Subordinate Peak Research Articles

Detrital zircon geochronology and heavy mineral composition constraints on provenance evolution in the western Pearl River Mouth basin, northern south China sea: A source to sink approach

Investigating the provenance evolution of sedimentary basins with complex tectonic histories is challenging because of the continuously evolving tectonic framework and changing source areas. Pearl River Mouth Basin (PRMB) in the northern South China Sea preserves a large volume of Cenozoic sediments derived from both intrabasinal and extrabasinal sources. However, rare study has been conducted to investigate the provenance evolution of the western PRMB. In this study, we report new detrital zircon U–Pb geochronological and heavy mineral data from the western PRMB, attempting to identify its potential sources and provenance evolution from Eocene to early Miocene. Our data from distinct structural units and formations reveal spatial-temporal differences in provenance. In the northern part, a similar age pattern with a major peak at ∼425 Ma and a subordinate peak at ∼230 Ma is preserved in the Eocene-late Oligocene sediments and suggests that sediments were mainly derived from the Yunkai Massif via Nanduhe River. By contrast, in the southern part, the Eocene-late Oligocene sediments display a dominant age population ranging from 100 Ma to 300 Ma, which implies that the sediments were mainly eroded from nearby Shenhu Uplift and Hainan Island. The heavy mineral data also record such spatial differences in provenance. However, during the early Miocene, the northern and southern parts show similar detrital zircon age patterns with multiple clusters at ∼245 Ma, ∼450 Ma, ∼850 Ma, 970–980 Ma, 1825–1845 Ma, and ∼2500 Ma, indicating that the Miocene sediments across the whole basin were mainly provided by the Pearl River system. The increase of Paleozoic and Precambrian zircons in the lower Miocene sediments suggests a profound provenance shift from multiple nearby sources to the South China Block via the Pearl River between Oligocene and Miocene in the western PRMB, and its timing is posterior to other regions of the PRMB. Finally, four-stage source-to-sink evolution for the PRMB is proposed, showing that sediment provenance in the PRMB is controlled by regional tectonic movement, drainage evolution, and basin architecture. This study suggests that the small-scale drainage system Nanduhe River sourced by Yunkai Massif contributed significantly to the PRMB between Eocene and Oligocene, and highlights its complex processes of provenance evolution that are relevant to the evolution of marginal sea basins globally.

The Proto- and Palaeo-Tethys tectonic evolution in Southeastern Tibetan Plateau: Constraints from detrital zircon dating of metasedimentary rocks from the Diancang Shan complex

ABSTRACT Metamorphic rocks from the Diancang Shan (DCS) complex along the Ailao Shan-Red River belt between the South China plate and Simao-Indochina block are studied in this contribution to constrain the Proto- to Palaeo-Tethys tectonic evolution of the eastern Tethys domain. LA-ICP-MS zircon U-Pb geochronological dating is conducted in this study on the metasedimentary rocks (garnet-biotite-plagioclase gneisses, biotite-quartz schists and phyllonites) from different stratigraphical horizons (Proterozoic and Triassic) of the DCS complex. The analyses yielded three major age peaks at ca. 248 Ma, ca. 441 Ma, ca. 1000–900 Ma and one subordinate age peak at ca. 828 Ma. The youngest ages for the samples help to constrain the maximum ages of deposition of the complex at Early Carboniferous and Late Triassic, respectively. The existence of the diagnostic age peak at ca. 440 Ma and the euhedral-subhedral morphology of the detrital zircons in the Palaeozoic and Mesozoic strata may indicate that there were early Palaeozoic magmatic activities along the eastern margin of the Simao-Indochina block. At the meantime, the age peak at ca. 440 Ma was never reported in the early Palaeozoic strata from the western margin of the South China plate, which supports the existence of an early Palaeozoic rift zone, i.e., the Proto-Tethys Jinsha Jiang-Ailao Shan-Song Ma rift zone, being consistent with geochemical discriminations. Furthermore, we conclude, from the significant difference between detrital zircon age data of Silurian to Devonian sedimentary rocks from the Simao-Indochina block and South China plate, the opening of the Palaeo-Tethys ocean since Early Carboniferous, the absence of evidence for the Palaeozoic orogeny, and the successive sedimentation from the Cambrian to Triassic along the western margin of the South China plate, that the Proto-Tethys rifting and subsequent Palaeo-Tethys ocean evolution along the Jinsha Jiang-Ailao Shan-Song Ma zone formed actually a complete ‘Wilson Cycle’ from early Palaeozoic to the Late Triassic.

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

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

The Pre-Grenvillian assembly of the southeastern Laurentian margin through the U–Pb–Hf detrital zircon record of Mesoproterozoic supracrustal sequences (Central Grenville Province, Quebec, Canada)

AbstractThe detrital zircon perspective on the pre-collisional crustal evolution of the Grenville Province remains poorly explored. In this study, we conducted in situ laser ablation U–Pb–Hf isotopic microanalysis on detrital zircon grains from three pre-orogenic (>1 Ga) supracrustal sequences that crop out in the Central Grenville Province (Lac Saint-Jean region, QC, CA). Detrital zircon grains from vestiges of these sequences record three dominant age peaks at c. 1.46 Ga, 1.62 Ga, 1.85 Ga, and a subordinate peak at 2.7 Ga. The 1.46 Ga and 1.62 Ga age peaks are recorded in detrital zircon grains from a quartzite associated with a metavolcanic sequence (i.e. Montauban Group) with a maximum depositional age of c. 1.44 Ga. In contrast, the c.1.85 Ga age peak is observed from recycled zircon grains in metasediments with maximum depositional ages between 1.2 and 1.3 Ga. The suprachondritic Hf isotope composition in detrital zircon grains of the 1.46 Ga and 1.62 Ga age populations records juvenile crustal growth during peri-Laurentian accretionary orogenesis related to the Pinwarian (1.4–1.5 Ga) and Mazatzalian–Labradorian (1.6–1.7 Ga) events. The detrital zircon grains associated with Penokean–Makkovikian (1.8–1.9 Ga) source rocks record reworking of c. 2.7 Ga continental crust derived from a near-chondritic mantle reservoir. Overall, crust-forming and basement reworking events associated with accretionary orogenesis in southeastern Laurentia are retained in the detrital zircon load of Precambrian basins even after the terminal Grenvillian collision and assembly of Rodinia.

GEOCHEMICAL CHARACTERISTICS AND CHARGE HISTORY OF OIL IN THE UPPER CRETACEOUS M1 SANDSTONES (NAPO FORMATION) IN BLOCK T, ORIENTE BASIN, ECUADOR

Major oil discoveries have recently been made in Block T in the north of the Oriente Basin, Ecuador. The oil is reservoired in the M1 Sandstones of the Upper Cretaceous Napo Formation. To investigate the origin and charge history of the petroleum, a detailed geochemical study was carried out on 43 crude oil samples from 42 producing wells in Block T together with fluid inclusion analyses of three core samples from two wells.According to the results of GC/GC‐MS analyses of the oil samples, the oils contain n‐alkanes with a peak carbon number at C15‐C17 and a subordinate peak at C25‐C30. The nC21‐/nC22+ ratio ranges from 0.64 to 1.69, and the Carbon Preference Index from 0.95 to 1.23. The odd‐over‐even predominance is 1.02–1.27. A cross‐plot of C22/C21 versus C24/C23 tricyclic terpanes indicates that the source rock is a marine marl mixed with a small amount of terrigenous material. C27 regular steranes are more dominant than C28 ≈ C29 and the C29/C27 ratio ranges from 0.67 to 0.94 indicating a source rock dominated by marine algal material with minor terrigenous input. Rc calculated using the MPI index was 0.83% to 1.11%, indicating that the oils were generated during the early to peak oil generation stage. A cross‐plot of C29ααα20S/(20S+20R) versus C29αββ/(ββ+αα), and ratios of C31L‐hopane 22S/(22S + 22R) and C32L‐hopane 22S/(22S + 22R), gave similar maturity results.The presence in the same oil samples of a complete n‐alkane series together with an unresolved UCM hump and 25‐norhopanes indicates at least two stages of oil charging, with severe biodegradation of the early‐stage oil and a later charge of fresh, unaltered oil.The homogenization temperatures of 36 fluid inclusions in samples from Block T wells F20 and F67 range from 81 to 95°C. A reconstructed burial and geothermal history of well F20 indicates that the M1 Sandstones in this area reached a temperature of 81°C at 19–16 Ma, after which temperatures increased continuously to 95–100°C at the present day. The homogenization temperatures of the analysed fluid inclusions combined with the geothermal history indicate that oil charging into the M1Sandstones began in the early Miocene and continues at the present day.

Sediment trap and deep sea coretop sediments as tracers of recent changes in planktonic foraminifera assemblages in the southeastern ultra-oligotrophic Levantine Basin

Sediment trap and core top sediments were used to study the seasonal and longer-term variability in the distribution and assemblage composition of planktonic foraminifera (PF) in the ultra-oligotrophic Eastern Mediterranean Levantine Basin (LB). A continuous time series of particulate flux sampled every 11–12 days were retrieved from a sediment trap deployed at 1300 m between May 2017 and May 2018. The core top sediments were collected close to the sediment trap mooring site at ~1500 m water depth. The average annual planktonic foraminiferal (PF) flux was 93 shells m-2 d-1, the lowest value yet recorded among traps located in tropical-subtropical oligotrophic regions. A bimodal increase in PF flux is observed, with highest numbers of 452 shells m-2 d-1 occurring in winter (February), responding directly to maxima in particulate mass flux. A lower flux occurs in late summer from mid-August to mid-September with up to 197 shells m-2 d-1.Ten species were found in the trap, the majority were symbiont-bearing spinose species that contribute 96% of the total flux. Globigerinoides ruber white predominate the assemblage composition during the winter peak together with Globoturborotalita rubsecens and Globigerinella calida. During the subordinate summer peak the dominating species were G. ruber white, Orbulina universa and Globigerinoides ruber pink.The relative abundance of G. bulloides and G. ruber pink is much lower in the sediment trap samples compared to their abundance in nearby coretop sediments. This trend seems to indicate a recent drop in their numbers. At the same time G. rubescens and Globoturborotalita tenella occur in higher numbers in the sediment trap compared with the coretop samples. These opposite trends may reflect the current adjustment of certain PF species to the ongoing sea surface warming and decrease in food availability in the LB.

Detrital Zircon U‐Pb Ages and Geochemistry of the Silurian to Permian Sedimentary Rocks in Central Inner Mongolia, China: Implications for Closure of the Paleo‐Asian Ocean

The Solonker suture zone has long been considered to mark the location of the final disappearance of the Paleo‐Asian Ocean in the eastern Central Asian Orogenic Belt (CAOB). However, the time of final suturing is still controversial with two main different proposals of late Permian to early Triassic, and late Devonian. This study reports integrated whole‐rock geochemistry and LA‐ICP‐MS zircon U‐Pb ages of sedimentary rocks from the Silurian Xuniwusu Formation, the Devonian Xilingol Complex and the Permian Zhesi Formation in the Hegenshan‐Xilinhot‐Linxi area in central Inner Mongolia, China. The depositional environment, provenance and tectonic setting of the Silurian‐Devonian and the Permian sediments are compared to constrain the tectonic evolution of the Solonker suture zone and its neighboring zones. The protoliths of the silty slates from the Xuniwusu Formation in the Baolidao zone belong to wacke and were derived from felsic igneous rocks with steady‐state weathering, poor sorting and compositional immaturity. The protoliths of metasedimentary rocks from the Xilingol Complex were wackes and litharenites and were sourced from predominantly felsic igneous rocks with variable weathering conditions and moderate sorting. The Xuniwusu Formation and Xilingol Complex samples both have two groups of detrital zircon that peak at ca. 0.9–1.0 Ga and ca. 420–440 Ma, with maximum deposition ages of late Silurian and middle Devonian age, respectively. Considering the ca. 484–383 Ma volcanic arc in the Baolidao zone, the Xuxiniwu Formation represents an oceanic trench sediment and is covered by the sedimentary rocks in the Xilingol Complex that represents a continental slope sediment in front of the arc. The middle Permian Zhesi Formation metasandstones were derived from predominantly felsic igneous rocks and are texturally immature with very low degrees of rounding and sorting, indicating short transport and rapid burial. The Zhesi Formation in the Hegenshan zone has a main zircon age peak of 302 Ma and a subordinate peak of 423 Ma and was deposited in a back‐arc basin with an early marine transgression during extension and a late marine regression during contraction. The formation also crops out locally in the Baolidao zone with a main zircon age peak of 467 Ma and a minor peak of 359 Ma, and suggests it formed as a marine transgression sedimentary sequence in a restricted extensional basin and followed by a marine regressive event. Two obvious zircon age peaks of 444 Ma and 280 Ma in the Solonker zone and 435 Ma and 274 Ma in Ondor Sum are retrieved from the Zhesi Formation. This suggests as a result of the gradual closure of the Paleo‐Asian Ocean a narrow ocean sedimentary environment with marine regressive sedimentary sequences occupied the Solonker and Ondor Sum zones during the middle Permian. A restricted ocean is suggested by the Permian strata in the Bainaimiao zone. Early Paleozoic subduction until ca. 381 Ma and renewed subduction during ca. 310–254 Ma accompanied by the opening and closure of a back‐arc basin during ca. 298–269 Ma occurred in the northern accretionary zone. In contrast, the southern accretionary zone documented early Paleozoic subduction until ca. 400 Ma and a renewed subduction during ca. 298–246 Ma. The final closure of the Paleo‐Asian ocean therefore lasted at least until the early Triassic and ended with the formation of the Solonker suture zone.

Postrift stress field inversion in the Potiguar Basin, Brazil – Implications for petroleum systems and evolution of the equatorial margin of South America

Rifting and related normal stress regime in the equatorial continental margin of Brazil ceased during the Late Cretaceous, when the stress regimes in eastern South America and West Africa changed to induce strike-slip or reverse motion. In this study, we explore the postrift tectonic, geomorphic, magmatic, and sedimentary responses to stress changes using the Potiguar Basin, the easternmost basin in the equatorial margin of Brazil, as a case study. We use field and topographic data, 2D seismic reflection lines, vertical electric soundings, and geochronological and borehole data to constrain the stress evolution of the Potiguar Basin from the Late Cretaceous to the Quaternary, discussing the role of basin inversion on sedimentation and landforms. Our results indicate the presence of two strike-slip stress regimes after rifting. The first stress field (SF1) occurred from Late Cretaceous to the middle Miocene and consisted of a N-S-oriented maximum subhorizontal compression and an E-W-oriented extension. The second stress field (SF2) took place from the middle Miocene to the present day and included subhorizontal E-W to NW-SE compression combined with N-S and NE-SW subhorizontal extension. Emplacement of volcanic rocks occurred along transtensional faults, with a principal peak during SF1 at 20–30 Ma and a subordinate peak during SF2 at 5–10 Ma. In response to shortening during SF2, a 70-km-long and 50-km-wide dome formed, where marine Miocene strata were uplifted to ~250 m asl. This uplift induced the displacement of alluvial channels away from the dome. Anticlines formed by transpression along the main NE-SW-striking faults during both SF1 and ST2 acted as traps in the petroleum system. Similar shifts and stress field inversions documented in other areas of the Brazilian continental margin are consistent with the Neogene rise of the Andes and may have implications for reconstructing the tectonic history of the Equatorial Atlantic margin of South America.

Sulfur K-edge XAS study of sulfur transformation behavior during pyrolysis and co-pyrolysis of biomass and coals under different atmospheres

Three low rank coals and one biomass, YiMa (YM) and Chifeng (CF) with comparatively high FeS2, and Ximeng (XM) coals with high organic sulfur contents, and sawdust (SD), were selected to investigate sulfur transformation behavior during pyrolysis and co-pyrolysis under Ar and CO2 atmospheres. The sulfur transformation of those samples was investigated by X-ray absorption spectroscopy (XAS) combined with X-ray fluorescence (XRF). For SD, the coals and their mixtures, the subordinate peak of CaS is formed during pyrolysis under Ar atmosphere, but not under CO2 atmosphere. For XM and CF coals, sulfate peak of their chars and the chars of their mixture becomes more intense after pyrolysis under Ar atmosphere, while remain low under CO2 atmosphere. This indicates that CO2 atmosphere can impede the formation of CaS and sulfate. In addition, CO2 atmosphere and SD can promote the decomposition of FeS in CF coal before 900 °C, while SD has no significant effect on FeS in YM coal at the ratio of 3:1 (YM:SD). However, SD can also help the decomposition of FeS in YM coal at the ratio of 1:1. This suggests that SD is not enough for FeS to decompose at the ratio of 3:1. Thiophene peaks of all samples are more intense under CO2 atmosphere than under Ar atmosphere, meaning that more stable organic sulfur is formed and retained in the char after pyrolysis and co-pyrolysis under CO2 atmosphere.

Final Subduction Processes of the Paleo‐Asian Ocean in the Alxa Tectonic Belt (NW China): Constraints From Field and Chronological Data of Permian Arc‐Related Volcano‐Sedimentary Rocks

AbstractThe timing of final subduction and closure of the Paleo‐Asian Ocean (PAO) is controversial. Located in a key position within the southern Central Asian Orogenic Belt, the Alxa Tectonic Belt (ATB) provides a crucial window to evaluate the final subduction processes of the PAO. This study presents field and geochronological data for Permian volcano‐sedimentary rocks from the southwestern ATB. Field observations revealed a syntectonic unconformity between the Middle and Upper Permian strata. Detrital zircon U‐Pb analyses show a major peak at ~273 Ma and a subordinate peak at ~440 Ma for the Middle Permian sample. The Upper Permian samples show consistently unimodal age spectra with single peaks at ~261 and ~263 Ma, respectively. The Permian zircons from the analyzed samples yield predominately positiveεHf(t) values, indicating major juvenile magmatic processes mixed with limited recycled Precambrian basement. The diagnostic zircon U‐Pb‐Hf isotopic characteristics and ubiquitous intermediate and felsic volcanic detritus in these rocks indicate rapid sediments accumulation sourced from a proximal magmatic terrane in a suprasubduction zone environment. The Paleozoic zircon U‐Pb age peaks from this study are comparable to those for the Permian arc‐related sediments along the Solonker Suture Zone, thus linking the Alxa active margin with the northern margin of the North China Craton during Middle‐Late Permian times. Our study thus provides key constraints for the final subduction processes of the PAO, documented within the ATB, before the terminal amalgamation of the southern Central Asian Orogenic Belt.

Investigation on Characteristic Variation of the FBG Spectrum with Crack Propagation in Aluminum Plate Structures.

In order to monitor the crack tip propagation of aluminum alloy, this study investigates the variation of the spectrum characteristics of a fiber Bragg grating (FBG), combined with an analysis of the spectrum simulation. The results identify the location of the subordinate peak as significantly associated with the strain distribution along the grating, corresponding to the different plastic zones ahead of the crack tip with various crack lengths. FBG sensors could observe monotonic and cyclic plastic zones ahead of the crack tip, with the quadratic strain distribution along the grating at the crack tip-FBG distance of 1.2 and 0.7 mm, respectively. FBG sensors could examine the process zones ahead of the crack tip with the cubic strain distribution along the grating at the crack tip-FBG distance of 0.5 mm. The spectrum oscillation occurs as the crack approaches the FBG where the highly heterogeneous strain is distributed. Another idea is to use a finite element method (FEM), together with a T-matrix method, to analyze the reflection intensity spectra of FBG sensors for various crack sizes. The described crack propagation detection system may apply in structural health monitoring.

The opening subplinian phase of the Hekla 1991 eruption: properties of the tephra fall deposit

The 1991 Hekla eruption started on 17th of January with an intense 50-min-long explosive phase that transitioned into fire fountain activity lasting for 2 days. The eruptive plume rose to maximum height in about 10 min and the total mass of tephra deposited from the opening phase was 8.6 × 109 kg (VEI 3 event). The principal axis of tephra fall is to the NNE of Hekla and grain-size analysis reveals a systematic decrease in grain-size away from source. Majority of sample sites show typically unimodal grain-size distributions, although a few have bimodal distributions where the secondary mode is a subtle finer peak. The calculated total grain-size distribution (TGSD) is bimodal, with a coarse primary peak (−3.5 to −2.5 φ) and a subordinate fine peak (2.5 to 3.5 φ). The coarse peak is lapilli-dominated and was deposited within the first 25 km of transport, whereas the fine peak is coarse-ash-dominated and fits well with the modal grain-size of samples deposited >65 km from Hekla. Ascent rate of the magma and conditions for vesiculation in the shallow conduit became increasingly uniform with time through the 1991 opening phase.

Mechanism of Subordinate Peak Skewing of FBG Sensor during Cracks Propagation Monitoring on Aluminum Alloy Structure

This study investigates the variety of the spectra features of fiber Bragg grating (FBG) around the crack tip during fatigue crack propagation. The study results reveal that the turning of the subordinate peak is significantly associated with crack lengths and corresponds to strain gradient along the FBG. Meanwhile, the strain distribution sensed by the FBG changes with the sensing section of the grating. FBG sensors could observe the monotonic plastic zone ahead of the fatigue crack tip. The cubic strain is distributed along the grating, with monotonic plastic zone propagation at the initial and terminal part of the grating, at approximately a 30% ratio of the entire grating. However, the monotonic plastic zone is sensed by the FBG, at ±15% bias of the grating center, with the quadratic strain gradient pattern along the grating. In particular, when the initial and terminal parts of the grating experience highly inhomogeneous strain distribution, the spectrum distortion occurs.

Constraints on the thermal evolution of the Adriatic margin during Jurassic continental break-up: U–Pb dating of rutile from the Ivrea–Verbano Zone, Italy

The Ivrea–Verbano Zone (IVZ), northern Italy, exposes an attenuated section through the Permian lower crust that records high-temperature metamorphism under lower crustal conditions and a protracted history of extension and exhumation associated partly with the Jurassic opening of the Alpine Tethys ocean. This study presents SHRIMP U–Pb geochronology of rutile from seven granulite facies metapelites from the base of the IVZ, collected from locations spanning ~35 km along the strike of Paleozoic fabrics. Rutile crystallised during Permian high-temperature metamorphism and anatexis, yet all samples give Jurassic rutile U–Pb ages that record cooling through 650–550 °C. Rutile age distributions are dominated by a peak at ~160 Ma, with a subordinate peak at ~175 Ma. Both ~160 and ~175 Ma age populations show excellent agreement between samples, indicating that the two distinctive cooling stages they record were synchronous on a regional scale. The ~175 Ma population is interpreted to record cooling in the footwall of rift-related faults and shear zones, for which widespread activity in the Lower Jurassic has been documented along the western margin of the Adriatic plate. The ~160 Ma age population postdates the activity of all known rift-related structures within the Adriatic margin, but coincides with extensive gabbroic magmatism and exhumation of sub-continental mantle to the floor of the Alpine Tethys, west of the Ivrea Zone. We propose that this ~160 Ma early post-rift age population records regional cooling following episodic heating of the distal Adriatic margin, likely related to extreme lithospheric thinning and associated advection of the asthenosphere to shallow levels. The partial preservation of the ~175 Ma age cluster suggests that the post-rift (~160 Ma) heating pulse was of short duration. The regional consistency of the data presented here, which is in contrast to many other thermochronometers in the IVZ, demonstrates the value of the rutile U–Pb technique for probing the thermal evolution of high-grade metamorphic terrains. In the IVZ, a significant decoupling between Zr-in-rutile temperatures and U–Pb ages of rutile is observed, with the two systems recording events ~120 Ma apart.

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.

Xigaze forearc basin revisited (South Tibet): Provenance changes and origin of the Xigaze Ophiolite

Our new stratigraphic, sedimentological, and micropaleontological analysis, integrated with basalt geochemistry, sandstone petrography, and detrital-zircon U-Pb and Hf isotope data, suggests the revision of current models for the geological evolution of the Asian active margin during the Cretaceous. The Xigaze forearc basin began to form in the late Early Cretaceous, south of the Gangdese arc, during the initial subduction of the Neotethyan oceanic lithosphere under the Lhasa terrane. Well-preserved stratigraphic successions document the classical upwardshallowing pattern of the forearc-basin strata and elucidate the origin of the associated oceanic magmatic rocks. The normal midocean-ridge basalt (N-MORB) geochemical signature and stratigraphic contact with the overlying abyssal cherts (Chongdui Formation) indicate that the Xigaze Ophiolite formed by forearc spreading and represents the basement of the forearc sedimentary sequence. Volcaniclastic sedimentation began with thick turbiditic sandstones and interbedded shales in the late Albian–Santonian (Ngamring Formation) followed by shelfal, deltaic, and fl uvial strata (Padana Formation), with fi nal fi lling of the basin by the Campanian age. Forearc sandstones do not show the classical trend from feldspatholithic volcaniclastic to quartzo-feldspathic plutoniclastic compositions, indicating limited unroofi ng of the Gangdese arc prior to collision. U-Pb age spectra of detrital zircons are unimodal with a 107 Ma peak in the lower Ngamring Formation (104–99 Ma), bimodal with a subordinate additional peak at 157 Ma in the middle Ngamring Formation (99– 88 Ma), and multimodal with more abundant pre-Mesozoic ages in the upper Ngamring and Padana Formations (88–76 Ma). These three petrofacies with distinct provenances document the progressive erosional evolution of the Gangdese arc, with uplift of the central Lhasa terrane and expanding river catchments to include the central Lhasa terrane during the Late Cretaceous.

Zircon U–Pb geochronology and Hf isotopes of major lithologies from the Jiaodong Terrane: Implications for the crustal evolution of the Eastern Block of the North China Craton

The Jiaodong Terrane of the Eastern Shandong Complex in the Eastern Block of the North China Craton (NCC) consists predominantly of Archean granitoid gneisses with minor supracrustal rock enclaves or lenses. This study presents new zircon LA-ICP-MS U–Pb and Lu–Hf isotopic data for these lithologies, which help to better understand the Archean crustal evolution of the Eastern Block of the NCC. Magmatic zircon U–Pb data reveal that zircons in the supracrustal rocks and granitoid gneisses were generated by multi-stage events at ~2.9Ga, ~2.7Ga and ~2.5Ga. Metamorphic zircon U–Pb data obtained for these rocks show distinct metamorphic ages at ~2.50 and ~1.9–1.8Ga, suggesting that the Jiaodong Terrane experienced a regional metamorphic event at the end of the Neoarchean and encountered reworking by a tectonothermal event that was associated with the formation of the Paleoproterozoic Jiao–Liao–Ji Belt. Magmatic zircons have variable εHf(t) values from −5.5 to +7.7 with model ages of 3.92–2.57Ga, of which most εHf(t) values are positive with a predominant peak of model ages at 3.4–3.1Ga and a subordinate peak at 2.8–2.7Ga. These Hf features reveal major juvenile crustal growth stages with significant additions of older crustal materials at 3.4–3.1Ga and 2.8–2.7Ga, and a crustal reworking event with minor juvenile additions at ~2.5Ga in the Jiaodong Terrane.

Zircon U[sbnd]Pb geochronology and Hf isotopes of major lithologies from the Yishui Terrane: Implications for the crustal evolution of the Eastern Block, North China Craton

As an important component of the Western Shandong Complex in the Eastern Block of the North China Craton, the Yishui Terrane consists of Neoarchean high-grade supracrustal rocks, granitoid gneisses and charnockites. LA-ICP-MS zircon UPb dating and Hf isotopic analyses on these lithologies have been carried out and the results provide new insights into the Neoarchean crustal evolution of the Eastern Block of the North China Craton. New zircon dating results reveal that the magmatic precursors of the supracrustal metapelites and granitoid gneisses were generated at 2.54–2.53Ga and 2.57–2.55Ga, respectively, and the charnockites were emplaced contemporaneously around 2.56–2.53Ga. Single metamorphic zircon grains and overgrowth rims from these rocks document consistent metamorphic ages at ~2.50Ga, suggesting that the Yishui Terrane experienced a high-grade metamorphic event at the end of the Neoarchean. Detrital zircons from pelitic gneisses yield 207Pb/206Pb ages of 2.89–2.65Ga, with a major age peak at ~2.53Ga and a subordinate age peak at ~2.70Ga, implying that the sedimentary protoliths of the pelitic gneisses may have been sourced from ~2.53Ga rocks in the Yishui Terrane and ~2.70Ga rocks in the adjacent Luxi Granite-Greenstone Terrane. Hf isotopic compositions show that the Neoarchean magmatic zircons have positive εHf(t) values ranging from +1.4 to +7.8 and depleted mantle model ages of 2.92–2.60Ga with a prominent peak at 2.8–2.7Ga, suggesting that the Neoarchean crust was derived mainly from juvenile sources and partly from the recycling of old continental crust in the Yishui area. Combined with previous data from the adjacent Luxi Granite–Greenstone Terrane and other complexes in the Eastern Block, it is concluded that the Neoarchean was an important period of crust accretion in the Eastern Block of the North China Craton.

Detrital zircon U–Pb geochronology, Hf-isotopes and geochemistry—New clues for the Precambrian crustal evolution of Cathaysia Block, South China

This paper reports some new results from U–Pb geochronological, Hf isotopic and REE geochemical studies of detrital zircons in the Ordovician sandstones from South Jiangxi within Cathaysia. 426 groups of U–Pb age determinations define five major age populations: 2560–2380 Ma (a peak of 2460 Ma), 1930–1520 Ma (a peak of 1700 Ma), 1300–900 Ma (a major peak at 970 Ma and two subordinate peaks at 1250 Ma and 1130 Ma), 850–730 Ma (a prominent peak of 780 Ma) and 670–530 Ma (a major peak at 540 Ma and a subordinate peak at 650 Ma). We also report zircon U–Pb concordia age of 3.96 Ga, which is the oldest age so far obtained from Cathaysia. The age peak at 2460 Ma correlates with similar ages reported for Neoarchean global continental growth. The 1930–1520 Ma population broadly overlaps with the time of amalgamation and disruption of the Columbia supercontinent. The major age peak at 970 Ma and two secondary peaks at 1250 Ma and 1130 Ma reflect multiple tectonothermal events associated with the assembly of Rodinia. Similar ages are widely reported from the South China Craton (SCC). Our study reveals that the 850–730 Ma population is consistent with the breakup period of Rodinia, suggesting that the SCC within Rodinia began to break up since 850 Ma. Geologically, the evidence for this breakup event is widespread and presented by Neoproterozoic granites, bimodal igneous rocks, basic dyke swarms and formation of continental rift type basins. Our study also reveals a 670–530 Ma population that correlates well with the assembly of Gondwana during end Neoproterozoic. However, direct geological evidence for this event has not yet been found within the studied area. Furthermore, the Hf isotopic model age data suggest two major stages of crustal evolution within Cathaysia. The first is the event dated at 1.6–2.8 Ga and the second one at 3.5–3.9 Ga. The zircons show a large range of εHf(t) values from + 8.64 to − 30.54, suggesting that they have different origins with a similar age of crystallization. The fact that most detrital zircons show negative εHf(t) values suggests the ancient provenances of Cathaysia were dominated by reworked crustal materials.

Provenance record from Mesoproterozoic-Cambrian sediments of Peary Land, North Greenland: Implications for the ice-covered Greenland Shield and Laurentian palaeogeography

In North Greenland, Precambrian crystalline basement forms restricted outcrops bordering the Inland Ice. The coverage and nature of this basement is of key importance in understanding the evolution of the Greenland Shield and its palaeogeography. Specifically, the extent of the Grenville Orogen within Greenland is difficult to resolve due to overprinting deformation and ice cover. In an effort to remove some of this uncertainty, we have examined autochthonous sedimentary deposits in Peary Land. Detrital zircon crystals in siliciclastic units of the Mesoproterozoic Independence Fjord Group (Inuiteq Sø Formation) yield ages from 1814 to 3299 Ma. The detrital population in these samples contains significant Palaeoproterozoic peaks at c. 1900 and 1990 Ma and a subordinate Neoarchaean peak at c. 2700 Ma. Detrital zircon grains from the overlying Neoproterozoic (?Marinoan) Morænesø Formation, range from 970 to 3970 Ma and include a substantial 1000–1400 Ma population that peaks at c. 1020 Ma. The (?Neoproterozoic-Lower Cambrian) Portfjeld Formation, higher in the stratigraphy, also contains late Palaeoproterozoic and late Mesoproterozoic peaks. The Palaeoproterozoic and older populations in the Morænesø and Portfjeld formations are comparable to those in the Inuiteq Sø Formation. Within these formations, the similarity of both the detrital ages and palaeocurrent directions, predominantly to the NE, suggests a consistent provenance area sourced throughout the Proterozoic. This source region was, however, affected by Grenville events after the deposition of the Inuiteq Sø Formation. Granitoid clasts within diamictites of the Morænesø Formation contain high uranium metamict zircon grains but yield best age estimates for unfoliated clasts of c. 2700 Ma. However, foliated clasts suggest c. 1250 Ma crystallization or overprinting. The age range of detritus and palaeocurrent directions is consistent with a dominant provenance from the Greenland Shield to the south-west. Potential sources include the Committee-Melville Orogen (Archaean), the Ellesmere-Inglefield Mobile Belt (Palaeoproterozoic) and the sub ice continuation of the Victoria Fjord complex (Archaean). A proximal source of late Mesoproterozoic detritus is unknown in North Greenland. It is conceivable that some of the sand-grade material may have been transported across the shield from a Grenville foreland basin, but the presence of cobble-sized clasts with indications of an Elzevirian history, strongly implies that the North Greenland basement was near to a zone of c. 1250 Ma reworking.