High Sr Contents Research Articles

Recycling of continental crust in the southern North China Craton: Constraints from the Sr–Nd–Pb–Hf–O isotopic compositions of Early Cretaceous Funiushan granites

This paper reports new zircon U–Pb ages, whole-rock geochemistry, and Sr–Nd–Pb–Hf–O isotopic compositions for the Funiushan (FNS) pluton of the southern North China Craton (NCC). These data and statistical analyses of previously reported compositions of late Mesozoic granites from the southern NCC are used to constrain late Mesozoic continental recycling and geodynamic processes. The FNS pluton includes coexisting early Early Cretaceous (140 Ma), late Early Cretaceous (130–116 Ma) and highly evolved granites (HEGs; 126–125 Ma). The early Early Cretaceous granites have high Sr contents (332–566 ppm), high Sr/Y (53–138) and (La/Yb)N (29–52) ratios, and low MgO contents (0.15–0.48 wt%). They have relatively low (87Sr/86Sr)i values (0.7051–0.7054), relatively high εNd(t) values (−4.11 to −3.96) and variable εHf(t) values (−22.9 to −0.53). They are also characterized by high initial 206Pb/204Pb values (17.893–17.975) and relatively low δ18O values (5.34‰–7.48‰) as well as Neoproterozoic (851–734 Ma) inherited zircons, suggesting that they have an adakitic affinity formed by recycling of subducted continental crust of the Yangtze Craton (YC) with input from a mantle component. In contrast, the late Early Cretaceous granites have relatively high (87Sr/86Sr)i values (0.7077–0.7085), low εNd(t) values (−14.2 to −12.0), relatively high initial 206Pb/204Pb values (17.398–17.497), εHf(t) values of −23.7 to −10.7, and δ18O values of 5.76‰–6.55‰. These data, and the Neoproterozoic zircon ages (716–702 Ma), indicate that the primary magmas formed from recycled YC crust with a minor contribution from the NCC basement. The late Early Cretaceous HEGs have relatively high εNd(t) values (−9.33 to −8.70), high initial 206Pb/204Pb values (17.656–17.885), intermediate εHf(t) values (−12.3 to −6.18), and relatively low δ18O values (5.22‰–6.72‰), indicating that they formed from subducted YC and mantle material. Previous work on granites of the southern NCC has established two phases of granite formation. Late Jurassic to early Early Cretaceous I-type granites (160–130 Ma) occur throughout the southern NCC. These are adakitic and formed from thickened lower continental crust (LCC). Late Early Cretaceous A-type granites (130–110 Ma) formed from thinned LCC. The differences between Late Jurassic to early Early Cretaceous granites and late Early Cretaceous granites reflect a transformation in tectonic regime from thickening to thinning, which is attributed to rollback of the subducting Paleo-Pacific Plate.

Petrogenesis and U–Pb zircon dating of the Chaitma Alkaline Complex from the southern margin of the Central Indian Tectonic Zone: geodynamic implications

Abstract In this study, we constrain the petrogenesis and U–Pb zircon age of a newly discovered alkaline complex, christened the Chaitma Alkaline Complex at the southern margin of the Central Indian Tectonic Zone in central India. The Chaitma Alkaline Complex comprises syenites and gabbros, emplaced coevally, and show features consistent with magma mixing. Geochemically, syenites are potassic–ultrapotassic (K 2 O/Na 2 O: 0.79–3.42), and contain high Ba ( c. 800–2700 ppm) and Sr ( c. 1400–3200 ppm). They show enrichment of the light rare earth elements (LREEs) relative to the heavy rare earth elements (HREEs) (La/Yb: 32–103) and do not display any Eu anomaly. Based on their geochemical signatures, such as low MgO (<0.87 wt%), Ni (8–16 ppm) and Cr (7–44 ppm) contents and prominent Zr–Hf negative anomaly, the syenites are inferred to have been derived by partial melting of a carbonated/metasomatized thickened lower crustal source. The coeval gabbros are undersaturated in silica (41–44 wt%), with relatively high total alkalis (Na 2 O + K 2 O: 3.7–5.1 wt%), Fe 2 O 3 (17–19 wt%), P 2 O 5 (3.1–4.9 wt%), Sr (1600–3400 ppm) and Ba (300–3500 ppm) contents. These have low MgO (<4.8 wt%), Ni (13–30 ppm) and Cr (18–84 ppm). Their chemistry is interpreted to be the result of interaction with the syenitic magma. These geochemical characters along with the high LREE/HREE ratio, negative trough in Nb–Ta, Zr–Hf, Ti, Sr and Rb, and positive spike of Pb in a multielement diagram, and enrichment of LILEs over HFSEs indicate their derivation from a metasomatized subduction-modified garnet–peridotite mantle source. Our study indicates that syenites and gabbros of the Chaitma Alkaline Complex were formed from genetically unrelated parental magmas derived from distinct sources. U–Pb dating of zircon yielded a magmatic emplacement age of 1626 ± 15 Ma for the syenites. The Chaitma Alkaline Complex was presumably formed during a short period of crustal extension in the midst of a protracted period of continent–continent collision and granulite-grade metamorphism ( c. 1.71–1.58 Ga) at the southern margin of the Central Indian Tectonic Zone.

Petrogenesis and Geodynamic Implications of Miocene Felsic Magmatic Rocks in the Wuyu Basin, Southern Gangdese Belt, Qinghai-Tibet Plateau

Miocene felsic magmatic rocks with high Sr/Y ratios are widely distributed throughout the Gangdese belt of southern Tibet. These provide a good opportunity to explore the magmatic process and deep dynamic mechanisms that occurred after collision between the Indo and the Asian plates. In this paper, felsic volcanic rocks from the Zongdangcun Formation in the Wuyu Basin in the central part of the southern Gangdese belt are used to disclose their origin. Zircon U-Pb geochronology analysis shows that the felsic magmatism occurred at ca. 10.3 ± 0.2 Ma, indicating that the Zongdangcun Formation formed during the Miocene. Most of these felsic magmatic rocks plot in the rhyolite area in the TAS diagram. The rhyolite specimens from the Zongdangcun Formation have the characteristics of high SiO2 (>64%), K2O, SiO2, and Sr contents, a low Y content and a high Sr/Y ratio, and the rocks are rich in LREE and depleted in HREE, showing geochemical affinity to adakitic rocks. The rocks have an enriched Sr-Nd isotopic composition (εNd(t) = −6.76 to −6.68, (87Sr/86Sr)i = 0.7082–0.7088), which is similar to the mixed product of the juvenile Lhasa lower continental crust and the ancient Indian crust. The Hf isotopes of zircon define a wide compositional range (εHf(t) = −4.19 to 6.72) with predominant enriched signatures. The Miocene-aged crustal thickness in southern Tibet, calculated on the basis of the Sr/Y and (La/Yb)N ratios was approximately 60–80 km, which is consistent with the thickening of the Qinghai-Tibet Plateau. The origin of Miocene felsic magmatic rocks with high Sr/Y ratios in the middle section of the Gangdese belt likely involved a partial melting of the thickened lower crust, essentially formed by the lower crust of the Lhasa block, with minor contribution from the ancient Indian crust. After comprehensively analyzing the post-collisional high Sr/Y magmatic rocks (33–8 Ma) collected from the southern margin of the Gangdese belt, we propose that the front edge tearing and segmented subduction of the Indian continental slab may be the major factor driving the east-west trending compositional changes of the Miocene adakitic rocks in southern Tibet.

Composition of ore-forming fluids in the Huangshuian carbonatite-related Mo-(REE) deposit: Insights from LA-ICP-MS analyses of fluid inclusions

The carbonatites in the southern margin of the North China Craton are distinguishable by containing abundant quartz and are closely spatially associated with Mo-(REE) deposits. Unveiling the nature of ore-forming fluids is key to understand the genesis of these Mo-(REE) deposits and to explore their potential genetic relationships with the quartz-rich carbonatites, but such issues were currently not convincingly addressed. Here, we provide detailed petrographic, microthermometric and LA-ICP-MS analyses of the fluid inclusions hosted in the primary quartz from the carbonatites in the Huangshuian Mo-(REE) deposit which is the largest Mo-(REE) one in the region, containing 0.4 million tons of Mo metal with REEs as the major by-product. Our results show that the fluid inclusions in the quartz of the carbonatites are two- and three-phase CO2-bearing types with high homogenization temperatures (average at 396 °C) and low salinities (average at 3.88 wt% NaCl equiv). The LA-ICP-MS analyses of these inclusions reveal that the primary fluids contain high concentrations of La, Ce, Pr, Nd, Sr, and Ba, similar to typical carbonatite-related fluids. In addition, they are characterized by high Y, Cu, Pb, and Zn. Such a metal association is broadly consistent with the mineral assemblages of the Huangshuian Mo-(REE) deposit, such as the widespread barite, bastnäsite, xenotime, chalcopyrite, galena, and sphalerite, strongly supporting the close genetic relation of the deposit with the quartz-rich carbonatites. Although the concentrations of Mo are extremely low in these inclusions (below the detect limit), it was constrained to be gradually enriched in evolved fluids. Considering that the recorded fluids in quartz represent earliest generation of fluids exsolved from carbonatite magmas, our new results highlight that quantifying metal budgets of fluid inclusions could be a robust way to evaluate fertility of carbonatites that are widespread in the southern margin of the North China Craton.

Migration of Arc Magmatism Above Mantle Wedge Diapirs With Variable Sediment Contribution in the Aegean

AbstractCompiled data show the age progression of magmatic centers along the two approximately linear profiles from NE Greece and NW Turkey to the South Aegean Volcanic Arc. The age progression reveals the southwestward migration of arc magmatic activity from Oligocene to present, perpendicular to the Hellenic Trench. This is in accordance with the migration of the Aegean subduction zone due to the collision of oceanic and continental blocks, trench retreat, mantle flow, and coeval extension. We suggest that the subduction of large volumes of sediments and their contribution to the sub‐arc magma source controlled the composition of calc‐alkaline to high‐K calc‐alkaline and shoshonitic arc magmas during the past 30 Ma. The magma geochemistry and the approximately linear age‐progressive migration of magmatic activity suggest focused ascent of mixed material from the subducted slab into the mantle wedge, most likely in the form of mélange diapirs. Geochemical data along the profile reveals increasing Sr and decreasing Nd isotopes during Upper Miocene in agreement with the ongoing subduction of continental blocks, low subduction rates, and development of an accretionary wedge. The different K‐rich arc magmas reflect the variable subduction of sediments, whereas crustal assimilation often plays a minor role. Magmas with variable 87Sr/86Sr, P/Nd, and Ba/La indicate a variable contribution of clastic, phosphate‐bearing, and barite‐bearing sediments. Low‐degree partial melting in sediment‐dominated mélange diapirs causes the formation of shoshonitic magmas with high Sr and P2O5 contents and high La/Yb in the northern Aegean.

Petrogenesis of early Paleozoic granitoids in the Dunhuang Block, NW China: Insights into magma evolution and crustal thickening

The occurrence of adakitic rocks can provide insight into the evolution of continental crust and deep geodynamic processes in subduction zones. In this paper, we investigated zircon U-Pb ages and Hf isotope, whole-rock major and trace elements, and whole-rock Sr-Nd-Pb isotopes of the Lianghu quartz diorites and Shigong monzogranites in the Dunhuang Block, to understand their petrogenesis and tectonic setting as well as the tectonic evolution of the Dunhuang Block in the early Paleozoic. LA-ICP-MS zircon U-Pb dating results suggest that the Lianghu quartz diorites and Shigong monzogranites were emplaced at ca. 455 ± 3 Ma and 431 ± 3 Ma, respectively. The Ordovician quartz diorites exhibit relatively high Sr (734–904 ppm) contents, negative-to-negligible Eu anomalies (Eu/Eu* = 0.87–0.99), high Sr/Y (52.5–124) ratios, but low Yb (0.68–1.32 ppm) and Y (7.27–14.0 ppm) contents. Moreover, they exhibit relatively high Mg# (52.0–54.7) values, Cr (23.1–88.0 ppm) and Ni (15.0–53.3 ppm) contents, similar to those of adakitic rocks originating from subducted oceanic crust. The quartz diorites display low initial 87Sr/86Sr (0.703464–0.704783), negative εNd(t) of −3.2 to −1.3, and positive εHf(t) of +3.8 to +8.0, with two-stage model ages for the Nd and Hf systems of 1.12 to 1.09 Ga and 1.17 to 0.91 Ga, respectively, indicative of a heterogeneous magma sources. They have relatively high radiogenic 206Pb/204Pb(t) (18.219–19.066), 207Pb/204Pb(t) (15.616–15.669), and 208Pb/204Pb(t) (39.042–39.198), signifying that some subduction-related materials (e.g., ocean island basalts) may be involved as sources. These characteristics indicate that the Lianghu quartz diorites were derived from the partial melting of subducted oceanic slabs (sediments + fluids), and that they underwent subsequent interaction with peridotite in the mantle wedge, with limited assimilation of crustal materials during magma ascent. The Silurian monzogranites contain high Sr content (655–674 ppm) but very low contents of Y (2.49–4.19 ppm) and Yb (0.24–0.37 ppm), yielding high Sr/Y ratios (161–263); those values, together with low MgO (0.30–0.41 wt.%), Mg# (40.6–41.4), Cr (2.39–3.28 ppm), and Ni (2.19–2.95 ppm) contents, resemble those of thickened lower crust-derived adakitic rocks. They show εHf(t) and εNd(t) values of −2.5 to +3.0 and −3.6, with the respective two-stage model ages of 1.55 to 1.20 Ga and 1.32 Ga. Their low Pb values, 206Pb/204Pb(t) = 18.184, 207Pb/204Pb(t) = 15.595, and 208Pb/204Pb(t) = 37.717, also suggest addition of minor mantle-like melts. These geochemical features indicate that the parent magmas of the monzogranites originated either from the melting of heterogeneous crustal sources, or through mixing of thickened juvenile crust, Mesoproterozoic crust materials, and minor mantel-derived materials in the stability field of garnet-bearing amphibolite. Given the coeval regional magmatism and tectonic setting, we propose that the continental crust thickening of the Dunhuang Block began roughly in the late Ordovician (~35 km) and culminated in the early Silurian (~50–55 km), as evidenced by the La/Yb ratios of quartz diorites (12.2–25.2) and monzogranites (57.6–60.9). The corresponding transition of the tectonic regime from subduction to collisional setting occurred at ~440 Ma. The Dunhuang Block could undergo thickening processes associated with underplating of mantle-derived magmas during subduction of the southern Paleo-Asian Ocean, and subsequently collided with the Shibanshan terrane (a Paleozoic continental arc) along the southern Beishan orogen at ca. 440–430 Ma. Our results show that the Dunhuang Block represents a continental arc in the early Paleozoic, and was involved in the Paleozoic orogenesis of the Central Asian Orogenic Belt.

The Effects of Source Mixing and Fractional Crystallization on the Composition of Eocene Granites in the Himalayan Orogen

Abstract Granites are generally the final products of crustal anatexis. The composition of the initial melts may be changed by fractional crystallization during magma evolution. Thus, it is crucial to retrieve the temperature and pressure conditions of crustal anatexis on the basis of the composition of the initial melts rather than the evolved melts. Here we use a suite of ∼46–41 Ma granites from the Himalayan orogen to address this issue. These rocks can be divided into two groups in terms of their petrological and geochemical features. One group has high maficity (MgO + FeOt = 2–4 wt%) and mainly consists of two-mica granites, and is characterized by apparent adakite geochemical signatures, including high Sr concentrations and Sr/Y and La/Yb ratios, and low concentrations of heavy rare earth elements and Y. The other group has low maficity (MgO + FeOt <1 wt%) and consists of subvolcanic porphyritic granites and garnet/tourmaline-bearing leucogranites. This group does not possess apparent adakite signatures. The low-maficity group (LMG) has lower MgO + FeOt contents and the high-maficity group (HMG) has higher Mg# compared with initial anatectic melts determined by experimental petrology and melt inclusions studies. Petrological observations indicate that the HMG and the LMG can be explained as a crystal-rich cumulate and its fractionated melt, respectively, such that the initial anatectic melt is best represented by an intermediate composition. Such a cogenetic relationship is supported by the comparable Sr–Nd isotopic compositions of the two coeval groups. However, these compositions are also highly variable, pointing to a mixed source that was composed of amphibolite and metapelite with contrasting isotope compositions. We model the major and trace element compositions of anatectic melts generated by partial melting of a mixed source at four apparent thermobarometric ratios of 600, 800, 1000 and 1200 °C GPa–1. Modeling results indicate that melt produced at 1000 °C GPa–1 best matches the major and trace element compositions of the inferred initial melt compositions. In particular, a binary mixture generated from 10 vol% partial melting of amphibolite and 30 vol% melting of metapelite at 850 ± 50 °C and 8·5 ± 0·5 kbar gives the best match. Therefore, this study highlights that high thermobarometric ratios and subsequent fractional crystallization are responsible for the generation of the apparent adakitic geochemical signatures, rather than melting at the base of the thickened crust as previously proposed. The thermal anomaly responsible for the Eocene magmatism in the Himalayan orogen was probably related to asthenosphere upwelling in response to rollback of the subducting Neo-Tethyan oceanic slab at the terminal stage of continental collision between India and Asia. As such, a transition in dynamic regime from compression to extension is necessary for the generation of high thermobarometric ratios in continental collision zone. Therefore, after correcting for potential effects of fractional crystallization and crystal accumulation on melt composition, granite geochemistry coupled with thermodynamic modeling can better elucidate the petrogenesis of granites and the geodynamic mechanisms associated with anatexis at convergent plate boundaries.

Zircon U–Pb ages and petrogenesis of late Miocene adakitic rocks from the Sari Gunay gold deposit, NW Iran

AbstractLate Miocene volcanic rocks host the Sari Gunay epithermal gold deposit in NW Iran. These rocks are located within the Hamedan–Tabriz volcanic belt and occupy the northwestern part of the Sanandaj–Sirjan zone (SaSZ). The volcanic rocks span in composition from latite to dacite and rhyolite. Plagioclase, hornblende, biotite and quartz are the main phenocrysts in a fine-grained and glassy matrix. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating yielded crystallization ages of 10.10 ± 0.01 Ma and 11.18 ± 0.14 Ma for rhyolite and dacite, respectively. High ratios of Sr/Y (> 20) and La/Yb (> 20), high contents of Sr (≥ 400 ppm), low contents of MgO (≤ 6 wt%), Y ≤ 18 ppm (c. 16.5 ppm), Yb ≤ 1.9 ppm (c. 1.53 ppm) and weak negative Eu anomalies (Eu*/Eu c. 0.81) are compatible with a high-silica adakitic signature of the rocks. Regarding the location of the study area nearly 100 km from the Zagros suture zone, we argue that delamination of lithospheric mantle beneath the SaSZ has played a key role in the development of the adakitic rocks in a post-collision tectonic regime. The adakitic melts are suggested to have formed by partial melting of delaminated continental lithosphere and/or lower crustal amphibolite following the collision of the Arabian and Iranian plates.

Generation of Cretaceous high-silica granite by complementary crystal accumulation and silicic melt extraction in the coastal region of southeastern China

Abstract It is generally hypothesized that high-silica (SiO2 > 75 wt%) granite (HSG) originates from crystal fractionation in the shallow crust. Yet, identifying the complementary cumulate residue of HSG within plutons remains difficult. In this work, we examine the genetic links between the porphyritic monzogranite and HSG (including porphyritic granite, monzogranite, and alkali feldspar granite) from the coastal area of southeastern China using detailed zircon U-Pb ages, trace elements, Hf-O isotopes, and whole-rock geochemistry and Nd-Hf isotopic compositions. Zircon U-Pb ages indicate that the porphyritic monzogranite and HSG are coeval (ca. 96–99 Ma). The HSG and porphyritic monzogranite have similar formation ages within analytic error, identical mineral assemblages, similar Nd-Hf isotopic compositions, and consistent variations in their zircon compositions (i.e., Eu/Eu*, Zr/Hf, and Sm/Yb), which suggests that their parental magma came from a common silicic magma reservoir and that the lithological differences are the result of melt extraction processes. The porphyritic monzogranite has relatively high SiO2 (70.0–73.4 wt%), Ba (718–1070 ppm), and Sr (493–657 ppm) contents, low K2O and Rb concentrations and low Rb/Sr ratios (0.1–0.2), and it displays weak Eu anomalies (Eu/Eu* = 0.57–0.90). Together with the petrographic features of the porphyritic monzogranite, these geochemical variations indicate that the porphyritic monzongranite is the residual silicic cumulate of the crystal mush column. The HSG (SiO2 = 75.0–78.4) has variable Rb/Sr ratios (2–490) and very low Sr (1–109 ppm) and Ba (9–323 ppm) contents. Zircon from the HSG and porphyritic monzogranite overlap in Eu/Eu*, Zr/Hf, and Sm/Yb ratios and Hf contents; however, some zircon from the HSG show very low Eu/Eu* (<0.1) and Zr/Hf ratios. These features suggest that the HSG represents the high-silica melt that was extracted from a crystal-rich mush. The injection of mantle-derived hotter mafic magma into the mush column and the exsolution of F/Cl−-enriched volatiles (or fluids) from the interstitial melt rejuvenated the pre-existing highly crystalline mush. Subsequent extraction and upward migration of silicic melt resulting from compaction of the mush column formed the HSG at shallow crustal levels, which left the complementary crystal residue solidified as porphyritic monzogranite at the bottom.

Geochronological, geochemical, and Sr–Nd–Pb–Hf isotopes of Cretaceous gneissic granite and quartz monzonite in the Tongbai Complex: Record of lower crust thickening beneath the Tongbai orogen

A comprehensive study of zircon U–Pb ages, major and trace elements, whole‐rock Sr–Nd–Pb isotopes and zircon Hf isotopes of the gneissic granite and quartz monzonite in the Tongbai Complex is conducted in an attempt to unravel their petrogenesis and shed new light on the tectonic evolution and crust thickening process of the Tongbai orogen. Zircon U–Pb dating indicates that the emplacement of gneissic granite was early at 144.2 ± 1.3 Ma, whereas the quartz monzonite formed later at 130.2 ± 1.7 Ma. Both the gneissic granite and quartz monzonite samples share many chemical similarities, such as high Al2O3, K2O, Sr contents and low MgO contents, together with high Sr/Y, high La/Yb ratios, suggesting an C‐adakitic affinity and possibly derived from partial melting of the thickened lower crust. The later quartz monzonites may have involvement of much more proportion of mantle‐derived materials (such as the metamorphosed mafic rocks, ecologite) in the lower crust during partial melting for its petrogenesis, due to its higher MgO, Cr, Ni, and V contents than the gneissic granites. The formation of the gneissic granite and quartz monzonite records the evolution history for the lower crust thickening beneath the Tongbai orogen at the Cretaceous. Nearly all granitoids in the Tongbai orogen currently found have an emplacement age of >130 Ma and have higher Sr/Y ratios and lower MgO, Cr, Ni, and V contents with respect to the granitoids in the Dabie orogen which occurs in two stages of granitic magmatism of >130 Ma and <130 Ma. The Tongbai orogen lacks the granitoids formed by significant crust–mantle mixing that occurred in the Dabei area at <130 Ma. These results indicate that the lower crust was continuing thickening but probably not delaminated beneath the Tongbai orogeny during the Early Cretaceous.

Origin, petrogenesis and geodynamic implications of the early Eocene Altınpınar adakitic andesites in the eastern Sakarya Zone, northeastern Turkey

Early Cenozoic magmatism in the eastern Sakarya Zone (NE Turkey) provides an important constraint on the regional tectono-magmatic evolution of the region. Early Eocene syn-collisional adakitic rocks are observed as small stocks with outcropping areas commonly less than 10 km2. This study presents petrography, whole-rock geochemistry and Sr-Nd-Pb isotope data, as well as in-situ 40Ar/39Ar age constraints on one of these adakitic andesites in the Altınpınar area of Gümüşhane, and discusses source region, petrological processes and geodynamic setting prevailed during their genesis. Andesites commonly show microlitic porphyric and vitrophyric porphyric textures, and include significant amounts of mafic microgranular enclaves (MMEs). Plagioclase, hornblende, Fe-Ti oxides and minor pyroxene are the main mineral phases. In-situ 40Ar-39Ar amphibole dating constrains the cooling age of andesites into a time span from 52.8 ± 1.3–48.8 ± 1.9 Ma. Andesites are medium to high-K calc-alkaline and display most of the signatures typical of those of the adakites. They are characterized by moderate MgO (1.7–4.1 wt%), low Y (9−14 ppm), Yb (0.9–1.5 ppm), and HREE and high Sr (325−964 ppm) contents, and high Sr/Y (36–76) ratios. 87Sr/86Sr(t) (0.704948−0.705100) and 143Nd/144Nd(t) (0.512588−0.512628) ratios are in the isotopic range of the adakites. All these geochemical and isotopic data suggest that the parental magma of adakitic andesites has been produced by partial melting of oceanic basalts under amphibole-eclogite facies conditions during the breakoff of the northern Neotethyan oceanic slab.

Investigation of meteoric water and parent fluid mixing in a two-phase geothermal reservoir system using strontium isotope analysis: A case study from Southern Bandung, West Java, Indonesia

Determinations of the recharge area and recharge mechanism in geothermal systems are essential for reservoir management and a sustainable resource use. To address this problem, studies aplenty have aimed to identify the recharge elevation using stable water isotopes, δ2H and δ18O. Nevertheless, the physical and chemical processes involved in the generation of a reservoir fluid from a deeply infiltrated recharge flow remain poorly understood. This study aims to clarify this process using strontium (Sr) concentrations and isotope composition from water and well rock samples by selecting a geothermal field with a two-phase reservoir system in Southern Bandung, West Java, Indonesia. The water samples are characterized by variable Sr isotopic compositions (87Sr/86Sr) (0.70450–0.70725) and low Sr concentrations (0.01–0.72 ppm). The 87Sr/86Sr of the well rocks is also variable (0.70400–0.70827) with particularly high Sr concentrations (9.1–53 ppm). Three types of domain that are the combinations of the reservoir fluid mixing with groundwater are identified. The first two types are shallow and deep groundwater composed of 90 % meteoric water and 10 % upflow fluids with Sr concentration 0.01 to 0.11 ppm and the 87Sr/86Sr from 0.7055 to 0.70725. The shallow groundwater may possibly carry a 87Sr/86Sr anomaly (higher than 87Sr/86Sr of plagioclase: 0.7065) from the anthropogenic activities through the pathways created by the intersection of the NW-SE and NE-SW inferred regional faults in the west part of the field, hosted by the Wayang Windu Formation. The deep groundwater type is also a mixture of 10 % parent fluid hosted by the deeper aquifer rocks Malabar Formation, with lower strontium isotopes ratio than the first aquifer (87Sr/86Sr 0.7045–0.7055). The third groundwater refers to the perched aquifer with mixture of 30 %–70 % parent fluid that has undergone condensation and mixing processes in Pangalengan Formation (87Sr/86Sr 0.70452–0.7052). This groundwater is thought to be the source of mostly hot springs in the study area.

Compositional Variations of Apatite and REE-Bearing Minerals in Relation to Crystallization Trends in the Monchepluton Layered Complex (Kola Peninsula)

Abstract ––We have investigated the compositional variations of apatite (Ap) and rare-earth element (REE) minerals in the Monchepluton layered complex on the Kola Peninsula. On the basis of large sets of pertinent analytical data, we have estimated geochemical trends involving major, minor, and trace elements and studied their relation with the compositions of rock-forming silicate and oxide minerals. The variations observed in Ap differ considerably from trends reported for other layered intrusions. The composition fields of Ap are not consistent with the variations in the chemical composition of the bulk rocks and their constituent minerals, as determined along the representative cross sections of the entire complex. The compositional variations of Ap are fairly similar in all units of the complex. Chlorapatite (>6 wt.% Cl) is invariably abundant. There is no relationship between the Cl content of Ap and the degree of magnesium enrichment of the coexisting early magmatic silicates. In the F–Cl–OH diagram, broad fields of ternary solid solution are observed. There are no compositions along the Cl–F axis. The compositions of Ap are notably poor in Cl in the marginal series (the Nyud massif) and correspond to hydroxylapatite with a high content of fluorapatite component. Two composition fields of Ap are recognized in the Monchepluton complex: ≤3 wt.% and >6 wt.% Cl; there are, however, extensive overlaps. Two generations of apatite are thus implied. The first nucleated at the early stage of crystallization of H2O-bearing intercumulus melt as a result of substantial increase in the contents of P, F, Cl, and other incompatible components. The following stage of degassing of the crystallizing melt caused a decoupling of Cl and F. Fluorine remained mostly in the melt; in contrast, Cl was partitioned efficiently into an H2O-bearing fluid phase. At the early stage, the apatite incorporated combinations of hydroxylapatite and fluorapatite, with a low content of Cl. At the late stage, chlorapatite crystallized from a Cl-rich fluid, and ferrochloropargasite (4.1 wt.% Cl) formed in the Poaz massif as a result of autometasomatic alteration via reactions of this fluid with plagioclase and pyroxene. The apatite has high Sr contents (up to 4.1 wt.% SrO) in the highly magnesian cumulates of the Dunite block and the massifs of mounts Kumuzh’ya, Nittis, and Travyanaya. This enrichment illustrates the accumulation of Sr in the intercumulus melt, in which Ap was the only Sr-bearing phase in the absence or scarcity of intercumulus plagioclase. The REE contents also increased in the intercumulus melt and led to the formation of monazite-(Ce), REE-bearing Ap, and allanite-(Ce) in the remaining microvolumes of melt. Loveringite and Ap crystallized as coexisting phases in Mt. Sopcha. For the first time in a layered intrusion, an extensive range of compositions is documented in the Ce–La–Nd diagram for the REE-bearing phosphates (monazite and REE-rich apatite), which display a predominant La ↔ Nd substitution at the constant contents of Ce.

Geology and geochemistry of deformed granites from the Querari Complex, Rio Negro Province, NW-Amazonian Craton, Brazil

The Querari Complex corresponds to the basement rocks from Uaupes Domain and represents one of the least studied units in the northwest of the Rio Negro Province, Amazonian Craton. In this paper, we present new field geology, petrographic, and geochemical data of deformed granites from the Querari Complex. Based on our results, we suggest the differentiation of the Querari Complex into two magmatic facies. The Pana-Pana Facies comprise mainly porphyritic syeno to monzogranites with biotite as the main mafic mineral, and titanite, epidote, and allanite as accessory phases. The rocks of the Pana-Pana Facies have calc-alkaline and metaluminous affinities. The Matapi Facies have a syenogranite composition, coarse to porphyritic texture with magmatic muscovite and biotite, normative corundum higher than 1% (1.85-2.06), and mostly a peraluminous character. Both facies are generally enriched in silica and have a small spectrum of variation. (67.5 to 70.1 wt.% Pana-Pana Facies - 71.1 to 73 wt.% Matapi Facies), but they differ by the high Al2O3, Fe2O3, MgO, CaO, Sr, and Ba contents in the Matapi Facies. Geological and geochemical compositions suggest that the magmatic precursors of these rocks of Matapi Facies may be derived from partial melting of metasedimentary sources, whereas the Pana-Pana Facies are probably derived from a meta-ignea source of intermediate composition, such as tonalitic gneisses. The rocks of the Querari Complex would have been generated in the collisional tectonic settings during the Paleoproterozoic (between 1778 and 1740 Ma). During this 1.78-1.74 Ga tectono-magmatic event (D1), the magmatic fabric (S0) and the parallel S1 foliation have been developed, with NE-SE orientation. A subsequent tectonic event (D2) was responsible for the folding S1 foliation, creating the S2 axial planar foliation with an approximate orientation E-W. This D2 event is thought to represent a Calymmian (1.52 - 1.48 Ga) tectono-metamorphic event, associated with widespread I- and S-type granite emplacement in the Rio Negro Province. The deformation textures, as well as the mineral paragenesis for the Pana-Pana and Matapi facies, reveal temperature conditions at upper amphibolite facies, up to 700oC. Finally, the D3 tectono-metamorphic event comprises the reactivation of many NE-SW ductile shear zones with sinistral kinematic, creating a mylonitic foliation (S3) in the rocks of the Querari Complex. This D3 tectono-metamorphic event is probably linked to the intracratonic K´Mudku tectono-metamorphic event (between 1317 and 1198 Ma) of the Amazonian Greenvillian-Sunsas continental collision.

Source of 226Ra in Ramsar spring water, Iran: implication of water–rock interaction and stable isotopes

This study was carried out primarily to understand the hydrogeochemical processes controlling the 226Ra anomalies in Ramsar area. Analyses revealed two types of water: (1) non-thermal Ca–HCO3 type and (2) thermal Na–Cl type, mainly of meteoric and hydrothermal origin, respectively. Non-thermal springs have higher concentrations of U due to silicate weathering. Thermal springs are characterized by high concentrations of 226Ra, As, Fe, Li, Cs, Rb, Sr, Ba, B, Br−, F−, NO3−, PO43− and SiO2 resulting from high-temperature water–rossck interaction and mixing with hydrothermal fluids. Thermal springs are manifestations of an old hydrothermal system with subsurface reservoir temperatures varying between 83 and 100 °C. Radium activity is negatively correlated with pH and positively correlated with TDS, Cl−, Ba, and Ca, reflecting competitive ion effects of alkaline-earth metals, complexing with Cl−, and co-precipitation with barite and calcite. These processes are thought to be the dominant factors in controlling 226Ra mobility in spring water.

Identification and Geological Significance of Early Jurassic Adakitic Volcanic Rocks in Xintaimen Area, Western Liaoning

The Western Liaoning area, where a large number of Jurassic-Cretaceous volcanic rocks are exposed, is one of the typical areas for studying the Mesozoic Paleo-Pacific and Mongolia-Okhotsk subduction process, and lithospheric destruction of North China Craton. The identification and investigation of Early Jurassic adakitic volcanic rocks in the Xintaimen area of Western Liaoning is of particular significance for exploring the volcanic magma source and its composition evolution, tracking the crust-mantle interaction, and revealing the craton destruction and the subduction of oceanic plates. Detailed petrography, zircon U–Pb dating, geochemistry, and zircon Hf isotope studies indicate that the Early Jurassic intermediate-acidic volcanic rocks are mainly composed of trachydacites and a few rhyolites with the formation ages of 178.6–181.9 Ma. Geochemical characteristics show that they have a high content of SiO2, MgO, Al2O3, and total-alkali, typical of the high-K calc-alkaline series. They also show enrichment of light rare earth elements (LREEs) and large ion lithophile elements (LILEs), depletion of heavy rare earth elements (HREEs) and high field strength elements (HFSEs), and have a high content of Sr and low content of Y and Yb, suggesting that they were derived from the partial melting of the lower crust. The εHf(t) values of dated zircons and two-stage model ages (TDM2) vary from −11.6 to −7.4 and from 1692 to 1958 Ma, respectively. During the Early Jurassic, the study area was under long-range tectonic effects with the closure of the Mongolia-Okhotsk Ocean and the subduction of the Paleo-Pacific plate, which caused the basaltic magma to invade the lower crust of the North China Craton. The mantle-derived magma was separated and crystallized while heating the Proterozoic lower crust, and part of the thickened crust melted to form these intermediate-acidic adakitic volcanic rocks.

Recycling of crustal materials and implications for lithospheric thinning: Evidence from Mesozoic volcanic rocks in the Hailar–Tamtsag Basin, NE China

Late Mesozoic Nb-rich basaltic andesites and high-Mg adakitic volcanic rocks from the Hailar–Tamtsag Basin, northeast China, provide important insights into the recycling processes of crustal materials and their role in late Mesozoic lithospheric thinning. The Late Jurassic Nb-rich basaltic andesites (154 ± 4 Ma) are enriched in large-ion lithophile and light rare earth elements, slightly depleted in high-field-strength elements, and have high TiO2, P2O5, and Nb contents, and (Nb/Th)PM and Nb/U ratios, which together with the relatively depleted Sr–Nd–Hf isotopic compositions indicate a derivation from a mantle wedge metasomatized by hydrous melts from subducted oceanic crust. The Early Cretaceous high-Mg adakitic volcanic rocks (129–117 Ma) are characterized by low Y and heavy rare earth element contents, and high Sr contents and Sr/Y ratios, similar to those of rocks derived from partial melting of an eclogitic source. They also have high Rb/Sr, K2O/Na2O, and Mg# values, and high MgO, Cr, and Ni contents. These geochemical features suggest that the adakitic lavas were derived from partial melting of delaminated lower continental crust, followed by interaction of the resulting melts with mantle material during their ascent. Our data, along with available geological, paleomagnetic, and geophysical evidence, lead us to propose that recycling of Paleo-Pacific oceanic crustal materials into the upper mantle due to flat-slab subduction and rollback of the Paleo-Pacific Plate during the late Mesozoic likely provided the precondition for lithospheric thinning in northeast China, with consequent lithospheric delamination causing recycling of continental crustal materials and further lithospheric thinning.

Lithium-mica composition as pathfinder and recorder of Grenvillian-age greisenization, Rondonia Tin Province, Brazil

The tin-greisens of the Rondonia Tin Province, Brazil, are related with the intrusion of a 995−975 Ma evolved rapakivi granite suite interpreted as post-collisional with respect to the Grenvillian orogeny during assembly of Rodinia. Lithium-iron mica (‘zinnwaldite’) is the main mineral in late- to post-magmatic and ore stages of such greisens, and has the potential of being a recorder of the mineralization processes. We provide bulk rock geochemistry of granite, greisen, and greisenized granite, coupled with in-situ major and trace element analyses in mica. Trace element and Li contents in mica were assessed via LA-ICP-MS analysis to avoid interference from ore-mineral inclusions. There is a large-scale zoning (hundreds of meters) of the composition of magmatic mica within the massif. Within 200 m of greisen zones, the mica composition in granite becomes similar to hydrothermal greisen mica, i.e. mica composition is suggested as a proximity indicator for greisen. Mica records the evolution of the system from magmatic to hydrothermal. Early-magmatic mica is Li, Rb and F poor and Mg, Ti and Fe rich, as opposed to greisen mica. Rare metals (e.g. Sn, Ta, W) display complex behavior, as their content in mica increases from magmatic to transitional stages, but decreases from transitional to ore (greisen and vein) stages. This can be explained by a complex interaction between enrichment of metals in the fluid, crystallization order of HFSE-bearing minerals, a decrease in the acceptance of HFSE in mica due to Ti depletion, and a change in the system from melt-dominated to fluid-dominated. Depletion of rare metals in mica can be an important factor for mineralization, since binding these metals to silicates reduces the amount of ore minerals. In granite, up to 86 % of Sn is bound to mica, while in greisen, up to 95 % of it is available to form cassiterite. Niobium behaves differently than other rare metals, likely due to its very high initial partition coefficient in mica and its lower solubility in fluids when compared to Sn and Ta. As such, changes in the Nb/Sn ratio in mica can be used as a proxy for the rock/fluid ratios. Mica pseudomorphs after feldspar in greisenized granite have anomalously high Sr contents inherited from their albite precursor.

Sr- and C-Chemostratigraphy Potential of the Paleoproterozoic Sedimentary Carbonates under Medium-Temperature Metamorphism: the Ruskeala Marble, Karelia

Comprehensive petrological and isotope-geochemical study of marble was carried out in the upper part of the Sortavala Group of the northeastern lense at the Ruskeala deposit in the Northern Ladoga area. The petrological study showed that the carbonate rocks of the Sortavala Group underwent medium-temperature low-pressure amphibolite-facies metamorphism. The mineral assemblages of Ruskeala marbles were formed at temperature of 550–600°C and pressure of ~3–5 kbar in equilibrium with a mixed water-carbon dioxide fluid with $${{X}_{{{\text{C}}{{{\text{O}}}_{2}}}}}$$ ~ 0.5–0.8. Dolomite marbles contain admixture (up to 2%) of finely disseminated carbonaceous matter and about 8–15% of calcite. Dolomites contain small amounts of Mn (70–110 ppm) and Fe (1600–3600 ppm) and high content of Sr (122–256 ppm). The initial 87Sr/86Sr ratio in the dolomites is within 0.70465–0.70522, δ13C values vary between +0.6…+1.9 ‰, and δ18О within –13.2 … –10.2‰ (V-PDB). Calcite marbles are free of carbonaceous matter, have very low contents of Mg (0.2–0.8%), Mn (10–90 ppm) and Fe (160–640 ppm) and very high Sr concentration (850–2750 ppm). The initial 87Sr/86Sr ratios in the calcite marbles range from 0.70482 to 0.70489, δ13С from 1.5 to 2.1‰, and δ18О from –10.9 to ‒8.1 ‰ (V-PDB). Tremolite-bearing marbles have higher 87Sr/86Sr ratio (up to 0.70522), while their δ13С and δ18О values decrease to 0.1‰ and –12.2‰, respectively. The metamorphism of Ruskeala carbonate even under medium-temperature amphibolite-facies conditions was essentially isochemical process, which retained the unique Sr and C chemostratigraphic potential of calcite and dolomite marbles for the reconstruction of 87Sr/86Sr and δ13C in the Paleoproterozoic seawater. The 87Sr/86Sr ratio in the 1.9–2.0 Ga Svecofennian ocean was 0.70463–0.70492, and δ13С value +1.5 ± 1‰. New Sr-isotope data record an increase in radiogenic Sr input in the ocean about 2 billion years ago, which was probably related to the growth of continental crust and more intense weathering. The δ13С in Ludicovian carbonates mark the beginning of C-isotope stasis in ocean after the Lomagundi-Jatulian anomaly of 13Ccarb.

High-Mg andesitic rocks formed through crustal magmatic differentiation

High-Mg andesitic rocks are enriched in both compatible (Mg, Cr and Ni) and incompatible elements (Si, Ba and Sr), which indicates the complexity of their petrogenesis. Models involving hybridization of the mantle sources and input of adakitic melts have been invoked, but struggle to explain the low Mg# values (<0.65) of some low Sr/Y (<40) high-Mg andesitic rocks, because these rocks cannot represent primary melts (Mg# ≥ 0.72) produced by the partial melting of mantle peridotite. This study presents a petrological and geochemical analysis of the Xinsi diorite (443 ± 3 Ma) and Tiechang gabbro (440 ± 3 Ma) from the Early Paleozoic Wuyi-Yunkai Orogen in South China, and demonstrates the role of magmatic differentiation in the petrogenesis of high-Mg andesitic rocks. These rocks contain high SiO2, MgO, Ba and Sr concentrations with low Mg# values (≤0.69) and Sr/Y ratios (≤16.7), resembling typical low Sr/Y high-Mg andesitic rocks. Amphiboles and clinopyroxenes in the Xinsi diorite contain variable contents of Ba and Sr, both of which negatively correlate with Mg#. This indicates that their parental melts had low Ba and Sr and underwent significant enrichment of Ba and Sr through the fractionation of Mg-rich minerals within upper crust (3.1–4.4 kbar). Clinopyroxene, plagioclase and biotite in the Tiechang gabbro all contain lower Ba and Sr than those in the Xinsi diorite, suggesting that their parental melts were also initially low in Sr and Ba and experienced enrichment of these elements during magma evolution at middle crustal levels (5.7–6.3 kbar). The low Ba and Sr concentrations and Sr/Y ratios for parental melts of the Xinsi diorite and Tiechang gabbro suggest their derivation from the partial melting of mantle sources with input from slab melts at shallow depths without involvement of abundant garnet in petrogenesis. This study demonstrates the importance of fractional crystallization in the genesis of low Sr/Y high-Mg andesitic rocks and is conflict with past views that their geochemical features were related to the involvement of adakitic melts in their mantle sources. Therefore, this study presents an alternative model for the production of low Sr/Y and high Sr/Y high-Mg andesitic rocks, particularly in the Late Archean, which reflects the intense melting of subducted slab at different depths in the hotter mantle regime at that time.