Hf Isotope Research Articles

Petrogenesis of the Newly Discovered Neoproterozoic Adakitic Rock in Bure Area, Western Ethiopia Shield: Implication for the Pan-African Tectonic Evolution

The Neoproterozoic Bure adakitic rock in the western Ethiopia shield is a newly discovered magmatic rock type. However, the physicochemical conditions during its formation, and its source characteristics are still not clear, restricting a full understanding of its petrogenesis and geodynamic evolution. In this study, in order to shed light on the physicochemical conditions during rock formation and provide further constraints on the petrogenesis of the Bure adakitic rock, we conduct electron microprobe analysis on K-feldspar, plagioclase, and biotite. Additionally, we investigate the trace elements and Hf isotopes of zircon, and the Sr-Nd isotopes of the whole rock. The results show that the K-feldspar is orthoclase (Or = 89.08~96.37), the plagioclase is oligoclase (Ab = 74.63~85.99), and the biotite is magnesio-biotite. Based on the biotite analysis results, we calculate that the pressure during rock formation was 1.75~2.81 kbar (average value of 2.09 kbar), representing a depth of approximately 6.39~10.2 km (average value of 7.60 km). The zircon thermometer yields a crystallization temperature of 659~814 °C. Most of the (Ce/Ce*)D values in the zircons plotted above the Ni-NiO oxygen buffer pair, and the calculated magmatic oxygen fugacity (logfO2) values vary from −18.5 to −4.9, revealing a relatively high magma oxygen fugacity. The uniform contents of FeO, MgO, and K2O in the biotite suggest a crustal magma source for the Bure adakitic rock. The relatively low (87Sr/86Sr)i values of 0.70088 to 0.70275, positive εNd(t) values of 3.26 to 7.28, together with the positive εHf(t) values of 7.64~12.99, suggest that the magma was sourced from a Neoproterozoic juvenile crust, with no discernable involvement of a pre-Neoproterozoic continental crust, which is coeval with early magmatic stages in the Arabian Nubian Shield elsewhere. Additionally, the mean Nd model ages demonstrate an increasing trend from the northern parts (Egypt, Sudan, Afif terrane of Arabia, and Eritrea and northern Ethiopia; 0.87 Ga) to the central parts (Western Ethiopia shield; 1.03 Ga) and southern parts (Southern Ethiopia Shield, 1.13 Ga; Kenya, 1.2 Ga) of the East African Orogen, which indicate an increasing contribution of pre-Pan-African crust towards the southern part of the East African Orogen. Based on the negative correlation between MgO and Al2O3 in the biotite, together with the Lu/Hf-Y and Yb-Y results of the zircon, we infer that the Bure adakitic rock was formed in an arc–arc collision orogenic environment. Combining this inference with the whole rock geochemistry and U-Pb age of the Bure adakitic rock, we further propose that the rock is the product of thickened juvenile crust melting triggered by the Neoproterozoic Pan-African Orogeny.

Complementarity of Hf isotopes from detrital and igneous zircon: an example from the Central Gneiss Belt, Grenville Province, Ontario

Combined U–Pb and Hf isotopic analysis of detrital and igneous zircon provides information about variations in crustal addition vs. reworking through time. However, whereas detrital zircon data from only a few samples can provide information about extended periods of orogenic activity, this approach lacks the geological context that comes with studying igneous zircon and may not record mid- and deep-crustal sources or sources isolated from sites of deposition. Conversely, igneous zircon is likely to miss sources that were removed by later tectonic activity, but which may be preserved in the detrital record. The Central Gneiss Belt of the SW Grenville Province in Ontario has a relatively well-understood orogenic architecture and records active-margin growth and reworking between ca. 1900–1200 Ma. We present U–Pb and Hf isotope data of zircon from 30 orthogneiss samples ranging in age from ca. 1750 to 1250 Ma, covering all tectonostratigraphic levels of the Central Gneiss Belt. As expected, the detrital and igneous datasets display many of the same overall features, such as crustal growth along the SW Laurentian active margin; however, there are also some distinct differences. In particular, sedimentation appears to have taken place near the active margin, with little or no input from distal inboard sources, thus missing this significant component of reworked crust. This study highlights the need for a combination of detrital and igneous samples in order to provide the most complete picture of long-lived accretionary orogenic systems.

Late Triassic paleogeography of southern Laurentia and its fringing arcs: Insights from detrital zircon U-Pb geochronology and Hf isotope geochemistry, Auld Lang Syne basin (Nevada, USA)

Fluvial strata of the Upper Triassic Chinle Formation and Dockum Group, exposed across the Western Interior of North America, have long been interpreted to record a transcontinental river system that connected the ancestral Ouachita orogen of Texas and Oklahoma, USA, to the Auld Lang Syne basin of northwestern Nevada, USA, its inferred marine terminus. Fluvial strata are well-characterized by existing detrital zircon data, but the provenance of the Auld Lang Syne basin is poorly constrained. We present new detrital zircon U-Pb and Hf isotopic data that characterize the provenance of Norian siliciclastic strata that dominate the Auld Lang Syne basin. Mixture modeling of Auld Lang Syne basin data identifies the Alleghany−Ouachita−Marathon belt of eastern Laurentia as a dominant source of sediment, but the presence of Triassic detrital zircon grains in Auld Lang Syne basin strata indicates that at least one peri-Laurentian arc segment had to have also contributed sediment. A comparison of new Hf isotopic data with those characterizing various peri-Laurentian volcanic arcs demonstrates that although multiple arc segments may have simultaneously contributed zircons to the Auld Lang Syne basin, the west Pangean arc of northern Mexico stands out as a unique source of highly evolved Permian to Triassic detrital zircon grains in samples from the Auld Lang Syne basin. Altogether, our data and analyses demonstrate source-to-sink connectivity between the Late Triassic (Norian) Cordilleran margin and remnant late Paleozoic highlands of southern to eastern Laurentia, which ultimately framed a Mississippi River−scale, transcontinental watershed that traversed the topographically subdued Laurentian continental interior.

Geochronology, geochemistry and Hf isotope of the quartz monzonite and the diorite in Dachaigou, the East Kunlun Orogenic Belt, China, and their geological significance

This study focuses on quartz monzonite and diorite plutons in Dachaigou, East Kunlun, examining their formation, age, petrogenesis, magmatic source and tectonic setting. Through comprehensive field observations, zircon geochronology, geochemistry, and Hf isotope analysis, new insights into the Paleozoic tectonic evolution of the proto-Tethys Ocean in the East Kunlun orogenic belt are provided. Zircon U-Pb dating reveals that quartz monzonite and diorite formed at 417.4 ± 2.1 Ma and 404.6 ± 1.8 Ma, respectively. Geochemical analysis shows that the A/CNK value of quartz monzonite ranges from 0.98 to 1.07, with the Pb content proportional to SiO2, which aligns with the characteristics of I-type granite. The εHf(t) values for quartz monzonite and diorite are -0.84 to 2.2 and -13.22 to 2.04, respectively. Considering the formation age, geochemical characteristics, and regional tectonic evolution, it is concluded that quartz monzonite has a crust-derived origin, whereas diorite has a crust-mantle mixing origin. Both were formed in a post-collision extensional tectonic setting resulting from slab break-off, implying the Proto-Tethys Ocean East Kunlun entered a post-collisional extension stage in the Late Silurian-Early Devonian.

Continental Crust Rejuvenation Across the Paleo‐Mesoarchean Transition Resulted From Elevated Mantle Geotherms

AbstractThe increase in initial Hf isotopes identified in early Mesoarchean detrital zircon is commonly interpreted as a reflection of the geodynamic transition from stagnant‐lid to mobile‐lid tectonics. However, given the lack of petrogenetic context, interpreting detrital zircon may lead to spurious conclusions. In this contribution, we use zircon U‐Pb‐Hf‐O isotopic and bulk rock compositions of newly identified 3.05–2.9 Ga granitoids from the SW Yangtze Block to posit petrogenesis within an isotopically juvenile magmatic system. A statistical analysis of these data with a global igneous zircon Lu‐Hf isotopic compilation reveals an increase in average initial radiogenic Hf isotopes during the Paleoarchean to Mesoarchean transition. We posit that the Earth's continental crust underwent a global rejuvenation across the Paleo‐Mesoarchean transition. This rejuvenation can be explained by an independently observed increase in mantle temperatures resulting from mantle thermal evolution and does not require a change in tectonic style.

First identification of Late Mesozoic intraplate magmatism in the Chinese North Tianshan: Implications for the orogenic architecture and crustal evolution

The formation and dynamics of granitoids in an intra-continental setting are crucial for understanding the architecture and evolution of continental crust. Here, we report geochronological, geochemical, and Sr-Nd-Hf isotopic data for newly discovered late Mesozoic granitic intrusions in the Tianshan belt, northwestern China. These granitoids are I-type granites derived from an igneous precursor and were emplaced during ∼145-132 Ma. They have positive ε Nd (t) values and young Nd model ages, together with relatively low Sr/Y ratios, indicating that they might have originated from partial melting of the juvenile lower crust. There is a prominent decoupling between zircon Hf and bulk rock Nd isotopes, which may have resulted from the early crystallization of Ti-rich minerals. These granitic intrusions also display subduction-related geochemical characteristics, which are likely inherited from the Paleozoic crustal sources that were metasomatized by subduction-related fluids. We conclude that these late Mesozoic granitoids were emplaced in an intra-continental setting, and were likely triggered by thermal relaxation due to crustal shortening and thickening. These data further imply that the Tianshan has changed into crustal reworking during the Mesozoic from its prominent crustal growth in the Paleozoic. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.7167890

Hf-Nd isotope decoupling in S-type granitoids caused by disequilibrium melting of metasedimentary rocks: Evidence from the North Qinling Terrane, Central China

The intrinsic assumption of radiogenic isotope tracing is that isotope systems maintain equilibrium between melt and source. However, this assumption is not naturally correct, particularly for S-type granites, which are formed by partial melting of metasedimentary rocks. The S-type metagranites from the North Qinling Terrane show various degrees of HfNd isotope decoupling and discrepancies between whole-rock and zircon Hf isotopes. Zircon UPb dating yields emplacement ages from 946 to 890 Ma. Their high δ18O values, (87Sr/86Sr)i ratios, and negative εNd(t) values overlapped with metasedimentary rocks in the Qinling Group imply that they are derived from partial melting of the Qinling Group. The low Rb/Ba, Rb/Sr, Al2O3/TiO2, and high CaO/Na2O ratios indicate that their sources are metagraywackes. The negative correlation between decoupling degrees of HfNd isotopes and Zr concentrations suggests that the incomplete dissolution of zircon during partial melting results in the decoupling. The discrepancy between whole-rock and zircon Hf isotopes can be attributed to the combined effect of incomplete dissolution of zircons and the release of various Hf isotope compositions from partly dissolved inherited zircons to local melts. The compiled literature data suggest that whole-rock HfNd isotope decoupling of most metagraywacke-derived S-type granites is caused by incomplete melting of zircons, whereas those of metapelite-derived S-type granites may be controlled by both incomplete melting of zircons and source inheritance.

Zircon provenances of the late Paleoproterozoic metasedimentary rock in the South Yangtze Block: Implications for paleogeographic reconstruction

ABSTRACT The zircon provenances of the late Paleoproterozoic metasedimentary rocks are important for assembling Proto-Yangtze and its reconstruction in the Nuna supercontinent. We present a dataset involving 363 detrital zircon U-Pb dating and 165 Hf isotope analyses from the Laochanghe Formation of the Dahongshan Group in the southwestern Yangtze Block. New detrital zircon U-Pb ages, combined with the heterogeneity of sedimentary strata and available magmatic age data, suggest that the maximum depositional age of the Laochanghe Formation cloud be younger than 1.81 Ga and older than 1.74 Ga. The zircon U-Pb-Hf isotope compositions of the volcanic and metamorphic rocks overlap with those of the late Paleoproterozoic metasedimentary rock, suggesting the southwestern Yangtze Block provided provenance at 1.9, 2.3, and 2.7 Ga. This characteristic is significantly different from the northern Yangtze Block only provided partial provenance at 1.9 and 2.7 Ga. The northern and southwestern of the Yangtze Block jointly provide material for the late Paleoproterozoic metasedimentary rocks, combining synchronous late Paleoproterozoic magmatism and metamorphism, indicative of the formation of the proto-Yangtze Block in response to the accumulation of the Nuna supercontinent. Additionally, the potential provenance areas of the late Paleoproterozoic metasedimentary rock in the southwestern Yangtze include the northwestern Laurentia and southern Siberia, excluding the northern Australian, and Cathaysia. These findings indicate that the southwestern Yangtze may have been located between northwestern Laurentia and southern Siberia during the partial fragmentation of the Nuna supercontinent, enhancing our understanding of changes in the Nuna supercontinent over time.

Petrogenesis of newly identified mantle-plume-related ca. 3.3 Ga tholeiitic-komatiitic rocks in the Anshan area, North China Craton

The geodynamic regime that governed the crustal evolution of Earth during the early Archean remains intensely debated. The North China Craton (NCC) preserves a geological history spanning 3.8–2.5 Ga, particularly in the Anshan area, making it an ideal natural laboratory for probing the formation and evolution of the NCC and its associated geodynamic regime. Here, we document new geochronology, geochemistry, and zircon Hf-O isotope data from newly discovered Paleoarchean meta-mafic rocks in the Anshan area. Based on their whole-rock geochemistry, these unit can be divided into tholeiitic and komatiitic series. Of which, the komatiitic rocks are characteristic by high MgO contents (up to 20.6 wt%). Zircon U-Pb dating shows that all meta-mafic rocks formed contemporaneously, with crystallization ages of ca. 3.3 Ga. Most of the studied meta-mafic rocks display radiogenic zircon Hf isotopes, with TDM1 ages ranging from 3592 to 3346 Ma and εHf(t) values from −1.94 to + 3.49. They also exhibit mantle-like zircon δ18O values (+4.92 ‰ to + 5.98 ‰). These zircon Hf-O isotope data indicate that the protoliths of the ca. 3.3 Ga meta-mafic rocks originated from the partial melting of a depleted mantle without significant crustal contamination. Furthermore, the parental magmas of the komatiitic rocks and some of tholeiitic rocks were generated from 20 % and 5–10 % partial melting of spinel-lherzolite, respectively, whereas other tholeiitic rocks were the result of a low degree (1–5 %) of partial melting of spinel-garnet lherzolite. The ca. 3.3 Ga tholeiitic-komatiitic rocks were most likely formed in an intraplate rifting setting, associated with a mantle plume.

U-Pb geochronology and Hf isotopes of the Grenvillian Río Hondo gneisses, Puebla: redefining the western edge of Oaxaquia

In situ Río Hondo (Puebla, southern Mexico) gneiss samples, as well as clastic samples recovered from the nearby-outcropping latest Paleozoic Matzitzi Formation, a fluvial unit mainly sourced by Grenvillian rocks,  were historically interpreted as representative of the northernmost exposures of the Oaxacan Complex, the largest outcrop of ortho and metasedimentary units, made up of mostly 1.0–1.3 Ga protoliths, affected cfby local migmatization (ca. 1.1 Ga) and granulite facies metamorphism at ca. 0.98 Ga, constituting the most prominent outcrop of the Oaxaquia microcontinent.
 U-Pb geochronology and Lu-Hf isotopic determinations in zircon by LA-(MC)-ICP-MS were performed on both in situ and clast samples. In situ basement samples record a ca. 1.2 crystallization event, together with a younger one at ca. 1.02 Ga. both lacking inherited >1.3 Ga components. The clasts have an unimodal zircon U-Pb age distribution, recording a crystallization event at ca. 1.2–1.27 Ga. Scarce inherited zircon cores between ca. 1.4–1.6 Ga were found, with only a few samples with a broader age distribution, suggesting a detrital protolith with zircon cores as old as ca. 1.8 and 2.4 Ga. No zircon overgrowths or geochemical-petrographic evidences are indicative of granulite metamorphism. Furthermore, all the studied metaigneous samples show discordant zircon ages produced by Pb loss events barely constrained between the latest Paleozoic to the Mesozoic.
 Hf isotopes reveal that zircon crystals from clasts have a range of εHf (1.25 Ga) ≈+1 to +5 and yield Hf model ages from 1.7 to 1.9 Ga. On the other hand, the The zircon Hf isotopes of one analyzed basement sample reveal a higher range of εHf (1.25 Ga) ≈+7 to +9, and Hf model ages from 1.5 to 1.6 Ga.
 Both ≈1.2 Ga and 1.02 Ga events are consistent with magmatic ages previously documented elsewhere in Oaxaquia, interpreted as indicating portions of the NW Amazonia-Oaxaquia arc system with cratonic influence or to slices of Baltica thrust over Oaxaquia during the Grenville orogeny. However, the absence of granulite facies indicators, such as zircon metamorphic ages and/or granulite paragenesis (typically, in other Oaxaquia samples, orthopyroxene and garnet) are interpreted as prime evidence that the studied samples didn’t undergo such high grade of metamorphism. Río Hondo gneisses, as this sequence is informally named, must belong to a source that had the influence of an older continental crust and can be tentatively associated either with rocks recently described in the Sierra de Juárez, or those belonging to the central basement of the Maya block, currently exposed farther to the SE in Chiapas.

Neoproterozoic low-T/P metamorphism in the Yangtze Block manifests a long-lived subduction girdle around Rodinia

Identifying long-lived subduction at the periphery of supercontinents provides insights into the processes of block assembly and dispersal within the supercontinent cycle. The Yangtze Block of South China stands as a key component during the transition from Rodinia to Gondwana, characterized by active tectono-magmatic processes throughout the early to middle Neoproterozoic. However, the lack of metamorphic records associated with accretionary orogenesis results in ambiguity about the tectonic regime and its evolution in Rodinia during this period. Here, we present evidence of low-temperature/pressure ratio (low-T/P) metamorphism in phengite-bearing orthogneisses from the western margin of the Yangtze Block (WYB). Through petrographic investigations and zircon U–Pb–Hf–O isotopic analysis in core and rim domains, we identify two distinct metamorphic rock types, with protolith ages of 1419 ± 19 Ma and 831 ± 9 Ma. Both rock types record metamorphism at ca. 830–820 Ma, accompanied by infiltration of externally-derived melts with high-δ18O and unradiogenic Hf isotopes. Our phase equilibria modeling, combined with mineral thermometry and Si-in-phengite content, shows peak metamorphic conditions of ∼550 °C and ∼8.2–8.6 kbar, corresponding to a cold geothermal gradient (19.0–20.5 °C/km). The low-T/P metamorphism is interpreted to occur either in a subduction zone accretionary wedge or in an overriding forearc continental crust, providing robust evidence for Neoproterozoic orogenesis of the WYB within a subduction framework. Based on petrological, isotopic, and paleomagnetic data, we conclude that the WYB represents part of a long-lived subduction girdle (at least ca. 970–750 Ma) at the periphery of Rodinia. Since the early stage of Rodinia breakup, this girdle was involved in alternating advance and retreat accretionary orogenesis as the Yangtze Block continuously drifted away from a mantle upwelling toward the degree-2 girdle of mantle downwelling. Our study provides a snapshot of the evolution of a complete long-lived circum-Rodinian subduction girdle during the transition from Rodinia to Gondwana.

Carboniferous–Early Permian volcano-sedimentary units from the northern margin of the North China Craton recorded subduction initiation in the Paleo-Asian Ocean

The precise timing of subduction initiation of the Paleo-Asian Ocean (PAO) in the northern margin of the North China Craton (NCC) remains controversial. In this study, we have conducted zircon UPb dating, whole-rock major and trace elements, and zircon Hf isotope analyses on metadacites and metamorphic greywackes from the Changde volcano-sedimentary rocks, feldspar quartz sandstones and argillaceous siltstones from the Luquantun Formation and the Sidao sedimentary rocks in central-eastern Jilin Province (NE China), to constrain the initial closure of the PAO. We obtained Early Carboniferous zircon UPb ages (345 ± 2 Ma and 351 ± 7 Ma) from the Changde volcano-sedimentary rocks. The metadacites are characterized by the enrichment in light rare earth elements and large ion lithophile elements, depletion in heavy rare earth elements and high field strength elements, and rare earth element ratios similar to those of the continental crust, indicating that these rocks originated from crustal melting. The metadacites exhibit affinity with the peraluminous A-type granite, with high zircon εHf(t) values (+3.46 − +12.21) and TDM2 of 1132–571 Ma, suggesting that they formed in a post-collisional extensional setting. Detrital zircon UPb ages from the Luquantun Formation and Sidao sedimentary rocks constrain their maximum depositional ages to the Late Carboniferous (319 ± 5 Ma) and Early Permian (284 ± 4 Ma), respectively. Most detrital zircons have age peaks at 1800 Ma with negative zircon εHf(t) values, and 2500 Ma with positive zircon εHf(t) values, suggesting that the Carboniferous–Early Permian sediments from these two formations were mainly sourced from the NCC. Moreover, the chemical index of alteration, index of compositional variability, and plagioclase index of alteration values suggest that the sediments of the Changde volcano-sedimentary rocks originated from a mafic igneous source with a low degree of weathering and a sedimentary recycling history, while the samples from the Luquantun Formation and Sidao sedimentary rocks were sourced from an intermediate-felsic igneous rock with a moderate to intense degree of weathering and mainly influenced by source composition. The crystallization age curves and summary plots of detrital zircons indicate that the Early Carboniferous metamorphic greywackes from the Changde Formation were mainly deposited in a passive margin, while the Carboniferous–Early Permian sediments of the Luquantun Formation and Sidao sedimentary rocks were mainly deposited in an active margin. We suggest that the tectonic transition from passive to active margin occurred at ∼333 Ma, marking subduction initiation in the PAO close to the northern margin of the NCC.

North Lhasa terrane in the Precambrian originated from Western Australia

Constraining the origin and Paleogeographic positions of ancient continental fragments plays a crucial role in reconstructing and validating supercontinent cycles. The Lhasa terrane in southern Tibet is the key to revealing the early formation and evolution of the Himalayan–Tibetan orogen. Although previous origin models of the Lhasa terrane are supported by Phanerozoic evidence, Precambrian geological records have not been comprehensively considered. The U–Pb age and Hf isotope data on detrital zircons from newly discovered Precambrian basement in the North Lhasa terrane define two distinctive age populations of ca. 1170 Ma with εHf(t) values identical to the coeval detrital zircons from Western Australia, and ca. 950 Ma with a similar εHf(t) range to the contemporaneous detrital zircons from South Qiangtang and Tethyan Himalaya terranes. The ca. 1170 Ma detrital zircons were most likely derived from Western Australia, whereas the ca. 950 Ma detrital zircons might have been sourced from the norther Indian margin. Compiled detrital zircon data shows that in the early Neoproterozoic, the affinity between northern Lhasa and Western Australia decreased, while the predilection between northern Lhasa and northern India increased. Combined with ca. 930–870 Ma rift, ca. 870–700 Ma arc igneous rocks and ∼650 Ma high-pressure granulites, we propose that the North Lhasa terrane was a ribbon continent that rifted from Western Australia in the early Neoproterozoic (ca. 930–870 Ma), drifted westward along the northern edge of Rodinia in the middle Neoproterozoic (ca. 870–700 Ma), and was emplaced in the Northern East African Orogen during the late Neoproterozoic (∼650 Ma).

Petrogenesis of early-middle jurassic igneous rocks in the Central Jilin Province, NE China: implications for the early subduction of the Paleo-Pacific ocean and crustal growth

ABSTRACT Crustal growth is closely associated with the oceanic subduction process, although the precise mechanism involved remains poorly constrained. Northeast (NE) China is an important component of the largest accretive orogenic belt worldwide – Central Asian orogenic belt. Its accretionary process was dominated by the Paleo-Asian and Paleo-Pacific Oceans; thus, NE China can provide a promising insight to explore this complex mechanism. We report new geochronological, geochemical and Hf isotopic compositions of the igneous rocks found in the Central Jilin Province, NE China. The geochronological results reveal that these igneous rocks were formed during 174.7 − 167.7 Ma (i.e. Early−Middle Jurassic). The quartz diorite and monzogranites from the northeastern margin of the North China Craton have high Sr (314 − 757 ppm) content, (La/Yb)N (7.11 − 29.9) and Sr/Y (41.50 − 157) ratios, low Y (2.03 − 12.97 ppm) and Yb (0.30 − 1.34 ppm) contents, exhibiting adakitic features. Coupling with their significant negative εHf(t) values (−32.51 to − 5.45), we propose that these igneous rocks were originated from the partial melting of an ancient thickened lower crust. In contrary, the syenogranite, granite porphyry, and porphyritic monzogranite from the Zhangguangcai and Jiamusi blocks are characterized by high K calc-alkaline, low MgO (0.03 − 0.88 wt.%), Zr + Nb + Ce + Y (141 − 462 ppm) contents and Sr/Y (0.93 − 17.40) ratios, indicating an affinity of I−type granite. In view of their positive εHf(t) values (5.41 to 9.47), we suggest that they were originated from the partial melting of a juvenile lower mafic crust. Despite they have different magma sources, all the Jurassic igneous rocks exhibit typical geochemical signatures associated with subduction, such as enriched in large ion lithophile elements and depleted in high field strength elements. Considering the spatial-temporal distribution of coeval igneous rocks within the region, we propose that the Early Jurassic is the early subduction of the Paleo-Pacific Ocean. The Jurassic igneous rocks can be divided into two categories, one with high Sr/Y ratios and negative Hf isotope, and the others with low Sr/Y ratios and positive Hf isotope, which may indicate that crustal architecture in subduction zone has a significant effect on continental crustal growth and reworking in NE China.

Vestiges of Earth’s earliest depleted mantle reservoir

There is a paucity of evidence preserved in the rock record regarding Earth’s earliest enriched crust and its complementary depleted mantle during the Hadean. In recent years, vestiges of these early reservoirs have been inferred by examination of Hf isotope systematics compiled from zircons. The Singhbhum craton of Eastern India, for example, preserves only the existence of an enriched (εHf <0) crustal reservoir during the Hadean−Eoarchean, with the notable absence of a depleted mantle reservoir signature (εHf >0) until ca. 3.5 Ga. Here we report a new Sm-Nd isochron for the Lower Lava greenstones of the western Iron Ore Group from the Singhbhum craton, confirming a 3.42 ± 0.14 Ga crystallization age with an initial εNd of +5.7 ± 2.5. This is the highest positive εNd value derived from an isochron of this age. We infer that this depleted mantle source is a vestige complementary to the primary crust following planetary differentiation. Furthermore, we present U-Pb zircon ages for a 3.39 ± 0.02 Ga tuff that lies stratigraphically above the Lower Lava and <30 cm below an extensive conformable banded iron formation (BIF). This age implies that the western Iron Ore Group’s BIF is the largest economic-grade iron formation of its Paleoarchean age, suggesting that free atmospheric oxygen existed as more than just whiffs at this time.

A special ore formation of the newly discovered Hamaling Au-Cu-Mo polymetallic deposit in the Tongling ore-cluster region: Constraints from geochronology and geochemistry

The Hamaling deposit represents the first discovery of a gold-copper-molybdenum deposit situated within the Ordovician strata of the Tongling ore-cluster region. It comprises three distinct types of ore, including porphyry-type Cu-Au ore found in granodiorite, skarn-type Cu-Au ore at the contact zone, and breccia-type Mo-Cu ore within the Ordovician strata. However, the exact mineralization age, ore genesis, and mineralization processes of the Hamaling deposit remain uncertain. To address these uncertainties, the present study employed LA-ICP-MS to date zircon in granodiorite and garnet in skarn, revealing ages of 139.3 ± 0.44 Ma and 142.3 ± 0.89 Ma, respectively. Additionally, the age of 140.0 ± 1.1 Ma was obtained through Re-Os dating of molybdenite from breccia-type ore. These findings suggest a connection between the Hamaling deposit and the early Cretaceous magmatic activity in the Tongling region. The granodiorite intrusion exhibits a high-potassium calc-alkaline affinity and formed under oxidized conditions at temperatures ranging from 721 to 832 °C (average 769 °C). The Hf isotope composition of the granodiorite implies its formation through the mixing of mantle-derived magma from an enriched lithospheric mantle with partially melted lower crustal source magma. The sulfur isotopes found in the ore minerals range from δ34S = 5.55 ‰ to 11.99 ‰, indicating a magmatic sulfur source. The H-O isotopic compositions of quartz during the quartz-sulfide stage suggest that the magmatic water was the primary component of the fluids responsible for ore formation, possibly with some contribution from meteoric water. The identification of the Hamaling deposit highlights the significant potential for mineral exploration within the Lower Paleozoic strata in the Tongling ore-cluster area and even the broader Middle-Lower Yangtze River Valley Metallogenic Belt (MLYB).

Tectonic and Crustal Processes Drive Multi-Million Year Arc Magma Evolution Leading up to Porphyry Copper Deposit Formation in Central Chile

Abstract Subduction zone magmatism is a major control of volcanism, the generation of modern continental crust and the formation of economically important porphyry Cu–(Mo–Au) deposits. Reading the magmatic record of individual arc segments and constraining the rates of magmatic changes are critical in order to fully understand and quantify the processes that drive magma evolution in subduction settings during arc growth. This study focuses on the San Francisco Batholith and the Rio Blanco-Los Bronces porphyry deposit cluster in central Chile, which provides an igneous rock record over ~13.5 Myr of arc evolution. We use whole-rock geochemistry, zircon geochronology and Hf isotope geochemistry to track changes in the crustal magmatic system of this arc segment during crustal thickening and porphyry Cu deposit formation. By combining the analytical dataset with Monte Carlo fractional crystallisation and assimilation fractional crystallisation modelling, we test a model for significant crustal involvement during magma evolution. Systematic and continuous increases in Dy/Yb, La/Yb, V/Sc and Sr/Y in the magmas over time indicate a transition in the main fractionation assemblage from plagioclase-dominated to amphibole-dominated that reflects deeper crystallisation and/or a higher meltwater content. Concomitant decreases in εHf and Th/La as well as increasing Ba/Th are best explained by assimilation of progressively deeper crustal lithologies from low (Chilenia) to high Ba/Th (Cuyania) basement terranes. Our study highlights that an increasingly hydrous magma and a deepening locus of crustal magma differentiation and assimilation, driven by crustal thickening contemporaneous with increased tectonic convergence and ingression of the aseismic Juan Fernandez ridge, can account for all investigated aspects of the multi-Myr magmatic evolution leading up to the formation of the Rio Blanco-Los Bronces porphyry Cu deposits. Our findings corroborate the importance of high-pressure differentiation of hydrous magma for the formation of Andean-style porphyry deposits. Once magmas favourable for porphyry Cu mineralisation were generated in the lower crust, multiple episodes of efficient magma migration into the upper crust fed several, discrete, shallow magmatic-hydrothermal systems over ~3.5 Myr to form the world’s largest known Cu resource at Rio Blanco-Los Bronces.

Mesozoic-Cenozoic tectonic-paleogeographic evolution of Bayingobi basin: response to subduction and collision of the Mongol-Okhotsk Ocean plate

The structures, sedimentary fill, and magmatic rocks of sedimentary basins are the products of regional tectonic evolution and are crucial to studying the basin's tectonic-paleogeographic environment and regional tectonic evolution. The present study discussed the zircon U-Pb dating of volcanic rocks samples, in-situ Hf isotope, and whole rock geochemistry analysis of the Bayingobi basin, the paleogeographic, sedimentary filling, and tectonic background of the Bayinggobi basin through the outcrop and core description of Meso-Cenozoic strata, stratigraphic correlation and lithofacies analysis. The U-Pb age of the volcanic rocks is 132–102 Ma, and the in-situ Hf isotopic values range from -20.99 to +29.48. The 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopic ratios of the volcanic rocks are 0.707049–0.879761 and 0.511846–0.512540, respectively, and the Nd isotopic values range from -0.62 to -6.83. The volcanic rocks in the basin have the characteristics of congenital margin island arc volcanic rocks (CAA) with loss of Nb, Ta, and enrichment of Pb, originating mainly from dehydration melting of the plate subduction. The lower Cretaceous Bayingobi, Suhongtu, and Yingen Formations developed specifically delta-lacustrine deposits. The lower and upper member of the Bayinggobi Formation was deposited at Berriasian to Valanginian and Valanginian to late Aptian, respectively. The Suhongtu Formation was deposited during the late Aptian to early Albian and controlled by the strike of Engeer Us fault. The Yingen Formation was deposited in the late faulted depression stage at late Albian. Because of the subduction of the Mongol-Okhotsk Ocean plate in the Early Cretaceous, several depressions (sags) were formed in the Bayingobi basin, accompanied by the eruption of continental plate margin island arc magmas. With the closure of the Mongol-Okhotsk Ocean in the late early Cretaceous, the basin uplifted as a whole and the Upper Cretaceous Ulansuhai Formation was deposited. Supplementary material: https://doi.org/10.6084/m9.figshare.c.7105807

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.

New geochemical and geochronological insights on forearc magmatism across the Sanak-Baranof belt, southern Alaska: A tale of two belts

Abstract The Sanak-Baranof belt includes a series of near-trench plutons that intrude the outboard Chugach–Prince William terrane over ~2200 km along the southern Alaskan margin. We present new petrological, geochronological, and geochemical data for comagmatic microgranitoid enclaves and granitoid rocks from the Crawfish Inlet (ca. 53–47 Ma) and Krestof Island (ca. 52 Ma) plutons on Baranof and Krestof Islands, as well as the Mount Stamy (ca. 51 Ma) and Mount Draper (ca. 54–53 Ma) plutons and associated mafic rocks that intrude the Boundary block at Nunatak Fiord near Yakutat, Alaska, USA. These data suggest that intrusion of the Sanak-Baranof belt plutons is actually a tale of two distinct belts: a western belt with crystallization ages that young systematically from west to east (63–56 Ma) and an eastern belt with crystallization ages ranging from 55 to 47 Ma, but with no clear age progression along the margin. Hf isotope analyses of magmatic zircon from the western Sanak-Baranof belt become increasingly evolved toward the east with εHft = 9.3 ± 0.7 on Sanak Island versus εHft = 5.1 ± 0.5 for the Hive Island pluton in Resurrection Bay. The Hf isotope ratios of eastern Sanak-Baranof belt rocks also vary systematically with age but in reverse, with more evolved ratios in the oldest plutons (εHft = +4.7 ± 0.7) and more primitive ratios in the youngest plutons (εHft = +13.7 ± 0.7). We propose that these findings indicate distinct modes of origin and emplacement histories for the western and eastern segments of the Sanak-Baranof belt, and that the petrogenesis of eastern Sanak-Baranof belt plutons (emplaced subsequent to 57–55 Ma) was associated with an increasing mantle component supplied to the youngest eastern Sanak-Baranof belt magmas. These plutons reveal important information about offshore plate geometries and a dynamic period of plate reorganization ca. 57–55 Ma, but a clearer picture of the tectonic setting that facilitated these Sanak-Baranof belt intrusions cannot be resolved until the magnitude and significance of lateral translation of the Chugach–Prince William terrane are better understood.