Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: Pre-Nagssugtoqidian crustal evolution in West Greenland: geology, geochemistry and deformation of supracrustal and granitic rocks north-east of Kangaatsiaq

The area north-east of Kangaatsiaq features polyphase grey orthogneisses, supracrustal rocks and Kangaatsiaq granite exposed within a WSW–ENE-trending synform. The supracrustal rocks are comprised of garnet-bearing metapelites, layered amphibolites and layered, likewise grey biotite paragneisses. Their association and geochemical compositions are consistent with a metamorphosed volcano-sedimentary basin (containing both tholeiitic and calc-alkali lavas) and is similar to other Archaean greenstone belts. The Kangaatsiaq granite forms a 15 × 3 km flat, subconcordant body of deformed,pink, porphyritic granite occupying the core of the supracrustal synform, and is demonstrably intrusive into the amphibolites. The granite displays a pronounced linear fabric (L or L > S). Thepost-granite deformation developed under lower amphibolite facies conditions (400 ± 50°C), and is characterised by a regular, NE–SW-trending subhorizontal lineation and an associated irregular foliation, whose poles define a great circle; together they are indicative of highly constrictional strain. The existence of a pre-granite event is attested by early isoclinal folds and a foliation within the amphibolites that is not present in the granite, and by the fact that the granite cuts earlier structures in the supracrustal rocks. This early event, preserved only in quartz-free lithologies, resulted in high-temperature fabrics being developed under upper amphibolite to granulite facies conditions

From the roots to the roof of a granite: the closepet granite of South India

The Dharwar craton exposes a natural cross-section of the continental crust. This crust has been intruded during the Late Archaean by a large volume of granites. One of these is the Closepet Granite, which outcrops at different structural levels from deep (corresponding to palaeopressures of 7-8 Kbar) to shallow (2-3 Kbar) crust. This crosssection allows the study of all components of this granite: the root zone, displaying strong crust-mantle interaction, resulting in highly heterogeneous, enclave-rich monzonilic to granitic magmas; the transfer zone, with inferred upward movement of these magmas; and a rheological interface in the shallow crust at which the ascent of the magmas was arrested. At this level, only the less viscous (differenciated and enclave-free) magmas were able to rise through a network of dykes and fill small pockets, forming typical, elliptic granitic intrusions (the "intrusion zone")

Diversity in Earth's early felsic crust: Paleoarchean peraluminous granites of the Barberton Greenstone Belt

Earth's oldest preserved granitoid crust dates back to the Paleoarchean and consists predominantly of sodic tonalite-trondhjemite-granodiorite (TTG) granitoids that arose through the partial melting of hydrated metabasalts. In contrast, granites (sensu stricto) typically appear relatively late in the plutonic record of the old cratons. However, the existence of Hadean zircons with mineral inclusion suites that are consistent with crystallization from peraluminous granitic magmas indicates that granitic rocks formed part of the earliest felsic crust; although we have direct evidence, this earliest felsic crust is not preserved. Here we present evidence of an unusual variety of markedly low-CaO, K2O-rich, rutile-bearing, peraluminous granite and rhyolite that was produced concurrently with TTG magmas during three magmatic cycles in the Barberton Greenstone Belt (BGB), southern Africa. This material is not preserved as in situ rock units, but occurs as clasts within a younger conglomerate. Within these rocks, plagioclase feldspar is a rare inclusion in zircon, relative to alkali feldspar, and has low anorthite contents (An < 15%), attesting to the primary nature of the low-Ca signature of the magmas. This, along with Eu/Eu* ~1, high K2O and Sr content, as well as the peraluminous character of the magmas, is a consequence of phengite melting in a metagraywacke source at pressures in excess of those of plagioclase stability. This process contributed to each episode of continental crustal growth through the Paleoarchean to Mesoarchean in the BGB, despite leaving no plutonic record at the typical mid-crustal level of exposure that the TTG plutons around the belt represent