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The Yangtze Block in South China constitutes an important Precambrian landmass in the present East Asian continent. The Neoproterozoic sedimentary successions of the Hengdan Group in the NW Yangtze Block record essential information for deciphering the Neoproterozoic tectonics along the NW margin. However, its depositional age, provenance and tectonic properties remain uncertain. Here, a combined analysis of detrital zircon U–Pb dating and geochemistry is performed on representative samples from the Hengdan Group. Concordant dating results of samples from the bottom and upper parts constrain the maximum depositional age at c. 720 Ma. Detrital zircon age patterns of samples reveal a uniformly pronounced age peak at c. 915–720 Ma, which is consistent with the magmatic pulses in domains at the NW end of the Yangtze Block. In addition, these samples display left-sloping post-Archaean Australian shale (PAAS)-normalized rare-earth element patterns and variable trace element patterns, resembling sediments accumulated in a basin related to an active continental margin geodynamic setting. Provenance analysis reveals that the main sources featured intermediate to felsic components, which experienced rapid erosion and sedimentation. These integrated new investigations, along with previous compilations, indicate that the Hengdan Group might have been deposited in a fore-arc basin controlled by subduction beneath the Bikou Terrane. Thus, such interpretation further supports proposals for subduction-related tectonics along the western margin of the Yangtze Block during the early Neoproterozoic. [ABSTRACT FROM AUTHOR]

A study of heavy mineral assemblages, rutile compositions, and detrital zircon age populations in Namurian to Westphalian sandstones in North Wales, deposited in the southwestern part of the Pennine Basin of the United Kingdom, has revealed considerable complexity in their provenance history. The Pendleian to Marsdenian Cefn‐y‐fedw Sandstone Formation, which is known to have been derived from the Wales–Brabant Massif (WBM) to the south on the basis of palaeocurrent and petrographic information, has a heavy mineral assemblage characteristic of this southerly provenance, and includes Late Neoproterozoic zircons apparently of local WBM origin. However, the formation is dominated by zircons that were most probably recycled from sandstones of northern origin from the Caledonian Belt that had been previously deposited over the massif during Late Devonian times, and, as such, has a comparable history to the sedimentologically‐equivalent Morridge Formation of the English Midlands. Heavy mineral analysis shows that sandstones in the Brigantian Minera Formation and Yeadonian part of the Bowland Shale Formation are of similar southern provenance. The Yeadonian Gwespyr Sandstone, previously interpreted as having a northern origin, similar to the time‐equivalent Rough Rock, has variations in heavy mineral analysis and zircon spectrum that suggest a complex provenance history and includes sand bodies with northern, western, and southern origins. [ABSTRACT FROM AUTHOR]

The gneisses outcropping in the Larsemann Hills of East Antarctica are ideal for studying the composition and evolution of the Prydz tectonic belt. In this study, detailed petrological analyses, phase equilibrium modelling, and zircon analyses were performed on a felsic orthogneiss from the Broknes Peninsula in the Larsemann Hills. The study results show that the protolith of the felsic gneiss is granite, which is further identified to have been an S-type granitoid. The felsic orthogneiss intruded into the basement complex at ~976 Ma. The magmatic zircons in the felsic orthogneiss have lower LREE and higher HREE contents than those of the metamorphic zircons in the same rock. The felsic gneiss consists of the mineral assemblage garnet +ilmenite+ plagioclase +K-feldspar + sillimanite + quartz and underwent granulite facies metamorphism in the Grenvillian period (～899 Ma), with peak conditions of ～870°C and ～9.5 kbar. The Larsemann Hills should be categorized as the orogenic process from arc-continent collision to continent-continent collision during the Grenvillian period, crust thickening(~899 Ma) and subsequent collapse(550–500 Ma). [ABSTRACT FROM AUTHOR]

The absence of a fully preserved foreland basin system in the central-eastern Yarlung-Zangpo Suture Zone (YZSZ) of Tibet has hindered the understanding of the initial timing of the India-Asia collision along strike. To address this issue, remnant foredeep and wedge-top deposits of the foreland basin system are described from the Tethyan Himalaya sequence and the YZSZ in the Xigaze area. The foredeep is defined by the olistostrome of the Zongzhuo Formation, which consists of matrix and blocks, including chert, limestone, sandstone and volcanic rocks. Based on the matrix properties, the Zongzhuo Formation is divided into two units: a lower member (Zhilong unit) with a matrix composed of black shale and thin layers of siltstone and an upper member (Yongla unit) with a matrix composed of distinctly red shale or yellow-green siliceous mudstone with interbedded siltstone and limestone. The Zongzhuo Formation is dated to 65–57 Ma by detrital zircon U - Pb chronology and radiolarian assemblages. In the YZSZ, the Puxia and Jiabi units are interpreted as wedge-top deposits consisting of mudstone matrix and exotic blocks, such as sandstone, chert and limestone. The maximum depositional ages (MDAs) of the sandstone blocks from both units are ca. 65–59 Ma. Detrital zircon provenance analysis and trace element data exclude an intraoceanic arc origin and point to a source from the Gangdese arc and recycled accretionary wedge in the suture zone. Therefore, we propose that the initial collision between India and Asia occurred at 65 Ma in the central-eastern YZSZ. • We report a remnant peripheral foreland basin at the Yarlung-Zangpo Suture Zone. • The foredeep consists of the Zongzhuo Formation on the Tethyan Himalaya. • The wedge-top, exposed on the accretionary wedge, contains Jiabi and Puxia units. • The foredeep implies the India-Asia collision is no later than 65 Ma. • The ages and provenance of wedge-top and foredeep support a single-stage collision. [ABSTRACT FROM AUTHOR]

• The Huangcheng basin has undergone three compression events since 100 Ma. • Slickenside analysis reveals north–south and east–west compression stresses. • Cretaceous sedimentary rocks in the area are sourced from the Qilian Shan-Nan Shan Block and Alashan Block. The sedimentary rocks in the Hexi Corridor, north-eastern Tibetan Plateau, contain information about crustal deformation during and after the closure of the Meso-Tethys Ocean and the growth of the Tibetan Plateau. This study examines the origin and deformation of Late Mesozoic sedimentary rocks in the Huangcheng basin where the source of Late Mesozoic sedimentary rocks and deformation styles of faults and folds remain controversial. Results from field mapping, fault kinematic analysis, and detrital zircon analysis suggest that the study region might have experienced three episodes of compression events since 100 Ma. The first episode is characterized by north–south compression, which could reflect the convergence between the Alashan and the Qilian Shan-Nan Shan. The second episode reflects the reactivation of the thrust faults related to the far-field effect resulting from the closure of the Neo-Tethys Ocean. The third episode is the regional east–west trending thrust due to the block extrusion. One set of slickensides indicates north–south compression while a second set implies nearly east–west compression, which could represent different stress orientations between the first two episodes and the third episode. Eleven detrital zircon samples from the Cretaceous to Neogene strata were collected for detrital zircon U-Pb dating and rare earth element analysis. Zircon U-Pb ages show major peaks around 265 Ma and 455 Ma with a notable lack of ages around 1.0 Ga. We infer that the source of the Neogene sedimentary rocks was the Qilian Shan while the sources of the Cretaceous sedimentary rocks were the Qilian Shan and Alashan. [ABSTRACT FROM AUTHOR]

• Closure of the Ediacaran-Cambrian ocean between the OMAS and Africa. • Multiple metamorphic events in the Central Ribeira belt. • Tectonic setting of two superposed basins: The Costeiro and Búzios basins. The Ribeira Belt represents a deeply eroded orogen which exposes rocks from the different stages of magmatic arcs and associated metasedimentary basins. This contribution focus on the last collisional episode between the Outer Magmatic Arc System (OMAS) and the Cabo Frio Terrane (Angola craton). The OMAS represents a long-lived magmatic arc that collided against the Inner Magmatic System (IMAS) at ca. 590 Ma (M1 metamorphism), and against the Cabo Frio Terrane at ca. 530 Ma (M2 metamorphism). The nature of the magmatism recorded in the first collisional episode, and the subduction polarity of the second is a current topic of debate. New U-Pb age and Lu-Hf analyses in zircon grains from units close to the contact are presented to propose a tectonic model for the closure of the oceanic space between the OMAS and the Cabo Frio Terrane. The results in combination with published data suggest that the metasedimentary rocks of the São Fidélis Group are in a back-arc position of the OMAS and were affected by both the M1 and M2 metamorphic episodes, reflected by the presence of metamorphic zircons with ages between ca. 592–553 Ma and 543–533 Ma. The orthogneiss of the Tinguí Complex intrusive in the back-arc metasedimentary units yielded a crystallization age of 578 ± 9 Ma, coeval with the syn -collisional stage M1. A younger metamorphic overprint at 529 ± 7 Ma was also detected (syn -M2). The orthogneiss of the Região dos Lagos Complex (Cabo Frio Terrane) rendered a crystallization age of 1968 ± 26 and a M2 metamorphic overprint at 522 Ma. Zircon analyses from folded leucosomes in the orthogneiss also indicated a crystallization age of 523 ± 10 Ma, which constrain the time of folding after thrusting. Undeformed post-collisional granitoids and pegmatites yielded crystallization ages between 496 and 499 Ma, closing the tectonic evolution of the belt with the orogen collapse. Our results corroborate with terrane accretion model for the Central Segment of the Ribeira Belt. [ABSTRACT FROM AUTHOR]

[Display omitted] • Basalt and underlying tephra-rich carbonate olistostrome occur as interlayers in middle Permian limestone. • Basalt and basaltic tuff in olistostrome are products of syn-rifting magmatism in ca. 267 Ma. • Parent magma of basalt was sourced from low-degree partial melting of the asthenospheric mantle. • Asthenosphere upwelling resulted in the rifting of the upper Yangtze carbonate platform, SW China. Rifting of the upper Yangtze carbonate platform in the middle Permian gave rise to Kaijiang-Liangping (KL) and Deyang-Wusheng (DW) rifts in the NE Sichuan basin, SW China. These rifts are well-endowed in gas, hosting eight out of nine discovered gas fields in the Sichuan basin. However, the initiation time and geodynamics driving the rifting are poorly understood, which restricts petroleum evaluation and exploration in the KL and DW regions. Our field surveys found that the basalt and underlying volcano-carbonate olistostrome in Huayingshan Mountain (Mt.) in the NE Sichuan basin are the interlayers within the limestone of the middle Permian Maokou Formation (Fm.). Stratigraphically, the Maokou Fm. and the late Permian sedimentary rocks above it form a mega-sequence from rifting to subsidence. Within the Maokou Fm., the rifting sequence comprises the basalt, volcano-carbonate olistostrome (tephra-rich polymictic breccia limestone) and limestone oligomictic breccia of the slope facies. A new data set composed of stratigraphic, petrologic, geochemical, isotopic and zircon U-Pb analyses shows that the basalt is sub-alkaline basalt and displays OIB-like geochemical signatures. The tephra block is basaltic tuff with abundant lath-shaped plagioclase crystals. Parent magma of the basalt originated from low-degree partial melting of the slightly enriched asthenospheric mantle at the garnet-spinel peridotite transition zone. The basalt and volcano-carbonate olistostrome reveal syn-rifting magmatism in ca. 267 ± 3 Ma. The KL and DW rift basins developed on the substratum of the upper Yangtze carbonate platform, and were triggered by asthenosphere upwelling during the Wordian stage. [ABSTRACT FROM AUTHOR]

Multiple parting bands within Permo–Carboniferous coal that are generally enriched in critical metals in the northern North China have been confirmed to be altered from volcanic ash (tonsteins). The tonsteins and adjacent coal in some areas contain boehmite with varying contents. Whether or not the boehmite has a relationship with the volcanic-ash-altered kaolinite remains poorly understood. Herein, petrographical, mineralogical, whole-rock geochemical, and in-situ elemental analyses, combined with U–Pb–Hf isotopic analysis of zircon, were performed for the boehmite-bearing/rich partings and coal collected from the eastern edge of the Datong and Jungar coalfields. Except for the boehmite, well-ordered kaolinite is predominant in the parting samples, where the columnar/tabular and vermicular kaolinite are commonly present. Additionally, the zircons separated from the representative parting and coal samples are mostly igneous origin with only one age population of ca. 300 Ma, almost same with the depositional age of the coal, suggesting that the kaolinite in the inorganic constitutes of the investigated coal seams were mainly altered from volcanic ash. Numerous fine-grained boehmite exhibit textural features of replacement for columnar/tabular and vermicular kaolinite along the cleavage cracks in the parting samples, suggesting that such boehmite were formed from desilication of volcanic-ash-altered kaolinite. The tonsteins and coal along the eastern edge of the coalfields were uplifted and influenced by fault activities due to Indosinian and Yanshan orogeny, which were probably experienced intensive leaching by silica-undersaturated percolating water and groundwater, resulting in desilication of volcanic-ash-altered kaolinite and precipitation of residual Al as boehmite. The Ga, preserved in the alumina octahedral sheets of volcanic-ash-altered kaolinite, were retained by boehmite due to its very similar geochemical behavior with Al. The formation of boehmite and its retention for Ga made a contribution to the genesis of high–Al–Ga coal in the northern North China. • Boehmite was formed from desilication of volcanic-ash-altered kaolinite. • Formation of boehmite and its retention for Ga contributed to genesis of high–Al–Ga coal. • Volcanic ash play a role in enrichment of critical metals in Permo–Carboniferous coal of North China. [ABSTRACT FROM AUTHOR]

[Display omitted] Evolution of internal or external oceanic domains can bring decisive indications into the mode of formation of supercontinents, which is key to understand the supercontinent cycle. Defining the type of ocean evolving in the Central Asian Orogenic belt (CAOB) is thus critical to better understand the Earth's supercontinental evolution. In this contribution, we provide systematic and combined U-Pb, trace-element in zircon and hafnium-in-zircon analyses of four turbidites of the Altai accretionary wedge. These turbiditic rocks provide constraints into the early Paleozoic subduction-accretionary stages of the Mongolian Accretionary Collage (MAC) and show a major detrital age peak in the Cambro-Ordovician (∼490–500 Ma), with minor Neo- and Paleo-Proterozoic to Archean peaks. The zircon trace-elemental patterns are consistent with derivation mostly from magmatic arc (with granitoids affinity), interpreted as detritus sourced from the Ikh-Mongol continental arc system further north-east (present coordinates). The main detrital zircon peak together with the zircon magmatic arc origin suggest that the subduction-accretionary stage was active from 550 to 430 Ma showing mixed ε Hf (t) values (-20 to + 15). A summary of the detrital zircon ε Hf (t) values from 550 to 430 Ma suggests a continuous increase of ε Hf (t) mean values from + 0.2 to + 6.1 towards younger ages. The younging juvenile trend can be compared to the evolution of external orogeny, therefore consistent with a Pacific-type accretionary system facing an external ocean. At last, the results combined with two paleo-geographic reconstructions from the literature imply that the MAC may have been part of the Peri-Siberian accretionary orogeny in the early Paleozoic. [ABSTRACT FROM AUTHOR]

An increasing number of detrital zircon U–Pb geochronological data have been reported to trace sediment provenance for the Cenozoic Qaidam basin, which is crucial to understanding crustal deformation, paleoclimate change and basin development in northern Tibetan Plateau and to assessing geodynamic models of plateau growth. However, the existing provenance interpretations are highly diverse and how the northern Tibet has evolved remains controversial. This contribution presents new detrital zircon dating results from Cenozoic outcrop and borehole samples and compiles published data from the whole Qaidam basin, adjacent small Cenozoic basins and the surrounding mountains. Our new synthesis indicates that, Paleoproterozoic signals (1800–2000 Ma and 2350–2500 Ma), rather than the Permian–Triassic ages, can be applied effectively to distinguish the Qilian, Altun and Eastern Kunlun-sourced detrital zircons. The Cenozoic Qaidam basin exhibits spatiotemporally variable detrital zircon age populations. Most sandstones from the western and southern basin are characterized by Phanerozoic bimodal age spectra (i.e., 400–480 Ma and 220–280 Ma) with minor Precambrian signals, indicating major contributions from the neighboring Altun and Eastern Kunlun ranges. By contrast, almost all the northern and eastern basin sandstones display prominent early Paleozoic detrital zircon ages; but Paleoproterozoic, Neoproterozoic (750–950 Ma) and Permian–Triassic signals only appear as dominant age clusters in some samples. Different temporal variation trends are observed from the investigated sections in this region, revealing variable zircon supply from different micro-terranes in the Qilian Mountains. This implies that using detrital zircon provenance data from a single section or from a local area of the Qaidam basin to address regional tectonic and climatic issues of the northern Tibetan Plateau unlikely provide useful results. We propose that the Cenozoic Qaidam basin deposits were derived from localized, adjacent source regions, rather than cross-basinal, distant mountains. Our conclusions support models with synchronous deformation throughout most of northern Tibet in the Cenozoic. The observed spatiotemporal variations in detrital zircon populations are not only attributed to tectonic deformation-induced source changes, but can also be due to heterogeneity of the source terranes (e.g., durability and zircon fertility) and variable factors (e.g., hydrodynamic sorting, recycling and sedimentary microenvironment) in transport-deposition processes. This study also highlights the importance of involving detrital zircon textural and sedimentological parameters to zircon provenance interpretations. An integrated provenance analysis combining other detritus components is helpful to comprehensively characterize source-to-sink systems for sedimentary basins. • Spatiotemporal variations in Qaidam basin detrital zircon ages are evident. • Paleoproterozoic zircon ages are unique signatures for the Qilian Mountains. • Cenozoic deposits were from nearby sources, rather than cross-basinal mountains. • Varied source-to-sink systems contribute to detrital zircon provenance variations. • Detrital zircon analysis on a local area cannot address regional tectonic issues. [ABSTRACT FROM AUTHOR]

The Cenozoic sedimentary infill of the Qaidam Basin in the northern Tibetan Plateau provide significant insights into the uplift history and the tectonic evolution of the basin-bounding mountain ranges. Along the SW basin margin, a continuous record is preserved in the ~3000-m-thick Cenozoic succession at the Changweitai area. An up-section switch from marginal and deep lacustrine sedimentation to lacustrine delta-alluvial fan deposition indicates progradation and increasingly basinward advance of sediment transportation systems. Provenance data from sandstone petrology, palaeocurrent analysis and zircon U-Pb geochronology suggest that the Eastern Kunlun Range has been consistently providing material to the SW Qaidam basin since the deposition of the upper Xiaganchaigou Formation, indicating its latest uplift episode prior to the Late Eocene (before 35.5 Ma). However, variation in depositional systems indicates a clear shift in sediment provenance between the deposition of the Xiayoushashan Formation and the Shangyoushashan Formation. We propose that the Cenozoic Eastern Kunlun Range experienced a northward encroachment of shortening into the Qaidam Basin. During the Early Miocene, extensive topographic growth of the Altyn Tagh Range caused by reactivation of the Altyn Tagh strike-slip fault, provided the main source of sediment for the western Qaidam basin. Subsequently, a new source for the basin was provided by the uplifting Qimen Tagh subrange since ~15 Ma. [ABSTRACT FROM AUTHOR]

The Paleozoic strata are widely distributed in the northwest of the Ordos Basin, and the provenance attributes of the basin sediments during this period are still controversial. In this paper, the detrital zircon LA-MC-ICPMS U-Pb age test was conducted on the drilling core samples of the Shanxi Formation of the Upper Paleozoic in the Otuokeqi area of the Ordos Basin, and the provenance age and the characteristic of the Shanxi formation in the Otuokeqi area in the northwest were discussed. The cathodoluminescence image shows that the detrital zircon has a clear core-edge structure, and most of the cores have clear oscillatory zonings, which suggests that they are magmatic in origin. Zircons have no oscillatory zoning structure that shows the cause of metamorphism. The age of detrital zircon is dominated by Paleoproterozoic and can be divided into four groups, which are 2500~2300 Ma, 2100~1600 Ma, 470~400 Ma, and 360~260 Ma. The first two groups are the specific manifestations of the Precambrian Fuping Movement (2.5 billion years) and the Luliang Movement (1.8 billion years) of the North China Craton. The third and fourth groups of detrital zircons mainly come from Paleozoic magmatic rocks formed by the subduction and collision of the Siberian plate and the North China plate. The ε Hf t value of zircon ranges from -18.36 to 4.33, and the age of the second-order Hf model T DM 2 ranges from 2491 to 1175 Ma. The source rock reflecting the provenance of the sediments comes from the material recycling of the Paleoproterozoic and Mesoproterozoic in the crust, combined with the Meso-Neoproterozoic detrital zircons discovered this time, indicating that the provenance area has experienced Greenwellian orogeny. [ABSTRACT FROM AUTHOR]

In the Transdanubian Range, Pannonian Basin, Hungary, karstic sinkholes on a planation surface of Triassic carbonates are filled by grey clayey–silty kaolin deposits. The provenance and accumulation age of these strongly altered terrestrial karst-filling sediments are constrained by X-ray powder diffraction, heavy mineral analysis and zircon U–Pb dating. The heavy minerals of the Southern Bakony Mountains samples are dominated by the ultra-stable zircon–rutile–tourmaline association. Zircon U–Pb data indicate accumulation between 20 and 16 Ma. Furthermore, Archaean to Palaeogene grains were also determined, reflecting the principally fluvial recycling of Eocene bauxites and their cover sequences. In contrast, the sample from the Keszthely Hills consists almost exclusively of airborne material including zircons of 18–14 Ma, reflecting a dominant contribution from the Carpathian–Pannonian Neogene volcanism. The shift in the Miocene age components is inferred to have been caused by the landscape evolution and burial history of the planation surface remnants controlled by local block tectonics. [ABSTRACT FROM AUTHOR]

The Wulian complex is located on the northern margin of the Sulu orogenic belt, and was formed by collision between the North China Craton (NCC) to the north and South China Craton (SCC) to the south. It consists of the metasedimentary Wulian Group, gneissic granite and meta-diorite. The U–Pb analyses for the detrital zircons from the Wulian Group exhibit one predominant age population of 2600–2400 Ma with a peak at c. 2.5 Ga and several secondary age populations of > 3000, 3000–2800, 2800–2600, 2200–2000, 1900–1800, 1500–1300 and 1250–950 Ma; some metamorphic zircons have metamorphic ages of c. 2.7, 2.55–2.45, 2.1–2.0 and 1.95–1.80 Ga, which are consistent with magmatic-metamorphic events in the SCC. Additionally, the Wulian Group was intruded by the gneissic granite and meta-diorite at c. 0.76 Ga, attributed to Neoproterozoic syn-rifting bimodal magmatic activity in the SCC and derived from partial melting of Archaean continental crust and depleted mantle, respectively. The Wulian Group therefore has tectonic affinity to the SCC and was mainly sourced from the SCC. The detrital zircons have positive and negative ϵHf(t) values, indicating that their source rocks were derived from reworking of both ancient and juvenile crustal rocks. The major early Precambrian crustal growth took place during c. 3.4–2.5 Ga with a dominant peak at 2.96 Ga and several secondary peaks at 3.27, 2.74 and 2.52 Ga. The two oldest zircons with ages of 3307 and 3347 Ma record the recycling of ancient continental crust (> 3.35 Ga) and crustal growth prior to c. 3.95 Ga in the SCC. [ABSTRACT FROM AUTHOR]

In the present work, a natural zircon megacryst SA02 (the exact provenance unknown) is investigated as a new potential reference material for U–Pb geochronology and Hf–O isotopic composition analysis via micro-beam methods. The precise and accurate U–Pb age is determined by the chemical abrasion isotope dilution thermal ionization mass-spectrometry (CA-ID-TIMS) method. The resultant mean 206Pb/238U date is 535.10 ± 0.24 Ma (2s, n = 2), interpreted as the crystallization age of the zircon megacryst. The mean ID-TIMS 206Pb/238U date of 533.7 ± 3.7 Ma (2s, n = 8) is recommended as the working value for micro-beam analyses when using untreated SA02 zircon grains as the primary reference material. 206Pb/238U dates of 533.0 ± 6.2 Ma (2s, n = 57) and 534 ± 8 Ma (2s, n = 101) obtained by secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) respectively are reproducible and in agreement with the results of ID-TIMS within < 0.3% relative analytical errors. Solution data of Hf isotope compositions measured by multi-collector ICP-MS (MC-ICP-MS) from SA02 zircon yield a mean 176Hf/177Hf of 0.282287 ± 0.000016 (2s, n = 31), which is recommended as a reference value for microbeam analysis. Hf isotope analyses by LA-MC-ICP-MS yield homogeneous Hf isotopic compositions with a mean 176Hf/177Hf of 0.282289 ± 0.000033 (2s, n = 142) identical to the solution value. The mean δ18O value measured by laser fluorination is 6.03 ± 0.28‰ (2s, n = 13), which is consistent with the result of SIMS analysis. [ABSTRACT FROM AUTHOR]

The Yanliao Biota is notable for producing rare and well-preserved Jurassic vertebrate fossils. Many discoveries in the Bawanggou section, northern Hebei Province have greatly enhanced our knowledge of important vertebrate fossils from the Yanliao Biota, including an arboreal euharamiyidan mammal, maniraptoran theropods, salamanders and pterosaurs. However, lacking of precise dating for the sediments bearing these fossils in the Bawanggou section hampered further understanding of the evolution of this biota. Here we report a chronology based on secondary ion mass spectrometry (SIMS) U-Pb zircon analyses from the Tiaojishan Formation bearing the Yanliao Biota in the Bawanggou section. Three bentonite layers dated to 159.0 ± 1.1 Ma, 159.5 ± 0.8 Ma, and 159.8 ± 0.8 Ma, respectively, were found to be interstratified with the fossil-bearing layer in this area. These data place the Yanliao Biota from Qinglong in the Oxfordian Stage of the Upper Jurassic and provide stringent constraints on vertebrates discovered in the Bawanggou section. Previous biostratigraphic studies and our geochronology show that fossil assemblage in the Bawanggou section is coeval with the Linglongta Biota (late Yanliao Biota) preserved in the Daxishan section (western Liaoning Province). [ABSTRACT FROM AUTHOR]

As a record of oceanic subduction, an accretionary complex plays a key role in the reconstruction of plate tectonic history. The Kekesentao ophiolitic mélange between the Chinese Altai orogen to the north and the Kazakhstan collage to the south played an important role in the subduction–accretion of the Chinese Altai in the Palaeozoic. This article provides new structural field relations, and petrographic, geochemical, and geochronologic data for the Kekesentao ophiolitic mélange, and detrital zircon analyses of turbidites that are imbricated with the mélange. The Kekesentao mélange consists of ultramafic rocks, meta‐gabbros, pillow basalts, cherts, and imbricated trench turbidites, tuffaceous sandstones and quartz schists (ocean plate stratigraphy). The mélange shows a 'block in matrix' structure in the field, and the general imbricated dip of the thrust system is to the N‐NE, indicating southward accretion. Pillow basalts and meta‐gabbros have a typical N‐MORB geochemical signature, and the U–Pb zircon age of a meta‐gabbro, interpreted as the age of pre‐subduction oceanic crust, is Early Devonian (399–393 Ma). The upper time limit of accretion of the mélange is constrained by a Late Devonian (361 Ma) intrusive granitic pluton. Detrital zircon ages of surrounding turbidites range from 369 to 3,114 Ma, which is typical of magmatic 540–460 Ma zircons from the Chinese Altai, suggesting that the Chinese Altai arc was the source of zircons in the mélange. The Kekesentao ophiolite was accreted to the accretionary complex before the Late Devonian. Our analysis of structures, ocean plate stratigraphy, and zircon isotopic provenance of the Kekesentao ophiolitic mélange and turbidites provides a robust conclusion that southward growth of the accretionary complex in the Kekesentao area of the Chinese Altai was semi‐continuous from the Early Palaeozoic to Devonian. [ABSTRACT FROM AUTHOR]

Apatite and zircon (U-Th) = He thermochronological data are obtained through a combination of crystal selection, He content measurement by crystal heating with analysis using noble gas mass spectrometry, and measurement of U, Th, and Sm contents by crystal dissolution as well as solution analysis using inductively coupled plasma mass spectrometry (ICP-MS). This contribution documents the methods for helium thermochronology used at the GEOPS laboratory, Paris-Saclay University, between 2007 and the present that allow apatite and zircon (U-Th) = He data to be obtained with precision. More specifically, we show that the He content can be determined with precision (at 5 %) and accuracy using a calibration of the He sensitivity based on the Durango apatite, and its use also appears crucial to check for He and U-Th-Sm analytical problems. The Durango apatite used as a standard is therefore a suitable mineral to perform precise He calibration and yields (U-Th) / He ages of 31.1±1.4 Ma with an analytical error of less than 5% (1σ). The (U-Th) / He ages for the Fish Canyon Tuff zircon standard yield a dispersion of about 9% (1σ) with a mean age of 27.0±2.6 Ma, which is comparable to other laboratories. For the long-term quality control of the (U-Th) / He data, attention is paid to evaluating the drift of He sensitivity and blanks through time as well as that of (U-Th) / He ages and Th / U ratios (with Sm / Th when possible), all relying on the use of Durango apatite and Fish Canyon Tuff zircon as standards. [ABSTRACT FROM AUTHOR]

Zircon Raman dating based on irradiation damage is a debated concept but not an established geo- /thermochronological method. One issue is the temperature range of radiation-damage annealing over geological timescales. We conducted isochronal and isothermal annealing experiments on radiation-damaged zircons between 500 and 1000 °C for durations between 10 min and 5 d to describe the annealing kinetics. We measured the widths (Γ) and positions (ω) of the ν1(SiO4), ν2(SiO4), and ν3(SiO4) internal Raman bands, and the external rotation Raman band at ~ 974, 438, 1008, and 356 cm-1 after each annealing step. We fitted a Johnson--Mehl--Avrami--Kolmogorov and a distributed activation energy model to the fractional annealing data, calculated from the widths of the ν2(SiOO4), ν3(SiOO4), and external rotation bands. From the kinetic models, we determined closure temperatures Tc for damage accumulation for each Raman band. Tc ranges from 330 to 370 °C for the internal ν2(SiO4) and ν3(SiO4) bands; the external rotation band is more sensitive to thermal annealing (Tc ~ 260 to 310 °C). Our estimates are in general agreement with previous ones, but more geological evidence is needed to validate the results. The Tc difference for the different Raman bands offers the prospect of a multi-closure-temperature zircon Raman thermochronometer. [ABSTRACT FROM AUTHOR]

Zircon U-Pb geochronology is a staple of crustal evolution studies and sedimentary provenance analysis. Constructing (detrital) U-Pb age spectra is straightforward for concordant 206Pb/238U and 207Pb/206Pb compositions. But unfortunately, many U-Pb datasets contain a significant proportion of discordant analyses. This paper investigates two decisions that must be made when analysing such discordant U-Pb data. First, the analyst must choose whether to use the 206Pb/238U or the 207Pb/206Pb date. The 206Pb/238U method is more precise for young samples, whereas the 207Pb/206Pb method is better suited for old samples. However there is no agreement which "cutoff" should be used to switch between the two. This subjective decision can be avoided by using single-grain concordia ages. These represent a kind of weighted mean between the 206Pb/238U and 207Pb/206Pb methods, which offers better precision than either of the latter two methods. A second subjective decision is how to define the discordance cutoff between "good" and "bad" data. Discordance is usually defined as (1) the relative age difference between the 206Pb/238U and 207Pb/206Pb dates. However, this paper shows that several other definitions are possible as well, including (2) the absolute age difference; (3) the common-Pb fraction according to the Stacey-Kramers mantle evolution model; (4) the p value of concordance; (5) the perpendicular log ratio (or "Aitchison") distance to the concordia line; and (6) the log ratio distance to the maximum likelihood composition on the concordia line. Applying these six discordance filters to a 70 869-grain dataset of zircon U-Pb compositions reveals that (i) the relative age discordance filter tends to suppress the young age components in U-Pb age spectra, whilst inflating the older age components; (ii) the Stacey--Kramers discordance filter is more likely to reject old grains and less likely to reject young ones; (iii) the p-value-based discordance filter has the undesirable effect of biasing the results towards the least precise measurements; (iv) the log-ratio-based discordance filters are strictest for Proterozoic grains and more lenient for Phanerozoic and Archaean age components; (v) of all the methods, the log ratio distance to the concordia composition produces the best results, in the sense that it produces age spectra that most closely match those of the unfiltered data: it sharpens age spectra but does not change their shape. The popular relative age definition fares the worst according to this criterion. All the methods presented in this paper have been implemented in the IsoplotR toolbox for geochronology. [ABSTRACT FROM AUTHOR]

The same unetched and chemically etched apatite crystals from five rock samples were dated by the U--Pb method via laser ablation inductively coupled plasma mass spectrometry (LA--ICP-MS). The objective of this study is to test whether chemical etching required for apatite fission track analysis impacts the precision and accuracy of apatite U--Pb geochronology. The results of this experiment suggest that etching has insignificant effects on the accuracy of apatite U--Pb ages obtained by LA--ICP-MS. Therefore, LA--ICP-MS is reliable for U--Pb analysis as part of apatite fission track and U--Pb double dating. [ABSTRACT FROM AUTHOR]

Up to 2 km of siliciclastic and chemical sedimentary rocks, metamorphosed to greenschist facies, are preserved in the Baraboo Hills of southern Wisconsin. The strata compose two sedimentary successions separated by an angular unconformity. The lower succession includes the Baraboo quartzite, Seeley slate, and Freedom Formation, and the upper includes the Dake quartzite and Rowley Creek slate. Despite being studied for more than 100 y, the exposed section is only recently subdivided into informal members based on identification of sedimentary lithofacies and geologic mapping. This study integrates detrital zircon and paleocurrent analyses with sedimentologic and stratigraphic observations derived from detailed field mapping of the Baraboo and Dake quartzites. Our purpose is twofold: (1) characterize lithofacies of the Baraboo quartzite to interpret the environments of deposition for this unit and (2) evaluate sediment provenance and constrain depositional age. Lithofacies, paleocurrent, and detrital zircon U-Pb analyses of the Baraboo quartzite record fluvial braid plain, eolian, and fluvial-, tide- and wave-influenced deltaic depositional environments with sediments sourced from the north and deposited after 1714 ± 17 Ma. Lithofacies compose two backstepping alluvial to marine successions separated by a thick, laterally continuous coastal dune deposit. North-directed paleocurrents and detrital zircon ages confirm the Dake quartzite is a distinct unit with maximum depositional age of less than 1630.1 ± 8.6 Ma. Deposition of the Dake quartzite reflects basement uplift that postdates deposition of the Baraboo quartzite. The hiatus represented by the unconformity beneath the Dake quartzite is unconstrained and may represent more than 100 My. [ABSTRACT FROM AUTHOR]

The provocative hypothesis that the Shinumo Sandstone in the depths of Grand Canyon was the source for clasts of orthoquartzite in conglomerate of the Sespe Formation of coastal California, if verified, would indicate that a major river system flowed southwest from the Colorado Plateau to the Pacific Ocean prior to opening of the Gulf of California, and would imply that Grand Canyon had been carved to within a few hundred meters of its modern depth at the time of this drainage connection. The proposed Eocene Shinumo-Sespe connection, however, is not supported by detrital zircon nor paleomagneticinclination data and is refuted by thermochronology that shows that the Shinumo Sandstone of eastern Grand Canyon was >60 °C (~1.8 km deep) and hence not incised at this time. A proposed 20 Ma (Miocene) Shinumo-Sespe drainage connection based on clasts in the Sespe Formation is also refuted. We point out numerous caveats and non-unique interpretations of paleomagnetic data from clasts. Further, our detrital zircon analysis requires diverse sources for Sespe clasts, with better statistical matches for the four "most- Shinumolike" Sespe clasts with quartzites of the Big Bear Group and Ontario Ridge metasedimentary succession of the Transverse Ranges, Horse Thief Springs Formation from Death Valley, and Troy Quartzite of central Arizona. Diverse thermochronologic and geologic data also refute a Miocene river pathway through western Grand Canyon and Grand Wash trough. Thus, Sespe clasts do not require a drainage connection from Grand Canyon or the Colorado Plateau and provide no constraints for the history of carving of Grand Canyon. Instead, abundant evidence refutes the "old" (70-17 Ma) Grand Canyon models and supports a <6 Ma Grand Canyon. [ABSTRACT FROM AUTHOR]

The South Altyn Block (SAB), located along the southern margin of the Altyn Tagh in Qaidam Basin, has a significant relationship with the tectonics of the Qaidam Basin basement. This study presents the petrological features, geochemical compositions, and zircon U–Pb and Hf isotope data of four granitic plutons from the eastern segment of the SAB to constrain the petrogenesis and tectonic setting of this region during the Palaeozoic. Basing on previous U–Pb dating results, the zircon U–Pb analysis in this study suggests that Palaeozoic magmatic events can be subdivided into four episodes: Late Cambrian (approximately 502 Ma), Late Ordovician (approximately 444 Ma), Early Devonian, and Middle Permian (approximately 271 Ma). The Palaeozoic granitoids were derived mainly from Neoproterozoic juvenile crustal components, with minor palaeoproterozoic ancient materials. The S‐ and I‐type granitoids in Late Cambrian indicate a compressional tectonic environment with respect to subduction, and A‐type granitoids suggest post‐collision regime. The Late Ordovician granodiorites of A‐type imply typical magmatism within a post‐collision extensional setting. Ascribing to the subduction of Palaeo‐Tethys Ocean during the Devonian, S‐type granites were emplaced in the Early Devonian accompanied with the crust thickening. The Middle Permian magmatic events include a series of S‐type granitoids, demonstrating the setting of oceanic subduction along with the closure of the Palaeo‐Tethys Ocean. [ABSTRACT FROM AUTHOR]

The Jiangshan gold deposit is the largest, most recently‐discovered gold deposit in the Bengbu Uplift. The ore bodies are located in the structural fracture zone of the Zhuangzili Formation (Ar3), with major Pb‐Zn and Au reserves. In this study, LA‐ICP‐MS zircon U‐Pb analyses yielded a crystallization age of 111.5 ± 1.8 Ma for the quartz diorite porphyry in Jiangshan. The quartz diorite porphyry has high Ba and Sr content, with low Y and Yb content, which is similar to the characteristics of adakitic rocks. They are enriched in large ion lithophile elements (LILEs, e.g., Ba, U) and light rare earth elements (LREEs), while depleted in high field strength elements (HFSEs, e.g., Nb, Ti) and heavy rare earth element (HREEs). They have zircon ∊Hf(t) values of –23.52 to –21.14 (mean = –22.32). and Hf model ages of 2419.76 to 2569.39 Ma. The magma source area is the lower crust. Magma primarily came from the partial melting of the lower crust, with the addition of some mantle material. The quartz diorite porphyries are characterized by high zircon TTi‐in‐zircon values (608–757°C), Ce4+/Ce3+ ratios (71.97–1387.10) and Eu/Eu∗ ratios (0.46–1.08), indicating high temperature and magmatic oxygen fugacities. High temperatures can provide heat to fluids and highly oxidized magmas can control the behavior and speciation of sulfides, thus controlling the behavior of Au. Finally, the ore‐forming fluid is enriched and precipitated in a favorable structural space to form the Jiangshan Au deposit. [ABSTRACT FROM AUTHOR]

BACKGROUND: The zircon epoxy resins are commonly used for LA - ICP - MS zircon research. OBJECTIVES: To study the influence of the surface morphology of zircon epoxy for zircon analysis by LA - ICP - MS. METHODS: The surface morphologies of zircon epoxy were investigated by AFM. The AFM was also used to study and compare the surface morphology of zircons under different modes and conditions with 193 nm laser system. The Ar - ion milling was used for zircon epoxy. RESULTS: The surface of the zircon epoxy resins was generally smooth but slightly uneven. There are scratches from a few to tens nm on the surface of zircon. The height differences and gaps are between zircons and epoxy resin. The results show that the slightly uneven has less impact on the analysis accuracy than other laser parameters such as energy density, frequency, and movement rate. The depth and morphology of different matrixes by linear scanning were different. The scanning depths on the NIST610, CGSG, 91500 are decreases under the same laser condition. The scratches of zircon surface were not obvious after Ar - ion milling, but the zircons may be damaged. CONCLUSIONS: The surface morphology of zircon in epoxy resins has less impact on the analysis accuracy for LA - ICP - MS. The influence and application of Ar - ion milling for LA - ICP - MS need to be further studied. [ABSTRACT FROM AUTHOR]

The sedimentary architecture and provenance of the early Mesozoic incipient northern Gulf of Mexico basin remains controversial due to both lack of outcrop exposure and sample scarcity across the southern United States with subcrop depths approaching 6 km. The Eagle Mills Formation and coeval deposition across the northern Gulf of Mexico provides both a stratigraphic foundation for some ~15-km-thick overlying Mesozoic and Cenozoic deposits, and a coeval pre-salt equivalent for southern synrift deposits, in one of the most economically significant hydrocarbon basins in the world. This study presents more than 3200 new detrital zircon U-Pb analyses from sixteen Late Triassic presalt, siliciclastic, subcrop well samples, and combines over 14,000 linear kilometers of 2-D multi-channel seismic reflection data, 1511 geophysical well logs, and biostratigraphic data from 2478 wells to construct basin-scale pre-salt isochore and structure maps spanning the northern Gulf of Mexico margin from Florida to the USA-Mexican border. The data show that incipient Gulf of Mexico paleodrainage pathways held individual distinctions between basement sources and tectonic controls in three primary regions across the northern Gulf of Mexico: (1) The western Gulf of Mexico paleodrainage extended from the Central Texas uplift highlands to the submarine Potosi Fan on the western margin of Laurentia with local tributary sources from the East Mexico Arc, Yucatán/Maya, and Marathon-Ouachita provinces as evidenced by inverse Monte Carlo unmixing of peri-Gondwanan (ca. 700-500 Ma), Appalachian/Ouachita (500-280 Ma), Grenville (1250-950 Ma), and Mid-Continent/Granite- Rhyolite Province (1500-1300 Ma) detrital zircon ages. Isochore and associated geophysical well and seismic data suggest that by Early Jurassic time this depocenter had shifted into the present-day western Gulf of Mexico as East Mexico Arc development continued. (2) Southerly drainage in the northcentral Gulf of Mexico region bifurcated around the Sabine and Monroe uplifted terranes with southwestern flow characterized by peri-Gondwanan detrital zircon ages from late Paleozoic accreted basement or discrete flexural successor basins, and southeastern fluvial networks distinguished by traditional North American basement province sources including Grenville, Mid-Continent, and Yavapai-Mazatzal. (3) Eastern Gulf of Mexico regional paleodrainage, with regional southern flow dictated by the brittle extensional tectonics of the South Georgia Rift as well as the regional southern flexure of the South Florida Basin, resulted in almost all pre-salt detrital zircon siliciclastic ages from this region to be dominated by local Gondwanan/peri-Gondwanan aged sources including the proximal Suwannee terrane and Osceola Granite complex. These regional, synrift sediment provenance models provide the first critical allochthonous evidence of Late Triassic- Early Jurassic paleodrainage stemming from the Appalachian-Ouachita hinterlands into the incipient northern Gulf of Mexico basin with critical implications for pre-salt hydrocarbon exploration and carbon sequestration reservoir potential. [ABSTRACT FROM AUTHOR]

The South China Block (SCB) has been regarded by many as an integral part of Gondwana, but proposed timing and processes for its accretion to Gondwana vary and remain contentious, largely owing to the lack of reliable Pan‐African age paleomagnetic data and tectono‐magmatic records from the SCB. Integrated in situ U‐Pb ages and Hf‐O isotope analyses of detrital zircons from geochronologically well‐calibrated Ediacaran‐Cambrian sedimentary rocks of western SCB reveal age populations of 2.51, 1.85, 1.20, 0.80, and 0.52 Ga. Detrital zircon age spectra indicate a major tectonic transition for the SCB during 0.56–0.54 Ga, interpreted to reflect the beginning of the collision between SCB‐Indochina and NW India blocks. The collisional event lasted until early Ordovician, leading to the suturing of the SCB‐Indochina to the northern margin of East Gondwana. Plain Language Summary: The South China Block is thought to be a part of the Gondwana superterrane, which was composed of more than half of all continents 650–400 million years ago (Ma). However, questions of when and how the South China Block collided with Gondwana are yet to be answered. In this study, we conducted provenance analyses of sedimentary rocks whose depositional ages were known via radioisotopic dating and chemo‐biostratigraphy in the western South China Block. The results reveal a change in tectonic setting of the South China Block at 560–540 Ma, interpreted as the onset of the collision between the South China Block and India along the northern margin of East Gondwana. Key Points: 1.2‐Ga detrital zircon population is present in age‐calibrated Ediacaran‐Cambrian strata of western South China BlockA major change in tectonic setting of the South China Block occurred in 0.56–0.54 GaThe connection between the South China Block and NW India Block started in the late Ediacaran [ABSTRACT FROM AUTHOR]

Post-orogenic alkaline intrusions from the Sulu Orogenic Belt of eastern North China Craton consist of A-type granites. In this study, we report U–Pb zircon ages, geochemical data, Sr–Nd–Pb, and zircon Hf isotopic data for these rocks. The LA-ICP-MS U–Pb zircon analyses yield consistent ages ranging from 127.1 ± 2.4 to 119.5 ± 4.8 Ma for four samples. The alkaline rocks are characterized by high total alkalis (K2O + Na2O = 8.32–10.11 wt%), light rare-earth element enrichment, and heavy rare-earth element depletion, with a wide range (La/Yb)N values (20–48), moderate negative Eu anomalies (Eu/Eu* = 0.50–0.74), enrichment in large-ion lithophile elements (LILEs, i.e., Rb, Th, U and Pb), and depletion in Ba, Sr and high field strength elements (HFSEs, i.e., Nb, Ta, and Ti), high (87Sr/86Sr)i ranging from 0.708 to 0.7089, low εNd (t) values from −19.4 to −16.8, (206Pb/204Pb)i = 16.751 – 16.935, (207Pb/204Pb)i = 15.381−15.535, (208Pb/204Pb)i = 37.472–37.838, negative εHf (t) values between −21.3 and −25.7 for the magmatic zircons, and larger TDM2 model ages from 2.5 to 2.8 Ga. These results suggest that the rocks were derived from a common enriched lithospheric mantle source that was metasomatized by foundered lower crustal eclogitic materials before magma generation. Furthermore, the geochemical and isotopic feature implies that the primary magma of these rocks originated through partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from lower crust eclogite. These rocks in this study may have been generated by subsequent fractionation of potassium feldspar, plagioclase, ilmenite, and/or rutile. However, negligible crustal contamination occurred during the diagenesis process. [ABSTRACT FROM AUTHOR]

The Mount Gee Sinter and the Radium Ridge Breccia within the Mount Painter Inlier, South Australia, preserve evidence of a hydrothermal event peaking during the Late Devonian (ca 365 Ma). Prior to this study, limited data relating to this event were available, but our results of 846 LA-ICPMS U–Pb monazite analyses indicate the timing of this hydrothermal event. The dominant monazite population age of ca 363 Ma for the Mount Gee Sinter represents earlier phases of a protracted hydrothermal–epithermal system, whereas a later epithermal phase cross-cuts rocks hosting ca 220 Ma age zircon. Parts of the Radium Ridge Breccia have been recently interpreted as a series of Early Cretaceous glacial events. Zircon ages (604 zircon analyses) from the Radium Ridge Breccia define a detrital population dominated by ca 1585 Ma ages, consistent with derivation of clasts within the breccia from local granitic and metasedimentary basement. The Radium Ridge Breccia is, however, dominated by a ca 367 Ma aged monazite population, probably reflecting overprinting of the local Mesoproterozoic granitic basement rock during the same hydrothermal event as formed the earlier phase of the Mount Gee Sinter. It is interpreted that the monazite ca 365 Ma age reflects a significant Late Devonian hydrothermal event, evidenced locally in the southern Mount Painter Inlier, resulting from localised heat flow but with thermal implications for the regional geology of the northwestern Curnamona Province. [ABSTRACT FROM AUTHOR]

The Grès Singuliers unit represents an anomalous occurrence of a siliciclastic-dominated sedimentary system typifying a restricted geographic area around the Mont Blanc massif. Deposited during Early Jurassic rifting, this unit was influenced by the tectonic processes responsible for its development. This contribution integrates and reconciles sedimentological, stratigraphic and tectonic data and discusses the tectono-sedimentary evolution of the Mont Blanc basement and its autochthonous sedimentary cover. Based on depositional facies, a petrographic and detrital zircon provenance analysis, we propose that the Grès Singuliers unit is mainly derived from erosion of the local basement and pre-rift sedimentary cover. Furthermore, recognition of Jurassic cataclasites and black gouges capping the Mont Blanc basement confirms the hypothesis that the Mont Blanc domain formed an extensional core complex. The source to sink relationship between the Mont Blanc detachment system and the Grès Singuliers unit, as well as timing and location within the Alpine rift system, allows us to interpret this unit as the syn-tectonic sedimentary response to crustal necking, responsible for the onset of localized severe crustal/lithospheric thinning in the European margin of the Alpine Tethys rift system. The main result of this study was to show that the exhumation and uplift of basement during crustal/lithospheric necking produced a new source area for clastic sedimentary systems. Therefore, the local occurrence of a siliciclastic unit similar to the Grès Singuliers along passive margins may be symptomatic of necking zones in other rift systems. [ABSTRACT FROM AUTHOR]

The Sanshilipu monzogranites is located in the northern margin of the South Qinling Block, with an outcrop of about 10 km2, and as an intrusion into Palaeozoic Danfeng ophiolitic mélange. The samples consist mainly of plagioclase, K‐feldspar, quartz, biotite, and minor titanite, apatite, magnetite, with contents of SiO2 (61.73–68.49%), Al2O3 (14.58–16.61%), K2O + Na2O (5.79–8.87%), MgO (1.07–2.91%), and low TiO2 (0.55–0.83%), similar to those of I‐type granite. They also show high concentrations of LREE, Pb, and Sr, slightly negative Eu, but low HREE, Nb, Ta, and Y. High Sr and Sr/Y, low Y characteristics are similar to those of adakite. High precision LA‐ICP‐MS U–Pb dating and trace element analysis of zircon in the Sanshilipu granite yielded a concordant age of 205 ± 1 Ma. This age is apparently younger than the closure age of the Mian‐Lue Ocean (242–221 Ma). We propose that the Sanshilipu monzogranites formed by magma mixing of thickened lower crust and limited mantle‐derived mafic magma during post‐collision of the South China and North China blocks. [ABSTRACT FROM AUTHOR]

To detect the exhumation history of the southwestern South China Block (SCB), we performed fission track (FT) analysis on zircon and apatite grains in granitoid and sedimentary samples. From east to west, the study area includes the Yunkai Massif, Lingshan granitic belt, Shiwandashan Basin, and eastern margin of the Youjiang Basin. The granite sample of the Yunkai Massif has two peaks of 75 and 92 Ma for zircon FT dating. The Lingshan granitic belt samples yield zircon FT central ages from 135 to 132 Ma. The Permian bauxite samples of the Youjiang Basin yield zircon FT central ages from 109 to 93 Ma and display age peaks at ~97–93 Ma. The Yunkai Massif granite sample has two peaks at 74 and 104 Ma for apatite FT dating, while the Lingshan granitic belt sample has two peaks at 81 and 111 Ma. The cooling paths of the Yunkai Massif sample started with an Early Cretaceous (~120–100 Ma) cooling event that brought the granitoids into the apatite partial annealing zone (PAZ). Through comparative studies, we suggest that the southwestern SCB underwent three periods of crustal uplift during ~135–132, ~111–92, and ~ 81–74 Ma, respectively, which is consistent with the regional stratigraphic unconformity and crustal extension. Only the Yunkai Massif and Lingshan granitic belt were uplifted during ~135–132 Ma. During ~111–92 Ma, the southwestern SCB experienced crustal uplift, and the basal conglomerate began to deposit in the Shiwandashan Basin. Late Cretaceous uplifted occurred during ~81–74 Ma, and the Yunkai Massif was uplifted throughout the Cretaceous. From 97 to 92 Ma, the Permian bauxite deposits in the Youjiang Basin were uplifted, which provided the basis of the later transformation to Quaternary bauxite. [ABSTRACT FROM AUTHOR]

The retrieval of accurate thermal histories recorded by the (U-Th)/He system relies on empirical estimates of diffusion kinetics from natural minerals, although the difficulty in obtaining samples with homogeneous gas concentrations (required for accurate diffusivities) has limited the collection of such datasets. Whole-grain analyses are relatively time- and cost-effective, but natural 4He concentration heterogeneities caused by α-ejection, diffusional rounding, and/or parent nuclide zonation present an unquantified source of error. We employ a 1D spherical finite difference diffusion model to simulate effects of natural sources of He concentration heterogeneities, with a focus on the zircon (U-Th)/He (ZHe) system. Using He concentration profiles affected by various natural heterogeneities, models consistently predict that diffusion kinetics are strongly underestimated using such methods, especially at low gas release fractions. These underestimations are driven by He depletion near the grain boundary caused by α-ejection, and exacerbated by U and Th depletion. Conversely, models with parent nuclide (and therefore He) enrichment near the grain boundary compensate for ejection-based loss, yielding more accurate diffusion kinetics overall. A comparison of these results to real step-heating data yields few similarities, however, with He releases from real zircons either being linear in Arrhenius space, or having anomalously high diffusivities at low fractional releases. Radiation damage and its annealing are also significant factors affecting He diffusional mechanics. Using diffusivities and annealing as predicted by the current ZHe forward model, cycled step-heating of high-dose zircons (>1 × 1018 α/g) predict that diffusion decreases consistently with increased heating temperatures, similar to observations. The forward model predicts that annealing beyond this threshold dose should increase diffusivity, which is not observed, however. These results suggest that whole-grain step-heating data may provide a reasonable proxy for empirically measuring damage annealing kinetics in zircon. Major discrepancies between model results and real data reveal the need for more cycled-step heating data to understand the full complexities of He diffusion dynamics. [ABSTRACT FROM AUTHOR]

Previously dated zircon crystals from the Amalia-Kraaipan granite-greenstone belts and Makoppa Dome were analysed for their Lu-Hf isotopic characteristics to refine the geological evolution of these areas. Samples from the Makoppa Dome, belonging to the Pietersburg Block, largely fall within the epsilon Hf-age range for granitoids from the eastern part of the block. However, the oldest 3.01 to 3.03 Ga trondhjemitic gneisses show that reworking of juvenile mafic crust started earlier in the western than the eastern part of the block, suggesting a diachronous tectonic evolution. The three granitoids from the Amalia-Kraaipan area fall within the field for Pietersburg and Kimberley block granitoids. Contribution from older crustal material is seen in a 3.08 Ga schist, likely derived from a volcanic protolith, from the Madibe Belt, in the far east of the Kimberley Block, with a mantle extraction age of 3.25 to 3.45 Ga. The data suggest that the Kimberley Block, like the Pietersburg Block, also contains (minor) ancient crustal components, derived from a depleted mantle source prior to 3.1 Ga. The new data suggest that the Kimberley and Pietersburg blocks underwent a very similar Paleo- to Mesoarchean crustal evolution, with a major crust formation event at 3.1 to 3.0 Ga followed by successive crust reworking until 2.77 Ga. Lavas of the Ventersdorp Supergroup, for which zircon grains from a ca. 2.75 lapilli tuff give Hfi of +2, are the first evidence of a juvenile source, after 300 Myr of crustal reworking. [ABSTRACT FROM AUTHOR]

In the northwest of the Himalayan-Tibetan Orogen, the ∼250 km-long Kongur Shan extensional system in the eastern Pamir was formed during the convergence between the Indian and Asian plates. Tectonic activity of the Kongur Shan normal fault and the Tashkurgan normal fault can help to reveal the origin of east-west extension along the Kongur Shan extensional system. The Kongur Shan fault has been extensively studied, while the Tashkurgan fault calls for systemic research. In this study, low-temperature thermochronology including apatite fission track analysis and apatite and zircon (U-Th)/He analyses is applied to constrain the timing of activity of the Tashkurgan fault. Results indicate that the Tashkurgan fault initiated at 10−5 Ma, and most likely at 6−5 Ma. The footwall of the Tashkurgan fault has been exhumed at an average exhumation rate of 0.6−0.9 mm/a since the initiation of the Tashkurgan fault. Combined with previous research on the Kongur Shan fault, we believe that the origin of east-west extension along the Kongur Shan extensional system was driven by gravitational collapse of over-thickened Pamir crust. [ABSTRACT FROM AUTHOR]

The study of the petrogenesis of some magmatic rocks with special geochemical attributes provides effective information for us to explore the deep geodynamic background of their formation. A series of granitic porphyry dykes have been found in the mélange zone of the Asa region in southern Tibet, whose genesis may be closely related to the evolution of the Meso-Tethyan Ocean. Regional geodynamic evolution is investigated by whole-rock geochemical analysis, zircon U–Pb dating and Lu–Hf isotopic analysis of two porphyritic granites. The Asa porphyritic granites have high SiO2 (74.29–78.65 wt %) and alkalis (Na2O + K2O = 6.51–9.35 wt %) contents, and low Al2O3 (11.60–14.51 wt %), CaO (0.04–0.19 wt MgO (0.01–0.10 wt %) contents. They are enriched in Zr, Nb, Ce, Y and Hf and depleted in Ti, Ba, Sr and P, consistent with A-type granites. The samples are relatively rich in LREEs, with LREE/HREE ratios of 1.73–3.04. They display negative Eu anomalies (Eu/Eu* = 0.24–0.28) and obvious Ce anomalies in some samples. Zircon U–Pb analyses show that the porphyritic granites formed in late Early Cretaceous time, 107.4 to 105.5 Ma. Zircon εHf(t) values are in the range of 6.9 to 12.0. These data indicate that the porphyritic granites were sourced from interaction between mantle-derived and juvenile lower crust-derived melts, with the addition of oceanic sediment-derived melts. This occurred when the subducting Bangong–Nujiang oceanic crust split to create a slab window. Rising asthenosphere triggered re-melting of lower crust basalts, resulting in the formation of the late Early Cretaceous A-type granites around Asa. [ABSTRACT FROM AUTHOR]

Structural analysis and new zircon U/Pb geochronology were performed in the Cuonadong Dome in order to test the hypothesis that the top‐to‐North deformation in the North Himalayan Gneiss Domes (NHGD) has been correlated with deformation along the South Tibetan detachment system (STDS). Structural analysis suggests that the X‐axes of sheath folds at the different flanks of the dome are consistent, and show average a trend and plunge of 350° and 18°. Many shear sense indicators are recorded in the ductile shear zone during the top‐to‐north deformation, including the augen structure, σ‐type and δ‐type rotating porphyroclast, S–C fabric and pressure shadow structure. The development of the sheath folds first provide a direct‐field structural evidence that represents a deeper ductile manifestation of the STDS, and further suggests that the top‐to‐north deformation in the NHGD have been correlated with deformation along the STDS. The emplacement of the synkinematic granites at ca. 32 Ma exposed at the core of the sheath folds is also interpreted as the initiation of slip along the STDS. [ABSTRACT FROM AUTHOR]

The eastern Hexi Corridor, northwest China, is located at the tectonic junction of the Alxa Block, the North China Craton, and the Qinling‐Qilian Orogen. The early Paleozoic Xiangshan Group record critical information regarding paleoenvironment, paleoclimate and paleotectonic setting, from which we here present a focused study on the chert beds within the Xiangshan Group. Through field mapping, microstructural observation, whole‐rock geochemistry analyses and detrital zircon dating, we suggest that the Xiangshan Group chert was deposited along a passive continental margin, formed primarily through biological activity with minor hydrothermal influence and terrestrial input. The characteristics of the chert support a low latitude sedimentary paleoenvironmental origin, and reveal the fact that the Alxa Block was separated from the North China craton, while emerged some paleogeographic affinity with the Qilian region in the Middle‐Late Cambrian. [ABSTRACT FROM AUTHOR]

In the supercontinent of Rodinia, Baltica occurred next to Amazonia, then the two drifted away when Rodinia broke up. By the end of the Neoproterozoic, Baltica became an independent continent. At that time, Timanide orogen developed at its modern northeastern margin. In most paleogeographical reconstructions, the opposite (SW, Tornquist) edge faced the Tornquist Ocean and remained just a passive margin till the arrival of the Gondwana-born East Avalonia in the late Ordovician. However, preliminary isotopic studies of detrital zircons from the Tornquist passive margin succession hinted that rock components of Gondwana derivation reached Baltica already in the early Cambrian. In this paper, we examine 18 drill-cores of Ediacaran-Cambrian and Ordovician siliciclastic rocks from the tectonostratigraphic units along the SW–NE transect from Upper Silesia (USB) via Małopolska (MB) and the Holy Cross Mts (HCM) to the East European Platform (EEP), SE Poland, in terms of the provenance data gained from the LA-ICP-MS and SHRIMP analyses of 32 zircon samples. Rocks from all the units revealed abundant Cadomian 0.7–0.55 Ga detrital zircons (15–50% of the total analyzed grains) and other grains that yielded peaks at 0.9–1.2, 1.4–1.6, 1.8–2.2, 2.7–3.0 Ga assignable to Baltica rather than Amazonia. Such age spectra in the USB, HCM and EEP prove the proximity of peripheral (peri-Gondwanan) fragments of the Cadomian orogen to Baltica. These fragments formed the Teissyere-Tornquist Terrane Assemblage (TTA) that obliquely docked and overrode the thinned southwestern edge of Baltica which earlier accumulated Neoproterozoic rift and passive margin deposits. Our data show that in the late Ediacaran-early Cambrian, parts of the Cadomian orogenic belt became accreted to Baltica. [ABSTRACT FROM AUTHOR]

Although continental crust is characterized by the widespread occurrence of granitoids, the causal relationship between continental crust growth and granitic magmatism still remains enigmatic. While fractional crystallization of basaltic magmas (with or without crustal contamination) and partial melting of mafic lower crust are two feasible mechanisms for the production of granitoids in continental arc regions, the problem has been encountered in discriminating between the two mechanisms by whole-rock geochemistry. This can be resolved by an integrated study of zircon U-Pb ages and Hf-O isotopes together with whole-rock major-trace elements and Sr-Nd-Pb isotopes, which is illustrated for Mesozoic granitoids from the Gangdese orogen in southern Tibet. The results provide geochemical evidence for prompt reworking of the juvenile mafic arc crust in the newly accreted continental margin. The target granitoids exhibit high contents of SiO2 (65.76-70.75 wt%) and Na2O + K2O (6.38-8.15 wt%) but low contents of MgO (0.19-0.98 wt%), Fe2O3 (0.88-3.13 wt%), CaO (2.00-3.82 wt%), Ni (<5.8 ppm), and Cr (⩽10 ppm). They are enriched in large ion lithophile elements, Pb, and light rare earth elements but depleted in high field strength elements. The granitoids are relatively depleted in whole-rock Sr-Nd isotope compositions with low (87Sr/86Sr)i ratios of 0.7043-0.7048 and positive Nd(t) values of 0.5-2.6, and have relatively low 207Pb/204Pb and 208Pb/204Pb ratios at given 206Pb/204Pb ratios. Laser ablation-inductively coupled plasma-mass spectrometry and secondary ion mass spectrometry U-Pb dating on synmagmatic zircons yield ages of 77 ± 2-81 ± 1 Ma in the Late Cretaceous for their emplacement. Relict zircons have two groups of U-Pb ages in the late Mesozoic and the late Paleozoic, respectively. The whole-rock Sr-Nd isotopes in the granitoids are quite similar to those of Late Cretaceous mafic rocks in the Gangdese batholith. In addition, both synmagmatic zircons and relict zircons with Late Cretaceous U-Pb ages exhibit almost the same Hf-O isotope compositions to those of the slightly earlier mafic rocks. All these observations indicate that the granitoids were mainly derived from partial melting of the juvenile mafic arc crust. Therefore, reworking of the juvenile mafic arc crust is the mechanism for the origin of isotopically depleted granitoids in southern Tibet. It is this process that leads to differentiation of the juvenile mafic arc crust toward the felsic lithology in the continental arc. In this regard, the granitoids with depleted radiogenic isotope compositions do not necessarily contribute to the crustal growth at convergent plate boundaries. [ABSTRACT FROM AUTHOR]

Uranium--lead (U--Pb) geochronology was conducted by laser ablation -- inductively coupled plasma mass spectrometry (LA-ICPMS) on 7175 detrital zircon grains from 29 samples from the Coconino Sandstone, Moenkopi Formation, and Chinle Formation. These samples were recovered from ~520m of drill core that was acquired during the Colorado Plateau Coring Project (CPCP), located in Petrified Forest National Park (Arizona). A sample from the lower Permian Coconino Sandstone yields a broad distribution of Proterozoic and Paleozoic ages that are consistent with derivation from the Appalachian and Ouachita orogens, with little input from local basement or Ancestral Rocky Mountain sources. Four samples from the Holbrook Member of the Moenkopi Formation yield a different set of Precambrian and Paleozoic age groups, indicating derivation from the Ouachita orogen, the East Mexico arc, and the Permo-Triassic arc built along the Cordilleran margin. A total of 23 samples from the Chinle Formation contain variable proportions of Proterozoic and Paleozoic zircon grains but are dominated by Late Triassic grains. LA-ICPMS ages of these grains belong to five main groups that correspond to the Mesa Redondo Member, Blue Mesa Member and lower part of the Sonsela Member, upper part of the Sonsela Member, middle part of the Petrified Forest Member, and upper part of the Petrified Forest Member. The ages of pre-Triassic grains also correspond to these chronostratigraphic units and are interpreted to reflect varying contributions from the Appalachian orogen to the east, Ouachita orogen to the southeast, Precambrian basement exposed in the ancestral Mogollon Highlands to the south, East Mexico arc, and Permian--Triassic arc built along the southern Cordilleran margin. Triassic grains in each chronostratigraphic unit also have distinct U and thorium (Th) concentrations, which are interpreted to reflect temporal changes in the chemistry of arc magmatism. Comparison of our LA-ICPMS ages with available chemical abrasion thermal ionization mass spectrometry (CA-TIMS) ages and new magnetostratigraphic data provides new insights into the depositional history of the Chinle Formation, as well as methods utilized to determine depositional ages of fluvial strata. For parts of the Chinle Formation that are dominated by fine-grained clastic strata (e.g., mudstone and siltstone), such as the Blue Mesa Member and Petrified Forest Member, all three chronometers agree (to within ~1 Myr), and robust depositional chronologies have been determined. In contrast, for stratigraphic intervals dominated by coarse-grained clastic strata (e.g., sandstone), such as most of the Sonsela Member, the three chronologic records disagree due to recycling of older zircon grains and variable dilution of syn-depositional-age grains. This results in LAICPMS ages that significantly predate deposition and CA-TIMS ages that range between the other two chronometers. These complications challenge attempts to establish a well-defined chronostratigraphic age model for the Chinle Formation. [ABSTRACT FROM AUTHOR]

The gold mineralization in the Central Aldan ore district is genetically related to potassic calc-alkaline and alkaline magmatism dated at 115–150 Ma. The objective of this study is to establish the age of hydrothermal processes that accompanied the formation of Au-Te mineralization at the Samolazovsky Deposit. Based on the isotope-geochemical study of zircons from quartz-feldspar metasomatic rocks of the deposit, the granitoids and charnokites of the Nimnyr Complex (1 900–1 960 Ma) at the contact with the Yukhta monzonite-syenite massif (∼127 Ma) were studied. Zircon U-Pb dating was performed on a SHRIMP-II ion microprobe, and rare-earth and trace elements analyses of zircon were carried out in the same craters by secondary-ion mass spectrometry on a Cameca IMS-4f ion microprobe. It is revealed that the studied zircons have heterogeneous structures: dark core and lighter rim, which differ greatly in isotope-geochemical parameters. Zircon rims are cut by a network of fractures, extending into the central part of zircon grains. The rims yield a subconcordant age of 1 937±24 Ma, with an average total REE content of 550 ppm, which corresponds to the formation age of the Nimnyr Complex. All zircon cores yield a discordant age of 83±11 Ma and are characterized by a higher total REE content (∼1 812 ppm), as well as higher contents of U and non-formula elements (Ca, Sr, and Y) with respect to rims, due to the effect of fluid on zircons. Despite the limited number of zircon grains, the additional geochronological study of zircons from syenites of the ore-bearing Ryabinovy Massif has revealed the presence of two distinct age clusters: ∼125–138 and 76–83 Ma. The older ages of zircons from syenites are typical for the Central Aldan ore district. Until now, there is still no explanation for an age range (76–83 Ma) of single zircon grains from ore-bearing syenites of the Ryabinovy Massif. The obtained data suggest that the processes of activation (the effect of fluid) within the Central Aldan ore district continued until Late Mesozoic. With regards to the equivocal geotectonic position of the Mesozoic potassic magmatism in the study area and its high metallogenic potential, there exists an absolute necessity to determine the geochronological age of the rock formations. Therefore this study presents the Late Cretaceous geochronological data for the first time which can constrain the time-frame for the formation of gold-bearing magmatic and metasomatic rocks of the Aldan ore district. [ABSTRACT FROM AUTHOR]

Zirconium (Zr) plays a key role in the development of phases like zircon (ZrSiO4) and baddeleyite (ZrO2) in magmatic systems. These minerals are crucial for the study of geologic time and crustal evolution, and their high resistivity to weathering and erosion results in their preservation on timescales of billions of years. Although zircon and baddeleyite may also preserve a robust record of Zr isotope behavior in high-temperature terrestrial environments, little is known about the factors that control Zr isotope partitioning in magmatic systems, the petrogenetic significance of fractionated compositions, or how these variations are recorded in Zr-rich accessory phases. Here, we describe a new analytical protocol for accurately determining the Zr stable isotope composition of zircon by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), using the double-spike method to correct for procedural and instrumental mass bias. We apply this technique to test whether zircon crystallization in carbonatite magmatic systems is a driver of Zr isotope fractionation by interrogating the internal zonation of a zircon megacryst from the Mud Tank carbonatite (MTUR1). We find the MTUR1 megacryst to lack internal zoning within analytical uncertainties with a mean μ94/90ZrNIST = −55 ± 28 ppm (2 SD, n = 151), which suggests that zircon crystallization is not a driver of Zr isotope fractionation in carbonatite magmas. This observation is in stark contrast with those made in silicate magmatic systems, raising the possibility that the bonding environment of Zr4+ ions may be fundamentally different in carbonatite vs. silicate melts. Because of its remarkable homogeneity, the MTUR1 megacryst is an ideal natural reference material for Zr isotopic analysis of zircon using both solution and spatially resolved methods. The reproducibility of a pure Zr solution and our chemically purified zircon fractions indicate that the external reproducibility of our method is on the order of ±28 ppm for μ94/90Zr, or ±7 ppm per amu, at 95% confidence. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau, the largest highland on Earth, formed due to the collision of India-Asia over the past 50-60 m.y., and the evolution of the Tibetan Plateau impacts our knowledge of continental tectonics. Examination of the northernmost margin of the Tibetan Plateau is key to unravelling the deformation mechanisms acting in northern Tibet. The left-slip Altyn Tagh fault system defines the northwest margin of the Tibetan Plateau, separating the Western and Eastern Kunlun Ranges in the southwest. Both Cenozoic and pre-Cenozoic crustal deformation events at this junction between the Altyn Tagh and Kunlun Ranges were responsible for the construction of northwestern Tibet, yet the relative contribution of each phase remains unconstrained. The western domain of the Eastern Kunlun Range is marked by active NE-trending, left-slip deformation of the Altyn Tagh fault and an E-striking Cenozoic thrust system developed in response India-Asia collision. To better constrain the Paleozoic Altyn Tagh and Kunlun orogens and establish the Cenozoic structural framework, we conducted an integrated investigation involving detailed geologic mapping (~1:50,000 scale), U-Pb zircon geochronology, and synthesis of existing data sets across northwestern Tibet. Our new zircon analyses from Paleoproterozoic-Cretaceous strata constrain stratigraphic age and sediment provenance and highlight Proterozoic-Paleozoic arc activity. We propose a tectonic model for the Neoproterozoic-Mesozoic evolution of northwestern Tibet wherein restoration of an ~56-km-long balanced cross section across the western domain of the Eastern Kunlun suggests that Cenozoic minimum shortening strain was ~30% (~24 km shortening). Field evidence suggests this shortening commenced after ca. 25-20 Ma, which yields an average long-term shortening rate of 1.2-0.9 mm yr-1 and strain rates of 4.7 × 10-16 s-1 to 2.3 × 10-16 s-1. Geometric considerations demonstrate that this contractional deformation did not significantly contribute to left-slip offset on the Altyn Tagh fault, which has ~10 mm/yr slip rates. [ABSTRACT FROM AUTHOR]

Recent research on Paleo-Tethys tectonics has identified a huge late Paleozoic to Mesozoic igneous belt that extends more than 2500 km in the northeast Tibetan Plateau. However, the magma genesis and evolution in this belt remains a subject of considerable debate. This paper presents a combination of zircon U-Pb ages, mineral compositions, major and trace element concentrations, and Sr-Nd-Hf isotopic data for the plutons across the Zhiduo arc belt that marks the site connecting different tectonic-magmatic units. The studied rocks from one quartz diorite, two granodiorite plutons, and their mafic enclaves define a continuous compositional evolution varying from high- to medium- K calc-alkaline gabbroic diorite to granodiorite. Laser ablation-inductively coupled plasma-mass spectroscopy U-Pb analyses of zircons from these three plutonic suites and one mafic enclave yield Late Triassic ages of 222-217 Ma, establishing that the mafic and felsic magmas were nearly coeval. All these rocks are featured by zoned hornblende and plagioclase with Mg- and Ca-rich mantles or oscillatory change in compositions. They exhibit high and variable MgO (up to 4.88-5.66 wt%), Cr, and Ni contents except that one granitoid pluton (Dangjiangrong) possesses high Co (up to 145.0 ppm). They are characterized by subduction-type trace element patterns, with prominent positive Rb, Th, Pb, and K anomalies and negative Ba, Nb, P, and Ti. Together with continuous and heterogeneous Sr-, Nd-, and zircon Hf-isotopic compositions, it suggests that these Late Triassic high-Mg diorites and associated granitoids were generated through magma mixing and fractional crystallization accompanied by chemical exchange. Taking into account the magmatic record from nearby regions, we suggest that double-sided subduction and rollback of the subducting Paleo-Tethys oceanic slab is the main mechanism to generate geochemically-varied magmatism in the northeast Tibetan Plateau, and eventually close the Paleo-Tethys Ocean during much of the Late Triassic. [ABSTRACT FROM AUTHOR]

In situ U-Pb geochronology has been conducted using laser ablation inductively coupled mass spectrometry (LA-ICP-MS) on shocked and thermally metamorphosed apatite, titanite, and zircon grains from the Steen River impact structure, Canada. The dated relict mineral phases occur within impact melt-bearing breccias that underwent post-deposition sintering at 450 °C > T < 800 °C. Apatite yields a refined lower intercept age of 141 ± 4 Ma, which we interpret as the best estimate age for the Steen River impact event. Titanite was only partially reset; yielding a lower intercept age of 113 ± 41 Ma. Zircon yields a lower intercept impact age of 120 ± 14 Ma, which is considered a minimum best-estimate impact age. The most reset zircon analyses that control this lower intercept are complicated by combinations of common-Pb incorporation and recent Pb loss associated with granularized and radiation-damaged (metamict) domains. All three phases preserve Paleoproterozoic crystalline basement ages, with a single concordant 206Pb/238U age of 1914 ± 39 Ma from apatite, an upper intercept age of 1882 ± 11 Ma from zircon, and an upper intercept age of 1842 ± 9 Ma from titanite. For apatite, the degree of isotopic resetting is largely thermally controlled, with the extent of reset closely associated with textural setting (degree of grain armouring, melt proximity and sample temperature) and, to a lesser extent, by shock/thermally generated microstructures (i.e., planar fractures, micro-vesicles, and recrystallized domains). While titanite records an impact age that falls within error of apatite and zircon, the majority of grains experienced only partial isotopic resetting, which we attribute to incomplete Pb loss associated with rapid cooling and post-depositional sintering of the breccia matrix below the titanite closure temperature (∼800 °C). In zircon, ancient (impact) Pb loss was facilitated along defect-related, fast-diffusion pathways within pre-impact metamict domains, shock defects, and via recrystallization. These same domains were also subject to recent (post-impact) Pb loss and common Pb contamination, significantly compromising the reliability of zircon ages. The distribution of U-Pb ratios in apatite and titanite is unlike those obtained in crystalline targets, a feature we interpret to be characteristic of impact structures developed in mixed (sedimentary – crystalline) targets, such as Steen River. In this case, disaggregated melt systems create thermal regimes distinct from those derived from predominantly igneous/metamorphic targets. With an age of 141 ± 4 Ma, Steen River joins the Dellen (Sweden), Gosses Bluff (Australia), Mjølnir (Barents Sea), and Morokweng (South Africa) impact structures in being formed at, or close to, the Jurassic-Cretaceous boundary. [ABSTRACT FROM AUTHOR]

The Ganjiang River, one of eight major tributaries of the Yangtze River, located in the western hinterland of the Cathaysia Block, SE China, has a length of 823 km and a drainage area of 82 809 km2, whose detrital zircons provide a valuable means to trace sediment provenances of the river and explore the crustal growth and evolution of the Cathaysia Block. In the current study, 389 concordia zircon U–Pb age spots and rare earth element (REE) contents, in combination with 201 Lu–Hf isotope analyses, have been determined. Oscillatory zoning, high Th/U ratios and REE distribution patterns indicate that most detrital zircon grains are of magmatic origin. The age can be further divided into seven groups: 130–185 Ma with a peak at 153 Ma (7 %); 217–379 Ma with a peak at 224 Ma (16 %); 390–494 Ma with a peak at 424 Ma (37 %); 500–698 Ma with a peak at 624 Ma (5 %); 716–897 Ma with a peak at 812 Ma (10 %); 902–1191 Ma with a peak at 976 Ma (13 %); and 2232–2614 Ma with a peak at 2471 Ma (5 %). The sources of almost all the zircon age groups can be found from the exposed rocks. In particular, Yanshanian, Hercynian to Indosinian, Pan-African, Grenvillian and Palaeoproterozoic–Archaean zircons can be mainly sourced from the northern Guangdong – southern Jiangxi – western Fujian region, while Caledonian zircons come from southern and central Jiangxi, and Jinningian zircons are from central and northern Jiangxi. Most determined zircon grains exhibit negative ε Hf(t) values and TDM2 ages of 797 to 4016 Ma with a wide peak at 1500–2100 Ma and a keen peak at 1824 Ma, suggesting that most zircons are sourced from the reworked ancient crustal materials or crust–mantle mixing. The zircon Hf model age cumulative probability diagram shows that rapid crustal growth took place at the Palaeo- to Mesoproterozoic and that about 90 % of the crust of the Cathaysia Block was formed before 1.5 Ga. [ABSTRACT FROM AUTHOR]

Analysis of the distribution of detrital zircon grains is one of the few parameters by which Precambrian palaeogeography may be interpreted. However, the break-up of Pangea and the subsequent dispersal of some of its fragments around the Indian Ocean demonstrate that zircon analysis alone may be misleading, since zircons indicate their original derivation and not their subsequent plate-tectonic pathways. Based on analysis of Precambrian–Ordovician zircon distributions, the presence of microcontinents and separating oceans in the north Gondwanan realm has been rejected in favour of an undivided pre-Variscan continental northwards extension of Africa to include Iberia, Armorica and neighbouring southern European terranes, based on analysis of Precambrian–Ordovician zircon distribution. However, contrasting views, indicating the presence of three peri-Gondwanan oceans with complete Wilson cycles, are reinforced here by a critical reappraisal of the significance of that Variscan area detrital zircon record together with a comparison of the evolution of the present-day Indian Ocean, indicating that Iberia, Armorica and other terranes were each separate from the main Gondwanan craton during the early Palaeozoic Era. [ABSTRACT FROM AUTHOR]