Tectonism rather than “snowball Earth” glaciation is responsible for the Great Unconformity
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.
Article Details
Journal Info
Proceedings of the National Academy of Sciences
National Academy of Sciences
Authors (12)
Rong-Ruo Zhan
State Key Laboratory of Continental Evolution and Early Life, and Department of Geology, Northwest University
Liang Duan
State Key Laboratory of Continental Evolution and Early Life, and Department of Geology, Northwest University
Massimiliano Zattin
Department of Geosciences, University of Padova
Nicholas Christie-Blick
Department of Earth and Environmental Sciences, and Lamont-Doherty Earth Observatory of Columbia University
Bo Wan
State Key Laboratory of Lithospheric and Environmental Coevolution, Institute of Geology and Geophysics, Chinese Academy of Sciences
Rong-Hao Wei
State Key Laboratory of Continental Evolution and Early Life, and Department of Geology, Northwest University
Zhao Yang
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry
Jianqiang Wang
College of Polymer Science and Engineering, National Key Laboratory of Advanced Polymer Materials
Longlong Gou
State Key Laboratory of Continental Evolution and Early Life, and Department of Geology, Northwest University
Valerio Olivetti
Department of Earth and Environmental Sciences, and Lamont-Doherty Earth Observatory of Columbia University
Kai-Yun Chen
State Key Laboratory of Continental Evolution and Early Life, and Department of Geology, Northwest University
Xingliang Zhang
State Key Laboratory of Continental Evolution and Early Life, and Department of Geology, Northwest University