About
71
Publications
33,732
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
6,064
Citations
Introduction
Additional affiliations
September 1992 - May 2005
Publications
Publications (71)
The Precambrian shield of Madagascar is reevaluated with recently compiled geological data and new U-Pb sensitive high-resolution ion microprobe (SHRIMP) geochronology. Two Archean domains are recognized: the eastern Antongil-Masora domain and the central Antananarivo domain, the latter with distinctive belts of metamafic gneiss and schist (Tsarata...
The Precambrian shield of south-central Madagascar, excluding the Vohibory region, consists of three geologic domains, from north to south: Antananarivo, Ikalamavony-Itremo, and Anosyen–Androyen. The northern Antananarivo domain represents the Neoarchean sector of the Greater Dharwar Craton amalgamated at 2.52–2.48Ga. The Greater Dharwar Craton is...
Newly determined U–Pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the Devonian time-scale. They are: (1) 417.6±1.0 Ma for an ash within the conodont zone of Icrioduswoschmidti/I. w. hesperius (early Lochkovian); (2) 408.3±1.9 Ma for an ash of early Emsian age correlated with the conodont zones of Po. dehi...
The olivine melilitites from the southern part of the 6.8 Ma-old Takarindiona volcanic field (Eastern Madagascar) are olivine ± chromite -phyric lavas, with zoned titanaugite, perovskite, melilite, nepheline, monticellite, Ba–Ti-mica and Fe–Ti oxides as microphenocrysts and groundmass phases. The rocks are very primitive, rich in incompatible trace...
New U-Pb detrital zircon ages prove a Neoproterozoic sedimentation age of the Ambatolampy Group in central Madagascar. The youngest detrital zircons are most likely derived from the Imorona-Itsindro suite, a calc-alkaline, bimodal suite related to crustal extension between 855 and 720 Ma. Mafic gneisses and amphibolites show a geochemical signature...
The Itasy is a Pleistocene-Holocene volcanic field in central Madagascar, located to the west of the Ankaratra volcanic complex. It comprises scoria cones and lava domes (>120), with associated pyroclastic fall and mafic lava flows, covering an area of ab. 400 km². The last volcanic episodes probably dated ca. 6000–7100 y BP; warm springs and geyse...
Determining the possible tectonic regimes active during the Neoproterozoic is crucial for the knowledge of the evolution of the super-continent Gondwana. In Madagascar, that occupies a key position in Gondwana, there is an on-going debate regarding the location of possible suture zones and the implications in terms of paleo-geography. Recognizing h...
The Ampasindava alkaline province consists of a series of circular and elliptical intrusions, lava flows, dyke swarms and plugs of Cenozoic age emplaced into the Mesozoic-Cenozoic sedimentary rocks of the Antsiranana basin (NW Madagascar) and above the crystalline basement. The magmatism in the Ampasindava region is linked to a NW-SE trending exten...
Available U–Pb geochronology of the Precambrian shield of Madagascar is summarized and integrated into a synthesis of the region’s geological history. The shield is described in terms of six geodynamic domains, from northeast to southwest, the Bemarivo, Antongil–Masora, Antananarivo, Ikalamavony, Androyan–Anosyan, and Vohibory domains. Each domain...
The REE-mineralized Khanneshin carbonatite complex in southern Afghanistan is an economically light rare earth element (LREE)-enriched carbonatite complex of Quaternary age. Geological studies have suggested that the LREE-enriched rocks at Khanneshin are comparable in grade to many economic REE deposits, including parts of the world-class Bayan Obo...
New geochronologic data from basement rocks support the interpretation that the Argentine Precordillera (Cuyania) terrane was rifted from the Ouachita embayment of the Iapetan margin of Laurentia. New data from the Ozark dome show a range of ages in two groups at 1466 +/- 3 to 1462 +/- 1 Ma and 1323 +/- 2 to 1317 +/- 2 Ma, consistent with existing...
The rapid rise in world demand for the rare-earth elements (REEs) has expanded the search for new REE resources. We document two types of light rare-earth element (LREE)-enriched rocks in the Khanneshin carbonatite complex of southern Afghanistan: type 1 concordant seams of khanneshite-(Ce), synchysite-(Ce), and parisite-(Ce) within banded barite-s...
New detrital zircon U–Pb age data obtained from various quartzite units of three spatially separated supracrustal packages in central and northern Madagascar, show that these units were deposited between 1.8 and 0.8Ga and have similar aged provenances. The distribution of detrital zircon ages indicates an overwhelming contribution of sources with a...
Abstract Late Cretaceous dykes and lavas from central-eastern coastal Madagascar (Vatomandry and Mahatsara districts) span a compositional range from basalt to rhyolite. The dykes strike N–S, parallel to the coast, and intrude the Precambrian schists and gneisses of the area. 40Ar/39Ar age determinations on rhyolite from Sakanila massif (western Va...
This chapter summarizes and interprets results for the Balkhab copper area of interest (AOI) and
its subarea that have come from geologic and compilation activities that were conducted jointly between
2009 and 2011 by the U.S. Geological Survey (USGS), the U.S. Department of Defense Task Force for
Business and Stability Operations (TFBSO), and the...
We summarize and interpret results for the Dusar volcanogenic massive sulfide, Shaida porphyry
copper, and Misgaran tin skarn subareas of interest. These subareas have been surveyed by joint
geologic and compilation activities conducted between 2009 and 2011 by the U.S. Geological Survey
(USGS), the U.S. Department of Defense Task Force for Busines...
The Khanneshin carbonatite is a deeply dissected igneous complex of Quaternary age that rises
approximately 700 meters above the flat-lying Neogene sediments of the Registan Desert, Helmand
Province, Afghanistan. The complex consists almost exclusively of carbonate-rich intrusive and
extrusive igneous rocks, crudely circular in outline, with only t...
Late tectonic, post-collisional granite suites are a feature of many parts of the Late Neoproterozoic to Cambrian East African Orogen (EAO), where they are generally attributed to late extensional collapse of the orogen, accompanied by high heat flow and asthenospheric uprise. The Maevarano Suite comprises voluminous plutons which were emplaced in...
The broadly east-west trending, Late Neoproterozoic Bemarivo Belt in northern Madagascar has been re-surveyed at 1:100 000 scale as part of a large multi-disciplinary World Bank-sponsored project. The work included acquisition of 14 U–Pb zircon dates and whole-rock major and trace element geochemical data of representative rocks. The belt has previ...
The Ellsworth terrane is one of a number of fault-bounded blocks that occur along the eastern margin of Ganderia, the western-most of the peri-Gondwanan domains in the northern Appalachians that were accreted to Laurentia in the Paleozoic. Geologic relations, detrital zircon ages, and basalt geochemistry suggest that the Ellsworth terrane is part o...
The Precambrian geology of west-central Madagascar is reviewed and re-interpreted in light of new field observations, Landsat Thematic Mapper image analysis, and U–Pb geochronology. The bedrock of the area consists of: (1) late Archean (to Paleoproterozoic) migmatite gneiss and schist; (2) Mesoproterozoic stratified rocks (Itremo, Amborompotsy, and...
The Precambrian geology of west-central Madagascar is reviewed and re-interpreted in light of new field observations, Landsat Thematic Mapper image analysis, and U–Pb geochronology. The bedrock of the area consists of: (1) late Archean (to Paleoproterozoic) migmatite gneiss and schist; (2) Mesoproterozoic stratified rocks (Itremo, Amborompotsy, and...
New data from an Upper Triassic to Lower Cretaceous deep marine succession—the herein reinstated and restricted Gemuk Group—provide a vital piece of the puzzle for unraveling southwestern Alaska's tectonic history. First defined by Cady et al. in 1955, the Gemuk Group soon became a regional catchall unit that ended up as part of at least four diffe...
A distinctive yet enigmatic suite of fault-bounded ultramafic massifs occurs within accretionary complex mélange of the McHugh Complex on the Kenai Peninsula of southern Alaska. The largest and most significant of these include Red Mountain and the Halibut Cove Complex, consisting of dunite and pyroxenite with chromite seams and lesser quantities o...
The timing of continental building in the Sveconorwegian orogen of SW Scandinavia is evaluated with zircon U-Pb geochronology. ID-TIMS,
LA-ICPMS and SIMS data are reported for 21 samples of orthogneiss, metarhyolite and metasandstone in S Norway, with emphasis on the Suldal
area. The Sveconorwegian orogen is divided into a reworked Fennoscandian 1....
The most complete Neoproterozoic successions in south China contain three diamictite intervals in the Changan, Tiesiao, and Nantuo Formations. The youngest and most widespread Nantuo glacial deposit overlies the Datangpo Formation and underlies the fossil- rich Doushantuo Formation. Previous authors have correlated the Nantuo diamictite to either S...
A region of metamorphosed supracrustal rocks (pelite, quartzite, marble, and graywacke) and coeval intrusive igneous rocks crop out in a 250 km long orogenic belt in northern Madagascar. The NW-SE trending belt is situated between a juvenile Neoproterozoic magmatic arc terrane (to the north) and an Archean craton, strongly reworked in early Neoprot...
The Saghand area of East-Central Iran exposes rocks that comprise the substratum of the Central Iranian continental terrane, as part of the larger Alpine- Himalayan orogenic system. Our new U-Pb ages and geochemical data from the magmatic, metamorphic and siliciclastic rocks of the Saghand area unravel three main episodes of orogenic activity in th...
The Goochland terrane is an isolated block of Mesoproterozoic crust in the Piedmont Province of central Virginia. We report U-Pb zircon dates and whole-rock major and trace element data for the State Farm gneiss, one of the main units in the terrane, and additional results for a newly recognized suite of Neoproterozoic granitoids that intrude the g...
Landsat TM and radar JERS-1 SAR (L-Band) imagery of the Itremo area, central Madagascar, were processed to emphasize structural geology features including folded quartzite ridges and plutons. TM band ratios 5/7, 5/1, 5/4∗3/4 were assigned to RGB. Band 5/7 highlights pelitic schist, band 5/1 emphasizes mafic igneous rocks, and 5/4∗3/4 distinguishes...
The Sveconorwegian and Grenville orogenic belts display widespread 1.19–1.13Ga Early Grenvillian continental magmatism including A-type granitoids. In the Sveconorwegian province, S Norway, bimodal 1.17–1.14Ga metavolcanic rocks of the Telemark sector are part of this magmatism. Volcanic rocks in low- to medium-metamorphic grade are interlayered wi...
The Acadian deformation front in the northern Appalachians of Maine and New Hampshire can now be closely located during the early Emsian (Early Devonian; 408–406 Ma). Tight correlations between paleontologically and isotopically dated rocks are possible only because of a new 408-Ma time scale tie point for the early Emsian. The deformation front la...
We report a thick, laterally extensive 2505 +/- 2.2-million-year-old (uranium-lead ratio in zircon) Archean ophiolite complex in the North China craton. Basal harzburgite tectonite is overlain by cumulate ultramafic rocks, a mafic-ultramafic transition zone of interlayered gabbro and ultramafic cumulates, compositionally layered olivine-gabbro and...
Two platformal stratigraphic sequences occur on Islesboro, Penobscot Bay, Maine. The older Seven Hundred Acre Island Formation is at least 200 m thick, its base is not exposed, and it makes up fault-bounded blocks of siliceous colour-banded dolomitic marble, muscovite-rich quartzite, coarse-grained splendent muscovite-garnet-staurolite-andalusite s...
The zone of Acadian collision between the Medial New England and Composite Avalon terranes is well preserved in Maine. A transect from northwest (Rome) to southeast (Camden) crosses the eastern part of Medial New England comprising the Central Maine basin, Liberty-Orrington thrust sheet, and Fredericton trough, and the western part of Composite Ava...
New U-Pb geochronology constrains the timing of the Acadian orogeny in the Central Maine Terrane of northern New Hampshire. Sixteen fractions of one to six grains each of zircon or monazite have been analyzed from six samples: (1) an early syntectonic diorite that records the onset of the Acadian; (2) a schist, a migmatite, and two granites that to...
The Huqf Supergroup, Oman, contains volcanic horizons with the potential
to calibrate Neoproterozoic events and chemostratigraphy using U-Pb
zircon geochronology. A tuffaceous bed near the base, within the lower
(Ghubrah) diamictite and beneath a lower cap carbonate, provides the
first U-Pb zircon date obtained from within a Neoproterozoic glacial...
We reconstruct seven sequential positions of the Acadian deformation front and foreland basin to illustrate the northwestward migration of the orogenic belt across Maine and adjacent areas from Late Silurian to Middle Devonian time. The reconstructions are based on (1) U-Pb and 40Ar/39Ar ages of pretectonic, syntectonic, and posttectonic plutons; (...
In the Stuyahok area of the south-central Holy Cross quadrangle, Alaska, felsic to intermediate dikes and sills intrude Lower Cretaceous volcanic and volcaniclastic rocks of the Koyukuk terrane. These previously undated intrusions are the probable source of at least 933 kg (30,000 oz) of past placer gold production. Additional placer, and perhaps l...
New U-Pb zircon ages and Sm-Nd and Rb-Sr isotopic data are presented for orthogneisses from north-central Mad-agascar, including I ˆ le Sainte Marie, Alaotra-Beforona, Maevatanana, and Ambatolampy-Ambatomarina. A migmatite tonalite gneiss from I ˆ le Sainte Marie is dated precisely at Ma and has a Sm-Nd model age (T DM) of 3204 3187 2 Ma, thereby e...
The common spatial relationship in convergent orogenic belts between a crustal-scale shear-zone system, high-grade metamorphic rocks, and granites suggests a feedback relation between crustal anatexis and contractional deformation that helps granite extraction and focuses granite ascent. Such a feedback relation has been proposed for ascent of Earl...
Stratigraphy and isotope geochronology in the crystalline core of the Appalachians suggest revised interpretations of the extent, nature and timing of Paleozoic orogens in New England. Five major episodes of magmatism, deformation, and high-grade regional metamorphism are recognized: Taconian (455-442 Ma), Acadian (423-385 Ma), Neo-Acadian (366-350...
The North Dabie Complex (NDC) comprises a high-temperature metamorphic suite dominated by amphibolite-facies granitoid orthogneiss intruded by voluminous granites. U-Pb zircon dating on these rocks yields the following new results: (1) Two of the granitoid orthogneiss samples have Early Cretaceous protolith emplacement ages of 133.7 ± 2.3 Ma and 13...
The Dabie Shan contains two rare geologic features. One, the occurrence of ultra-high pressure metamorphic rocks (peak P > 2.7 GPa = UHP) in the east-central part of this belt, and two, some of these UHP rocks are characterized by anomalously 18O-depleted oxygen isotopic compositions. Geochronological data are presented that constrain the age of th...
The U-Pb dating of 18 samples, representing the principal rock types of the 4000 km2 Salmi anorthosite-rapakivi granite complex and its satellite Uljalegi pluton, southeastern Baltic (Fennoscandian) Shield,
reveals that six temporally distinct episodes of igneous activity occurred in a timespan of 17 million years. From oldest
to youngest they are:...
Distinct groupings of late Neoproterozoic tectonomagmatic and depositional events at 760 Ma, 685-670 Ma, 635-590 Ma and 590-545 Ma are recognized within the peri-Gondwanan margin of the Newfoundland Appalachians. This pre-Iapetan orogenic activity resulted in amalgamation of distinctive tectonic packages prior to deposition of a shale-rich platform...
The Pinware terrane in the eastern Grenville Province of Labrador is characterized by abundant granitoid rocks but a lack of metasedimentary gneiss. On the basis of newly obtained U-Pb zircon ages, the following history is outlined. Supracrustal rocks, including felsic volcanics, were formed at $1640 \pm 7 Ma$. These rocks were migmatized and injec...
Recent geochronological data show that geon 14 and older rocks are found
at least 700 km south of the Grenville front in the eastern Grenville
province. In the southwestern Grenville province, comparable rocks
extend only 200 km south; farther south, in the Central metasedimentary
belt and the Adirondack Mountains, the crust mostly postdates 1350 M...
New geochronologic data combined with structural and petrologic studies have radically changed concepts of the tectonic framework in the Bronson Hill anticlinorium, central Massachusetts. The authors focus on a striking coincidence of structural, metamorphic and geochronologic transitions on the east limb of the Warwick dome and Kempfield anticline...
The Shelburne Falls arc (SFA) is over 185 km long and comprises the following gneiss-cored domes in western Mass. and Conn.: Shelburne Falls, Goshen, Granville, Granby, Collinsville, Bristol, and Waterbury. Arc related rocks from these domes have been correlated with lithologically similar rocks in the Bronson Hill magmatic arc (BHA) dated previous...
Through a combination of low analytical blanks, clean Pb-205 enriched tracer-solution, and refined procedures of sample preparation, it is possible to isolate and measure minute quantities of radiogenic Pb in concordant zircon, thereby permitting accurate isotopic age determinations of small multigrain samples of Paleozoic zircon with 7--20 ppm rad...
U-Pb age determinations on six newly identified examples of Grenvillian plutonism from eastern Labrador have yielded the following ages: Gilbert Bay granite 1132−6⁺⁷ Ma; Second Choice Lake pegmatite 1003±6 Ma; Southwest Pond granite 963±6 Ma; Chateau Pond granite 964±2 Ma; Rivière Bujeault headwaters quartz syenite 964±5 Ma; Upper St Lewis River (w...
High initial parent/daughter element ratios and a unique dual decay scheme make UPb zicron ages more precise and reliable than most isotopic ages, and thus inherently superior for time-scale calibration. Employing improved techniques to the conventional method of UPb dating, we have analyzed microgram-size (2–12 × 10−8 g) zircon fractions from bios...
Results of U-Pb zircon, titanite and monazite dating from 29 Proterozoic gneissic rocks from an area of ca. 9800 km² in the central portion of the Western Gneiss Region (WGR), Norway are presented. The major period of crust formation is identified, and the age and approximate domains of Middle Proterozoic (Sveconorwegian) and Phanerozoic (Caledonia...
The geochronologic history of the northern portion of the Western Gneiss Region, south-central Norway has been investigated by UPb analyses of zircon and titanite from various basement units and one supracrustal gneiss. A six-point (four zircon and two titanite) discordia line from a migmatite melt-pod and its host-gneiss (Åstfjord migmatite gneiss...
The tectonostratigraphy and regional structure of the area is described. The basement gneisses of probable Proterozoic age are divided into three principal members: an oldest series of migmatite tonalite gneisses; a complex of granitic and porphyroclastic augen gneisses with a distinctive unit of microcline-rich potassic granite; and a suite of cro...
Landsat TM and Radar JERS-1 SAR (L-Band) imagery of the Itremo area, central Madagascar, were processed to emphasize structural features including folded quartzite ridges and pluton/country rock relationships. Late Archean to Paleoproterozoic migmatitic gneiss and schist are overlain by Mesoproterozoic stratified rocks. Proterozoic (˜1000 Ma--720 M...
