Detrital Zircon Analysis Research Articles

Precambrian evolution of the Tarim Block and its tectonic affinity to other major continental blocks in China: New clues from U–Pb geochronology and Lu–Hf isotopes of detrital zircons

The Tarim Block, one of the largest Precambrian cratonic blocks in East Asia, is located in northwestern China. The Precambrian formation and evolution of the Tarim Block, and its tectonic affinity to other major continental blocks in China, specifically the North China Craton (NCC) and the South China Block (SCB), remain poorly understood, in spite of their implications for understanding the ancient tectonic framework of East Asia. To achieve a better understanding of the Precambrian tectonothermal history of the Tarim Block, we have undertaken U–Pb dating and Lu–Hf isotopic analyses of detrital zircons from late Neoproterozoic–early Permian sandstones in the Aksu area of the northwestern Tarim Basin. The morphologies, Th/U ratios, U–Pb ages and Lu–Hf isotopes of these detrital zircons indicate magmatic episodes took place in the late Neoarchaean–early Palaeoproterozoic (ca. 2.6–2.4Ga, peak at 2.48Ga), middle Palaeoproterozoic (ca. 2.0–1.8Ga, peak at 1.87Ga), latest Mesoproterozoic–early Neoproterozoic (ca. 1.05–0.9Ga, peak at 0.94Ga), middle Neoproterozoic (ca. 0.85–0.7Ga, peak at 0.78Ga), and early Palaeozoic (ca. 0.45–0.4Ga, peak at 0.43Ga). By integrating our results with previous geological observations, we argue that the Tarim Block as a whole was affected by Precambrian tectonothermal events at ca. 2.6–2.4, 2.0–1.8, 1.05–0.9 and 0.85–0.7Ga. These events are respectively thought to have been associated with a late Neoarchaean–early Palaeoproterozoic global continent-building event, the assembly of the Palaeoproterozoic Columbia supercontinent, the latest Mesoproterozoic–early Neoproterozoic accretion of the Tarim Block to the Rodinia supercontinent, and the middle Neoproterozoic separation of the Tarim Block from Rodinia. Comparisons of detrital zircon U–Pb age spectra, geochronological data for magmatic and metamorphic rocks, in situ zircon Lu–Hf isotopes, and other geological data from among the Tarim Block, the NCC and the SCB point to a close tectonic affinity between the Tarim Block and the SCB in the Neoproterozoic. However, during 2.6–1.8Ga, the Tarim Block underwent a different tectonic evolution from the SCB, and instead was tectonically linked to the NCC.

Characterization of the Paleoproterozoic Hottah terrane, Wopmay Orogen using multi-isotopic (U-Pb, Hf and O) detrital zircon analyses: An evaluation of linkages to northwest Laurentian Paleoproterozoic domains

The Paleoproterozoic Wopmay orogen is modeled as a simple arc-continent collision involving the Archean Slave craton and an enigmatic continental arc terrane termed the Hottah terrane. Hottah is a composite terrane that includes a juvenile 2.6-2.1 Ga basement and a younger 1.93-1.90 Ga continental arc. The extent and crustal age structure of the terrane is poorly known which limits interpretations as to its origin, and eventual role in the development of the orogen. Multi-isotopic (U-Pb, Hf, O) analyses of detrital zircon from rocks of the Hottah terrane and its cover sequence are used to indirectly evaluate its age and crustal characteristics. The data confirm that ca 2.6-2.1 Ga crust is an important component of the terrane but Hf isotopic data indicate mostly non-juvenile compositions consistent with recycled Neoarchean crust sources. Ages of detrital zircon are distinct from those expected of the Slave craton but are similar to adjacent 2.0-1.90 Ga Paleoproterozoic terranes of northwestern Laurentia. The similarity to terranes such as the Ksituan/Buffalo Head and Taltson-Thelon magmatic zones, south and east of the Wopmay Orogen indicate that Hottah could represent a terrane that initially evolved adjacent to the earliest assembled parts of the Nuna continent between 2.0 and 1.9 Ga, and was rifted prior to the collision with the Slave margin that produced the Calderian orogeny.

Geological characteristics and age of the Dahongliutan Fe-ore deposit in the Western Kunlun orogenic belt, Xinjiang, northwestern China

The large-scale Dahongliutan hematite-rich Fe deposit in the Tianshuihai terrane (Western Kunlun orogenic belt), Xinjiang, northwestern China, contains proven Fe ore reserves exceeding 100Mt at an average grade of 35wt.% Fe(t) (maximum 53wt.%). The deposit is hosted in the Neoproterozoic Tianshuihai Group, a suite of neritic, siliciclastic and sedimentary carbonate rocks subjected to greenschist-facies metamorphism. The Fe orebodies are laminate, stratoid, lenticular and interlayered with marbles and schists. Ore minerals mainly contain hematite, with minor siderite and limonite and rare sulfides, whereas gangue minerals mainly comprise quartz, dolomite, ankerite, calcite, muscovite and chloritoid. Most Fe ores display lepidoblastic, blastopsammitic, crystalloblastic and metasomatic textures with massive or banded structures. Based on mineral assemblages, the Fe ores are divided into four types, namely: (1) Quartz–hematite; (2) Quartz–dolomite–calcite–muscovite–hematite; (3) Quartz–ankerite–hematite; (4) Quartz–siderite–hematite.Zircon U–Pb analyses on the marbles and schists yielded a Neoproterozoic age (Ediacaran; 593±7Ma), whereas those on the ore-intruding medium-grained porphyritic biotite-quartz monzonite, medium to fine grained biotite-quartz monzonite and metagabbro yielded Cambrian–Early Ordovician ages (i.e., 484.5±2.7, 527.9±2.8 and 532.3±3.1Ma), which altogether constrain the ore formation to the Late Neoproterozoic to Early Cambrian (532–593Ma). In addition, the 163 detrital zircon analyses on the Dahongliutan marble and schist define five major age populations, namely: 2561–2329, 2076–1644, 1164–899, 869–722 and 696–593Ma. Provenance studies show that the detritals at Dahongliutan were mainly sourced from the North Kunlun and Tianshuihai terranes.Comparison with typical BIF deposits in the world, we infer that the deposit belongs to Neoproterozoic (Ediacaran) BIF-related sedimentary metamorphic type iron deposit and resembles Superior-type BIF, probably reflecting the recurrence of anoxic ferruginous conditions in the Neoproterozoic–Early Cambrian deep sea.

Implications of U–Pb and Lu–Hf isotopic analysis of detrital zircons for the depositional age, provenance and tectonic setting of the Permian–Triassic Palaeotethyan Karakaya Complex, NW Turkey

New zircon U–Pb age data, combined with Lu–Hf isotopic data, are presented here for sandstones of mainly arkosic composition from the Permian–Triassic Karakaya Complex. Predominantly, Carboniferous, Triassic and Devonian zircon age groups are recognised, most of which have a Late Triassic (Carnian–Norian) maximum depositional age. Carboniferous- and Devonian-aged zircon populations exhibit intermediate e Hf(t) values (−11 to +2), consistent with formation in a continental margin arc setting where juvenile mantle-derived magma mixed with (recycled) old crust of Palaeoproterozoic Hf model age. In contrast, the Triassic-aged zircon population exhibits higher e Hf(t) values (−5 to +4), consistent with mixing of juvenile mantle-derived melts with (recycled) old crust of Neoproterozoic Hf model age. Potential igneous source rocks for the sandstones of the Karakaya Complex exist in the Devonian and Carboniferous granitic rocks of the Sakarya continental basement to the north. Their e Hf(t) and corresponding model ages are nearly identical to the age-equivalent zircon populations within the Karakaya Complex sandstones. However, the Triassic granitic rocks of the Sakarya continental crust differ significantly in e Hf(t) and corresponding model age from the sandstones of the Karakaya Complex. Late Triassic sandstones from the Tauride continental unit to the south lack the dominant Late Palaeozoic and Triassic zircon populations of the Karakaya Complex sandstones. Triassic granitic bodies and intermediate-composition extrusive rocks in the Tauride continental unit also differ in e Hf(t) and corresponding Hf model ages from the Karakaya Complex sandstones. In addition, Late Triassic sandstones of the Kocaeli Triassic unit (Istanbul Terrane) in the north differ strongly from the Karakaya Complex sandstones in zircon population ages and e Hf(t). In the regional context, the new zircon age and lutetium–hafnium isotopic data are consistent with derivation of the Late Triassic Karakaya Complex sandstones from a Late Palaeozoic–Triassic continental margin arc located somewhere along the southern margin of Eurasia, although its exact position cannot be pinpointed at present owing to lack of suitable outcrop and comparable isotopic data.

SHRIMP U–Pb zircon provenance of the Sullavai Group of Pranhita–Godavari Basin and Bairenkonda Quartzite of Cuddapah Basin, with implications for the Southern Indian Proterozoic tectonic architecture

Proterozoic basins in cratonic India, referred to as “Purana Basins”, cover about 20% of the Archean basement of the subcontinent. Although the stratigraphy of most of these basins has been well established, it is only recently that radiometric age constraints have been obtained for some of the sedimentary sequences. This study provides new data for two of the Purana Basins in southern India using SHRIMP U–Pb analysis of detrital zircons. For the Pranhita–Godavari Basin, an age limit of 709Ma is provided for the age of deposition of the Sullavai Group. This prolongs the duration of Proterozoic sedimentation to approximately one billion years (ca. 1700–709Ma) and establishes the Venkatpur Sandstones of Sullavai Group as the youngest Purana Basin succession identified in India so far. A major zircon provenance age peak at about 1000Ma, and zircon ages between 800 and 750Ma, are correlated with major tectonothermal events in the Eastern Ghats Mobile Belt (EGMB) and intrusion of granites and associated pegmatites at that time. The main provenance area of the Venkatpur Sandstones is interpreted to be the EGMB, with subordinate supply of sediments from the Eastern Dharwar craton. It is suggested that portions of the EGMB must have been an integral part of Peninsular India at the time of deposition of these sediments. For the Cuddapah Basin, new U–Pb detrital zircon age constraints are provided for the Nallamalai Group sediments (Bairenkonda Quartzites within the Nallamalai Fold Belt), the youngest population of which yielded an age of ca. 1550Ma. This age is similar to the emplacement age of the Vinukonda Granite (1589±4.4Ma) in the Nellore Schist Belt. This suggests that the Nellore Schist Belt was a source region for the Bairenkonda Quartzites and that deposition continued until at least 1550Ma. A high-precision Archean age (ca. 3366Ma) for a detrital zircon grain indicates the presence of Paleoarchean components within the sediment source region. Provided that Paleoarchean rocks are as yet unknown from the largely juvenile Neoarchean Eastern Dharwar craton, there exists a possibility that the Nallamalai Group was sourced from the Ongole Domain of the EGMB.

Detrital zircon geochronology and provenance of the Chubut Group in the northeast of Patagonia, Argentina

The Chubut Group constitutes the most widespread sedimentary unit in NE Patagonia, characterized by variable-energy fluvial deposits. U–Pb analysis of detrital zircons from two sections of the Chubut Group constraint the age of the oldest sedimentary rocks in the northeast of the Somuncurá – Cañadón Asfalto Basin. In the Cañadón Williams area, at San Jorge section, 20 km NW of Telsen locality, dating of 56 detrital zircons from a medium to coarse sandstone indicated a maximum depositional age of 109 ± 1 Ma (n = 4). These sandstones were interpreted to represent shallow channels, associated with a lacustrine system. In the Telsen locality, a laser ablation analysis of 115 detrital zircons from a medium to coarse-grained sandstone, from fluvial channel facies, yielded a maximum depositional age of ca. 106 ± 1 Ma (n = 8). Both ages are consistent with volcanic events of the Barremian to Albian age in the central Patagonian Andes Region. Cathodoluminescence images of zircons from the San Jorge sample suggest an igneous origin, which is further supported by Th/U values above 0.5 in most of the grains. The distribution of the statistical modes of the main age populations of detrital zircons for the two samples [182, 185 and 189 Ma for Telsen sample (T2S) and 181 ± 1 Ma for San Jorge sample (SJS)] matches the age of the volcanic Marifil Formation. The rocks of the Marifil Formation of these ages are exposed NE to SE of the study area. The abundance of zircons of similar Jurassic ages (n = 52 for SJS and n = 105 for T2S) and the external morphology of the zircons in the sample SJS, implies a close proximity of the source area. Suggestion that the Marifil Formation was the main provenance source is also supported by northeast–southeasterly paleocurrents measured at the San Jorge and Telsen sections.

Reconstruction of tectonic events on the northern Eurasia margin of the Arctic, from U-Pb detrital zircon provenance investigations of late Paleozoic to Mesozoic sandstones in southern Taimyr Peninsula

The Taimyr fold-and-thrust belt records late Paleozoic compression, presumably related to Uralian orogenesis, overprinted by Mesozoic dextral strike-slip faulting. U-Pb detrital zircon analyses of 38 sandstones from southern Taimyr were conducted using laser ablation–inductively coupled plasma–mass spectrometry to investigate late Paleozoic to Mesozoic sediment provenance and the tectonic evolution of Taimyr within a regional framework. The Pennsylvanian to Permian sandstones contain detrital zircon populations of 370–260 Ma, which are consistent with derivation from the late Paleozoic Uralian orogen in northern Taimyr and/or the polar Urals. Late Neoproterozoic through Silurian ages (688–420 Ma), most consistent with derivation from Timanian and Caledonian age sources, suggest an ultimate Baltica source. Southern Taimyr represents the proforeland basin of the bivergent Uralian orogen in the late Paleozoic. Triassic sedimentary rocks contain detrital zircon populations of Carboniferous–Permian (355–260 Ma), late Neoproterozoic to Early Devonian (650–410 Ma), and minor Neoproterozoic (1000–700 Ma) ages, which suggest a similar provenance as the Carboniferous to Permian strata. The addition of a Permian–Triassic (260–220 Ma) zircon population indicates derivation of detritus from Siberian Trap–related magmatism. Jurassic samples have a dominant age peak at 255 Ma and a distinct reduction in Carboniferous–Permian and late Neoproterozoic to Early Devonian input, suggesting that erosion and contributions from Uralian sources ceased while greater input from Siberian Trap–related rocks of Taimyr dominated. Comparison of these results to the published literature demonstrates that detritus from the Uralian orogen was deposited in Taimyr, Novaya Zemlya, and the New Siberian Islands in the Permian, but not in the Lisburne Hills or Wrangel Island. In the Triassic, Taimyr, Chukotka, Wrangel Island, the Kular Dome in the northern Verkhoyansk of Siberia, Lisburne Hills, Franz Josef Land, and Svalbard shared sources from Taimyr, the Siberian Traps, and the polar Urals, indicating that there were no geographic barriers among these locations prior to opening of the Amerasia Basin. Detritus from the Uralian orogen in Taimyr was shed northward into the retroforeland basin and was then transported farther 20–30 m.y. after Uralian orogenesis. The widespread distribution of material eroded from Taimyr and the polar Urals during the Triassic is likely due to the arrival of, and sublithospheric spreading associated with, the Siberian mantle plume head at ca. 250 Ma. The subsequent motion of the lithosphere relative to the plume-swell likely caused a northwestward migration of the uplifted regions. Taimyr and the polar Urals were probably affected. In the Jurassic, detrital zircon spectra from Taimyr, Chukotka, the Kular Dome, and Svalbard show great differences, suggesting that these locations no longer shared the same provenance from Taimyr and the Urals. The restricted distribution of detritus from Taimyr and the Urals indicates that erosion of the Uralian orogen was reduced. In the Late Jurassic, the depositional setting of southern Taimyr probably changed from a foreland to an intracratonic basin.

Provenance and tectonic setting of the Paleoproterozoic metasedimentary rocks from the Liaohe Group, Jiao-Liao-Ji Belt, North China Craton: Insights from detrital zircon U–Pb geochronology, whole-rock Sm–Nd isotopes, and geochemistry

Geochronological, geochemical and isotopic studies were carried out on the Paleoproterozoic metasedimentary rocks from the Jiao-Liao-Ji Belt, North China Craton, to constrain their provenance and tectonic setting, as well as to evaluate the effects of weathering and sedimentary processes on the source rock signature. U–Pb isotopic dating using the LA-ICP-MS method on zircons from the Paleoproterozoic metasedimentary rocks reveals that the depositional age can be constrained in the period between 1.98 and 1.9Ga. Geochemical data reveal low-intermediate degrees of weathering of the source, compositionally immature and poorly sorted. Detailed analysis of detrital zircon U–Pb geochronology, whole-rock Sm–Nd isotope, and geochemistry show that these metasedimentary rocks are derived from a mixed provenance. The predominant derivation is from metavolcanic rocks of the Liaohe Group and Paleoproterozoic gneissic granitoids. There is also an input of Archean continental crust. The metasedimentary rocks were probably deposited in a back-arc basin within an arc system, thus supporting the Paleoproterozoic arc-continent collision model as already proposed by some authors.

Provenance of Cretaceous trench slope sediments from the Mesozoic Wandashan Orogen, NE China: Implications for determining ancient drainage systems and tectonics of the Paleo-Pacific

The Wandashan Orogen of NE China is a typical accretionary orogen related to Paleo-Pacific subduction. The Raohe Complex, as a major part of the orogen, consists of mid-Triassic to mid-Jurassic radiolarian chert and intraoceanic igneous rocks in an accretionary prism overlain by weakly sheared terrestrial-sourced clastic trench slope sediments. Sensitive high-resolution ion microprobe U-Pb dating and LA-MC-ICPMS Hf isotopic analysis of detrital zircons from the terrestrial-sourced Yongfuqiao Formation sandstone show that most zircons are Phanerozoic (90%): 140–150 Ma (10%), 180–220 Ma (25%), 240–270 Ma (15%), 300–360 Ma (15%), 391–395 Ma (3%), and 450–540 Ma (20%), whereas 10% are Precambrian in age. About 90% of the zircons have eHf(t) values ranging from +11.1 to −12.8. This suggests that the major provenance of the trench slope sediments was from the adjacent eastern segment of the Central Asian Orogenic Belt and the Jiamusi Block. The age of the Yongfuqiao Formation is constrained to the earliest Cretaceous, which represents the accretion time of the mid-Triassic to mid-Jurassic oceanic complexes. When compared with the Mino Complex in Japan and the Tananao Complex in Taiwan, three different provenances are identified suggesting three ancient drainage systems which transported sediments from NE China, North China, and South China to the Paleo-Pacific subduction-accretion system.

Provenance Analysis of Lower Cretaceous Sindong Group Sandstones in the Gyeongsang Basin, Korea, Using Integrated Petrography, Quartz Sem-Cathodoluminescence, and Zircon Zr/Hf Analysis

The Sindong Group (Aptian–Albian) in southeastern Korea is a 2–3-km-thick fluvio-lacustrine sedimentary package deposited in an elongated basin (the Nakdong Trough), which was formed by extension in an active-continental-margin setting. The provenance of the Sindong Group was studied to understand spatial and temporal variation in composition in three different parts of the basin by using integrated data on petrography, quartz SEM-cathodoluminescence (CL) analysis, and zircon Zr/Hf analysis. Although Sindong Group sandstones display wide variation in the composition of framework grains, they generally have increasing amounts of feldspar and decreasing amounts of quartz up sequence. Significant amounts of volcanic rock fragments and volcanic quartz are observed in the late-stage sediments. Metamorphic quartz is predominant in all Sindong Group sandstones, indicative of the exposure of metamorphic rocks in the source terrane, mostly from Precambrian basement and Triassic granites. The occurrence of significant amounts of plutonic quartz from early-stage sediments suggests that Jurassic granites were widely exposed in the source terranes. In addition, the episodic increase in volume of plutonic quartz content in the sequence, especially in the northern part of the basin, suggests that episodic tectonic activity occurred in the catchment. The increasing feldspar content up sequence could support the occurrence of tectonic activity in the catchments. The Zr/Hf analysis of detrital zircons revealed that the majority of zircons are of continental-crust origin formed in orogenic settings, but zircons in the lowest strata in the northern part of the basin were derived largely from anorogenic magmatic rocks of mantle origin. Our results demonstrate that source terranes for the Sindong Group have heterogeneous spatial and temporal distribution and were composed mainly of Precambrian basement and Triassic to Jurassic granitic rocks, with minor (meta)sedimentary rocks and syndepositional volcanic rocks. The detritus derived from syndepositional volcanic rocks became significant in the late stage of basin filling, representing the transition from extensional tectonism to continental-arc magmatism. The differences in characteristics of quartz SEM-CL and zircon Zr/Hf ratios in different parts of the basin are best explained by deposition on different alluvial fans and river systems.

Unravelling the complexities in high-grade rocks using multiple techniques: the Achankovil Zone of southern India

The Achankovil Zone of southern India forms a distinct isotopic and structural boundary separating the Madurai Block to the north from the Trivandrum Block to the south. We combine isotopic and trace element geochemistry of major and accessory phases with phase equilibria modelling to provide quantitative constraints on the timing and conditions of peak metamorphism and the nature of the protoliths within the Achankovil Zone. The results suggest a clockwise pressure–temperature path with peak metamorphic temperatures of up to 950 °C at pressures of around 0.7 GPa followed by high-temperature decompression. The metamorphic peak occurred at 545–512 Ma. U–Pb and Hf isotopic analysis of detrital zircon shows that the rocks have a strong affinity with the southern part of the Madurai Block. The Achankovil Zone is interpreted as the reworked southern margin of the Madurai Block, which was metamorphosed during the final stages of the assembly of Gondwana.

Detrital zircon U–Pb geochronology, Hf isotopes and geochemistry constraints on crustal growth and Mesozoic tectonics of southeastern China

In situ U–Pb geochronological, Hf isotopic and REE geochemical analyses of detrital zircons from Mesozoic sandstones in central Jiangxi and east Hunan of the South China Block (SCB) are used to provide not only information about crustal evolution process, but more importantly new constraints on sedimentary provenances as well as Mesozoic basin evolutions in central SCB. A total of 417 concordant zircon analyses define five U–Pb age populations at ca. 2.6–2.3Ga, ca. 2.0–1.7Ga, ca. 1.0–0.7Ga, ca. 500–400Ma and ca. 300–200Ma. Integrated analyses of zircon U–Pb ages and Hf isotopes of detrital zircons reveal five episodes of juvenile continental crust growth: ca. 2.5Ga, ca. 1.7Ga, ca. 850Ma, ca. 440Ma and ca. 230Ma, with all but the ca. 2.5Ga episode likely represent that of the SCB.None of the three samples from T3–J1 strata showed strong ca. 1850Ma and ca. 230Ma peaks suggesting that the T3–J1 sediments probably sourced from the Yangtze Block. In contrast, stronger peaks of ca. 1850Ma and ca. 250–230Ma in post-J1 strata relative to that of T3–J1 strata suggest a dominantly local Cathaysian provenance. In addition, the distinct low εHf(T) values for zircons of ca. 430Ma from T3–J1 strata in comparison with higher εHf(T) values for that from post-J1 strata also support aforementioned viewpoint. Such sharp changes between the pre-J1 and post-J1 strata coincide with the remarkable change in regional palaeogeography from a broad shallow marine basin in the Late Triassic–Early Jurassic time to a basin-and-range-style province in the Middle Jurassic. The characteristics and time evolution of detrital zircons from the studied area are consistent with the flat-slab subduction model which involves the development of a broad sag basin during the T3–J1 time, and a rapid regional uplift in the Cathaysia Block caused by the reinitiating of normal subduction along the coastal region at ca. 190Ma.

Analysis of the Ragged Basin, Western Australia: Insights into syn-orogenic basin evolution within the Albany–Fraser Orogen

Sedimentary basins occur within a variety of tectonic settings, both within plates and near plate boundaries. We explore the complex history of the Mesoproterozoic Ragged Basin, located in the eastern Nornalup Zone of the Albany–Fraser Orogen, which is part of the West Australian Craton. Sediments of the Ragged Basin were deposited within a shallow basin by a large fluvial system dominated by shifting, sandy braided channels, forming a quartz-rich succession defined as the Mount Ragged Formation. The gradual coarsening upwards sequence indicates a distal fluvial environment characterised by channel migration and abandonment, changing to a proximal fluvial environment characterised by rapid periods of sedimentation and coarser deposits. Ion microprobe (SHRIMP) U–Pb analysis of detrital zircons constrain a maximum depositional age of 1314±19Ma for the Mount Ragged Formation, so it is feasible that deposition started during the latter part of Stage I (c. 1330–1260Ma) of the Albany–Fraser Orogeny. The detrital zircon U–Pb data demonstrates that the Mount Ragged Formation contains c. 1810–1320Ma detritus, most of which appears to be derived locally from the reworked craton margin that forms the Albany–Fraser Orogen basement. However, the smaller c. 1560 and c. 2490Ma zircon age components have no known source within the West Australian Craton, and were potentially originally sourced from the Gawler Craton or other unknown sources beneath the Eucla and Bight Basins. These exotic ages support the interpretation that outboard accretion occurred prior to Stage II of the Albany–Fraser Orogeny. New structural data, field observations and aeromagnetic image interpretation indicate that the Mount Ragged Formation was deformed by a northwest-vergent fold and thrust system. A minimum age for deposition, and structural emplacement, is provided by a crystallisation age of 1175±12Ma for a cross-cutting monzogranite exposed at Scott Rock, part of the Esperance Supersuite. Upper-crustal thrusting in the Mount Ragged Formation can be linked to deeper, large-scale regional structures such as the Tagon and Rodona Shear Zones, the latter of which represents the eastern edge of the Albany–Fraser Orogen.

Generation and preservation of continental crust in the Grenville Orogeny

Detrital zircons from modern sediments display an episodic temporal distribution of U-Pb crystallization ages forming a series of ‘peaks’ and ‘troughs’. The peaks are interpreted to represent either periods of enhanced generation of granitic magma perhaps associated with mantle overturn and superplume events, or preferential preservation of continental crust during global collisional orogenesis. The close association of those peaks with the assembly of supercontinents implies a causal relationship between collisional orogenesis and the presence of zircon age peaks. Here these two end-member models (episodic periodicity of increased magmatism versus selective preservation during collisional orogenesis) are assessed using U-Pb, Hf, and O analysis of detrital zircons from sedimentary successions deposited during the ∼1.3–1.1 Ga accretionary, ∼1.1–0.9 Ga collisional, and < 0.9 Ga extensional collapse phases of the Grenville orogenic cycle in Labrador and Scotland. The pre-collisional, accretionary stage provides a baseline of continental crust present prior to orogenesis and is dominated by Archean and Paleoproterozoic age peaks associated with pre-1300 Ma Laurentian geology. Strata deposited during the Grenville Orogeny display similar Archean and Paleoproterozoic detrital populations along with a series of broad muted peaks from ∼1500 to 1100 Ma. However, post-collisional sedimentary successions display a dominant age peak between 1085 and 985 Ma, similar to that observed in modern North American river sediments.Zircons within the post-orogenic sedimentary successions have progressively lower ɛHf and higher δ18O values from ∼1800 to ∼1200 Ma whereupon they have higher ɛHf and δ18O within the dominant 1085–985 Ma age peak. Furthermore, the Lu-Hf isotopic profile of the Grenville-related age peak is consistent with significant assimilation and contamination by older crustal material. The timing of this dominant age peak coincides with the peak of metamorphism and magmatism associated with the Grenville Orogeny, which is a typical collisional orogenic belt. The change from broad muted age peaks in the syn-orogenic strata to a single peak in the post-orogenic sedimentary successions and in the modern river sediments implies a significant shift in provenance following continental collision. This temporal change in provenance highlights that the source(s), from which detrital zircons within syn-orogenic strata were derived, was no longer available during the later stages of the accretionary and collisional stages of the orogenic cycle. This may reflect some combination of tectonic burial, erosion, or possibly recycling into the mantle by tectonic erosion of the source(s). During continental collision, the incorporated continental crust is isolated from crustal recycling processes operative at subduction margins. This tectonic isolation combined with sedimentary recycling likely controls the presence of the isotopic signature associated with the Grenville Orogeny in the modern Mississippi and Appalachian river sediments. These results imply that zircon age peaks, which developed in conjunction with supercontinents, are the product of selective crustal preservation resulting from collisional orogenesis.

Late Miocene provenance change on the eastern margin of the Yinggehai-Song Hong Basin, South China Sea: Evidence from U–Pb dating and Hf isotope analyses of detrital zircons

Understanding the provenance of the reservoir in a sedimentary basin is of great importance in hydrocarbon exploration and production. The Yinggehai-Song Hong Basin is one of the most important Cenozoic petroliferous basins in the South China Sea. To better understand the provenance characteristics of the Upper Miocene Huangliu Formation (Tortonian-Messinian) on the eastern margin of the basin and test the influence of uplift of the Tibetan Plateau in the South China Sea, 172 single zircons from two sandstone samples in the Lingtou gas field were dated by U–Pb chronometer, and 54 of these grains were spot analyzed for Hf isotopes. The results indicate that the upper member of the Huangliu Formation in this gas field shows two major peaks of U–Pb ages at ca. 250 Ma and ca. 432 Ma, along with four subordinate peaks at ca. 757 Ma, ca. 1926 Ma, ca. 2529 Ma and ca. 2775 Ma. The initial Hf isotope ratios [εHf (t)] of these zircons are negative to positive for each age group, suggesting that existing crustal materials were mixing with new mantle melts in some magmatic episodes. In contrast, the lower member of the Huangliu Formation show two major age peaks at ca. 98 Ma and 248 Ma, with a subordinate peak at ca. 1453 Ma. The εHf(t) values are concentrated between −11.6 and −3.4, revealing that they were derived from older crust. Comparing with the source characteristics of tectonic units surrounding the basin, the source of the upper member in the gas field was mainly from the southern Yangtze Block, whereas the lower member was derived from the Hainan Uplift. Together with the change of climate and sedimentation rate after 10 Ma on the northern margin of the South China Sea, we attribute the provenance change to the uplift of the Tibetan Plateau at the same time.

Proterozoic Evolution of the North Atlantic–Arctic Caledonides: Insights from Detrital Zircon Analysis of Metasedimentary Rocks from the Pearya Terrane, Canadian High Arctic

AbstractThe Pearya Terrane, recognized as the only exotic terrane along the Canadian Arctic margin, includes a Neoproterozoic–early Paleozoic basinal or passive-margin metasedimentary sequence that is structurally juxtaposed with arc-related Paleozoic rocks and a metamorphic basement complex containing early Neoproterozoic orthogneiss. The Neoproterozoic siliciclastic sequence is similar to other clastic sections formed at the breakup of Rodinia, but its paleogeographic origin and crustal affinity are uncertain. Detrital zircon age spectra from seven samples reveal three groups: Group A, with numerous peaks at c. 1100–1800 Ma and the youngest population at c. 1020 Ma; Group B, defined by a dominant c. 970 Ma age peak; and Group C, with dominant peaks from c. 970–1800 Ma and a small population of c. 635–710 Ma grains. Spectra from Group A resemble data from the latest Mesoproterozoic units in Svalbard, East Greenland, and the Scandinavian Caledonides, with the ubiquitous Mesoproterozoic ages observed in al...

Contrasting crustal evolution processes in the Dharwar craton: Insights from detrital zircon U–Pb and Hf isotopes

New in situ U–Pb-Hf analyses of detrital zircons from across the Archaean Dharwar craton indicate significant juvenile crustal extraction events at ~3.3 and 2.7Ga, and continuous extraction from 3.7 to 3.3Ga. Reworking in the older western block at ~3.0Ga marks the onset of cratonisation, most likely due to ‘modern’ plate tectonic processes, whilst reworking in both the western and younger eastern block at 2.55–2.50Ga indicates accretion of the two terranes and final cratonisation much later than in most other Archaean terranes (~2.7Ga). Different patterns of disturbance to the zircon U–Pb systematics reflect variations in both the U content of parent rocks and later metamorphic conditions. Tectonic links are observed between the Kaapvaal and western Dharwar cratons, and between the north China and eastern Dharwar cratons, though none of these links necessarily requires a consanguineous origin.

Salt domes of the UAE and Oman: Probing eastern Arabia

The emergent salt domes of the United Arab Emirates (UAE) have been investigated in detail and examples from central Oman have been studied for comparison. The salt domes contain exotic clasts of igneous, sedimentary and low-grade metamorphic rocks of the Arabian basement that have been brought to the surface from depths of over 8km. The clasts thus provide an opportunity to examine the lithology, geochemical composition and age of the “basement” underlying this part of eastern Arabia, where no other outcrops are available for direct study. Five volcanic rocks give consistent latest Ediacaran U-Pb zircon crystallisation dates of ca. 560–545Ma, with Neoproterozoic, Palaeoproterozoic and Neoarchaean ages of inherited zircons. These rocks, although strongly altered, preserve geochemical characteristics compatible with formation in a within-plate, extensional setting along the northern edge of Gondwana, adjacent to Prototethys. U-Pb analyses of detrital zircons in sedimentary and low-grade metamorphic rocks indicate deposition younger than ca. 597Ma in UAE and <734Ma in Oman. The two UAE sedimentary rocks may correlate with the Shuram and Khufai Formations of the Nafun Group (Huqf Supergroup) in Oman. Like the volcanic rocks, the two sedimentary samples from the UAE show derivation from the erosion of Neo-, Palaeoproterozoic and Neoarchaean sources. These sources could be from the Arabian basement itself or from other basement blocks such as those embedded in present-day Iran and Afghanistan, the precise whereabouts of which in Neoproterozoic times remains somewhat uncertain. The zircon age spectra of samples from the UAE show Neoproterozoic age peak characteristics of sources from both the western and eastern Arabian basement blocks, indicating that the two segments were juxtaposed by about 597Ma, the maximum age of their deposition.

Cretaceous provenance change in the Hegang Basin and its connection with the Songliao Basin, NE China: evidence for lithospheric extension driven by palaeo-Pacific roll-back

Abstract The Cretaceous Hegang Basin is located on the Jiamusi Block, NE China, and separated from the Songliao Basin by the Lesser Xing'an Range (LXR). Seismic interpretation shows that the Chengzihe, Muling and Dongshan formations of the Hegang Basin thicken eastwards with westwards onlap, indicating that the LXR existed as a palaeo-uplift during that period, whereas the Houshigou Formation shows no thickness change, indicating that the LXR was possibly under water at this time. This is supported by results of detrital zircon analysis from the Hegang Basin in which the Chengzihe Formation is dominated by approximately 180 Ma zircons, which can only be provided by the LXR, whereas the Houshigou Formation records no Early Jurassic ages. This view is consistent with previous studies of the Songliao Basin for a provenance change between the Denglouku and Quantou formations. We conclude that the LXR was a highland during deposition of the Chengzihe, Muling and Dongshan formations but that it was under water when the Houshigou Formation was deposited. There was thus a connection between the Hegang and Songliao basins, which marks an eastwards migration of the depositional and extensional centre of the Songliao–Hegang basin system. This eastwards migration implies lithospheric extension driven by palaeo-Pacific roll-back.

Sedimentology, U-Pb detrital geochronology, and Hf isotopic analyses from Mississippian–Permian stratigraphy of the Mystic subterrane, Farewell terrane, Alaska

The Farewell terrane of western Alaska is one of the more remote and understudied crustal fragments in the North American Cordillera. Although it is generally accepted that the oldest, Precambrian parts of the Farewell terrane originated along the Arctic margin (i.e., Siberia), the paleogeographic history of the Farewell terrane during much of the middle and late Paleozoic remains unknown. Here, we present new sedimentologic and provenance data from upper Paleozoic clastic strata of the Mystic subterrane, which represents the youngest part of the Farewell terrane. Sedimentary facies consist of high- and low-density sediment-gravity-flow deposits and are interpreted to represent a submarine fan depositional system. Sandstone modal composition trends show a relative abundance of lithic volcanic fragments (∼65%) and subordinate occurrences of lithic sedimentary fragments (∼15%) and chert (∼13%). Laser-ablation–inductively coupled plasma–mass spectrometry analyses of detrital zircons reveal a bulk U-Pb age distribution of Precambrian–Paleozoic grains. U-Pb detrital zircon age spectra from Mississippian strata have a primary peak age between 400 and 325 Ma and secondary peak ages between 480 and 415 Ma and 2000 and 1800 Ma. Devonian–Mississippian zircons exhibit enriched e Hf, isotopic values (–3 to –35), whereas Ordovician–Silurian zircons have both enriched (–5 to –25) and depleted (+5 to +14) e Hf, values. Age spectra from Permian strata show primary peaks between 320 and 275 Ma and 460 and 415 Ma, with isolated occurrences of Precambrian-age zircons. Pennsylvanian–Permian zircons exhibit depleted e Hf, values (+2 to +14). Youngest peak ages support a Mississippian–Early Permian maximum depositional age for this part of the Mystic subterrane. Overall, provenance trends reflect primary detrital contributions from arc and recycled orogen source areas, which included both enriched and primitive magmatic sources. New U-Pb and Hf isotope analyses from the Mystic assemblage match most closely with magmatic source areas of the Alexander and Wrangellia terranes. Findings are consistent with a model where the Farewell terrane was proximal to both the Alexander and Wrangellia terranes by Mississippian–Permian time.