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Abstract Ophiolites, mostly formed via subduction initiation at proto-forearcs, exhibit a unique variation of mantle-derived magmatism from MORB-like to low-Ti tholeiitic and bainitic-like affinities. Such variation was suggested to form chromite deposits spanning high-Al to high-Cr types. Nevertheless, the origin of diverse magmatism during subduction initiation and their linkages to different chromite deposits has long been enigmatic. Here we show elemental and Os isotopic compositions of different chromitites from the Zambales ophiolite, Philippines. Combined with data from ophiolites worldwide, high-Al and high-Cr chromitites are revealed to result from low-Ti tholeiitic and boninitic-like magmatism, respectively. Proto-forearc mantle had few chromitites generated during MORB-like magmatism, but afterwards, it was modified first by slab fluids and later by continuous asthenospheric upwelling in the context of slab densification and rollback. The latter modification elevated the geothermal gradient and replenished fertile components in the proto-forearc mantle progressively, inducing increasingly higher degrees of mantle melting and Cr-richer magmatism and chromitites.

At the Le Thor Seminar in 1969, Heidegger characterises his thinking as taking the form of what he calls a ‘topology of being’ (Topologie des Seins) and as thereby giving a key role to place (topos, Ort/Ortschaft). Much of my work over the last 25 years has been devoted to exploring how such a topology is indeed present in Heidegger’s thinking, both early and late, and so to showing how place figures in that thinking – to showing, in effect, how the questioning of being is also the thinking of place. The aim here is to provide a summary introduction to the topology that this exploration has aimed at uncovering, but to do so in a way that is focussed on the early work, especially Being and Time. To this end, the discussion proceeds through an explication of the topological elements that are present in the form of key terms and ideas such as facticity, questionability, being-in, existential spatiality, and there-being or Dasein. There is also a brief exploration of the way the term Dasein figures in German philosophical discourse prior to Heidegger in ways that are not only reflected in Heidegger’s early work, but also draw directly upon that term’s topological connotations.