recrystallized groundmass of quartz, actinolite, and epidote. Contains local 

amygdules filled with chlorite and epidote and local calcite veins. Plagioclase 

is largely replaced by saussurite. Faint pillow structure occurs locally. Unit 

locally contains interbedded, dark-gray to black, generally fine grained 

carbonaceous pelitic phyllite and phyllonite. Unit is over 600 m thick. Occurs 

in fault-bounded lens within margin of Aurora Peak terrane in northwest 

Mount Hayes B-4 quadrangle 

pis Metasedimentary rock, chiefly phyllite (Triassic to Silurian)—Chiefly fine 

grained, pale-yellow, pale-green, and graphitic black metasedimentary phyllite 

and locally extensive phyllonite and blastomylonite. Predominant lithologies 

are metachert, quartz-mica phyllite, quartz-calc-phyllite, quartzite, marble, 

and metavolcanic schist. Protoliths are siltstone, shale, marl, limestone, 
17

quartz-rich volcanic rocks, and volcanic graywacke. West of the map area, in 

the central Healy quadrangle, metasedimentary rocks yielded Silurian and 

Devonian age megafossils (Sherwood and Craddock, 1979)

Intense ductile deformation has obliterated most relict minerals and 

textures. Local relict meter-scale bedding occurs. Metamorphosed at lower to 

middle greenschist facies. Diagnostic lower greenschist facies metamorphic 

minerals are white mica, chlorite, graphite, and calcite. Structural thickness of 

a few thousand meters is estimated for the unit 

Quartz-mica phyllite and phylonite composed of subangular to 

subrounded quartz clasts in a fine-grained matrix of granular quartz, schistose 

white mica, and, locally, biotite. Minor minerals are graphite, plagioclase, 

chlorite, calcite, hematite, opaque minerals, and rare andalusite. Unit contains 

local, millimeter-scale, quartz-rich, mica-rich, and calcite-rich layers that 

parallel schistosity. Relict subrounded to subangular clastic quartz grains to 

2 mm. Local fine to coarse bands of graphite along schistosity 

Quartz-calc-phyllite and phyllonite composed mainly of sparse to 

abundant relict clasts of quartz and calcite to 2 mm in matrix, very fine 

grained quartz, schistose sericite, feldspar, and abundant calcite. Contains 

local thin graphite-rich layers. Marble is granoblastic to schistose and locally 

contains minor quartz, white mica, and graphite 

Quartzite contains local quartz-mica phyllonite. Compositional 

layering defined by variably proportioned bands of quartz and white mica and 

minor biotite, chlorite, and calcite 

Metavolcanic schist is composed mainly of relict phenocrysts of 

plagioclase and lesser quartz and K-feldspar to 3 mm long, variably fractured 

and granulated in a matrix of fine granular quartz and schistose sericite. Minor 

minerals are calcite, chlorite, and opaque minerals. Resorbed outlines of 

quartz and plagioclase are locally preserved. Plagioclase is partially replaced 

by sericite 

Unit is intensely deformed and exhibits strong schistosity. Schistosity 

dips moderately to steeply south and strikes west to northwest, generally 

parallel to the Denali and Hines Creek Faults. Remnant small-scale isoclinal 

folds occur in outcrop and thin section with axial planes parallel to schistosity 

that deforms an older, less apparent schistosity. Most folds obliterated by 

intense deformation along younger schistosity 

Unit occurs in fault-bounded wedges. Intruded by gabbro of Mount 

Moffit (pimg) and by smaller bodies, dikes, and sills of granite and gabbro 

piv Mafic to siliceous metavolcanic rock with lesser phyllite, metasiltstone, and chert 

(Triassic to Silurian)—Chiefly fine grained metavolcanic rock and lesser 

metasedimentary phyllite and phyllonite. Major lithologies are 

metamorphosed quartz keratophyre and metaandesite and sparse metalatite, 

metarhyodacite, metadacite, and metabasalt. Structural thickness estimated to 

be a few thousand meters. West of map area, in central Healy quadrangle, 

metasedimentary rocks in this unit have yielded Pennsylvanian and Triassic 

megafossils (Sherwood and Craddock, 1979). A U-Pb zircon age from a 

metarhyodacite layer in the terrane is 375±8 Ma (Aleinikoff and Nokleberg, 

1983; Nokleberg and others, 1992a) 
18

Metavolcanic rocks mainly composed of relict phenocrysts, to 3.5 mm 

and averaging about 1.5 mm, of quartz and plagioclase in a groundmass of 

very fine grained granular quartz, feldspar, abundant schistose chlorite, 

sericite, K-feldspar, calcite, epidote, actinolite, and sparse biotite. Unit is 

locally intensely deformed into blastomylonite. Relict plagioclase phenocrysts 

occur and are commonly fractured and locally recrystallized to augen-shaped 

aggregates. Unit is intensely deformed into phyllonite. Plagioclase and 

K-feldspar are partly replaced by white mica; biotite by chlorite 

Metasedimentary rocks are chiefly quartz-mica phyllite and phyllonite, 

quartzite, and quartz-calc phyllite and phyllonite. Protoliths for the 

metasedimentary rocks are siltstone, sandstone, graywacke, marl, and 

limestone 

Quartz-mica phyllite and phyllonite are predominantly quartz-white 

mica phyllonite with lesser quartz biotite phyllite and phyllonite, quartzbiotite-K-feldspar phyllite and phyllonite, and white mica-biotite-quartzgraphite phyllite and phyllonite. Common minor minerals are plagioclase, 

chlorite, calcite, epidote, hematite, andalusite, graphite, chlorite, and opaque 

minerals. Generally fine grained. Patches of calcite occur locally. 

Compositional layering, preferred orientation of elongate quartz grains, and 

grain-size segregation are parallel to schistosity. Compositional layering 

defined by layers of quartz alternating with layers of mica and, locally, layers 

of K-feldspar, graphite, and rare andalusite. Local relict rounded quartz 

pebbles. Unit exhibits local intense granulation and fracturing of quartz and 

plagioclase. Plagioclase partially replaced by calcite and white mica. Biotite 

partially replaced by chlorite 

Unit intensely recrystallized and ductily deformed. Metamorphosed at 

lower to middle greenschist facies with local metamorphic biotite. Schistosity 

dips moderately to steeply south and strikes west to northwest, generally 

parallel to the Denali and Hines Creek Faults. Remnant, small-scale, isoclinal 

folds with axial planes are parallel to schistosity that deforms an older 

schistosity. Most folds obliterated by intense deformation along younger 

schistosity 

Unit occurs in fault-bounded wedges and is intruded by metagabbro of 

Mount Moffit (pimg) and smaller gabbroic stocks, dikes, and sills. U-Pb 

zircon isotopic analysis of samples of metavolcanic rocks (piv; interlayered 

and metasedimentary rocks) in eastern Mount Hayes quadrangle yields an age 

of 375 Ma (Nokleberg and others, 1992b, table 2, localities 32, 34, 36) 

AURORA PEAK TERRANE—SOUTH OF NENANA GLACIER FAULT AND NORTH OF 

DENALI FAULT 

The Aurora Peak terrane (Nokleberg and others, 1985, 1992b: Nokleberg and Richter, 2007) 

occurs north of the Denali Fault in the western part of the Mount Hayes quadrangle. The terrane consists 

of (1) a relatively older unit of metasedimentary rocks, chiefly fine to medium grained and polydeformed calc-schist, marble, quartzite, and pelitic schist (aps) and (2) a relatively younger unit of 

regionally metamorphosed and penetratively deformed gneissic granitic rocks derived from quartz 

diorite, granodiorite, granite, gabbro, and diorite (apg). The protoliths for metasedimentary rocks are 

marl, quartzite, and shale. The Aurora Peak terrane was twice ductility metamorphosed and deformed, 

once into mylonitic schist during an earlier period of upper amphibolite facies metamorphism and later 
19

into blastomylonite during a period of middle greenschist facies metamorphism (Nokleberg and others, 

1992b). The general parallelism of the schistosity in the gneissic granitic rocks with the Denali and 

Nenana Glacier Faults suggests that metamorphism and deformation occurred while the faults were 

active. 

Like the Maclaren terrane to the south, the Aurora Peak terrane is interpreted as a displaced 

fragment of the Kluane schist and the Ruby Range batholith that occur northeast of the Denali Fault 400 

km to the southeast in the Yukon Territory (Nokleberg and others, 1985, 1992b; Nokleberg and Richter, 

2007). Although somewhat similar, the Aurora Peak and Mclaren terranes are distinct terranes because 

of occurrence of the structural mélange of sedimentary and volcanic rocks of the Paleozoic and 

Cretaceous Windy terrane between the two terranes. 

apg Metamorphosed granitic rock (lower Tertiary to middle Cretaceous)—Consists 

chiefly of stocks, dikes, and sills of metadiorite and minor metamorphosed 

quartz diorite, granite, granodiorite, and gabbro. Metadiorite and 

metamorphosed quartz diorite composed of variable amounts of hornblende, 

clinopyroxene, quartz, and biotite and lesser orthopyroxene, quartz, calcite, 

sericite, clinozoisite, sphene, apatite, and hematite. Unit is fine to medium 

grained with relict hypidiomorphic granular texture. Hornblende and 

plagioclase are variably recrystallized. Hornblende rims clinopyroxene and 

opaque minerals. Plagioclase partially replaced by white mica 

Metagranite and metagranodiorite are fine to medium grained and are 

composed of variable amounts of biotite and white mica and lesser chlorite, 

epidote, calcite, sericite, sphene, garnet, andalusite, and actinolite. Relict 

hypautomorphic granular texture occurs. Metagranodiorite locally contains 

relict K-feldspar phenocrysts to 7 mm across. Plagioclase and K-feldspar 

variably replaced by sericite and minor epidote; clinopyroxene by biotite and 

chlorite; biotite by chlorite 

Unit moderately deformed; exhibits moderate schistosity that dips 

steeply to vertically and strikes west-northwest. Variably fractured, deformed, 

and granulated and is metamorphosed to amphibolite facies. Diagnostic 

amphibolite facies minerals are biotite, garnet, hornblende, and clinopyroxene. 

Local retrogressive metamorphism indicated by partial replacement of 

plagioclase and K-feldspar by sericite and epidote; clinopyroxene by biotite 

and chlorite; and biotite by chlorite 

Unit occurs principally in the southern Mount Hayes C-6 quadrangle. 

Unit is faulted against the Maclaren terrane to the south along the Denali Fault 

and against the Pingston terrane to the north along the Nenana Glacier Fault. 

Unit intrudes metamorphosed sedimentary rocks (aps) in stocks, dikes, and 

sills and is intruded by slightly metamorphosed granite dikes approximately 

1 m wide 

In map area, U-Pb zircon isotopic analysis of a metadiorite yields a 

Late Cretaceous age of 71 Ma (Nokleberg and others, 1992a, table 2, locality 

38). To the west in the east-central Healy quadrangle, 40Ar/39Ar isotopic 

analysis of hornblende in correlative (meta)granitic rocks yields a middle 

Cretaceous age of 106 Ma (Csejtey and others, 1992, locality 33). These 

isotopic ages are interpreted as middle Cretaceous to lower Tertiary intrusion 

of metagranitic rocks in the Aurora Peak terrane 

Isotopic analyses of schistose biotite and hornblende in metagranitic 

rocks are interpreted as forming during uplift and cooling of the Aurora Peak 
20

terrane in the middle Tertiary. K-Ar isotopic analysis of biotite yields isotopic 

ages of 18.2, 24.0, and 27 Ma (Nokleberg and others, 1992b, table 2, localities 

37, 38). K-Ar isotopic analysis of hornblende yields an isotopic age of 36.8 

Ma (Nokleberg and others, 1992b, table 2, locality 37). Because of the older 

U-Pb zircon isotopic ages and because the Aurora Peak terrane occurs 

adjacent to the Denali Fault, these K-Ar isotopic dates are interpreted as ages 

of uplift and cooling of the Aurora Peak terrane during Cenozoic migration 

along the Denali Fault (Nokleberg and others, 1985, 1989, 1992b) 

apmg Metagabbro (lower Tertiary to middle Cretaceous)—Chiefly fine-grained 

hornblende and plagioclase and minor biotite, clinopyroxene, calcite, chlorite, 

quartz, white mica, and sphene. Contains local compositional layering defined 

by alternating bands of schistose biotite and nematoblastic hornblende. 

Clinopyroxene partially replaced by hornblende and biotite; plagioclase by 

white mica 

aps High-grade metasedimentary schist and carbonate (Triassic to Silurian)—

Chiefly fine- to medium-grained, mylonitic, calc-schist, marble, quartz-mica 

schist, and quartzite. Protoliths are marl, limestone, pelite, and sandstone. 

Structural thickness is estimated at a few thousand meters 

Calc-schist consists predominantly of quartz-calcite schist grading to 

marble but includes some chlorite-calcite schist, plagioclase-calcite schist, 

biotite-quartz-calcite-hornblende schist, and quartz-epidote-biotite-calcite 

schist. Minor minerals are white mica, K-feldspar, actinolite, wollastonite, 

tremolite, clinopyroxene, garnet, graphite, sphene, zoisite, and opaque 

minerals. Marble locally contains clinopyroxene and garnet. Compositional 

layering generally consists of alternating quartz and calcite-rich layers with 

lesser schistose mica. Quartz, plagioclase, and calcite are commonly elongate 

parallel to schistosity. Variably fractured, granulated, and recrystallized quartz 

and plagioclase porphyroclasts form augen and augen-shaped aggregates to 

1.5 mm in blastomylonites. Sparse relict clastic quartz grains occur locally. 

Plagioclase partially replaced by white mica and clinozoisite; clinopyroxene 

by actinolite and clinozoisite 

Quartz-mica schists consist of quartz-white mica schist, white micaquartz schist, quartz-biotite schist, chlorite-white mica-quartz schist, and 

quartz-chlorite-white mica-graphite schist. Minor minerals are plagioclase, 

graphite, garnet, calcite, biotite, and opaque minerals. Displays compositional 

layering defined by alternating quartz-rich and mica-rich layers. Variably 

distorted, fractured, and granulated quartz and plagioclase commonly form 

elongate grains parallel to schistosity. Plagioclase is partially recrystallized to 

white mica 

Intense ductile deformation. Schistosity and parallel compositional 

layering dip steeply to vertically and strike west-northwest, parallel to the 

Hines Creek, Nenana Glacier, and Denali Faults. Unit is located in the Mount 

Hayes B-5 and C-5 quadrangles. Small isoclinal folds, defined by folding of 

an older schistosity, possess axial planes parallel to the dominant and younger 

schistosity. Local extreme ductile deformation that occurs along schistosity 

produces mylonitic schist and local blastomylonite 

Unit exhibits two periods of metamorphism: (1) an older period at 

upper amphibolite facies and (2) a younger period at middle greenschist 
21

facies. Diagnostic upper amphibolite facies minerals are hornblende, 

clinopyroxene, garnet, biotite, and wollastonite. Diagnostic middle greenschist 

facies minerals are chlorite, epidote, biotite, white mica, actinolite, and biotite. 

Lower grade rocks mainly occur along the margins of the terrane near the 

Denali, Nenana Glacier, and Hines Creek Faults. Retrogressive 

metamorphism indicated by partial replacement of clinopyroxene by actinolite 

and clinozoisite; plagioclase by white mica 

Unit occurs in a fault-bounded wedge, in the west-central part of the 

Mount Hayes quadrangle, between the Hines Creek Fault to the northeast, the 

Nenana Glacier Fault to the north, and the Denali Fault to the south. Unit 

intruded by stocks, dikes, and sills of metamorphosed and deformed diorite, 

granodiorite, and granite and by stocks, dikes, and sills of weakly schistose 

and weakly metamorphosed gabbro. Intrusive contacts are locally faulted 

Age of the protolith of the metasedimentary rocks constrained to 

Silurian through Triassic as determined from conodont fragments of postOrdovician morphotype from one marble body (Nokleberg and others, 1992a, 

table 1, locality 7) 

WINDY TERRANE—WITHIN SPLAYS OF DENALI FAULT 

The Windy terrane (Jones and others, 1987; Nokleberg and others, 1985, 1992b; Nokleberg and 

Richter, 2007) occurs across the Mount Hayes B-4 and B-5 quadrangles within branches of the Denali 

Fault, north of the Maclaren terrane, and south of the Aurora Peak and Yukon-Tanana terranes. Unlike 

the adjacent terranes to the north and south, the Windy terrane exhibits primary sedimentary or volcanic 

textures and structures. Relict sedimentary structures are bedding, graded bedding, and crossbedding. 

The Windy terrane occurs in narrow slivers that occur discontinuously for several hundred kilometers 

along the Denali Fault (Jones and others, 1987; Nokleberg and Richter, 2007). 

The major units in the structural mélange of the Windy terrane are (1) fault-bounded lenses of 

Cretaceous flysch and volcanic rocks consisting mainly of argillite; weakly metamorphosed quartz 

siltstone, quartz sandstone, metagraywacke, and metaconglomerate; and minor andesite and dacite and 

(2) small to large, fault-bounded lenses of Silurian(?) and Devonian limestone and marl. Estimated 

structural thickness of the terrane is about 3,000 to 4,000 m. 

The two major units occur in narrow, interleaved, fault-bounded lenses. Local intense schistosity 

strikes northwest parallel to branches of Denali Fault and dips moderately to steeply northeast in the 

western part of Mount Hayes quadrangle and moderately southwest in the eastern part of quadrangle. 

Local intense deformation occurs with development of phyllonite and protomylonite. Local abundant 

brittle shears (microfaults) and fault gouge occur along the southern margin of unit. Unit exhibits 

incipient greenschist facies metamorphism. Diagnostic minerals are very fine grained chlorite, graphite, 

sericite, epidote, and actinolite. 

The terrane is faulted against the Jarvis Creek Glacier subterrane and the Pingston and Aurora 

Peak terranes north of the Denali Fault and the Wrangellia and Maclaren terranes south of the Denali 

Fault. The terrane is intruded by a weakly schistose granite pluton in the Mount Hayes B-4 quadrangle 

and by small granitic and gabbroic dikes and sills. 

The Cretaceous flysch and associated volcanic rocks are interpreted as remnants of the Kahiltna 

terrane and associated Gravina arc (Stanley and others, 1990; Nokleberg and Richter, 2007). The 

Silurian(?) and Devonian limestone and marl are interpreted as possibly derived from weakly 

metamorphosed parts of the Yukon-Tanana terrane to the north. The terrane is a structural mélange of 

the two major units that have been tectonically mixed during Cenozoic dextral-slip movement along the 

Denali Fault (Nokleberg and others, 1989; Nokleberg and Richter, 2007). 
22

The terrane contains one known fragment of a Cretaceous ammonite (Nokleberg and others, 

1992a, table 1, locality 8) that was found in float but is interpreted as derived from the unit of flysch and 

volcanic rocks (J.H. Stout, written commun., 1976). Marl and limestone unit contains Silurian(?) and 

Devonian megafossils and microfossils (Nokleberg and others, 1992a, table 1, localities 8, 9, 10, 11). 

wp Phyllite, argillite, and minor metagraywacke and marl (Cretaceous)—Chiefly 

medium- to dark-gray, fine-grained phyllite and argillite with lesser mediumgrained metagraywacke, marl, and sparse limestone 

Phyllite and argillite are composed of quartz grains, to 0.2 mm, in very 

fine grained matrix of quartz, chlorite, graphite, and sericite. Contains local 

plagioclase and quartz-rich silty layers and minor hematite and opaque 

minerals. Sandy to pebbly siltstone composed of subangular quartz clasts in 

variable matrix of quartz and sericite and minor calcite, biotite, epidote, 

actinolite, opaque minerals, and sphene 

Marl is mainly black to light gray and well bedded. Exhibits sparse 

crossbedding and consists mainly of fine-grained phyllitic white mica and 

calcite enclosing granular quartz and epidote. Major minerals are quartz, 

calcite, epidote, and white mica. Minor minerals are chlorite, graphite, sphene, 

tourmaline, and opaque minerals. Unit contains sparse relict angular quartz 

grains. Unit locally grades into calcareous sandstone. Locally contains sparse 

quartz pebbles 

Unit also contains local fine- to medium-grained, light- to dark-gray 

limestone composed mainly of calcite and minor dolomite. Local abundant 

corals. Local sparse grains of quartz and variable amounts of graphite 

wa Andesite, dacite, and volcanic graywacke (Cretaceous)—Chiefly andesite 

composed of phenocrysts of plagioclase, to 1.0 mm long, and sparse quartz 

and biotite in groundmass composed predominantly of plagioclase and minor 

calcite, epidote, chlorite, white mica, and opaque minerals. Dacite composed 

of phenocrysts of quartz, plagioclase, and biotite to 1.0 mm across in 

groundmass of plagioclase microlites with epidote, white mica, and opaque 

minerals. Exhibits relict fine-grained igneous textures. Plagioclase and 

K-feldspar are partially replaced by white mica. Unit also contains minor 

dacite and volcanic graywacke 

wg Metagraywacke and lesser phyllite (Cretaceous)—Chiefly angular clasts of quartz, 

plagioclase, and, locally, K-feldspar, to 0.4 mm, in matrix of sparse, very fine 

grained quartz, white mica, and calcite. Plagioclase clasts are locally twinned 

and zoned. Minor minerals are epidote, biotite, chlorite, sphene, and opaque 

minerals 

Unit also contains local conglomerate composed of medium- to 

coarse-grained, angular fragments of argillite, silty argillite, chert, and 

metavolcanic graywacke in a matrix of very fine grained quartz and mica. 

Relict radiolarians occur in chert clasts. Sandstone composed of fine- to 

medium-grained, subangular grains of quartz in a fine-grained matrix 

predominantly of sericite. Plagioclase and K-feldspar are partially replaced by 

white mica 
23

MACLAREN TERRANE—SOUTH OF DENALI FAULT AND NORTH OF BROXSON 

GULCH THRUST 

The Maclaren terrane occurs in the southeast corner of the map, south of the Denali Fault. The 

terrane consists of two major units: (1) the penetratively deformed and regionally metamorphosed 

granitic plutonic rocks of the East Susitna batholith to the north and (2) the schist, amphibolite, phyllite, 

argillite, and metagraywacke of the Maclaren Glacier metamorphic belt to the south (Nokleberg and 

others, 1982, 1985, 1989, 1992b). The contact between the East Susitna batholith and the Maclaren 

Glacier metamorphic belt is a faulted intrusive contact named the Meteor Peak Fault (Nokleberg and 

others, 1982, 1985, 1992b). 

The Maclaren terrane is interpreted as a tectonically detached part of a prograde Barrovian-type 

metamorphic belt and a companion composite continental-margin arc batholith, both intensely 

metamorphosed and deformed (Smith and Turner, 1973; Nokleberg and others, 1985; Davidson and 

others, 1992; Nokleberg and Richter, 2007). The increase of metamorphic grade in the Maclaren Glacier 

metamorphic belt toward the East Susitna batholith indicates metamorphism occurred in response to 

syntectonic emplacement and overthrusting of the batholith. In addition, similar middle amphibolite 

facies metamorphism occurs in both the schist and amphibolite unit of the Maclaren Glacier 

metamorphic belt and the East Susitna batholith, and both contain a parallel or subparallel schistosity. 

This relation indicates that both were regionally deformed and metamorphosed together during the 

synkinematic intrusion of the batholith from the Late Cretaceous to the middle Tertiary. 

East Susitna Batholith 

mes East Susitna batholith (lower Tertiary and Upper Cretaceous)—South of Denali 

Fault and north of Meteor Peak Fault. Chiefly gneissose granodiorite and 

quartz diorite and minor granite. Fine to medium grained, with relict 

hypidiomorphic granular, seriate, and porphyritic textures containing relict 

phenocrysts of plagioclase and K-feldspar to 6 mm across. Relict igneous 

minerals are plagioclase, quartz, K-feldspar (locally perthitic), biotite, 

hornblende rimmed by biotite, and clinopyroxene rimmed by biotite and 

hornblende. Minor zircon and apatite. Relict igneous hornblende rimmed by 

igneous biotite; clinopyroxene by biotite and minor hornblende. Contains 

clinopyroxene and hornblende with poikiloblastic texture containing abundant 

inclusions of feldspar and quartz. Strong undulose extinction occurs in 

feldspar and quartz augen. Relict igneous plagioclase occurs with complex 

twinning, normal zoning, and oscillatory zoning. The gneissose granitic 

plutonic rocks of the East Susitna batholith are derived from diorite, 

granodiorite, and minor granite and locally grade into units of migmatite, 

migmatitic schist, and schist and amphibolite. The unit locally contains sparse 

crosscutting dikes of nonfoliated gabbro, diabase, rhyodacite, and rhyolite 

The unit exhibits a single pervasive schistosity that generally strikes 

northwest to southwest, dips moderately to steeply west, and parallels the 

younger structures in the schist and amphibolite unit (msh) of the Maclaren 

Glacier metamorphic belt to the south in the Mount Hayes B-6 quadrangle. 

Unit is metamorphosed at middle to upper amphibolite facies 

Three groups of isotopic ages are determined for the East Susitna 

batholith: (1) a sample of schistose quartz diorite from the batholith yielded a 

U-Pb zircon age of 70 Ma (Davidson and others, 1992), (2) various and 

abundant K-Ar ages for metamorphic biotite and hornblende range from 87.4 
24

to 29.8 Ma (Nokleberg and others, 1992a), and (3) a sample from the Valdez 

Creek tonalite in the southern part of batholith in the Healy quadrangle 

yielded U-Pb zircon ages of 64 to 60 Ma (Davidson and others, 1992; 

Ridgway and others, 2002). Several observations indicate intrusion of the 

batholith during regional deformation (syntectonic intrusion) (Nokleberg and 

others, 1985, 1992b): (1) occurrence of a parallel regional metamorphic fabric 

formed at amphibolite facies in both the East Susitna batholith and the 

structurally subjacent Maclaren metamorphic belt (described below) and 

(2) overlapping U-Pb zircon intrusive ages and the older ranges of hornblende 

and biotite metamorphic ages (Upper Cretaceous and lower Tertiary) 

Maclaren Glacier Metamorphic Belt 

The Maclaren Glacier metamorphic belt occurs to the south of the East Susitna batholith (south 

of Meteor Peak Fault and north of Broxson Gulch Thrust) and is a pro-grade Barrovian-type 

metamorphic belt. From south to north, the major units are (1) Upper Jurassic or older argillite and 

metagraywacke; (2) phyllite; and (3) quartz-mica schist, calc-schist, and amphibolite (Nokleberg and 

others, 1985, 1992b). Contacts between the three major units are faults exhibiting abundant brittle shears 

(microfaults) and abrupt changes of metamorphic facies at each surface. 

The Maclaren Glacier metamorphic belt is ductility deformed into protomylonite and phyllonite 

in the argillite and metagraywacke unit, phyllonite in the phyllite unit, and mylonitic schist in the quartzmica schist, calc-schist, and amphibolite unit. A general increase in metamorphic grade occurs from the 

argillite and metagraywacke unit in the south to the quartz-mica schist, calc-schist, and amphibolite unit 

in the north, grading from lower greenschist facies in the argillite and metagraywacke unit to lower or 

middle amphibolite facies metamorphism in the quartz-mica schist, calc-schist, and amphibolite unit 

(Nokleberg and others, 1985, 1989). 

mb Maclaren Glacier metamorphic belt (Upper Jurassic?)—Chiefly high-grade 

metasedimentary schist. Unit consists mainly of quartz-mica schist, 

amphibolite, and calc-schist. Protoliths are chiefly pelite, sandstone, 

graywacke, and minor marl, andesite, and gabbro. Grain size is 0.1 to 0.3 mm. 

Estimated structural thickness is about 6,700 m 

Quartz-mica schist consists of fine-grained white mica-quartz schist, 

biotite-white mica-quartz schist, garnet-white mica-quartz schist, biotitequartz schist, plagioclase-white mica-quartz schist, and plagioclase-chloritequartz-white mica schist. Amphibolite, derived from marl, is composed of 

schistose hornblende, garnet, biotite, quartz, plagioclase, and calcite. Unit is 

metamorphosed to amphibolite facies 

Unit is intensely deformed with a strong schistosity. Two generations 

of isoclinal folds occur with opposite vergences, with axial planes parallel to 

schistosity. Older generation folds generally show north vergence, whereas 

younger generation folds generally show south vergence 

A latest Cretaceous to lower Tertiary age of regional metamorphism 

for the Maclaren Glacier metamorphic belt is indicated by (1) K-Ar 

hornblende and biotite ages ranging from 64.1 to 28.5 Ma (Nokleberg and 

others, 1992a) and (2) 40Ar/39Ar plateau ages of 69 to 60 Ma for metamorphic 

biotite in the highest-grade part of the metamorphic belt (schist and 

amphibolite unit) in the Healy quadrangle (Davidson and others, 1992; 

Ridgway and others, 2002). The latter data indicate that regional 
25

metamorphism and deformation of the metamorphic belt ended at about 

62 Ma (Davidson and others, 1992; Ridgway and others, 2002) 

WRANGELLIA TERRANE 

The Wrangellia terrane occurs in the southeast corner of the map and is faulted against the 

Maclaren terrane to the north along the Broxson Gulch thrust. 

In the map area, the Wrangellia terrane contains only three units: (1) a unit of ultramafic plutonic 

rock; (2) a unit of gabbro and metagabbro; and (3) the Slana Spur Formation. The unit of ultramafic 

plutonic rock may be fault-bounded slices juxtaposed along the Broxson Gulch thrust or may be derived 

from the base of the Wrangellia terrane. The unit of gabbro and metagabbro may have similar origins or 

may be part of the late Paleozoic Skolai island arc that formed the volcanoclastic and volcanic rocks of 

the Slana Spur Formation or may be related to extrusion of basalt that formed the Middle to Upper 

Triassic Nikolai Greenstone. 

In the map area, three major geologic events occurred in the origin and evolution of the 

Wrangellia terrane. The first event was formation of the Upper Paleozoic submarine volcanic, 

sedimentary, and plutonic rocks of the Skolai arc (Bond, 1973, 1976; Richter and Jones, 1973; 

Nokleberg and others, 1985; Barker and Stern, 1986; Nokleberg and Richter, 2007). The second event is 

interpreted as back-arc rifting that formed the Upper Triassic Nikolai Greenstone and associated gabbro 

dikes and cumulate mafic and ultramafic sills (Richter and Jones, 1973; Jones and others, 1987; 

Nokleberg and others, 1985; Nokleberg and Richter, 2007). The third event was formation of a marginal 

flysch basin in which the Upper Jurassic and Lower Cretaceous argillite, graywacke, conglomerate, and 

andesite of the Gravina-Nutzotin belt was deposited onto the northern edge of the Wrangellia terrane 

(Berg and others, 1972; Richter and Jones, 1973; Nokleberg and others, 1985; Nokleberg and Richter, 

2007). 

wrum Ultramafic plutonic rock (Cretaceous to Triassic?)—Chiefly dunite, olivineclinopyroxene cumulate, serpentinite, metagabbro, and metadiabase. 

Ultramafic rocks contain both cumulate and metamorphic textures and are 

interpreted as a dismembered alpine peridotite. Relations of the mafic rocks to 

the ultramafic rocks is unclear. Relatively younger mafic dikes locally intrude 

the alpine peridotite and may be part of the unit of gabbro, diabase, and 

metagabbro (wrgm) that intrudes Upper Triassic and older rocks throughout 

the Wrangellia terrane. Structural thickness is estimated at about 1,500 m. 

Olivine is partially to completely replaced by serpentine; pyroxene, 

hornblende, and biotite by chlorite 

wrgb Gabbro and metagabbro (Cretaceous to Triassic?)—Metagabbro composed 

principally of fine- to medium-grained, diabasic-texture hornblende 

metagabbro and minor hornblende-clinopyroxene metagabbro and 

clinopyroxene metagabbro. A relict fine- to medium-grained, hypidiomorphic 

granular and lesser subophitic texture occurs locally. Relict minerals are 

hornblende, plagioclase, clinopyroxene, olivine, quartz, biotite, ilmenite, and 

opaque minerals. Metagabbro and metadiabase are variably metamorphosed at 

lower greenschist facies. Relict minerals are plagioclase, clinopyroxene, and 

hornblende. Metadiabase is composed of hornblende-plagioclase metadiabase 

and clinopyroxene-plagioclase metadiabase 

wrs Slana Spur Formation (Lower Permian to Middle Pennsylvanian)—Chiefly 

calcareous and volcaniclastic rocks composed of a thick sequence of marine 

calcareous and noncalcareous volcaniclastic rocks and lesser limestone, tuff, 

and volcanic breccia. Occurs in the southeastern and south-central parts of the 
26

Mount Hayes quadrangle. Ages of megafossils and microfossils in both 

members of formation, mainly brachiopods, corals, and foraminifers, range 

from Middle Pennsylvanian through Lower Permian (Nokleberg and others, 

1992a, table 1, localities 13–16, 52–57, 59–63, 65–69, 71–72, 76, 86, 107–

108). Thickness of unit is estimated at 700 to 1,400 m. Unit exhibits lower 

greenschist facies metamorphism and is locally intruded by diabase and 

andesite dikes, sills, and small plutons 

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30

Figure 1. Representative images and SHRIMP U-Pb data from zircon from plutonic rocks near the Hines Creek 

fault zone. White-filled error-ellipses are U-Pb data used to calculate the weighted average age (see inset). 

Gray error ellipses are U-Pb data excluded from age calculation. A, CL images of zircon from 10ANK001 

(leucodiorite). B, Tera-Wasserburg plot of SHRIMP data from 10ANK001. Only data from cores used in age 

calculation. Unfilled ellipses with dashed borders are data from dark (in CL) tips of grains. C, CL images of 

zircon from 10ANK004 CL images of zircon from 10ANK004 (porphyritic granodiorite). D, Tera-Wasserburg plot 

of SHRIMP data from 10ANK004 (porphyritic granodiorite). 
31

Table 1. SHRIMP U-Th-Pb data for zircon from two granitic plutons near the Hines Creek Fault, Alaska. 

[---, not measured]

___________________________________________________________________________________________________________________________________________________ 

Sample1 Measured Measured % Ages (Ma) 

(Location) 204Pb 207Pb common U Th/U 206Pb2 err3

 238U4 err3 207Pb4 err3

 206Pb 206Pb 206Pb (ppm) 238U 206Pb (%) 206Pb (%)

___________________________________________________________________________________________________________________________________________________

10ANK001-1ozc -0.000026 0.0458 -0.27 1066 0.216 99.4 2 64.5 1.9 0.0462 4.9

10ANK001-2ozc 0.000123 0.0459 -0.25 856 0.246 89.4 1 72.0 1.5 0.0440 5.3

10ANK001-3ozc -0.000028 0.0498 0.25 1093 0.154 91.7 1 69.6 1.5 0.0502 4.6

10ANK001-4ozc 0.000138 0.0488 0.12 810 0.216 92.2 1 69.5 1.5 0.0468 5.7

10ANK001-5uzt 0.000147 0.0477 -0.04 1086 0.215 100 2 64.0 1.6 0.0455 5.5

10ANK001-6ozc -0.000085 0.0557 0.98 779 0.211 96.7 2 65.4 1.7 0.0570 5.3

10ANK001-7ozc 0.000149 0.0500 0.25 539 0.193 96.5 2 66.3 1.7 0.0478 6.8

10ANK001-8ozc 0.000138 0.0514 0.43 1363 0.178 96.0 1 66.6 1.5 0.0493 4.6

10ANK001-9uzt -0.000038 0.0445 -0.44 1894 0.111 99.1 2 64.8 1.6 0.0450 4.2

10ANK001-10ozc --- 0.0482 0.03 568 0.290 98.5 2 64.9 1.7 0.0482 6.2

10ANK001-11ozc -0.000187 0.0440 -0.49 610 0.196 93.6 1 68.4 1.5 0.0468 6.8

10ANK001-12ozc 0.000045 0.0435 -0.57 650 0.198 98.2 4 65.6 3.6 0.0428 6.9

10ANK001-13ozc 0.000126 0.0481 0.03 1072 0.243 94.5 1 67.8 1.5 0.0463 5.6

10ANK001-14uzt --- 0.0501 0.28 1317 0.136 92.6 1 68.9 1.5 0.0501 4.0

10ANK001-15ozc 0.000044 0.0460 -0.24 635 0.215 91.9 1 69.8 1.5 0.0453 6.3

10ANK001-16uzt -0.000045 0.0487 0.12 2008 0.095 90.4 1 70.7 1.5 0.0494 3.8

10ANK001-17ozc --- 0.0472 -0.09 675 0.191 96.0 2 66.7 1.7 0.0472 6.1

10ANK001-18ozc 0.000130 0.0482 0.04 910 0.253 92.6 1 69.2 1.5 0.0463 5.0

10ANK001-19uzt 0.000370 0.0574 1.20 1192 0.142 93.4 1 68.2 1.5 0.0520 4.8

10ANK001-20ozc --- 0.0477 -0.04 717 0.181 98.7 2 64.9 1.7 0.0477 9.9

10ANK001-21ozc 0.000147 0.0452 -0.34 618 0.197 92.5 1 69.6 1.5 0.0430 7.5

10ANK001-22ozc 0.000291 0.0501 0.27 644 0.179 95.2 4 67.4 4.2 0.0458 7.3

10ANK004-1ozc 0.000159 0.0508 0.36 1011 0.304 96.0 2 66.6 1.6 0.0485 5.5

10ANK004-2ozc 0.000040 0.0494 0.18 664 0.274 98.5 2 64.9 1.7 0.0488 5.6

10ANK004-3ozc 0.000085 0.0506 0.34 636 0.269 95.2 2 67.1 1.7 0.0493 6.0

10ANK004-4ozc -0.000060 0.0479 -0.01 939 0.278 98.4 2 65.0 1.6 0.0488 5.0

10ANK004-5ozc -0.000042 0.0477 -0.04 684 0.303 101 2 63.2 1.7 0.0483 2.9

10ANK004-6ozc --- 0.0444 -0.43 744 0.351 92.0 1 69.9 1.5 0.0444 5.6

10ANK004-7ozc -0.000038 0.0433 -0.59 736 0.262 99.0 2 64.9 2.0 0.0438 5.9

10ANK004-8ozc 0.000069 0.0462 -0.23 875 0.259 99.6 2 64.5 2.1 0.0452 5.9

10ANK004-9ozc -0.000034 0.0467 -0.15 952 0.285 94.2 1 68.0 1.5 0.0472 5.4

10ANK004-10ozc -0.000145 0.0448 -0.41 608 0.273 102 2 62.7 1.7 0.0469 3.8

10ANK004-11ozc --- 0.0526 0.58 518 0.298 96.4 3 66.0 2.8 0.0526 6.1

10ANK004-12ozc --- 0.0465 -0.18 725 0.305 97.9 3 65.4 2.8 0.0465 5.3

10ANK004-13ozc 0.000152 0.0471 -0.10 804 0.273 93.7 1 68.5 1.5 0.0449 5.7

10ANK004-14ozc -0.000158 0.0521 0.53 623 0.277 94.7 4 67.1 4.6 0.0544 5.5

10ANK004-15ozc -0.000059 0.0464 -0.20 975 0.265 98.9 3 64.8 3.2 0.0472 5.2

10ANK004-16ozc 0.000128 0.0492 0.18 579 0.260 90.6 1 70.7 1.6 0.0473 6.4

10ANK004-17ozc 0.000144 0.0496 0.22 752 0.265 92.3 1 69.4 1.5 0.0475 3.5

10ANK004-18ozc 0.000160 0.0459 -0.26 524 0.245 99.1 2 64.9 1.7 0.0436 7.9

___________________________________________________________________________________________________________________________________________________

1 Samples analyzed September 2011 by USGS/Stanford SHRIMP-RG. Abbreviations: ozc, oscillatory-zoned core; uzt, unzoned tip. 2 206Pb/238U ages corrected for common Pb using the 207Pb-correction method. Decay constants from Steiger and Jäger (1977). 3

 1-sigma errors. 4

 Radiogenic ratios, corrected for common Pb using the 204Pb-correction method, based on the Stacey and Kramers (1975) model.