LREE Depletion Research Articles

The Ediacaran metamorphosed banded iron formation (BIF) at Gohar Zamin mine (Gol-e-Gohar #3 anomaly), Sirjan (southeastern Iran): Perspective from ore structures, bulk ore-rock geochemistry and O-S-Pb isotopic signatures

Little is known about the occurrence of the Neoproterozoic banded iron formations (BIFs), except few cases of the glaciogenic Cryogenian BIFs. In this investigation, we describe an Ediacaran metamorphosed BIF interbedded with metamorphosed rocks. The Gohar Zamin iron deposit (643 Mt @ 54.3 % Fe, 2.04 % S, 0.12 % P) is hosted by mica schist, quartz schist and meta-basite that formed by metamorphism of the Fe-oxy-hydroxides, terrigenous (pelitic)-chemical (carbonate) sediments, silica gel and repeated phases of MORB-type submarine basic eruptions in shallow marine syn-rift basins. The sediments, basaltic eruptions and iron oxides were lithified to BIFs and then metamorphosed to greenschist facies during Cimmerian orogeny. The presence of macro-meso-microbandings in BIFs, coarse-grained quartz dropstones and magnetite clasts in the ores-host rocks, chemical index of alteration (CIA) (41.83 to 95.42 %) and positive correlation of Al2O3 against TiO2 and SiO2 values suggests a possible syn-glaciogenic BIF deposition. Fe/Ti-Al (Al + Fe + Mn), Fe-P, Co-Ni, V-Ti, V-Ni and Ni/ (Cr + Mn)-Ti + V diagrams suggest similarity to BIFs rather than the I-type granitoid magmatic-hydrothermal-skarn iron ores. REE + Y patterns display LREE depletion to slight enrichment, low-moderate Y/Ho ratios, HREE flat patterns, a nearly-zero to a seawater-like negative Ce anomaly and negative Eu anomaly. Such signatures may reflect low-T (300–200 °C) hydrothermal fluids for the origin of Fe-oxy-hydroxides formed by seawater-basaltic interaction and syn-glaciogenic meltwater influxes. Delta 18O values in magnetite-hematite (+3.3 to + 9.5 ‰) are in equilibrium with seawater and global BIFs. Delta 34S values in pyrite (+21.51 to + 26.59 ‰) reflect similarity to the Ediacaran pyrite composition formed by both thermal sulfate reduction (TSR) and bacterial sulfate reduction (BSR) processes. The radiogenic ratios of 206Pb/204Pb (19.228–25.105), 207Pb/204Pb (15.50–16.158) and 208Pb/204Pb (38.526–39.895) plot on the right side of 0.0 Ga geochron and were probably originated from the highly radiogenic zircon or galena clasts deposited by glaciogenic deposits. Geochemostratigraphy records zigzag elemental halos with the highest values of Fe (59.08 wt%) and Au (49.9 ppb). Exploration guides may be oriented to surficial sampling of the gossanized outcrops and heavy mineral surveys in drainage crosscutting the schistose rocks.

The Paleoarchean Buffalo River komatiites: Progressive melting of a single large mantle plume beneath the growing Kaapvaal craton

Several Archean granitoid-greenstone terranes are exposed on the southeastern Kaapvaal craton in South Africa, but they received little scientific attention compared to the archetypal greenstone belt successions of the Barberton Mountain Land at the eastern craton margin. This study reports on a detailed field and geochemical survey of the Buffalo River Greenstone Belt at the southern Kaapvaal craton margin in KwaZulu-Natal, with focus on hitherto unstudied komatiites and basaltic rocks from this volcanic succession. Cross-cutting relationships and new U-Pb zircon age determinations for several granitoid units establish a minimum age of 3.26 Ga for komatiitic volcanism, possibly as old as ca. 3.5 Ga if a 3.47 Ga granodiorite sheet is interpreted as ‘intrusive’ into the greenstone succession.Geochemical data reveal three types of Paleoarchean komatiites at Buffalo River. Spinifex textured lava flows represent Al-depleted komatiites, with subchondritic Al2O3/TiO2 ratios and enrichment of LREE over HREE. The second type comprises Al-undepleted komatiites that have chondritic Al2O3/TiO2 and flat REE patterns. The third type identified comprises Al-enriched komatiites that display suprachondritic Al2O3/TiO2 ratios, with significant LREE depletion. The Al-depleted and Al-undepleted komatiites from Buffalo River are geochemically similar to komatiites from the 3.48 Ga Komati and 3.26 Ga Weltevreden formations of the Barberton Supergroup respectively, whereas the Al-enriched komatiites resemble the 3.33 Ga Commondale komatiites on the southeastern Kaapvaal craton.To explain the co-occurrence of three discrete komatiite types within a single volcanic succession at Buffalo River, we suggest that each major komatiite magmatic pulse originated from the same upwelling mantle source, from which melt was extracted at different pressure but similarly hot temperature conditions. 187Os/188Os data for the Al-depleted komatiites suggest an ultimate magma origin from a primitive mantle reservoir. The contrasting γOs values for Kaapvaal craton komatiites (zero to positive) and peridotitic mantle xenoliths (zero to negative) support a complementary nature of these lithologies as high-degree melts and depleted residues linked by vigorous mantle plume activity at around 3.5 Ga. Such a relationship can explain the contrasting Re/Os systematics of komatiites and lithospheric mantle peridotites, which creates the contrasting γOs over time.The highly siderophile element patterns of the Al-depleted komatiites from Buffalo River are similar to those of Barberton-type komatiites, for which an origin from the deepest upper mantle with high melt retention in an upwelling plume source was suggested. We confirm that this ca. 3.5 Ga mantle source had only 60–80 % of the platinum-group element budget of the modern ambient mantle, which points indirectly to a location at great depth in the aftermath of the meteoritic late accretion. Progressive melting of such an upwelling mantle source, to the point of majoritic garnet exhaustion, may explain the Al-undepleted and Al-enriched komatiites at Buffalo River. The presence of all three major komatiite types within a single volcanic succession may be linked to deep critical melting of a large mantle plume associated with growth of the Kaapvaal ‘continent’ at 3.5 Ga.

Unravelling magmatic-hydrothermal processes at Salobo and GT-46 IOCG deposits, Carajás mineral province, Brazil: Constraints from whole-rock geochemistry and trace elements in apatite

The iron oxide-copper-gold (IOCG) deposits of the northern portion of the Carajás Province, Amazonian Craton, Brazil, were primarily formed at the 2.5 Ga IOCG event. These deposits commonly exhibit wide Fe–K hydrothermal alteration halos (i.e., almandine-grunerite-biotite-magnetite) and display a temporal and spatial association with the 2.5 Ga granitic bodies, particularly in the GT-46 and in the world-class Salobo deposit. However, this association still lacks investigation concerning the metallogenic influence of the 2.5 Ga granitic bodies in the IOCG formation. Within these deposits, ca. 2.5 hydrothermally altered granites are recognized and include the Old Salobo, at the Salobo deposit, and G1 and G2, at the GT-46 deposit. Whole-rock geochemistry combined with petrography has pointed out that the G1 and Old Salobo are represented by granites to monzogranites, ferroan, metaluminous to weakly peraluminous with negative Eu anomaly. On the contrary, the G2 granite seems to represent a distinct body with granite composition, ferroan, metaluminous to weakly peraluminous with positive Eu anomaly. This granite exhibit pegmatitic textures, high Sr/Y ratios and listric-shaped normalized REE patterns, which suggest crystallization under high water contents. These granites primarily plots in the field of the volcanic arc granites, though some shifts towards to syn-collisional granites are observed. Effects of hydrothermal alteration are commonly seen in these granites both in textural aspects and geochemistry. Apatite mineral chemistry studies shows that magmatic signature in apatite is preserved in the G2 granite (G2core apatite), Old Salobo granite (OSA) and in the GT-46 ore zone (OZGT-A apatite), represented by enrichment in LREE and negative Eu anomaly. Hydrothermally altered apatite is recognized in the Old Salobo (OSB) and G2 granite (G2rim) and in the ore zone of GT-46 deposit and (OZGT-B) with depletion in LREE, which suggest that the same fluid might have affected both deposits. Truly hydrothermal apatite crystals from the Salobo and GT-46 ore zones shows high (Eu/Eu*)N values, indicative of high oxygen fugacity and alkaline fluids. Strong HREE depletion of the apatite grains from the central zone of the deposits suggest coeval almandine crystallization in the Fe–K alteration halos and evolved hydrothermal fluids. These results indicate that magmatic and hydrothermal process coexist in the IOCG deposits from the northern sector of Carajás Province. This might suggest that the 2.5 Ga IOCG deposits from the Carajás Province can have formed during the development of wide magmatic-hydrothermal systems.

The Coorg Block, southern India: Insights from felsic and mafic magmatic suites on Mesoarchean plate tectonics and correlation with supercontinent Ur

The Coorg Block in southern India is one of the oldest crustal fragments on the globe and is composed of Mesoarchean magmatic suites, dominantly charnockites, gabbros and their variants that were metamorphosed under granulite facies conditions. Here we investigate a suite of charnockites, metagabbros and amphibolite from this block by undertaking detailed field studies, petrological and geochemical analysis, and zircon and monazite isotope geochronology. Phase equilibria modeling using pseudosection computations shows ultrahigh-temperature metamorphic conditions yielding a P-T range of 10–11 kbar at 1000 °C for the charnockite assemblage and 8–9 kbar at 950 °C for the metagabbro. Geochemistry indicates that the felsic and mafic rocks are sub-alkaline and represent a tholeiitic magma series. The rocks were derived possibly through fractionation of a reduced primary magma in a Mesoarchean subduction-related setting. Zircon grains from the charnockites and gabbros show magmatic textures, with LREE depletion and HREE enrichment, negative La, Pr, Nd, Eu and positive Ce, Sm, Gd anomalies, and Th/U ratios consistent with magmatic crystallization. We present zircon and monazite U–Pb data from a comprehensive suite of samples that indicate timing of peak of magmatic emplacement for both the charnockite and gabbroic suites occurred at ∼ 3.15 Ga, closely followed by metamorphism at ∼ 3.0 Ga. The presence of magmatic xenocrysts of up to ∼ 3.5 Ga in some of these rocks suggest older crustal components in the basement. Zircon Lu–Hf analyses suggest that the amphibolite and gabbro were mostly derived from depleted mantle sources whereas the charnockite suite involved both juvenile and reworked Paleoarchean components. The tectonic setting of these felsic and mafic magmatic rock suites correlates with a Mesoarchean subduction system, complementing recent models on the emergence of modern-style plate tectonics in the early Earth. We correlate the Mesoarchean arc magmatic suites in the Coorg Block to the building blocks of the core of the Earth’s oldest supercontinent Ur, with the surrounding Neoarchean granulite blocks and their equivalents in other cratonic fragments to the ‘expanded Ur’.

Characteristics of REEs and Trace Elements in Scheelite and Muscovite Ar–Ar Isotopic Dating of the Daping Tungsten Deposit

The recently discovered Daping tungsten deposit is located about 25 km north of Tongcheng County, Hubei Province, in the northern margin of the Sijiapu granite deposit of the Mufushan composite batholith. The ore body is produced in the northeast-oriented greisenization granite and quartz vein, and belongs to the greisen-vein-type scheelite deposit. The resources of the Daping W deposit have a value of 7935 t W and the average grade is 0.201% WO3. Based on mineralogical and petrographic studies, scheelite is classified into two types. A study of the geochemical characteristics of rare earth elements (REEs) and trace elements indicated that some scheelite specimens showed LREE depletion. Meanwhile, the total amount of scheelite rare earth elements (REEs) is low and the ratio of LREE/HREE ranges from 0.40~2.72 in the Daping W deposit. The contents of REEs and trace elements in the two types of scheelite differ significantly. Type I scheelite has an average ∑REE content of 195.65 ppm, an LREE/HREE value of 0.5, an Eu anomaly (δEu) of 0.78, Mo of 366.20 ppm, Sn of 22.62 ppm, and Sr of 264.80 ppm. However, type II scheelite features an average ∑REE of 111.28 ppm, an LREE/HREE ratio of 1.43, a δEu of 1.56, Mo of 188.48 ppm, Sn of 0.15 ppm, and Sr of 829.93 ppm. The content level of Mo in the two types of scheelite is not high, indicating that this whole metallogenic environment is a reduction environment. However, this is a complex process. The presence of type I scheelite with negative Eu anomalies and relatively high Mo content indicates that the ore-forming environment in the early period of the greisen stage was relatively oxidizing. In contrast, type II scheelite contains large amounts of Sr and large positive Eu anomalies, which are likely to be released from plagioclase in the granite during greisenization. The extremely low composition of Mo in type II scheelite is closely related to the reducing environment in the later period of the greisen stage. Because Mo probably exists in its Mo4+ state, it may be difficult for it to replace W6+ in the scheelite lattice. Additionally, comparing the contents of Sn and Sr in different types of scheelite shows that the metallogenic environment changes from relative oxidation to the reduction of scheelite. The variation in trace elements and REEs in scheelite over time reflects a complex magmatic–hydrothermal mineralization environment. Additionally, the Ar–Ar system dating results for muscovite that is closely associated with scheelite in the greisenization granite vein indicate that a muscovite 40Ar/39Ar plateau age of about 133 Ma represents the time of tungsten mineralization. This muscovite 40Ar/39Ar dating result is close to the previous zircon U-Pb age data of the biotite monzogranite (ca. 140–145 Ma), which is the largest intrusion in the orefield. Meanwhile, the new age data reported here confirm that the Daping tungsten deposit represents a Mesozoic magmatic–hydrothermal mineralization event with a setting of lithospheric extension in the Mufushan composite batholith.

Geochemical Characterization of Laminated Crystalline Crust Travertines Formed by Ca2+-Deficient Hot Springs at Sobcha (China)

Travertines formed of crystalline crust have been widely reported, but there has not been focus on their geochemical characteristics. We therefore carefully conducted a series of geochemical investigations and U-Th dating on a travertine mound mainly composed of crystalline crust from Sobcha (southwest China) to determine their geochemical features and geological implications. The Sobcha travertines dominantly consist of granular crystals and fan crystals and show δ13C from 3.4‰ to 4.9‰ V-PDB, δ18O from −26.7‰ to −23.7‰ V-PDB, and 87Sr/86Sr from 0.712458 to 0.712951. When normalized to PASS, the Sobcha travertines exhibit MREE enrichment relative to HREE and LREE, HREE enrichment relative to LREE, and positive Eu anomalies. The δ13C signatures and mother CO2 evaluation of the Sobcha travertines show that the Sobcha travertines were thermogene travertines largely receiving mother CO2 from (upper) mantle (i.e., magmatic CO2) or a mixture of soil-derived CO2 and CO2 related to carbonate decarbonation. The 87Sr/86Sr of the Sobcha travertines is out of the 87Sr/86Sr ranges of local deposits exposed at Sobcha and surrounding areas but is well matched with the mean 87Sr/86Sr of Nadi Kangri volcanic rocks which cropped out to the northeast of the studied travertines (over 20 km away). This might indicate the important role of the Nadi Kangri volcanic rocks in suppling Sr to the studied travertines, but more studies are required. The LREE depletion compared to MREE and HREE in the Sobcha travertines was interpreted to be caused by the difference in geochemical mobility between LREEs and HREEs during water–rock interaction at depth, while the MREE enrichment compared to HREE was considered to be most likely inherited from reservoir/aquifer rocks. The positive Eu anomalies of the Sobcha travertines may result from very high reservoir temperatures and/or preferential dissolution of Eu-rich minerals/rocks (especially plagioclase). The Sobcha travertine mounds displays no or very slight vertical variations in δ13C, 87Sr/86Sr, and REE patterns, indicating the compositional stability of mother CO2 and paleo-fluids. However, a significant vertical increase in δ18O was observed and was explained as the result of gradual water temperature decrease related to climate cooling, self-closure of the vents, or mound vertical growth. The findings in this study might help us better understand the deposition of crystalline crust in Ca2+-deficient hot spring systems.

Geochemical and Characteristics of Mafic and Ultramafic Rocks of the Suprasubduction Zone Mawat Ophiolite, NE Iraq

New geochemical data were presented for the mafic (basalts and gabbros) and ultramafic (dunites, serpentinites and pyroxenites) rocks from the Mawat ophiolite exposed in the Zagros suture zone in northeastern Iraq. The mantle section of the ophiolite is composed of serpentinized peridotites, harzburgites, dunites, chromitites and pyroxenite dykes. The crustal section is composed of layered amphibole-rich gabbros, pegmatitic gabbros as well as basalts and minor felsic dykes. The ultramafic rocks are highly depleted in the LILEs and most of the HFSEs. The mafic rocks are tholeiitic, characterized by depletion of LREEs and display a positive trend from LREE to HREE with low Ti/V ratios. The younger gabbros are mostly calc-alkaline, characterized by enrichments of LREE with a negative REE trend and high Ti/V ratios. The basaltic and ultramafic samples plot below the N-MORB reference line suggesting that these elements have been mobile. They fall within the boninitic field in the Ti/V diagram and are related to the subduction initiation setting. The younger gabbros are related to rifting which postdated the formation of ophiolite. These geochemical data are consistent with the subduction-related suprasubduction zone tectonic setting.

Constraints on Paleoproterozoic crustal growth from Birimian Supergroup lavas of the Bui belt (Ghana) in the West African Craton

The volcano-metasedimentary Bui belt in Ghana is one of the lesser known Birimian belts of the West African Craton that provide constraints on Paleoproterozoic crustal growth. This study presents the first major, trace element and Nd-Hf isotope data for the mafic suite of the Bui belt to constrain their petrogenesis and geodynamic setting. Although alteration is prevalent, the volcanic, volcaniclastic and plutonic rocks show tholeiitic signatures, with Mg# 35–65. Chondrite-normalised REE patterns are mainly flat, with slight LREE enrichment or depletion, and multi-element diagrams show Th and LREE depletion relative to other immobile incompatible trace elements. These features suggest derivation from a moderately depleted mantle source. Whole rock Sm-Nd isotope data yields an errorchron at ca. 2.2 Ga, with an initial εNd of +3.4 but the Lu-Hf isotopic system appears to be disturbed. The lack of arc related geochemical signatures (absence of negative Nb-Ta and Ti peaks, a nearly flat to depleted REE pattern) in the Bui mafic suite, together with the volcanic-sedimentary rock association, point towards magma generation in an oceanic plateau or divergent setting similar to a mid-ocean ridge, contrasting with the subduction setting that has been proposed for most other instances of Birimian magmatism in the West African Craton.

Žune Ba-F epithermal deposit Part 1: Mineralogical and geochemical characteristics

The Žune Ba-F epithermal deposit is situated in the Ljubija ore field (NW Bosnia and Herzegovina), within Upper Palaeozoic dolostone. A typical ESE-WNW Variscan vergency fault zone separates the dolostone from Lower Triassic schists and sandstones. External and internal pseudo-bedding, with massive, homogenous structure and partial limonitization characterizes the dolostone. Its geochemical composition exhibits low SiO2 (1.33 – 2.06 mass. %), Al2O3 (0.27 –0.38 mass. %), BaO (0.02 – 0.83 mass. %), ƩREE (5.7 – 9.4 ppm), Sr (61.7 – 120.4 ppm), Sm (0.3 – 2.2 ppm) and Eu (0.1 – 0.6 ppm), while having high CaO (30.24 – 32.38 mass. %), MgO (16.47 – 17.35 mass. %) and LOI (44.6 – 45.58 mass. %). The dolostone-mineralization contact zone consists of metasomatically recrystallised host dolostone with quartz and pyrite, where the presence of accessory tremolite, magnesiochloritoid and pyknite indicates peak formation conditions in the pre-mineralization phase with temperatures above 300°C. Two ore types are described: (i) Ba-F vein-type mineralization composed of barite – fluorite ± quartz, and (ii) hydrothermal breccia composed of coarse-grained fluorite and barite, surrounding fragments of dolostone, and occupying ≈20 % of the deposit. Mineralized samples show slightly elevated SiO2 (2.20 – 5.53 mass. %) and Al2O3 (0.24 – 0.74 mass. %), low MgO (below 0.02 mass. %) and LOI (0.3 – 3.1 %), with high BaO (up to 50.74 mass. %), CaO (up to 66.03 mass. %), ƩREE (20 – 166 ppm), Sr (exceeding 1 mass. %), Sm (up to 118 ppm) and Eu (up to 44 ppm). Elevated Sr can be correlated to other barite epigenetic hydrothermal deposits in the Dinarides, interpreted as BaSr substitution in the barite crystal lattice. Fluorite-rich samples are characterized by Y (0.6 –49.2 ppm) and HREE enrichment, accompanied by depletion of LREE. The Ba-F deposit Žune, having variable REE concentration and a negative cerium and ytterbium anomaly corresponds geochemically to world-class fluorite deposits associated with carbonate sedimentary rocks.

Magmatic Garnet and Magma Evolution in Cuonadong Leucogranites: Constraints from Petrology and Mineral Geochemistry

Located at the eastern segment of the Tethyan Himalayan tectonic unit, the Cuonadong leucogranites (muscovite granite and pegmatite) have a mineral assemblage of quartz, plagioclase, and alkali feldspar, as well as muscovite and garnet. Garnets in both muscovite granite and pegmatite belong to the almandine–spessartine solid solution, with minor andradite, grossular, and pyrope, and show a specific Mn zoning of a relatively rim-ward Mn depletion trend. However, a few garnets in pegmatite show grossular enrichment towards the rim. All the analyzed garnets are characterized by HREE enrichment and LREE depletion with obvious Eu anomalies. The difference is that garnets from the muscovite granite show distinct left-declined or flat HREE patterns, while those from the pegmatite are featured by flat or right-declined HREE patterns. Moreover, garnets from the pegmatite show relatively more distinct HREE- and Y-rich cores compared with those from the muscovite granite. The MnO concentration, spessartine content, and MnO/(MnO + FeO) ratio of the garnets from the Cuonadong dome increase from the muscovite granite to the pegmatite, suggesting that the pegmatite likely formed from a more evolved environment. Elevated grossular and CaO contents of the garnet rim in the pegmatite may reflect an influence of fluids in their composition. The major and trace element compositions and zoning textures of garnets from the Cuonadong leucogranites suggest a magmatic origin and a formation at moderately low temperatures and relatively low-pressure conditions. From the muscovite granite to the pegmatite, the system entered a fluid-rich environment and the garnets from the pegmatite likely crystallized from a lower-temperature fluid.

Petrographic, Rare Earth Elemental and Isotopic Constraints on the Dolomite Origin: A Case Study from the Middle-Upper Cambrian Xixiangchi Formation in Eastern Sichuan Basin, Southwest China

The Middle-Upper Cambrian Xixiangchi Formation in the Sichuan Basin is regarded as an important reservoir with great potential for hydrocarbon exploration. It is previously indicated that the Xixiangchi carbonates have experienced extensive dolomitization, however, the origin of dolomitizing fluids and the dolomitization mechanism still remain uncertain. In this study, a set of petrographic and geochemical examinations, including rare earth elements (REE) and isotopic (C, O, and Sr) compositions were used to trace the origins of dolomitizing fluids and associated diagenetic processes. The petrographic examination revealed three types of matrix dolomites (D1, D2, D3) and one cement saddle dolomite (SD). These phases have crystal size ranges of less than 30 μm (very fine to fine crystals, D1), 30–100 μm (fine to medium crystals, D2), 100–300 μm (medium to coarsely crystalline dolomite, D3), and 0.3–4 mm (fracture filling cements, SD), respectively. D1 is characterized by non to very weak luminescence, weakly negative Ce anomalies (Ce/Ce* = 0.84 ± 0.02), strongly negative Eu anomalies (Eu/Eu* = 0.65 ± 0.03), and high 87Sr/86Sr ratios (0.71062 ± 0.00122). In combination with δ13C (−1.5‰ ± 0.2‰) and δ18O (−9.7‰ ± 0.5‰) compositions, D1 is interpreted to be formed by penecontemporaneous dolomitization in the near-surface environment with seawater as the dolomitizing fluid. In contrast, D2 is characterized by intercrystalline pores, dirty crystal surfaces, similar δ13C (−1.4‰ ± 0.4‰) compositions but higher δ18O (−8.9‰ ± 0.7‰) compositions, and lower 87Sr/86Sr ratios (0.70992 ± 0.00035), similar Ce anomalies (Ce/Ce* = 0.87 ± 0.04) and higher Eu anomalies (Eu/Eu* = 0.85 ± 0.04). The coarser D2 is regarded to be formed by the post-penecontemporaneous seepage-reflux dolomitization or by recrystallization of D1 dolomite in a near-surface or shallow burial environment. D3 is distinguished by a cloudy core with clear rims, showing slightly higher Eu anomalies (Eu/Eu* = 0.88 ± 0.02) and similar Ce anomalies (Ce/Ce* = 0.88 ± 0.02) than those of D1 and D2. Combined with the δ18O compositions (−10.4‰ ± 0.4‰) and 87Sr/86Sr ratios (0.70989 ± 0.00048), D3 is thought to be formed by the overgrowth or recrystallization of D1 and D2 dolomites in a shallow to moderate burial environment. The fractures filling SD dolomite consists of nonplanar and much coarser crystals with undulatory extinctions and brighter red luminescence. The lower δ18O (−11.1‰ ± 0.3‰) compositions, lower negative Eu anomalies (Eu/Eu* = 0.70 ± 0.01) of SD than the matrix dolomites, and similar Ce anomalies (Ce/Ce* = 0.83 ± 0.01) are indicative of hydrothermal dolomitization, with possible fluids associated with the magma during the period of Emei taphrogenic movement. In addition, the 87Sr/86Sr ratios (0.70941 ± 0.00003) of SD suggest probable origin from the coeval seawater partially. Therefore, SD dolomite is interpreted to be formed by hydrothermal dolomitization with mixed dolomitizing fluid of seawater and hydrothermal fluids. In summary, all the matrix dolomites have almost the same ΣREE concentrations and exhibit similar near-flat REE partition patterns with weak LREE enrichments, weakly negative Ce anomalies, and negative Eu anomalies. Such characteristics of REE compositions are indicative of similar evolved dolomitizing fluid, such as seawater or seawater- derived fluids. By contrast, SD dolomites have a different REE partition pattern with left-leaning characteristics, LREE depletions, and negative Eu anomalies, thus suggesting a different dolomitizing fluid source from the matrix dolomites. In addition, the development of intercrystalline pores associated with D2 dolomite makes it more likely to be a potential reservoir, indicating that the dolomitizing history of carbonate has a strong influence on the quality of potential dolomite reservoirs.

Geochemistry of Volcano-sedimentary and Plutonic Formations of the Agbaou Gold Deposit, Ivory Coast

Located in the south-west part of the Fettekro greenstone belt, Agbaou gold deposit is marked by three major lithological units: (i) a volcano-plutonic unit composed of basaltic to andesitic lavas, amphibolites, chlorite-schists and sills of microdiorite and microgabbro; (ii) a volcano-sedimentary unit containing pyroclastic lavas (basaltic and dacitic) and sediments (shale and grauwacke); (iii) the late felsic dikes (rhyolite and rhyodacite) probably contemporary with the formation of granitoids form the third unit. These host rocks are mostly intensely deformed and altered. Alteration phenomena were revealed by the high values in fire loss, the decreasing of silica contents, the sometimes high values of alkaline for rocks also basic, the constant depletion in LREE and LILE. The Eu and Nb negative anomalies reveal a crustal contamination of magmatic series. Basaltic lavas are volcanic arc tholeiites nearing N-MORB type; they are associated to a magmatogenesis of ocean floor. Their magmatic source would probably be spinel lherzolitic type. Andesites have a calc-alkaline composition and seem far link to active subduction margin. Geodynamics context would be that of an area where transcurrent faults of lithospheric extension generate heat corridors able of generating by fusion the andesitic calc-alkaline magma. This context would probably be the one that prevailed during the establishment of the gold mineralization. Pyroclastic rocks of dacitic composition as acid lavas (rhyolite and rhyodacite) have also evolved in this same geotectonic context. Plutonic rocks are located in arc-volcanic granites field, while metasediment are linked to active continental margin field.

Shallow-ocean and atmospheric redox signatures preserved in the ca. 1.88 Ga Sokoman iron formation, Labrador Trough, Canada

Detailed mineralogical and geochemical analysis of drill core samples from three previously unstudied localities (Sheps Lake, Lac Ritchie, Hayot Lake) of the ca. 1.88 Ga Sokoman continental margin-type iron formation (IF) was undertaken to better understand tectonically stable, shallow-marine environments and surface redox conditions during the late Paleoproterozoic. Suboxic (Fe-oxide-rich including paragenetically early hematite) and anoxic (Fe-silicate/carbonate-rich) mineral paragenetic pathways operated during IF deposition. Post-depositional alteration beyond late diagenesis/metamorphism was negligible, based on petrographic examination and analysis of bulk Fe(III)/Fe(II) ratios. High-precision trace element (TE) data of the Sokoman IF, in the context of new analyses of IF/iron ore reference materials (IOC-1, FeR-3, FeR-4), reveal similarities to contemporaneous continental margin-type IF. However, both the analytical approach and integration of chemostratigraphic variations in detrital element, rare earth element and yttrium (REE + Y), and other TE (Cr, V, U, Ni, Co, Zn) parameters with a previously published sequence-stratigraphic framework provides refined insight into the ca. 1.88 Ga marine surface environment. Specifically, this study dissects new details on the effects of base-level fluctuations, terrigenous input, basin redox stratification, and microbial activity that are collectively captured within the mineralogically and texturally complex units of the Sokoman IF.The REE + Y signature of the Sokoman IF is confirmed to have developed during deposition/early diagenesis through a comparison of geochemical signatures of chert (jasper) intraclasts and surrounding bulk IF. Furthermore, the Sokoman IF REE + Y data show patterns reminiscent of modern seawater (LREE depletion, small negative Ce anomalies, small positive La, Gd, and Y anomalies), but in some cases also strong positive Ce anomalies. Modelling of hyperbolic trends in Ce/Ce*-Pr/Pr* plots, preserved despite varying detrital admixtures, provides supporting evidence for interaction of dissolved REE + Y with marine Fe- and Mn-(oxyhydr)oxides, and quantitatively constrains the amount of detritus required to overprint Ce anomalies. The co-existence of positive and negative bulk-rock Ce anomalies, similar to those of other ca. 1.88 Ga IF, implies the presence of a shallow marine redoxcline at that time. However, the absence of any strong covariations between these Ce anomalies and (1) Mn- or Fe-enrichments, (2) Y anomalies, (3) LREE/HREE ratios, or (4) tetrad coefficients (τ) is best explained by the separation of a shallow Mn-redoxcline from a slightly deeper and more diffuse Fe-redoxcline inferred here to be controlled by cyanobacteria and photoferrotrophs, respectively.Combined plots of chemostratigraphic and TE/ΣFe vs. enrichment factors highlight variable input/scavenging of different TEs within the Sokoman IF; authigenic TE enrichment is more readily captured in deeper, suboxic to anoxic units relative to shallower, nearshore units where even low amounts of continental detritus can obscure low-magnitude, authigenic redox signatures. This approach confirms the low magnitude and limited range of authigenic enrichments in redox-sensitive and nutrient-type TEs in the Sokoman IF as being similar to those of other ca. 1.88 Ga IF localities, but reveals which depositional environments best capture specific authigenic signatures (e.g., Cr-V-U-P enrichments). Detritus-poor samples record highly fractionated Nb/Ta and Zr/Hf ratios (m/m; Nb/Ta: median 56.4, range 15.5–680; Zr/Hf: median 97.8, range 42.9–409) that exceed those observed in the modern hydrosphere, and are interpreted to reflect greater interaction of the “dissolved” load of these elements with abundant marine Fe/Mn colloids/fine-particulates. Detritus-rich samples have Nb/Ta and Zr/Hf ratios converging towards crustal values similar to those of shales within the Sokoman basin; both datasets support a model for a predominantly felsic (Archean plutonic/metamorphic rock) source.New inferences from our data on the Sokoman IF support a close link between atmosphere–ocean oxygenation and microbial ecosystems via continental weathering under an oxygen-poor atmosphere (aided locally by arid conditions). In this model, such conditions limited the terrestrial supply of redox-sensitive and nutrient-type elements (most notably P) into the ocean, largely restricting the spatial extent of primary productivity to the photic zone of coastal regions. These processes are consistent with collective evidence from other ca. 1.88 Ga IF deposits that suggest low-O2 and nutrient-limited Earth surface conditions relative to preceding time intervals in the Paleoproterozoic.

Stable isotope geochemistry and microfossil assemblages of carbonate rocks in the ophiolite mélange zone of the Indo–Myanmar orogenic Belt, NE India: Implications on age and depositional environment

A comprehensive data of whole‐rock and stable isotopic geochemistry along with microfossil assemblages of the carbonate rocks of the ophiolite mélange zone of the Indo–Myanmar orogenic Belt (IMOB), north‐east India are discussed, to determine the influence of terrigenous contamination during the formation of these carbonate rocks and also to understand their depositional environment and ages. These carbonate rocks contain a diverse fauna with the dominance of foraminiferal assemblages of planktonic foraminifera (Globotruncana sp. and Heterohelix sp., etc.) which indicates they were formed during the Santonian to Maastrichtian age. Based on chemical compositions, these carbonate rocks have been identified as limestone (CaO/MgO > 50.1) to slightly dolomitic limestone (9.1 < CaO/MgO < 50.1). Total rare earth element (REE) contents in these carbonates are variable (22.39–146.05 ppm). The Post‐Archean Australian Shale (PAAS)‐normalized REE + Y patterns of these carbonates exhibit seawater‐like REE patterns with LREE depletion and relative HREE enrichment with negative Ce anomalies (Ce/Ce* = 0.32–0.79) and positive Y (4.42–27.81 ppm) and Eu anomalies (Eu/Eu* = 1.11–1.86), suggesting that they were deposited under an oxygenated environment with contamination by hydrothermal activity. They are also depleted in δ13C 0/00 (PDB) (1.02–1.570/00) and δ18O 0/00 (PDB) (−6.37 to −9.00%) values which characterize marine precipitates. Eu anomalies and spread in negative δ18O 0/00 (PDB) values to a lesser extent of δ13C 0/00 (PDB) values of these carbonates suggest their formation was altered by diagenesis in the shallow marine environment. Our new whole‐rock and stable isotope geochemical characteristics, in conjunction with microfacies, suggest that the investigated carbonate rocks might have been formed in low‐energy environments, and deposited in neritic to bathyal palaeoenvironments during the Santonian to Maastrichtian interval.

Late Cretaceous fore–arc spreading in the northern Kuching Zone of West Borneo, SE Asia: Constraints from the Pakong Mafic Complex

• The Pakong Complex formed at ∼ 100–78 Ma, more widely than expected. • The Pakong Complex comprises N-MORB- and E-MORB-type mafic rocks with arc-like imprints. • Fore-arc spreading resulted in the generation of the Pakong Complex. • The Cretaceous tectonic evolution of West Borneo was related to the paleo-Pacific subduction . The tectonic evolution of West Borneo and its paleogeographic correlation with other blocks/terranes in Southeast Asia during the Mesozoic remain unclear. Here we present newly obtained zircon U–Pb ages and whole-rock elemental and Sr–Nd isotopic data for the Pakong mafic rocks along the Lupar Line in the northern Kuching Zone of West Borneo. The zircon U–Pb dating results show that the Pakong gabbros were formed at 82.0 ± 1.9 Ma, while the diabases were emplaced at 78.5 ± 0.9 Ma. Geochemically, all the Pakong mafic rocks can be divided into two groups. The Group 1 samples show an affinity to N–MORB with negative anomalies in Nb, Ta and Ti, while Group 2 is characterized by E–MORB–like REE pattern with slight enrichment in LREE but similar depletion in Nb, Ta and Ti to Group 1. Isotopically, the former (ε Nd (t) = 6.23–9.87) has more depleted Nd isotopic compositions than the latter (ε Nd (t) = 4.25–5.71). The combined signatures indicate that the N–MORB–like mafic rocks (Group 1) were derived from 10 to 30% partial melting of a depleted lherzolite mantle modified by subduction–related fluids and that the E–MORB–like mafic rocks (Group 2) were the results of mixing between the Group 1 magmas and the OIB-type melts. Integrating with regional data, we propose the Late Cretaceous fore–arc spreading development along the Lupar Line in the northern Kuching Zone of West Borneo, which was induced by the rollback of the subducting Paleo–Pacific plate rather than the Proto–South China Sea slab.

Using titanite to constrain geochronology and physicochemical conditions of hydrothermal mineralization events: A case study of the Duotoushan Fe–Cu deposit, Eastern Tianshan, NW China

As a common Ca‐ and Ti‐ bearing silicate mineral in many types of hydrothermal deposits, titanite usually contains high concentrations of trace elements. Its mineral chemistry and U–Pb isotope can reveal the physicochemical conditions and geochronology of the ore‐forming systems. In this contribution, we present a detailed study on titanite which precipitated during the Fe mineralization in the Duotoushan deposit. Due to coexistence with hydrothermal minerals, low Th/U ratios (0.02–0.3), and depletion in rare earth elements (REE), all the studied titanites are classified into a hydrothermal group. The negative correlation between [REE3+ + (Al, Fe)3+] and [Ca2+ + Ti4+] indicates that REE mainly entered the lattice of titanite via the mechanism of substitution. In addition, titanite grains are characterized by HREE, Zr, and Nb enrichments with LREE depletion, suggesting that the complexation of F− at neutral to alkaline pH conditions may have caused the fractionation of REE. At Duotoushan, the titanite grains coexist with quartz, epidote, amphibole, and magnetite, and exhibit positive Eu anomalies (δEu = 1.04–1.31) but lack Ce anomalies, indicating that ore‐forming fluids may have been derived from a relatively low oxygen fugacity and high fH2O environment. Titanite yielded an in‐situ U–Pb lower‐intercept age of 307.2 ± 4.8 Ma (MSWD = 0.97), consistent with the syn‐ore amphibole 40Ar‐39Ar plateau age (305 ± 6 Ma). Since the mineralization ages are obviously younger than country rocks, the previous syn‐sedimentary ore‐forming model for Duotoushan Fe–Cu mineralization can be excluded. Integrating the characteristics from ore deposit geology, periods of mineralization events, and spatial–temporal distribution of magmatism, we proposed that the Duotoushan Fe–Cu mineralization event may be linked with a hidden granite in its orefield.

Genesis of the Xiarihamu Magmatic Ni-Co Sulfide Deposit in the East Kunlun Orogen, Northern Tibetan Plateau: In Situ Oxygen Isotope and Geochemical Perspectives

Abstract Convergent margins are commonly deemed to have poor potential to form giant magmatic Ni-Cu-(platinum group element) sulfide deposits, due to the possibly low lithospheric geothermal gradient and the small basaltic magma fluxes. This view, however, is challenged by the recent discovery of the Xiarihamu Ni-Co deposit in the East Kunlun orogen (northern Tibetan Plateau), which contains ~157 million metric tons (Mt) of sulfide ores at 0.65% Ni, 0.013% Co, and 0.14% Cu, making it the world’s 20th largest magmatic sulfide deposit. To investigate the mantle source nature, magmatic processes, and their genetic linkage to Ni-Co mineralization in orogenic belts, we presented new in situ orthopyroxene oxygen isotope and pyroxene trace element data from the mafic-ultramafic cumulate rocks at Xiarihamu. Our results show that orthopyroxene crystals have much higher δ18O (6.40–8.58‰) than those in unmodified mantle peridotite (5.72 ± 0.14‰). Orthopyroxene grains in the primitive harzburgite cumulates have the lowest δ18O values (6.40–7.71‰) and the highest Mg# contents (88.7–83.9). From the harzburgite to the evolved lithologies (e.g., websterite and gabbronorite), the δ18O values of orthopyroxene increase, whereas the Mg# values, Ni contents, and heavy/light rare earth element (HREE/LREE) ratios of orthopyroxene decrease, implying crustal contamination during magma fractionation. The δ18O variations and sharp increases in V/Sc and LREE/HREE ratios from the primitive orthopyroxene crystals (with the highest Ni and Mg#) to the evolved ones (with low Ni and Mg#) indicate that crustal contamination played a critical role in sulfide saturation. The absences of any trend in orthopyroxene δ18O values versus Mg# contents, Ni concentrations, and La/Yb ratios toward unmodified mantle values suggest an enriched mantle source. On the mid-ocean ridge basalt (pyroxene)-normalized multielement plots, both orthopyroxene, clinopyroxene, and calculated parental magma show LREE and large ion lithophile element (LILE) enrichments and depletions in Nb-(Ta), Sr, and Zr-(Hf). The predicted primitive magma trace element compositions and the high-δ18O characteristics of the high-Mg# orthopyroxene grains suggest that the Xiarihamu primitive magma was partly originated from the pyroxenite mantle metasomatized by subducted slab-derived melts and fluids. Given the lower solidus temperature of clinopyroxene relative to olivine, pyroxenites in the mantle wedge may generate voluminous high-Ni magmas during partial melting. The high-Ni magmas are likely conducive to magmatic Ni-Cu sulfide mineralization in orogenic belts.

Early Diagenetic Dolomite as a Potential Archive of Paleo‐redox Fluctuations in an Early Tonian Marine Basin?

AbstractThe Tonian Period witnessed important environmental changes and critical evolutionary innovations. Published iron speciation data suggest a global redox transition of mid‐depth seawaters from euxinic to ferruginous in early Tonian, but details of this transition remain unknown. This study explores Tonian stromatolitic carbonates as a possible archive of paleoenvironmental changes, through the investigation of dolomitic limestones and dolostones associated with stromatolites of the Weiji Formation in the Huaibei region of North China. Three types of dolomitization are recognized on the basis of petrographic and geochemical data. Type I and II dolomitization resulted in dolomitic limestones characterized by LREE depletions, MREE enrichments, positive yttrium anomalies, and a lack of europium anomalies, indicating early diagenetic dolomitization, possibly in the iron reduction zone and under the influence of bottom seawater. The lack of cerium anomalies in these carbonates suggests anoxia in shallow marine environments. The coexistence of ferroan/non‐ferroan dolomite crystals and overgrowth bands is interpreted as possible evidence for rapid fluctuations between iron‐rich and iron‐depleted conditions in pore‐waters or seawaters. In contrast, type III dolomitization resulted in pervasively dolomitized stromatolitic carbonates and likely represents late diagenetic processes. This study highlights the potential of early diagenetic dolomite as an archive for paleoenvironmental investigations.

Chemical composition of garnet from the Xintianling skarn W deposit in southern Hunan and its geological significance

新田岭矿床是南岭钨锡成矿带中的一个大型矽卡岩型钨矿床，产于骑田岭岩体东北部与石炭系碳酸盐地层的接触带位置。本文运用LA-ICP-MS技术对该矿床矽卡岩中的石榴子石进行了系统的成分分析，获得了其主量、微量和稀土元素含量。结果显示，新田岭矿床中的石榴子石属于钙铁榴石-钙铝榴石固溶体系列（And₂₄Gro₆₆-And₇₁Gro₂₂），石榴子石的端元成分在富钙铝榴石和富钙铁榴石之间变化。稀土元素的配分模式也同时出现了左倾、Eu负异常和右倾、Eu正异常两种类型，暗示新田岭矿床石榴子石结晶过程中热液流体存在不同的氧化还原环境和水/岩比条件，这也与其晶体中是否出现振荡环带相对应。将不同矽卡岩型矿床中石榴子石的W、Sn含量进行对比显示，含W矿化的矽卡岩型矿床中石榴子石的W、Sn含量整体上显著高于不含W矿化的矿床，指示石榴子石中的W、Sn含量在一定程度上具有预测矽卡岩型矿床成W矿潜力的作用。此外，石榴子石中Fe、Eu、U等元素的含量还可以进一步区分矽卡岩W矿床中的伴生金属元素类型（包括W-Mo、W-Sn、W-Cu-Fe和W-Mo-Cu-Fe等）。本文研究表明，石榴子石的成分特征不仅可以指示矽卡岩的成矿环境，还可用于评估矽卡岩中金属（尤其是W）的成矿潜力，具有一定的理论意义和应用价值。;Xintianling is a large skarn W deposit in the Nanling W-Sn metallogenic belt, and it is located in the contact zone between the northeastern Qitianling pluton and the Carboniferous carbonate rocks. In this study, the typical skarn mineral, garnet, has been analyzed by LA-ICP-MS to quantify the concentrations of major elements, trace elements, as well as rare earth elements (REEs). The results reveal that the garnet from the Xintianling deposit mainly belongs to the andradite-grossular solid solution (And₂₄Gro₆₆ to And₇₁Gro₂₂), which shows a transitional trend dominated by either andradite or grossular. The REEs of the garnet show two distinct patterns, one is characterized by HREE enrichment and LREE depletion with negative Eu anomaly, and the other is featured with LREE enrichment and HREE depletion with positive Eu anomaly. These differences suggest that the garnet crystals grow under variable redox conditions and water/rock ratios in the hydrothermal system, which has also been reflected in the oscillatory zones. A compilation of available data from other skarn deposits combined with the results from this study indicates that W and Sn concentrations of garnet from skarn deposits with economic W mineralization are significantly higher than those without W mineralization, implying that the W and Sn concentrations could probably predict the potential economic metals (especially W) in a skarn system. Furthermore, the results also indicate that the Fe, Eu and U concentrations of garnet can provide useful information for distinguishing the associated metal(s) of a W skarn system, including W-Mo, W-Sn, W-Cu-(Fe) and W-Mo-Cu-(Fe). In conclusion, the current study shows that the compositional characteristics of garnet have certain guiding significance in understanding the ore-formation conditions and evaluating mineralization potentials of metals in a skarn system, especially for these W skarns like Xintianling.

Genesis and tectonic setting of Late Jurassic-Early Cretaceous granites in Nachatang area, Central Lhasa Terrane: Constraints from geochemistry, chronology and Hf isotopes

西藏中拉萨地块东段大规模侏罗纪-白垩纪花岗岩类的成因类型及构造背景尚未得到有效约束，该时期岩浆作用的时空分布、岩石成因以及深部动力学机制等问题亟需新的深入研究。本文对中拉萨地块东段南缘那茶淌地区的花岗岩类进行了系统的岩相学、元素地球化学、年代学和锆石Hf同位素研究。LA-MC-ICPMS锆石U-Pb定年结果显示，那茶淌地区黑云母二长花岗岩成岩年龄为147±1.4Ma，花岗闪长岩年龄为140.6±1.3Ma，系晚侏罗世-早白垩世中酸性岩浆活动的产物。在元素地球化学组成上，黑云母二长花岗岩和花岗闪长岩的主量元素组成具有富SiO₂（分别为71.02%~71.81%和65.17%~66.73%）、Al₂O₃（分别为13.45%~13.57%和14.43%~15.20%）、碱金属（Na₂O+K₂O）（分别为6.79%~7.48%和6.55%~7.37%），贫TiO₂（分别为0.15%~0.21%和0.10%~0.13%）等特征，显示Ⅰ型准铝-弱过铝质（A/CNK=0.98~1.14）的高钾钙碱性系列特征。微量元素以富集K、Rb、Ba、Th等大离子亲石元素，亏损Ta、Nb、P、Ti等高场强元素为特征。花岗闪长岩稀土元素总量（ΣREE=263.9×10^-6~313.8×10^-6）高于黑云母二长花岗岩（ΣREE=116.3×10^-6~168.8×10^-6），均表现为轻稀土元素富集，重稀土元素相对亏损，具弱的负Eu异常。两种岩石锆石Hf同位素均以负的ε_Hf（t）值和古老的地壳模式年龄为特征，黑云母二长花岗岩ε_Hf（t）值为-21.64~-7.66，地壳模式年龄（t_DM^C）为1.68~2.56Ga，花岗闪长岩锆石ε_Hf（t）值为-11.95~-8.15，地壳模式年龄（t_DM^C）为1.71~1.95Ga。结合前人研究资料，认为中拉萨地块东段那茶淌地区晚侏罗世-早白垩世花岗岩类形成的构造背景与班公湖-怒江洋南向俯冲有关，岩浆来源于俯冲作用诱发古老下地壳物质的重熔。;The genetic types and tectonic settings of the large-scale Jurassic-Cretaceous granites in the eastern part of the Central Lhasa Terrane in Tibet have not been well constrained, and the temporal and spatial distribution of their magmatism, petrogenesis and deep dynamic mechanism in this period are in urgent need of further research. In this paper, the lithography, chronology, geochemistry and zircon Hf isotope of the biotite monzogranite and granodiorite from the Nachatang area in the southern margin of the eastern segment of the Central Lhasa Terrane are systematically studied. LA-MC-ICPMS zircon U-Pb dating results show that the biotite monzogranite and granodiorite are 147±1.4Ma and 140.6±1.3Ma, respectively, showing they are the products of magmatism in Late Jurassic-Early Cretaceous. In terms of geochemical compositions, the biotite monzogranite and granodiorite have low TiO₂(0.15%~0.21% and 0.10%~0.13%), high SiO₂ (71.02%~71.81% and 65.17%~66.73%), Al₂O₃ (13.45%~13.57% and 14.43%~15.20%) and alkali (Na₂O+K₂O) (6.79%~7.48% and 6.55%~7.37%) contents, showing the characteristics of Ⅰ-type peraluminum to weak peraluminum calc-alkaline series (A/CNK=0.98~1.14). Trace element compositions of the measured samples are characterized by enrichment of large ion lithophile elements such as K, Rb, Ba and Th, and depletion of high field strength elements such as Ta, Nb, P and Ti. The total amount of REE in the granodiorite (ΣREE=263.9×10^-6~313.8×10^-6) is higher than that in the biotite monzonite (Σ REE=116.3×10^-6~168.8×10^-6), which shows the enrichment of LREE and relative depletion of HREE, with weak negative Eu anomaly. The zircon Hf isotopes are characterized by negative ε_Hf(t) values and ancient crustal model ages. The ε_Hf(t) values of the biotite monzogranite range from -21.64 to -7.66, and the crustal model ages (t_DM^C) range from 1.68Ga to 2.56Ga. Zircon ε_Hf(t) values of the granodiorite vary from -11.95 to -8.15, and the crustal model ages (t_DM^C) from 1.71Ga to 1.95Ga. Finally, we conclude that the tectonic setting of Late Jurassic to Early Cretaceous granites in the Nachatang area is related to the southward subduction of the Bangong-Nujiang Ocean seafloor, and the magma is derived from the remelting of ancient lower crust material induced by subduction.