Subordinate Peaks Research Articles

Continental-scale sediment mixing and dispersal across northern Gondwana: detrital zircon U-Pb-O-Hf isotopic evidence from the Cambro-Ordovician sandstones overlying the Arabian Shield

ABSTRACT The juvenile Neoproterozoic basement of the Arabian Shield is overlain with angular unconformity by a voluminous Cambro-Ordovician cover sequence known as the Saq Formation and Wajid Group. Provenance studies of this vast siliciclastic cover over the Saudi Arabian part of the Arabian-Nubian Shield (ANS) have to date been based solely on U-Pb zircon data and heavy minerals. We present the first combined in-situ U-Pb, δ18O and Lu-Hf isotopic data for detrital zircon from the Saq and Wajid units exposed along the northeastern margin and southern part of the Arabian Shield. U-Pb age spectra reveal prominent age peaks at ca. 0.8–0.55 Ga and 1.1–0.9 Ga with subordinate peaks at ca. 2.2–1.7 Ga and 2.7–2.5 Ga. The δ18O secular variation mirrors global compilations with Archaean zircon defining a restricted δ18O range of ca. 4.0–8.0 ‰ and younger zircon showing wide variation in δ18O up to ca. 14 ‰. The ca. 0.8–0.55 Ga age peak has the largest variation in εHf(t) with about half of all these Neoproterozoic zircon grains being juvenile (εHf(t) > 5), which are interpreted to be sourced from the juvenile terranes of the ANS. Neoproterozoic zircon with evolved εHf(t) signatures require a more distal source beyond the ANS. As extensive ca. 1.1–0.9 Ga crust is lacking in the vicinity of the ANS, the ca. 1.1–0.9 Ga age peak is interpreted to be derived from either contemporaneous orogenic belts in Central Africa or recycled from older sedimentary rocks containing these age components. Extreme variations in δ18O of post–Archaean zircon, together with the evolved εHf(t), indicate crustal thickening and increased incorporation of supracrustal material associated with collisional orogenesis. The remarkable similarities in age spectra and isotopic compositions of the Saq Formation and Wajid Group sandstones with those from other regions in northern Gondwana indicate a continental–scale homogenization and dispersion process.

The diversity of spectral shapes of hydrogen Lyman lines and Mg II lines in a quiescent prominence

Context. Broad sets of spectroscopic observations comprising multiple lines represent an excellent opportunity for diagnostics of the properties of the prominence plasma and the dynamics of their fine structures. However, they also bring significant challenges when they are compared with synthetic spectra provided by radiative transfer modeling. Aims. In this work, we provide a statistical spectroscopic analysis of a unique dataset of coordinated prominence observations in the Lyman lines (Lyα to Lyδ) and the Mg II k and h lines. The observed data were obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrograph on board of the Solar and Heliospheric Observatory (SoHO) satellite and the Interface Region Imaging Spectrograph (IRIS) on 22 October 2013. Only a few similar coordinated datasets of Lyman and Mg II k and h observations have ever been obtained in prominences and we present here the first analysis using these two sets of spectral lines. Moreover, for the first time, we assess the influence of noise on the statistical properties of the studied profile characteristics. Methods. We focus on the following profile characteristics: the shape of the observed line profiles based on the number of distinct peaks, the integrated line intensity, the center-to-peak ratio describing the depth of the reversal of two-peaked profiles, and the asymmetry of these peaks. Results. We show that the presence of noise has a negligible effect on the integrated intensity of all observed lines, but it significantly affects the classification of spectral profiles using the number of distinct peaks, the reversal depth, and also the peak asymmetry. We also demonstrate that by taking the influence of noise into account, we can assess which profile characteristics in which spectral lines are suitable for diagnostics of different properties of the observed prominence. For example, we show that the subordinate peaks (peaks below error bars) in the Lyman line profiles are mostly caused by noise, which means that only the dominant peaks should be used for statistical analyses or comparisons with synthetic spectra. On the other hand, in the Mg II k and h profiles, the key role in the distinction between the multi-peaked profiles with low peaks and the profiles with deep reversals is played by the dynamics of multiple fine structures located along a line of sight. The complex, multi-peaked profiles are observed in places where multiple fine structures with different line-of-sight velocities are crossing the line of sight, while the profiles with deep reversals likely correspond to instances when we observe single fine structures or more fine structures but with similar line-of-sight velocities. Conclusions. This study allows us to conclude that if we are interested in the diagnostics of the dynamics of prominence fine structures, the best approach is to use a combination of profile asymmetry in the Lyman lines together with the complex profiles of Mg II k and h lines. On the other hand, if we want to diagnose the temperature and pressure properties of individual prominence fine structures, we need to focus on the deeply reversed Mg II k and h lines in combination with the Lyman lines and to analyze the depth of the central reversal and the integrated intensities.

Detrital composition and sedimentary provenance of Early Carboniferous Al-bearing rock series in central Guizhou

The Early Carboniferous Al-bearing rock series in central Guizhou is an important bauxite ore-bearing and Li-rich stratigraphic unit. The origin and correlation of detrital zircon ages from different types of Al-bearing rock series will provide new insights into the sedimentary processes and metallogenic mechanisms. We present the detrital zircon U-Pb ages and Hf isotopic compositions from the Early Carboniferous Al-bearing rock series and underlying Ordovician clastic rocks (Tongzi and Meitan Formation). The early Carboniferous Al-bearing rock series in the central Guizhou show two dominant age peaks at ca. 980–960 Ma and 540–530 Ma and several subordinate age peaks (ca. 2500 Ma, 820–780 Ma, and 630–610 Ma). The deposition of the Al-bearing rock series occurred near the direct source and the provenance of the Jiujialu Formation mainly originated from the recycled sedimentary bedrock of underlying Ordovician stratigraphic units. Most recycled clastic materials of the Early Carboniferous Al-bearing rock series originated from external sources outside the South China Block. Ferrous clay rocks and Aluminous clay rocks show two age peaks at ca. 540 Ma and 970 Ma. Detrital zircon from the bauxite diposits shows multiple detrital age peaks, reflecting the supply of multiple provenances. Aluminous or Ferrous clay rocks are more widespread in the southern segment of central Guizhou may be related to the early carboniferous transgression.

Provenance of Ordovician Malieziken Group, Southwest Tarim and Its Implication on the Paleo-Position of Tarim Block in East Gondwana

Tarim is inferred to have a close connection with East Gondwana during the Ordovician, but the position in East Gondwana remains controversial. In this study, we report 316 detrital zircons U-Pb data from three samples of Ordovician Malieziken Group sedimentary rocks, collected in the Qiate Section, Southwest Tarim, provided new insight into the position of Tarim in East Gondwana. Detrital zircons data indicated the maximum depositional age for the three samples is 489.5 Ma, 478.1 Ma, and 465 Ma, respectively, indicating the Qiate and Kandilike Formation of the Malieziken Group was deposited in Early—Middle Ordovician. The detrital zircons are characterized by two main peaks at ~490 Ma and ~1100 Ma, and three subordinate peaks at ~880 Ma, ~1400 Ma, and ~1650 Ma, suggesting most of the detritus of Malieziken Group from the South Kunlun Terrane (SKT) itself. However, the source of the ~1650 Ma peak is not found in the Tarim block, and the ~1400 Ma and the ~1650 Ma peak are absent in the middle of the three samples, which implied that there is an exotic source. The Paleoproterozoic sediment strata in the Albany–Fraser belt shows dominant peaks at ~1400 Ma and ~1650 Ma may have been transported to SKT and redeposited in the Malieziken Group during the Ordovician. The Malieziken Group shows detrital zircon age patterns resembling those of East Sumatra, Lhasa, and Western Australia which, in combination with the Albany–Fraser belt provenance, enables us to propose that the Tarim block has a close linkage with Western Australia, East Sumatra, and Lhasa in East Gondwana.

U–Pb Zircon Ages and Geochemistry of the Wuguan Complex and Liuling Group: Implications for the Late Paleozoic Tectonic Evolution of the Qinling Orogenic Belt, Central China

The tectonic evolution of the Qinling orogen is key to understanding the process of convergence between the North China Block (NCB) and the South China Block (SCB). The Wuguan Complex and Liuling Group, situated along the southern margin of the Shangnan–Danfeng suture zone (SDSZ) between the North Qinling Terrane (NQT) and the South Qinling Terrane (SQT), are important indicators of the late Paleozoic tectonic evolution of the Qinling orogen. In this paper, the detrital zircon U–Pb geochronology and geochemical analysis of the Wuguan Complex and Liuling Group are carried out. Detrital zircons from two metasedimentary rock samples of the Liuling Group yield a major age peak at 460 Ma and two subordinate peaks at 804 Ma and 920 Ma, with a few older grains having formed between 1000–2549 Ma. One metasedimentary rock sample of the Wuguan Complex has a similar age spectrum as that of the Liuling Group, which shows the main age peak at 440 Ma and two subordinate peaks at 786 and 927 Ma, indicating all detrital zircon age results have the same source area. Geochemical analyses suggest that the sedimentary rocks of the Liuling Group and part of the Wuguan Complex were deposited in the tectonic setting of the continental island arc (CIA), while the geochemical characteristics of the other group of sedimentary rocks of the Wuguan Complex indicate the mixing of basic rock sources. The protolith of garnet amphibolite and hornblende schist, which were collected from the Wuguan Complex, were classified as andesite and basalt, with the nature of arc andesite and oceanic island basalt, respectively. In combination with regional data, we suggest that the Liuling Group and the Wuguan Complex were deposited in a fore-arc basin. Additionally, the Wuguan Complex was subsequently incorporated into the tectonic mélange by the northward subduction of the Paleo-Qinling Ocean. Zircons from the subduction-related metamorphic igneous rocks in the Wuguan Complex yielded a weighted mean age of 365 ± 19 Ma, indicating that the Paleo-Qinling Ocean between the SQT and NQT was still subducted at the end of Devonian.

Sandstones of the Itmurundy accretionary complex, central Kazakhstan, as archives of arc magmatism and subduction erosion: Evidence from U-Pb zircon ages, geochemistry and Hf-Nd isotopes

Sandstones hosted by Pacific-type orogenic belts and related accretionary complexes carry records of their source intra-oceanic or continental magmatic arcs. Study of arc-derived sandstones is important for reconstructing tectonic evolution of Pacific-type convergent margins in case such arcs get partly or completely eroded during subduction. In this paper, we present first U-Pb detrital zircon ages and Hf-in-zircon isotope ratios and whole-rock geochemical and Nd data from Ordovician to early Silurian clastic sediments (sandstones) of the Itmurundy Pacific-type orogenic belt and its hosted accretionary complex (AC). The Itmurundy AC is located in the northern Balkhash area of central Kazakhstan and includes sandstones of the Itmurundy and Kazyk fms. (central segment) and Tyuretai Fm. (eastern segment). The U-Pb ages of detrital zircons from Group 1 sandstones show unimodal distributions with major peaks at ca. 467–456 Ma and the youngest clusters of ages from 442 to 439 Ma Ma suggesting post-Llandovery deposition. The distributions of the U-Pb ages of detrital zircons from Group 2 sandstones are polymodal with major peaks at ca. 462–461 Ma and subordinate peaks at 788, 992, 2472 Ma. The Group 2 zircons yielded two youngest clusters of U-Pb ages: 458 Ma and 424 Ma suggesting post-middle Ordovician and post-Ludlow maximum depositional ages. According to petrographic classifications, both Group 1 and 2 sandstones are poorly-sorted and poorly-rounded greywacke or litharenite. The chemical compositions imply that these sandstones are immature and weakly weathered sediments. The Group 1 greywackes are characterized by relatively low SiO2 (63 wt%) compared to Group 2 greywackes (SiO2 = 66 wt% in average). The major and trace element compositions of both groups of sandstones resemble those of supra-subduction andesitic to dacitic volcanic rocks. The positive values of whole-rock ɛNd(t) (+1 to + 5.3) and zircon ɛHf(t) (+9.8 to +17.5) obtained from the Group 1 greywackes suggest juvenile igneous rocks in the source area. On the contrary, the negative values of ɛNd(t) (−7.2) and variable values of zircon ɛHf(t) (−24.5 to +11.5) from the Group 2 sandstones suggest that their parental igneous rocks were derived from mantle sources possessing both juvenile and recycled characteristics. Conclusively, the greywacke sandstones of both groups formed by erosion of an Ordovician intra-oceanic volcanic arc once existed at an active margin of the Paleo-Asian Ocean, however those of Group 1 deposited in a fore-arc basin and trench, while those of Group 2 deposited in a back-arc basin.

Provenance and tectonic setting of the Statherian Hangaoshan Group: Implications for evolution of the North China Craton during late Paleoproterozoic

The Hangaoshan Group, mainly composed of siliciclastic rocks, is one of the best-preserved sedimentary units exposed in the central North China Craton (NCC) from the Statherian Period. The Hangaoshan Group overlies the Paleoproterozoic Jiehekou Group and underlies Cambrian strata, with both contacts representing unconformities. Detrital zircon U-Pb dating and regional stratigraphic correlation constrain the depositional age of the Hangaoshan Group during ca. 1.8–1.69 Ga. High CIA (>62), low ICV (mostly 0.25–1.12) values and high SiO2/Al2O3 (2.5–22.2) ratios are suggestive of mature sources that experienced moderate to intensive chemical weathering. Low textural and compositional maturity indicate that the provenance of the Hangaoshan Group is mainly proximal deposition. Large proportion of quartz grains, light REEs enrichment relative to heavy REEs ((La/Yb)N = 4.37–33.7), negative Eu anomalies (δEu = 0.41–0.79), high Th/Co (0.44–20.5), high La/Sc (1.35–17.2) ratios, low La/Th (0.99–9.64) ratio and low Hf content (1.34–24.5) suggest that the provenances are mainly composed of felsic magmatic rocks with minor contributions from intermediate-basic meta-volcanic rocks, which is also supported by the A-CN-K, Al2O3-Fe2O3T*2-MgO*2 and Co-Nb-Y diagram. Detrital zircon ages from the Hangaoshan Group are mostly between 2.26 Ga and 1.84 Ga with a notable peak at 2.18 Ga and two subordinate peaks at 2.08 Ga and 1.98 Ga. Geochronological and isotopic similarity suggests that the Chijianling-Guandishan TTG and the Jiehekou Group in the Lvliang area are the dominant sources for the Hangaoshan Group, while the Yejishan Group, 2.2 Ga mafic meta-volcanic rocks, and Huijiazhuang and Xiyupi granite also contributed to lesser degrees. In terms of petrological characteristics, most gravels in the lower conglomerate of the 3rd Formation (Fm) are sandstone fragments of the 1st and 2nd Fm, suggesting that the 3rd Fm is mainly derived from the older diagenetic rocks of the Hangaoshan Group, with a lesser amount of basement rocks. Generally, the Hangaoshan Group was likely deposited in a rift basin. In combination with previous studies on other late Paleoproterozoic volcanic-sedimentary sequences, we consider that the Xiong’er rift in southern NCC extended into the midcontinent at the Lvliang area during ca.1.78 Ga and then the continental crust was uplifted in the Lvliang area during the Mesoproterozoic–Neoproterozoic.

Mechanism of Spectral Distortion for Real-Time Crack Propagation on Aluminum Alloy Structure

This study investigates four characteristic damage mechanisms of fiber Bragg grating (FBG) sensors, with fatigue crack propagation in aluminum alloy. The multipeak wavelength distinguish algorithm was developed for FBG spectrum quantitative analysis. The results distinguish a subordinate peak skewing significantly, associated with strain patterns along the FBG, corresponding to various crack lengths. For parallel bonded direction grating, the subordinate peak skewing appears at the strain pattern transition region. This is located at the ratio 32%-34% of crack length lying in the crack tip. Meanwhile, the four damage characteristics correspond to subordinate peak skewing. When the strain is distributed along the grating, spectral distortion occurs. In this region, the cubic strain pattern determines the shorter wavelength location of subordinate peaks. This corresponds to the 15%-17% ratio of crack length lying in the grating, causing spectral oscillations.

Provenance of the Paleozoic to Mesozoic Siliciclastic Rocks of the Istanbul Zone Constrains the Timing of the Rheic Ocean Closure in the Eastern Mediterranean Region

AbstractThe Intra‐Pontide Suture between the Istanbul and Sakarya zones was regarded debatably either as a Neotethyan Suture or a trace of the Rheic Suture in Turkey. Here, we present U‐Pb ages and Lu‐Hf isotopic compositions of detrital zircons from the Silurian to Triassic sandstones of the Istanbul Zone. Upper Silurian‐Lower Devonian sandstone is dominated by Mesoproterozoic zircons (1950–900 Ma), with subordinate peaks at the latest Neoproterozoic to Silurian (750–420 Ma) and mid‐Archean (2850–2750 Ma) confirming their Avalonian affinity. Detrital zircon ages from Carboniferous‐Triassic sandstones show major peaks at Carboniferous‐Early Permian (360–270 Ma) and Late Neoproterozoic–Cambrian (750–480 Ma) while Mesoproterozoic zircons are insignificant. The εHf(t) values of the detrital zircons exhibit a wide range from −21.3 to +11.7, and over 62% of zircon grains have negative values, largely coinciding with those of the Paleozoic igneous rocks in the Sakarya Zone. The Istanbul Zone is devoid of Carboniferous igneous and/or metamorphic rocks. Therefore, abundant Carboniferous zircons and the disappearance of the Mesoproterozoic zircons in the Carboniferous‐Triassic sandstones of the Istanbul Zone require juxtaposition with a continental domain similar to the Sakarya and Strandja zones, which are characterized by widespread Carboniferous magmatism. We suggest that the Intra‐Pontide Suture represents the trace of the Rheic Suture in Turkey, along which Avalonia and Armorica collided during the Early Carboniferous.

U-Pb Geochronology and Hf Isotope Geochemistry of the Turtleback Complex and East Sound Group, San Juan Islands, Northwestern North American Cordillera

Abstract This study focuses on Paleozoic rocks of the Turtleback Complex (TBC) and East Sound Group (ESG) of northwestern Washington. These assemblages record a long and complex history of magmatism, sedimentation, and volcanism as part of the Chilliwack composite terrane. This study investigates the tectonic setting and magmatic evolution of the Chilliwack terrane by analyzing U-Pb geochronologic and Hf isotopic data from zircons extracted from igneous and sedimentary rocks of the TBC and ESG. Igneous rocks of the TBC yield U-Pb ages of ~420-~370 Ma for zircon rims, which are interpreted to record pluton crystallization, and ages of ~500-370 Ma for inherited cores and antecrysts. Zircons older than 410-400 Ma yield typical igneous values of U/Th and U concentration and somewhat more evolved εHft values (+5 to +10), whereas younger grains yield values of U/Th and U concentrations that record ongoing metamorphism and have more juvenile εHft values of +10 to +15. This evolution is interpreted to have occurred in a long-lived island arc that experienced a transition at ~410-400 Ma from crustal thickening to regional crustal extension. Detrital zircon grains from the ESG yield dominant ages of ~421-~366 Ma and εHft values of +8 to +15, both of which overlap with values from igneous rocks of the underlying TBC. Strata of the ESG also contain abundant older zircon grains, with a dominant age peak of ~1860 Ma and subordinate peaks at 2673, 2570, 1485, 1113, 736, and 553 Ma. When compared with similar results from other assemblages and terranes in the northern Cordillera, our results suggest possible connections with the Yellow Aster Complex of the nearby North Cascade Range. Our results also suggest general similarities with the Alexander terrane, Wrangellia terrane, and southeast Alaska portion of the Yukon-Tanana terrane. These similarities are consistent with previous interpretations that the Chilliwack composite terrane formed in association with the Alexander, Wrangellia, and southeast Alaska portion of the Yukon-Tanana terrane along the paleo-Arctic margin of Laurentia during early Paleozoic time. Our work also illustrates the importance of recycling of older magmatic rocks over millions of years within a juvenile island arc system.

Episodic Archean crustal accretion in the North China Craton: Insights from integrated zircon U-Pb-Hf-O isotopes of the Southern Jilin Complex, northeast China

Recent advances in high-precision in-situ analysis of zircon U-Pb-Hf-O isotopes have significantly improved our approach to studying the origin and evolution of Archean crust. This study presents high-precision in-situ zircon U-Pb-Hf-O isotopes for the Southern Jilin Complex (SJC) on the northeastern margin of the North China Craton (NCC) and explores the potential of such an integrated approach in understanding the Archean crust evolution and its tectonic implications. The SJC consists mainly of Archean granitoid gneisses hosting minor supracrustal rock xenoliths. Zircon U-Pb data from representative lithologies reveal three episodes of magmatism at ~2.78, ~2.69 and ~2.55 Ga, respectively. The former two granitoid magmatic events are recognized for the first time in NE NCC, while the latest one is widespread over the NCC. All metamorphic zircon domains document similar metamorphic ages of 2.51–2.48 Ga, consistent with the widespread metamorphism of ~2.50 Ga in the NCC. Most concordant magmatic zircons preserve “mantle-like” O isotopic signatures, indicating the magma sources were not contaminated by large amounts of high δ18O supracrustal sediments. Hf depleted mantle model ages of magmatic zircons display one predominant peak at 2.9–2.8 Ga and two subordinate peaks at 3.3–3.2 Ga and 2.7–2.6 Ga, indicating possible episodic crust-mantle differentiation in Southern Jilin. Integrated zircon U-Pb-O-Hf data from the SJC suggest that magma sources were mainly derived from multiple episodes of reworking of juvenile or ancient crust with mantle component addition, while recycling of sediments was trivial during the Neoarchean in this region. The spatial–temporal relations of magmatism, lack of supracrustal addition to magma sources, and other geological evidence from the NCC are in favor of a bottom-up geodynamic regime possibly related to plume activities, arguing against a widespread top-down mechanism involving modern-style subduction in the NCC during the Neoarchean.

Zircon U–Pb age constraints on the provenance of Upper Oligocene to Upper Miocene sandstones in the western Qiongdongnan Basin, South China sea

The provenance of Upper Oligocene to Upper Miocene sandstones in the western Qiongdongnan Basin was studied by zircon U–Pb ages. More than 200 zircon grains were separated from the sandstone of the Upper Oligocene Lingshui, Lower Miocene Sanya, and Upper Miocene Huangliu formations, and spot analysed for U–Pb dating. Most zircon grains from the Upper Oligocene Lingshui and Upper Miocene Huangliu formations had rounded corners, suggesting that the grains were transported a relatively long distance before deposition, while grains from the Lower Miocene Sanya Formation were usually angular in shape, implying a shorter transport distance from their provenance. The Lingshui Formation contained exclusively Cenozoic, Mesozoic, Palaeozoic, and Proterozoic zircon ages, and the age spectrum showed two major peaks at ca. 247 and 441 Ma, along with nine subordinate age peaks at ca. 35, 305, 517, 623, 811, 852, 911, 1158, and 1905 Ma. This indicates that Upper Oligocene sediments in the northwestern area of the Qiongdongnan Basin may have originated from the Red River system, which had four major peaks at 254, 418, 751, and 1848 Ma, and five subordinate peaks at ca. 32, 81, 514, 606, and 967 Ma. Results suggest that sediments from the Red River system entered the Qiongdongnan Basin as early as the Late Oligocene. The zircon age spectrum of the Sanya Formation had two major peaks at 99 and 237 Ma, indicating that Lower Miocene sandstones in the northwestern area of the Qiongdongnan Basin were mainly from Hainan Island, with ages ranging from 110 to 90 to 280–220 Ma. This study infers that the sandstones may be the paleo-Red River capture by the Yangze River, which resulted in a large decrease of sediment supply from the paleo-Red River system, such that the sediments of the paleo-Red River did not develop in the western area of the Qiongdongnan Basin during the Early Miocene. Results indicate that if the Red River capture existed, it would have predated the Early Miocene. The zircon age spectrum from Upper Miocene sediments of the western Qiongdongnan Basin showed five major age peaks at ca. 27, 88, 256, 415, and 785 Ma, indicating that its provenance was the Red River system. The Late Miocene provenance change from Hainan Island to the Red River may have been in response to a major phase of the Tibetan Plateau uplift.

Detrital zircon in the Huashan Group, northern Yangtze Block: Implications for the nature of Neoproterozoic sedimentary basins and Precambrian crustal evolution

The Huashan Group preserves Neoproterozoic volcanic‐sedimentary sequences in the northern Yangtze Block and is an ideal target for determining the provenance and characteristics of Neoproterozoic sedimentary basins and the Precambrian crustal evolution of the Yangtze Block. Here, we report LA‐ICP‐MS detrital zircon U–Pb–Hf isotopes from four metamorphic clastic rock samples in the Huashan Group. Detrital zircons ages yield four major peaks at ca. 2,670, 2,040, 940, and 840 Ma and five subordinate peaks at greater than or equal to ca. 2,850, 2,490, 1,840, 1,600, and 1,240 Ma. The provenance of the Huashan Group includes Archean to mid‐Neoproterozoic magmatic rocks, and reworked sedimentary rocks from the northern Yangtze Block. The Huashan Group was deposited from ca. 830 to 800 Ma and represents sedimentation accompanying the development of a mid‐Neoproterozoic continental rift basin in Yangtze Block associated with the breakup of the Rodinia supercontinent. Hafnium isotope analyses of detrital zircon from the Huashan Group suggest that most crustal growth in the northern Yangtze Block occurred during the Late‐Mesoproterozoic and early to Middle Neoproterozoic and crustal reworking occurred from the Archean to the Neoproterozoic.

Early Triassic Conversion from Source to Sink on the Southern Margin of the North China Craton: Constraints by Detrital Zircon U-Pb Ages

Provenance analysis of sediments provides important constraints on basin formation and orogenic processes. With the aim to define the sedimentary provenance and tectonic evolution of the southern margin of the North China Craton, this paper presents new detrital zircon U-Pb data from Early Triassic sediments in the Yiyang area. The results showed major peaks at 1848, 458, 425, and 268 Ma and subordinate peaks at ca. 2500, 872, and 957 Ma on age spectra from the Liujiagou Formation. The Heshanggou Formation exhibited a major age peak at 445 Ma and subordinate peaks at 755 and 947 Ma. Integrated with the analysis of sandstone detrital compositions, we suggest that the sources of the Liujiagou Formation were mainly a mixture of the southern margin of the North China Craton and the North Qinling Orogenic Belt, whereas the Heshanggou Formation was derived primarily from the North Qinling Orogenic Belt. Age comparisons of detrital zircon geochronology collected from different basins in the North China Craton indicated that the paleogeography of the North China Craton during the Early Triassic was strongly asymmetric, wherein the uplifted highland along the southern margin of the North China Craton was relatively lower than the northern margin. Meanwhile, the marked shift in source region from the Liujiagou to the Heshanggou formations provides a constraint regarding the conversion from denuded zone to deposited zone along the southern margin of the North China Craton in the Early Triassic, which controlled the evolution of the provenance and sedimentary system.

Depositional Age, Provenance Characteristics and Tectonic Setting of the Ailaoshan Group in the Southwestern South China Block

The depositional and metamorphic ages and provenances of the Ailaoshan (ALS) Group in the Ailaoshan‐Red River (ALS‐RR) shear zone, southwestern South China Block (SCB), were investigated to constrain the tectonic history of the southwestern SCB. In this study, we use petrology, geochemical analysis, zircon cathodoluminescence imaging and U‐Pb geochronology to analyse samples of quartzite, garnet‐bearing two‐mica schist and metapelite. The age spectra of detrital zircon grains from these metasediments show two dominant age peaks at 550–424 Ma and 876–730 Ma and two subordinate peaks at 970–955 Ma and ∼2450 Ma. The youngest peak, corresponding to the early Palaeozoic, accounts for more than 20% of the total dates and constrains the deposition of the ALS Group to the Palaeozoic rather than the Palaeoproterozoic as traditionally thought. Moreover, two peaks of metamorphic ages corresponding to the Permo‐Triassic and Cenozoic were also identified, and these ages document the tectonothermal events associated with the Indosinian collision between the Indochina Block and the SCB and the Himalayan collision between the Indian and Asian plates. Geochemical data suggest that the provenances of the ALS Group were dominated by continental arc and recycled metasedimentary rocks. The comparison of probability density distribution plots of the detrital zircon U‐Pb age data indicates that the Neoproterozoic detritus in the ALS Group was probably derived from the arc‐related Neoproterozoic intrusive bodies in the northwestern and southwestern SCB. Furthermore, the early Palaeozoic detritus might have been sourced from eroded early Palaeozoic strata and magmatic plutons in Cathaysia and volcanic rocks in the western Indochina Block.

Subduction and collision processes between the North China and South China blocks constrained by the geochronology and geochemistry of the Wuguan Complex in the Qinling orogen, China

ABSTRACT The Qinling orogen is a key area for understanding the processes of subduction and collision between the South China Block (SCB) and North China Block (NCB). The Wuguan Complex, distributed along the southern margin of the Shangdan suture zone, can provide important constraints on the age of collision between NCB and SCB and the tectonic evolution of the Qinling orogen in Late Paleozoic. Detrital zircons from meta-sedimentary rocks of the Wuguan Complex in the Danfeng-Shangnan area have an age spectrum with two main peaks at ~448 Ma and ~819 Ma, and two subordinate peaks at ~938 and ~1440 Ma, respectively, and are interpreted to have been derived from the North Qinling terrane (NQT). The petrographic and geochemical characteristics of the meta-sedimentary rocks indicate that they were deposited in a fore-arc basin along the southern margin of the NQT. The youngest detrital zircons yield a weighted mean age of 378 ± 3 Ma, indicating that the fore-arc deposition was continuing at least to this time, which implies that the Paleo-Qinling Ocean between the NCB and SCB was not finally closed until at least the late Devonian. In combination with regional data, we propose that sedimentary rocks of the Wuguan Complex might once have been a sequence of late Ordovician to late Devonian strata with intercalated mafic rocks, which has been dismembered by the later tectonic activity. It was metamorphosed during northward subduction of the Paleo-Qinling Ocean at ca. 320 Ma, and slowly cooled through ca. 350°C at ca. 247 Ma (muscovite 40Ar/39Ar age). It has recorded the detailed processes of subduction and collision between the NCB and SCB.

Combined detrital zircon fission track and U-Pb dating of the Late Paleozoic to Early Mesozoic sandstones in the Helanshan, western Ordos fold-thrust belt: Constraints for provenance and exhumation history

In order to unravel the Mesozoic sedimentation in response to multistage deformation of the western Ordos fold-thrust belt, combined zircon U-Pb and fission track analyses of single zircon grain are conducted for seven sandstone samples in the Helanshan area. Zircon FT ages are calculated using absolute uranium concentration determined by LA-ICP-MS during the procedure of zircon U-Pb dating. The newly-obtained zircon FT data show age features that are comparable with the previous zircon FT ages obtained by conventional FT methods (by which uranium contents are determined through an external detector to map induced fission tracks). The newly-obtained zircon FT ages have four subordinate FT age peaks (i.e., 225 Ma, 165 Ma, 125 Ma and 80 Ma) which are well matched with the regional geodynamic events occurred in the Late Triassic, Late Jurassic, Late Cretaceous and Early Cenozoic, respectively; and the zircon U-Pb ages have two main peaks at the Paleoproterozoic and the Late Paleozoic. The zircon U-Pb ages, integrating with the FT ages and available paleocurrents, suggest that the Paleoproterozoic basement rocks and Late Paleozoic plutonic rocks of the Alxa Block are the source rocks for the Triassic sandstones, and the Jurassic sandstones are associated with a multi-cycling sedimentation. The Jurassic sandstones contain recycled zircons that firstly deposited in the Triassic strata and subsequently exhumed during the Late Triassic-Early Jurassic.

Depositional age and provenance in the San Luis Formation, Sierras Pampeanas, Argentina: Evidence from detrital zircon studies

The San Luis Formation is one of the lithostratigraphic units constituting the early Paleozoic crystalline basement of the Sierras de San Luis, which are part of the Sierras Pampeanas of central Argentina. The low-grade metamorphic overprint of the San Luis Formation makes it a key unit for the modelling of its sedimentary environment, which belongs to a deep-marine environment. This formation crops out in two belts named as Eastern and Western, whose stratigraphic correlation has not been clarified. Five samples from both belts of the San Luis Formation show U-Pb age distributions of detrital zircons with dominant peaks that are characteristic of orogenic systems of the West Gondwanan landmasses. However, detrital zircon age spectra and maximum depositional ages differ substantially in each belt of the San Luis Formation. While the Western belt displays polymodal age patterns with its most prominent age peaks at ∼635 Ma, a second most important population appears at 535–575 Ma with subordinate groups at 720–775 Ma and 1.7–2.2 Ga; the Eastern belt shows an almost unimodal age pattern dominated by an age peak at ∼535 Ma, with very subordinate peaks at ∼620 Ma, ∼780 Ma and ∼1,017 Ma. Regarding the maximum depositional age, two different ages have been recognized in the Western belt, ∼555 Ma at its bottom and ∼530 Ma at its top; whereas in the Eastern belt the maximum depositional age is ∼515 Ma. The age spectra of detrital zircons from the San Luis Formation record the evolution of the nearby Pampean orogen. At an early stage of exhumation, the Pampean orogenic system chiefly liberated recycled sedimentary detritus containing zircons with Neoproterozoic (∼635 Ma), Mesoproterozoic (∼1,000 Ma) and subordinate amounts of Paleoproterozoic (∼2,200 Ma) ages. Upon advanced unroofing and active erosion, the Pampean sequences sourced first-cycle detritus with latest Neoproterozoic to early Cambrian ages (555–525 Ma). A major conclusion is that the San Luis Formation accumulated in at least two stages, filling successive deep-marine basins that were marginal to the Pampean orogen during and after its latest Neoproterozoic to Cambrian development.

Provenance and tectonic setting transition as recorded in the Neoproterozoic strata, western Jiangnan Orogen: Implications for South China within Rodinia

The Neoproterozoic Tonian strata (ca. 870–725 Ma) in the western Jiangnan Orogen archive the records of sedimentary provenance and tectonic setting which can be used to understand the geological evolution of the South China Continent. These strata are separated into the basement and cover sequences by a regional angular unconformity. The basement sequence can be subdivided into the lower and the upper parts by the widespread interbedded ca. 840 Ma basalt with pillow structure. In the present work, 234 concordant detrital zircon analyses are obtained from three Tonian sandstone samples in the Fanjingshan district, Guizhou Province. Combined with previous results, a total of 1736 analyses of detrital zircon U-Pb ages derived from 12 formations of Tonian strata in the western Jiangnan Orogen are used to decipher the integrated sedimentary and tectonic histories. The zircons from the lowermost part of the basement sequence (the Yujiagou Formation) show oval morphology and display two Paleoproterozoic age peaks at 2325 Ma and 1845 Ma which are similar with the detrital zircon age peaks from the Late Paleoproterozoic to Early Mesoproterozoic Dongchuan/Dahongshan/Hekou groups, suggesting a passive margin basin in which the sediments were mainly sourced from the southwestern Yangtze Block. However, the zircon age population of the lower part of the basement sequence (the Xiaojiahe, Huixiangping formations and their equivalents) indicates the sedimentary derivation from bidirectional sources (the ca. 870 Ma arc materials in the south and the old detritus from the southwestern Yangtze Block) which is consistent with a back arc setting for the deposition of the sediments. Zircons from the upper part of the basement sequence (the Duyantang Formation and its equivalent) show euhedral and subangular morphology and display a unimodal age peak at ca. 835 Ma. This sequence was possibly deposited in a convergent setting and the detritus were came from the locally distributed syn-collisional igneous rocks. The lower part of the cover sequence (the Xinzhai and Wuye formations and their equivalents) shows a distinct zircon age peak at 815–809 Ma and two subordinate peaks at 2485 Ma and 2018 Ma, suggesting that the basin had gradually transformed into a continental rift basin and received the detritus from the ca. 815 Ma post-collisional magmatic rocks as well as from different Paleoproterozoic source rocks in the northern Yangtze Block. We propose a tectonic evolution model that envisages eruption of ca. 840 Ma basalt in a back arc basin that existed during ca. 870–835 Ma, an angular unconformity was formed during amalgamation of the Yangtze Block and the Cathaysia Block at ca. 835–820 Ma and the rifting of the South China Continent was initiated at ca. 800 Ma. Our study concludes that the South China Continent was formed on the periphery of the Rodinia supercontinent.

Detrital zircon U–Pb geochronology and geochemistry of late Neoproterozoic – early Cambrian sedimentary rocks in the Cathaysia Block: constraint on its palaeo-position in Gondwana supercontinent

AbstractWe present updated U–Pb ages and Hf isotopic compositions of detrital zircons and whole-rock geochemical data to investigate the provenance and tectonic setting of late Neoproterozoic and early Cambrian sandstones from the Cathaysia Block, in order to offer new constraints on its tectonic evolution and its palaeo-position within the supercontinent. The source rocks for the studied sandstones were dominated by felsic–intermediate materials with moderate weathering history. U–Pb dating results show major populations atc. 2500 Ma, 1000–900 Ma and 870–716 Ma with subordinate peaks at 655–532 Ma, consistent with the global Neoarchean continental crust growth, assembly and break-up of Rodinia, and Pan-African Event associated with the formation of Gondwana. Zircon U–Pb ages and Hf isotopic data suggest that most derived from exotic terranes once connected to the Cathaysia Block. Using whole-rock geochemical analysis, it was determined that the studied sedimentary rocks were deposited in a passive continental margin and the Cathaysia and Yangtze blocks were part of the same continent; no Cambrian ocean existed between them. Compiling a detrital zircon dataset from Qiangtang, northern India, the Lhasa Terrane and Western Australia, the Cathaysia Block seems to be more similar to the Qiangtang and western part of the northern India margin, instead of having a direct connection with the Lhasa Terrane and Western Australia in the Gondwana reconstruction during the late Neoproterozoic and Cambrian eons.