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A variety of felsic and mafic granulites and ultramafic rocks occur as xenoliths within a 12.7 Ma ultrapotassic dyke intruding Xigaze flysch immediately to the north of the Yarlung-Tsangpo suture zone in southern Tibet. Garnet-clinopyroxene-plagioclase-quartz thermobarometry on mafic granulite xenoliths gives temperatures of 1130-1330[degrees]C and pressures between 22 and 26 kbar indicating equilibration in the high-pressure and ultrahigh-temperature granulite field and defining a geotherm of c. 16[degrees]C [km.sup.-1]. Ultramafic xenoliths consist mainly of hornblende and biotite, probably of restitic crustal rather than mantle origin, and attained peak metamorphic conditions of 920-1130[degrees]C and 17-24 kbar, whereas felsic granulites equilibrated at 870-900[degrees]C at an inferred pressure of 17 kbar. In situ U-(Th)-Pb laser ablation inductively coupled plasma mass spectrometry dating of zircons shows that protoliths may include Proterozoic basement rocks, Late Cretaceous calc-alkaline tonalites of the Gangdese batholith root and/or remnants of a Neo-Tethyan oceanic arc. Certain zircons from a felsic granulite and an ultramafic xenolith have mean [sup.206]Pb/[sup.238]U ages of 16.8 [+ or -] 0.9 Ma and 15.6 [+ or -] 0.6 Ma, respectively, and monazites from a micaceous xenolith yielded a mean [sup.208]Pb/[sup.232]Th age of 14.4 [+ or -] 0.4 Ma. These results show that the southern Tibet basement reached a thickness of c. 80 km by 17-14 Ma at the latest and has remained unchanged until the present day. Supplementary material: Mineral analyses used for pressure temperature estimations and results of [sup.40]Ar/ [sup.30]Ar laser single-grain fusion experiments are available at http://www.geolsoc.org.uk/SUP18325.

New Caledonia preserves evidence that constrains models for the tectonic evolution of the southwest Pacific region. Onland geology reflects four main tectonic phases: (1) early Mesozoic development of subduction-related terranes and their accretion to the Gondwana margin; (2) Cretaceous passive margin development and sea-floor spreading during the Gondwana breakup; (3) foundering of an oceanic basin and the Eocene arrival of thinned Gondwana margin crust at a southwest-facing subduction zone, resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast; and (4) detachment faulting during extensional collapse, resulting in unroofing of metamorphic core complexes. The last phase explains supposedly anomalous metamorphic gradients in the northeast of the island.

Recent field mapping has refined our understanding of the stratigraphy and geology of southeastern Bohol, which is composed of a Cretaceous basement complex subdivided into three distinct formations. The basal unit, a metamorphic complex named the Alicia Schist, is overthrust by the Cansiwang mélange, which is, in turn, structurally overlain by the Southeast Bohol Ophiolite Complex. The entire basement complex is overlain unconformably by a ∼2000 m thick sequence of Lower Miocene to Pleistocene carbonate and clastic sedimentary rocks and igneous units. Newly identified lithostratigraphic units in the area include the Cansiwang mélange, a tectonic mélange interpreted as an accretionary prism, and the Lumbog Volcaniclastic Member of the Lower Miocene Carmen Formation. The Cansiwang mélange is sandwiched between the ophiolite and the metamorphic complex, suggesting that the Alicia Schist was not formed in response to emplacement of the Southeast Bohol Ophiolite Complex. The accretionary prism beneath the ophiolite complex and the presence of boninites suggest that the Southeast Bohol Ophiolite Complex was emplaced in a forearc setting. The Southeast Bohol Ophiolite Complex formed during the Early Cretaceous in a supra-subduction zone environment related to a southeast-facing arc (using present-day geographical references). The accretion of this ophiolite complex was followed by a period of erosion and then later by extensive clastic and carbonate rock deposition (Carmen Formation, Sierra Bullones Limestone and Maribojoc Limestone). The Lumbog Volcaniclastic Member and Jagna Andesite document intermittent Tertiary volcanism in southeastern Bohol. [ABSTRACT FROM AUTHOR]