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Elazığ volcanites, defined within the Eastern Anatolian Volcanic Province, are distributed in three regions (Cip, Harput, Yeniköy) around the center of Elazığ. While the lava of volcanites consisting of effusive and explosive volcanism products do not form thick stacks, pyroclastics, which generally form basaltic slag cones, have a relatively much thicker thickness. Petrographic examinations of the lavas have shown that the main mineral composition consists of weakly altered, porphyritic, vesicular and flow-textured olivine basalts consisting of plagioclase, olivine and pyroxene minerals, and alkaline basalts containing nepheline and leucite. According to mineral chemistry analysis data, while labradorite is the most common plagioclase mineral in all samples, a change from anorthite to sanidine is observed in Yeniköy samples and from andesine to sanidine in Harput samples. Pyroxene minerals have a bronzite and diopside composition and appear to crystallize from a system with high Mg and Ca content. In the variation diagrams related to minerals, weak differences are observed between the samples depending on their mineral composition. In terms of olivine mineral content, Cip village samples are relatively poorer in Al, Mn and Ca than pyroxene minerals, but richer in Fe and Mg, although they are particularly weak in Mg and rich in Ca content, compared to Harput samples. The orientations of the element contents of petrographic and mineral compositions indicate that these volcanics may be the product of two differentiated magmas formed under low pressure conditions, affected by the magma mixture along with fractionation. The fact that amphiboles also have magmatic and metamorphic properties suggests that metasomatism and the subduction components that because it may be important in magma differentiation. [ABSTRACT FROM AUTHOR]

The Lower Oligocene basic dikes are cropped out in the Chah-e-Alikhan area (Northeast of Isfahan province, North of the Daq-e-Sorkh desert). These dikes show NE-SW and NW-SE trends and cross cut the Eocene volcanic rocks and associated flysches. NW-SE dikes are younger and cut the NE-SW ones. These dikes are similar in petrography and are composed of plagioclase, clinopyroxene, olivine, sanidine, Cr-spinel and ilmenite. Zeolite, serpentine, calcite and magnetite are secondary minerals. These dikes represent the porphyritic, glomeroporphyritic, poikilitic and trachytic textures. Intergranular and granular textures can be seen at the center of the larger dikes. These basalts are enriched in alkalis (Na2O+K2O), LREE and LILE (Cs, Rb, Ba, Pb) and have high values of LREE/HREE ratio (La/Yb=8.9-10). In the classification diagrams, which are based on the incompatible elements and HFSEs, they are classified as alkali basalts. The primitive magma of these basaltic dikes has been produced by partial melting of a garnet-spinel lherzolite of the mantle previously suffered the carbonate metasomatism. The formation of the alkali basalt dikes of the Chah-e-Alikhan area can be ascribed to the former subduction of the Central- East Iranian Microcontinent (CEIM) confining oceanic crust and decompression melting induced by the extensional basin of the Anarak‒Jandaq area in Early Oligocene. The primary basaltic magma has been formed by low degree of partial melting of a metasomatised mantle lherzolite during continental crust extension episode in the lower Oligocene and has been ascent through the faults. Introduction In the Northwest of CEIM (Central-East Iranian Microcontinent), along the Great Kavir fault, volumes of alkali basalts with the lower Oligocene age are outcropped as volcanic and subvolcanic (Dike) rocks. In this research, the subvolcanic exposures of this basic magmatism in the the Chah-e-Alikhan area is discussed. The Lower Oligocene basic dikes are cropped out in the Chah-e-Alikhan area (Northeast of Isfahan, Northeast of Zavareh, and Northwest of the CEIM). These dikes show NE-SW and NW-SE trends and cross cut the Eocene volcanic rocks and associated flysches. In this paper, the geological and petrological aspects, as well as the geodynamic setting of alkali basalt dikes of the Chah-e-Alikhan area are discussed. Study of these dikes, as a part of the Cenozoic alkaline magmatism from Northwest of the CEIM, will be useful in understanding the geodynamical evolution of the Central Iran. Analytical method The method of study is including petrography (field, library and microscopic studies) and whole rocks geochemical analysis of rocks. 13 fresh whole rock samples of alkali basalts from the Chah-e-Alikhan area were selected for the major and trace elements chemical analyses. Whole rock geochemical analyses carried out by using a Bruker S4 Pioneer XRF at the Central Laboratory of the University of Isfahan. Trace element compositions of the selected samples were achieved by ICP-MS (Inductively coupled plasma-mass spectrometry) at the Zarazma Mineral Studies Company (Tehran, Iran). Results and discussion The rock-forming minerals of the Chahe-e-Alikhan basic dikes are Cr-spinel, olivine, clinopyroxene, plagioclase, sanidine and ilmenite. Zeolite, serpentine, calcite and magnetite are secondary minerals which are formed as a result of the alteration of primary minerals. Petrographical characteristics indicate that these dikes are alkali basalt and represent the porphyritic, glomeroporphyritic and trachytic textures. Intergranular and granular textures can be seen at the center of the larger dikes. These basalts are enriched in alkalis (Na2O+K2O=4.5-5.4 wt%), LILEs (Cs, Rb, Ba, Pb) and have high values of LREE/HREE ratio (La/Yb=8.9-10). Trace elements ratio diagrams such as La/Nb versus La/Yb, Dy/Yb against La/Yb, Sm/Yb versus La/Yb (Bogaard and Worner, 2003) and Ce/Yb-Ce (Ellam, 1992) are used in order to determination of the depth, type and degree of partial melting of the source rock. Based on the geochemical characteristics and diagrams, the primitive magma of the Chah-e-Alikhan alkali basalts possibly have been produced by about 5 to 10 percent partial melting of a garnet-spinel lherzolite, which is located at the depth of about 105 km, as a part of a mixed asthenospheric–lithospheric mantle. The elevated values of the Zr/Hf ratio and the Na2O + K2O versus TiO2 diagram (Zeng et al., 2010) indicate that the primitive magma of the studied basic dikes previously suffered the carbonate metasomatism. The Chah-e-Alikhan alkali basalts show high values of the Alkalis (Na2O + K2O), enrichment in LREE, HFSE and LILE. The subducted oceanic slab is the source of carbon and LILEs are the mobile components of subduction (Shaw et al., 2003). Considering that Cs is a highly fluid mobile element, enrichment in Cs relative to Rb suggests that the fluid phases derived from a subducting slab are probably the metasomatic agents. The lower Oligocene alkaline magmatism in the Chah-e-Alikhan area and the enrichment of the mantle with incompatible elements (metasomatism) can be attributed to two oceanic crust subduction events: (1) Northeast ward Neotethys subduction along the Zagros Thrust Zone beneath the Central Iran from the Triassic to the Eocene (Torabi, 2010); and (2) Subduction of an oceanic crust along the Great Kavir Fault, which is situated to the western margin of the CEIM. The spreading of the last ocean crust started in the Triassic and ended in the Eocene. The remnants of this oceanic crust are found as ophiolitic melanges on the western side of the CEIM, such as the Nain, Surk, and Ashin ophiolites (Rajabi and Torabi, 2012; Torabi, 2010). The geological history and position of the Chah-e-Alikhan alkali basalt dikes suggests that the the carbonate metasomatism of the mantle peridotites can be attributed to the subduction of the CEIM confining oceanic crust. Several tectonic discrimination diagrams have been used for determination of the tectonic setting of the Chah-e-Alikhan basalts. The La/Yb versus Th/Nb (Hollocher et al., 2012), Ta/Yb against Th/Yb (Gorton and Schandl, 2000) and DF1 versus DF2 (Verma and Agrawual, 2011) diagrams suggest a within-plate (continental) tectonic setting. The activity of the major faults of the area such as Great Kavir, Chah Mishury and Chah Gireh Faults has been created a suitable inter-plate extensional system to ascending the Lower Oligocene alkali basalt magma in the Chah-e-Alikhan area. Conclusion The Lower Oligocene alkali basalts of the Chah-e-Alikhan area is a part of the intra-continental alkaline magmatism crosscuts the Eocene volcanic rocks. The area provides a setting to study the Cenozoic alkaline magmatism of the northwest of the CEIM. These basalts are enriched in total Alkalis, TiO2, LREE and LILEs. They have been produced by about 5 to 10 percent degree of partial melting of a garnet-spinel bearing lherzolite of a mixed lithospheric-asthenospheric mantle which is previously metasomatised. The mantle enrichment can be ascribed to the subduction of the CEIM confining oceanic crust beneath the Central Iran from the Triassic to the Eocene. The Grate Kavir Fault and related faults have played an important role in the Lower Oligocene alkaline magmatism in northwest of the CEIM.

The northeast Jordan is part of the large intra-continental volcanic province of Harrat Al-Shaam (also written: Harrat Ash- Sham), which covers an area of about 50.000 km². In Jordan, the volcanic province covers an area of about 12.000 km². They are represented by basalt flows and tephra cones. Twenty-four basaltic rock samples were collected and covered about 25 km² area 7 km northeast of the village Dear Al-Kahef were studied. The petrographical data show that the samples are olivine-, plagioclase- and pyroxene-phyric basalt type. The geochemical investigation of the rocks shows that they are under-saturated regarding the silica content, which ranges between 46.00 and 49.86 wt.%. They are mainly alkali basalts and belong to the alkaline to sub-alkaline rocks series containing 2.26 to 4.55 wt. % alkali oxides. The geochemical parameters of these by the silica content (< 50 wt%) the high MgO content (>7 wt%), the Mg-number (0.60-0.65), and the high Ni contents lies between 100 to 170 ppm, and the high Cr content in the studied rocks range from 125 to 260 ppm. This magma shows low variable abundances of compatible and incompatible trace elements reflecting a homogenous source. Their Geochemical trend hints that the parental magma ascended rapidly, and underwent only limited fractional crystallization without crustal contamination. The primitive nature of the magma is reflected the distinct chemical similarity of the studied rocks suggests that they were derived from a single enriched and homogeneous mantle source, and initiated by a low degree of partial melting (4-13 %) of garnet peridotite at a depth >100 km. [ABSTRACT FROM AUTHOR]

The Lower Oligocene basic dikes are cropped out in the Chah-e-Alikhan area (Northeast of Isfahan province, North of the Daq-e-Sorkh desert). These dikes show NE-SW and NW-SE trends and cross cut the Eocene volcanic rocks and associated flysches. NW-SE dikes are younger and cut the NE-SW ones. These dikes are similar in petrography and are composed of plagioclase, clinopyroxene, olivine, sanidine, Cr-spinel and ilmenite. Zeolite, serpentine, calcite and magnetite are secondary minerals. These dikes represent the porphyritic, glomeroporphyritic, poikilitic and trachytic textures. Intergranular and granular textures can be seen at the center of the larger dikes. These basalts are enriched in alkalis (Na2O+K2O), LREE and LILE (Cs, Rb, Ba, Pb) and have high values of LREE/HREE ratio (La/Yb=8.9-10). In the classification diagrams, which are based on the incompatible elements and HFSEs, they are classified as alkali basalts. The primitive magma of these basaltic dikes has been produced by partial melting of a garnet-spinel lherzolite of the mantle previously suffered the carbonate metasomatism. The formation of the alkali basalt dikes of the Chah-e)Alikhan area can be ascribed to the former subduction of the Central-East Iranian Microcontinent (CEIM) confining oceanic crust and decompression melting induced by the extensional basin of the Anarak‒ Jandaq area in Early Oligocene. The primary basaltic magma has been formed by low degree of partial melting of a metasomatised mantle lherzolite during continental crust extension episode in the lower Oligocene and has been ascent through the faults. [ABSTRACT FROM AUTHOR]

The lithosphere--asthenosphere boundary (LAB), which can be seismically detected, stabilizes plate tectonics. Several conflicting hypotheses have been proposed as the causes of LAB discontinuity, such as the contribution of hydrated minerals, mineral anisotropy, and partial melts. The petit-spot melts ascending from the asthenosphere, owing to subducting plate flexures, support the partial melting at the LAB. Here, we observed the lava outcrops of six monogenetic volcanoes formed by petit-spot volcanism in the western Pacific. Thereafter, we determined the 40Ar/39Ar ages, major and trace element compositions, and Sr, Nd, and Pb isotopic ratios of the petit-spot basalts. The 40Ar/39Ar ages of two monogenetic volcanoes were ca. 2.6 Ma (million years ago) and ca. 0 Ma, respectively. The isotopic compositions of the western Pacific petit-spot basalts suggest their geochemically similar melting sources. They were likely derived from a mixture of high-μ (HIMU) mantle-like and enriched mantle (EM) -1-like components related to carbonatitic/carbonated materials and recycled crustal components. A mass balance-based melting model implied that the characteristic trace element composition (i.e., Zr, Hf, and Ti depletions) of the western Pacific petit-spot magmas could be explained by the partial melting of garnet lherzolite with a small degree of carbonatite melt flux with crustal components. This result confirms the involvement of carbonatite melt and recycled crust in the source of petit-spot melts and provides an implication for the genesis of tectonic-induced volcanism with similar geochemical signatures to those of petit-spots. [ABSTRACT FROM AUTHOR]

Volcanic clasts from the International Ocean Discovery Program Site U1431 in the South China Sea (SCS) were analyzed for V isotopic compositions in this study. These volcanic clasts represent mantle-derived carbonated melts and record the transition from carbonated melts to alkali basalts. Based on the formation sequence, these clast samples were divided into early-stage (> 8.3 Ma) and late-stage (< 8.3 Ma) clasts. The early-stage volcanic clasts have δ51V values of −0.76‰ to −0.67‰, which provide an estimate for the V isotopic composition of primary carbonated melts. Their V isotopic compositions are slightly heavier than those of mid-ocean ridge basalts (−0.84‰ ± 0.10‰) and bulk silicate Earth (−0.86‰ to −0.91‰), reflecting the control of low-degree partial melting under conditions of high oxygen fugacity. The late-stage volcanic clasts have δ51V values ranging from −0.62‰ to 0.29‰, which are systematically heavier than those of early-stage volcanic clasts. The carbonated melts rose through and reacted with the lithospheric mantle and were transformed into alkali basalts by dissolving orthopyroxene and precipitating olivine and/or clinopyroxene. Because the reactants and reaction products do not lead to significant V isotope fractionation, the V isotopes show limited variations during transformation from carbonated melts to alkali basalts. The alkali basalts were emplaced into shallow crust by multiple pulses, in which the magma experienced variable degrees of magma differentiation, with δ51V values close to those of the initial alkali basalts or increasing due to fractional crystallization of Fe Ti oxides. The change in V isotopic compositions from early-stage volcanic clasts to late-stage volcanic clasts was driven by the varying magnitude of influence exerted by different magmatic processes en route from the deep mantle to the shallow crust. [ABSTRACT FROM AUTHOR]

The Tarom- Masuleh area (western Alborz) exposes considerable Late Paleozoic volcanic rocks. Stratigraphic relationships indicate that the igneous units are of Carboniferous- Permian age. Based on whole- rock chemical data, the samples are compositionally basic (SiO2= 45.3- 50.7 wt.%) and alkaline (TiO2= 1.1- 4.4 wt.%; Nb/Y=0.9- 2.3). Furthermore, these rocks are characterized by nearly primitive to evolved compositions (MgO= 14.5- 2.5 wt.%). Major and trace elements data show that chemical variations were predominantly controlled by crystal fractionation and, mantle source processes or crustal contamination was not so effective. Trace element theoretical modeling of crystallization process also shows that fractional crystallization of olivine + clinopyroxene has played a major role in the chemical evolution of the melt. The chemical characteristics of the samples in terms of HFSE enrichment and elevated LREE/HREE ratio ((La/Yb)N= 4.8- 17.5) are identical to those of oceanic island basalts (OIB). Thus, the Late Paleozoic magmatism of the Tarom-Masouleh region took place in an intraplate setting (passive continental margin) influenced by the extensional tectonic regime. Coeval magmatism in other parts of Iran, including Central Iran, Sanandaj- Sirjan and Azerbaijan, as well as other areas of the northern margin of Gondwana (Oman, North Africa) and China, similarly represent intraplate magmatic signature attributed to the mantle plume and/or hot spot activity or extensional tectonics and rifting concurrent with the early stages of the appearance of the Neotethys Ocean.

Ocean island basalts (OIBs) with Zn isotopic ratios higher than the normal mantle (δ66Zn = 0.17 ± 0.08‰) or mid-ocean ridge basalts (MORBs; δ66Zn = 0.27 ± 0.06‰) generally also have an enriched Sr-Nd isotopic signature, suggesting carbonate-bearing eclogites, whose protolith is inferred to be subducting altered oceanic crust, in their mantle source. On the contrary, continental intraplate basalts with high δ66Zn usually show depleted Sr-Nd isotopic signatures (i.e., decoupled Zn-Sr-Nd isotopic composition). To elucidate the origin of the decoupled Zn-Sr-Nd isotopic composition in continental intraplate basalts, we report the discovery of both coupled and decoupled Zn-Sr-Nd isotopic data for a suite of Cenozoic continental intraplate basalts from the Zhejiang province, Southeast China. These basalts display clear spatial and temporal geochemical variations, with early-stage inland low-silica samples presenting moderately enriched Sr-Nd isotopic signatures and high δ66Zn (coupled Zn-Sr-Nd isotopic composition, similar to OIBs), and later-stage coastal high-silica samples that display a pronounced δ66Zn decrease with increasing SiO 2 and 87Sr/86Sr and with decreasing alkali contents and 143Nd/144Nd (decoupled Zn-Sr-Nd isotopic composition). The early-stage basalts with coupled high Zn-Sr-Nd isotopic signatures are also more enriched in incompatible elements than any other basalts from eastern China reported so far. We explain the spatial and temporal geochemical variations of these basalts as the result of two main melting events: 1) the low-silica early-stage magmatism mostly occurs inland and results from high-pressure partial melting of a carbonated eclogite-bearing asthenospheric mantle. Because of the presence of a thick lithosphere limits the melting of the depleted mantle component, the signature of the Zn-Sr-Nd isotopically enriched, and more fusible carbonated eclogite is preserved. 2) At the later stage, magmatism mostly occurs on the coast where the subcontinental lithosphere is thinner. Hence, decompression melting progresses to shallower depth, resulting in an increase of the contribution from the depleted peridotite matrix and a dilution of the signal from the isotopically enriched fusible component. Further upwelling and in-situ melting at the base of the subduction-modified sub-continental lithospheric mantle (SCLM) explains both the decoupled Zn-Sr-Nd isotopic signature of the coastal basalts and their major and trace element variability. We further propose that decompression melting is driven by small-scale convection resulting from variations of lithospheric thickness. Our data highlight the importance of dynamic melting of carbonated eclogite-bearing asthenosphere and subsequent lithospheric melting in preservation and destruction of the coupled enriched Zn-Sr-Nd isotopic signature of carbonated eclogite component and generation of the apparent decoupled Zn-Sr-Nd isotopic signal commonly observed in continental intraplate basalts. [ABSTRACT FROM AUTHOR]

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The Yarmouk River gorge extends along the Israel–Jordan–Syria border junction. It marks the southern bound of the Irbid–Azraq rift and Harrat Ash Shaam volcanic field at their intersection with the younger Dead Sea Transform plate boundary. During the last ∼13 Ma, the gorge has repeatedly accumulated basaltic units, chronologically named the Lower, Cover, Yarmouk and Raqqad Basalt formations. We examined their origin and distribution through aerial photos, and geological and geophysical evidence. Our results define a southern Golan magmatic province, which includes exposed Miocene (∼13 Ma) basalts, gabbro–diabase intrusions below the gorge and the adjacent Dead Sea Transform valley, and numerous Pliocene–Pleistocene volcanic sources along the gorge. Cover Basalt (∼5.0–4.3 Ma) eruptions formed two adjacent 0–100 m thick plateaus on the transform shoulder before flowing downslope to fill the topographically lower Dead Sea Transform valley with ∼700 m thick basalts. Later incision of the Yarmouk River and displacement along its associated fault divided the plateaus and formed the gorge. The younger Yarmouk (0.8–0.6 Ma) and Raqqad (0.2–0.1 Ma) basalts erupted in the upper part of the gorge from volcanos reported here, and flowed downstream toward the Dead Sea Transform valley. Consequently, eruptions from six phreatic volcanic vents altered the Yarmouk River morphology from sinuous to meandering. Our results associate the ∼13 Ma long southern Golan volcanism with the proposed SW-trending extensional Yarmouk Fault, located east of the Dead Sea Transform. Hence, the Yarmouk volcanism is associated with the ongoing Harrat Ash Shaam activity, which is not directly linked to the displacement along the Dead Sea Transform. [ABSTRACT FROM AUTHOR]

Crust–mantle interaction induced by continental subduction occurs through metasomatic reaction of continental crust-derived materials with mantle wedge peridotite in continental subduction channels. Mantle-derived igneous rocks above continental subduction zones can provide insights into the nature of crust–mantle interaction and the types of metasomatism. The Laixi region is located on the southeastern margin of the North China Craton adjacent to the Sulu orogen. Here, we present K–Ar dating, whole-rock major and trace elements, Sr–Nd–Pb isotopes, and olivine and clinopyroxene major and trace elements of the Laixi basalt to investigate the nature of metasomatism at the crust–mantle interface. These basalts exhibit geochemical inheritance of island arc basalt (IAB)-like trace-element patterns, moderately enriched Sr–Nd isotopic compositions, and variable Pb isotopic compositions from upper-crustal materials of the subducted South China Block. The olivine and clinopyroxene contents of the Laixi basalts indicate a mixed source composed of ~ 51% pyroxenite and ~ 49% peridotite which is the result of carbonate metasomatism. On the basis of the typical differences in MgO, CaO and Al2O3 contents between the Laixi basaltic magmas and experimental melts, the metasomatic agents are identified as carbonated eclogite-derived melts. These features of the IAB-like basalts suggest metasomatic reaction of mantle-wedge peridotite with carbonated silicate melt derived from the subducted upper crust in the continental subduction channel, with olivine being consumed to generate ultramafic metasomatites enriched in pyroxene. [ABSTRACT FROM AUTHOR]

We report multistage geochemical evolution of off-cratonic subcontinental lithospheric mantle by studying mantle xenoliths hosted in alkali basalts from the northwestern part of the Deccan volcanic province in Kutch. The xenolithic fragments are peridotites, composed of Cr-rich diopside, Mg-rich olivine, orthopyroxene and aluminous spinel. Compositionally, these peridotites belong to type I: Cr-diopside lherzolite group. Primarily they possess protogranular texture, but, secondary textures such as reaction corona are also present. High forsterite content of primary olivine (Fo89–92), high Mg# (>92) in orthopyroxene along with low Cr# (0.09–0.35) and TiO2 content (up to 1.12 wt.%) in spinel indicate their upper mantle origin. Higher values of AlVI/AlIV (0.99–2.4) of primary clinopyroxenes provide evidence for their high-pressure upper mantle origin, consistent with their high Mg#. Clinopyroxene displays light rare-earth element- and mid-rare-earth element-enriched pattern along with pronounced negative spike for Nb, Ta, Ti, Zr and Hf. They record multiple metasomatic imprints; high Ti/Eu (>1500) ratio attests silicate metasomatism whereas negative high-field-strength element anomalies indicate a carbonate metasomatism. Olivine-spinel mantle array trend suggests low degrees of partial melting and melt extraction (1–15 wt.%). The primary mineralogy of peridotite xenoliths affirms that they have been equilibrated at a temperature and pressure range of 786–1159°C and 8–23 kb, respectively. They record high mantle heat flow between 62 and 66 mW m−2, may be interpreted as a consequence of thermal perturbation by additional heat input into a relatively thin mantle lithosphere via upcoming magma(s) due to upwelling of Réunion plume beneath western part of the Indian subcontinent. Summarising we conclude that the lithospheric mantle beneath western India suffered a complex multistage evolutionary history followed by rifting at the end of the Mesozoic era. [ABSTRACT FROM AUTHOR]

The Ghezelhesar alkali olivine basalt flows as dark horizontal flows with about 20 m thickness covered the Quaternary deposits, 2 km southwest of Ghezelhesar village, 60 km northeast of Hamedan and in the Sanandaj-Sirjan geological and tectonic zone. The phenocrysts of these rocks are olivine and clinopyroxene often as euhedral crystals and common porphyritic, vitrophyritic and glomeroporphyric textures. The matrix of the rocks studied formed from volcanic glass, leucite, nepheline and microliths of pyroxene. The Ghezelhesar basalts, with continental within plate alkaline nature, are silica-under saturated and characterized by normative minerals of Diopside, Hematite, Anorthite, Albite, Orthoclase, ±Hypersthene, ±Olivine, ±Nepheline, and ±Quartz. REE normalized patterns show enrichment in LREEs rather than HREEs and fractionation between LREE and HREE is relatively high (LaN/YbN = 37.05–43.43). A negative anomaly in High Field Strength Elements (Nb, Ta, Zr, Ti, P, and Rb) and positive anomaly in Large Ion Lithophile Elements (i.e. Ba, Pb) and elements such as Th, La, Ce, Nd, and Sm are remarkable geochemical features of the rocks under study. These criteria along with parameters of their trace elements such as the ∆Nb indicate that the parent magma of the rocks under investigation derived from the low-grade degree partial melting of an enriched garnet-mantle, and the fractional crystallization has affected their chemical properties.

The Tarom- Masuleh area (western Alborz) exposes considerable Late Paleozoic volcanic rocks. Stratigraphic relationships indicate that the igneous units are of Carboniferous- Permian age. Based on whole- rock chemical data, the samples are compositionally basic (SiO2= 45.3- 50.7 wt.%) and alkaline (TiO2= 1.1- 4.4 wt.%; Nb/Y=0.9- 2.3). Furthermore, these rocks are characterized by nearly primitive to evolved compositions (MgO= 14.5- 2.5 wt.%). Major and trace elements data show that chemical variations were predominantly controlled by crystal fractionation and, mantle source processes or crustal contamination was not so effective. Trace element theoretical modeling of crystallization process also shows that fractional crystallization of olivine + clinopyroxene has played a major role in the chemical evolution of the melt. The chemical characteristics of the samples in terms of HFSE enrichment and elevated LREE/HREE ratio ((La/Yb)N= 4.8- 17.5) are identical to those of oceanic island basalts (OIB). Thus, the Late Paleozoic magmatism of the Tarom-Masouleh region took place in an intraplate setting (passive continental margin) influenced by the extensional tectonic regime. Coeval magmatism in other parts of Iran, including Central Iran, Sanandaj- Sirjan and Azerbaijan, as well as other areas of the northern margin of Gondwana (Oman, North Africa) and China, similarly represent intraplate magmatic signature attributed to the mantle plume and/or hot spot activity or extensional tectonics and rifting concurrent with the early stages of the appearance of the Neotethys Ocean. [ABSTRACT FROM AUTHOR]

The Tabas Black Land volcanic field (14 Ma) is on the major right lateral Nayband fault, on the Lut Block, Iran. It has a central area of eroded ventd, surrounded by lavas. Lavas are tilted and folded on the east by the Nayband fault. To the west lavas are undeformed and are in inverted relief. We study the evolution of the volcanic field and assess its relationship to the regional tectonics. The Tabas Black Land products are basaltic trachyandesite – basaltic andesite, with intraplate sodic alkaline affinity and represent post-collisional magmatism. Geochemical and isotopic data show that magmas formed from 5% partial melting of garnet peridotite mantle. Modest K2O values, ~1.25 wt%, indicate hydrous phases (e.g., phlogopite) in the source. The average of P2O5/K2O ratios (0.31) indicate very low crustal contamination caused a sub-alkaline tendency in few differentiated samples. Comparing with other studies, we conclude that partial melting in Tabas is higher than at other Lut Block volcanoes, but have the least crustal contamination. Tabas magma storage and differentiation happened in the middle crust (400-500 MPa = 15-19 km), for temperatures of 1150 - 1200 oC. The Nayband has caused several destructive earthquakes during the 20th century. Volcanism has localised along the fault since 14 million years, with a similar source, but decreasing degrees partial melting and a shift towards the south from Tabas Black Lands. Thus, Nayaband magmatism appears to be dwindling, even if the fault itself remains active.

The Beishan orogenic belt, located in the southern Central Asian Orogenic Belt, includes several discrete arc terranes. Here, we report on a newly discovered Early Neoproterozoic volcano‐sedimentary sequence in the eastern Beishan orogenic belt in order to constrain the composition and origin of the Shuangyingshan‐Huaniushan Terrane. The ~766‐m‐thick volcano‐sedimentary sequence is very low‐grade metamorphosed, and characterized by muddy and silty slate with the well‐developed parallel laminations and minor thinly‐bedded limestone in its lower and upper sections, and thick packages of sandstone‐conglomerate and basaltic rocks in the middle section. Lava flow units in the basalt are very common, and the sandstone‐conglomerate exhibits sedimentary structures typical of gravity currents, including erosional and slump features, and Bouma sequences. These features suggest that syn‐sedimentary volcanism occurred and the sequence formed in an active, deep marine environment. The basalt has a zircon U–Pb age of 901 ± 10 Ma, indicating that this sequence formed during the Early Neoproterozoic. Basalt samples have moderate SiO2 (45.33–49.18%), and high TiO2 (1.27–4.04%) contents, Mg# values of 25–48, and plot in the alkali basalt field in the Nb/Y versus Zr/TiO2 diagram, indicative of an evolved alkali basalt magma. They show inclined chondrite‐normalized REE patterns with (La/Yb)N ratios of 4.74–6.53, no pronounced negative Eu anomalies (Eu/Eu* = 0.87–1.22), no obvious negative Zr, Hf, Nb, and Ta anomalies in the primitive‐mantle‐normalized trace‐element diagram, consistent with oceanic island basalts. Considered together, these lithologies resemble those of an oceanic seamount. Our results, and the presence of the previously reported Gubaoquan granitic and mafic rocks (905–865 Ma) that formed in an active continental margin setting and underwent an amphibolite‐facies metamorphism, suggest that the Shuangyingshan‐Huaniushan Terrane may be an accreted terrane that consists of different lithologies with various origins that formed during the Neoproterozoic. [ABSTRACT FROM AUTHOR]

The Payas region bauxite deposits occur as a sandwiched layer that is a few kilometers long and an average of 10 m thick between the lower and upper Cretaceous carbonates of the Arabian Platform. The bauxites occur as 2 types, comprising blanket and pocket, are chemically and texturally homogeneous, and have a thrust structure with ophiolitic mélange formations. The bauxite varies in color, from reddish-brown to grayish-green to black, and has a massive, patchy, and very rare oolitic-pisolitic texture. The bauxite mainly consists of diaspore, hematite, rutile, anatase, rare kaolinite, boehmite, and pyrite minerals. The prismatic and lath-shaped euhedral rutile within the bauxites indicated in situ formation of the bauxites from Ti-rich basaltic pyroclastics. The chondrite-normalized rare earth element pattern of the bauxite was similar to the basalt pattern and had a very weak Eu anomaly (0.9). There are 2 groups of elements have been enriched in the Payas region bauxite: the first group contains TiO2 (9.67wt%), Cr (752 ppm), V (617 ppm) and Ni (72 ppm), and the second group comprises Zr (993 ppm), Nb (86 ppm) and Sn (7 ppm). These 2 groups of element enrichment indicated that the parental material of bauxite had an alkali basalt character. The carbon and oxygen isotope stratigraphy throughout the carbonate section from the bottom to the top indicated that the climate was warm during bauxitization (mean δ18OVPDB: -6.15‰) and relatively cold after bauxite deposition (mean δ18OVPDB: -4.71‰). A marine regression during the warm climate could have been related to the uplifting of the coastal zone, which was linked to the vertical fault movements of the normal faults. A rapid transgression after bauxite formation during the cold climate period can be explained by subsidence of the continental margin, which was associated with episodic ophiolitic nappe loading during the closure of the Neotethyan Ocean in the region. [ABSTRACT FROM AUTHOR]

The Ghezelhesar alkali olivine basalt flows as dark horizontal flows with about 20 m thickness covered the Quaternary deposits, 2 km southwest of Ghezelhesar village, 60 km northeast of Hamedan and in the Sanandaj-Sirjan geological and tectonic zone. The phenocrysts of these rocks are olivine and clinopyroxene often as euhedral crystals and common porphyritic, vitrophyritic and glomeroporphyric textures. The matrix of the rocks studied formed from volcanic glass, leucite, nepheline and microliths of pyroxene. The Ghezelhesar basalts, with continental within plate alkaline nature, are silica-under saturated and characterized by normative minerals of Diopside, Hematite, Anorthite, Albite, Orthoclase, ±Hypersthene, ±Olivine, ±Nepheline, and ±Quartz. REE normalized patterns show enrichment in LREEs rather than HREEs and fractionation between LREE and HREE is relatively high (LaN/YbN = 37.05–43.43). A negative anomaly in High Field Strength Elements (Nb, Ta, Zr, Ti, P, and Rb) and positive anomaly in Large Ion Lithophile Elements (i.e. Ba, Pb) and elements such as Th, La, Ce, Nd, and Sm are remarkable geochemical features of the rocks under study. These criteria along with parameters of their trace elements such as the ∆Nb indicate that the parent magma of the rocks under investigation derived from the low-grade degree partial melting of an enriched garnet-mantle, and the fractional crystallization has affected their chemical properties. [ABSTRACT FROM AUTHOR]

Ostrá Lúka basalts are a product of the final phase of Neogene volcanism in Central Slovakia. Their major and trace elements composition is alkaline, a feature confirmed by light rare earth elements (LREE) relative enrichment and some incompatible trace elements ratios. The basalts contain rare surrounded gabbro cumulates. Their peculiarity is a strong zonation of olivines and clinopyroxene. The significant zonation probably indicates a short stop of the melt at shallow depth. The Sr, Nd and Pb isotope compositions indicate an origin from a moderately depleted mantle source. The mineral and chemical composition of the basalts is similar to the Pannonian basin alkali basalts and the Western and Central Europe alkali basalts.

Skarnoid calc-silicate xenoliths composed of anorthite, clinopyroxene and Mg-Al spinel occur in alkali basalts of the Pliocene-Pleistocene intra-plate magmatic province in the northern part of the Pannonian Basin. Randomly oriented and elongated pseudomorphs are tschermakite crystals replaced by olivine, spinel and plagioclase. The relict amphibole within the pseudomorphs is characterized by high VIAl, between 1.95 and 2.1, and very low occupancy of the A-site (3+Al)AlSiO6 endmember with an equal proportion of VIAl3+ and Fe3+. Concentrations of kushiroite CaAlAlSiO6 endmember, up to 47.5 mol%, are the highest recorded in terrestrial samples. The AlFe3+-rich pyroxenes originated at the expense of diopside-augite during the interaction with carbonate-aluminosilicate melt. Forsterite (Fo72–83) and hemoilmenite with up to 32 mol% geikielite (9.3 wt% MgO) also crystallized from the melt, leaving behind the residual calcic carbonate with minor MgO (1–3 wt%). Columnar habit of neoformed olivine growing across diopside-augite layers indicates rapid crystallization from eutectic liquid. Euhedral aragonite and apatite embedded in fine-grained calcite or aragonite groundmass indicate slow crystallization of the residual carbonatite around the calcite-aragonite stability boundary. Corundum exsolutions in rock-forming anorthite are products of superimposed low-pressure pyrometamorphic reworking during transport in alkali basalt. Concomitant alkali metasomatism produced neoformed interstitial sodalite, nepheline, sanidine, albite, biotite, Mg-poor ilmenite (10–18 mol% MgTiO3), Ti-magnetite and fluorapatite. Olivine-ilmenite-aragonite-calcite thermobarometry returned temperatures of 770–860 °C and pressures of 1.8–2.1 GPa, whereas plagioclase-amphibole thermobarometer yielded 781 ± 13 °C and 2.05 ± 0.03 GPa. The calculated pressures correspond to depths of 60–70 km. The calc-silicate xenoliths are most likely metamorphosed marbles; however, a magmatic protolith (metagabbro, metaanorthosite) cannot be ruled out owing to high Cr contents in spinels (up to 30 mol% chromite) and abundant Cu-sulfides.

The Antalya Complex in southern Turkey comprises a number of autochthonous and allochthonous units that originated from the Southern Neotethys. Late Triassic volcanic rocks are widespread in the Antalya Complex and are important for the onset of the rifting stage of the southern Neotethys. The studied Late Triassic volcanic rocks within the Antalya Complex are exposed in the southern part of Saklıkent (Antalya) region. They are represented by pillow, massive, and columnar-jointed lava flows with volcaniclastic breccias and pelagic limestone intercalations. Spilitic basalts exhibit intersertal, microlithic porphyritic, and ophitic textures and are represented by plagioclase, pyroxene, and olivine. Secondary phases are characterized by serpentine, calcite, chlorite, epidote, zeolite, and quartz. Based on Zr/Ti vs. Nb/Y ratios, the volcanic rocks are represented by alkaline basalts (Nb/Y = 1.54-2.82). A chondrite normalized REE diagram for the volcanic rocks displays significant LREE enrichment with respect to HREE ([La/Yb]N = 15.14-19.77). Trace element geochemistry of the studied rocks suggests that these rocks are more akin to ocean island basalt (OIB) and were formed by small degrees (~2-4%) of partial melting of an enriched mantle source (spinel + garnet-bearing lherzolite). The volcanic rocks of the Saklıkent region exhibit similarities to the Late Triassic volcanics of the Koçali Complex in SE Anatolia and the Mamonia Complex (Cyprus) in terms of their geochemical features. All evidence suggests that the Late Triassic alkaline volcanics in Antalya, Mamonia (Cyprus), and the Koçali (Adıyaman) Complexes were formed in an extensional environment at the continent-ocean transition zone during the rifting of the southern Neotethyan Ocean. [ABSTRACT FROM AUTHOR]

A geochemical study was undertaken on basaltic lava flows intercalated with Oligocene to Miocene strata in the Sabzevar region, northern Iran, to examine their petrogenesis in a regional tectonic framework. The lavas are either aphyric or have phenocrysts and micro-phenocrysts of olivine and, to a lesser extent, clinopyroxene. Geochemically, the lavas are silica-undersaturated alkali basalts characterized by relatively high Mg# (~ 57–66) and Na2O/K2O (~ 2.0–6.7). They have distinctive trace element patterns characterized by strong rare-earth element fractionation, negative Nb–Ta and Zr-Hf anomalies and a positive Sr anomaly. Significant contamination by crustal materials either in the magma source or during ascent is ruled out on the basis of trace element compositions and Sr–Nd isotopic compositions (87Sr/86Sr = 0.7037–0.7048 and 143Nd/144Nd = 0.5128–0.5130), both of which differ markedly from continental crustal rocks. Phenocryst assemblage, analysis of multiple saturation points in lherzolite systems, and covariations of La/Yb with MgO of the studied lavas are generally consistent with an origin involving high-pressure fractionation of peridotite-derived melts. Primary magma compositions calculated by reversed fractionation of clinopyroxene and olivine for the relatively primitive samples (> 9 wt.% MgO), however, do not plot on the lherzolite multiple saturation points. Also, high-pressure fractionation predicts increasing trends of silica undersaturation and alkalinitiy with differentiation, and such trends are not indicated by the geochemical data. We suggest that the mixed trends shown by the data might be related to melt generation from both peridotite and silica-deficient pyroxenite sources, superimposed by variable degrees of high-pressure fractionation. The role of pyroxenite in magma genesis is indicated not only by the positive Sr anomaly shown by the trace element patterns, but also first-row transition element systematics of the studied lavas. The silica-deficient pyroxenites contributing to melt generation might have been transformed from mafic–ultramafic cumulates in subducted, lower oceanic crust, or might have formed in the lower crust or mantle lithosphere under continents during earlier magmatic episodes. [ABSTRACT FROM AUTHOR]

• Large Fe isotopic variation for continental intraplate basalts from SE China. • A two-stage melting process explains both heavy and light Fe isotope data. • Early-stage low-degree melt preserves heavy Fe isotopes of carbonated pyroxenite. • Further decompression and mixing with SCLM melt causes light Fe isotope signature. • Fe isotopes provide insights into generation of continental intraplate basalts. Iron isotope studies on ocean island basalts (OIBs) and mid-ocean ridge basalts (MORBs) have disclosed the contribution of pyroxenite lithologies in the generation of basaltic magmas. Whether Fe isotopic compositions of continental intraplate basalts can be applied to trace lithological heterogeneity within the mantle source regions remains poorly investigated. To explore the systematics of stable Fe isotopes as a potential probe of lithological heterogeneity in the source of continental intraplate basalts, we present twenty-four Fe isotope data on a suite of well-characterized Cenozoic basalts from SE China. The samples show a large range of Fe isotope values (δ56Fe = +0.09‰ to +0.20‰), which correlate with SiO 2 , CaO/Al 2 O 3 , Ti/Eu, Hf/Hf*, Zr/Nb, Dy/Yb, La/Yb, Nb/Y, K/La, Sr/Ce, δ66Zn and estimated equilibrium pressures. The samples with the highest δ56Fe values represent early-stage low-silica basalts with moderately enriched Sr-Nd isotope ratios and high δ66Zn values, while the late-stage high-silica basalts display a broad δ56Fe decrease with increasing 87Sr/86Sr and with decreasing ε Nd and δ66Zn. We demonstrate that the heaviest Fe isotope signatures cannot be derived from a pure peridotite source and require a pyroxenite component in the source. Combined with other geochemical proxies, we show that the heaviest basalt compositions are consistent with low-degree melts produced by the adiabatic decompression of a carbonated pyroxenite-bearing asthenospheric mantle. Mixing of these hybrid melts with melt produced from in-situ melting of the subduction-modified sub-continental lithospheric mantle (SCLM) reproduces the Fe-isotope variability of the late-stage basalts. Our results demonstrate the significance of lithological heterogeneity in the mantle source of continental intraplate basalts and highlight the subsequent imprint of mantle lithosphere in the evolution of their Fe isotope compositions. Finally, this study exemplifies the potential of the Fe-Zn stable isotope pair for mantle geochemistry; coupled with traditional radiogenic isotopes and major and trace element concentrations, they formed an efficient tool to trace the nature and contribution of the mantle source components in the formation of intraplate basalts. [ABSTRACT FROM AUTHOR]

Introduction Basaltic volcanoes are one of the volcanisms that have occurred in different parts of the world. The study of these lavas is important for petrologists, because they are seen in different tectonic settings and therefore diverse mechanisms affect their formation (Chen et al., 2007). Young volcanic rocks such as Quaternary basalts are one of latest products of magmatism in Iran that are related to deep fractures and active faults in Quaternary (Emami, 2000). The study area is located at 140km east of Birjand at Gazik 1:100000 geological map (Guillou et al., 1981) and have 60̊ 11' to 60̊ 15 '27" eastward longitude and 32̊ 33' 24" to 32̊ 39' 10" northward latitude. On the basis of structural subdivisions of Iran, this area is located in the northern part of the Sistan suture zone (Tirrul et al., 1983). Because of the importance of basaltic rocks in Sistan suture, this research is done with the aim of investigating the petrography and mineralogy of basaltic lavas, the nature of basaltic and intermediate magmatism and finally determination of tectonomagmatic regime. Materials and methods After field studies and sampling, 85 thin sections were prepared and carefully studied. Then ten samples with the lowest alteration were analyzed for major elements by inductively coupled plasma (ICP) technologies and trace elements were analyzed using inductively coupled plasma mass spectrometry (ICP-MS), following a lithium metaborate/tetraborate fusion and nitric acid total digestion at the Acme laboratories, Vancouver, Canada. Electron probe micro analyses of clinopyroxene and olivine were done at the Iranian mineral processing research center (IMPRC) by Cameca SX100 machine. X-ray diffraction analysis of minerals was done at the X-ray laboratory of the University of Birjand. Results In 60km south of GaziK at the east of the southern Khorasan province and the northern part of the Sistan suture zone, volcanic rocks with intermediate (Oligomiocene) and basic (Quaternary) compositions outcropped above ophiolitic units. Electron probe micro analyzer (EMPA) data indicated that clinopyroxene in basalt is diopside and olivine from chrysolite type with Mg# around 81-82 percent. The whole rocks geochemical data prove calc-alkaline and alkaline nature for andesites and basalts, respectively. Trace element patterns, especially for andesites show enrichment in Ba, K, Cs, Sr and Th, depletion in P, Nb, Ti and enrichment in LREE relative to HREE. Electron probe micro analyses of clinopyroxene in olivine basalt support alkaline nature and within plate tectonic setting for this rock. Thermobarometry of clinopyroxene in olivine basalt record crystallization conditions about 1200 oC and 6-10kbars. Discussion The origin of intraplate volcanism is diverse and not always well understood. Most intraplate volcanos have been attributed to (i) mantle plumes and hot spots, (ii) continental rift, (iii) back-arc extension and (iv) lithosphere delamination and thinning (Chen et al., 2007). Although volcanism at intraplate settings is less common than along mid-ocean ridges and subduction zones, it is of significant importance for both preventing geological hazards and understanding mantle geochemistry. It is believed that alkaline oceanic island basalts (OIB) are only derived from the asthenospheric mantle (Alici et al., 2002). However, the intracontinental alkaline magmas can be produced by partial melting of metasomatized mantle enriched in LREE and LILE (Upadhyay et al., 2006). On the basis of trace element diagrams, Ratouk basaltic rocks placed within plate volcanic zone (WPVZ) and andesitic samples have been located within the active continental margin (ACM). The studies that took place about young basaltic volcanism (Alishahi, 2012; Mollashahi et al., 2011; Ghasempour et al., 2011; Pang et al., 2012; Walker et al., 2009) have shown that the mechanisms of their occurrence are similar such that all of them have been formed in intraplate extensional environments and active fault zone and originated from enriched mantle or asthenosphere. Lithospheric thickness maps derived from the speed of shear waves show that the lithosphere is thin in east of Iran and volcanic activity has occurred along strike-slip faults (Walker et al., 2009). Therefore, according to other similar basaltic eruptions that have occurred in the Sistan suture zone, we can say that all of them are from the same origin and as a result of deep fractures within continental plates that provide conditions for the eruption of basaltic magma. Andesitic units in the Ratouk area are located within the active continental margin and show similar characteristics to rocks of the Subduction Zone in terms of composition. Acknowledgements The authors would like to thank reviewers for the constructive comments which greatly contributed to the improvement of the manuscript. References Alici, P., Temel, A. and Gourgaud, A., 2002. Pb-Nd Sr isotope and trace element geochemistry of Quaternary extension-related alkaline volcanism: a case study of Kula region western Anatolia, Turkey. Journal of Volcanology and Geothermal Research, 115(3): 487-510. Alishahi, E., 2012. Petrology and Geochemistry of volcanic rocks in Nasfandeh area (east of Nehbandan) –Iran. M.Sc. Thesis, University of Birjand, Birjand, Iran, 211 pp. (in Persian with English abstract) Chen, Y., Zhang, Y., Graham, D., Su, S. and Deng, J., 2007. Geochemistry of Cenozoic basalts and mantle xenoliths in Northeast China. Lithos, 96(1): 108–126. Emami, M.H., 2000. Magmatism in Iran. Geological Survey of Iran, Tehran, 608 pp. Ghasempour, M.R., Byabangard, H., Boomeri, M. and Moridi, A., 2011. Geochemistry and tectonic setting of Plio-Quaternary basaltic rocks in SE Nehbandan, eastern Iran. Iranian Journal of Crystallography and Mineralogy, 18(4): 695-708. (in Persian with English abstract) Guillou, Y., Maurizot, P., Vaslet, D. and Dellavillen, H., 1981. Geological map of Gazik, Scale1:100000. Geological Survey of Iran. Mollashahi, N., Zarrinkoub, M.H., Mohammadi, S.S. and Khatib, M.M., 2011. Petrology of young volcanic in Hamun Lake area (East of Iran). Iranian Journal of Crystallography and Mineralogy, 19(3): 519-528. (in Persian with English abstract) Pang, K.W., Chung, S.L., Zarrinkoub, M.H., Mohammadi, S.S., Yang, H.M., Chu, C.H., Lee, H.Y. and Lo, C.H., 2012. Age, geochemical characteristics and petrogenesis of Late Cenozoic intraplate alkali basalts in the Lut–Sistan region, eastern Iran. Chemical Geology, 306-307: 40-53. Tirrul, R ., Bell, L.R., Griffis, R.J. and Camp, V.E., 1983. The Sistan suture zone of eastern Iran. Geological Society of America Bulletin, 94(1): 134-150. Upadhyay, D., Raith, M.M., Mezger, K. and Hammerschmidt, K., 2006. Mesoproterozoic rift-related alkaline magmatism at Elchuru, Prakasam Alkaline Province, SE India. Lithos, 89(3): 447-477. Walker , R.T., Gans, P., Allen, M., Jackson, J., Khatib, M.M. and Zarrinkoub, M.H., 2009. Late Cenozoic Volcanism and rates of active faulting in eastern Iran. Geophysical Journal International, 177: 783-805.

Introduction The study area is located 12km away from the north east of Sarbisheh at the eastern border of the Lut block (Karimpour et al., 2011; Richards et al., 2012). The magmatic activity in the Lut blockhas begun in the middle Jurassic (165-162 Ma) and reached its peak in the Tertiary age (Jung et al., 1983; Karimpour et al., 2011). Volcanic and subvolcanic rocks in the Tertiary age cover over half of the Lut block with up to 2000 m thickness and they were formed due to subduction prior to the collision of the Arabian and Asian plates (Jung et al., 1983; Karimpour et al., 2011). In the Kangan area, the basaltic lavas cropped out beyond the above intermediate to acid volcanic rocks. In this area, bentonite and perlite deposits have an economic importance. The main purpose of this paper is to present a better understanding of the tectono-magmatic settings of volcanic rocks in the northeast of Sarbisheh, east of Iran based on their geochemical characteristics. Materials and methods Fifteen samples were analyzed for major elements by inductively coupled plasma (ICP) technologies and trace elements by using inductively coupled plasma mass spectrometry (ICP-MS), following a lithium metaborate/tetraborate fusion and nitric acid total digestion, at the Acme laboratories, Vancouver, Canada. Results The Kangan area is located at the northeast of Sarbishe, Southern Khorasan and the eastern border of the Lut block. In this area, basaltic lavas have cropped out above intermediate to acid lavas such as andesite, dacite, rhyolite (sometimes perlitic) .The main minerals in the basalt are plagioclase, olivine and pyroxene, in andesite contain plagioclase, pyroxene, biotite and amphibole and in acid rocks include plagioclase, quartz, sanidine, biotite and amphibole. Intermediate to acid rocks have medium to high-K calc-alkaline nature and basalt is alkaline. Enrichment in LREE relative to HREE (Ce/Yb= 21.14-28.7), high ratio of Zr/Y(4.79- 10.81), enrichment in LILE and negative anomaly of Eu, Nb, P, Ti, Ba and Sr in intermediate to acid lavas are characteristics of subduction related calc-alkaline magmatism. Geochemical characteristics such as high ratio of La/Yb (8.18), low content of Rb with tectonic setting discriminant diagrams show within plate environment for basalt. The constituent magma of the studied rocks originated from an enriched garnet lherzolite source in 100 to 110km depth. Discussion Enrichment in LREE relative to HREE (Ce/Yb= 21.14-28.7), high ratio of Zr/Y (4.79- 10.81), enrichment in LILE and negative anomaly of Eu, Nb, P, Ti, Ba and Sr in intermediate to acid lavas are characteristics of subduction related calc-alkaline magmatism. Tectonic setting discrimination diagrams show that andesite to dacitic rocks are located in active continental margin (Schandle and Gorton, 2002) and basalt is placed within the volcanic plate zone and continental rift type (Verma et al., 2006). Intermediate to acid rocks of Kangan area originated from lithospheric mantle (Moharami et al., 2014) that is enriched by sediment melt related metasomatism (Ersoy et al., 2010) whereas Kangan basaltic lava origin is Nb enriched (Wang et al., 2008; Sajona et al., 1996) mixed lithospheric - asthenospheric mantle (Moharamiet al., 2014). According to the trace elements diagrams (Ellam, 1992), partial melting depth for generation of Kangan area lavas was determined to be about 100 to 110Km. Because of absent crustal contamination instances in the basalt, it can be argued that ascending of magma has been rapid and probably similar to other alkali basalts in east of Iran, it may be related to deep fault systems. Acknowledgements The authors would like to thank the reviewers for their constructive comments which greatly contributed to the improvement of the manuscript. References Ellam, R.M., 1992. Lithospheric thickness as a control on basalt geochemistry. Geology, 20(2): 153-156. Ersoy, E.Y., Helvaci, C. and Palmer, M.R., 2010. Mantle source characteristics and melting models for the early-middle Miocene mafic volcanism in western Anatolia: implications for enrichment processes of mantle lithosphere and origin of K-rich volcanism in post-collisional settings. Journal of Volcanology and Geothermal Research, 198(1-2): 112-128. Jung, D., Keller, J., Khorasani, R., Marcks, C., Baumann, A. and Horn, P., 1983. Petrology of the Tertiary magmatic activity the northern Lut area, East of Iran. Geological Survey of Iran, Tehran, Report 51, 519 pp. Karimpour, M.H., Stern, C.R., Farmer, L., Saadat, S. and Malekezadeh, A., 2011. Review of age, Rb-Sr geochemistry and petrogenesis of Jurassic to Quaternary igneous rocks in Lut block, eastern Iran. Geopersia, 1(1):19-36. Moharami, F., Azadi, I., Mirmohamadi, M., Mehdipour Ghazi, J. and Rahgoshay, M., 2014. Petrological and Geodynamical Constraints of Chaldoran Basaltic Rocks, NW Iran: Evidence from Geochemical Characteris. Iranian Journal of Earth Sciences, 6(1): 31-43. Richards, J.P., Spell, T., Rameh, E., Razique, A. and Fletcher, T., 2012. High Sr/Y magmas reflect arc maturity, high magmatic water content, and porphyry Cu ± Mo ± Au potential: examples from the Tethyan arcs of central and eastern Iran and western Pakistan. Economic Geology, 107(2): 295–332. Sajona, F.G., Maury, R.C., Bellon, H., Cotton, J. and Defant, M., 1996. High field strength element enrichment of Pliocene-Pelistocene island arc basalts, Zomboanga Peninsula, Western Mindanao Philippines. Journal of Petrology, 37(3): 693–726. Schandl, E.S. and Gorton, M.P., 2002. Application of high field strength elements to discriminate tectonic setting in VMS environment. Economic Geology, 97(3): 629-642. Verma, S.P., Guevara, M. and Agrawal, S., 2006. Discriminating four tectonic settings: Five new geochemical diagrams for basic and ultrabasic volcanic rocks based on log- ratio transformation of major-element data. Journal of Earth System Science, 115(5): 485-528. Wang, Q., Wyman, D.A., Xu, J., Wan, Y., Li, C., Zi, F., Jiang, Z., Qiu, H., Chu, Z., Zhao, Z. and Dong, Y., 2008. Triassic Nb-enriched basalts, magnesian andesites, and adakites of the Qiangtang terrane (Central Tibet): evidence for metasomatism by slab-derived melts in the mantle wedge. Contributions to Mineralogy and Petrology, 155(4): 437-490.

Quaternary alkali basalts and related rocks are located in the northern portion of the Sanandaj–Sirjan zone in Iran (SaSZ). These rocks, also known as the Salmas Quaternary volcanic rocks (SQVR), consist primarily of basalts and trachy basalts (mafic parts) and basaltic trachy andesites and trachy andesites (intermediate parts), which are highly sodic alkaline and high-K calc-alkaline in character, respectively. These mafic to intermediate samples contain variable proportions of pyroxene, olivine and plagioclase, alongside ubiquitous accessory levels of biotite, amphibolte and oxides. Based on the negative Nb, Ta, Zr, and Hf, and also positive Th and U anomalies in some samples, the SQVR formed in a widely-recognized syn -collision environment following the termination of oblique Neotethys subduction beneath the Central Iranian microplate. Following slab break-off of the remnants of the oceanic lithosphere under the Arabia-Eurasia collision zone, a combination of asthenospheric upwelling, small-scale mantle convection, and localized crustal extension promoted magmatism. We model that decompression melting occurred on the boundary of the lithosphere and asthenosphere at around 65–70 km. The magma of the SQVR resulted from relatively small degrees of partial melting (<5%) of a metasomatized amphibole-bearing garnet-spinel lherzolite. Fractional crystallization, combined with a small amount of assimilation and fractional crystallization occurred during transfer to the surface and resulted in the evolution of basaltic parent magmas towards intermediate compositions. Unlabelled Image • The Salmas volcanic rocks are composed of alkaline and high-K calc-alkaline basalt and andesite. • The rocks are related with a syn-collision tectonic environment. • Magma were generated by slab break-off of the remnants of Neotethys in a subduction zone. • Formation of the rocks may have involved in assimilation and fractional crystallization process. [ABSTRACT FROM AUTHOR]

Two kinds of basalts with different chemical compositions were obtained in the Sanshui Basin, they share the same eruption period. Although they have significant differences in major and trace element concentrations, their isotopic ratios suggest a similar magma source. Based on mineral geochemical analysis, orthopyroxene with reaction rim and zoned clinopyroxene are observed in Zidong (ZD) basalts, but not found in Wangjiegang (WJG) basalts. Linear scanning of these minerals suggests compositional variation between within-plate tholeiite and within-plate alkali-basalt. Presence of a double-layer magma chamber under the Sanshui Basin, and occurrence of magma mixing between upper and lower chambers is proposed. This magma mixing leads to different chemical composition and mineral constitution of two kinds of basalts, as well as reaction rim and compositional variation of minerals in ZD basalts. [ABSTRACT FROM AUTHOR]

In this paper we present the petrography and geochemistry of a recently collected lherzolite-websterite xenolith series and of clinopyroxene xenocrysts, hosted in Upper Cretaceous–Paleogene basanites of Poiana Ruscă (Romania), whose xenoliths show notable orthopyroxene-enrichment. In the series a slightly deformed porphyroclastic-equigranular textured series could represent the early mantle characteristics, and in many cases notable orthopyroxene growth and poikilitic texture formation was observed. The most abundant mantle lithology, Type A xenoliths have high Al and Na-contents but low mg# of the pyroxenes and low cr# of spinel suggesting a low degree (< 10 %) of mafic melt removal. They are also generally poor in overall REE-s (rare earth elements) and have flat REY (rare earth elements+ Y) patterns with slight LREE-depletion. The geochemistry of the Type A xenoliths and calculated melt composition in equilibrium with the xenolith clinopyroxenes suggests that the percolating melt causing the poikilitization can be linked to a mafic, Al-Na-rich, volatile-poor melt and show similarity with the Late Cretaceous–Paleogene (66–72 Ma) subduction-related andesitic magmatism of Poiana Ruscă. Type B xenoliths, with their slightly different chemistry, suggest that, after the ancient depletion, the mantle went through a slight metasomatic event. A subsequent passage of mafic melts in the mantle, with similar compositions to the older andesitic magmatism of Poiana Ruscă, is recorded in the pyroxenites (Fe-rich xenoliths), whereas the megacrysts seem to be cogenetic with the host basanite. The Poiana Ruscă xenoliths differ from the orthopyroxene-enriched mantle xenoliths described previously from the Carpathian-Pannonian Region and from the Dacia block.

This study presented whole-rock elemental and Sr-Nd isotope geochemistry data with the purpose to decipher the origin and evolution of the Miocene Elmadağ Volcanic Complex, Central Anatolia (Ankara, Turkey). Volcanic products spanned in composition from mildly alkaline basaltic (47–52 wt% SiO2) and medium- to high-K calc-alkaline intermediate (54–62 wt% SiO2; andesite to trachyandesite) to felsic (64–74 wt% SiO2; dacite to rhyolite) units. Despite a homogeneous major element composition, basaltic rocks were characterized by two distinct trace element and isotopic signatures, which have been correlated with different mantle sources. The first group of basaltic rocks was similar to those of oceanic island basalts (OIB) and was derived from asthenospheric mantle source. The second group had geochemical characteristics of orogenic basalts derived from subduction-modified lithospheric mantle source and represented parental magma of the intermediate to felsic rocks. By coupling geochemical and textural analyses of the rocks from the Elmadağ Volcanic Complex, I suggest that crystallization of olivine + clinopyroxene + apatite played an important role in the evolution of basaltic rocks, while plagioclase + amphibole + apatite + Fe-Ti oxides ± zircon crystallization was major process involved in the evolution of intermediate to felsic rocks. The EVC basaltic rocks were associated with the post-collisional extensional tectonic regime in the Central Anatolia, but the coexistence of the OIB-like volcanism implies variations in the extension dynamics during Miocene.

Feldspar megacrysts in Late Miocene-Pliocene maars, diatremes and basaltic lava flows in the northern part of the Pannonian Basin span the compositional range from Na-sanidine, through anorthoclase to oligoclase and andesine. Newly formed An82 plagioclase (bytownite) crystallized within composite melt inclusions hosted by the oligoclase. Powder X-ray diffraction data indicate strong structural disorder diagnostic of the high albite-high sanidine series typical of magmatic feldspars. The magmatic origin is also corroborated by chemical compositions, which plot along the 700 ± 50 °C solvus, with the exception of the most sodic Ab79 plagioclase megacryst projecting along the 600 °C isotherm. Vibrational spectroscopic records document that the basic groups of magmatic feldspars can be identified by the specific pattern of the group I and IV bands in the 350-600 cm-1 range. The IVa band at 560-570 cm-1 is diagnostic for triclinic feldspars. The anorthite and orthoclase contents can be inferred from the 506-515 cm-1 (Ia) and 473-486 cm-1 (Ib) peak separation values combined with the Ia bandwidth. [ABSTRACT FROM AUTHOR]

The pyroclastic rocks in the Cretaceous Abakaliki basin occur mostly as oval-shaped bodies, consisting of lithic/lava and vitric fragments. They are commonly characterized by parallel and cross laminations, as well contain xenoliths of shale, mudstone and siltstones from the older Asu River Group of Albian age. The rocks are basic to ultrabasic in composition, comprising altered alkali basalts, altered tuffs, minor lapillistones and agglomerates. The mineral compositions are characterized mainly by laths of calcic plagioclase, pyroxene (altered), altered olivines and opaques. Calcite, zeolite and quartz represent the secondary mineral constituents. Geochemically, two groups of volcaniclastic rocks, are distinguished: alkaline and tholeiitic rocks, both represented by fresh and altered rock samples. The older alkali basalts occur within the core of the Abakaliki anticlinorium while the younger tholeiites occur towards the periphery. Though most of the rocks are moderate to highly altered [Loss on ignition (LOI, 3.43–22.07 wt. %)], the use of immobile trace element such as Nb, Zr, Y, Hf, Ti, Ta and REEs reflect asthenospheric mantle source compositions. The rocks are enriched in incompatible elements and REEs (∑REE = 87.98–281.0 ppm for alkaline and 69.45–287.99 ppm for tholeiites). The ratios of La/Yb n are higher in the alkaline rocks ranging from 7.69 to 31.55 compared to the tholeiitic rocks which range from 4.4 to 16.89 and indicating the presence of garnet-bearing lherzolite in the source mantle. The spidergrams and REEs patterns along with Zr/Nb, Ba/Nb, Rb/Nb ratios suggest that the rocks were generated by a mantle plume from partial melting of mixed enriched mantle sources (HIMU, EMI and EMII) similar to the rocks of the south Atlantic Ocean such as St. Helena (alkaline rocks) and Ascension rocks (tholeiitic rocks). The rocks were formed in a within-plate setting of the intra-continental rift type similar to other igneous rocks in the Benue Rift and are not related to any subduction event as previously suggested. [ABSTRACT FROM AUTHOR]

Intra-plate basalts of ~ 35–0 Ma in East Eurasia formed in a broad backarc region above the stagnant Pacific Plate slab in the mantle transition zone. These basalts show regional-scale variations in Nd-Hf isotopes. The basalts with the most radiogenic Nd-Hf center on the Shandong Peninsula with intermediate Nd-Hf at Hainan and Datong. The least radiogenic basalts occur in the perimeters underlain by the thick continental lithosphere. Shandong basalts possess isotopic signatures of the young igneous oceanic crust of the subducted Pacific Plate. Hainan and Datong basalts have isotopic signatures of recycled subduction materials with billions of years of storage in the mantle. The perimeter basalts have isotopic signatures similar to pyroxenite xenoliths from the subcontinental lithospheric mantle beneath East Eurasia. Hainan basalts exhibit the highest mantle potential temperature ( T p ), while the Shandong basalts have the lowest T p . We infer that a deep high- T p plume interacted with the subducted Pacific Plate slab in the mantle transition zone to form a local low- T p plume by entraining colder igneous oceanic lithosphere. We infer that the subducted Izanagi Plate slab, once a part of the Pacific Plate mosaic, broke off from the Pacific Plate slab at ~ 35 Ma to sink into the lower mantle. The sinking Izanagi slab triggered the plume that interacted with the stagnant Pacific slab and caused subcontinental lithospheric melting. This coincided with formation of the western Pacific backarc marginal basins due to Pacific Plate slab rollback and stagnation. [ABSTRACT FROM AUTHOR]

Many seamounts on the Ontong Java Plateau (OJP) occur near the Stewart Arch, a topographic high that extends parallel to the North Solomon Trench along the southern margins of the plateau. Despite the thick sediment cover, several volcanic cones with strong acoustic reflection were discovered on the submarine flank of the Nuugurigia Seamount. From such volcanic cones, basalts were successfully sampled by dredging. Radiometric dating of basalts and ferromanganese encrustation indicate eruption age of 20–25 Ma, significantly younger than the ~ 122 Ma main OJP plateau and post-plateau basalts. The age range coincides with the collision of the OJP with the Solomon Arc. The Nuugurigia basalts geochemically differ from any other rocks sampled on the OJP so far. They are alkali basalts with elevated Sr, low Zr and Hf, and Enriched Mantle-I (EMI)-like isotopic composition. Parental magmas of these alkali basalts may have formed by small-degree melting of peridotitic mantle impregnated with recycled pyroxenite material having enriched geochemical composition in the OJP's mantle root. We conclude that small-volume alkali basalts from the enriched mantle root migrated through faults or fractures caused by the collision along the Stewart Arch to form the seamount. Our results suggest that the collision of the OJP with the Solomon arc played an important role in the origin of similar post-plateau seamounts along the Stewart Arch. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spinel seams can be formed through interaction between alkali basaltic melts and fertile lherzolite. • Re-classification of chromitite into four types, namely high-Cr, intermediate, high-Al, and extremely high-Al, covering the entire chromite series. • Significant compositional feedback of spinel seam to peridotite. It has long been known that an indisputable fact that chromite/spinel deposits are genetically related exclusively with komatiitic, tholeiitic or boninitic magmas derived from high-degree mantle melting. Here we report formation of a seam of Cr-bearing spinel through interaction between an alkali basaltic magma and fertile lherzolite. The thin seam occurrence of spinel resembles concordant podiform chromitites in ophiolites and stratiform chromitites in layered intrusions. We show that the Cr-bearing spinel seam formed by melt-rock reaction that observed in ophiolitic peridotites. The most significant difference is that the Cr-bearing spinel produced from the alkali basaltic melt-lherzolite interaction is extremely rich in Al with Cr# values of 3–6. We consequently re-classify chromitite into four types based on their Cr# values namely: high-Cr (chromite Cr# > 70), intermediate (Cr# = 70–50), high-Al (Cr# = 50–40), and extremely high-Al (Cr# < 10) with a Cr# gap between 40 and 10. The chromite/spinel compositions correspond closely to diagnostic parental magmas and the lithologies of the host peridotites. [ABSTRACT FROM AUTHOR]

Introduction In the east and northeast of Sanandaj in the Qorveh-Bijar-Takab axis, there are series of basaltic composition volcanoes with Quaternary age. The study area is part of the Sanandaj-Sirjan zone and is located between 47°52' and 47°57' E longitudes and 35°26 and '35°30' N latitudes. Due to the location of the volcanic cone on Pliocene clastic sediments and Quaternary travertine, the age of these volcanoes is considered to be Quaternary. The cones mostly consist of low scoria, ash, volcanic bombs, lapilli deposits and basaltic lava (Moein Vaziri and Aminsobhani, 1985). Petrological and geochemical studies have been carried out to evaluate Quaternary magmatism in the area and to determine the nature of the lithological characteristics, such as the evaluation of source rocks and magma type, degree of partial melting and the tectonic setting of Ghezel Ghaleh rocks (Moein Vaziri, 1997). Simplified geological map of the study area is characterized by ER-Mapper software. Materials and methods In the course of field studies in the region, 40 samples were taken, 30 thin sections were prepared and polished. XRD analyses were performed on some whole rock samples. All major, minor and trace elements were assessed by ICP-MS at Lab Weft Laboratory in Australia. Results Based on the classification of structural zones, the area is located in the Sanandaj-Sirjan zone, hundred kilometers away from the main Zagros thrust along the NW-SE direction. After early Cimmerian orogeny, andesitic volcanic activity took place (Moein Vaziri and Aminsobhani, 1985). A major secondary mineral in these rocks is iddingsite, formed by hydration and oxidation of the olivine (Shelley, 1993). According to SiO2 against Na2O + K2O (TAS) diagram (Irvine and Baragar , 1971) and cationic R1 and R2 diagram (De La Roche et el., 1980), volcanic rocks of the area indicate alkaline series. Discussion To obtain more information on the tectonic setting of these rocks, the Zr/Y-Zr diagram by Pierce (Pearce and Norry, 1979) as well as Nb/Y versus Ti/Y diagram of Pierce (Pearce and Cann, 1973), show that alkali basalt rocks in the study area are fitted in the field of within plate basalts. To determine the genesis of rocks from melting curve of Aldanmaz and Colleagues (Aldanmaz et al., 2006) based on changes in REE (La on Sm/Yb), the samples show approximately 1 to 5% partial melting of garnet lherzolites. The spider diagrams indicate that the studied rocks are enriched in LREE and LILE, depleted in HFSE with no Eu anomaly, Cs, Sr, and Pb positive anomalies which are the characteristics of alkaline magmas and high concentrations of incompatible elements and alkaline elements in the lava, implying the melting of the lower part of the mantle source. Light rare earth elements, are incompatible with the primary crystallized phases such as olivine, clinopyroxene and plagioclase, consequently focused increasingly during phase crystallization and fractionation in the remaining fluid (Hirschman, 1998). Conclusions Based on microscopic and geochemical data, these rocks are alkali basalt, basanite and tephrite. The rocks contain olivine, pyroxene, feldspar, and minerals such as iddingsite, opaque and secondary minerals, calcite with porphyritic texture and microlitic and glassy matrix, vesicular and some glomeroporphyritic, vitrophyric and amygdaloidal textures. Most minerals have undulose extinction which indicates mantle deformation. Geochemical data for the rocks indicate high-K alkaline characteristic of the primary magma. The spider diagrams indicate that the studied rocks are enriched in LREE and LILE, depleted in HFSE with no negative Eu anomaly, positive anomalies of Cs, Sr, Pb which are characteristics of alkaline magmas. These rocks are produced by partial melting of garnet-lherzolite rich under lithospheric mantle. Based on tectonomagmatic diagrams, they are within plate basalts and by magmatic series graphs are alkali basalts. Microscopic evidence such as disequilibrium textures in the minerals (zoned state, solution and twinning) shows a magmatic contamination in mixing volcanic mass. References Aldanmaz, E., Koprubasi, N.O., Gurer, F., Kaymakci, N. and Gournaud, A., 2006. geochemical constraints on the Cenozoic, OIB-type alkaline volcanic rocks of NW Turkey: implications for mantle sources and melting processes. Lithos, 86 (1–2) pp. 50–76. De La Roche, H., Leterrier, J., Grand claude, P. and Marchel, M., 1980. A classification of volcanic and plutonic rocks using R1-R2 diagrams and major elements, it’s relationships with current nomenclature. Chemical Geology, 29(1-4): 183–210. Hirschman, M., 1998. Origin of the transgressive granophyres in the layered series of the Skaergaard intrusion, East Greenland. In: D.J. Geist and C.M. White (Editors.). Journal of Volcanology and Geothermal Research, 52(1-3): 185–207. Irvine, T.N. and Baragar, W.R.A., 1971. A guide to chemical classification of the common volcanic rocks. Canadian Journal of Earth Sciences, 5(8): 448– 523. Moein Vaziri, H., 1997. The history of magmatism in Iran. Tehran University Press, Tehran, 440 pp. (in Persian) Moein Vaziri, H. and Aminsobhani, A., 1985. Study of young volcanic region being involved in –Qorveh- Takab. Tehran University Press, Tehran, 350 pp. (in Persian) Pearce, J.A. and Cann, J.R., 1973. Tectonic setting of basaltic volcanic rocks determind using traceelements analysis. Earth and Planetary Science Letters, 19(2): 290– 300. Pearce, J.A. and Norry, M.J., 1979. Petrogenetic implications of Ti, Zr, Y and Nb variation in volcanic rocks. Contributions to Mineralogy and Petrology, 69(1): 33– 47. Shelley, D. (Translated by Mohamadzadeh, F.), 1993. Igneous and metamorphic rocks under the microscope, classification, textures, microstructures and mineral preferred-orientations. Chapman and Hall, Unwin, London, 445 pp.

A1-type granite xenoliths occur in alkali basalts erupted during Pliocene−Pleistocene continental rifting of Carpathian back-arc basin (Central Europe). The Pliocene (5.2 Ma) peraluminous calc-alkalic granite contains unusually high concentrations of critical metals bound in Nb, Ta, REE, U, Th-oxides typical for silica-undersaturated alkalic granites, and syenites: columbite-Mn, fergusonite-Y, oxycalciopyrochlore, Nb-rutile, and Ca-niobate (fersmite or viggezite). In contrast, it does not contain allanite and monazite—the main REE-carriers in calc-alkalic granites. The crystallization of REE-bearing Nb-oxides instead of OH-silicates and phosphates was probably caused by strong water deficiency and low phosphorus content in the parental magma. Increased Nb and Ta concentrations have been inherited from the mafic parental magma derived from the metasomatized mantle. The strong Al- and Ca-enrichment probably reflects the specific composition of the mantle wedge modified by fluids, alkalic, and carbonatitic melts liberated from the subducted slab of oceanic crust prior to the Pliocene-Pleistocene rifting.

Geochemical compositions of continental basalts are generally considered as the best proxy record of the chemical and isotopic evolution of subcontinental lithosphere and convective mantle. There are voluminous Cretaceous continental basalts in the North China Craton (NCC), which are mainly composed of alkali basalts with minor sub-alkali basalts. Abrupt changes in chemical and isotopic compositions of these basalts were often ascribed to subcontinental lithosphere thinning of the NCC. However, processes responsible for such changes and its implications for subcontinental lithosphere evolution remain obscure. Here we report major geochemical changes at ~ 108 Ma in the north part of the NCC. The > 108 Ma alkali basalts are characterized by negative ε Nd (t) and declining “island arc-like” geochemical characteristics from the east to the west, implying decreasing slab-derived components from westward subducting slabs in their metasomatized lithospheric mantle sources. In contrast, the < 108 Ma Cretaceous alkali basalts have depleted Sr-Nd isotopic compositions and “OIB-like” geochemical features. These observations suggest that westward subduction of the Paleo-Pacific plate was responsible for the Cretaceous basaltic activities in the NCC. Combined with plate reconstructions and geophysical observations, we propose that flat subduction of the “extinct” ridge between the Izanagi and the Pacific plates controlled this major transition as well as the destruction of the NCC. The transition from a supra-subduction zone environment to a within-plate extensional environment around 108 Ma is probably due to the eastward slab rollback and the northward shift of the spreading ridge. [ABSTRACT FROM AUTHOR]

We present a comprehensive major and trace element and Sr-Nd-Pb isotope dataset from the major volcanic units exposed on La Palma and show how geochemical and volcanic evolution can be linked to asthenospheric and lithospheric processes. Lavas from the northern shield (from Basal Complex to Taburiente to Bejenado volcanism, 3-4Ma to 400 ka) become more alkalic and SiO2- undersaturated with decreasing age, but show little change in MgO-normalized trace element compositions. Their high (Nb,Ta)/U and Ba/Th but low La/Nb ratios suggest assimilation of amphibole, probably in the lithospheric mantle that was metasomatized by earlier melts. Lavas from the Cumbre Vieja unit (<125 ka) in the southern half of La Palma are more incompatible-element enriched and probably formed through lower degrees of melting than those from the northern shield, which are nearly identical isotopically. Their Nb/U ratios are mostly within the range 47 ± 10, significantly below those of the earlier lavas. In 206Pb/204Pb versus 143Nd/144Nd, 208Pb/204Pb and 208Pb/206Pb isotope diagrams, the Basal Complex rocks and lavas from the adjacent El Hierro island form a separate trend compared with the younger subaerial La Palma lavas. Both groups share a common depleted end-member but require separate, enriched HIMU-like end-members, believed to be located within the asthenosphere. The temporal and spatial variations in the composition of La Palma and El Hierro lavas could be explained within the context of NE-directed plate motion over a zoned Canary plume. After La Palma moved away from the asthenospheric source domain of the Basal Complex, El Hierro formed above the same domain, whereas the younger units on La Palma tapped a distinct asthenospheric domain located further north. The short-lived Bejenado volcano that formed directly after the giant Cumbre Nueva sector collapse at c. 560 ka produced the isotopically most depleted lavas reported from La Palma thus far. Their compositions suggest incorporation of a depleted pyroxenitic component. The Bejenado lavas also extend to the highest Nb/U and Ba/Th and lowest La/Nb ratios of all La Palma lavas, consistent with increased melting of amphibole within the lithospheric mantle or lower crust. We propose that the collapse is related to the migration of magmatism to the south of La Palma, and led to short-term enhanced decompression melting of amphibole and pyroxenite within the lithosphere. [ABSTRACT FROM AUTHOR]

Volatiles play an important role in magmatic and volcanic processes. Melt inclusions are a powerful tool to study pre-eruptive volatiles, but interpretation of their H2O and CO2 variations can be difficult. The H2 O and CO2 contents of melt inclusions from nine basanites from Hut Point Peninsula, Mt Terror and Mt Bird on Ross Island, Antarctica, were studied to understand better the behavior of volatiles in the magmas and to provide insight into magma transport and storage processes. Ninety olivine-hosted (Fo78-88) melt inclusions were examined along with the composition of the associated bulk-rock samples. The H2 O (0.4-2.0wt %) and CO2 (0.2-9wt %, or 0.2-1-8wt % after correction for vapor bubbles) variations in the melt inclusions cannot be explained by equilibrium degassing. A strong correlation between melt inclusion radius and H2 O content for Hut Point samples indicates that diffusive loss of Hþ has occurred. Based on vapor saturation pressure trends, it is inferred that a magma reservoir existed below Hut Point at a depth of ∼18 km and by modeling diffusive loss of H+ for melt inclusions, it is shown that the magmas ascended from this depth in less than a year. Melt inclusions from Terror and Bird lack evidence of diffusive loss of H+ and there are no strong chemical indicators of CO2 fluxing. Compositional heterogeneities in melt inclusions indicate that magma mixing occurred, making it difficult to interpret H2 O and CO2 trends. Melt inclusions from these volcanoes were entrapped polybarically, inconsistent with entrapment in a single storage region. Published analyses of 54 olivine-hosted (Fo53-83) melt inclusions in seven samples from Erebus volcano on Ross Island were re-examined for comparative purposes. Low H2 O (∼0.1wt %) and CO2 (0-0.2wt %) contents and the evolved compositions of these indicate that Erebus magmas undergo shallow (<6 km) crystallization before eruption, probably in a shallow storage region. Magmas from the surrounding volcanoes show no sign of shallow storage. [ABSTRACT FROM AUTHOR]

It is well known that vanadium (V) is redox-sensitive during magmatism, but whether V isotopes can be used as a mantle oxygen fugacity (f O 2) sensor remains controversial. Before using V isotopes as a redox proxy, it is crucial to understand the fractionation behavior and controlling factors of V isotopes during mantle melting. This study reports high-precision V isotopic data for alkali basalts with high f O 2 in eastern China, which were derived from carbonated mantle by a low degree of partial melting. Our results show that their δ51V values (−0.85‰ to −0.61‰) are higher than those of bulk silicate Earth (BSE) and mid-ocean ridge basalts (MORBs). Chemical alteration, crustal contamination or fractional crystallization negligibly affect the δ51V values of alkali basalts. Although subducted carbonates are involved in the mantle source region under eastern China, mass balance calculations show that the incorporation of carbonates did not significantly increase the δ51V values of alkali basalts. In contrast, the observed high δ51V values probably reflect that mantle melting controls the V isotopic compositions of mantle-derived melts. The relative abundances of V5+, V4+ and V3+ in silicate melt are influenced by the variation of f O 2 and/or the degree of partial melting. Basaltic melts tend to be enriched in V with high valence at the condition of high f O 2 during mantle melting, which contributes to the enrichment of 51V in alkali basalts because of the affinity of high valence V and 51V. Because mantle minerals are overall more compatible of V with low valence, the valence states of V in silicate melt tend to be higher at low degree of partial melting, resulting in more significant fractionation of V isotopes. Therefore, this study validates discernable V isotope fractionation during partial melting of the mantle and examines the potential of using V isotopes to trace the redox state of magmatic systems. • Report V isotopic data of alkali basalts. • Validate discernable V isotope fractionation during mantle partial melting. [ABSTRACT FROM AUTHOR]

Twins in plagioclase, which are abundant in rocks, have important implications for the growth history and subsequent transformation. There are many twin laws in plagioclase and some of them are difficult to identify. This paper presents an electron backscatter diffraction (EBSD) analysis combined with electron microprobe analysis of plagioclase twinning in the Niutoushan alkali basalt. Theoretical pole figures of 12 different twin laws for plagioclase were generated. By comparing the pole figures obtained from EBSD with the theoretical ones, 11 twin laws have been identified in the alkali basalt, and their frequency has also been determined: Albite (28%), Carlsbad (25%), Albite-Carlsbad (34%), Pericline (3%), Ala (2%), Manebach (1%), Albite-Ala (1%), Prism {110} (2%), Prism {10} (1%), Prism {130} (1%) and Prism {10} (1%). All the plagioclase twins in the alkali basalt are growth twins. The anorthite content of the plagioclase has a negative correlation with the frequency of the Pericline and Albite twin laws but a positive correlation with the frequency of all the other twin laws, which is consistent with previous results. The theoretical pole figures of twin laws for plagioclase introduced in this paper can be applied to investigating plagioclase twin laws in all plagioclase-bearing rocks, and the relationship between twin pattern and crystallization conditions of the rocks can be established. [ABSTRACT FROM AUTHOR]