Partial melting and subduction-related metasomatism recorded by geochemical and isotope (He-Ne-Ar-Sr-Nd) compositions of spinel lherzolite xenoliths from Coyhaique, Chilean Patagonia

One hundred mantle xenoliths were collected from a hawaiite flow of Miocene–Pliocene age near Rayfield River, south-central British Columbia. The massive host hawaiite contains subrounded xenoliths that range in size from 1 to 10 cm and show protogranular textures. Both Cr-diopside-bearing and Al-augite-bearing xenoliths are represented. The Cr-diopside-bearing xenolith suite consists of spinel lherzolite (64%), dunite (12%), websterite (12%), harzburgite (9%), and olivine websterite (3%). Banding and veining on a centimetre scale are present in four xenoliths. Partial melting at the grain boundaries of clinopyroxene is common and may be due to natural partial melting in the upper mantle, heating by the host magma during transport, or decompression during ascent.Microprobe analyses of the constituent minerals show that most of the xenoliths are well equilibrated. Olivine is Fo89 to Fo92, orthopyroxene is En90, and Cr diopside is Wo47En48Fs5. More Fe-rich pyroxene compositions are present in some of the websterite xenoliths. The Mg/(Mg + Fe2+) and Cr/(Cr + Al + Fe3+) ratios in spinel are uniform in individual xenoliths, but they vary from xenolith to xenolith. Equilibration temperatures for the xenoliths are 860–980 °C using the Wells geothermometer. The depth of equilibration estimated for the xenoliths using geophysical and phase equilibrium constraints is 30–40 km.

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Geochemistry and petrology of spinel lherzolite xenoliths from Xalapasco de La Joya, San Luis Potosi, Mexico: Partial melting and mantle metasomatism

Journal of Geophysical Research Atmospheres ◽

10.1029/jb095ib10p15859 ◽

1990 ◽

Vol 95 (B10) ◽

pp. 15859 ◽

Cited By ~ 36

Author(s):

Yan Liang ◽

Don Elthon

Keyword(s):

Partial Melting ◽

Mantle Metasomatism ◽

Spinel Lherzolite ◽

San Luis ◽

San Luis Potosi ◽

La Joya ◽

San Luis Potosí

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Noble Gas Isotopes and Mineral Chemistry Recording Partial Melting and Subduction-Related Metasomatism in Spinel-Lherzolites from Coyhaique, Chilean Patagonia

10.46427/gold2020.1950 ◽

2020 ◽

Author(s):

Eduardo Novais-Rodrigues ◽

Tiago Jalowitzki ◽

Fernanda Gervasoni ◽

Hirochika Sumino ◽

Yannick Bussweiler ◽

...

Keyword(s):

Partial Melting ◽

Noble Gas ◽

Mineral Chemistry ◽

Spinel Lherzolites ◽

Chilean Patagonia ◽

Noble Gas Isotopes ◽

Gas Isotopes

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Amphibole in a spinel lherzolite xenolith: evidence for volatiles and partial melting in the upper mantle beneath southern British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e84-111 ◽

1984 ◽

Vol 21 (9) ◽

pp. 1067-1072 ◽

Cited By ~ 7

Author(s):

Mark Brearley ◽

Christopher M. Scarfe

Keyword(s):

British Columbia ◽

Partial Melting ◽

Upper Mantle ◽

Stability Field ◽

Spinel Lherzolite ◽

Ultramafic Xenolith ◽

Metasomatic Fluid ◽

Small Grains ◽

First Time

Pargasitic amphibole has been observed for the first time in an ultramafic xenolith from British Columbia. The xenolith is a chrome diopside-bearing spinel lherzolite trapped within an alkali basaltic lava flow at Lightning Peak, near Vernon, British Columbia. Amphibole (<5%) occurs within the xenolith as small grains, interstitial between other xenolith mineral phases, and always shows evidence of melting. Microprobe analyses of the amphibole reveal that it is a pargasite rich in MgO (MgO = 17.1–17.7 wt.%; Mg/(Mg + Fe2+) = 0.89) and CaO (10.4–10.7 wt.%). Textural and chemical evidence suggests that the pargasite is in equilibrium with the other phases in spinel lherzolite. The pargasite probably crystallized within the spinel stability field of the upper mantle from a volatile-rich metasomatic fluid that was produced by dehydration of subducted material. Melting in the amphibole may have been caused by one of three processes: superheating by the host alkali basalt, decompression as the magma ascended, or by in situ partial melting within the upper mantle. The partial melting of amphibole-bearing spinel lherzolite provides a possible mechanism for the generation of late Cenozoic alkalic magmas of the Intermontane Belt of British Columbia.

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The Effects of Small Amounts of H2O, CO2 and Na2O on the Partial Melting of Spinel Lherzolite in the System CaO–MgO–Al2O3–SiO2 ± H2O ± CO2 ± Na2O at 1·1 GPa

Journal of Petrology ◽

10.1093/petrology/egi081 ◽

2005 ◽

Vol 47 (2) ◽

pp. 409-434 ◽

Cited By ~ 36

Author(s):

XI LIU ◽

HUGH ST. C. O'NEILL ◽

ANDREW J. BERRY

Keyword(s):

Partial Melting ◽

Spinel Lherzolite

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ORIGIN AND EVOLUTION OF THE OPHIOLITIC COMPLEX OF ZDRALJICA (CENTRAL SERBIA)

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.16757 ◽

2004 ◽

Vol 36 (1) ◽

pp. 597

Author(s):

K. Resimic-Saric ◽

A. Koroneos ◽

V. Cvetkovic ◽

K. Balogh

Keyword(s):

Partial Melting ◽

Fractional Crystallization ◽

Upper Jurassic ◽

Geochemical Data ◽

Spinel Lherzolite ◽

Origin And Evolution ◽

Variation Patterns ◽

One Step ◽

Ophiolitic Complex ◽

Batch Melting

The ophiolitic complex of Zdraljica (Central Serbia) belongs to the Eastern Branch of the Vardar suture zone. It was emp'aced during the Upper Jurassic. The complex consists predominately of a MORB/VAB-like tholeiitic suite, represented mostly by gabbros and diabases. Small occurrences of cummulitic peridotites, basalts and plagiogranites also appear. The tholeiitic suite is intruded by calc-alkaline intermediate and acid magmas. Geochemical data suggest that the ZOC tholeiitic rocks originated by partial melting of a spinel-lherzolite source. Non-modal batch melting modeling indicates 10 to 15 % of partial melting of such a source. The magmas were later modified by fractional crystallization. One-step major element modeling requires 40% (F=0.60) of fractional crystallization of a mineral assemblage: PI52 gCpxi2 5OI26 iTtn2 9Ap4.4Mgt1.0- The model is supported by the variation patterns of most trace elements.

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The Volcano‐Tectonic Evolution of the Macquarie Ridge Complex, Australia‐Pacific Plate Boundary South of New Zealand

10.26686/wgtn.16997290 ◽

2021 ◽

Author(s):

◽

Christopher Edward Conway

Keyword(s):

New Zealand ◽

Partial Melting ◽

Plate Boundary ◽

Pacific Plate ◽

Seafloor Spreading ◽

Spinel Lherzolite ◽

Low Degree ◽

Mid Ocean Ridge ◽

Group 2 ◽

Ocean Ridge

The Macquarie Ridge Complex (MRC) forms the submarine expression of the Australia‐Pacific plate boundary south of New Zealand, comprising a rugged bathymetry made up of numerous seamounts along its length. Tectonic plate reconstructions show that the plate boundary evolved from divergent to transpressional relative plate motion from ca. 40 – 6 Ma. However, only limited geological observation of the products of past seafloor spreading and present transpressional deformation has been achieved. This study presents new high-resolution multibeam, photographic, petrologic and geochemical data for 10 seamounts located along the MRC in order to elucidate the current nature and evolution of the plate boundary. Seamounts are oriented parallel to the plate boundary, characterized by elongate forms, and deformed by transform faulting. Three guyot‐type seamounts display summit plateaux that were formed by wave and current erosion. MRC seafloor is composed of alkaline to sub‐alkaline basaltic pillow, massive and sheet lava flows, lava talus, volcaniclastic breccia, diabase and gabbro. This oceanic crust was formed during effusive mid‐ocean ridge volcanism at the relic Macquarie spreading centre and has since been sheared, accreted and exhumed along the modern transpressional plate boundary. Major element systematics indicate samples originated from spatially distinct magmatic sources and have since been juxtaposed at seamounts due to transpressional relative plate motion. MRC seamounts have formed as discrete elevations as a result of dip‐slip and strike‐slip faulting of the ridge axis. Thus, MRC seamounts are volcanic in origin but are now the morphological manifestations of tectonic and geomorphic processes. Petrologic and geochemical characteristics of volcanic glass samples from the MRC indicate that both effusive and explosive eruption styles operated at the relic Macquarie spreading centre. Primitive and sub‐alkaline to transitional basaltic magma that rose efficiently to the seafloor was erupted effusively and cooled to form lava flows with low vesicle and phenocryst contents or was granulated on contact with seawater to form hyaloclasts deposited in volcaniclastic breccias. More alkaline magmas that underwent crystal fractionation and volatile exsolution in shallow reservoirs were fragmented and erupted during submarine hawaiian‐type eruptions. Such a scenario is likely to have occurred during the final stages of magmatism at the Australia‐Pacific plate boundary south of New Zealand when seafloor spreading was ultraslow or had ceased, which induced low degrees of partial melting and retarded magma ascent rates. All MRC samples display enriched mid‐ocean ridge basalt (E‐MORB) trace element characteristics. The sample suite can be divided into two groups, with Group 1 samples distinguished from Group 2 samples by their lower concentrations of highly incompatible trace elements, flatter LREE slopes, higher MgO contents and lower alkali element contents. Group 1 basalts were derived from low degree partial melting of spinel lherzolite generated during the late stages of mid‐ocean ridge volcanism at the plate boundary when seafloor spreading rates were slow to ultraslow (full spreading rate < 20 mm yr⁻¹). Group 2 basalts were derived from low degree partial melting of spinel lherzolite, mixed with small amounts of very low degree partial melting of garnet lherzolite, during post‐spreading volcanism at the MRC. Remnant heat from previous seafloor spreading induced buoyant ascent of the sub‐ridge mantle and enriched heterogeneities were preferentially tapped by the ensuing low melt fractions. Magma ascent was stalled due to the cessation of extension at the ridge and the melts underwent crystal fractionation prior to eruption, which accounts for the lower MgO contents of Group 2 basalts. The pervasive incompatible element‐enrichment of MRC basalts and similarity to lavas from fossil spreading ridges in the eastern Pacific Ocean may reflect regional enrichment of the Pacific upper mantle.

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Early Carboniferous Paleo-Asian oceanic plate subduction: Implications from geochronology and geochemistry of early Carboniferous magmatism in southern West Junggar, NW China

10.5194/egusphere-egu21-11906 ◽

2021 ◽

Author(s):

Pengde Liu ◽

Xijun Liu ◽

Zhiguo Zhang ◽

Yujia Song ◽

Yao Xiao ◽

...

Keyword(s):

Rare Earth ◽

Rare Earth Elements ◽

Partial Melting ◽

Early Carboniferous ◽

Orogenic Belt ◽

Island Arc ◽

Spinel Lherzolite ◽

Oceanic Plate ◽

Island Arcs ◽

West Junggar

&#160; &#160; The subduction and closure of the Paleo-Asia Ocean generated the Central Asian Orogenic Belt (CAOB), which extends from the Urals in the west through Kazakhstan, northwestern China, Mongolia, and northeastern China to the Russian Far East. It is generally accepted that the CAOB comprises a complicated and varied collage of terranes, including island arcs, ophiolites, accretionary prisms, seamounts, and microcontinents. The CAOB is the world&#8217;s largest accretionary orogen and is also considered a type area for studying Phanerozoic continental growth. The accretionary processes of the orogen might have resulted from either the progressive duplication of a single and long-lived island-arc system or the collision of several island arcs and micro-continents, similar to the complex archipelago systems in the modern southwestern Pacific. West Junggar is located in a key area of the CAOB, has been a focus of studies of the tectonic evolution and crustal growth of the orogenic belt. West Junggar has been considered by some geologists as a paleo-Asian intra-oceanic subduction system, whereas others have variously argued that West Junggar was formed by single subduction, arc&#8211;arc collision, or ridge subduction, or by post-collisional processes after the early Carboniferous. An understanding of the Carboniferous tec-tonic setting is critical for determining the evolution of West Junggar. A series of early Carboniferous volcanic and intrusive rocks occur in the southern West Junggar. Our new zircon U&#8211;Pb geochronological data reveal that diorite intruded at 334.1 &#177; 1.1 Ma, and that basaltic andesite was erupted at 334.3 &#177; 3.7 Ma. These intrusive and volcanic rocks are calc-alkaline, display moderate MgO (1.62&#8211;4.18 wt.%) contents and Mg# values (40&#8211;59), low Cr (14.5&#8211;47.2 ppm) and Ni (7.5&#8211;34.6 ppm) contents, and are characterized by enrichment in light rare-earth elements and large-ion lithophile elements and depletion in heavy rare-earth elements and high-field-strength elements, meaning that they belong to typical subduction-zone island-arc magma. The rocks show low initial 87Sr/86Sr ratios (0.703649 to 0.705008), positive &#400;Nd(t) values (+4.8 to +6.2, mean +5.4), and young TDM Nd model ages ranging from 1016 to 616 Ma, indicating a magmatic origin from depleted mantle involving partial melting of 10%&#8211;25% garnet and spinel lherzolite. Combining our results with those of previous studies, we suggest that these rocks formed as a result of northwestward subduction of the Paleo-Asian Junggar oceanic plate, which caused partial melting of sub-arc mantle. We conclude that intra-oceanic arc magmatism was extensive in southern Paleo-Asian Ocean during the early Carboniferous.This study was financially supported by the National Natural Science Foundation of China (41772059) and the CAS &#8220;Light of West China&#8221; Program (2018-XBYJRC-003).

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