Comparisons Between Tethyan Anorthosite‐Bearing Ophiolites and Archean Anorthosite‐Bearing Layered Intrusions: Implications for Archean Geodynamic Processes

Abstract

Elucidating the petrogenesis and geodynamic setting(s) of anorthosites in Archean layered intrusions and Tethyan ophiolites has significant implications for crustal evolution and growth throughout Earth history. Archean anorthosite‐bearing layered intrusions occur on every continent. Tethyan ophiolites occur in Europe, Africa, and Asia. In this contribution, the field, petrographic, petrological, and geochemical characteristics of 100 Tethyan anorthosite‐bearing ophiolites and 155 Archean anorthosite‐bearing layered intrusions are compared. Tethyan anorthosite‐bearing ophiolites range from Devonian to Paleocene in age are variably composite, contain anorthosites with highly calcic (An44–100) plagioclase and magmatic amphibole. These ophiolites formed predominantly at convergent plate margins, with some forming in mid‐ocean ridge, continental rift, and mantle plume settings. The predominantly convergent plate margin tectonic setting of Tethyan anorthosite‐bearing ophiolites is indicated by negative Nb and Ti anomalies and magmatic amphibole. Archean anorthosite‐bearing layered intrusions are Eoarchean to Neoarchean in age, have megacrystic anorthosites with highly calcic (An20–100) plagioclase and magmatic amphibole, and are interlayered with gabbros and leucogabbros and intrude pillow basalts. These Archean layered intrusions are interpreted to have predominantly formed at convergent plate margins, with the remainder forming in mantle plume, continental rift, oceanic plateau, postorogenic, anorogenic, mid‐ocean ridge, and passive continental margin settings. These layered intrusions predominantly crystallized from hydrous Ca‐ and Al‐rich tholeiitic magmas. The field, petrographic, and geochemical similarities between Archean and Tethyan anorthosites indicate that they were produced by similar geodynamic processes mainly in suprasubduction zone settings. We suggest that Archean anorthosite‐bearing layered intrusions and spatially associated greenstone belts represent dismembered subduction‐related Archean ophiolites.

Metamorphic evolution of the Sittampundi Layered Complex, India, during the Archaean–Proterozoic boundary: insight from pseudosection modelling and zircon U–Pb SHRIMP geochronology

“…Analogous to SLC, suprasubduction zone arc-related tectonic environment for the development of Archaean layered complex and greenstone belt is commonly reported from Greenland (Ivisaartoq Greenstone Belt and Fiskenaesset Anorthosite Complex) and Canada (Doré Lake Complex) (Polat et al 2008(Polat et al , 2009(Polat et al , 2011b(Polat et al , 2018. A majority of the Archaean anorthosite complexes were formed in an arc setting, similar to the ophiolite-hosted Tethyan anorthosites, which suggest that throughout Earth's history most of the anorthosite complexes formed as a consequence of collisional tectonics (Sotiriou & Polat, 2020).…”

Why the pounamu? Low- to medium grade metabasites and metaultrabasites of New Zealand from a geoheritage perspective

“…These rocks are almost without exception metamorphic rocks, dominantly metabasites and metaultrabasites (eclogite, Na-pyroxenite, omphacite/jadeite schists, metabasalt, metadolerite, nephrite, serpentinite) hence their source regions had to be associated with some sort of (meta)ophiolite belts [5] or ancient suture zones [7] that are common mostly in the Eastern Mediterranean region [8], Apennine Peninsula in Italy [5,9,10], in the older cratonic regions such as Fennoscandia [11][12][13][14] or associated with a low viscosity Archean lava flows of komatiites [15]. In the formation of greenstone, the post-emplacement seafloor processes as well as the long-lasting hydrothermal effect in the mafic to ultramafic, mostly oceanic crustal material together with subsequent regional metamorphism generate a very diverse rock assemblage [16].…”

Growth of continental crust in intra-oceanic and continental-margin arc systems: Analogs for Archean systems

“…Another component of oceanic arc and supra-subduction ophiolite development and evolution through time is the formation of layered calcic anorthosite-gabbro-ultramafic complexes, which form in the magma chamber of modern oceanic arcs as evidenced from exposed sections (e.g., Davidson and Arculus, 2005;Jagoutz and Kelemen, 2015;Sotiriou and Polat, 2020), cognate xenoliths (Arculus and Wills, 1980;Conrad and Kay, 1984) and seismic sections (Kiddle et al, 2010;Sotiriou and Polat, 2020). The lower magma chamber or "root' of the Cretaceous (greenschistlow amphibolite facies) chromite-layered Kohistan islandarc in Pakistan (Khan et al, 1989;Jagoutz et al, 2007;Dhuime et al, 2009;Petterson, 2010;Bilqees et al, 2016) was separated and partially subducted farther down the Himalayan Yarlung-Tsangpo subduction zone, metamorphosed, and exhumed as the Tora Tigga (amphibolite facies- Jan and Tahirkheli, 1990) and Jijal (granulite and eclogite facies) complexes (Ringuette et al, 1999).…”

“…In this section (Figure 6a), between 30-35 km depth the rocks are garnet-rich plagioclase-free residues (Clarke et al, 2013), and below 50 km the rocks are pyroxene-amphibole ± garnet eclogites, garnet clinopyroxenites, and amphibole clinopyroxenites (Figures 5, 6) that are complementary to the melts in the higher crustal levels, thus, colloquially dubbed arclogites (Ducea and Saleeby, 1996;Lee and Anderson, 2015;Ducea et al, 2021aDucea et al, , 2021b. The Carboniferous Black Giant Anorthosite and surrounding granitoid gneisses of Fiordland (Figure 6) share many geological and geochemical features of Archean anorthositebearing layered intrusions and associated gneisses (Gibson and Ireland, 1999), suggesting that both Archean and Pa-leozoic anorthosite-gneiss associations originated in magmatic arcs (Sotiriou and Polat, 2020).…”