PRELIMINARY GEOCHRONOLOGY AND GEOCHEMISTRY OF PRELIMINARY GEOCHRONOLOGY AND GEOCHEMISTRY OF THE HICKS BUTTE COMPLEX, CENTRAL CASCADES, THE HICKS BUTTE COMPLEX, CENTRAL CASCADES,

WASHINGTON: POSSIBLE LINKS BETWEEN POLYGENETIC WASHINGTON: POSSIBLE LINKS BETWEEN POLYGENETIC MESOZOIC ARC ROCKS OF THE CENTRAL CASCADES AND THE MESOZOIC ARC ROCKS OF THE CENTRAL CASCADES AND THE

BLUE MOUNTAINS PROVINCEBLUE MOUNTAINS PROVINCE

James MacDonald, Florida Gulf Coast University, James MacDonald, Florida Gulf Coast University, and Mark Pecha, University of Arizonaand Mark Pecha, University of Arizona

Geologic province sketch map Geologic province sketch map displaying the location of the displaying the location of the Washington’s Mesozoic units Washington’s Mesozoic units

south of the North Cascades with south of the North Cascades with respect to the Blue Mountains, respect to the Blue Mountains,

Klamath Mountains, and Northern Klamath Mountains, and Northern Sierra Nevada. Sierra Nevada.

Simplified geologic map Simplified geologic map displaying pre-Cenozoic displaying pre-Cenozoic tectonic elements of the tectonic elements of the central and northwest central and northwest

Cascades.Cascades.

Terranes east of the Terranes east of the Straight Creek-Fraser Straight Creek-Fraser River fault have been River fault have been

dextrally displaced to the dextrally displaced to the south. south.

Modified from Miller et al. (1993), Modified from Miller et al. (1993), Tabor (1994), and Brown and Dragovich Tabor (1994), and Brown and Dragovich

(2003) (2003)

Restoration of Restoration of northern northern

Cordillera strike-Cordillera strike-slip faulting at 100 slip faulting at 100

Ma.Ma.

BT = Baker terraneBT = Baker terraneIO = Ingalls IO = Ingalls ophioliteophiolite

Hicks Butte Hicks Butte complex would be complex would be

outboard of IOoutboard of IO

Wyld et al., 2006Wyld et al., 2006

Simplified geologic map Simplified geologic map displaying pre-Cenozoic displaying pre-Cenozoic tectonic elements of the tectonic elements of the central and northwest central and northwest

Cascades.Cascades.

Terranes east of the Terranes east of the Straight Creek-Fraser Straight Creek-Fraser River fault have been River fault have been

dextrally displaced to the dextrally displaced to the south. south.

Modified from Miller et al. (1993), Modified from Miller et al. (1993), Tabor (1994), and Brown and Dragovich Tabor (1994), and Brown and Dragovich

(2003) (2003)

Simplified geologic map displaying Simplified geologic map displaying the tectonic elements east of the the tectonic elements east of the Straight Creek fault and south of Straight Creek fault and south of the Cascades Crystalline Core. the Cascades Crystalline Core.

From the north to the south, the From the north to the south, the Late Jurassic arc rocks within Late Jurassic arc rocks within

these inliers include:these inliers include:

Hicks Butte complex Hicks Butte complex 153 ± 153 ± 2 Ma 2 Ma (Miller et al., 1993)(Miller et al., 1993)

Quartz Mountain stock Quartz Mountain stock 157.4 ± 157.4 ± 1.2 Ma 1.2 Ma (Miller et al., 1993; (Miller et al., 1993; MacDonald, 2006)MacDonald, 2006)

Indian Creek complex Indian Creek complex 154 ± 154 ± 2 Ma 2 Ma (Miller et al., 1993) (Miller et al., 1993)

Modified from Tabor et al. (1982, 1987, 1993, 2000), Miller (1985,

1989) and Miller et al. (1993)

Simplified geologic Simplified geologic map of the Hicks map of the Hicks

Butte inlier.Butte inlier.

Tonalite, diorite, and quartz diorite are the most common rock Tonalite, diorite, and quartz diorite are the most common rock types within the Hicks Butte complex. Lesser hornblende types within the Hicks Butte complex. Lesser hornblende

gabbro, dacite, and hornblendite also occur. gabbro, dacite, and hornblendite also occur.

All of these rock are deformed to gneiss or amphibolite.All of these rock are deformed to gneiss or amphibolite.

Tonalite cut by a dike of Tonalite cut by a dike of hornblende gabbrohornblende gabbro

Dacite intruding tonalite and Dacite intruding tonalite and hornblende gabbro gneiss hornblende gabbro gneiss

Tonalite gneiss cut by a Tonalite gneiss cut by a dike of hornblende gabbro dike of hornblende gabbro

gneiss -- displaying gneiss -- displaying boudinage.boudinage.

Annotated folded and Annotated folded and faulted dike of hornblende faulted dike of hornblende

gabbro that is located gabbro that is located within tonalite gneisswithin tonalite gneiss

Tonalite gneiss cut by Tonalite gneiss cut by two dikes of dacite– one two dikes of dacite– one displaying boudinage and displaying boudinage and the other slightly folded..the other slightly folded..

100 μm

Igneous zircons from Igneous zircons from a Hicks Butte a Hicks Butte

complex tonalite complex tonalite (HB-1).(HB-1).

Zircon cores typically Zircon cores typically display sector to display sector to complex zoning. complex zoning.

Rims display Rims display oscillatory zoning. oscillatory zoning.

Spots 4R and 4C Spots 4R and 4C yield Carboniferous yield Carboniferous

ages. ages.

11 igneous zircons from the tonalite yield a U-Pb age of 11 igneous zircons from the tonalite yield a U-Pb age of 150.0 ± 6.8 Ma (2σ; total error = 4.5 %; MSWD = 0.2).150.0 ± 6.8 Ma (2σ; total error = 4.5 %; MSWD = 0.2).

This This corroboratescorroborates the published date of 153 ± 2 Ma from a the published date of 153 ± 2 Ma from a tonalite gneiss from this complex (Miller et al., 1993).tonalite gneiss from this complex (Miller et al., 1993).

This sample also contains 3 concordant Paleozoic age This sample also contains 3 concordant Paleozoic age zircon spot analyses (317 ± 12; 356 ± 12; & zircon spot analyses (317 ± 12; 356 ± 12; & 464 ± 8 Ma464 ± 8 Ma).).

Igneous zircons Igneous zircons from a Hicks Butte from a Hicks Butte

complex dacite complex dacite (HB-12).(HB-12).

Zircon cores Zircon cores typically display typically display

oscillatory, sector oscillatory, sector or complex zoning. or complex zoning.

Rims display Rims display oscillatory zoning.oscillatory zoning.

Few zircons are Few zircons are not zoned.not zoned.

28 igneous zircons from the dacite yield a U-Pb age of 28 igneous zircons from the dacite yield a U-Pb age of 144.0 ± 2.4 Ma (2σ; total error = 1.7%; MSWD = 1.1).144.0 ± 2.4 Ma (2σ; total error = 1.7%; MSWD = 1.1).

Mesozoic ages in some Washington Mesozoic ages in some Washington Cascades plutonsCascades plutons

Hicks Butte inlieHicks Butte inlier r Hicks Butte complexHicks Butte complex 150 - 153 Ma U-Pb zircon 150 - 153 Ma U-Pb zircon 144 ± 2.4 Ma dacite 144 ± 2.4 Ma dacite (Miller et al., 1993; This study)(Miller et al., 1993; This study)

Manastash inlierManastash inlier Quartz Mt. stocQuartz Mt. stock k 157 Ma U-Pb zircon 157 Ma U-Pb zircon Hereford Meadow amphibolite Hereford Meadow amphibolite 143 ± 0.7 Ma Ar-Ar hbl 143 ± 0.7 Ma Ar-Ar hbl (Miller et al., 1993; MacDonald, 2006)(Miller et al., 1993; MacDonald, 2006)

Rimrock Lake inlierRimrock Lake inlier Indian Creek complexIndian Creek complex 154 Ma U-Pb zircon 154 Ma U-Pb zircon 142 ± 9 Ma K-Ar hbl 142 ± 9 Ma K-Ar hbl (Conley, 1980; Miller et al., 1993)(Conley, 1980; Miller et al., 1993)

Modified from Tabor et al. (1982, 1987, 1993, 2000), Miller (1985,

1989) and Miller et al. (1993)

Complex ranges from mafic Complex ranges from mafic to felsic in composition. to felsic in composition.

Includes dacites.Includes dacites.

All samples from the All samples from the complex are low-K, complex are low-K,

tholeiitictholeiitic

Le Maitre (2002) Compiled by Rollinson (1993)

All samples from the All samples from the complex are calciccomplex are calcic

150 Ma = metaluminous150 Ma = metaluminous

144 Ma = peraluminous144 Ma = peraluminous

Frost et al. (2001) Frost et al. (2001)

150 Ma = “normal” Sr/Y ratios150 Ma = “normal” Sr/Y ratios

144 Ma = high Sr/Y ratios of 144 Ma = high Sr/Y ratios of 197 and 419197 and 419

Samples from the complex Samples from the complex are predominantly are predominantly

magnesian. Two are magnesian. Two are ferroan.ferroan.

Frost et al. (2001) Drummond and Defant (1990)

144 MA dacite are low in Ni, Cr, and Mg#144 MA dacite are low in Ni, Cr, and Mg#

Chondrite-normalized Chondrite-normalized diagram for Hicks diagram for Hicks

Butte complex Butte complex samples.samples.

Normalization values Normalization values are from McDonough are from McDonough

and Sun (1995)and Sun (1995)

ConclusionsConclusions::

1)1)Main phase of the Hicks Butte complex is 150-153 Ma Main phase of the Hicks Butte complex is 150-153 Ma and Paleozoic xenocrystic zircons suggest that the complex and Paleozoic xenocrystic zircons suggest that the complex is not exotic to the North American cratonis not exotic to the North American craton

2)2)144 Ma high Sr/Y dacite intrudes the 150-153 Ma portion 144 Ma high Sr/Y dacite intrudes the 150-153 Ma portion of the complexof the complex

3)3)150-153 Ma preliminary geochemistry suggests partial 150-153 Ma preliminary geochemistry suggests partial melting of a hydrous depleted mantle source in an arc melting of a hydrous depleted mantle source in an arc settingsetting

4)4)Two high Sr/Y 144 Ma dacites have geochemistry that is Two high Sr/Y 144 Ma dacites have geochemistry that is consistent with partial melting of an enriched mantle consistent with partial melting of an enriched mantle source in an arc setting with garnet as a residual phase. source in an arc setting with garnet as a residual phase. Possibly low oxygen activities?Possibly low oxygen activities?

Regional linksRegional links::

1)1)Ca. Ca. 144 Ma high Sr/Y magmatism within the central 144 Ma high Sr/Y magmatism within the central Cascades is coeval to the Blue Mountains provinceCascades is coeval to the Blue Mountains province

2)2)Ca. Ca. 144 Ma high Sr/Y magmatism within the central 144 Ma high Sr/Y magmatism within the central Cascades could be related to widespread orogenic Cascades could be related to widespread orogenic thickening and partial melting that has been identified thickening and partial melting that has been identified within the Klamath and Blue Mountains (Barnes et al., within the Klamath and Blue Mountains (Barnes et al., 1996, 2006; Schwartz et al., 2011) 1996, 2006; Schwartz et al., 2011)

Discussions with Bob Miller and Joe Dragovich were of a Discussions with Bob Miller and Joe Dragovich were of a great help.great help.Josh Schwartz kindly provided a draft of his Lithos paperJosh Schwartz kindly provided a draft of his Lithos paperFunding was provided by Florida Gulf Coast University Funding was provided by Florida Gulf Coast University (MacDonald) and NSF (Pecha).(MacDonald) and NSF (Pecha).