Tectonic Regime Research Articles

Curie point depth from airborne magnetic data analysis for geothermal exploration in southern Thailand

Southern Thailand is a high heat flow region, which implies to high-potential area of geothermal resources. Direct heat flow measurements are only available from petroleum wells in Gulf of Thailand. Therefore, indirect method of Curie Point Depth (CPD) calculation has been used to evaluate the heat flow on land of southern Thailand. CPD is the theoretical depth at which subsurface temperature reaches the value of the Curie point of magnetite, which is 578 °C. CPD can be calculated by deriving the depth of the bottom of the magnetic body to the surface using spectral analysis from airborne magnetic data, and the calculated values can produce the CPD map of southern Thailand. The results show that CPD ranges from 7.88 to 19.75 km with an average of 13.74 km, and heat flow ranges from 61.54 to 154.25 mW/m2 with an average of 90.36 mW/m2. This study suggests that the high heat flow in southern Thailand, which is higher than the regular continental crust heat flow of 65 mW/m2, is possibly caused by a high heat anomaly from mantle upwelling and expressed through weak zones of faults and sutures in extensional tectonic regimes. The high heat from mantle has elevated by five zones: (1) Ranong faults zone, (2) Khlong Marui faults zone, (3) Coastline of Surat Thani and Nakhon Si Thammarat, (4) Trang and Satun zone, and (5) Bentong-Roab suture. These five zones are considered to be high-potential areas for future geothermal resources exploration.

Neoproterozoic Buchan-type metamorphism of the northwestern margin of the Yangtze Craton and tectonothermal implications

The tectono-metamorphic mechanism along the margins of the Yangtze Craton in the Neoproterozoic has been a controversy for a long time. The Micangshan terrane is located at the northwestern margin of the Yangtze Craton and is mainly composed of Neoproterozoic metamorphosed volcanic and sedimentary sequences. In this work, two representative garnet-bearing two-mica schist samples and two representative garnet-bearing biotite-plagioclase gneiss samples were performed detailed petrological and geochronological research. Three generations of mineral assemblages include the prograde (M1), peak (M2) and retrograde (M3) stages, respectively. Conventional geothermobarometry and phase equilibria modeling define the respective P–T conditions to be 2.0–3.0 kbar/596–686 °C for the M1, 2.6–4.8 kbar/632–693 °C for the M2 and 1.3–2.7 kbar/500–550 °C for the M3 stages and thus anticlockwise P–T paths were retrieved. The regional peak Buchan-type metamorphism with a higher geothermal gradient of ca. 40–75 °C/km was firstly identified in the northwestern margin of the Yangtze Craton. Secondary ion mass spectrometry (SIMS) U-Pb dating of magmatic zircon yielded the formation ages of the protolith of the rocks to be 838–863 Ma. SIMS U-Pb dating of metamorphic zircon and monazite LA-ICP-MS U-Pb dating yielded the metamorphic ages to be 820–794 Ma and 810–761 Ma, respectively, for the prograde (M1) to peak (M2) stage. Biotite 40Ar/39Ar dating yielded similar plateau ages and normal isochron ages of 750–745 Ma and are interpreted to represent the retrograde (M3) stage. Combined with previous studies, we propose that there was a transition of tectonic regime from compressional continental arc environment to extensional back-arc environment for the Micangshan terrane, which may be related to the southwards subduction of the South Qinling belt beneath the NW margin of the Yangtze Craton in the Neoproterozoic.

Variations of the effective elastic thickness evidence for a wide diffusive boundary between the North American and Eurasian plates in Siberia

Northeastern Eurasia is one of the least explored regions in the world. Very little geophysical data is available for this inaccessible area. Even the exact location of the plate boundary between Eurasia and North America remains a subject of ongoing debate. The effective elastic thickness (EET) of the lithosphere is a proxy for lithospheric strength and can provide insight into the thermal regime and tectonic processes. We have computed a high-resolution map of the EET for northeastern Eurasia using the fan wavelet coherence technique applied to the Bouguer gravity anomalies and topography/bathymetry data, appropriately adjusted to account for the influence of density variations within sediments. The results obtained provide insights into different tectonic regimes within this predominantly understudied region. In particular, we identify the boundary between the Eurasian and North American plates in Siberia as a rheologically weak diffusive zone extending from the Verkhoyansk and Sette-Daban Ranges to the eastern boundary of the Chersky Range. Unlike the Sette-Daban and Verkhoyansk Ranges, which were formed by plate collision and have an EET of 30–50 km, other mountainous regions have much lower EET values, usually less than 15 km. These areas have recently experienced tectonic activity that has weakened the lithosphere.

Petrogenesis and Tectonic Implications of the Qulihai Pluton in the Northern Margin of the Yili Block, NW China

Abstract Despite extensive research work that has been done, whether the northern margin of the Yili Block (YB) is still an active continental margin during the early Carboniferous period is still in debate. Herein, we conducted zircon U–Pb geochronology, geochemistry, and zircon Lu–Hf isotope studies on the Qulihai pluton in the northern margin of the YB to constrain the petrogenesis and dynamic process. The Qulihai pluton is a granitoid complex that is composed of quartz diorite, quartz monzonite, and syenogranite. The zircon U–Pb dating results revealed that the pluton was formed and emplaced between 346 and 342 Ma. The three different Qulihai pluton rock types had comparable εHf(t) values, ranging from +3 to +8. The corresponding two-stage model ages of 817–1182 Ma indicated their potential derivation from the Meso-Neoproterozoic juvenile crust. The Qulihai pluton typically features medium-to-high SiO2, K2O, and Al2O3 contents and low MgO and Fe2O3T contents. The quartz diorite and quartz monzonite samples had Mg# values of 43–47, indicating the input of mantle-derived melts in the source area. In contrast, the source region of syenogranite was purely crustal material. The Qulihai pluton is mainly characterized as strong metaluminous moderate-to-high-K cal-alkaline rocks of the I-type granite series, which are enriched in large-ion lithophile elements and depleted in high field strength elements while exhibiting active continental margin island arc magmatism. Our findings, combined with the comprehensive analysis of previous studies, suggest that the Qulihai pluton formation resulted from the subduction of the North Tianshan oceanic crust beneath the YB during the early Carboniferous period, contemporary with the tectonic regime transition from subduction advance to subduction retreat.

Basin provenance and its control on mineralisation within the Early Devonian Cobar Basin, western Lachlan Orogen, eastern Australia

The Cobar Basin, in central New South Wales, is an Early Devonian extensional basin that formed in the western Lachlan Orogen. The basin was filled with shallow- to deep-water sequences of the Cobar Supergroup and hosts small to large polymetallic deposits. Detrital zircon geochronology and whole-rock geochemical data collected from the Amphitheatre Group of the Cobar Supergroup provide constraints on the history of basin fill and illustrate the dynamic interplay between basin provenance and mineralisation, corresponding to the evolving tectonic regime. Data reveal provenance dissimilarity between the southern and northern parts of the basin. In the south, units of the Amphitheatre Group received abundant detritus from ca 430–410 Ma magmatic rocks situated to the southwest and southeast of the basin. By contrast, the northern successions were predominately sourced from recycled Ordovician basement found to the northwest, north, northeast of the basin, along with contributions associated with the Macquarie Arc. This spatial provenance variation, however, is less significant in the younger formations: the northern and southern sequences both exhibit an increase in older recycled detritus upwards with time. This reflects a progressive modification of basin paleogeography, during the transition from rift phase to sag phase. The rift-phase basin geography is characterised by fault-restricted deposition with predominant sediments derived from local proximal sources. The subsequent sag-phase subsidence exhibits a uniform depositional system with more homogenised basin input. This provenance variation is coeval with the stratigraphically controlled mineralisation features within the Amphitheatre Group successions, implying a provenance influence on mineralisation. Data suggest the different sediment source regions have produced distinct detrital mineral compositions between the major mineral-hosting and mineral-barren formations. The enrichment of some detrital minerals in the mineral-hosting units, such as feldspar, muscovite, Ti-minerals (and carbonate), is suggested to be an important factor for mineralisation in the basin.

Integrated assessment of global carbon capture, utilization, and storage projects

In recent decades, Carbon Capture, Utilization, and Storage (CCUS)/Carbon Capture and Storage (CCS) projects at commercial scale have been evaluated from economic, technical, and operational approaches. However, there is a lack of research comprising both the technical aspects and the geological properties. In this investigation, we have developed a full description of active commercial CCUS/CCS projects in terms of technical guidelines and geological properties of reservoirs and caprocks. In addition, we built letter-value plots and cross-plots for 43 pairs of reservoirs and caprocks used for CO₂ geological storage. Then, Principal Component Analysis (PCA) was performed to assess correlations among reservoir and caprock parameters and understand which parameters are more relevant. Thus, our findings suggested that peripheral foreland and post-rift sag basins may contain suitable carbon storage sites, with Carboniferous and Cretaceous as the prevalent reservoir ages. We also noted that reservoirs have mostly been deposited in transitional and marine environments, with shale representing the prevalent caprock lithology. From the multivariate analysis, caprock and reservoir ages, reservoir porosity, reservoir depth, reservoir lithology, and caprock porosity exhibited the highest parameter weight. To finish, an integrated model correlating all geological and petrophysical parameters with classifications based on reservoir depositional environment and basin tectonic sub-regime is presented. Thus, significant correlations regarding reservoir rock and caprock parameters and tectonic regimes were found, which may contribute to future assessments of carbon storage sites.

Arc magmatism associated with continental convergence in the SE segment of the UDMA, Iran: Insights from zircon geochronology and Hf–Sr–Nd–Fe isotopes

Magmatic suites provide the keys to evaluate the growth and reworking of continental crust. Late Cretaceous to Pleistocene convergence in the Urumieh–Dokhtar magmatic arc (UDMA) of Iran produced continental-arc magmatism that traces the transition from subduction to collision. The extent and origin of some magmatic segments in the SE UDMA remain poorly understood. The Oligocene (31 to 25 Ma) Jiroft plutonic rocks here investigated encompass the compositional spectrum from gabbro to granodiorite. Zircon εHf(t) (−1.3 to +8.1), whole rock εNd(t) (+0.8 to +3) and δ56Fe (0.07‰ to 0.16‰) are intermediate between values of depleted mantle and arc-related magmas, and indicate low degrees of oxidization of metasomatized mantle. Modelling indicates that the trace element patterns of Jiroft parental melts can be closely replicated by 4% partial melting (i.e., F = 4%) of a mantle source which was metasomatized by 2% of sediment melt. The parental melt fits well with a model pattern of ∼97% batch melt (i.e., 98% DM + 2% sediment at F = 4%) and contaminated with ∼3% upper crustal components. The 31–25 Ma magmas of the SE UDMA formed before the main collision event (< 20 Ma) between Arabia and Iran, in conjunction with changing tectonic regime from extensional to compressional. Compilation of the Cenozoic magmatic front (i.e., UDMA) and rear-arc (NE Iran and Alborz–Azerbaijan) data reveals variable degrees of crustal cannibalization during the flare-up episodes. We find that individual segments of the UDMA experienced different geodynamics conditions, further documenting the diachronous collision and correspondingly non-uniform crustal thickening across the UDMA.

Uplift rate calculation based on the comparison between marine terrace data and river profile analysis: A morphotectonic insight form the Ionian coastal belt of Basilicata, Italy

Geomorphological analyses of a wide coastal belt between northern Calabria and Puglia, where a well-exposed staircase of marine terraces extensively crops out, were performed in order to unravel the uplift history of this key-area. As a matter of fact, the Ionian coast of southern Italy represents a strategic sector for investigating the middle-late Quaternary morphotectonic evolution of the orogenic system of southern Italy.The main goal of our research was the reconstruction of a detailed uplift history using spatial distribution of marine terraces and river profile inversion. This was achieved by producing a new, detailed and complete map of the entire sequence of marine terraces and associated palaeoshorelines along the entire coastal sector. A critical review of the literature related to geochronological data from the study area, integrated with a modeling of the interaction between eustatic changes and tectonic uplift allowed demonstrating that the different terraces are correlated to many highstand peaks, dating the highest/oldest terrace to mid-Pleistocene times. Additional constraints on the spatio-temporal variation of tectonic uplift (or base-level fall) have been derived from the inversion of longitudinal river profiles. Such an approach adopts an independent geomorphic marker than the marine terraces and allowed us to obtain an additional estimation the uplift history of the area. The uplift values from the two methods differ in some cases by an order of magnitude, which could be attributed to the rigorous assumption of the river profile inversion or a limitation related to the chronological scheme of marine terraces.Our results highlight a spatial and temporal variation in the uplift rates, which can be only explained with a morphotectonic framework and likely the whole chain-foredeep-foreland system, remained under a prevailingly compressional tectonic regime during the Quaternary, with significant consequences for the seismic hazard of the region.

Deep-sourced CO2 emissions from the Eastern Himalaya Syntaxis and the Tengchong Volcanic Field, southeast Tibet

The India-Asia collision zone is believed to play a central role in Earth's geological carbon budget. The processes controlling soil CO2 flux and mechanism at this continental subduction zone margin remain however poorly constrained. Here, we focus on hydrothermal CO2 emissions from southeast Tibet, specifically from the Eastern Himalaya Syntaxis (EHS) and the Tengchong Volcanic Field (TVF), with the twin goals of informing models of carbon cycling and ascertaining the source of hydrothermal degassing systems. In-situ measurements of soil CO2 flux from the Aqiong, Caquka, Nongchaka, Rongduo, and Woka hydrothermal fields of the EHS yield average soil CO2 fluxes of 72, 5, 13, 66, and 10 g m−2 day−1, respectively. Regional heat flow, tectonic regimes, and CO2 content in the spring gas are plausible controlling factors for soil CO2 flux, which is crucial to quantifying total CO2 output in continental collision zones. The compositions and He-C-N isotopes of hydrothermal volatiles from two study regions are reported here as well. Analysis of the He-C-N isotopes in terms of distances to the Jiali fault and the nearest Holocene volcano confirms that the Jiali fault and Holocene volcanoes have a significant impact on discharging deep-sourced CO2 from the EHS and TVF hydrothermal systems to the surface. The 3He/4He values of EHS hydrothermal volatiles (92 to 98°E), combined with previous data (82 to 92°E), show a clear increasing trend from south to north. Thus, we propose an updated model of enriched mantle wedge source for the EHS hydrothermal volatiles, based on multi-component mixing calculations of the He-CO2 systematics. The EHS hydrothermal volatiles exhibit systematics spatial variations from the core location to the bilateral segments, suggesting the highest 3He/4He ratio and carbonate-rich characteristics at the core location possibly controlled by the asthenosphere upwelling caused by the deep fragmentation structure.

Review of temporal trend in Archean granitoid chemistry- implications for Eoarchean (3.7–3.9 Ga) transition in geodynamic regime of crust formation

In this study, we review changes in Archean granitoid chemistry using stacked probability density estimation and statistical change-point analyses. A significant change in Archean sodic granitoid composition occurs in the 3.9–3.75 Ga period, marked by a shift of SiO2, Al2O3, Na2O, V, Cr, Sr, Sr/Y to higher, and TiO2, FeOT, MnO, P2O5, A/NK, A/CNK, Sc, Ba, Ta, Nb, Hf, Y, and rare earth elements to lower values, which reflects different formation P-T regime and petrogenetic processes. Using phase equilibria and trace element modelling, we demonstrate that the pre-3.9 Ga Acasta Tonalite Gneiss (ATG)-like granitoids formed at shallow depths (∼3 km) but are chemically distinct from impactites of all known large impact craters with basaltic/mixed target rocks. Impact melting produces MgO-rich melts at relatively greater “apparent” depths, reflecting target rock chemistry and contribution from the upwelling mantle, and is unlikely to have produced the shallow-seated ATG rocks. The ATG trace element chemistry is similar to many modern-day non-arc settings felsic rocks, which suggests that the melting regime in these extensional settings also existed before 3.9 Ga and ATG formed in a mantle plume-driven extensional tectonic regime involving melting of long-lived mafic proto-crust at shallow crustal depths above mantle upwelling. In contrast, the 3.9–3.75 Ga transitional and post-3.75 Ga TTGs formed by deep-seated (25–50 km) melting in equilibrium with garnet-bearing amphibolite. When considered together with Ti isotopic evidence of shift from tholeiitic to calc-alkaline magmatism in the 4.0–3.75 Ga period, the evidence for a transition from a regime dominated by crustal reworking to one of significant juvenile input at 3.60–3.85 Ga, noted in trace element/Hf-isotope composition of detrital zircon from several cratons and the reported ultra-high pressure metamorphism/interleaving arc-plume sequence, require a greater depth of melting. We interpret this transition to mark a gradual shift from stagnant-lid to intermittent mobile-lid-type plate tectonics involving deeper subduction of oceanic lithosphere. However, from the single occurrence of pre-3.9 Ga ATG rocks and their similarity with some Archean Fe-rich silica-saturated rocks chemistry, it is unknown whether plume magmatism was the only active mechanism or operated in conjunction with mobile-lid tectonics on early Earth, like in Archean.

Crustal architecture of the Dharwar craton and Southern Granulite Terrane, Southern India, from the analysis of gravity-magnetic data

The potential field (gravity & magnetic) data, along with results of available seismic and magnetotelluric studies over the Southern India Shield comprising the Dharwar craton (DC), Southern Granulite Terrane (SGT) and southern part of the Eastern Granulite Mobile Belt (EGMB), were synthesized. The study attempts to elucidate the geometry and continuity of greenstone belts/shear zones, isostatic condition and deeper crustal architecture. We observed a characteristic elevation-gravity relationship for each of the tectonic domains. The greenstone belts of the DC are characterized by N-S to NW-SE trending positive residual gravity anomalies and continue beneath the Cuddapah sediments. The basement of the Cuddapah basin is characterized by NW-SE trending greenstone belts with low-density intrusive rocks. The gravity anomaly suggests occurrence of a high-density rock unit occurs at mid-crustal depth beneath the ‘Closepet granite’ and ‘Chitradurga schist belt’. The potential field signatures of the DC and SGT are distinctly different. The Cauvery Shear Zone is characterized by positive residual gravity and magnetic anomalies with ∼E-W to ENE-WSW trend that continues further east under sediment covers of the east coast. The residual gravity signatures and horizontal gravity gradient signatures suggest that the orogenic systems encompassing the Cauvery Shear Zone and the eastern part of the EGMB may be a part of a common structural belt or tectonic regime associated with the assembly of the Gondwana supercontinent. The potential field modelling reveals the presence of a thick, high-density material resting over the base of the crust in the entire stretch of the east-coast of India.

Seismotectonic Stress Regime and Airborne-Gravity Lineament Investigation of the Caribbean region and its Kinematic implications

The tectonic stress regime of the Caribbean region has been studied by stress tensor inversion analysis for the area bounded by Latitudes 17.32o to 23.79o N and Longitudes 81.47o to -60.56o E. A total of two hundred and twenty (220) fault plane solutions (FPS), made up of the seismic (earthquake) events that have occurred in the region of the study were found on the data catalog of the project website of the global centroid moment tensor, were employed in this study. To characterize the stress regimes of the region of study, the classification of the region based on the global moment tensor project is as follows: Cuba-zone, Haiti-zone, Dominican-republic, Monapassage, Puerto Rico, Virgin-Island and the Leeward Island. The gravity geophysical method revealed the presence of multiple or swarms of fractured lines within the same geographical range of study which might have developed over the years as a result of the interaction and coupling effect of the plate boundaries that have close proximity to the region of study. The seismicity pattern indicates that none of the provinces or countries located within the Caribbean region is devoid of large-magnitude earthquake occurrences capable of wreaking severe havoc on the immediate environment. Obviously, our stress tensor inversion result indicates two types of stress regimes namely compression and the strike-slip with different orientations. Cuba-zone, Haiti-zone, Dominican Republic, Monapassage, and Leeward Island are governed mainly by compression stress regimes. In contrast, the strike-slip stress regimes mainly govern the Puerto Rico and the Virgin Island.

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

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

A Tectonic Manifesto

AbstractTectonics is the scientific discipline that studies the relationship between planetary convection and surface deformation and magmatism. In recent years global tectonic regimes and planetary evolution have become foci of astronomical and planetological research dealing in particular with potential habitability of planets orbiting other stars in our galaxy (exoplanets). This broadens the scientific impact of “tectonics” and makes it useful to outline a few guiding principles. For many, the term “tectonics” is synonymous with Plate Tectonics on Earth, but it should not be limited to only the planet we know best. Specifically, the concept should be generalized to encompass other rocky planets and moons in our Solar System and exoplanets. This article summarizes 15 general concepts about how such bodies are expected to behave.

Metasomatized mantle sources for orogenic gold deposits hosted in high-grade metamorphic rocks: Evidence from Hg isotopes

Abstract Investigation of Hg isotope ratios of gold-related sulfides and penecontemporaneous mafic dikes from four orogenic gold provinces on the margins of the North China Craton and Yangtze Craton identifies three orogenic gold deposit (OGD) groups from different tectonic regimes. Ore-related sulfides of group 1 OGDs and mafic dikes from the craton margin reworked via oceanic subduction mostly have positive Δ199Hg values. The group 2 OGDs and mafic dikes from the margin that witnessed complex oceanic and continental subductions have mixed positive to negative Δ199Hg values. The group 3 OGDs on the margin that experienced continental subduction have dominantly negative Δ199Hg values. These isotopic differences indicate subduction histories have a first-order control on the distinct sources for the OGDs. It indicates that OGDs were derived from fluids from the mantle lithosphere metasomatized by contrasting subduction components, not from metamorphic fluids as is widely accepted. Group 1 OGDs and dikes were sourced from metasomatized mantle, which inherited the positive Δ199Hg of both recycled marine sediments and seawater during oceanic subduction, whereas group 3 with negative Δ199Hg was derived from mantle lithosphere metasomatized by subduction of mainly continental components. This genetic model identifies regions with high-grade metamorphic rocks above metasomatized mantle lithosphere as promising new OGD exploration targets.

A late Neoarchean continental arc system in the northeastern North China Craton: constrain from the Guanghua mélange in the Tonghua area, southern Jilin Province

ABSTRACT The late Neoarchean tonalite – trondhjemite – granodiorite (TTG) and mafic rocks record essential information regarding the early tectonic evolution of the North China Craton, which is crucial for understanding the onset and development of the plate tectonic regime. In this study, we present a comprehensive analysis of petrography, geochronology, and geochemistry of the Guanghua Mélange from the Tonghua area in NE China. The mélange comprises basalt, gabbro, pyroxene diorite, and trondhjemite, and is classified into three groups: basaltic – gabbroic rocks (Group #1), dioritic rocks (Group #2), and trondhjemites (Group #3). Zircon U-Pb analyses indicate that they formed at 2596–2550 Ma, 2531–2515 Ma, and 2502 Ma, respectively, with metamorphism occurring during ~ 2500–2450 Ma. Meanwhile, geochemical data indicate that the calc – alkaline basaltic rocks (Group #1) exhibit slight depletion of Nb or Ta with weakly negative Eu anomalies, suggesting derivation from the lithospheric mantle and formation within a continental arc environment. The pyroxene diorites (Group #2) display similar geochemical characteristics to Group #1, likely formed by partial melting of depleted mantle that underwent sgignificant metasomatism due to variable amounts of slab-derived fluids or melts. The tholeiitic granitoids (Group #3) exhibit strongly fractionated chondrite-normalized REE patterns with high (La/Yb)N and Sr contents, low Y contents, and depletion of Nb, Ta or Ti, resembling adakites generated in arc setting, indicating likely formation through partial melting of subducted oceanic crust. This process was controlled by the initial plate tectonics under a higher geothermal gradient. Consequently, when combined with previous findings, we conclude that an initial subduction of oceanic plate operated in the northeastern North China Craton during the late Neoarchean (>2.55 Ga). Subsequently, it transformed into modern-type plate tectonics during ~ 2.55–2.53 Ga, eventually followed by the continent-continent collision at ~ 2.50–2.45 Ga, resulting in the formation of the Ji – Liao – Ji (Jilin – Liaoning – Hebei) Collision Orogenic Belt.

Late Neoarchean and Paleoproterozoic tectonothermal and metamorphic evolution recorded in high-pressure granulites: Evidence from the Xuanhua Complex, northern North China Craton

Archean cratons usually underwent reworked processes during the late Paleoproterozoic orogeny, which may result in multiple tectonothermal records preserved in some high-grade metamorphic rocks; thus, these rocks provide a key opportunity on understanding the tectonic styles during different periods. In this study, we report new petrological, mineral chemical and geochronological data of a suite of newly discovered mafic and felsic metamorphic rocks in the Xuanhua Complex from the northern North China Craton (NCC), revealing the complex metamorphic thermal history and the transition of tectonic regime from the late Neoarchean to the late Paleoproterozoic. The mafic granulite preserves the prograde quartz and clinopyroxene inclusions within garnets (M1), and the peak stage (M2) is recorded by garnet, clinopyroxene, hornblende, plagioclase, quartz and ilmenite. The first retrograde (M3a) and final cooling stages (M3b) are defined by the appearance of orthopyroxene, and the amphibolite-facies overprinting, respectively. The felsic granulite records the similar peak mineral assemblage (M2), but has higher volumes of feldspar and quartz than the mafic granulite. The retrograde stage (M3) is represented by amphibolite-facies assemblage (hornblende ± biotite ± clinopyroxene) and fine-grained intergrowth of hornblende + plagioclase around garnet. Pseudosection modeling and thermobarometry results suggest that both high-pressure (HP) mafic and felsic granulites record clockwise P–T paths, including isothermal decompression and cooling from the peak stage (M2: 10.4–10.8 kbar/830–860 °C and 9.6–11.2 kbar/850–930 °C, respectively) to the retrograde stages (M3a and M3b: 7.5–8.0 kbar/840–870 °C and 7.8–8.2 kbar/650–700 °C, respectively; M3: 7.2–8.6 kbar/670–800 °C). Zircon U–Pb dating shows that the magmatic precursors of these rocks were emplaced at c. 2.5–2.47 Ga. The metamorphic zircons reveal two groups metamorphic ages of c. 2.51–2.45 Ga and c. 1.90–1.85 Ga. The c. 2.51–2.45 Ga ages indicate a late Neoarchean tectonothermal event, and the c. 1.95–1.85 Ga ages are interpreted to represent the Paleoproterozoic HP granulite-facies metamorphism overprinting. The highest positive εHf(t) value of 7.64 and 2.8–2.6 Ga Hf model ages of c. 2.5 Ga magmatic zircons indicate that the c. 2.5 Ga mantle-derived mafic magma and the c. 2.5 Ga partial melting of 2.8–2.6 Ga basaltic juvenile crust generated the protoliths of mafic and felsic granulites, respectively, revealing 2.8–2.6 Ga and 2.5 Ga crustal growth and c. 2.5 Ga crustal reworking in the northern NCC.To sum up, we consider that the late Neoarchean magmatism and coeval metamorphism recorded in our samples are probably resulted from the amalgamation of micro-blocks. The Paleoproterozoic clockwise P–T–t paths with near-isothermal decompression segments and low geothermal gradients (c. 21–26 °C/km) of HP mafic and felsic granulites indicate a rapid post-collisional exhumation process after the significantly crustal thickening, and this long-term orogeny along the TNCO (c. 1.95–1.85 Ga; > 100 Myr) is related to the incorporation of the NCC into the Columbia supercontinent.

O–Hf isotope ratios of Alvand S-type granite, western Iran, reveal crustal melting in an extensional regime

There are a few intrusive bodies in the central Sanandaj-Sirjan Zone (C-SaSZ), which is parallel to the Zagros suture zone, in western Iran. The Alvand batholith in the Hamedan area is one of these bodies and consists of rock types with large variation, in particular, two-mica garnet-bearing granite with an S-type signature. Zircon UPb dating gives crystallization ages of 170–163 Ma for the S-type granite. The 176Hf/177Hf ratios in the zircon grains vary from 0.282001 to 0.282780 (rim), with low 176Lu/177Hf ratios (0.002 to 0.018). The εHf(t) values (rim) are clustered into two main groups: a negative εHf(t) group (−6.9 to 0.0, n = 39), with some highly negative εHf(t) values (−25.8 to −21.9, n = 3), and slightly positive εHf(t) values (+0.3 to +2.9, n = 14) of inherited grains. The δ18O values for the zircon grains are positive and range from +10.4‰ to +11.8‰. The high δ18O (positive) and mostly negative εHf(t) values are more consistent with continental crustal sources for these rocks, and the Hf model ages (TDM2) show a wide range from 2.7 to 0.8 Ga, suggesting the heterogeneity of the crustal components. The long incubation time (2089 to 544 Ma) indicates a long history of crustal residence and crustal reworking. The incubation age of the zircon grains, >300 Ma, confirms the recycling of crustal material by partial melting. The simultaneous occurrence of S-type granites with mafic bodies, such as gabbro and diorite members with tholeiitic signatures, suggests that the injection of mafic magma increased the geothermal gradient from the bottom and sides along the major faults, which was the trajectory for the injection of hot mafic melts to shallow depths. These processes abnormally increased the geothermal gradients locally, and the partial melting of crustal and supracrustal materials produced S-type granites and migmatization among the hot blade-shaped mafic bodies. Therefore, the partial melting of crustal material in an extensional tectonic regime and/or in a thin continental crust occurred in a continental rift and/or in the Neo-Tethys passive margin. The present work concludes that the passive margin can be suggested as the tectonic setting for the generation of S-type granites, without the collisional regime that has been widely considered for the sources of this type of granite in the world.

Sulfide Pb-Zn mineralization in the Tianshuihai terrane, northwest Tibetan plateau: A case study of the Huoshaoyun Pb-Zn deposit

The Tianshuihai terrane, located in the northwest of the Tibetan plateau, is a newly known metallogenic district of Pb-Zn deposits in China, with a prospective resource of Pb and Zn over 30 Mt. Lead and Zn mineralization in the terrane comprises two types of non-sulfide and sulfide. However, the genesis of sulfide Pb-Zn mineralization and its relationship to regional geological evolution remain enigmatic. In this paper, a detailed mineralogical and geochemical study of the Huoshaoyun Pb-Zn deposit combine with a synthesized review of the evolution of the Tianshuihai terrane provide comprehensive constraints on the genesis of sulfide Pb-Zn mineralization and what geological events of which it may have been part. Economic orebodies in the Huoshaoyun deposit are hosted by a sequence of unmetamorphosed, flat-lying carbonate complex of Middle Jurassic age. Ore minerals consist predominantly of smithsonite and cerussite with variable sphalerite and galena. The sulfide minerals are texturally early and were replaced by non-sulfide minerals. Sulfur isotope compositions of galena are remarkably inhomogeneous, range from −18.52 to 25.40 ‰. Conversely, lead isotope compositions of galena display fairly uniform 206Pb/204Pb (18.485–18.785), 207Pb/204Pb (15.640–15.764), and 208Pb/204Pb (38.781–39.303) ratios. We thus propose that sulfide Pb-Zn mineralization in the Huoshaoyun deposit belongs to Mississippi Valley (MVT) - type. The metals were most probably sourced from the regional strata, e.g., the Permian Shenxianwan, Triassic Keleqinghe, and Jurassic Longshan formations. Sulfide Pb-Zn mineralization in the Tianshuihai terrane likely occurred sometime between the Oligocene to Early Miocene in a paleo-forland basin, coincided with the widespread potassic and ultra-potassic magmatic activities, a marked change in tectonic regime from compressional to extensional, an elevated heat flow in the Tibetan Plateau, and a great MVT-type Pb-Zn mineralization event in the Tethys tectonic domain. This study raises awareness about the presence of MVT-type Pb-Zn deposits in the Tianshuihai terrane and the great potential for Pb-Zn exploration in this region.

Mechanisms for generating elevated zircon δ18O in Archean crust: Insights from the Saglek-Hebron Complex, Canada

The Saglek-Hebron Complex (northern Labrador, Canada) is a polymetamorphic terrane preserving felsic crustal rocks as old as 3.87 Ga. Crustal rocks of this age are rare and offer opportunities to interrogate how Earth's earliest continent forming processes may have differed from the modern plate tectonic regime. Oxygen isotope ratios (δ18O) in primary crystalline zircon are strongly affected by the incorporation of supracrustal materials during magmatism and can provide useful information about the character of early crustal reworking events. While zircon δ18O signatures >+6.4 ‰ indicate the incorporation of supracrustal material into the source of crustal anatexis, questions remain regarding the volumetric scale, sources, and processes by which supracrustal and magmatic mixing occurred during the Archean. Here, we present 271 zircon in-situ oxygen isotope analyses for a suite of seven Saglek-Hebron granitoids emplaced between 3.87 and 2.79 Ga in age, significantly expanding the temporal and lithologic diversity of the magmatic SHC zircon δ18O record. Collected from carefully characterized grain domains, primary zircon δ18O values range from 5.0 to 8.4 ‰ and include some of the highest igneous Archean zircon oxygen isotope ratios recorded to date. Leveraging an integrated workflow for identifying preserved zircon geochemistry, and correlating our new data with previous information from zircon Hf and whole-rock 142Nd/144Nd isotopes, we identify three periods of contribution from high-δ18O supracrustal material to crustal melts during reworking events in the SHC at 3.63, 3.33, and 2.79 Ga. Our work points towards repeated episodes of interaction between a maturing surface environment and magmatism from 3.6 Ga onwards at this locality.