Granitic Bodies Research Articles

Granite rock towers shaped by mesh‐like joint sets, which formed in the shallower portion of a granite body during cooling at depth

AbstractGranite is fractured according to the stress state during the cooling stage, providing predispositions for later topographic evolution. This study clarified that triangular mesh‐like joints can be made during granite cooling and that they can become the structural causes for the formation of rock towers and corestones on the ground. Tengu rock, which consists of rock towers and granite corestones in Hiroshima, was investigated using an unmanned air vehicle. The rock towers were shaped by high‐angle mesh‐like joints, which were likely made during the cooling of the granite and are dominated by three joint sets. All the joint sets have sharp planar surfaces, which suggests that they are brittle fractures. One joint set is cut by the other two joint sets, frequently accompanies aplite and quartz veins and is developed in the whole exposed granite; this set likely formed first during cooling and then was penetrated by aplite from depth. The other two joint sets are high‐angle conjugate joint sets, are limited to the shallower portion of the granite pluton and do not extend deeper, which strongly suggests that they formed in a rapidly cooled shallower portion of the pluton, probably near its roof. These three joint sets form rock columns with parallelogram cross‐sections, in which incipient corestones were made. Subsurface weathering along the joints and subsequent exhumation of the weathering products formed the present rock towers and corestones only in the shallower portion of the granite.

Geochemical Studies of Rare Earth Elements (REE) in Ion Adsorption Clays (IAC) in Gua Musang, Kelantan

Rare earth element (REE) become the ‘critical metals’ for green technology development that have been rapidly expanded worldwide in these days. REE is mainly originated from granitic rocks. REE in ion adsorption clay (IAC) is the product from weathering of granite. IAC are believed to store high concentration of heavy rare earth element (HREE) and light rare earth element (LREE). Gua Musang is selected for this study because it is located on the three longitudinal belts that composed of acid volcanic igneous rocks from Main Range, Senting and Boundary Range Granites. In this study, the characteristics of ion adsorption clays and REE distribution in Gua Musang have been studied by mineralogy and geochemical analyses. Rocks and soil samples were collected closed to the granite bodies and its surrounding to represent its weathering products. Polarised optical microscopy was used for petrography and mineralogy studies. From fieldwork observation, Gua Musang lithologies composed of carbonate facies, argillaceous facies and pyroclastic facies. X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD) and Inductive Coupled Plasma Microspectrometry (ICP-MS) were used accordingly to characterise the composition of major and trace elements in IAC samples. REE value in Pulai are the highest concentration as iron nodule have been found in the sampling area. Sample from Boundary Range granite also reported store high concentration of REEs in this study.

The gravity field and gravity data reduction across the continental area of Nigeria

This research presents the variation of the gravity field and associated gravity field components over the continental area of Nigeria to provide data for geoscience research, geodetic and engineering works, aerodynamic studies and deep crustal inferences. Accurate positions and elevations were observed at 58 of the 59 base stations of the Primary Gravity Network of Nigeria (PGNN), whose absolute gravity values had been accurately determined. The absolute gravity values were plotted against their respective positions to reveal the distribution pattern and strength of the gravity field within the study area. Theoretical gravity values at each base station were generated using the Somigliana's equation. The free-air gravity and free-air anomaly gravity values were generated with respect to the World Geodetic System 1984 (WGS84) ellipsoid using GPS-derived elevation data. Then, the perturbing potential, free-air gravity with respect to the geoid, and the indirect effects were evaluated. The average of the indirect effects was used to adjust the WGS84 gravity formula to produce a gravity formula that better approximates the geoid across the continental area of Nigeria, compatible with the heights measured relative to the geoid, which can serve as a reference for establishing a vertical height control. The Bouguer gravity and Bouguer gravity anomalies across Nigeria revealed a “trans-southern gravity high strip” interpreted to be associated with mantle upwelling. Two new major mega-lineaments related to mantle upwelling were mapped. A batholith province trending NW–SE was delineated, occurring from north central Nigeria to the north western region and containing closures of “Bouguer gravity lows” interpreted as batholiths. A separate closure of “Bouguer gravity low” was detected at Azare, north eastern Nigeria, which may be due to the presence of intrusive granitic body. It is recommended that the mantle structure beneath “the trans-southern gravity high strip”, “delineated batholith province” and “isolated gravity closures” around the northeast of Nigeria should be studied from seismic shear wave splitting analysis for better understanding of the deep lithospheric structures and moho relief.

The emplacement, alteration, subduction and metamorphism of metagranites from the Tso Morari Complex, Ladakh Himalaya

AbstractEclogite-facies mineral assemblages are commonly preserved in mafic protoliths within continental terranes. It is widely accepted that the entirety of these continental terrains must also have been subducted to eclogite-facies conditions. However, evidence that the felsic material transformed at eclogite-facies conditions is lacking. Low-strain metagranites of the ultrahigh-pressure metamorphic Tso Morari Complex in Ladakh, Himalaya, are host to eclogite-facies mafic sills and preserve evidence of subduction to eclogite-facies conditions. Following the eclogite-facies metamorphism, the granites and their gneissic equivalents were overprinted by amphibolite-facies Barrovian metamorphism, obscuring their earlier metamorphic history. We present evidence that the Tso Morari metagranites preserve a complex magmatic, hydrothermal and polymetamorphic history that involved four stages. Stage 1 was magmatic crystallisation, a record of which is preserved in the primary igneous mineralogy and relict igneous microstructures. Monazite grains record a U–Pb age of 474.0 ± 11.6 Ma, concurrent with a published zircon crystallisation age. Stage 2 represents pervasive late-magmatic hydrothermal alteration of the granite during emplacement and is evident in the mineral composition, particularly in the white micas preserved in the igneous domains. Stage 3 involved the (ultra)high-pressure metamorphism of these granite bodies during the Himalayan subduction of continental material. The high-pressure stage of the metamorphic history (>25 kbar at 550–650°C) is preserved as thin coronas of garnet and phengite around igneous biotite, garnet with kyanite inclusions in pseudomorphs after cordierite, and rare palisade quartz textures after coesite. Stage 4 was a result of Barrovian metamorphism of the Tso Morari Complex and is evident in the replacement of garnet by biotite. Many of these features are preserved in localised textural domains in the rock, where local equilibrium was important and the anhydrous conditions limited reaction progress, though aided preservation potential. Collectively, these four stages record a 480 Myr history of metamorphism and reworking of the northernmost Indian plate.

Middle-Late Jurassic chronology and source-to-sink system of the Sikeshu section in the southern margin of the Junggar Basin, Xinjiang

With the improvement of isotopic testing technology, high-precision dating methods such as SHRIMP or LA-ICP-MS of detrital zircon have been used to analyze and infer the formation age of sedimentary basins, the source of detrital materials, and the tectonic background of the formation and widely used. The LA-ICP-MS zircon U-Pb dating method was used to study the detrital zircon in the Middle-Late Jurassic sandstone in the Sikeshu section of the southern margin of the Junggar Basin, Xinjiang. The results show that the detrital zircon ages are mainly 270~447Ma,240~440Ma,245~432Ma, and 286~360Ma. There are also several ancient zircon ages, mainly 945~1080Ma. Combined with zircon mineralogical characteristics, CL images, Th/U ratio, sandstone petrographic characteristics, and regional chronological data, the primary provenance of the Middle-Late Jurassic sandstone is mainly from the Yilinghabilga Mountains in the North Tianshan, and Carboniferous-Permian volcanic rocks, pyroclastic rocks and Carboniferous granites exposed in the Borokonu Mountains of the Central Tianshan Mountains. By comparing the age changes between the four sampling points, the change process of the North Tianshan-Middle Tianshan source-sink system is obtained. From west to east, the upper Devonian glutamate, the Middle Devonian carbonate, and the large granite bodies of the Carboniferous series constituted the early watershed. From the middle to late period of the Toutunhe Formation to the Xishanyao Formation, from east to west, the Cambrian and Silurian carbonate rocks and the large granites and other rocks formed the late water line.

New Targets of Potential Mining Interest Using Gravimetric and Satellite Data: Case Study of Hercynian Rehamna Massif, Morocco

The known mineralization in the Rehamna Massif is essentially vein type and linked to the presence of granitic bodies and pneumatolytic - hydrothermal fluid circulations. This part of western Moroccan Meseta, belongs to the Hercynian belt, was the seat of enormous mining productions mainly base metals during the 20th century. Subsequently, exploitations are ended with artisanal extractions, in relation to exploration decline. The present work aims to search for new favourable mining targets, using gravimetric and remote sensing data. Gravimetric data allowed us to delineate leucogranitic apexes of shallow depth. Data filtering and processing consist of separation between Regional and Residual fields from Bouguer anomaly, then, calculation of horizontal, vertical and tilt derivatives to get different gravity anomalies. A Satellite image is used to obtain structural lineaments of the study region through directional filters (N0°, N45°, N90°, N135°). These treatments, supported by field investigations, enabled us to discriminate potential areas, suitable for tactical mining exploration.

Evolution of arc magmatic cycles from the Carboniferous to the Early Cretaceous in the western paleomargin of Gondwana, north of the Andes

This work presents a considerable volume of new and compiled data indicating that arc magmatism in the western paleomargin of Gondwana began in the Carboniferous and continued during the Permian and Early Triassic. Subsequently, the magmatism reactivated during the Early and Middle Jurassic due to the subduction of the Farallon Plate under the continental paleomargin. The arc pluton belts are distributed from the edge of the paleomargin toward the interior of the continent in the same orientation as the slab (west–east direction). During the Carboniferous, between ca. 333 Ma and ca. 300 Ma, magmatism formed small calcic metaluminous gabbro and leucotonalite plutons of tholeiitic to calc-alkaline affinity on the western margin of Gondwana. Later, the second belt of arc plutons formed during the Permian/Triassic (between ca. 300 Ma and ca. 234 Ma) and are represented by metaluminous to peraluminous calc-alkaline to high-K calc-alkaline batholiths and stocks of heterogeneous composition (granites, granodiorites, diorites, quartz monzonites, and monzonites), which were intruded by dikes and minor granite bodies during the Middle Triassic. Between ca. 214 Ma and ca. 186 Ma, peraluminous plutons of batholithic dimensions of monzogranitic to syenogranitic composition developed in the back-arc. Between ca. 197 Ma and ca. 186 Ma, back-arc magmatism occurred, while a new magmatic cycle began along the arc axis. At the end of the Jurassic, the magmatic arc cycle ended in the northwestern paleomargin of Gondwana (ca. 164 Ma). The intrusion ca. 159 Ma of porphyritic bodies of alkaline andesitic basalts toward the edge of the continental margin suggests the strangulation and collapse of the subduction zone in the mantle. To the west, off the continental margin, a new arc magmatic cycle began over a different continental terrane ca. 171 Ma and extended to ca. 138 Ma, giving rise to a belt of calcic to calcic-alkaline plutons emplaced in the Ordovician metamorphic (Anacona Terrane), Triassic (Tahamí Terrane), and Upper Jurassic (Tierradentro Orogen) rocks. The assemblage amalgamated to the western margin of Gondwana in this period.

Age and Origin of the Massangana Intrusive Suite and Associated Mineralizations, in the Rondônia Tin Province: Petrography, U-Pb, and Lu-Hf Isotopes Zircons

Rondônia intrusive suites represent the youngest A-type magmatism that occurred in the SW of the Amazon craton, with mineralizations in Sn, Nb, Ta, W, and topaz. Petrological and isotopic studies (U-Pb and Lu-Hf by LA-ICP-MS) allowed the Massangana granite to be subdivided into São Domingos facies (medium to fine biotite-granite), Bom Jardim facies (fine granite), Massangana facies (pyterlites and coarse granites) and Taboca facies (fine granites). The crystallization ages obtained were between 995.7 ± 9.5 Ma to 1026 ± 16 Ma, and the εHf values vary significantly between positive and negative, showing predominantly crustal sources for forming these rocks. Petrographic studies on ore samples indicate the action of co-magmatic hydrothermal fluids enriched in CO2, H2O, and F. These ores are characterized by endogreisens, exogreisens, pegmatites, and quartz veins that are explored in the São Domingos facies area. The endogreisens and exogreisens are formed by topaz-granites and zinnwaldite-granites; the pegmatites are formed by topaz-zinnwaldite-cassiterite-granites; and the veins by cassiterite-sulfides and quartz. The geometries of the mineralized bodies indicate a dome-shaped contact with the host rocks in the magma chamber and can be attributed to residual accumulation. In this sense, the origin of these ores is related to the evolution of intrusive granitic bodies where the terminal phases of the fluid-enriched magma are lodged in the apical portions, and the origin of the mineralized bodies present a biotite-granite, albite-granite, and endogreisens evolution (potassium series), or biotite-granite, alkali-granite and endogreisens (sodic series) and these rocks present TDM ages that indicate a concerning relation to the non-mineralized rocks of Massangana granite.

Development of Open Transport of Aqueous Fluid from Pegmatite Revealed by Trace Elements in Garnet

We investigated the fluid flow and elemental transport from a granitic body to the middle crust by determining the trace element compositions of garnet in pegmatites related to a quartz diorite intrusion and metamorphic rocks on Kinkasan Island, northeast Japan. Garnet in the pegmatites and biotite schists is characterized by spessartine– (Sps–) almandine- (Alm-) rich compositions of Sps14–69Alm22–70Prp2–14Grs1–13 and Sps16–30Alm54–66Prp9–16Grs3–6, respectively. A garnetite pod in the metamorphic unit has grossular- (Grs-) rich compositions (Sps1–4Alm8–11Prp0.1–0.4Grs80–87Adr3–4). The peak temperature ( T ) and pressure ( P ) conditions of the biotite schist during contact metamorphism were 600–650°C and 0.27–0.41 GPa, respectively. The primary fluid inclusions in quartz crystals within the pegmatites hosted by the quartz diorite and hosted by the metamorphic rocks have a wide range of homogenization temperatures (200–380°C). These correspond to the trapping temperature of 500–700°C, assuming a salinity of 4 wt.% NaClequivalent at pressure of the crystallization of the quartz diorite. Chondrite-normalized rare earth element (REE) patterns of garnets in the pegmatites in the quartz diorite and metamorphic unit are generally characterized by enrichment of heavy REEs and negative Eu anomalies with the REE contents in the schists which are systematically lower than in the pegmatites. However, garnet in the biotite schists close to the pegmatites has similar REE contents to garnet in the adjacent pegmatites. These geochemical features suggest that garnet in the biotite schists grew in response to fluid infiltration from the pegmatites. Besides, the Grs-rich garnet in the garnetite pod and its host quartz schist have flat heavy REE patterns and no Eu anomalies, which probably reflect a metasomatic process related to plagioclase replacement that produced Ca-Al-rich fluids. Our results suggest that the infiltration of pegmatitic fluids enhances elemental transport and metamorphic reactions in the middle crust.

Geochemistry and origin of listwaenites within the Northern Branch of Neo-Tethyan ophiolites, Turkey

The study presents geological field observations, petrographic characteristics and bulk rock geochemical data of listwaenitic occurrences related to Jurassic–Cretaceous IAESZ ophiolites of the northern part of Turkey. Listwaenites of the Jurassic–Cretaceous Eldivan ophiolite and the Cretaceous Dağküplü ophiolite occur as mineralised or non-mineralised blocks and/or veins associated with serpentinised peridotites and ophiolitic mélanges along major thrust zones within the Izmir–Ankara–Erzincan Suture Zone (IAESZ) of the Northern Branch of the Neo-Tethys, Turkey. The silica–carbonate listwaenites (Type I) consist mainly of dolomite and minor calcite with quartz and minor phyllosilicates (chlorite, mica), serpentine and hematite. They are formed by circulation of meteoric hydrothermal fluids, along major décollement faults and thrust faults during the emplacement of serpentinised peridotites. The Kaymaz listwaenites (Type II) are composed mainly of fine-grained microcrystalline quartz with negligible dolomite, calcite, magnesite, serpentine and Fe-hydroxides. They display hard resistant masses, and are adjacent to the Eocene granitic bodies. Listwaenites are gentically related to the serpentinised peridotites, while the mineralisation appears to be related to the granite-related hydrothermal fluids.

Magnetic shape fabric analysis from syntectonic granites: a study based on the eigenvalue method

AbstractWe investigate the shape and strength of the magnetic fabrics (anisotropy of magnetic susceptibility (AMS) data) of various massive granitic plutons from different parts of India, using the eigenvalue method. The study aims to analyse eigenvalues and establish their relationship with various deformational attributes. It involves: (1) calculating eigenvectors and their corresponding eigenvalues from magnetic fabric datasets; (2) finding a link between the geometrical appearance of eigenvectors and the mechanistic issues involved with a specific deformation scenario; and (3) determining shape and strength parameters from the magnetic foliation data distribution.The statistical analysis for the unimodal magnetic fabric dataset of orthorhombic symmetry class implies that the plane, consisting of intermediate (V2) and minimum (V3) eigenvectors with pole V1, accurately traces the instantaneous stretching axis (ISAmax) of a particular material flow system under a pure shear regime. Moreover, for the distributions of similar symmetry and modality, we infer that the rotational characteristics of eigenvectors with respect to a fixed coordinate cause a distinct shift of such planes (V2–V3) from the ISAmax of a steady-state flow system under simple shear, where a substantial amount of rotational strain is involved. However, our findings also suggest that variation in symmetry and modality of magnetic fabric data distribution of different studied granitoids can directly influence the relative disposition of V2–V3 with respect to the direction of ISAmax. We conclude that eigenvalue analysis of magnetic fabrics is a powerful approach, which can be utilized while studying the salient deformational aspects of any syntectonic massive granitic body.

Nature and origin of anorthosite enclaves within Proterozoic granite of Chotanagpur Granite Gneiss Complex of Eastern India

The Central Indian Tectonic Zone (CITZ) is a Proterozoic suture along which the Northern and Southern Indian Blocks are inferred to have amalgamated, forming the Greater Indian Landmass. The Chotanagpur Granite Gneiss Complex (CGGC) represents the eastern extension of the CITZ and exposes several granite plutons. Enclaves of diverse origin are present as minor constituents within these granitic bodies. This study reports new major and trace element data for anorthosite enclaves hosted within granites in the Pattharkatti and Rajgir area from the northern margin of CGGC to get modern insights into the petrogenesis of anorthosites. Anorthosite enclaves show sharp contact with the host granite. They contain cumulus plagioclase (An87–94), intercumulus amphibole (magnesiohornblende and ferrotschermakite), and biotite (Mg-biotite and phlogopite) along with minor iron oxides. Amphibole crystallization pressure and temperature are constrained between 0.5 and 6.4 kbar and 653–780°C for the anorthosites. The studied anorthosites display a very gradual and steady increase in whole-rock rare earth element (REE) contents from Lu to La [(La/Yb)N = 1.22–13.08]. They also show a sharp decline in Fe2O3(t) and MgO, whereas Al2O3 increases with increasing silica contents from 45.69 to 51.16 wt%. In the chondrite normalized REE diagram, plagioclase exhibits LREE enriched patterns with strong positive Eu anomaly. The composition of parental liquid for anorthosite from the study area was estimated by adopting the equilibrium distribution method. Parental melt curves from Sm to La are near parallel and constrained broadly between trapped melt fractions (TMF) = ∼5%–15%. Anorthosites of the study area may have formed from the plagioclase-saturated basaltic melt.

Geochronology and Geochemistry of the Xianghualing Granitic Rocks: Insights into Multi-Stage Sn-Polymetallic Mineralization in South China

Multi-stage magmatic events associated with large tungsten-tin polymetallic deposits in the Nanling Range have been the subject of extensive research spanning many years. In this paper we report the results of a systematic study of the petrology, whole-rock geochemistry, zircon U-Pb chronology, and trace element geochemistry of granite bodies exposed in the Xianghualing ore field. They show that the granites in the study area are characterized by high SiO2 (63.83%–75.29%), Al2O3 (13.12%–18.87%), Rb (565–3260 ppm), Nd (67.3–113.5 ppm) and Ta (23.2–129.0 ppm) and by low MgO (0.02%–0.22%), TiO2 (0%–0.02%), Sr (5.3–80.5 ppm) and Ba (7.9–66.4 ppm). The rocks are highly differentiated A-type peraluminous granite, which originated in an extensional within-plate tectonic setting. Based on U-Pb dating and trace element analysis, the following multi-stage magma-hydrothermal events were identified: (1) Paleozoic (~347 Ma) and Triassic (~206 Ma) magmatic stages (initial enrichment epochs of ore-forming elements), (2) Jurassic (~161 Ma) magmatic-hydrothermal stage (mineralization epoch), and (3) Cretaceous hydrothermal overprinting stage (with peaks in the Early Cretaceous ~120 Ma and Late Cretaceous ~80 Ma). From an economic point of view, the Late Cretaceous appears to have great potential for tungsten-tin mineralization. Zircon trace element geochemistry indicates that the ore-forming fluids related to tin mineralization in the Cretaceous originated from the crust and underwent highly differentiated evolutionary processes under relatively reducing conditions. This paper emphasizes the Cretaceous tungsten-tin metallogenic events in the Nanling Range and provides an essential basis and new ideas for further tin-tungsten exploration.

Metallogenic model of the Fengyan stratabound Zn-Pb deposit in Fujian of southeastern China: Constraints from fluid inclusions, C[sbnd]O[sbnd]S-Pb isotopes, and pyrite chemistry

The Fengyan stratabound Zn-Pb deposit (total resources: 24.7 Mt of ore @ 4.09 % Zn and 1.92 % Pb) is hosted by Neoproterozoic marble and metavolcanic rocks in the Meixian ore field of southeastern China. Hitherto, the genesis of this deposit has been a matter of debate, including a Neoproterozoic volcanogenic massive sulfide genesis (VMS) or an Early Cretaceous magmatic-hydrothermal origin. Based on fluid inclusion data from various hydrothermal stages, stable isotope data of hydrothermal minerals, and in-situ trace element analyses of poly-stage pyrite (Py1-3), the deposit can be classified as a distal skarn-type. A complex paragenesis reflects four hydrothermal stages: stage I (pyroxene + garnet + Py1), stage II (epidote + hematite + magnetite + Py2), stage III (quartz + sphalerite + galena + Py3a + Py3b), and stage IV (calcite). The prograde skarn comprises andradite-rich garnet (on average Ad57Gr34Py9) and pyroxene (on average Hd58Di10Jo32) with high Mn contents. Fluid inclusion data reveal salinity and temperature ranges for the prograde and retrograde skarn fluids as 11.5 to 14.6 wt% NaCl equiv. at 278 to 338℃ and 7.5 to 11.2 wt% NaCl equiv. at 235 to 275℃, respectively. The entrapment pressure is calculated as 130 bars. The sulfide ore minerals of stage III were precipitated at lower temperatures (186 to 259℃) from aqueous fluids with lower salinities (<6.6 wt% NaCl equiv.). Late-stage calcite was deposited from a more dilute (<2.2 wt% NaCl equiv.) and cooler (<200℃) fluid with extremely depleted δ18Ofluid values of −10.1 to −2.0 ‰ (V-SMOW), consistent with a meteoric origin. A mean δ34SV-CDT of 1.7 ± 0.9 ‰ of sulfide minerals points to a magmatic sulfur source. Lead isotopic compositions of sphalerite separates (206Pb/204Pb = 18.295–18.381, 207Pb/204Pb = 15.644–15.662, and 208Pb/204Pb = 38.494–38.724) are similar to those of the Yanshanian granitic bodies in the region but different from those of the ore-hosting marble and metavolcanic rocks. Calcite in the late stage has δ13CV-PDB values of −5.4 to −1.5 ‰, consistent with a predominant magmatic origin. Variations of Co, Ni, Se, and As in pyrite of different generations are interpreted to reflect changes in temperature during hydrothermal evolution. The Co/Ni ratios in all generations of pyrite, mainly between 1 and 10, indicate a magmatic-hydrothermal source. Overall, our new data indicate progressive mixing of a granite-derived magmatic fluid with meteoric waters, as is expected in a distal skarn deposit.

Velocity Structure and Cu-Au Mineralization of the Duobaoshan Ore District, NE China: Constrained by First-Arrival Seismic Tomography

The genesis of deeply buried deposits in the Duobaoshan ore district, the largest porphyry-related Cu-Mo-Au ore field in northeastern China, is not well understood and their exploration is lacking because the fine velocity structure of this region is not comprehensively understood. Herein, first-arrival seismic travel times were picked along a deep seismic reflection profile and inverted using the tomographic method to obtain a detailed velocity profile of the upper 2900 m of the crust beneath this region. The profile showed that the velocity varied from 1900 to 6100 m/s and that the crust was subdivided into five parts by two low-velocity (2500–4000 m/s) blocks. Based on previous studies, the boundaries between the high-speed and low-speed bodies were interpreted as hidden fractures, and the 5000–6100 m/s parts were interpreted as concealed granite bodies in these sections. Porphyry copper deposits in the Duobaoshan ore district were related to the occulted granite bodies, and epithermal Au deposits were associated with the occulted fracture zones. Comprehensive evaluation of hydrothermal activity, regional magnetic anomalies, and deposit distribution indicated that the hidden fractures served as channels for ore-related magmas. Combining previous research on the Duobaoshan ore district with our results of the high-velocity interface, we infer that the prospecting range of the Tongshan deposit is below the depth of 1000 m.

Geochemical and radiogenic isotopic signatures of granitic rocks in Chanthaburi and Chachoengsao provinces, southeastern Thailand: Implications for origin and evolution

The Chanthaburi, Pliew, Klathing, Khao Cha Mao, and Khao Hin Son granitic bodies in Chanthaburi and Chachoengsao provinces in southeastern Thailand, which are located on the southwestern side of the Mae Ping Fault and eastern side of the Klaeng Fault, were investigated. In this study, magnetic susceptibility measurements, whole-rock chemical composition and Nd-Sr isotope analyses, and zircon U-Pb dating were conducted on these granitic bodies. The surveyed granitic rocks are classified as I- to A-type granites, are of the ilmenite series, and show clearly negative Eu anomalies, which suggest they formed under reducing conditions. Nd-Sr isotope ratios indicate continental crust material involvement in the formation of these granite bodies. The magnetic and geochemical signatures are similar to those of granite bodies in southwestern Cambodia. The study area is thus considered an extensional area of southwestern Cambodia, corresponding to the Sukhothai Zone (the Chanthaburi-Kampong Chhnang Zone). Zircon U-Pb dating yields ages of 208–214 Ma (the Late Triassic) for granite bodies except for the Khao Cha Mao granitic body, which dates to 55 Ma. The former age corresponds to the collision time of the Sibumasu and Indochina terranes, and the latter age is likely related to the collision time of the Indian and Eurasian continents.

Records of the oceanic propagator closure at the southern splay of the Palaeo‐Tethys

The Palaeo-Tethys is known to have diverged into several splays throughout East and South-east Asia. Several researchers have widely studied the importance and geometries of the Palaeo-Tethys' branches. Plate reconstruction geometries for the southern Palaeo-Tethys splay suggest that the ocean either connects to the proto-Pacific or dies out. We review and discuss the Late Palaeozoic to the Early Mesozoic lithologies attributed to the Palaeo-Tethys, from the Himalayan Syntaxis in the north to the Bangka and Belitung islands in western Indonesia to the south. Relics of oceanic crust and deep-sea sediments related to the main Palaeo-Tethys Basin can be traced from the South China (Yunnan)-Thailand border to Peninsular Malaysia. A sub-parallel back-arc suture exists in eastern Thailand in the north and vanishes towards the south at the latitude of the Gulf of Thailand. Towards the south of Peninsular Malaysia, the material that constitutes the suture zone of main Palaeo-Tethys is found offshore in the Riau Archipelago, Indonesia, and has been extensively eroded. Thus, we rely on gravity signatures to extrapolate the extension of the structures to the Bangka and Belitung islands, which show only minor serpentine and pillow basalts occurrences along a line that curves towards Borneo. The metamorphic rocks associated with the suture zones range from high grade (gneiss) in Thailand to low grade (mica schist and minor amphibolite) in Peninsular Malaysia. The syn- and post-collisional granitic bodies that form large batholiths in Thailand and Malaysia are comparatively smaller in Indonesia, particularly on Belitung Island, suggesting the lack of large underplating of the Sibumasu crust within the region. We interpret the stratigraphic and tectonic observations of the southern Palaeo-Tethys to support the theory of the southward (present orientation) opening of a propagating oceanic basin from Devonian to Carboniferous, which began to close from the Permian to Triassic period.

Late Carboniferous intracontinental magmatism in the northernmost Sierras Pampeanas, Argentina: The case study of the Tres Cerritos pluton

The Tres Cerritos pluton, a composed, shallow intrusive body, represents the northernmost Late Carboniferous intracontinental magmatism emplaced in the Eastern Sierras Pampeanas of Argentina. Our geochronological study has yielded a U–Pb zircon age of 318 ± 1.7 Ma. It is located between two juxtaposed structural metamorphic domains of the Tolombón Complex in the Sierra de Quilmes that are in contact through old shear zones with N–S to NE-SW orientation. The emplacement of the Tres Cerritos pluton was highly conditioned by the high rheological constrast between the intrusive magma and metasediments in low metamorphic grade. Main magmatic structures and the external shape of the pluton domains are roughly parallel to the regional shear zones. On the contrary, the contacts of the intrusive body crosscut the principal fabrics of the metamorphic host, which show negligible deflection close to the granitic body. Therefore, the magma emplacement would have been through stoping mechanism, assisted by hydraulic forces and favored by Famatinian shear zones reactivated.The Tres Cerritos pluton is mostly composed of alkali-calcic, felsic and peraluminous granites, plotted between the magnesian and ferroan fields. Geochemical characteristics point to a clear A-type affinity, with low La/Yb (MBU: La/Yb = 28.72–21.27; MU: La/Yb = 13.58–2.41) and Sr/Y (MBU: Sr/Y = 5.40–3.86; MU: Sr/Y = 1.80–1.32) ratios. εHf isotopic values between −12 and −15, the most negative results obtained from the Carboniferous magmatism in the Eastern Sierras Pampeanas, relate the pluton to an old metasedimentary source. The comparative analysis with other intrusive bodies of the Devonian-Carboniferous silicic and alkali-calcic magmatism scattered along the Eastern Sierras Pampeanas, suggests a homogeneous and long-lasting crustal source for these granitic rocks, with a similar crustal affinity. In this regard, the contribution of juvenile basic magmas at the source decreased during the thermal, likely extensional, event that promoted the Devonian-Carboniferous intracontinental magmatic suite.

Petrophysical Characterization of Non-Magnetic Granites; Density and Magnetic Susceptibility Relationships

In this work we establish reliable correlations between density and magnetic susceptibility in three paramagnetic granites from the Pyrenees. In total, 128 sites (310 density measurements and &gt;2600 susceptibility ones) were studied in the Mont Louis-Andorra, Maladeta and Marimanha granitic plutons covering the main range of variability of magnetic susceptibility. Regressions were calculated for every granitic body and an integrated linear function was obtained for the entire dataset: ρ (kg/m3) = 2566 (kg/m3) + 0.541κ (10−6 S.I.) (R:0.97). This relationship is only valid in the paramagnetic domain, where iron is mostly fractioned in iron-bearing phyllosilicates and the occurrence of magnetite is negligible (or at least its contribution to the bulk susceptibility). This relationship, likely different in other bodies, allows for transforming magnetic susceptibility data into density data, helping to constrain gravity modelling when density data from rock samples are scarce. Given the large amount of AMS studies worldwide, together with the quickness and cost-effectiveness of susceptibility measurements with portable devices, this methodology allows for densifying and homogenizing the petrophysical data when modelling granite rock volumes based on both magnetic and gravimetric signals.

The buried Variscan granites and associated structures in the High Moulouya basin from gravity data and their role during the Triassic-Liassic extensional tectonics (Moroccan Meseta-Atlas domain).

The High Moulouya Basin (HMB) occupies a key location between the Southern Middle Atlas and the Central High Atlas. Gravity data from the HMB show the presence of three gravity lows. Borehole data show a thin Meso-Cenozoic cover in the HMB that eliminates the possibility that these lows are due to sedimentary rocks. The gravity anomalies may therefore be related to hidden granitic bodies within the Paleozoic basement. In order to map these granite bodies and associated structures, gravity data sets were processed and enhanced using various mathematical techniques, transformations, and 2D gravity modeling. The following were either better defined or revealed: i) The High Moulouya Batholith is a large NE-SW trending batholith that crops out partially in the Aouli-Mibladen and Boumia Paleozoic inliers. Our study shows the continuity of this batholith with a 90 km long and 30 km wide granitic structure. ii) The Hidden Engil granite is a subcircular, relatively small granite body (20 × 18 km) located at the Middle Atlas's eastern boundary. The hidden granite of Zebzat (30 × 10 km) represents a narrow E-W trending pluton bounded by the High Atlas tectonic structures on its southern boundary. The tectonic influence of these granite bodies may explain, to some extent, the stability of the HMB throughout the development of the Atlasic subsiding basins. The two Atlas basins are separated by the High Moulouya granite-cored intrabasinal high. As shown by the horizontal gradient and Euler deconvolution methods, during Triassic-Liassic NW-SE extensional events, the formation of the Middle and High Atlas basins was guided by Variscan inherited faults bounding the granitic bodies of the HMB. The main factors responsible for the formation of the High Moulouya granite-cored intrabasinal high are the isostatic compensation that follows the granite emplacement during the Variscan orogeny, the distribution of strain and deformation around the granite bodies during the Triassic-Liassic extensional tectonics and their concomitant buoyancy forces.