Composite Sensitive High Resolution Ion Microprobe (SHRIMP) U–Pb zircon and 40Ar–39Ar step-heating biotite-hornblende ages are used to provide constraints on the timing and origin of the felsic gneissic rocks in the Baiyunshan Mountains region and to elucidate their tectonothermal history. SHRIMP dating and CL imaging of zircons give magmatic zircon crystallization ages between Late Ordovician and Early Silurian (c. 453.5 Ma, 446 Ma, and 439 Ma) for three representative felsic gneisses, suggesting that most of the Baiyunshan gneiss cannot represent basement rocks of the Cathaysia Block as previously thought. Including the present age information, a synthesis of available age data for regional Wuyun (Wuyi-Yunkai) events reflects the emergence of orogen-wide magmatism that could be syn-orogenic and have occurred mainly between 460 and 420 Ma in the South China Block. Inherited zircons are abundant, with ages clustering at late Mesoproterozoic (1189–1017 Ma) and middle Mesoproterozoic (772 Ma), which reveals that the Baiyunshan orthogneiss samples a crustal basement containing significant igneous or recycled components related to the Rodinia amalgamation and break-up. A SHRIMP date of 212 ± 12 Ma from a white rim of zircon provides evidence for metamorphic overprinting of an Indosinian tectonothermal event on the Baiyunshan gneiss. Incremental heating experiments with six biotite samples and one hornblende sample from a variety of metamorphic rocks yielded two distinct 40Ar–39Ar age groups: 150–155 and 94–98 Ma. The older ages are similar to zircon U–Pb dates for widespread granitic intrusions in central Guangdong. We attribute them to Late Jurassic magmatism-induced thermal resetting of the biotite K–Ar system. On the other hand, the younger age group is interpreted to record either cooling through the biotite closure temperature of ~300–350 °C or a second resetting of biotite Ar isotopes at c. 94–98 Ma due to contemporaneous magmatic activity. Our present age data suggest that the Maofengshan orthogneiss was exhumed to 8 to 10 km crustal levels at c. 150 Ma, whereas the eastward components of gneissic rock masses appear to have passed upward through the same crustal depth synchronously or later (by c. 94 Ma). Exhumation of middle crustal-level rocks in the study area since c. 155 Ma is roughly coeval with exhumation of gneissic rocks from elsewhere in the Wuyun Orogen, suggesting a large-scale mechanism for the exhumation pulse related to the Yanshanian extensional tectonic regime.

The Troodos ophiolite in Cyprus and Baer–Bassit ophiolite in Syria together form part of the Tethyan ophiolite belt. They were generated in a supra-subduction zone setting in Late Cretaceous times. As with many of the ophiolite occurrences in this belt, the sequences are closely associated with tectonic ‘coloured mélange’ zones, which contain, among a variety of lithologies, metre- to kilometre-size blocks of metamorphic rocks. Precise 40Ar–39Ar laser step-heating experiments performed on four amphibolites from SW Cyprus and six from NW Syria, yield plateau ages ranging from 75.7±0.3 Ma to 88.9±0.8 Ma in Cyprus and 71.7±0.5 to 88.4±0.4 Ma in Syria. The older limits of these time spans are coeval with the age of the formation of the associated ophiolites. Unlike other metamorphic sole rocks which seem to form in relatively short time spans, these metamorphic rocks found in Cyprus and Syria are interpreted to have formed in Late Cretaceous times by accretion below the overriding Troodos and Baer–Bassit crust for a period of 15–18 Ma. The metamorphic complexes were exhumed by extension and crustal thinning associated with subduction roll-back and the rotation of the overriding plate until the cessation of subduction in Maastrichtian times. In Cyprus, the exhumed metamorphic complex was incorporated into an accretionary prism constructed primarily of the collapsed Mamonia passive margin sequence intercalated with rocks of the Troodos ophiolite during plate collision in the Maastrichtian. Concomitantly, in Syria, the Baer–Bassit ophiolite and subcreted metamorphic complex were emplaced onto the Arabian passive margin and fragmented into blocks and knockers, forming the Baer–Bassit mélange.

The regionally significant 0.5–2 km thick Høybakken detachment in central Norway bounds the southern margin of the Central Norway Basement Window and exhibits a well-developed top-to-the-WSW fabric characteristic of late Scandian, Devonian ductile extension. 40Ar–39Ar data obtained from hornblende, mica and K-feldspar mineral separates of rocks collected in a transect through the Høybakken detachment yield well-defined plateau and isochron mineral ages. Early Devonian exhumation and cooling of the Høybakken detachment footwall is recorded by hornblende ages of ∼ 400 Ma and mica ages of ∼ 390 Ma. The mylonitic fabric overlying the footwall records younger Middle Devonian mica crystallization ages of 384–381 Ma that are among the youngest extensional ductile fabrics dated in the Caledonides and suggest prolonged extensional activity on the Høybakken detachment. After inferred cessation of ductile extension at 381 Ma, the rate of uplift and cooling was reduced, and the footwall records Late Devonian to Early Carboniferous K-feldspar ages of 371–356 Ma. Prolonged extensional activity at Høybakken is compatible with recent U–Pb ages of deformed titanite crystals and established Rb–Sr ages of white mica in shear-related pegmatites, both from the southwestern part of the Fosen Peninsula, and 40Ar–39Ar ages of syn-tectonic mica overgrowth from the adjacent Hitra–Snåsa Fault. Together, these ages suggest the onset of ductile extension soon after ∼ 401 Ma, and with the Middle Devonian crystallization ages determined here, suggest that ductile extension on the Høybakken detachment had a duration of 11–20 Ma. The youngest age of 320 Ma was obtained from a K-feldspar in a cataclastic granite of the Høybakken detachment's hangingwall and is considered to date a phase of post-Scandian brittle deformation that overprinted the mylonitic shear fabric.