In search for the missing arc root of the Southern California Batholith: P-T-t evolution of upper mantle xenoliths of the Colorado Plateau Transition Zone

Rautela, Ojashvi; Chapman, Alan D.; Shields, Jessie E.; Ducea, Mihai N.; Lee, Cin-Ty A.; Jiang, Huaidong; Saleeby, Jason B.

doi:10.1016/j.epsl.2020.116447

Cited by 13 publications

(10 citation statements)

References 39 publications

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“…The time of xenolith eruption was selected as these arclogites do not have widespread evidence of annealing, this indicates that their fabrics likely formed shortly before eruption. Along with this, Sm–Nd isotope data show that the arclogites were still hot near the time of xenolith eruption (Rautela et al., 2020), indicating that they likely had the ability to deform through creep. Pressure and temperature estimates on xenoliths from the Sullivan Buttes vent show that the geotherm at the time of eruption was around 60 mW/m 2 (Smith et al., 1994).…”

Section: Discussionmentioning

confidence: 90%

“…This has been argued to represent the bulldozing hypothesis described earlier given the coincidence with Mojave Province batholith formation (A. D. Chapman et al., 2020). Sm‐Nd dating of arclogite xenoliths from the Camp Creek and Sullivan Buttes vents (Esperança et al., 1988; Rautela et al., 2020) provide age constraints younger than those of zircon (∼60–30 Ma) and these are interpreted as cooling ages. Therefore, the U‐Pb data of zircon supports formation of the Arizona arclogites during two pulses of magmatism which were followed by 30–55 million years of slow cooling deep in the lithosphere prior to xenolith entrainment at ∼25 Ma.…”

Section: Geologic Backgroundmentioning

confidence: 99%

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Evolution of Microstructural Heterogeneity in the Deep Arc Lithosphere During Delamination

2023

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The microstructural properties of deep arc cumulates (arclogites) are poorly understood, but are essential in gaining a comprehensive picture of the rheology of continental lithosphere. Here, we analyze 16 arclogite xenoliths, comprising a low MgO and a high MgO suite, from Arizona, USA using electron backscatter diffraction to map microstructures, clinopyroxene shape preferred orientations (SPO), and clinopyroxene crystallographic preferred orientations (CPO). The lower pressure (∼1 GPa) low MgO arclogites show a variety of different clinopyroxene fabrics (S, L, and LS‐type), whereas the high pressure (>2 GPa) high MgO arclogites show predominantly LS‐type fabrics. Furthermore, clinopyroxenes in low MgO arclogites all show a pronounced correspondence between the long axis of their grain shape ellipsoids with the [001] crystal direction, indicating an SPO control on the CPO. In contrast, high MgO arclogite clinopyroxenes lack such a correspondence. We propose that both arclogite types originated as igneous cumulates, consistent with previous studies, but that the high MgO suite experienced substantial recrystallization which diminished the original igneous SPO‐induced CPO. Using strain rates appropriate for arc settings, we calculate a strength profile for the lithosphere and argue that the deepest arclogite textures are consistent with lithospheric foundering through ductile deformation under high shear strain (10−14–10−12 s−1). Our study shows that there is a high degree of shear strain localization in deep arc roots while shallower portions are relatively undeformed.

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Section: Discussionmentioning

confidence: 90%

Section: Geologic Backgroundmentioning

confidence: 99%

Evolution of Microstructural Heterogeneity in the Deep Arc Lithosphere During Delamination

2023

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“…These xenoliths, equilibrated at pressures and temperatures (P-T) of ca. 1.0-2.8 GPa and 600-850°C 26 , contain copper-bearing sulphides 25 and have been dated by U-Pb zircon at ca. 150 Ma and 75 Ma 26,27,28 , yet their origins remain unclear.…”

Section: Flat-slab Subduction and Crustal Anatexis During The Laramid...mentioning

confidence: 99%

“…1.0-2.8 GPa and 600-850°C 26 , contain copper-bearing sulphides 25 and have been dated by U-Pb zircon at ca. 150 Ma and 75 Ma 26,27,28 , yet their origins remain unclear. It is possible they originate from cumulate 'arclogites' derived from juvenile mantle-derived magmas 25,26,27,28 .…”

Section: Flat-slab Subduction and Crustal Anatexis During The Laramid...mentioning

confidence: 99%

The role of crustal anatexis in porphyry copper ore formation during flat-slab subduction: Insights from the Laramide Belt, SW USA

Lamont,

Loader,

Roberts

et al. 2024

Preprint

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The prevailing paradigm for the formation of porphyry copper deposits along convergent plate boundaries involves deep-crustal differentiation of metal-bearing juvenile magmas derived from the mantle-wedge above a subduction zone. However, many major porphyry districts formed during periods of flat-slab subduction when the mantle-wedge would have been reduced or absent, leaving unclear the source region of the ore-forming magmas. To resolve this paradox, we investigate deep crustal processes during the genesis of the Laramide Porphyry Province of Arizona, which formed between 80–50 Ma during flat-slab subduction of the Farallon Plate beneath North America. We show that: (1) Laramide granitic rocks have isotopic signatures implying a crustal origin suggesting that they were derived from Proterozoic aged crust; and (2) Proterozoic crustal rocks were pre-enriched in copper and underwent water fluxed anatexis between 73–60 Ma at a geothermal gradient of ~28°C/km, coincident with the zenith of granitic magmatism, porphyry genesis (73–56 Ma) and flat-slab subduction (75–65 Ma). To explain the formation of the Laramide Porphyry Province, we propose that volatiles derived from the leading edge of the Farallon flat-slab promoted anatexis of mafic (garnet pyroxenite and amphibolite) and felsic pre-enriched lower crust, without necessarily requiring significant juvenile mantle-wedge derived magmatism.

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“…One possibility is that the arc root at the time of tectonic obduction was partially molten. Temperatures of the orogenic lower crust approximated from thermometry of arclogite exposures (Esperança et al, 1988;Smith et al, 1994;Ducea & Saleeby, 1996;Ringuette et al, 1999;Weber et al, 2002;Yoshino & Okudaira, 2004;Lee et al, 2006;Dhuime et al, 2009;Gysi et al, 2011;Erdman et al, 2016;Rautela et al, 2020) and amphibolite/granulite terranes (Depine et al, 2008;Triantafyllou et al, 2018) range on average from 700-950 • C. This temperature range exceeds both the high-pressure water-saturated and water-absent solidi of typical lower crustal assemblages (Vielzeuf & Schmidt, 2001). Therefore, the arc root is likely to be a meltbearing region, with melt extraction out of the hot zone balanced by influx of hot mantle-derived magma (Ducea et al, 2021a).…”

Section: The Deep Crustal Hot Zone Of Cordilleran Arcs: Characteristi...mentioning

confidence: 99%

Arclogites in the Subarc Lower Crust: Effects of Crystallization, Partial Melting, and Retained Melt on the Foundering Ability of Residual Roots

Bowman¹,

Ducea²,

Triantafyllou³

2021

Geological Society of America Abstracts With Programs

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Thick-crusted (>45 km) Cordilleran arcs exhibit cyclic processes including periods of magmatic quiescence interspersed with pulses of high-flux magmatism. Most models assume that during high-flux events, fractional crystallization and partial melting within the deep crustal hot zone generate a dense (>3.4 g/cm 3 ) arclogitic subarc root that can readily founder into the mantle. Yet these models do not consider that: (1) the retention of low-density melt within the subarc root, and (2) the protolith lithology of the restitic portion of the subarc root may greatly impact the density evolution of the root and its susceptibility to foundering. In this article, we first address the effect of retained melt on the foundering ability of the subarc root by calculating the density and time for foundering of melt-bearing arclogitic residue at 1.5, 2, and 2.5 GPa. We find that melt volumes >10-18% are required to stabilize the root within the lower crust; melt volumes below this threshold lower the viscosity of the residue so much so as to decrease the time for foundering by an order of magnitude. We then constrain through phase equilibria modeling the effect of partial melting of different lower crustal protoliths on the density of the restitic subarc root. To do this, we model the density and mineralogical evolution of restites in equilibrium with their derivative melts during open-system, isobaric partial melting of typical crustal assemblages from 600-1100 • C at 1.5 (∼50 km) and 2 GPa (∼65 km). In our models, typical end-member assemblages in a lower crustal hot zone include basalt, metapelite, and metagraywacke. We find that melt-depleted restites derived from basaltic compositions are amphibole-bearing arclogites with densities conducive to foundering, which at 2 GPa can occur even in the presence of the coexisting hydrous felsic residual melt. Foundering of the amphibole ± melt-bearing root may refertilize the mantle wedge and induce melting of the surrounding asthenosphere as well as the arclogitic mass. However, if temperatures in a 50-km deep subarc hot zone are not sufficient to drive melt depletion of basaltic restites, these dense (3.1-3.3 g/cm 3 ) residues are gravitationally stable, increasing the density of the lower crust and lowering the elevation of the arc. In comparison, partial melting of metasedimentary country rock produces alkali feldspar-rich residues that never achieve densities conducive to foundering. Thus, if high-flux events are driven by the influx of melt-fertile lithosphere beneath the arc as envisioned by the Cordilleran cycle model, then partial melting of the metasedimentary portion will generate low-density residues that remain in the lower crust and contribute to the thickness, geochemistry, and seismic structure of the bulk arc.

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In search for the missing arc root of the Southern California Batholith: P-T-t evolution of upper mantle xenoliths of the Colorado Plateau Transition Zone

Cited by 13 publications

References 39 publications

Evolution of Microstructural Heterogeneity in the Deep Arc Lithosphere During Delamination

Evolution of Microstructural Heterogeneity in the Deep Arc Lithosphere During Delamination

The role of crustal anatexis in porphyry copper ore formation during flat-slab subduction: Insights from the Laramide Belt, SW USA

Arclogites in the Subarc Lower Crust: Effects of Crystallization, Partial Melting, and Retained Melt on the Foundering Ability of Residual Roots

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