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Notes: Abstract Fluid infiltration into fault zones and their deeper-level counterparts, brittle-ductile shear zones, is examined in diverse tectonic environments. In the 2.7 Ga Abitibi greenstone belt, major tectonic discontinuities, with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism. During reverse motion on the structures, accommodating shortening of the belt, these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids. Such fluids were characterised by δ18O=+6±2, δD=−50±20, δ13C=−4±4, and temperatures of 270 to 450°C, probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism. Hydrothermal fluids were more radiogenic (87Sr/86Sr=0.7010 to 0.7040) and possessed higher μ than did contemporaneous mantle, komatiites or tholeiites, and thus carried a contribution from older sialic basement. A provinciality of87Sr/86Sr and δ13C is evident, signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres. Mineralised faults possess enrichments of large ion lithophile (LIL), LIL elements, including K, Rb, Ba, Cs, B, and CO2, and rare elements, such as Au, Ag, As, Sb, Se, Te, Bi, and W. Fluids were characterised by XCO 2≈0.1, neutral to slightly acidic pH, low salinity ≤3 wt-%, K/Na=0.1, they carried minor CH4, CO, and N2, and they underwent transient effervescence of CO2 during decompression. Clastic sediments occupy graben developed at fault flexures. The40Ar/39Ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years. At the Grenville front, translation was accommodated along two mylonite zones and an intervening boundary fault. The high-temperature (580°C) and low-temperature (430 to 490°C) mylonite zones, formed in the presence of deep-level crust-equilibrated fluids of metamorphic origin. Late brittle faults contain quartz veins precipitated from fluids with extemely negative δ18O (−14 per mil) at 200 to 300°C. The water may have been derived from downward penetration into fault zones of precipitation of low18O on a mountain range induced by continental collision, with uplift accommodated at deep levels by the mylonite zones coupled with rebound on the boundary faults. Archean gneisses overlie Proterozoic sediments along thrust surfaces at Lagoa Real, Brazil; the gneisses are transected by brittle-ductile shear zones locally occupied by uranium deposits. Following deformation at 500 to 540°C, in the presence of metamorphic fluids and under conditions of low water-to-rock ratio, shear zones underwent local intense oxidation and desilication. All minerals undergo a shift of −10 per mil, indicating discharge of meteoric-water-recharged formation brines in the underlying Proterozoic sediments up through the Archean gneisses, during overthrusting; ≈1000 km3 of solutions passed through these structures. The shear zones and Proterozoic sediments are less radiogenic (87Sr/86Sr=0.720) than contemporaneous Archean gneisses (0.900), corroborating the transport of fluids and solutes through the structure from a large external reservoir. Major crustal detachment faults of Tertiary age in the Picacho Cordilleran metamorphic core complex of Arizona show an upward transition from undeformed granitic basement through mylonitic to brecciated and hydrothermally altered counterparts. The highest tectonic levels are allochthonous, oxidatively altered Miocene volcanics. This transition is accompanied by an increase of 12 per mil in δ18O, from +7 to +19, and a 400°C decrease in temperature. Lower tectonic levels acted as aquifers for the expulsion of large volumes of higher-temperature reduced metamorphic fluids and/or evolved formation brines. The Miocene allochthon was influenced by a lower-temperature reservoir inducing oxidative potassic alteration; mixing occurred between cool downward-penetrating thermal waters and the hot, deeper aqueous reservoir. In general, flow regimes in these fault and shear zones follow a sequence, from conditions of high temperature and pressure with locally derived fluids at low water-to-rock ratios, during initiation of the structures, to high fluxes of reduced formation or metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs. Later in the tectonic evolution and at shallower crustal levels there was incursion of oxidising fluids from near-surface reservoirs into the faults. In general, magmatism, tectonics, and fluid motion are intimately related.

Notes: The concentrations of 27 trace elements in the basalt BIR-1, as well as in other mafic rock reference materials, have been determined by ICP-MS, using pure elemental solutions for external calibration and standard additions. Concentrations of rare earth elements in BIR-1 for the new ICP-MS data, agree with compiled values, and previous ID-SSMS results, whereas ICP-MS data on HFSE's are systematically higher by about 40% to 70% than ID-SSMS, but are consistent with data generated at other ICP-MS laboratories.

Notes: [Auszug] In proximity to domains of U-mineralization hydrothermal metasomatism has overprinted the regional amphibolite grade metamorphism of the gneisses on a massive scale, sporadically 40km across and 100km along strike. Albitic plagioclase is the dominant mineral in 'ore grade' zones; uraninite is ...

Notes: Summary Archean shoshonitic lamprophyres are cotemporal and cospatial with gold mineralization in the Superior Province of Canada, both being emplaced along translithospheric structures that demark subprovince boundaries. By analogy with geochemically similar Phanerozoic counterparts, the dikes are a product of specific plate interactions rather than a deep asthenosphere plume-initiated event, and their onset in the late-Archean at ∼ 2.7 Ga signifies that Phanerozoic style plate-tectonics was operating at this time. Fresh shonshonitic dikes are characterized by normal background gold contents of 3.9 ± 8.1 ppb (lσ), close to the value of 3.0 ppb for the bulk continental crust, and average abundances of As, Sb, Bi, W, TI, B, Cu, Pb, Zn, and Mo are also close to their values in bulk continental crust. Thus, fresh lamprophyres are not intrinsically enriched either in Au or elements affiliated with gold in mesothermal deposits, and accordingly do not constitute a special source rock. Platinum group element contents (Ir = 0.4 ± 0.58 ppb; Pt = 5.9 ± 26.5, Pd = 5.5 ± 1.8), in conjunction with Cu, Au, and Ni abundances, define approximately flat patterns on primitive mantle-normalized diagrams, consistent with derivation of the alkaline magmas from a depleted mantle source variably enriched by incompatible elements. Comparable abundances and ratios of Pd/Au, Os/Ir, and Ru/Ir in Archean lamprophyres, Archean komatiites, and Gorgona komatiites signify that the Archean and Phanerozoic upper mantle had similar noble metal contents, such that the prolific greenstone belt Au-Ag vein deposits cannot be explained by secular variations in upper mantle Au abundance alone. The lack of covariation between Au and light rare earth elements in lamprophyres rules out mantle metasomatism as a process generating intrinsically Au-rich magmas. Emplacement of the lamprophyres was diachronous from north (2710 Ma) to south (2670 Ma) in the Superior Province, as was the gold mineralization. Both were related to late transpressional tectonics during successive accretions of individual subprovinces. Alkaline magmatism and gold mineralization are temporally and spatially related because they share a common geodynamic setting, but they are otherwise the products of distinct processes. Much of Archean time was devoid of shoshonites and mesothermal gold deposits. The first widespread inception of this duality at 2.71–2.65 Ga in the Superior and Slave Provinces, Canada, and in India and Australia, may reflect one of the first supercontinent aggregations involving accretionary, “Cordilleran style” tectonics. Giant mesothermal gold provinces and shoshonites recur through time in the Palaeozoic and Mesozoic in this geodynamic setting.

Notes: Zusammenfassung Die metamorphen Komplexe in Arizona sind charakterisiert durch Dehnungstektonik, in denen listrisch gestörte und unmetamorphe vulkanische Gesteine einer oberen Platte tektonisch auf hochgradig metamorphe Gesteine einer unteren Platte entlang einer flachwinkligen Abscherungsfläche verfrachtet wurden. Die Abscherungen werden markiert durch Mikrobrekzien und chloritische Brekzien, die sich durch hydraulisches Zerbrechen (»hydraulic fracturing«) und Metasomatose gebildet und damit die unterlagernden amphibolitfaziellen Mylonite überprägt haben. Sauerstoff- und Wasserstoff-Isotopendaten belegen, daß die Mylonite bei 500 °C unter einem niedrigen Wasser/Gesteins-Verhältnis gebildet wurden. Die chloritischen Brekzien entwickelten sich bei 300–305 °C während des Einbruchs hydrothermaler Fluide entlang der Abscherungsfläche. Die hydrothermalen Veränderungen hatten massive Zugabe von Fe, Mn und Mg zur Folge unter gleichzeitiger Wegnahme von K und Na, was sich in der Hydrolyse der K-Feldspäte und Plagioklase zu Chlorit widerspiegelt. In den vulkanischen Gesteinen des oberen Stockwerks ist es lokal zur Bildung von K-Feldspat, Kalzit und Fe-, Mn-Oxiden gekommen. Geochemisch sind die vulkanischen Gesteine charakterisiert durch eine gesteigerte Häufigkeit von Änderungen unempfindlicher, inkompatibler Elemente (Th, LREE, P2O5), fraktionierte REE-Verteilungen (Lacn/Ybcn = 18) und eine Zunahme an »basischen« Spurenelementen wie Cr, Co, Ni, Sc. Primäre K2O-Gehalte werden auf 3–6 wt.% geschätzt. Ein durchgehendes Merkmal ist in den Chondrit-normalisierten Diagrammen das Vorhandensein von Trögen für Ta-Nb und Ti. Dies ein Hinweis auf Magmen, die mit konvergierenden Plattengrenzen verknüpft sind. Hydrothermale Änderungen beinhalten massive Zugabe von K, Fe, Ca und CO2, und eine systematische Abnahme von Na und Mg. δ-18O-Werte im Gesamtgestein reichen von 4 bis 18 pro mil. und bestätigen damit die Breite des Isotopenaustausches mit einem wässrigen Reservoir. Alterationen anden bei Temperaturen zwischen 250 und 100 °C statt. Die δ18O-Werte der Fluide in den hydrothermalen Wässern liegen schätzungsweise mit ihren Grenzwerten zwischen −11 und +11 pro mil. Ein duales Fluidregime wirkt während der Dehnungstektonik. In den tiefen tektonischen Stockwerken mit hoher Temperatur konzentrieren sich reduzierende Fluidmengen von metamorphem oder meteoritischem Ursprung an Abscherungen unter lithostatischem Druck. Es tritt eine Fe, Mn, Mg-Metasomatose auf. Im Gegensatz dazu sind in den höheren tektonischen Stockwerken kühlere, oxidierende Thermalwässer unter hydrostatischen Bedingungen und meteorischen Ursprungs anzutreffen.