Zircon Hf Isotopic Data Research Articles

Crustal thickening and multipoint delamination for the ca. 90 Ma high-Sr/Y intrusions and the associated porphyry-skarn Cu-Au-Mo mineralization in the western central Lhasa terrane, Tibetan Plateau

The ca. 90 Ma (92−84 Ma) high-Sr/Y intrusions in the western central Lhasa terrane (WCLT) of the Tibetan Plateau record critical information about the late Mesozoic crustal architecture of the Lhasa terrane and may have provided favorable conditions for porphyry mineralization. However, conflicting geodynamic processes have been proposed, and their mineralization potential is unclear. Here, we report the newly discovered Banongzuosi porphyry-skarn Mo-Cu deposit and Qielong skarn Cu-Au and Rongqing porphyry-quartz vein-type Mo mineral prospects. They provide important constraints on the generation of the ca. 90 Ma high-Sr/Y magmas and their associated mineralization potential. Then, integrated studies of the ca. 90 Ma intrusions are performed to address the above issues. Dating shows that intrusions and mineralization in the three areas occurred at 92.4−84.1 Ma. Based on whole-rock geochemistry, the high-Sr/Y intrusions can be divided into low- and high-Mg#-Cr ones. Zircon Hf isotopic data indicate that both ancient and juvenile lower crust existed in the WCLT, with significant juvenile components in the high-Mg# and Cr-rich intrusions. The crustal thickness calculated from the zircon trace element data suggests that the WCLT had thickened crust (>64 km) with local areas thinned by lower crustal delamination at ca. 90 Ma. Regional thickening and local lower crustal delamination formed the low- and high-Mg#-Cr intrusions, respectively. Whole-rock and zircon trace element data reveal that most of the ca. 90 Ma high-Sr/Y intrusions are hydrous and oxidized. The thickened crust resulted in high H2O contents and fO2 of intrusions and promoted porphyry-skarn mineralization. However, crustal thinning and contamination by reduced Precambrian basement decreased the magma fO2 and hindered mineralization. The advantageous tectonic setting and high H2O and fO2 led to the ca. 90 Ma high-Sr/Y intrusions having the potential to form collisional porphyry-skarn Cu-Au-Mo deposits.

The Permian to late Triassic magmatic evolution of SW Pangea: Reconciling evidence from Patagonia and the Antarctic Peninsula

The geodynamic setting across the Paleozoic to Mesozoic transition in Patagonia and the Antarctic Peninsula (SW Pangea) has been strongly debated. Hypotheses of terrane accretion, episodes of shallower to flattened subduction, long-lived stages of crustal extension, or even subduction arrest have been variably proposed. We have compiled and re-evaluated the available whole-rock geochemistry and zircon Hf-isotope data for Permian to Triassic rocks from Patagonia and the Antarctic Peninsula, and compared these findings with the orogenic events in these regions.We have identified that two orogenic cycles occurred along the SW margin of Pangea during the Permian-Triassic interval, namely the Gondwanide and Chonide/Peninsula orogenies. Both orogenies coexisted with the development of magmatic arcs; the Permian arc exhibits an overall I-type signature that switched to A-type towards ca. 252 Ma, whereas the Triassic arc has an S-type signature in the Antarctic Peninsula and intraplate features in Patagonia. The Hf isotope data for zircon exhibit broadly subchondritic values, suggesting significant crustal contribution in the magmatic source during both cycles. The short- and long-term temporal behavior of the isotopic trends suggests variations that may be attributable to the participation of primitive and/or evolved sources. We conclude that the geochemical and isotopic signatures of the magmas, together with different styles of crustal deformation, resulted from the interaction of the upper and lower plates, consistent with the evolution of an accretionary-type margin along SW Pangea during Permian and Triassic times.

An isolated mildly depleted mantle source for the north atlantic craton

Generation of continental crust during early Earth was a vital step towards stabilizing the cratonic lithosphere. How and when this happened is, however, still poorly understood. Radiogenic isotope data from the oldest crust, and minerals therein, provide a unique insight into the timing and processes that operated during Earth’s earliest evolution. Using combined zircon U-Pb, O and Lu-Hf isotope data from a glacial stream-sediment within the Isukasia (Isua) terrane of southern West Greenland, we argue for an isolated mantle source for the ca. 1.3 Ga of initial stages of crustal growth in the North Atlantic Craton. Zircon Hf isotope data between 3939 and 2950 Ma yield strikingly homogeneous, near chondritic signatures, with the few analyses that deviate slightly being indicative of ancient Pb-loss. Combined with published data from carefully selected and well-characterized ca. 3.9–2.6 Ga magmatic rocks of the NAC, almost no indications of reworking of older crust can be detected, but all strongly sub-chondritic data rather fall on Pb-loss trends tracing back to chondritic sources. This long-lived and near-chondritic signature with negligible influence from a strongly depleted mantle, or from un-radiogenic sources, argues for protracted crust separation from an isolated mantle source. We suggest a scenario whereby primary melting to produce basaltic and komatiitic crust leaves an infertile harzburgitic residue, unlikely to re-melt, that becomes sequestered as mantle lithosphere. Hence, domains of primordial fertile mantle are continuously sourced from an undepleted mantle reservoir. Combined with small wavelength mantle convection, a near-chondritic to mildly depleted regional mantle is retained into at least the Mesoarchean.

Subduction history of the Paleo-Asian oceanic slab along the northern margin of the North China Craton: A case study of zircons and cherts from central Jilin Province, NE China

This paper presents U-Pb ages and Hf isotope data for detrital zircons and whole-rock geochemical data for siliceous-clastic sedimentary rocks of the Shitoukoumen Formation, central Jilin Province, NE China. The new data combined with published data for the northern North China Craton enable us to constrain the temporal changes in crustal thickness along the Solonker−Xar Moron−Changchun−Yanji suture belt (SXCYB). The Shitoukoumen Formation contains ophiolitic lenses, radiolarian-bearing cherts, and volcanic-sedimentary units of various ages. A radiolarian-bearing volcanic-sedimentary unit exhibits a Bouma sequence, in which detrital zircons from a rhyolitic tuff and siliceous-clastic sedimentary rocks yielded youngest ages of 278−273 Ma, which constrain the depositional age of the unit. The geochemical compositions of the cherts suggest the pelagic deposits contain some continent-derived clastic material and may be near-trench gravity flow deposits. The dominantly depleted zircon εHf(t) values of the sedimentary rocks in the Shitoukoumen Formation record extensive crustal growth during the Paleozoic. The variations in the crustal thicknesses during the Paleozoic to early Mesozoic record a tectonic transition from subduction initiation, mature continental arc, and finally to Paleo-Asian ocean closure. The thickest crust (∼58 km) at ca. 245 Ma might have been related to an orogenic peak during the final closure of the Paleo-Asian Ocean along the SXCYB.

Neoarchean and Paleoproterozoic magmatism in the Longjiang area, NE China: Implications for the recycling history of supracrustal components in the eastern Central Asian Orogenic Belt

Substantial Phanerozoic crustal growth and reworking in the eastern Central Asian Orogenic Belt has partly obscured the Precambrian geological record. Accurate identification of such Precambrian magmatism and its petrogenesis is paramount to unveiling the early crustal evolution of the eastern Central Asian Orogenic Belt. Two outcrops of Neoarchean and Paleoproterozoic magmatism in the Longjiang area of NE China, eastern Central Asian Orogenic Belt, were recently discovered. The Kaoquantun outcrop consists of monzogranites that yield a zircon 207Pb/206Pb age of 2568 ± 8 Ma and are similar to peraluminous A1-type granites. They were derived from the partial melting of a hybrid crustal source comprising newly accreted Mesoarchean crust and abundant supracrustal metapelites in a post-collisional extensional setting. Such metapelites were initially part of the upper crust but were buried in the middle−lower crust due to crustal thickening prior to ca. 2.6 Ga. In the Zhanbeitun outcrop, basaltic andesites overlie monzogranites, and both have been intruded by syenogranites. The monzogranites and syenogranites yield zircon 207Pb/206Pb ages of 1881 ± 10 Ma and 1843 ± 3 Ma, respectively, whereas the basaltic andesites are inferred to have formed at 1.88−1.84 Ga. The 1.88 Ga monzogranites have relatively enriched zircon Hf-O isotopic compositions and were derived from a hybrid melt of mafic rocks in the lower crust and ancient metabasalts that had undergone low-temperature alteration at supracrustal depths. The 1.88−1.84 Ga basaltic andesites are Nb-rich and were generated by the partial melting of a mantle wedge that was metasomatized by subduction-derived fluids, recycled sediments, and slab-derived melts. The 1.84 Ga syenogranites are peraluminous and K-rich, and record a profound mixing and assimilation process involving melts derived from supracrustal sediments and the lower crust. Three stages of Paleoproterozoic magmatism emerged from subduction-related crustal thickening, slab breakoff, and collision, respectively. The zircon Hf isotopic data further indicate that the eastern Central Asian Orogenic Belt underwent at least one stage of proto-crustal growth at ca. 3.0 Ga, followed by multiple phases of crustal reworking during the Neoarchean and Paleoproterozoic, with dominant involvement of supracrustal components.

Connection between tectonothermal events of the Yakutian kimberlite province and assembly of the Siberian craton

The tectonic framework of the Siberian craton is still under debate. It is generally assumed that the Markha and Daldyn terranes collided at 2.2–2.1 Ga and the final assembly of the Siberian craton occurred at 1.9–1.8 Ga. However, previous study on zircons from xenoliths of the Zapolyarnaya pipe, which is located in the Upper Muna kimberlite field and close to the boundary between the Markha and Daldyn terranes, do not show tectonothermal evidence younger than 2.7 Ga. To clarify the tectonothermal evolution of the Siberian craton, we present U-Pb ages and Hf isotope data of zircons from crustal xenoliths in the Novinka and Komsomolskaya Magnitnaya kimberlite pipes in the Upper Muna field. The zircon ages confirm only one major tectonothermal event at 2.7 Ga in the Upper Muna field, which doubts the existence of the collision zone between the Markha and Daldyn terranes. The middle-lower crust beneath the Upper Muna field is mainly composed of mafic and intermediate granulites and experienced long-term cooling. The negative values of εHf(2.7) suggests ignorable addition of juvenile component during partial melting of the Paleoarchean crust at 2.7 Ga. Compared with crustal xenoliths from other kimberlite pipes in the Yakutian diamondiferous province, the crust of the Anabar province shows vertical and lateral heterogeneity and the absence of a relationship between the crustal reworking degree and the main collision zones. We propose that the widespread 2.7 and 1.9 Ga tectonothermal events in the Anabar tectonic province were associated with the episodic rise of superplumes, which not only caused the crustal growth and reworking but also facilitated collision and amalgamation of terranes.

Controls on apatite compositional variations in magmatic rocks: A case study of Mesozoic mafic–felsic intrusions from the eastern North China Craton

Compositional variations of apatite are mainly determined by parameters such as partition coefficients and the composition of parental magma. However, the relative importance of these parameters in relation to apatite geochemistry in different lithologies of magmatic rocks is not well constrained. In this study, six Mesozoic (219–154 Ma) mafic–felsic intrusions from the eastern North China Craton, were selected for detailed apatite microanalyses (trace elements and Nd isotopes). Apatite from the studied intrusions has uniform textures in the cathodoluminescence image. They exhibit high abundances of rare earth elements (REE) and are characterized by light REE enriched patterns, indicative of a magmatic origin. Alongside compiled apatite data, these findings suggest that compositional variations of REE + Y in apatite from mafic to felsic magmatic rocks are controlled primarily by elemental partitioning between apatite and melts. The competitive crystallization of other accessory minerals prior to apatite can be responsible for compositional variations of Sr, Pb, Th, and U. New Nd isotope data for apatite are discussed and compared with whole-rock Nd and zircon Hf isotope data for the same sample. The Nd isotopic compositions between the whole-rock and apatite are identical. The integrated dataset provides an alternative interpretation for the isotopic decoupling between apatite Nd and zircon Hf isotope systems. In conclusion, apatite REE concentrations and Nd isotopes have the potential to serve as geological indicators.

Petrogenesis of Neoarchean granitic gneisses from the Daqishan area of the Dabie orogen and implications for the early crustal evolution of the Northern Yangtze Craton

ABSTRACT The Yangtze Craton is one of the crucial cratons constitued the eastern Asia continent. It is characterized by Archaean to Paleoproterozoic basement rocks, making it an excellent area to study the Precambrian geologic and tectonic regime. Recently, abundant Archaean rocks have been reported from the Dabie Orogen, which providing important information to understanding the early evolution of the Northern Yangtze Craton. In this contribution, we present petrological, whole-rock geochemical, and zircon U – Pb – Hf isotopic analyses on newly discovered Neoarchean granite in the Dabie Orogen. We identified 2744 ± 10 Ma and 2715 ± 11 Ma (~2.74 Ga) Na-rich granitic gneisses, 2691 ± 6 Ma and 2696 ± 8 Ma (~2.69 Ga) A2-type granitic gneisses, and 2664 ± 8 Ma, 2664 ± 6 Ma, 2672 ± 7 Ma, 2642 ± 10 Ma (~2.66 Ga) A1-type granitic/syenite gneisses from the Daqishan area of the Dabie Orogen. Geochemical and zircon Hf isotope data indicate that the ~ 2.74 Ga Na-rich granitic gneisses were partial melting products of thickened mafic crust with limited depleted mantle input, while the 2.69 Ga and 2.66 Ga A-type granitic gneisses represent felsic magmatism in a post-collisional to an extensional tectonic setting. Based on our research, we categorized the Northern Yangtze Craton into the Kongling domain and Dabie domain by comparing with the distribution of the zircon U-Pb magmatic ages and metamorphic events. We suggest that the initial unified basement of the northern proto-Yangtze Craton formed during the Nuna supercontinent cycle at ~ 2.0 Ga.

Genesis of the Early Indosinian Darongshan Granitoid in South China: Response to the Subduction of the Eastern Paleo-Tethys Ocean

The Bangxi–Chenxing suture zone is an essential area from which information about the closure history of the eastern Paleo-Tethys Ocean can be obtained. The Darongshan granitoid, which is adjacent to this suture, lies among the widely distributed granitic rocks and few basic rocks in the southern Guangxi Province. Herein, we report the petrogeochemistry, zircon U–Pb ages, and zircon Hf isotopic data of the Darongshan pluton in this region. The LA-ICP-MS U–Pb zircon analysis indicates that the Darongshan pluton had formed at 249.9±2.6 Ma. The Darongshan granites are silica-rich (SiO2=65.68–72.91 wt%, mean=69.89 wt%) with high Na2O contents (Na2O=0.46–6.58 wt%, mean=3.49), relatively high Mg (Mg#=35.12–73.31, mean=57.73), and an average Fe2O3T+TiO2+MnO+MgO of 4.96. These features are similar to those of the Mg-andesitic/dioritic rock- (MA-) like tonalite–trondhjemite–granodiorites (TTGs). Chemical analyses show that all rocks are enriched in large-ion lithophile elements (Rb, Th, and U) and light rare earth elements, with weak negative Eu anomalies (Eu/Eu∗=0.27–0.67), and Ta, Nb, and Ti depletion, with typical arc-like affinity. The zircon Hf isotopic results show zircon ƐHft values ranging from -18.2 to -7.4 and the TDM2 model ages 1.74–2.41 Ga. The petrogeochemistry and zircon Hf isotopic signatures indicate the magma generation of the Darongshan granitoid with fluid/melt released from the subducted slab and the fluid/melt assimilated and mixed with the mantle peridotite during ascent. Combining previous extant information on Permo–Triassic subduction/collision-related magmatism in the Bangxi–Chenxing with that of the Jinshajiang–Ailaoshan–Song Ma suture zones, the Darongshan granitoid is interpreted as a magmatic formation that was generated in an active continental margin arc environment during the subduction of the Early Indosinian eastern Paleo-Tethys Ocean and the South China Block, further supporting the idea that closure occurred during the Middle–Late Triassic.

Cretaceous magmatism in the northern Lhasa Terrane: Implications for the tectonic evolution and crustal growth tempos of central Tibet

The subduction and demise of an ocean plate are generally recognized as essential processes that result in the reworking and maturation of the continental crust. The northern Lhasa Terrane in central Tibet represents the forefront of the Lhasa-Qiangtang collision belt following the closure of the Bangong-Nujiang Ocean. Thus, it is a pivotal location to study the transition processes from oceanic lithosphere subduction to continental collision as well as pertinent crustal growth mechanisms. Here, we present zircon U-Pb dating, whole-rock major and trace element and Sr-Nd isotope, and zircon Hf isotope and trace element data of the Mendang igneous complex, Baingoin County, northern Lhasa Terrane. Geochronological results show that the granodiorites, trachydacites, and rhyolites in the Mendang igneous complex formed at ca. 122−116 Ma, 97 Ma, and 73 Ma, respectively. The Early Cretaceous granodiorite samples are peraluminous with high SiO2, Al2O3, and K2O contents, and moderate A/CNK (molar ratio of Al2O3/[CaO + Na2O + K2O]) values, which are similar to those of typical felsic peraluminous I-type granites. The granodiorites are characterized by enrichment in light rare earth elements and large ion lithophile elements (e.g., Rb) and depletion in high field strength elements (e.g., Nb, Ta). They also show the most enriched whole-rock Sr-Nd [(87Sr/86Sr)i = 0.7072−0.7078; εNd(t) = −7.60 to −5.08] and zircon Hf [εHf(t) = −4.46 to +1.02] isotope compositions, indicating that the Early Cretaceous granodiorites were likely derived from an ancient basement under a subduction setting. The trachydacites have uniform SiO2, high Al2O3, Sr contents, and Sr/Y values, and low Y and Yb contents, belonging to adakitic rocks. They show more depleted whole-rock Sr-Nd [(87Sr/86Sr)i = 0.7065−0.7066; εNd(t) = −0.56 to −0.22] and zircon Hf [εHf(t) = 4.36−7.84] isotopes than the granodiorites, suggesting that the trachydacites may have generated from partial melting of the juvenile thickened lower continental crust. The rhyolites have the highest SiO2 and K2O contents in the Mendang igneous complex, and significant depletion of Ba, Sr, Eu, P, and Ti. They have slighter more enriched whole-rock Nd [εNd(t) = −3.71 to −1.16] and zircon Hf [εHf(t) = 1.03−4.31] isotope compositions than the trachydacites. These features suggest that the rhyolites were highly fractionated products of the crustal melts. Whole-rock Sr-Nd and zircon Hf isotopes of the Mendang igneous complex show a kink trend from enrichment to depletion and then transfer to enrichment again, signifying an increased contribution of juvenile materials in the northern Lhasa Terrane toward progressively replacing the ancient lower crust and accumulating to newly formed crust. The estimated crustal thickness beneath the northern Lhasa Terrane shows a sharp increase from the Early to Late Cretaceous and peak at ca. 97 Ma, whereas it largely decreases in the Late Cretaceous. Integrated with previous studies, we propose that the formation of the Mendang igneous complex (122−73 Ma) elaborately documents the regional tectonic transition from oceanic lithosphere subduction to demise as well as continental crustal differentiation and maturation. The rollback and breakoff of the southward subducted Bangong-Nujiang oceanic slab in the Early Cretaceous initiated diverse magmatism in the northern Lhasa Terrane. During the early Late Cretaceous, the widespread adakitic and Mg-rich magmatism was attributed to the delamination of the thickened lithosphere following the final amalgamation of the Lhasa and Qiangtang Terranes. In the late Late Cretaceous, post-collisional extension induced the formation of the rhyolites in the northern Lhasa Terrane. The growth and destruction of the continental crust had certain tempos from the oceanic lithosphere subduction to continental post-collision stage.

Compositionally variable basement and tectonic affinity of the Bainaimiao arc belt: Implications for crustal growth of the Central Asian Orogenic Belt

As an important part of the southeastern boundary of the Central Asian Orogenic Belt (CAOB), the Bainaimiao arc belt, particularly its tectonic affinity and Precambrian basement composition, is an important element to provide new insights about the crustal growth of the CAOB. However, these remain poorly understood. This paper presents new geochronological, whole-rock geochemical and zircon Hf isotope data on early Paleozoic intrusive rocks from the Bainaimiao arc belt in the southeastern CAOB. The Ordovician gabbroic diorites in the Zhengxiangbaiqi area of the western Bainaimiao arc belt have low SiO2 contents (51.73–54.82 wt%), high TiO2 (0.99–1.07 wt%) and TFe2O3 contents (9.68–9.89 wt%), depletions in Nb, Ta and Ti, and positive εHf(t) values (6.8–11.3). These rocks generated from partial melting of a mantle wedge that has been metasomatized by subducted-derived fluids. The Silurian monzogranites in the Zhengxiangbaiqi area have high contents of SiO2 (72.61–75.12 wt%) and K2O (2.75–4.12 wt%), positive εHf(t) values (0.7–9.3) and abundant Precambrian inherited zircons. These monzogranites originated from partial melting of the thickened juvenile crustal components with significant ancient crustal contamination. The Silurian granites and granodiorites in the Faku area of the eastern Bainaimiao arc belt are characterized by high Na2O contents (4.00–4.52 wt%), high Sr/Y ratios, low MgO (1.15–1.74 wt%) and K2O contents (0.52–1.42 wt%), low K2O/Na2O ratios, and positive εHf(t) values ranging from 0.6 to 8.1. These rocks were derived from partial melting of a subducted slab interacted with mantle peridotite. New zircon U-Pb-Hf isotope data from these early Paleozoic intrusive rocks combined with previous results indicate that the Precambrian basement of the Bainaimiao arc belt is laterally heterogeneous, with Neoarchean-Paleoproterozoic basement beneath the western Bainaimiao arc belt and Paleo-Mesoproterozoic basement beneath the central Jilin area in the eastern Bainaimiao arc belt. The Bainaimiao arc belt has a tectonic affinity different from the North China Craton (NCC) and represents a composite arc system consisting of an ensialic island arc with a basement composition similar to that of the Precambrian microcontinents in the CAOB in the Bayan Obo-Damaoqi-Bainaimiao-Zhengxiangbaiqi and central Jilin areas and an oceanic island arc in the Ongniud-Faku and southern Jilin areas. The involvement of composite arc systems in the amalgamation of the accretionary orogenic belt could be an important mechanism for crustal growth in the CAOB.

Structural patterns and ages of Permian-Triassic multistage strike-slip faulting in the Chifeng area, southeastern Inner Mongolia, China: Implications for the final closure of the Paleo-Asian Ocean

The closure of the Paleo-Asian Ocean (PAO) to the north of the North China Craton (NCC) holds significance in comprehending the Phanerozoic continental evolution of East Asia. However, the timing of the final closure of the PAO, tectono-magmatic records of this process in the northern margin of the NCC, and related geodynamics remain to be resolved. Here we undertaken detailed macro- and micro-structural investigations on the E-W-striking and NNE-striking fault system in the Chifeng area, northern edge of the NCC. Combined with new zircon U-Pb and muscovite 40Ar/39Ar dating, we delineated three phases of strike-slip faulting in the research region during the Permian-Triassic, including WNW-ESE-striking and NE-SW-striking ductile sinistral shearing at ∼ 270–258 Ma and 258–246 Ma, respectively, and subsequent ∼ E-W-oriented ductile–brittle dextral shearing at ∼ 230–209 Ma. Based on analysis of paleotectonic stress fields, we propose that the first two-stage deformation shared a regional unified N-NNE contractional setting, while the late ∼ E-W-striking dextral shearing reflected a distinct regional NNW-SSE shortening event. The regional magmatism reveals three age peaks of ∼ 270 Ma, ∼250 Ma and ∼ 230 Ma, corresponding well to the above three-phase deformation. Further, zircon Hf isotopic data imply that the composition of juvenile material in regional deep-seated crust gradually increased from Permian to Triassic. The N-NNE contraction may be controlled by the eastward scissor-like final closure of the PAO during the Middle Permian-Early Triassic. The middle-late Late Triassic NNW-SSE contraction is likely influenced by the remote effect of the low-angle southward subduction of the Mongol-Okhotsk oceanic plate.

U–Pb Geochronology of the Baguio Area, a Major Mining District in Northern Luzon (Philippines)

ABSTRACTThe Baguio District, located in northern Luzon (the Philippines), is one of the major gold and copper mining districts in the Philippines and SE Asia. U–Pb zircon ages for igneous rocks and for detrital zircons extracted from sediment samples of the principal formations of the Baguio District reveal major magmatic pulses at ca. 1, 3, 16, and 20 Ma. The oldest zircon dated in this study has an age of 27.3 ± 1.6 (2σ) indicating earlier activity which has, however, left only a small imprint on the zircon inventory of the sediments. The absence of older zircons suggests that northern Luzon formed as an intra‐oceanic arc. Zircon Hf isotope data suggests that the magmas, from which the zircons crystallized, were derived from time‐integrated highly depleted mantle sources, compatible with an intra‐oceanic origin of the island. The results of the U–Pb dating of zircons mostly confirm previous estimates of the ages of the rock units. Mid‐Miocene ages obtained for samples thought to represent the Pugo Formation, the lowermost unit, which is thought to be Cretaceous‐Eocene in age, most likely date magmatic rocks that intruded the Pugo Formation.

New early Oligocene age for the Mouding Basin, Southwestern China: Source and paleoenvironment

Sedimentary basins in the southeastern margin of the Tibetan Plateau yield valuable geophysical and fossil records, documenting the paleoenvironmental and biodiversity changes in the Tibetan Plateau and the Hengduan Mountains. Constraining the age of sediment deposition is fundamental in understanding the evolutionary history of biodiversity, climate (e.g. development of the monsoon), and regional landscape changes. Many basins in this area were originally considered as Miocene basins based on regional lithostratigraphic comparison and biostratigraphy, although this has been challenged recently for several basins (e.g. Lühe, Markma, Jianchuan, Wenshan and Relu basins). Here we report a new age for the Mouding Basin, Central Yunnan, China. We arrive at an early Oligocene (33 ± 1 Ma) instead of a Miocene age for the fossil-bearing strata of this basin. UPb and 40Ar/39Ar dating of a volcanic ash layer from the Mouding Basin and one from the Lühe Basin in combination with zircon Hf isotope data suggest that the early Oligocene Laojiezi eruption is a likely source for ash layers in both basins. Fossilized dicot leaves were used to reconstruct the paleoclimate and the paleo-elevation of the Mouding Basin. This paleoclimate reconstruction indicates that the paleoclimate in the Mouding Basin closely resembles that of the Lühe Basin. The paleoclimate between the two floras is in fact more similar than their respective modern climates. During the early Oligocene, the Mouding Basin experienced colder and more humid winters with a milder monsoonal climate compared to today. Despite this, the Mouding flora exhibits high floristic similarities with its contemporary Lühe and Markam floras, as well as with the modern vegetation in southwestern China, supporting that the modernization of the biodiversity in the SE margin of the Tibetan Plateau has initiated since the Paleogene.

Chronological and Mineralogical Records of the Langqi Pluton, Fuzhou: Constraints on the Magma Mixing Process

The mafic microgranular enclaves (MMEs) from Mesozoic intermediate-acid magmatic rocks, widely developed along the Fujian coast, are considered to be the results of large-scale crust–mantle interaction by magma mixing. This paper is based on zircon U-Pb chronology, along with zircon Hf isotope and mineral analyses for the host granite and MMEs from Langqi Island, in order to investigate the magma mixing mechanism of the Langqi pluton in Fuzhou, Southeast China. The results indicate that the MMEs were emplaced during the late Early Cretaceous (98.9 ± 2.2 Ma), identical to the age of the granite (100.1 ± 1.1 Ma) within the error range. The zircon εHf(t) values for the granite and MMEs are in the ranges of −2.1~0.0 and −1.7~+1.1. The zircon Hf isotope data indicate that both the granite and MMEs were predominantly derived from the ancient crustal basement of Cathaysia, with a partial mantle-derived contribution. The An values of plagioclase phenocrysts with oscillatory zoning patterns in the MMEs show oscillatory changes from the core to the rim, indicating multiple mixing events between the two magmas with different compositions. Amphiboles in the MMEs show characteristics of crust–mantle contamination, and the Ti migrated from the mafic magma with high concentration to the felsic magma with low concentration during the magma mixing process. Biotites in the host rock and MMEs belong to primary biotite, and they have relatively high MgO contents (ave. 12.78 wt.%) and relatively low FeOT/(MgO + FeOT) ratios (ave. 0.56), showing characteristics of crust–mantle contamination. The crust–mantle magma interaction in a crystal, mushy state played a significant role in controlling the formation and evolution of the Langqi pluton. The magmatism was predominantly sourced from mixing between the mantle-derived mafic magma and the crust-derived felsic magma during the subduction of the Paleo-Pacific Plate, resulting in the formation of the Langqi doleritic veins, granites, and MMEs.

Late Neoarchean plume-induced crust-mantle interaction and crustal reworking: Evidence from the Jianping Complex, North China Craton

The Archean basement of the North China Craton (NCC) is predominantly composed of 2.6–2.5 Ga lithological assemblages, while the tectonic regime that governed the formation and evolution of these Neoarchean basement rocks has been a controversial issue. Based on field relationships, petrographical features, whole-rock chemistry and zircon Hf isotope data, diverse late Neoarchean granitoids exposed in the Jianping Complex of the NCC are categorized into TTGs, sanukitoids and potassic granites. Their petrogenesis are associated with partial melting of metabasalts, melting of metasomatized mantle, and melting of crustal lithologies including tonalite and metasediments, respectively. Zircon U-Pb results suggest that different types of Neoarchean granitoids in the Jianping Complex are nearly coeval with crystallization ages of ∼ 2.54–2.52 Ga and metamorphic ages of ∼ 2.49–2.48 Ga. New Hf isotopic data reveal that these granitoids show positive εHf(t) values, with the tonalitic gneisses of εHf(t) values closer to the depleted mantle than those of granodioritic gneiss, sanukitoids and potassic granite. This result reflects potentially more enriched source for other granitoids than the tonalitic gneisses, which is linked with increasing level of crustal-mantle interaction and crustal reworking the late Neoarchean. Integrating other evidence from geochemical, structural and metamorphic studies, it is inferred that the plume activities play an important role in the emplacement of late Neoarchean granitoids in the Jianping Complex, with TTGs formed through the partial melting of juvenile crust induced by plume activity, sanukitoids produced from melting of metasomatized mantle resulted from sagduction process, and potassic granites formed by reworking of earlier crustal lithology caused by sustained underplating of mantle material. Overall, we interpreted that the late Neoarchean crustal growth and crustal-mantle interaction in the Jianping Complex can be attributed to upwelling of mantle plume and potential sagduction process in a vertical tectonic regime.

Genetic link between Mesozoic magmatism and Makeng-type iron polymetallic deposits in the central Cathaysia Block, southeast China

Makeng-type Fe polymetallic deposits occur in the central Cathaysia Block, southeast China, and are an important part of the Wuyishan mineralization belt. To determine the origins of the deposits, we analyzed whole-rock geochemical, zircon U–Pb and molybdenite Re–Os geochronological, and zircon Lu–Hf and sulfide S–Pb isotopic data. The deposits are associated with granites that yield ages of 160–150 and 135–130 Ma. The Mo mineralization is genetically related to the younger granites (135–130 Ma), whereas the Fe mineralization is likely related to the older granites (160–150 Ma). The whole-rock geochemical and zircon Hf isotope data indicate the granites formed by the melting of Paleoproterozoic − Mesoproterozoic crustal materials. The S–Pb isotope data indicate that the ore-forming materials were derived mainly from the upper crust, with some input of mantle-derived material that was transported by deeply sourced fluids in the orogenic belt. Based on our results and previously published data, it is inferred that Fe mineralization occurred in a transitional tectonic setting (i.e., from compression to extension), whereas the Mo mineralization formed in an extensional setting associated with rollback of the Paleo-Pacific Plate.

The Singhbhum Craton (India) records a billion year of continental crust formation and modification

The petrogenesis of continental crust from its ultimate mantle source can be reconstructed from the element abundances and radiogenic isotope compositions of ideally pristine igneous rocks. The initial isotope compositions of igneous rocks provide geochemical constraints on the age, composition and evolution of their source(s). Determining initial isotope ratios for rock samples can be challenging, especially in rocks with a long and protracted thermal history. The Rb-Sr system is highly sensitive to parent-daughter element fractionation during magma differentiation. This makes the Rb-Sr isotope systematics ideal to trace the precursor composition of Archean felsic crust and constrain the time of element fractionation during the formation and subsequent modification of continental crust. Initial isotope compositions can be obtained directly from minerals that strongly prefer the daughter element and effectively exclude the parent element of the radio-isotope system of interest. Apatite, having a near zero Rb/Sr ratio, is ideal for preserving its initial 87Sr/86Sr and zircon records initial 176Hf/177Hf compositions. Combined modelling of Sr and Hf isotope data from granitoids of the Archean Singhbhum Craton, indicates that the older Paleoarchean granitoids, emplaced between 3.53 Ga and 3.44 Ga, were derived from a mafic precursor (∼52–54 wt% SiO2) sourced from a depleted mantle at ∼3.71 Ga. Initial 87Sr/86Sr isotope signatures of matrix apatite and apatite inclusions in zircon from the younger Paleoarchean granitoids (3.4–3.2 Ga) of the Singhbhum Craton indicate these younger granitoids were produced by mixing of magma generated from an older mafic source and partial melts derived from the older granitoids. The combined Sr-Hf isotope modelling links the timing of mantle extraction of the precursor material for Paleoarchean Singhbhum granitoids with a known mafic crust extraction event at ∼3.71 Ga. In combination, the new Sr isotope data from apatite combined with whole rock and zircon Hf isotope data from the literature reveal a ∼1 Ga protracted crustal growth and differentiation history of the nucleus of the Singhbhum Craton. By combining radio-isotope systems like 87Rb-87Sr and 176Lu-176Hf, the petrogenesis of Archean felsic crust from the extraction of mafic material from the mantle to reworking in an orogenic cycle to emplacement can be reconstructed. This approach can be applied to other greenstone-gneiss terranes to quantify the spatio-temporal and compositional evolution of voluminous felsic crust and the formation of cratons in the Archean.

Building and reworking of Archean continental crust in the nucleus of the Yangtze Craton: Constraint from 3.4 Ga and 2.94 Ga granitoid gneisses in the Southern Kongling Complex

The TTG gneisses, a dominant lithological assemblage within Archean cratonic provinces, provide a window into the early evolution of the continental crust. The Kongling complex in South China preserves voluminous Archean granitoids, recording the early formation and evolution history of the Yangtze Craton. We present results of a comprehensive study involving field investigation, petrographic characterization, zircon U–Pb geochronology and Lu-Hf isotope tracing, and whole-rock geochemistry for the Archean granitoid gneisses from the Southern Kongling Complex. Igneous zircons from two granitic gneisses yielded weighted mean 207Pb/206Pb ages of 3399 ± 15 Ma (MSWD = 0.99, n = 24) and 3389 ± 12 Ma (MSWD = 1.02, n = 20). Zircons from the 3.4 Ga granitic gneiss also record a ca.3.0 Ga anatexis event which is contemporaneous with the widespread granitoid gneisses in the Kongling Complex. Geochemical and zircon Hf isotope data (εHf(t) values of − 3.41 to + 0.77 and two-stage Hf model ages of 3.65–3.80 Ga) for the granitic gneisses support a derivation from pre-existing Eoarchean (TDM2 = 3.73 Ga) crust. LA-ICP-MS zircon U-Pb dating yielded emplacement ages of 2948 ± 17 Ma for a migmatized trondhjemitic gneiss, and 2928 ± 14 Ma for a quartz monzonite gneiss. These two gneisses have similar zircon Hf model ages (TDM2 = 3.45 Ga) and both were emplaced during a major phase of mafic magma diapiric process that significantly reworked the old crust. The occurrences of 2.94 Ga trondhjemite and associated mafic blocks suggest intra-crustal differentiation by partial melting of low-K mafic rocks. We suggest that intra-crustal remelting and differentiation played a key role in the formation, evolution, and maturation of the micro-continents in Kongling during the Paleo- to Meso-Archean. The whole-rock geochemical and zircon Hf isotopic compositions of the different generations of granitoid gneisses from the Southern Kongling Complex are similar to those of the coeval gneisses (3.45 Ga and 2.95 Ga) from the northern part of the Kongling Complex, indicating a common tectono-magmatic history shared by both segments tracing back to as early as 3.4 Ga. The Archean granitoid gneisses from the Kongling Complex record remelting and differentiation of Eo- to Paleo-Archean crusts during the Paleo- to Meso-Archean, implying that Eoarchean crust is likely to have been preserved within the Kongling complex.

Tracing the crustal evolution of the Precambrian Southern Granulite terrane in East Gondwana: New insights from zircon U-Pb/Hf geochronology

The Precambrian Southern Granulite terrane of south India has a crustal evolution history broadly bracketed between the late Archean and Cambrian with records of polyphase deformation, metamorphism, and magmatism. The Southern Granulite terrane comprises distinct crustal blocks bounded by shear/suture zones that have been variably correlated with supercontinent fragments including Madagascar, Sri Lanka, Africa, Eastern Ghats, and Antarctica. However, the timing and mechanism of assembly of different crustal blocks within the Southern Granulite terrane and its linkages with counterparts in East Gondwana are highly debated. This study aimed to unravel the complex crustal evolutionary pattern of the terrane by generating robust zircon U-Pb/Hf isotopic data from basement charnockites, gneisses, granitoids, and alkaline intrusive units from the central part of Southern Granulite terrane and comparing these results with similar data from different East Gondwanan terranes. The study identified four distinct crustal growth episodes in the Madurai block: (1) Neoarchean−early Paleoproterozoic, (2) Rhyacian−Orosirian, (3) late Tonian, and (4) Ediacaran−Cambrian. Analysis of zircon Hf isotope data revealed that the first two events are marked by juvenile magmatic signatures, whereas the latter two are distinctly associated with intense reworking and remelting of older crust with no significant juvenile input. Our new results combined with existing data from other Gondwanan terranes suggest a common Paleoproterozoic ancestry for the Southern Granulite terrane and its corresponding Gondwanan fragments, proposing a revision to the existing geodynamic models.