Cretaceous Granites Research Articles

Genesis and Tectonic Implications of Early Cretaceous Granites in the Haobugao Area, Southern Great Xing’an Range: Insights from Zircon U–Pb Geochronology, Hf Isotopic Composition, and Petrochemistry

In the Huanggangliang–Ganzhuermiao metallogenic belt in the southern Great Xing’an Range, the Haobugao Pb‒Zn deposit is the most widespread skarn-type polymetallic deposit. The observed mineralization processes in this area are closely associated with both magmatic and tectonic activity. The zircon U‒Pb ages of two granitoid phases are 134.0 ± 0.6 Ma and 133.4 ± 0.9 Ma (Early Cretaceous). High SiO2 content (average mass fractions of 77.98 wt.% and 73.25 wt.%), high alkalinity (average mass fractions of 6.19 wt.% and 8.78 wt.%), and low CaO levels (average mass fractions of 0.16 wt.% and 0.12 wt.%) are characteristic of these rocks. They are also enriched in high-field-strength elements (HFSEs) (Th, U, Ta, Zr, Hf, etc.) and depleted in large ion lithophile elements (LILEs) (Ba, Sr, etc.). Furthermore, the Nb/Ta ratios (7.80~8.82, 10.00~10.83) point to a crustal origin of the magma. The zircon Hf isotopic compositions suggest that the melting of young crust derived from Meso-Neoproterozoic and Neoproterozoic depleted mantle gave rise to the magma in these granite porphyries. These rocks formed in an extensional environment driven by the subduction and retreat of the Paleo-Pacific plate during the Early Cretaceous.

Light δD apatites reveal deep origin water in North China Craton intracontinental granites and basalts

Water is essential to the formation of intracontinental granites, but its origin remains elusive. Here we address this scientific problem by analyzing D/H isotopes of apatites, hydrous minerals in Jurassic and Early Cretaceous granites and basalts from eastern North China Craton, where water was previously interpreted as derived from subducting slab. Results reveal extremely low δD values in pristine Early Cretaceous granitic (−203‰ to −127‰) and basaltic (−197‰ to −107‰) apatites, contrasting with relatively high δD values (−137‰ to −47‰) in Jurassic granites. Given the depth-dependent D/H isotopic fractionation during slab dehydration and high-water contents in coeval primitive mafic magmas, the Early Cretaceous magma water is attributed to the stagnant slab within the mantle transition zone. Secular change in the depth of water aligns with steepening of subducting Paleo-Pacific plate from Jurassic to Early Cretaceous, demonstrating the potential of apatite H isotopes in tracing water origin in granites and basalts.

Late Mesozoic ductile deformation and exhumation along the Shangdan suture zone in the Qinling Orogenic Belt, China

The Qinling Orogenic Belt (QOB) is a multi‐stage orogenic belt recording subduction and collision processes. The ductile shearing deformation with different properties and ages is developed on the boundary of the different litho‐tectonic units, which can be used to decipher the tectonic evolution of the QOB. Previous studies mainly concentrated on the pre‐Late Mesozoic shearing deformation, while the Late Mesozoic shearing deformation received less attention. It restricts the understanding of the Late Mesozoic tectonic evolution of the QOB. Hence, we conducted detailed field structural analysis and laboratory analysis of the Shagou shear zone (SGSZ) in the middle part of the Shangdan suture zone (SDSZ). The SGSZ, developed in the southern margin of the Baliping pluton, is an S–SSW‐dipping sinistral strike‐slip ductile shear zone with a top‐to‐the‐ESE shear sense. The mylonite protoliths are voluminous Late Triassic granites (200–215 Ma) and a small amount of Neoproterozoic granites (759 Ma) and Early Cretaceous granites (145 Ma). Microstructures and geothermobarometer results suggest that the ductile shearing deformation occurred under high greenschist–low amphibolite‐facies conditions (400–650°C) at middle crustal depths (13–21 km). Zircon U–Pb and amphibole‐biotite 40Ar/39Ar dating results constrain the timing of shearing deformation to 135–145 Ma and the rapid exhumation of the SGSZ to 115–135 Ma. Combining with the regional data, we consider that the sinistral strike‐slip shearing deformation in the SGSZ controls and accommodates the south‐eastward extrusion of the East SQB under the intracontinental compression. Subsequently, the intracontinental extension led to the rapid exhumation of the SGSZ.

Magmatic evolution and sources of metals and fluids in the large granite-related Xiasai vein-type Ag–Pb–Zn(–Sn) deposit, northern Yidun terrane, SW China

The Xiasai Ag–Pb–Zn–(Sn) deposit in the northern Yidun terrane (eastern Tethys), hosted in Late Triassic metasandstones, is genetically associated with Late Cretaceous granites. We present chemical and Sr–Nd–Pb–Li–B isotope data of Late Cretaceous granites and their mafic microgranular enclaves (MME), late aplites, and Late Triassic metasedimentary rocks. The narrow range of 87Sr/86Sr99 (0.70627–0.70953) and εNd99 (–6.1 to –5.2) values of most Late Cretaceous granites reflects a mixed source with contributions from the mantle and Paleoproterozoic felsic crust. These granites have high SiO2 contents (>69 wt%) and strong depletions in Sr, Ba, and Eu. Major and trace element contents correlate with the fractionation index 1/TiO2, indicating that they experienced extensive fractionation. Local late aplite dikes were derived from similar source rocks, but seem to be younger.The Pb isotopic compositions reflect that the metal Pb was derived from the granite with variable contributions from the Late Triassic sedimentary rocks. Weakly and moderately altered metasandstones have similar δ7Li and δ11B values as most granites (δ7Li: 0.00 to 2.68 ‰; δ11B values: –14.93 to –12.36 ‰), indicating magmatic fluid sources. The magmatic fluids resulted in the initial enrichment of Sn, Cu, Pb, and Zn. Strong alteration of feldspar and biotite resulted in the metasandstones in negligible change of Li concentrations, significant loss of Sr, Na2O, CaO, MgO, and Fe2O3, but significant addition of B. This alteration lowered δ7Li from 1.01 to –3.65 ‰ and lowered δ11B from –9.43 to –19.18 ‰. The low δ7Li values and extremely low δ11B values reflect external fluids from the Late Triassic sedimentary wall rocks, which interacted with granites and mobilized metals (e.g., Sn, Ag, Pb, and Zn) from the granite and/or the sedimentary wall rocks. The location of the Xiasai deposit is controlled by regional NNW-trending faults induced by Late Cretaceous extension.

Tectonic evolution of the South Pamir Orogen: Insights from the Permian to cretaceous magmatism

The Pamir orogen originated through the amalgamation of various arc terranes. Despite undergoing numerous studies, the subduction polarity and time regarding the accretion processes remain inadequately constrained. To address these issues, we carried out a detailed study of zircon and apatite U-Pb ages, zircon Hf isotopes, and whole-rock geochemistry for the Permian to Cretaceous gabbro, volcanic rocks and granitoids from the Southern Pamir and the Rushan-Pshart suture. Three stages of magmatism are identified, including 279–266 Ma gabbro and andesite to dacite, 209–208 Ma granitoids, and 108–103 Ma gabbro and granitoids, respectively. The Permian gabbro and basaltic andesite to dacite in Pshart Range are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), but are depleted in Ta, Nb, and Ti, suggesting formation from an enriched mantle source in a subduction zone. The Late Triassic I-type granitoids are typical arc calc-alkaline magmatic rocks with εHf(t) values varying from −8.7 to −3.5, which mainly sourced from the partial melting of mixed crustal sources predominately consisting mafic rocks with minor metasedimentary rocks. The Early Cretaceous Pshart granites are I-type granites with relatively low εHf(t) values ranging from −14.6 to −2.9, suggesting that they were crust-derived rocks. The Early Cretaceous Bazardara granites are identified as A2-type granites with the εHf(t) values ranging from −18.3 to +5.3, and were derived from mixing of mantle-derived and crust-derived magmas, or interaction between mantle melts and old crustal rocks. The early Cretaceous gabbro exhibits -MORB-like geochemical characteristics with flat REE pattern (La/YbN = 4.96), moderate enrichment of LILEs and weak depletion of Nb, Ta and Ti (Nb/LaPM = 0.94). Thus, the early Cretaceous A2-type granite, E-MORB-like gabbro and volcanic rocks were formed in an extensional setting. Our new data indicate that the southward subduction of the Rushan-Pshart oceanic slab started in the Early Permian and continued to the Late Triassic. Moreover, combining the previous data, we conclude that the Early Cretaceous granites and gabbro in the Southern Pamir formed in an extensional environment due to the southward rollback after northward near-flat subduction of the Neo-Tethyan oceanic lithosphere.

Magmatic evolution and metallogenic diversity of the late Cretaceous granites in the Yidun terrane: Constraints from zircon and apatite geochemistry

Porphyry-hydrothermal type Cu-Mo(−W) deposits in the southern Yidun terrane (SYT) and hydrothermal-skarn type Sn-Pb-Zn-Ag deposits in the northern Yidun terrane (NYT) are closely related to late Cretaceous granitic intrusions in time and space. However, the genetic mechanisms and controlling factors responsible for the metallogenic diversity remain unclear. We investigated zircon and apatite compositions of the Sn-Pb-Zn-Ag-associated granites in northern Yidun terrane and the Mo-W-Cu and Mo-Cu-associated granites in southern Yidun terrane. The Cretaceous granites are distributed along a N–S-trending belt having ages ranging from 106 to 73 Ma, with a transition from predominant plagioclase crystallization to amphibole-dominated crystallization. Our data show that the granites from the NYT have lower zircon Eu/Eu* (0.06 ± 0.04), Ce4+/Ce3+, and ΔFMQ (FMQ is fayalite-magnetite-quartz) values compared to the granites in the SYT, indicating that the granites from the NYT are relatively reduced (ΔFMQ = -1.03 ± 1.02) in contrast to the oxidized granites in the SYT (ΔFMQ = 1.10 ± 1.05). Furthermore, apatite can record the volatile compositions of magma before fluid exsolution. Apatites in granites from the NYT with low XF/XCl ratios (≤120) are interpreted to have crystallized from volatile-undersaturated magma. These apatites are characterized by low Cl contents ranging from 0.04 to 0.12 wt% (0.07 ± 0.02 wt%; n = 21) and low SO3 contents of 0.01–0.06 wt%. In contrast, apatites in granite from the SYT with low XF/XCl ratios (≤80) have high Cl contents of 0.05 to 0.34 wt% (0.16 ± 0.07 wt%; n = 52) and SO3 contents of 0.01–0.46 wt%. The chemical compositions of zircon and apatite indicate that the Mo-W-Cu and Mo-Cu-associated granites in the SYT have higher fO2 and melt S contents before fluid exsolution than the Sn-Pb-Zn-Ag-associated granites in the NYT. Therefore, the contrasting magmatic oxidation states and S contents are critical in controlling the metallogenic diversity of the Cretaceous granites in the Yidun terrane. The Xingguolongba and Cuopu granites, first reported in this article, have U-Pb ages consistent with the Rongyicuo and Cuomolong granites. Furthermore, they exhibit similar geochemical properties, such as oxygen fugacity and volatiles, suggesting the possibility of forming Sn-Pb-Zn-Ag deposits.

Thermophysical properties and geochemical characteristics of granites in the Tengchong area: indications for resource potential of hot dry rocks

Ascertaining regional radiogeochemical characteristics and lithospheric thermal structure characteristics is paramount for identifying the resource potential of hot dry rocks. This study conducted thermal conductivity testing and whole-rock analyses of outcrop granites of different formation epochs from the Tengchong area. Moreover, combined with the previously published whole-rock data and the data related to radioactive heat production rates, this study conducted geological, geophysical and geothermal analyses. Key findings are: (1) Granites in the Tengchong area exhibit an average radioactive heat generation rate of 5.54 μ W m −3 . Among them, the Late Cretaceous granites have an average radioactive heat generation rate of 8.08 μ W m −3 , suggesting high heat production granites. (2) Granites in the Tengchong area present an average thermal conductivity of 3.135 W.m −1 K −1 , relatively akin to the average values of granitic rocks worldwide. Compared to granites of other epochs, the Late Cretaceous granites manifest significantly higher thermal conductivities, with an average of 3.28 W.m −1 K −1 . (3) There is a negative correlation between the mica content and the thermal conductivity of the granites in the Tengchong area. (4) The Tengchong area holds potential for hot dry rocks exploitation and is inferred to have a lithospheric structure characterized by hot mantle and cold crust.

The power of modern 3-D visualization of high-resolution terrain models in geologic mapping: Complex fold geometries revealed by 3-D mapping in the Panamint metamorphic complex, eastern California, USA

We use structure from motion–multiview stereo (SM) terrain models developed from ground-based images and images acquired from uncrewed aircraft (aka drones) as a base map for three-dimensional (3-D) mapping on the walls of a deep canyon in the Panamint Range of eastern California, USA. The ability to manipulate the 3-D model with views from arbitrary look directions and broad scale range revealed structures that were invisible to conventional two-dimensional (2-D) mapping because of both the scale of the structures and their exposure on vertical to near-vertical cliff faces. The analysis supports field evidence for four phases of ductile deformation, with only one of the younger phases documented on early geologic maps of the area. The oldest deformational event (D1) produced the main metamorphic fabric and pre-dates Late Cretaceous plutons. This deformation produced a 200–250-m-thick high-strain zone localized along marbles at the top of the Kingston Peak Formation and lower Noonday Formation. Geometric analysis from the model suggests strongly that large sheath folds at scales of 100–300 m are developed within these marbles. Large measured finite strains indicate displacement across this apparent shear zone of at least 4–5 km and displacements of tens of kilometers are allowable, yet the structure is invisible to conventional mapping because the high-strain zone is stratabound. The main fabric shows two clear overprints and a third that is likely an even younger deformation. D2 and D3 generated tight to close, recumbent folds and open to tight, upright folds, respectively, both folding the main foliation with localized development of crenulation cleavages axial planar to the folds. An additional overprint shows no clear cross-cutting relationship with D2 or D3 fabrics and could be a manifestation of either of those events, although the deformation is spatially limited to a narrow shear zone beneath a brittle, dextral-normal fault with the same kinematics as a mylonitic fabric in a Cretaceous granite in the footwall. This observation suggests an extensional, core complex–style deformation to produce this structure. We suggest that 3-D mapping has the potential to revolutionize geologic mapping studies, particularly where steep topography provides 3-D views that are virtually invisible on conventional 2-D maps. Previously bewildering geologic puzzles can be solved by the ability to visualize large cliff exposures from arbitrary angles and map the features in true 3-D at resolutions to the centimeter level. Although this study emphasized intermediate scales imaged by a drone, our methods here are easily extended to larger scales using a crewed aircraft for imaging. We suggest these methods should be used routinely in frontier areas with steep terrain where aviation is already in use for access, but the methods can be employed anywhere steep terrain “hides” major rock exposures on conventional 2-D maps.

Использование метода главных компонентов для анализа геохимических данных и ассоциаций элементов Колумбинского перспективного участка (Кемский террейн, Сихотэ-Алиньский складчатый пояс)

Native manifestations and deposits of precious metals of folded belts of surrounding of the North Asian and Sino-Korean cratons are of lesser resources and areas; that requires growth of research and technological potential for discoveries of the mineralizations. In Sikhote-Alin folded belt, which is typical example of boundary folded belts developed over a subduction zone, terranes of different age are described. Basements of these terranes are of accretion, island arc and turbidite origin, intruded by magmatic rocks and overlain by volcanic-sedimentary cover. Conducted researches consider area of island arc Kema terrane, which occupies large territories of the Strait of Tartary continental coast. Au-Ag deposits here are related to the origin and development of the active volcanic boundary. Genesis of the ore objects here is epithermal and related to intrusive and effusive complexes of Upper Cretaceous and Paleogene ages. Detailed field lithogeochemical surveys were held on a prospective Kolumbe site where Upper Jurassic–Lower Cretaceous siliceous and terrigenous rocks are intruded by Cretaceous granites of Tatibinski and Olginsky complexes. Research of the geochemical features was done using Principal Component Analysis, the effective method of dimensional reduction and data filtration. Implementation of that method in geochemical data analysis facilitates outlining of the associations of the elements by unifying them into principal components and discover their spacial distribution related to geological complexes of the research area. Determining of the number of principal components used explained variance covered by these components. Derived maps of the spatial distribution of principal components that include elements associations allowed to determine the locations of the local geochemical extrema. Grouping of elements into principal components made it possible to assume the staging in ore deposition in a prospective Kolumbe site. Conducted studies could invigorate further more detailed researches of the minerageny of the considered area.

Multi-isotopes (H, O, Sr, and Li) and element geochemistry constrain the formation of Kongchutso helium-rich geothermal field in western Tibet, China

The Kongchutso geothermal field hosts helium-rich hot springs with helium contents (up to 1.54 vol.%) higher than industrial grade of He resources (0.05 – 0.1 vol.%). However, the geochemical signature of helium-rich geothermal fluids, reservoir feature, and their genesis remain poorly understood. Here, we present element geochemistry (major and trace elements) and multi-isotopes (H, O, Sr, and Li) compositions of hot and cold springs, lake, calcareous sinters, and rocks from Kongchutso to determine the formation mechanism of helium-rich geothermal system. The major elements studies of water samples show that most helium-rich hot spring waters belong to the Na-HCO3-Cl type, possibly affected by water-rock interaction in the deep and mixing of geothermal fluids with groundwater in the shallow. Based on chalcedony geothermometers and silica enthalpy mixing model, the reservoir temperature has been calculated to be 106 – 118 °C. The H and O isotopic compositions of water samples manifest that the Kongchutso geothermal system was recharged by snow-melt water and meteoric precipitation from the surrounding mountains at an elevation of 5366 m. The widespread Cretaceous granites in the region featured by high enrichment of uranium (up to 34.15 ppm) and thorium (up to 37.49 ppm) are considered as helium and heat sources, and also are reservoir rocks. The interpretation is supported by consistent signatures of rare earth elements and Sr-Li isotopes for waters, calcareous sinters, and granites. Therefore, we suggest that the helium was initially generated via radioactive decay by U-Th in granites and then dissolved in the deep circulated and heated meteoric waters, and finally ascended to surface through the main fault systems to form the helium-rich hot springs at Kongchutso. Some other hydrothermal manifestations, such as calcareous sinters, formed accompanying the fluids migrated to the surface. Based on these new findings, we further proposed that high radioactive granite, together with tectonic system and surface hydrothermal manifestations can be used as indicators for exploration of helium-rich geothermal resources in Tibet and elsewhere in the world.

Paleogene mid-crustal intrusions in the Ruby Mountains–East Humboldt Range metamorphic core complex, northeastern Nevada, USA

Abstract Middle Eocene to early Oligocene intrusions, widespread in the Ruby Mountains–East Humboldt Range metamorphic core complex, Nevada, USA, provide insights into a major Paleogene magmatic episode and its relation to tectonism in the northeastern Great Basin. These intrusions, well-exposed in upper Lamoille Canyon, range in composition from gabbro to leucomonzogranite. They form small plutons, sheets, and dikes that intrude the metamorphic and granitic infrastructure of the core complex. Two types of Paleogene monzogranite were recognized. The first is exemplified by two of the larger intrusive bodies, the Snow Lake Peak and Castle Lake intrusions, which occur as sheet-like bodies near and at the structural base of metamorphosed Neoproterozoic and Cambrian Prospect Mountain Quartzite where it is inverted above Cambrian and Ordovician marble of Verdi Peak in the Lamoille Canyon nappe. Swarms of dikes are associated with these intrusions. U-Pb (zircon) ages range ca. 40–33 Ma and typically display relatively simple and minor inheritance. The rocks have the lowest εHf (zircon) and εNd (whole rock) of any of the middle Cenozoic granites. The second type of monzogranite, Overlook type, typically occurs as thin, isolated dikes and leucosome-like bodies in Late Cretaceous granites of the infrastructure, with no obvious relationship to the large monzogranite bodies. Overlook-type monzogranite displays complex zircon inheritance, yields igneous ages ca. 37–32 Ma, and has εHf (zircon) and εNd (whole rock) identical to those of Late Cretaceous granites in the core complex. These isotopic and field data indicate that Overlook-type monzogranite formed in situ through anatexis of host Cretaceous granites. A pervasive thermal event was required to stimulate this crustal melting. Gabbros from Lamoille Canyon and quartz diorite dated from 32 km away signal mantle-derived magmatism ca. 39–37 Ma (U-Pb, zircon) was a driver of crustal melting and hybridization. Eocene 40Ar/39Ar apparent ages on hornblende and biotite are consistent with syn- to post-magmatic extensional exhumation and decompression. Thus, the core complex provides a window into trans-crustal magmatism and insight into how such magmatism affected the Nevadaplano orogenic plateau. This Paleogene thermal pulse, which may relate to removal of the Farallon slab by delamination of mantle lithosphere, involved partial melting of the upper mantle and transfer of magma and heat to the Nevadaplano crust. Lower-crustal melting of Archean(?) to Paleoproterozoic rocks resulted in Snow Lake Peak–type magmas, and middle-crustal melting of granite in the infrastructure yielded Overlook-type magmas. This crustal magmatism, as exemplified by the intrusions in the core complex, likely played a role in destabilizing the Nevadaplano and its later collapse during middle Miocene extension. The Paleogene intrusions and associated structural features also provide insight into the evolution of the core complex through either the buoyant upwelling of a melt-rich diapir (gneiss-dome model) or buoyant upwelling of the melt-rich middle crust synchronous with a west-rooted mylonitic shear zone (extensional shear-zone model). We favor a hybrid that incorporates both models.

Geodynamics and nature of the basement of the northern Lhasa Terrane: Insights from Early Cretaceous highly fractionated I-type granites in the Beila and Dongga areas, central Tibetan Plateau

Collisional orogenic belts serve as excellent places for investigating geodynamic process and growth mechanism of the continental crust. As one of the largest collisional orogenic belts worldwide, the Tibetan Plateau is formed by the amalgamation of multiple tectonic terranes. However, the nature and composition of the crustal basement beneath the northern Lhasa Terrane, located in central Tibetan Plateau, is still a matter of debate. Here, we investigated a series of Early Cretaceous granites in the Beila and Dongga areas, northern Lhasa Terrane. Zircon U-Pb dating reveals that the Beila and Dongga granites were emplaced at ca. 118 Ma and 110 Ma, respectively. These granites are characterized by high SiO2 and K2O, low TiO2 and P2O5 contents and low Mg#. They exhibit enrichment in light rare earth elements, significant negative Eu anomalies, and depletion in Ba and Sr. These geochemical features suggest that they belong to highly fractionated I-type granites. Both the Beila and Dongga granites display similar and enriched whole-rock Sr-Nd and zircon Hf isotope compositions, implying a likely common ancient crustal origin. Given the temporal sequences and redox conditions during their formation, it is highly probable that the Beila and Dongga granites formed during the syn-collision stage between the Lhasa and Qiangtang Terranes and the breakoff of the Bangong-Nujiang oceanic slab, respectively. Integrated with coeval magmatism in the central Tibetan Plateau, our new data reveal the presence of a regionally preserved ancient basement beneath the northern Lhasa Terrane, analogous to the equivalent basement beneath the central Lhasa Terrane.

Petrogenesis of high heat producing granites and their contribution to geothermal resource in the Huangshadong geothermal field, South China

The Huangshadong geothermal field (HGF), situated in the contact zone between Mesozoic granites and NE-striking dominant faults in South China, has great geothermal potential. Petrogenesis of reservoir rock plays an important role in understandings its genetic mechanism and assessing geothermal potential. However, due to the lack of rock sample at depth collected from the geothermal reservoir, the petrogenesis of granites in the geothermal reservoirs of the HGF, remains an enigma. This study elucidated the petrogenetic characteristics of these granites sampled directly from geothermal reservoir at the depth of ∼3,000 km and their geothermal implications through zircon U-Pb dating, geochemical analysis, and Hf isotopic analysis. The zircon U-Pb ages indicate that the magmatism evolution of HGF contains three eras, namely, Cretaceous (135 ± 4 to 143.6 ± 2.8 Ma), Jurassic (152.7 ± 2.7 to 176.7 ± 1.8 Ma), and Permian granites (251 ± 9.1 to 251 ± 5 Ma) from the youngest to oldest. The reservoir granites were emplaced during the latest stage of Cretaceous intrusion, as indicated by the zircon U-Pb ages (135 ± 4 Ma and 135.3 ± 2.4 Ma) of rock samples from the deep part of well HR-1. These Cretaceous rocks are highly fractionated I-type granites, featuring high SiO2, K2O, and Na2O contents, high Rb/Sr ratios, low Zr/Hf, Nb/Ta, and Th/U ratios, and A/CNK values of 1.05–1.13. Compared to other Cretaceous granites outcropping on the margin of the HGF, these granites have undergone the strongest fractional differentiation. The Cretaceous granites in the HGF are high-heat-producing rocks (>5 μW/m3), with an average heat production rate of 6.63 μW/m3. Notably, the Cretaceous reservoir granites (as reservoir rocks) serve as an important heat source for the formation of geothermal resources in the HGF. In addition, the zircon Hf isotopic composition indicates that the reservoir Cretaceous granites originated from Meso-to Paleo-Proterozoic lower crustal materials (TDM2: 1,385 to 1907 Ma).

Extraction of gravity components related to W-Sn polymetallic deposits using Bi-dimensional empirical mode decomposition (BEMD) in the Laojunshan Ore Cluster Region, SW China

The Laojunshan ore cluster region is situated at the north Song Chay dome, which is the junction of the Yangtze, the Cathaysia, and the Indo-China Blocks. The north Song Chay dome characterized by the Laojunshan metamorphic core complex is an important ore-forming region for W-Sn-Pb-Zn-In elements related to the Late Cretaceous granitic magmatism. In this paper, the Bi-dimensional empirical mode decomposition (BEMD) is applied to separate gravity components from the original gravity data, combined with the known geological and mineralized information, to explore the relationships between the gravity components and various ore-controlling factors at different depths. Four intrinsic mode functions (IMFs) and a residue are obtained. They may imply the spatial distribution of the geological bodies with featured gravity components at different depths. The results are shown as follows:(1) The low-pass filtering gravity component (BIMF4) implies the deeply buried geological units in the study region. The Cretaceous Laojunshan granitic complex and the Nanwenhe gneissic granite display negative gravity components and weak positive gravity components, respectively. The former is closely related to Sn-Zn-In mineralization, the latter is closely related to W polymetallic deposits. Therefore, the negative gravity components showing the Laojunshan granitic complex are the prospecting targets for deeply buried Sn-Zn-In deposits. The weak positive gravity components displaying the Nanwenhe gneissic granite are the prospecting targets for deeply buried W polymetallic deposits.(2) The band-pass filtering gravity component (BIMF3) implies the geological units at middle depth. The skarn-type Sn-W polymetallic deposits are observed in the transition zones from the positive to the negative gravity components, which coincide with the contact metasomatic zones between the Cretaceous granite and the Cambrian-Devonian carbonate rocks. Some small quartz vein W deposits occur within the Cretaceous Laojunshan granite with negative gravity components, and some layered W deposits occur in the Silurian gneissic granite with a weak positive gravity component.(3) High-pass filtering gravity component (BIMF2) implies geological units at the shallow crust, which shows that most of the deposits (occurrences) are located within the positive gravity component zones. These positive gravity component zones should be ore-finding targets for further prospecting for the undiscovered Sn and W polymetallic deposits.(4) The gravity components separated by BEMD coincide with the spatial distribution of the granites associated with various types of mineralization and alteration zones at different depths, which will give insights for further prospecting for concealed ore bodies in this study region.

Petrogenesis of the Mesozoic granitoids from the Yuanlinzi Sn-Cu deposit, Northeast China: Implications for Cu-rich Sn mineralization

Granite-related hydrothermal Sn deposits are commonly expected to contain little or no Cu because Cu and Sn have markedly different geochemical properties. However, examples of Sn deposits rich in Cu are well-known in many Sn belts worldwide. So far, the magmatic processes of ore-related rocks and genesis of Cu-rich Sn deposits remain controversial. The newly discovered Yuanlinzi Sn-Cu deposit is located in the southern Great Xing’an Range (SGXR), Northeast China. It is a typical Cu-rich Sn deposit in the SGXR. This contribution reports new cassiterite and zircon U-Pb ages, geochemical compositions, and Sr-Nd isotopic data for the granitoids in the Yuanlinzi deposit to decipher the genesis of Cu-rich Sn deposit. Cassiterite U-Pb dating reveals that the Sn mineralization at Yuanlinzi was formed at ∼ 138 Ma. Zircon U-Pb dating of the granitoids yielded two age clusters: Early Triassic (247.6–246.3 Ma) for the granodiorite, and Early Cretaceous (145.3–141.9 Ma) for the granites, including K-feldspar granite (145.3 ± 0.5 Ma), granite porphyry (143.6 ± 0.9 Ma), fine-grained granite (142.8 ± 1.1 Ma) and albite granite (141.9 ± 1.3 Ma). The Early Cretaceous granites have geochemical affinities for A-type granites, for example, A/CNK = 0.98–1.07, high TFeO/(TFeO + MgO) ratios, total alkali (Na2O + K2O), and Ga/Al ratios. The Early Triassic granodiorite have relatively low (87Sr/86Sr)i values of 0.7034–0.7041, whereas the Early Cretaceous granite has slightly variable and higher (87Sr/86Sr)i values, varying from 0.7020 to 0.7065. The Early Triassic granodiorite and Early Cretaceous granites have similar bulk-rock εNd (t) values and TDM2 ages, ranging from + 1.89 to + 3.53 and 732 to 845 Ma, respectively. The geochemical data and Sr-Nd isotopes indicate that the Early Cretaceous granites were derived from partial melting of the juvenile middle-upper crust. This study further suggests that the 145.3–141.9 Ma granites are associated with back-arc extension environment during the low-angle subduction of Paleo-Pacific plate. In addition, the whole-rock and zircon compositions show that the Cu-Sn magma is characterized by relatively oxidized and less evolved features compared to the Cu-poor Sn deposits in the region. The rapid increase of oxygen fugacity of the latest episode of the Early Cretaceous magma is supposed to have initiated by the injection of mafic magma, which supported the Cu source for the deposit. Our studies suggest that the Cu-bearing mafic magma/fluid injection plays a key role on the formation of Cu-rich Sn deposit.

Decoding the Link Between Magmatic Cyclicity and Episodic Variation of Tectonics and Crustal Thickness in the Overriding Plate

AbstractCyclical change in subduction angle is the favorable mechanism to elucidate the cyclicity of continental arc magmatism, however, the role of episodic tectonics and variation of the lithosphere in overriding plates is much underestimated. Here we focus on structural, magnetic, and gravitational features of the Late Jurassic to Early Cretaceous granites in the Mesozoic Paleo‐Pacific arc system of the North China block. By unraveling the emplacement process and regional tectonics, we establish a three‐staged extension‐contraction cycle with crustal thickness variation controlling the magmatic flux and behavior. The Late Jurassic extension produced high‐flux crustal‐derived magma (1.87 × 103 km2/Myr), but the thick crust >45 km accumulated large granitic batholiths by multi‐feeders emplacement at the middle‐lower crust and prevented magma ascent and eruption. Subsequently, the Latest Jurassic to Earliest Cretaceous contraction resulted in the magmatic lull and thickened crust of ca. 60 km, fueling crustal material for the ensuing magmatism. In the Early Cretaceous, intense crustal extension thinned the crust to 30 km and largely enhanced the magmatic flux (3.03 × 103 km2/Myr). The magma is prone to penetrate the thin crust with an intensive eruption. A small amount of magma was stored, and the emplacement was controlled by ductile detachments or normal faults. Our model emphasizes episodic the deformation of lithosphere and associated crustal thickness variation in controlling magma production, which may shed new light in understanding the magmatic cyclicity under continuous subduction.

Multiple stages of continental rifting in Eastern Peninsular Malaysia: new insights from Jurassic–Cretaceous granitoids

Mesozoic granitoids in Peninsular Malaysia provide crucial information on the temporal–spatial relationship between the Tethyan and Palaeo-Pacific domains. This paper presents new ages and geochemical data for newly identified Jurassic–Cretaceous granites and meta-granites from East Malaya. These granitoids can be divided into three groups. Group 1 consists of high-K calc-alkaline granites and granodiorites (171–162 Ma) with variable ε Nd ( t ) values of −7.4–+0.5, zircon ε Hf ( t ) values of −7.4–+8.6, and high initial ratios for 206 Pb/ 204 Pb (20.04–20.65), 207 Pb/ 204 Pb (15.73–15.79) and 208 Pb/ 204 Pb (39.80–40.20). The melting of metasedimentary rocks with a juvenile mafic component formed Group 1 samples. Group 2 granite porphyries ( c. 131 Ma) with A-type affinities and Group 3 granitic gneisses ( c. 130 Ma) with I-type affinities share similar ε Nd ( t ) values (−7.2 to −5.5), zircon ε Hf ( t ) values (−10.1–+6.5), and initial ratios for 206 Pb/ 204 Pb (18.81–19.02), 207 Pb/ 204 Pb (15.71–15.77) and 208 Pb/ 204 Pb (38.95–39.59). Although Group 2 and 3 samples were derived from an ‘ancient’ meta-mafic source region, Group 2 shows evidence for the involvement of a juvenile mafic component. All these granitoids are akin to the Permian–Triassic igneous rocks in East Malaya. The Jurassic–Cretaceous igneous rocks in Eastern Peninsular Malaysia were formed during multiple stages of continental rifting in response to Palaeo-Pacific slab rollback pulses rather than by Tethyan evolutionary processes. Supplementary material : Data for the Middle Jurassic–Early Cretaceous granitoids of East Malaya are available at https://doi.org/10.6084/m9.figshare.c.6689085 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Possible genetic relationship between Mesozoic magmatic rocks and gold mineralization in the Jiaodong Peninsula (Eastern China): constraints of magmatic evolution and physicochemical conditions

The Jiaodong Peninsula is China’s largest gold province and the third largest in the world. Although gold mineralization is associated with Mesozoic granites temporally and spatially, the specific genetic association remains unclear, leading to ambiguity regarding the genetic type of gold deposits. To address this issue, we conducted whole-rock major and trace elements, LA–ICP–MS zircon U–Pb geochronology and trace elements geochemical analyses on the Linglong (Linglong suite), Yashan, and Nansu (Weideshan suite) plutons, and compiled contemporaneous magmatic rock data. Our results show that the granites were emplaced at 161 ± 2, 118 ± 1, and 121 ± 2 Ma, respectively. Geochemically, these rocks exhibit high Al2O3 (12.73–14.10 wt%) content and Sr/Y (35.54–136.50) ratio, and low Y (3.26–11.20 ppm) and Yb (0.33–0.97 ppm) contents, indicating the adakitic rock properties. They were formed through partial melting of the thickened lower crust associated with subduction of the paleo-Pacific Plate. The Early Cretaceous granites contain a large amount of mafic microgranular enclaves, indicating the presence of mantle material mixing in the source area. Zircon trace elements show that the pre-mineralization magma (Linglong) had relatively low oxygen fugacity and temperature (ΔFMQ = −2.5 to +1.9, T-Ti in zircon (mean) = 740°C) compared to the mineralization magma (ΔFMQ = +0.5 to +3.9, T-Ti in zircon (mean) = 755°C). The physicochemical conditions in the pre-mineralization magma source area may be favorable for sulfide accumulation (may including gold). During the Early Cretaceous, North China Craton decratonization reached its climax, and a large number of adakitic crust-mantle mixed oxidized magma upwells, allowing for the migration and mineralization of a large amount of sulfides and gold. This model helps explain the transient, explosive, and genetic categories in Jiaodong gold deposits.

Petrogenesis of early Cretaceous granites in Mufushan complex, northeastern Hunan Province: Insights on middle-late Mesozoic tectonic evolution of eastern South China

We present new field observations, whole-rock major and trace elements, Sr-Nd-Pb-Hf isotopes and zircon UPb ages for the Mesozoic granites in the Mufushan complex, eastern South China. The age determinations by LA-ICP-MS UPb dating of zircons indicate that the porphyritic biotite granites and two-mica monzogranites have ages of ∼136 Ma and ∼ 130 Ma, respectively. These granites display highly evolved S-type granite geochemical characteristics, with high SiO2 (70–74 wt%) contents, high 10000*Ga/Al ratios (2.3–3.2, average of 2.8) and weakly peraluminous (A/CNK > 1.1). Both types of granites are enriched in large ion lithophile elements (LILEs, e.g., Rb, K, Ba, Sr) and depleted in high field strength elements (HFSEs, e.g., Nb, Ta, Ti), with negative anomalies of Eu and positive anomalies of Pb, which are akin to continental arc rocks. The two-mica monzogranites have high 87Sr/86Sr(i) (0.71355–0.71535), 206Pb/204Pb(i) (18.105–18.157), low εNd(t) (−9.1 to −9.6) and εHf(t) (−4.1 to −10.4), similar to those of the porphyritic biotite granites which are characterized by high 87Sr/86Sr(i) (0.717337–0.71692), 206Pb/204Pb(i) (18.134–18.580), low εNd(t) (−9.1 to −9.7) and zircon εHf(t) (−6.8 to −3.3). The similar emplacement ages and mineral assemblages as well as Sr-Nd-Hf isotopic signatures indicate their derivations were likely derived from a common magma source. These early Cretaceous granites yield two-stage Nd model ages of 1.6–1.7 Ga, similar to the two-stage Hf model ages of 1.3–1.8 Ga. The presence of Neoproterozoic and subordinate Mesoproterozoic zircons within the granitic rocks suggest a significant contribution of ancient crustal materials involved in the genesis of the magmas. In combination with comprehensive studies on the magmatic rocks, the early Cretaceous Mufushan granitic rocks may have experienced an extensive enrichment process, contemporaneously with partial melting of the Neoproterozoic volcanic-sedimentary sequences that produced the arc-like rocks. Almost simultaneously, an extensional event caused by the subduction and slab roll-back of the Paleo-Pacific plate (Izanagi plate) dominates the middle-late Mesozoic tectonics in eastern South China. This extensional regime was accompanied by the underplating of mantle-derived magma and crustal melting, producing the widespread early Cretaceous granites in adjacent regions. The development of coeval basin-and-range structures with the production of contemporaneous magmatic rocks and related polymetallic deposits in eastern South China are all related to slab roll-back tectonics.

Igneous records of transformation from ocean to continent of Mongolia–Okhotsk Ocean: Evidence from granitoids of Woduhe area, Heilongjiang Province, China

The Woduhe area of Heilongjiang Province is located in the eastern side of the Greater Xing'an Range. This area has experienced the evolution of the Palaeo‐Asian Ocean, the Palaeo‐Pacific, and the Mongolia–Okhotsk Ocean, and it can be used to discuss the transformation process of these palaeo‐oceanic plates to continental plates. However, controversies exist over its time period and the process of transformation. The 1:250000 Woduhe Geological Map shows that Early Cretaceous granitic batholith developed near the Dajinshan area. However, the LA‐ICP‐MS zircon U–Pb dating presented in this paper shows that the trondhjemites from the southern part of the Dajinshan area were formed at 156.9 ± 2.2 Ma, syenogranites were formed at 131.7 ± 1.6 Ma, and diorite porphyrite dikes were formed at 126.0 ± 3.1 Ma. Therefore, Early Cretaceous batholiths should be reclassified as different, separate units. The Late Jurassic intrusive rocks belong to TTGG assemblages (tonalite–trondhjemite–granodiorite‐granite). Trace element spider diagrams show that the rocks are enriched in K, Pb, Zr, and Hf; depleted in Nb, Ta, and Eu; with higher Sr; and lower Y content. The rare earth element pattern is right‐sloping (La/Yb > 12). The Early Cretaceous intrusive rocks belong to G assemblages (granodiorite). Combined with the tectonic settings, we determined that the Late Jurassic and the Early Cretaceous granites were formed in a magmatic arc setting related to subduction. Late Jurassic intrusive magma mainly originated from the partial melting of the thickened lower crust under the Xing'an arc, and was likely contaminated by mantle material. Early Cretaceous intrusive magma originated from the partial melting of the Xing'an sub‐arc crust. Based on the distribution of the Late Jurassic TTG (N and NE) and G (S and SW) assemblages, intrusive records of the southward and southwestward subduction of the Mongolia–Okhotsk Ocean can be observed. In addition, the grade of maturity of the Xing'an arc is increasing during Late Jurassic to Early Cretaceous.