Granite Batholith Research Articles

Characteristics of Radiogenic Heat Production of Widely Distributed Granitoids in Western Sichuan, Southeast Tibetan Plateau

Abstract Investigating the genesis of geothermal resources requires a thorough understanding of the heat source mechanism, which is also a vital basis for the efficient exploration and utilization of geothermal resources. Situated in the eastern Himalayan syntax, western Sichuan is considered to be one of the main concentration regions of high-temperature geothermal resources in China. To date, various studies have been carried out to reveal the heat source and genesis of the abundant high-temperature resources in this area; however, studies on the contribution of the radioactive heat generated by the widely distributed granitoids to the high-temperature geothermal resources remain scarce. In order to resolve this knowledge gap, we attempted to obtain evidence from the geochemical data published in the literature in the past few decades. A total of 548 radiogenic heat production rate data were determined. The statistical data indicate that the average concentrations of the heat-producing elements U, Th, and K are 6.09±5.22 ppm, 26.74±16.78 ppm, and 3.51±0.82%, respectively. The calculated heat production values of the granitoids vary from 0.52 to 10.86 μW/m3, yielding an arithmetic average value of 3.74±2.15 μW/m3, which is higher than that of global Mesozoic–Cenozoic granites (3.09±1.62 μW/m3). Based on the heat production values, the capacity of the granitic batholiths to store heat was assessed, and the Dongcuo pluton was found to be the largest heat reservoir (382.88×1013 J/a). The distribution of the crustal heat flow was examined using the calculated heat production data and the stratigraphic structure obtained via deep seismic sounding in the study area. The results indicate that the crustal heat flow is 48.3–56.2 mW/m2, which is mainly contributed by the radioactive decay in the granitoids in the upper crust. The fact that it accounts for nearly half of the regional background heat flow indicates that the radiogenic heat from the granitoids is an important heat source for the formation of the thermal anomaly and the high-temperature geothermal resources in the study area. Thus, the results obtained in this study highlight the importance of the widely distributed granitoids to high-temperature geothermal resources in western Sichuan.

The fractures-controlled tin mineralization at the end of Late Cretaceous in the Songshan deposit, southwestern China: Constraints from U–Pb dating of zircon, garnet, and cassiterite

The Songshan tin deposit is located in the northern Lincang granitic batholith along the Lancangjiang tin belt, Western Yunnan, southwestern China. The ore bodies mainly occur as tourmaline-quartz veins with NNE- and/or NW-trending in the Triassic Pinghejie granitic pluton, and the schist of the Proterozoic Songshan Formation. The previous study suggested the tin mineralization in the Songshan deposit should occur in the Triassic, but no directed age data support it. This hinders the understanding of the genesis of the Songshan tin deposit, especially the tin mineralization in the Lancangjiang tin belt. Here, we report the zircons U-Pb ages of 222.7 ± 1.6 and 222.0 ± 2.4 Ma for the granodiorite, 215.1 ± 1.5 and 223.0 ± 2.0 Ma for the biotite monzogranite, and 222.3 ± 2.3 Ma for the alter granite from the Pinghejie granitic pluton. The monazite from the monzogranite yields a U-Pb age of 212.8 ± 1.9 Ma. We also obtain two garnet U-Pb ages of 215.1 ± 8.7 Ma and 213.5 ± 7.2 Ma from skarn, and two cassiterite U-Pb ages of 76.6 ± 1.5 Ma and 79.6 ± 3.6 Ma from tin ores. These data suggest that tin mineralization in the Songshan deposit occurred at the end of Late Cretaceous, which is quite different from the ages of the Pinghejie granitic pluton emplaced and the formation of skarn. The zircon Hf isotopes (εHf(t) = –22 ∼ -12) and monazite Nd isotopes (εNd(t) = -13.04 ∼ -11.80) indicate that the Pinghejie granitic pluton was derived from the remelting of Paleoproterozoic crust. The paper concluded that the tin mineralization in the Songshan deposit occurred at the end of Late Cretaceous. It is another important metallogenic period in the Lancangjiang tin belt, which may be related to the subduction of the NeoTethys oceanic crust. The tin mineralization can not only occur in the magmatic arc, but also in the hinterland behind the magmatic arc.

Peraluminous granite related to tin mineralization formed by magmatic differentiation and fluid exsolution of metaluminous melt: A case study from the Bozhushan batholith, South China Block

Most primary tin deposits are closely temporally and spatially related to peraluminous granites. These granites usually exhibit highly evolved geochemical characteristics that disguise their specific origin. This paper reports a study of whole-rock geochemistry and Sm–Nd isotopes, zircon U–Pb geochronology and Lu–Hf isotopes, and mineral chemistry of the Bozhushan granitic batholith in the Youjiang basin, South China. The Bozhushan batholith, producing the Bainiuchang large tin–polymetallic deposit, consists of metaluminous tin-barren monzogranites and peraluminous tin-bearing monzogranites. LA-ICP-MS zircon U-Pb dating suggests that the peraluminous rocks were emplaced during the Late Cretaceous (88.5 ± 0.7 Ma), which is largely consistent with the emplacement age of the metaluminous rocks. These granitic rocks have similar Nd-Hf isotopic compositions, supporting a common crustal source. Relative to the metaluminous monzogranites, the peraluminous tin-bearing rocks exhibit more evolved geochemical compositions with higher Si and lower Ca, P, Mg, Fe, and Ti and stronger depletion in Eu, Ba, Sr, Zr, Hf, and rare earth elements. These differing geochemical characteristics can be explained by the differentiation of biotite, plagioclase, zircon and apatite. The extremely low Nb/Ta (<5) and K/Rb (<150) ratios of the peraluminous rocks indicate a fluid exsolution process. We suggest that the peraluminous tin-bearing rocks were derived by magmatic differentiation and fluid exsolution of the metaluminous melts. Combining our new results with previous studies, we conclude that on a worldwide scale some peraluminous granites related to tin mineralization are derived by magmatic differentiation and fluid exsolution of metaluminous melts rather than from metasedimentary rocks.

Monazite geochronology and geochemistry constraints on the formation of the giant Zhengchong Li-Rb-Cs deposit in South China

The giant Zhengchong Li-Rb-Cs deposit (ore resource: 270 k tonnes (t) Li2O @ 0.557 wt%, 110 kt Rb2O @ 0.225 wt%, and 6 kt Cs2O @ 0.013 wt%) in South China is associated with quartz-zinnwaldite-topaz rock, which is composed mainly of quartz, zinnwaldite and topaz with a porphyritic texture. However, the genetic link between these rocks and their Jiuyishan granite batholith host is unclear, and the magmatic-hydrothermal process involved in the rare-metal mineralization remains enigmatic. In this study, we analyzed the in-situ U-Pb age and mineral chemistry of monazite, a ubiquitous accessory phase at Zhengchong, to reconstruct the precise geochronological framework of this highly-fractionated felsic magmatic system, and the origin of the Li-Rb-Cs-rich quartz-zinnwaldite-topaz rock. Based on petrographic observations and back-scattered electron (BSE) imaging, monazite crystals in different rocks at Zhengchong have the following characteristics: (1) Mnz-I is mainly BSE-zoned monazite disseminated in granite porphyry, coexisting with zircon or included in zinnwaldite, (2) Mnz-II consists of relatively fine-grained BSE-zoned or homogeneous monazite distributed in feldspar phenocryst-bearing quartz-zinnwaldite-topaz rock, (3) Mnz-III is BSE-zoned monazite with embayed texture in the core, distributed in coarse-grained quartz-zinnwaldite-topaz rock, and (4) Mnz-IV is homogenous, BSE-gray monazite from fine-grained porphyritic quartz-zinnwaldite-topaz rock (as the main orebodies). All monazite crystals are characterized by high Th content, indicating magmatic origin. The LA-ICP-MS monazite U-Pb ages indicate granitic magmatism and mineralization cluster around 150 Ma, implying a close genetic link between the granite porphyry host and the quartz-zinnwaldite-topaz rock. We compared the chondrite-normalized REE distribution patterns and principal component analysis and partial least squares-discriminant analysis of the monazite analyzed, and suggested that the BSE-zoned Mnz-I, II and III are likely of the same type, significantly different from the homogenous Mnz-IV. The gray rims (under BSE) of Mnz-I, II and III are similar to Mnz-IV, and differ markedly from the bright core (under BSE) in their lower HREE and ThO2, but higher Eu and Eu/Eu* contents. When combined with the whole-rock composition data, the monazite compositional variation cannot be attributed to rapid changes in magma composition, depressurization, and increased water content, but rather to the increasing oxygen fugacity and the decreasing temperature and Si activity, accompanied by the elevated fractionation of granitic magma. Thus, the variation in monazite composition reflects the formation of Zhengchong Li-Rb-Cs deposit, which may be the result of high magmatic differentiation of fluorine-rich A-type magmas. Although multistage rare metal metallogenic events have been identified in the Nanling region, it is suggested that the Late Jurassic Zhengchong Li-Rb-Cs mineralization occurred within a short duration (<1 million years). Overall, the monazite chemical and geochronological signatures are good pathfinders for magmatic evolution and Li-Rb-Cs mineralization in the Jiuyishan complex, which could be used as a potential prospecting tool for highly-evolved granite-related rare metal deposits.

The Kalba batholith dyke swarms (Eastern Kazakhstan): Mafic magmas effect on granite formation

The Kalba granitoid batholith formed in Early Permian is one of the largest in the western part of the Central Asian Orogenic Belt. Batholith granites are intruded by mafic and intemediate dykes forming several swarms. Previously it was believed that the dykes were Mesozoic and had no relationship with the formation of the batholith. Our geochronological studies allow to determine the age of the dykes at 279 Ma (also Early Permian). Dyke rocks are represented by dolerites, variolites, monzodiorites, and plagioclase porphyrites. The petrographic study of plagioclase porphyrites allow to find the sign of magma mixing. The another indicator of magma mixing are the contacts between mafic and felsic rocks in largest dykes of complex structure. A model for the interaction of mafic magmas with crustal substrates is proposed. Mafic magmas intruded from sublithospheric mantle, provoked a partial melting and then interacted with granitic melts at the basement level of granite batholith. Dyke swarms were formed after the cooling and consolidation of main volume of Kalba batholith by inrtusion of mafic and hybride magmas from the basement level of granite batholith. Chemical diversity of the mafic dykes was caused mainly by the differentiation of parental mafic magmas and also a lesser extent by their interaction with the granitoid magmas. Comparison with data on coeval magmatism in neighboring regions suggests that the Kalba batholith may be included in areal of Early Permian Tarim Large Igneous Province. • The dyke swarms cut the granites of the Kalba batholith in Eastern Kazakhstan. • The dykes and the Kalba batholith granites are Early Permian. • Dyke rocks composition was caused mainly by the differentiation of mafic magmas. • Parent mafic magmas formed in lithospheric mantle and provoked melting in crust. • Geodynamic setting was a post-orogenic extension with effect of Tarim mantle plume.

A simplified GIS and google-earth-based approach for lineaments and terrain attributes mapping in a basement complex terrain

In this study, we use an integrated geologic mapping technique for remote mapping of lineaments and geologic terrain. Our workflow is based on geographic information system tools and consists of stream network delineation, lineaments mapping, terrain roughness index calculation, and interpretation of structural fabrics from google earth aerial photographs. The case study area, the Idanre Hills in southwestern Nigeria, has a protracted history and is characterized by steep-sided outcrops of a granitic batholith and migmatite-gneiss. Lineaments are widespread and dense around the batholith, occurring in areas of high elevation, and slope gradient. Terrain roughness indices are high at the outcrops and lineament sites. Streams in the area exhibit variable flow and partly align with the lineaments. The high roughness indices observed have tectonic connotations and are related to the occurrence of lineaments, strain domains, and high degree of rock weathering. Importantly, our method is effective in remote mapping of lineaments and terrain attributes within the study area and has wider applications in other basement complex terrains.

Magmatism and tectonic setting of proto-Japan during the Early Carboniferous: Constraints from the geochemical characteristics of mafic volcanic rocks in the Hida Gaien Belt, SW Japan

• Early Carboniferous subduction-related basalts–andesites are found in SW Japan. • High-Al basalts were generated by arc tholeiitic magma near crust–mantle boundary. • Basaltic andesites were generated by fractional crystallization of the high-Al magma. • Early Carboniferous tectonic setting of proto-Japan was a primitive island arc . The Hida Gaien Belt in southwest Japan consists mainly of Paleozoic to Mesozoic shelf-facies rocks and records the tectonic evolution of East Asia. Here we report a study of the geochemistry of mafic volcanic rocks from the Early Carboniferous Arakigawa Formation of this belt. Two types of mafic volcanic rock are identified: (1) high-Al basaltic lavas, which were generated by island arc tholeiitic magma that formed under high-pressure conditions near the crust–mantle boundary and in which the nucleation of plagioclase was suppressed and delayed; and (2) basaltic andesitic lavas, which were generated by fractional crystallization of the high-Al tholeiitic magma. Combining our new results with previous geological findings, we consider that the tectonic setting of proto-Japan during the Early Carboniferous was a primitive island arc characterized by active island arc tholeiitic magmatism and the absence of a granitic batholith.

Evolution of the Paleo-Tethys Ocean in Eastern Kunlun, North Tibetan Plateau: From continental rift-drift to final closure

The dynamic evolution of the Paleo-Tethys Ocean from continental rift-drift and seafloor spreading to initial subduction and final closure has been hotly debated. This paper tries to bring new constraints to this longstanding debate based on the compiled the latest data and investigations into Carboniferous-Triassic magmatism in the westernmost segment of the Eastern Kunlun orogenic belt, North Tibetan Plateau. New results indicate that the ca. 335 Ma appinite stocks were derived from the asthenosphere mantle wedge slightly modified by slab-derived materials. The ca. 244 Ma dioritic appinite stocks were sourced from the partial melting of hydrothermally altered upper oceanic crust following the closure of the Paleo-Tethys Ocean. The ca. 231 Ma adakitic granite stock originated from the partial melting of the thickened eclogitic lower crust in the syn -collisional setting, and the ca. 219–215 Ma granite batholith had a mafic source in the post-collisional setting. By integrating records available, new scenarios of the evolution of the Paleo-Tethys Ocean in Eastern Kunlun were established. The ca. 390–380 Ma continental rifting leading to the opening of the Paleo-Tethys Ocean is attributed to the post-collisional gravitational instability subsequent to the closure of the Proto-Tethys Ocean and the far-field extensional stress induced by the retreating subduction of the Paleo-Asian Oceanic lithosphere along the northern margin of Tarim-Qaidam. The Paleo-Tethys Oceanic lithosphere initially northward subducted at ca. 366–335 Ma. The closure of the Paleo-Tethys Ocean leading to the “soft” collision between the Eastern Kunlun and Bayanhar terranes occurred at ca. 235–225 Ma followed by the ca. 225–200 Ma post-collisional extension. • The ca. 390–380 Ma opening of the PTO due to gravitational instability and retreating subduction. • The initial northward subduction of PTO occurred at ca. 366–335 Ma. • The closure occurred at 235–225 Ma followed by 225–200 Ma post-collisional extension.

U-Pb geochronology of the Silurian-Devonian Bega Batholith, south-eastern Australia: Insights into the origin and development of I-type granites

Earth’s continental crust is primarily composed of buoyant, felsic igneous (granitic) material that has been extracted from the mantle along convergent plate margins. Establishing the timescales of subduction-related granite batholith assembly is key to understanding the processes of magma generation, segregation, and transport that define the dynamics and rates of crustal growth. The ‘Cordilleran’ Bega Batholith is the largest I-type granite batholith in the Lachlan Fold Belt (LFB) of south-eastern Australia. The product of accretionary orogenesis along the Terra Australis Orogen, it has been extensively characterised by isotopic and geochemical studies yet lacks a robust geochronological framework. We present new ID-TIMS and SHRIMP U-Pb zircon ages for twenty-two plutonic rocks of the Bega Batholith. This geochronological survey indicates a prolonged duration for I-type magmatism, with crystallisation ages ranging from ca. 420 Ma in the west, to 385 Ma in the eastern Bega Batholith. These I-type granites collectively occupy ∼90,000 km3 and were emplaced over a period of ∼20–35 Ma, corresponding to a magma production rate of ∼8–15 km3/Ma km−1, considerably lower than that of S-type granites of the region and other subduction-related granite terranes globally. Fundamentally, the temporal overlap between the Bega I-type granites and S- and A-type granites also argues against a hiatus between each phase of granite magmatism in the LFB, suggesting a continuum between the granite types and derivation from common source components. This new geochronological data provides the first comprehensive compilation of U-Pb ages from across the Bega Batholith, establishing initial constraints on the development and evolution of I-type magmatism in south-eastern Australia. Our results demonstrate that I-type granite petrogenesis is linked with crustal growth processes, requiring the modification of global crustal growth curves during the Phanerozoic to account for new continental crust generated within I-type granite terranes of the Paleo-Pacific Gondwanan margin.

Development of Tourmaline-Bearing Lithologies of the Peraluminous Tusaquillas Composite Granitic Batholith, NW Argentina: Evidence from Quartz and Tourmaline

ABSTRACT Textural and chemical characteristics of quartz and tourmaline found in tourmaline-rich orbicules, greisens, pegmatites, and tourmalinite segregations associated with the peraluminous leucogranitic Tusaquillas Batholith Complex of northwest Argentina exhibit both magmatic and hydrothermal features. Imaging of quartz by optical cathodoluminescence and scanning electron microscopy cathodoluminescence shows three stages of development. Stage-1 quartz, considered magmatic, develops as large grains in pegmatites that have optical cathodoluminescence homogeneity; as anhedral relict grains partially replaced by stage-2 hydrothermal quartz in tourmalinite segregations, orbicules, and greisens; and as idiomorphic grains with irregularly spaced oscillatory zoning seen in scanning electron microscopy cathodoluminescence in orbicules. Stage-2 quartz, interpreted as hydrothermal, partially replaces stage-1 quartz and generation-1 tourmaline in most lithologies. Stage-3 quartz, a late hydrothermal stage, occurs in all lithologies as weakly luminescing quartz in healed quartz fractures with abundant fluid inclusions, commonly associated with the crystallization of irregular late-stage tourmaline. Multiple generations of tourmaline span magmatic to hydrothermal phases of development. In all lithologies, generation-1 tourmaline is compositionally similar: highly aluminous (range of average values of Altotal = 6.31–6.95 apfu), markedly Fe- and X□-rich (XMg = 0.01–0.17, X□= 0.21–0.51), and having variable F and WO (F = 0.00–0.57 apfu, WO = 0.00–0.40). Generation-1 tourmaline is interpreted as magmatic with compositions reflecting the chemical environment of the host lithologies and with compositional zoning patterns characteristic of both closed- and open-system behavior, possibly related to the transition to subsolidus conditions. Similar to generation-1 tourmaline, later-stage generations-2 and -3 tourmaline compositions are highly aluminous (range of average values of Altotal = 6.38–6.79 apfu), markedly Fe- and X□-rich (XMg = 0.00–0.20, X□= 0.28–0.40), and variably F- and WO-enriched (F = 0.07–0.57 apfu, WO = 0.00–0.31), but notably poorer in Ca and Ti (&amp;lt;0.01 apfu). The later-stage tourmaline is considered to have developed during the subsolidus hydrothermal conditions. External chemical contributions to tourmaline compositions from the country rocks appear to be minor to nonexistent. The X-site and W-site occupancies of the late-generation tourmaline implies subsolidus invasive alkaline, saline aqueous fluids with high Na but minimal Ca contents derived from the crystallizing leucogranites and related rocks across the solidus-to-subsolidus transition.

Geology, geochemistry and mineralogy of indium resources at Pitkäranta Mining District, Ladoga Karelia, Russia

This study is aimed at substantiating the prospects of the Pitkäranta Mining District for indium, assessing its resources and elucidating the mineralogical and geochemical features of the distribution of indium in ores. The skarn deposits genetically related to the Salmi anorthosite-rapakivi granite batholith of Early Riphean age were studied. The deposits were divided into two groups, depending on the degree of the greisen alteration of skarns: 1) Sn-Zn-Cu-Fe deposits (the Old Ore Field, Kitelä, Hopunlampi, Heposelkä and Kulismajoki) with little or no greisenization and 2) Be-Sn-Zn deposits with fluorite and magnetite (the New Ore Field, Lupikko, Uksa and Ristiniemi) with well-defined greisenization. Deposits of group 1 are located in the external zone of the Salmi Batholith with a steeply plunging roof (Kitelä), and deposits of group 2 commonly lie above LiF granite domes unexposed by erosion, and are spatially associated with the dykes of these granites and stockscheiders. The distribution of In and associated elements in skarn ores and major ore minerals (sphalerite, chalcopyrite, magnetite and cassiterite) were studied by ICP MS, LA ICP MS and electron probe microanalysis. A total of over 200 samples were analyzed. The results obtained show that In is closely associated geochemically with Zn and Cd, less closely with Cu, Bi and Te is not associated practically with Mo, W, As, Sn and Ag. The content of In in ores from various mines varies from <1 ppm to 0.33 %, and the average In content is 66 ppm. These variations are mainly due to different sphalerite contents in ores and the degree of manifestation of propylitic and greisen alteration of ore-bearing skarns. The main indium-bearing mineral is sphalerite (average In content is 1927 ppm). Other high-In minerals (stannoidite and mawsonite) are uncommon (<0.01 %) and, therefore, do not markedly affect the In balance in ore. The same applies with rare exception to roquesite, the only indium's mineral known here. In-richest (up to 1.5 %) sphalerites with 3–6 % Fe, up to 300–400 ppm Mn and 0.1–0.2 % Co were identified in ore mineral associations of propylitized skarns, which contain no or small amounts of chalcopyrite. Sphalerite-chalcopyrite association is characteristic of roquesite. It occurs mainly in low-tin aposkarn greisens with abundant arsenopyrite-löllingite-sphalerite mineralization. The formation of roquesite seems to have been supported by indium, which was released upon the decomposition of its solid solutions in chalcopyrite and sphalerite and upon the hydrothermal-temperature effect of the late intrusion phases of the Salmi Batholith, LiF granites, on ores. The indium distribution pattern in sphalerite, which is also rich Cd, Ag and Au, shows that roquesite-free propylitized skarns with Sn-Zn-Fe mineralization have the greatest potential for indium and these metals in the zones where the roof of the Salmi Batholith plunges steeply (40–50°) and LiF granites do not occur (Kitelä, Kulismajoki and Hopunlampi deposits). Predicted indium resources in the sphalerite ores of the Pitkäranta Mining District are estimated at 1585–2536 t (as shown by various calculations), cadmium resources at 18424 t, silver resources at 226 t and gold resources at 2 t.

New U-Pb zircon ages of plagiogranites from the Coastal Complex ophiolite and Twillingate batholith, Newfoundland: Evidence for the oldest and overlapping silicic magmatism in the nascent Cambrian peri-Laurentia forearc and arc terranes

The Coastal Complex (CC) and Bay of Islands Complex (BOIC) represent two supra-subduction zone (SSZ) forearc ophiolitic assemblages of different ages within the Taconic Humber Arm Allochthon of the Western Newfoundland Appalachians. To further constrain age relationships between the CC and BOIC and earliest initiation of Iapetus subduction, we acquired LA-ICP-MS U-Pb zircon ages for eleven plagiogranites sampled along strike of the CC belt. These ages combined with three prior legacy ages establish an age range of 514.3–502.7 Ma for the six CC plagiogranite plutons. The oldest precise ca. 514.3 Ma CC pluton age represents the oldest Taconic arc-related plutonic activity yet documented in Western Newfoundland and provides a minimum age for the intruded CC ophiolite basement and initiation of westerly vergent subduction within the peri-Laurentian Iapetus Ocean. This confirms the Early Cambrian CC mafic–ultramafic basement is significantly older than the juxtaposed SSZ BOIC, which formed by later rifting of the CC forearc along younger forearc spreading center in the Late Cambrian by ca. 488.3 Ma. After subduction initiation a prolonged early period CC forearc silicic magmatism lasted at least ∼ 11.6 Ma until ca. 502.7 Ma, a range consistent with age spans of magmatism in modern juvenile forearcs. We also reinvestigated the Central Newfoundland Twillingate Granite batholith thought to be one of the earliest major felsic batholiths formed within the adjacent juvenile arc massif of the Notre Dame Subzone, part of the same peri-Laurentian arc. We determined a precise 3-sample composite age of 504.3 ± 1.8 Ma that signals the formation of earliest Notre Dame arc edifice developed by Middle Cambrian. It overlaps the end-stage CC forearc plagiogranite magmatism and places a minimum mid-Cambrian age constraint on intruded ophiolitic arc tholeiitic and boninitic pillow lavas of the Sleepy Cove and correlated Lushs Bight volcanics, suggesting basement continuity with the CC.

Large zircon age spans record multi-stage history of batholith assembly: Insights from the Late Triassic Dongcuo batholith in the eastern Tibetan Plateau

Large and homogeneous plutons can assemble incrementally over millions of years, yielding large age spans. Determination of the age span is crucial to constrain the timing and nature of the batholith assembly. This paper reports comprehensive whole-rock geochemical data, LA-ICP-MS zircon U-Pb age, and zircon Hf isotopic data to constrain the timing and assembly process of the Late Triassic Dongcuo batholith, the largest batholith in the Yidun Terrane, eastern Tibetan Plateau. Samples from the batholith consist of metaluminous to weakly peraluminous granitoids (SiO2 = 69.91–79.85 wt%). These granitoids show large variation of zircon Hf isotopic compositions with εHf(t) of -17.15 to +0.13. The multiple zircon populations in single hand specimens revealed by kernel density estimation spread over 20 Myr (ca. 225–204 Ma), which is also confirmed by core-rim ages of single zircon grains, suggesting prolonged magmatism of the Dongcuo batholith. Our data indicate that the assembly of the batholith resulted from emplacement of discrete magma batches which derived from spatially varied sources and underwent variable differentiation. The assembly mainly involved three stages, including an early episode of magmatism (ca. 228 Ma), a high-flux magmatism between ca. 220 Ma and ca. 216 Ma, and a late-stage thermal event (ca. 211–204 Ma) possibly related to high temperature and localized remelting of the batholith. This study highlights the complexity of zircon populations in composite granitic batholith, showing that the search for single crystallization ages for a sample is fraught with difficulties and may mask rather than elucidate the crystallization history of the magmatic body.

What Makes A Hot Spring, Hot?

Hot springs naturally are groundwater that emerges to the surface after being heated up by geothermal activities. There are various classifications of hot springs according to the surface temperature. Still, in Malaysia, it is referred to as the spring that is higher than an average body temperature or 40 °C and above. Two types of hot spring origin are volcanic and non-volcanic sources. The Quaternary magmatic intrusion of Maria volcanic complex in Sabah is the only volcanic-related hot spring. Meanwhile, Sungai Klah, Ulu Slim, Gadek, and other hot springs in Malaysia originated from regional granite intrusion that slowly cooled down since the Triassic period. In Peninsular Malaysia, there is a geological trend of hot springs distribution based on three different intrusion and localities of granite batholiths: Eastern, Central and Western belts of granite. Tectonically, most of these hot springs are associated with fault zones related to highly fractured and deep-seated fault areas with high permeability host rock, such as Bok Bak Fault. Later it can conduit meteoric water to seep deep beneath the subsurface and be subjected to a high geothermal gradient zone. High dissolved minerals in the hot springs are beneficial for balneotherapy, while the excess heat and brine can be harnessed into electrical energy. The development of geothermal potential in Malaysia is still unhurried compared to our neighbouring countries, for example, Thailand’s Fang Geothermal Power Plant is a non-volcanic hot spring with a sound temperature of 130°C which can generate 300 kW of electricity. Lastly, effort has been made by researchers in gathering the data on hot spring distribution in Malaysia which can be viewed with just a click. A new app is developed for Android user named Malaysia’s Hot Springs that can be freely downloaded from the ‘Apps Store’ in hope that the application can serve as hot springs tourism and publication reference purposes.

Permian Remelting and Maturity of Continental Crust Revealed by the Daqing Peraluminous Granitic Batholith, Inner Mongolia

AbstractThe Phanerozoic granites in northeast China bear key information for studying the tectonic evolution and crustal growth or reworking in the Central Asian Orogenic Belt (CAOB). The Daqing granitic batholith widely outcrops as a high-level intrusion in the Xing’an-Mongolia Orogenic Belt, southeastern CAOB. Three types of enclaves in granites have been identified: (1) mafic magmatic enclaves (MMEs), (2) volcanic xenoliths, and (3) biotite-rich enclaves. The batholith is mainly composed of peraluminous biotite granite and granodiorite with SiO2=63.95−69.48 wt.%, A/CNK=1.15−1.27, and 2.54 to 4.30 wt.% of normative corundum. They exhibit remarkable enrichment in large ion lithophile elements (LILEs; K, Rb, Th, and Pb) and depletion in high field strength elements (HFSEs; Nb, Ta, and Ti), P, Eu, and Sr, as well as relatively enriched Sr-Nd isotopes (87Sr/86Sri=0.70530−0.70576, εNdt=–0.1−+0.2). Zircon U-Pb dating suggests that this batholith was emplaced in the Early Permian (ca. 283-282 Ma), consistent with a period of intensive magmatic activities in northern Inner Mongolia. The Nb/Ta ratios of MMEs (17.6-20.1) are higher than those of the host granites (11.4-12.5), together with the reaction rims where biotite crystals cluster around the amphibole cores, suggesting magma mixing between mantle- and crust-derived melts. Zircons from a biotite-rich enclave define a protolith age of ca. 320 Ma and an anatectic age at ca. 281 Ma. Whole-rock Sr-Nd isotopic modelling and zircon Hf isotopes reveal that the batholith was mainly produced by remelting of newly accreted continental crust with minor addition of mantle-derived materials. The geochemical compositions imply that their precursor magmas originated from a relatively high crustal level (&amp;lt;5 kbar) with crystallization temperatures ranging from 800 to 850°C. We suggest that the Daqing peraluminous granitoids were derived from partial melting of newly accreted crustal materials at a relatively shallow crustal depth, associated with a ridge subduction-related heat source. Such mantle-derived magmas through a slab tear window resulting from ridge subduction provide not only the heat for the widespread crustal remelting and therefore maturity but also juvenile materials for crustal growth.

Episodic emplacement of the Lingshan Granitic Complex and related two-stage molybdenum mineralization in the Dabie orogenic belt

The Lingshan Granitic Complex consists of a granitic batholith and its proximal Mushan and Xiaofan porphyry stocks, and hosts stockwork-type Mo mineralization within the porphyry stocks and the fine-grained monzogranite, and several vein-type Mo occurrences in the coarse-grained porphyritic monzogranite. All these rocks show similar values of the whole-rock initial 87Sr/86Sr (0.70442–0.70987), εNd(t) (–17.2 to –11.0), and zircon εHf(t) (–27.2 to –9.3), indicating their derivation from partial melting of the Paleoproterozoic-Neoarchean recycled continental crust induced by basaltic underplating at the crust-mantle boundary. The zircon U-Pb and molybdenite Re-Os geochronological results indicate that the Lingshan Granitic Complex was formed by at least two pulses of magmatism at 140–137 Ma and 128–125 Ma, accompanied by two periods of Mo mineralization, which is the epitome of the peak granitic magmatism and related Mo mineralization in the whole Dabie orogenic belt. Combined with previous data, it can be concluded that the discontinuous and episodic nature of magma emplacement in the whole Dabie Mo metallogenic belt has significant consequences for large-scale, multi-staged Mo mineralization. Although Mo mineralization can occur in various lithofacies of the Lingshan Granitic Complex, the industrial Mo enrichment mainly lies within the small shallow emplacement granite porphyry stocks and subordinately within the fine-grained phase of the pluton. These features indicate that the Mo industrial enrichment is not only related to the highly evolved magma, but also more closely related to mechanism of magma emplacement. Rapid decompression induced by rapid ascent of the Mo-bearing granite porphyry stocks, and rapid crystallization of magma induced by quickly cooling due to conductive heat loss to the sidewalls of the fine-grained phase of the outer zone of the granite batholith, are favorable for the ore-fluid exsolution responsible for the magmatic-hydrothermal Mo mineralization.

Geochemical, zircon U–Pb–Hf–O isotopic evidence and molybdenite Re–Os dating from the Cuojiaoma batholith, eastern Tibetan Plateau: Implications for molybdenum potential and tectonic evolution

Subduction of oceanic plates beneath continental lithosphere is critical for understanding tectonic evolution and evaluation of prospecting and exploration. Within the Yidun Terrane (YDT) of southwestern China, a number of Mesozoic to Cenozoic granitoid intrusions are exposed and they are useful for investigating the tectonic evolution of the Paleo-Tethys system. However, Mesozoic magmatism of the northern portion of the YDT, remains ambiguous regarding to their magmatic spatial–temporal evolution and their mineralization potential. As the largest pluton in the northern YDT, the Cuojiaoma batholith mainly consists of monzogranite and granodiorite. In this study, we present new zircon U–Pb and molybdenite Re–Os ages, whole-rock geochemical, and zircon Hf–O isotopic data for the Cuojiaoma batholith. LA-ICP-MS zircon U-Pb dating of granodiorite and monzogranite exhibit ages of 221.8 ± 1.4 Ma (n = 22, MSWD = 2.4) and 216.7 ± 2.2 Ma (n = 14, MSWD = 0.03), respectively. A total of 9 molybdenite samples differing Re-Os model ages of 205.4 ± 3.3 and 220.6 ± 5.5 Ma, yield a robust weighted mean model age of 209.9 ± 1.8 Ma (MSWD = 2.4, n = 9) representing the depositional age of molybdenite. The monzogranite and granodiorite’s mineralogical and geochemical characteristics indicate they are classified as (medium-) high-K calc-alkaline and metaluminous to weakly peraluminous I-type granite. Geochemically, they are enriched in large-ion lithophile elements (LILEs, e.g., Rb, U, K) and light rare earth elements (LREEs), and depleted in high-field-strength elements (HFSEs, e.g., Nb, Ta, Ti and P) and heavy rare earth elements (HREEs), and contain distinctly or slightly negative Eu anomalies and no significant Ce anomalies, indicating an affinity to classical island arc magma. Combined with their negative zircon εHf(t) values (−16.24 to −2.49 and −16.41 to −1.43) and two-stage Hf model ages (2019–1255 Ma and 2027–1200 Ma), plus their zircon δ18O values, which range from 5.96 to 8.01 and from 5.05 to 7.61 for monzogranite and granodiorite, respectively, these geochemical indexes indicate that the Cuojiaoma batholith shares similar petrogenesis to other intrusions within the YDT. The formation of the early granodiorite may be genetically related to the slab subduction and is most likely formed by mixture of lower crustal melts and mafic magma derived from partial melting of mantle wedge induced by the influx of slab derived melt (fluid). Subsequent slab break-off and the upwelling asthenosphere at ∼ 216 Ma to 210 Ma led to high heat flow and extensive melting of the overlying mantle wedge, followed by the highly crystallization differentiation, which finally contributed to the monzogranite and the subsequential disseminated molybdenite in a post-subduction extension setting. The northern YDT possesses high Mo metallogenic prospectivity, especially for the magmatic activity that dominantly by lower crustal melt and genetically related to the slab break-off occurred at ∼ 216 Ma and represented by the highly fractionated granite derived from the large Cuojiaoma granitic batholith.

Activation of Ad Damm shear zone, western Saudi Arabian margin, and its relation to the Red Sea rift system

Abstract The Ad Damm shear zone (ADSZ) is a major mylonitic right-lateral structure that bounds the Jeddah terrane to the north from the Asir terrane to the south. High-resolution field mapping coupled with petrological and geochemical analyses indicate that Jeddah terrane is characterized by heterogeneous magmatism with extensive meta-basalt intruded by silicic plutons of varying size. South of the ADSZ, Asir terrane is characterized by larger scale granitic batholiths. A younger generation of Eocene–Miocene basaltic dikes cut the mylonitic shear zone at a high angle. Petrographic analyses of the ADSZ mylonitic rocks indicate dynamic recrystallization and grain-size reduction, suggesting high-temperature recrystallization. Field observations also found a lack of low-temperature fault zone rocks (e.g. gouge) except for isolated brittle slickensides. Spider diagrams of Jeddah, Asir terranes, and ADSZ rocks are characterized by an arc-related signature, which related to the amalgamation of Jeddah and Asir terranes and defined ADSZ as Neoproterozoic structure. In contrast, Eocene–Miocene basaltic dikes and southern basaltic flow are represented by a rift-related signature, which associated with the development of the Red Sea rift system. Offshore, south of the ADSZ, the Red Sea rift exhibits well-developed linear magnetic anomalies and large topographic escarpment perpendicular to the rift margin, but they are not present north of it. In addition, recent seismicity recorded along the ADSZ and differences in the crustal thickness and characteristics of Asir and Jeddah terranes, collectively, make ADSZ acted as an active crustal boundary and still influence the ongoing tectonic evolution of the Red Sea rift.

Uranium in groundwaters: Insights from the Leinster granite, SE Ireland

Uranium concentrations in groundwaters from >100 private wells in the Caledonian Leinster Granite Batholith of SE Ireland range from a few μg/l to >300 μg/l. Approximately 10% of the wells exhibit uranium concentrations that exceed the current WHO provisional guideline of 30 μg/l and a further 10% exceed the original WHO guideline value of 15 μg/l. New whole-rock geochemical analyses and laboratory batch leaching experiments confirm the granite as the ultimate source of the groundwater uranium, but carbonate-bearing glacial deposits that overlie the granite play an important role in facilitating the generation of soluble and mobile anionic uranyl carbonate complexes. Whilst the granite has average uranium concentrations broadly similar to other Irish and British Caledonian granites, it is enriched locally in uranium, with whole-rock values up to c. 30 mg/kg. Uraniferous zircon, apatite, monazite and associations with secondary Fe-bearing oxide minerals were detected in drillcore whole-rock samples that had the highest uranium concentrations, but uraninite was not detected. Broad positive correlations between groundwater uranium concentrations and bicarbonate alkalinity and electrical conductivity are found in both the sampled groundwaters and in laboratory leachates of the granite and surficial glacial deposits. Leachates from the granite had approximately an order of magnitude higher uranium concentrations compared with those from the overlying limestone-bearing glacial tills. (234U/238U) ratios for the groundwaters and the leachates always exceed unity, indicating preferential leaching of loosely bound radiogenic 234U from mineral surfaces or grain boundaries into the groundwaters, rather than wholescale dissolution of the primary uraniferous minerals in the granite. Strontium isotopes ratios in the groundwaters constrain the balance between limestone and granite-derived Sr, and by extension the sources of dissolved Ca. These data indicate that calcite dissolution is the main source of dissolved calcium, highlighting the role of weathering of overlying limestone-bearing glacial tills during recharge in determining the geochemistry of the groundwaters. Geochemical modelling indicates that in the oxidising groundwaters of the study area U6+ is dominant, in the form of UO2(CO3)3−4 at the high pH values (7.49–7.69) of waters from wells overlain by limestone-bearing till. By contrast, in a small number of wells overlain by granite-bearing till, modelling indicates that the dominant species is UO2(CO3)2−2 reflecting their lower pH (6.22–6.30). Overall, carbonate species play a major role in uranium solubility and mobility in these granite-hosted groundwaters.

Ultrahigh-temperature granites and a curious thermal eye in the post-collisional South Bohemian batholith of the Variscan orogenic belt (Europe)

Abstract Comprehensive zircon thermometry that takes into account zircon saturation temperatures, Ti-in-zircon measurements, and zircon morphologies and microstructures can provide key information on the thermal evolution of a granite batholith. The Variscan South Bohemian batholith (Germany, Austria, and Czech Republic) comprises a series of granitoid units that intruded between ca. 330 and ca. 300 Ma. We categorize the granitic rocks according to their emplacement temperature into very low temperature (T) (VLT; &amp;lt;750 °C), low T (LT; 750–800 °C), medium T (MT; 800–850 °C), high T (HT; 850–900 °C), and ultrahigh T (UHT; &amp;gt;900 °C). The first stage of batholith formation (ca. 330–325 Ma) is characterized by LT to MT melting of mainly metasedimentary sources driven by their isothermal exhumation. In turn, ca. 322 Ma HT and UHT granites in the southern half of the batholith reveal an ephemeral thermal anomaly in the subbatholithic crust, which is presumably linked to a hidden mafic intrusion. The HT and UHT granites are weakly peraluminous, high-K, I-type rocks. Although sharing some features with A-type granites such as high Zr and rare earth element contents, they differ from classical A-type granites in being magnesian, not enriched in Ga over Al, and having high Ba and Sr contents. A ring structure of ca. 317 Ma MT and/or LT plutons is observed around the HT and/or UHT granite complex and interpreted as an aftermath of the hotspot event. This study is an example of how deep-crustal hotspots, presumably caused by mantle magmatism, can significantly enhance the effects of decompressional crustal melting in a post-collisional setting.