! 2005 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org.Geology; December 2005; v. 33; no. 12; p. 937–940; doi: 10.1130/G21856.1; 3 figures. 937

Large-scale pseudotachylytes and fluidized cataclasites from anancient subduction thrust faultChristen D. RoweJ. Casey Moore

Earth Science Department, University of California–Santa Cruz, 1156 High Street, Santa Cruz, California95064, USA

Francesca Meneghini Dipartimento di Scienze della Terra, Universita di Pisa, via S. Maria, 53, 56126 Pisa, ItalyAlexander W. McKeirnan Department of Geosciences, Pennsylvania State University, 320 Deike Building, University Park,

Pennsylvania 16802, USA

ABSTRACTIn the Kodiak accretionary complex, Kodiak Island, Alaska, pseudotachylyte occurs in

black, locally vitreous ultrafine-grained fault rock. Microscopic observations show thatthe pseudotachylytes are composed of glass, with vesicles, amygdules, microlites, and flowstructures, indicating a frictional melt. The pseudotachylyte is gradational to cataclasiteand shows outcrop-scale injection and ductile deformation structures. The cataclasite wasductily mobile (i.e., fluidized) simultaneous with the formation and emplacement of pseu-dotachylyte melt. The pseudotachylytic rocks postdate the stratal disruption fabric of as-sociated shear-zone melanges and show similar direction of thrust transport, and haveundergone limited subsequent deformation. We interpret the stratal disruption as result-ing from underthrusting of the subducting plate and pseudotachylyte development as thefinal activity of this thrust surface. The gradational contacts between pseudotachylyte andcataclasite demonstrate that the cataclasite also formed as a seismic product and mayrepresent paleoseismic rupture zones, possibly of very great earthquakes, with or withoutaccompanying pseudotachylytes. The pseudotachylytes are voluminous, and many are spa-tially disconnected from generation surfaces. This style is distinct from pseudotachylytesdescribed in other environments, and this may explain the rarity of documented examplesof subduction-thrust pseudotachylyte.

Keywords: pseudotachylyte, Kodiak accretionary complex, subduction thrust, paleoseismicity,fluidized gouge, cataclasite.

INTRODUCTIONSubduction thrust faults generate the

world’s largest earthquakes and are the site of!90% of global moment release (Pacheco etal., 1993). Studies of exhumed subductioncomplexes provide the only means of geolog-ically observing the seismogenic zone. How-ever, explicit geological evidence of paleo-seismicity in subduction-zone rocks exhumedfrom seismogenic depths has been elusive.Fisher and Byrne (1987) recognized that me-lange zones preserved in accretionary prismsrepresent ancient subduction thrust faults.However, deformation in these systems isbroadly distributed. Ikesawa et al. (2003),Austrheim and Andersen (2004), and Kita-mura et al. (2005) discovered direct evidenceof paleoseismicity as frictional melts or pseu-dotachylytes in ancient subduction thrustfaults. These pseudotachylytes satisfy thestrictest criteria for identifying paleoseismicity(Cowan, 1999). Pseudotachylyte-bearingfaults are uniquely able to record dynamicrupture processes during earthquakes(Bjørnerud and Magloughlin, 2004; Lan-Binet al., 1997) . Given that the majority of mod-ern subduction zones are seismogenic, directevidence of paleoseismicity seems strangelyabsent in the rock record.

PseudotachylytesMany pseudotachylytes are associated with

cataclasites, suggesting that ultracomminutionis a stage in the development of pseudotachy-lyte, and possibly a necessary precursor(Bjørnerud and Magloughlin, 2004; Mag-loughlin, 1992; Spray, 1995). It is the generalconsensus that both ultracataclasis and fric-tional melting play a role in pseudotachylyteformation (Magloughlin, 1992), and that pseu-dotachylytes are formed exclusively duringseismic slip (Sibson, 1975). Otsuki et al.(2003) documented association of cataclasiteand pseudotachylyte horizons in the Nojimafault zone over millimeter scales, reinforcingthe genetic relationship between cataclasis andmelting.

GEOLOGIC SETTINGThe Kodiak accretionary complex (Fig. 1)

comprises a mid-Mesozoic to early Tertiaryaccretionary prism constructed of accreted,NW-dipping, thrust-bounded units. These rockunits are progressively younger toward thesoutheast, with modern equivalents forming inthe Aleutian Trench (Plafker et al., 1994).Decollement-system thrust faults are pre-served in several accreted units, recording the

history of the decollement during its activityat some discrete depth (Fisher and Byrne,1987).The structurally lowest part of the Paleo-

cene Ghost Rocks Formation of the accretion-ary complex is an argillaceous melange andFisher and Byrne’s (1987) prime example ofa decollement zone. We have studied this me-lange at Pasagshak Point, where it primarilyconsists of variably disrupted turbiditic argil-lites with a few continuous massive sand-stones ("10 m thick). Prehnite-pumpellyitefacies greenstones occur locally (Fig. 1). Wa-ter and methane fluid inclusions in synmel-ange quartz veins indicate melange formationat depths of 12–14 km and temperatures of230–260 #C (Byrne, 1984; Rowe et al., 2002;Vrolijk et al., 1988). As the melange forma-tion occurred before, during, and up to basalaccretion of the unit (Byrne, 1984), this is tak-en as an estimate of minimum burialconditions.

SHEAR ZONES AND ULTRAFINE-GRAINED FAULT ROCKS: FIELDRELATIONSThe melange of Pasagshak Point includes at

least three 5–15-m-thick shear zones that aresubparallel to local fabric (Figs. 1 and 2). Theshear zones are characterized by argillite ma-trix with pervasive scaly fabric, containing ro-tated and rounded sandstone boudins, andstrong downdip lineations on both matrix pha-coids and sandstone boudins (shear-zone fab-ric; Figs. 2A, 2B). Extensional veins existwithin clasts and fabric-parallel veining israre. Sandstone clasts vary from submillimeterto 10 cm along fabric strike, and up to 20 cmdown fabric dip. These shear zones are in asense ‘‘micromelange,’’ but are easily distin-guished from background argillite-matrix me-lange by a more pervasive shear fabric, androunding, smaller scale, and rotation of sand-stone clasts (Figs. 2A, 2B). One shear zone isexposed for 1 km along strike and can be cor-related for a total of 3 km along strike. Its basegrades into disrupted argillite with variablesandstone bed fragments and boudins. The up-per surface of this most continuous shear zonefollows the base of a massive sandstone layer.Dark gray to black, locally vitreous,

938 GEOLOGY, December 2005

Figure 1. A: Geologic map of Kodiak Islands showing seaward-younging Mesozoic andCenozoic accretionary prism. B–C: Geologic map and cross-section detail Paleocene argil-laceous melange identified as subduction decollement (Fisher and Byrne, 1987). Disruptedsandstone and greenstone units in argillite matrix are cut by more continuous shear zonesand ultrafine-grained fault rock intervals. D: Equal-area lower-hemisphere projection showscontoured poles to NW-dipping melange foliation (N ! 51, contoured at 2%/1% area). Foldaxes and S-C intersections from melange and shear zones indicate NW underthrusting oflower plate; great circle (dashed) with northwesterly trending line separates fields of alter-nate fold and S-C asymmetry (Hansen, 1971). Mean value of shear indicators from ultrafine-grained fault rock nearly coincides with separation line showing kinematic consistency ofmelange and shear-zone deformation, and slip on ultrafine-grained fault zones. Where vis-ible, steps on slickenlines bounding ultrafine-grained fault rock show underthrusting to NW,similar to melange and shear-zone deformation. Image was plotted with Stereonet by R.Allmendinger.

ultrafine-grained fault rock crosscuts andintrudes the shear zones. The base of theultrafine-grained layers is sharp and cutsshear-zone scaly fabric at a low (!20#) angle(Figs. 2A–2C). Outcrops show intrusive sills,dikelets, and flow structures, some of whichresemble flame structures. These intrusivestructures often deform the shear-zone fabricaround them (Figs. 2B, 2C). Asymmetricaland sheath folds of the ultrafine-grained faultrock occur along contacts of, and within, theshear zones (Fig. 2C). The massive ultrafine-grained fault rock frequently shows blocky,layer-perpendicular jointing (Figs. 2A, 2C).The structurally highest and most continuousexample occurs at the top of the most contin-uously mapped shear zone, just below a mas-sive sandstone (Fig. 1). The ultrafine-grainedfault rock layers sometimes occur singly (Fig.2A), sometimes as a double horizon encasingvariably organized fabric of mixed lithologicmaterial, or are overlain by horizons that aretransitional to a shear zone and characterizedby flow-banding folds (Fig. 2C).

MICROSCOPIC OBSERVATIONS ANDCLASSIFICATION OF ULTRAFINE-GRAINED FAULT ROCKSUltrafine-grained fault rocks contain pre-

dominantly quartz, feldspar, illite, and chlo-

rite. Quartz and feldspar matrix grains aregenerally 300 $m or smaller in diameter. Thefabric is characterized by unsorted grains ofquartz and feldspar in a microaphanitic matrix(microaphanitic is used here as a nongeneticterm for microscopically irresolvable faultrock). The matrix grades from very finegrained chlorite % clays to completely mi-croaphanitic matrix (Fig. 3A). Where grainsare discernable, the matrix varies from slightlyfoliated chlorite and/or clay to a random fabricmat of lathes.

Overall AppearanceThe optical appearance of the microaphan-

itic fault rocks varies. Some samples havefine, patchy birefringence textures due to veryfine grained chlorite, clay, and quartz. Othersare opaque, even in overly thin sections (sub–30 $m thickness). In some layers, the concen-tration of clastic material is so great and thematrix so opaque as to obscure the nature ofthe groundmass.

Vesicles and AmygdulesRare vesicles and amygdules occur in the

most fine-grained matrix (Fig. 3B). They arevery small, isolated, and subspherical (aspectratio " 1/3). Rarely, radiating cracks extend

outward from the vesicle walls. Some are par-tially to totally infilled with quartz, calcite, py-rite, and/or apatite.

Rounded GrainsRounded grains are plentiful within apha-

nitic horizons (Figs. 3A, 3C, 3D); the bound-aries of dominantly aphanitic horizons are of-ten gradational into cataclasite, where grainproportion increases over 1 mm or less from&10% to near 100% of the rock. In the mi-croaphanitic regions, rounded grain popula-tions are entirely quartz, but where grain pop-ulation increases, grains become more angular,and feldspar grains become more common.

Oxide and Sulfide CrystalsThe aphanitic rocks are generally free of

microlite crystals. The exceptions are skeletalpyrite grains, and tiny spherical grains or nod-ules of titanium oxide and zinc sulfide, whichoccur in scattered clusters or rows of sub-spherical grains within the aphanitic matrix(Fig. 3C). Rutile is extremely rare as a detritalmineral in the wall rock, and sphalerite hasnever been observed elsewhere in the rocks.Pyrite occurs in the host rock in detrital andauthigenic fragments, but the grain size in thehost argillite and shear zone is very small,while the skeletal and framboidal grains foundin the ultrafine-grained fault rocks are an orderof magnitude larger (Fig. 3D).

Interpretation and Identification ofPseudotachylyteMany of the features described here are

consistent with previously reported observa-tions of melt-derived pseudotachylyte, andhold some clues to the conditions under whichmelting occurred. The microaphanitic faultrock material is interpreted to be pseudotachy-lyte glass, which is variably devitrified. Theamygdules are identified as mineral-filled ves-icles formed during cooling of pseudotachy-lyte glass immediately after formation (Mad-dock et al., 1987). Amygdule mineral growthmay or may not have been coeval with thedevelopment of veins in fine extensionaljoints, which also characterize the glassiestlayers of the fault rock.The rounded grains observed in the apha-

nitic groundmass are interpreted to be survi-vor grains. This interpretation is supported bythe mineralogy (quartz is more refractory thanmicas and clays, which dominate source rock)and the smooth rounding of grains, distinctfrom the angular shape of detrital grains in thesource rock and crushing-derived grains in thecataclasite. The pattern of rounded quartzgrains within a microaphanitic layer, gradingto increasingly angular grains of less refrac-tory minerals (feldspars, clasts of older pseu-dotachylyte), is consistent with the pattern ob-served by Otsuki et al. (2003) in variably

GEOLOGY, December 2005 939

Figure 2. Field photos of ultrafine-grained fault rock within shear zones. A: Field photo andsketch of cherty massive blocky pseudotachylyte. Pseudotachylyte cuts earlier melangefabric at low angle (indicated by tip of pencil). Boundaries are sharp and semiplanar. B:Field photo and sketch of fluidized intrusion of ultrafine-grained fault rock. Large dike feedsseveral smaller sills. Shear-zone fabric is deformed (curved white arrows) by upward intru-sions, suggesting mobility of shear-zone fabric during intrusion event. Basal layer cutsbackground shear-zone fabric at low angle and may be rupture surface where ultrafine-grained material was generated. Sills in upper part of intrusion penetrate along shear-zonefoliation (black arrows), suggesting that foliation surfaces were weak during intrusion. C:Field photo and sketch of massive blocky pseudotachylyte layers (white arrows) with foldedcataclasite layers (dotted white lines indicate axial trace). Asymmetrical folds are seawardvergent, consistent with overall vergence of shear zones and surrounding melange. Baseof blocky pseudotachylyte layer crosscuts shear fabric at low angle.

Figure 3. Microphotographs of ultrafine-grained fault rock. A: Photomicrograph ofglass-fluidized cataclasite contact. Lowerlight colored material is translucent brownpseudotachylyte glass. Note fiamme-like flu-idly folded shard of banded glass. This ma-terial grades upward to increasing concen-trations of quartz and glass clasts,increasing angularity, and eventually to ca-taclasites at top of image. Large angularclast of glass is included at top in cataclas-ite. Plane polarized light. B: Vesicle alongboundary between clast-poor pseudotachy-lyte and cataclasite. Vesicle rim is coated inapatite. Vesicle is empty; bright specks in-side vesicle are bits of dust caught in thin-section cement. Backscattered-electron(BSE) image. C: Linear train of TiOx beads(white arrows) in pseudotachylyte glassvein in cataclasite (white brackets) (BSE). D:Skeletal pyrite grain grown along similarboundary to that shown in C. Pyrite hasgrown around quartz survivor grains inglass matrix (BSE).

melted gouge from the Nojima fault zone. Thegradational transition between glass-rich, toglass-matrix, to clast-dominated cataclasites(i.e., Fig. 3A) is similar to that described byBerlenbach and Roering (1992).The oxide and sulfide mineral grains are

distinct from any in the source rock, either bymineralogy (rutile, sphalerite) or by grain sizeand morphology (coarse skeletal pyrite).Therefore it is likely that these grains are en-demic to the ultrafine-grained fault rocks, andthat they originated by crystallization from amelt. Skeletal pyrite grains from pseudotachy-lytes may be indicative of crystallization froma melt. The isotropic, aphanitic ultrafine-

grained rocks, which display vesicles, roundedsurvivor grains, skeletal pyrite, and metallicmicrolites, are consistent with the identifica-tion of pseudotachylyte.

DISCUSSIONGlobally, the upper limit of seismicity in

subduction zones varies in depth, but roughlycorrelates with the 100–150 #C isotherm inthermal models (Hyndman et al., 1997; Oles-kevich et al., 1999). This locality, as well asthe Japanese subduction thrust pseudotachy-lyte locality (Ikesawa et al., 2003), likelyformed in the middle to upper seismogeniczone, while the Corsican locality likely

formed in the brittle-ductile transition zone(Austrheim and Andersen, 2004; Hyndman etal., 1997). It has been suggested that pseudo-tachylyte formation is restricted to dry faults(Bjørnerud and Magloughlin, 2004; Sibson,1975), because the presence of water could lu-bricate the fault and/or act as a heat sink andprevent the heat buildup needed to cause fric-tional melting during earthquakes. In contrast,calculations by Dixon and Dixon (1989) dem-onstrated that the presence of vesicles in amelt requires entraining of available volatilesduring pseudotachylyte cooling, because thereis insufficient time to nucleate bubbles by de-gassing, as previously suggested (Maddock etal., 1987). O’Hara and Sharp (2001) demon-strated that microlite isotopic compositions re-quired melt-groundwater interaction duringpseudotachylyte formation.The thickness of the Kodiak pseudotachy-

940 GEOLOGY, December 2005

lytes (! !10 cm) exceeds predications for themaximum melt thickness that could be pro-duced on a single surface (!1 cm), as meltproduction is modeled as inherently self-limiting (McKenzie and Brune, 1972). Workby Di Toro et al. (2005) suggests that a thick-ness of 2–3 cm could be correlated to coseis-mic slip of !10 m, so by that relation, a10-cm-thick fault vein would require extraor-dinarily large slip. It is possible that this con-flict could be resolved by considering at leastthree factors: (1) the thick pseudotachylyteveins that are dense with survivor grains con-tain less melt than a completely glass vein ofthe same dimension, (2) melting of phyllosil-icate source rocks may require less energyconsumption (lower heat capacity) than themodels assumed, and (3) even pseudotachy-lyte fault veins that are semiplanar for tens orhundreds of meters could represent accumu-lated melt from a larger generation plane thathas ponded locally. Despite these qualifica-tions, the very thick pseudotachylytes fromthe Kodiak Islands may well be the productsof great earthquakes, which would be expect-ed in this environment.Dixon and Dixon (1989) showed that the

residence time of thin tabular bodies of silicatemelt is short (seconds to hours). Flow bandingand intercalation with fluidized gouge and en-trainment of volatiles and clasts must have im-mediately followed melt generation and there-fore occurred during or immediately afterseismic rupture. This association requires thatthe transiently fluidized cataclasite is an earth-quake product, formed in the same environ-ment as, and adjacent to, the frictional meltingthat formed the pseudotachylyte. This deter-mination does not require that all cataclasiteshave a seismic origin, but demonstrates thepossibility that cataclasite could be a seismicsignature in the rock record (Otsuki, 2003).

CONCLUSIONSThe Pasagshak Point locality hosts the

thickest and most voluminous subductionthrust pseudotachylytes described to date. Theflow-banded bodies indicate that considerablevolumes of frictional melt and ultracataclasiticmaterial were rapidly created during seismicrupture. Pseudotachylyte was likely producedin a wet fault, suggesting that the contentionthat pseudotachylytes form in dry faults mayhave some exceptions. The pseudotachylytecrosscuts background scaly fabric of a shearzone at a low angle; therefore, it formed by aseismic event that postdated slower stratal dis-ruption processes, which characterize the pre-existing melange and shear zones. The lack ofsignificant overprinting deformation suggeststhat the pseudotachylyte formation was fol-lowed by transfer to a lower strain-rate envi-

ronment, probably the upper plate of the sub-duction thrust. The recognition of thispseudotachylyte occurrence style widens ourunderstanding of the record of paleoseismicityin subduction zones. Such deformationallylate, outcrop-scale fluidization structures mayindicate paleoseismicity in accretionaryprisms, even in the absence ofpseudotachylyte.

ACKNOWLEDGMENTSWe thank Alan Rempel for discussions on the

thermodynamics of frictional melting. We appreci-ate the helpful comments of Gaku Kimura, YuzuruYamamoto, and an anonymous reviewer that sub-stantially improved this manuscript. The Institute ofGeophysics and Planetary Physics at the Universityof California–Santa Cruz provided assistance forfield logistics. This work was supported by the Na-tional Science Foundation grant OCE-0203664.

REFERENCES CITEDAustrheim, H., and Andersen, T.B., 2004, Pseudo-

tachylytes from Corsica: Fossil earthquakesfrom a subduction complex: Terra Nova,v. 166, p. 193–197.

Berlenbach, J.W., and Roering, C., 1992, Sheath-fold-like structures in pseudotachylytes: Jour-nal of Structural Geology, v. 14, p. 847–856,doi: 10.1016/0191-8141(92)90045-X.

Bjørnerud, M.G., and Magloughlin, J.F., 2004,Pressure-related feedback processes in thegeneration of pseudotachylytes: Journal ofStructural Geology, v. 26, p. 2317–2323, doi:10.1016/j.jsg.2002.08.001.

Byrne, T., 1984, Early deformation in melange ter-ranes of the Ghost Rocks Formation, KodiakIslands, Alaska, in Raymond, L.A., ed., Me-langes; their nature, origin and significance:Geological Society of America Special Paper198, p. 21–51.

Cowan, D.S., 1999, Do faults preserve a record ofseismic slip? A field geologist’s opinion: Jour-nal of Structural Geology, v. 21, p. 995–1001,doi: 10.1016/S0191-8141(99)00046-2.

Di Toro, G., Pennacchioni, G., and Teza, G., 2005,Can pseudotachylytes be used to infer earth-quake source parameters? An example of lim-itations in the study of exhumed faults: Tec-tonophysics, v. 402, p. 3–20.

Dixon, J.E., and Dixon, T.H., 1989, Vesicles,amygdules and similar structures in fault-generated pseudotachylytes: Comment: Lith-os, v. 23, p. 225–229, doi: 10.1016/0024-4937(89)90007-8.

Fisher, D., and Byrne, T., 1987, Structural evolutionof underthrusted sediments, Kodiak Islands,Alaska: Tectonics, v. 6, p. 775–793.

Hansen, E.C., 1971, Strain facies: New York,Springer-Verlag, 207 p.

Hyndman, R.D., Yamano, M., and Oleskevich,D.A., 1997, The seismogenic zone of subduc-tion thrust faults: The Island Arc, v. 6,p. 224–260.

Ikesawa, E., Sakaguchi, A., and Kimura, G., 2003,Pseudotachylyte from an ancient accretionarycomplex; evidence for melt generation duringseismic slip along a master decollement?: Ge-ology, v. 31, p. 637–640, doi: 10.1130/0091-7613(2003)0312.0.CO;2.

Kitamura, Y., Sato, K., Ikesawa, E., Ikehara-Ohmori, K., Kimura, G., Kondo, H., Ujiie, K.,Onishi, C.T., Kawabata, K., Hashimoto,Y.M.H., and Masago, H., 2005, Melange and

its seismogenic roof decollment: A plateboundary fault rock in the subduction zone—An example from the Shimanto Belt, Japan:Tectonics, (in press).

Lan-Bin, S., Chuan-Yong, L., Chen, X.-D., Xiao-Ou, Z., and Mei-Xiang, B., 1997, Character-istics of fault rocks and paleo-earthquakesource along the Koktokay-Ertai fault zone,Xinjiang, China: Acta Seismologica Sinica,v. 10, p. 365–373.

Maddock, R.H., Grocott, J., and Van Nes, M., 1987,Vesicles, amygdules, and similar structures infault-generated pseudotachylytes: Lithos,v. 20, p. 419–432, doi: 10.1016/0024-4937(87)90019-3.

Magloughlin, J.F., 1992, Microstructural and chem-ical changes associated with cataclasis andfrictional melting at shallow crustal levels:The cataclasite-pseudotachylyte connection:Tectonophysics, v. 204, p. 243–260, doi:10.1016/0040-1951(92)90310-3.

McKenzie, D., and Brune, J.N., 1972, Melting onfault planes during large earthquakes: RoyalAstronomical Society Geophysical Journal,v. 29, p. 65–78.

O’Hara, K., and Sharp, Z.D., 2001, Chemical andoxygen isotope composition of natural and ar-tificial pseudotachylyte: Role of water duringfrictional fusion: Earth and Planetary ScienceLetters, v. 184, p. 393–406.

Oleskevich, D.A., Hyndman, R.D., and Wang, K.,1999, The updip and downdip limits to greatsubduction earthquakes: Thermal and structur-al models of Cascadia, south Alaska, SW Ja-pan, and Chile: Journal of Geophysical Re-search, v. 104, p. 14,965–14,991, doi:10.1029/1999JB900060.

Otsuki, K., Monzawa, N., and Nagase, T., 2003,Fluidization and melting of fault gouge duringseismic slip: Identification in the Nojima faultzone and implications for focal earthquakemechanisms: Journal of Geophysical Re-search, v. 108, p. 18 p.

Pacheco, J.F., Sykes, L.R., and Scholz, C.H., 1993,Nature of seismic coupling along simple plateboundaries of the subduction type: Journal ofGeophysical Research, v. 98, p. 14,133–14,159.

Plafker, G., Moore, J.C., and Winkler, G.R., 1994,Geology of the southern Alaska margin, inPlafker, G., and Berg, H.C., eds., The geologyof Alaska: Boulder, Colorado, Geological So-ciety of America, Geology of North America,v. G-1, p. 389–449.

Rowe, C.D., Thompson, E., and Moore, J.C., 2002,Contrasts in faulting and veining across theaseismic to seismic transition, Kodiak accre-tionary complex, Alaska: Eos (Transactions,American Geophysical Union), ConferenceProceedings, v. 83, no. 47, Fall Meet. Suppl.,Abstract T21A-1060.

Sibson, R.H., 1975, Generation of pseudotachylyteby ancient seismic faulting: Royal Astronom-ical Society Geophysical Journal, v. 43,p. 775–794.

Spray, J., 1995, Pseudotachylyte controversy: Factor friction?: Geology, v. 23, p. 1119–1122,doi: 10.1130/0091-7613(1995)0232.3.CO;2.

Vrolijk, P., Myers, G., and Moore, J.C., 1988, Warmfluid migration along tectonic melanges in theKodiak accretionary complex, Alaska: Journal ofGeophysical Research, v. 93, p. 10,313–10,324.

Manuscript received 13 May 2005Revised manuscript received 1 August 2005Manuscript accepted 5 August 2005

Printed in USA