EVOLUTION OF THE IGNEOUS MINERALS: A GEOINFORMATICS APPROACH

We catalog 1665 mineral species associated with a wide range of igneous rock types through > 4.5 billion years of Earth history. Mineral modes of 1850 igneous rocks reveal that 115 minerals are frequent major and/or accessory phases, including 69 silicates, 19 oxides, 13 carbonates, and 6 sulfides. Patterns of coexistence among these minerals, revealed by network, Louvain community detection, and agglomerative hierarchical clustering analyses, point to four major communities of igneous primary phases, corresponding to different compositional regimes: (1) quartz- and/or alkali feldspar-dominant rocks, including rare-element granite pegmatites; (2) mafic/ultramafic rock series with major calcic plagioclase and/or mafic minerals; (3) rocks with major feldspathoids and/or analcime, including agpaitic rocks and their rare-element pegmatites; and (4) carbonatites and related carbonate-bearing rocks.

Igneous rocks display characteristics of an evolving chemical system, with significant increases in mineral diversity and chemical complexity over Earth’s first 2 billion years. The first igneous rocks (>4.56 Ga) were ultramafic in composition with 122 different minerals, followed closely by mafic rocks that were generated in large measure by decompression melting of those ultramafic lithologies (4.6 Ga). Quartz-normative granitic rocks and their extrusive equivalents (> 4.4 Ga), formed primarily by partial melting of wet basalt, added to the mineral inventory, which reached 246 different mineral kinds. Subsequently, four groups of igneous rocks with diagnostic concentrations of rare element minerals – layered igneous intrusions, complex granite pegmatites, alkaline igneous complexes, and carbonatites – all appeared < 3 billion years ago. These more recent igneous rocks hold > 700 different minerals, 500 of which are unique to these lithologies. Network representations and heatmaps of primary igneous minerals illustrate Bowen’s reaction series of igneous mineral evolution, as well as his concepts of mineral associations and antipathies. Furthermore, phase relationships and reaction series associated with the minerals of a dozen major elements, as well as numerous minor elements, are embedded in these multi-dimensional visualizations.