TDM Values Research Articles

Age, clinopyroxene geochemistry and petrogenesis of post-collisional magmatic rocks in the Jonob-e-Sechangi area, Lut block, eastern Iran

The Lut-Sistan region, eastern Iran has an extensive record of Eocene-Oligocene magmatism the origin of which is not fully understood. In this study, we analyze a set of volcanic rocks in the Jonob-e-Sechangi area of the Lut block. U-Pb zircon analyses demonstrate that magmatism can be divided into two age groups. Group 1 formed at ∼45 Ma and involved different felsic (calc-alkaline rhyolitic to dacitic) and intermediate (high-K calc-alkaline andesitic) rocks. All samples from Group 1 display nearly identical initial 87Sr/86Sr values (87Sr/86Sri = 0.7045-0.7056). However, the felsic rocks show higher ԐNdt (+2.21 to +2.73) and lower TDM (0.51-0.61 Ga). In contrast, intermediate rocks have ԐNdt values of +1.27 to +2.23 and TDM values between 0.63 and 0.74 Ga. Additional geochemical variations suggest that the felsic and intermediate rocks of Group 1 are not co-genetic. The felsic extrusive rocks in the Jonob-e-Sechangi area likely formed from the partial melting of the amphibolitic arc crust. In contrast, the high-K calc-alkaline andesitic rocks of Group 1 may have originated from low-degree partial melting of a spinel-peridotite mantle source.Group 2 formed basaltic andesite to andesitic rocks at37-40 Ma, showing high-K calc-alkaline to shoshonitic compositions, relatively high 87Sr/86Sri (0.7047- 0.7076) and relatively low ԐNdt (0.48 to-5.86). These geochemical features require magma derivation from a mantle source that is not only elementally but also isotopically enriched, followed by variable fractionation and crustal contamination. The enriched mantle source was most likely resided in the lithosphere and formed by metasomatism by continental crust-derived materials. Clinopyroxene trace elements compositions display marked variations between different magmatic rocks. Clinopyroxene in dacitic samples of Group 1 shows relatively high contents of Sr, Rb, and Ba whereas that in Group 2 rocks has relatively high contents of Sc, V, Ga, Nb, Zr, Hf, Y and rare earth elements (REE). The findings of this study show that the intricate interactions between the lithosphere and asthenosphere, stemming from post-collisional delamination processes following the closure of the Sistan Ocean and the collision of the Lut-Afghan blocks, led to differing levels of partial melting in the region's heterogeneous metasomatized mantle. This phenomenon explains the diverse range of volcanic rocks found not just in the Jonob-e-Sechangi area but also in other regions of the Lut Block.

Variability in the sources of North Gondwana Cadomian basins tracked by Nd isotopic systematics (Iberian Massif)

The Cadomian Orogeny encompassed the opening and closure of oceanic domains and associated sedimentary basins in the northern margin of Gondwana from Ediacaran to Early Cambrian time. In the Iberian Massif, these Cadomian basins are included in autochthonous and allochthonous (far-travelled) terranes of the Variscan Orogen. A compilation of Nd isotope information of Ediacaran-Lower Cambrian siliciclastic series supports previous proposal for variability in the sources along the North Gondwanan margin that continued during the Early Paleozoic. Older TDM model ages ranging from 1361 to 2357 Ma of the Variscan allochthonous Ediacaran-Lower Cambrian siliciclastic series indicate proximity to Archean and Paleoproterozoic old crustal sources of the West African Craton and represent deposition on a western Cadomian basin. In turn, the autochthonous Ediacaran-Lower Cambrian siliciclastic series show relatively younger TDM values ranging from 1179 to 2114 Ma, suggesting derivation from more juvenile magmatic rocks that are well represented further east. The Ediacaran-Lower Cambrian siliciclastic series of the autochthonous terranes formed in an eastern Cadomian basin located near the Sahara Metacraton, the Trans-Saharan Orogen and the Tuareg and Arabian-Nubian shields.

A complex history of extension, subduction and collision in west Gondwana: Clues from the Riacho do Pontal orogen, Borborema Province (NE Brazil)

The geodynamic understanding of the Riacho do Pontal Orogen, in the Borborema Province, NE-Brazil, has progressed substantially in the last decade, mainly from geochemical and isotopic studies. However, the role of the Neoproterozoic magmatism has not totally been unraveled and has left some crucial questions unanswered. In order to contribute to this debate, we present petrographic, geochemical and isotopic (U–Pb, Sm–Nd and Sr–Sr) data obtained for a set of granitoids and metavolcanic rocks from the Internal and Central domains of the Riacho do Pontal Orogen. The Neoproterozoic granitoids comprise a major alkaline pluton of the Serra da Aldeia suite; two syenitic plutons – Nova Olinda and Caboclo –, and high-K, sub-alkaline granitoids from the Betânia granite. The alkaline pluton from the Serra da Aldeia suite yielded a zircon U–Pb age of 578 ± 5 Ma, while the Nova Olinda and Caboclo syenites yielded ages of 613 ± 2 Ma and 620 ± 3 Ma, respectively. The Betânia granite, displaying a volcanic-arc geochemical signature, yielded the age of 627 ± 4 Ma. Tonian ages were also obtained between 956 ± 8 Ma and 965 ± 3 Ma for three unclassified orthogneisses from the Internal Domain of the Orogen. A sample of metarhyolite from the Paleoproterozoic basement yielded an age of 1631 ± 21 Ma. The isotopic data for the Nova Olinda and Caboclo syenites revealed εNd(620 Ma) values between −7.72 and −8.45 and TDM values from 1.76 to 1.97.87Sr/86Sr ratios of 0.71594 ± 2 and 0.74432 ± 1 suggest mixing of crustal and mantle materials during their evolution. In contrast, the Betânia granite presented a ratio of 0.70669 ± 1, reinforcing the correlation with mantle sources. The integrated analysis of the data indicate that the Betânia granite is part of an Ediacaran magmatic-arc system, with the Nova Olinda and Caboclo syenites characterized as products of the late-orogenic magmatism, while the alkaline rocks of the Serra da Aldeia suite represent the final of post-orogenic stages of one of the multiple collisions of the West Gondwana.

Isotopic compositions and geological significance of sediments from the Heihe River, North Qilian Orogen, NW China

Strontium (Sr), neodymium (Nd), and hafnium (Hf) isotopic analyses of different size-fractions of sediments collected from the Heihe River in the North Qilian Orogen (NQO) were carried out to trace the sediment sources and to determine the relationships between the Sr–Nd–Hf isotopic behaviors, and the grain-size and hydraulic sorting effects during fluvial transport. Our results demonstrate that the sand and suspended load samples collected from the same site have different Nd isotopic compositions, while their 87Sr/86Sr ratios are only slightly different. These features indicate that contributions to the sediments from different sources with different grain sizes vary greatly. Coarse-grained sand may more intuitively reflect the variations in local sources than the suspended load. The suspended load samples are distributed along the Clay Array on the ԐHf vs. ԐNd diagram due to zircon sorting. A similar NdHf decoupling phenomenon is widespread in the global oceans and large river systems, indicating that the NdHf isotopic behavior depends on the hydrodynamic sorting of minerals during fluvial transport. Moreover, the crustal accretion of the NQO from the depleted mantle occurred in the Proterozoic based on the constraints provided by the TDM values of the river sediments. The Nd isotopic compositional characteristics of the river sediments indicate that the NQO has an affinity with the Yangtze Craton. The determination of the basement tectonic affinity of the NQO significantly contributes to our understanding of the Neoproterozoic evolution of the Gondwana continental margin.

A new record of continental arc magmatism in the Ceará Central Domain, Borborema Province (NE Brazil): evidence from the Pacatuba-Maranguape Complex

The amalgamation of continental masses during the formation of West Gondwana at the end of the Neoproterozoic (ca. 0.6 Ga) resulted in the closure of oceans and associated generation of magmatic arcs. To better understand episodes of high magma production, compositional and isotopic evolution of arc magmatism in the western active margin of Gondwana, this work presents new U-Pb zircon ages, lithogeochemistry, whole-rock Nd and in situ zircon Hf isotopes from plutonic and metaplutonic rocks of a dismembered arc-related unit (Pacatuba-Maranguape Complex) from the Ceará Central Domain, Borborema Province (NE Brazil). The Pacatuba-Maranguape Complex is exposed in the northeastern portion of the Ceará Central Domain and comprises pre- to late-tectonic granitoids bordered by migmatitic-gneisses that have experienced variable partial melting and deformation. Zircon U-Pb analyses yielded concordant ages of 675 Ma, 655–640 Ma, 630–625 Ma and 610 Ma, with inherited grains of 880–700 Ma, 700–650 Ma and 2200–2000 Ma. Geochemically, the granitoids are medium- to high-K calc-alkaline, metaluminous to slightly peraluminous, magnesian and calc-alkalic to alkali-calcic. Lu-Hf and Sm-Nd model ages provided TDM (Hf) model ages between 920 Ma and 1470 Ma with ɛHf(t) values of + 12.75 to −5.44, and TDM (Nd) values between 950 Ma and 1470 Ma with ɛNd(t) values between −1.06 and + 4.35. These data indicate that these granitoids were generated from the mixture of juvenile magmas and older crustal components on an active continental margin setting. Petrogenetic and geochronological constraints indicate a synchronous evolution with the Santa Quitéria Magmatic Arc, exposed approximately 100 km to the west. The compilation of geochronological and geochemical data from the Pacatuba-Maranguape Complex and the Santa Quitéria Arc suggests that arc magmatism developed mainly as a result of a magmatic flare-up between 660 and 620 Ma during the subduction of the Goiás-Pharusian oceanic crust in the central portion of West Gondwana.

Lithostratigraphy of the Mesoproterozoic Donkieboud Granodiorite (Komsberg Suite), South Africa and Namibia

Abstract The Donkieboud Granodiorite pluton forms an extensive intrusion across the border region between South Africa and southeast Namibia. The mesocratic grey, weakly to moderately K-feldspar porphyritic biotite ± hornblende ± orthopyroxene granodiorite represents the most extensive member of the late- to post-tectonic Komsberg Suite (~1 125 to 1 105 Ma) which intruded as sheet-like bodies into the older high grade paragneisses and orthogneisses (~1 230 to 1 140 Ma) of the Kakamas Domain of the Mesoproterozoic Namaqua-Natal Province. The Donkieboud Granodiorite comprises three main textural variations namely:a porphyritic to weakly porphyritic, relatively undeformed rock with randomly orientated ovoid and twinned feldspar phenocrysts;a weakly- to well-foliated gneiss with between 3 to 10% feldspar phenocrysts set in a medium-grained matrix anda patchy metamorphic charnockite variety. Large inclusions of the strongly foliated Twakputs (~1 210 Ma) and the Witwater (~1 140 Ma) garnetiferous granite gneisses occur within the Donkieboud Granodiorite and mafic xenoliths are common. The Donkieboud Granodiorite is variably deformed ranging from unfoliated to being gneissic. The foliation developed during its intrusion into an existing but waning regional stress field with the strain increasing towards the contacts with the surrounding country rocks. Subsequent km-scale open folding resulted in the reorientation of the gneissic foliation and locally, intense reworking of the fabrics along the margins of the folds. In places, the Donkieboud unit is crosscut by discrete mylonitic shears with a west to northwest trend. U-Pb zircon dating of the Donkieboud Granodiorite samples yielded concordia ages of between 1 118 and 1 107 Ma. Overall the Donkieboud Granodiorite has an intermediate to felsic composition (mean SiO2: 63.9 ± 2.2 wt.%) and is strongly metaluminous. This, together with its biotite-hornblende ± orthopyroxene mineral assemblage and the abundance of mafic xenoliths, suggests it is an I-type granitoid, with the source magma produced by partial melting of older igneous rocks that had not undergone any significant amount of chemical weathering. The εNd values of -1.15 and -0.11 and TDM values of 1 615 and 1 505 Ma are typical of the Komsberg Suite and indicate a significant contribution of older crustal material to the magma of the Donkieboud pluton.

Early Paleozoic subduction in the Indochina interior: Revealed by Ordo-Silurian mafic-intermediate igneous rocks in South Laos

The early Paleozoic tectonic nature and subsequent orogenic process remain poorly known in the Indochina interior. This study introduces the general geology of South Laos and presents a set of new zircon UPb and HfO isotopic analyses, and whole-rock elemental and Sr-Nd-Pb isotopic data for the mafic-intermediate igneous rocks in South Laos. The representative samples from the previously-mapped Ordo-Silurian strata in the southern Truong Son zone give the formation ages of 434–438 Ma. Five samples from the Tam Ky-Phuoc Son tectonic zone yield zircon UPb ages of 447–485 Ma. The corresponding zircon εHf(t), δ18O and TDM values are in range of +1.6~ −6.5, 6.1–8.6‰, and 1.02–1.79 Ga, respectively. Forty-five mafic-intermediate igneous rocks in South Laos with mg-number = 42–69 have SiO2 = 53.04–61.66 wt%, Al2O3 = 12.13–20.92 wt% and MgO = 2.73–9.55 wt%, and are characterized by enrichment in LILEs and depletion in HFSEs with NbTa negative anomalies. Their (87Sr/86Sr)i ratios range from 0.7044 to 0.7109 and εNd(t) values from −6.2 to −2.6, with (206Pb/204Pb)i = 18.08–18.68, (207Pb/204Pb)i = 15.50–15.77, and (208Pb/204Pb)i = 38.04–38.97. Ten gabbroic samples, with mg-number = 77–79, show similar incompatible elemental ratios and Sr-Nd-Pb-Hf-O isotopic compositions with the other mafic-intermediate igneous rocks, but have lower SiO2 and higher MgO, Cr, Ni and V contents, reflective of a primary mafic magma. Such characteristics suggest a newly-modified wedge source by recycled sediment-derived components. In combination with other geological observations in Central Vietnam, we propose a northerly-younging early Paleozoic igneous event in response to the on-growing accretionary orogenesis in the Indochina interior. The southward consumption of the early Paleozoic Tam Ky-Phuoc Son Ocean in the Indochina interior continued until at least ~430 Ma and the assemblage of the Northern Indochina with the Kontum terrane likely terminated at the early Devonian.

Complex Neoarchean mantle metasomatism: Evidence from sanukitoid diorites-monzodiorites-granodiorites in the northeastern North China Craton

Mantle metasomatism is a major factor leading to diverse arc magmatism. Late Neoarchean sanukitoid diorites-quartz diorites-monzodiorites-granodiorites (DQMGs) are widespread in the North Liaoning Block, northeastern North China Craton, and were evidently emplaced into Neoarchean tonalite-trondhjemite-granodiorite (TTG) gneisses and metamorphic calc-alkaline volcanic rocks. Integrated with these slightly earlier arc-related TTGs and volcanic rocks, DQMG magmatism may preserve crucial signatures of complicated Neoarchean mantle metasomatism.These DQMGs show emplacement ages of ~2.56 to 2.53 Ga and wide ranges of SiO2 (51.34–68.74 wt%), K2O (1.67–4.56 wt%), MgO (1.48–6.68 wt%), Cr (29–334 ppm) and V (46–329 ppm) concentrations and high Mg# values of 45 to 65, with zircon ɛHf(t2) values from +0.0 to +6.9, suggesting that the DQMGs are typical Archean sanukitoids. According to geochemical characteristics and petrogenesis, these sanukitoid DQMGs are subdivided into Group #1 and Group #2. The Group #1 magma was derived from partial melting of a fluid-metasomatized mantle source altered further by adakitic melts, and the Group #2 magma from the mantle source was further metasomatized by subducted sediment melts. The relatively high K2O contents, K2O/Na2O, Nb/Zr ratios and various TDM(Hf) values of the sanukitoid DQMGs were derived from a lithospheric mantle source that was metasomatized by subducted fluids, slab- and sediment-derived melts. Therefore, the complex mantle metasomatism may be an essential reason for the appearance of a mass of K-rich granitoids with sanukitoid composition and the Neoarchean diversity of granitoid rocks.

Isotopic age constraints and geochemical results of disseminated ophiolitic assemblage from Neoproterozoic mélange, central Brazil

The Neoproterozoic Brasília belt, central Brazil, formed during the amalgamation of West Gondwana, and contains a magmatic arc and a large metasedimentary pile. An ophiolitic mélange is contained within one of the metasedimentary units from the pile, and includes bodies of metamafic and ultramafic assemblages in a metasedimentary rock matrix. One of these metamafic bodies encompasses a serpentinite body, which displays a well-developed metasomatic “black-wall” alteration zone at its contact. Samples of metamafic, serpentinite and black-wall rocks were collected, as well as two garnet-mica schists in contact with the metamafic assemblage. The metamafic assemblage is composed of epidote-amphibole schist, chemical analysis of which indicates that its protolith was a tholeiitic basalt with a MORB signature that may have been formed in a back-arc environment. U-Pb analyses indicate an age of crystallization of c. 800 Ma for the protolith of the epidote-amphibole schist. The black-wall is mostly composed of chlorite schist, with the exception of an albite-hornblende fels at the contact with the epidote-amphibole schist. The black-wall has a range of ages from c. 800 to 760 Ma. ƐHf values of selected zircon grains of the epidote-amphibole schist sample range from −21.67 to + 13.66, with TDM ages of 0.80–4.22 Ga, while the black-wall samples have highly depleted ƐHf values ranging from + 9.16 to + 23.98, with TDM model ages of 0.34–0.96 Ga. The studied garnet-mica schists have zircon population peaks of c. 790 to 890 Ma. ƐHf ranges from −14.87 to + 6.46 and TDM ages from 1.47 to 1.91 Ga. The epidote-amphibole schist, serpentinite and black-wall assemblages all have positive ƐNd values from + 4.95 to + 7.89, indicating a mantle signature. ƐNd values for the mica schists are −8.31 and −8.16, and their TDM values are 1.83 and 2.36 Ga, which indicate continentally derived components. The results suggest that the ophiolitic component of the Araxá mélange formed in a back-arc basin environment, which formed at c. 800 Ma and lasted till c. 760 Ma, while the studied schists probably represent sediments deposited in the newly formed back-arc basin.

New geochronological and isotope data for the Las Chacras – Potrerillos and Renca batholiths: A contribution to the Middle-Upper Devonian magmatism in the pre-Andean foreland (Sierras Pampeanas, Argentina), SW Gondwana

The Las Chacras-Potrerillos together with the Renca batholith (Sierras de San Luis) are the largest Devonian igneous bodies in the Sierras Pampeanas after the Achala batholith (Sierra de Córdoba), all emplaced in the Devonian foreland region. The Achala batholith has U–Pb zircon ages (using SHRIMP or LA-ICP-MS methodology, ranging from 366 to 379 Ma), while comparable ages for the Las Chacras-Potrerillos batholith remain absent (a single U–Pb conventional zircon age is available for this batholith), and one weighted mean age (U–Pb zircon SHRIMP data) is available for Renca batholith. U–Pb zircon LA-MC-ICP-MS data sets from a monzogranite sample of the biotite-amphibole porphyritic granite unit (CHA-101), the largest granitic unit of the Las Chacras-Potrerillos batholith, yielded three ages: 377 ± 3, 384 ± 2, and 393 ± 3 Ma. These ages (outside error limits), suggest the existence of a long-lived magmatic plumbing system, of around 15 Ma, with intrusion of younger batches into older crystal mushes. This interpretation leads us to assume a long period of heating in the source through the earliest Middle - early Upper Devonian ranging from 377 to 393 Ma. Based on previous studies of ascent and emplacement of granitic magmas, we propose that the majority of the zircon ages measured could be inherited from a deeper level of the magmatic system (i.e., antecrysts) and only some could be assigned to in-situ crystallization during the emplacement in middle-upper crust. Additionally, U–Pb zircon SHRIMP data sets from a monzogranite sample of the biotite-amphibole porphyritic granite unit (REN-103), the largest granitic unit of the Renca batholith, yielded two ages: 353 ± 4 Ma and 393 ± 3 Ma. The older age is equal to that obtained for the CHA-101 sample and confirms that the magmatism started in the earliest Middle Devonian. The younger age is comparable to previous ages determined in micas crystallized in intragranitic pegmatites as well as cooling ages from biotite hosted in granites of the Las Chacras-Potrerillos batholith, strongly suggesting a long-lasting cooling history of ca. 24 or 40 Ma (according to the crystallization age assumed, 377 or 393 Ma) or a reheating effect at around 350 Ma as was suggested in previous works. Recent Carboniferous crystallization ages determined in granites of the Sierras Pampeanas produced similar values (i.e., close to 350 Ma), and suggest a longer time of magmatic activity embracing the Middle-Late Devonian – Early Carboniferous (∼40 Ma), in the Devonian foreland (present-day Eastern Sierras Pampeanas). Nd and Sr isotopes data from CHA-101 and REN-103 samples (εNdt and 87Sr/86Srt ranging from −3.0 to −1.1 and from 0.706861 to 0.707275, respectively), are consistent with previous data reported for the studied granitic units and suggest a continental source with probable participation of subcontinental lithospheric mantle. TDM values (1.2 and 1.4 Ga) support the idea of an older Gondwana lithosphere source for the studied monzogranites.

Neoarchean sanukitoids and associated rocks from the Tengzhou-Pingyi intrusive complex, North China Craton: Insights into petrogenesis and crust-mantle interactions

Quartz monzodiorites, granodiorites and monzogranites constitute the dominant lithological assemblage in the Neoarchean Tengzhou-Pingyi intrusive complex (TPIC) in the southwestern part of western Shandong Province (WSP) in the eastern part of the North China Craton (NCC), and mafic magmatic enclaves (MMEs) are widely developed only in granodiorites of the TPIC. LA–ICP–MS zircon U-Pb isotopic dating reveals that the TPIC was emplaced at ~2.54–2.52 Ga. The ~2.54 Ga monzogranites display geochemical affinities with high-K granites, and they were likely derived from the partial melting of metamorphic greywackes at lower crustal levels. The ~2.54–2.52 Ga quartz monzodiorites and granodiorites show significant geochemical similarities to the Archean sanukitoids of the western Karelian Province of Finland with higher Mg# (43–57) values, Cr (24–88 ppm), Sr (547–1154 ppm), and Ba (662–1961 ppm) contents and K2O/Na2O (0.42–1.00) ratios. Therefore, we define the quartz monzodiorites and granodiorites as Neoarchean sanukitoids. Based on their lithological assemblages and geochemical characteristics, these sanukitoids can be subdivided into sanukitoid quartz monzodiorites (SQMs) and porphyritic sanukitoid granodiorites (PSGs). The SQMs exhibit higher positive ɛHf(t2) values from +1.9 to +3.6 with TDM values of 2.70 to 2.77 Ga and are strongly enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), implying a mantle source that was enriched by either fluids or melts. The PSGs have a wide range of ɛHf(t2) values from −3.4 to +3.8, suggesting that they were formed by crust-mantle magma mixing. This interpretation is also supported by the petrological textural and compositional disequilibrium of plagioclase phenocrysts from the PSGs. Moreover, the MMEs and their host PSGs have identical crystallization ages (~2.54 Ga), similar mineral chemistries and zircon Lu-Hf isotopic compositions, indicating that the MMEs are cumulates from the earlier host PSGs magma. Petrogenetic studies and zircon Lu-Hf isotopic features of these lithological assemblages indicate that the interval of ~2.55–2.52 Ga in the TPIC represents an important period of crustal growth and crust-mantle interactions. Considering the spatial-temporal relationships and the petrogenesis of the diverse lithological assemblages, we propose that the Neoarchean TPIC was most likely formed in an active continental margin setting.

Implications of 770 Ma Rhyolitic Tuffs, eastern South China Craton in constraining the tectonic setting of the Nanhua Basin

Mid-Neoproterozoic magmatic rocks from the southeastern part of the Nanhua Basin constrain the tectonic setting of the basin. Data from rhyolitic tuffs of the Louqian Formation that overlie the Cathaysia Block in southeastern South China indicate accumulation of the unit at ca. 770 Ma, and provide an upper age limit on collisional assembly of the Yangtze and Cathaysia blocks. The zircons within the tuffs display largely positive εHf(t) (−3.66 to +13.94) and juvenile TDM (Hf) values (1.74–0.90 Ga), which indicate involvement of Neoproterozoic to late Paleoproterozoic crustal materials in their generation. Geochemically, the tuffs are peraluminous and characterized by both A-type and arc affinities with high SiO2, Ga, accentuated negative Eu anomalies, strong depletion in high field strength elements and high zircon saturation temperatures (TZr), which are comparable to contemporaneous (800–750 Ma) felsic rocks from the northwestern of the Nanhua Basin. These characteristics suggest the Nanhua Basin lay inboard of a convergent plate margin arc. This arc is represented by 860–730 Ma magmatism along the western and northern margin of the South China Craton (Panxi-Hannan Belt), with the Nanhua Basin occupying an upper plate, back arc setting.

Recurrent intrusive episodes in the Paleozoic metasedimentary upper crust during the Early Carboniferous time: The Veladero granitoid stock and the peraluminous andesite

The Veladero hill is a well-exposed upper crustal block located between the basement of Sierra de Umango (Western Sierras Pampeanas), and the Devonian - Carboniferous sedimentary sequence of Precordillera, at western Argentina. The hill is formed by schists, metaluminous granitoids and a subalkaline peraluminous andesite studied in this work. The country rocks are schists with mineralogy typically developed during a thermal event (e.g., cordierite, andalusite, biotite). The magmatic assemblage of the peraluminous andesite consists of K-feldspar + plagioclase + quartz + biotite + cordierite, with zircon, monazite, and oxides as accessory minerals. One representative sample from this rock was analyzed and has contents of SiO2 = 61%, Fe2O3t + MgO = 9.03, Na2O + K2O = 6.6%, and aluminium saturation index = 1.5, consistent with the mineralogy. A U-Pb zircon Concordia age of 347 ± 4 Ma was acquired by LA-MC-ICP-MS from zircon hosted in the peraluminous andesite, which together with an age of 342 ± 2 Ma recently published for the metaluminous Veladero granitoid stock, indicate that these two ages overlap within error. Combined mineral assemblage and Al-in-hornblende geobarometric data from the Veladero granitoid stock reveal that the granitic magma passed through ∼10 km of continental crust before reaching its final emplacement level. Field evidence indicates that the Veladero granitoid stock was emplaced under dominantly brittle deformation mechanisms and that the peraluminous andesite magma was generated and subsequently intruded into a previously emplaced magma mush close to solidification, making space by the displacement of large blocks of the host granite. Documented mingling relationships between granite and peraluminous andesite also support emplacement while the granite remained partially crystallized so that the time interval between the two was relatively short, probably on the scale of hundreds of thousands of years. We propose that the peraluminous magma was generated during the ascent of the metaluminous Veladero granitoid stock magma and that the most of the zircon crystallized in high middle crust from the Veladero granitoid stock. These zircons were subsequently recycled and incorporated in the peraluminous andesite. Zircons in the Veladero granitoid stock and the peraluminous andesite have indistinguishable morphology and support this interpretation. In situ Hf isotope data were obtained from igneous zircons in the peraluminous andesite and reveal a dominantly continental source (average εHf,t = −8.0, excluding one just positive value). εHf,t and TDM values from zircon in the Veladero granitoid stock and hosted in the peraluminous andesite are indistinguishable, which is consistent with their original crystallization in the Veladero granitoid stock. TDM values mainly range from 1.5 to 1.9 Ga (average = 1.7 Ga) and reveal a continental Gondwana signature. Consistently, detrital zircon ages from schists in which the igneous rocks were emplaced indicate Ordovician depositional ages and original Gondwanan provenance. However, based on previous studies a Devonian depositional age cannot be ruled out.

Sr, Nd, and Hf Isotope Composition of Rocks of the Reft Gabbro–Diorite–Tonalite Complex (Eastern Slope of the Middle Urals): Petrological and Geological Implications

This paper reports Rb–Sr and Sm–Nd isotope data on the gabbro–diorite–tonalite rock association of the Reft massif (eastern margin of the Middle Urals) and Lu–Hf isotope data on zircon populations from these rocks. In terms of Nd and Hf isotope composition, the rocks of the studied association are subdivided into two distinctly different groups. The first group consists of gabbros and diorites, as well as plagioclase granites from thin dikes and veins cutting across the gabbros. In terms of 43Nd/144Nd i = 0.512518–0.512573 (eNd(T) = +8.6...+9.7) and 176Hf/177Hf i = 0.282961–0.283019 (eHf(T) = +15.9...+17.9), these rocks are practically identical to depleted mantle. Their Nd and Hf model ages show wide variations, but in general are close to their crystallization time. The second group is represented by tonalites and quartz diorites, which compose a large body occupying over half of the massif area. These rocks are characterized by the lower values of 143Nd/144Nd i = 0.512265–0.512388 (eNd(T) = +3.7...+6.0) and 176Hf/177Hf i = 0.282826–0.282870 (eHf(T) = +11.1...+12.7). The TDM values of the second group are much (two–three times) higher than their geological age (crystallization time), which indicates sufficiently long crustal residence time of their source. The initial 87Sr/86Sr in the rocks of both the groups varies from 0.70348 to 0.70495. This is likely explained by the different saturation of melts with fluid enriched in radiogenic Sr. The source of this fluid could be seawater that was buried in a subduction zone with oceanic sediments and released during slab dehydration. Obtained data make it possible to conclude that the formation of the studied gabbro–diorite–tonalite association is a result of spatially and temporally close magma formation processes in the crust and mantle, with insignificant contribution of differentiation of mantle basite magma.

Petrological, geochemical, isotopic, and geochronological constraints for the Late Devonian–Early Carboniferous magmatism in SW Gondwana (27–32°LS): an example of geodynamic switching

We report a study integrating 13 new U–Pb LA-MC-ICP-MS zircon ages and Hf-isotope data from dated magmatic zircons together with complete petrological and whole-rock geochemistry data for the dated granitic rocks. Sample selection was strongly based on knowledge reported in previous investigations. Latest Devonian–Early Carboniferous granite samples were collected along a transect of ~ 900 km, from the inner continental region (present-day Eastern Sierras Pampeanas) to the magmatic arc (now Western Sierras Pampeanas and Frontal Cordillera). Based on these data together with ca. 100 published whole-rock geochemical analyses we conclude that Late Devonian–Early Carboniferous magmatism at this latitude represents continuous activity (ranging from 322 to 379 Ma) on the pre-Andean margin of SW Gondwana, although important whole-rock and isotopic compositional variations occurred through time and space. Combined whole-rock chemistry and isotope data reveal that peraluminous A-type magmatism started in the intracontinental region during the Late Devonian, with subsequent development of synchronous Carboniferous peraluminous and metaluminous A-type magmatism in the retro-arc region and calc-alkaline magmatism in the western paleomargin. We envisage that magmatic evolution was mainly controlled by episodic fluctuations in the angle of subduction of the oceanic plate (between flat-slab and normal subduction), supporting a geodynamic switching model. Subduction fluctuations were relatively fast (ca. 7 Ma) during the Late Devonian and Early Carboniferous, and the complete magmatic switch-off and switch-on process lasted for ~ 57 Ma. Hf TDM values of zircon (igneous and inherited) from some Carboniferous peraluminous A-type granites in the retro-arc suggest that Gondwana continental lithosphere formed during previous orogenies was partly the source of the Devonian–Carboniferous granitic magmas, thus precluding the generation of the parental magmas from exotic terranes.

K-rich granitoid magmatism at the Archean–Proterozoic transition in southern Jilin: Insights into the Neoarchean crustal evolution of the northeastern part of the North China Craton

Massive Neoarchean to early Paleoproterozoic K-rich granitoid rocks are widely distributed in the southern Jilin metamorphic basement terrane, which is located in the northeastern part of the North China Craton (NCC). Based on newly obtained petrological, geochemical and geochronological data, these K-rich granitoid rocks can be subdivided into: ~2.50Ga porphyritic monzogranites in the Jingyu–Tonghua area, and ~2.50–2.49Ga medium-grained and coarse-grained monzogranites and ~2.47Ga porphyritic quartz syenites in the Huadian–Jingyu area. The ~2.50Ga porphyritic monzogranites are characterized by rare earth element (REE) patterns with high (La/Yb)N and low (Gd/Yb)N ratios and weakly negative Eu anomalies, as well as zircon εHf(t2) values of +1.7 to +5.3 with TDM(Hf) values of 2748 to 2612Ma. These results suggest that the monzogranitic magma was produced under low-pressure conditions by partial melting of a heterogeneous crustal source, with residual plagioclase, hornblende, orthopyroxene, and clinopyroxene. The ~2.50–2.49Ga medium- to coarse-grained monzogranites show low MgO and CaO contents, Mg# values of 1–42 and zircon εHf(t2) values of −0.7 to +4.6, as well as TDM(Hf) values of 2847 to 2634Ma. These results indicate that these rocks were also generated from partial melting of pre-existing juvenile crustal materials that were enriched in potassium by either fluid alteration or surface processes at middle to lower crustal levels. The ~2.47Ga porphyritic quartz syenites have zircon εHf(t2) values of +2.8 to +5.6 and TDM(Hf) values of 2678 to 2571Ma; display the highest K2O concentrations of the rocks examined in this study; are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs); have low MgO contents and Mg# values; and display strongly differentiated chondrite-normalized REE patterns with no significant Eu anomalies. These results indicate that these rocks may have been produced by partial melting of juvenile mantle-derived basaltic rocks associated with recycled K-rich metasediments in the lower crust.Combined with previous studies on the southern Jilin metamorphic basement terrane, our data indicate that the ~2.50–2.47GaK-rich granitoid rocks are products of Neoarchean intracrustal recycling. The K-rich granitoid rocks are coeval with regional amphibolite- to local granulite-facies metamorphism, which were most likely triggered by the arc-continent collision between an intra-oceanic arc system along the northwestern margin of the NCC and the ancient continental margin in southern Jilin and by the post-collisional delamination of the thickened crust. These processes led to crustal differentiation and the final stabilization of the cratonic continental crust.

Chemical and Sr-Nd compositions and 40Ar/39Ar ages of NW-trending dolerite dikes of Burkina Faso: Evidence for a Mesoproterozoic magmatism in the West African Craton

The Paleoproterozoic basement of the northeastern part of the Leo-Man craton is intruded by generally NW-trending dikes. These regional scale dikes extend over 1000 km in Burkina Faso, Mali and Niger. We present chemical and Sr-Nd isotope compositions, as well as 40Ar/39Ar ages of these dikes with the following strikes N98°–N112°, and N114°–N124° in NE Burkina Faso. Field relationships show that the dikes are posterior to all other rock types dated between 2.26 Ga and 2.0 Ga. Chemical data indicate that the dikes are continental flood basalts and composed of low-Ti (TiO2 ≤ 2 wt.%) sub-alkaline basalts and andesites. They exhibit a minor negative Europium anomaly (0.86–0.99) and slightly fractionated REE patterns ((La/Yb)N = 2.5–9.1; YbN = 9.5–19.9). The ratios of Th/Ta (1.3–11.4) and Ce/Pb (5.2–58.5) suggest a varying crustal assimilation of the dike magmas during ascent in the continental crust for all studied samples. Calculated P-T conditions indicate that the magma reached temperatures of 1285 °C (calculated from olivine compositions) and pressures of 6.9 kbar (calculated for pyroxene minerals). Calculated initial 87Sr/86Sr (0.70040–0.70260) and ɛNd(t) = +2.1 to −3.5 at 1575 Ma, also point to a crustal contamination with the most primitive samples showing TDM values of 1946 Ma and 2154 Ma. The low values of La/Ba (<0.2) and Nb/La (<1.0), contrast with the low Th/Nb (<0.9), and suggest a lithospheric mantle or subduction-modified mantle as possible source for the dikes. Sr-Nd data, Mg# and Nb-Ta-Zr-Y-Th-Tb-Yb compositions further suggest that the most primitive samples were emplaced in a none orogenic setting and their magmas were subjected to variable crustal contaminations. Literature and the present whole rock 40Ar/39Ar age determinations show that the dikes were emplaced during a widespread Mesoproterozoic magmatism between 1.6 Ga and 1.2 Ga, and were affected by a thermal event causing the argon systematics resetting, best constrained by the date of sample KK1 (1236 ± 20 Ma, 40Ar/36Ar = 294 ± 13, MSWD = 2.2). Contemporaneous 1590–1570 Ma extensive magmatism is reported in other crustal blocks in Baltica (Sveconorw-Goth, svecofennian) NW Laurentia (Slave craton, Yukon), and Australia (Gawler craton), and together with the 1575 studied dikes, are related to the breakup of the supercontinent Nuna.

A source-depleted Early Jurassic granitic pluton from South China: Implication to the Mesozoic juvenile accretion of the South China crust

Source-depleted granites were rarely reported in South China. Hereby we identified such a granitic pluton, the Tiandong pluton, at Northeastern Guangdong province in Southeastern (SE) China. Whole-rock Sr-Nd and zircon Hf isotopes of the Tiandong granites both revealed obviously depleted source signatures, with initial isotopic values of initial 87Sr/86Sr=0.7032–0.7040, εNd(t)=1.1–1.5, and εHf(t)=6–13, respectively. Zircon U-Pb dating implied the granite was intruded in Early Jurassic (188Ma). The dominant minerals of the Tiandong granite consist of K-feldspar, plagioclase, quartz and biotite, with accessory mineral assemblage of apatite+zircon+magnetite. Based on the mineralogy and the depleted isotopic signature, the granites chemically show I-type affinity such as low Zr+Nb+Ce+Y (131.6 to 212.2), 104×Ga/Al (2.12–2.27), A/CNK values <1.1 (0.97–1.03), corundum molecule <1 (0–0.55) and extremely low P2O5 contents (0.05wt%). The one-stage and two-stage depleted mantle Nd model ages (TDM=0.89 to 0.84Ga, T2DM=0.88 to 0.85Ga) are consistent. TDM(Hf) values of 0.31–0.63Ga are also indistinguishable from T2DM(Hf) values of 0.35–0.75Ga. The Nd and Hf isotopic compositions confirm that the Tiandong granites are juvenile crustal accretion but decoupled Nd-Hf isotopic systems. The juvenile crust is likely to originate from a mixed source of the primary asthenospheric mantle and the subordinate EMII. Combined with early studies of adjacent rocks, we propose that the early Jurassic (~200–175Ma) magmatism as evidenced by the Tiandong granites might be driven by upwelling of asthenosphere and subsequent underplating of mafic melts in an intra-plate extensional setting as a response to far-field stress during early stage subduction of the paleo-pacific plate.

The Mesoarchean Tiejiashan-Gongchangling potassic granite in the Anshan-Benxi area, North China Craton: Origin by recycling of Paleo- to Eoarchean crust from U-Pb-Nd-Hf-O isotopic studies

Mesoarchean and older potassic granites are important indicators of recycling of ancient continental crust early in Earth's history. This study of integrated whole rock and zircon geochemistry and geochronology reports the age and identification of the source materials of the >200km2 Mesoarchean Tiejiashan-Gongchangling granite in the Anshan-Benxi area, North China Craton, the largest pre-Neoarchean granite domain in the craton. SHRIMP U-Pb zircon dating on 15 samples indicates the magmatic crystallization of the granites between 2.95 and 3.0Ga and reveals a superimposed tectonothermal event at ~2.91Ga. The granites are characterized by high SiO2 and K2O, low CaO, FeOt, MgO and TiO2 with peraluminuous features. They show large variations in (La/Yb)n and strong negative Eu and Ba anomalies and Nb, P and Ti depletions. Whole rock Nd and magmatic zircon Hf isotopic compositions show large variations, but with most having εNd(t) and εHf(t) values <0, with tDM(Nd) and tDM(Hf) values varying from 3.3 to 3.9Ga and 3.3 to 4.0Ga, respectively. Magmatic zircons without very strong lead loss (discordance ≤20%) have δ18O values of +3.14 to +8.39. 3.3–3.7Ga xenocrystic zircons occur in some samples. The granite formed as a result of recycling of Paleo- to Eoarchean continental material in an intracontinental environment, with little if any contribution from Mesoarchean mantle sources. The sources could be predominantly unaltered ancient gneisses, together with yet to be identified Paleo- to Eoarchean materials affected by early low temperature alteration (weathered rocks or clastic sediment).

Designing novel bioconjugates of hydroxyethyl cellulose and salicylates for potential pharmaceutical and pharmacological applications

This deals with fabrication of macromolecular prodrugs (MPDs) of salicylic acid (SA) and aspirin (ASP) based on a hydrophilic cellulose ether, hydroxyethyl cellulose (HEC). Degrees of substitution (DS) of SA and ASP per HEC repeating unit (HEC-RU) were achieved ranging from 0.60 to 2.18 and 0.53 to1.50, respectively. The amphiphilic HEC-SA conjugate 2 assembled into nanowire-like structures, while HEC-ASP conjugate 6 formed nanoparticles (diameter 300–00nm) at a water/DMSO interface. After oral administration in rabbit models, conjugates 2 and 6 showed plasma half-life of 6.96 and 7.01h with maximum plasma concentration (Cmax) of 15.27 and 23.01μg L−1, respectively, and each reached peak plasma concentration (tmax) at 4.0h. Immunomodulatory assays (interleukin 6 and tumor necrosis factor-α values) revealed that anti-inflammatory properties of SA and ASP were unaltered in conjugates. Swelling inhibition of 61 and 71% was observed for conjugates 2 and 6, respectively, in a carrageenan induced paw edema test. Cytotoxic profiling (MTT assay) showed that conjugates were safe for administration in the concentration range of 2–10mM up to 24h. Thermal analyses revealed that Tdm values of SA and ASP conjugates were increased by 99 and 154̊C, respectively, indicating extraordinary thermal stability imparted to drugs after MPD formation.