Mineral Evolution: Episodic Metallogenesis, the Supercontinent Cycle, and the Coevolving Geosphere and Biosphere
Robert M. Hazen, Xiao-Ming Liu, Robert T. Downs, Joshua Golden, Alexander J. Pires, Edward S. Grew, Grethe Hystad, Charlene Estrada, Dimitri A. Sverjensky, 2014. "Mineral Evolution: Episodic Metallogenesis, the Supercontinent Cycle, and the Coevolving Geosphere and Biosphere", Building Exploration Capability for the 21st Century, Karen D. Kelley, Howard C. Golden
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Analyses of temporal and geographic distributions of the minerals of beryllium, boron, copper, mercury, and molybdenum reveal episodic deposition and diversification. We observe statistically significant increases in the number of reported mineral localities and/or the appearance of new mineral species at ~2800 to 2500, ~1900 to 1700, ~1200 to 1000, ~600 to 500, and ~430 to 250 Ma. These intervals roughly correlate with presumed episodes of supercontinent assembly and associated collisional orogenies of Kenorland (which included Superia), Nuna (a part of Columbia), Rodinia, Pannotia (which included Gondwana), and Pangea, respectively. In constrast, fewer deposits or new mineral species containing these elements have been reported from the intervals at ~2500 to 1900, ~1700 to 1200, 1000 to 600, and 500 to 430 Ma. Metallogenesis is thus relatively sparse during periods of presumed supercontinent stability, breakup, and maximum dispersion.
Variations in the details of these trends, such as comparatively limited Hg metallogenesis during the assumed period of Rodinia assembly; Proterozoic Be and B mineralization associated with extensional environments; Proterozoic Cu, Zn, and U deposits at ~1600 and 830 Ma; and Cenozoic peaks in B, Cu, and Hg mineral diversity, reveal complexities in the relationship between episodes of mineral deposition and diversification on the one hand, and supercontinent assembly and preservational biases on the other. Temporal patterns of metallogenesis also reflect changing near-surface environments, including differing degrees of production and preservation of continental crust; the shallowing geotherm; changing ocean chemistry; and biological influences, especially those associated with atmospheric oxygenation, biomineralization, and the rise of the terrestrial biosphere. A significant unresolved question is the extent to which these peaks in metallogenesis reflect true episodicity, as opposed to preservational bias.
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Earth’s near-surface mineralogy has diversified over more than 4.5 b.y. from no more than a dozen preplanetary refractory mineral species (what have been referred to as “ur-minerals” by Hazen et al., 2008) to ~5,000 species (based on the list of minerals approved by the International Mineralogical Association; http://rruff.info/ima). This dramatic diversification is a consequence of three principal physical, chemical, and biological processes: (1) element selection and concentration (primarily through planetary differentiation and fluidrock interactions); (2) an expanded range of mineral-forming environments (including temperature, pressure, redox, and activities of volatile species); and (3) the influence of the biosphere. Earth’s history can be divided into three eras and ten stages of “mineral evolution” (Table 1; Hazen et al., 2008), each of which has seen significant changes in the planet’s near-surface mineralogy, including increases in the number of mineral species; shifts in the distribution of those species; systematic changes in major, minor, and trace element and isotopic compositions of minerals; and the appearance of new mineral grain sizes, textures, and/or morphologies. Initial treatments of mineral evolution, first in Russia (e.g., Zhabin, 1979; Yushkin, 1982) and subsequently in greater detail by our group (Hazen et al., 2008, 2009, 2011, 2013a, b; Hazen and Ferry, 2010; Hazen, 2013), focused on key events in Earth history. The 10 stages we suggested are Earth’s accretion and differentiation (stages 1, 2, and 3), petrologic innovations (e.g., the stage 4 initiation of granite magmatism), modes of tectonism (stage 5 and the commencement of plate tectonics), biological transitions (origins of life, oxygenic photosynthesis, and the terrestrial biosphere in stages 6, 7, and 10, respectively), and associated environmental changes in oceans and atmosphere (stage 8 “intermediate ocean” and stage 9 “snowball/hothouse Earth” episodes). These 10 stages of mineral evolution provide a useful conceptual framework for considering Earth’s changing mineralogy through time, and episodes of metallization are often associated with specific stages of mineral evolution (Table 1). For example, the formation of complex pegmatites with Be, Li, Cs, and Sn mineralization could not have occurred prior to stage 4 granitization. Similarly, the appearance of large-scale volcanogenic sulfide deposits may postdate the initiation of modern-style subduction (stage 5). The origins and evolution of life also played central roles; for example, redox-mediated ore deposits of elements such as U, Mo, and Cu occurred only after the Great Oxidation Event (stage 7), and major Hg deposition is associated with the rise of the terrestrial biosphere (stage 10; Hazen et al., 2012).