The mantle source of basalts from Reunion Island is not more oxidized than the MORB source mantle

Glasses quenched from relatively undegassed ocean island magmas erupted from volcanoes at Iceland, Hawaii, the Canary Islands, and Erebus have elevated Fe3+/∑Fe ratios compared to glasses quenched from mid-ocean ridge basalts. This has been ascribed to elevated fO2 of their mantle sources, plausibly due to subducted, oxidized near-surface-derived components in their mantle sources. The basaltic magmas from Reunion Island in the Indian ocean have Sr–Nd-Hf-Pb-Os isotopic compositions suggesting that their mantle sources contain little or no subducted near-surface materials and contain the C/FOZO/PREMA mantle component. To constrain the fO2 of the C/FOZO/PREMA mantle component and test the link between oxidized OIB and recycled surface-derived materials in their sources, we measured major and volatile element abundances and Fe3+/∑Fe ratios of naturally glassy, olivine-hosted melt inclusions from Piton de La Fournaise volcano, La Reunion. We conclude that the fO2 of the mantle source of these Reunion lavas is lower than of the mantle sources of primitive, undegassed magmas from Hawaii, Iceland, the Canary Islands, and Mt. Erebus, and indistinguishable from that of the Indian-ocean upper mantle. This finding is consistent with previous suggestions that the source of Reunion lavas (and the C/FOZO/PREMA mantle component) contains little or no recycled materials and with the suggestion that recycled oxidized materials contribute to the high fO2 of some other OIBs, especially those from incompatible-element-enriched mantle sources. Simple mixing models between oxidized melts of EM1 and HIMU components and relatively reduced melts of DMM can explain the isotopic compositions and Fe3+/∑Fe ratios of lavas from Hawaii, Iceland, the Canary Islands, and Mount Erebus; this model can be tested by study of additional OIB magmas, including those rich in the EM2 component.

Oxidized Mantle Sources of HIMU and EM-type Ocean Island Basalts

Oxygen fugacity (fO2) is a fundamental variable in igneous petrology with utility as a potential tracer of recycled surficial materials in the sources of mantle-derived lavas. It has been postulated that ocean island basalts (OIB) have elevated fO2 relative to mid-ocean ridge basalts (MORB) owing to more oxidized source regions. To clarify this issue, trace-element systematics of olivine grains are reported from OIB lavas with HIMU (high-; Mangaia, Canary Islands), enriched mantle (EM; Samoa; São Miguel, Azores Islands) and depleted MORB mantle (DMM; Pico, Azores) Sr-Nd-Pb-Os isotopic signatures, to constrain the fO2 of each magmatic system. Despite sampling distinct mantle reservoirs based on radiogenic isotope systematics, these OIB suites show similar fO2, ranging from +1.5 to +2.9 FMQ, with an average of 2.0 ± 0.7 FMQ, significantly higher than MORB at +0.6 ± 0.2 FMQ using the same oxybarometer. OIBs show no correlation between fO2 and bulk rock isotopic ratios or parental magma compositions. The lack of correlations with isotopic signatures likely results from radiogenic isotope signatures being hosted in volumetrically minor trace element enriched mantle lithologies, while fO2 reflects the volumetrically dominant mantle component. Higher fO2 in OIB relative to MORB implies a uniformly oxidizing plume source mantle that may be the result of either a common oxidized oceanic crust-rich reservoir parental to all modern plume lavas, or preservation of un-degassed and oxidized mantle domains formed early in Earth history.

Petrological and geochemical characteristic of the rocks of the Voznesensky intrusive massif (Southern Urals): Оn the question of the composition and sources of magma producing gold and copper porphyry mineralization

Research subject. The petrological and geochemical features of the rocks of the Voznesensky intrusive massif and its dyke series were studied in order to clarify the composition, possible sources and geodynamic settings of magma generation that produced Au- and Cu-porphyry mineralization.Methods. The content of petrogenic oxides was determined by the chemical method, trace elements – by ICP-MS analysis.Results. Among the rocks of the Voznesensky massif, which have the geochemical characteristics of suprasubduction formations, varieties with calc-alkaline and adakite-like properties were established. The main phase of the massif is represented by gabbro-diorites and diorites belonging to the calc-alkaline series. Ore-bearing dykes of gabbro-diorites, diorites and granodiorites of the Au-porphyry Bolshekaransky deposit are of calc-alkaline composition, while the post-ore dykes of granodiorites and plagiogranites of this deposit exhibit adakite-like characteristics.Conclusions. The ore-bearing dyke series of the Voznesensky deposit is represented by calc-alkaline diorites and adakite-like granodiorites and plagiogranites. The metallogenic specialization of the dykes was influenced by the silicic acidity and the redox state of the ore-generating melts. Granitoids with Cu-porphyry mineralization, compared to their gold-bearing varieties, crystallized from more acidic melts with a higher degree of oxidation. It is assumed that the main mantle component of magmas for the Voznesensky rocks were relatively weakly depleted spinel peridotites of the suprasubduction lithospheric mantle. Calc-alkaline magmas were melted from a mantle substrate previously metasomatized by aqueous fluids, and magmas with adakite-like properties – metamorphosed by melts of basalts and sedimentary rocks of slab. Melting of slab rocks may have been associated with additional heating due to friction caused by changes in direction and/or velocity of oblique subduction.

West Antarctic mantle deduced from mafic magmatism

Distinct mantle compositions recorded in primitive West Antarctic magmatic rocks vary by tectonic setting and time. Deep asthenospheric mantle plume sources or shallow metasomatised mantle sources may operate either coincidently or independently to supply melts for magmatism. For example, contemporaneous subduction–plume dynamics produced the Ferrar-Karoo large igneous province; subduction-related melting followed by slab-rollback or melting of slab-hosted pyroxenite explains Antarctic Peninsula volcanism through time; Marie Byrd Land magmatism results from plume materials variably mixed with subduction modified mantle; while magmatism in Victoria Land and western Ross Sea is best explained by plate dynamics and melting of asthenospheric and metasomatised lithospheric sources and not by an upwelling plume. Element and isotopic ratios show a fundamental change between Marie Byrd Land and Victoria Land mantle domains. Specifically, Pb isotopes indicate that Victoria Land magmatism sources have a stronger focal zone (FOZO) mantle component while Marie Byrd Land magmatism possesses more of the HIMU mantle component. The chemical and isotopic heterogeneity of relatively unfractionated igneous rocks in West Antarctica reflects fundamental differences in mantle domains and melting conditions. This mantle variability coincides with changes in crustal structure and composition and has a geophysical signature that is manifest in seismic data and tomographic models.

Defining the composition of the deep mantle and the primordial He inventory of the Afar plume

<p>Basaltic rocks generated by upwelling mantle plumes display a range of trace element and isotope compositions indicative of strong heterogeneity in deep material brought to Earth surface.  Helium isotopes are an unrivalled tracer of the deep mantle in plume-derived basalts.  It is frequently difficult to identify the composition of the deep mantle component as He isotopes rarely correlate with incompatible trace element and radiogenic isotope tracers. It is supposed that this is due to the high He concentration of the deep mantle compared to degassed/enriched mantle reservoirs dominating the He in mixtures, although this is far from widely accepted.  The modern Afar plume is natural laboratory for testing the prevailing paradigm.</p><p>The <sup>3</sup>He/<sup>4</sup>He of basalt glasses from 26°N to 11°N along the Red Sea spreading axis increases systematically from 7.9 to 15 R<sub>a</sub>. Strong along-rift relationships between <sup>3</sup>He/<sup>4</sup>He and incompatible trace element ratios are consistent with a binary mixture between moderately enriched shallow asthenospheric mantle in the north and plume mantle evident in basalts from the Gulf of Tadjoura, Djibouti (the Ramad enriched component of Barrat et al. 1990).  The high-<sup>3</sup>He/<sup>4</sup>He basalts have trace element-isotopic compositions that are similar, but not identical, to the high <sup>3</sup>He/<sup>4</sup>He (22 R<sub>a</sub>) high Ti (HT2) flood basalts erupted during the initial phase of the Afar plume volcanism (Rogers et al. in press). This suggests that the deep mantle component in the modern Afar plume has a HIMU-like composition. From the hyperbolic <sup>3</sup>He/<sup>4</sup>He-K/Th-Rb/La mixing relationships we determine that the upwelling deep mantle has 3-5 times higher He concentration than the asthenosphere mantle beneath the northern Red Sea.</p><p>Barrat et al. 1990.  Earth and Planetary Science Letters 101, 233-247.</p>

Sr-Nd-Pb isotopic significance of mantle source components from Central and Western Anatolia: Melting evidences from peridotite and pyroxenite source domains

<p>Extensive magmatic activities were developed in  Central and Western Anatolia,  since middle miocene to quaternary times,   the most primitive lavas are situated in eastern end of Central (Sivas) and also western (Kula) Anatolia, besides Kula basalts are  one of the most recent basaltic rocks together with  basalts  from south-central Anatolia.   Although the magmatism is generally   observed at several different  locations, the recent   basaltic rocks in both of the regions   seem to be derived from  the melting  of the peridotite and pyroxenite  source  domains and the latter one  was ignored in previous studies as source component.</p><p> The previous studies indicate that many of the basaltic rocks from Central and Western Anatolia  are related with spinel-garnet transition, but typical Tb/Yb(N) (>1.8; [1]) and Zn/Fe   (separates peridotite-derived (Zn/Fe <12; [2]) and pyroxenite-derived (Zn/Fe 13-20); [2] melts)  Co/Fe  ratios of the basaltic rocks from  several volcanic centers from Central and Western Anatolia  reveal that   melting from the single  source component  are not solely capable of  the producing  basaltic  rocks. </p><p> Sr-Nd and Pb isotopic  compositions  clearly display the distinction  of samples which are  linked to    asthenospheric source. The lead isotopic systematic  shows  no siginificant differences  among the Central and Western Anatolian basalts,  of all the samples are above the NHRL line and close to EM II  mantle component,  Sr- Nd  isotopes  also display similar compositions as well, the majority of the samples are in and close to mantle array,   but the  Sr isotopic composition   of  Miocene aged  Gediz and Simav lavas have high radiogenic values. </p><p>Tb/Yb(N),  Zn/Fe ratios  and   as well as the Pb isotopic  compositions and REE-based melting model reveal  that Sivas, Erciyes Hasandağ, and Develidağ samples in central Anatolia,  and Kula, Gediz basalt in western Anatolia  seem to be  derived from the amalgamated melting of  pyroxenite and peridotite sources,   besides,  the sources melting is capable of  the producing     elemental variations in  basaltic rocks related with either lithospheric delamination or lithospheric  unstability</p><ul><li>1.Wang et al., 2002, J.Geophys.Res.vol:107,ECV 5 1-21</li> <li>2 .Le Roux, et al.,2011,EPSL, vol:307, 395-408</li> </ul><p>This study is financially supported by Hacettepe University, BAB project no: FHD-2018-17283</p><p> </p>

No continuous suture between Kudi and Oytag: new evidence from geochronology and geochemistry data

<p>A lateral continuity between belts of mafic and ultramafic Paleozoic rocks found in the West Kunlun of Northern Tibet and comparable rocks, known from an outcrop in the Chinese North Pamir, has long been proposed. This led to the concept of an originally generally straight, E–W trending Oytag–Kudi suture zone. In turn, this paleogeographic model formed a key constraint for the hypothesis, that the Pamir has indented 300 km northward with respect to Tibet during the Cenozoic. We show, that the arc volcanic rocks found in the North Pamir are distinguishable from the units known from the West Kunlun.<br>The North Pamir is dominated by Paleozoic arc volcanic rocks. We present new geochemical and geochronological data to give a holistic view of an early to mid-Carboniferous arc complex. This belt was previously identified as an intraoceanic arc in the northeastern North Pamir. Our data yields evidence for a gradual lateral change towards the west into a Cordilleran-style arc in the Tajik North Pamir. Large leucocratic granitoid intrusions are hosted in part by Devonian to Carboniferous oceanic crust and the metamorphic Kurguvad basement block of Ediacaran age (maximum deposition age) in Tajikistan. LA-ICP-MS U-Pb dating of zircons, together with whole rock geochemistry derived from tonalitic to granodioritic intrusions, reveal a major Visean to Bashkirian intrusive phase between 340 and 320 Ma ago.<br>The West Kunlun experienced two major intrusive phases, connected with arc-volcanic activity — a first phase during Proto-Tethys closure in Ordovician and Silurian times and a second phase connected to the Triassic Paleo-Tethys closure. The Carboniferous arc-volcanic phase in the North Pamir clearly postdates Paleozoic arc-magmatic activity in the West Kunlun by ~100 Ma. This observation, along with geochemical evidence for a more pronounced mantle component in the Carboniferous arc-magmatic rocks of the North Pamir, disagrees with the common model of a continuous Kunlun belt from the West Kunlun into the North Pamir. Moreover, Paleozoic oceanic units younger than and west of Tarim cratonic crust challenge the idea of a continuous cratonic Tarim-Tajik continent beneath the Pamir.</p>

The Carboniferous Arc of the North Pamir

In this study, we investigate the age and geochemical variability of volcanic arc rocks found in the Chinese, Kyrgyz, and Tajik North Pamir in Central Asia. New geochemical and geochronological data together with compiled data from the literature give a holistic view of an early to mid-Carboniferous intraoceanic arc preserved in the northeastern Pamir. This North Pamir volcanic arc complex involves continental slivers in its western reaches and transforms into a Cordilleran-style collision zone with arc-magmatic rocks. These are hosted in part by Devonian to Carboniferous oceanic crust and the metamorphic Kurguvad basement block of Ediacaran age (maximum deposition age) in Tajikistan. We discuss whether a sliver of Carboniferous subduction-related basalts and intruded tonalites close to the Chinese town of Mazar was part of the same arc. LA-ICP-MS U-Pb dating of zircons, together with whole rock geochemistry derived from tonalitic to granodioritic intrusions, reveals a major Visean to Bashkirian intrusive phase between 340 and 320 Ma ago. This clearly postdates Paleozoic arc-magmatic activity in the West Kunlun by ~100 Ma. This observation, along with geochemical evidence for a more pronounced mantle component in the Carboniferous arc-magmatic rocks of the North Pamir, disagrees with the common model of a continuous Kunlun belt from the West Kunlun into the North Pamir. Moreover, Paleozoic oceanic units younger than and west of the Tarim cratonic crust challenge the idea of a continuous cratonic Tarim-Tajik continent beneath the Pamir.

Duobagou Permian–Triassic granites from the Dunhuang orogenic belt, NW China: implications for the tectonic evolution of the southernmost Central Asian Orogenic Belt

The Duobagou Permian–Triassic granites of the Dunhuang orogenic belt are of great importance in understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt. LA-ICP-MS U–Pb zircon ages indicate that Permian–Triassic granitic intrusions from the Duobagou area formed at 276–274 Ma and 246 ± 1 Ma. These granites have high SiO2, Na2O and K2O, but low Al2O3, CaO and MgO contents and belong mainly to the high-K calc-alkaline I-type granite series. Based on whole-rock geochemistry and Sr–Nd and zircon Hf isotopes, the Duobagou Permian–Triassic granites were dominantly derived from the partial melting of lower continental crust formed during late Palaeoproterozoic to Mesoproterozoic times in a post-collisional extensional setting. Permian granites with zircon ϵHf(t) values of −5.4 to +3.1 and Hf model ages of TDM2 = 1.14–1.70 Ga indicate the involvement of a mantle component in their petrogenesis. Triassic granites with higher zircon ϵHf(t) values (+0.5 to +3.8) and TDM2 = 1.08–1.31 Ga suggest more juvenile sources caused by a greater contribution of mantle-derived melts, indicating a significant crustal growth. Regional extension from lithospheric delamination and heating from asthenospheric upwelling were proposed to have triggered the partial melting of lower crust, resulting in the generation of the Permian–Triassic magmatism. This may have been the mechanism for the significant crustal growth during Permian and Triassic times in the southernmost Central Asian Orogenic Belt.