Figure 1. Tectonic map of Betic-Rif arc. Internal Betics, Internal Rif, and floor of Alboran Sea constitute Alboran domain. Prebetic, Subbetic, and External Rif form external Betic-Rif arc. Line of section in Figure 2 is shown as dotted line. Inset: Alpine orogenic system in Mediterranean.

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Combining Lu-Hf garnet geochronology with in situ trace element analyses in garnet allowed us to gain new insight into the metamorphic evolution of UHP-UHT rocks in the Stary Gierałtów region, in the Polish Sudetes. Prograde garnet growth recorded by Rayleigh-type heavy REE (HREE) zoning in the felsic granulites indicates that the obtained 386.6 ± 4.9 Ma Lu-Hf age represents the time of

Prograde P-T paths and thermal modelling suggest metamorphism in the Sanbagawa belt represents unusually warm conditions for subduction-type metamorphic belts, and these likely reflect conditions of a convergent margin a few million years before the arrival of an active spreading ridge. Radiometric age data and kinematic indicators of ductile deformation suggest the Sanbagawa belt formed in a Cretaceous convergent margin associated with a plate movement vector that had a large sinistral oblique component with respect to the belt, the East Asian margin. Plate reconstructions for the Cretaceous to Tertiary for this region show that the only plausible plate compatible with such motion at this time is the Izanagi plate. These reconstructions also show that progressively younger sections of the Izanagi plate were subducted beneath eastern Asia, i.e. a spreading ridge approached, until 85-83 Ma when the Izanagi Plate ceased to exist as an independent plate. The major reorganization of plates and associated movements around this time is likely to be the age of major interaction between the ridge and convergent margin. The ridge-approach model for the Sanbagawa metamorphism, therefore, predicts that peak metamorphism is a few million years older than this age range. New Lu-Hf dating of eclogite in the Sanbagawa belt gives ages of 89-88 Ma, in excellent agreement with the prediction. Combining this estimate for the peak age of metamorphism with published P-T-t results implies vertical exhumation rates of greater than 2.5 cm yr )1 . This high rate of exhumation can explain the lack of a significant thermal overprint in the Sanbagawa belt during subduction of the ridge.

Low-angle detachment faults are common features in areas of large-scale continental extension and are typically associated with metamorphic core complexes, where they separate upper plate brittle extension from lower plate ductile stretching and metamorphism. In many core complexes, the footwall rocks have been exhumed from middle to lower crustal depths, leading to considerable debate about the relationship between hangingwall and footwall rocks, and the role that detachment faults play in footwall exhumation. Here, garnet-biotite thermometry and garnet-muscovite-biotite-plagioclase barometry results are presented, together with garnet and zircon geochronology data, from seven locations within metapelitic rocks in the footwall of the northern Snake Range de´collement (NSRD). These locations lie both parallel and normal to the direction of footwall transport to constrain the preexhumation geometry of the footwall. To determine P-T gradients precisely within the footwall, the DPT method of Worley & Powell (2000) has been employed, which minimizes the contribution of systematic uncertainties to thermobarometric calculations. The results show that footwall rocks reached pressures of 6-8 kbar and temperatures of 500-650°C, equivalent to burial depths of 23-30 km. Burial depth remains constant in the WNW-ESE direction of footwall transport, but increases from south to north. The lack of a burial gradient in the direction of footwall transport implies that the footwall rocks, which today define a sub-horizontal datum in the direction of fault transport, also defined a subhorizontal datum at depth in Late Cretaceous time. This suggests that the footwall was not tilted about the normal to the fault transport direction during exhumation, and hence that the NSRD did not form as a low-angle normal fault cutting down through the lower crust. Instead, the following evolution for the northern Snake Range footwall is proposed. (i) Mesozoic contraction caused substantial crustal thickening by duplication and folding of the miogeoclinal sequence, accompanied by upper greenschist to amphibolite facies metamorphism. (ii) About half of the total exhumation was accomplished by roughly coaxial stretching and thinning in Late Cretaceous to Early Tertiary time, accompanied by retrogression and mylonitic deformation. (iii) The footwall rocks were then ÔcapturedÕ from the middle crust along a moderately dipping NSRD that soled into the middle crust with a rolling-hinge geometry at both upper and lower terminations.

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The Day Nui Con Voi massif bears a record of the Red River shear zone (RRSZ) activity in North Vietnam. It forms a large‐scale antiformal “core complex”‐type structure, bounded by the Song Hong and Song Chay faults. The kinematics of both faults are identical and reflect transtensional shear initiated under upper amphibolite facies conditions and propagated into greenschist facies. Microfabric analysis establishes that both extensional and strike‐slip shearing initiated between 700 and 500°C. The RRSZ evolved from a single, subvertical fault, which, due to strike‐perpendicular extension, underwent progressive dilation. The created space was “intruded” by already metamorphosed and deformed ductile middle crust in the form of a gneissic “dome.” Both strike‐slip and extensional shearing were accommodated in the limbs of the antiform, while its core was uplifted from midcrustal level bearing only a minor record of sinistral shear.

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