Whole rock geochemical data For paleozoic sedimentary rocks of the western Brooks Range, Alaska

The paper presents U–Pb ages for zircons of the calc-alkalic to alkalic igneous suite and associated alluvial–fluvial sedimentary rocks of the Timiskaming Group in the late Archean Abitibi greenstone belt, Superior Province. The Timiskaming Group rests unconformably on pre-2700 Ma komatiitic to calc-alkalic volcanic sequences and is the expression of the latest stages of magmatism and tectonism that shaped the greenstone belt. An age of 2685 ± 3 Ma for the Bidgood quartz porphyry, an age of about 2685–2682 Ma for a quartz–feldspar porphyry clast in a conglomerate, and ages ranging from 2686 to 2680 Ma for detrital zircons in sandstones appear to reflect an early stage in the development of the Timiskaming Group. The youngest detrital zircons in each of three sandstones at Timmins, Kirkland Lake, and south of Larder Lake define maximum ages of sedimentation at about 2679 Ma; the latter sandstone is cut by a porphyry dyke dated by titanite at [Formula: see text], identical to the 2677 ± 2 Ma age for a volcanic agglomerate of the Bear Lake Formation north of Larder Lake. Similar ages have previously been reported for syenitic to granitic plutons of the region. The dominant period of Timiskaming sedimentation and magmatism was thus 2680–2677 Ma. Xenocrystic zircons found in a porphyry and a lamprophyre dyke have ages of 2750–2720 Ma, which correspond to the ages of the oldest units in the belt, predating the volumetrically dominant ca. 2700 Ma greenstone sequences. The presence of these xenocrysts and the onlapping of the Timiskaming Group on all earlier lithotectonic units of the southern Abitibi belt support the concept that the 2700 Ma ensimatic sequences were thrust onto older assemblages during a phase of compression that culminated with the generation of tonalite and granodiorite at about 2695–2688 Ma. Published geochemical data for the Timiskaming igneous suite, notably the enrichments in large-ion lithophile elements and light rare-earth elements and the relative depletion of Nb, Ta, and Ti compare with the characteristics of suites at modern convergent settings such as the Eolian and the Banda arcs and are consistent with generation of the melts from deep metasomatized mantle in the final stages of, or after cessation of, subduction. Late- and post-Timiskaming compression caused north-directed thrusting and folding. Turbiditic sedimentary units of the Larder Lake area which locally structurally overly the alluvial–fluvial sequence and were earlier thought to be part of the Timiskaming Group, appear to be older "flyschoid" sequences, possibly correlative with sedimentary rocks deposited in the Porcupine syncline at Timmins between 2700 and 2690 Ma.

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Paleozoic Sedimentary Rocks in the Red Dog Zn-Pb-Ag District and Vicinity, Western Brooks Range, Alaska: Provenance, Deposition, and Metallogenic Significance

Economic Geology ◽

10.2113/gsecongeo.99.7.1385 ◽

2004 ◽

Vol 99 (7) ◽

pp. 1385-1414 ◽

Cited By ~ 22

Author(s):

J. F. Slack ◽

J. A. Dumoulin ◽

J. M. Schmidt ◽

L. E. Young ◽

C. S. Rombach

Keyword(s):

Sedimentary Rocks ◽

Brooks Range

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Provenance and Tectonic Implications of Sedimentary Rocks of the Paleozoic Chiron Basin, Eastern Transbaikalia, Russia, Based on Whole-Rock Geochemistry and Detrital Zircon U–Pb Age and Hf Isotopic Data

Minerals ◽

10.3390/min10030279 ◽

2020 ◽

Vol 10 (3) ◽

pp. 279 ◽

Cited By ~ 1

Author(s):

Ludmila I. Popeko ◽

Yulia N. Smirnova ◽

Victor A. Zaika ◽

Andrey A. Sorokin ◽

Sergey I. Dril

Keyword(s):

Siberian Craton ◽

Detrital Zircon ◽

Sedimentary Rocks ◽

Source Area ◽

Major And Trace Elements ◽

Geochemical Data ◽

Island Arcs ◽

Isotopic Data ◽

Tectonic History ◽

Eastern Transbaikalia

The Chiron Basin extends along the southern periphery of the Siberian Craton and the western margin of the Mongol–Okhotsk Belt. Here, we present whole-rock geochemical data (major and trace elements and Sm–Nd isotopes) along with zircon U–Pb geochronology and Lu–Hf isotopic data from Paleozoic sedimentary rocks within the Chiron Basin to investigate their provenance and tectonic history. εNd(t) values of the siliciclastics rocks of the Khara–Shibir, Shazagaitui, and Zhipkhoshi formations vary from −17.8 to −6.6, with corresponding two-stage Nd model ages (tNd(C)) ranging from 2.56 to 1.65 Ga. Detrital zircon grains from these rocks are predominantly Archean, Paleoproterozoic, and Carboniferous–Devonian in age. The data suggest that the southern flank of the Siberian Craton is the only viable source area for Archean and Paleoproterozoic zircon grains with Hf model ages (tHf(C)) of >2.20 Ga. The majority of zircon grains from sandstones from the Khara–Shibir, Shazagaitui, and Zhipkhoshi formations are Devonian–Carboniferous in age. With respect to their Hf model ages, the zircon grains can be subdivided into two groups. The first group of Devonian–Carboniferous zircon grains is characterized by relatively old (mainly Paleoproterozoic) tHf(C) model ages of 2.25–1.70 Ga and the source was the southern margin of the Siberian Craton. The second group of Devonian–Carboniferous zircon grains is characterized by significantly younger (mainly Neoproterozoic) tHf(C) model ages of 1.35–0.36 Ga, which are consistent with a juvenile source, most likely eroded island arcs. Our data, show that sedimentary rocks of the Chiron Basin likely formed in a back-arc basin on the southern periphery of the Siberian Craton facing the Paleozoic Mongol–Okhotsk Ocean.

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Tectonochemistry of the Brooks Range Ophiolite, Alaska

Lithosphere ◽

10.2113/2020/7866789 ◽

2020 ◽

Vol 2020 (1) ◽

Author(s):

Joseph Biasi ◽

Paul Asimow ◽

Ronald Harris

Keyword(s):

Continental Margin ◽

Mineral Chemistry ◽

The Arctic ◽

Geochemical Data ◽

New Mineral ◽

Trace Element Geochemistry ◽

Element Geochemistry ◽

Brooks Range ◽

Arctic Alaska ◽

Intrusive Rocks

Abstract We present new whole-rock geochemical data from the Brooks Range ophiolite (BRO) together with new mineral chemistry data from the BRO, South Sandwich forearc, Izu-Bonin forearc, and Hess Deep. The analyses reveal that the Brooks Range ophiolite (BRO) was most likely created in a forearc setting. We show that this tectonic classification requires the Brookian orogeny to begin at ~163-169 Ma. The middle-Jurassic BRO contains abundant gabbros and other intrusive rocks that are geochemically similar to lithologies found in other forearc settings. Based on major, minor, and trace element geochemistry, we conclude that the BRO has clear signals of a subduction-related origin. High-precision olivine data from the BRO have a forearc signature, with possible geochemical input from a nearby arc. The Koyukuk terrane lies to the south of the Brooks Range; previous studies have concluded that the BRO is the forearc remnant of this arc-related terrane. These studies also conclude that collision between the Koyukuk Arc and the Arctic Alaska continental margin marks the beginning of the Brookian orogeny. Since the BRO is a forearc ophiolite, the collision between the Koyukuk Arc and the continental margin must have coincided with obduction of the BRO. Previously determined 40Ar/39Ar ages from the BRO’s metamorphic sole yield an obduction age of 163-169 Ma. Since the same collisional event that obducts the BRO also is responsible for the Brookian orogeny, we conclude that the BRO’s obduction age of ~163-169 Ma marks the beginning of this orogenic event.

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A Silurian U–Pb age for the Cape St. Mary's sills, Avalon Peninsula, Newfoundland, Canada: implications for Silurian orogenesis in the Avalon Zone

Canadian Journal of Earth Sciences ◽

10.1139/e93-138 ◽

1993 ◽

Vol 30 (8) ◽

pp. 1607-1612 ◽

Cited By ~ 13

Author(s):

John D. Greenough ◽

Sandra L. Kamo ◽

Thomas E. Krogh

Keyword(s):

Sedimentary Rocks ◽

Geochemical Data ◽

Mobile Belt ◽

Ridge Basalt ◽

Tectonic Environment ◽

Mid Ocean Ridge ◽

Mafic Magmas ◽

Ocean Ridge ◽

Avalon Peninsula ◽

Orogenic Events

Mafic sills from Cape St. Mary's on the Avalon Peninsula of Newfoundland give an U–Pb baddeleyite age of 441 ± 2 Ma. This age corresponds with the earliest ages recorded for the climactic Silurian orogenic event that dominantly affected rocks of the Central Mobile Belt in Newfoundland. The age is consistent with but in no way necessitates that the Avalon and Gander zones were juxtaposed during the Silurian. Because sills tend to form in poorly lithified and undeformed sedimentary rocks, it is unlikely that Cambrian sediments hosting the sills were affected by Ordovician orogenic events that strongly affected central Newfoundland. Negative Nb and Ti anomalies on mid-ocean-ridge basalt normalized diagrams show that the sill geochemistry is consistent with formation in a transpressional tectonic environment. Mafic magmas clearly associated with the Silurian event share these chemical and tectonic affinities. Thus both the age and geochemical data are consistent with but do not require a link between the Gander and Avalon zones during the Silurian. If the two zones were joined prior to the Silurian then the Avalon must have been distal to both the Ordovician and Silurian orogenic activity. Further, considerable post-Silurian movement would have had to occur along the bounding Hermitage–Dover fault to account for contrasts in the intensity of metamorphism, plutonism, and deformation between the Gander and Avalon zones.

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Reappraisal of the Mesozoic tectonic transition from the Paleo-Tethyan to Paleo-Pacific domains in South China

Geological Society of America Bulletin ◽

10.1130/b35755.1 ◽

2021 ◽

Author(s):

Chengshi Gan ◽

Yuzhi Zhang ◽

Yuejun Wang ◽

Xin Qian ◽

Yang Wang

Keyword(s):

South China ◽

Middle Jurassic ◽

Late Jurassic ◽

Sedimentary Rocks ◽

Early Jurassic ◽

Igneous Rocks ◽

Late Triassic ◽

Geochemical Data ◽

South China Block ◽

Tectonic Transition

The southeastern (SE) South China Block was mainly influenced by the Paleo-Tethyan and Paleo-Pacific dynamic domains during the Mesozoic. The initial timing of the tectonic transition between these two domains in the SE South China Block still remains debated. The transition would affect the nature of the lithosphere and material provenance of sediments, and, therefore, igneous and sedimentary rocks in the area could record such dynamic processes. In this study, published geochronological and geochemical data of the Triassic and Jurassic igneous rocks and detrital zircon data of contemporaneous sedimentary rocks in the SE South China Block were compiled, aiming to provide constraints on the tectonic transition via tracing the spatial-temporal variations in the nature of the lithosphere and sedimentary provenance signals. The compiled results suggest that the magmatic intensity and volume decreased significantly from the Late Triassic to Early−Middle Jurassic, with an obvious magmatic quiescence between them, and increased from the Early−Middle Jurassic to Late Jurassic. The εNd(t) and zircon εHf(t) values of mafic rocks, granitoids, and shoshonitic rocks remarkably increased from the Late Triassic to Early−Middle Jurassic, indicative of variations in the lithospheric mantle and continental crust. Such variations suggest that the initial tectonic transition occurred at the earliest Early Jurassic. Based on the southward paleocurrents from Early Jurassic sandstone, E-W−trending extension of Early−Middle Jurassic mafic and shoshonitic rocks, and similar sedimentary provenances of Late Triassic and Early−Middle Jurassic sedimentary rocks, these features imply that the SE South China Block was not immediately influenced by the Paleo-Pacific domain during the Early−Middle Jurassic. However, from the Early−Middle Jurassic to Late Jurassic and Early Cretaceous, the spatial distribution, geochemical signatures, magmatic intensity, and magmatic volume of igneous rocks and provenance of sedimentary rocks exhibit obvious variations, and the regional fold hinge direction changed from E-W−trending to NE-trending, suggesting significant effects from Paleo-Pacific subduction on the SE South China Block. Thus, the Mesozoic tectonic transition from the Paleo-Tethyan to the Paleo-Pacific dynamic domain in the SE South China Block likely occurred during the Early−Middle Jurassic.

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Multiple episodes of Cenozoic denudation in the northeastern Brooks Range: fission-track data from the Okpilak batholith, Alaska

Canadian Journal of Earth Sciences ◽

10.1139/e95-092 ◽

1995 ◽

Vol 32 (8) ◽

pp. 1106-1118 ◽

Cited By ~ 13

Author(s):

Paul B. O'sullivan ◽

Catherine L. Hanks ◽

Wesley K. Wallace ◽

Paul F. Green

Keyword(s):

Fission Track ◽

Middle Eocene ◽

Sedimentary Rocks ◽

Late Oligocene ◽

Brooks Range ◽

Rapid Cooling ◽

Zircon Fission Track ◽

Fault Bend ◽

Thrust Sheets ◽

Uplift And Erosion

The northeastern Brooks Range of Alaska is a complex Mesozoic to Cenozoic northward-verging fold and thrust belt. In response to regional compression, shortening in the upper crust has occurred through the duplexing of thrust sheets and formation of associated fault-bend folds. Apatite and zircon fission-track data from the Okpilak batholith and adjacent sedimentary rocks exposed within the northeastern Brooks Range provide new constraints on the timing, magnitude, and rate of cooling of these thrust sheets as they were rapidly denuded in response to uplift during Cenozoic time. Fission-track results indicate that a previously recognized episode of Paleocene cooling was followed by at least two younger episodes of rapid cooling during Middle Eocene and Late Oligocene time. The two younger episodes of rapid cooling are interpreted to reflect denudation in response to uplift resulting from Cenozoic thrusting and related folding. As a result of structural thickening, up to 8 km of material was eroded from the top of the batholith between ~41–45 Ma (Middle Eocene). Renewed shortening and emplacement of an underlying thrust sheet at ~25 Ma (Late Oligocene) resulted in at least 2 km of uplift and erosion of sedimentary rocks immediately north of the batholith. These results suggest that, even though Paleocene uplift and erosion may have occurred across the northeastern Brooks Range, the major episode of thrust faulting, responsible for structural emplacement of the batholith into its present position and kilometre-scale denudation, most likely occurred during Middle Eocene time.

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Organic geochemical data for Mesozoic and Paleozoic shales, central and eastern Brooks Range, Alaska

Open-File Report ◽

10.3133/ofr81551 ◽

1981 ◽

Author(s):

William Peters Brosge ◽

H.N. Reiser ◽

J.T. Dutro ◽

R.L. Detterman

Keyword(s):

Geochemical Data ◽

Brooks Range

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Intrusion history of the Portrush Sill, County Antrim, Northern Ireland: evidence for rapid emplacement and high-temperature contact metamorphism

Geological Magazine ◽

10.1017/s0016756811000537 ◽

2011 ◽

Vol 149 (1) ◽

pp. 67-79 ◽

Cited By ~ 5

Author(s):

MORGANE LEDEVIN ◽

NICHOLAS ARNDT ◽

MARK R. COOPER ◽

GARTH EARLS ◽

PAUL LYLE ◽

...

Keyword(s):

Northern Ireland ◽

Sedimentary Rocks ◽

Lower Jurassic ◽

Contact Metamorphism ◽

Geochemical Data ◽

Contact Aureole ◽

The North ◽

Geochemical Analyses ◽

Element Enrichment ◽

County Antrim

AbstractThe gabbroic Portrush Sill in Northern Ireland, part of the North Atlantic Igneous Province, intruded Lower Jurassic mudstones and siltstones about 55 Ma ago. We used petrologic observations and geochemical analyses to study how the sill interacted with the sedimentary rocks. Field relationships show that an Upper Sill and numerous associated Minor Intrusions were emplaced in the sedimentary host rocks before intrusion of the Main Sill, some 10 m above its upper contact. Geochemical analyses reveal two magma contamination processes: Nb and Ta anomalies, coupled with incompatible element enrichment, record contamination by deep crustal rocks, whereas Li, Pb and Ba anomalies reveal a superficial contamination through fluid circulation at the contact between magmatic and sedimentary rocks. Analysis of mineral assemblages and geochemical data from the contact aureole demonstrate uniform metamorphic conditions between the two main intrusions and an absence of a thermal gradient. The identification of pyrrhotite by magnetization analyses and of orthopyroxene by microprobe analyses indicates very high temperatures, up to 660°C. Thermal modelling explains these temperatures as the coupled effects of the Main Sill and the earlier intruded Upper Sill and Minor Intrusions. Even though the chemical composition of the Main Sill suggests another type of parental liquid, all three units were emplaced in a very short time, certainly less than five years.

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