Structural elements in southeastern Quebec,northwestern Appalachians,Canada

An attempt is made to correlate and separate in terms of style and time two contrasting sets of structural elements in the northwestern part of the Appalachian Uplands in the Province of Quebec, Canada. There is sufficient evidence to indicate that a fold system with north-south trending axes is superimposed on a fold system with east-west axes. It is suggested that the two sets of structures represent pulses of one long-continued deformation accompanied by corresponding early and late phases of metamorphism.

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Zusammenfassung Es wurde versucht, in den Appalachen des südöstlichen Teiles der Provinz Quebec, Kanada, zwei ungleichzeitige tektonische Systeme verschiedenen Baustils zu trennen. Die komplexen Kleinstrukturen zeigen, da\ Ost-West streichende Faltenachsen von einer jüngeren Nord-Süd-Faltung überprägt worden sind. Der Autor ist der Meinung, da\ die zwei tektonischen Systeme, die von einer frühen und späten Phase der Metamorphose begleitet werden, den zeitlich getrennten Verformungsstadien einer Orogenese entsprechen.

     

Origin of red beds in a Cambrian flysch sequence, Canadian Appalachians, Quebec

The basal unit of this flysch sequence consists of about 700 m of rhythmically interlayered red and green claystone intercalated with feldspathic sandstone and lithic conglomerate. Chemical analyses show that both types of claystones have approximately the same Fe₂O₃ content (8%). The presence within green claystone of inarticulate brachiopods, thin laminations of phosphate and pyrite, coupled with a high Mn content (Fe/Mn : 27) together with the composition of the chlorites, suggest that green mud was deposited slowly in a marine environment under reducing conditions. The hematite content of red claystone averages 4%. The Fe/Mn is high (71), and the clay fraction contains chamosite in addition to chlorite and illite. These characteristics favour a paralic oxidizing environment for the red muds. Rapid resedimentation of red sediment from a paralic environment into the green lithotope, rather than a lateral variation of facies, is suggested by: (1) the distribution of the two hemirhythms in the stratigraphic column, (2) the presence in the red hemirhythm of large slump structures, contorted laminations, and pebbly claystone, and (3) by the internal sedimentary structures of the coarse fraction.     

Metamorphism at the northwest contact of the Stanhope Pluton,Quebec Appalachians: Mineral equilibria in interbedded pelite and calc-schist

The interbedding of pelite and calc-schist in part of the contact aureole of a Devonian (biotite K-Ar age 346±4 Ma) granite pluton that straddles the Quebec-Vermont border offers an opportunity to compare metamorphic conditions prevailing in both rock types, and to test for internal consistency among several different geothermometers and geobarometers.Microprobe analyses and recent thermodynamic data are used with simple activity-composition models to estimate P-T-X _fluid conditions near the sillimanite zone. Calculations yield the following results: P=2 to 3 kb, and T =400° to 600° C in the inner one kilometre of the aureole; was around 0.8. Estimates are based on the calc-silicate isobaric invariant assemblages tremolite-K-feldspar-plagioclase-clinozoisite-phlogopite-calcite-quartz and diopside-tremolite-plagiolase-clinozoisite-calcite-quartz, and the paragonite-andalusite-sillimanite-albite-quartz equilibrium. The solid-solid reaction phlogopite+2 diopside + 4 quartz=tremolite+K-feldspar in the calc-schist (combined with the andalusite-sillimanite equilibrium), and phase relations in the granite yield apparently inconsistent results.The implied 6 to 10 km of cover at the time of intrusion may have been provided by subsequently eroded thrust sheets.     

Volcanic red-bed copper mineralisation related to submarine basalt alteration,Mont Alexandre,Quebec Appalachians,Canada

Two types of native copper occur in Upper Silurian basaltic rocks in the Mont Alexandre area, Quebec Appalachians: (1) type 1 forms micrometric inclusions in plagioclase and is possibly magmatic in origin, whereas (2) type 2 occurs as coarse-grained patches rimmed by cuprite in altered porphyritic basalt. Type 1 has higher contents of sulphur (2,000–20,263 ppm) and arsenic (146–6,017 ppm), and a broader range of silver abundances (<65–2,186 ppm Ag) than type 2 (149–1,288 ppm S, <90–146 As, <65–928 ppm Ag). No mineral inclusions of sulphide or arsenide in native copper were observed at the electron-microprobe scale. Primary igneous fabrics are preserved, but the basaltic flows are pervasively oxidised and plagioclase is albitised. Chlorite replaces plagioclase and forms interstitial aggregates in the groundmass and has Fe/(Fe+Mg) ratios ranging from 0.29 to 0.36 with calculated temperatures between 155°C and 182°C. Copper sulphides in vacuoles and veinlets are associated with malachite, fibro-radiating albite and yarrowite (Cu₉S₈ with up to 0.3 wt% Ag). Bulk-rock concentrations of thallium and lithium range from 70 to 310 ppb and 10 to 22 ppm, respectively, and thallium is positively correlated with Fe₂O₃. Such concentrations of thallium and lithium are typical of spilitisation during heated seawater–basalt interaction. Spilitisation is consistent with the regional geological setting of deepwater-facies sedimentation, but is different from current models for volcanic red-bed copper, which indicate subaerial oxidation of volcanic flows. The volcanic red-bed copper model should be re-examined to account for native copper mineralisation in basalts altered by warm seawater.     

Diagenetic and low-grade metamorphic terranes of Gaspé Peninsula related to the geological structure of the Taconian and Acadian orogenic belts, Quebec Appalachians

Abstract Illite crystallinity (IC) measurements, determination of the proportion of 2M mica-polytypes and organic-matter reflectance measurements establish regional diagenetic/low-grade metamorphic trends for the Taconian and Acadian belts of Gaspé Peninsula. IC varies as a function of many factors besides maximum burial temperature and heating time. Correlation between IC and %2M illite polytypes for the Fortin Group and Temiscouata Formation suggests (i) that the amount of high-grade detrital mica in the samples is low, and (ii) that IC can be used with some confidence as an estimator of regional thermal maturation levels. Correlation of these parameters with available organic reflectance values further supports this assumption. The illites of the Temiscouata and western Fortin groups are mostly phengitic in composition, whereas in the eastern outcrop belt they are more Mg- and Fe-rich (celadonitic), but generally also of lower grade and lower 2M content. The d(060) values for illites measured on the unorientated <2-μm fraction of samples fall between 1.502 and 1.503 Å (range: 1.500–1.504 Å), indicating relatively low octahedral occupancy by Mg and Fe (between one-fifth and one-third of the available spaces). Pyrophyllite and paragonite were not detected. Chlorites are Fe-rich and ripidolitic. The IC map for the Acadian belt of the peninsula displays general congruence between IC contours (2200 sample points) and structural trends for the 27,000-km² area. The highest grades (anchimetamorphic) are associated with the oldest rocks (Honorat and Matapedia groups) exposed in the cores of major anticlines. Anchimetamorphic grades associated with the western outcrop belt of the Lower Devonian Fortin Group require 7–8 km of subsidence to accommodate sufficient thickness of overlying younger rocks (on top of 4–5 km of Fortin Group deep-water clastics) to explain the grades in terms of burial metamorphism assuming a geothermal gradient of 30° C km^?1. The lowest-grade diagenetic rocks occupy a large area in the northeastern part of the peninsula, smaller areas in the northwestern part of the Acadian belt, in the centre of Chaleurs Bay synclinorium, and in the Ordovician Mictaw Group. The contact between the Taconian and Acadian belt is marked by a distinct maturation discontinuity. The Grand Pabos fault juxtaposes rocks of contrasting maturation levels (Matapedia Group against Fortin Group) in the west, but shows no maturation offset further east in the Honorat Group. The fault zone limiting the Fortin Group in the north is also associated with a major IC jump.     

The New Geophysics

New Geophysics of critically microcracked rock is a new understanding of fluid‐rock deformation that matches much of the behaviour of in situ rock observed throughout the Earth's crust and uppermost mantle. The behaviour of rock in New Geophysics: is self‐similar; can be monitored, calculated, predicted, even in principle controlled; prevails in almost all rocks; and has ‘butterfly‐effect’ sensitivity. All of these remarkable features (except controllability) have been observed, in some cases many times. However, New Geophysics is innovative, controversial, and currently “ridiculed” and “violently opposed” (Schopenhauer Stages 1 and 2), and is difficult to get published via consensus‐driven peer‐review. Consequently, in the last 10 years, various aspects of New Geophysics have been published in some 20 different journals and conference proceedings making it difficult to access by the general reader. This review presents a synopsis of what is believed to be a fundamental advance in solid Earth geoscience.     

Umbrella structure and channel-wall stoping in the Cambrian St. Roch Formation,Quebec Appalachians: significance for particle support mechanisms and turbulence development in hyper-concentrated sediment gravity flows

Umbrella structure is a newly recognized sedimentary structure associated with large platy clasts in resedimented boulder-bearing pebble conglomerate with a sandy matrix. It consists of a sand rim that lacks pebbles on parts or the entire underside of platy boulders, whereas on the upper side, pebbles are in direct contact with the boulders. The depositing processes were high- to hyper-concentrated sediment gravity flows in a submarine channel or canyon on the Cambrian continental slope of North America bordering the Iapetus Ocean. The structure occurs predominantly where clasts dip moderately in the down-current direction. Based on the association of the structure with slightly forward dipping slabs, it is proposed that these down-current dipping slabs may have been in the process of counter-clockwise rotation that was aborted and may have generated a pressure shadow on the underside enabling the inrush of fluid and the infiltration of sand into the anomalous low-pressure zone. The structure has implications for particle support mechanisms in high- to hyper-concentrated sedimentary gravity flows, in that it redirects attention to the much debated mechanism of dispersive pressure and alternatives. It provides an observable sediment structure that supports dispersive pressure which so far depended on experimental evidence and theoretical arguments alone. Vrolijk and Southard’s (1997) concept of a ‘laminar sheared layer’ is here for the first time interpreted as having an upward-moving ‘free-surface’ layer effect during deposition from hyper-concentrated flows. Channel-wall stoping involves unlithified turbiditic spillover sand in the levee sediment of the canyon wall that was washed out by the upper diluted parts of the high-concentration flows coming down the channel and leaving a niche in the wall that was filled with coarser channel-axis facies by the same flow (or later flows) when its aggradation reached the level of the niche. The contact between turbidite and pebble conglomerate occurs now more than 2 m laterally into the exposed channel wall. Channel-wall stoping tracks turbulence development in hyper-concentrated gravity flows.     

Nd Isotopic Characteristics of Granitoids from the New foundland Appalachians

正The Appalachian orogen in North America is currently considered to be a Paleozoic accretion-type orogenic belt,or a collage,formed by collision of many ancient blocks between Laurentian and Gondwanan margins (Williams,1979;Williams et al.,1988;van Staal et al.,2007).Recently,major progress has been made in understanding the characteristics and tectonic evolution of the outboard peri-Laurentian and peri-Gondwanan terranes of the Iapetus Ocean (van Staal et al.,2009,2012).     

Reprocessing and enhanced interpretation of the initial COCORP Southern Appalachians traverse

Reprocessing of the 1978–1980 COCORP Southern Appalachian seismic reflection data has produced improved images of structures related to the emplacement of the Blue Ridge–Inner Piedmont allochthon. The results enhance and extend the interpretation presented previously that the Blue Ridge and Inner Piedmont are allochthonous above a shallow, and shallow dipping, detachment that can be followed from outcrop at the Blue Ridge/Valley and Ridge transition to at least beneath the Carolina terrane. The continuity of reflections in the new images supports the interpretation that the southern Appalachian detachment is not rooted on the east side of the Inner Piedmont, but rather projects as a low-angle detachment (or zone of decoupling) to beneath the Coastal Plain. An implication of this geometry is that terranes, such as the Carolina terrane, between autochthonous North America and the Alleghanian suture beneath the Coastal Plain are detached, thin flakes.     

Terrane sutures in the Maine Appalachians,USA and adjacent areas

Terrane sutures in the Maine Appalachians and adjacent areas are recognized as melange dominated, deformed accretionary prisms of Ordovician age, and as a broad synmetamorphic transcurrent fault zone of probable Late Silurian-Early Devonian age. Although the accretionary prisms are associated with present day aeromagnetic and Bouguer gravity anomalies, they are probably not associated with present day crustal penetrating boundaries. The geology of the accretionary prisms indicates subduction-obduction dominated regimes during which (1) the Gander and Boundary Mountain (Dunnage) terranes amalgamated and (2) the composite Boundary Mountain-Gander terrane accreted to the Laurentian margin. The Penobscottian orogeny produced and deformed the older of the two accretionary prisms. This accretionary prism indicates that the Penobscottian was a continuous or perhaps diachronous event which spanned the late Cambrian to early Late Ordovician. The younger accretionary prism was produced and deformed during the Taconian orogeny during late Middle to early Late Ordovician. Initial deformation of this accretionary prism may have overlapped the waning stages of the Penobscottian. Portions of the Taconian arc locally overlie the Penobscottian accretionary prism. A synmetamorphic fault zone lies within Precambrian(?) to Ordovician(?) bimodal metavolcanic and metapelitic rocks assigned here to the Avalon terrane. This zone is several kilometres wide and is interpreted to be the postsubduction suture between the Avalon and Gander terranes, and may, in part, represent a fossil transform fault system. The fault zone contains phyllonites as well as shear zones which generally record dextral motion. The phyllonites were previously interpreted as a stratigraphic unit, whereas the shear zones span or are contained within mappable compositional units. Formation of and movement along these phyllonites and shear zones ceased before the intrusion of Early Devonian plutons. Not all faults in south-western Maine are related to the suture. Younger dip and/or strike-slip and thrust faults are approximately parallel to, or may lie within, the older shear zones and they complicate the recognition of the older faults.     

Radon reduction in homes constructed on saprolite in the Central Appalachians

 A 3-year study of indoor radon in more than 1000 homes in northern Virginia and southern Maryland was conducted using 3-month exposure alpha-track monitors. In a study set of 200 homes, first-floor indoor radon concentrations, which most closely approximates home exposure levels, averaged slightly more than 3 pCi/l. In a study set of 100 homes, sub-slab ventilation was used to reduce indoor radon concentrations. Interest in remediation was related to public perception of the hazardous nature of radon; people living in homes with indoor radon measurements of more than 4 pCi/l were more likely to participate in the remediation phase of the project. Sub-slab ventilation was successful in more than 90% of the homes in reducing indoor radon from concentrations as high as 30 pCi/ to less than 4 pCi/l, at least for the entire year of post-remediation radon measurements. Received: 29 February 1996 · Accepted: 29 May 1996     

海洋地球物理技术的发展

海洋地球物理的海底探测技术在20世纪里的迅猛发展推动了地球科学的进展。高精度的导航定位技术是实现海底高精度探测的基础。高精度的导航定位包括水面船只和水下探测系统的精确定位。现代水面船只定位依赖以全球卫星定位技术为主的导航定位系统；水下定位系统主要发展有超短基线定位系统(USBL)、短基线定位系统(SBL)和长基线定位系统(LBL)等。海洋重力测量系统的主体技术得到改进，陀螺稳定平台广泛采用光纤陀螺技术，开发出改正交又耦合效应的新技术，系统实现数字化控制，卫星测高技术引入海洋重力测量领域。海洋地磁测量发展出光泵式测量技术、多分量测量技术和梯度测量技术，近数十年快速发展起来的海底声学探测技术有多波束测深技术、声纳侧扫技术和浅层剖面测量技术等，这些技术已经在当代海底科学研究、海底资源勘查、海洋工程和海洋开发等方面发挥出极其重要的作用。在新的世纪里，海洋地球物理仍然保持着前沿科学的地住。     

Geophysics of proposed proterozoic sutures in Canada

Sutures have been identified or proposed at several sites in the Canadian Shield. Although many authors have suggested that some form of primitive plate tectonic processes have played a major role in the formation of the Archean crust of the Superior structural province, Proterozoic sutures, resembling Phanerozoic examples, have been proposed only within the younger Churchill and Grenville provinces, and at or near the boundaries between the older Superior and Slave provinces and the younger provinces. Gravity, magnetic, seismic and paleomagnetic data related to three proposed sutures in the latter category have been interpreted and generally support the view that the Shield comprises a mosaic of once separated, but now joined cratonic blocks. The sutures vary in complexity from wide zones, containing distinctive rocks formed at ancient accreting and consuming plate margins, to cryptic sutures marked only by abrupt changes in metamorphism and zones of cataclasis. Paired negative and positive gravity anomalies associated with these sutures have been interpreted in terms of juxtaposed crustal blocks of different density and thickness. Magnetic anomaly patterns change abruptly at structural province boundaries. Available seismic results support the concept of thickened crust in the younger province as derived from gravity modelling. Most authors prefer interpretation of Proterozoic pole positions in terms of one-plate models, but in some cases the interpretation of paleomagnetic data is equivocal and two-plate models have been proposed.     

Synthesis of Palaeozoic deformational events and terrane accretion in the Canadian Appalachians

Plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion, with some deformation associated with transform/transcurrent movements. Deformation associated with subduction varies between two end members: (1) where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes, a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over-riding plate; and (2) where continent-continent collision is occurring, a wide surface zone of accretionary deformation starts synchronously or with limited diachronism. Palaeozoic deformational events in the Canadian Appalachians correspond to narrow diachronous events in the Ordovician and Silurian, whereas Devonian, Carboniferous and Permian deformational events are widespread and broadly synchronous. Along the western side of the Canadian Appalachians, the Taconian deformational event starts diachronously throughout the Ordovician and corresponds to the north-north-west accretion of the Notre Dame, Ascot-Weedon, St Victor and various ophiolitic massifs (volcanic arc and peri-arc terranes) over cratonic North America. Within the eastern half of the Central Mobile Belt, the Late Cambrian-Early Ordovician Penobscotian deformational event corresponds to the ?south-easterly accretion of the Exploits subzone (various volcanic are and peri-arc terranes) over the Gander Zone (?continental rise). In the centre of the orogen, the Late Ordovician-Silurian Beothukan deformational event corresponds to the south-easterly accretion of the Notre Dame over the Exploits-Gander subzones. Along the south-eastern side of the Central Mobile Belt, the Silurian Ganderian deformational event corresponds to the north-north-east, sinistral transcurrent accretion of the Avalon Composite Terrane (microcontinent) over the Gander-Exploits zones. Along the south-eastern half of the orogen, the Late Silurian-Middle Devonian Acadian deformation event corresponds to the westerly accretion of the Meguma terrane (intradeep or continental rise) over the Avalon Composite Terrane. Affecting the entire orogen, the Late Devonian, Carboniferous and Permian, Acadian-Alleghanian deformational events correspond to the east-west convergence between Laurentia and Gondwana (continent-continent collision).     

Ages of regional metamorphism and ductile deformation in the central and southern Appalachians

A summary of available geochronology of deformational fabrics formed at greenschist and higher grades in the central and southern Appalachians is presented as a map showing the ages of regional metamorphism and ductile deformation. The ca. 480-435 Ma Taconic event affected most of the Piedmont and Blue Ridge provinces. The ca. 380-340 Ma Acadian event was milder and was centered in the west central Piedmont and eastern Blue Ridge. The 330-230 Ma Alleghanian event exhibits an abrupt ductile deformation front in the eastern Piedmont and extends an unknown distance eastward below the Atlantic Coastal Plain.     

Petrogenesis of sapphirine-bearing metatroctolites from the Buck Creek ultramafic body,southern Appalachians

The Buck Creek ultramafic body, North Carolina, includes aluminous lenses that have been described as troctolites. These lenses preserve mineral assemblages which record several different stages of metamorphism. The first stage is characterized by anhydrous reactions between olivine and plagioclase to produce coronas of orthopyroxene+ clinopyroxene/spinel symplectite. Thermo barometric results indicate minimum pressures of c. 6 kbar and c. 800 ^oC. Sapphirine replaces spinel in some clinopyroxene symplectites, and occurs as anhedral grains within amphibole, observations which in combination suggest peak metamorphic conditions of c. 9-10 kbar and c. 850 ^oC. Sapphirine-bearing hydrous assemblages formed at the expense of the coronas, indicating a second metamorphic episode involving deeper burial, deformation and hydration. Schistose rocks from the margins of the lenses are composed of anorthite+amphibole+margarite+corundum, and probably record a later, lower P-T event. Whole rock analyses for the Buck Creek lenses suggest an accumulate protolith of magnesian olivine and calcic plagioclase. Trace element data for the troctolites are consistent with data for adjacent amphibolites in suggesting that the Buck Creek mafic and ultramafic cumulates crystallized from magmas derived from a mantle source similar to that which produces modern intraplate or rift-related basalts. We propose that the Buck Creek ultramafics represent basal cumulates(± uppermost mantle) from ocean crust formed in a marginal basin in the latest Precambrian. Subduction-induced burial to at least 18 km under dry conditions induced corona formation. Collisional events of the Taconic orogeny thrust the Buck Creek rocks into the orogenic pile to at least 30 km depth and hydrated them along zones of weakness, locally producing P-T -P_H2O conditions appropriate for formation of sapphirine and hydrated assemblages, but still preserving some dry symplectites.     

Basement massifs in the Appalachians: their role in deformation during the Appalachian Orogenies

Basement is constituted of rocks which belong to a previous orogenic cycle which have been reactivated and incorporated into a younger cycle. Basement massifs may be classified according to their relative position in an orogen as external or internal massifs. They may also be categorized according to their role in deformation, as thrust-related, fold-related and composite massifs. All Appalachian external massifs were transported following their removal from the overridden edge of the ancient North American continental margin. Most of the internal massifs are also probably transported, but several (Pine Mountain and Sauratown Mountains) may be present as windows exposing parautochthonous basement beneath the main thrust sheet. The latter reside immediately west of the low (west) to high (east) gravity gradient which probably outlines the old edge of Grenvillian crust. Reactivated crustal material generated during early Palaeozoic orogeny plays the same mechanical role in reactivation as basement from the previous Grenville cycle. The domes of the Bronson Hill anticlinorium cored with Ordovician or older gneisses illustrate this behaviour. Basement (Grenville) massifs are distributed throughout the Appalachians as a belt of external massifs (Blue Ridge, Reading Prong, Hudson and Berkshire Highlands, Green Mountains, and Long Range Mountains) along the western edge of the crystalline metamorphic core. Additionally, internal massifs are also present (Pine Mountain belt, Tallulah Falls and Toxaway domes, Sauratown Mountains anticlinorium, State Farm gneiss dome, Baltimore Gneiss domes, Mine Ridge anticline, and Chain Lakes massif). Basement internal massifs probably served to localize thrusts by causing them to ramp over and around the massifs. Their antiformal shape may in part be as much related to thrust mechanics as to folding.