2026-03-11 コロンビア大学
＜関連情報＞
- https://news.climate.columbia.edu/2026/03/11/earths-missing-billion-years-study-links-the-great-unconformity-to-early-tectonics/
- https://www.pnas.org/doi/10.1073/pnas.2523891123
大不整合の原因は、「スノーボールアース」と呼ばれる氷河作用ではなく、地殻変動である Tectonism rather than “snowball Earth” glaciation is responsible for the Great Unconformity
Rong-Ruo Zhan , Liang Duan , Massimiliano Zattin, +8 , and Xingliang Zhang
Proceedins of the National Academy of Sciences Published:February 23, 2026
DOI:https://doi.org/10.1073/pnas.2523891123
Significance
The Great Unconformity (GUn) is arguably the most iconic but enigmatic gap in Earth’s stratigraphic record. Among puzzling features requiring explanation is evidence for many kilometers of exhumation and a hiatus of hundreds of millions to billions of years in continental interiors. Existing models call for either a glacial or a plate tectonic origin in the Neoproterozoic. We provide evidence that erosion below the unconformity was protracted in North China, and that the most pronounced erosion at a global scale occurred during the late Paleoproterozoic and was driven by tectonics associated with supercontinent cycle of Columbia.
Abstract
The Great Unconformity (GUn)—a widely recognized discontinuity and associated gap in the rock record between Precambrian and Cambrian rocks—represents a globally important interval of continental exposure and erosion that is notable also for the first appearance of all major animal phyla on Earth. However, its origin remains the subject of vigorous debate. Here, we present field relationships, and zircon and monazite U–Pb, biotite and muscovite Rb–Sr, and zircon (U–Th)/He thermochronology data for Precambrian crystalline basement rocks from North China to constrain the exhumation history below the unconformity. Dates from multichronometers and thermal history inversions show that the most substantial cooling of continental basement took place from ~2,100 to 1,600 Ma. Comparison with thermal history data from Laurentia, Baltica, and Amazonia suggests that protracted plate tectonics broadly modulated by supercontinent cycles, and not “snowball Earth” glaciation, is responsible for crustal exhumation below the unconformity. The most pronounced erosion evident in both the thermochronologic record and geochemical indicators of continental weathering is shown to correspond with development of Earth’s first true supercontinent (Columbia), rather than with either the Cambrian explosion or the emergence of modern plate tectonics.
