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Controversies and knowledge gaps in Geology (Part 1): Formation of ‘Archean granitoids’ (TTGs)

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What are TTGs? A suite of granitoids comprising tonalites , trondhjemite and granodiorites collectively referred to as tonalite-trondhjemite-granodiorite (TTG) granitoids are the main constituents of Archean terranes 1 . TTGs were mostly emplaced in the Archean and are not generated in modern-day subduction zones 1 . Thus, these rocks have invariably undergone multiple episodes of metamorphism and usually occur as strongly deformed gneisses (Fig. 1). Figure 1. TTG specimen (Source: Wikipidea) Geochemically, TTGs are sodic (K 2 O/Na 2 O<0.5), contain high contents of light rare earth elements (LREE) and low contents of high rare earth elements (HREE) resulting in strongly fractionated REE patterns (average La/Yb N of 32.4), exhibit negative Nb-Ti anomalies, and lack pronounced Eu and Sr anomalies 2 . The fractionated REE patterns and the Nb-Ti anomalies are interpreted to be indicative of the presence of garnet, amphibole and/or rutile in the melt residue 3 , whereas the Sr and
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Adding crushed rocks to soils absorbs atmospheric carbon and curb global warming

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Summary Enhanced Rock Weathering involves the application of pulverized rocks to soils. It is one of the proposed ways of reducing effects of global warming. The Paris Agreement on climate change adopted the limiting of the increase in global warming to well below 2 o C. Quick and efficient removal of carbon dioxide (CO 2 ) is thus an urgent requirement to achieve the set targets. The natural chemical weathering of rocks (a process involving the reaction of atmospheric CO 2 with water to form a weak carbonic acid (H 2 CO 3 ), and the attack of silicate and carbonate minerals by the carbonic acid) normally absorbs only 0.3% of the atmospheric CO 2 . Enhanced rock weathering (ERW) - the modification by acceleration of the removal of atmospheric CO 2 by the application of pulverized magnesium-rich silicate rocks (mostly basalts) and calcium-rich rocks (carbonates) - is one of the cost-effective methods of extracting CO 2 from the atmosphere.  A recent study has shown that ERW has the
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New study proposes ‘Goldilocks’ temperature zones as factories for generation of mineral deposits

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Current understanding of the formation of porphyry deposits Porphyry deposits are a major source of copper (Cu), gold (Au), and molybdenum (Mo) (Fig. 1). These deposits contribute 75%, 50%, and 20% of the Cu-, Mo-, Au produced in the world, respectively 1 . Figure 1. Molybdenite (dark grey molybdenum-sulphide mineral) hosted in quartz (grey) veins in a porphyry deposit (Source 2 ) Typically, porphyry deposits form in magmatic arcs (oceanic and continental) above subduction zones in a series of processes beginning with (i) the expulsion of metal-enriched fluids from the subducting slab into the mantle wedge resulting in partial melting of the mantle wedge, followed by, (ii) the migration and stalling of such magmas in the magma chambers in the mid to lower crust, and subsequently, (iii) the migration of metal-rich fluids produced during the crystallisation of magmas in magma chambers into the upper crust where they form pipe- and dyke-like porphyry deposits  3 , 4 (Fig. 2). Figur
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