TY - JOUR
T1 - Interpreting date-eU correlations in zircon (U-Th)/He datasets
T2 - A case study from the Longmen Shan, China
AU - Guenthner, William R.
AU - Reiners, Peter W.
AU - Tian, Yuntao
N1 - Funding Information:
We acknowledge support from NSF grant EAR-0910577 to P.W.R. We appreciate helpful discussions with Rich Ketcham and Raphael Pik, and constructive reviews, and editorial handling, from Cécile Gautheron and David Shuster, and Mark Harrison.
PY - 2014/10/1
Y1 - 2014/10/1
N2 - Zircon (U-Th)/He (zircon He) dates from the Longmen Shan (LMS, on the eastern margin of the Tibetan Plateau) show a distinctive compositional dependence consistent with a strong effect of radiation damage on He diffusion. Using a new model accounting for the evolution of damage and diffusivity as a function of time and temperature, we use these data, together with constraints from other low-. T thermochronometers, to interpret the Precambrian to Neogene thermal and exhumation histories of LMS basement rocks. For most samples, several features of the inverse correlations between single-grain zircon He dates and effective uranium (eU) concentrations, combined with geologic constraints, require near-surface exposure in the Precambrian, followed by burial and heating to temperatures less than about 200°C over hundreds of Ma, and a final episode of cooling (exhumation) to surface temperatures after ~30 Ma. In contrast, samples from the hanging wall of the Wenchuan-Maowen thrust fault in the LMS show weak or no date-eU correlations, requiring exhumation from greater depths than corresponding footwall rocks. Our modeling focuses particularly on maximum temperatures prior to Cenozoic exhumation, as well as the timing of the Cenozoic rapid cooling event, as these thermal history segments are most pertinent to debates about the timing and kinematics of recent exhumation in the LMS. Models for one sample near the front of the range in the central LMS (LME-18) require rapid Cenozoic cooling from ~180°C to less than ~50°C from ~30-25 Ma. Model results from a more hinterland transect in the central LMS (Wenchuan) require a later rapid cooling event from ~190°C to the surface, beginning at ~15 Ma. Finally, our models for samples from the southern LMS (WMF footwall transect) require rapid cooling from ~200°C to the surface beginning at ~12 Ma. Taken together, these reinterpretations of previously published results lead to a cohesive burial and exhumation history for samples from a large area of the orogen and require large-magnitude exhumation in hinterland regions of the LMS more than 10 Ma after exhumation in the frontal part of the range.
AB - Zircon (U-Th)/He (zircon He) dates from the Longmen Shan (LMS, on the eastern margin of the Tibetan Plateau) show a distinctive compositional dependence consistent with a strong effect of radiation damage on He diffusion. Using a new model accounting for the evolution of damage and diffusivity as a function of time and temperature, we use these data, together with constraints from other low-. T thermochronometers, to interpret the Precambrian to Neogene thermal and exhumation histories of LMS basement rocks. For most samples, several features of the inverse correlations between single-grain zircon He dates and effective uranium (eU) concentrations, combined with geologic constraints, require near-surface exposure in the Precambrian, followed by burial and heating to temperatures less than about 200°C over hundreds of Ma, and a final episode of cooling (exhumation) to surface temperatures after ~30 Ma. In contrast, samples from the hanging wall of the Wenchuan-Maowen thrust fault in the LMS show weak or no date-eU correlations, requiring exhumation from greater depths than corresponding footwall rocks. Our modeling focuses particularly on maximum temperatures prior to Cenozoic exhumation, as well as the timing of the Cenozoic rapid cooling event, as these thermal history segments are most pertinent to debates about the timing and kinematics of recent exhumation in the LMS. Models for one sample near the front of the range in the central LMS (LME-18) require rapid Cenozoic cooling from ~180°C to less than ~50°C from ~30-25 Ma. Model results from a more hinterland transect in the central LMS (Wenchuan) require a later rapid cooling event from ~190°C to the surface, beginning at ~15 Ma. Finally, our models for samples from the southern LMS (WMF footwall transect) require rapid cooling from ~200°C to the surface beginning at ~12 Ma. Taken together, these reinterpretations of previously published results lead to a cohesive burial and exhumation history for samples from a large area of the orogen and require large-magnitude exhumation in hinterland regions of the LMS more than 10 Ma after exhumation in the frontal part of the range.
KW - Longmen Shan
KW - Low-temperature thermochronology
KW - Radiation damage
KW - Tibetan Plateau
KW - Zircon (U-Th)/He dating
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U2 - 10.1016/j.epsl.2014.06.050
DO - 10.1016/j.epsl.2014.06.050
M3 - Article
AN - SCOPUS:84905252322
SN - 0012-821X
VL - 403
SP - 328
EP - 339
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -