Isotopic Data Of Detrital Zircons Research Articles

Mid-Cretaceous to early Eocene Neo-Tethyan subduction records in West Sulawesi, Indonesia

Situated in the heart of the Indonesian archipelago, Sulawesi records well-developed Cenozoic magmatism, yet its Cretaceous magmatic evolution remains enigmatic. Here, we report new U-Pb-Hf isotopic data of detrital zircons from West Sulawesi, Indonesia to constrain its Cretaceous to Eocene magmatic tempo. Detrital zircons aged at ca. 105−80 Ma and ca. 70−45 Ma occur as the most dominant age populations and show high positive εHf(t) values, indicating derivation from juvenile sources with limited continental crustal contamination. Our new data, combined with available results, support the existence of an Andean-type continental margin in West Sulawesi during mid-Cretaceous to early Eocene times. Importantly, the magmatic tempo of West Sulawesi is also consistent with those of southern Lhasa (Tibet) and Sumatra (Indonesia), but contrasts with those of Paleo-Pacific subduction-related arcs in SE China, SE Vietnam, East Malaysia, and NW Borneo. Therefore, we put forward that West Sulawesi may be the southeasternmost component of the Neo-Tethyan arc system that spreads over 7500 km, from southern Tibet to SE Sundaland. Such a huge arc system with concurrent magmatic flare-ups and lulls in South Asia may have played a significant role in global-scale plate reorganization.

Locating the Yangtze Block in Nuna: Constraints from age and isotopic data from Paleoproterozoic sedimentary rocks in the Phan Si Pan Zone, northwest Vietnam

New U-Pb ages and Hf isotopic data for detrital zircons from the late Paleoproterozoic sedimentary rocks (Suoi Chieng Formation) in the Phan Si Pan Zone of northwest Vietnam constrain their depositional ages, provenance, and tectonic setting. The weighted average age of the youngest coherent zircon population is 1769 ± 31 Ma (MSWD = 1.3, n = 8), which provides a maximum depositional age for the Suoi Chieng Formation. The detrital zircons obtained from six Paleoproterozoic samples exhibit various ages, showing multiple magmatic and metamorphic events. The detrital zircon age pattern shows that magmatic activities in the source areas occurred at 2650 Ma, 2350–2150 Ma, and 2050 Ma, as well as minor activities at 2850 Ma, 1850 Ma, and 1780 Ma. Additionally, a prominent metamorphic age peak is observed around ca. 1850 Ma, while a few metamorphic zircons exhibit ages ranging from 2600 to 2500 Ma and 2100 Ma. This pattern indicates that the primary source of these zircons is the local basement rocks of the Phan Si Pan Zone and SW Yangtze. However, contributions from other adjoining cratonic blocks are also possible and these likely included the Rae craton of North Laurentia. Our new data verifies and expands earlier results, showing that the SW Yangtze and north Yangtze have distinct Archean-Paleoproterozoic crustal evolutionary histories prior to their assembly in the late Paleoproterozoic. Regional correlations based on detrital zircon spectra, stratigraphic and tectono-thermal histories show strong similarities between the SW Yangtze and the Rae craton of north Laurentia throughout the Paleoproterozoic, suggesting the proximity of the two blocks before or during the formation of the Nuna supercontinent. We further suggest that the north Yangtze adjoined southern Siberia in the Archean to late Paleoproterozoic as supported by their identical tectono-thermal histories and detrital zircon age spectra. In combination with published data, we propose that the Yangtze Block was located between north Laurentia and south Siberia during the Nuna assembly.

Caribbean–South America interactions since the Late Cretaceous: Insights from zircon U–Pb and Lu–Hf isotopic data in sedimentary sequences of the northwestern Andes

The Northern Andes in Colombia developed along an active, convergent margin with a complex subduction-accretion/collision history since Triassic times. Sedimentary basins that developed within, or close to, the evolving margin provide an important record for the tectonic history. Here we present U–Pb and Hf isotopic data of detrital zircons from Late Cretaceous and Miocene sedimentary strata. Two sedimentary sequences deposited in an active margin setting are analyzed in this study along two roughly E–W trending transects. Targeted sedimentary sequences are the Late Cretaceous-Paleocene siliciclastic member of the Penderisco Formation outcropping in the Western Cordillera and the hemipelagic Miocene Beibaviejo Formation overlying the suture zone between the Western Cordillera and the Panama-Chocó Block (PCB). Provenance and Hf isotopic signatures for sediments and volcaniclastic sandstones associated with the Penderisco Formation indicate a maximum depositional age of ca. 57 Ma with input of detrital material from mixed sources from two major domains: an eastern ancient continental domain, and a western Cretaceous oceanic domain that defines the present Western Cordillera. The record from continental sources suggests a para-autochthonous to autochthonous syn-tectonic history. For the Beibaviejo Formation provenance and Hf isotopic data suggest the Penderisco Formation and Eocene rocks with oceanic affinity within the PCB as the main sources and define a middle Miocene maximum depositional age (∼16 Ma). Our results provide a new insight into the evolution of volcaniclastic sequences at the northwestern margin of South America and provide a new constraint on the timing of collision between the PCB and the Andean margin during the middle Miocene.

Timing of the Meso-Tethys Ocean opening: Evidence from Permian sedimentary provenance changes in the South Qiangtang Terrane, Tibetan Plateau

Timing of the opening of the Meso-Tethys Ocean, represented by the Bangong–Nujiang Suture Zone on the Tibetan Plateau, remains controversial. Further research is required to understand the breakup of the northern Gondwana margin and the tectonic evolution of the Tethyan realm. In this study, we present petrography, U-Pb dating and Hf isotopic data for detrital zircons from Upper Carboniferous–Upper Permian strata in the South Qiangtang Terrane on the Tibetan Plateau. These data, together with data from previous literature, indicate a youngest detrital zircon age peak of ca. 550 Ma for Upper Carboniferous–Lower Permian strata. This is far older than the depositional age of ca. 300 Ma and indicates a source in the stable Gondwana Continent. Upper Permian strata yield younger ages (490–247 Ma) with peaks at ca. 460, 355, 290 and 260 Ma, indicating a source in the active South Qiangtang Terrane. Combined with the unconformity between the Lower and Upper Permian strata in the western South Qiangtang Terrane, we conclude that a significant change in sedimentary provenance occurred at 280–260 Ma. This provenance change might have resulted from the 300–279 Ma rifting magmatism on the northern Indian margin of Gondwana (e.g., South Qiangtang). The 300–279 Ma magmatism is interpreted to reflect the early stages of rifting, and the subsequent 280–260 Ma sedimentary provenance change is interpreted as the later stage, both of which established a complete Early–Middle Permian (300–260 Ma) rifting process that marks the opening of the Meso-Tethys Ocean.

Protracted northward drifting of South China during the assembly of Gondwana: Constraints from the spatial-temporal provenance comparison of Neoproterozoic–Cambrian strata

Abstract Neoproterozoic to Paleozoic sedimentation shows systematic temporal-spatial variations within South China, which must be considered in reconstructing geological evolution of South China in response to global plate reorganization from the breakup of Rodinia to the assembly of Gondwana. We use >1000 new U-Pb and Hf isotopic data for detrital zircons from Neoproterozoic–Cambrian strata across the western (i.e., Longmenshan) and eastern (i.e., Wuyishan) margins of South China, coupled with compiled stratigraphic and magmatic information, to constrain change in provenance through time. First-order conclusions are as follows: (1) detrital zircons from the Neoproterozoic strata of the two margins were mainly sourced from the Panxi-Hannan arc and the Jiangnan orogen, signaling a rough self-sufficient sedimentary system; (2) newly identified Cambrian molasse-like sediments in the western margin, in which abundant detrital zircons are 550–500 Ma old with positive εHf(t) values, were mainly derived from the 580–500 Ma Cadomian arc belt along the Iran-Turkey margin; and (3) the Cambrian sediments in the eastern margin document more increased contributions from the Grenvillian-age provinces most possibly in Australia. Such spatial-temporal provenance variations signal the northward drifting of South China, from a position connecting with Iran-Turkey and northern India to that approaching Australia during the late Neoproterozoic–Cambrian period. We highlight that the activity of oblique oceanic-continental convergence accreted Asian terranes onto the northern margin of Gondwana, hence contributing to the ultimate Gondwana architecture under global plate reorganization.

Two types of accretionary complexes in the eastern Mongol–Okhotsk Belt: Constraints from U–Pb and Hf isotopic data of detrital zircons from metasedimentary rocks of the Selemdzha and Tokur terranes

The Mongol–Okhotsk Belt is a major structural element of East Asia. However, a number of important aspects of its evolution remain unresolved, in particular, the timing and scenarios of accretion and collision. This paper presents first detrital zircon U–Pb–Hf and whole-rock Nd isotope data from metasedimentary rocks of the Selemdzha and Tokur terranes in the eastern Mongol–Okhotsk Belt. Our new data suggest that these terranes are not part of a single sedimentary sequence, as has been previously assumed, but likely form a set of thrust sheets. The eastern Mongol–Okhotsk Belt hosts at least two types of accretionary complexes. The first type includes the Talyma, Zlatoust, Sagur-1, Tokur, and Ekimchan formations, which contain abundant Paleoproterozoic and Archean zircons, as well as Paleozoic zircons with two-stage model ages (tHf(C)) of >1.7 Ga. These formations are interpreted as fragments of a Paleozoic accretionary complex emplaced at the southern edge of the Siberian Craton. The second type includes the Afanas'ev and Sagur-2 formations, which lack Paleoproterozoic and Archean zircons but contain early Mesozoic zircons with tHf(C) ages of <1.4 Ga. The Afanas'ev and Sagur-2 formations are probably fragments of an early Mesozoic accretionary complex formed at the northern edge of the Amur Block. Our new model focuses on stratigraphic architecture of the Selemdzha and Tokur terranes and implies that two subduction zones of opposite polarities existed during the suturing of the Mongol–Okhotsk Ocean.

Proterozoic tectonic evolution of the Tarim Craton: New insights from detrital zircon U-Pb and Lu-Hf isotopes of metasediments in the Kuruktag area

The Proterozoic is the longest Eon in geological history and witnessed the assemblies and breakups of the Columbia and Rodinia supercontinents. The Tarim Craton has been proposed to be a building block of these supercontinents. However, its tectonic evolution during late Paleoproterozoic to earliest Neoproterozoic (ca. 1.8–0.8 Ga) has been poorly understood, due to the paucity of geological record. In this paper, we present U-Pb and Lu-Hf isotopic data for detrital zircons from the metasediments of the early Neoproterozoic Paergangtag Group and the Paleoproterozoic Xinditag Group in the Kuruktag area, northern Tarim Craton.Although formed approximately 1 billion years later, the Paergangtag Group contains detrital zircons almost identical to those inthe Xinditag Group. LA-ICP-MS U-Pb dating yields a ca. 2.0 Ga age peak, as well as a group of older zircons of ca. 2.5 Ga in six samples from these two groups. Lu-Hf data show that the ca. 2.0 Ga zircons have variableεHf(t) values (−28.1 to 0.1), indicating the detritus were mostly derived from reworked continental crusts. The older zircons around 2.5 Ga have both negative and positiveεHf(t) values (−28.5 to 9.5), indicating a prolonged and complicated crustal growth and reworking process in the source area. It is inferred that the zircons in these samples were likely derived from southeastern Tarim Craton, where a ca. 2.0 Ga orogenic event has been documented.The fact that the Neoproterozoic Paergangtag Group contains only Paleoproterozoic and older zircons suggests that the Tarim Craton was not involved in the Grenville Orogeny, which developed between the colliding continents in the interior of the Rodinia Supercontinent. In contrast, the Tarim Craton was probably on the periphery of the Rodinia Supercontinent and was involved in the peripheral subduction zone of the supercontinent shortly after the deposition of the Paergangtag Group. Our new data imply that the Tarim Craton might have been a tectonically stable continent for nearly 1 billion years from ca. 1.8 to 0.9 Ga.

Timing of closure of the eastern Mongol–Okhotsk Ocean: Constraints from U–Pb and Hf isotopic data of detrital zircons from metasediments along the Dzhagdy Transect

The Mongol–Okhotsk Belt, a major structural element of East Asia, is probably the youngest orogenic segment within the Central Asian Orogenic Belt. However, the timing of final closure of the Mongol–Okhotsk Ocean remains unresolved. Here, we present detrital zircon U–Pb–Hf isotopic data and whole-rock geochemical data (major and trace elements and Sm-Nd isotopes) for the metasedimentary rocks from the Un'ya–Bom Terrane, Dzhagdy Terrane, and the eastern part of the Tukuringra Terrane. Our new zircon U-Pb ages suggest that all sedimentary formations along the Dzhagdy Transect are early Mesozoic in age, rather than Paleozoic as previously thought. The detrital zircons from the metasedimentary rocks in the Un'ya–Bom Terrane, the Dzhagdy Terrane, and the eastern part of the Tukuringra Terrane yielded the youngest concordant ages of 194 ± 4, 193 ± 2, and 171 ± 2 Ma, respectively. Moreover, we note that the so-called sedimentary formations of these terranes are not single sedimentary sequences as previously suggested, but a set of an olistostrome or tectonic mélanges composed of rocks of different ages and origins. These sedimentary formations are probably relics of the Mongol–Okhotsk remnant basin that formed in the “gaps” between the southern margin of the North Asian Craton and the Amur Block during their collision. The absence of detrital zircons younger than 171 Ma in the sedimentary rocks of the Mongol–Okhotsk basin implies that the final closure of this basin could have taken place at the boundary of the Early and Middle Jurassic as a result of the collision or the development of the Mongol–Okhotsk orogenic belt in this region. After that, the Mongol–Okhotsk Belt underwent intense deformation related to within-plate strike-slip faulting, which could be attributed to the late Mesozoic rotation of the North Asian Craton relative to the continental massifs of East Asia.

Provenance investigation for the Cambrian–Ordovician strata from the northern margin of the western Yangtze Block: implications for locating the South China Block in Gondwana

AbstractWe report new U–Pb isotopic data for detrital zircons from Cambrian–Ordovician strata on the northern margin of the western Yangtze Block, which together with published U–Pb isotopic data for coeval strata in the South China Block, provide critical constraints on the provenance of these sediments and further shed light on the early Palaeozoic position of the South China Block in the context of Gondwana. Detrital zircons in this study yield four major age peaks in the early Palaeoproterozoic, early Neoproterozoic, middle Neoproterozoic and late Neoproterozoic – early Palaeozoic. The dominant age population of 900–700 Ma matches well with magmatic ages from the nearby Panxi–Hannan Belt, which indicates that Cambrian–Ordovician sedimentary rocks in the western Yangtze Block were mainly of local derivation. However, compilations of detrital zircon ages for the Cambrian–Ordovician strata from the Cathaysia Block and the eastern Yangtze Block show that both blocks are dominated by late Mesoproterozoic- and early Neoproterozoic-aged detrital zircons, which suggests a remarkable exotic input with typical Gondwana signatures. According to the integrated detrital zircon age spectra of the Cambrian–Ordovician sedimentary rocks from the entire South China Block and palaeocurrent data, the South China Block should have been linked with North India and Western Australia within East Gondwana. Specifically, the Cathaysia Block was located adjacent to Western Australia, while the Yangtze Block was connected with North India.

Detrital zircon provenance investigation from the Neoproterozoic successions of the South China Block: Paleogeographic implications

We report U-Pb isotopic data for detrital zircons from the Late Neoproterozoic Dengying Formation on the northern margin of the Yangtze Block and the other published Neoproterozoic U-Pb isotopic data in the South China Block (SCB), which provide critical constraints on the provenance of these sediments and further shed light on the Neoproterozoic paleogeographic evolution of the SCB in the context of the Rodinia and the succeeding Gondwana supercontinents. The SCB-northern India provenance linkage has started from the Cryogenian. Single Neoproterozoic zircon population from the Upper Cryogenian suggests local detritus supply and the western margin of the Yangtze Block was possibly on an arc setting. Therefore, we speculate that the SCB was independent or located along the margin of Rodinia supercontinent during the Cryogenian. Detrital zircon age spectrum of this study shows similarity with the Cryogenian samples in the eastern Yangtze Block, but with the addition of ‘Pan-African’ age population, which implies that the SCB-India assemblage had been linked with the Gondwana supercontinent during the Ediacaran. Except for a small amount of recycled materials, the Late Neoproterozoic detritus in part of the western Yangtze Block were predominantly derived from the Panxi-Hannan Belt. Early Paleozoic detrital zircon age spectrum of the Tethyan Himalaya is similar with the Late Neoproterozoic age spectra of the Cathaysia Block, whereas appears to be different from the Late Neoproterozoic age spectra of the western Yangtze Block, which implies that the northern India was probably linked with the southern margin of the SCB during the Ediacaran time interval. Finally, the SCB assembled with the western Australia during the Early Paleozoic.

Early Neoproterozoic (ca. 900 Ma) rift sedimentation and mafic magmatism in the North Lhasa Terrane, Tibet: Paleogeographic and tectonic implications

The origin and evolution of the Precambrian North Lhasa Terrane in the central Tibetan Plateau remain enigmatic. Here we present UPb age and Hf isotopic data for detrital zircons from early Neoproterozoic quartzites in the North Lhasa Terrane, Tibet. An integrated petrological, geochronological, geochemical, and Sr–Nd–Hf isotopic study was also undertaken on amphibolites associated with the quartzites. The depositional age of the quartzites is constrained to be between ca. 931 Ma (youngest detrital igneous zircon core) and 869 Ma (oldest metamorphic zircon rim). The detrital zircons have a main age population from 1200 to 1000 Ma, and lack zircons with ages of 1000–900 Ma. Zircons from the amphibolites yield concordant ages of ca. 913–902 Ma, which are comparable to the depositional age of the quartzites. The amphibolites have N-MORB-like compositions and are characterized by high positive zircon εHf(t) (+7.2 to +14.0) and whole-rock εNd(t) (+5.5 to +6.0) values. Their compositions have been modified by crustal contamination. The formation of these quartzites and amphibolites was related to an early Neoproterozoic rift adjacent to the African side of the northern East African Orogen, followed by opening of part of the Mozambique Ocean.

Geochronology, geochemistry, and tectonic implications of upper Silurian – Lower Devonian meta-sedimentary rocks from the Jiangyu Group in eastern Jilin Province, Northeast China

In this study, we present detrital zircon U–Pb ages and Hf isotopic data and whole-rock geochemical data from meta-sedimentary rocks of the Jiangyu Group in eastern Jilin Province (Northeast China) to constrain the late Silurian – Early Devonian tectonic evolution of the southeastern Xing’an–Mongolia Orogenic Belt. Two samples of the meta-sedimentary rocks from the Jiangyu Group yielded concordant ages ranging from 2926 to 415 Ma, and the youngest zircon populations of the two samples yielded weighted mean ages of 427 ± 3 and 426 ± 3 Ma, respectively. Combined with reliable published muscovite 40Ar-39Ar ages of 408 Ma from the overlying metamorphic ophiolitic mélange, these data indicate that the protoliths of the Jiangyu Group were deposited during the late Silurian – Early Devonian Era. A comparison of the U–Pb ages and Hf isotopic data for detrital zircons from northeastern Gondwana and the Jiangyu Group indicates a probable tectonic affinity. The whole-rock geochemical data indicate that the protoliths of the meta-sedimentary rocks from the Jiangyu Group were graywackes deposited in a continental arc setting. Based on the recognition of the early to middle Paleozoic subduction–accretion events along the eastern segment of the northern margin of the North China Craton (NCC), we infer that the subduction–accretion events may have occurred in the Yanbian area followed by one or more arc–continent collisions after the Early Devonian.

The delimitation between the mature and juvenile crustal provinces in SE Asia: Insights from detrital zircon U-Pb and Hf isotopic data for the Salween drainage, Myanmar

To understand the geological control and tectonic forcing on the development of a major river system in SE Asia, new detrital zircon U-Pb and Hf isotopic data from the Salween drainage, Myanmar is reported. Three samples with a range of deposition ages corresponding to different tectonic periods of the Sibumasu Terrane reveal a dramatic change in the drainage system. Differing from the detrital compositions of modern sediments from the Salween river mouth, a Late Triassic sandstone sample shows zircon age distribution implying that the Salween drainage may have been connected at that time to the northeastern part of the Songpan-Ganzi Terrane and western part of the South China Block.U-Pb ages and ɛHf(T) isotopic data of detrital zircons from other major rivers in SE Asia, including the Yangtze, Red, and Mekong Rivers in the east and the Irrawaddy River and the Yalu-Tsangpo in the west are further synthesized. A marked discrepancy in zircons younger than Jurassic ages is identified. Similar to results from the Salween samples, these young zircons from the eastern rivers are overwhelmed by an old, recycled crustal component exhibiting negative ɛHf(T) values. In contrast, those from the western rivers are dominated by juvenile components that are characterized by high and positive ɛHf(T) values. The Salween drainage, therefore, lies in the frontier with its western outline broadly depicting the boundary between mature and juvenile crustal provinces in SE Asia.

New U–Pb isotopic data for detrital zircons from metasedimentary sequences of northwestern Taimyr

This work presents the U–Pb (LA–ICP–MS) data of detrital zircons from metasedimentary sequences of northwestern Taimyr. An analysis of the youngest populations of detrital zircons testifies to the wide distribution of Cambrian sequences in the study area, but not Precambrian sequences as was considered earlier, and the need for a substantial revision of the stratigraphic scheme of this area. The detrital zircon age distribution shows that the Timan margin of the Baltic paleocontinent was a major provenance area of the Cambrian sediments in northern and northwestern Taimyr, as well as the coeval sediments of the Severnaya Zemlya archipelago.

Detrital zircon ages in Korean mid-Paleozoic meta-sandstones (Imjingang Belt and Taean Formation): Constraints on tectonic and depositional setting, source regions and possible affinity with Chinese terranes

Sensitive High-Resolution Ion Microprobe (SHRIMP) U–Th–Pb isotopic data of detrital zircons from mature, quartz-rich meta-sandstones are used to constrain possible tectonic affinities and source regions of the rhythmically layered and graded-bedded series in the Yeoncheon Complex (Imjingang Belt) and the correlative Taean Formation. These metamorphic marine turbidite sequences presently occur along the Paleoproterozoic (1.93–1.83Ga) Gyeonggi Massif, central Korea’s main high-grade metamorphic gneiss terrane. Yet, detrital zircons yielded highly similar multimodal age spectra with peaks that do not match the age repartition in these basement rocks, as late (1.9–1.8Ga) and earliest (∼2.5Ga) Paleoproterozoic detrital modes are subordinate but, in contrast, Paleozoic (440–425Ma) and Neoproterozoic (980–920Ma) spikes are prominent, yet the basement essentially lacks lithologies with such ages. The youngest concordant zircon ages in each sample are: 378, 394 and 423Ma. The maturity of the meta-sandstones and the general roundness of zircons of magmatic signature, irrespective of their age, suggest that sediments underwent considerable transport from source to sink, and possibly important weathering and recycling, which may have filtered out irradiation-weakened metamorphic zircon grains. In combination with these isotopic data, presence of a low-angle ductile fault contact between the Yeoncheon Complex and the Taean Formation and the underlying mylonitized Precambrian basement implies that they are in tectonic contact and do not have a stratigraphic relationship, as often assumed. Consequently, in all likelihood, both meta-sedimentary formations: (1) are at least of early Late Devonian age, (2) received much of their detritus from distant (reworked) Silurian–Devonian and Early Neoproterozoic magmatic sources, not present in the Gyeonggi Massif, (3) and not from Paleoproterozoic crystalline rocks of this massif, or other Korean Precambrian basement terranes, and (4) should be viewed as independent tectonic units that had sources not exposed in Korea.A thorough literature review reveals that the Yeoncheon Complex and the Taean Formation were potentially sourced from the Liuling, Nanwan and Foziling groups in the Qinling–Dabie Belt, which all show very similar detrital zircon age spectra. These immature middle–late Devonian sandstones were deposited in a pro-foreland basin formed as a result of the aborted subduction of the South Qinling Terrane below the North Qinling Terrane, which was uplifted and eroded during post-collision isostatic rebound. The submarine fans where the mature distal turbiditic Yeoncheon and Taean sandstones were deposited may have constituted the eastern terminal part of a routing system originating in the uplifted and eroded middle Paleozoic Qinling Belt and adjacent part of the foreland basin.

Provenance study for the Paleozoic sedimentary rocks from the west Yangtze Block: Constraint on possible link of South China to the Gondwana supercontinent reconstruction

The early Paleozoic and Devonian sedimentary rocks in the western part of the Yangtze Block were suggested to be derived from an exotic source that was once connected to South China. This conclusion was mainly based on that detrital zircons from these rocks give U-Pb age populations of 2400–2600Ma, 1750–1850Ma, 900–1000Ma, 750–870Ma and 500–680Ma, but corresponding magmatic rocks of such late Archean, Grenvillian and latest Neoproterozoic-Cambrian ages do not outcrop in this area or adjacent regions. Zircons from the Cambrian sedimentary rocks of this study show the youngest age peak at ca. 550Ma, and these zircons are mostly euhedral with positive εHf(t) values of +0.6 to +7.4. Because the unconformity between the Cambrian and Ordovician is evident in both west and south sides of South China, which is synchronous with its counterpart along the northern margin of the East Gondwana blocks (e.g. Himalaya region, Qiangtang, Western Australia), it is possible that these zircons were likely derived from a late Neoproterozoic-early Cambrian accretionary orogen (e.g. Bhimphedian orogeny) associated with the initial subduction of a proto-Tethys ocean beneath the margins of Gondwana continents. In contrast, the 500–680Ma zircon population of the Silurian-Devonian sedimentary rocks give an older age peak at ca. 650Ma and their εHf(t) values for the <540Ma grains are all negative (−27.8 to −0.3). These detrital zircons are rounded and could be possibly sourced from ‘Pan-African’ orogenic belts that formed during the amalgamation of the Gondwana, such as the East African and Prydz-Darling orogens between the segments of Gondwana. Early Neoproterozoic ages are dominant in the above sedimentary rocks of this study and correlate well with the large volume of 900–1000Ma magmatism in Grenville-age provinces (e.g. Rayner-Eastern Ghats belt in India-East Antarctica) formed from ocean closure and collision tectonics during the Rodinia assembly. Our Hf isotopic data for detrital zircons of above ages suggest different origins, i.e. crustal reworking and growth at episodes of ca. 2.5Ga, 0.9–1.0Ga, 0.75–0.87Ga and 0.6–0.68Ga. Coupled with the stratigraphic relationship, these age and Hf isotopic data support a South China-North India-Qiangtang continental margin system along the northern margin of the East Gondwana. The west portion of South China was possibly connected to the uplifted Himalaya region in the early Cambrian with continuous detrital inputs from India and surrounding orogenic belts.

Chapter 8 The Eastern (Back-arc) Basin of Central Myanmar: Basement rocks, lithostratigraphic units, palaeocurrents, provenance and developmental history

The Eastern Basin (Back-arc Trough) was initiated on the West Myanmar Block (WMB) and occupies the eastern half of the Central Myanmar Basin (CMB), between the Central Volcanic Line (CVL) and the Sagaing Fault. Sub-basins of the CMB share a similar origin, related to the collision between India and Asia. Field evidence shows that Upper Palaeozoic carbonates and Mesozoic ophiolitic sediments and their metamorphosed derivatives form the basement rocks in the eastern and northern parts of Eastern Basin (EB), while igneous rocks of the Wuntho-Salingyi Mesozoic Arc form the basement in the western portion of the basin. The basal Tertiary unit of the EB is the Lower Eocene Tonkyauk Chaung Conglomerate, overlying the eroded surface of the pre-Tertiary rocks in the Shwebo Basin (SBB). With the exception of the SBB, Oligocene strata have not been recorded in the Eastern Basin province. The ages of the Tertiary units in the Bago Yoma and Shwebo basins, assigned by Myint Thein (1966) and Myint Thein et al. (1982), are now supported by detrital zircon ages and palaeobotanical findings. More than 3000 measurements of cross-bedding azimuths reveal that the siliciclastic sediments were brought into the basin by southwards-directed longitudinal currents, causing the retreat of the sea. Recent research on U–Pb and Hf isotopic data of detrital zircons from the CMB has demonstrated that the Gangdese Batholith of the Lhasa Terrane in South Tibet was the dominant source during the Palaeogene. By the Early Miocene, terrains of the eastern Transhimalayan and intra-Myanmar Dianxi-Burma batholiths became important areas of provenance while the western section of the Sibumasu Block, with its S-type batholiths, played a secondary role and the Wuntho-Salingyi Magmatic Arc provided a relatively minor provenance. The Tertiary sequence of the CMB contains a record of filling of the foreland (orogen-parallel) basin by river-borne sediments; …

A rhythmic source change of the Neoproterozoic basement meta-sedimentary sequences in the Jiangnan Orogen: Implications for tectonic evolution on the southeastern margin of the Yangtze Block

The amalgamation of South China Block and its role in the assembly and breakup of Rodinia supercontinent have been hotly debated in recent decades. However, the intensity of accreted arcs around South China and the following exhumation were poorly constrained. Here we present combined U–Pb dating and Hf isotopic analyses of detrital zircons for a stratigraphic section of the upper Shuangqiaoshan Group in the eastern part of the Jiangnan Orogen (JO). U–Pb dating results suggest a general younging trend of the maximum depositional ages from the Anlelin to the Xiushui Formations of the upper Shuangqiaoshan Group, indicating a co-magmatic sedimentation in association with continental-arc magmatism along the SE margin of the Yangtze Block. The Anlelin and Xiushui Formations were constrained to form in the periods of ca. 845–836Ma and ca. 835–815Ma, respectively. Provenance analysis suggests two sources for these Neoproterozoic basement sequences. Neoproterozoic zircons with positive-εHf(t) values represent detritus derived from the arc-related magmatic rocks to the southeast, whereas >1000Ma zircons and the other Neoproterozoic detrital zircons with negative εHf(t) values are proposed to be sourced from the interior of the Yangtze Block to the northwest. Simultaneously, the Hf isotope results of detrital zircons indicate that there was a rhythmic source change for the sediments in the upper Shuangqiaoshan Group, with the amounts of two separate sources from the Yangtze Block to the west and from the arc terranes to the east increasing alternatively. This provides solid evidence for a bidirectional water flow and supports a back-arc basin setting for the deposition of the sediments. Combined with the published U–Pb and Hf isotopic data for detrital zircons from the Neoproterozoic folded sedimentary sequences in the JO, we calculated the relative contribution of arc-derived crustal materials in the basement sequences of the JO. The calculations suggest that the proportion increases progressively from west to east and the back-arc basins represented by the folded sedimentary sequences could be divided into three regions, plus an arc terrane region to the east. This comparison further suggests that the orientation of Neoproterozoic accretion on the Southeastern margin of the Yangtze Block was in a W–E direction, and the JO in Neoproterozoic may not have extended 1500km as what we see today.

Detrital zircon provenance constraints on the initial uplift and denudation of the Chinese western Tianshan after the assembly of the southwestern Central Asian Orogenic Belt

U–Pb and Lu–Hf isotopic data of detrital zircons from late Paleozoic and Mesozoic strata along the southern flank of the Chinese western Tianshan enable to identify provenance changes and reconstruct early stage uplift and denudation history of the Tianshan range. Detrital zircons from Permian and Early–Middle Triassic siliciclastic rocks show two prominent age populations at 500–390Ma and 310–260Ma, and subordinate Precambrian ages at ~2.5Ga, 2.0–1.7Ga, 1.2–0.9Ga and 900–600Ma, with rare ages between 390 and 310Ma. These characteristics and zircon εHf(t) data consistently suggest a sediment source predominantly from the Tarim Craton, rather than the Central Tianshan–Yili Block. In contrast, Late Triassic to Cretaceous strata additionally contain abundant 390–310Ma and 260–220Ma detrital zircons, implying multiple source regions from the Central Tianshan–Yili Block, Tarim Craton, and Western Kunlun Orogen. A significant switch of sedimentary provenances occurred in the mid-Triassic and is consistent with contemporaneous change of paleocurrent directions and the onset of intense tectonothermal events in the broad region of the Chinese western Tianshan and Kyrgyz Tianshan. These data collectively indicate that the significant surface uplift and denudation of the Tianshan range were probably initiated in the mid-Triassic (~240Ma) after the assembly of the southwestern Central Asian Orogenic Belt. This uplifting event represents an intracontinental orogeny most likely in response to the collision between the Qiangtang Block and southern Eurasia, following the closure of the western part of the Paleo-Tethys Ocean.

Tectonic evolution from subduction to arc-continent collision of the Junggar ocean: Constraints from U-Pb dating and Hf isotopes of detrital zircons from the North Tianshan belt, NW China

The Junggar ocean, once situated north (present coordinate) of the Yili and Central Tianshan blocks during early Paleozoic to late Carboniferous time, was a major southern branch of the Paleo–Asian Ocean, the opening, expansion, and final closure of which led to the development of the Central Asian Orogenic Belt between Eastern Europe–Siberia and Tarim–North China. However, the detailed evolution of the Junggar ocean has not been well constrained. This paper reports U-Pb and Lu-Hf isotopic data of detrital zircons from sandstones in the North Tianshan belt, which can provide new insights into understanding the Paleozoic development of the Junggar ocean. Most detrital zircons exhibit oscillatory zoning and high Th/U ratios, typical of igneous origin. The predominant Paleozoic zircons yield major age populations at ca. 294, 313–327, 338–375, 440–455, and 474–502 Ma and are interpreted to have been derived from the long-lived volcanic- and island-arc systems formed by the southward subduction of the Junggar ocean and subsequent collisional and postcollisional magmatism. The minor Precambrian zircons yield ages scattering at ca. 550, 680–765, 890, 970–990, 1160–1250, 1500, 1690–1750, 1840–1970, 2440–2500, and 2615–2700 Ma, which are nearly, but not fully, congruent with those from the adjacent Beishan and Kuluketage Precambrian terranes. Therefore, our results indicate that the Central Tianshan block was once part of the Tarim block during Precambrian time. Most of the 541–440 Ma zircons possess low negative eHf(t) values, while the <440–300 Ma zircons exhibit dominantly positive eHf(t) values, which can be linked to the Junggar oceanic slab rollback since ca. 440 Ma. This event, subsequently, gave rise to the opening of the South Tianshan back-arc basin/ocean between the Central Tianshan and Tarim blocks, exhumation of high-pressure granulites, and formation of a series of island arcs in the Junggar ocean. Combined with previous studies, we suggest that the Junggar ocean was probably closed at ca. 300 Ma in association with arc-continent collision, followed by postcollisional magmatism. It deserves mentioning that the ca. 0.5 and 1.4–1.5 Ga (detrital) zircons and contemporaneous magmatic rocks only occur in the Central Tianshan block, not in the Tarim block. Therefore, more detailed investigations are needed to better elucidate the origin and Precambrian evolution of the Central Tianshan block.