A DETRITAL APPROACH TO EVALUATING THE ROLE OF DEEP LITHOSPHERE REMOVAL IN OROGENESIS

Removal of dense lower lithospheric material maintains gravitational equilibrium and mass balance in convergent orogens, and can be a primary driver of orogenic uplift. However, unlike magmatic and accretionary processes that add mass to the lithosphere, the removal of mass at depth must often be inferred from the absence of evidence (e.g. unexplained topographic uplift, missing mantle lithosphere). Even when foundering events do leave traces of their occurrence (e.g. low-volume magmatism, serendipitous xenolith eruptions, transient hinterland sedimentary basins), the low preservation potential of such evidence leaves incomplete and ambiguous records. This limits our ability to evaluate the role of lithosphere removal in orogenesis and in its energy budget to only orogens where magmatism and hinterland basins have been preserved, or to the realm of numerical geodynamic models. To develop a more comprehensive record of this process, and facilitate comparisons between regions with copious surface evidence of lithospheric foundering (e.g. Puna Plateau) with regions where the evidence is scant, whether poorly preserved or not yet recognized (e.g. Tibet, Pamir, Colorado Plateau), we investigate the detrital record from young strata in internally-drained hinterland basins as a proxy for foundering-related magmatism. Integration of isotope geochemistry, trace element geochemistry, and thermochronology of detrital zircon and apatite presents a promising approach to reconstruct a continuous record of low-volume magmatism, both eroded and preserved. Ti-in-zircon thermometry, Ce-U-Ti oxybarometry, and REE proxies for depth of magmatic differentiation potentially provide a means of distinguishing zircon crystals associated with hinterland magmatism from that associated with arc magmatism. We consider whether lithospheric foundering can be associated with recognizable patterns that are similar across orogens, and whether geochemical shifts in hinterland magmatism reveal first-order differences in the temporal scale of mass and energy removal in different orogens.