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During the differentiation of arc magmas, fractionating liquids follow a series of cotectics, where the co-crystallization of multiple minerals control the melt compositional trajectories, commonly referred to as liquid lines of descent (LLD). These cotectics are sensitive to intensive properties, including fractionation pressure and melt H2O concentration, and changes in these variables produce systematic differences in the LLDs of arc lavas. Based on a compilation of experimental studies, we develop two major element proxies that exploit differences in LLDs to constrain the fractionation conditions of arc magmas. Near-primary fractionating magmas evolve along the olivine-clinopyroxene cotectic, which is pressure-sensitive. We use this sensitivity to develop a proxy for early fractionation pressure based on the normative mineral compositions of melts with 8 ± 1 wt.% MgO. Fractionation in more evolved magmas is controlled by the clinopyroxene-plagioclase cotectic, which is strongly sensitive to magmatic H2O contents. We use this relationship to develop an H2O proxy that is calibrated to the normative mineral components of melts with 2–4 wt.% MgO. These two proxies provide new tools for estimating the variations in pressure and temperature between magmatic systems. We applied these proxies to compiled major element data and phenocryst assemblages from modern volcanic arcs and show that in island arcs early fractionation is relatively shallow and magmas are dominantly H2O-poor, while continental arcs are characterized by more hydrous and deeper early fractionation. These differences likely reflect variations in the relative contributions of decompression and flux melting in combination with distinct upper plate controls on arc melt generation., Geochemistry, Geophysics, Geosystems, 24 (5), ISSN:1525-2027

The magma-poor West Iberian Margin, as part of the Peri-Atlantic alkaline province, records multiple evidence for intra-plate post-rift magmatism. Based on high-resolution multichannel seismic data, this work discusses the presence of large volcanic and intrusive features in the Estremadura Spur, providing evidence for important magmatic activity during the drifting of the continental margin. Our observations reveal distinct voluminous fissure-fed effusive sequences and the details of the 2800 m-high Fontanelas compound volcano, including its external and internal architecture, secondary vents and associated lava flows, all of which were probably extruded at intermediate water depths. Numerous and morphologically diverse sills and sill complexes are also described, attesting to the presence of a Late Cretaceous shallow magmatic plumbing system in the area. Magmatism in this region is interpreted as having occurred during two main pulses and types of activity: 1) Coniacian to lower Campanian(?) age, characterized by fissural and fault-controlled volcanism, which mostly extruded massive lobate/sheet lava flows; and 2) a second voluminous intrusive and extrusive event of mid to late Campanian age, which includes the intrusion of the Estremadura Spur laccolith and the prominent Fontanelas compound volcano with associated dendritic lava flows. The inferred volumes of the first fissure-fed effusive event suggest a large eruption magnitude, comparable to some of the largest historical effusive eruptions. The second magmatic pulse led to the emplacement of discrete clusters of sills and sill complexes, as well as the construction of the ~2.8 km-high Fontanelas volcano, suggesting a syn-rift structural inheritance that controlled the location of the Estremadura Spur Intrusion and the Fontanelas volcanic area. Altogether, a total volume of rock exceeding 1.452 km3 is estimated to have been emplaced or extruded in this region in a relatively short period, attesting to the prominence of the magmatism in this sector of the West Iberian Margin.

Earth's mantle undergoes convection on million-year timescales as heat is transferred from depth to the surface. Whilst this flow has long been linked to the large-scale horizontal forces that drive plate tectonics and supercontinent cycles, geologists are increasingly recognising the signature of convection through transient vertical motions in the rock record, known as "dynamic topography". A significant component of topography is supported by lithospheric isostasy, and changes in lithospheric thermal structure are sometimes included in the definition of dynamic topography. An additional component arises from active flow within the underlying convecting mantle, and this process causes dynamic topography that has lengthscales varying from 10,000 km down to 500 km and typical amplitudes of ±1 km. Transient uplift and subsidence events are often slow, but might evolve at rates as fast as 500 m/Myr over cycles as short as ~3 Myr, leading to periodic overwriting of the geological record that results in complex interpretational challenges. Despite these difficulties, a growing number of observational and computational studies have highlighted the important role of dynamic topography in fields as diverse as intraplate magmatism, sedimentary stratigraphy, landscape evolution, paleo-shorelines, oceanic circulation patterns, and ice sheet stability. This review provides a brief overview of our current understanding of the topic and explores some basic insights that can be gained from simple three-dimensional numerical simulations of mantle convection under different convective regimes. We summarise a suite of observational techniques used to estimate dynamic topography, and finish by laying out some key unanswered questions to stimulate debate and inspire future studies.

[Ultramafic‐derived or magmatic‐sourced fluids transported upward along strike‐slip faults, and contributed to the local precipitation of hydrothermal dolomites and cherts. , Abstract Ordovician carbonate rocks on the northern slope of the Tazhong Uplift in the Tarim Basin are modified to varying degrees by hydrothermal fluids related to multiple tectonic‐thermal events, but the nature, origin and circulation mechanisms of such hydrothermal fluids remain debated. In this article, in situ rare‐earth elements and yttrium (REE + Y) concentrations, previously published geochemical datasets and petrographic investigations are integrated to develop a thermo‐tectonic evolution model to improve understanding of silicification and dolomitisation occurring in the interior of the craton basin. δ30Si values, REE + Y ratios and fluid mixing models using modern black smoker fluid and seawater indicate that magma‐sourced hydrothermal fluids, rather than basinal brine heated by magmatism, are responsible for the precipitation of cherts. Petrological and geochemical evidence suggests that deep‐seated, ultramafic‐derived hydrothermal fluids and/or magmatic fluids associated with Permian volcanism may have been involved in the formation of hydrothermal dolomites in the study area. Accompanying formation and reactivation of the strike‐slip faults on the northern slope of the Tazhong Uplift, small volumes of hydrothermal fluids might have been triggered by seismic pumping. The early formed strike‐slip fault systems may also have served as conduits for the subsequent large‐scale transport of deep‐seated, ultramafic‐derived thermal fluids and/or Permian magmatic fluids, along which fluids were transported upwards at high flow rates. Carbonation of ultramafic rocks through interaction with deep‐seated hydrothermal fluids rich in CO2 may have served as a magnesium and silica source for dolomitisation and silicification. Trans‐tensional troughs on NNE‐trending strike‐slip faults with positive flower structure are favourable locations for dolomitisation and silicification.]

[Abstract The combined effects of post‐rift magma emplacement and tectonic inversion on the hyper‐extended West Iberian Margin are unravelled in detail using multichannel 2D/3D seismic data. The Estremadura Spur, acting as an uplifted crustal block bounded by two first‐order transfer zones, shows evidence of four post‐rift tectonic events each with a distinctive seismic‐stratigraphic response that can be used to demonstrate the tectono‐magmatic interplay, namely: (a) the Campanian onset of magmatism (including the Fontanelas Volcano, the widespread evidence of multiple sill complexes and the detailed description of a >20 km long laccolith, the Estremadura Spur Intrusion; (b) the Campanian‐Maastrichtian NE‐SW event pervasively affecting the area, resulting in regional uplift, reverse faulting and folding; (c) the Paleocene‐mid Eocene inversion that resulted in widespread erosion and; (d) the Oligocene‐mid Miocene evidence of rejuvenated NW‐SE inversion marked by crestal faulting and forced‐fault folding establishing the final geometry of the area. The distinct deformation styles within each tectonic phase document a case of decoupled deformation between Late Cretaceous and Tertiary units, in response to the predominant stress field evolution, revealing that the magnitude of Late Cretaceous inversion is far more significant than the one affecting the latter units. A detailed analysis of the laccolith and its overburden demonstrate the distinct deformation patterns associated both with magma ascent (including extensional faulting, forced‐folding and concentric reverse faulting) and its interference as a rigid intrusive body during subsequent transpressive inversion. This reinforces the role that the combined tectono‐magmatic events played on the margin. Also analysed is the wider impact of post‐rift magmatism and the associate emplacement of sub‐lithospheric magma on the rheology of a thinned continental crust. This takes into account the simultaneous tectonic inversion of the margin, the implied alternative views on characteristic heat flow, and on how these can be incorporated in source rock organic maturity modelling., The combined effects of multiphase margin inversion and Late Cretaceous magmatism on the Central West Iberian Margin reveals that deformation is decoupled between Cretaceous and Tertiary strata, with a laccolith accommodating significant shortening and acting as a rigid body. ]

To simulate the outgassing of CO2 and water from Martian mantle, I used a two-dimensional numerical model of magmatism in the convecting mantle. The mantle is internally heated by incompatible heat...

Fluid-flux melting is commonly attributed as the primary driver of magmatism in arcs; however, decompression melting, mantle heterogeneity, and the amount and compositions of slab-derived materials...

The Himalayan–Tibetan orogen is the world's largest active orogen with the thickest continental crust on Earth. However, the timing of crustal thickening of this orogen remains controversial. In recent years, magmatic rocks with adakitic affinities have been widely used to constrain the crustal thickness. Here, we present zircon U–Pb ages, geochemical and Sr–Nd–Pb–Hf isotopic data for the Dala two‐mica granites (eastern Tethyan Himalaya) that may shed light on this issue. Zircon U–Pb dating shows that the Dala two‐mica granites were emplaced at ca. 43 Ma. The granites display adakitic signatures, including high SiO2, Al2O3 and Sr contents, low Y and Yb contents with high Sr/Y (27−67) and La/Yb (35−99) ratios. High K2O and Th contents, low Nb/U, Ce/Pb, Ti/Eu and Nd/Sm ratios and low MgO, Mg#, Cr and Ni contents suggest that the Dala two‐mica granites were derived from partial melting of a thickened lower crust. Low negative zircon eHf(t) values (−10.4 to −0.5) with old two‐stage Hf model ages (1.1–1.8 Ga), high (87Sr/86Sr)i (0.715861–0.717665) with low eNd(t) (−12.5 to −11.3) and high Pb isotopes [(206Pb/204Pb)i=18.783–18.861, (207Pb/204Pb)i=18.783–18.861 and (208Pb/204Pb)i=39.052–39.285], together with previous literature data, indicate that the magma source for the Eocene granites in the Yardoi area was composed of ancient lower crust consisting mainly of garnet‐amphibolite and probably subordinate metapelites of the High Himalayan Crystalline Sequence. The residual mineral assemblage of garnet + rutile + plagioclase ± amphibole in the source region demonstrates that the crust beneath the Himalaya could have been thickened to ﹥50 km in the Eocene. Combining with previous studies, we propose that the Eocene magmatic rocks in the Tethyan Himalaya (e.g. ca. 43 Ma old Dala two‐mica granites) can be best interpreted as the consequence of breakoff of the Neo‐Tethyan oceanic slab.

Fracture-fissure systems found at mid-ocean ridges are dominating conduits for the circulation of metallogenic fluid.Ascertaining the distribution area of active faults on both sides of mid-ocean ridges will provide a useful tool in the search for potential hydrothermal vents,thus guiding the exploration of modem seafloor sulfides.Considering the MidAtlantic Ridge 20°N-24°N (NMAR) and North Chile Rise (NCR) as examples,fault elements such as Fault Spacing (ΔS) and Fault Heave (ΔX) can be identified and quantitatively measured.The methods used include Fourier filtering of the multi -beam bathymetry data,in combination with measurements of the topographic slope,curvature,and slope aspect patterns.According to the Sequential Faulting Model of mid-ocean ridges,the maximal migration distance of an active fault on either side of mid-ocean ridges—that is,the distribution range of active faults—can be measured.Results show that the maximal migration distance of active faults at the NMAR is 0.76-1.01 km (the distance is larger at the center than at the ends of this segment),and at the NCR,the distribution range of active faults is 0.38-1.6 km.The migration distance of active faults on the two study areas is positively related to the axial variation of magma supply.In the NCR study area,where there is an abundant magma input,the number of faults within a certain distance is mainly affected by the variation of lithospheric thickness.Here a large range of faulting clearly corresponds to a high proportion of magmatism to seafloor spreading near mid-ocean ridges (M) value,and in the study area of the NMAR,there is insufficient magmatism,and the number of faults may be controlled by both lithospheric thickness and magma supply,leading to a less obvious positive correlation between the distribution range of active faults and M.