Melting Of Juvenile Mafic Crust Research Articles

An Overview on the Composition and Age of Upper Crust of Proto‐Tethyan Lajishan Intra‐oceanic Arc, NE Tibet Plateau

AbstractIdentification and anatomy of oceanic arcs within ancient orogenic belt are significant for better understanding the tectonic framework and closure process of paleo‐ocean basin. This article summarizes the geological, geochemical, and geochronological characteristics of upper crust of Proto‐Tethyan Lajishan intra‐oceanic arc and provides new data to constrain the subduction evolution of the South Qilian Ocean. The intra‐oceanic arc volcanic rocks, including intermediate–mafic lava, breccia, tuff, and minor felsic rocks, are distributed along southern part of the Lajishan ophiolite belt. Geochemical and isotopic compositions indicate that the intermediate–mafic lava were originated from depleted mantle contaminated by sediment melts or hydrous fluids, whereas the felsic rocks were likely generated by partial melting of juvenile mafic crust in intra‐oceanic arc setting. Zircons from felsic rocks yield consistent and concordant ages ranging from 506 to 523 Ma, suggesting these volcanic rocks represent the relicts of upper crust of the Cambrian intra‐oceanic arc. Combined with the Cambrian forearc ophiolite and accretionary complex, we suggest that the Cambrian intra‐oceanic arc in the Lajishan ophiolite belt is belonging to the intra‐oceanic arc system which was generated by south‐directed subduction in the South Qilian Ocean at a relatively short interval between approximately 530 and 480 Ma.

Plagioclase as archive of the incremental assembly of the Quxu batholith, South Tibet: Implication for the nature of magma reservoir

The formation of magma reservoir and resultant construction of large batholith are increasingly recognized as long-term incremental processes. Here we employed back-scattered electron and cathodoluminescence images, in-situ major and trace elements, and Sr isotopes of plagioclase for five lithological groups from the Quxu complex batholith (south Tibet), which shed new light on the nature and incremental construction processes of batholith. Our results show that plagioclases display diverse textures and show systematic differences in geochemistry and Sr isotopes for different lithologies, indicating that their host rocks originated from multiple magma sources and/or underwent distinct magmatic processes. Plagioclases in Group I granodiorites and Group III mafic dykes and mafic magmatic enclaves exhibit comparable textural features (e.g., resorption and sieved textures) and share similar Sr (< 1500 ppm) and Ba (< 200 ppm) contents, and 87Sr/86Sr ratios (ISr) (0.7035–0.7050) at given lower An (20–50) values, suggesting that they were evolved from similar mafic magma sources. The significant variations in An (20–90), Sr and Ba contents of plagioclase in Group III indicate both fractional crystallization and magma mixing. Plagioclases in Group II monzogranites have a similar An ranges to Group I but higher Sr (900–2200 ppm) contents and ISr (mostly 0.7045 to 0.7066) values, suggesting that they formed from partial melting of juvenile mafic crust without significant mantle contribution. Plagioclases in Group IV granodiorites and Group V monzogranites exhibit higher Sr (500–3000 ppm) contents than other groups at given An values. Their ISr values fall within the range of Group II, indicating a similar magma source. Abundant plagioclases displaying normal and oscillatory zonings in them implies that fractional crystallization occurred, while the presence of typical glomerocrysts in Group V indicates mush disaggregation. The simulation results of the trace elements indicate that the different lithologies of the Quxu batholith represent different states of magma reservoirs, corresponding to crystal mushes with varying degrees of extracted melts. The incremental growth processes of lager batholith operate as an open system, in which magma convection, mixing and recharge, crystal accumulation, recycling and reaction with melts, and mush disaggregation commonly occur.

Permian-Triassic tectonic evolution of the Ailaoshan orogenic belt in SW China: insights from magmatic records

ABSTRACT The Ailaoshan orogen in SW China records the evolution of the Ailaoshan Paleo-Tethyan ocean and the amalgamation history between the South China and Indochina blocks, an important process for the formation of Southeast Asia. However, its tectonic evolution remains ambiguous with various competing models. We have carried out an integrated geochronological–petrological–geochemical study for the granites, dacites-rhyolites, granodiorites and trachyandesites in this orogen to give new constraints on this issue. The 255–254 Ma granites and the 250–248 Ma dacites-rhyolites show similar geochemical features and are characterized by strongly peraluminous nature, continental crust-like trace element patterns and negative zircon εHf(t) values (−14.4 to −6.6), indicating they derived from partial melting of ancient crust. The 229 Ma hornblende-bearing granodiorites are metaluminous to weakly peraluminous (A/CNK = 0.96–1.01) and belong to high-K calc-alkaline I-type granites. They show depleted whole-rock Sr-Nd and zircon Hf isotope compositions (initial 87Sr/86Sr = 0.7027 to 0.7038, εNd(t) = 4.0 to 4.1, εHf(t) = 9.3 to 11.5), suggestive of derivation from partial melting of juvenile mafic crust. The 226 Ma trachyandesites are characterized by high MgO (4.1–4.6 wt.%), high Mg# (56) and arc-type geochemical affinities with enriched isotope compositions (initial 87Sr/86Sr = 0.7108 to 0.7111, εNd(t) = −7.7 to −7.5, εHf(t) = −6.3 to −3.5). These features indicate that their parental magmas derived from partial melting of enriched lithospheric mantle metasomatized by oceanic sediment-derived melts. These new data, in conjunction with spatial-temporal-temperature variations of igneous rocks, metamorphic records and stratigraphic changes in the region, suggest that the Ailaoshan Paleo-Tethyan ocean closed at the Early Triassic (ca. 250 Ma) which was followed by the Late Triassic postcollisional slab breakoff, and the ocean experienced westward unipolar subduction during its evolution with no assumed eastward subduction.

The Fundamental Role of H2O in the Generation of Coeval Sodic and Potassic Granitoids at Continental Arcs: An Example from the Yangtze Block, South China

AbstractThe bulk rock composition of granitoids reflects the composition of their source and the conditions of partial melting, which are functions of the geodynamic setting in which they formed. Granitoids in active continental margins (continental arcs) are dominated by calc-alkaline rocks with subordinate alkaline compositions, although how these different magma compositions formed is not well understood. Neoproterozoic magmatic rocks are widely distributed along the western margin of the Yangtze Block in South China to form the &amp;gt;1000-km long Panxi continental arc system, which is dominated by granitoids with minor mafic–ultramafic and intermediate plutons. The granitoids are subdivided into sodic and potassic variants that occur as belts along the western and eastern sides of the continental arc, respectively. Sodic granitoids from the western part consist of tonalite, granodiorite, and monzogranite with crystallisation ages ranging from 870 Ma to 740 Ma. They have low K2O/Na2O ratios (0.1–1.0) and high Na2O contents (3.5–6.7 wt%), high but variable SiO2 (61–75 wt%) concentrations, and negative to positive whole-rock εNd(t) values (−1.7 to +2.9). Zircon grains from the sodic granitoids have εHf(t) values ranging from +0.3 to +9.6 and δ18O from 3.90‰ to 7.71‰. The potassic granitoids from the eastern side consist of monzogranite and syenogranite with crystallisation ages from 820 Ma to 790 Ma. They have high K2O/Na2O ratios (0.6–2.2), K2O (2.6–5.9 wt%) and SiO2 contents (69–78 wt%), but whole-rock εNd(t) (−0.9 to +2.9) and zircon εHf(t) (+1.8 to +12.9), and δ18O values (2.98‰ to 6.41‰) similar to those of the sodic granitoids. The isotopic compositions of both the sodic and potassic granitoids are similar to those of spatially- and temporally-related mantle-derived (mafic to ultramafic) rocks, and are considered to have been derived from juvenile mafic continental crust. Phase equilibrium modelling shows that the H2O content of the granitoid source rocks played a key role in their petrogenesis, both in lowering solidus temperatures and in controlling the compositions of the derived partial melts. Our results indicate that calc-alkaline sodic granitoids can be formed by water-fluxed melting of juvenile mafic crust at 750–900°C and 9–12 kbar in which the required H2O was derived from the dewatering of underplating mafic arc magmas. By contrast, the potassic granitoids were generated by fluid-absent (H2O-undersaturated) partial melting of a similar juvenile mafic source at 725–900°C and 6–9 kbar. We conclude that the sodic granitoids were derived from partial melting of the newly-formed mafic lower crust in the continental arc, whereas the potassic granitoids were likely generated in the back-arc setting induced by upwelling of asthenospheric mantle.

Crustal growth and evolution in convergent margin: Evidence from three Paleozoic granitic pulses in the junction zone between Qinling and Qilian orogenic belt

Paleozoic igneous rocks in the junction zone between the western Qinling and Qilian orogenic belts preserve important message about the deep crustal structure and their tectonic relationship. By means of zircon U Pb dating, Lu Hf isotope, bulk-rock geochemistry for a suite of Paleozoic granites from the western Qinling and Qilian orogenic belt, three main granite pulses were identified: 1) First pulse (~500 to 450 Ma) quartz diorite with typical island-arc affinity, i.e., intermediate SiO 2 (56.42 to 61.44 wt%) contents, variable Na 2 O/K 2 O ratios of 0.9 to 1.7, high MgO contents (3.14 to 4.40 wt%) with high Mg# values of 55.6 to 60, moderate Sr/Y (22 to 29) ratios and insignificant Eu*/Eu anomalies (0.77 to 0.84), zircons from the quartz diorite have positive ε Hf (t) values of +2.2 to +5.5; all these features indicate that the quartz diorite was formed by hydrous melting of depleted mantle wedge in subduction setting; 2) Second pulse (ca. 440 to 430 Ma), monzogranite (e.g., the Dangchuan and Caochuanpu monzogranite), they display higher SiO 2 (71.23 to 73.91 wt%) contents, K 2 O/Na 2 O (1.10 to 2.26) ratios, lower MgO (0.34 to 0.43 wt%) contents, significant negative Eu anomalies of 0.36 to 0.48, evolved Sr Nd isotopic compositions, and variable zircon Lu Hf (ε Hf (t) = −5.0 to +10.6) compositions, suggesting dehydration melting of heterogeneous crust; 3) Third pulse (ca. 420 to 410 Ma), biotite granite that display typical A-type affinity, i.e., high FeO T /MgO and Ga/Al (10,000 × Ga/Al = 2.7 to 3.0) ratios, high Zr (230 to 313 ppm), Nb (3.49 to 34.6 ppm) and Zr + Nb + Ce + Yb (351 to 512 ppm) contents, most zircons from these biotite granites have negative ε Hf (t) values of −2.7 to −26.6, in combination with their higher Zr saturation temperatures (822 to 842 °C), suggesting high temperature melting of matured continental crust in extensional setting. These results indicate that the western Qinling and Qilian orogenic belts experience a tectonic switch from subduction to extension in Early-Paleozoic (ca. 460 to 410 Ma). All these granites record the crustal evolution and switch of melting regime in convergent margin. • Three Paleozoic magmatic pulses in the junction zone between North Qinling and Qilian. • Hydrous melting of depleted mantle wedge formed the first pulse. • Dehydration melting of juvenile mafic crust formed the second pulse. • High temperature melting of heterogeneous crust in extensional setting formed the third pulse.

Chronological framework of Precambrian Dantazi Complex: Implications for the formation and evolution of the northern North China Craton

The Dantazi Complex in the North Hebei Terrane is located in the middle segment of the northern North China Craton, and plays a crucial role for understanding the early Precambrian crustal evolution of the craton. The Dantazi Complex is composed mainly of late Neoarchean tonalites-trondhjemites-granodiorites, potassic granites, sanukitoid granodiorites-monzodiorites and quartz syenites, which were emplaced by Paleoproterozoic gabbroic stocks. SHRIMP and LA–ICP–MS zircon dating analyses have revealed that the Neoarchean diversified granitoids of the Dantazi Complex were formed in ∼2.52–2.47 Ga, and preserved ∼2.60–2.53 Ga inherited/captured zircon ages. All these rocks experienced early metamorphism and deformation at ∼2.40 Ga, later granulite facies metamorphism at ∼1.80 Ga, and alterations at ∼1.73 Ga. Whole-rock chemical characteristics and Sm–Nd–Lu–Hf isotopes indicate that (1) The ∼2.52 Ga tonalites-trondhjemites-granodiorites were derived from partial melting of juvenile mafic crust; (2) the ∼2.51 Ga sanukitoid monzodiorite-granodiorite series came from slab-mantle interaction with different melt/rock ratios; (3) The ∼2.50–2.47 Ga potassic granites were generated by intracrustal recycling of metagreywacks that sourced from the mixture between juvenile and ancient crustal materials; and (4) The ∼2.50 Ga quartz syenites were originated from fractional crystallization of mantle-derived magmas. These petrogenetic processes reveal that the subduction-related crust-mantle interaction is the key reason for the diversity of late Neoarchean granitoids in the Dantazi Complex. Regional comparison indicates that the Precambrian North Hebei Terrane show distinct structure in the chronology and lithological assemblages from other basement terranes in the trans-North China Orogen and Western Block, implying that they were formed in different crust-mantle dynamic systems. Therefore, the Precambrian North Hebei Terrane was probably an independent micro-continental block at least until the early Paleoproterozoic. In the Archean crystalline basement range of the North Hebei–West Liaoning–East Hebei, from NW to SE, the magmatic crystallization ages gradually became older, and the granitoid assemblages transformed from sodium-rich to potassium-rich, the spatio-temporal evolution of chemical composition and lithological assemblages further indicates that the North Hebei Terrane was most likely developed in an arc environment with continuous retreat subduction caused by the slab roll-back.

Cambrian intra-oceanic subduction within the southern branch of the Proto-Tethyan Ocean: Constraints from rhyolites in the Lajishan suture, NE Tibetan Plateau

The South Qilian suture in the Qilian Orogen is an early Paleozoic belt that developed as a result of closure of the southern branch of the Proto-Tethyan Ocean. It is characterized by widespread Cambrian intermediate-basic volcanic rocks which record the early-stage evolution of the paleo-ocean basin. However, Cambrian evolution of the paleo-ocean basin remains controversial due to the lack of research on the age and tectonic affinity of these volcanic rocks. In this study, we identified rhyolites from the intermediate-basic volcanic rocks in the South Qilian suture. They occur as pebbles in the breccias, or as veins and interlayers within the intermediate-basic volcanic rocks. Zircon U-Pb datings yield ages of 514.0 ± 2.8 Ma, 521 ± 4 Ma, 523 ± 5 Ma, and 513 ± 9 Ma for four rhyolites, respectively. The Cambrian rhyolites show variable La/Sm ratios and Rb contents and positive zircon εHf(t) values (+6.8 to +14.6) and whole-rock εNd(t) values (+2.1 to +4.6), suggesting that they were derived from partial melting of juvenile mafic crust. They also have high Al2O3 and CaO contents, as well as low K2O and trace element concentrations, which are similar to those of oceanic arc rhyolite. These early Cambrian oceanic arc rhyolites, along with the SSZ-type ophiolite (ca. 530–520 Ma) to the north and late-stage granitoid intrusions (ca. 474–450 Ma), indicate that the southern branch of the Proto-Tethyan Ocean experienced southward intra-oceanic subduction during the early Cambrian-early Ordovician period.

Relicts of a Cambrian oceanic arc in the Lajishan suture, NE Tibetan Plateau: Evidence for early-stage subduction within the Proto-Tethyan Ocean

Lajishan suture in the Qilian Orogen records subduction process of the southern branch of the Proto-Tethyan Ocean. However, when and where the subduction started remain controversial issues. We present a study of the Cambrian volcanic rocks from the Lajishan suture. These volcanic rocks are coherent and composed of basalt, andesite, and volcanic breccia with minor interlayers or veins of dacite and rhyolite. Zircons from the dacite and rhyolite yield concordant Early-Middle Cambrian ages ranging from 521 to 510 Ma. Basalt and andesite exhibit subduction-related geochemical signatures with enrichment in large ion lithophile elements and depletion in high field strength elements. They have evolved REE, LREE, ε Nd (t) (+2.6 to +8.2), and (La/Sm) N ratios, suggesting derivation from depleted mantle wedge with addition of hydrous fluid or various amounts of sediment-derived melts. Dacite and rhyolite have positive zircon ε Hf (t) values (+6.1 to +11.6) and whole-rock ε Nd (t) values (+1.7 to +4.2). They were generated by partial melting of juvenile mafic crust resulting from magma underplating. These Cambrian volcanic rocks in the Lajishan suture are exposed to the south of the accretionary complex and therefore are likely to be relicts of Cambrian oceanic arc built on the oceanic crust during southward subduction of the South Qilian Ocean. Considering the Cambrian-Ordovician intra-oceanic trench-arc-basin system reconstructed in the North Qilian suture, it is suggested that both southern and northern branches of the Proto-Tethyan Ocean have experienced intra-oceanic subduction process which initiated at ca. 530 Ma. • Cambrian volcanic rocks are coherent and widely exposed in the Lajishan suture. • They represent the relicts of an oceanic arc within the South Qilian Ocean. • Early-stage subduction of the Proto-Tethyan Ocean initiated at ca. 530 Ma.

Paleo-Mesoarchean crustal growth and reworking in the western Dharwar Craton, southwestern India: Evidence from trondhjemitic gneiss and granitic gneiss

Paleo-Mesoarchean felsic orthogneisses are widely exposed in the southern part of the western Dharwar Craton (WDC), southern India shield. The felsic orthogneisses studied in this paper from the WDC can be divided into two groups based on their geological, geochronological, and geochemical data: the 3.4–3.3 Ga trondhjemitic gneiss (including trondhjemitic veins) and the ∼3.1–3.0 Ga granitic gneiss. The 3.4–3.3 Ga trondhjemitic gneiss is characterized by high contents of SiO2 (70.4–73.1 wt%), Na2O (5.49–5.91 wt%) and Sr (647–740 ppm), high ratios of Na2O/K2O (4.7–7.7) and Sr/Y (53–106), but relatively lower Mg# values (32–39), and Cr (9.5–28.7 ppm) and Ni (1.34–5.33 ppm) concentrations, as well as insignificant Eu anomalies, fractionated REE patterns and mostly positive zircon εHf(t) values (+0.8-+5.9). These data indicate that the trondhjemitic gneiss was derived from partial melting of juvenile mafic crust in a relatively moderate-shallow depth, with residual mineral assemblage of garnet, amphibole and clinopyroxene, implying crustal growth event at 3.4–3.3 Ga. By contrast, the ∼3.1–3.0 Ga granitic gneiss is characterized by relatively lower contents of Na2O (3.82–4.63 wt%) and Sr (96.9–291 ppm), low ratios of Na2O/K2O (1.4–1.7) and Sr/Y (3.02–8.65), as well as significantly negative Eu anomalies and negative to positive zircon εHf(t) values (-5.6-+4.5). Therefore, the granitic gneiss was probably derived from partial melting of pre-existing crustal rocks, suggesting a prominent crustal reworking event at ∼3.1–3.0 Ga. This study emphasizes that the western Dharwar Craton is dominated by Paleoarchean (3.4–3.2 Ga) crustal growth event and a strong crustal reworking event in early Mesoarchean (∼3.1–3.0 Ga), though the Mesoarchean crustal growth event is discernible, evidenced by regional ∼3.0 Ga TTG rocks. The early Mesoarchean (∼3.1–3.0 Ga) crustal reworking event, represented by series of potassium-rich granites, is also reported in other Archean cratons, and thus it may have global significances.

The Aksug Porphyry Cu–Mo Ore-Magmatic System (Northeastern Tuva): Sources and Formation of Ore-Bearing Magma

Abstract ––Two stages are recognized in the evolution of the Aksug ore-magmatic system (OMS): (1) formation of the Aksug granitoid pluton and (2) emplacement of small ore-bearing intrusions. Intrusive bodies of the two stages are composed of rocks of the same type and bear copper mineralization: poor dispersed and large-scale veinlet-disseminated, respectively. The pluton and small intrusions are formed by gabbroid and granitoid rocks, with similar petrogeochemical characteristics of igneous rocks of the same type. The plutonic gabbroic association includes gabbro, gabbrodiorites, and pyroxene–amphibole diorites/quartz diorites. The small subvolcanic gabbroic intrusions are gabbrodiorite and diorite porphyrites. The trace element patterns of the gabbroids are similar to those of igneous rocks in subduction zones. The gabbroids are characterized by isotope parameters εNd(500) = +6.1 to +7.2 and (87Sr/86Sr)500 = 0.7022–0.7030 and model age TNd(DM) = 0.85–0.74 Ga. As follows from the geochemical parameters, the depleted mantle metasomatized by subduction fluids was the source of basaltic magma. The plutonic granitoid association includes tonalites, plagiogranites, and amphibole diorites/quartz diorites; the small subvolcanic granitoid intrusions are tonalite porphyry and quartz diorite porphyrites. The trace element patterns and Nd and Sr isotope compositions of the granitoids are much similar to those of the gabbroids. According to the geochemical parameters, tonalitic and plagiogranitic magmas formed through the melting of juvenile mafic crust, and dioritic magma resulted from the mixing of basaltic and tonalitic/plagiogranitic magmas. In the course of the OMS formation, metals and volatiles were introduced by basaltic and granitoid magmas from the metasomatized mantle and juvenile mafic crust. The compression setting during the pluton formation hampered the separation of ore-bearing fluids, which led to poor dispersed mineralization. The extension setting during the emplacement of small intrusions favored the intense separation of ore-bearing fluids. The interaction of magma and fluids of the small intrusions with rocks of the pluton was accompanied by the removal of metals from the latter and their involvement in the ore-forming process. This increased the ore potential of the magmatic system and favored the formation of rich mineralization at the final stage of its evolution.

Petrogenesis of Archean TTGs and potassic granites in the southern Yangtze Block: Constraints on the early formation of the Yangtze Block

The southern Yangtze is underlain by Mesoarchean igneous rocks that were emplaced in two pulses, including trondhjemites at ca. 3092–3071 Ma followed by potassic granites at 2920 Ma. These represent the oldest TTG suites identified in the southern Yangtze and the oldest potassic granites in the entire Yangtze Block. Hf isotopic analysis reveals εHf(t) values of −2.49–7.49 and Hf crustal model ages (TDMC) of 3601–3000 Ma for zircons from the trondhjemites, whereas those from the potassic granites show εHf(t) values of −1.79–4.18 and TDMC ages of 3453–3043 Ma. The trondhjemites have high SiO2, Mg# and low Al2O3 and K2O/Na2O, and are highly evolved with low Ni, Cr and Co. The trondhjemites are characterized by low Sr/Y, Eu/Gd and (La/Yb)N, and high Y and HREE, typical of high-HREE and low-pressure TTGs. Their geochemical and isotopic compositions indicate that they are derived from melting of juvenile mafic crust with little contribution from older crustal materials, consistent with a plagioclase-bearing basaltic source. The multielement patterns of potassic granites are similar to that of the trondhjemites, albeit with lower HREE and Y contents. Their high K2O values, strongly fractionated REE patterns and low Y contents indicate the presence of garnet and/or amphibole as residual phases in the source region, which indicates they formed at higher pressure than the trondhjemites. The isotopic and geochemical data imply that the formation of the potassic granites could be related to reworking of older TTGs. The increasing K2O/Na2O of the 3092–3071 Ma trondhjemites to potassic 2920 Ma granites corresponds with stabilization, maturation and thickening of the Archean continental crust in the southern Yangtze. The geochemical data of the TTGs in the Kunming region show important differences from that of contemporaneous TTGs from the Kongling Complex, suggesting that southern Yangtze is composed by an independent old nucleus, which is exotic to the northern Yangtze. A synthesis of petrogenesis, geochronology, geochemistry and isotope data of Archean granites of the Yangtze Block provides important insights into the architecture of its Archean crust. We propose that the Yangtze Block can be subdivided into discrete northwestern, northeastern and southern domains, but which are all affected by late Paleoproterozoic tectonothermal events, suggesting that they had been assembled together by then to form the united Yangtze Block.

Petrogenesis and tectonic setting of the Chaheilingashun pluton, North Alxa Block, NW China: constraints from whole-rock geochemistry, zircon U–Pb ages, and Hf isotope compositions

To better constrain the petrogenesis and tectonic setting of the Chaheilingashun pluton in the southern Ya-Gan Fault, North Alxa Block, NW China, this study presents new zircon U–Pb ages, whole-rock geochemistry, and Hf isotopes of diorites from the Chaheilingashun pluton. The Chaheilingashun pluton is composed of medium- to coarse-grained monzonitic diorite, with moderate to high SiO2 contents (58.22–62.77 wt.%), moderate total alkali contents (Na2O + K2O, 5.72–7.66 wt.%), and high Al2O3 contents (14.26–17.69 wt.%), which indicate that the diorite exhibits calc-alkaline to alkaline and metaluminous to peraluminous series. The correlations of SiO2 with oxides and the right-dipping oblique trends of rare earth elements (REEs) demonstrate that the magma experienced fractional crystallization. In particularly, the correlations of Rb with Ba and Sr, and the weak negative Eu anomalies indicate that the plagioclase has undergone fractional crystallization. In addition, this paper has shown that both fractional crystallization and partial melting also contributed to the magmatic process through the Eu anomalies and La/Sm-La diagram. The positive eHf(t) values (2.2–4.6) and low Mg#, Cr, and Ni indicate that diorite was generated from the partial melting of juvenile mafic crust. Together with previous results, the diorites are inferred to have formed in an post-collisional extensional environment. The zircon U–Pb age of diorite from the Chaheilingashun pluton is dated at 289.3 Ma, suggesting that the final closure time of the Paleo-Asian Ocean was might before 289.3 ± 2.3 Ma.