O–H–Sr–Nd isotope constraints on the origin of the Famatinian magmatic arc, NW Argentina

AbstractWe report a study of whole-rock O–H–Sr–Nd isotopes of Ordovician igneous and metamorphic rocks exposed at different crustal palaeodepths along c. 750 km in the Sierras Pampeanas, NW Argentina. The isotope compositions preserved in the intermediate rocks (mostly tonalite) (average δ18O = +8.7 ± 0.5‰, δD = −73 ± 14‰, 87Sr/86Srt = 0.7088 ± 0.0001 and εNdt = −4.5 ± 0.6) show no major difference from those of most of the mafic rocks (average δ18O = +8 ± 0.8‰, δD = −84 ± 18‰, 87Sr/86Srt = 0.7082 ± 0.0016 and εNdt = −4 ± 1.1), suggesting that most of their magmas acquired their crustal characteristics in the mantle. The estimate of assimilation of crustal material (δ18O = +12.2 ± 1.7‰, δD = −89 ± 21‰, 87Sr/86Srt = 0.7146 ± 0.0034 and εNdt = −6.9 ± 0.7) by the tonalite is in most samples within the range 10–20%. Felsic magmas that reached upper crustal levels had isotope values (δ18O = +9.9 ± 1.5‰, δD= −76 ± 5‰, 87Sr/86Srt = 0.7067 ± 0.0010, εNdt = −3.5 ± 1.4) suggesting that they were not derived by fractionation of the contaminated intermediate magmas, but evolved from different magma batches. Some rocks of the arc, both igneous (mostly gabbro and tonalite) and metamorphic, underwent restricted interaction with meteoric fluids. Reported values of δ18O of magmatic zircons from the Famatinian arc rocks (+6 to +9‰) are comparable to our δ18O whole-rock data, indicating that pervasive oxygen isotope exchange in the lower crust was not a major process after zircon crystallization.

Download Full-text

Lower Palaeozoic and Precambrian igneous rocks from eastern England, and their bearing on late Ordovician closure of the Tornquist Sea: constraints from U-Pb and Nd isotopes

Geological Magazine ◽

10.1017/s0016756800023190 ◽

1993 ◽

Vol 130 (6) ◽

pp. 835-846 ◽

Cited By ~ 80

Author(s):

S. R. Noble ◽

R. D. Tucker ◽

T. C. Pharaoh

Keyword(s):

Volcanic Rocks ◽

Igneous Rocks ◽

Calc Alkaline ◽

Nd Isotopes ◽

Nd Isotope ◽

Magmatic Arc ◽

The North ◽

Basement Rocks ◽

Continental Arc ◽

Lower Palaeozoic

AbstractThe U-Pb isotope ages and Nd isotope characteristics of asuite of igneous rocks from the basement of eastern England show that Ordovician calc-alkaline igneous rocks are tectonically interleaved with late Precambrian volcanic rocks distinct from Precambrian rocks exposed in southern Britain. New U-Pb ages for the North Creake tuff (zircon, 449±13 Ma), Moorby Microgranite (zircon, 457 ± 20 Ma), and the Nuneaton lamprophyre (zircon and baddeleyite, 442 ± 3 Ma) confirm the presence ofan Ordovician magmatic arc. Tectonically interleaved Precambrian volcanic rocks within this arc are verified by new U-Pb zircon ages for tuffs at Glinton (612 ± 21 Ma) and Orton (616 ± 6 Ma). Initial εNd values for these basement rocks range from +4 to - 6, consistent with generation of both c. 615 Ma and c. 450 Ma groups of rocksin continental arc settings. The U-Pb and Sm-Nd isotope data support arguments for an Ordovician fold/thrust belt extending from England to Belgium, and that the Ordovician calc-alkaline rocks formed in response to subductionof Tornquist Sea oceanic crust beneath Avalonia.

Download Full-text

Calc-alkaline volcanic rocks and zircon ages of the late Tonian: early Cryogenian arc-related Big Naryn Complex in the Eastern Djetim-Too Range, Middle Tianshan block, Kyrgyzstan

International Journal of Earth Sciences ◽

10.1007/s00531-020-01956-z ◽

2020 ◽

Author(s):

Baiansuluu Terbishalieva ◽

Martin Jan Timmerman ◽

Alexander Mikolaichuk ◽

Uwe Altenberger ◽

Jiří Sláma ◽

...

Keyword(s):

Volcanic Rocks ◽

Metamorphic Rocks ◽

Magmatic Arc ◽

Lower Member ◽

Short Time Span ◽

Zircon Crystallization ◽

Arc Setting ◽

Late Neoproterozoic ◽

Continental Magmatic Arc ◽

Short Time

AbstractThe Big Naryn Complex (BNC) in the East Djetim-Too Range of the Kyrgyz Middle Tianshan block is a tectonized, at least 2 km thick sequence of predominantly felsic to intermediate volcanic rocks intruded by porphyric rhyolite sills. It overlies a basement of metamorphic rocks and is overlain by late Neoproterozoic Djetim-Too Formation sediments; these also occur as tectonic intercalations in the BNC. The up to ca. 1100 m thick Lower Member is composed of predominantly rhyolites-to-dacites and minor basalts, while the at least 900 m thick pyroclastic Upper Member is dominated by rhyolitic-to-dacitic ignimbrites. Porphyric rhyolite sills are concentrated at the top of the Lower Member. A Lower Member rhyolite and a sill sample have LA-ICP-MS U–Pb zircon crystallization ages of 726.1 ± 2.2 Ma and 720.3 ± 6.5 Ma, respectively, showing that most of the magmatism occurred within a short time span in the late Tonian–early Cryogenian. Inherited zircons in the sill sample have Neoarchean (2.63, 2.64 Ga), Paleo- (2.33–1.81 Ga), Meso- (1.55 Ga), and Neoproterozoic (ca. 815 Ma) ages, and were derived from a heterogeneous Kuilyu Complex basement. A 1751 ± 7 Ma 40Ar/39Ar age for amphibole from metagabbro is the age of cooling subsequent to Paleoproterozoic metamorphism of the Kuilyu Complex. The large amount of pyroclastic rocks, and their major and trace element compositions, the presence of Neoarchean to Neoproterozoic inherited zircons and a depositional basement of metamorphic rocks point to formation of the BNC in a continental magmatic arc setting.

Download Full-text

Subduction erosion and crustal material recycling indicated by adakites in central Tibet

Geology ◽

10.1130/g48486.1 ◽

2021 ◽

Author(s):

Zong-Yong Yang ◽

Qiang Wang ◽

Lu-Lu Hao ◽

Derek A. Wyman ◽

Lin Ma ◽

...

Keyword(s):

Crustal Material ◽

Convergent Margins ◽

Nd Isotopes ◽

Magmatic Arc ◽

Material Recycling ◽

Intrusive Rocks ◽

Subducted Oceanic Crust ◽

Subduction Erosion ◽

Central Tibet ◽

Qiangtang Terrane

Subduction erosion is important for crustal material recycling and is widespread in modern active convergent margins. However, such a process is rarely identified in fossil convergent systems, which casts doubt on the importance of subduction erosion through the geological record. We report on ca. 155 Ma Kangqiong (pluton) intrusive rocks of a Mesozoic magmatic arc in the southern Qiangtang terrane, central Tibet. These rocks mainly consist of trondhjemites and tonalites and are similar to slab-derived adakites with mantle-like zircon oxygen isotope compositions (δ18O = 5.2‰–5.6‰), they display more evolved Sr-Nd isotopes and higher Th/La relative to mid-oceanic ridge basalts from the Bangong-Nujiang suture, and they contain abundant amphibole and biotite. These characteristics indicate magma generation via H2O-fluxed melting of eroded forearc crust debris with subducted oceanic crust at 1.5–2.5 GPa and 700–800 °C. In addition, the intrusions are exposed <20 km north of the Bangong-Nujiang suture. Given the formation of adakites, narrow arc-suture distance, migration of the Jurassic frontal arc toward the continent interior, and other independent geological archives, we suggest that the hydrated forearc crust materials were removed from the overlying plate and carried into the mantle by subduction erosion. Our study provides the first direct magmatic evidence for a subduction erosion process in pre-Cenozoic convergent systems, which confirms an important role for such processes in subduction-zone material recycling.

Download Full-text

Extensional Carboniferous magmatism at the western margin of Gondwana: Las Lozas valley, Catamarca, Argentina

Andean geology ◽

10.5027/andgeov43n1-a06 ◽

2016 ◽

Vol 43 (1) ◽

pp. 105 ◽

Cited By ~ 14

Author(s):

Beatriz Coira ◽

Clara E. Cisterna ◽

Horstpeter H. Ulbrich ◽

Umberto G. Cordani

Keyword(s):

Mantle Source ◽

Granitic Rocks ◽

Magma Source ◽

Crustal Material ◽

Nd Isotopes ◽

Sierras Pampeanas ◽

Juvenile Material ◽

Lithospheric Extension ◽

Eastern Sierras Pampeanas ◽

Volcanic Succession

The Las Lozas volcanic sequence, which crops out at northwestern border of the Famatina belt-southeastern Puna, NW Argentina, is constituted mainly by rhyolites and a lesser volume of basalts and trachytes, and volcanoclastic deposits. These rocks, previously considered of Early Paleozoic age, are now assigned to the Lower Pennsylvanian (320 Ma U-Pb age). They represent a bimodal volcanic succession that plot in the subalkaline/tholeiitic (rhyolites), alkaline basalts (basalts) and alkaline (trachytes) fields on the total alkali-silica diagram. The basalts display features comparable to transitional MORB and within-plate tholeiites, with contributions from a mantle source affected by crustal contamination. The acid members also show geochemical affinities to within-plate magmas, and their composition suggest a derivation from continental crustal material with mantle source interaction or a juvenile essentially mantle derived crust. The 320 Ma age from the Las Lozas volcanic succession as well as the 342 and 348 Ma U-Pb ages, from rocks in the nearby Cazadero Grande section, to the south, and the U-Pb ages from Sierra Pampeanas granites (332-357 Ma) highlight the importance achieved by Carboniferous magmatic activity in that region, framed between 320 and 350 Ma. Low strontium initial ratios from the Las Lozas (0.70479-0.70164) indicate a predominant contribution by a juvenile component, while the ratios in the nearby Cazadero Grande (0.71433-0.71233) and Sierras Pampeanas granites (0.717 to 0.7124) point to an input by enriched sources with restricted contribution of a mantle component. Nd isotopes from a basalt from the Las Lozas section (εNd(320) with +3.11, TDM with 774.6 Ma) indicates a possible asthenospheric source, with evidence for some mixture between juvenile and reworked crustal material. In contrast Sr-Nd isotopes in a rhyolite from Cazadero Grande (εNd(t) of -2.91 and -0.3, TDM of 1.09 and 1.1 Ga) and of Sierra Pampeanas granites (εNd(t) of -0.6, TDM of 1.19 and 1.1 Ga) suggest a crustal source with minor juvenile input. Taking in account the age difference in the region between Mississippian and the Lower Pennsylvanian magmatism, this would indicate a change in the magma source consistent with a more pronounced extensional tectonic regime for the Lower Pennsylvanian. This assumption need to be considered together with observations along a transect at 27º30’S, where the Carboniferous Eastern Sierras Pampeanas granitic rocks show, regardless of age, a greater contribution of juvenile material of mantle character to the west. Among these rocks, with a major juvenile component, are those of the Las Lozas succession as well the Cerro Gloria Granite, the eastern manifestations of the Carboniferous Eastern Sierras Pampeanas magmatism. From the foregoing emerges that the contribution of juvenile material could be continuously varied in the region through the Carboniferous, due to varying lithospheric extension. An example of this arise from the presented data of the Lozas succession, which indicate that this rocks resulted from reworking of supra-crustal material with input of juvenile magmas, linked to the change in the lithospheric extension

Download Full-text

Diachronous Redistribution of Hf and Nd Isotopes at the Crystal Scale—Consequences for the Isotopic Evolution of a Poly-Metamorphic Crustal Terrane

Geosciences ◽

10.3390/geosciences12010036 ◽

2022 ◽

Vol 12 (1) ◽

pp. 36

Author(s):

Adrien Vezinet ◽

Emilie Thomassot ◽

Yan Luo ◽

Chiranjeeb Sarkar ◽

D. Graham Pearson

Keyword(s):

Metamorphic Rocks ◽

Nd Isotopes ◽

Nd Isotope ◽

Isotopic Evolution ◽

Metamorphic Terrane ◽

O Isotope ◽

Pt Path ◽

Hand Specimen ◽

North Atlantic Craton

In metamorphic rocks, mineral species react over a range of pressure–temperature conditions that do not necessarily overlap. Mineral equilibration can occur at varied points along the metamorphic pressure–temperature (PT) path, and thus at different times. The sole or dominant use of zircon isotopic compositions to constrain the evolution of metamorphic rocks might then inadvertently skew geological interpretations towards one aspect or one moment of a rock’s history. Here, we present in-situ U–Pb/Sm–Nd isotope analyses of the apatite crystals extracted from two meta-igneous rocks exposed in the Saglek Block (North Atlantic craton, Canada), an Archean metamorphic terrane, with the aim of examining the various signatures and events that they record. The data are combined with published U–Pb/Hf/O isotope compositions of zircon extracted from the same hand-specimens. We found an offset of nearly ca. 1.5 Gyr between U-Pb ages derived from the oldest zircon cores and apatite U–Pb/Sm–Nd isotopic ages, and an offset of ca. 200 Ma between the youngest zircon metamorphic overgrowths and apatite. These differences in metamorphic ages recorded by zircon and apatite mean that the redistribution of Hf isotopes (largely hosted in zircon) and Nd isotopes (largely hosted in apatite within these rocks), were not synchronous at the hand-specimen scale (≤~0.001 m3). We propose that the diachronous redistribution of Hf and Nd isotopes and their parent isotopes was caused by the different PT conditions of growth equilibration between zircon and apatite during metamorphism. These findings document the latest metamorphic evolution of the Saglek Block, highlighting the role played by intra-crustal reworking during the late-Archean regional metamorphic event.

Download Full-text

Geoquímica e Isotópos de Nd de Rochas Metavulcânicas da Antiforme Capané, Complexo Metamórfico Porongos, RS

Pesquisas em Geociências ◽

10.22456/1807-9806.17939 ◽

2008 ◽

Vol 35 (2) ◽

pp. 83 ◽

Cited By ~ 7

Author(s):

KARINE GOLLMANN GOLLMANN ◽

JULIANA CHARÃO MARQUES ◽

JOSÉ CARLOS FRANTZ ◽

FARID CHEMALE JUNIOR

Keyword(s):

Isotope Composition ◽

Metamorphic Complex ◽

Nd Isotope ◽

Mafic Rocks ◽

Magmatic Arc ◽

Eastern Flank ◽

Group 4 ◽

Dom Feliciano Belt ◽

Group 3 ◽

Nd Isotope Composition

The Capané Antiform, located in the northern part of the Neoproterozoic Porongos Metamorphic Complex (RS), is composed of a supracrustal sequence metamorphosed under greenschist (eastern flank) to amphibolite (western flank) facies. Four groups of rocks were recognized. Groups 1 and 2 are constituted of felsic and mafic rocks from the central and western part of the antiform, respectively. They show high LREE and LILE and low HREE and HFSE. The εNd (t) varies from strongly negative (-20) in felsic rocks to moderately negative (-6 to -11) in mafic rocks, with Nd TDM ages that varies from Paleoproterozoic to Mesoproterozoic. The Group 3 consists of metarhyolites from the eastern flank and is geochemically similar to former groups, but shows differences in Nd isotope composition. The εNd(t) is slightly negative (-2 to -4) and the model ages are restricted to the Mesoproterozoic. Group 4, constituted of metabasalts, shows chemical similarities with OIB-MORB and has juvenile isotope signature. The first three groups were interpreted as evolved from a magmatic arc, related probably to the collision of the São Gabriel block with the Encantadas microcontinent during the Neoproterozoic. The Nd differences observed were considered as a result of more or less interaction between mantle and crust components and, particularly, the characteristics observed in the Group 3 can point out a correlation with the syn-tangential granitoids from the eastern part of the Dom Feliciano Belt. The metabasalts of the group 4 were correlated to the antiform's previously described ophiolite remains.

Download Full-text

Origin of the Ordovician Mansehra granite in the NW Himalaya, Pakistan: constraints from Sr–Nd isotopic data, zircon U–Pb age and Hf isotopes

Geological Society London Special Publications ◽

10.1144/sp481.5 ◽

2018 ◽

Vol 481 (1) ◽

pp. 277-298 ◽

Cited By ~ 2

Author(s):

Masatsugu Ogasawara ◽

Mayuko Fukuyama ◽

Rehanul Haq Siddiqui ◽

Ye Zhao

Keyword(s):

Granitic Magma ◽

Geochemical Data ◽

Large Contribution ◽

Crustal Material ◽

Sr Isotope ◽

Nw Himalaya ◽

Nd Isotope ◽

Isotope Data ◽

Late Neoproterozoic ◽

T Values

AbstractThe Mansehra granite in the NW Himalaya is a typical Lesser Himalayan granite. We present here new whole-rock geochemistry, Rb–Sr and Sm–Nd isotope data, together with zircon U–Pb ages and Hf isotope data, for the Mansehra granite. Geochemical data for the granite show typical S-type characteristics. Zircon U–Pb dating yields 206Pb/238U crystallization ages of 483–476 Ma. The zircon grains contain abundant inherited cores and some of these show a clear detrital origin. The 206Pb/238U ages of the inherited cores in the granite cluster in the ranges 889–664, 1862–1595 and 2029 Ma. An age of 664 Ma is considered to be the maximum age of the sedimentary protoliths. Thus the Late Neoproterozoic to Cambrian sedimentary rocks must be the protolith of the Mansehra granitic magma. The initial Sr isotope ratios are high, ranging from 0.7324 to 0.7444, whereas the εNd(t) values range from −9.2 to −8.6, which strongly suggests a large contribution of old crustal material to the protoliths. The two-stage Nd model ages and zircon Hf model ages are Paleoproterozoic, indicating that the protolith sediments were derived from Paleoproterozoic crustal components.

Download Full-text

Mafic magmatism associated with the Goiás magmatic arc in the Anicuns region, Goiás, central Brazil: Sm–Nd isotopes and new ID-TIMS and SHIMP U–Pb data

Journal of South American Earth Sciences ◽

10.1016/j.jsames.2003.11.001 ◽

2004 ◽

Vol 16 (7) ◽

pp. 599-614 ◽

Cited By ~ 34

Author(s):

Jorge Henrique Laux ◽

Márcio Martins Pimentel ◽

Elton Luiz Dantas ◽

Richard Armstrong ◽

Alan Armele ◽

...

Keyword(s):

Nd Isotopes ◽

Mafic Magmatism ◽

Magmatic Arc ◽

Central Brazil

Download Full-text

Zircon ages and the distribution of Archaean and Proterozoic rocks in the Rauer Islands

Antarctic Science ◽

10.1017/s0954102093000252 ◽

1993 ◽

Vol 5 (2) ◽

pp. 193-206 ◽

Cited By ~ 88

Author(s):

P. D. Kinny ◽

L. P. Black ◽

J. W. Sheraton

Keyword(s):

Granulite Facies ◽

Metamorphic Rocks ◽

Low Grade ◽

High Grade ◽

Ion Microprobe ◽

Rock Interaction ◽

Mafic Rocks ◽

Grade Fluid ◽

Vestfold Hills ◽

Intrusive Suite

The application of zircon U-Pb geochronology using the SHRIMP ion microprobe to the Precambrian high-grade metamorphic rocks of the Rauer Islands on the Prydz Bay coast of East Antarctica, has resulted in major revisions to the interpreted geological history. Large tracts of granitic orthogneisses, previously considered to be mostly Proterozoic in age, are shown here to be Archaean, with crystallization ages of 3270 Ma and 2800 Ma. These rocks and associated granulite-facies mafic rocks and paragneisses account for up to 50% of exposures in the Rauer Islands. Unlike the 2500 Ma rocks in the nearby Vestfold Hills which were cratonized soon after formation, the Rauer Islands rocks were reworked at about 1000 Ma under granulite to amphibolite facies conditions, and mixed with newly generated felsic crust. Dating of components of this felsic intrusive suite indicates that this Proterozoic reworking was accomplished in about 30–40 million years. Low-grade retrogression at 500 Ma was accompanied by brittle shearing, pegmatite injection, partial resetting of U-Pb geochronometers and growth of new zircons. Minor underformed lamprophyre dykes intruded Hop and nearby islands later in the Phanerozoic. Thus, the geology of the Rauer Islands reflects reworking and juxtaposition of unrelated rocks in a Proterozoic orogenic belt, and illustrates the important influence of relatively low-grade fluid-rock interaction on zircon U-Pb systematics in high-grade terranes.

Download Full-text

Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: A case study for the COSC-1 borehole, Sweden

10.5194/egusphere-egu2020-13955 ◽

2020 ◽

Author(s):

Felix Kästner ◽

Simona Pierdominici ◽

Judith Elger ◽

Christian Berndt ◽

Alba Zappone ◽

...

Keyword(s):

Seismic Anisotropy ◽

Seismic Velocity ◽

Metamorphic Rocks ◽

Seismic Velocities ◽

Mafic Rocks ◽

Seismic Properties ◽

The Core ◽

Nappe Complex ◽

Thrust Zone ◽

Mountain Belts

<p>Deeply rooted thrust zones are key features of tectonic processes and the evolution of mountain belts. Exhumed and deeply-eroded orogens like the Scandinavian Caledonides allow to study such systems from the surface. Previous seismic investigations of the Seve Nappe Complex have shown indications for a strong but discontinuous reflectivity of this thrust zone, which is only poorly understood. The correlation of seismic properties measured on borehole cores with surface seismic data can help to constrain the origin of this reflectivity. In this study, we compare seismic velocities measured on cores to in situ velocities measured in the borehole. The core and downhole velocities deviate by up to 2 km/s. However, velocities of mafic rocks are generally in close agreement. Seismic anisotropy increases from about 5 to 26 % at depth, indicating a transition from gneissic to schistose foliation. Differences in the core and downhole velocities are most likely the result of microcracks due to depressurization of the cores. Thus, seismic velocity can help to identify mafic rocks on different scales whereas the velocity signature of other lithologies is obscured in core-derived velocities. Metamorphic foliation on the other hand has a clear expression in seismic anisotropy. To further constrain the effects of mineral composition, microstructure and deformation on the measured seismic anisotropy, we conducted additional microscopic investigations on selected core samples. These analyses using electron-based microscopy and X-ray powder diffractometry indicate that the anisotropy is strongest for mica schists followed by amphibole-rich units. This also emphasizes that seismic velocity and anisotropy are of complementary importance to better distinguish the present lithological units. Our results will aid in the evaluation of core-derived seismic properties of high-grade metamorphic rocks at the COSC-1 borehole and elsewhere.</p>

Download Full-text