Granitoid Plutons Research Articles

Sources and petrogenesis of Late Triassic granitoids in the Yajiang gneiss dome group (eastern Songpan-Ganze orogenic belt) with tectonic implications

Numerous Mesozoic granitoid plutons with a substantial variety of petrologic and geochemical signatures intrude the Triassic metasedimentary rocks of the Songpan-Ganze accretionary-orogenic wedge in the eastern Tibetan Plateau. These granitoid rocks generally exhibit sharp contact with the Triassic sedimentary rocks. To better understand the genesis and emplacement of magmas associated with tectonic accretion along convergent plate boundaries, we present new LA-ICP-MS zircon U-Pb geochronology, major and trace elements, and Sr–Nd–Pb–Hf isotopic compositions for intermediate-to-felsic plutons in the Yajiang gneiss dome group (YGDG), including the Changzheng pluton, the Jiajika (Majingzi) pluton, the Rongxuka pluton, the Xiya pluton, the Xinduqiao pluton, and the Waduo diorite dikes in the eastern margin of the Songpan-Ganze orogenic belt (SGOB). By their typical petrological and geochemical characteristics, these plutons are classified as I-type granodiorite-diorite (Rongxuka, Xiya, Xinduqiao plutons, Waduo dikes) or S-type granite (Changzheng and Jiajika plutons). I-type granodiorite-diorites exhibit a high Mg# (average 49), medium-K cala-alkiline signature and are enriched in large-ion lithophile elements (e.g., Rb, Th, and U) but depleted in high field strength elements (e.g., Nb, Ta, and Ti), and with lower initial 87Sr/86Sr values (0.70622 to 0.70863) but a relatively high and concentrated εHf(t) (−27 to −1.9) and εNd(t) (−4.02 to −7.51); while S-type granites exhibit a high silica, high-K cala-alkiline signature with strong negative Eu anomalies (Eu/Eu* = 0.17–0.64), and possess high initial 87Sr/86Sr values but low εHf(t) (−40.1 to −0.9) and εNd(t) (−8.72 to −12.14) signatures, forming through partial melting of metasedimentary rocks from an ancient crust source. LA–ICP–MS zircon U-Pb dating indicates that they were emplacement between 207.2 ± 1.4 and 223.6 ± 2.2 Ma. Both types of granitoid rock were formed by the crustal partial melting followed by extensive fractional crystallization under high-temperature (700–850 °C), low-pressure (<15 kb) conditions. In combination with previous studies, our data provide evidence for an affinity between the eastern Songpan-Ganze andthe Yangtze craton basements, and suggest that the granitoid plutons formed in a syn-collisional to post-collisional setting at ca. 207–223 Ma.

Petrogenesis of the Triassic Dongjiangkou pluton in the South Qinling orogenic belt, Central China: Insufficient magma mixing of mafic and felsic magmas

Magma mixing or mingling between mafic and felsic magmas is a common phenomenon in granitoid magmatism, and chemical and mechanical interactions between the magmas are frequently observed in granitic rocks. The Dongjiangkou pluton is an example of magma mixing among the numerous early Mesozoic granitoid plutons that are exposed in eastern South Qinling. This pluton is predominantly composed of granodiorite and contains abundant mafic/intermediate microgranular enclaves (MMEs) and is sporadically intruded by mafic dykes. Both the granodiorite and MMEs were crystallized at 224–214 Ma and have inherited zircons of similar age ranges. The granodioritic rocks had metaluminous to weak peraluminous features and adakitic signatures and belong to the high-K calc-alkaline series, whereas the MMEs and dioritic dykes had low SiO2 contents and metaluminous features and belong to the high-K calc-alkaline to shoshonite series. All of the rocks had high Mg# values and similar geochemical characteristics regarding trace elements and Sr isotopes, but they had diverse whole-rock Nd-Pb and zircon Hf isotopic compositions. The Dongjiangkou granodiorite was produced by partial melting of old basement rocks and Paleozoic juvenile crust beneath South Qinling triggered by asthenospheric upwelling. Magma(s) of the Dongjiangkou MMEs may have been derived from deep mantle and injected into and mixed with the magma(s) of the granodiorite, but chemical and isotopic homogenization was not achieved during the magma mixing process. Clastic rocks may have played a major role in the formation of crust-derived magma(s), causing strong Nd-Hf isotopic decoupling of several granitoid plutons in South Qinling.

Deciphering the parent-daughter relationship between Ediacaran high-silica ignimbrites and their complementary silicic cumulates: Insights from zircon trace element composition

The Ediacaran Campo Alegre-Corupá Basin (CACB) comprises a rare and excellent exposure of caldera-forming pyroclastic rocks and their cogenetic underlaying plutons. The CACB experienced at least two major episodes of bimodal volcanic activity. The Basin Stage (∼605–590 Ma), characterized by transitional OIB-like basaltic lava flows with minor trachydacites and rhyolites, interbedded with surge-like, silicic pyroclastic deposits, and the Caldera Stage (∼583–577 Ma), marked by at least one cycle of silicic alkaline, caldera-forming eruption, dominated by rhyolitic to trachytic ignimbrites and lava flows/domes with subordinate IAB-like basalts. During the Caldera Stage, granitoid plutons were emplaced at shallow crustal levels (∼5–8 km deep), correlating with the depth of the magma chamber responsible for the contemporaneous large silicic eruption(s). Previous studies have suggested a genetic connection between the post-collisional volcanic and plutonic rocks based on their similar ages, composition, and Sr-Nd-Hf isotopic signatures. In this study, we analyze zircon trace elements from the volcanic rocks of both stages in the CACB to constrain their evolutive compositional patterns, redox conditions, and Ti-in-zircon saturation temperatures. We compare our results with zircon compositions of the cogenetic granitoids, focusing on the Corupá Pluton, which likely supplied the magma for the caldera-forming eruption(s). By examining whole-rock and zircon chemical compositions, we establish a petrogenetic link between the volcanic rocks and their potential remnant magma reservoir. Our findings indicate that the silicic volcanic rocks from the Caldera Stage represent highly evolved compositions extracted from a crystal mush that solidified as a syenitic intrusion. During the evolution of the volcanic-plutonic system, zircon crystals tracked compositional changes associated with the extraction of residual silicic liquids from crystal mushes and the formation of intermediate-silicic cumulates. Unique variations in zircon compositions of volcanic and plutonic rocks, such as Eu/Eu*, Zr/Hf, and Th/U ratios support such a connection and suggest crystal-melt segregation processes at relatively low crystallinities (< 30 vol%). Additionally, our trace element data supports the occurrence of intense hydrothermal-induced recrystallization of zircon within the caldera structure, as suggested by the morphologic aspects of crystals previously analyzed for UPb and LuHf isotopes.

Native silver in the eastern part of the Karkonosze granitoid pluton, Lower Silesia, Poland

This article describes silver specimens of the size of tenths to a few millimetres, found in small pegmatites and quartz veinlets of the porphyritic granitoid area in 22 sites in the eastern part of the Variscan granitoid Karkonosze pluton, from 20 of which native silver occurrences were previously not known. The sites are scattered on the whole surface of the granitoid. The native silver occurred in wire, rod, platy, dendritic, anhedral granular and euhedral cubic and octahedral habits; in some specimens twins and fenster faces were also found. Associated with native silver small amounts of acanthite crystallized commonly, sometimes apparently formed by sulphur diffusion into silver. Inclusions of native gold, electrum, galena, chalcopyrite and pyrite occurred in the native silver. The parent fluids of the specimens were epithermal, because the homogenization temperature (Th) of inclusions in quartz, calcite and cleavelandite that were the host minerals of the native silver was generally 91–165ºC and for individual samples the Th range was 4–11ºC. The total salinity of the fluid was 2.4–7.2 wt. % with Na and Ca (hydro)carbonates as the main dissolved components and admixtures of K, Mg, Fe, Al, S, Cl and F. The parent granitoid contains Ag in trace amounts (0.034–0.056 ppm) and was probably the source of this element for the crystals of native silver. Migration of Ag was made easier by the presence of fluoride ions in fluids.

Zircon melt inclusion study on the Miocene Miuchi granitoid pluton, SW Japan: A new approach to estimate crystallization pressures of granitic rocks

Granitic rocks (sensu lato) are a major rock type in orogenic belts. The crystallization pressures of granitic rocks can help to unravel the magmatic processes and tectonic evolution of these regions, particularly in areas where metamorphic rocks are not exposed. However, geobarometric techniques that are suitable for granitoids are quite limited. In this study, we propose a new approach to estimate crystallization pressures of granitoid magmas using melt inclusions in zircon, a ubiquitous accessory mineral in these lithologies. Homogenization experiments of polymineralic inclusions hosted in zircon have been conducted from a biotite granite sample in the Miocene Miuchi pluton, southwest Japan arc, using a piston-cylinder high-pressure–high-temperature apparatus. The homogenized compositions of the inclusions have high SiO2 contents (76–80 wt%) implying that they represent fractionated interstitial melts trapped in growing zircon crystals. The rhyolite-MELTS geobarometer for the homogenized melt inclusions in oscillatory-zoned zircon rim yields pressures ranging from 80 to 114 MPa (with error of ±25 MPa), interpreted as the crystallization pressures of the Miuchi pluton. These results are consistent with field and petrographic observations suggestive of a shallow emplacement level. The approach presented here would be applicable to most granitoids, which could provide fundamental data to better understand granite petrogenesis and the tectonic evolution of orogenic belts.

Раннемеловые гранитно-метаморфические ассоциации и оруденение Золотого хребта (Восточная Чукотка)

The geological characteristic of the Golden Ridge, one of the oldest gold-bearing areas in the North-East, is presented. The important role of the Early Cretaceous metamorphism and the associated granitoid plutonism controlling the orogenic gold mineralization and the placer gold content, which is typical for the granite-metamorphic domes of Chukotka, is demonstrated. The area prospects for the Late Cretaceous copper-molybdenum-porphyry mineralization are characterized. The potential of ore and placer gold in the area discussed is assessed.

From magmatic arc to a post-accretionary setting: Late Palaeozoic granitoid plutons in the northwestern Trans-Altai Zone, Mongolia

From magmatic arc to a post-accretionary setting: Late Palaeozoic granitoid plutons in the northwestern Trans-Altai Zone, Mongolia

Logan Medallist 7. Appinite Complexes, Granitoid Batholiths and Crustal Growth: A Conceptual Model

Appinite bodies are a suite of plutonic rocks, ranging from ultramafic to felsic in composition, that are characterized by idiomorphic hornblende as the dominant mafic mineral in all lithologies and by spectacularly diverse textures, including planar and linear magmatic fabrics, mafic pegmatites and widespread evidence of mingling between coeval mafic and felsic compositions. These features suggest crystallization from anomalously water-rich magma which, according to limited isotopic studies, has both mantle and meteoric components. Appinite bodies typically occur as small (~2 km diameter) complexes emplaced along the periphery of granitoid plutons and commonly adjacent to major deep crustal faults, which they preferentially exploit during their ascent. Several studies emphasize the relationship between intrusion of appinite, granitoid plutonism and termination of subduction. However, recent geochronological data suggest a more long-lived genetic relationship between appinite and granitoid magma generation and subduction.Appinite may represent aliquots of hydrous basaltic magma derived from variably fractionated mafic underplates that were originally emplaced during protracted subduction adjacent to the Moho, triggering generation of voluminous granitoid magma by partial melting in the overlying MASH zone. Hydrous mafic magma from this underplate may have ascended, accumulated, and differentiated at mid-to-upper crustal levels (ca. 3–6 kbar, 15 km depth) and crystallized under water-saturated conditions. The granitoid magma was emplaced in pulses when transient stresses activated favourably oriented structures which became conduits for magma transport. The ascent of late mafic magma, however, is impeded by the rheological barriers created by the structurally overlying granitoid magma bodies. Magma that forms appinite complexes evaded those rheological barriers because it preferentially exploited the deep crustal faults that bounded the plutonic system. In this scenario, appinite complexes may be a direct connection to the mafic underplate and so its most mafic components may provide insights into processes that generate granitoid batholiths and, more generally, into crustal growth in arc systems.

Silver compounds as minerals in the eastern Karkonosze granitoid pluton, Sudetes, Poland

Twenty silver minerals of the sulphide, arsenide, selenide, telluride, sulphosalt and chloride groups were found in 13 locations in the Variscan Karkonosze granitoid pluton. Previously only one of these minerals was known from this area. The findings include species characterized in publications as rare or exceptionally rare, e.g., muthmannite and tsnigriite. They occur in pegmatites and quartz veins; their parageneses are described. The studies include determination of chemical compositions, formulae calculations and recording of XRD patterns. Inclusion studies in paragenetic quartz indicate that they crystallized from epithermal fluids with a common but low component of CO 2. The results suggest that the minerals formed from trace elements (Ag included) in the Karkonosze granitoid due to very local degrees of recrystallization of the host granitoid.

Petrogenesis and Metallogenesis of Granitoids in the Yangla Cu-W Polymetallic Deposit, Southwest China: Evidence from Zircon Trace Elements and Hf Isotope

Magmatic zircon tends to present characteristic trends in trace element compositions in response to magma petrogenesis and metallogenesis, such that zircon may provide a window into melt evolution not accessible by whole rock chemistry. The Yangla large Cu deposit is located in the central part of the Jinshajiang Suture Zone, southwest China, constrained between the Jinshajiang and Yangla Faults. In this study, the trace elements and hafnium isotopic compositions of zircons from quartz diorite were studied. Previous published relevant data of Yangla granitoid plutons (i.e., dioritic enclave, granodiorite, and quartz monzonite porphyry) also have been systematically cited and discussed. The result shows that the crystallization temperature and two-stage Hf mode ages (tCDM; the age of the source rocks for the magmas) gradually increased while the oxygen fugacity (fO2) and εHf(t) values gradually decreased, corresponding to the diorite enclave (~232 Ma), through granodiorite (~208 Ma) and quartz monzonite porphyry (~202 Ma), and to quartz diorite (~195 Ma). It is suggested that four plutons were from the same three-component mixing of upper crust + lower crust + mantle magmas, while the upper crustal metasediments ratios were gradually increased from the early to late stage. The increasing upper crust inputs resulted in higher melting temperatures and compositions of the initial magma. All melts experienced distinct fractional crystallization of apatite, titanite, and amphibole, and the later granite melts experienced higher assimilation and fractional crystallization degrees than the early ones in the evolution processes four stages of intrusive rocks. These Yangla granitoids are the products of large-scale acid magmatic emplacement activities in the Triassic-early Jurassic and have a good metallogenic potential of the Cu-W polymetallic deposit.

Paleozoic tectonic setting and evolution of the Central Tianshan Block: Insights from Devonian arc-related granitoids

• Distinct Devonian arc-related granitoids record three phases of magmatism . • Devonian granitoids were derived from remelting of Mesoproterozoic rocks with addition of mantle and juvenile crustal components. • The Central Tianshan Block was a continental arc during the Paleozoic bipolar subduction of the Kangguer oceanic slabs. The Central Tianshan Block of the Central Asian Orogenic Belt (CAOB) contains Precambrian metamorphic basement and voluminous Paleozoic granitoids, but its Paleozoic tectonic setting remains debated. This study presents new geochronological and geochemical data for the granitoids in the Shuangqing district in combination with published data from the Central Tianshan Block to constrain the tectonic setting and evolution of the Central Tianshan Block. Zircon U–Pb dating of the different granitoid plutons identified three phases of magmatism, a foliated granite (408.9 ± 2.6 Ma), a K-feldspar granite (397.7 ± 2.5 Ma), and a granodiorite (porphyry) (ca. 390–388 Ma). These Devonian granitoids show medium- to high-K calc-alkaline affinities, large ion lithophile elements (LILE; e.g., Rb and Ba) enrichment, and high field strength elements (HFSE; e.g., Nb, Ta, and Ti) and Eu depletion, consistent with subduction-related I-type granitoids. They have negative ε Nd (t) values (−5.2 to −3.4), old zircon T DM C ages (1623–1036 Ma), and variable zircon ε Hf (t) values (−3.54 to +5.70), indicating they were mainly sourced from remelting of Mesoproterozoic rocks with variable incorporation of mantle and juvenile crustal components in their magma sources. Combining with published data and this study, we suggest the Central Tianshan Block was a continental arc in the Ordovician to Carboniferous during the bipolar subduction of the Kangguer oceanic slabs. During the Devonian, the subduction of the Kangguer oceanic slabs formed the Central Tianshan continental arc to the south, accompanied by emplacement of multiphase arc-related granitoids in the Shuangqing district.

In-situ plagioclase geochemistry and Pb isotopic compositions from Mesozoic granitoids in the northeastern North China Block and its petrogenetic implications

Plagioclase has been widely used to reflect the magmatic evolution and the crust-mantle interaction based on its compositional zoning. However, the abilities in recording the adakitic characteristics and the reworking of continental crust are not understood. This paper reports new in-situ plagioclase geochemistry and Pb isotopic compositions of eight Mesozoic granitoid plutons in the northeastern North China Block (NCB). Based on our previous whole-rock and in-situ apatite geochemistry, we divided them into two groups as adakitic rocks and non-adakitic rocks. Comparison and analysis of plagioclase geochemistry in this paper and previous data between these two groups show that plagioclase crystallized from adakitic rocks possesses higher Sr (735–1588 ppm, generally >1000 ppm) concentrations, δEu (δEu = 2EuN / (SmN + GdN; N represents after primitive mantle normalize) and Sr/Y (1159–81,344, generally >5000) values than those from non-adakitic rocks. Therefore, we believe that the geochemical index of plagioclase Sr–Y–δEu could reserve the adakitic characteristics and then propose two plagioclase geochemical diagrams (Sr/Y versus Y and δEu versus Sr/Y) to identify the adakitic characteristics. Furthermore, the in-situ plagioclase Pb isotopic compositions (206Pb/204Pb ranging from 16.948 to 18.146, 207Pb/204Pb ranging from 15.403 to 15.656 and 208Pb/204Pb ranging from 37.250 to 39.088), together with the rock-assemblages and spatial-temporal distributions of Mesozoic rocks as well as the variations of whole-rock Sr–Nd–Pb and zircon HfO isotopic compositions reveal the variation of crustal properties during Mesozoic. Late Triassic magmatism originated from reworking of juvenile lower crust in normal thickness. Early Jurassic magmatism were formed by partial melting of ancient thickened lower crust. Late Jurassic magmatism were derived from remelting of ancient lower crust in normal thickness. Early Cretaceous magmatism were derived from reworking of ancient lower crust in different depth.

Zircon U–Pb and titanite U–Th–Pb ages of the Ghorveh mixed granitoid pluton: Implications for the Late Jurassic supra‐subduction extension of the Sanandaj–Sirjan Zone, Iran

The Ghorveh batholith, located in the central part of the Sanandaj–Sirjan Zone (SSZ), Iran, preserves several sequences of Mesozoic plutonic and volcanic rocks. This study presents systematic analyses of the calc‐alkaline granites and monzodiorites from the southern part of the Ghorveh pluton. The granites are metaluminous to slightly peraluminous with A/CNK ratios of 0.97–1.02, indicating an A‐type granitic affinity. High Rb, Th, and K and low Sr, P, and Ti concentrations indicate an involvement of crustal materials. Whole‐rock negative εNd(t) values and relatively high TDM1 model ages support a continental crustal source. Thus, the granites are of fractionated A‐type in composition produced by partial melting of crustal materials. The monzodiorites have incompatible trace element patterns with enrichment in light rare earth elements (LREEs) and large‐ion lithophile elements (LILEs) relative to heavy rare earth elements and high‐field strength elements. This combined with the high Mg# values and the positive εNd and εHf(t) values, indicate a mantle‐derived origin. Dating results show that the granites and monzodiorites have uniform crystallization ages of ~150 Ma. Previous results and our new data suggest that the Jurassic subduction of Neo‐Tethyan Oceanic crust under the Eurasian continent was followed by slab rollback that induced back‐arc extension. Heat transfer from arc magmas increased the degree of decompressional melting in the thinned lithosphere. Melting of the presumably homogeneous crust was concurrent with emplacement of the intermediate composition magmas. Consequently, we propose that the Ghorveh area of the central SSZ developed in a supra‐subduction extensional phase during the Late Jurassic.

The Ouarzazate Supergroup and its plutonic keel: the relicts of an Ediacaran silicic large igneous province in North Africa

Ouarzazate igneous rocks from Sidi Ifni, SW Morocco, define a &gt;3 km thick pile of mostly pyroclastic falls and flows of rhyolitic and dacitic ignimbrite and tuff, underlain by co-magmatic granitoid plutons. These rocks formed during two closely spaced periods of magmatism dated to c. 595–585 and 575–560 Ma, with the majority of rocks comprised of ferroan alkali feldspar rhyolite, syenorhyolite or monzorhyolite. They can be divided into high and low heavy rare earth element types that discriminate as both volcanic arc and within-plate magma types. Coeval, but less common, mafic rocks consist of olivine-normative trachybasalt and basaltic trachyandesite. Temporal and compositional equivalents of the Ouarzazate volcanic and intrusive rocks crop out widely across North Africa and extend into the previously contiguous regions of NE North America. Collectively, these erupted/shallowly emplaced Ouarzazate-like rocks represent asthenospheric partial melts that are variably hybridized by additions from the lithospheric mantle and crust. The root cause of asthenospheric upwelling remains unknown, although the foundering of pre-collison subducted oceanic lithosphere may provide a plausible explanation. The vast geographical extent over which Ouarzazate-like igneous rocks are found, together with their composition and intra-plate setting, support the conclusion that these rocks represent the remnants of a late Ediacaran silicic large igneous province. Supplementary material: A tabulation of the geochronologic and geochemical datasets from Sidi Ifni is available at https://doi.org/10.6084/m9.figshare.c.5945756

Albian–Cenomanian granitoid magmatism in Eastern and Central Tibet as a result of diachronous, continental collision induced slab tear propagation

AbstractA discrete belt of Albian–Cenomanian granitoid plutons occurs in the Lhasa and Qiangtang terranes in the Central (CTP) and Eastern Tibetan Plateau (ETP) and represents a major magmatic pulse in the plateau’s crustal evolution during the Cretaceous. The geochemistry, petrogenesis, and magmatic development of these granitoids are different from those of magmatic arc granitoids along the southern edges of the Lhasa and Qiangtang terranes, indicating different heat and melt sources and tectonic setting of their formation. We present here new mineral, whole-rock and isotope geochemistry, and zircon U-Pb age data from the Xiasai pluton in the ETP and discuss its geochemical-petrological characteristics and magmatic development in comparison to the other Cretaceous plutons in the ETP and CTP, and within the tectonic framework of the Mesotethyan geology of Tibet. Zircons from the Xiasai and other plutons in the ETP have yielded U-Pb ages ranging from 106 Ma to 93 Ma in comparison to 115 Ma and 100.3 Ma zircons from the Southern Qiangtang Terrane (SQT) and 113.4 Ma and 109 Ma zircons from the Northern Lhasa Terrane (NLT) farther west. The Cretaceous granitoids in the ETP and CTP range in composition from granite, K-feldspar granite to monzogranite and biotite monzogranite, representing highly fractionated I-type granites with relatively high SiO2 and K2O contents, variable (Na2O + K2O)/CaO and FeOT/MgO ratios, and (Zr + Nb + Ce + Y) abundances. They display significant negative Eu anomalies (Eu/*Eu) = 0.04–0.12) and strong depletions in Sr and Ba, and are strongly enriched in large ion lithophile elements but depleted in high field strength elements. Their εHf(t) values correspond to wide ranging Hf isotope crustal model ages (TDMC) of 0.3–1.9 Ga, and their Sr-Nd isotopic signatures show elevated (87Sr/86Sr)i ratios (0.7034–0.7105) and negative εNd(t) values of –8.8 to –4.9. These high whole-rock (87Sr/86Sr)i ratios and relatively high Th/Nb and Th/Yb ratios indicate incorporation of melts derived from partial melting of subducted sediments into the melt evolution of these granitoids that involved partial melting of the subduction-metasomatized lithospheric mantle and the mafic- to intermediate-composition continental crust. The extant zircon crystallization ages of the granitoid intrusions in the CTP and ETP show eastward younging of their emplacement from 115 Ma to 93 Ma, suggesting an apparent eastward migration of the heat source through time. A diachronous collision of the NLT with the SQT during 145–120 Ma and the subsequent slab breakoff induced, eastward propagated slab tear and asthenospheric upwelling produced the hybrid melts of the Albian–Cenomanian granitoids and their emplacement in a discrete, narrow magmatic belt in the CTP and ETP.

СТАНОВЛЕНИЕ ГРАНИТОИДНЫХ (ГАББРО-ГРАНИТНЫХ) ПЛУТОНОВ И СВЯЗАННОГО С НИМИ ОРУДЕНЕНИЯ

Deep geological and geophysical modeling by a large number of granitoid plutons for the first time showed a completely different nature than was commonly believed. As a result, ideas about the connection of mineralization with them have changed dramatically. Many petrological contradictions and puzzles were solved logically and scientifically grounded. The complete and comprehensive review of the problem from the beginning (source of the initial magma) to the end (formation of the granite ore-magmatic system) is given. Three stages of the volatiles and ore matter concentration in the history of the plutons formation were established: the first (planetary) - during the intrachamber differentiation of the initial basalt magma with an isolation of granitoid melting; the second (regional) - during the formation of a residual leukogranite chamber the third, main (local) - during the intrusion of ore-generating apophyses from the chamber.

Association of A‐ and I‐type granitoids in the central Aravalli orogen, Rajasthan: Implications for the Neoproterozoic tectonic evolution of north‐west India

We present new mineralogical and geochemical data for the granitoid plutons of the Neoproterozoic Sendra Granitoid Suite, central Aravalli orogen, north‐west India to constrain their petrogenesis and tectonic setting. The granitoids can be classified into two groups: (a) A‐type Chang, Chitar, Borwar, and Seliberi plutons and (b) I‐type Jaitpura pluton. The available geochronological data (zircon U–Pb ages) suggest that all the granitoids are coeval at 990–970 Ma. The granitoids are mostly granite sensu stricto, with subordinate granodiorite and rare tonalite. The rocks are metaluminous to mildly peraluminous and have high total REE abundances. Nevertheless, there are also certain geochemical differences between A‐type and I‐type granitoids. The I‐type granitoids have relatively high Al2O3 and CaO concentrations and show significant fractionation with increasing SiO2. The least fractionated sample contains low abundances of the HFSE and has low Fe‐number and Ga/Al ratios. In contrast, the A‐type granitoids have lower CaO and higher HFSE concentrations, Fe‐number, and Ga/Al ratios. Both A‐type and I‐type granitoids show negative Ba, Sr, Nb, P, Ti, and Eu anomalies, and are characterized by high zircon‐saturation temperatures (801–977°C). The present data suggest that rocks of the Sendra Granitoid Suite were generated predominantly by partial melting of mafic sources at high temperatures and emplaced in a post‐collisional extensional regime. Moreover, our study provides evidence of the preserved post‐collisional extensional magmatism subsequent to the subduction during the assembly of the Rodinia supercontinent, which is otherwise relatively less prevalent over intra‐plate or within‐plate magmatism during this time period.

Geodynamic Formation Conditions and Age of Granitoids from Small Intrusions in the West of the Yana–Kolyma Gold Belt (Northeast Asia)

Abstract We report results of geological, mineralogical-petrographic, geochemical, isotope-geochemical (Sm–Nd, Rb–Sr), and geochronological (U–Pb, 40Ar/39Ar) studies of acid and intermediate intrusive rocks (granodiorites, leucocratic granites, subalkaline granites, and subalkaline leucocratic granites, diorites, and quartz diorites) of the Bukeschen and Samyr small plutons in the western part of the Yana–Kolyma gold belt (northeast Asia). These rocks are combined with Late Jurassic (151–145 Ma) dikes of basic, intermediate, and acid compositions into a single complex of small intrusions. They intrude the Upper Triassic–Middle Jurassic terrigenous deposits of continental margin blocks in the eastern part of the Verkhoyansk–Kolyma folded area. Our new U–Pb data for zircon (SHRIMP-II) indicate that the Bukeschen and Samyr pluton granitoids formed in the Berriasian, at 144.5 and 143 Ma, respectively. The small-intrusion granitoids have geochemical and isotope (Sm–Nd and Rb–Sr) characteristics similar to those of Late Jurassic dikes of varying composition. Therefore, they can be united into a single complex of small intrusions generated from a mixed source with the participation of mantle (OIB- and E-MORB type), lower crust, and subduction components and with Paleoproterozoic–Mesoproterozoic Sm–Nd model age estimates for the magma sources. Late Jurassic–Early Cretaceous magmatic and postmagmatic events and cooling of the intrusions played an important role in the processes of gold localization in the western part of the Yana–Kolyma gold belt. This is reflected in two tectonothermal stages (accounting for closing temperatures of the U–Pb, 40Ar/39Ar, and Re–Os isotope systems for different minerals) estimated at 151–141 and 138–137 Ma. These results for the small-intrusion complex agree with the tectonic model of the evolution of an active continental margin (northeastern Siberia) in the Mesozoic era, whose final development stage in the Berriasian age saw the formation of mostly small granitoid plutons.

Constraints on the timescales and processes that led to high-SiO2 rhyolite production in the Searchlight pluton, Nevada, USA

Abstract Plutons offer an opportunity to study the extended history of magmas at depth. Fully exploiting this record requires the ability to track changes in magmatic plumbing systems as magma intrudes, crystallizes, and/or mixes through time. This task has been difficult in granitoid plutons because of low sampling density, poorly preserved or cryptic intrusive relationships, and the difficulty of identifying plutonic volumes that record the contemporaneous presence of melt. In particular, the difficulty in delineating fossil magma reservoirs has limited our ability to directly test whether or not high-SiO2 rhyolite is the result of crystal-melt segregation. We present new high-precision U-Pb zircon geochronologic and geochemical data that characterize the Miocene Searchlight pluton in southern Nevada, USA. The data indicate that the pluton was built incrementally over ~1.5 m.y. with some volumes of magma completely crystallizing before subsequent volumes arrived. The largest increment is an ~2.7-km-thick granitic sill that records contemporaneous zircon crystallization, which we interpret to represent a fossil silicic magma reservoir within the greater Searchlight pluton. Whole-rock geochemical data demonstrate that this unit is stratified relative to paleo-vertical, consistent with gravitationally driven separation of high-SiO2 melt from early-formed crystals at moderate crystallinity. Zircon trace-element compositions suggest that our geochronologic data from this unit record most of the relevant crystallization interval for differentiation and that this process occurred in &amp;lt;150 k.y.

Arc-continent collision during culmination of Proto-Tethyan Ocean closure in the Central Qilian belt, NE Tibetan Plateau

Abstract Accurate lithostratigraphy framework of the Central Qilian belt is key to understand subduction-collision of the Proto-Tethyan Ocean in the NE Tibetan Plateau. The Dongchagou and the Moshigou formations share similar detrital zircon age populations with youngest age peak at ca. 1.15–1.21 Ga, which is consistent with the granitoid gneiss of the Liujiatai Formation. In combination with rock assemblages, metamorphic facies, and associated oldest granitoid plutons, we revised Precambrian lithostratigraphy of the Central Qilian belt as the &amp;gt;1.2 Ga Huangyuan Group and the ca. 1200–930 Ma Huangzhong Group in this study. The former is the same as the Liujiatai Formation, whereas the later includes the Dongchagou and Moshigou formations. Siliciclastic turbidites of the Qingshipo Formation gradually pass upward into carbonates of the Huashishan Group, we therefore ascribe them to the Huashishan Group. This group unconformably overlies the Precambrian basement of the Central Qilian belt and consists of continental slope to coastal plain deposits with a bi-direction of the S- and N-ward paleocurrent. These sediments contain abundant metamorphic, magmatic, and minor ophiolitic detritus with main age populations of ca. 910 Ma, ca. 487 Ma, and ca. 447 Ma detrital zircons, probably derived from the Central and South Qilian belts. The basement of the Huangzhong Group experienced 440– 430 Ma continent-continent collision-related metamorphism and deformation. These results and regional geology demonstrate that the Huashishan Group was formed by arc-continent collision deposition during culmination of the Proto-Tethyan Ocean closure in the Qilian orogenic belt, NE Tibetan Plateau.