Dioritic Enclaves Research Articles

Diorite enclaves and host granite of the early Miocene Gorontalo pluton in the North Sulawesi Arc, Indonesia: Implications for recycled oceanic crust and crust-mantle interaction

• Granites from the Early Miocene Gorontalo pluton were derived from a juvenile crust. • Diorite enclaves originated from mixing of depleted mantle- and juvenile crust-derived magmas . • Sub-normal mantle δ 18 O values suggest the involvement of recycled altered oceanic crust . • Early Miocene crust-mantle interaction occurred in the North Sulawesi Arc. Zircon Hf-O isotopes, combined with whole-rock Sr-Nd-Pb isotopes, can provide unambiguous evidence for crustal recycling and crust-mantle interaction processes. The North Sulawesi Arc (Indonesian) was traditionally regarded as an intra-oceanic arc, and the diorite enclaves and host granites of the Gorontalo pluton provide excellent opportunities for evaluating these issues, based on our zircon U-Pb geochronological and Hf-O isotopic, and whole-rock geochemical analyses. This study firstly reports the zircon U-Pb ages of ∼20.1–22.4 Ma for the host granites and ∼19.5–20.4 Ma for the diorite enclaves. The host granites have high SiO 2 , and low 10000*Ga/Al, A/CNK and Rb/Sr, classified as unfractionated I-type granites. They are characterized by high εNd (t) (from +4.8 to +5.7), high zircon εHf (t) (from +11.1 to +16.4), sub-normal mantle zircon δ 18 O (4.6–5.4‰), moderate ( 206 Pb/ 204 Pb) i (18.29–18.45), and young two-stage Hf model ages (52–394 Ma), deriving from partial melting of a juvenile mafic crust. The diorite enclaves show typical magmatic textures and contain abundant acicular apatite and plagioclase megacrysts with an obvious rim-core texture. They also have high εNd (t) (from +4.8 to +5.1), high zircon εHf (t) (from +10.7 to +15.2), sub-normal mantle zircon δ 18 O (4.1–5.1‰) and moderate ( 206 Pb/ 204 Pb) i (18.3), interpreted as the products of mixing of magmas derived from a depleted mantle and a juvenile crust. The diorite enclaves have sub-normal mantle δ 18 O values, positive εNd (t) and zircon εHf (t) , suggesting recycled altered oceanic crust into depleted mantle prior to magma generation. The presence of the host granites and diorite enclaves provides robust evidence for early Miocene (or prior to early Miocene) crust-mantle interaction in the North Sulawesi Arc.

Petrogenesis and Geodynamic Implications of Late Triassic Mogetong Adakitic Pluton in East Kunlun Orogen, Northern Tibet: Constraints from Zircon U–Pb–Hf Isotopes and Whole-Rock Geochemistry

Adakites or adakitic rocks usually show special geochemical signatures and are petrological probes to reveal the tectono–magmatic evolutionary history of paleo–orogenic belts. Here, we present a comprehensive study on the zircon U–Pb geochronology, whole-rock geochemistry, and zircon Lu-Hf isotopes of Mogetong adakitic pluton in East Kunlun orogen, Northern Tibetan Plateau, to constrain its petrogenesis and tectonic setting, and thus to reveal its implications for the Paleo–Tethyan orogeny. The studied pluton comprises of quartz monzonite porphyry with zircon U–Pb crystallization age of ca. 215 Ma, which is coeval to their diorite enclaves (ca. 212 Ma). The quartz monzonite porphyries have intermediate SiO2 (63.31–65.74 wt%), relatively high Al2O3 (15.52–16.02 wt%), K2O (2.83–3.34 wt%), and Sr (462–729 ppm), but low Y (9.14–15.7 ppm) and Yb (0.73–1.39 ppm) with high Mg# (47–55), Sr/Y (30–57) and La/Yb ratios resembling typical high–K calc-alkaline and high Mg# adakitic rocks. Zircon Lu–Hf isotopes show that the studied samples have weakly juvenile zircon Lu-Hf isotopes (εHf(t) = 1.80–4.03) with older model age (1.00–1.14 Ga). The relative low content of Cr (14–59 ppm) and Ni (8–30 ppm), as well as the petrological, geochemical, and Lu-Hf isotopic data, indicates that the Mogetong adakitic rocks were generated by partial melting of thickened lower crust with a certain contribution of the underplated mantle-derived magma in slab break-off setting. This study shows that the Late Triassic adakitic magmatism in East Kunlun orogen may be the response of tectonic transition from oceanic subduction to post–subduction extension, and the reworking of ancient continental crust with subsequent variable crust-mantle magma mixing is the major mechanism of continental crust evolution in the Paleo–Tethyan orogenic belt.

Cerium and Ytrium in apatite as records of magmatic processes: Insight into fractional crystallization, magma mingling and fluid saturation

Apatite is a versatile mineral crystallizing at different stages of silicic magma evolution. Its composition may record that of magma, but could also be affected by interaction with fluids. The focus of this study is the well-recognized magma mingling process that was previously detected using plagioclase composition and in this study complementary record is sought in apatite. The apatite was analysed in two dioritic enclaves (primitive and hybrid) and host quartz monzonite, which is an igneous rock emplaced at ca. 340 Ma in mylonitized Góry Sowie gneisses (NE Bohemian Massif). The apatite was analysed in-situ by microprobe that allowed for chemical characterization of different apatite populations in quartz monzonite and analyses of thin acicular apatite in the enclaves. Apatite population in the quartz monzonite was chemically distinct from that in both enclave types and characterized by higher Y and lower Ce contents, such values are usually typical for peraluminous magmas. As such, the apatite transfer from felsic to mafic magma should be well recorded in apatite composition, which was not the case. Monzonite apatite composition was not commonly observed in the hybrid enclave despite massive plagioclase transfer and only rare resorbed cores with low Ce and Y contents were present. However, such low Ce and Y cores crystalized at the latest stage of apatite crystallization in the quartz monzonite, whereas the plagioclase transfer was an early episode. Therefore, we conclude that apatite transfer was limited during mingling and the apatite composition in the quartz monzonite is best explained by an early Cl-Ce-rich fluid removal and then fractional crystallization, while apatite in the primitive enclave is affected only by fractional crystallization. Altogether, Ce and Y composition of apatite is a valuable tool to record diverse magmatic processes such as fluid removal and precipitation from fluid in addition to fractionation of different REE phases and should be further explored.

Late Devonian transition from advancing to retreating subduction in the SW Central Asian Orogenic Belt: Insights from multiple deformation and magmatic events in the southern Yili Block, NW China

In order to better constrain the Late Paleozoic tectonic evolution of the SW Central Asian Orogenic Belt, we conducted field structural investigations, zircon U-Pb dating, whole-rock geochemical and Sr-Nd isotopic studies on the meta-sedimentary rocks and intruding granites and mafic dykes in the Dahalajunshan area, southern Yili Block of NW China. Our results allow us to recognize five tectonic/magmatic events. Field-scale and microscopic structures of the low-grade meta-sedimentary rocks showed a regional top-to-the-SE thrusting (Event 1). Undeformed granites that contain dioritic enclaves (Event 2) crosscut the regional foliations and thus post-date Event 1 after ca. 379–369 Ma. Mafic dykes intruded all these rocks after ∼328 Ma (Event 4–1), posterior to brittle-ductile thrusting (N-S contraction) (Event 3) and prior to normal faulting (N-S extension) (Event 4–2). All the magmatic rocks formed in a subduction-related setting. The granites and dioritic enclaves derived from a mixing of crustal- and mantle-derived sources variously modified by slab-derived hydrous melts. The primary magma of the diabase dykes derived from a mantle source modified by the slab fluids with 5% crustal contamination. Variation from regional compression (ductile and brittle-ductile thrusting) to extension (normal faulting) and increasing mantle input in arc-related magmatism reveals a transition from Early Paleozoic advancing subduction (events 1 to 3) to Late Paleozoic retreating subduction (events 4–1 and 4–2) of the Junggar oceanic plate beneath the Yili Block.

Linking ocean subduction with early Paleozoic intracontinental orogeny in South China: Insights from the Xiaying complex in eastern Guangxi Province

The tectonic setting of the early Paleozoic orogeny in the South China Block (SCB) has been hotly controversial. Although most studies have ascribed it to an intracontinental orogeny, there are various views on the geodynamic drivers of the intracontinental orogeny. This study reports on the Ordovician Xiaying igneous complex in the eastern part of Guangxi province, southern South China. This complex is composed of granodiorite, monzogranite and micro-granular diorite enclosed by granodiorite. The zircon U–Pb dating suggests that these three types of rocks emplaced synchronously at around 464–442 Ma, significantly older than those S- and I-type granites (450–400 Ma) distributed in the interior of the SCB. One monzogranite collected in the border of the complex has an older age (480 Ma). The Xiaying hornblende–bearing granodiorites have low SiO2 (61.8–68.7 wt%), P2O5 (0.07–0.10 wt%), Rb/Sr (0.52–1.30) and Rb/Ba (0.13–0.34) and high Fe2O3t (3.84–5.57 wt%), MgO (1.48–2.35 wt%), CaO (2.28–4.54 wt%) and Na2O/K2O (0.90–1.91), with metaluminous to weakly peraluminous features (most A/CNK = 0.87–1.07), showing typical I-type granitoid characteristics. The Nd–Hf isotopic model ages (ca 1.6–1.8 Ga) indicate that the Xiaying granodiorites were probably formed by partial melting of a late Paleoproterozoic basement in the deep crust. The micro–granular dioritic enclaves (MMEs) have similar formation ages and Nd–Hf isotopic compositions to the host granodiorites, and show geochemical evolution relation with granodiorites, suggesting that they resulted from the mixing of mafic and granodioritic magmas, which derived from a depleted mantle and a Paleoproterozoic crust, respectively. Based on their similar formation ages and zircon Hf-isotope compositions and the assimilation and fractional crystallization (AFC) modelling, it is suggested that major monzogranites were generated from the granodioritic magma through the AFC process. The rock associations and arc-related geochemical characteristics of the granodiorites and dioritic MMEs suggest that they probably formed in a subduction-related tectonic setting. Combined with the spatial distribution of the rock types and formation ages of these early Ordovician to early Devonian magmatic rocks in the SCB from southeast to northwest, it is inferred that there was an Ordovician northwestward subduction of the proto–South China Ocean occurring to the south of the SCB, which may connect with the Tam Ky–Phuoc Son Suture Zone in the eastern Indochina Block. It was the subduction of the proto–South China Ocean and subsequent collision between the southern SCB and an unknown continent that triggered early Ordovician to early Devonian intracontinental orogeny in the interior of the SCB.

Genetic relations between enclaves and their host granitoids from Doumer Island, northern Antarctic Peninsula: Evidence from mineral chemistry, Sr–Nd and Li isotopes

Dark enclaves in the late Paleocene granitoids of Doumer Island, northern Antarctic Peninsula, were examined by field investigations, zircon U–Pb geochronology, mineral chemistry, whole-rock major- and trace-elements, and Sr-Nd-Li isotopes to elucidate their origins and genetic relationships with host granitoids. The enclaves and host granitoids have similar zircon U–Pb ages of 54.6–55.7 Ma and indistinguishable Nd–Sr isotopes of εNd(t) = 4.7–6.1, ISr = 0.7036–0.7039, indicating a cogenetic relationship. A pyroxene-dioritic enclave (WA16–06-3) is a cognate restite with peritectic phases that resulted from amphibole-dehydration melting at temperatures above 800 °C and at low-P (7–10 kbar). Two other enclaves (WA16–07-2 and WA15–27-3) are fragments of the chilled margins of the conduits entrained in the later insurgent felsic magma. The flat, right-leaning REE patterns are accompanied by positive Eu anomalies (Eu/Eu* = 1.07–1.16) in the dark enclaves and negative Eu anomalies (Eu/Eu* = 0.72–0.88) in the host intrusions. The accumulation of restitic plagioclase and peritectic pyroxene could have induced the positive Eu anomalies in the dark enclaves. The P–T conditions estimated from cummingtonite rims on pyroxene in the pyroxene-dioritic enclave suggest near-isothermal decompression in an environment of fast exhumation. Enclave WA16–07-2 is part of an intense swarm of enclaves near the pluton margin, and crystallized from a less evolved melt that was mechanically eroded by the host magma, indicating a transient state of magma flow. The dioritic enclaves were transported in the form of ductile crystal–melt mushes that were rotated in the insurgent viscous granitoid magma. The enclaves become rounder and sparser towards the interior of the host pluton. Dehydration melting of metabasalt could have produced these melts that are rich in δ7Li while leaving a lighter δ7Li pyroxene-rich residue at the source. The underlying cause of these events was the retreat of the subducting proto-Pacific (Phoenix) oceanic slab beneath the western Antarctic Peninsula that triggered melting of asthenospheric mantle, with basaltic magma underplating and melting a juvenile metabasaltic lower crust.

Late Ediacaran post-collisional magmatism in the Guéra Massif, South-Central Chad

ABSTRACT The Guéra Massif of South-Central Chad is composed of collisional and post-collisional intrusive rocks related to the Central African Orogenic Belt. Collisional granites were emplaced at 595–590 Ma but there are a series of post-collisional intrusions that were emplaced at 570–560 Ma. The older granites have zircon U-Pb weighted-mean ages of 569 ± 6 Ma, 568 ± 7 Ma, and 568 ± 6 Ma, whereas the younger granites are 556 ± 7 Ma and 561 ± 6 Ma but all ages are within their maximum uncertainty. Both groups of post-collisional granites are peraluminous, ferroan, and alkali calcic to calc-alkalic but dioritic microgranular enclaves were observed within the older granites. The chemical variability of each group can be explained by fractional crystallization and it is likely that their parental magmas were derived by partial melting of the lower crust. The Nd isotopes of the older rocks (εNd(t) = −9.5 to −1.2) are slightly less enriched than the younger rocks (εNd(t) = −13.1 and −9.1). Moreover, the Nd isotopic compositions appear to indicate the existence of two isotopically distinct regions of the Guéra Massif with one centred on the Mongo (west) region and the other near the El Hidjer to Zan (east) region. The older group was emplaced during a period of crustal thinning after oblique collision and shearing related to the final suturing of the Congo-Saõ Francisco Craton and the Saharan Metacraton. The younger group was likely emplaced after a period of regional WNW-ESE directed crustal shortening. The punctuated nature of deformation/crustal relaxation cycles in the southern Saharan Metacraton suggests that there may have been many small terranes rather than larger cratonic blocks involved in the lithotectonic evolution of the Central African Orogenic Belt north of the Congo-Saõ Francisco Craton.

Triassic magmatism and tectonic setting of the eastern Tianshan, NW China: Constraints from the Weiya intrusive complex

The Weiya intrusive complex, located in the eastern part of the middle Tianshan terrane can provide crucial constraints on the tectonic evolution of the eastern Tianshan during the Triassic period. Here, we perform detailed zircon U–Pb chronological and Hf–O isotopic as well as whole-rock geochemical and Sr–Nd isotopic analyses on the hornblende gabbro, syenogranite, and granodiorite of the Weiya intrusive complex. The hornblende gabbro with a zircon U–Pb age of 241.6 ± 1.0 Ma is an alkaline gabbro and characterized by enrichments in large iron lithophile elements with depletions of Nb and Ta. It has uniform initial 87Sr/86Sr ratios (0.707173–0.707211) and positive εNd(t) values (+0.58 to +0.61) with zircon δ18O and εHf(t) values ranging from 6.0‰ to 7.6‰ and from +6.1 to +10.5, respectively. Geochemical modelling indicates that the mantle source of the hornblende gabbro was metasomatized by ~10% oceanic sediments associated with previous subduction events. The syenogranite (238.1 ± 2.0 Ma), emplaced nearly simultaneously with the hornblende gabbro, is an A-type granite with slightly metaluminous to peraluminous characteristics (A/CNK = 0.99–1.02), and it has high initial 87Sr/86Sr ratios (0.711740–0.713603) and negative εNd(t) values (−0.94 to −0.76). By contrast, the granodiorite (230.8 ± 0.9 Ma), which contains minor late Carboniferous dioritic enclaves (314.4 ± 3.3 Ma) belongs to the high-K calc-alkaline I-type granite with metaluminous characteristics (A/CNK = 0.95–0.98), and it has relatively low initial 87Sr/86Sr ratios (0.706731–0.707081) and negative εNd(t) values (−1.11 to −1.33). The δ18O and εHf(t) values of zircons from the syenogranite vary from 6.1‰ to 7.5‰ and from +2.8 to +5.3, respectively, while those of zircons from the granodiorite vary from 7.6‰ to 9.0‰ and from −8.1 to −3.4, respectively. These geochemical and isotopic data imply that the syenogranite formed by partial melting of Neoproterozoic calc-alkaline granitoids at high temperatures, whereas the granodiorite was derived from partial melts of (meta)-igneous rocks with additions of supracrustal sedimentary materials. Taking account into all available geological data, we suggest that the eastern Tianshan was in an intra-continental setting during the Triassic period, and the Weiya intrusive complex was generated related to lithospheric extension and thinning.

Compositional Variation of Amphiboles During Magma Mixing: A Case Study of Huangyangshan A-Type Granite in Kalamaili Metallogenic Belt, East Junggar, China

The Huangyangshan A-type granitic pluton, distributed along the thrust fault in the Kalamaili region of East Junggar, Xinjiang, China, consists of alkaline granite containing abundant dioritic enclaves that formed via magma mixing. Both the host granite and the enclaves contain sodic amphiboles. The textural evidence indicates that amphiboles crystallized as a magmatic phase in both units. We determined major and trace element contents of amphiboles from both units to investigate the compositional variation of the amphiboles during the magma mixing process. The results show that cations of W- and C-site are influenced by chemical compositions of the magma whereas cations of A-, B- and T-site and Al3+ are controlled by crystal structure. Therefore, the variations of W- and C-site cations can reflect magma evolution. The core and rim of the amphiboles show similar trace element patterns, which also suggests that the amphiboles are late-stage phases. Furthermore, the amphibole-only thermometers yield reasonable estimates that are consistent with petrographic evidence. However, thermometers based on partition coefficients and all the currently available amphibole-based barometers that rely on Al contents or DAl cannot be applied to Fe-rich and Al-poor amphiboles.

Origin of Carboniferous intra-oceanic arc granitoids from the eastern Pamir and implications for the Paleo-Tethyan ocean

The expanding and diminishing of the Paleo-Tethyan ocean recorded in the Pamir, and relationships between different segments of the Paleo-Tethyan suture from Pamir to Tibet are poorly constrained. Here we present new zircon U–Pb ages and geochemical data of the Waqia granitoid pluton from the eastern Pamir. Both the host granitoids and gabbroic to dioritic enclaves have similar zircon U–Pb ages of 323–318 Ma, being contemporaneous in origin. These rocks are metaluminous, calc-alkaline, tholeiitic series. They exhibit low K2O, low Sr/Y ratios, low REE contents with depleted to flat LREE patterns, slight enrichment in Rb, Ba, Zr, Hf, and negative Nb, Ta, P, and Ti anomalies. They have similar initial 87Sr/86Sr ratios of 0.7040 to 0.7045, positive εNd(t) (+4.63 to +5.02) and εHf(t) (+9.9 to +14.7) values. Detailed elemental and isotopic data indicate that these coeval rocks in the Waqia pluton were cognate and formed by hydrous partial melting of a juvenile mafic crust within an intra-oceanic arc setting. This study is the first to report reliable isotopic ages of the early Paleo-Tethyan subduction in the eastern Pamir. Further, the Tanymas-Mazha Paleo-Tethyan suture in the eastern Pamir should be the western extension of the Jinshanjiang Paleo-Tethyan suture in the central to eastern Tibetan plateau. An integration of published results leads us to conclude that closure of the Jinshanjiang Paleo-Tethyan ocean was diachronous along its 3000–4000 km length, with closure times of ca 240 Ma in the Pamir and ca 220 Ma in the Sanjiang region.

The Ediacaran Rio Doce magmatic arc in the Araçuaí – Ribeira boundary sector, southeast Brazil: Lithochemistry and isotopic (Sm–Nd and Sr) signatures

The Rio Doce magmatic arc, developed from ca. 630 to ca. 580 Ma on an active continental margin, linking the Araçuaí and Ribeira orogens in southeastern Brazil. The arc plutonic portion comprises the G1 supersuite, a calc-alkaline, magnesian, I-type pre-collisional rock-assemblage, mostly composed of tonalite to granodiorite, frequently containing dioritic to mafic enclaves, and their metamorphosed equivalents. We carried out field, petrographic, lithochemical and isotopic (Sm–Nd and Sr) studies on a segment of the Rio Doce arc located in the transition region between the Araçuaí and Ribeira orogens. The studied samples include metamorphozed granitic rocks (referred to by their igneous names in the QAP diagram), consisting of syenogranite, monzogranite, granodiorite, tonalite, quartz diorite, orthopyroxene-bearing tonalite and orthopyroxene-bearing quartz diorite. This rock assemblage defines an I-type, magnesian, metaluminous to slightly peraluminous, medium-to high-K, expanded calc-alkaline series. The numerous mafic to dioritic enclaves and related features indicate magma mixing processes. Isotopic data show moderately to strongly negative εNd(t) values (−2.9 to −13.6) and intermediate to high 86Sr/87Sr ratios (0.7067–0.7165) suggests assimilation of older crustal material (i.e., the Juiz de Fora and Pocrane complexes, enclosing paragneisses), which is also indicated by Nd TDM model ages from 1.19 Ga to 2.13 Ga. Magmatic orthopyroxene and high content of CaO in garnet suggest magma crystallization in the deep crust. Together, our data point out to a combination of partial melting of mantle wedge in the subduction zone, deep crustal anatexis, host rock assimilation, and crystal fractionation for magma genesis in the southeastern Rio Doce arc.

Recycling of K-feldspar antecrysts in the Baishiya porphyritic granodiorite, East Kunlun orogenic belt, northern Tibet Plateau: Implications for magma differentiation in a crystal mush reservoir

It is popular in geochemical models to assume that chemical differentiation occurs by crystal fractionation from high-melt-fraction magma reservoirs. However, a “crystal mush” reservoir characterized by low-melt-fraction has been gradually accepted in the past decade. Magma differentiation in this scenario remains poorly understand. Located in the East Kunlun orogenic belt, northern Tibet Plateau, the Baishiya granodiorite is an ideal example to investigate magma reservoir processes. Although major elements of the Baishiya granodiorite are relatively homogeneous, there is a distinct variation of magmatic texture, trace elements concentrations, and isotopic ratios from top to bottom. The textural and geochemical signatures above cannot be explained by assimilation-fractionation crystallization, magma mixing or convective self-mixing alone. Within the concept model of crystal mush, we propose a multistage formation process of the studied granodiorite. First, a rhyolitic mushy reservoir once existed. It was replenished by episodic basaltic melts from below, resulting in the textural coarsening of K-feldspar. When the heat and/or melts injection was high enough, the crystal mush could be gradually rejuvenated and subsequently stirred. Some K-feldspar antecrysts would be partly recycled to form mantled plagioclase through convective self-mixing. Thus, the evolved and buoyancy melts exhibited an equilibrated geochemical signature with plagioclase, and ultimately formed the porphyry phase on the top. Moreover, recycling of K-feldspar antecrysts contributed to a depletion of heavy rare earth elements and Y contents, as well as an elevation of Cr concentrations and Eu/Eu* ratios in the residual crystal mush, and finally formed the porphyritic granodiorite. Due to a continuous injection and convective self-mixing, the overall magma reservoir became more mafic gradually until it reached a granodioritic composition. Within a waning intensity of magma flux, the magma reservoir would be locked again. The injected melts would go through a rapid crystallization, and subsequently form microlites, such as the dioritic enclaves and the ground mass of the studied granodiorite. Consequently, traditional mechanisms that are based on low-crystallinity magmas may be a specific part of the protracted history rather than the whole story of the magma reservoir. Geochemical index of granitoid rocks should be used with caution due to this inherited affinity. It should be prerequisite to investigate crystal genesis carefully before utilizing geochemical diagrams.

Early Cretaceous granitoids in the Southern Pamir: Implications for the Meso-Tethys evolution of the Pamir Plateau

Although it is generally accepted that the Pamir was formed by long-term terrane drifting and accretion to the south margin of the Asia, the tectonic evolution during the Mesozoic remains unclear. The voluminous Cretaceous intrusions in the Southern Pamir-Karakorum provide key information for understanding the Mesozoic evolution in this region. In this contribution, we report detailed petrography, ages, mineral geochemistry, whole-rock elemental and SrNd geochemistry and in situ zircon LuHf isotopic compositions of the Early Cretaceous granitoids from the Chinese Wakhan Corridor, Southern Pamir. These granitoids are composed primarily of granodiorite and minor monzogranite and host dioritic enclaves. The granitoids were emplaced at 107–102 Ma, based on their zircon UPb ages. They have 63–73 wt% SiO2, Mg# between 39 and 53 and ACNK mostly lower than 1.1, and are I-type granites. The granitoids display arc-like geochemical signatures characterized by LREE-enriched patterns, variable negative Eu anomalies (LaN/YbN = 11.38–23.27; Eu/Eu* = 0.36–0.74), and a significant NbTa trough (Nb/La = 0.24–0.41). Isotopically, the granitoids have negative whole-rock εNd(t) (−8.73–7.35) and zircon εHf(t) (−17.7–5.3) values. The coeval dioritic enclaves (ca. 104 Ma) contain 57–63 wt% SiO2, and have high Mg# (46–57), low Cr (6.86–79.50 ppm), and Ni (2.88–10.00 ppm). These enclaves exhibit arc-like trace element patterns (Nb/La = 0.34–0.43) with variable negative Eu anomaly (Eu/Eu* = 0.52–0.87), uniform whole-rock εNd(t) (−4.74–4.73), and a large range of zircon εHf(t) values (−13.3–3.7). In line with their rock association and geochemistry, we suggest that the dioritic enclaves were derived from melting of a phlogopite-bearing mantle source modified by subduction-related process, followed by fractional crystallization and later assimilation by granitic hosts. These Early Cretaceous granitoids were most likely generated by partial melting of the Precambrian lower crust with variable involvement of mafic magma parental to the dioritic enclaves. Our new data, combined with the previous studies, reveal that the widespread Early Cretaceous magmatism in the Southern Pamir-Karakorum were most likely generated by flat-slab subduction of the Meso-Tethys Ocean during the Cretaceous.

Origin of the Triassic Lincang granites in the southeastern Tibetan Plateau: Crystallization from crystal mush

The crustal generation of the Paleo-Tethys orogenic belt in the southeastern Tibetan Plateau is a major unresolved geological problem. The Changning-Menglian suture in the southeastern Tibetan Plateau represents a remnant of the Paleo-Tethys Ocean. The Lincang batholith and associated volcanic rocks (the Manghuai rhyolites and Xiaodingxi basalts) are located to the east of the Changning-Menglian suture, and represent important constraints for the abovementioned geological problem. New zircon UPb ages, together with previously published results, indicate that the Manghuai rhyolites were emplaced at 229–239 Ma and the Lincang batholith yielded longer age span (211–239 Ma). Broad age span of zircons (to 28 million years) from these rocks record a long-lived crustal magmatic system in the Changning-Menglian Paleo-Tethys orogenic belt. These intrusive and associated volcanic rocks have significant differences between them in terms of geochemistry. In this study, these rocks are geochemically classified into three groups: (1) Group 1 comprises biotite granite and granodiorite rocks; (2) Group 2 includes alkali feldspar granite, two-mica granite, and rhyolite, which are high-silica (generally >70 wt%) rocks that have low TiO2, Al2O3, FeOtot, MgO, CaO, P2O5, Eu, and Sr contents, compared to those of Group 1. Based on their geochemical relationships and mineral textures, Groups 1 and 2 include cumulative- and fractionated-type granitoids, respectively; (3) while Group 3 is comprised of dioritic enclaves and the Xiaodingxi basalts. Based on more robust evidence, dioritic enclaves are derived from a mantle source magma. The Lincang granites have high and variable initial 87Sr/86Sr ratios (0.703122–0.728476), significantly negative εNd (t = 220 Ma) values (−13.4 to −7.5), negative εHf (t) values (−17.7 to −6.8), and old TDM2 ages. The Manghuai rhyolites and Xiaodingxi basalts have lower initial 87Sr/86Sr ratios (0.695970–0.709398), and higher εNd (t) values (−3.4 to −0.6) and εHf (t) values (−1.2 to +3.7) than those of the Lincang granites. Geochemical data suggest that the Manghuai rhyolites could be seen as fractionated and erupted melts from crystal mush reservoirs, which later crystallized to form the Lincang granites. The Manghuai rhyolites provide an instantaneous snapshot of the state of the crystal mush at the time of eruption. The Lincang granites are interpreted to record prolonged histories of open-system magmatic evolution, involving magma mixing, wall-rock assimilation, and multiple cycles of crystallization from the crystal mush reservoirs. Magmatic evolution was likely related to mantle upwelling in a post-collisional setting, forming large-volume granites and volcanics in the Changning-Menglian Paleo-Tethys orogenic belt. Thus, this crystal mush model provides an integrated picture of the Triassic silicic magmatism, linking the evolution of the Lincang batholith and Manghuai rhyolites before storage in the Changning-Menglian Paleo-Tethys orogenic belt.

Triassic arc mafic magmatism in North Qiangtang: Implications for tectonic reconstruction and mineral exploration

The North Qiangtang continental block in central Tibet is a critical piece of the Pangea puzzle. This paper uses integrated geochronological and geochemical data for selected mafic dykes and dioritic enclaves in this block to evaluate its tectonic evolution in the Triassic. Zircons from two mafic dykes and the dioritic enclaves of a large arc granodiorite pluton in eastern North Qiangtang yield indistinguishable U-Pb ages from 248 ± 2 to 251 ± 3 Ma, contemporaneous with widespread arc basaltic andesites and crust-derived rhyolites in the region. The mafic dykes and coeval arc basaltic andesites have almost identical Sr-Nd isotopes (initial 87Sr/86Sr = 0.707 to 0.708, εNd = −4.4 to −3.6), and are all characterized by light REE enrichments and pronounced negative Nb-Ta anomalies. The dioritic enclaves and the hosts have indistinguishable zircon U-Pb ages, almost identical Sr-Nd isotopes (initial 87Sr/86Sr = 0.709 to 0.711, εNd = −7.4 to −5.9), and similar zircon εHf (−13.7 to −5.7), but contrasting chondrite-normalized REE patterns due to hornblende fractionation. The Sr-Nd isotope data indicate that the dioritic enclaves formed from the hybrid melts produced by mixing at depth between the arc basaltic andesites and the crust-derived rhyolites. We propose that the Early Triassic arc igneous suites are related to the northward subduction of the southern Paleo-Tethys beneath the North Qiangtang block from Early to Middle Triassic. The occurrence of several Late Triassic porphyry Cu deposits plus a VMS Ag-Pb-Zn deposit in the Yidun arc, which is the product of the southward subduction of the northern Paleo-Tethys beneath the North Qiangtang block in the Late Triassic, indicates that the arc magmas generated during the subduction of the Paleo-Tethys are fertile in ore metals. Therefore, exploration for Early–Middle Triassic porphyry Cu and VMS deposits in the southern part of the North Qiangtang block is warranted.

Genetic links between granitic and related dioritic rocks in Liaodong Peninsula, China: Sr–Nd–Hf–O isotopic evidence

Syenogranite and related dioritic rocks (dioritic microgranular enclaves and quartz diorite) from the Early Cretaceous Shihuzhen–Jiudaogou pluton, NE China, were studied to investigate the formation and evolution of the granitic magma driven by the mantle-derived magma. All selected rocks were formed contemporaneously, with zircon UPb ages of 125–121 Ma. Field and petrographic observations show that magma mixing happened between mafic and felsic magmas represented by dioritic enclaves and syenogranite. The dioritic enclaves with quenching textures have low SiO2 and high MgO contents, variable zircon εHf(t) compositions (−8.7 to +2.4), coupled with low initial 87Sr/86Sr ratios (0.70647–0.70772) and variable εNd(t) values (−8.8 to −3.9) for apatite, suggesting they were derived from an enriched mantle source with contamination of crustal materials. The syenogranites have relatively high 87Rb/86Sr ratios (2.92–22.0), variable zircon εHf(t) compositions (from −11.1 to −3.6), coupled with low initial 87Sr/86Sr ratios (0.70727 to 0.70791) and variable εNd(t) values (from −9.9 to −7.3) for apatite, requiring a juvenile crust origin with participation of mantle-derived magma. They were characterized by high SiO2 (> 74.0 wt.%) and low MgO, P2O5 contents, with conspicuous negative Ba, Sr, and Eu anomalies, implying a late fractionation phase. The quartz diorites have relatively high initial 87Sr/86Sr ratios (0.70781–0.70928) for apatite, with negative zircon εHf(t) values (−11.6 to −7.8) and apatite εNd(t) values (−10.5 to −8.9), which are identical to those of the felsic parental magma of syenogranite. They show complementary geochemical compositions with the syenogranite, including low SiO2 (< 60.0 wt.%), high MgO (Mg# up to 44.2) and Sr (> 744 ppm) contents, with obvious positive Ba and Sr anomalies and weakly positive Eu anomalies. Coupled with petrological observations (e.g., cumulate texture), we argue the crystal-melting segregation model account for the genetic link between the quartz diorite and syenogranite, representing residual crystal accumulations and segregated interstitial melt from a crystal-rich magma chamber.The partial melting of juvenile lower crust and the subsequent crystallization differentiation of intermediate-acid magma developed a crystal-rich magma chamber. The mantle-derived magma then drove the rejuvenation of pre-exist magma chamber, promoted the crystal-melt segregation process and mixed with the felsic magma, and then formed quartz diorite and syenogranite in the Shihuzhen-Jiudaogou pluton. Mantle-derived magma played an important role in the formation of the granitic rocks, providing heat for partial melting, materials, and the driving force for their compositional evolution.

Rapid magma ascent and formation of the Águas Belas-Canindé granitic batholith, NE Brazil: evidence of epidote dissolution and thermobarometry

Abstract Mineral chemistry and intensive parameter estimates for the Major Isidoro (626 Ma) and Monteiropolis (627 Ma) magmatic epidote-bearing granitic plutons, emplaced along the Jacare dos Homens transpressional shear zone (JHSZ), Borborema Province, are focused in this study. These plutons consist of medium-to-coarse grained equigranular to porphyritic tonalite to granite that show abundant dioritic enclaves. These granites contain biotite (Fe# 0.44 to 0.55), Fe-edenite (Major Isidoro), hastingsite (Monteiropolis), titanite, and epidote that often show allanite core as key mafic mineral phases. Pistacite molecular content in epidote is in the interval of 27 to 31 mol%, presenting TiO2 < 0.30%, typical for magmatic epidote. Estimated intensive parameters reveal crystallization at 6.5 ± 1 (Major Isidoro) and 4.7 ± 0.6 kbar (Monteiropolis), temperatures from ~940°C (near-liquidus) to 675 ± 35°C (near-solidus) and oxidizing conditions. Partial corrosion of epidote took place during 15.6 to 32 (Major Isidoro) and 27-49 years (Monteiropolis), corresponding to rather high magma ascension rates of 365 to 750 and 395 to 635 m.years-1, respectively. The JHSZ likely favored upward magma transport at the Sergipano and Pernambuco-Alagoas domains boundary, during the onset of the Brasiliano orogeny (650-620 Ma).

Late Triassic ridge subduction of Paleotethys: Insights from high-Mg granitoids in the Songpan-Ganzi area of northern Tibet

The time of final closure of the Paleotethys Ocean is still hotly debated in particular regarding the Jinsha Ocean in northern Tibet. This study reports new geochronologic, geochemical and zircon Hf isotopic data of six granodiorites-diorites, which intrude the Mid-Late Triassic Songpan-Ganzi complex (SGC). LA-ICP-MS zircon U-Pb analyses of three quartz diorites (214.9 ± 2.2, 211.0 ± 1.3, 205.8 ± 1.4 Ma) and three granodiorites (210.8 ± 2.7, 206.7 ± 3.3, 205.9 ± 3.5 Ma) gave a Late Triassic age range (214.9–205.8 Ma). These granodiorite-diorite rocks have relatively high MgO (up to 9.1%) and Mg# (up to 70.2), Al2O3, Cr, Ni, but low TiO2, and high magnesium andesite/diorite (HMA) chemical signatures with low Sr and Y content, and slight-moderate negative Eu anomaly. Also, the dioritic enclaves and Late Triassic detrital zircons (as young as 208 Ma) were captured by studied rocks. Hf isotope data show overall slight to moderate negative zircon εHf(t) values (−1.97 to −5.76, −4.12 to −6.72) and heterogeneous TDMC ages (1.38−1.61Ga, 1.51−1.68Ga) for quartz diorites and granodiorites respectively, together with other published Hf isotopic data in SGC, are in highly concert with those around ~240 and ~440Ma magmas (as potential sources for SGC turbidites) in east Kunlun orogenic belt. Taken together, the HMA magmas were probably derived from a reaction between subducted marine sedimentary siliceous melts and peridotites from a mantle wedge.The linear distribution of Late Triassic HMAs and their eastward-younging trend (from northern Qiangtang to southern SGC), in combination with the contrasting distribution of volcanic rocks in the northern Qiangtang terrane, lead us to suggest that a slab window opened in the downgoing oceanic crust with two diverse slab angles during oblique subduction. Accordingly, the final closure of the Paleotethys Ocean was later than 205 Ma, and most likely in the end of the Late Triassic to Early Jurassic.

Role of magma mixing in generating of the Gheshlagh–Aftabrow intrusions, SW Buin Zahra, Iran: Evidence for a juvenile origin from geochemical and Sr–Nd isotopic data

In this paper, we investigate host granodiorites and associated mafic microgranular enclaves (MMEs), including gabbroic to quartz diorite enclaves from the Middle Eocene Gheshlagh–Aftabrow granitoid, to assess magma mixing and crust–mantle interaction in the Urumieh–Dokhtar magmatic arc. The host granodiorites yield zircon U–Pb ages of ca. 40 Ma. Geochemical and bulk rock Nd–Sr isotopic modelling, together with the widespread occurrence of mafic microgranular enclaves with ellipsoidal and spherical shapes and chilled margins, K‐feldspar and plagioclase megacrysts in the enclaves, and the presence of acicular apatite, ocellar quartz, plagioclase with oscillatory zoning and resorption surfaces, suggests that the mafic microgranular enclaves are globules of a more mafic magma derived from the mantle that was injected into and mixed/mingled with the magma derived from partial melting of a lower crust. Geochemically, the granitoid rocks are high‐K calc‐alkaline and metaluminous (A/CNK = 0.87–0.92) and belong to I‐type suite. These granitoid host rocks have much higher SiO2 (65.4–67.3 wt%) and relatively low Fe2O3 (1.8–2.1 wt%) and MgO (1–1.58 wt%), so compared with the host rocks, the mafic microgranular enclaves have much lower SiO2 contents (50.5–55 wt%), considerably higher Fe2O3 (3.4–4.2 wt%) and MgO (3.9–4.8 wt%). Both the host intrusion and enclaves are enriched in LREE relative to HREEs (LREE/HREE = 3.1–4.1; (La/Yb)N = 2.1–4.1) and show slightly negative Eu anomalies (δEu = 0.75–0.90) and nearly flat HREE patterns ((Gd/Yb)N = 0.86–1.26). Analyses of Sr–Nd isotopes in the host granodiorites and associated enclaves show (87Sr/86Sr)i host = 0.705070–0.705174, εNd(t) host = 0.21–2.31, TDM1 host = 782–983 Ma, (87Sr/86Sr)i enclave = 0.704997–0.705170, εNd(t) enclave = 2.15–2.17, and TDM1 enclave = 874–980 Ma, indicating of juvenile nature for these granites. This characteristic together with similar trace‐element compositions indicates intense magma mixing and a high degree of geochemical equilibration between the host granodiorites and their enclaves.A binary mixing model based on Sr–Nd isotopic compositions of the GAG indicates that rocks were mostly generated by mixing of 7–12% melts produced by partial melting of meta‐igneous old lower crust rocks with 88–93% contribution of mantle‐derived juvenile basaltic magmas.

Late Paleozoic magmatism and metallogenesis in the Aqishan-Yamansu belt, Eastern Tianshan: Constraints from the Bailingshan intrusive complex

The Aqishan-Yamansu belt in the Eastern Tianshan (NW China) contains many intermediate to felsic intrusive rocks and spatially and temporally associated Fe (-Cu) deposits. Zircon U-Pb dating of the Bailingshan granitoids, including diorite enclaves (in granodiorite), diorite, monzogranite and granodiorite, and andesitic tuff from the Shuanglong Fe-Cu deposit area yielded ages of 329.3 ± 2.1 Ma, 323.4 ± 2.6 Ma, 313.0 ± 2.0 Ma, 307.5 ± 1.7 Ma and 318.0 ± 2.0 Ma, respectively. These new ages, in combination with published data can be used to subdivide magmatism of the Bailingshan intrusive complex into three phases at ca. 329–323 Ma, ca. 318–313 Ma and ca. 308–297 Ma. Of the analyzed rocks of this study, the Shuanglong diorite enclave, diorite and andesitic tuff show calc-alkaline affinities, exhibiting LILE enrichment and HFSE depletion, with negative Nb and Ta anomalies. They have high MgO contents and Mg# values, with depleted εHf(t) and positive εNd(t) values, similar crustal-derived Nb/Ta and Y/Nb ratios, low Th/Yb and Th/Nb, and high Ba/La ratios, which are consistent with them being sourced from a depleted mantle wedge metasomatized by slab-derived fluids and crustal contamination. However, the monzogranite and granodiorite are metaluminous with characteristics of low- to high-K calc-alkaline I-type granites. The granitic rocks are enriched in LILE, depleted in HFSE and have significant Eu anomalies, with high Y contents and low Sr/Y ratios, resembling typical of normal arc magmas. Depleted εHf(t) and positive εNd(t) values with corresponding young TDMC ages of zircons, as well as Nb/Ta, Y/Nb, Th/U and La/Yb ratios suggest that the granitic rocks were probably formed by re-melting of juvenile lower crust or pre-existing mantle-derived mafic–intermediate igneous rocks. Integrating published data, we conclude that the Bailingshan granitoids (excluding the Shuanglong diorite and diorite enclave) were derived from re-melting of juvenile lower crust and mantle-derived mafic–intermediate igneous rocks, with mantle components playing a more prominent role in the formation of the younger and more felsic rocks. A comprehensive review, including our new data, suggests that the Aqishan-Yamansu belt formed as a fore-arc basin during the Carboniferous (ca. 350–300 Ma) when the Kangguer oceanic slab subducted beneath the Yili-Central Tianshan block. The ongoing southward subduction of the slab resulted in the closure of the Aqishan-Yamansu fore-arc basin (ca. 320–300 Ma), due to slab steepening and rollback followed by slab breakoff and rebound. During the Aqishan-Yamansu fore-arc basin inversion, the main phase of the Bailingshan granitoids emplaced in the Aqishan-Yamansu belt, accompanied by contemporary Fe and Fe-Cu mineralization.