ALBERT

Description: 〈p〉The chemical composition of different rocks as well as volatile-bearing and volatile-free minerals has been used to assess the presence of fluids in the Closepet batholith and to estimate the intensity of the fluid–rock interactions. The data were processed using polytopic vector analysis (PVA). Additional data include measurements of water content in the structure of volatile-free minerals and an examination of growth textures. The composition of mineral domains indicated formation/transformation processes with common fluid–mineral interactions. In general, the results suggested that the processes occurred in a ternary system. Two end-members were likely magmas and the third was enriched in fluids. In contrast, analysis of the apatite domains indicated that they likely formed/transformed in a more complex, four-component system. This system was fluid-rich and included hybrid magma with a large mafic component. PVA implies that the fluids do not appear to come from one source, given their close affinity and partial association with mantle-derived fluids. A dynamic tectonic setting promoting heat influx and redistribution, and interaction of fluids suggests that the formation/transformation processes of minerals and rocks occurred in a hot-spot like environment.〈/p〉 〈p〉〈b〉Supplementary material:〈/b〉 〈a href="https://doi.org/10.6084/m9.figshare.c.4356926"〉Fig. S1 (〈b〉a〈/b〉) Representative raw-, (〈b〉b〈/b〉) fitted- and (〈b〉c〈/b〉) deconvolved-IR spectrum; 〈inter-ref locator="https://doi.org/10.6084/m9.figshare.c.4356926" locator-type="url"〉Table S1〈/inter-ref〉 Whole rock analyses of Closepet granite available at 〈inter-ref locator="https://doi.org/10.6084/m9.figshare.c.4356926" locator-type="url"〉https://doi.org/10.6084/m9.figshare.c.4356926〈/inter-ref〉〈/a〉〈/p〉

Description: 〈p〉This paper descibes the petrology, geochemistry and petrogenesis of Archaean granitoids. Archaean granites define a continuum of compositions, between several end-members: (i) magmas that originated by partial melting of a range of crustal sources, from amphibolites to metasediments ("C-type" granitoids); (ii) magmas that formed by partial melting of an enriched mantle source, the most common agent of enrichment being felsic (TTG) melts. Differences in the degree of metasomatim results in different primitive liquids for these "M-type" granitoids.〈/p〉 〈p〉Mixed sources, differentiation and interactions between different melts resulted in a continuous range of compositions, defined by variable proportions of each end-member.〈/p〉 〈p〉During the Archaean, evolved crustal sources (sediments or felsic crust) and metasomatized mantle sources become increasingly more important, mirroring the progressive maturation of crustal segments, and the stabilization of the global tectonic system.〈/p〉

Description: 〈p〉The origin of large I-type batholiths remains a disputed topic. One model states that I-type granites form by partial melting of older crustal lithologies (amphibolites or intermediate igneous rocks). In another view, granite are trapped rhyolitic liquids occurring at the end of fractionation trends defining a basalt-andesite-dacite-rhyolite series.〈/p〉 〈p〉This paper explores the thermal implications of both scenarios, using a heat balance model that abstracts the heat production and consumption during crustal melting. Heat is consumed by melting and by losses through the surface (conductive or advective, as a result of eruption). It is supplied as a basal conductive heat flux, as internal heat production, or as advective heat carried by an influx of hot basalt into the crust.〈/p〉 〈p〉Using this abstract approach, it is possible to explore the role different parameters have on the balance of granites formed by differentiation of basalts or by crustal melting. Two end-member situations appear equally favorable to generate large volumes of granites: (i) short-lived environments dominated by high basaltic flux, where granites result mostly from basalt differentiation. (ii) long-lived systems with no or minimal basalt flux, with granites resulting chiefly of crustal melting.〈/p〉 〈p〉Supplementary material at 〈a href="https://doi.org/10.6084/m9.figshare.c.4386545"〉https://doi.org/10.6084/m9.figshare.c.4386545〈/a〉〈/p〉

Description: 〈p〉Whole-rock geochemistry represents a powerful tool in deciphering petrogenesis of magmatic suites, including granitoids, that can be used to formulate and test hypotheses qualitatively and often also quantitatively. Typically, it can rule out impossible/improbable scenarios and further constrain the process inferred on geological and petrological grounds. With the current explosion of high-precision data, both newly acquired and retrieved from extensive databases, the whole-rock geochemistry-based petrogenetic modelling of igneous rocks will gain further importance. Especially promising is its combination with thermodynamic modelling into a single, coherent and comprehensive software, using the R and Python languages.〈/p〉 〈p〉Supplementary material at 〈a href="https://doi.org/10.6084/m9.figshare.c.4386692"〉https://doi.org/10.6084/m9.figshare.c.4386692〈/a〉〈/p〉

Description: 〈p〉This paper describes the petrology, geochemistry and petrogenesis of Archean granitoids. Archean granites define a continuum of compositions between several end members: (i) magmas that originated by partial melting of a range of crustal sources, from amphibolites to metasediments (‘C-type’ granitoids); and (ii) magmas that formed by partial melting of an enriched mantle source, the most common agent of enrichment being felsic (TTG) melts. Differences in the degree of metasomatism results in different primitive liquids for these ‘M-type’ granitoids.〈/p〉 〈p〉Mixed sources, differentiation and interactions between different melts resulted in a continuous range of compositions, defined by variable proportions of each end member.〈/p〉 〈p〉During the Archean, evolved crustal sources (sediments or felsic crust) and metasomatized mantle sources become increasingly more important, mirroring the progressive maturation of crustal segments and the stabilization of the global tectonic system.〈/p〉

Description: 〈p〉Modern quantitative phase equilibria modelling allows the calculation of the stable phase assemblage of a rock system given its pressure, temperature and bulk composition. A new software tool (Rcrust) has been developed that allows the modelling of points in pressure–temperature–bulk composition space in which bulk compositional changes can be passed from point to point as the system evolves. This new methodology enables quantitative process-oriented investigation of the evolution of rocks. Procedures are outlined here for using this tool to model: 1) the control of the water content of a subsolidus system based on available pore space; 2) triggering of melt loss events when a critical melt volume threshold is exceeded, while allowing a portion of melt retention; 3) entrainment of crystals during segregation and ascent of granitic magmas from its source; 4) modification of the composition of granite magmas due to fractional crystallization and 5) progressive availability (through dissolution) of slow diffusing species and their control on the effective bulk composition of a system. These cases collectively illustrate thermodynamically constrained methods for modelling systems that involve mass transfer.〈/p〉 〈p〉Supplementary material at 〈a href="https://doi.org/10.6084/m9.figshare.c.4388291"〉https://doi.org/10.6084/m9.figshare.c.4388291〈/a〉〈/p〉

Description: Granitoids form the bulk of the Archean continental crust and preserve key information on early Earth evolution. India hosts five main Archean cratonic blocks (Aravalli, Bundelkhand, Singhbhum, Bastar and Dharwar). This book summarizes the available information on Archean granitoids of Indian cratons. The chapters cover a broad spectrum of themes related to granitoid typology, emplacement mechanism, petrogenesis, phase-equilibria modelling, temporal distribution, tectonic setting, and their roles in fluid evolution, metal delivery and mineralizations. The book presents a broader picture incorporating regional- to cratons-scale comparisons, implications for Archean geodynamic processes, and temporal changes thereof. This synthesis work, integrating modern concepts on granite petrology and crustal evolution, offers an irreplaceable body of reference information for any geologist interested in Archean Indian granitoids.