Identifying ultrahigh-temperature (UHT) metamorphism in granulite-facies metamorphic terrains and determining its pressure-temperature-time (P-T-t) paths are crucial steps toward elucidating the anomalously hot geodynamic evolution process. This study presents the inaugural identification of chloritized sapphirine-bearing granulites in the Helanshan Complex, located in the western segment of the Khondalite Belt, North China Craton. Three stages of metamorphic evolution were identified based on petrographic analyses, mineral chemistry, and phase equilibrium modelling: the pre-Tmax stage involves the presence of rutile-stable phase assemblage, wherein rutile is partially substituted by ilmenite; the Tmax stage involves the assemblage of garnet + plagioclase + K-feldspar + sillimanite + spinel ± sapphirine + quartz + ilmenite + melt, as evidenced by microscale (<5 μm) blebs of variably chloritized sapphirine within spinel; and the retrograde cooling stage features the solidus assemblage of garnet + plagioclase + biotite + K-feldspar + sillimanite + cordierite + quartz + ilmenite + melt. Phase equilibrium modelling indicates Tmax conditions of 958–1055 °C and 6.4–7.8 kbar, suggesting UHT conditions accompanied by a high geothermal gradient of approximately 150 °C/kbar. Furthermore, a clockwise P-T trajectory was established, involving pre-Tmax decompression and post-Tmax near-isobaric cooling. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon and monazite U-Pb dating of UHT pelitic granulites produced ages clustering around 1.91 Ga, marking the era of UHT metamorphism within the Helanshan Complex. This discovery broadens the scope of UHT metamorphism and indicates that the entire Khondalite Belt experienced a regional UHT metamorphic event during 1.93–1.91 Ga, which was likely induced by an initial radiogenic heating synergy followed by an augmented mantle heat flux.

Continental subduction has been identified in many orogens, such as the Alps, the Himalayas, and the Dabie; however, better understanding of the mechanism and outcome of different subduction processes remains desirable. The Qinling–Dabie orogen in Central China shows an asymmetric distribution of Triassic ultrahigh-pressure metamorphic rocks and syn- and post-tectonic granitoid plutons, thereby providing an excellent means by which to probe the diverse processes of continental subduction. Many late Mesozoic granitoid plutons that formed in post-orogenic or even anorogenic settings are widely distributed in both the Qinling and Dabie tectonic units and can be useful for studying the composition of materials beneath the crust because of their conspicuous compositional diversity. In the present study, we report zircon ages and NdHf isotopic compositions for the Shangcheng and Heyu granite plutons, which represent late Mesozoic plutons in Dabie and Qinling. When compared with those of the Shangcheng pluton, the wide range of Nd isotopic values and the slightly depleted Hf isotopic compositions of the Heyu pluton indicate that there may be juvenile crust beneath the Qinling tectonic unit that is not present beneath the southern margin of North China. The currently undetectable juvenile material in this region may be an important candidate source of the late Mesozoic magmatism and metal mineralization in the southern margin of North China. The compositional diversity of these granites, as indicated by the NdHf isotopic compositions, is attributed to the nature of the deep crust within the orogenic belt, and the magmatic origins of this region are discussed in the present study.

Dating deformation is key to unravel the evolution of orogens. Unfortunately, this is commonly challenged by the occurrence in the rock record of multiple overprinting deformation stages that lead to repeated blastesis and form multiple fabrics during both prograde and retrograde evolutions. Additionally, recrystallization is not always complete, which causes a mixture of inherited and neoblastic mineral phases. Therefore, an approach integrating age dating with microstructural and petrographic analyses is necessary to extract structurally constrained ages from the rock record. We used this approach to contribute to the long-lasting debate about exhumation of continental metamorphic units subducted to high-pressure conditions. We studied continental metasedimentary sequences of the Tuscan Metamorphic Units of the Northern Apennines (Italy) from two localities: the Island of Giglio to the west and the Monticiano-Roccastrada Unit to the east. We obtained two analytically distinct 40Ar/39Ar age ranges: an older 21–16 Ma age cluster is related to syn-orogenic top-to-the E contractional deformation occurring at ca. 1 GPa and 350 °C. A younger 15–11 Ma age group is related, instead, to exhumation to shallower structural levels and retrogression of these units to greenschist facies conditions. The interpretation of the results is based on white mica chemical compositions and rock fabrics. By integrating our results with published literature, we conclude that the investigated high-pressure continental metasedimentary sequences experienced early syn-orogenic exhumation from blueschist to greenschist facies conditions predominantly by a combination of extrusion and out- and in-sequence thrusting, with only minor contributions by extensional shearing during regional crustal thinning. Therefore, this study highlights the role of contractional fabrics in accommodating significant exhumation amounts of deeply subducted continental rocks.

Deciphering the origin of granitoids with enriched isotopic compositions is essential to understanding the mechanism of continental growth and reworking. Establishing their origin is also an effective solution to the decoupled interpretations between geochemical and isotopic observations in competing petrogenetic models. This paper reports on the whole-rock major and trace elements, Sr-Nd-Pb-Hf isotopes, and zircon UPb age and Hf isotope data of samples from the Late Triassic Lincang Batholith in SW China. The hornblende-bearing granodiorites are weakly peraluminous, whereas the coeval biotite monzogranites are generally strongly peraluminous. These two types of granitoids show identical and extremely enriched isotopic compositions with (87Sr/86Sr)i ratios of 0.71991 to 0.74302, whole-rock εNd(t) values of −13.5 to −10.1, and εHf(t) values of −13.4 to −10.3, as well as a large variation of zircon εHf(t) values of −17.6 to +0.6. The inherited zircons from both suites of samples show similar age peaks (ca. 950 Ma and ca. 1150 Ma), trace element concentrations, and εHf(t) variations to those of the detrital zircons from the Lancang Group. These similarities indicate that these rocks are most likely derived from the anatexis of the Lancang Group that is mainly composed of quartz schist, sericite schist, greenschist, chlorite albite schist, and minor eclogite. On the other hand, the Lancang Group is characterized by more enriched isotopic compositions than the granitic batholith with whole-rock εNd(225 Ma) value of −13.3 and εHf(225 Ma) value of −19.1, but identical to those of the average εHf(225 Ma) values of inherited and detrital zircons (−18.1 and − 16.3). This isotopic fractionation between the granitoids and the Lancang Group may result from disequilibrium melting of the Lancang Group with different dissolution behavior of accessory minerals (i.e., zircon, monazite, apatite, titanite, etc.). The Lincang Batholith is on average more silicic and richer in incompatible elements than the upper continental crust, suggesting that the isotopically enriched giant granitic batholith is a mature magmatic response to continental reactivation and reworking.

The rheological properties of the interface between the down-going and overriding plates in subduction zones provides insight into how plate convergence is accommodated and the controls on seismic and aseismic slip. This interface is known as the subduction channel and exhumed examples provide the only direct information on deformation mechanisms and the impact of metamorphism on rheology. The Rocky Beach Metamorphic Mélange in eastern Australia is one such exhumed subduction channel, composed of eclogite, blueschist and greenschist facies blocks within a mélange matrix. Previous phase equilibria modelling indicates that high pressure blocks were subducted to ca. 100 km depth and then retrogressed during return flow and exhumation. We found that the rheology of blocks is modified by metasomatism, consistent with studies on other subduction channels. However, through comparison of blocks from different metamorphic grades we found that the effect of metasomatism on rheology varied depending on the pressure and temperature conditions of metasomatism. While unmetasomatised eclogites behaved as rigid objects in the mélange matrix, rocks with mineral assemblages that equilibrated during eclogite facies metasomatism accumulated significant strain, forming isoclinal folds and refolded folds. Deformation of these blocks began at eclogite facies and continued during return flow and retrogression to blueschist facies. At blueschist facies, metasomatised blocks developed mm-scale isoclinal folds with shearing parallel to fold limbs forming rootless isoclinal folds. At the transition between blueschist and greenschist facies, pressure solution became important, preferentially focusing along layers of lawsonite, dissolving it from the rock. At greenschist facies, dissolution-precipitation processes caused significant mass loss, producing mm-spacing between pressure solution seams and cuspate folds, analogous to dewatering structures in sediments. In the Rocky Beach Metamorphic Mélange eclogite facies metasomatism reduces the competence of rigid blocks, reducing overall subduction channel heterogeneity during return flow. We suggest that subduction channels that experience widespread eclogite facies metasomatism may be less likely to generate seismic slip during return flow, since the proportion of rigid blocks and block strength are both reduced.

The southernmost Mariana convergent margin (SMCM) is a distinct segment of the Izu-Bonin-Mariana (IBM) subduction system with unique east-west orientation, however, its nature and tectonic history remains enigmatic. Here, for the first time, we present the detailed geochemical data of detrital minerals and UPb ages of accessory minerals from two sediment samples recovered at the deepest part of Southern Marianna Trench including the Challenger Deep. Detrital magmatic zircon UPb ages can be divided into three groups. Group 1 zircons show a weighted mean age of 50.3 ± 1.2 Ma, contemporary to the published boninites from northern IBM. The εHf(t) of these zircons (11.1–16.4) are also similar to the boninites (12.6–16.8) and volcanic arc rocks (4.2–14.2), but lower than forearc basalts (17.8–22.1), suggesting that these zircons are from boninitic or arc magmatism. The apatite UPb dating obtained a similar age of 55.0 ± 5.5 Ma. Therefore, if they are all from boninites, then subduction initiation magmatism ended at SMCM was likely coeval with northern IBM. Group 2 and Group 3 zircons have εHf(t) values similar to Group 1 zircons, but recorded younger 206Pb/238U ages of 16.8 ± 1.8 Ma and 11.0 ± 0.2 Ma, respectively, which are most likely related to the arc volcanism at West Mariana Ridge (WMR). Additionally, a rutile age of 19.0 ± 0.6 Ma is identified, which is also likely related to WMR. The chemical composition and calculated P-T conditions of clinopyroxenes indicate that they are mainly from the Mariana forearc basalts and arc volcanic rocks. In situ Sr isotopic compositions of plagioclases also show strong affinity to the Mariana forearc basalts and arc volcanic rocks. Therefore, our study indicates that sediments at the deep trench can record the long-term tectonic and magmatic evolution of the convergent margin.

The analysis of εHf(t) time series data from zircon reveals notable discrepancies based on sample type (igneous versus detrital), statistical weighting methodology, and geographic sampling bias. These differences warrant caution when interpreting data in the context of tectonic settings and the history of supercontinents. In terms of tectonic setting, accretionary orogens dominate in both sedimentary basins that host detrital zircons and in igneous zircon sources. Because of differences between the various time series, emphasis in this study is on peaks, valleys and secular trends and not on absolute εHf(t) values. Specifically, the igneous time series for εHf(t) in zircons shows more peaks and valleys than corresponding detrital time series for both weighted and unweighted data (weighting corrects for disproportionate geographic sampling). Also, sample-based (each sample considered separately) and site-based (samples grouped by geographic location and age) results align closely to the igneous time series, whereas the site-based detrital series displays more negative εHf(t) values. Regardless of the type of time series, the failure to compensate for disproportionate geographic sampling increases the prospects of producing an unrepresentative time-series. Nine zircon age peaks (both detrital and igneous) have corresponding εHf(t) peaks (3200, 2700, 2500, 2150, 1500, 1100, 750 Ma) and two have corresponding age valleys (1800–2000, 550 Ma). With exception of a geographically widespread 1500 Ma peak, most of the εHf(t) peaks and valleys are controlled by specific geographic regions and are likely not be global in extent.Two distinct periods (200–0 and 1800–1600 Ma) display εHf(t) signatures that rise steadily for 100–200 Myr, coinciding with the final stages of supercontinent assembly and the transition to the retreat of exterior orogens. An εHf(t) peak at 750 Ma and a high at 1400–1100 Ma partly overlap with supercontinent breakup and valleys at 550 Ma and 900 Ma with supercontinent assembly. A large εHf(t) valley at 2000–1800 Ma corresponds with the onset of craton collisions that led to the final assembly of Columbia at 1800–1600 Ma. The steep rise in εHf(t) in the last 200 Myr in both igneous and detrital zircons is controlled by sites in Circum-Pacific orogens in North and South America and Southwest Asia, and it parallels the breakup of Pangea. The general increase in zircon εHf(t) in the last 500 Myr in both detrital and igneous data reflects an increase in the proportion of isotopically juvenile components in accretionary orogens.

The early Paleoproterozoic Era has been largely recognized as a period of global magmatic slowdown (~2.3–2.2 Ga). The Lagoa Dourada Suite, located in the Mineiro Belt – southern São Francisco Craton - Brazil, is a juvenile high‑aluminum 2350 Ma TTG suite and spatially associated with a network of dykes that received little attention in the literature. Based on field features, petrography, whole-rock geochemistry, U-Th-Pb, and Hf isotopes in zircons, we propose that these dykes represent three different magmatic pulses produced via intracrustal melting of oceanic crust. Pulse 1 (<2347 Ma) is syn-plutonic with low-SiO2, high-Mg# and HREE, moderate [La/Yb]N, and low Ba+Sr contents. Pulse 2 (ca. <2330 Ma) shows high-SiO2, low-Mg# and HREE, moderate [La/Yb]N, and high Ba+Sr. Pulse 3 (ca. <2325 Ma) has intermediate-SiO2, low-Mg#, high HREE, moderate to high [La/Yb]N, and high Ba+Sr values. Their Hf compositions are broadly similar to those of the host rock, with positive εHf(t) values and the Hf-TDM model ages ranging from 2.65 to 2.46 Ga, attesting to their juvenile nature. These characteristics, coupled with their homogeneous Hf signature (176Hf/177Hf = 0.281382 to 0.281481), suggest that all these magmatic pulses came from a similar source. However, the whole-rock chemical diversity of the dykes and host rock suggests chemical heterogeneities within this source rock and/or the different magmatic pulses were generated by variable degrees of partial melting of a tholeiitic metabasaltic source throughout approximately 25 Ma. These findings reveal a wide compositional diversity of magmas that gave rise to a network of dykes crosscutting the Lagoa Dourada Suite and, consequently, to the framework of a juvenile continental crust on the southern margin of the São Francisco Craton. Furthermore, these rocks constitute a singular example of juvenile magmatism and contribute to a better understanding of the tectono-magmatic lull and potential petrological processes during this period.

Titanite is a valuable tool for studying polymetamorphism and understanding the evolution of orogenic belts as it potentially records different stages of metamorphic evolution. The combination of geochronology and Zr-in-titanite geothermometry has been widely used in petrochronology studies. However, there is ongoing debate regarding the significance of ages and temperatures obtained from titanite. Here, we conducted the first integrated titanite, zircon, and apatite UPb study, along with Zr-in-titanite geothermometry, on calc-silicate rocks from a polymetamorphic complex of the central Dom Feliciano Belt (Western Gondwana). Our aim was to investigate the impact of various metamorphic events on titanite grains. We carried out a geochronological, geochemical, and petrographic analysis of a calc-silicate sequence of the Passo Feio Complex, which was intruded by the Caçapava do Sul Granitic Complex (CSGC). The metamorphic complex experienced regional, contact, and hydrothermal metamorphism during the Neoproterozoic, but the ages and conditions of these metamorphic events remain widely debated. UPb analyses on over one hundred titanite grains from a K-feldspar-diopside schist revealed three distinct titanite populations. The older group, dated at 638.6 ± 2.8 Ma (2 s; n = 19), was associated with the regional metamorphism event (M1), likely initiated by the primary collision of the Dom Feliciano Belt. The intermediate group exhibited an age of 596.3 ± 1.1 Ma (2 s; n = 91). Given the presence of high-K magmatism and a carbonatite intrusion in the study area, producing zircon UPb ages around 600 Ma, this group was associated with contact metamorphism (M2), belike influenced by these intrusive igneous activities. The youngest titanite population showed an age of 565.7 ± 3.0 Ma (2 s; n = 6), which closely aligns, within analytical error, with the age of 561.4 ± 1.3 Ma (2 s; n = 46) obtained from UPb dating on apatite sourced from a diopside-phlogopite schist. The younger ages observed in both titanite and apatite are attributed to alterations resulting from interactions with hydrothermal fluids (M3) during the cooling phase of the CSGC. Chemical analyses conducted with an electron microprobe assessed the Zr concentrations in fifty titanite grains, examining both bright and dark zones observed in back-scattered electron images. The lowest temperature recorded among the 50 grains was 629 °C, which corresponds to dark BSE zones. In the light zones, the minimum temperature was 639 °C. While temperatures estimated using the Zr content in titanite may not correspond precisely with UPb ages, combining titanite ages with those from other accessory minerals like zircon and apatite, along with microstructural analysis, can provide a more comprehensive understanding of orogenic belt evolution.

In the present study, we integrate bulk rock chemistry and in-situ zircon U-Pb-Hf isotopes of high-K Neoarchean granitoids from the northeastern part of the Eastern Dharwar Craton (EDC) to investigate their source, petrogenesis, and plausible tectonic setting. Based on the mineral assemblage, in coherence with their geochemical characteristics, these granitoids are classified as Hornblende-biotite granite (HBG) with Microgranular enclaves (ME), Biotite granite (BTG) and Monzogranite (MG). Field observations and zircon UPb ages reveal coeval emplacement of these granitoids between 2.53 and 2.50 Ga. The HBG, including ME, has low silica, metaluminous affinity, and high ferromagnesian element content, consistent with their derivation from a mafic source. Some of the HBG and ME samples are strongly enriched in incompatible elements, similar to the sanukitoids. The geochemical attributes and strongly evolved zircon Hf isotopic compositions (ɛHf(t) = −4.3 to +1.8 and − 7.3 to +0.2) of the HBG and ME suggest their derivation from a mantle source metasomatized by subducted sediments. The BTG and MG are compositionally similar, with high silica, low ferromagnesian element content, and moderate peraluminous affinity, suggesting the involvement of felsic crustal sources. The sub-chondritic to chondritic zircon Hf isotopic compositions (ɛHf(t) = −2.7 to +1.4 and − 6.9 to +1.9) of these granitoids support the involvement of heterogeneous ancient crustal sources. While all granitoids exhibit similar zircon Hf isotopic compositions, their geochemical attributes suggest distinct sources. The HBG reflects juvenile crustal additions, whereas BTG and MG are products of the crustal reworking. We propose that these granitoids formed during the continent-continent collision between Western and Eastern Dharwar cratons, that took place after the break-off of the eastward subducting slab. The asthenospheric upwelling induced by slab break-off and/or lithospheric delamination of thickened crust led to the genesis of metasomatized mantle derived magma, which drove the crustal reworking. The observed zircon Hf isotopic composition of the EDC granitoids are similar to the present day Phanerozoic Alpine-Himalayan type orogenies supporting subduction followed by continental collision model for the stabilisation of Archean cratons. Evidence for the existence of Paleo- Mesoarchean felsic crust from this area warrants further studies to test the three-terrane model for the Dharwar Craton.