J. Stephen Daly

The Grenville Orogenic Cycle (ca. 1350-1000 Ma): an Adirondack perspective

Abstract The Adirondack Mountains are characterized by three major events that took place during the interval ca. 1350-1000 Ma. The earliest of these is the arc-related Elzevirian Orogeny (ca. 1350-1185 Ma) during which substantial volumes of juvenile calc-alkaline crust were added to the Adirondacks as well as to the northwest segment of the Central Metasedimentary Belt. Data from the southwestern United States as well as from Ireland and Baltica indicate that Elzevirian magmatism and orogeny were of global dimensions. Within the southwestern sector of the Grenville Province, the Elzevirian Orogeny culminated at ca. 1185 Ma when accretion of all outboard terranes was completed. Compressional orogeny related to this convergence resulted in overthickened crust and lithosphere which subsequently delaminated giving rise to orogen collapse and AMCG magmatism that swept southeastward from the Frontenac Terrane into the Adirondack Highlands during the interval ca. 1180-1130 Ma. Localized compressional events within neighboring parts of the Grenville Province emphasize the continued existence of contraction during this interval, although crustal extension caused local in sedimentary basins in which were deposited the Flinton and the St. Boniface Groups. The Adirondacks have not yet provided any record of events within the interval ca. 1125-1100 Ma, although there is evidence of contraction elsewhere in the southwestern Grenville Province at that time. At 1100-1090 Ma the northern Adirondack Highlands were invaded by mildly A-type hornblende granites (Hawkeye suite) that are interpreted to be the result of local crustal thinning contemporaneous with rifting and mafic magmatism taking place in the Midcontinent rift. Immediately following, at ca. 1090 Ma, the global-scale continental collision of the Ottawan Orogeny was initiated. Strong convergence, deformation, and metamorphism continued to at least ca. 1070 Ma, and rocks older than this are profoundly affected by this event. During the waning stages of the Ottawan Orogeny, overthickened crust and lithosphere delaminated and the orogen underwent collapse. Large extensional faults such as the Carthage-Colton-Labelle shear zone developed and rapidly exhumed granulite facies rocks in the mobile core of the orogen which centers on the Adirondack-Morin terranes and extends southeastward into the New York-New Jersey Highlands. Extensional faulting along the Carthage-Colton mylonite zone dropped the amphibolite facies Lowlands down to the west and into juxtaposition with granulite facies rocks of the Highlands. UPb cooling ages from garnet, monazite, and titanite exhibit a sufficiently broad spectrum to accommodate an initial rapid rate of rebound-related cooling followed by a slower, erosion-controlled cooling history. During delamination, late- to post-tectonic granites of the Lyon Mt. Gneiss (ca. 1070-1045 Ma) were emplaced. The youngest member of this suite is an undeformed fayalite granite dated at ca. 1045 Ma which crosscuts all older rocks and fabric. High-potassium, post-tectonic granites of similar age are common in other parts of the southwestern Grenville Province. Renewed contraction and metamorphism at ca. 1030 Ma demonstrate that the Ottawan Orogen was still experiencing convergence well after the peak of orogeny. However, most of the manifestations involve reactivation of older thrust faults, including the Grenville Front Tectonic Zone. The intrusion of small bodies of anorthosite at ca. 1015 Ma (i.e., Labrieville) provide further evidence for the emplacement of these rocks within collisional orogens, albeit in their collapsing phase.

The Lapland-Kola orogen: Palaeoproterozoic collision and accretion of the northern Fennoscandian lithosphere

Abstract A tectonic model is proposed for the Palaeoproterozoic Lapland-Kola orogen (LKO) in the northern Fennoscandian Shield. Although long regarded as an Archaean craton, integrated geological, geochemical and geophysical observations show that the Lapland-Kola orogen is a Palaeoproterozoic collisional belt containing both Archaean terranes and an important component of juvenile Palaeoproterozoic crust. Rifting, from 2.5 to 2.1 Ga, began under the influence of a mantle plume (> 1000 km diameter), related to the break-up of the Kenorland supercontinent. Two linear suture zones within the orogeriic core mark the sites of continental separation, ocean formation and closure. One of these is identified as a belt of 1.98-1.91 Ga juvenile crust of both arc magmatic and sedimentary origin, marked by the Lapland Granulite, Umba and Tersk terranes. Palaeomagnetic data and ancient sedimentary detritus within these terranes suggest limited oceanic separation. Collision of juvenile terranes with the surrounding Archaean took place mainly between 1.93 and 1.91 Ga, resulting in a Himalayan-scale mountain belt, manifest by a thick-skinned region of high-P granulite-facies metamorphism, including the classical Lapland Granulite Belt and a broad zone of compressional deformation extending southwards into the Belomorian Mobile Belt. Protracted cooling and exhumation, possibly related to the buttressing effect of surrounding lithosphere, culminated in the intrusion of 1.80-1.77 Ga post-tectonic granites.

Provenance and Terrane Evolution of the Kalak Nappe Complex, Norwegian Caledonides: Implications for Neoproterozoic Paleogeography and Tectonics

The Kalak Nappe Complex (KNC) within the northernmost Arctic Norwegian Caledonides has traditionally been interpreted as representing the tectonically shortened margin of Baltica, consisting of a Precambrian basement and a late Precambrian to Cambrian cover deposited on the margin of the Iapetus Ocean. However, new geochronology indicates a distinctly different scenario. Detrital zircon U‐Pb dating, together with the magmatic and deformation history, shows that the KNC metasediments, previously considered as a single stratigraphic sequence, belong to at least two distinct successions. Metasediments of the Svaerholt Succession, within the lower (Kolvik and Olderfjord) nappes of the KNC and affected by the late Grenvillian Rigolet deformation phase, were deposited between ca. 980 and 1030 Ma, constrained by intrusive granites and the youngest detrital zircons. The Sørøy Succession occurs within the Sørøy‐Seiland Nappe, the Havvatnet Imbricate Stack, and Veines Nappe (the upper nappes of the KNC). It was affected by the Porsanger Orogeny at or before ca. 840 Ma and contains detrital zircons as young as \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Sm-Nd and U-Pb Isotopic Evidence of Juvenile Crust in the Adirondack Lowlands and Implications for the Evolution of the Adirondack Mts.

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470 Ma granitoid magmatism associated with the Grampian Orogeny in the Slishwood Division, NW Ireland

\end{document} Ma, and it was thus deposited between ca. 840 and 910 Ma. The Eidvågeid Paragneiss, classically interpreted as the basement to the KNC metasediments, has a similar detrital zircon population to the Sørøy Succession and may be correlative to it. It cannot represent the basement to the entire KNC and was affected by metamorphic events at ca. 710, 670, 560, and 520 Ma. The detrital zircon populations of both KNC successions are consistent with a Laurentia‐Baltica affinity, with age peaks corresponding to Labradorian/Gothian, Pinwarian, and Grenville/Sveconorwegian events. The detrital age populations of the Sørøy Succession bear strong similarity to those from the Moine Supergroup of Scotland, while the Svaerholt Succession is comparable with the Krummedal supracrustal sequence in Greenland. The provenance data are consistent with episodic amalgamation of two terranes, exotic to the Baltoscandian margin of Iapetus, which developed in successor basins to the Grenville Orogen along the indented Rodinia margin.

Age and composition of crystalline basement rocks on the Norwegian continental margin: offshore extension and continuity of the Caledonian–Appalachian orogenic belt

This study addresses the timing and pressure-temperature (P-T) conditions of ophiolite obduction, one of the proposed causes of the ca. 470 Ma Grampian orogeny of Scotland and Ireland. This event gave rise to the main structural and metamorphic characteristics of the Grampian terrane-the type area for Barrovian metamorphism, the cause of which remains enigmatic despite a century of research. Zircons from the Highland Border ophiolite, Scotland, define a 499 +/- 8 Ma U-Pb concordia age, which is interpreted as dating magmatism. Its metamorphism is dated by a 490 +/- 4 Ma Ar-40-Ar-39 hornblende age, and a 488 +/- 1 Ma Ar-40-Ar-39 muscovite age from a metasedimentary xenolith within it, from which P-T estimates of 5.3 kbar and 580 degrees C relate to ophiolite obduction. Metamorphism of the Deerpark complex ophiolitic melange (Irish correlative of the Highland Border ophiolite) is constrained by a 514 +/- 3 Ma Ar-40-Ar-39 hornblende age, while mica schist slivers within it yield detrital zircon U-Pb ages consistent with Laurentian provenance and Rb-Sr and Ar-40-Ar-39 muscovite ages of ca. 482 Ma. P-T values of 3.3 kbar and 580 degrees C for the mica schist constrain the conditions of ophiolite obduction. Metamorphic mineral ages from the Grampian terrane (Dalradian Supergroup) are substantially younger (ca. 475-465 Ma) than those from the ophiolites. If conductive heating in overthickened crust was the cause of Barrovian metamorphism, then collisional thickening must have started soon after ophiolite obduction at ca. 490 Ma in order to generate the ca. 470 Ma metamorphic peak in the Grampian terrane. (Less)

Grampian and late Grenville events recorded by mineral geochronology near a basement–cover contact in north Mayo, Ireland

Sm-Nd investigations of Hyde School Gneiss yield

Large-scale, linked drainage systems in the NW European Triassic: insights from the Pb isotopic composition of detrital K-feldspar

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