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Abstract The widespread Cenozoic alkaline magmatism within and around the Tibetan Plateau offers a prime opportunity to probe the nature of the mantle at the depths where basalt magmas originate. The close temporal and spatial relationship between volcanism and regional strike‐slip fault systems also helps better understand the geodynamics of outward growth of the plateau in response to the continued India‐Asia convergence. We present a comprehensive study of the deeply sourced alkaline basalts formed along the Kunlun strike‐slip fault with the aim of understanding their petrogenesis and the composition of mantle sources beneath the northeastern Tibetan Plateau. High Nb/U and Ce/Pb ratios and relatively depleted bulk‐rock Sr‐Nd‐Pb isotope compositions corroborate the mantle origin of these alkaline basalts. Homogeneous and low 87Sr/86Sr of clinopyroxene indicates negligible crustal contamination during magmatic evolution. Low δ26Mg in the alkaline basalts and positive correlations with Hf/Sm and Ti/Ti* indicate that the basalts were derived from mantle that was metasomatized by melts derived from sedimentary carbonates during the Paleo‐Tethyan seafloor subduction. Based on 40Ar/39Ar dating results, it appears that the alkaline basaltic magmatism in the northeastern Tibetan Plateau occurred simultaneously with Kunlun strike‐slip faulting. These observations suggest that the India‐Asia convergence must have reactivated ancient subduction plate boundaries and resulted in strike‐slip faulting along these suture zones within and around the Tibetan Plateau. The eruption of low‐volume and deeply rooted alkaline basalts may have been controlled by fractures associated with the strike‐slip fault systems.

Abstract Decades of research have resulted in characterization of the ocean floor manifestations of mid‐ocean ridge (MOR) hydrothermal systems, yet numerical models accounting for the connections between heat transfer, hydrology and geochemistry have been slow to develop. The Thermo‐hydro‐chemical code ToughReact can be used to describe the coupled effects of fluid flow, heat transfer, and fluid‐rock chemical interactions that occur in MOR systems. We describe the results of 2‐dimensional simulations of steady state flow in fractured diabase with mineral‐fluid chemical reactions. Basal heating and specified permeability yield maximum temperature of 400°C. Total fluid flux and high fracture flow velocities are in accord with observations. Fluid chemistry, mineralogical changes and 87Sr/86Sr ratios can be compared to observations to assess and calibrate models. Simulated high temperature fracture fluids have Mg and SO4 near zero, elevated Ca and 87Sr/86Sr of about 0.7040. Total alteration is 10%–50% for simple models of spreading. Anhydrite forms mainly near the base of the upwelling zone and results in substantial local fracture porosity reduction. A calibrated model is used to predict how Sr isotopes and other features of altered oceanic crust would be different in the Cretaceous (95 Ma) early Proterozoic (1,800 Ma) and Archean (3,800 Ma), when seawater may have had high Ca and Sr concentrations, lower pH, higher temperature, and lower Na, Mg, and SO4. The simulations are offered as a start on what ultimately may require a longer‐term community effort to better understand the role of MOR thermo‐hydro‐chemical systems in Earth evolution.