Advances in Earth Science ›› 2020, Vol. 35 ›› Issue (10): 991-1005. doi: 10.11867/j.issn.1001-8166.2020.089

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Garnet Geochronology of Metamorphic Rocks

Hao Cheng( ),Naixiao Xu   

  1. State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092,China
  • Received:2020-08-02 Revised:2020-09-30 Online:2020-10-10 Published:2020-11-30
  • About author:Cheng Hao (1975-), male, Guiding City, Guizhou Province, Professor. Research areas include geochronology and thermochronology on metamorphic rocks. E-mail:
  • Supported by:
    the National Natural Science Foundation of China “Metamorphic Petrochronology”(41925013)

Hao Cheng,Naixiao Xu. Garnet Geochronology of Metamorphic Rocks[J]. Advances in Earth Science, 2020, 35(10): 991-1005.

The determination of the Pressure-Temperature-time (P-T-t) path of metamorphic rocks has an essential role in understanding the tectonic evolution of metamorphic rocks. Garnet has played a crucially important part in our understanding of metamorphic and tectonic processes and conditions. The potential of garnet geochronology in metamorphic rock studies lies in the use of the compositional zoning in garnet to elucidate quantitative P-T paths and the coupled application of multiple geochronometers to constrain the timescales of garnet growth. Garnet has long been the mineral of choice for metamorphic chronology because it hosts a remarkable number of long-lived radioactive isotopes and their stable decay products. These include: 238U, 235U and 232Th, which decay via intermediate steps to 206Pb, 207Pb and 208Pb, respectively; 87Rb, which decays to 87Sr; 176Lu, which decays to 176Hf; and 147Sm, which decays to 143Nd. This makes garnet one of the most versatile mineral phases available to geochronologists. As a result of advances in the techniques for sample preparation and measuring Nd-Hf isotopes by Thermal Ionization Mass Spectrometry (TIMS) and Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS), garnet Lu-Hf and Sm-Nd geochronology has been increasingly used to constrain the rates and timing of tectonometamorphic processes in orogenic studies over the last two decades. Metamorphic geochronologists have developed new techniques, such as microsampling, to link garnet ages with textural and petrological fingerprints of particular metamorphic processes, leading to major advances in petrogenesis and tectonics. When combined with petrographic and chemical observations, Lu-Hf and Sm-Nd ages in garnets are able to give unprecedented resolution of the timing and processes of metamorphism, although there are many potential pitfalls in the acquisition and interpretation of these data. This paper provides a brief review of the basic science and development of the garnet Lu-Hf and Sm-Nd systems, highlights the potential of garnet Lu-Hf and Sm-Nd geochronology, and reviews several crucial issues related to the complexities of interpretation of the radiometric ages. Examples, limitations, advantages and potential research directions are presented.

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