Detrital zircon U-Pb ages and whole-rock geochemistry of early Paleozoic metasedimentary rocks in the Mongolian Altai: Insights into the tectonic affinity of the whole Altai-Mongolian terrane

2019 ◽  
Vol 132 (3-4) ◽  
pp. 477-494
Author(s):  
Xiaoping Long ◽  
Jin Luo ◽  
Min Sun ◽  
Xuan-ce Wang ◽  
Yujing Wang ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Age Distribution ◽  
Isotopic Analysis ◽  
Detrital Zircons ◽  
Cumulative Distribution ◽  
Early Paleozoic ◽  
Zircon Age ◽  
Western Margin ◽  
Metasedimentary Rocks ◽  
Mongolian Altai

Abstract The tectonic affinity of the terranes and microcontinents within the Central Asian Orogenic Belt (CAOB) remains controversial. The Altai-Mongolian terrane (AMT), as a representative tectonic unit in the Mongolian collage, plays a vital role in reconstructing evolution history of the CAOB. The well-preserved early Paleozoic sedimentary sequence covering in this terrane could be considered as a fingerprint to track its provenance and tectonic affinity. Here, we present new whole-rock geochemistry, detrital zircon U-Pb dating, and Hf isotopic analysis for the metasedimentary rocks from the Mongolian Altai in order to shed new light on the tectonic affinity of the AMT. The youngest detrital zircon ages and the regional intrusions constrain the depositional time of the Mongolian Altai sequence to between Late Silurian and Early Devonian, which is consistent with the Habahe group in the western Chinese Altai. The features of whole-rock geochemistry and the cumulative distribution curves of the detrital zircon age spectra indicate that the Mongolian Altai sequence was probably deposited in an active continental setting during early Paleozoic. The zircon age spectra of our samples are all characterized by a main age group in the early Cambrian (peak at 541 Ma, 522 Ma, 506 Ma and 496 Ma, respectively), subdominant age populations during the Tonian, as well as rare older zircons. The nearby Lake Zone of Ikh-Mongol Arc most likely provided plenty of early Paleozoic materials, the subdominant Neoproterozoic detrital zircons could be supplied by the felsic intrusions along the western margin of the Tuva-Mongol microcontinent, and the sparse older zircons may be derived from its basement material. The Precambrian age distribution of the AMT is quite similar to both the Tarim and Siberia cratons, but the Siberia Craton displays a closer resemblance in Hf isotopic composition with the AMT. Thus, we believe that the Siberia Craton contains a closer tectonic affinity with the AMT, and that the Tuva-Mongol microcontinent possibly rifted from the western margin of this craton after the Tonian. To the south of the AMT, recent studies indicated the Yili and Central Tianshan blocks in the Kazakhstan collage of the western CAOB likely have a closer affinity with Gondwana. Therefore, the microcontinents in the CAOB most likely derived bilaterally from both the Siberia Craton and the Gondwana supercontinent. Moreover, our Hf isotopic compositions indicate two significant continental growth events in the Tonian and early Paleozoic, respectively.

Enigmatic provenance signature of sandstone from the Okwa Group, Botswana

2020 ◽  
Vol 123 (3) ◽  
pp. 331-342
Author(s):  
T. Andersen ◽  
M.A. Elburg ◽  
J. Lehmann
Keyword(s):  
South Africa ◽  
Detrital Zircon ◽  
Sedimentary Rock ◽  
Age Distribution ◽  
Sedimentary Rocks ◽  
Detrital Zircons ◽  
Significant Shift ◽  
Zircon Age ◽  
Three Samples ◽  
Isotope Distributions

Abstract Detrital zircon grains from three samples of sandstone from the Tswaane Formation of the Okwa Group of Botswana have been dated by U-Pb and analysed for Hf isotopes by multicollector LA-ICPMS. The detrital zircon age distribution pattern of the detrital zircons is dominated by a mid-Palaeoproterozoic age fraction (2 000 to 2 150 Ma) with minor late Archaean – early Palaeoproterozoic fractions. The 2 000 to 2 150 Ma zircon grains show a range of epsilon Hf from -12 to 0. The observed age and Hf isotope distributions overlap closely with those of sandstones of the Palaeoproterozoic Waterberg Group and Keis Supergroup of South Africa, but are very different from Neoproterozoic deposits in the region, and from the Takatswaane siltstone of the Okwa Group, all of which are dominated by detrital zircon grains younger than 1 950 Ma. The detrital zircon data indicate that the sources of Tswaane Formation sandstones were either Palaeoproterozoic rocks in the basement of the Kaapvaal Craton, or recycled Palaeoproterozoic sedimentary rocks similar to the Waterberg, Elim or Olifantshoek groups of South Africa. This implies a significant shift in provenance regime between the deposition of the Takatswaane and Tswaane formations. However, the detrital zircon data are also compatible with a completely different scenario in which the Tswaane Formation consists of Palaeoproterozoic sedimentary rock in tectonic rather than depositional contact with the other units of the Okwa Group.

Early-Paleozoic geodynamics of the Altai orogen: Constraints from geochemical and zircon U-Pb-Hf isotopic study of paragneissic rocks from the southern Chinese Altai

2020 ◽  
Author(s):  
Xing Cui ◽  
Min Sun ◽  
Guochun Zhao ◽  
Yunying Zhang ◽  
Jinlong Yao ◽  
...  
Keyword(s):  
Active Continental Margin ◽  
Detrital Zircons ◽  
Igneous Rocks ◽  
Cumulative Distribution ◽  
Geochemical Data ◽  
Accretionary Wedge ◽  
Early Paleozoic ◽  
Isotopic Study ◽  
Zircon Age ◽  
Southern Chinese

<p>The high-grade metamorphic complexes in the Chinese Altai were previously regarded as the Precambrian basement and thus important for unravelling tectonic evolution of the Altai orogen. This study reports detailed filed investigation, zircon U-Pb-Hf isotopic and whole-rock geochemical data for the paragneissic rocks from Northern Fuyun Complex (NFC), southern Chinese Altai. Detrital zircons from the paragneisses have a predominant early Paleozoic age population (ca. 535-435 Ma), with minor Neoproterozoic and sparse Mesoproterozoic to Archean ages. The geochemical analyses together with the euhedral shape of the detrital zircons suggest that their sedimentary protoliths mainly came from felsic-intermediate igneous rocks with low maturity. In combination with the cumulative distribution curves of zircon age spectra, the variable zircon εHf(t) values (-25 to +13), as well as the immature geochemical compositions, we infer that the protoliths were most likely deposited on an active continental margin in the early Paleozoic and sourced mainly from proximal igneous rocks, which are comparable to the Habahe Group. Similar detrital zircon age spectra of early Paleozoic sequences from the Chinese Altai, Mongolia Altai and Khovd Zone support the existence of a giant accretionary wedge developed along the western margin of the Ikh-Mongol Arc system, resulting from continuous northeast-dipping oceanic subduction. This research was financially supported by the National Key R&D Program of China (2017YFC0601205), Hong Kong RGC GRF (17302317 and 17303415) and NSFC Projects (41730213 and 41190075).</p>

Detrital zircon age distribution characteristics of Jurassic sandstone from the Southern Yili basin, China

2020 ◽  
pp. 002072092094060
Author(s):  
Chao Wang ◽  
Wenjian Jiang ◽  
Xin Shi ◽  
Huaisheng Zhang
Keyword(s):  
Detrital Zircon ◽  
Middle Jurassic ◽  
Age Distribution ◽  
Orogenic Belt ◽  
Detrital Zircons ◽  
The South ◽  
Zircon Age ◽  
Clastic Sediments ◽  
Wide Range ◽  
South Tianshan

The Central Asia orogenic belt contains a wide range of structural elements, including micro continent, back arc system, ocean island/plateau, ophiolite and subduction accretion complex. But its final closing time has been controversial. Based on the magmatic age of the surrounding orogenic belt, the source of this set of clastic sediments is determined, which provides new important evidence for the evolution of the South Tianshan orogenic belt. The results show that the Jurassic detrital zircons from the study area were mainly derived from magmatic zircons and are deposited in a proximal source. The detrital zircon age of the Lower Jurassic Badaowan and Sangonghe Formation are concentrated in 290–260 Ma, and in 350–290 Ma and 460–390 Ma, respectively. The detrital zircon age of the Middle Jurassic Xishanyao Formation concentrates in 370–320 Ma and 450–390 Ma. There are very few zircons from the Precambrian period. These ages are consistent with the timing, indicating these clastic sediments were mainly originated from the southern margin of the Yili - Middle Tianshan Block. The Late Permian - Middle Triassic detrital zircons almost do not exist, implying that there were no contemporary magmatism related to collision or post-collision in the South Tianshan district, its complex evolution and orogenic stage are still a challenging topic. In the ancient active plate margin, the sedimentary records in the pre-arc basin can provide more information about the magmatic arc and basin-orogen coupling than the present exposed arc itself. The rhyolite, trachyte, and trachyandesite of the Dahalajunshan Formation were widely developed in the Yili - Middle Tianshan Block during the Early Carboniferous. During the formation of Wulang Formation in the Early Permian, a large number of rhyolite were developed. The age data of 75 detrital zircons were obtained from the sandstone (J1s-5) of the Sangonghe Formation, of which 74 zircons have a concordance degree of over 90%, and their age data also fall on the harmonic curv. In addition, the age of the youngest zircons increased gradually from Early to Middle Jurassic, indicating that the sediments in this period had the feature of uncovering. Our study provides a good reference for the analysis of provenance and regional tectonic evolution.

Preliminary detrital zircon U-Pb Geochronology of the Wasatch Formation, Powder River Basin, Wyoming

2019 ◽  
Vol 56 (3) ◽  
pp. 247-266
Author(s):  
Ian Anderson ◽  
David H. Malone ◽  
John Craddock
Keyword(s):  
River Basin ◽  
Detrital Zircon ◽  
Middle Part ◽  
Detrital Zircons ◽  
Powder River Basin ◽  
Zircon Age ◽  
Lower Eocene ◽  
The North ◽  
Mountain Front ◽  
Fluvial Sandstone

The lower Eocene Wasatch Formation is more than 1500 m thick in the Powder River Basin of Wyoming. The Wasatch is a Laramide synorgenic deposit that consists of paludal and lacustrine mudstone, fluvial sandstone, and coal. U-Pb geochronologic data on detrital zircons were gathered for a sandstone unit in the middle part of the succession. The Wasatch was collected along Interstate 90 just west of the Powder River, which is about 50 km east of the Bighorn Mountain front. The sandstone is lenticular in geometry and consists of arkosic arenite and wacke. The detrital zircon age spectrum ranged (n=99) from 1433-2957 Ma in age, and consisted of more than 95% Archean age grains, with an age peak of about 2900 Ma. Three populations of Archean ages are evident: 2886.6±10 Ma (24%), 2906.6±8.4 Ma (56%) and 2934.1±6.6 Ma (20%; all results 2 sigma). These ages are consistent with the age of Archean rocks exposed in the northern part of the range. The sparse Proterozoic grains were likely derived from the recycling of Cambrian and Carboniferous strata. These sands were transported to the Powder River Basin through the alluvial fans adjacent to the Piney Creek thrust. Drainage continued to the north through the basin and eventually into the Ancestral Missouri River and Gulf of Mexico. The provenance of the Wasatch is distinct from coeval Tatman and Willwood strata in the Bighorn and Absaroka basins, which were derived from distal source (>500 km) areas in the Sevier Highlands of Idaho and the Laramide Beartooth and Tobacco Root uplifts. Why the Bighorn Mountains shed abundant Eocene strata only to the east and not to the west remains enigmatic, and merits further study.

U–Pb geochronology of Late Cretaceous and early Tertiary plutons in the northern Coast Mountains batholith

1991 ◽  
Vol 28 (6) ◽  
pp. 899-911 ◽  
Author(s):  
George E. Gehrels ◽  
William C. McClelland ◽  
Scott D. Samson ◽  
P. Jonathan Patchett ◽  
David A. Brew
Keyword(s):  
Shear Zone ◽  
Late Cretaceous ◽  
Detrital Zircons ◽  
Northern Coast ◽  
Coast Mountains ◽  
Western Margin ◽  
Early Proterozoic ◽  
Isotopic Signatures ◽  
Metasedimentary Rocks ◽  
Early Tertiary

U–Pb geochronologic studies demonstrate that steeply dipping, sheetlike tonalitic plutons along the western margin of the northern Coast Mountains batholith were emplaced between ~83 and ~57 (perhaps ~55) Ma. Less elongate tonalitic–granodioritic bodies in central portions of the batholith yield ages of 59–58 Ma, coeval with younger phases of the tonalitic sheets. Large granite–granodiorite bodies in central and eastern portions of the batholith were emplaced at 51–48 Ma. Trends in ages suggest that the tonalitic bodies generally become younger southeastward and that, at the latitude of Juneau, plutonism migrated northeastward across the batholith at ~0.9 km/Ma. Variations in the age, shape, location, and degree of fabric development among the various plutons indicate that Late Cretaceous – Paleocene tonalitic bodies were emplaced into a steeply dipping, dip-slip shear zone that was active along the western margin of the batholith. Postkinematic Eocene plutons were emplaced at shallow crustal levels. Inherited zircon components in these plutons range in age from mid-Paleozoic to Early Proterozoic and are coeval with detrital zircons in adjacent metasedimentary rocks. These old zircons, combined with evolved Nd isotopic signatures for most plutons, record assimilation of continental crustal or supracrustal rocks during the generation and (or) ascent of the plutons.

Detrital zircon geochronology of metasedimentary rocks in the southern Omineca Belt, Canadian Cordillera

1991 ◽  
Vol 28 (8) ◽  
pp. 1254-1270 ◽  
Author(s):  
Gerald M. Ross ◽  
Randall R. Parrish
Keyword(s):  
Detrital Zircon ◽  
Bimodal Distribution ◽  
Detrital Zircons ◽  
Detrital Zircon Geochronology ◽  
Early Proterozoic ◽  
Metasedimentary Rocks ◽  
Basement Rocks ◽  
Two Samples ◽  
Alberta Basin ◽  
Detrital Zircon Ages

We address two problems of Cordilleran geology in this study using U–Pb dating of single detrital zircon grains from metasedimentary rocks: the provenance of the Windermere Supergroup, and the age and correlation of metasedimentary rocks within the Shuswap Complex that are at high metamorphic grade. Because some of these rocks are clearly of North American affinity, the ages of zircons provide indirect constraints on the age and distribution of continental basement from which the zircons were derived.A consistent pattern emerges from ages of about 50 grains from six rocks. Nearly all samples analyzed (48–53°N) are characterized by a bimodal distribution of zircon ages of 1.65–2.16 Ga and > 2.5 Ga, with a distinct lack of ages between 2.1 and 2.5 Ga. Exceptions to this pattern are young zircons from two samples, from Valhalla and Grand Forks – Kettle complexes of southeastern British Columbia, that have grains 1435 ± 35 and 650 ± 15 Ma, respectively. These younger grains are inferred to have been derived from magmatic rocks, and they have no obvious source in either the Canadian Shield or the Alberta subsurface basement to the east. The Early Proterozoic and Archean ages of detrital zircons resemble those of dated basement rocks beneath the Alberta Basin as well as basement exposed within the Cordilleran hinterland (gneisses of Thor–Odin, Frenchman Cap, and Malton regions). However, 2.1–2.4 Ga rocks that are extensive in the subsurface of northern Alberta are not represented in the inventory of detrital zircon ages presented in this paper.This pattern suggests that much of the Cordilleran basement between these latitudes is underlain by Archean crust of the Hearne–Wyoming provinces that may be mantled to the west by an orogenic–magmatic belt of Early Proterozoic (1.7–1.9 Ga) age which may largely have been parallel to the present Cordilleran orogen.

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