Foundering Triggered by the Collision of India and Asia Captured in Xenoliths

Abstract

Xenoliths that erupted in the SE Pamir of Tajikistan from 1000 to 1050°C and 90 km depth illuminate what happens when crust founders into the mantle. 40Ar/39Ar dating of minerals from the xenoliths and volcanic host rocks of the shoshonitic Dunkeldik pipe and dike field indicates eruption at 11.2 ± 0.2 Ma. U‐Pb and trace element laser‐ablation split stream inductively coupled plasma mass spectrometry of zircon shows that the igneous and metasedimentary xenoliths were likely derived from the crustal section into which they were intruded: the Jurassic‐Cretaceous Andean‐style magmatic arc and its Proterozoic‐Mesozoic host rocks along the southern margin of Asia. Recrystallization of these zircons was extensive, yielding a range of dates down to 11 Ma. The zircons show distinct changes in Eu anomaly, Lu/Gd ratio, and Ti concentrations compatible with garnet growth and minimal heating at 22–20 Ma and then 200‐300°C of heating, ~25 km of burial, and alkali‐carbonate melt injection at 14–11 Ma. These changes are interpreted to coincide with (i) heat input due to Indian slab breakoff at ~22–20 Ma and (ii) rapid thickening and foundering of the Pamir lithosphere at 14‐11 Ma, prior to and synchronous with collision between deep Indian and Asian lithospheres beneath the Pamir.

Prolonged (>100 Ma) ultrahigh temperature metamorphism in the Napier Complex, East Antarctica: A petrochronological investigation of Earth's hottest crust

“…The Th/U ratios of zircon grains are typically greater than the suggested metamorphic value of 0.1, but consistent with the Th/U ratios from other UHT terranes as documented in Rubatto (), Shaffer et al. () and Yakymchuk, Kirkland, and Clark (). Ti‐in‐zircon thermometry yielded temperatures >900°C for four of the six concordant populations; however, the youngest sector‐zoned population and the high‐CL response cores have calculated temperatures of 847 and 894°C (Figure a).…”

“…A number of studies have demonstrated that the zircon–garnet relationship can withstand long durations of metamorphism at high temperature (Clark, Collins, Santosh, Taylor, & Wade, ; Harley & Nandakumar, ; Hermann & Rubatto, ; Kelly & Harley, ; Štípská, Powell, Hacker, Holder, & Kylander‐Clark, ; Taylor, Clark, Johnson, Santosh, & Collins, ), further establishing the utility of zircon–garnet relationships in interrogating the evolution of metamorphic terranes. The recently established ability to rapidly acquire in situ isotopic and trace elemental data sets through techniques such as laser ablation split stream petrochronology means that large coupled geochronological–geochemical data sets can be applied to understanding high‐ T events (Horton et al., ; Kylander‐Clark, Hacker, & Cottle, ; Shaffer, Hacker, Ratschbacher, & Kylander‐Clark, ).…”

Miocene Volcaniclastic Sequence Within the Xiyu Formation from Source to Sink: Implications for Drainage Development and Tectonic Evolution in Eastern Pamir, NW Tibetan Plateau

“…Petrographic, petrological, geochronological, and whole‐rock geochemical evidence indicates that the AVS in the foreland basin was most likely derived from the Dunkeldik volcanic belt. The 40 Ar/ 39 Ar ages of the samples from the volcaniclastic sequence (ranging from 10.9 to 11.5 Ma) overlap those of the Dunkeldik complex rocks (10.8 ± 0.15 to 11.1 ± 0.15 Ma; Ducea et al, ; Kooijman et al, ; Shaffer et al, ). Only the Dunkeldik volcanic belt shows unambiguous volcanic‐subvolcanic lithofacies among ~11‐Ma igneous rocks in the southeastern Pamir region (Dmitriev, ; Lutkov et al, ; Pan, ). The volcaniclastic deposits and the Dunkeldik volcanic complex share similar rock types. Pseudoleucitite breccia, pseudoleucite phonolite blocks, and trachyte blocks of volcanic origin within the volcaniclastic sequence, respectively, correspond to the fergusite, pseudoleucitic tinguaite, and trachyte in the Dunkeldik volcanic complex (Ducea et al, ; Lutkov et al, ).…”

“…Previous studies suggest that ~11 Ma igneous rocks in the Pamir region are distributed around the KSES, including an alkaline volcanic‐subvolcanic complex (Dunkeldik volcanic belt) (Figure d; e.g., Ducea et al, ; Hacker et al, ; Kooijman et al, ; Shaffer et al, ) and three alkaline plutons (Karibasheng, Kuzigan, and Zankan; Figure c; e.g., Dmitriev, ; Jiang et al, ; Ke et al, ; Lutkov et al, ). Petrographic, petrological, geochronological, and whole‐rock geochemical evidence indicates that the AVS in the foreland basin was most likely derived from the Dunkeldik volcanic belt.…”

“…A series of~11-Ma alkaline rocks along the KSES (e.g., Ducea et al, 2003;Jiang et al, 2012;Kooijman et al, 2017;Shaffer et al, 2017) are included in the scope of this study (Figures 1c and 1d). The alkaline rocks, which are found in three plutons (Karibasheng, Kuzigan, and Zankan) called the Tashkorgan plutons along the Tashkorgan valley (Jiang et al, 2012;Ke et al, 2006), as well as in a volcanic-subvolcanic complex called the Dunkeldik volcanic complex, are the youngest igneous rocks in the Pamir (Figure 1c; Lutkov et al, 2005).…”