Greenland from Archaean to Quaternary, Descriptive text to the 1995 Geological Map of Greenland 1:2 500 000, 2nd edition

The geological development of Greenland spans a period of nearly 4 Ga, from Eoarchaean to the Quaternary. Greenland is the largest island on Earth with a total area of 2 166 000 km2, but only c. 410 000 km2 are exposed bedrock, the remaining part being covered by a major ice sheet (the Inland Ice) reaching over 3 km in thickness. The adjacent offshore areas underlain by continental crust have an area of c. 825 000 km2. Greenland is dominated by crystalline rocks of the Precambrian shield, which formed during a succession of Archaean and Palaeoproterozoic orogenic events and stabilised as a part of the Laurentian shield about 1600 Ma ago. The shield area can be divided into three distinct types of basement provinces: (1) Archaean rocks (3200–2600 Ma old, with local older units up to >3800Ma) that were almost unaffected by Proterozoic or later orogenic activity; (2) Archaean terrains reworked during the Palaeoproterozoic around 1900–1750 Ma ago; and (3) terrains mainly composed of juvenile Palaeoproterozoic rocks (2000–1750 Ma in age).Subsequent geological developments mainly took place along the margins of the shield. During the Proterozoic and throughout the Phanerozoic major sedimentary basins formed, notably in North and North-East Greenland, in which sedimentary successions locally reaching 18 km in thickness were deposited. Palaeozoic orogenic activity affected parts of these successions in the Ellesmerian fold belt of North Greenland and the East Greenland Caledonides; the latter also incorporates reworked Precambrian crystalline basement complexes. Late Palaeozoic and Mesozoic sedimentary basins developed along the continent–ocean margins in North, East and West Greenland and are now preserved both onshore and offshore. Their development was closely related to continental break-up with formation of rift basins. Initial rifting in East Greenland in latest Devonian to earliest Carboniferous time and succeeding phases culminated with the opening of the North Atlantic Ocean in the late Paleocene. Sea-floor spreading was accompanied by extrusion of Palaeogene (early Tertiary) plateau basalts in both central West and central–southern East Greenland. During the Quaternary Greenland was almost completely covered by ice, and the present day Inland Ice is a relic from the Pleistocene ice ages. Vast amounts of glacially eroded detritus were deposited on the continental shelves around Greenland. Mineral exploitation in Greenland has so far encompassed cryolite, lead-zinc, gold, olivine and coal. Current prospecting activities in Greenland are concentrated on gold, base metals, platinum group elements, molybdenum, iron ore, diamonds and lead-zinc. Hydrocarbon potential is confined to the major Phanerozoic sedimentary basins, notably the large basins offshore North-East and West Greenland. While reserves of oil or gas have yet to be found, geophysical data com bined with discoveries of oil seeps onshore have revealed a considerable potential for offshore oil and gas

Palaeoproterozoic and Archaean gneiss complexes in northern Greenland: Palaeoproterozoic terrane assembly in the High Arctic

The Precambrian shield of northern Greenland has been investigated by SHRIMP U-Pb zircon dating of 14 orthogneisses and granitoids plus 5 metasediments, integrated with mapping by the Geological Survey of Denmark and Greenland and whole-rock Nd isotopic studies. The Inglefield Mobile Belt is a tract of Palaeoproterozoic sedimentation, plutonism, polyphase deformation and high-grade metamorphism that underlies Inglefield Land and northern Prudhoe Land. In the southern part of the belt at 78 degrees 30\u27N, the E-W-trending Sunrise Pynt Straight Belt is a high-grade, but structurally late, shear zone with contrasts in the geology on either side. South of the Sunrise Pynt Straight Belt, ca. 1980 Ma diorites and tonalites were emplaced into older orthogneisses and metasediments. Detrital zircons from two metaquartzites (deposited on Archaean basement?) yielded complex age spectra from ca. 3250 Ma to 2350 Ma, with 2600-2450 Ma grains dominant. In associated mica schist, low Th/U, 1923 +/- 8 Ma zircons date high-grade metamorphism. The most southern orthogneiss investigated (77 degrees 45\u27N) is Neoarchaean (ca. 2600 Ma), in agreement with previously published isotopic data. North of the Sunrise Pynt Straight Belt to 79 degrees 10\u27N an amphibolite-granulite-facies complex with extensive pelitic to psammitic paragneisses are the oldest rocks recognised. Two psammitic paragneisses yielded unrounded zircons with a unimodal detrital age population centred on 2000-1980 Ma. Their source could be ca. 1980Ma orthogneisses from south of the Sunrise Pynt Straight Belt, or from basement inliers in the North-East Greenland Caledonian fold belt. The metasediments were intruded by tonalites and diorites with dates of 1949 +/- 13 Ma and 1943 +/- 11 Ma, and then by granitoids (free of zircon inherited from older rocks) with ages of 1924 +/- 29 Ma to 1915 +/- 19 Ma. The metasediments show development of low Th/U zircon overgrowths at ca. 1920 Ma, coeval with the granitoids. Finally, other granites, some locally transformed into gneisses, have ages of 1783 +/- 22 Ma to 1741 +/- 15 Ma. Inherited zircons in the latter are up to 2650 Ma old. A granite dyke with a zircon age of 1783 Ma has an T(DM) age of 2981 Ma and a strongly negative epsilon(Nd) at 1.78 Ga, indicating derivation by melting or reworking of Archaean crust. Thus, by 1800 Ma this juvenile Palaeoproterozoic, terrane had probably over-ridden crust with Archaean components. North of Inglefield Land, Precambrian crystalline rocks are obscured until Victoria Fjord (81 degrees 30\u27N). One reconnaissance orthogneiss sample from there contains ca. 3400 Ma oscillatory-zoned zircons, which probably date the rock, rather than being a xenocrystic component in a younger rock. Thus, from north to south there is an assemblage of Archaean, Palaeoproterozoic and Archaean to early Palaeoproterozoic gneiss terranes. The Inglefield Mobile Belt is dominated by juvenile Palaeoproterozoic arc crust trapped between two unrelated blocks of Archaean crust of contrasting age. The collision, and probably thrusting of a Palaeoproterozoic arc over a southern Archaean foreland, occurred at ca. 1920Ma-dated by metamorphic zircon. The new isotopic results consolidate the regional mapping of Archaean and Palaeoproterozoic complexes across northern Baffin Bay that show continuity from Canada into Greenland, without displacement across the Nares Strait. (C) 2007 Elsevier B.V. All rights reserved

Co-operation with the Geological Survey Department of Ghana

Between October 2001 and the end of 2003 there was a close co-operation between the Geological Survey of Denmark and Greenland (GEUS) and the Geological Survey Department of Ghana (GSD), as part of a project to enhance GSD’s institutional capabilities and effectiveness, mainly in the fields of management, geological mapping, map production and data handling. During this period a team of geologists, GIS (Geographic Information System) and database experts as well as administrative staff from GEUS have visited GSD, and GSD officers have visited GEUS in Copenhagen. The main obstacles to GSD becoming an effective organisation are its status as a department under the Ghana Ministry of Mines, insufficient funding by the government, and poor remuneration of its professional staff. To overcome these obstacles, attempts are being made to change the status of GSD from a ‘civil servant organisation’ into a semiautonomous institution, which will permit the Survey to generate funding for its core activities by providing services to outside organisations, and pay better salaries to its personnel. Despite many problems, geological mapping has been resumed and three new geological maps have been produced by GSD during the project and stored in GIS format. A mapping manual has been prepared, and the structure and ‘Mission and Vision Statements’ for the Survey have been revised

Colophon, contents, preface

The present volume marks the completion of a large research project by the Geological Survey of Denmark and Greenland (GEUS), focused on the northern part of the Palaeoproterozoic Nagssugtoqidian orogen of central West Greenland, and carried out by a team of Danish and international participants. The project comprised geological mapping as well as structural, geochronological, geochemical and economic geological studies. This volume contains reports on both Archaean and Palaeoproterozoic geology as well as a study of neotectonic brittle structures. The field work was carried out in 2000-2003 in the region between Nordre Strømfjord and Jakobshavn Isfjord (see e.g. van Gool & Piazolo 2006, this volume, fig. 1). The project had two immediate purposes, namely to establish an overview of the mineral resource potential of supracrustal rocks in the region between 66° and 70°15'N, and produce four new geological sheets in the Survey's 1:100 000 map series

The nagssugtoqidian orogen in South-East Greenland: evidence for paleoproterozoic collision and plate assembly

The 200 km wide, east-west trending Paleoproterozoic mobile belt of the Ammassalik region of South-East Greenland contains a diverse assemblage of Paleoproterozoic and Archean rocks, variably affected by Paleoproterozoic deformations and high-grade low or high pressure metamorphism. By using previous field and geochemical data combined with new zircon dating and zircon trace element geochemistry, this mobile belt is confirmed as a 1870 to 1840 Ma collisional orogen, which contains one or more 1900 to 1880 Ma magmatic suites and northern and southern Archean basement terranes. The most studied 1900 to 1880 Ma magmatic suite is the Ammassalik Intrusive Complex, which is dominated by diorites (with arc-like geochemical signatures and with Paleoproterozoic Nd depleted mantle model ages), which was intruded into sedimentary rocks, (with predominantly Paleoproterozoic detrital zircons). Both these associated rock types show 1900 to 1880 Ma moderate pressure granulite facies metamorphism (7 kbar, \u3e= 850 degrees C). Paleoproterozoic mylonites separate the Ammassalik Intrusive Complex from Archean orthogneisses containing 1870 Ma eclogite (11 kbar, 650-700 degrees C) and high-pressure granulite facies assemblages in Palaeoproterozoic diabase dike remnants. Associated with these Archean gneisses are pelitic metasediments, marbles and orthoquartzites (with Archean detrital zircon with complex 1870 to 1740 Ma metamorphic rims) that contain kyanite, thereby also showing high-pressure metamorphism. In the Ammassalik area we propose that one or more Paleoproterozoic magmatic arcs with syn-magmatic moderate pressure, high temperature metamorphism were emplaced over the edge of southern Archean continental crust. This resulted in at least doubling of crustal thickness, causing the transient 1870 Ma eclogite to high-pressure granulite facies metamorphic conditions in the buried southern Archean terrane. Archean orthogneisses in the north of the mobile belt preserve low-pressure Archean granulite facies assemblages, and are interpreted as a different terrane at a higher structural level, which was juxtaposed with the southern eclogite-bearing Archean terrane and the lower pressure metamorphism Paleoproterozoic arc rocks during the collisional event(s). This new information from the Ammassalik region is used in a synthesis of Paleoproterozoic crustal accretion and collisional orogeny in Greenland