Gregory Harper - Academia.edu (original) (raw)
Papers by Gregory Harper
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ABSTRACT
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The polygenetic Ingalls ophiolite complex in the central Cascades, Washington, is one of several ... more The polygenetic Ingalls ophiolite complex in the central Cascades, Washington, is one of several Middle to Late Jurassic ophiolites of the North American Cordillera. It consists primarily of mantle tectonites. High-temperature mylonitic peridotite, over-printed by serpentinite mélange (Navaho Divide fault zone), separates harzburgite and dunite in the south from lherzolite in the north. Crustal units of the ophiolite occur as steeply dipping, kilometer-scale fault blocks within the Navaho Divide fault zone. These units are the Iron Mountain, Esmeralda Peaks, and Ingalls sedimentary rocks. Volcanic rocks of the Iron Mountain unit have transitional within-plate– enriched mid-ocean-ridge basalt affi nities, and a rhyolite yields a U-Pb zircon age of ca. 192 Ma. Minor sedimentary rocks include local oolitic limestones and cherts that contain Lower Jurassic (Pliensbachian) Radiolaria. This unit probably formed as a seamount within close proximity to a spreading ridge. The Esmeralda Peaks...
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The Ingalls ophiolite complex, central Cascades, Washington, mainly consists of mantle-derived ul... more The Ingalls ophiolite complex, central Cascades, Washington, mainly consists of mantle-derived ultramafi c tectonite, with crustal rocks consisting of gabbro, diabase, basalt, and sedimentary rocks. The crustal rocks occur as faulted blocks within ser-pentinite mélange (Navaho Divide fault zone). Mafi c rocks in most of these blocks comprise the Late Jurassic Esmeralda Peaks unit. Herein, we defi ne an older, Early Jurassic unit within the Ingalls ophiolite complex, which we call the Iron Mountain unit. This unit occurs along the southern edge of the complex and consists domi-nantly of mafi c volcanic rocks with minor sedimentary rocks. A rhyolite within the Iron Mountain unit yields a ca. 192 Ma U-Pb zircon age, consistent with an Early Jurassic age assignment based on radiolarians in cherts. The presence of volcanic rocks that have within-plate basalt magmatic affi nities and oolitic limestone suggests that the Iron Mountain unit formed as a seamount. Magmatic affi nities range fr...
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The Ingalls Ophiolite Complex is a suprasubduction-zone ophiolite formed largely in a fracture-zo... more The Ingalls Ophiolite Complex is a suprasubduction-zone ophiolite formed largely in a fracture-zone setting. Mantle tectonites are cut by a large, high-T shear zone overprinted by sheared serpentinite. Mafi c complexes of ca. 161 Ma gabbro, sheeted dikes, and pillow lava occur as large blocks in the sheared serpentinite. An overlying Late Jurassic argillite unit contains minor chert, graywacke, and pebble conglomerate, along with lenses of ophiolite breccias. Detrital serpentinite forms some of these breccias, and mafi c blocks in other breccias range up to hundreds of meters in diameter. Older basement is locally present in the ophiolite complex, including (1) phyllite, metachert, and pillow basalt of the undated De Roux unit overlain by (2) Early Jurassic pillow lava, basalt breccia, and minor chert and oolitic limestone of the Iron Mountain unit (fossil seamount). This older basement indicates that at least part of the ophiolite is polygenetic. The presence of a high-T mantle she...
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The Upper Jurassic Galice Formation of the Klamath Mountains, Oregon-California, overlies the ca.... more The Upper Jurassic Galice Formation of the Klamath Mountains, Oregon-California, overlies the ca. 162-Ma Josephine ophiolite and the slightly younger Rogue–Chetco volcano-plutonic arc complex. The Galice Formation that overlies the Josephine ophiolite consists of a siliceous hemipelagic sequence, which grades upward into a thick turbidite sequence. Bedded hemipelagic rocks and scarce sandstone, how-ever, also occur at several localities within the Josephine ophiolite pillow basalts. Corrected paleoflow current data suggest that the Galice Formation was derived predominantly from the east and north. Detrital modes of sandstones from the Galice Formation indicate an arc source as well as a predominantly chert-argillite source with minor metamorphic rocks. A sandstone located ~20 m below the top of the Josephine ophiolite has detrital modes and heavy mineral suites similar to the turbidite sand-stones. Detrital Cr-spinel compositions from the turbidite and intra-pillow lava sandstones ...
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Fe[sup +3](Fe+3) contents have been studied in a suite of over 30 chlorites from a variety of pro... more Fe[sup +3](Fe+3) contents have been studied in a suite of over 30 chlorites from a variety of provenances representing a range of F[sub O[sub 2]](FO2) conditions, including: (a) metapelites in western Maine, ranging from lower garnet to upper staurolite grade rocks, coexisting with graphite and Fe+3-poor ilmenite at 375--575 C; (b) extension veins cutting the Josephine ophiolite, formed at [approximately]430
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The Journal of Geology, 2002
... In Hawkins, JW; Parson, LM; Allan, JF; Abrahamsen, N.; Bednarz, U.; Blanc, G.; Bloomer, SH; e... more ... In Hawkins, JW; Parson, LM; Allan, JF; Abrahamsen, N.; Bednarz, U.; Blanc, G.; Bloomer, SH; et al., eds. Proc. Ocean Drilling Program Sci. Results 135:565–583. ... Geol. Surv. Dep., p. 182–192. First citation in article. Coulton, AJ; Harper, GD; and O'Hanley, DS 1995. ...
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The Journal of Geology, 1982
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The Journal of Geology, 1985
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Tectonophysics, 1982
ABSTRACT
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Tectonics, 1996
... Received 16 August 1995; accepted 21 August 1995; . Citation: Harper, GD, K. Grady, and AJ Co... more ... Received 16 August 1995; accepted 21 August 1995; . Citation: Harper, GD, K. Grady, and AJ Coulton (1996), Origin of the amphibolite “sole” of the Josephine ophiolite: Emplacement of a cold ophiolite over a hot arc, Tectonics, 15(2), 296–313, doi:10.1029/95TC02525. ...
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Tectonics, 1984
The geochronology, stratigraphy, and spatial relationships of Middle and Late Jurassic terranes o... more The geochronology, stratigraphy, and spatial relationships of Middle and Late Jurassic terranes of the Klamath Mountains strongly suggest that they were formed in a single west-facing magmatic arc built upon older accreted terranes. A Middle Jurassic arc complex is ...
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Tectonics, 1985
Geophysical evidence, especially microearthquakes that extend into the upper mantle beneath the i... more Geophysical evidence, especially microearthquakes that extend into the upper mantle beneath the inner floor of the Mid-Atlantic and Gorda Ridges, indicates that the axial magma chamber episodically freezes beneath slow spreading ridges. Freezing of the axial magma ...
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Journal of Structural Geology, 2004
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Journal of Geophysical Research, 1982
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Journal of Geophysical Research, 1988
JB_description.
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Journal of Geophysical Research, 1993
Based upon detailed mapping (1:10 and 1:100) of a large water-polished outcrop of the sheeted dik... more Based upon detailed mapping (1:10 and 1:100) of a large water-polished outcrop of the sheeted dike/gabbro transition zone in the Josephine ophiolite of NW California and SW Oregon, the following history of alternating episodes of magmatic, structural, and hydrothermal events ...
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Journal of Geophysical Research, 1988
ABSTRACT
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Bookmarks Related papers MentionsView impact
ABSTRACT
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The polygenetic Ingalls ophiolite complex in the central Cascades, Washington, is one of several ... more The polygenetic Ingalls ophiolite complex in the central Cascades, Washington, is one of several Middle to Late Jurassic ophiolites of the North American Cordillera. It consists primarily of mantle tectonites. High-temperature mylonitic peridotite, over-printed by serpentinite mélange (Navaho Divide fault zone), separates harzburgite and dunite in the south from lherzolite in the north. Crustal units of the ophiolite occur as steeply dipping, kilometer-scale fault blocks within the Navaho Divide fault zone. These units are the Iron Mountain, Esmeralda Peaks, and Ingalls sedimentary rocks. Volcanic rocks of the Iron Mountain unit have transitional within-plate– enriched mid-ocean-ridge basalt affi nities, and a rhyolite yields a U-Pb zircon age of ca. 192 Ma. Minor sedimentary rocks include local oolitic limestones and cherts that contain Lower Jurassic (Pliensbachian) Radiolaria. This unit probably formed as a seamount within close proximity to a spreading ridge. The Esmeralda Peaks...
Bookmarks Related papers MentionsView impact
The Ingalls ophiolite complex, central Cascades, Washington, mainly consists of mantle-derived ul... more The Ingalls ophiolite complex, central Cascades, Washington, mainly consists of mantle-derived ultramafi c tectonite, with crustal rocks consisting of gabbro, diabase, basalt, and sedimentary rocks. The crustal rocks occur as faulted blocks within ser-pentinite mélange (Navaho Divide fault zone). Mafi c rocks in most of these blocks comprise the Late Jurassic Esmeralda Peaks unit. Herein, we defi ne an older, Early Jurassic unit within the Ingalls ophiolite complex, which we call the Iron Mountain unit. This unit occurs along the southern edge of the complex and consists domi-nantly of mafi c volcanic rocks with minor sedimentary rocks. A rhyolite within the Iron Mountain unit yields a ca. 192 Ma U-Pb zircon age, consistent with an Early Jurassic age assignment based on radiolarians in cherts. The presence of volcanic rocks that have within-plate basalt magmatic affi nities and oolitic limestone suggests that the Iron Mountain unit formed as a seamount. Magmatic affi nities range fr...
Bookmarks Related papers MentionsView impact
The Ingalls Ophiolite Complex is a suprasubduction-zone ophiolite formed largely in a fracture-zo... more The Ingalls Ophiolite Complex is a suprasubduction-zone ophiolite formed largely in a fracture-zone setting. Mantle tectonites are cut by a large, high-T shear zone overprinted by sheared serpentinite. Mafi c complexes of ca. 161 Ma gabbro, sheeted dikes, and pillow lava occur as large blocks in the sheared serpentinite. An overlying Late Jurassic argillite unit contains minor chert, graywacke, and pebble conglomerate, along with lenses of ophiolite breccias. Detrital serpentinite forms some of these breccias, and mafi c blocks in other breccias range up to hundreds of meters in diameter. Older basement is locally present in the ophiolite complex, including (1) phyllite, metachert, and pillow basalt of the undated De Roux unit overlain by (2) Early Jurassic pillow lava, basalt breccia, and minor chert and oolitic limestone of the Iron Mountain unit (fossil seamount). This older basement indicates that at least part of the ophiolite is polygenetic. The presence of a high-T mantle she...
Bookmarks Related papers MentionsView impact
The Upper Jurassic Galice Formation of the Klamath Mountains, Oregon-California, overlies the ca.... more The Upper Jurassic Galice Formation of the Klamath Mountains, Oregon-California, overlies the ca. 162-Ma Josephine ophiolite and the slightly younger Rogue–Chetco volcano-plutonic arc complex. The Galice Formation that overlies the Josephine ophiolite consists of a siliceous hemipelagic sequence, which grades upward into a thick turbidite sequence. Bedded hemipelagic rocks and scarce sandstone, how-ever, also occur at several localities within the Josephine ophiolite pillow basalts. Corrected paleoflow current data suggest that the Galice Formation was derived predominantly from the east and north. Detrital modes of sandstones from the Galice Formation indicate an arc source as well as a predominantly chert-argillite source with minor metamorphic rocks. A sandstone located ~20 m below the top of the Josephine ophiolite has detrital modes and heavy mineral suites similar to the turbidite sand-stones. Detrital Cr-spinel compositions from the turbidite and intra-pillow lava sandstones ...
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Fe[sup +3](Fe+3) contents have been studied in a suite of over 30 chlorites from a variety of pro... more Fe[sup +3](Fe+3) contents have been studied in a suite of over 30 chlorites from a variety of provenances representing a range of F[sub O[sub 2]](FO2) conditions, including: (a) metapelites in western Maine, ranging from lower garnet to upper staurolite grade rocks, coexisting with graphite and Fe+3-poor ilmenite at 375--575 C; (b) extension veins cutting the Josephine ophiolite, formed at [approximately]430
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
The Journal of Geology, 2002
... In Hawkins, JW; Parson, LM; Allan, JF; Abrahamsen, N.; Bednarz, U.; Blanc, G.; Bloomer, SH; e... more ... In Hawkins, JW; Parson, LM; Allan, JF; Abrahamsen, N.; Bednarz, U.; Blanc, G.; Bloomer, SH; et al., eds. Proc. Ocean Drilling Program Sci. Results 135:565–583. ... Geol. Surv. Dep., p. 182–192. First citation in article. Coulton, AJ; Harper, GD; and O'Hanley, DS 1995. ...
Bookmarks Related papers MentionsView impact
The Journal of Geology, 1982
Bookmarks Related papers MentionsView impact
The Journal of Geology, 1985
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Tectonophysics, 1982
ABSTRACT
Bookmarks Related papers MentionsView impact
Tectonics, 1996
... Received 16 August 1995; accepted 21 August 1995; . Citation: Harper, GD, K. Grady, and AJ Co... more ... Received 16 August 1995; accepted 21 August 1995; . Citation: Harper, GD, K. Grady, and AJ Coulton (1996), Origin of the amphibolite “sole” of the Josephine ophiolite: Emplacement of a cold ophiolite over a hot arc, Tectonics, 15(2), 296–313, doi:10.1029/95TC02525. ...
Bookmarks Related papers MentionsView impact
Tectonics, 1984
The geochronology, stratigraphy, and spatial relationships of Middle and Late Jurassic terranes o... more The geochronology, stratigraphy, and spatial relationships of Middle and Late Jurassic terranes of the Klamath Mountains strongly suggest that they were formed in a single west-facing magmatic arc built upon older accreted terranes. A Middle Jurassic arc complex is ...
Bookmarks Related papers MentionsView impact
Tectonics, 1985
Geophysical evidence, especially microearthquakes that extend into the upper mantle beneath the i... more Geophysical evidence, especially microearthquakes that extend into the upper mantle beneath the inner floor of the Mid-Atlantic and Gorda Ridges, indicates that the axial magma chamber episodically freezes beneath slow spreading ridges. Freezing of the axial magma ...
Bookmarks Related papers MentionsView impact
Journal of Structural Geology, 2004
Bookmarks Related papers MentionsView impact
Journal of Geophysical Research, 1982
Bookmarks Related papers MentionsView impact
Journal of Geophysical Research, 1988
JB_description.
Bookmarks Related papers MentionsView impact
Journal of Geophysical Research, 1993
Based upon detailed mapping (1:10 and 1:100) of a large water-polished outcrop of the sheeted dik... more Based upon detailed mapping (1:10 and 1:100) of a large water-polished outcrop of the sheeted dike/gabbro transition zone in the Josephine ophiolite of NW California and SW Oregon, the following history of alternating episodes of magmatic, structural, and hydrothermal events ...
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Journal of Geophysical Research, 1988
ABSTRACT
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