Youngest Detrital Zircon Age Research Articles

Detrital zircon U–Pb and Hf analyses of Silurian–Devonian sediments in the Sukhothai Terrane, northern Thailand: implications for the Mid-Paleozoic arc belt

The Sukhothai Terrane in northern Thailand consists of continental basement and a Permo-Triassic magmatic arc related to the subduction of the main Palaeo-Tethys Ocean. The Donchai Group represents the oldest sedimentary sequence of the Sukhothai Terrane and consists mainly of meta-sandstone, quartzo-feldspathic schist, phyllite and silty slate. We present new detrital zircon U–Pb geochronology, Lu–Hf isotope data and geochemical data for the sedimentary rocks of the Donchai Group to elucidate the depositional age, provenance and nature of the group. The youngest detrital zircon ages (433–403 Ma) suggest that the Donchai Group accumulated between 433 and 368 Ma, revealing Silurian–Devonian arc magmatic rocks on the western margin of the Sukhothai Terrane. Sediments of the Donchai Group were sourced from both the continental basement and a Silurian–Early Devonian magmatic arc, suggesting a depositional setting on the continental slope of a back-arc basin along the western flank of the Sukhothai Terrane. The Silurian–Devonian arc belt in SW China probably extends to the Chiang Rai region to the west of the Sukhothai Terrane, northern Thailand, revealing the northwards subduction of the Proto-Tethys Ocean along the western Simao and Sukhothai margin during the mid-Paleozoic. The inferred arc and back-arc configuration of the Proto-Tethys Ocean in northern Thailand is comparable with that recently established in Yunnan, SW China. Supplementary material: Detrital zircon U–Pb ages and trace element analyses, zircon in-situ Lu–Hf isotopic compositions and whole-rock geochemical data are available at https://doi.org/10.6084/m9.figshare.c.6858373

Foreland basin unconformity, Western Himalaya, Pakistan: timing gap, regional correlation and tectonic implications

This study estimates the timing of unconformity between marine–continental transitional sequence of the Kuldana Formation and continental sequence of the Murree Formation for the first time across the Hazara-Kashmir syntaxis, western Himalaya, Pakistan. The ages of the studied units are constrained using detrital zircon U–Pb geochronology. The maximum depositional ages constrained by weighted mean and youngest detrital zircon age are 37 ± 1.7 Ma and 22.5 ± 0.6 Ma for top of Kuldana and base of Murree formations, respectively. Based on this age, the duration of hiatus is estimated to be ~ 14.5 Ma. The comparison of this unconformity and sedimentation pattern along strike suggests that the initial collision occurred in the central segment causing its early uplift and erosion with development of the unconformity. The sedimentation in the central segment culminated at ~ 37 Ma and resumed at ~ 22.5 Ma. The wider gap in central segment becomes narrower at western and eastern margin suggesting discontinuous deposition due to gradually closure of western and eastern margin. This supports the diachronous collision of the Indian and Asian plates with initial contact at the central segment.

Subduction–Accretion History of the Paleo-Pacific Plate Beneath the Eurasian Continent: Evidence from the Tongjiang Accretionary Complex, NE China

Detrital zircons in the matrix of an accretionary complex play an important role in providing evidence to reconstruct oceanic plate subduction and accretion processes. The Nadanhada accretionary complex (NAC) dominated by the Yuejinshan, Raohe and Tongjiang accretionary complexes provides significant geological evidence to better understand the Paleo-Pacific subduction–accretion process. Most previous studies have focused on the Yuejinshan and Raohe accretionary complexes, while those of the Tongjiang accretionary complex on the north side have focused on blocks. In this study, we present zircon U–Pb dating and Hf isotopic data for the matrix of metasedimentary rock in the Tongjiang accretionary complex. The analysis results show that the zircons in the fine silty mudstone, phyllonite and fine argillaceous siltstone define the youngest weighted mean ages (youngest detrital zircon ages) of 261.4 ± 2.9 Ma (247 Ma), 175.2 ± 4.9 Ma (169 Ma) and 168.6 ± 2.1 Ma (162 Ma), respectively, and yield a younging trend of the accretion materials from west to east. Provenance analysis indicates that the matrix was mainly sourced from the neighboring Jiamusi and Xingkai blocks. Based on previous results of the Permian and Late Triassic blocks in the Yuejinshan region, the Permian and Early Jurassic blocks in the Tongjiang region, and the Late Triassic and Early–Middle Jurassic blocks in the Raohe region, as well as the lower limit of the depositional age of the Late Triassic matrix in the Yuejinshan region and the Middle Jurassic and Early Cretaceous matrices in the Raohe region, we propose that the NAC may record the Late Permian–Triassic, Jurassic and Early Cretaceous oceanic accretion events, representing the westward subduction and accretion process of the Paleo–Pacific Ocean Plate.

Challenges of dating metasedimentary successions in collisional orogens: A case study of a Neoproterozoic passive margin in West Gondwana

Metasediments in collisional orogens critically record tectonic conditions during sediment formation and the thermal evolution during orogenesis. However, Precambrian metasediments can be difficult to date to a reasonable precision. Maximum depositional ages based on detrital zircon can vary considerably from sample to sample, even within a single formation. Although associated igneous bodies can yield depositional ages, their relationship with associated metasediments can be hard to constrain in poly-deformed terranes, as thrusting leads to the imbrication of rocks of different origins and ages. We present new U-Pb zircon ages for metasediments and tectonically-intercalated basement rocks from the Neoproterozoic Southern Brasília Orogen, West Gondwana, and explore the challenges of dating metasedimentary sequences in collisional orogens more widely. Our approach has been to constrain a metasedimentary succession based on field and petrographic analyses and to consider the youngest detrital zircon age, of all samples, as the maximum depositional age. Most samples yield youngest ages older than the maximum depositional age and are thus referred to as “apparent” maximum depositional ages. This results from the age distributions in the source regions, where there is major peak magmatism at ∼ 2.2–2.1 Ga, and small volumes of rocks with younger ages. Hence, apparent maximum depositional ages of ∼ 2.1 Ga, common in the studied succession, appear to be related to source characteristics. Five metasedimentary rocks were analyzed here, three yielded apparent maximum depositional ages between 1.8 and 1.6 Ga, and two samples provided ages of ∼ 1.0 Ga, considered the maximum depositional age. The Archean-Paleoproterozoic basement of the Southern Brasília Orogen is the main source region for overlying Neoproterozoic metasedimentary successions, with some material derived from the adjacent Southern São Francisco Craton. P-T obtained for the studied succession is consistent with sedimentary facies and geochronological studies that suggest it is the passive margin of the Southern São Francisco Craton.

Stratigraphic Constraints on Sandy Conglomerates in Huanghekou Sag, Bohai Bay Basin, via In Situ U-Pb Dating of Vein Calcite and Detrital Zircons, and XRD Analysis

The discovery of the BZ19-6 large-scale condensate gas field illustrates the great potential of the sandy conglomerate reservoirs in the Bohai Bay Basin. However, the stratigraphic correlation of the sandy conglomerate sequence in northern Huanghekou Sag remains a challenge due to the lack of syn-depositional volcanic layers and biostratigraphic constraints. The challenge limits understanding the regional strata distribution and further exploration deployment. In this study, we conducted in situ U-Pb dating of vein calcite and detrital zircons of the sandy conglomerate samples from borehole BZ26-A. The vein calcite age and the youngest age of detrital zircons provide the upper and lower bounds of the depositional age, respectively. We also correlated the samples with those from well-understood strata through a comparison of XRD mineral components. The absolute age of 47.0 Ma of the vein calcite and the youngest detrital zircon age of 103.5 Ma suggest the sedimentary sequence is supposed to be referred to as the Kongdian Formation (65–50.5 Ma). The XRD data and petrological analysis suggest that the lithostratigraphy of the Kongdian Formation in Huanghekou Sag could be divided into at least three members, with Member 3 consisting of red sediment deposited in a hot and dry climate; Member 2 and Member 1 deposited as fan delta with major parent rock of Mesozoic volcanic rocks and Precambrian meta-granitoid, respectively. Member 1 shows significant potential for energy exploration due to high brittle mineral components and fracture development.

Detrital zircon U–Pb ages of metasedimentary rocks from the Neoproterozoic Zhoutan Group in the northern Cathaysia Block (South China): Provenance and tectonic implications

ABSTRACT The Neoproterozoic Zhoutan Group, located at the conjunction area between the Yangtze and the Cathaysia Blocks, preserves an important record of the Neoproterozoic sedimentary system of the South China Block. However, its accurate depositional age, provenance, and tectonic affinity remain poorly studied. Here, we report new LA-ICP-MS detrital zircon U–Pb age data of four meta-sedimentary samples from the Zhoutan Group in the Nancheng area for complemental decipherment of its sedimentary and tectonic histories. Concordant detrital zircon ages reveal proportions of 54% latest Mesoproterozoic to early Neoproterozoic (ca. 1050–820 Ma), 24% early Paleoproterozoic (ca. 2500–2150 Ma), and 22% late Paleoproterozoic to early Mesoproterozoic (ca. 2000–1500 Ma) populations. Youngest detrital zircon age clusters exhibit a consistent weighted mean age of ca. 827 Ma, suggesting the maximum Tonian depositional age of the Zhoutan Group. Provenance interpretations reveal that the detritus of investigated samples were mainly sourced from the proximal Jiangnan Orogen with some additionally derived from the Cathaysia Block, the interior Yangtze Block, and/or extraneous terranes. In addition, the appearance of some later early Palaeozoic-aged (ca. 437 Ma) metamorphic rims and grains suggest that the Zhoutan Group has locally experienced an intense metamorphism during the early Palaeozoic (Silurian) time, which has been consistently recorded by the Neoproterozoic meta-strata in the Cathaysia Block. These new data, together with those from previous studies, indicate that the Zhoutan Group belongs to the early Neoproterozoic sedimentary successions between the Yangtze and the Cathaysia Blocks. Subsequently, it might be thrusted onto the present side of the Cathaysia Block during later tectonic processes and was affected by locally metamorphism during the Silurian time. Thus, such observations suggest that the potential border between the Yangtze and the Cathaysia Blocks should be to the north of the current position of the Zhoutan Group.

Study of molasse within the middle segment of the Bangong‐Nujiang suture zone, central Tibet: Constraints of ocean–continent transform

The Bangong‐Nujiang suture zone, separating the Lhasa and South Qiangtang terranes of the Tibetan Plateau, is marked by remnants of the Bangong‐Nujiang oceanic basin. In the Zanzong Co area of central Tibet, non‐marine molasse deposits of the newly identified Jingzhushan Formation record the eventual collision between these two terranes and subsequent ocean–continent transform along the middle segment of the Bangong‐Nujiang suture zone. In this contribution, it is observed that the Jingzhushan Formation, characterized by lacustrine facies and braided delta facies, rests unconformably on the underlying marine strata and ophiolite. Zircon U–Pb dating has been conducted with samples of four interlayer volcanic rocks and two sandstones from the Jingzhushan Formation. The interlayer volcanic rocks constrain the depositing age from ca. 115 to 72 Ma. Based on the youngest detrital zircon ages, the maximum depositional ages of the Jingzhushan Formation are suggested to be ca. 78 Ma. Petrographic and detrital zircon isotopic results indicate that sediments in the Jingzhushan Formation have mixed sources from the South Qiangtang terrane and the intervening Bangong‐Nujiang suture zone. Provenance analysis, together with regional data, suggests that the newly identified Jingzhushan Formation reflects continental molasse deposition in an intermontane basin during the post‐collisional stage. The development of the intermontane basin evidenced by molasse deposition of the Jingzhushan Formation reveals that the ocean–continent transform of the middle segment of the Bangong‐Nujiang Ocean had been completed in the late Early Cretaceous (ca. 115 Ma).

Tourmaline 40Ar/39Ar geochronology and thermochronology: Example from Hadean-zircon-bearing siliciclastic metasedimentary rocks from the Yilgarn Craton

We present 40Ar/39Ar ages and boron isotopes of tourmalines from a quartz-tourmaline intrusion cross-cutting the Hadean detrital-zircon-bearing metasedimentary rocks from the Mt. Alfred and Brooking Hills localities of the Illaara Greenstone Belt, Western Australia. Concordant 40Ar/39Ar plateau ages on the tourmalines at Mt. Alfred give a weighted mean age of 2935 ± 9 Ma (2σ). These results are the first reported Archean 40Ar/39Ar ages directly obtained on tourmaline, and provide a minimum depositional age for this sequence, placing constraints on the depositional timing of detrital Hadean zircons to between 2935 ± 9 Ma and c.a. 3250 Ma (youngest detrital zircon age in sequence). This is the last known occurrence of abundant detrital Hadean zircons having been directly deposited in a sedimentary sequence, and thus suggests that most Hadean zircon sources have been exhausted by this time. The 2935 ± 9 Ma tourmalines occur within a quartz-tourmaline intrusion with associated stratiform layers and veins, inferred to have grown during a hydrothermal fluid circulation event. A younger generation of tourmalines from the Brooking Hills, 30 km south of Mt. Alfred yielded concordant 40Ar/39Ar plateau ages with a weighted mean age of 2624 ± 16 Ma. These tourmalines occur within and along the margins of post-kinematic quartz veins, parallel to the foliation fabric and marks the end stage of high temperature tectono-thermal events within the Illaara Greenstone Belt. The retention of 2935 ± 9 Ma tourmaline ages within the Illaara Greenstone Belt shows that the K/Ar system of tourmaline remained closed throughout repeated upper-greenschist metamorphic events (∼450 °C) between the ages of c.a. 2930 to 2630 Ma in contrast to muscovite recording plateau ages of about 2600 Ma. This is in agreement with an approximate Ar closure temperature between ∼534 and 628 °C experimentally determined in this study.

Formation and evolution of the Eastern Kunlun Range, northern Tibet: Evidence from detrital zircon U-Pb geochronology and Hf isotopes

The Eastern Kunlun Range, as a high-elevation and granitoid-rich tectonic element in northern Tibet, records Paleozoic–Mesozoic amalgamation process of the East Asia continent and Cenozoic uplift of the Tibetan Plateau. However, Precambrian evolution of the Eastern Kunlun remains poorly understood and relations between Eastern Kunlun and adjacent terranes (e.g., Qaidam and Qilian) during the Phanerozoic accretion process are still highly controversial. We use detrital zircon U-Pb geochronological and Hf isotopic data of Proterozoic and Paleozoic metasedimentary rocks from the Eastern Kunlun Range, to reconstruct its origin and subsequent evolutionary history. Detrital zircons of the Proterozoic rocks are dominated by early–middle Neoproterozoic ages (700–1000 Ma), with two age peaks at ca. 800 Ma and ca. 920 Ma and εHf(t) values ranging from −10 to 5. The youngest detrital zircon ages (648–788 Ma) demonstrate that these investigated Proterozoic strata, which were previously mapped as Paleoproterozoic to Mesoproterozoic, were most likely deposited in the middle–late Neoproterozoic. Abundant 0.9–1.0 Ga detrital zircon crystals are consistent with those crystalline rocks of similar ages across the Kunlun-Qaidam and Qilian terranes, which are generally interpreted as the product of Grenvillian orogenesis. These findings support the hypothesis that these terranes were probably within a single continental landmass (named as KQQ block) during the Neoproterozoic. The high similarity of detrital zircon ages, Hf isotopes and Neoproterozoic lithostratigraphy between western Yangtze and KQQ blocks, supports a temporary connection of the KQQ block to western Yangtze in Rodinia supercontinent. Detrital zircons of the analyzed Paleozoic rocks are characterized by 390–490 Ma age populations. These results, in combination with published granitoids data of the northern Tibet, favor a scenario in which the Kunlun-Qaidam and Qilian terranes underwent separated subduction and accretion processes during the late Cambrian–Devonian, but together formed an upper plate to northward subduction of the Paleo-Tethys during the Permian–Triassic.

Detrital zircon provenance and palaeogeographic implications of the Ediacaran Shigu Group in the Zhongza Terrane, SW China

ABSTRACT The palaeogeographic positions of South China in the Rodinia and Gondwana supercontinents have long been controversial. We report petrological, detrital zircon U-Pb geochronological, trace element geochemical and Lu-Hf isotopic compositions for metasedimentary rocks from the Shigu Group in the Zhongza Terrane, SW China. The Shigu Group has been regarded as the Precambrian basement of the Zhongza Terrane, and comprises mainly a suite of medium-/low-grade metamorphosed terrigenous clastic rocks. The youngest zircon age population of two metasedimentary rock samples from the bottom Shigu Group yields a weighted average age of 633 ± 9 Ma, indicative of a late Neoproterozoic (ca. 630 Ma) maximum deposition age. The youngest detrital zircon age of a metasedimentary rock from the upper Shigu Group is 597 ± 7 Ma, it may suggesting a considerably later deposition. Detrital zircon age distribution patterns of the Shigu Group metasedimentary rocks are similar to those of coeval sedimentary rocks in the western Yangtze Block. According to Hf isotope compositions and zircon morphology, the Neoproterozoic Shigu Group detritus may have sourced from Neoproterozoic magmatic rocks in the western Yangtze Block, whilst the pre-Neoproterozoic zircons might originate from recycling of the underlying metasedimentary rocks. Our results indicate that the basement of the Zhongza Terrane was a continuation of the Yangtze Block, which implies that Precambrian Yangtze basement rocks were present beyond the current boundary of the Block. In the late Neoproterozoic (ca. 630–570 Ma), the western Yangtze Block may have been facing the Proto-Tethys and received detritus mainly from the local Neoproterozoic magmatic rocks. During the late Neoproterozoic-earliest Palaeozoic (ca. 570–520 Ma), the seaway closure between the Yangtze (incl. Zhongza) Block and northern India likely created new pathways for delivery of the earliest Neoproterozoic and Pan-African detrital zircons into the lowermost Palaeozoic sequences in South China.

A synthesis of late Paleozoic and early Mesozoic sedimentary provenances and constraints on the tectonic evolution of the northern North China Craton

The North China Craton (NCC) and its adjacent areas experienced a series of complex tectonic events during the late Paleozoic–early Mesozoic, the closure of the Paleo-Asian Ocean (PAO), the collision between the Central Asian Orogenic Belt (CAOB) and the NCC, and the subduction of the Yangtze Plate. This paper provides an overview of the provenances and tectonic implications of late Paleozoic and early Mesozoic sediments in the northern NCC based on a comprehensive analysis of the available geological and geochronological data together with our new clast compositions, paleocurrents, detrital zircon ages and Hf isotope data. Detrital zircons from the middle Permian Shihezi Formation in the Yungang basin have age distributions of 442–264 Ma, 2179–1606 Ma and 2665–2249 Ma and are characterized by negative εHf(t) values that match the age population and Hf isotope peculiarities of the Yinshan–Yanshan Orogenic Belt (YYOB). These observations suggest that these zircons were derived from the YYOB, which is consistent with most regions of the NCC. The CAOB became a minor source of sediments in the northern NCC no earlier than the late Permian, and the ultimate closure time of the PAO can be constrained to 267–261 Ma by the youngest detrital zircon ages. The tectonic evolution of the northern NCC in the late Paleozoic was closely related to the southward subduction of the PAO and the amalgamation of the CAOB and the NCC. The angular unconformity underlying the Early Jurassic strata and the absence of Triassic strata in the Yungang basin might be ascribed to the continuous collision of the CAOB and the NCC during the Late Triassic.

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

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.

Sedimentology and detrital zircon geochronology of the Nanduan Formation (Carboniferous) of the Changning-Menglian Belt: indications for the evolution of Paleo-Tethys in western Yunnan, China

The Changning-Menglian Belt in western Yunnan, China, has been considered for decades as a remnant of Paleo-Tethys in this region. However, the understanding of the geological evolution of the belt remains sketchy and incomplete. As a significant component of the stratigraphic successions in the eastern part of the belt, the siliciclastic Nanduan Formation preserved essential information of the developing history of the belt. Petrologic studies of the formation show that it was deposited in a neritic environment. The increase of mudstone beds and decrease of grain size of sandstones upwards suggest a gradual deepening of sedimentary environment. Petrographic and geochemical characteristics of sandstones show that they were derived from mature continental provenance and deposited in a passive continental margin setting. Detrital zircon ages of the formation range from 362 to 3685 Ma. The youngest detrital zircon age (362.2 ± 5.5 Ma) confines the deposition age of the sandstones to being younger than the latest Devonian. Dominant age populations of ca. 950 Ma and ca. 550 Ma can be correlated with the magmatic events that occurred in Eastern Ghats-northern Prince Charles (India–Antarctica) (ca. 950 Ma) and Pan-African orogens (Australia–India) (ca. 550 Ma), which are considered, therefore, to be the main provenance of the Nanduan Formation. These results let us consider that the Nanduan Formation and the underlying Lancang Group were formed on the margin of the Baoshan-Shan Block (therefore, autochthonous), and the Carboniferous‒Permian limestones of seamount resemblance, the oceanic bedded cherts, and basic and ultra-basic igneous rocks in the central zone of the belt are overthrusted slices (allochthonous).

Discovery of Middle Jurassic trench deposits in the Bangong-Nujiang suture zone: Implications for the timing of Lhasa-Qiangtang initial collision

The Mesozoic trench deposits in the Bangong-Nujiang suture zone in central Tibet can provide critical information for reconstructing the paleotectonic evolution of the Bangong-Nujiang Ocean and constraining the timing of the Lhasa-Qiangtang initial collision. In this paper, the Gamulong Formation, which is well exposed in the Dong Co area, western Bangong-Nujiang suture, central Tibet, was studied. The sedimentological analysis shows that the Gamulong Formation was deposited in a submarine fan environment. The youngest detrital zircon age and fossils from limestone pebbles within the Gamulong Formation combine to determine a Middle Jurassic age. The pebbles in the conglomerate are dominated by limestones and sandstones, which is consistent with the sandstone petrology showing limestone and sandstone fragments as the main framework components. Detrital zircon U-Pb ages from the sandstones yield age populations of 164–178 Ma, 200–500 Ma, 700–1000 Ma, 1700–2100 Ma and ~2500 Ma. The corresponding zircon εHf(t) values are distributed between −23.5 and +11.1. These zircon features are similar to those from the Qiangtang terrane. Accordingly, the provenance results imply that the Gamulong Formation was recycled from the accretionary complex (Mugagangri Group mélange) in the Bangong-Nujiang suture zone and the forearc basin deposits (Lower-Middle Jurassic Sewa/Shaqiaomu/Jiebuqu formations) in the southern Qiangtang subterrane. The Gamulong Formation is characterized by sedimentary recycling in the trench, likely in response to a tectonic event (possibly the continental collision). Together with the previous studies, this work on the occurrence of the Gamulong Formation indicates that the Lhasa-Qiangtang initial collision could have occurred in Middle Jurassic time (~166 Ma).

Zircon U-Pb Geochronology of Two Basement Cores (Kentucky, USA): Implications for Late Mesoproterozoic Sedimentation and Tectonics in the Eastern Midcontinent

AbstractBasement cores from two wells drilled west and east of the Grenville front consist of feldspathic litharenite and granitic orthogneiss, respectively. Detrital zircon U-Pb ages for the litharenite define a broad dominant U-Pb age mode at ca. 1115 Ma. The dominant mode matches that for the type locality of the Middle Run Formation in the Ohio subsurface and is interpreted to consist of detrital zircons sourced from East Continent Rift volcanic sources (ca. 1100 Ma) and Grenville Shawinigan granites/gneisses (1120–1180 Ma). The youngest detrital zircon ages (ca. 1020 Ma) require a maximum depositional age that is at least 70 My younger than the time of Midcontinent and East Continent rifting and magmatism. We propose that the litharenite is correlative with the Middle Run Formation in Ohio and was deposited in an evolving late Grenville rift/foreland basin adjacent to the exhuming Grenville orogen. Zircon U-Pb secondary-ion mass spectrometry ages from orthogneiss define a discordant array with interc...

Provenance of Mesozoic clastic rocks within the Bangong-Nujiang suture zone, central Tibet: Implications for the age of the initial Lhasa-Qiangtang collision

The Bangong-Nujiang suture zone, separating the Lhasa and Qiangtang blocks of the Tibetan Plateau, is marked by remnants of the Bangong-Nujiang oceanic basin. In the Gaize area of central Tibet, Mesozoic sedimentary strata recording the evolution of the basin and subsequent collision between these two blocks include the Upper Triassic-Lower Jurassic turbidites of the Mugagangri Group, the Upper Jurassic-Lower Cretaceous sandstone-dominated Wuga and Shamuluo formations, and the Upper Cretaceous molasse deposits of the Jingzhushan Formation. The Shamuluo and Jingzhushan formations rest unconformably on the underlying Mugagangri Group and Wuga Formation, respectively. In this contribution, we analyze petrographic components of sandstones and U-Pb-Hf isotopic compositions of detrital zircons from the Wuga and Jingzhushan formations for the first time. Based on the youngest detrital zircon ages, the maximum depositional ages of the Wuga and Jingzhushan formations are suggested to be ∼147–150Ma and ∼79–91Ma, respectively. Petrographic and isotopic results indicate that sediments in the Wuga Formation were mainly sourced from the accretionary complex (preserved as the Mugagangri Group) in the north, while sediments in the Jingzhushan Formation have mixed sources from the Lhasa block, the Qiangtang block and the intervening suture zone. Provenance analysis, together with regional data, suggests that the Upper Jurassic-Lower Cretaceous Wuga and Shamuluo formations were deposited in a peripheral foreland basin and a residual-sea basin, respectively, in response to the Lhasa-Qiangtang collision, whereas the Upper Cretaceous Jingzhushan Formation reflects continental molasse deposition during the post-collisional stage. The development of the peripheral foreland basin evidenced by deposition of the Wuga Formation reveals that the age of the initial Lhasa-Qiangtang collision might be the latest Jurassic (∼150Ma).

The subduction-accretion history of the Bangong-Nujiang Ocean: Constraints from provenance and geochronology of the Mesozoic strata near Gaize, central Tibet

The Mesozoic strata, within the Bangong-Nujiang suture zone in central Tibet, recorded critical information about the subduction-accretion processes of the Bangong-Nujiang Ocean prior to the Lhasa-Qiangtang collision. This paper reports detailed field observations, petrographic descriptions, sandstone detrital zircon U-Pb ages and Hf isotopic analyses from an accretionary complex (preserved as Mugagangri Group) and the unconformably overlying Shamuluo Formation near Gaize. The youngest detrital zircon ages, together with other age constraints from literature, suggest that the Mugagangri Group was deposited during late Triassic-early Jurassic, while the Shamuluo Formation was deposited during late Jurassic-early Cretaceous. Based on the differences in lithology, age and provenance, the Mugagangri Group is subdivided into the upper, middle and lower subunits. These units are younging structurally downward/southward, consistent with models of progressive off-scrapping and accretion in a southward-facing subduction complex. The upper subunit, comprising mainly quartz-sandstone and siliceous mud/shale, was deposited in abyssal plain environment close to the Qiangtang passive margin during late Triassic, with sediments derived from the southern Qiangtang block. The middle and lower subunits comprise mainly lithic-quartz-sandstone and mud/shale, containing abundant ultramafic/ophiolitic fragments. The middle subunit, of late Triassic-early Jurassic age, records a transition in tectono-depositional setting from abyssal plain to trench-wedge basin, with sudden influx of sediments sourced from the central Qiangtang metamorphic belt and northern Qiangtang magmatic belt. The appearance of ultramafic/ophiolitic fragments in the middle subunit reflects the subduction initiation. The lower subunit was deposited in a trench-wedge basin during early Jurassic, with influx of Jurassic-aged zircons originating from the newly active southern Qiangtang magmatic arc. The lower subunit records the onset of arc magmatism related to the northward subduction of the Bangong-Nujiang Ocean. The Shamuluo Formation, comprising mainly lithic-feldspar-sandstone with limestone interlayers, was deposited in a post-collisional residual-sea or pre-collisional trench-slope basin, with sediments derived entirely from the Qiangtang block.

Maximum sedimentation ages and provenance of metasedimentary rocks from Tinos Island, Cycladic blueschist belt, Greece

U–Pb zircon ages of five metasedimentary rocks from the Lower Unit on Tinos Island (Cycladic blueschist belt, Greece) document supply of detritus from various Proterozoic, Paleozoic and Mesozoic source rocks as well as post-depositional metamorphic zircon formation. Essential features of the studied zircon populations are Late Cretaceous (70–80 Ma) maximum sedimentation ages for the lithostratigraphic succession above the lowermost dolomite marble, significant contributions from Triassic to Neoproterozoic source rocks, minor influx of detritus recording Paleoproterozoic and older provenance (1.9–2.1, 2.4–2.5 and 2.7–2.8 Ga) and a lack or paucity of zircons with Mesoproterozoic ages (1.1–1.8 Ga). In combination with biostratigraphic evidence, the new dataset indicates that Late Cretaceous or younger rocks occur on top of or very close to the basal Triassic metacarbonates, suggesting a gap in the stratigraphic record near the base of the metamorphic succession. The time frame for sediment deposition is bracketed by the youngest detrital zircon ages (70–80 Ma) and metamorphic overgrowths that are related to high-pressure/low-temperature overprinting in the Eocene. This time interval possibly indicates a significant difference to the sedimentation history of the southern Cyclades, where Late Cretaceous detrital zircons have not yet been detected.

Soft-sediment deformation structures in the Cretaceous Zhucheng depression, Shandong Province, East China; their character, deformation timing and tectonic implications

Various plastic and brittle soft-sediment deformation structures (SSDS) are recognized in Cretaceous sedimentary rocks of the Zhucheng depression, East China record important information on the different sediment characteristics, depositional settings and tectonic movements involved in their formation. The recognized SSDS include undulate folds, mound-and-sag structures, diapirs, convolute features and a seismically induced unconformity. The Lower Cretaceous sedimentary rocks are fine grained, lacustrine deposits, whereas those of the Upper Cretaceous are coarse-grained sandstones and conglomerates formed in an alluvial fan or flood-plain setting. These SSDS with coarse-grained rocks are characterized by fault grading, load cast structures, ball and pillow structures and plunged sediment mixture structures. We propose that the SSDS was triggered by paleo-earthquakes. Alternating deformed and undeformed layers suggest frequent and repeated seismic activity. Stratigraphic correlations, the evaluation of magmatic events and the youngest detrital zircon ages indicate that the deformational events occurred mainly in the Early Cretaceous between 118Ma to 105Ma, and in the Late Cretaceous at approximately 100Ma. Numerous giant hadrosaurid fossil skeletons have been found in the Upper Cretaceous Wangshi Group, and unusual and abundant dinosaur tracks are preserved in the Lower Cretaceous Yangzhuang Formation of the Laiyang Group. The zones of widespread SSDS closely underlie and overlie the dinosaur fossil-bearing strata. The depositional setting changed in response to multiple paleoseismic events and regional tectonic movements. After many paleoearthquakes and environmental changes in the Early Cretaceous, many dinosaurs appear to have migrated, based on the presence of many tracks with a similar orientation in lacustrine sedimentary rocks. In the Late Cretaceous strata, large-scale dinosaur fossil layers are associated with paleo-earthquake records, suggesting that the dinosaur fossil burial may be associated with large-scale debris flows triggered by frequent earthquakes. Based on regional tectonic setting, the distribution of SSDS and the predicted paleo-earthquake magnitudes, the seismogenic fault may have been the Wulian Fault.

Closing the Canada Basin: Detrital zircon geochronology relationships between the North Slope of Arctic Alaska and the Franklinian mobile belt of Arctic Canada

Constraining the pre-opening paleogeography of the Canadian and Alaskan margins of the Canada Basin is a first-order objective in resolving the plate tectonic evolution of the Amerasia Basin of the Arctic Ocean. The most widely accepted model for opening of the Canada Basin involves counterclockwise rotation of Arctic Alaska away from Arctic Canada about a pole of rotation in the Mackenzie Delta region, although numerous other kinematic models have been proposed. The rotation model is tested using detrital zircon U-Pb geochronology of 12 samples from Middle Mississippian to Early-Middle Jurassic strata (Ellesmerian and lower Beaufortian megasequences) obtained from wells and outcrop along Alaska’s North Slope. These northerly-derived strata were deposited in fluvial to nearshore marine environments along the south-facing (present-day) shelf margin of the Arctic Alaska Basin and contain 360–390 Ma, 415–470 Ma, 500–750 Ma, 0.9–2.1 Ga, and 2.4–3.2 Ga zircon populations. Detrital zircon age populations in Ellesmerian and lower Beaufortian strata are remarkably similar to detrital zircon populations from Devonian foreland clastic wedge strata in the Canadian Arctic Islands and northern Yukon Territory. A paleogeographic setting in which Arctic Alaska received sediments recycled from the Devonian foreland clastic wedge and underlying Franklinian Basin strata is most consistent with the model of [Embry (1990)][1] in which northern Alaska lay within the foreland fold and thrust belt of the Franklinian mobile belt prior to the opening of the Canada Basin. The sequences that are inferred to have been the long-lived source region for Ellesmerian and lower Beaufortian strata were uplifted by Paleozoic (predominantly Late Devonian) deformation that has been documented along the Canadian and Alaskan margins. Triassic and Jurassic strata deposited along the Arctic Canada, Arctic Alaska, and northern Yukon shelves have detrital zircon ages that are significantly older than the youngest detrital zircon ages (Mesozoic) in coeval strata that were deposited west of Hanna Trough and north of the Sverdrup Basin axis, supporting continuity of these bathymetric features prior to opening of the Canada Basin. [1]: #ref-32