Depletion In High Field Strength Elements Research Articles

The Borborema province (NE Brazil) Neoproterozoic magmatic arcs: A review of geochemical and isotopic data of granitic rocks

The Borborema Province in NE Brazil is assumed to have been formed by Cryogenian-Ediacaran convergent events during the assembly of western Gondwana. Among the many geological markers of such episodes, the granitic record is widespread, representing the best testimony of the Brasiliano-Pan African Orogeny that took place between 800 and 500 Ma. Several granitic batholiths and stocks are interpreted as root remnants of arc edifices that grew during the consumption of large tracts of oceanic crust, such as the Goiás-Pharusian and Transordestino-Central África realms. Most of them share geochemical signatures that are typical for subduction-related magmas, such as enrichment in large-ion lithophile elements, aligned with depletion in high-field strength elements, including negative anomalies in Nb, Ta, P, and Ti, as well as systematic plots consistent with convergent-related settings in classical tectonic discrimination diagrams. The older record is represented by the Lagoa Caiçara unit (ca. 880-800 Ma) of the Santa Quitéria magmatic arc of the Northern Subprovince, interpreted as relics of an intra-oceanic setting, responsible for lithospheric growth in the region. A subsequent magmatic episode is marked by the injection ca. 650-620 Ma cordilleran and peraluminous magmas that formed a large set of batholiths and stocks in the Santa Quitéria and Conceição (Transversal Subprovince) magmatic arcs, as well those related to the Pernambuco-Alagoas Terrane and Sergipano Belt in the Southern Subprovince. Rocks crystallized in this age interval share similarities with those of the calc-alkalic and alkali-calcic series, interpreted to have been emplaced in the continental crust via upper mantle melting and subsequent crustal contamination. Finally, rocks aged between ca. 620-550 Ma are widespread and represent high-K, meta-to peraluminous and alkali-calcic precursor magmas, that also share geochemical similarities with S-type granites (crustal anatexis), being interpreted as syn-collisional with respect to the final assembly of Gondwana. The final framework of the Borborema Province is marked by extrusion tectonics that is materialized by the complex network of shear zones deforming the previous formed granites and injecting of non-subduction related melts. Although there is a lack of consensus regarding the assembly of the province during the Neoproterozoic, we suggest that accretionary-collisional events played a major role, as testified by the geochemical-isotopic signature of the arc-related granites, in addition to a number of structural, geophysical, and geological mapping data published in the recent years.

Recycling of subducted continent slab in an accretionary orogen: Insight from the Liangwan potassic granitoids in the Tongbai orogen, Central China

Granitoids provide a vital window to probe the lithological configuration and chemical evolution of orogenic belts. In this contribution, we present an integrated study of mineral compositions, zircon UPb ages and HfO isotopes, titanite UPb ages and SmNd isotopes, as well as whole-rock element and Sr–Nd–Hf isotope compositions of the Liangwan granitic pluton in the northern Paleozoic accretionary orogenic unit of the Tongbai orogen, central China. The Liangwan pluton is composed mainly of monzogranites and contains abundant mafic microgranular enclaves (MMEs). The monzogranites have relatively high silica contents (SiO2 = 67.40–69.91 wt%) and mainly exhibit shoshonite to high-K calc-alkaline and metaluminous features. The MMEs have similar mineral and geochemical compositions and zircon and titanite UPb ages of ca. 129 Ma to the monzogranites, suggesting that they are likely early-crystalized cumulates of the host monzogranites. The MMEs and monzogranites are both characterized by enrichment of large ion lithophile elements but depletion of high field-strength elements. The monzogranites have whole-rock initial Sr (Isr) of 0.7069–0.7074, εNd(t) of −14.2 to −13.7, and εHf(t) of −17.5 to −17.2, zircon εHf(t) of −17.8 to −17.0 and δ18O values of 5.27–5.98 ‰, and titanite εNd(t) of −14.50 to −13.78. These features are distinct from the rocks in the northern Tongbai accretionary orogenic unit but similar to those of the post-collisional granitoids in the southern Tongbai collisional orogenic unit. The Liangwan pluton was likely stemmed from the subducted South China Block (SCB) underneath the northern segment of the Tongbai orogen. Our results show that the subducted continental mass can act as an alternative source for the magmatic rocks occurred in the accretionary unit.

Subduction retreating caused the external breakup of Rodinia: Constraints from the Neoproterozoic igneous rocks in the western Yangtze Block, South China

The western Yangtze Block is an ideal place for investigating the Precambrian tectonic evolution of the South China Craton and the geodynamic mechanism responsible for the breakup of Rodinia. However, the Neoproterozoic tectonic evolution of the western Yangtze Block has not been fully elucidated; in particular, the driving mechanism has changed from an arc setting to a rift setting. Here, we present new zircon U–Pb geochronology and O–Hf isotopic compositions, whole-rock geochemistry, and Sr–Nd isotope data for Yanbian andesites and Shimian gabbros from the western Yangtze Block, South China. The ca. 850–840 Ma Yanbian andesites are high-Mg andesites with moderate SiO2 (56.75–60.21 wt%) and high MgO (4.24–6.44 wt%) and Mg# (52–66). These rocks show enrichments in large-ion lithophile elements (LILEs; e.g., Rb, Ba, Sr, and K) and light rare earth elements (LREEs) and depletions in high-field strength elements (HFSEs; e.g., Nb, Ta and Ti) and display decoupled Nd–Hf isotopes (εNd(t) = +3.9 to + 5.0, εHf(t) = +9.7 to + 13.1) and relatively high zircon δ18O values (5.82–7.72 ‰); these findings indicate that these rocks were derived from a mantle wedge enriched by slab fluids and sediment melts. The ca. 820–810 Ma Shimian calc-alkaline gabbros are characterized by enriched LREEs and LILEs (e.g., Rb, Sr, and K) and depleted HFSEs (e.g., Nb, Ta and Ti). These rocks show decoupled Nd–Hf isotopes (εNd(t) = +3.2 to + 4.2, εHf(t) = +3.1 to + 7.5) and relatively low zircon δ18O values (4.28–5.31 ‰), indicating that they were formed by partial melting of mantle wedge metasomatized by sediment and oceanic slab melts. Compiled geochronological data suggest that Neoproterozoic subduction-related magmatism along the western Yangtze Block formed a long-term active arc system. Slab retreat in this subduction zone led to a shift in the tectonic setting from a compressional setting to an extensional setting in the Yangtze Block during the middle to late Neoproterozoic. Moreover, the temporal link between retreating subduction zone and extensional tectonics in the Yangtze Block suggests that protracted subduction retreating resulted in external rifting in Rodinia.

Mantle Sources and Geochemical Evolution of the Picture Gorge Basalt, Columbia River Basalt Group

The Columbia River Basalt Group (CRBG) is the youngest continental flood basalt province, proposed to be sourced from the deep-seated plume that currently resides underneath Yellowstone National Park. If so, the earliest erupted basalts from this province, such as those in the Picture Gorge Basalt (PGB), aid in understanding and modeling plume impingement and the subsequent evolution of basaltic volcanism. Using geochemical and isotopic data, this study explores potential mantle sources and magma evolution of the PGB. Long known geochemical signatures of the PGB include overall large ion lithophile element (LILE) enrichment and relative depletion of high field strength elements (HFSE) typical of other CRBG main-phase units. Basaltic samples of the PGB have 87Sr/86Sr ratios on the low end of the range displayed by other CRBG lavas and mantle-like δ18O values. The relatively strong enrichment of LILE and depletion of HFSE coupled with depleted isotopic signatures suggest a metasomatized upper mantle as the most likely magmatic source for the PGB. Previous geochemical modeling of the PGB utilized the composition of two high-MgO primitive dikes exposed in the northern portion of the Monument Dike swarm as parental melt. However, fractionation of these dike compositions cannot generate the compositional variability illustrated by basaltic lavas and dikes of the PGB. This study identifies a second potential parental PGB composition best represented by basaltic flows in the extended spatial distribution of the PGB. This composition also better reflects the lowest stratigraphic flows identified in the previously mapped extent of the PGB. Age data reveal that PGB lavas erupted first and throughout eruptions of main-phase CRBG units (Steens, Imnaha, Grande Ronde Basalt). Combining geochemical signals with these age data indicates cyclical patterns in the amounts of contributing mantle components. Eruption of PGB material occurred in two pulses, demonstrated by a ~0.4 Ma temporal gap in reported ages, 16.62 to 16.23 Ma. Coupling ages with observed geochemical signals, including relative elemental abundances of LILE, indicates increased influence of a more primitive, potentially plume-like source with time.

Insights from Dikes for Multistage Granitic Magmatism in the Huayangchuan Uranium Polymetallic Deposit, Qinling Orogen

The Huayangchuan U-polymetallic deposit in the Qinling Orogen is a newly verified carbonatite-hosted deposit on the southern margin of the North China Craton (NCC) in Central China. Granitic magmatism is extensively developed in the Huayangchuan deposit area and is lacking analysis on the reasons for these situations; however, its ages, petrogenesis, and relationship with uranium mineralization are not well constrained. Zircon U–Pb ages for the hornblende-bearing granite porphyry and medium-fine-grained biotite granites in close proximity to carbonatite rocks are 229.8 ± 1.1 and 135.3 ± 0.6 Ma, respectively. High-K calc-alkaline series and weakly peraluminous Triassic hornblende-bearing granite porphyry are slightly enriched in light rare earth elements (LREE) with flat heavy rare earth element (HREE) patterns, enriched in Ba and Sr, and depleted in Nb, Ta, P, and Ti, i.e., geochemical characteristics similar to those of adakite-like rocks. The Early Cretaceous medium-fine-grained biotite granites are characterized by LREE enrichment and flat HREE patterns, which belong to high-K calc-alkaline series, and metaluminous belong to weakly peraluminous I-type granite, with U and large ion lithophile element (LILE) enrichment and high field strength element depletion. The high initial 87Sr/86Sr ratios and enriched Nd (εNd(t) = −10.7 to −9.5 and −19.9 to −18.9, respectively) and Hf (εHf(t) = −21.8 to −13.0 and −30.5 to −19.0, respectively) isotopes revealed that both granitic rocks from the Huayangchuan deposit mainly originated from lower crustal materials, generated by partial melting of the ancient basement materials of the Taihua Group. Triassic hornblende-bearing granite porphyry is significantly different from the mantle origin of the contemporaneous U-mineralization carbonatite. In combination with tectonic evolution, we argue that the Qinling Orogenic Belt was affected by the subduction of the North Mianlian Ocean during the Late Triassic. The ongoing northward subduction of the Yangtze Craton resulted in crustal thickening, forming large-scale Indosinian carbonatites, U-polymetallic mineralization, and contemporaneous intermediate-acid magmatism. Additionally, due to the tectonic system transformation caused by Paleo-Pacific Plate subduction, intracontinental lithosphere extension and lithospheric thinning occurred along the southern NCC margin in the Early Cretaceous. Intense magma underplating of the post-orogeny created a large number of magmatic rocks. The tremendous heat could have provided a thermal source and dynamic mechanism for the Yanshanian large-scale U-polymetallic mineralization events.

New Insights on the Early Proto-Tethys Subduction History: Evidence from Ages and Petrogenesis of Volcanic Rocks in the Bulunkuole Complex, West Kunlun Orogen

Abstract The Proto-Tethys Ocean has played a significant role in the geological history of Earth. However, ongoing debates persist regarding the timing and polarity of its early subduction. Volcanic rocks associated with iron deposits in the Bulunkuole Complex, West Kunlun Orogen, offer insights into both the complex’s formation age and Proto-Tethys evolution. This study presents newly obtained zircon U–Pb age data (~536 Ma) along with comprehensive whole-rock major and trace element and Sr–Nd–Hf isotope analyses of these volcanic rocks. Our dataset implies that the Bulunkuole Complex partly formed in the early Paleozoic rather than entirely in the Paleoproterozoic, as previously suggested. Geochemically, the volcanic rocks exhibit enrichments in large ion lithophile elements and light rare earth elements, along with depletions in high-field strength elements. They also display elevated initial 87Sr/86Sr values (0.71093, 0.72025) and negative εNd(t) values (−5.13, −6.18), classifying them as continental arc volcanic rocks. These geochemical fingerprints, complemented by zircon εHf(t) values (−12.7 to −1.6), indicate that the parental magmas of the volcanic rocks were produced by partial melting of the lithospheric mantle wedge, which had been metasomatized by subducted sediment-derived melts. The available data, in conjunction with previously published findings, strongly suggest that the Proto-Tethys Ocean subducted southward prior to approximately 536 Ma due to the assembly of Gondwana. Subsequent slab rollback may have resulted in a crustal thinning of 9–25 km during 536–514 Ma. Further shifts in subduction dynamics led to the transition from high-angle subduction to either normal or low-angle subduction, facilitating the formation of a thicker crust ranging from 39 to 70 km between 514 and 448 Ma. This study, therefore, provides valuable insights into the early evolution of the Proto-Tethys Ocean and contributes significantly to our understanding of the tectonic history of the West Kunlun Orogen.

Geochemistry and geochronology of the Neyshabur meta-volcanic rocks, Binalood mountains, NE Iran: witnesses of Paleo-Tethys rifting and closure

Geochemical and geochronologic data are presented for meta-mafic to meta-felsic rocks along the Paleo-Tethys Suture in the Binalood Mountains east of Neyshabur, NE Iran. The rocks have a late Cambrian age (U–Pb zircon, ~ 490 Ma) and were metamorphosed in the Early Jurassic (40Ar/39Ar amphibole and plagioclase, 199–192 Ma). The rocks of this suite are alkaline and sub-alkaline (tholeiitic). The alkaline rocks are enriched in light relative to heavy rare earth elements, and do not show depletion of high-field strength elements on primitive mantle-normalized multi-element diagrams; they are similar to ocean island basalts (OIB). The tholeiitic rocks are depleted in Nb and Ta and have higher MgO and lower TiO2 than the alkaline rocks. Both types have similar, high and variable 87Sr/86Sr(i) isotopic compositions of 0.7044 to 0.7082 and 143Nd/144Nd(i) values of 0.5118 to 0.5122. The alkaline rocks are lower-degree partial melts than the tholeiitic rocks and were generated at greater depths; they likely originated from a garnet pyroxenite-rich source. The spatial, temporal, and geochemical relationships of early Paleozoic meta-mafic to felsic rocks along the Paleo-Tethys Suture (e.g., Shahrud, Jajarm, Binalood, Torbat-e-Jam) substantiate the role of a mantle plume in continental breakup along the northern margin of Gondwana and a late Cambrian-Ordovician onset of rifting that resulted in the opening of the Paleo-Tethys Ocean. The Early Jurassic metamorphism post-dates its closure.Graphical abstract

Petrogenesis and metallogenic implications of Eocene–Oligocene magmatism in the Yulong porphyry copper belt, eastern Tibet: a review and analysis of geochronological, geochemical, and Sr–Nd–Pb–Hf isotopic data

The Eocene Yulong porphyry copper belt (YPCB) in eastern Tibet contains more than 10 Mt of Cu metal, associated with subvolcanic to volcanic porphyry systems intruding Cenozoic sedimentary basins. Geochemical data analysis shows that all samples belonged to high-K calc-alkaline and shoshonite series with metaluminous–peraluminous characteristics, light rare earth elements and large ion lithophile elements enrichment, high field strength elements depletion, and share geochemical similarities to adakitic rocks. We have established a spatiotemporal evolution framework through geochronological data analysis, combined with calculated bulk zirconium saturation temperature, calculated crustal thickness and geophysical evidence. We identified three magmatic processes triggered by asthenospheric upwelling and thermal erosion of thickened crust: (1) ultrapotassic magma derived from metasomatized mantle; (2) coeval ultrapotassic melt that promoted the partial melting of eroded lower crust and the generation of high-K adakitic felsic melt; high-K and Mg# adakitic fertile magma was formed by interaction between the eroded sulfide-rich juvenile lower crust-derived melt and mantle peridotite; (3) high-K adakitic fertile magma was derived from sulfide-rich juvenile lower crust, triggered by injecting hydrous ultrapotassic magma into thinned lower crust. The difference between deposit size in the north/south section of Yulong belt may be caused by the temperature of magmatic source and the volume of coeval potassic–ultrapotassic magmatism. Our analysis of the YPCB suggests that magmatism after 175 Ma within Intermontane arc complex of the Canadian Cordillera has high potential for porphyry deposits.

Geochemical characteristics of arc fractionated I-type granitoids of eastern Tak Batholith, Thailand

Abstract The Tak Batholith is located in the western part of Thailand’s eastern granitoid belt. To better understand the geochemical characteristics of granitoid and identify their occurrence, rock samples collected from the eastern part of the Tak Batholith were used for petrographical, mineralogical, and geochemical analyses. According to field investigation and lithology, petrography classifies these granitic rocks as medium-grained granodiorite and granodioritic dike. The granodiorites are composed chiefly of plagioclase, orthoclase, quartz, hornblende, and biotite, with tiny amounts of zircon, apatite, and opaque minerals. Meanwhile, the granitic dike shows a highly porphyritic texture, presenting mostly plagioclase phenocrysts, with a small amount of orthoclase and unidentified mafic phenocrysts sitting in a fine-grained groundmass comprising K-feldspar and quartz with a small amount of plagioclase and present granophyric intergrowth. Geochemical data of the amphiboles classified them as Ferro-edenite symbolizing the I-type granite. Whole-rock geochemistry indicates that these rock suites are I-type metaluminous granodiorite, and diorite fractionated from the high K calc-alkaline magma melted from the mafic crust of arc magmatism agreeable with the enrichment of large ion lithophile elements and depletion of highfield-strength elements, and rare earth element patterns.

Development of a back-arc basin from initial rifting to seafloor spreading: Constraints from Paleozoic basic rocks in the North Qinling accretionary orogen, central China

The progression from initial back-arc rifting to back-arc opening in ancient orogenic collages is important for reconstructing subduction histories, constraining tectonic switching, and understanding crustal growth and evolution. However, it is difficult to constrain this transition in ancient arcs. The Qinling-Dabie orogenic belt is one of the most important orogenic belts in eastern Asia, yet the history of Paleozoic accretionary processes in this belt remains equivocal, owing to a poor understanding of back-arc opening processes in the Erlangping unit. In this study, we present whole-rock geochemical analyses of mafic dikes in the Erlangping unit, along with U-Pb ages and Hf-O isotope compositions of zircon from these dikes. Zircon secondary ion mass spectrometry (SIMS) dating of these mafic dikes yielded U-Pb ages of 453 ± 3 Ma. The mafic dikes are calc-alkaline and are characterized by high K2O contents (1.16−3.16 wt%). They have enriched ([La/Yb]N = 4.3−14.9) light rare earth elements (REEs) and relatively flat heavy REE ([Dy/Yb]N = 0.9−1.5) patterns, and they exhibit enrichment in large ion lithophile elements (LILEs) but depletion in high field strength elements (HFSEs), resembling arc-like magmatism. These mafic dikes are characterized by relatively enriched initial 87Sr/86Sr (0.7049−0.7059), chondritic to slightly radiogenic εNd(t) (−0.36 to 1.33), and radiogenic whole-rock and zircon εHf(t) (+7.2−7.6 and +7.5−7.8, respectively). The zircons have δ18O values (5.0‰ ± 0.1‰) similar to those of normal mantle zircon. Accordingly, we interpret that the mafic dikes were derived from an enriched lithospheric mantle source metasomatized by subducted Proto-Tethys (Shangdan) ocean material. In contrast, previously reported ca. 440 Ma gabbros from the Erlangping unit are tholeiitic and have lower incompatible trace-element concentrations with less enrichment in LILEs and less depletion in HFSEs than the mafic dikes presented here. Whole-rock Nd and zircon Hf isotopic compositions suggest that these Silurian gabbros were derived from partial melting of a more depleted mantle with the involvement of asthenosphere, and they have a close geochemical affinity with back-arc basin basalts. In addition, trace-element ratios and geochemical modeling suggest higher melting pressures for the mafic dikes than the gabbros. The geochemical differences show systematic variations from island-arc basalt into back-arc basin basalt types, which is consistent with the magma source evolution of the Mariana Trough. Thus, we interpret that the ca. 454 Ma mafic dikes were emplaced when the infant arc split, and they record initial back-arc rifting in the Erlangping unit, whereas the Silurian gabbros subsequently formed during the opening of the back-arc basin. Our study provides a paradigm for deciphering the evolution of back-arc basins through the study of spatiotemporal geological and geochemical variations of mafic intrusions in ancient accretionary orogens.

From arc accretion to within-plate extension: Geochronology and geochemistry of the Neoproterozoic magmatism on the northern margin of the Yangtze Block

Early Neoproterozoic arc magmatism and arc accretion processes are fundamental issues in reconstructing the Rodinia supercontinent. In this study we present new data of zircon U-Pb geochronology, Hf-O isotopes and whole-rock geochemistry for the magmatic rocks (including 12 felsic volcanic rocks, 3 granodioritic intrusions, 8 basaltic extrusive rocks and 12 gabbroic intrusions), which are spatially independent, in the Dahongshan area on the northern margin of the Yangtze Block. The investigated intermediate-felsic rocks are dated at ca. 970 Ma, ca. 885–865 Ma, ca. 840–830 Ma and ca. 810–790 Ma by in situ ion probe and laser zircon U-Pb dating methods. The mafic rocks are dated at ca. 870 Ma by in situ ion probe. Combined with previous age data, our new geochronology results suggest continuous magmatic activities from ca. 970 Ma to ca. 790 Ma in the Dahongshan area with a magmatic flare-up at ca. 840 Ma. The ca. 970–840 Ma mafic rocks, as well as the contemporaneous intermediate-felsic rocks, show enrichments in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depletions in high-field strength elements (HFSEs), representing arc-related tectonic settings. Zircon grains from these rocks generally have positive εHf(t) values from +7.3 to +14.7 and slightly elevated δ18O values from +5.59 to +6.89, indicating a dominant juvenile source with minor supracrustal incorporation. In contrast, the ca. 830–790 Ma mafic rocks are characterized by E-MORB- (enriched mid-ocean ridge basalt) and OIB- (oceanic island basalt) like and the contemporaneous felsic rocks show characteristics of A2-type granites, implying a within-plate extension environment. Zircon grains from the ca. 830–790 Ma felsic rocks display broad εHf(t) values from −5.7 to +15.3 and low mantle δ18O values from +3.81 to +6.11, implying multiple magma sources for their generation and the imprinting of high-temperature hydrothermal alteration. The relative contributions of the mature crustal component in the Dahongshan magmas decreases from 10–20 % in the ca. 970–840 Ma felsic rocks to 0–10 % in the ca. 830–790 Ma felsic rocks. The Neoproterozoic magmatic activity on the northern margin of the Yangtze Block recorded an integrated evolution from accretion of previous oceanic arc (ca. 970–870 Ma) at ca. 870–840 Ma to within-plate extension (ca. 830–790 Ma) in response to the convergence and divergence of the supercontinent Rodinia.

Chronolgy and Geochemistry of the Sijiaying Iron Deposit in Eastern Hebei Province, North China Craton: Implications for the Genesis of High-Grade Iron Ores

The Sijiaying iron deposit is located in the Eastern Hebei area of the southern section of the northern margin of the North China Craton (NCC) and is the largest single iron deposit in China. The deposit contains many banded iron formations (BIFs) and was proven to have more than 3 million tons of high-grade iron ore resources. This study carried out geochemistry and zircon U–Pb analysis of normal-grade iron ore, high-grade iron ore, and wall rock (biotite–leptynite, chlorite–sericite schist) in the Sijiaying deposit and discussed the genesis and metallogenic age of high-grade iron ore. BIFs have low concentrations of Al2O3 and TiO2 and high field strength element (HFSE) depletion, indicating almost no contamination via terrestrial debris. The standardized post-Archean Australian shale (PAAS) rare earth element (REE) distribution pattern indicates that the iron formation exhibits positive Eu, Y, and heavy rare earth element (HREE) anomalies and lacks negative Ce anomalies, indicating that the Sijiaying BIF was enriched with iron sources via high-temperature hydrothermal fluids from the seabed and deposited in an anoxic ancient marine environment. In addition, geological field work identified two types of high-grade iron ore in the mining area: primitive sedimentary and hydrothermally altered high-grade iron ore. Further ore geochemical research showed that the primitive sedimentary-type iron ore is similar in geochemistry to the BIF. In addition to low Eu/Eu* values, the hydrothermally altered high-grade iron ore shows geochemical characteristics similar to those of the BIF, suggesting that they share the same iron source but did not form at the same time. The total large ion lithophile element (LILE) (Sr, Ba, Pb) contents in primitive sedimentary-type high-grade iron ore are higher than those in hydrothermally altered high-grade iron ore, indicating that LILEs are carried away via fluids during the hydrothermal alteration process in normal-grade iron ore. The geochemical characteristics of biotite–leptynite and chlorite–sericite schist include high contents of SiO2 and Al2O3, light rare earth elements (LREEs), LILE enrichment (Rb, Ba, Sr, Zr), and HFSE depletion (Nb, Ta, P, Ti), characteristics that are similar to island arc volcanic rocks. The reconstruction of the original rock indicates that the wall rock is a product of volcanic sedimentary cycles in an island arc setting. Zircon cathodoluminescence images and LA–ICP–MS zircon U–Pb dating can be divided into four age groups (3283 Ma, 2547 Ma, 2500 Ma, and 2407 Ma), which correspond to the earliest volcanic activity in eastern Hebei, the main mineralization age of the Sijiaying BIF (the mineralization age of primitive sedimentary high-grade iron ore), a regional tectonic–metamorphic event, and the occurrence of migmatization (the mineralization age of hydrothermally altered high-grade iron ore), respectively. Therefore, the Sijiaying BIF and primitive sedimentary high-grade iron ores were deposited and mineralized at 2547 Ma, and the iron orebody was later altered via the hydrothermal solution at 2407 Ma, forming large-scale high-grade iron ores.

Making Andesite Through Shallow Hybridization of Magmas Derived From Variably Enriched Lithospheric Mantle

AbstractWe integrate textural and in situ compositional information from plagioclase and clinopyroxene (Cpx) phenocrysts together with groundmass compositions in early Cretaceous andesite dykes within the Sulu belt of China to propose a new petrogenetic model for andesite. Plagioclase phenocrysts are mostly andesine; they are depleted in high field strength elements (HFSE). However, Cpx phenocrysts are either reversely zoned (type I) or homogeneous (type II), with the zoned Cpx divided into subtypes IA and IB. All Cpx has high Mg#, low Na2O and generally low Al2O3, with depletions in HFSE and variably high 87Sr/86Sr ratios, suggesting crystallization above the Moho from magmas derived from enriched lithospheric mantle. The cores of type IA/IB and type II Cpx have normal major‐ and trace‐element compositional variations and similar 87Sr/86Sr ratios to each other and to plagioclase, consistent with fractional crystallization from a common magma (magma 1). The rims of type IA and IB Cpx also have normal major‐ and trace‐element compositional variations, but these are not as evolved as the cores, and the rims have lower 87Sr/86Sr ratios, demonstrating crystallization from an isotopically distinct magma (magma 2). Based on modeled major and rare earth element compositions of magmas inferred to have been in equilibrium with different Cpx (±plagioclase) domains, the measured groundmass compositions can be reproduced by variable mixing between the two magmas. Our study demonstrates for the first time that andesite magma can be made through fractionation and shallow hybridization of magmas derived from variably enriched lithospheric mantle.

Petrogenesis and geochemical evidence from early Jurassic intrusive rocks and their implications for subduction of the Paleo-Pacific Plate in the Yanbian area, Northeast China

Subduction of the Paleo-Pacific Plate plays a key role in the Early Jurassic magmatism evolution in the Yanbian area, Northeast China. In this paper, zircon U–Pb ages, whole-rock geochemical, and Sr–Nd–Hf isotopic compositions are presented. The Early Jurassic gabbros, diorite enclaves, granodiorites, and granites ages range from 183 to 189 Ma. They are characterized by enrichment in large-ion lithophile elements and depletion in high-field strength elements. The gabbros are classified as low- and medium-K tholeiitic, granodiorites and granites are high-K calc-alkaline I-type, and diorite enclaves are calc-alkaline transitional series. The gabbros have zircon εHf(t) values of 6.81–9.89, whole-rock 87Sr/86Sr(i) = 0.7043–0.7044, and εNd(t) from 2.72 to 2.80. The diorite enclaves have zircons with εHf(t) values of 8.26–12.80, whole-rock 87Sr/86Sr(i) = 0.7051, and εNd(t) from 0.96 to 1.09. The granodiorites and granites have zircon εHf(t) values of 7.59–12.87, whole-rock 87Sr/86Sr(i) = 0.7042–0.7066, and εNd(t) from 2.33 to 2.61. These data indicate that gabbroic magmas were derived from partial melting of a depleted mantle wedge metasomatized by subduction-related fluids. The basaltic magma underplated and heated the juvenile crust, whereas the granodiorites and granites might be the product of fractional crystallization of a mixture of basaltic and felsic magmas or derived from partial melting of the juvenile lower crust. Our data constrain the petrogenesis of these Early Jurassic intrusive rocks which are attributed to subduction of the Paleo-Pacific Plate beneath Eurasia continent in northeastern China.

Late Neoarchean crust–mantle interaction and tectonic implications in western Shandong Province, North China Craton: Evidence from a granodiorite pluton and associated magmatic enclaves

This study presents original data on the microstructure, mineralogy, whole–rock geochemistry, and isotopes of a Late Neoarchean granodiorite pluton and associated mafic microgranular enclaves (MMEs) in western Shandong Province of the eastern part of the North China Craton (NCC). The MMEs hosted in the granitic pluton are more mafic, and amphibole and biotite are the predominant mafic minerals. The sharp contacts and fine–grained textures of the MMEs indicated a rapid quenching process during a magma mingling event. Zircon and titanite UPb dating indicated that the host granodiorite pluton formed at circa 2546 Ma, and the MMEs formed at approximately 2538 Ma. The dating results indicated a crust–mantle interaction. Geochemically, the host pluton has high silica contents (SiO2 = 67.68–68.51 wt%), Mg# values (51–53) and low Aluminum Saturation Index ratios (A/CNK = 0.92–0.95), which are indicative of I–type granitic affinity. Moreover, they show arc–type trace element features characterized by enrichment of light rare earth elements (LREEs) and large ion lithophile elements (LILEs) (e.g., Cs, Rb, K, and Pb), but depletion in high field strength elements (HFSEs) (e.g., Nb, Ta, P, and Ti). In contrast, the MMEs have lower silica contents (SiO2 = 52.07–56.03 wt%), but higher Mg# values (56–68) and Cr, Ni and Cu contents of 454–633, 159–225 and 98.3–207 ppm, respectively, corresponding to a mantle component. Similar to the host pluton, the MMEs show enrichment of LREEs and LILEs, but depletion of HFSEs, reflecting an arc–type magma origin. Isotopically, the host granodiorite and MMEs both have relatively depleted NdHf isotopic compositions, with εNd(t) values of −0.67–1.22 and − 0.31–1.89, and εHf(t) values of 5.63–2.03 and − 0.18–4.48, respectively. Zircon oxygen isotopes reveal that the host granodiorite and MMEs have slightly higher oxygen isotopes than the normal mantle zircon (5.3‰), with mean δ18O values of 6.35‰ and 6.81‰, respectively, indicating assimilation of minor supracrustal materials in the magma source. However, a combination of Nd–Hf–O isotopes suggests that the MMEs haveslightly enriched isotopic compositions than the host granodiorite pluton, suggesting a “reversed isotope” feature. This important finding also enlightens that “reversed isotope” phenomenon represented magma mingling between isotopically relatively enriched mafic and relatively depleted felsic magmas. Furthermore, the Ce4+/Ce3+ ratios in zircon from the host granodiorite and MMEs indicated a low oxygen fugacity, with mean values of 24.25 and 39.69, respectively. Although the host granodiorite and MMEs have the similar oxygen fugacity ranges, the MMEs have high Cu concentrations of 98.3–207 ppm (mean value = 151 ppm), indicating a Cu–rich magma source. Integrating the petrogenesis of the Late Neoarchean granodiorite pluton and associated MMEs, it is inferred that the host granodiorite pluton was derived from partial melting of mafic lower crust with minor insignificant ancient materials, and the MMEs were derived from partial melting of depleted mantle metasomatized by sulfur–rich sediment melts/fluids (chalcophile element). Tectonically, our samples reveal an affinity with an arc in a syn–collisional setting. Together with regional rock assemblages, we suggest that the onset of plate tectonics (subduction) was to occur by the end of Neoarchean in the NCC.

Triassic volcanism on the North margin of the North China Craton: Insights for lithospheric modification during closure of Paleo-Asian Ocean

As a key tectonic region linking the northern margin of the North China craton (NCC) and eastern Central Asian Orogenic Belt (CAOB), western Liaoning, with extensively distributed magmatic activity, provides natural samples to investigate the evolutionary history of the Paleo-Asian Ocean plate subduction to closure. The Middle Triassic (ca. 241 Ma) trachyandesites and Late Triassic (ca. 223 Ma) basaltic andesites were first identified from the Tiaojishan Formation, western Liaoning. They have variable SiO 2 contents (52.48–60.31 wt%) and alkaline or high-K calc-alkaline to shoshonite compositions, and belong to the metaluminous series. Middle Triassic trachyandesites are enriched in large ion lithophile elements (LILEs), high field strength elements (HFSEs), and light rare earth elements (LREEs) with high Nb/La ratios (0.63–0.76). They have homogeneous whole-rock Sr Nd ( 87 Sr/ 86 Sr i = 0.704684–0.704808, ε Nd (t) = −4.6 to −4.0) and variable zircon Hf isotopic signatures (ε Hf (t) = −10.3 to 8.2), indicating that they probably originated from the partial melting of the subcontinental lithospheric mantle with the addition of asthenosphere materials. In contrast, the Late Triassic basaltic andesites show arc-related geochemical affinities, such as LILEs and LREEs enrichment and HFSEs depletion. They have more enriched whole-rock 87 Sr/ 86 Sr i (0.704895–0.705394), ε Nd (t) (−16.1 to −14.0), and zircon ε Hf (t) (−13.1 to −8.8) than the Middle Triassic trachyandesites, suggesting that they probably represent partial melts of the subduction-related fluids-modified lithospheric mantle. The modification of the northern margin of the NCC lithospheric mantle is closely related to the final subduction of the Palaeo-Asian oceanic plate and the subsequent post-orogenic extension. • Triassic volcanic rocks are founded in Tiaojishan Formation, Western Liaoning. • Study area was in a post-orogenic extensional setting in the Middle-Late Triassic. • Ocean Subduction modified the North China Craton lithosphere in the Triassic.

Metamorphic Evolution and Orogenic Process Related to the Eastern Paleo-Tethyan Warm Subduction and Indochina–South China Collision

Abstract The eastern Paleo-Tethyan Jinshajiang–Ailaoshan–Song Ma orogenic belt in the Southeast Tibetan Plateau represents the tectonic boundary between the Indochina and South China blocks. Regional Cenozoic lithospheric strike-slip movements caused by the India–Asia collision have modified many of the pristine geological records associated with the Indosinian orogeny. The lack of reliable petrological evidences, particularly of high-pressure (HP) metamorphism, has hindered the tracing of the evolutionary history of the Paleo-Tethyan orogenic belt. We report the mineralogy, geochemistry, geochronology and thermodynamic modelling of eclogite lenses/blocks and their host garnet–phengite schists from the Song Ma Suture Zone of Northwest Vietnam and reveal their protolith origins and metamorphic evolution. The eclogites are geochemically similar to mid-ocean ridge basalt, showing weak depletions in high field-strength elements, positive to slightly negative whole-rock ɛNd(t) ratios (−1.69 to +5.15) and slightly high 87Sr/86Sr(t) ratios (0.70466–0.70834). The igneous protolith of the eclogites formed in the late Silurian (425.4 ± 3.6 Ma; igneous zircon dating, 638–459 Ma TDM dating), which makes them the oldest known mid-ocean ridge mafic rocks in an ancient Paleo-Tethyan Ocean. Various eclogites preserve similar peak mineral assemblages (garnet + omphacite + phengite + rutile + quartz ± epidote/clinozoisite ± kyanite ± winchite) under indistinguishable peak conditions. Their prograde P–T trajectories show a uniform pattern of progressive heating and weak compression along a geothermal gradient of 8°C–10°C/km, indicating a warm subduction setting at a low angle that contrasts with the cold oceanic subduction recorded in the adjacent Paleo-Tethyan suture zones. Combined with detrital U–Pb ages from previous studies, our geochronological data indicate that the host schists originated from continental crust within the South China Block and underwent a pervasive Triassic HP metamorphism related to the Indosinian orogeny. The eclogites and host schists yielded HP metamorphic ages of 239–234 Ma and retrogressive amphibolite-facies metamorphic ages of 231–229 Ma, suggesting rapid cooling (14.0°C–21.6°C/Myr) and exhumation (6.4 km/Myr) from the mantle to the crust. The Song Ma eclogites and their host schists formed when the final ocean closure transitioned to the initial Indochina–South China collision. The Song Ma eclogites and their host schists provide essential information on the opening and closure of the eastern Paleo-Tethys and the subsequent amalgamation of Southeast Asian continental fragments.

Petrogenesis and tectonomagmatic setting of gabbroic rocks in the Gisel area (northern Iran)

The Alborz-Azerbaijan magmatic zone in northern Iran is one of the important zones of magmatic activity in the Cenozoic. Lithologically, this complex consists of olivine gabbro, monzogabbro, dolerite, and gabbro with granular, intergranular, and porphyritic textures. The main phenocrysts of these rocks are clinopyroxene, plagioclase, and sometimes iddingsitized olivine. The rocks producing magma has potassic and shoshonitic nature. Enrichment in large-ion lithophile elements (LILEs), i.e., Ba, Rb, and Th, and depletion of high-field strength elements (HFSEs), i.e., Ti and Nb, in the spider diagrams are of the characteristics of subduction and active continental margin rocks. Also, these diagrams show enrichment in the light rare earth elements (LREEs) compared to heavy rare earth elements (HREEs). This feature also is representative of the rocks of subduction zones and active continental margins. The geochemical and petrogenetic studies indicate unique origin of the intrusive rocks in the study area and the role of fractional crystallization with simultaneous crustal assimilation (AFC) and magma contamination with crustal rocks in the evolution of the magma forming these rocks. This magma is obtained from the low-degree partial melting of an enriched mantle source beneath the continental lithosphere with garnet lherzolite composition at a depth of 100 to 110 km in a post-collision extensional basin.

SIMS Zircon U-Pb Ages and O Isotope Compositions of Gabbro from the Laguoco Ophiolite from Western Shiquanhe–Yonzhu Suture Zone (Tibet) and Their Geological Significance

The Shiquanhe–Laguoco–Yongzhu–Jiali ophiolite mélange belt in Tibet includes the Laguoco Tso ophiolite as part of its western segment. Researchers studying the evolution of the Tibetan Plateau and the Tethys have taken a keen interest in the debated relationship between this ophiolite belt and the Bangong–Nujiang ophiolite belt. However, there is little research in this field. This study reports the rock geochemistry, SIMS (the secondary ion mass spectrometry) zircon U-Pb ages, and O isotope compositions of gabbro from the Laguoco ophiolite. Gabbro has substantial depletion in HFSEs (the high field strength elements) such as Th, Nb, Zr, and Hf, as well as exhibits comparatively high Mg# (80.6 on average), and low K, N, P, and Ti contents. Therefore, it was possibly formed in an intra oceanic subduction island arc environment originating from ~30% partial melting of the depleted spinel lherzolite. The SIMS zircon U-Pb ages of the gabbro samples are 187 ± 1.2 Ma and 189 ± 2.1 Ma, and the weighted averages of δ18O are 5.24‰ ± 0.12‰ and 5.34‰ ± 0.13‰, which are close to mantle-derived zircon δ18O (5.3‰ ± 0.3‰). These results suggest that during the Early Jurassic, the Laguoco ophiolite recorded the intra oceanic subduction of the northern branch of the Neo-Tethys.

Late Permian-Triassic ridge subduction beneath the northeastern margin of the North China Craton: Evidence from the Kaiyuan appinitic to high-Mg intermediate intrusions in northern Liaoning, North China

Recognizing terminal ridge subduction is of first-order importance in chronicling the tectonic timeline of any accretionary orogens, but remains elusive in the final suturing zone of the Paleo-Asian Ocean along the Solonker−Xar Moron−Changchun−Yanji swath. Here we report two generations of ultramafic-mafic to intermediate intrusions from northern Liaoning, North China, linking eastern Central Asian Orogenic Belt and northern North China Craton. The ca. 259 Ma appinites show variable enrichment in large-ion lithophile elements (LILEs) but depletion in high-field strength elements (HFSEs), and variably enriched isotopic compositions with εNd(t) of −11.8 to −2.4 and zircon εHf(t) of −15.7 to +5.0. These petro-geochemical traits argue for their derivation from partial melting of subduction-modified lithospheric mantle. By contrast, the high-Mg diorites of 226−223 Ma display decoupling features between LILEs and HFSEs and juvenile isotopic signatures with εNd(t) of −0.3 to +2.6 and zircon εHf(t) of +5.4 to +11.4. These characters are consistent with a magmatic origin from partial fusion of sediment-fertilized asthenospheric mantle. Synthesizing the two mantle-melting events with regional coeval igneous activities leads to the identification of Late Permian (265−250 Ma) and Middle-Late Triassic (241−218 Ma) magmatic flare-ups with a 10−15 m.y. lull along the northern North China Craton. This magmatic tempo tends to record a salient mantle replacement from hydrous metasomatized lithosphere to anhydrous asthenosphere. In combination with ensuing progressive crustal growth, simultaneous metamorphism, and structural activities, these diverse manifestations make a compelling case of ridge subduction and concomitant slab window formation during the eventual closure of the Paleo-Asian Ocean along the Solonker−Xar Moron−Changchun−Yanji swath.