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Mantle xenoliths from Santo Domingo, Ventura-Espíritu Santo and Durango volcanic fields (Mesa Central in Mexico) experienced low degrees of partial melting in the stability fields of garnet (⁓ 2%) and spinel peridotites (⁓ 2–4%), and interacted with hydrous alkaline melts possibly during the Basin and Range extensional tectonism since Late Oligocene. Enclosed and intergranular grains of monosulfide solid solution (mss) in Santo Domingo peridotites are residues after the extraction of 0.1–0.5 fractions of Ni-Cu-rich sulphide melt during mantle melting events. On the other hand, glo˜bular sulphides (pentlandite ± chalcopyrite) hosted in glass veinlets in the Ventura-Espíritu Santo and Durango peridotites crystallized from Ni-Cu-rich droplets of sulphide melt, immiscible in the Quaternary silicate magmas that brought the xenoliths to the surface. Rhenium-depletion model ages of these sulphide populations indicate that part of the subcontinental lithospheric mantle (SCLM) of the Oaxaquia terrane (beneath Santo Domingo and Ventura-Espíritu Santo) originated in the Archaean-Paleoproterozoic as the southernmost extension of the Laurentia craton, and was assembled with the Central terrane (beneath Durango) during the Grenville orogeny (⁓ 1.0 Ga). Early Palaeozoic (⁓ 500 Ma) model ages common to sulphides from the peridotite xenoliths of the three volcanic fields suggest that the Oaxaquia-Central composite block split away from North America during the Rodinia break-up and experienced the Pan-African-Brasiliano orogeny that led to Gondwana assembly. During the Cenozoic, the reactivation of translithospheric faults bounding this composite old SCLM provided preferential pathways for focusing the ascent of ore-productive magmas/fluids associated with the subduction-related metallogeny of the Pacific active margin of Mexico.

Traditional inversion techniques applied to the problem of characterizing the thermal and compositional structure of the upper mantle are not well suited to deal with the nonlinearity of the problem, the trade-off between temperature and compositional effects on wave velocities, the nonuniqueness of the compositional space, and the dissimilar sensitivities of physical parameters to temperature and composition. Probabilistic inversions, on the other hand, offer a powerful formalism to cope with all these difficulties, while allowing for an adequate treatment of the intrinsic uncertainties associated with both data and physical theories. This paper presents a detailed analysis of the two most important elements controlling the outputs of probabilistic (Bayesian) inversions for temperature and composition of the Earth's mantle, namely the a priori information on model parameters, (m), and the likelihood function, L(m). The former is mainly controlled by our current understanding of lithosphere and mantle composition, while the latter conveys information on the observed data, their uncertainties, and the physical theories used to relate model parameters to observed data.The benefits of combining specific geophysical datasets (Rayleigh and Love dispersion curves, body wave tomography, magnetotelluric, geothermal, petrological, gravity, elevation, and geoid), and their effects on L(m), are demonstrated by analyzing their individual and combined sensitivities to composition and temperature as well as their observational uncertainties. The dependence of bulk density, electrical conductivity, and seismic velocities to major-element composition is systematically explored using Monte Carlo simulations. We show that the dominant source of uncertainty in the identification of compositional anomalies within the lithosphere is the intrinsic nonuniqueness in compositional space. A general strategy for defining (m) is proposed based on statistical analyses of a large database of nat, Australian Research Council, Science Foundation Ireland, IRETHERM, JAE-DOC programme (CSIC-España), Ministerio de Economía y Competitividad (España), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

New trace-element, radiogenic Sr-Nd-Pb isotopic and geochronological data from Middle-Late Cretaceous Zagros ophiolites of Iran give new insights into the tectono-magmatic history of these supra-subduction zone (SSZ)-type ophiolites. The distribution of Middle-Late Cretaceous SSZ-type ophiolites in Iran comprises two parallel belts: (1) the outer Zagros ophiolitic belt and (2) the inner Zagros ophiolitic belt. These Middle-Late Cretaceous ophiolites were generated by seafloor spreading in what became the fore-arc and back-arc during the subduction initiation event and now define a ∼3000-km-long belt from Cyprus to Turkey, Syria, Iran, the UAE, and Oman. The Zagros ophiolites contain complete (if disrupted) mantle and crustal sequences. Mantle sequences from both outer-belt and inner-belt ophiolites are dominated by dunites, harzburgites, and lherzolites with minor chromitite lenses. Peridotites are also intruded by gabbros and a variety of mafic to minor felsic (plagiogranite and dacite) dikes. Crustal rocks comprise ultramafic-mafic cumulates as well as isotropic gabbros, sheeted dike complexes, pillowed and massive lavas, and felsic rocks. Our new zircon U-Pb ages indicate that the outer-belt and inner-belt ophiolites formed near coevally during the Middle-Late Cretaceous; 100−96 Ma for the outer belt and 105−94 Ma for the inner belt. Both incompatible-element ratios and isotopic data confirm that depleted mantle and variable contributions of subduction components were involved in the genesis of outer-belt and inner-belt rocks. Our data for the outer belt and inner belt along with those from better-studied ophiolites in Cyprus, Turkey, the UAE, and Oman lead to the conclusion that a broad, ∼3000-km-long swath of fore-arc lithosphere was created during Middle-Late Cretaceous time.

We present the first global review on the Sm-Nd and Lu-Hf isotope systematics of the mantle; it includes all published data on peridotites and pyroxenites from all tectonic settings (>1100 combined Hf-Nd analyses), as well as previous compilations for oceanic basalts and material such as oceanic and continental sediments. We first provide a comprehensive overview of the main reservoirs and mechanisms accounting for the contrasting variability of radiogenic isotope systematics in the sub-oceanic mantle and the relative homogeneity of its volcanic products, highlighting the paradigm change promoted by the use of Hf isotopes. Secondly, we summarize the different models invoked to explain the decoupling/(re-)coupling of Hf and Nd isotopes. Decoupling above the mantle array is often related to melt-peridotite interaction involving ancient protoliths, whereas coupled Hf-Nd or decoupling below the array are shown to be insufficient criteria to exclude the involvement of such protoliths. The Hf-Nd isotope variability of the SCLM is then addressed using a tectono-thermal classification based on the Global Lithospheric Architecture Mapping (GLAM) project. The extreme variability that characterizes the cratonic SCLM reflects the long-term preservation of depleted signatures overprinted by ancient and recent metasomatic episodes. Refertilized SCLM domains fingerprinted by variably decoupled Hf-Nd isotope systematics record subduction-related processes, which also appears to be instrumental in the recycling of continental material into the convective mantle. We show that there is a critical “chicken-and-egg” question underpinning debates on the spatio-temporal evolution of the SCLM: whether ancient signatures are pre-existing in the lithosphere (e.g. “lithospheric memory” during refertilization) or introduced into the convective mantle (i.e. recycling). Importantly, our compilation shows that fertile lithologies such as pyroxenites can also carry extremely depleted isotopic sign

New trace-element, radiogenic Sr-Nd-Pb isotopic and geochronological data from Middle-Late Cretaceous Zagros ophiolites of Iran give new insights into the tectono-magmatic history of these supra-subduction zone (SSZ)-type ophiolites. The distribution of Middle-Late Cretaceous SSZ-type ophiolites in Iran comprises two parallel belts: (1) the outer Zagros ophiolitic belt and (2) the inner Zagros ophiolitic belt. These Middle-Late Cretaceous ophiolites were generated by seafloor spreading in what became the fore-arc and back-arc during the subduction initiation event and now define a ∼3000-km-long belt from Cyprus to Turkey, Syria, Iran, the UAE, and Oman. The Zagros ophiolites contain complete (if disrupted) mantle and crustal sequences. Mantle sequences from both outer-belt and inner-belt ophiolites are dominated by dunites, harzburgites, and lherzolites with minor chromitite lenses. Peridotites are also intruded by gabbros and a variety of mafic to minor felsic (plagiogranite and dacite) dikes. Crustal rocks comprise ultramafic-mafic cumulates as well as isotropic gabbros, sheeted dike complexes, pillowed and massive lavas, and felsic rocks. Our new zircon U-Pb ages indicate that the outer-belt and inner-belt ophiolites formed near coevally during the Middle-Late Cretaceous; 100−96 Ma for the outer belt and 105−94 Ma for the inner belt. Both incompatible-element ratios and isotopic data confirm that depleted mantle and variable contributions of subduction components were involved in the genesis of outer-belt and inner-belt rocks. Our data for the outer belt and inner belt along with those from better-studied ophiolites in Cyprus, Turkey, the UAE, and Oman lead to the conclusion that a broad, ∼3000-km-long swath of fore-arc lithosphere was created during Middle-Late Cretaceous time.

Much of the crust of Iran and Anatolia, including their oldest exposed rocks, formed during an episode of intense convergent margin (arc) magmatism as a result of subduction of oceanic lithosphere beneath northern Gondwana from ca 620 Ma to ca 500 Ma, the Cadomian crust-forming event. Most igneous rocks formed between ca 570 and 525 Ma. Cadomian crust is well-known from western and southern Europe and from eastern North America but is much less well-known from Iran and Anatolia. We use published age and compositional data and contribute new data in order to better understand this ancient magmatic system. Cadomian magmatism included calc-alkaline igneous rocks of arc affinity in the main arc and alkalic igneous rocks that formed in a back-arc setting; these igneous rocks are associated with sedimentary rocks. Geochemical and isotopic modelling reveals that basaltic magmas were the main input, that these formed by partial melting in the upper mantle, and that basaltic magmas evolved further in deep crustal hot zones to form granitic magmas through a combination of assimilating older continental crust and fractional crystalization of basaltic magmas.

How new subduction zones form is an ongoing scientific question with key implications for our understanding of how this process influences the behavior of the overriding plate. Here we focus on the effects of a Late Cretaceous subduction-initiation (SI) event in Iran and show how SI caused enough extension to open a back-arc basin in NE Iran. The Late Cretaceous Torbat-e-Heydarieh ophiolite (THO) is well exposed as part of the Sabzevar-Torbat-e-Heydarieh ophiolite belt. It is dominated by mantle peridotite, with a thin crustal sequence. The THO mantle sequence consists of harzburgite, clinopyroxene-harz burgite, plagioclase lherzolite, impregnated lherzolite, and dunite. Spinel in THO mantle peridotites show variable Cr# (10-63), similar to both abyssal and fore-arc peridotites. The igneous rocks (gabbros and dikes intruding mantle peridotite, pillowed and massive lavas, amphibole gabbros, plagiogranites and associated diorites, and diabase dikes) display rare earth element patterns similar to MORB, arc tholeiite and back-arc basin basalt. Zircons from six samples, including plagiogranites and dikes within mantle peridotite, yield U-Pb ages of ca. 99-92 Ma, indicating that the THO formed during the Late Cretaceous and was magmatically active for similar to 7 m.y. THO igneous rocks have variable epsilon Nd(t) of +5.7 to +8.2 and epsilon Hf(t) ranging from +14.9 to +21.5; zircons have epsilon Hf(t) of +8.1 to +18.5. These isotopic compositions indicate that the THO rocks were derived from an isotopically depleted mantle source similar to that of the Indian Ocean, which was slightly affected by the recycling of subducted sediments. We conclude that the THO and other Sabzevar-Torbat-e-Heydarieh ophiolites formed in a back-arc basin well to the north of the Late Cretaceous fore-arc, now represented by the Zagros ophiolites, testifying that a broad region of Iran was affected by upper-plate extension accompanying Late Cretaceous subduction initiation.

Highlights • Cadomian continental arc crust of NE Iran was built during ∼15 Myr of magmatism. • Magmatic flare-up in Iran Cadomia occurred over ∼45 Myr; 570 to 525 Ma. • Geochemical differentiation in “hot zones” built the stratified continental crust of Iran. Abstract The generation and differentiation of continental crust by arc magmatism is strongly influenced by episodes of high magmatic flux (“flare-ups”). Magmatic flare-ups encourage the development of deep crustal hot zones where magmatic differentiation and density stratification combine to form the upper felsic and lower mafic continental crust. Such processes, which are responsible for the construction of continental arc crust, are prolonged events, which build a ∼30-40 km arc crust over tens of million years (∼100 Myr). New zircon U-Pb data reveal that the construction of Cadomian crust from NE Iran occurred over ∼15 ± 0.3 Myr. However, compiled zircon U-Pb ages reveal a prolonged magmatic flare-up of ∼45 Myr; ∼570 to 525 Ma. Basement outcrops in NE Iran expose lower- and upper crust that show how magmatic-geochemical differentiation occurred deep beneath a Cadomian continental arc in a crustal hot zone. Isotopic data for igneous rocks produced during this 45 Myr episode reveal interactions between mantle-derived melts and old continental crust. Synthesis of new and published data indicates that this type of interaction is common during periods of high magmatic fluxes. Our results indicate that differentiation of mafic melts in the lower crust during prolonged magmatic flare-ups plays a key role in building a stratified continental crust.

This study analyzes the microstructures and deformational characteristics of spinel peridotite xenoliths from the Nógrád-Gömör Volcanic Field (NGVF), located on the northern margin of a young extensional basin presently affected by compression. The xenoliths show a wide range of microstructures, bearing the imprints of heterogeneous deformation and variable degrees of subsequent annealing. Olivine crystal preferred orientations (CPOs) have dominantly [010]-fiber and orthorhombic patterns. Orthopyroxene CPOs indicate coeval deformation with olivine. Olivine J indices correlate positively with equilibration temperatures, suggesting that the CPO strength increases with depth. In contrast, the intensity of intragranular deformation in olivine varies as a function of the sampling locality. We interpret the microstructures and CPO patterns as recording deformation by dislocation creep in a transpressional regime, which is consistent with recent tectonic evolution in the Carpathian-Pannonian region due to the convergence between the Adria microplate and the European platform. Postkinematic annealing is probably linked to percolation of metasomatism by mafic melts through the upper mantle of the NGVF prior to the eruption of the host alkali basalt. Elevated equilibration temperatures in xenoliths from the central part of the volcanic field are interpreted to be associated with the last metasomatic event, which only shortly preceded the ascent of the host magma. Despite well-developed olivine CPOs in the xenoliths, which imply a strong seismic anisotropy, the lithospheric mantle alone cannot account for the shear wave splitting delay times measured in the NGVF, indicating that deformation in both the lithosphere and the asthenosphere contributes to the observed shear wave splitting.