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How seismotectonics of convergent margins reconciles with the force balance of subduction is contentious. The comparison of seismotectonics and available slab pull forces along the Sunda convergent margin shows an enigmatic inverse relationship: upper plate thickening and seismicity magnitude are highest along Sumatra and Andaman, where the slab is shorter than ∼300 km; conversely, these are negligible along the Java segment, where the slab reaches deeper, ∼660 km. Using numerical models, we test the role of such slab pull gradients in the force balance of subduction in three‐dimensions, where the slab depth, and therefore its net pull, varies along the trench. We show that in the presence of a "slab step," the deeper slab drives the convergence of the rigid plate, causing upper plate compression and trench advance in the neighboring trench segments, where a short slab may have no pull to subduct the incoming plate. While neglecting convergence obliquity, the simplified models show relevant along‐trench variations of coupling, trench rotations, and minor strike‐slip shearing due to the slab step, providing a diagnostic strain pattern, with compression/extension atop the short/long slab and minor strike‐slip, increasing in magnitude with depth difference. The modeled tectonic patterns are compared to Sunda margin deformation across scales, from the Cenozoic tectonics to the seismic strain rates, showing remarkable consistency with deformation gradients from Sumatra to Java, potentially illustrating the contribution of the slab step to the seismotectonics of the region. Key Points: Sunda margin thickening and seismic strain are anti‐correlated with the slab depth and largest in the proximity of a step in the slab depths between Sumatra and JavaNumerical models of subduction with slab steps show compatible upper plate tectonics and trench motions due to deep slab lateral loadingStrain regimes and seismicity along the Sumatra‐Java margin support the role of trench‐parallel tectonic loading across timescales [ABSTRACT FROM AUTHOR]

Rifting in the Afar region is considered to be the only known example of the formation of an incipient divergent triple junction. Taking the Afar region as an example, we use three-dimensional lithospheric-scale laboratory experiments to constrain the factors controlling the structure and the tectonic evolution of the area. We systematically evaluate the role of different preexisting heterogeneities, such as those due to plume head impingement or inherited weak structures, and different kinematic boundary conditions, such as orthogonal versus rotational extension. The interaction between these inherited heterogeneities and the tested boundary conditions results in a range of complex rift geometries and structural features, such as rift segmentation and ridge jumps, which are comparable to those observed in the Afar region. At the plate scale, only under rotational extension, consecutive rift zones intersecting at high angles develop akin to the along-axis segmentation in the Red Sea and the Gulf of Aden. Under orthogonal extension, the dominant rifting trend is perpendicular to the stretching direction. Preexisting weaknesses, including that due to a mantle plume, trigger different rifting styles and influence the geometry of large-scale continental breakup. When compared to the Afar region, our results suggest that differing the degree of stretching, following the rotation of the Arabian plate since the Oligocene, led to the rifting in the Red Sea and the Gulf of Aden and likely did not cause the formation of the Main Ethiopian Rift. [ABSTRACT FROM AUTHOR]

Tectonic models for the latest Paleoproterozoic to earliest Mesoproterozoic evolution of eastern Australia (circa 1620-1500 Ma) are diverse and either emphasize plume or plate margin activity, neither of which satisfactorily explains all geological observations. The dichotomy is largely attributed to geochemical, spatial and temporal data that suggest voluminous A-type felsic magmas are plume related, whereas distribution of arc-related magmas and intense orogenic overprint suggest plate margin activity. The salient geological events include arc-related magmatism at circa 1620-1610 Ma followed by a magmatic hiatus coincident with north-south crustal shortening (1610-1590 Ma) and a magmatic flare-up of A-type felsic magmas throughout the Gawler Craton (circa 1595-1575 Ma). These magmas form the oldest component of a northward younging hot spot track that extends to the Mount Isa Inlier. At circa 1590-1550 Ma, arc magmatism resumed along the northern margin of the Gawler Craton and the rest of eastern Australia records a 90° shift in the regional shortening direction related to activity along the eastern margin of the Australian continent. A plume-modified orogenic setting satisfies all of the spatial and temporal relationships between magma generation and orogenic activity. In this model, the Gawler Craton and the adjacent subduction zone migrated over a mantle plume (circa 1620-1610 Ma). Resultant flat subduction caused transient orogenesis (1610-1595 Ma) in the overriding plate. Slab delamination and thermal assimilation of the plume and the subducting slab caused a switch to crustal extension in the overriding plate, resulting in extensive mantle-derived and crustal melting in the Gawler Craton (1595-1575 Ma). [ABSTRACT FROM AUTHOR]

Mesoproterozoic A-type magmatic rocks in the Gawler Craton, Curnamona Province and eastern Mount Isa Inlier, form a palaeo-curvilinear belt for reconstructed plate orientations. The oldest igneous rocks in the Gawler Craton are the Hiltaba Granite Suite: c. 1600–1575 Ma. The youngest in the Mount Isa Inlier are the Williams-Naraku Batholiths: c. 1545–1500 Ma. The belt is interpreted as a segment of a hotspot track that evolved between c. 1600 and 1500 Ma. This hotspot track may define a quasilinear part of Australia’s motion between 1636 and 1500 Ma, and suggests that Australia drifted to high latitudes. An implication of this interpretation is that Australia and Laurentia may not have been fellow travellers leading to the formation of Rodinia. A hotspot model for A-type magmatism in Australia differs from geodynamic models for this style of magmatism on other continents. This suggests that multiple geologic processes may be responsible for the genesis of Proterozoic A-type magmas. [ABSTRACT FROM AUTHOR]