Distinctly different parental magmas for calc-alkaline plutons and tholeiitic lavas in the central and eastern Aleutian arc

177

122

We extracted all volcanic arc rock analyses calculated to be in equilibrium with mantle olivine from the global georoc database. This results in 938 primitive melt compositions from 30 arcs. Based on geochemical criteria six principal types of primitive arc melts can be distinguished: calc‐alkaline basalts and andesites, tholeiitic basalts, highly depleted tholeiitic andesites, shoshonites and low‐Si basalts. Their major element systematics indicates that last mantle equilibration occurred mostly at 1.0–2.5 GPa, 1220–1350°C for tholeiitic and calc‐alkaline basalts, at 0.5–1.2 GPa and ∼1200°C for depleted tholeiitic andesites, and at 0.7–1.2 GPa, 1050–1150°C for calc‐alkaline andesites. Quantitative treatment of major and trace elements suggests that the different melt types can be explained by a combination of variable mantle wedge preconditioning (degree of depletion prior to slab component addition, metasomatism in the lithosphere), variation in the amount and nature of the slab component added, and ‐ for primitive calc‐alkaline andesites ‐ reactive fractionation in the lithospheric top of the mantle wedge. The different slab components are best characterized by high Na2O, TiO2, Zr and Th for slab melts; high K2O/Na2O and more pronounced Nb, Sr, and Pb anomalies for fluids; and high K2O at high K2O/Na2O for supercritical liquids. A slab component that is dominantly a slab melt is common in continental but rare in intra‐oceanic arcs, consistent with comparatively cooler slabs in intra‐oceanic subduction zones. A majority of the arcs has more than one melt type, testifying for heterogeneity in the mantle wedge and added slab component.

Section: Discussion Of Melt Typesmentioning

confidence: 99%

The global systematics of primitive arc melts

Schmidt

Jagoutz²

2017

177

122

“…Calc-alkaline intrusive rocks in Hidden Bay, Adak (36-31 Ma, Citron et al, 1980), Kagalaska (~13-14 Ma, Citron et al, 1980;Jicha et al, 2006), Amatignak (~31-30 Ma), Ilak (~12 Ma), and Atka Islands (~39-9 Ma, Cai et al, 2015), and granodiorites/tonalites from Medny in the Komandorsky Islands (~12-8 Ma, Tsvetkov, 1991). Calc-alkaline intrusive rocks in Hidden Bay, Adak (36-31 Ma, Citron et al, 1980), Kagalaska (~13-14 Ma, Citron et al, 1980;Jicha et al, 2006), Amatignak (~31-30 Ma), Ilak (~12 Ma), and Atka Islands (~39-9 Ma, Cai et al, 2015), and granodiorites/tonalites from Medny in the Komandorsky Islands (~12-8 Ma, Tsvetkov, 1991).…”

Section: Geochemistry Geophysics Geosystemsmentioning

confidence: 99%

“…Global comparison of Talamanca intrusive rocks, other arc plutonic rocks, and reference compositions of sodic (Na) and potassic (K) TTGs (Moyen, 2011) and Upper Continental Crust (Rudnick & Gao, 2003). Kagalaska pluton from Fraser and Barrett (1959), Citron (1980), Kay et al (1983), Kay et al (1986Kay et al ( , 1990, Romick et al (1990), Tsvetkov (1991, Yogodzinski et al (1995), and Cai et al (2015). Kagalaska pluton from Fraser and Barrett (1959), Citron (1980), Kay et al (1983), Kay et al (1986Kay et al ( , 1990, Romick et al (1990), Tsvetkov (1991, Yogodzinski et al (1995), and Cai et al (2015).…”

Section: Geochemistry Geophysics Geosystemsmentioning

confidence: 99%

“…Partial melting of subducted oceanic crust in eclogite facies, with subsequent reaction of these melts with peridotite from the mantle wedge, could be the origin for some primitive andesites found in the western Aleutians (Kay, 1978;Kelemen, Yogodzinski, et al, 2003); this contribution from a slab melt end-member is more evident in the Komandorsky Islands in Western Aleutians (Kelemen, Yogodzinski, et al, 2003;Yogodzinski et al, 1995). More recently, obtained isotopic evidence suggests that in central and eastern Aleutians, tholeiitic, and calc-alkaline magmas represent distinct magma sources (Cai et al, 2015), possibly reflecting variable amounts of subducted material in the two series. Therefore, a combination of subducted slab input in the form of a melt (Kelemen, Yogodzinski, et al, 2003) and the subsequent fractional crystallization of the arc primary magmas (Kay et al, 1990;Kay & Kay, 1994), yielded a composition very close to upper continental crust (Kay et al, 1990, and data in Figure 12a), but still not as enriched as the Talamanca suite ( Figure 12a).…”

Section: 1029/2018gc008128mentioning

confidence: 99%

See 1 more Smart Citation

The Record of the Transition From an Oceanic Arc to a Young Continent in the Talamanca Cordillera

Gazel

Hayes

Ulloa

et al. 2019

The Talamanca Cordillera in the Central America Arc (Costa Rica‐Panama) preserves the record of the geochemical evolution from an intraoceanic arc to a juvenile continental arc in an active subduction zone, making it a testbed to explore processes that resulted in juvenile continental crust formation and explore potential mechanisms of early continental crust generation. Here we present a comprehensive set of geochronological, geochemical, and petrological data from the Talamanca Cordillera that tracks the key turning point (12–8 Ma) from the evolution of an oceanic arc depleted in incompatible elements to a juvenile continent. Most plutonic rocks from this transition and postintrusive rocks share striking similarities with average upper continental crust and Archean tonalite, trondhjemite, and granodiorite. We complement these data with seismic studies across the arc. Seismic velocities within the Caribbean Plate (basement of the arc) show a relatively uniform lateral structure consistent with a thick mafic large igneous province. Comparisons of seismic velocity profiles in the middle and lower crust beneath the active arc and remnant Miocene arc suggest a transition toward more felsic compositions as the volcanic center migrated toward the location of the modern arc. Seismic velocities along the modern arc in Costa Rica compared with other active arcs and average continental crust suggest an intermediate composition beneath the active arc in Costa Rica closer to average crust. Our geochemical modeling and radiogenic isotopes systematics suggest that input components from melting of the subducting Galapagos hotspot tracks are required for this compositional change.

“…The number of published pre‐Miocene radioisotopic ages within the Aleutians is limited, and mainly consists of K‐Ar ages with age distributions suggesting pulses of concentrated arc magmatism at 38–29, 16–11, and 6–0 Ma [e.g., Scholl et al ., ; Kay et al ., 1982, 1994; Citron et al ., , Fournelle et al ., ; Jicha et al ., ]. Although, several recent studies [ Cai et al ., ; Kay et al ., ] have been begun to focus on refining the Eocene to Miocene record of Aleutian volcanism and plutonism.…”

Section: Introductionmentioning

confidence: 98%

Eocene to Pleistocene magmatic evolution of the Delarof Islands, Aleutian Arc

Schaen

Jicha

Kay

et al. 2016

The Delarof Islands in the Aleutian Arc near 179º W record ∼37 million years of discontinuous arc magmatism along a SW‐NE cross‐arc transect from near the trench to the active volcanic front. Geochemical and geochronologic data from the pre‐Pleistocene volcanic record in this region are limited and the 40Ar/39Ar, isotopic, and trace element data presented here are the first from units older than the Pleistocene‐Holocene volcanoes (Tanaga, Gareloi). Twenty‐two new 40Ar/39Ar ages establish a temporal framework for geochemical data and reveal that magmatism in the Delarof region was coincident with two arc‐wide magmatic flare ups in the late Eocene/early Oligocene and latest Miocene/Pliocene. Mafic lavas and plutons in the southern Delarofs give 40Ar/39Ar plateau ages ranging from 36.8 ± 0.2 to 26.9 ± 0.6 Ma on Amatignak Island and 37.0 ± 0.2 to 29.3 ± 1.0 Ma on Ulak Island. To the north 25 km, 40Ar/39Ar ages from the central Delarof Islands, Kavalga, Ogliuga, and Skagul are late Miocene (6.28 ± 0.04 Ma) to Pliocene (4.77 ± 0.18 Ma) with younger ages to the northeast. A significant transition in arc chemistry occurs in the Pleistocene where lavas from active volcanoes Gareloi and Tanaga exhibit higher sediment and hydrous fluid signatures (Th/La, Cs/Ta, La/Sm, LILE abundances) and lower 143Nd/144Nd than older Delarof Island units closer to the trench. Similar findings from Eocene‐Miocene lavas from Amchitka to Adak suggest that a previously minor sediment melt component became more pronounced in the Quaternary.