Prograde and retrograde history of the Junction School eclogite, California, and an evaluation of garnet–phengite–clinopyroxene thermobarometry

Page, F. Zeb; Armstrong, Lora S.; Essene, Eric J.; Mukasa, Samuel B.

doi:10.1007/s00410-006-0161-9

Cited by 73 publications

(80 citation statements)

References 63 publications

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“…Initially solidified as Farallon oceanic crust far from the North American margin, these rocks recrystallized in a relatively young, warm oceanic-continental convergence zone along an unrefrigerated, relatively warm mantle hanging wall, as reflected by HP/LT mineral parageneses indicating counterclockwise decompression P-T-time trajectories (Cloos 1982(Cloos , 1986Wakabayashi 1990Wakabayashi , 1999Saha et al 2005;Page et al 2007;Ukar and Cloos 2014). Most high-grade tectonic blocks were transformed at *10-12 kbar, and *400-600°C (Fig.…”

Section: Hp/lt Recrystallization Of the Franciscan Complexmentioning

confidence: 95%

Review of Late Jurassic-early Miocene sedimentation and plate-tectonic evolution of northern California: illuminating example of an accretionary margin

Ernst

2015

Chin. J. Geochem.

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Section: Hp/lt Recrystallization Of the Franciscan Complexmentioning

confidence: 95%

Review of Late Jurassic-early Miocene sedimentation and plate-tectonic evolution of northern California: illuminating example of an accretionary margin

Ernst

2015

Chin. J. Geochem.

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“…Many high-grade blocks are partly encased in "rinds" composed of minerals such as actinolite, chlorite, talc, and phengite: this rind apparently formed by metasomatic reaction between the block and the ultramafi c rocks under conditions of decreasing metamorphic grade (e.g., Coleman and Lanphere, 1971;Moore, 1984). High-grade metamorphism evolved along a counterclockwise P-T path (P on the positive y-axis; Wakabayashi, 1990;Krogh et al, 1994;Tsujimori et al, 2006;Page et al, 2007), whereas metamorphism in lower-grade metamorphic rocks took place under a mildly clockwise or hairpin P-T trajectory (Maruyama and Liou, 1988;Maruyama et al, 1985).…”

Section: Franciscan Complex Metamorphism and Geologic Settingmentioning

confidence: 99%

“…Peak temperatures of Franciscan metamorphism decrease with decreasing age, from amphibolites with temperatures of over 600 °C in the high-grade blocks (Wakabayashi, 1990) to 300-350 °C for epidote blueschists (Blake et al, 1988;Maruyama and Liou, 1988) at 154 Ma (Wakabayashi and Dumitru , 2007) to 150-250 °C for lawsonite blueschist-facies rocks (Ernst, 1971a;Maruyama et al, 1985) at 80-120 Ma (Wakabayashi and Dumitru, 2007), and ultimately to zeolite and prehnite-pumpellyite temperatures of <200 °C (Blake et al, 1988) for the last 95 Ma. Peak metamorphic pressures of high-grade metamorphic rocks range from ~5 kbar for the lowest pressure amphibolites (Wakabayashi, 1990) to 20-25 kbar for eclogites (Tsujimori et al, 2006;Page et al, 2007). Lower-grade blueschist gives pressures of ~6 to >10 kbar (Maruyama et al, 1985;Ernst, 1993), whereas sub-blueschist-grade rocks were metamorphosed at pressures at 4 kbar or less (Blake et al, 1988).…”

Section: Franciscan Complex Metamorphism and Geologic Settingmentioning

confidence: 99%

“…(1) High-T Franciscan metamorphism took place at medium-to very high-P rather than low-P conditions (Wakabayashi, 1990;Anczkiewicz et al, 2004;Tsujimori et al, 2006Tsujimori et al, , 2007Page et al, 2007). Metamorphic soles elsewhere in the world exhibit high-T and medium-to high-P metamorphism, rather than high-T and low-P metamorphism (e.g., Jamieson, 1986;Encarnación et al, 1995;Gnos, 1998;Önen and Hall, 2000;Searle and Cox, 2002;Guilmette et al, 2008).…”

Section: High-grade (Metamorphic Sole) Metamorphism: Inception Of Submentioning

confidence: 99%

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Suprasubduction-zone ophiolite generation, emplacement, and initiation of subduction: A perspective from geochemistry, metamorphism, geochronology, and regional geology

Wakabayashi

Ghatak

Basu

2010

Geological Society of America Bulletin

103

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Ophiolites are on-land remnants of oceanic lithosphere, and most of the more extensive ophiolites apparently formed above a subduction zone, a tectonic setting known as a suprasubduction-zone setting. Thin sheets of high-grade metamorphic rocks, known as metamorphic soles, crop out structurally beneath many suprasubduction-zone ophiolites. Such rocks may have formed during the inception of subduction beneath young and hot oceanic lithosphere. Disagreement exists as to whether suprasubduction-zone ophiolites are emplaced over the same subduction zone over which they once formed or over a later one. High-grade metamorphic rocks (blocks-in-mélange and coherent sheets) from the Franciscan Complex may represent a metamorphic sole beneath the suprasubduction-zone Coast Range ophiolite. Trace-element and isotopic data indicate that the Franciscan high-grade metamorphic rocks formed in a suprasubduction-zone envi ronment, requiring the existence of a pre-Franciscan sub duction zone, whereas later-subducted, lower-grade oceanic rocks are of mid-ocean-ridge or oceanic-island basalt affi ni ties. The Coast Range ophiolite and Franciscan high-grade rock protoliths formed over a pre-Franciscan subduction zone that may have dipped westward. The high-grade Franciscan rocks were metamorphosed at the inception of east-dipping subduction beneath the Coast Range ophiolite, and the ophiolite was subsequently emplaced over this later subduction zone. Suprasubduction-zone protolith signatures have been obtained for other metamorphic soles beneath suprasubduction-zone ophiolites, suggesting that our proposed model of suprasubduction-zone ophiolite generation over one subduction zone and emplacement over a second one may be globally applicable. Regional geology suggests that this dual subduction-zone model may also apply to suprasubduction-zone ophiolites with midocean-ridge and/or oceanic-island basalt soles.Generation of ophiolite over first subduction zone and emplacement over a later one.

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“…These high-grade blocks with Middle to Late Jurassic ages of metamorphism are relatively well studied (Coleman and Lanphere 1971;Wakabayashi 1992;Anczkiewicz et al 2004;Wakabayashi and Dumitru 2007;Ukar et al 2012). Initially solidified as Farallon or pre-Farallon oceanic crust distant from the North American margin, the rocks recrystallized in a relatively young, warm oceanic-continental convergence zone along an unrefrigerated hanging wall, as deduced from HP mineral parageneses indicating counterclockwise P-T-time trajectories (Cloos 1982(Cloos , 1986Wakabayashi 1990Wakabayashi , 1999Saha et al 2005;Page et al 2007;Ukar and Cloos 2014). Most highgrade tectonic blocks were transformed at ~10-12 kbar, and ~400-600 °C, but some evidently formed at even higher P-T ranges (e.g., Krogh et al 1994;Tsujimori et al 2006).…”

Section: Introductionmentioning

confidence: 98%

Franciscan geologic history constrained by tectonic/olistostromal high-grade metamafic blocks in the iconic California Mesozoic-Cenozoic accretionary complex

Ernst

2014

American Mineralogist

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Subduction generated a NW-trending Andean arc along the Californian margin beginning at ~175 Ma. Coeval high-pressure (HP) transformation of oceanic crust in an east-dipping, subduction zone probably accompanied plate convergence, but recovered Franciscan eclogite and garnet blueschist blocks chiefly possess younger recrystallization ages of ~165-150 Ma. These Jurassic HP metamafic rocks were sequestered in a low-temperature environment well into Cretaceous time. Fragments of actinolitic rinds partially surround many such high-grade blocks. Only slightly younger than the HP metamorphism, these rinds reflect metasomatic exchange between metabasalt and serpentinized harzburgite along the dynamic oceanic crust-mantle hanging wall during storage of the mafic rocks at moderate depth. High-grade tectonic blocks later were brought toward the surface in circulating, low-density, sheared mud-matrix mélange and/or in buoyant serpentinite bodies. Most exotic HP metamafic blocks occur in mélanges of the Franciscan Central Belt, reflecting tectonic insertion within the subduction zone-not near-surface additions to the clastic section. However, rare, high-grade clasts in feebly recrystallized Franciscan conglomerates suggest erosion and sedimentary deposition for some HP blocks. The addition of dense metabasaltic olistoliths to the mid-and Upper Cretaceous section requires that these HP material were carried surfaceward first as tectonic fragments, perhaps immersed in low-density serpentinite or mud-matrix mélange, then eroded and transported into the trench. HP rocks are conspicuously lacking in coeval Great Valley strata. Whatever the origin of particular high-grade rocks, widespread post-depositional shearing has largely obliterated their original natures, but all dense metamafic blocks of Jurassic recrystallization age must have been supplied to the Cretaceous Franciscan accretionary complex by entrainment in a low-density, circulating muddy matrix or serpentinite body. The vast majority of exotic HP blocks resides in Central Belt mélanges, and appears to be tectonic rather than olistostromal in origin.

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Prograde and retrograde history of the Junction School eclogite, California, and an evaluation of garnet–phengite–clinopyroxene thermobarometry

Cited by 73 publications

References 63 publications

Review of Late Jurassic-early Miocene sedimentation and plate-tectonic evolution of northern California: illuminating example of an accretionary margin

Review of Late Jurassic-early Miocene sedimentation and plate-tectonic evolution of northern California: illuminating example of an accretionary margin

Suprasubduction-zone ophiolite generation, emplacement, and initiation of subduction: A perspective from geochemistry, metamorphism, geochronology, and regional geology

Franciscan geologic history constrained by tectonic/olistostromal high-grade metamafic blocks in the iconic California Mesozoic-Cenozoic accretionary complex

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