The Angudan Orogeny affected Cryogenian to earliest Cambrian sedimentary rock formations of the Jabal Akhdar Dome of the Oman Mountains. These rocks were folded and cleaved at 525 ± 5 Ma. We studied the Cambro-Ordovician (Terreneuvian to Darriwillian) Amdeh Formation of the neighboring Saih Hatat Dome to see whether this formation was also affected by the Angudan Orogeny. The Angudan deformation within the Jabal Akhdar Dome is known for its folds and cleavage. Due to age considerations (see above), we studied the folds and cleavages within the two oldest members of the Amdeh Formation (Am 1 and Am 2) in order to compare them with the ones that are known from the Jabal Akhdar Dome to possibly detect Angudan-related deformation in Am 1 and Am 2. Angudan folds of the Jabal Akhdar Dome display fold axes that are oriented NE/SW, but the two lowest members of the Amdeh Formation reveal one set of folds with subhorizontal fold axes that trend NW-NNW/SE-SSE. The lack of Angudan-related folds suggests that the lowest Amdeh Member (Am 1) postdates the Angudan Orogeny. The age of Am 1 is uncertain. Based on our structural results, we consider an upper Terreneuvian age (late stage 2) for Am 1. The folds in Am 1 and 2 are related to the Late Cretaceous–Cenozoic Semail Orogeny (term introduced here). The observed fold vergences (mainly to the W and SW) were caused by shear deformation during descent into the subduction zone by simple shear. The contact between the stratigraphically underlying Hiyam Formation and the Amdeh Formation is generally considered to be an unconformity. We observed a distinct NW/SE-striking deformation zone along the contact of both formations which is located in proximity to the largest observed fold. Tectonically, this contact is defined by the sinistral Wadi Amdeh Fault (name introduced here). The unconformity should be present in the subsurface of the southwestern fault block. Near the contact between the Hiyam and the Amdeh formations, a 20 cm thick unit of reddish cataclasite/tectonic breccia occurs within the basal part of Am 1 which represents a deformed acidic layer or sill. This rock unit could be the first evidence for Cambrian igneous activity.

Contrary to the commonly accepted notion that the lithosphere in NE China thinned from the Late Jurassic through to the Early Cretaceous period, we report the discovery of a thickening episode in the backdrop of this long-term thinning. A series of lamprophyre dikes have been recently discovered in the Tuquan Basin of the western Songliao Basin that have been dated to 156.0 ± 2.3 Ma, 132.9 ± 1.2 Ma, and 126.2 ± 2.5 Ma by using the zircon U–Pb technique. These lamprophyres are subdivided into biotite orthoclase lamprophyre (BOL) from the Late Jurassic and quartz magnetite lamprophyre (QML) from the Early Cretaceous. The BOL and QMLs are shoshonite and calc-alkaline in series, are characterized by large amounts of FeO^T, TiO₂, MgO, and Mg#, and are rich in LREEs and LILEs but poor in HREEs and HFSEs. They have high ratios of (La/Yb)_N, La/Ta, La/Nb, Th/Y, Ba/Nb, Ba/Ta, and Ba/Th, and low ratios of Zr/Ba, La/Sm, and Nb/Zr. These features collectively point to the derivation of dike magmas from the partial melting of the enriched lithospheric mantle that had been previously metasomatized by subduction-related fluids. The BOL has high ratios of Rb/Sr (0.42) and K/Yb*1000 (28.3), and low ratios of Ba/Rb (13.5) and Dy/Yb (2.35), suggesting the derivation of magma from a high degree of partial melting of the phlogopite-bearing lherzolite mantle in the spinel–garnet transition zone at a depth of about 60 km. The QMLs have low ratios of Rb/Sr (0.02–0.06) and K/Yb*1000 (8.13–19.73), and high ratios of Ba/Rb (17.6–42.6) and Dy/Yb (3.48–4.09), indicating that the magmas were derived from a low degree of partial melting of the lherzolite mantle in the garnet zone at a depth of ca. 85 km. The younger QML (126.2 ± 2.5 Ma) has a lower Dy/Yb ratio (3.48–3.92) than the older QML (132.9 ± 1.2 Ma), with a Dy/Yb ratio of 4.09 implying that the younger magma was formed at a shallower depth of the mantle (<85 km) than the older one. These observations indicate that in 156–132 Ma, the lithosphere thickened by approximately 25 km at a rate of approximately 1.0 km/Myr. This is used to propose a model of geodynamic evolution in three stages.