Geochemical Atlas of the Yilgarn Granitoids/Western Australia. Sp. Papers 22

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The objectives of this study is to compile  previous  mineralogical, petrological, geochemical and geochronological data on Yilgarn granitoids in order to produce the tectonothermal model for the mid-to late-Archaean evolution of the craton, and through this, attempt to define those regions of the craton which are most likely to lie above a lithospheric keel and, hence, host diamondiferous alkaline intrusions if other conditions (e.g. sites of crustal extension) are met.  In the Yilgarn Craton, the granitoids are the most widely distributed rock type available for study and span the time period 3.8 to 2.6 Ga (most between 2.9 and 2.6 Ga).First three time slices (3.0-2.9, 2.75-2.8 and 2.72-2.68 Ga) represent the main growth of the Yilgarn Craton from the west to the east.  They comprise the volcanic and plutonic rocks originated above the subduction zones at the paleocontinental margins.  Incorporated calc-alkaline synvolcanic tonalite-granodiorite suites are always slightly younger, usually intruding into own volcanic ejecta.  In general these events initiated the melting within the continental crust and intrusion of the large granite batholiths in the foreland of the subduction suture zones. 2.7Ga volcano-magmatic event in the Eastern Goldfields Province has been simultaneously followed by a continent-continent collision in the western part of the craton.  In the foreland of the collision zone (dipping to the east) the extensive batholithic intrusions occur as a reaction to the crustal thickening.  These large batholithic intrusions at 2.65-2.62 are slightly younger than the post-subduction equivalents in the east (2.66Ga).Yilgarn granitoids are geochemically classified into high-K, calc-alkaline series and medium-K calc-alkaline series.  A minority of rocks belong to the low-K tholeiite and shoshonite series.  The regional distribution of the series corresponds to the major tectonic subdivision of the Yilgarn Craton.  High-K calc-alkaline series are dominant in the western part and medium-K and low-K, calc-alkaline series dominate in the eastern part of the Craton.  It reflects the difference in crustal composition between western (older) and eastern (younger) parts of the Craton.  The shoshonitic series occurs along the main structural boundaries and along the craton margins.Six main regional anomalies of high MgO, Cu, Cr, Ni, Na2O and low K2O, FeO, P2O5, MnO, Rb and Al2O3 in the Murchison, Southern Cross and Eastern Gold Provinces indicate the presence the granitoids with mantle signature.  They may represent fingerprints of the late Archaean hot spots in the Yilgarn Craton. Much of the thick lithosphere is expected in the western Yilgarn in contrast of the eastern Goldfields Province where presence of the thinner, metasomatised lithosphere is indicated.  The western lithospheric segment consists of three root structures, dislocated by major sutures.  The main lithospheric keel is proposed in the centre of the Yilgarn Craton where the negligible tectonothermal activity is indicated by the lowest heat flow (none or low thermal metamorphism since 2.8Ga) and crustal magmatic granite activity (lack of gravity lows).The gravity lows are indicative for batholithic roots and may represent main feeders of the granitic magmas.  Their size and distribution may indicate history within and above the main suture zones of the Yilgarn Craton.  The gravity lows show concentric distribution around the crustal core of the Yilgarn Craton.  Such a gravity arrangement may indicate the tectonothermal shadow above the thick and deep lithospheric keel.  Potential for diamond occurrence is therefore higher in the Western part of the Yilgarn Craton, specially in its central portion....................................................Cílem této studie je shromáždit předchozí mineralogická, petrologická, geochemická a geochronologická data o granitoidech Yilgarnského kratonu v Západní Austrálii za účelem vytvoření tektonotermálního modelu jeho evoluce ve středním až pozdním archaiku v časovém rozpětí 3,8 až 2,6 Ga. Prostřednictvím tohoto modelu se následně autoři pokoušejí definovat ty oblasti kratonu, které jsou s největší pravděpodobností hostiteli diamantonosných ultrabazických extruzí. Pozice hlavního litosférického kýlu je navrhována do středu Yilgarnského kratonu, kde je tektonotermální aktivita indikována nejnižším tepelným tokem a korovou magmatickou aktivitou granitoidů. Na základě analýzy velikosti a distribuce gravitačních minim autoři docházejí k závěru, že potenciál Yilgarnského kratonu pro výskyt diamantů je zejména v jeho centrální části.Brož., A4, 1. vyd., 102 s., r. 2021