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Liu, H., McKenzie, N. R., Colleps, C. L., Chen, W., Ying, Y., Stockli, L. D., Sardsub, A., Stockli, D. F., Zircon isotope-trace element compositions track Paleozoic–Mesozoic slab dynamics and terrane accretion in Thailand (In Review: Earth and Planetary Science Letters)
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Colleps, C. L., McKenzie, N. R., Guenthner, W. R., Sharma, M., and Stockli, D. F., Tracking the long-term burial and erosional evolution of central India: Low-temperature thermochronometric constraints from the Bundelkhand craton and Vindhyan basin
Colleps, C. L. and McKenzie, N. R., Global trends in burial and erosion within continental interiors with implications for deep-time Earth system processes
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Apatite (U-Th)/He thermochronometric constraints on the northern extent of the Deccan large igneous province
Colleps, C.L., McKenzie, N.R., Guenthner, W. R., Sharma, M., Gibson, T.M., Stockli, D.F.
2021 Earth and Planetary Science Letters
The volcanic emplacement and subsequent weathering of the Deccan Traps of India is believed to have had a significant influence in driving global climatic shifts from the Late Cretaceous and through the Cenozoic. The magnitude of the Deccan Traps’ impact on Earth’s surface environment is largely dependent on the speculated original footprint of the large igneous province. To test established estimates for the pre-erosive northern extent of the Deccan Traps, we applied low-temperature apatite (U-Th)/He thermochronology (AHe) on rocks from the Bundelkhand craton and overlying Proterozoic Vindhyan successions of central India ~150–200 km northeast of the northernmost preservation of Deccan basalts. New AHe data reveal young ~5–85 Ma AHe dates with low effective uranium concentrations (eU) between 5–22 ppm, with a steep positive date-eU correlation that plateaus at ~350 Ma in grains with eU values >50 ppm. Inverse thermal history modeling—utilizing AHe diffusion parameters of the Radiation Damage Accumulation and Annealing Model (RDAAM)—indicate that observed AHe date-eU correlations are most consistent with thermal histories that require the craton and Vindhyan strata to be at or near surface temperatures by ~66 Ma, followed by a discrete reheating event associated with Deccan volcanism. These results establish new minimal areal constraints for the northern extent of Deccan volcanism which thermally perturbed much of the Vindhyan succession. Thermal alteration of organic rich Vindhyan sediment may have provided an additional source of volatile emissions that facilitated late Maastrichtian warming at the onset of Deccan volcanism. New minimal northern constraints on Deccan volcanism additionally confirm that large volumes of Deccan basalts have been stripped away since the time of their emplacement, which poses considerable implications for unraveling their role in Cenozoic cooling.
Zircon and apatite U-Pb age constraints from the Bundelkhand craton and Proterozoic strata of central India: Insights into craton stabilization and subsequent basin evolution
Colleps, C.L., McKenzie, N.R., Sharma, M., Liu, H., Gibson, T.M., Chen, W., Stockli, D.F.
2021 Precambrian Research
The geologic processes involved in attaining strengthened cratonic lithosphere remain debated despite their importance for stabilization and long-term preservation. In central India, stabilization of the Bundelkhand craton has conventionally been attributed to the youngest magmatic event impacting the craton at ~2.5 Ga, though the post-amalgamation evolution of the craton prior to Proterozoic basin development is poorly understood. This study presents new basement zircon and apatite U-Pb age data along with new detrital zircon U-Pb age data from Proterozoic marginal sedimentary basin deposits to explore the post-magmatic and burial evolution of the Bundelkhand craton. Apatite from ~3.4–2.5 Ga granitoids and gneisses collected across the ~250 km wide craton yielded near uniform U-Pb ages between ~2.4–2.3 Ga, indicating broad-scale exhumation of the Bundelkhand craton through mid-crustal depths following amalgamation and felsic magmatism. Unroofing of the Bundelkhand craton at this time is corroborated by ~2.7–2.5 Ga detrital zircon U-Pb age peaks from basal sandstones of the Bijawar and Gwalior groups, which lie in direct nonconformable contact with the craton along both its southeastern and northwestern margins, respectively. These age populations reveal an abundance of zircon sourced directly from the Bundelkhand craton, and a sub-population of ~2.2–2.3 Ga grains provide a maximum depositional age for the oldest strata deposited on the craton. We speculate that the redistribution of heat producing elements associated with shallow emplacement of Bundelkhand granitoids and subsequent erosion may have enhanced lithospheric strengthening and facilitated a long-term thermal regime that promoted craton stability by ~2.2 Ga. Following stabilization, far-field marginal tectonism likely influenced the vertical motions within the Bundelkhand craton, inducing stages of broad subsidence and erosion recorded within the strata of the Lower and Upper Vindhyan successions.
Detrital zircon record of Phanerozoic magmatism in the southern Central Andes
Capaldi, T.N., McKenzie, N.R., Horton, B.K., Mackaman-Lofland, C, Colleps, C.L., Stockli, D.F.
The spatial and temporal distribution of arc magmatism and associated isotopic variations provide insights into the Phanerozoic history of the western margin of South America during major shifts in Andean and pre-Andean plate interactions. We integrated detrital zircon U-Th-Pb and Hf isotopic results across continental magmatic arc systems of Chile and western Argentina (28°S–33°S) with igneous bedrock geochronologic and zircon Hf isotope results to define isotopic signatures linked to changes in continental margin processes. Key tectonic phases included: Paleozoic terrane accretion and Carboniferous subduction initiation during Gondwanide orogenesis, Permian–Triassic extensional collapse, Jurassic–Paleogene continental arc magmatism, and Neogene flat slab subduction during Andean shortening. The ~550 m.y. record of magmatic activity records spatial trends in magma composition associated with terrane boundaries. East of 69°W, radiogenic isotopic signatures indicate reworked continental lithosphere with enriched (evolved) εHf values and low (<0.65) zircon Th/U ratios during phases of early Paleozoic and Miocene shortening and lithospheric thickening. In contrast, the magmatic record west of 69°W displays depleted (juvenile) εHf values and high (>0.7) zircon Th/U values consistent with increased asthenospheric contributions during lithospheric thinning. Spatial constraints on Mesozoic to Cenozoic arc width provide a rough approximation of relative subduction angle, such that an increase in arc width reflects shallower slab dip. Comparisons among slab dip calculations with time-averaged εHf and Th/U zircon results exhibit a clear trend of decreasing (enriched) magma compositions with increasing arc width and decreasing slab dip. Collectively, these data sets demonstrate the influence of subduction angle on the position of upper-plate magmatism (including inboard arc advance and outboard arc retreat), changes in isotopic signatures, and overall composition of crustal and mantle material along the western edge of South America.
Sediment provenance of pre- and post-collisional Cretaceous–Paleogene strata from the frontal Himalaya of northwest India
Colleps, C.L., McKenzie, N.R., Horton, B.K., Webb, A.A.G., Ng, Y.W., Singh, B.P.
2020 Earth and Planetary Science Letters
Whereas the timing for India–Asia collision remains debated, contrasting collisional models provide testable predictions in terms of sediment source contributions during the accumulation of Paleocene to middle Eocene deposits now exposed in the frontal Himalayan system. Within the Lesser Himalaya and frontal thrust system of northwest India, discontinuous exposures of the Cretaceous Singtali Formation and upper Paleocene–middle Eocene Subathu Formation yield a record of these early collisional stages. To test competing collisional models, we analyze the provenance of these deposits with new detrital zircon U-Pb and Hf isotopic data which can distinguish among Indian plate, Asian plate, Kohistan-Ladahk arc, and various Himalayan sources. Detrital zircon age distributions for the Singtali Formation are dominated by Paleoproterozoic zircons with a distinct Cretaceous age component, whereas age data from the Subathu Formation record (1) a marked increase in the relative abundance of Cambrian–Neoproterozoic grains, (2) a decrease in the proportion of Paleoproterozoic grains, and (3) distinct Permian and Late Cretaceous–Paleocene age components. All Cretaceous grains from the Singtali Formation yielded crustal Hf isotopic signatures, indicating a distinctive pre-collisional source of Cretaceous grains of Indian affinity. Zircon Hf isotopic signatures from <320 Ma grains in the Subathu Formation show a significant lower to middle Eocene increase in source diversity, including juvenile grains most likely originating from the Asian plate and Kohistan-Ladakh arc. This requires inception of India-Asia collision by ∼44–50 Ma—the depositional age of the uppermost Subathu Formation. This major provenance shift is similar to that observed for pre- and post-collisional Tethyan Himalayan strata in the north, which is suggestive of a single contiguous basin linking the Lesser Himalaya by ∼44–50 Ma and contests the notion that the Lesser and Tethyan Himalaya were separated by a “Greater India Basin” during the Eocene. When coupled with the well documented Paleocene–early Eocene provenance record of the Tethyan Himalaya, these new data provide support for a collisional model in which Asian detritus reached the northernmost edge of India by ∼59 Ma with terminal closure of both the Shyok and Indus-Yarlung suture zones by ∼54 Ma.
Neogene Kinematic Evolution and Exhumation of the NW India Himalaya: Zircon Geo‐ and Thermochronometric Insights From the Fold‐Thrust Belt and Foreland Basin
Colleps, C.L., Stockli, D.F., McKenzie, N.R., Webb, A.A.G., Horton, B.K.
The kinematic and exhumational evolution of the Lesser Himalaya (LH) remains a topic of debate. In NW India, the stratigraphically diverse LH is separated into the inner LH (iLH) of late Paleo‐Mesoproterozoic rocks and the outer LH (oLH) of Cryogenian to Cambrian rocks. Contradictory models regarding the age and structural affinity of the Tons thrust—a prominent structure bounding the oLH and iLH—are grounded in conflicting positions of the oLH prior to Himalayan orogenesis. This study presents new zircon (U‐Th)/He and U‐Pb ages from the thrust belt and foreland basin of NW India that refine the kinematic and exhumational evolution of the LH. Combined cooling ages and foreland provenance data support emplacement and unroofing of the oLH via southward in‐sequence propagation of the Tons thrust by middle Miocene time. This requires that, before India–Asia collision, the oLH was positioned as the southernmost succession of Neoproterozoic–Cambrian strata along the north Indian margin. This is further supported by detrital zircon U‐Pb ages from Cretaceous–Paleogene strata (Singtali Formation) unconformably overlying the oLH, which yield diagnostic Cretaceous detrital zircons correlative with coeval strata in the frontal Himalaya of Nepal. A pulse of rapid exhumation along the Tons thrust front at ~16 Ma was followed by east‐to‐west development of a midcrustal ramp at ~12 Ma which facilitated diachronous iLH duplexing. This duplexing shifted the locus of maximum exhumation northward, eroding away Main Central Thrust hanging wall rocks until the iLH breached the surface at ~9–11 Ma near Nepal and by ~3–7 Ma within the Kullu‐Rampur window.
Zircon (U‐Th)/He Thermochronometric Constraints on Himalayan Thrust Belt Exhumation, Bedrock Weathering, and Cenozoic Seawater Chemistry
Colleps, C.L., McKenzie, N.R., Stockli, D.F., Hughes, N.C., Singh, B.P., Webb, A.A.G., Myrow, P.M., Planavsky, N.J., Horton, B.K.
2018 Geochemistry, Geophysics, Geosystems
Shifts in global seawater 187Os/188Os and 87Sr/86Sr are often utilized as proxies to track global weathering processes responsible for CO2 fluctuations in Earth history, particularly climatic cooling during the Cenozoic. It has been proposed, however, that these isotopic records instead reflect the weathering of chemically distinctive Himalayan lithologies exposed at the surface. We present new zircon (U‐Th)/He thermochronometric and detrital zircon U‐Pb geochronologic evidence from the Himalaya of northwest India to explore these contrasting interpretations concerning the driving mechanisms responsible for these seawater records. Our data demonstrate in‐sequence southward thrust propagation with rapid exhumation of Lesser Himalayan strata enriched in labile 187Os and relatively less in radiogenic 87Sr at ∼16 Ma, which directly corresponds with coeval shifts in seawater 187Os/188Os and 87Sr/86Sr. Results presented here provide substantial evidence that the onset of exhumation of 187Os‐enriched Lesser Himalayan strata could have significantly impacted the marine 187Os/188Os record at 16 Ma. These results support the hypothesis that regional weathering of isotopically unique source rocks can drive seawater records independently from shifts in global‐scale weathering rates, hindering the utility of these records as reliable proxies to track global weathering processes and climate in deep geologic time.