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MULTIDATING OF THE INDIA-ASIA COLLISION ZONE We collected 12 samples of Kailas Formation and 5 samples of Gangdese batholith granite between ~80.9°E and ~86.7°E (see the GSA Data Repository 1) for geochronology and thermochronology. Samples of Kailas Formation from previously published sections (DeCelles et al., 2011) together with newly investigated sections near Xiao Gurla (Yagra Valley), Lopukangri, and Geydo (Fig. 1), were analyzed (for analytical details and information about the locations and stratigraphic positions of the analyzed samples, see the Data Repository). Phlogopite crystals were separated from two basaltic fl ows from a section of the middle Kailas Formation (lacustrine facies) at its type locality near Mount Kailas (Fig. 1) (4KR363 and 4KR388; DeCelles et al., 2011) and yielded 40 Ar/ 39 Ar plateau ages of 23.2 ± 0.2 Ma and 23.8 ± 0.3 Ma (Fig. 2; Fig. DR1 in the Data Reposi

Widespread mafic volcanism, elevated crustal temperatures, and plateau‐type topography in Central Anatolia, Turkey, could collectively be the result of lithospheric delamination, mantle upwelling, and tectonic escape. We use results from 40Ar/39Ar geochronology, basalt geochemistry, and a passive‐source broadband seismic experiment obtained in a collaborative international effort (Continental Dynamics‐Central Anatolia Tectonics) to investigate the upper mantle structure and evolution of melting conditions over an ∼2400 km2 area south and west of Hasan volcano. New 40Ar/39Ar dates for the basalts mostly cluster between 0.2 and 0.6 Ma, but some scoria cones are as old as 2.5 Ma. Basalts are dominantly Mg‐rich (Mg# = 62–71), moderately alkaline (normative Ne < 5 wt %), and, based on major and trace element signatures, derived from a peridotitic source. Covariations between radiogenic isotope and trace element signatures reveal contributions from a subduction‐related component and intraplate‐like mantle asthenosphere, as well as from ambient upper mantle. Central Anatolian basalts reflect maximum mantle potential temperatures of <1350°C and an average pressure of melt equilibration of 1.4 GPa, which are cooler and shallower than for basalts from Eastern and Western Anatolia. When considered in light of regionally slow upper mantle shear wave velocities, the mantle lithosphere may be thin and infiltrated by melts, or largely absent. An absence of secular changes in melting conditions suggests little to no lithospheric thinning over the past ∼1 Ma, despite evidence for lithospheric extension. Hasan basalts appear to be generated by decompression melting in response to the rollback of the Cyprean slab.

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Hydrogen isotope and 40 Ar/ 39 Ar geochronological data are presented from muscovite within a crustal-scale extensional detachment of the Shuswap Metamorphic Complex, North American Cordillera. The hydrogen isotope compositions (␦D ms ) of precisely dated muscovite attain values as low as ؊156‰ in the detachment mylonite, whereas footwall quartzite has a ␦D ms value of ؊81‰. The very low ␦D ms values in the detachment are best explained by infiltration of meteoric water, with maximum ␦D values of ؊135‰ ؎ 3‰, during extensional unroofing of the orogen at 49.0-47.9 Ma. On the basis of the empirically determined relationship between elevation and isotopic composition of precipitation, the reconstructed early Eocene paleoelevations of the orogen are 4060 ؎ 250 m to 4320 ؎ 250 m, at least 1000 m higher than the highest present-day peaks. We propose that the isotopic composition of surface-derived waters in extensional detachments represents a newly recognized method to estimate maximum paleoelevations attained immediately preceding extensional orogenic collapse. Figure 1. Muscovite vs. quartz ␦ 18 O values from mylonitic quartzite in footwall of detachment. Temperatures correspond to lines of constant quartz-muscovite oxygen isotope fractionation, ⌬ qtz-ms . Alignment of different mylonitic quartzite samples is consistent with quartz-muscovite equilibrium at temperatures of 420 ؎ 40 ؇C.