Part of the Slave Structural Province, the Hope Bay Greenstone Belt is a 82 km long north-striking sequence of supracrustal rocks dominated by mafic volcanic rocks with lesser felsic volcanic and sedimentary rocks. Mapping of two transects in the southern section and two transects in the northern section have contributed to a robust stratigraphic framework the belt. Three recently discovered Archean lode gold deposits in the Hope Bay Greenstone belt have associations with major structures and specific lithologies (Fe-Ti enriched basalts). The Flake Lake and the Clover Transects are in the southern part of the belt and the Wolverine and Doris-Discovery Transects are in the northern part of the belt. This work subdivides the volcanic rocks into distinct suites based upon field, petrologic, geochemical, and geochronologic criteria. Some of the suites are stratigraphically continuous and can be correlated tens of kilometres along strike thereby linking the two parts of the Hope Bay Greenstone Belt. U-Pb geochronology supports work by Hebel (1999) concluded that virtually all the supracrustal rocks in the Hope Bay Greenstone Belt were deposited over at least 53 m.y. (2716-2663 Ma), with the majority of the volcanism occurring after 2700 Ma. A number of basalt groups are identified and include the normal basalt, the LREE-enriched basalt, the Ti-enriched basalt and the Ti-enriched Al-depleted basalt groups. They have chemical signatures that vary in trace elements particularly HFSE and REE’s, and can be easily be distinguished by geochemical screening. The felsic volcanic suites are also divided into three main groups, tholeiitic rhyolite, calc-alkaline dacite and calc-alkaline rhyolite groups. Nd and Hf isotope signatures are consistent with trace element signatures in identifying mafic and felsic volcanic groups, with the tholeiitic rhyolite showing highly variable signature. The Hope Bay Greenstone Belt has been show to have a number of felsic and volcanic cycles. An early construction phase of the belt is made up of primarily mafic volcanics which is followed by felsic volcanism equalled mafic volcanism which lacks basalts enriched in Ti. The geodynamic environment that created the Hope Bay Greenstone Belt can be explained by plume influenced subduction zone.

Most researchers contend that the destruction of the Rheic Ocean culminated in the formation of the supercontinent Pangea. However, despite the importance of this ocean, there are major uncertainties in the identification of its margins, mechanisms and timing of its formation, and the geodynamics of its closure. Rocks recording the evolution of the Rheic are excellently preserved in the southern Iberian peninsula of Western Europe. Here, the Ossa Morena (OMZ) is separated from the South Portuguese (SPZ) zone by a sequence of polydeformed rocks know as the Pulo do lobo Zone (PDLZ). The PDLZ isinterpreted as a late Paleozoic accretionary prism, which contains potential vestiges of the ancient Rheic Ocean (ophiolites). The objective of this study is to better understand the processes associated with the formation of Pangea by determining the lithotectonic histories of both the PDLZ and SPZ. New field, geochronological and geochemical data are used to test and further constrain current models for the evolution of Pangea as recorded in the Variscan orogen. Fieldwork and geochronological data indicate that the PDLZ was derived from neither the OMZ (Gondwana) nor the SPZ suggesting that if the PDLZ is an accretionary prism it was not derived from the upper or lower plate. This apparent conundrum can be reconciled by a model involving excision of a crustal fragment during collision between an Iberian indenter (Gondwana) with Laurussia during the formation of Pangea. Geochronological and Geochemical data from the SPZ indicate that the lower crust isnot compositionally similar to the overlying Devonian-Carboniferous continental detritus. This unusual relationship is similar to the relationship between the relatively juvenile basement and ancient upper crust documented in the exposed portion of the Meguma terrane in the northern Appalachians, which paleogeographic reconstructions show was immediately outboard of southern Iberia in the Late Devonian. Taken together with the suggested complex tectonic history of the PDLZ the results of this thesis provide important insight into the geometry and timing of the formation of Pangea and indicate that re-interpretation may be required for what is known concerning the tectonic evolution of both the Variscan and Appalachian orogens.

The tectonometamorphic histories of allochthonous nappe units that were deeply buried and subsequently exhumed during the Scandian orogeny in the Western Gneiss Region (WGR) of Norway are poorly constrained and understood. One such unit is the Blåhø Nappe which underlies northern Harøya and Finnøya, two islands in the Nordøyane ultrahigh-pressure (UHP) metamorphic domain. The Blåhø Nappe contains a lower unit of garnet amphibolite gneiss with interlayered garnet-bearing quartzofeldspathic gneiss and marble, and an upper unit of migmatitic aluminous gneiss. Southern Harøya comprises orthogneisses attributed to the Baltican continental crust, and is separated from the Blåhø Nappe by the Finnøya migmatitic shear zone (FMSZ). Field and petrographic observations from these islands suggest that the Blåhø Nappe experienced peak metamorphism at high pressure amphibolite to granulite facies conditions before being overprinted by relatively lower pressure amphibolite facies conditions. In contrast, the adjacent Baltican basement gneiss contains coesite-eclogite pods, which attests to UHP conditions. However, the basement rocks are also overprinted by an amphibolite facies assemblage. To understand the implications of these observations, the metamorphic history of the Blåhø Nappe was investigated, and compared to that of the basement. This thesis presents thermobarometric and geochronologic analyses used to define a metamorphic pressure-temperature-time (PTt) path for the Blåhø Nappe on Harøya and Finnøya. The results suggest prograde metamorphism between ca. 440 Ma and 415 Ma, peak temperature metamorphism at 860?C and 15 kbar at around 410 Ma, equilibration at amphibolite-facies conditions of 680?C and 9 kbar by 395 Ma, and cooling below Ar-closure T in muscovite by ca. 360 Ma. The PTt data from the Blåhø Nappe demonstrate that these rocks did not share the UHP history of the adjacent basement rocks, but that both experienced similar amphibolite facies metamorphism and deformation. These units were likely juxtaposed along the FMSZ during isothermal decompression from their respective maximum burial depths to ~30 km depth.

Telšių (TDZ) ir Drūkšių-Polocko deformacijos zonos (DPDZ) kristaliniame pamate yra svarbios plastinės šlyties sistemos, priklausančios Kurzemės-Polocko lūžių juostai, esančiai vakariniame Rytų Europos kratono pakraštyje. Taikant petrografinį, mikrostruktūrinį ir izotopinės geochronologijos metodus kristalinių uolienų tyrimams, šiame darbe išaiškinti dar prekambre vykę magmatizmo, deformacijų ir metamorfizmo procesai bei stadijos tirtose deformacijos zonose, kurios kelis kartus reaktyvavosi proterozojuje ir fanerozojuje. Jų palyginimas su panašiomis deformacijos zonomis Baltijos skyde Švedijoje bei Baltarusijoje gali padėti atskleisti regiono aplink Baltijos jūrą, esančio Rytų Europos kratone, evoliuciją. / The Telšiai deformation zone (TDZ) and the Drūkšiai-Polotsk deformation zone (DPDZ) in the crystalline basement of Lithuania are important structures, belonging to the wide Polotsk-Kurzeme fault belt in the western part of the East European Craton (EEC). Combining microstructural, metamorphic and isotopic geochronological information is a tool constraining the time of deformation and metamorphism in shear zones. The TDZ and DPDZ were reactivated several times in the Proterozoic and Phanerozoic times. Their correlation with similar deformation zones of the Baltic Shield in Sweden and Belarus provides new insights into the regional structure and evolution of the East European Craton around the Baltic Sea.

The Barry gold deposit is an example of an Archean greenstone-hosted lode gold deposit located in the Urban-Barry greenstone belt in the Abitibi subprovince of Québec, Canada. Auriferous zones are spatially associated with NE-trending ductile shear zones with moderate south-easterly dip. Gold mineralization occurs within albite-carbonate-quartz veins that are straight N64ºE/64ºSE and folded N20ºE/60ºSE and within the surrounding carbonate-quartz-pyrite and locally biotite-carbonate alteration zones of the host mafic volcanic rocks. The deposit has gold resources indicated at 52,300 oz (385,000 mt at 4.23 g/t Au) and inferred at 126,600 oz (966,000 mt at 4.07 g/t Au). The host mafic volcanic rocks are part of the 2717 Ma Macho Formation that exhibit a geochemical signature transitional between mid-ocean and island arc. They are cut by pre-ore diorite, pre- and post-ore quartz-feldspar porphyry (QFP), and quartz monzonite dikes and plugs interpreted to have formed in a volcanic arc to syn-collisional setting. The auriferous veins comprise 5-15% volume of the mafic volcanic rocks, are 1-5cm wide, and locally pinch and swell or are boudinaged. Although the volcanic units strike N55-60ºE and dip 40ºSE, the ore envelope (>2 g/t Au) is constrained from surface to 30m depth in an antiformal shape. Free gold is found in albite-carbonate-quartz veins, syn-mineralization altered host rocks, and locally within quartz veins cutting early QFP dikes. The timing of gold mineralization at the Barry deposit is well constrained by U-Pb zircon dating of pre-mineralization diorite and post-mineralization QFP dikes. Analyses of single zircon grains by thermal ionization mass spectrometry (TIMS) give concordant and overlapping data with indistinguishable ages, yielding an average age of 2697 ± 0.6 Ma that is interpreted as the age of gold mineralization at the Barry deposit. This date indicates that gold mineralization was coeval with regional deformation and magmatism, and is, to our knowledge, the most precise age yet established for Archean lode gold mineralization. This confirms that the Barry lode gold deposit formed during an earlier, pre-2686, deformational period in the late Archean, similar to what was documented in the Kiena, Norlartic and Siscoe (Main Zone) mines in the Southern Abitibi greenstone belt. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2009-05-12 17:18:25.925

The Miguel Auza mine, located in Zacatecas State, Mexico, is a vein-type polymetallic epithermal deposit hosted in deformed argillite, siltstone and greywacke of the Cretaceous Caracol Formation. Silver-rich base metal veins (0.2 m to >1.5 m wide) are spatially associated with NE-striking, steeply SE- dipping (70-80º) faults over a strike length of 1.6 km and a depth of 460 m. Three distinct structural stages are correlated with hydrothermal mineral deposition: Stage I is characterized by normal faulting and early hypogene alteration of the sedimentary rock. Stage II is associated with reverse-sense reactivation of early normal faults, dilation of bedding planes/fractures, and deposition of barren calcite + pyrite veinlets. Sub-stages IIA and IIB are related to the development of reverse-fault-hosted quartz-carbonate sulphide veins and characterize the main stage of mineralization. Associated hydrothermal minerals during the main stage of mineral deposition are quartz, muscovite, and calcite. Stage III involves late NW-SE striking block faulting, brecciation and calcite veining. Later supergene oxidation of veins led to deposition of Fe-oxides and hydroxides. The main Ag-bearing minerals comprise pyrargyrite, tetrahedrite- freibergite, polybasite-antimonpearceite, and acanthite, with associated sulphides including galena, sphalerite, chalcopyrite, arsenopyrite and pyrite. In the main ore zone, base metal sulphides are commonly intergrown with the Ag-bearing sulfosalts. Compositions of Ag-rich tetrahedrite + pyrargyrite + sphalerite indicate a primary depositional temperature around 325-350ºC for the late phase of sub-stage IIB. 40Ar/39Ar dating of wall-rock illite associated with stage I alteration yields an age of 46.58 ± 0.30 Ma. Ages of 46.01 ± 0.55 Ma, and 44.55 ± 0.22 Ma were obtained for vein muscovite related to the main stage (sub-stage IIB) of ore deposition. These ages correspond to the later stage of the Laramide orogeny in Northern Mexico. The geometric relationship between the various structures, vein types, and the regional Miguel Auza fault zone suggest episodic reverse-sense reactivation of normal faults. Based on (1) the tectonic setting, (2) spatially related igneous rocks, (3) ore and gangue mineralogy, and textures (4) geochemical signature, and (5) inferred temperature of formation, the Miguel Auza deposit is interpreted to be an intermediate-sulfidation type deposit. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-04-15 13:04:06.104

The Alto Chicama district, Central Andean Cordillera Occidental, La Libertad, northern Perú, hosts the 14 M oz, Miocene Lagunas Norte high-sulphidation epithermal Au-(Ag) deposit (Latitude 7° 56ʹ30ʺ S; Longitude 78°14ʹ50ʺ W), in addition to several important, epithermal and mesothermal precious ± base-metal vein systems and porphyry Cu-Au-(Mo) deposits and prospects. The district is underlain by lower Oligocene-to-Middle Miocene, subaerial, Calipuy Supergroup volcanic rocks, unconformably overlying Upper Jurassic – Lower Cretaceous marine sedimentary strata affected by late Eocene-early Oligocene thin-skinned fold and thrust deformation. Mineralization at Lagunas Norte is largely hosted by intensely-folded Valanginian Chimú Formation quartz arenite, but extends into overlying, weakly-deformed, Lower Miocene dacitic volcaniclastic deposits. Fold- and thrust-related deformation at the deposit, and subsequent magmatic and hydrothermal activity, were localized along a long-lived, crustal-scale cross-strike discontinuity. Hydrothermal activity at Lagunas Norte was associated with local extension within an overall regional compressive regime. Ore formation occurred during the terminal stages of andesitic-to-dacitic magmatism in the deposit area, immediately following the sector collapse of an adjacent volcanic centre, and during eruption of late-stage peripheral dacitic domes. Intense advanced-argillic alteration occurred in at least two major pulses over a ~ 0.9 m.y. period, implying repeated magma influx in a shallow subjacent chamber. The ensuing Au-(Ag)-pyrite-enargite deposition resulted from mixing of magmatic vapour with oxidized groundwaters, a process stimulated by the contiguous incision of a steep-walled valley-pediment. The local volcanic rocks record a transition from “normal arc” to higher-pressure “adakitic” magmatism, initiated during ore deposition at Lagunas Norte, but exhibited by the entire Calipuy arc in northern Perú, and interpreted to reflect the destabilization of plagioclase and stabilization of garnet in inferred lower-crustal magmas. The progressive depletion of 18O and D in meteoric water recorded in late Oligocene-to-Late Miocene hypogene and supergene minerals is in permissive agreement with major uplift from ~ 1000 m to over 3000 m a.s.l. during hydrothermal activity. Hydrothermal activity and related ore deposition at Lagunas Norte unambiguously predated, by at least 2 m.y., the impingement of the aseismic Nazca Ridge at the Perú Trench and the ensuing flattening of the subducting slab / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2012-04-05 11:09:14.751

Field mapping and, structural, microstructural, and chronological analyses confirm the existence of a segment of the Gurla-Mandhata-Humla fault, an orogen-parallel strike-slip dominated shear zone in the upper Karnali valley of northwestern Nepal. This shear zone forms the upper contact of, and cuts obliquely across the Greater Himalayan Sequence (GHS). Data from this study reveal two phases of GHS deformation. Phase 1 is characterized by U-Th-Pb monazite crystallization ages (~26–12 Ma, peak ~18–15 Ma), consistent with typical Neohimalayan metamorphic ages, and the final stages of south-directed extrusion of the GHS. Phase 2 is characterized by south-dipping high-strain foliations and intensely developed ESE-WNW trending, shallowly plunging mineral elongation lineations, indicating orogen-parallel extension. Thermochronology of muscovite defining these fabrics implies that the area was cooling and experiencing orogen-parallel extension by ~15–9 Ma. Mineral deformation mechanisms and quartz c-axis patterns of these fabrics record a rapid increase in temperature from ~350°C along the shear zone, to ~650°C at ~2.5 structural km below the shear zone. Such temperature gradients may be remnants of telescoped and/or flattened isotherms generated during south-directed extrusion of the GHS. Overprinting ESE-WNW fabrics record progressive deformation of the GHS at lower temperatures. Progressive deformation included a significant component of pure shear, as indicated by symmetric high-temperature quartz c-axis fabrics and a lower-temperature vorticity estimate (~59% pure shear). A transition in c-axis fabrics from type I to type II cross-girdles at ~ 1.2 km below the fault could indicate a transition from plane strain towards constriction. Together, these data suggest orogen-parallel extension was occurring as a result of transtension. This study reveals a transition from south-directed extrusion of the GHS to orogen-parallel extension between ~15–13 Ma. Comparing these data with tectonic events across the Himalaya reveals an orogen-wide middle Miocene transition, coeval with the uplift of eastern Tibet. This is consistent with interpretations invoking radial spreading of Tibet and east-directed lower-crustal flow to explain orogen-parallel extension. Our study leads to the suggestion that a transition affecting mid- to lower-crustal processes may be responsible for the cessation of south-directed extrusion of the GHS and onset of east-directed lower-crustal flow. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-09-23 02:16:09.326

No description available.

Terrane discrimination in polycyclic continental basement rocks is challenging due to high-grade metamorphism and intense deformation. Based on early USGS mapping the Blue Ridge basement in the Dellwood quadrangle of the eastern Great Smoky Mountains was proposed to consist of augen orthogneisses of Laurentian (Grenvillian) affinity interfolded with migmatitic hornblende and biotite paragneisses (“Carolina Gneiss”) and amphibolites of uncertain affinity. However, detailed study reveals that the hornblende gneiss of Hadley and Goldsmith (1963) is a heterogeneous map unit consisting of (1)metaplutonic rocks; (2) variably foliated and folded felsic orthogneisses; (3) strongly migmatitic, folded Hbl+Bt-bearing gneisses; (4) foliated and lineated garnet amphibolites Field relations, petrology, and geochemistry demonstrate that felsic orthogneisses are related to metaplutonic rocks via (post-Taconian) progressive deformation and reconstitution. Whole rock XRF geochemistry reveals likely protoliths of Hbl gneiss and Bt gneiss are geochemically similar and have common sources. U-Pb zircon geochronology and field relationships suggest felsic orthogneisses (1050 Ma,1150-1190 Ma, 1250-1300 Ma) are components of the Mesoproterozoic Grenville basement, and not part of a metamorphosed Neoproterozoic syn-rift Laurentian margin cover sequence. A previously unknown age mode for Mesoproterozoic plutonism in the southern Appalachians was discovered (~1250-1300 Ma) suggesting the presence of a component exotic to pre-Grenvillian Laurentia (Amazonia?).