Post-collisional Tectonic Setting Research Articles

Petrogenesis of shoshonitic granitoids, eastern India: Implications for the late Grenvillian post-collisional magmatism

Many elongated, lenticular plutons of porphyritic granitoids are distributed mainly near the southern and northern margin of the Chhotanagpur Gneissic Complex (CGC) which belongs to the EW to ENE–WSW tending 1500 km long Proterozoic orogenic belt amalgamating the North and South Indian cratonic blocks. The late Grenvillian (1071 ± 64 Ma) Raghunathpur porphyritic granitoid gneiss (PGG) batholith comprising alkali feldspar granite, granite, granodiorite, tonalite, quartz syenite and quartz monzonite intruded into the granitoid gneisses of southeastern part of CGC in the Purulia district, West Bengal and is aligned with ENE–WSW trending North Purulia shear zone. Mineral chemistry, geochemistry, physical condition of crystallization and petrogenetic model of Raghunathpur PGG have been discussed for the first time. The petrographic and geochemical features (including major and trace-elements, mineral chemistry and 87Sr/86Sr ratio) suggest these granitoids to be classified as the shoshonitic type. Raghunathpur batholith was emplaced at around 800 °C and at 6 kbar pressure tectonic discrimination diagrams reveal a post-collision tectonic setting while structural studies reveal its emplacement in the extensional fissure of North Purulia shear zone. The Raghunathpur granitoid is compared with some similar granitoids of Europe and China to draw its petrogenetic model. Hybridization of mantle-generated enriched mafic magma and crustal magma at lower crust and later fractional crystallization is proposed for the petrogenesis of this PGG. Mafic magma generated in a post-collisional extension possibly because of delamination of subducting slab. Raghunathpur batholith had emplaced in the CGC during the final amalgamation (∼1.0 Ga) of the North and South Indian cratonic blocks. Granitoid magma, after its generation at depth, was transported to its present level along megadyke channel, ways within shear zones.

GRADE DISTRIBUTION OF THE GIANT OK TEDI Cu-Au DEPOSIT, PAPUA NEW GUINEA

The Ok Tedi porphyry Cu-Au deposit in Papua New Guinea is a world-class mineral deposit. In its pre-mining stage, it contained 5.5 Mt Cu and 18.1 Moz Au; skarn accounts for ~80% of the current 1.9 Mt Cu and 7.7 Moz Au in total resources. Two composite felsic stocks intruded a tectonostratigraphic sequence of clastic and carbonate rocks at ~1.16 ± 0.10 Ma, in a postcollisional tectonic setting. Ensuing magmatic-hydrothermal mineralization occurred within a geologically short time span of ~200 k.y. On the mine scale, heterogeneous metal grades (0–2.5% Cu) reflect contrasting styles of mineralization, conforming to classic skarn- and porphyry-type mineralization. A three-dimensional geologic model, alteration distribution, mineralization styles, and grade distribution indicate that fluids, exsolved from a deeper magma chamber, used shallow stocks as their preferred permeable pathway upward. Where limestone was present at depth, high-grade skarn formed, with the permeable stock having very low (<0.1% Cu) grade. In contrast, where the intrusions were encapsulated solely by impermeable silicified siltstone, economic grade (avg 0.6% Cu) developed within the intrusion, showing concentric patterns interpreted to represent individual magmatic pulses within the stock. The rare opportunity to visualize this in three dimensions and interact with the model is provided in the interactive electronic supplementary material.

Geodynamic setting of Mesozoic magmatism in NE China and surrounding regions: Perspectives from spatio-temporal distribution patterns of ore deposits

North-eastern China and surrounding regions host some of the best examples of Phanerozoic juvenile crust on the globe. However, the Mesozoic tectonic setting and geodynamic processes in this region remain debated. Here we attempt a systematic analysis of the spatio-temporal distribution patterns of ore deposits in NE China and surrounding regions to constrain the geodynamic milieu. From an evaluation of the available geochronological data, we identify five distinct stages of ore formation: 240–205Ma, 190–165Ma, 155–145Ma, 140–120Ma, and 115–100Ma. The Triassic (240–205Ma) magmatism and associated mineralisation occurred during in a post-collisional tectonic setting involving the closure of the Paleo-Asian Ocean. The Early-Mid Jurassic (190–165Ma) events are related to the subduction of the Paleo-Pacific Ocean in the eastern Asian continental margin, whereas in the Erguna block, these are associated with the subduction of the Mongol–Okhotsk Ocean. From 155 to 120Ma, large-scale continental extension occurred in NE China and surrounding regions. However, the Late Jurassic magmatism and mineralisation events in these areas evolved in a post-orogenic extensional environment of the Mongol–Okhotsk Ocean subduction system. The early stage of the Early Cretaceous events occurred under the combined effects of the closure of the Mongol–Okhotsk Ocean and the subduction of the Paleo-Pacific Ocean. The widespread extension ceased during the late phase of Early Cretaceous (115–100Ma), following the rapid tectonic changes resulting from the Paleo-Pacific Oceanic plate reconfiguration.

Geology and evolution of pegmatite-hosted U-Th &amp;plusmn; REE-Y-Nb Mineralization, Kulyk, Eagle, and Karin Lakes region, Wollaston Domain, northern Saskatchewan, Canada: examples of the dual role of extreme fractionation and hybridization processes

*Corr esponding author In northern Saskatchewan, granitic pegmatites intruded Early Paleoproterozoic Wollaston Group metasedimentary rocks and interfolded granitoids that unconformably overlie Late Archean gneisses, all of which have been subjected to deformation during the protracted 1.86 to 1.77 Ga Trans-Hudson Orogeny. The U–Th ± REE–Y–Nb pegmatite intrusions and fracture-controlled U mineralization characterize the occurrences at Kulyk Lake, Eagle Lake, and Karin Lake properties in the Wollaston Domain. The pegmatites are moderately to highly evolved, ranging from mineralogically simple to complex types. These are rare-earth element class, NYF pegmatites (Nb–Y–F), and are interpreted to have formed in a late syn- to post-collisional tectonic setting. The complex-type pegmatites are hybridized, due to metasomatic interaction with the host rocks and therefore are locally crudely zoned. Saturation of U–Th ± REE–Y–Nb occurred at the margins (predominately the border and wall zones) of the hybridized pegmatites. Partial melts were generated at depth, and then coalesced as they intruded to higher structural levels during exhumation of this orogen. This agrees with U–Pb geochronology of these granitic pegmatites, which constrains them between peak- and late-metamorphic events of the Trans-Hudson Orogeny. The age constraints and relatively high-T partial melting conditions (~750 °C) confine the pegmatite melt-forming conditions to an early deformational event (1835–1805 Ma) that was overprinted by high-T retrograde metamorphism at c. 1770 Ma. Field relationships, textures and geochemical variations provide strong evidence that the U, Th, REE ± Y– Nb phases in the studied pegmatites were progressively enriched through extreme fractionation effects of which are evident throughout multiple pegmatite injections. In addition, volatiles and other fluxing components further enriched U, Th, REE ± Y– Nb during complex hybridization reactions between pegmatite melt and wallrock, up to the final stages of pegmatite emplacement.

Heterogeneous Zircon Cargo in Voluminous Late Paleozoic Rhyolites: Hf, O Isotope and Zr/Hf Records of Plutonic to Volcanic Magma Evolution

Voluminous rhyolitic lavas and ignimbrites (c. 34 000 km3) were formed in the NE German Basin in a post-collisional setting at c. 295 Ma. Trace elements, eHf and δ18O have been measured in dated magmatic and inherited rhyolitic zircons from three drill cores across the basin. Magmatic zircons crystallized in two stages: the first stage in less differentiated and isotopically heterogeneous magmas and the second stage in more differentiated and isotopically homogeneous magmas. The first and second stages can be related to the crystallization of zircons within a heterogeneous pluton and in an evolved, silicic magma that was later erupted. Some zircons crystallized entirely during the evolved magma stage and provide good resolution for identifying and characterizing processes happening shortly before eruption. The isotopic compositions of the magmatic zircons constrain the proportions of juvenile and reworked materials involved in the formation of voluminous silicic magmas in a post-collisional tectonic setting. The advantage of studying the volcanic rocks from the NE German Basin is that their petrogenesis involved a relatively simple, two-source interaction during magma production, which permits quantitative estimation of the amount of each source component. AFC modelling shows that the first stage zircons crystallized from magmas containing 5–80% of the juvenile component, whereas the final rhyolitic magmas contained 30–40% of this material. The inherited zircons have Hf model ages of 1·9–2·2 Ga, suggesting that much of the local basement was initially derived from the mantle at that time and that it was subsequently reworked at around 1·5 Ga. Similar model ages are a feature of Baltica-derived sediments and the implication is that such sediments underlie large areas of the NE German Basin. The lack of any record of Avalonian basement in the NE German Basin may indicate that both the sedimentary cover and the underlying basement are part of Baltica.

Types, characteristics, and time–space distribution of molybdenum deposits in China

Molybdenum exploration activity in China has accelerated tremendously during the past decade owing to the continuous, increasing demand for Earth resources. China possesses the largest Mo reserves in the world (exceeding 19.6 Mt). The major ore deposits are of porphyry, porphyry–skarn, skarn, vein, and sedimentary types. Porphyry molybdenum deposits contain 77.5% of the Chinese Mo reserves, with lesser amounts in porphyry–skarns (13%), skarns (5.1%), and veins (4.4%). Exploitation of sedimentary-type molybdenum deposits thus far has been uneconomical. The six Mo provinces are in the Northeast China, Yanliao, Qinling–Dabie, middle–lower Yangtze River Valley, South China, and Sanjiang areas. We recognize six ore-forming periods: (1) Precambrian (>541 Ma), (2) Palaeozoic (541–250 Ma), (3) Triassic (250–200 Ma), (4) Jurassic–Early Cretaceous (190–135 Ma), (5) Cretaceous (135–90 Ma), and (6) Cenozoic (55–12 Ma). The abundance of Mo ore deposits in China reflects the occurrence of multiple periods of tectonism, involving interactions between the Siberian, North China, Yangtze, India, and Palaeo-Pacific plates. Precambrian molybdenum deposits are related to Mesoproterozoic volcanism in an extensional setting. Palaeozoic Cu–Mo deposits are related to calc-alkaline granitic plutons in an island arc or a continental margin setting. Triassic Mo deposits formed in the syn-collision–postcollision tectonic setting between the Siberian and North China plates and between the North China and Yangzi plates. Jurassic–Early Cretaceous molybdenum deposits formed along the eastern margin of Asia and are associated with the palaeo-Pacific plate-subduction tectonic setting. Cretaceous Mo deposits are related to high-K calc-alkaline granitic rocks and formed in a lithospheric thinning setting. Cenozoic molybdenum deposits formed in a collision setting between the Indian and Eurasian continents and the subsequent extensional setting.

Mid-Triassic felsic igneous rocks from the southern Lancangjiang Zone, SW China: Petrogenesis and implications for the evolution of Paleo-Tethys

The southern Lancangjiang magmatic belt is an important component of the Triassic San-Jiang igneous zone in Southwestern China and is mainly composed of the Lincang (LC) batholith and a Mesozoic volcanic belt that contains abundant rhyolites. Our new LA-ICP-MS zircon U–Pb results, together with previous SHRIMP and LA-ICP-MS ages, define two emplacement ages for the Lincang batholith: at ~230Ma and ~220Ma, corresponding to the eruption times of volcanic rocks of the Manghuai and Xiaodingxi formations, respectively. Most of the ~230Ma LC granites possess high A/CNK values (>1.1) and display strongly peraluminous characteristics, similar to S-type granite, whereas the Manghuai Formation (MHF) rhyolites show an affinity to A-type granite, especially their elevated FeOt/(FeOt+MgO) and Ga/Al ratios. Both of the granitic and volcanic rocks have strongly fractionated REE patterns ((La/Yb)N=2.66–33.2 and 13.1–19.7, respectively) and have conspicuous negative Eu anomalies (Eu*/Eu=0.06–0.65 and 0.52–0.74, respectively) with a similar depletion in HFSE (Nb, Zr, Hf), P, Ba and Sr. The Sr–Nd isotopic data and TDM2 model ages suggest that the LC granitic magma had a dominantly crustal source, whereas the MHF rhyolites were derived from mixing between middle/upper crustal rocks similar to the source of the LC granitic magma, with a small volume of mantle-derived melt.In combination with regional studies, our new geochemical data and geochronological results show that the mid-Triassic magmatism was generated in a post-collisional tectonic setting. The spatial distribution pattern of the Mesozoic igneous rocks along the Lancangjiang zone favors a slab breakoff model, which resulted in post-collisional extension and asthenospheric upwelling that induced large-scale partial melting of the middle-lower crust to produce voluminous amounts of felsic magma. Therefore, the occurrence of the mid-Triassic post-collisional magmatism clearly indicates that the final continent–continent/arc collision between the Gondwana-derived Sibumasu and Indochina blocks of Paleo-Tethys was completed by the early mid-Triassic.

Geochronological and Geochemical Constrains on Petrogenesis of the Jietebutiao A‐type Granite in West Junggar, Xinjiang

AbstractLate Paleozoic post‐collisional granitoids are widespread in West Junggar, as well as northern Xinjiang. As a representative of those intrusions, the Jietebutiao granite occurs in the southwestern margin of the West Junggar (northwest China), and is mainly composed of mid‐coarse‐grained monzogranite and syenogranite. In the present study, we report the results of high‐precision zircon laser‐ablation–inductively‐coupled plasma mass–spectrometry U–Pb dating on the Jietebutiao granite for the first time, and yield weighted mean 206Pb/238U ages of 287 ± 9 Ma and 278 ± 3 Ma for monzogranite and syenogranite, respectively. The Jietebutiao granite has a pronounced A‐type affinity; it is metaluminons to slightly peraluminous; has a high‐K calc‐alkaline composition; high concentrations of Na2O + K2O, varying from 6.8 to 8.5 wt%; high FeOt/MgO; 10 000Ga/Al ratios, a low CaO, MgO, and TiO2 content; enriched in some large ion lithophile elements (LILE, such as Rb and Th) and high field strength elements (HFSE, such as Zr, Hf, and Y); and depleted in Sr, Ba, and Ti. In addition, the granite has a relatively high rare earth element (REE) content (except for Eu), with significant negative Eu anomalies (Eu/Eu*= 0.01–0.72), and showing slight tetrad REE patterns and non‐charge and radius controlled (CHARAC) trace element behavior. Petrographic, geochemical, and geochronological data suggest that the parental magma of Jietebutiao intrusions are of mixed origin, and are most probably formed by the interaction between the lower crust‐ and mantle‐derived magmas in the Early Permian post‐collisional tectonic setting. The basaltic magmas underplated and interacted with the lower crust that was dominated by deeply buried arc (and back‐arc basin) series and the oceanic crust formed in the Paleozoic, and then triggered the partial melting of the juvenile lower crust, producing voluminous granitic melts and forming the Jietebutiao A2‐type monzogranites, with the lithospheric mantle progressively thinning and rifting to form A‐type granites, such as syenogranites, in the Jietebutiao pluton. This further proves the important contribution of Late Paleozoic granitic magmatism in terms of vertical crustal growth in northern Xinjiang.

Perogenesis of granites, Sharm El-Sheikh area, South Sinai, Egypt: petrological constrains and tectonic evolution

Precambrian granites of the Sharm El-Sheikh area in south Sinai, Egypt belong to collisional and post-collisional Magmatism (610–580 Ma). The granites are widely distributed in the northern part of the Neoproterozoic Arabian-Nubian Shield. South Sinai includes important components of successive multiple stages of upper crust granitic rocks. The earliest stages include monzogranite and syenogranites while the later stages produced alkali feldspar granites and riebeckite-bearing granites. Numerous felsic, mafic dikes and quartz veins traverse the study granites. Petrographically, the granitic rocks consist mainly of perthite, plagioclase, quartz, biotite and riebeckite. Analysis results portray monzogranites displaying calc-alkaline characteristics and emplaced in island-arc tectonic settings, whereas the syenogranites, alkali-feldspar granites and the riebeckite bearing-granites exhibit an alkaline nature and are enriched in HFSEs similar to granites within an extensional regime. Multi-element variation diagrams and geochemical characteristics reinforce a post-collision tectonic setting. REEs geochemical modeling reveals that the rocks were generated as a result of partial melting and fractionation of lower crust basaltic magma giving rise to A1 and A2 subtype granites. They were subsequently emplaced within an intraplate environment at the end of the Pan-African Orogeny.

Geochemistry and zircon U–Pb–Hf isotopes of the late Paleoproterozoic Jianping diorite–monzonite–syenite suite of the North China Craton: Implications for petrogenesis and geodynamic setting

The late Paleoproterozoic Jianping diorite–monzonite–syenite suite (JDMSS), in the Western Liaoning Province (WLP) along the northern margin of the North China Craton (NCC), is composed mainly of magnetite diorites, clinopyroxene monzonites, syenites, and quartz syenites. LA-ICP-MS zircon U–Pb isotopic dating indicates that this complex emplaced between 1696 and 1721Ma, almost synchronously with the 1680–1750Ma anorthosite–mangerite–alkali granitoid–rapakivi granite suite (AMGRS) in northern Hebei Province. The JDMSS in the WLP is the eastwards extensional part of the AMGRS in northern Hebei Province along the northern margin of the NCC. All samples from the JDMSS are characterized by a wide and continuously variable geochemical spectrum of 46.3–64.9wt.% SiO2 and 0.528–4.14wt.% MgO, with high K2O (1.080–7.01wt.%) and total alkalis (Na2O+K2O, 5.08–12.55wt.%). These rocks are enriched in LREEs and LILEs but depleted in HFSEs (Nb, Ta, and Ti), and they show negative zircon εHf(t) values of −12.6 to −0.3 and a low whole-rock initial 87Sr/86Sr value of 0.703564. These geochemical features, together with trace element modeling, suggest that all the rocks of the JDMSS were generated chiefly by fractional crystallization of a common parental magma that was derived by partial melting of an amphibole-bearing enriched subcontinental lithospheric mantle source (mixed EMI and HIMU mantle), and that the magma assimilated crustal materials during ascent and emplacement. Integrating our data with those of previous studies of the contemporaneous magmatic rocks throughout the NCC (mafic dykes, volcanic rocks, and AMGRS; 1680–1780Ma), we propose that both the northern and southern margins of the NCC, as well as the TNCO (Trans-North China Orogen), evolved under a post-collisional tectonic setting during the late Paleoproterozoic, postdating the final amalgamation of the NCC, and that the NCC at this time was probably located between Laurentia (North America and Greenland) and Siberia within the interior of the Columbia supercontinent.

Xiba Granitic Pluton in the Qinling Orogenic Belt, Central China: Its Petrogenesis and Tectonic Implications

AbstractXiba granitic pluton is located in South Qinling tectonic domain of the Qinling orogenic belt and consists mainly of granodiorite and monzogranite with significant number of microgranular quartz dioritic enclaves. SHRIMP zircon U–Pb isotopic dating reveals that the quartz dioritic enclaves formed at 214±3 Ma, which is similar to the age of their host monzogranite (218±1 Ma). The granitoids belong to high‐K calc‐alkaline series, and are characterized by enriched LILEs relative to HFSEs with negative Nb, Ta and Ti anomalies, and right‐declined REE patterns with (La/Yb)N ratios ranging from 15.83 to 26.47 and δEu values from 0.78 to 1.22 (mean= 0.97). Most of these samples from Xiba granitic pluton exhibit εNd(t) values of –8.79 to –5.38, depleted mantle Nd model ages (TDM) between 1.1 Ga and 1.7 Ga, and initial Sr isotopic ratios (87Sr/86Sr)i from 0.7061 to 0.7082, indicating a possible Meso‐ to Paleoproterozoic lower crust source region, with exception of samples XB01‐2‐1 and XB10‐1 displaying higher (87Sr/86Sr)i values of 0.779 and 0.735, respectively, which suggests a contamination of the upper crustal materials. Quartz dioritic enclaves are interpreted as the result of rapid crystallization fractionation during the parent magmatic emplacement, as evidenced by similar age, texture, geochemical, and Sr‐Nd isotopic features with their host rocks. Characteristics of the petrological and geochemical data reveal that the parent magma of Xiba granitoids was produced by a magma mingling process. The upwelling asthenosphere caused a high heat flow and the mafic magma was underplated into the bottom of the lower continent crust, which caused the partial melting of the lower continent crustal materials. This geodynamic process generated the mixing parent magma between mafic magma from depleted mantle and felsic magma derived from the lower continent crust. Integrated petrogenesis and tectonic discrimination with regional tectonic evolution of the Qinling orogen, it is suggested that the granitoids are most likely products in a post‐collision tectonic setting.

Petrogenesis and magmatic–hydrothermal evolution time limitation of Kelumute No. 112 pegmatite in Altay, Northwestern China: Evidence from zircon U[sbnd]Pb and Hf isotopes

Granitic pegmatites and associated rare-metal deposits, unique features in the Altay orogen, are located in a key tectonic position of the southern Central Asian Orogenic Belt (CAOB) and document the tectonic evolution of the Paleo-Asian Ocean. The Kelumute No. 112 pegmatite, which intruded into the Jideke two-mica granites, hosts abundant rare-metal (e.g., Li, Be, Nb, Ta) ore deposits and ranks only second to the Koktokay No. 3 pegmatite in both size and reserves. To explore the evolution time limitation of magmatic, magmatic–hydrothermal and hydrothermal stages in the pegmatite magma system, the tectonic setting and the genetic relationship between pegmatites and granites, this study presents zircon UPb and Hf isotopic compositions of the Kelumute No. 112 pegmatite and the wall rocks (two-mica granite and biotite granite) as determined by LA-ICPMS and LA-MC-ICPMS. The weighted mean 206Pb/238U ages of the internal textural zones of the pegmatite, including zones I, II, III, V and VI, are 238.3±2.0Ma, 233.5±3.7Ma, 188.3±1.7Ma, 218.8±1.9Ma and 210.7±1.6Ma, respectively. Wall rocks of two-mica granite and biotite granite are dated at 445.6±4.3Ma and 455.6±5.4Ma, respectively. Zircons from the Kelumute No. 112 pegmatite have lower positive εHf(t) values (+0.03 to +2.35), with TDM model ages of 1112–1225Ma. Wall rocks show similar zircon εHf(t) values (−1.41 to +4.13) and TDM model ages (1172 to 1515Ma). However, three xenocrystic zircons from the granites are characterized by larger negative εHf(t) values (−5.85 to −9.83) and older TDM model ages (1839 to 2090Ma). Thus, the following conclusions can be drawn: 1) the Kelumute No. 112 pegmatite and its wall rocks (Jideke two-mica granite and biotite granite) have no genetic relationship, as indicated by the large gaps between their formation ages. However, they did originate from a common source composed of ancient crust and mantle-derived materials under two different tectonic settings; 2) the magmatic, magmatic–hydrothermal transition and hydrothermal stages of the No. 112 pegmatite magma lasted for ~5Ma, ~23Ma and ~22Ma, respectively; and 3) the No. 112 pegmatite magma was most likely formed in a post-collision tectonic setting, indicating that block amalgamation and collisional orogeny of the CAOB continued into the Triassic.

Source contamination and tectonomagmatic signals of overlapping Early to Middle Miocene orogenic magmas associated with shallow continental subduction and asthenospheric mantle flows in Western Anatolia: A record from Simav (Kütahya) region

The disappearances of mafic shoshonitic and ultrapotassic magma prior to Late Oligocene in Western Anatolia post-collisional tectonic settings, and the sudden appearance of Early-Middle Miocene potassic lavas with orogenic geochemical signatures, indicate a striking change of mantle sources during the Early-Middle Miocene period, and require a special explanation. In this regard, the Simav (Kütahya) region of Western Anatolia represents a critical area, where the Early-Middle Miocene mafic potassic (shoshonite, absarokite, ultrapotassic) and high-K calc-alkaline (andesite, dacite-rhyolite, granite) series rocks overlap in the extensional geotectonic setting in a back-arc position. The appraisal of petrological data obtained from Simav igneous complex indicates that there is a remarkable geochemical and isotopic similarity (e.g., negative Eu anomalies; Nb–Ta depletions; high Sr, low Nd and variable Pb isotope compositions) between coevally generated mafic potassic and high-K calc-alkaline magma series. The near primitive mafic potassic (MHKS) lavas with high Sr isotope compositions require a heterogeneous mantle source contaminated with crustal materials. Dragged and delaminated crustal components, caused by shallow continental subduction and the late arrived subducted terrigenous sediments from the Aegean trench are likely candidate sources of continental materials incorporated into the mantle source of the Simav mafic potassic (MHKS) magmas. The nature of these components also played a significant role in the compositional variations of Simav mafic series rocks. The Simav mafic potassic (MHKS) magmas were derived from a crust-contaminated, subduction-modified (metasomatized) EM-II type mantle source, interacting with influxed asthenosphere in a back-arc mantle wedge, whereas mixing of lower crustal silicic melts with underplated potassic mafic magmas resulted in coeval high-K calc-alkaline rocks, matched by the extent of crustal contamination observed in the more evolved silicic rocks. The petrogenesis of the Simav magmatism was triggered by multiple driving forces with kinematic linkage: such as asthenospheric mantle flows, trench retreat, shallow continental subduction, regional extensional uplifting (e.g., Menderes Massif), and concomitant extension and delaminations of subducted (accreted) crust and mantle lithosphere. Considering the Late Tertiary geodynamic picture of the Western Anatolia back-arc extensional province, the initiation of post-collisional potassic and ultrapotassic magma pulses, as a tectonomagmatic precursor, provide evidence for (i) the timing of last stage of regional uplifting (e.g., Menderes Massif) and onset of extensional basin formations in different periods, and (ii) rapid tectonic transitions.

Petrology and Geochemistry of Post‐Collisional Early Miocene Volcanism in the Karacadaǧ Area (Central Anatolia, Turkey)

Abstract:Early Miocene (ca. 21–18 Ma) volcanism in the Karacadaǧ area comprises three groups of volcanic rocks: (1) calcalkaline suite (andesitic to rhyolitic lavas and their pyroclastics), (2) mildly‐alkaline suite (alkali basalt, hawaiite, mugearite, benmoreite and trachydacite), and (3) a single trachyandesitic flow unit. Field observations, 40Ar/39Ar ages and geochemical data show that there was a progressive temporal transition from group 1 to 3 in a post‐collisional tectonic setting. The calcalkaline suite rocks with medium‐K in composition resemble those of subduction‐related lavas, whereas the mildly‐alkaline suite rocks having a sodic tendency (Na2O/K2O=1.5–3.2) resemble those of within‐plate lavas. Incompatible element and Sr‐Nd isotopic characteristics of the suites suggest that the lithospheric mantle beneath the Karacadaǧ area was heterogeneously enriched by two processes before collision: (1) enrichment by subduction‐related processes, which is important in the genesis of the calcalkaline volcanism, (2) enrichment by small degree melts from the astenosphere, which dominates the mildly alkaline volcanism. Perturbation of the enriched lithosphere by either delamination following collision and uplift or removal of the subducted slab following subduction and collision (i.e., slab breakoff) is the likely mechanism for the initiation of the post‐collision volcanism.

Geochemistry, zircon U–Pb age and Hf isotope compositions of Paleoproterozoic aluminous A-type granites from the Kongling terrain, Yangtze Block: Constraints on petrogenesis and geologic implications

An integrated study of petrology, zircon U–Pb age, and geochemistry was reported for a Paleoproterozoic granitic pluton from the Kongling terrain in the northern part of the Yangtze Block. The Quanqitang pluton is composed mainly of alkali feldspar, quartz, biotite and plagioclase. Zircon U–Pb dating yields a 207Pb/206Pb age of ca.1.85Ga, which represents its intrusion age. The Quanqitang pluton has high SiO2 (72.6–74.4wt.%), K2O (5.09–5.56wt.%) and Na2O (3.02–3.36wt.%), and low Fe2O3 (2.56–3.19wt.%) and MgO (0.25–0.37wt.%). It is metaluminous (A/CNK=0.93–0.98) and belongs to the high-K calc-alkaline series. On the chondrite-normalized REE diagram, all the samples invariably show a relatively enrichment in light rare earth elements (LREEs) with high (La/Yb)N ratios (10.6–21.7) and strong negative Eu anomalies. Their primitive-mantle normalized spidergrams display negative Ba, Nb, Ta, Sr, P, Eu and Ti anomalies. The calculated zirconium saturation temperatures range from 802 to 861°C with an average of 845°C. Zircons from the granites have εHf(t) values ranging from −17.6 to −20.9, corresponding to two-stage Hf modal ages of 3.6 to 3.8Ga. Based on the geochemical features, it is inferred that the granites were generated by the dehydration melting of Archean tonalitic gneisses with a plagioclase-rich residual assemblage. The granites chemically belong to the A2-type granites, and have an intrusion age younger than the possible ca. 2.0Ga collisional event in the Yangtze Block. This suggests that they formed in a post-collisional tectonic setting, and thus a tectonic regime switch from collision to extension might have occurred in the Yangtze Block before ca. 1.85Ga. The occurrence of the A2-type granite indicates that the Kongling microcontinental block became a stabilized craton at ca. 1.85Ga.

Late Neoproterozoic volcano-sedimentary successions of Wadi Rufaiyil, southern Sinai, Egypt: A case of transition from late- to post-collisional magmatism

The Neoproterozoic Wadi Rufaiyil volcano-sedimentary successions are exposed in southern Sinai (Egypt), at the northernmost segment of the Arabian–Nubian Shield (ANS). Two eruption phases have been recognized within these successions; both of them are intercalated with the Hammamat Clastics. The lower unit is composed predominantly of andesite to dacite and less commonly tuffs, while the upper one comprised mainly rhyolite with subordinate dacite–rhyodacite and their pyroclastics. The lower Hammamat Clastics are intermediate in compositions, contrary to the upper ones which are acidic and more mature. Geochemically, the volcanic rocks are mostly high-K calc-alkaline, corresponding to andesite through dacite–rhyodacite and rhyolite. Evolved parts of the younger phase (i.e., rhyolite) have transitional character to alkaline A-type magma, related most likely to their high fractionated nature rather than a switch in the tectonic regime. REE patterns are characterized by fractionated LREE [(La/Sm) n = 2.50–3.38] and nearly flat HREE [(Gd/Lu) n = 1.16–1.62], where the most evolved variants display prominent negative Eu anomalies (Eu/Eu * = 0.04–0.46). Dokhan Volcanics and associated Hammamat Clastics from Sinai and the Egyptian Eastern Desert (ED) share these geochemical characteristics. The Wadi Rufaiyil lavas display geochemical characteristics of both pre-collisional arc-type and post-collisional within-plate environments, suggesting eruption in a transition from late- to post-collisional tectonic setting. The integrated data point to generation by partial melting of mafic lower crust and/or upper mantle source to produce andesitic–dacitic (tonalite) magma with subsequent extensive fractional crystallization. The extrusion of the Wadi Rufaiyil volcanics was likely associated with extensive denudation of the pre-630 Ma orogenic edifice as well as the 630–600 Ma late-collisional products. Such a scenario implies delamination of thick lithosphere root during late- to post-collisional stage, facilitating the upwelling of hot asthenopsheric material and surface uplifting of northern ANS. This may have been the trigger to transition into the widespread post-collisional alkaline A-type magmatism at ∼600 Ma.

오대산 지역에 나타나는 맨거라이트와 반려암의 특징과 트라이아스기 한반도 지체구조 해석에 대한 의미

경기육괴 동부에 위치하는 오대산 지역에서는 맨거라이트와 반려암으로 구성된 화성암체가 원생대 초기에 형성된 혼성편마암을 관입하고 있다. 맨거라이트는 사방휘석, 단사휘석, 각섬석, 흑운모, 사장석, 퍼어사이틱 K-장석, 석영으로 이루어져 있으며 반려암의 광물군은 맨거라이트와 유사하나 반려암내에서는 각섬석이 사방휘석 주변에 적은 양으로 나타나며 퍼어사이틱 K-장석이 나타나지 않는다. 맨거라이트내에 반려암이 포획암 형태나 불규칙한 형태로 나타나며 두 암석의 경계가 불분명하다. 반려암질 포획암내에는 맨거라이트에서 볼 수 있는 퍼어사이틱 K-장석을 포함한 우백질부가 렌즈상으로 포함되어 있다. 이러한 것들은 두 개의 화성암이 액체상태에서 서로 혼합되었음을 지시한다. SHRIMP 저어콘 연대 측정결과 맨거라이트와 반려암으후부터 각각 <TEX>$234{\pm}1.2$</TEX> Ma와 <TEX>$231{\pm}1.3$</TEX> Ma의 트라이아스기 중기에 해당하는 연령을 얻었다. 이 연령은 홍성(226~233 Ma)과 양평 (227~231 Ma)지역의 트라이아스기 대륙충돌 후 화성암들의 연령과 유사하다. 맨거라이트와 반려암은 고함량 Ba-Sr 화성암(high Ba-Sr granite)이고 쇼쇼나이틱(shoshonitic) 하며, 대륙충돌 후 판 내부 환경에서 만들어졌다. 한편, 이 암석들은 대부분 경희토류와 친석원소가 부화되어 있으며 Nb-Ta-P-Ti 부(-) 이상을 보이는 섭입대 화성암의 특정도 보여준다. 위의 지화학적 특징들은 오대산 맨거라이트와 반려암은 대륙충돌 이전에 있었던 섭입시기에 지각물질에 의해 부화된 맨틀이 대륙충돌 후 분리된 대륙판과 해양판 사이 공간으로 유입된 연약권의 열에 의해 부분용융이 되면서 만들어졌음을 지시한다 오대산 지역의 맨거라이트와 반려암을 포함한 경기육괴와 임진강대 북부에 나타나는 약 230Ma의 대륙충돌 후 화성암의 분포는 이 시기에 일어난 한반도내 북중국판과 남중국판 충돌의 경계가 홍성 지역을 지나 양평-오대산지역과 옥천변성대 사이 지역으로 연결될 것임을 강하게 시사한다. The igneous complex consisting of mangerite and gabbro in the Odaesan area, the eastem part of the Gyeonggi Massif, South Korea, intruded early Paleo-proterozoic migmatitic gneiss. The mangerite is composed of orthopyroxene, clinopyroxene, amphibole, biotite, plagioclase, pethitic K-feldspar, quartz. The gabbro has similar mineral assemblage but gabbro has minor amounts of amphibole and no perthitic K-feldspar. The gabbro occurs as enclave and irregular shaped body within the mangerite, and the boundary between the mangerite and gabbro is irregular. Leucocratic lenses with perthitic K-feldspar are included in the gabbro enclaves. These textures represent mixing of two different magmas in liquid state. SHRIMP U-Pb zircon age dating gave <TEX>$234{\pm}1.2$</TEX> Ma and <TEX>$231{\pm}1.3$</TEX> Ma for mangerite and gabbro, respectively. These ages are similar with the intrusion ages of post collision granitoids in the Hongseong (226~233 Ma) and Yangpyeong (227~231 Ma) areas in the Gyeonggi Massif. The mangerite and gabbro are high Ba-Sr granites, shoshonitic and formed in post collision tectonic setting. These rocks also show the characters of subduction-related igneous rock such as enrichment in LREE, LILE and negative Nb-Ta-P-Ti anomalies. These data represent that the mangerite and gabbro formed in the post collision tectonic setting by the partial melting of an enriched lithospheric mantle during subduction which occurred before collision. The heat for the partial melting was supplied by asthenospheric upwelling through the gab between continental and oceanic slabs formed by slab break-off after continental collision. The distribution of post-collisional igneous rocks (ca. 230 Ma) in the Gyeonggi Massif including Odaesan mangerite and gabbro strongly suggests that the tectonic boundary between the North and South China blocks in Korean peninsula passes the Hongseong area and futher exteneds into the area between the Yangpyeong-Odaesan line and Ogcheon metamorphic belt.

Zircon SHRIMP U-Pb geochronology, geochemistry and petrogenesis of the upper Eocene Shuangmaidi peraluminous granite in Baoshan Block, Western Yunnan Terrain, southwestern China

The Baoshan Block is tectonically located in the middle segment of the Sibumasu plate. Granitic magmatism within the Baoshan Block has been considered weakly active due mainly to very limited exposures during the Himalaya orogenic episode. The geochronological study on the buried Shuangmaidi granite has confirmed the existence of the Cenozoic granitoids in the Baoshan Block. The present study indicates that: (1) It is medium- to coarse-grained two mica phyric granite, characterized by high SiO2 (73.55%–77.16%) and low CaO (0.34%–1.38%) contents, with a total alkalis (K2O+Na2O) of 5.22%–8.03%, K2O/Na2O ratios of 0.24–1.79, and total rare earth elements (ΣREE) of the granite between 85 and 125 ppb. All samples are enriched in light REE and exhibit medium negative Eu anomalies; and they show pronounced negative anomalies in Ba, Sr, Ti, and Nb but significant positive anomalies in K, Rb, U, Th, and Pb on mantle-normalized trace element patterns, indicating typically peraluminous to strongly peraluminous S-type granite. (2) The zircon SHRIMP U-Pb ages of the granite are 36.27±0.48 Ma for the samples from ZK7-1 and 35.78±0.49 Ma for those from ZK0-1, respectively. The similar zircon ages from these two drill cores may suggest that the granite samples come from the same buried pluton. (3) 206Pb/204Pb values of the granite vary from 20.115 to 25.359, 207Pb/204Pb from 15.776 to 16.160, and 208Pb/204Pb from 39.236 to 41.285, showing the characteristics of radioactive lead anomaly of the upper crust. The (87Sr/86Sr)i values calculated on the average age of the two-mica orthoclase granite (36 Ma) range from 0.72524 to 0.77503 and ɛNd(t) values vary from −10.9 to −11.7. These data, along with the depleted-mantle Nd modal ages of 1.73–1.80 Ga, imply that the granites might have formed from partial melting of the Precambrian crystal basements. (4) On the Hf-Rb-Ta diagram, almost all the samples fall within the field of post-collision tectonic setting. The CaO/Na2O and Al2O3/TiO2 ratios suggest that the granitic magma may have formed from partial melting of clay-rich crustal materials with a possible melting temperature of about 900°C and a possible crystallization temperature of 775–795°C. (5) During the post-collision of the Himalaya orogen, with the southeastward extrusion of the Indochina continent resulting from the continuous northward indentation of the India continent into the Asia, the Gaoligong Fault, as the western boundary of the Indochina continent, moved in the dextral strike-slip on a large scale to trigger partial melting of the thickened crust, and the peraluminous granitic magma from which the Shuangmaidi two-mica orthoclase granite derived was formed.

Pyrrhotite Re–Os and SHRIMP zircon U–Pb dating of the Hongqiling Ni–Cu sulfide deposits in Northeast China

The Hongqiling (HQL) magmatic Ni–Cu sulfide deposits (Jilin Province, NE China) are located at the southern margin of the eastern Xing'an–Mongolian Orogenic Belt (XMOB) of the eastern Central Asian orogenic belt (CAOB), situated between the Siberian Craton (SC) and the North China Craton (NCC). The HQL ore-bearing mafic–ultramafic intrusions intrude into the metamorphic rocks of the lowermost Huangyingtun Formation of the Hulan Group (HLG), whose lithology is herein identified as a hornblende–zoisite gneiss. SHRIMP zircon U–Pb dating for the HLG, country rock of the HQL deposits, indicated a maximum deposition age of 272.2 ± 4.3 Ma (95% confidence level, MSWD = 2.6, n = 14). Six pyrrhotite samples separated from massive Ni–Cu sulfide ores of the Fujia (No. 7) deposit yielded a Re–Os isotopic isochron age of 208 ± 21 Ma (95% confidence level, MSWD = 2.4, n = 6), indicating that the ore-formation age was Late Triassic. Re–Os isotope analyses showed an initial 187Os/ 188Os ratio of 0.315 ± 0.050. The γ Os values ranged from + 137 to + 161 with an average of + 151, indicating that its ore-forming materials were mainly derived from mantle with possibly < 30% crustal Os contamination. Large scale magmatic Ni–Cu mineralization in eastern Jilin occurred in post-collisional tectonic setting in the Late Triassic. Our new results suggest that the ages of the Ni–Cu sulfide deposits in the CAOB within China tended to become younger from west to east, as manifested by the Late Caledonian (~ 440 Ma), through the Late Hercynian (300–265 Ma) to the Late Indosinian (225–200 Ma). Such variation could reflect the gradual closure and post-collisional orogeny between the SC and the NCC from west to east.

Geochronological and geochemical constrains on petrogenesis of the Huangyangshan A-type granite from the East Junggar, Xinjiang, NW China

The Huangyangshan pluton occurs in the Kalamaili region which is situated in the central part of the Central Asian Orogenic Belt, East Junggar, Xinjiang (NW China). The granitoid rocks are composed of medium-grained biotite (richterite, arfvedsonite) alkali-feldspar granite, fine grained arfvedsonite alkali-feldspar granite and microgranular enclaves. The granites have a pronounced A-type affinity: they are metaluminous to weakly peraluminous and calc-alkaline to alkaline in composition with high concentrations of Na 2O + K 2O varying from 8.4 to 9.2 wt.%, high FeOt/MgO and 10,000 Ga/Al ratios, low abundances of CaO, MgO and TiO 2, enrichment in some LILEs (such as Rb and Th) and HFSEs (such as Zr, Y and REEs except Eu), depletion in Sr and Ba. Moreover, they display characteristic tetrad REE patterns and non-CHARAC trace element behavior, which is well demonstrated in highly differentiated rocks with strong hydrothermal interaction. The U–Pb zircon LA-ICP-MS ages of the host rocks and enclaves are 311 ± 5 Ma and 300 ± 6 Ma, respectively. The similar of these two ages suggests that host rocks and enclaves formed at a same time. Furthermore, the time span closely corresponds to known ages of post-collisional A-type granitoids of the Junggar terrane. Geochemical, geochronological and isotopic data ( ε Nd( T) in the range +5.2 to +6.6 and I Sr mostly in the range 0.7031–0.7041) suggest that the Huangyangshan intrusions, and the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas in the Late Carboniferous post-collisional tectonic setting (A 2 type granite). The magma for the Huangyangshan granites was derived by partial melting of an enriched subcontinental lithospheric mantle (SCLM) that was modified by slab-derived components from an earlier subduction event, this melting resulted from heat supplied from the asthenosphere through an opening created during the break-off of an oceanic slab. This further proves the important contribution of the Late Paleozoic granitic magmatism in terms of vertical crustal growth in northern Xinjiang.