Ichnological studies in deep-marine successions are of great use for detailing the evolution of these sedimentary environments, as well as highlighting the changes in ambient conditions. In order to investigate these aspects, the deep-marine Maghrebian Flysch Basin of Northern Morocco was chosen for study. Within this basin, two sedimentary successions – the Beni Ider and Tala Lakrah units, comprising calcareous and siliciclastic turbidite sediments and ranging in age from Late Cretaceous to Early Miocene, were examined in detail. An ichnoassemblage (31 ichnogenera, 41 ichnospecies), including 9 graphoglyptid ichnogenera, was recognised, with the ichnoassemblages belonging to the Nereites ichnofacies. Pre- and post-depositional ichnofossils were present in equal amounts, with ichnodiversity being higher in Eocene times.

Comparison and correlation of the ichnological data from Morocco (this study) with data from Spain indicated that the main influences on trace fossil distribution within the successions were broadly similar. Environmental factors, such as substrate, oxygen and nutrient contents, as well as the ambient hydrodynamic regime and the frequency and intensity of turbiditic events, all played an important role. However, the relative importance of these factors varied both spatially as well as temporally within the different parts of the Maghrebian Flysch Basin. Temporal variations were related both to changes in (orogenically-influenced) basin and lobe evolution, as well as changes in global oceanographic and climatic conditions at the Eocene–Oligocene transition.

The present study documents the lithostratigraphy, biostratigraphy, facies evolution and depositional environments of the Eocene El Kohol Formation exposed on the southern flank of the Central Saharan Atlas (Algeria), through the integration of lithological characteristics, fossil and ichnofossil assemblages, and microfacies analysis. The succession is subdivided into two formal members: the Marly El Kohol Member, comprising a lower marlstone-dominated interval, and the Siliciclastic Kheneg ed Dis Member, representing an upper sandstone-dominated succession. The boundary between these members is marked by a transition from pale, carbonate-rich deposits to darker clastic sediments.

Field observations and microscopic analyses have enabled the recognition of sixteen facies types (Ft1–Ft16), which are interpreted in terms of depositional environment and grouped into four main facies associations (FA1–FA4): (FA1) an inland lake environment; (FA2) a palustrine environment, characterized by carbonate deposition in freshwater to brackish conditions with subaerial exposure and paedogenic modification; and alluvial settings comprising (FA3) fluvial channel and (FA4) floodplain deposits.

Palaeontological analyses have produced new micropalaeontological data for the region, including charophytes (Sphaerochara parvula, Nodosochara [Turbochara] sp., Gyrogona sp., Harrisichara cf. leptocera, Lamprothamnium papulosum, Peckichara torulosa var. varians, Raskyella cf. sahariana and Nitellopsis cf. [Tectochara] dutempleii), ostracods (Neocyprideis meguerchiensis, Paracypris? sp. 1, Paracypris? sp. 2 and Thalassocypria? sp. 1) and actinopterygian fish microremains (primarily from polypterids and alestids). Additionally, fragmentary remains of the terrestrial proboscidean Numidotherium koholense have been recovered. Ichnological analysis of the succession identified five ichnotaxa: Ophiomorpha isp., Palaeophycus isp., Skolithos annulatus, Skolithos linearis and Thalassinoides horizontalis.

This study contributes to refining the regional and North African understanding of the spatial extent and palaeoenvironmental evolution of the Eocene succession and helps to complete the ichnological and palaeontological records of the Eocene in the area.

We present the mineralogy and whole rock geochemistry of the lamproites dykes from the Kawardha area of the Western Bastar Craton. These dykes are characterized by phenocrysts and microphenocrysts of olivine, phlogopite, ulvo-spinel, Cr-spinel and magnetite within the chlorite and carbonate-rich groundmass with rutile and apatite as accessory phases. Mineral chemistry indicates that the lamproites in Kawardha are similar to olivine-phlogopite lamproites and are geochemically similar to other lamproites in the eastern Bastar craton. The Kawardha lamproites are characterized by higher concentrations of MgO (12–20.29 wt%), V (193–502 ppm), Ni (206–823 ppm), Cr (146–1130 ppm), Nb (101–260 ppm), Zr (301–635 ppm), Hf (6–13 ppm) and LREEs. Positive Nb-Ta anomalies and Th, Hf and Zr variations are comparable to other intra-cratonic rift-related lamproites. The geochemical variations (such as REE, HFSE and LILE) are consistent with an asthenospheric mantle source similar to the other lamproites in Bastar craton. Trace element modelling implies a low-degree partial melting (0.1–2%) of phlogopite-bearing garnet-lherzolite and/or phlogopite-bearing spinel-lherzolite mantle source. The widespread Proterozoic rifting events in the Bastar craton likely led to the melting and upwelling of the asthenospheric mantle and which further interacted with the metasomatized lithospheric mantle to form the parental melts of the lamproite dykes of the Kawardha area.

The Deerni copper deposit is one of the largest in Qinghai province, China, with proven copper reserves of 0.556 Mt. To explore new copper orebodies, we conducted a geological study at western Deerni focusing on hydrothermal alterations and ore-controlling structures. Field investigation shows that the deposit is hosted mainly within the central segment of the Deerni ophiolite. Additional hosts include Lower-Permian slate, limestone, gabbro and volcanic rock, as well as the contact zone between granite and slate. Such observations indicate that the Deerni copper deposit is not only associated with the ophiolite, but its formation is also controlled by faults. Alterations including serpentinization, carbonatization, silicification and malachite, and magnetite mineralization occurred along fractures within the wall rocks and surrounding strata. This means the alteration post-dated structural activity that affected the Lower Permian strata in the region. The Deerni copper deposit is controlled by the NW-striking faults. This is evidenced by (1) slate fragments and breccias within the orebodies, (2) saw-toothed boundaries between the orebodies and host rocks, (3) copper ore veinlets and (4) striations and step patterns on the orebody surface and hanging-wall-hosted quartz veins. Mineralization controlled by NW-trending faults suggests a major orebody (‘No. 2’) likely extends to either northwest or southeast. Field investigations along with geophysical and geochemical data, thus predicted the presence of concealed copper orebodies in western Deerni. Subsequent drilling projects have verified this prediction and revealed three concealed orebodies with widths of 7.15–13.87 m and Cu grade of 1.00–11.34 wt.%, adding 10,000 tonnes to the copper reserves.

The Guanajuato Mining District of central Mexico is one of the main silver and gold deposits in the world. It is in the State of Guanajuato in the southern part of the Sierra Madre Occidental (SMO) volcanic province. The mining district developed within a mid-Tertiary volcano-sedimentary sequence that includes thick alluvial-fan deposits accumulated in a tectonic basin during the Eocene-Oligocene named the Guanajuato Red Conglomerate and an overlying volcanic sequence mostly pyroclastic of Oligocene age. The mid-Tertiary stratigraphy of Guanajuato is revised and reinterpreted in the light of new fieldwork and U-Pb ages, which document a close timing between all units of the volcanic succession at the top of the Guanajuato Red Conglomerate. This sequence is made of pyroclastic density current deposits formed during episodic events from the Guanajuato caldera. A new nomenclature of the caldera’s units is proposed; the Guanajuato Caldera Volcanic Group, which includes the Guanajuato Pyroclastic Formation represented by the Loseros PDC deposits and the Bufa-Calderones ignimbrites emplaced around 32.8 ± 0.2 Ma, and the post-collapse lava domes of El Rodeo and Chichíndaro formations emplaced at 31–30 Ma. Apparently, a resurgent pulse of the caldera uplifted the collapsed intra-caldera blocks, so that the caldera floor is now exposed. The caldera collapse was controlled by the pre-existing normal faults inherited from the previous tectonic basin; thus, it is classified as a graben-type caldera, with a square shape and a size of 15 × 16 km. By comparison with other similar calderas of Mexico, the Guanajuato caldera is another case study of graben-type calderas of the SMO coinciding with mineral districts, such as Bolaños (Jalisco).

The first precise, biostratigraphically bracketed U-Pb dates on the middle Middle Cambrian come from the Rte. 111 ash (new) in the lower Manuels River Formation of southern New Brunswick. Manuels River black mudstone (Avalonian depositional sequence [Ads] 8) unconformably overlies Fossil Brook Member greenish mudstone (Ads 7) of the Chamberlain’s Brook Formation, and the two units should not be combined into a ‘Forest Hills Formation’ (abandoned). This unconformity marks the trans-Avalonian (i.e., Rhode Island–Belgium) green–black boundary and onset of ca. 26 Ma of dysoxic/anoxic marine deposition. Trilobites and agnostids correlate the surprisingly endemic, upper Paradoxides abenacus Zone and Rte. 111 ash into the Hypagnostus parvifrons Zone (Drumian) in Avalonian Wales, Baltic upper ‘Acidusus’ atavus Zone and upper Mawddachites hicksii–lower Paradoxides davidis zones of Avalonian Newfoundland and Britain. The Manuels River Formation in SE Newfoundland and coeval Nant-y-big Formation in South Wales have not yielded ash dates. However, our U-Pb zircon analyses of the Rte. 111 ash in the lower Manuels River in southern New Brunswick yield statistically identical ages of 501.44 ± 0.10 and 501.45 ± 0.08 Ma. The Ads 7–8 unconformity is locally 6–10 m lower in New Brunswick and is somewhat older. Our ages for the Rte. 111 ash show the lower Drumian is significantly younger than previous estimates, is ca. 4.9 Ma younger than the Lower–Middle Cambrian boundary, and debunks claims of a continuous Lower–Middle Cambrian succession in Avalonian New Brunswick where a ca. 7 Ma hiatus is present.

Magnetostratigraphy, palynology and ammonite biochronology of the Staithes S-20 core are used in an integrated evaluation of the late Norian to early Hettangian successions in Britain. The polarity patterns of the Blue Anchor and Westbury formations differ from their counterparts in SW England, indicating younger and older ages, respectively, for those units in NE England. Magnetostratigraphy indicates an underlying Sevatian age hiatus coeval with the D5 disconformity of the German Keuper. The miospore succession from S-20 is divisible into zones like those from the St Audrie’s Bay section in SW England. Using magnetic susceptibility datasets for the earliest Hettangian chronozones from S-20, Lavernock, St Audrie’s Bay and Lyme Regis, a new method is used to derive a TimeOpt-based astrochronology for the earliest Hettangian. This is anchored to radioisotopic dates from Peru correlated into British sections using carbon isotope excursions. A brief reverse magnetozone in the basal Cotham Member in the Staithes S-20 core and the astrochronological evaluation demonstrate that CAMP volcanics are coeval with the end-Triassic extinction in UK sections. An eco-plant model assessment of the miospores indicates greater proportions of eurythermic and europhyte floras, suggesting stronger seasonality in palaeoclimate was probably a key factor in the end-Triassic extinction.

This study examines detrital garnet compositions from five samples spanning a Late Miocene–Pliocene section of Himalayan sedimentary rocks (Surai Khola, Siwalik Group and central Nepal) to assess provenance and tectonic implications. A total of 100 detrital garnets were analysed for edge-to-edge compositional zoning, revealing distinct groups linked to specific hinterland regions. Manual classification identified garnet Groups 1 and 2 as grossular, Group 3 as spessartine, and Groups 4 through 7 as almandine, varying in XCa, XMg and XMn. Most garnets exhibit low XMg and flat zoning, with Groups 6* and 7* containing slightly higher XMg. Statistical clustering aligns broadly with manual groupings, which strengthens provenance interpretations. Comparisons with hinterland garnet compositions expand provenance options to magmatic garnets and rocks outside the Himalayan core units. Eight Siwalik Group garnets were modelled for pressure–temperature conditions and paths. Group 4 and 6 garnets, potentially linked to blueschist/eclogites or metamorphosed arc/Himalayan core rocks, record conditions of 510–538°C and 4.6–6.8 kbar, with isothermal burial over 0.5–2 kbar. Group 2 garnet, resembling compositions from North Himalayan granitic enclaves, yields core conditions of 480°C and 6 kbar and an N-shaped pressure–temperature path. Two Group 5 garnets with zoning like those in the High Himalayan leucogranites yield 520–528°C at 3.2–3.6 kbar. These findings provide insights into Himalayan erosion dynamics, hinterland exhumation and sediment transport pathways. Integrating garnet compositional zoning with statistical clustering and thermodynamic modelling is valuable for provenance studies of garnet-bearing sedimentary sections.

The limestone and marlstone succession of the Pliensbachian Vale das Fontes and Lemede formations at the Global Boundary Stratotype Section and Point (GSSP) at Peniche (Portugal) received much attention in numerous studies. It contains abundant pyritic and limonitic aggregates, which are herein described and interpreted as remarkably preserved soft-bodied organisms (worms) for the first time. The slender to compact bodies with a cylindrical or dorsoventrally flattened cross-section are several centimetres long and have a diametre/width of 0.5–8 mm. They occur on bedding planes or are partly preserved within their burrows. Although their taphonomic history did not favour the preservation of many details, key features such as body shape, size and composition, as well as occasionally preserved segmentation and body appendages, allow a rough assignment to the phyla Nemertea, Annelida and Nematoda. Favourable circumstances such as intermittent dysoxic to anoxic bottom conditions, microbial activity and sudden burial have probably contributed to a reduced decay of the soft bodies. Comparison with similar successions globally shows that such a preservation of worms is not a unique process but occurs in several thick, fine-grained units throughout the Phanerozoic. Such inadequately preserved soft-bodied animals are still often overlooked but have the potential to add to our knowledge of the distribution and evolution of major clades of non-skeletal organisms.

A new species of flatfish (Pleuronectiformes) is described from early Oligocene deposits of the Keasey Formation near Mist, Oregon, USA. The rare preservation of an articulated fish in the Mist crinoid lagerstätte is likely because the specimen represents a relatively pelagic immature individual that had not yet settled into the typical benthic lifestyle of adult flatfishes. The new species is included in a phylogenetic analysis; although it is lacking many characters, it is recovered as an early diverging lineage, sister to the extant members of the superfamily Pleuronectoidea. This phylogenetic position fits well with the age of this fossil and conforms with the origin of flatfishes occurring in the early Cenozoic, followed by diversification and radiation throughout the Eocene, Oligocene and Miocene epochs.

The Central Indian Tectonic Zone (CITZ) formed during the Mesoproterozoic north-south collision between the Bundelkhand and Bastar Cratons. The origin of the deformation of the Late-Paleoproterozoic Lower Vindhyan Group (LVG), which occurs in the sedimentary basin adjacent to and north of the CITZ, is debated, with previous researchers supporting synsedimentary processes. To investigate the possibility of a collisional origin, we collected and analysed litho-structural data from the LVG and the Mid-Paleoproterozoic Mahakoshal Supracrustal belt (MSB), which lies within the CITZ. We report, for the first time, diverse structures from the LVG, such as various types of buckle folds including kink-folds, reverse faults and, most importantly, 5–20 meters long outcrops of pop-up structures, which are commonly encountered in fold-thrust belts. However, the adjacent MSB showes relatively complex polyphase deformation with three major deformation stages that produced: (i) E-W-trending regional foliation and diversely oriented folds (D1), (ii) E-W oriented steep folds associated with a large-scale shear zone along the Son-Narmada South Fault (D2) and (iii) local cross-folds (D3). Based on our field observations in the LVG and the MSB, we additionally propose and substantiate, through geological cross-sections and a kinematic model, that the LVG deformed between the D3 and the deposition of the Upper Vindhyan Group. Unlike previous studies, which attributed the deformation structures of the LVG to seismic or soft-sediment processes, our findings confirm that the Mesoproterozoic collision along the CITZ deformed the LVG as the deformation front, aided by detachment folding, propagated into it.

The Eastern Ghats Belt (EGB) has been extensively studied by the geoscientific community; however, this communication reports unique mineral assemblages that have not been documented previously. This study documents the occurrence of sapphirine, spinel, orthopyroxene, sodic-gedrite, calcic-amphibole, biotite and plagioclase assemblage indicating in ultrahigh temperature (UHT) metamorphic conditions. The significance of this study lies in the peculiarity of sapphirine being present within anorthite matrix which has been reported for the first time from the Indian subcontinent. The studied assemblage has been correlated with the more or less similar assemblage of rock called ‘Sakenites’ reported from southern Madagascar to correlate the most probable source rock ‘anorthosites’ that underwent metamorphic transformations and led to the unique UHT mineral assemblage. The Na-rich gedrite identified within the assemblage represents a relict mineral indicative of high-grade amphibolite-facies metamorphism. The derived pressure–temperature (P-T) trajectory reveals a decompression path with almost uniformly decreasing P-T conditions in contrast to the commonly reported isothermal decompression (ITD) path from various other domains and provinces of the EGB. The corresponding retrograde assemblage has been recalibrated by the sequential removal of sapphirine and corroborated with T-X (H2O) constraints.

The analyzed EMP U-Th-Pb monazite chemical age constraints suggest mesoproterozoic to neoproterozoic episodes corresponding to a pair of ∼959 Ma and ∼846 Ma thermal events. These metamorphic events have been correlated to reconstructing the Rodinian supercontinent at ∼959 Ma and the initiation of its subsequent break-up at ∼846 Ma.

The Lower Jurassic (Toarcian) Posidonienschiefer Formation of southwestern Germany is a classic konservat lagerstätte, yielding some of the world’s best-preserved fossils of marine vertebrates, including ichthyosaurs, thalattosuchian crocodylomorphs, plesiosaurs and fishes. Despite numerous studies concentrating on the taphonomy of ichthyosaurs in this formation, less taphonomic work has focussed on the thalattosuchians of the assemblage. Multiple thalattosuchian species displaying a wide range of body sizes have been recovered. We investigated indicators for seafloor arrival position in thirteen Macrospondylus bollensis and one Platysuchus multiscrobiculatus specimens representing various body sizes using three-dimensional (3D) photogrammetric models. False-colour depth maps were used to interpret the relative topography (depth level) of bone penetration into the sediment and were aligned on the XY plane, making them parallel to the stratigraphic plane. Our results show both headfirst and non-headfirst seafloor arrivals in observed specimens, with headfirst seafloor arrivals exhibiting deeply buried skulls, displacement of select cervical vertebrae and/or characteristic fractures in the cranium and mandible. We (1) interpret seafloor landing types in teleosauroids; (2) recognize and list specific characteristics that are consistently attributed to either a headfirst or non-headfirst seafloor arrival; (3) discuss possible factors that may have contributed to these features, such as body shape and size, substrate and velocity; and (4) provide a new definition for headfirst seafloor arrival that can be readily attributed to other marine vertebrates from various formations. Lastly, our results show that observers must carefully consider how historical specimens might have been prepared, as this may influence taphonomic interpretations.

Dating the shear zone activity remains challenging and depends on geochronometer reactivity. We investigate the Forno-Rosarolo Shear Zone (Ivrea-Verbano Zone, Italy), developed in the intermediate-low continental crust under amphibolite-facies conditions. Sheared paragneisses and calc-silicates were dated using in situ U–(Th–)Pb monazite and titanite geochronology. Three monazite generations (MNZI-III) were identified based on microstructural position, internal features, chemical zoning (Th, Y) and isotopic data. Deformation was mainly recorded by MNZII, with high-Y domains yielding Triassic dates (average ages of: 238±8 and 222±8 Ma). Rare, highly fractured or porous MNZIII grains provided younger dates (202±8 to 184±6 Ma). MNZI, abundant in protomylonites, retains regional metamorphism, linking monazite U–Th–Pb data to fabric evolution. Titanite shows different zoning features and chemistry as a function of the surrounding mineral assemblage: (i) strongly zoned grains are mostly associated with silicate-rich layers; (ii) homogeneous grains are generally within the silicate-poor layers. Both types show a decoupling between chemistry, almost completely related to the peak metamorphism, and U–Pb isotopes. Deformation microstructures promoted a total reset of the U–Pb dataset at the beginning of deformation and a subsequent volume diffusion through the grains: the innermost domains of both titanite types provide a Triassic lower intercept age (240±5 Ma) while the rims/tips, locally coinciding with high strained portions, define an alignment of isotopic data with a Jurassic lower intercept age (186±6 Ma). This study highlights how combining monazite and titanite geochronology refines the timing and duration of deformation, particularly in large-scale shear zones involving different lithologies.

The Iberian Pyrite Belt contains one of the largest accumulations of massive sulphide deposits on Earth. Many of these deposits are hosted by latest Devonian black shales rich in terrestrial and marine palynomorphs. Among the marine fossils, the most abundantly reported species is Maranhites mosesii. By means of a multi-analytical methodology, including (1) biometry of specimens, (2) TOFSIMS imaging and spectral analysis of selected specimens and (3) host-rock geochemistry, we detected that cysts of M. mosesii are smaller and lighter in massive sulphide-generating environments than in coeval non-massive sulphide-generating environment. Cysts of M. mosesii sank after encystment and maturated in the seafloor of different subbasins affected by disparate anoxic conditions. The specimens that maturated in anoxic settings enriched in pollutants, like Arsenic (As) and Lead (Pb), were smaller and lighter than those from non-polluted anoxic environments. Their organic walls were also enriched in As. Neither the anoxia nor the pollutants prevented the proliferation of M. mosesii, as this was the most abundant phytoplanktonic species in all environments. To explain this, we suggest that this species developed a successful adaptive mechanism that might involve anaerobic metabolic interchange with the surrounding oxygen-depleted media and high levels of tolerance to stressors. Whatever the reason, it entails a causal relationship between cyst size and seafloor environmental conditions. In consequence, the biometry of M. mosesii can be envisaged as a promising vector for sulphide deposit exploration in the Iberian Pyrite Belt.

Nd-Hf isotope evolution in arc magmas has been widely used to trace the advance and retreat of subduction zones over time. However, the reliability of this method has been questioned. One way to assess its validity is by comparing it with LaN/YbN or Sr/Yb ratios, which are well-established proxies for crustal thickness. In this study, we present new Nd-Hf isotopic data from the Permian to Triassic Hangay Batholith in the western Mongol-Okhotsk Orogen (Hangay Mountains), to evaluate the role of Nd-Hf isotopes in tracing crustal thickness variations along convergent plate boundaries. Our results show that granitoids from the Hangay Batholith likely originated from partial melting of crustal materials, with a possible mantle contribution. These granitoids have moderate εNd(t) and εHf(t) values, with no significant shift from Permian to Triassic, which contrasts with the continuous crustal thickening indicated by LaN/YbN ratios. This inconsistency between Nd-Hf isotope evolution and crustal thickness variation is likely due to the heterogeneous crustal architecture in this accretionary orogen. Our findings highlight the need for caution when linking Hf and Nd isotope evolution with extensional and contractional tectonics.

A previous study of the altitudes of the lowest part of the Upper Cretaceous–Eocene stratigraphic ensemble evidenced for the first time the existence of an east-west elongated dome between N53° and N54° Lat. on the western slope of the Southern Urals. This ridge which is superimposed on the remnants of the Sernovodsk–Abdullino Aulacogen and with the Belaya tear fault was the result of the rejuvenation of these deep basement features; it has been interpreted as a positive flower structure. Slightly to the north, the Southern Urals display a clear bend towards the East. In front of it, detailed microstructural studies show that this curvature was associated with a stress pattern typical of an indentation. Field studies concentrating on the intersection between the flower structure and the Belaya River Valley show (1) that there are two riverbeds more or less superimposed in the same valley, (2) that the older watercourse is offset by small east-west shear zones, (3) that the shear zones are in continuity with the flower structure and (4) that the recent riverbed is not affected by similar offsets. The vertical movements recorded along the Belaya River by geodetic measurements don’t support the existence of a recent activity of the indenter because they are always of a limited extent and associated with karst collapses. This conclusion is supported by the stratigraphic evolution of the fluvial sediments and confirms that the indentation of the Southern Urals did not continue after 10 ka.

Advances in analytical instrumentation over the past decade have facilitated the development of new geochronological methods. In particular, the triple quadrupole inductively coupled plasma mass spectrometers with in-line reaction cells have made it possible to investigate beta decay geochronological systems, including Lu-Hf in garnet, in situ via laser ablation. While these new methods allow different kinds of studies to be carried out, their utility relative to well-established methods has not been investigated in detail. Herein we present the results of in situ garnet Lu-Hf and monazite U(-Th)-Pb geochronological analyses of two adjacent Archean meta-pelitic rocks from the Northwest Territories, Canada. Whereas the garnet Lu-Hf analyses define single population isochrons of ca. 2570 Ma, monazite U(-Th)-Pb analyses define two chemically distinct populations. An older ca. 2570 Ma monazite population has low Y concentrations, while a younger, ca. 2530 Ma monazite population has high Y concentrations. The change in Y concentrations in the monazite is consistent with coeveal growth with garnet during prograde metamorphism whereas the younger high Y monazite is interpreted to reflect growth during garnet breakdown during decompression. The results presented herein demonstrate that incorporating both in situ garnet and monazite geochronological data takes advantage of each method (i.e. the spatial precision, variable (re)crystalization under different conditions, and the ability to determine a date without relying on an isochron for monazite U-Pb, and the ability to date a primary metamorphic phase for garnet Lu-Hf) to build a more robust geochronological history.

We present a study of the Gyangarh and Anjana granitoids in the Aravalli Craton, northwestern India, with new data on their whole-rock geochemistry, U-Pb zircon and U-Th-total Pb monazite geochronology and structures and microstructures. These granitoids are monzogranites with metaluminous and calc-alkalic geochemical characters. They show negative Eu anomalies with depletions in Sr and Ti, indicating fractionation of plagioclase and Fe-Ti oxides from their parental magmas. U-Pb zircon dating of granitoids yielded crystallization ages of 1776 ± 35 Ma to 1709 ± 29 Ma, indicating that the plutons were emplaced during the late stages of the Aravalli orogeny. These plutons have been variably deformed and show shallow- to moderately dipping mylonitic foliations (<40°) with shallow (<30°) NW- to NE-plunging stretching lineations (SL1). The pole distribution of the mylonitic foliation (S1) and lineation (SL1) data indicates that the gentle mylonitic foliations have been overprinted by steep (>65°), NE-SW-striking S2 mylonitic foliations. The kinematic indicators suggest that the D1 and D2 deformations were associated with dextral-normal and sinistral-reverse senses of shearing, respectively. Monazite dating of texturally constrained grains shows that the pluton experienced intense mylonitization (D1-S1; 1653 ± 30 Ma) during the waning stages of the Aravalli orogeny. Later, these plutons experienced a second episode of mylonitization (933 ± 11 Ma to 897 ± 9 Ma) due to sinistral-reverse shearing (D2-S2) during the late stages of the Delhi orogeny. These new results show that the Gyangarh and Anjana plutons record signatures of two major orogenies that have shaped the Sandmata Complex (Aravalli Craton) in the Palaeoproterozoic.

The Imalia polyphase polymetallic deposit, located in the Mahakoshal belt of Central India, is hosted by carbonate rocks. The major part of mineralisation at Imalia results from hydrothermal activity induced by the intrusion of quartz porphyry dykes, which also formed an alteration halo of silicate and oxide minerals during their interaction with the host lithology. The initial silicates to form were hydrothermal Ca-amphibole and a minor amount of garnet, followed by potassic phases including biotite and K-feldspar, as well as rutile, apatite, titanite, pyrite, magnetite and rare calcite and ilmenite. A subsequent, cooler pulse of hydrothermal fluid overprinted the earlier-formed silicates and was responsible for the bulk of the sulphide mineralisation at Imalia. During this transformation phase, propylitic silicates primarily consisting of chlorite and epidote, along with a modest proportion of actinolite, albite, titanite, sericite and calcite, formed, accompanied by iron-rich oxide phases including magnetite, hematite and ilmenite. These silicates mostly formed under high water-to-rock ratios with significant meteoric water influence. Geothermometric and fluid inclusion data indicate that alteration zone minerals formed at temperatures between approximately 150°C and 550°C, at pressures of around 1 kbar and depths of less than 10 km, with a mean oxygen fugacity of log fO2 -32, closely aligned with the FMQ buffer. The alteration zone minerals record the evolution of hydrothermal fluids in a predominantly brittle structural regime, characterised by episodic decompression due to fluid overpressuring and hydrofracturing, as evidenced by various types of breccias, diverse quartz veins, open space-filling textures and fluid inclusion data.