Lamprophyre Dykes Research Articles

Late Palaeozoic high-K calc-alkaline to shoshonitic series magmatism and related W(–Mo–Cu–Au) metallogeny of the Kyrgyz Tien Shan, Central Asia

In the Kyrgyz Tien Shan, numerous high-K calc-alkaline to shoshonitic series intrusions are associated with the large fault system known as the ‘Major structural line of Tien Shan’, or ‘Nikolaev Line’. During the Carboniferous, this lineament represented a zone of intracontinental, possibly back-arc rifting associated with a north-dipping subduction, whereas in the Late Carboniferous to Permian it was part of a larger continental collision structure. These Late Paleozoic high-potassic intrusions comprise numerous intrusive phases that vary in composition from the early mafic (monzogabbro, monzodiorite) through intermediate (monzonite, syenite, quartz syenite) to late stage and more evolved (quartz monzonite, granodiorite, monzogranite, leucogranite–alaskite) members locally intersected by monzodiorite–porphyry and lamprophyre dykes. They can be related to low degrees (from ∼1–2 to 2–2.5 vol%) of partial melting of metasomatically enriched upper mantle followed by magma fractionation and emplacement at shallower crustal levels. In summary, the high-K magmas formed in continental- and post-collisional arc settings with a progressive input of crustal material. From the west to the east, the potassic intrusions contain progressively higher Nb and Y concentrations, reflecting their derivation in a post-collisional setting. The A-type granite signatures also become more distinct in this direction. This is consistent with the tectonic model implying the ‘scissor-like’ closure of the Late Paleozoic Turkestan palaeo-ocean from east to west. These high-potassic intrusions are accompanied by W–Mo–Cu–Au skarn/porphyry to Au(–W) replacement-style deposits, which are part of the extended Au (Au–W–Mo–Cu) metallogenic belt of Tien Shan. The association of skarn and porphyry-style W–Mo to Mo–Cu–Au–W mineralization defines these ‘porphyry–skarn’ systems as a distinct group containing strongly oxidized andradite-dominant skarns. An early W partitioning into magmatic–hydrothermal fluid, together with Mo and Cu, is typical of this magmatic–hydrothermal system and can be explained by an early H 2 O saturation of the parental magma. The late-stage mafic dykes including lamprophyres probably reflect the presence of another, but concealed, mafic intrusion releasing CO 2 and metals, such as Au, As, Sb, Bi and Te, into the hydrothermal mineral system.

Transcrustal magmatic system in lamprophyre dyke constructed by multiple magma reservoirs

Transcrustal magmatic system in lamprophyre dyke constructed by multiple magma reservoirs

Neoproterozoic (ca. 830 Ma) carbonatite dykes from Qianlishan in the western North China Craton: Petrogenesis and metallogenic implications

Carbonatite and the associated alkaline intrusive complexes are the primary sources of light rare earth element (REEs). Our field investigations in the western margin of the North China Craton (NCC) have firstly identified over 20 carbonatite dykes and minor coeval carbonate-rich lamprophyre dykes intruding the Paleoproterozoic Qianlishan Group in the southern Qianlishan area. Zircon LA-ICP-MS U-Pb dating on six carbonatite samples yielded crystallization ages ranging from 835.2 ± 3.7 Ma to 828.9 ± 3.8 Ma, indicating emplacement of the carbonatite dykes at ca. 830 Ma during the Neoproterozoic. Geochemical data show that most of the carbonatite dykes are rich in light REEs with total light REEs > 600 ppm to 4932 ppm, and the carbonate-rich lamprophyre dykes are characterized by high Cr (1219–1267 ppm) and Ni concentrations (857–1076 ppm). Petrological and scanning electron microprobe (SEM) analytical results show that the dominant REE-bearing minerals in the carbonatites are monazite, and other REE-bearing minerals are parisite and bastnäsite. Geochemical and carbon–oxygen isotopic results indicate that the ca. 830 Ma carbonatite dykes were produced by low-degree partial melting of a previously metasomatised subcontinental lithospheric mantle with assimilation of crustal material. Emplacement of the ca. 830 Ma carbonatite and carbonate-rich lamprophyre dykes in the southern Qianlishan area and the previously reported ca. 810 Ma mafic dykes in the middle Qianlishan area occurred in a continental rift environment. Simultaneous development of the Neoproterozoic (830 − 810 Ma) continental rifting events in the western margin of the NCC and the eastern margin of the Alxa Block as previously suggested may indicate a connection between the eastern Alxa Block and the western NCC during and before the middle Neoproterozoic.

Petrology and Geochemistry of Lamprophyres from Tirthal Area, in Eastern Margin of the Eastern Dharwar Craton, Khammam, Telangana, India

The presence of lamprophyre dykes is very common in the Eastern Dharwar Craton (EDC), southern India. The present paper reports five new lamprophyre bodies from the Tirthal area near the bank of the Muneru River (80°08ʹ 13.00ʹʹ:17°19ʹ 9.0ʹʹ), north of Khammam, Telangana.Petrography and geochemistry of the lamprophyre dykes are also discussed in this paper. The study area mainly consists of granitoids of Peninsular Gneissic Complex-II (PGC-II) of the EDC. The lamprophyre intrudes the granitoids of the EDC.Petrographic studies revealed the presence of panidiomorphic texture. Euhedral crystals of clinopyroxene, biotite and amphibole are present as phenocryst in the lamprophyre,while k-feldspar, plagioclase feldspar, biotite and apatite are present in the groundmass.The lamprophyre is characterized by SiO2 (40.03%-45.23%), Fe2O3(9.09%-13.45%), MgO (9.78%-11.96%), CaO (8.25%-14.78%), K2O (0.69%-2.37%), TiO2 (1.3%-1.53%) and Al2O3 (9.76%-12.02%) contents. Similarly trace elements analysis gavehigher amounts of Ba (2030-10498ppm), Sr (438-925 ppm), Ni (156-225 ppm), Zr (417-590 ppm), V (141-169 ppm) and Cr(388-482 ppm). All the samples gave higher LREE values as compared to HREE with a total REE content within the range of 1108.50-2004.49 ppm. The lamprophyre is classified as minette belonging to Calc Alkaline Group based on geochemical and petrological studies.

Geochemistry and Zircon LA–ICP–MS U–Pb Geochronology of the Shuangwang Au Deposit, Shaanxi Province: Implications for Tectonic Evolution and Metallogenic Age

The Shuangwang Au deposit (with a gold resource of approximately 70 t Au), is located in the Fenxian-Taibai fore-arc basin in the West Qinling Orogen of central China. Igneous intrusions in the region include the Xiba granitic pluton and granite porphyry and lamprophyre dykes. The Xiba pluton is composed of granodiorite and monzonite granite. The granodiorite is typical I-type granite, and it yields a crystallization age of 221.1 ± 1.2 Ma and a two-stage Hf model age of 1432–1634 Ma. The monzonite granite shows a transitional characteristic between I-type and A-type granite, and it yields a crystallization age of 214.8 ± 1.2 Ma and a two-stage Hf model age of 1443–1549 Ma. The granitoid was derived mainly from a crust–mantle mixed source. The ages indicate that the granodiorite and monzonite granite formed during two different stages. The REE distribution patterns of the Xiba granitoid exhibit significant fractionation between LREE and HREE, showing right-dipping curves, with an enrichment of LREE and a deficit of HREE. The granodiorite displays a light negative Eu anomaly, while the monzonite granite displays an obvious negative Eu anomaly. The granite porphyry dikes are distributed in the No. I breccia and Jiupinggou granite porphyry, and they yield crystallization ages of 219.9 ± 1.5 Ma and 213.1 ± 0.89 Ma, respectively, and two-stage Hf model ages of 1382–1501 Ma and 1373–1522 Ma, respectively. The lamprophyre dikes in the deposit yield a crystallization age of 214.4 ± 2.7 Ma. After the collision event between the Yangtze and the North China Plates along the Qinling orogenic belt, at approximately 220 Ma in the Late Triassic, the detachment of the slab produced the upwelling of the asthenosphere material. Under conditions of mantle heat and tectonic stress, widespread partial melting of the subducted continental crust and the upper lithosphere mantle occurred, forming granitoids with various degrees of adakite characteristics.

Location and polarity of Variscan sutures based on petrological and seismological data from the Bohemian Massif and the implications for the European Variscides

The high- to ultrahigh-pressure ((U)HP) metamorphic rocks are present within the European Variscan belt between the Bohemian and Iberian massifs (the Galicia-Moldanubian zone) and they are partly incorporated into the Alpine orogenic system. Due to their involvement in various allochthonous units, the affiliation of the (U)HP rocks to the suture zones that were the sites of their initial exhumation, is not always clear. The Bohemian Massif preserves the best evidence of Variscan sutures with clear relationships to the exposed (U)HP rocks. They are the Moldanubian and the Saxo-Thuringian sutures bounding the Teplá-Barrandian block from the SSE and NNE, respectively. The distribution of (U)HP rocks coincides with the boundaries of mantle lithosphere domains, delimited from large-scale seismic anisotropy, and reveals the NW-ward inclination of the Moldanubian mantle lithosphere domain beneath the Teplá-Barrandian block and thus a subduction polarity to the NW. The eastern margin of the Teplá-Barrandian block contains a magmatic arc, which is in direct contact with the Moldanubian orogenic wedge, and both are penetrated by lamprophyre dykes (∼340 Ma), which dates the cessation of the collision-related shortening and crustal consolidation. The overall crustal geometry of the Saxo-Thuringian suture implies the SE-ward polarity of subduction during its formation. However, based on seismic tomography and anisotropy model, the suture at mantle depths appears as a sub-vertical boundary between the Saxo-Thuringian and the Teplá-Barrandian lithosphere domains. The Saxo-Thuringian zone bears evidence of blueschist facies metamorphism in the (para)autochthonous units, which are strongly retrogressed. Compared to the Moldanubian zone, (U)HP rocks are less common in the Saxo-Thuringian zone and occur as nappes and klippes, some of which are exposed near the Moldanubian suture. The similarities of the Saxo-Thuringian (U)HP rocks to those in the Moldanubian zone and their allochthonous positions favour formation of some of the (U)HP rocks along the Moldanubian suture and their subsequent emplacement into the Saxothuringian zone. The Moldanubian suture appears to control the distribution of most of the (U)HP rocks exposed along the European Variscan Belt. They all show similarities regarding lithology, mainly fragments of mantle rocks included in felsic materials, and their granulite-amphibolite facies thermal overprint.

Petrography and Geochemistry Study of the Madharam Lamprophyre Dyke, Western Margin of the Proterozoic Pakhal Basin Within Eastern Dharwar Craton, Khammam, Telangana, India

Various lamprophyre types are prevalent throughout the Cuddapah Igneous Province (CIP) and Prakasam Alkaline Province (PAP) in the Eastern Dharwar Craton (EDC), located in southern India. This study focuses on a newly identified lamprophyre dyke situated near the Madharam area in Khammam District, Telangana, India (coordinates 80°15ʹ:17°32ʹ) on the northeastern edge of the EDC. The paper provides an in-depth analysis of the petrography and geochemistry of this lamprophyre. The study area predominantly comprises granitoids from the Peninsular Gneissic Complex (PGC) within the EDC. Geographically, it is flanked by the Proterozoic sedimentary basins of Pakhal to the east and Cuddapah to the south. The Madharam lamprophyre exhibits a characteristic porphyritic-panidiomorphic texture, with clinopyroxene phenocrysts occurring alongside feldspar in the groundmass. Amphiboles present in the rock are of calcic variety (mainly actinolite group). Clinopyroxene is found to be diopside in nature (Wo48-50 En40-41 Fs9-10) and the feldspars show albitic (Or0Ab85-92 An 6-14) nature. Lower TiO2 content in the amphibole and clinopyroxene suggests the nature of the lamprophyre is calc-alkaline. The geochemical signatures, such as variable Ba/La ratios and low Nb/La values, suggest minimal to no crustal contamination in the lamprophyre magma. These findings are significant for understanding the evolution of the EDC and provide important constraints on the geodynamics of southern peninsular India.

Petrography and geochemistry study of the Thirtal lamprophyre dyke left bank of Muneru River, in eastern margin of the Eastern Dharwar Craton, Khammam, Telangana, India

Various types of lamprophyres are very common in different part of the Cudappah Igneous Provice (CIP)/Prakasham Alkaline Province (PAP) in Eastern Dharwar Craton (EDC), southern India. Present paper reports a lamprophyre dyke near the Thirtal lamprophyre left bank of Muneru River area, Khammam District, Telangana, India (80°08ʹ 12.9ʹʹ:17°19ʹ 10.13ʹʹ) at the northeastern margin of the EDC. In the present paper also discuss the detail petrography and geochemistry of the newly found lamprophyre. The study area mainly consists of granitoids of Peninsular Gneissic Complex (PGC) of the EDC. Regionally, the area is bounded by two Proterozoic sedimentary basins, i.e. in the east Pakhal basin and in the south Cuddapah basin. The lamprophyre of the study area has been intruded within granitoids of the EDC. This dyke is ~0.5 to 1 mt wide having ~50 mt exposed strike length on the bank of Pakhal River. Petrographically clinopyroxene and olivine are present as a phenocryst and biotite, plagioclase, kfeldspar, carbonate, amphibole, chlorite and epidote present in the groundmass. In some of the part carbonate replace the clinopyroxene and olivine. The mineral chemistry, whole rock, trace elements and REE geochemistry suggested that this lamprophyre belongs to calc-alkaline group (CAL)

Petrology and Geochemical Study of Calc-Alkaline Lamprophyres from South of Garla Area Bank of Munneru River, Eastern Dharwar Craton, Telangana South India

The Eastern Dharwar Craton (EDC) in southern India frequently features lamprophyre dykes, with the present study identifying two new dykes near South of Garla village. Petrographic and geochemical analyses were conducted on these dykes, which intrude the granitoids of the Peninsular Gneissic Complex-II (PGC-II) within the EDC. Petrographic examination revealed a panidiomorphic texture, with clinopyroxen, biotite, and amphibole as phenocrysts, and k-feldspar, plagioclase feldspar, and biotite in the groundmass. The lamprophyre's composition is characterized by varying levels of SiO2, Fe2O3, MgO, CaO, K2O, TiO2, and Al2O3, alongside elevated concentrations of trace elements such as Ba, Sr, Ni, Zr, V, and Cr. The lamprophyre is classified as minette of the Calc Alkaline Group based on its geochemical and petrological attributes.

Petrography of lamprophyres of the Endegechu area of the Yana-Adycha tin ore region

The article considers the features of the petrographic composition of the lamprophyre dyke; attributed to the kHunkhadi complex of Late Cretaceous age; established on the Endegechchu hill in the Yano-Adycha tin ore region located in the Adycha tectonic zone. The rocks have a porphyry structure; and mineral formations of their own magmatic stage; magmatic; metasomatic and late hydrothermal-metasomatic substitutions are isolated in their composition. A characteristic feature of these rocks are spherulites of concentric-zonal structure; covered with a shell of scaly or lamellar graphite; depending on the size of the spherulites; evenly distributed throughout the rock; which were studied for the first time and have not been established in other igneous rocks widely developed in the area. The study of spherulites is an important petrological task; which makes it possible to identify the mechanisms of their formation and causes; can indicate the conditions of formation and sources of matter of the rocks containing them. The morphology of graphite; its distribution and the nature of its relationship with surrounding minerals are also very informative for establishing the primary nature of graphite and epigenetic changes in host rocks as a result of various hydrothermal-metasomatic processes; which is possible due to the ability of carbonaceous matter to redistribute in the rock when exposed to various forces; rather than being removed from it.

Constraints from lamprophyre petrogenesis on the timing of Eocene lithospheric thinning and associated rifting of Borneo and Sulawesi

The petrogenetic history of well characterised magmatic rocks may contain invaluable information of paleo-lithospheric thickness and structure that can inform on tectonic evolution. Petrographically distinctive rocks, such as lamprophyres, provide temporal and spatial constraints to build, assess, and verify tectonic models.An alkaline lamprophyre dyke that intrudes the rift-related sediments of the Eocene Tanjung Formation of the Senakin Peninsula in South Kalimantan, Indonesia has been investigated using petrology, whole rock geochemistry and Ar-Ar geochronology.The Senakin lamprophyre dyke is mostly geochemically homogenous but petrographically stratified with vesicle free monchiquite alkaline lamprophyre mineralogy at the base and an amygdale bearing kaersutite phenocryst free upper zone. The major and trace element chemistry is consistent with an intra-plate Ocean Island Basalt like affinity. 40Ar/39Ar dating of hornblende and groundmass aliquots indicates an emplacement age of 37.45 ± 0.10 Ma (2σ), which is consistent with the Late Eocene age of the Tanjung Formation derived from microfossil analysis.The petrology and geochemistry of the Senakin lamprophyre dyke is consistent with magma genesis at > 2GPa beneath a thick lithosphere followed by fractional crystallisation at Moho depths equivalent to 0.5–0.8 GPa. This indicates a much thicker southeastern Kalimantan paleo-lithosphere. Lamprophyre magmatism was initiated by lithospheric extension associated with the opening of the Makassar Strait and also regional thermal upwelling. This extension continued to thin the lithosphere to its current thickness equivalent to 0.5 GPa.

Petrology, U-Pb titanite dating and Sr-Nd isotope geochemistry of a shoshonitic lamprophyre dyke near the Western Dharwar Craton-Southern Granulite Terrane contact, southern India: Implications for long-lived enriched mantle, widespread Tonian-Cryogenian rifting, and Rodinia configuration

We present petrology, U-Pb titanite geochronology, bulk-rock and Sr-Nd geochemistry of an undeformed and unmetamorphosed shoshonitic lamprophyre (spessartite) from the Mysuru area (Halaguru- Harohalli alkaline province) located approximately 80 km north of the tectonic contact between the Western Dharwar Craton and the Southern Granulite Terrane, southern India, to understand its origin and to evaluate its geodynamic significance. The lamprophyre shows a typical porphyritic-panidiomorphic texture with amphibole phenocrysts. Clinopyroxene occurs only as xenocrysts with feldspar, apatite, titanite and titano-magnetite confined to the groundmass. Amphibole mineral composition classifies them as pargasite and tremolite, and the groundmass is essentially constituted of alkali feldspar. High whole-rock Mg# (56–65), Ni + Cr (245 to 730 ppm), a lack of correlation between SiO2 and Rb/Sr as well as ɛNd(i) indicates that crustal contamination experienced by the lamprophyre magma is limited. U-Pb titanite (n = 18) SHRIMP-II dating yielded a Neoproterozoic Tera-Wasserburg concordia age of 820 ± 15 Ma (MSWD = 5.9). Whole-rock derived 87Sr/86Sr(i) (0.70425–0.70530) and ɛNd(i) (-6.3 to −4.3) suggest origin of the lamprophyre from an enriched lithospheric mantle source. Paleoproterozoic depleted-mantle model ages of ca. 1.8 Ga suggest the existence of a long-lived enriched mantle which correspond to the timing (ca.1.9–1.7 Ga) of widespread mafic dyke swarms’ emplacement in the Dharmapuri-Agali-Tiruvannamalai domain in the Salem block at the northernmost portion of the Southern Granulite Terrane. The Tonian emplacement age of the studied lamprophyre is synchronous with several co-spatial Neoproterozoic (i) alkaline complexes ± carbonatite ± lamprophyre from the northern part of the Southern Granulite Terrane, and (ii) other mafic alkaline dykes of the Halaguru-Harohalli alkaline province from the southern part of the Eastern Dharwar Craton. Our results highlight the importance of this lamprophyre dyke, present close to the’Fermor Line’ as well as near the boundary between Eastern and Western Dharwar Cratons, which provides a rare opportunity to understand its spatio-temporal link with alkaline dykes of the Southern Granulite Terrain. Our findings also help understand the role of repeated large-scale rifting, associated with the Rodinia break-up, leading to the generation of a wide spectrum of Tonian-Cryogenian alkaline magmas in southern Indian Shield. The new age data also have implications for the configuration of India’s paleoposition during the Neoproterozoic and support the idea that South China Block-India were located on the periphery of Rodinia or were already detached from the supercontinent.

Petrogenesis of Eocene Lamprophyre Dykes in Northern Qiangtang Terrane, Tibetan Plateau: Implications for the Tethyan Mantle Metasomatism and Tectonic Evolution

Post-collisional (ultra)potassic lamprophyre dykes are the key probes for understanding mantle metasomatism and reconstructing tectonic evolution. In this study, we present new petrological, geochronological, geochemical and zircon Lu-Hf isotopic data for lamprophyre dykes in the northern Qiangtang terrane (central Tibet), aiming to constrain their petrogenesis and geodynamic setting. The studied lamprophyres are minettes with phenocrysts of siderophyllite and phlogopite, which intrude into Triassic granite of 236.9 Ma. These lamprophyres yield zircon U-Pb ages of 39.7–40.9 Ma. They exhibit high contents of K2O (7.61–8.59 wt.%) and ultrapotassic features with high K2O/Na2O (11.43–14.38) ratios. They are characterized by increased values of Mg# (69.1 to 72.1) and high concentrations of compatible elements (e.g., Cr = 277–529 ppm, Ni = 232–322 ppm), which are diagnostic of mantle-derived primitive magma. The studied lamprophyres have a high abundance of rare earth elements (∑REE = 902–1061 ppm) with significantly fractionated REE patterns ((La/Yb)N = 66.3–100.6), and they are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), but depleted in high field strength elements (HFSE) (e.g., Nb, Ta and Ti) and heavy rare earth elements (HREE) with enriched zircon Hf isotopes (εHf(t) from −6.40 to 3.80). This indicates their derivation from an enriched mantle source which was metasomatized by subduction-related fluids and sediment-derived melts. A petrogenetic study suggests that the lamprophyres were generated by the partial melting of a phlogopite-bearing lherzolite within the garnet stability field. We propose that the Cenozoic ultrapotassic mafic rocks in the central Tibetan Plateau originated in the lithospheric mantle metasomatized by the subduction-related components, and are the magmatic response to the detachment of the subducted Tethyan slab.

Tithonian mafic intrusions in north-central Newfoundland: link to Atlantic rifting?

The small volume, Mesozoic alkali gabbro intrusions of the Budgell Harbour and Dildo Pond stocks and associated alkaline lamprophyre dykes in Notre Dame Bay in Newfoundland are an example of onshore magmatism that may be associated with North Atlantic Ocean opening. Chemical abrasion isotope dilution thermal ionization mass spectrometry U–Pb dating of zircon from Budgell Harbour Stock drill core samples yielded a weighted average 206Pb/238U age of 147.9 ± 0.5 Ma (95% confidence interval, mean square weighted deviation = 0.10). Five 40Ar/39Ar laser step-heating, single phlogopite grain analyses from the Budgell Harbour and Dildo Pond stocks, plus a lamprophyre dyke, yielded ages ranging from 146.3 ± 0.2 to 149.5 ± 0.5 Ma. The data demonstrate a ca. 148 Ma (Jurassic and Tithonian) alkaline magmatic event in Newfoundland, contemporaneous with rifting and offshore basin formation. These new age data and published determinations from magmatic rocks on conjugate margins and adjacent regions reveal long-lived episodic magmatism in the embryonic North Atlantic rift environment. We propose a new model whereby magmatism occurred in Notre Dame Bay at the convergence of older crustal-scale faults and localized Moho depth variations that may have triggered lithospheric mantle melting through isothermal, distal, and edge-driven upwelling related to regional extension.

Miocene lamprophyre and felsic volcanics in the outer zone of SW Japan: arc building through multiple sources in an active convergent margin

ABSTRACT Subduction-related magmatism is a significant contributor to arc building and continental growth. In the active convergent margin of the SW Japan arc, voluminous volcanic rocks and mafic dykes formed through subduction and back-arc rifting during Miocene. In this study, we investigate a suite of felsic volcanic rocks (rhyolite and dacite) and lamprophyres from central Shikoku Island, which occur in the north-central part of the Chichibu belt and Sanbagawa belt in the Outer zone of the SW Japan arc. Whole-rock geochemistry results show that the rhyolite and dacite samples are peraluminous, belong to the high-K calc-alkaline series, show LREE and LILE enrichment, HREE and HFSE depletion that suggest arc volcanic affinity. The lamprophyre samples belong to alkali lamprophyre, show LREE and HFSE enrichments, and display OIB (oceanic island basalt)-like geochemical features. The 206Pb/238U weighted mean ages of the zircons from the rhyolite and dacite samples range from 14.39 ± 0.21 Ma to 13.92 ± 0.30 Ma, whereas the lamprophyre shows 206Pb/238U weighted mean age of 12.21 ± 0.35 Ma. Zircon Lu-Hf isotope data suggest that the rhyolite and dacite were derived from the remelting of the arc crustal rocks and that the lamprophyre was derived from depleted mantle sources and was contaminated by crustal materials. The felsic volcanic rocks (rhyolite and dacite) can be correlated to Miocene (15.5 Ma to 13.5 Ma) magmatism in the Outer Zone of the SW Japan arc. The formation of lamprophyre dykes in the SW Japan arc may be related to the subhorizontal mantle flows beneath the SW Japan arc associated with the opening of the Japan Sea back-arc basin or asthenosphere upwelling through the slab-tear of the Philippine Sea Plate beneath the SW Japan arc. Our study shows that the SW Japan Arc was built by multiple magmatism from diverse sources in an active convergent margin.

Transcrustal magma plumbing process in the Cenozoic Dali potassic lamprophyre dyke formation in the southeastern Tibet Plateau

(Ultra-)potassic lamprophyres are volumetrically rare, but are widely distributed in diverse geological settings and extensively applied to trace the mantle source and melting processes. However, it is still debatable whether the lamprophyre formation involved transcrustal magmatic processes. In this study, we describe the diverse zoning patterns and textures of clinopyroxene (Cpx) from a Cenozoic potassic lamprophyre dyke in southeastern Tibet Plateau. Three types of Cpx macrocrysts with normal- and reverse oscillatory zoning and sieved textures, and Cpx microcrysts from Cpx–Phl nodules are recognized. The Cpx macrocrysts have highly variable Mg# (62–89) and chemical compositions. Their oscillatory-zoned mantle has alternating coarse layers or closely-packed layers, with distinct resorption surface shown in backscattered electron (BSE) images. High-amplitude oscillation of Mg# (±5 to ±12), Al, Cr and Sr at the boundary layers of mantle may reflect multiple magma mixing/recharge events. In contrast, low-amplitude and high-frequency oscillation of Mg# (varying from < ±3) across the closely-packed layers could be attributed to local magma mixing or kinetic effect at the crystal-melt interface. The sieved domains occur in the Cpx macrocrystic core with spongy space and linking the external groundmass by cracks, and have major and minor compositions and 87Sr/86Sr ratios similar to those of the rims. This indicates that the sieved domains are probably originated from dissolution of the Cpx macrocrysts by groundmass melt and later reprecipitation. The estimated pressure and temperature for the Cpx macrocryst high-Mg# cores and low Mg# rims are 580–1160 MPa (avg. 919 MPa) and 30–1270 MPa (avg. 681 MPa), and 1116–1266 °C (avg. 1216 °C) and 955–1215 °C (avg. 1110 °C), respectively, suggesting polybaric differentiation or Cpx-saturated magmas. The estimated pressure and temperature for the reverse-zoned Cpx marcocryst cores are 450–1310 MPa (avg. 953 MPa) and 1097–1209 °C (avg. 1166 °C), respectively, indicating that they are likely formed in equilibrium with a more evolved magma batch, and then were entrapped by more primitive mantle-derived potassic magmas during magma upwelling. The La/Yb and Dy/Yb modelling of equilibrium melts suggest that magmas of the Cpx–Phl nodules and their lamprophyre host were derived from similar mantle sources. Therefore, the complex zoning patterns and compositions of Cpx macrocrysts could indicate transcrustal magmatic processes in the potassic lamprophyre dyke formation.

U-Pb Neoproterozoic age and petrogenesis of a calc-alkaline shoshonitic lamprophyre from Simdega area, Chhotanagpur Gneissic Complex (Eastern India): Implication for the evolution of the Central Indian Tectonic Zone and Rodinia tectonics

The age of emplacement and geochemistry of the lamprophyres are of tectonic significance as they have potential to unravel global scale geodynamic processes. We present petrology, U-Pb SHRIMP apatite and titanite ages and bulk-rock Sr-Nd isotope data for an unmetamorphosed and undeformed lamprophyre dyke from the Simdega area of the Chhotanagpur Gneissic Complex (CGC) which is a component of the E-W trending Central Indian Tectonic Zone (CITZ), India. The CITZ is a major intercontinental suture which separates the northern Indian and the southern Indian blocks whose polarity of their subduction is a contentious issue. The lamprophyre exhibits a strong porphyritic-panidiomorphic texture imparted by the megacrysts/phenocrysts of mica and amphibole with feldspar, apatite, titanite, zircon and opaques confined to the groundmass. Based on combined mineralogy and geochemistry, the lamprophyre is classified to be of calc-alkaline variety (minette) with shoshonitic affinities. Mg# (70.7–78.2) contents highlight the primitive melt character whereas incompatible trace element ratios exclude crustal contamination and are indistinguishable from those of the subduction-related global as well as Eastern Dharwar craton (southern India) calc-alkaline lamprophyres. U-Pb dating of apatite gave an emplacement age of 944 ± 82 Ma which is indistinguishable, within the error limits, from the U-Pb titanite age of 942.1 ± 5 Ma demonstrating a Neoproterozoic magmatic emplacement age of the lamprophyre synchronous with the Rodinia assembly. Bulk-rock 87Sr/86Srinitial (0.707239 and 0.708910) and ɛNdinitial (-8.9 to -8.3) highlights the involvement of an enriched mantle source. Calculated Paleoproterozoic model ages (Nd depleted mantle) of 2.1 Ga of the lamprophyre are indistinguishable from those of the co-spatial amphibolite dykes. Petrogenetic modeling involving rare earth elements reveals that the derivation of the lamprophyre magma from 2 to 3% partial melting of a mixed garnet (70%) and spinel (30%) lherzolitic mantle source with minor phlogopite. Our study highlights that the western part of the CGC was less affected, relative to the eastern part, by the M3 regional amphibolite grade metamorphic event (ca. 920-880 Ma) and also supports the geodynamic models involving northward-directed subduction of the Southern Indian block under the Northern Indian block.-

Perovskite geochronology and petrogenesis of the Neoproterozoic Mad Gap Yards ultramafic lamprophyre dykes, East Kimberley region, Western Australia

Perovskite geochronology and petrogenesis of the Neoproterozoic Mad Gap Yards ultramafic lamprophyre dykes, East Kimberley region, Western Australia

Geochemistry, Petrogenesis and dating of lamprophyric dykes in the Kaleybar area, NW Iran

Geochemistry, Petrogenesis and dating of lamprophyric dykes in the Kaleybar area, NW Iran

Mesozoic tectonic transition from the Tethyan to Paleo-Pacific domains in South China: New insights from Mesozoic igneous rocks in the western Nanling Range

• The studied Mesozoic igneous in the Nanling Rang include post-orogenic ultramafic–mafic rock, subduction-related mafic rocks and other calc-alkaline intermediate-felsic rocks. • Those igneous rock assemblages in the Nanling Rang reflect the tectonic transition of the SCB. • The Nanling Rang was a Tethyan domain before ca. 170 Ma but a Paleo-Pacific domain after that. • The Mesozoic evolution of the SCB involved four stages: post-orogenic extension, slab foundering, and tectonic transition from subduction to rollback, followed by slab rollback. Mesozoic tectono-magmatic evolution of the Nanling Range in the South China Block (SCB) remains controversial, especially about the role of the Tethyan and Paleo-Pacific dynamics in the generation of Mesozoic igneous rocks. The Mesozoic magmatic events have produced a diverse variety of rocks, dominantly granites and spatially associated mafic–ultramafic rocks, lamprophyres and diorites. We present new zircon U-Pb ages and in-situ Hf isotope data, along with whole-rock elemental and Sr-Nd isotopic data for the Mesozoic igneous rocks from the western Nanling Range. The two ca. 200 Ma ultramafic–mafic rocks have low SiO 2 contents (40.00–44.94 wt%) and typical ocean island basalt (OIB)-like trace elemental affinities with positive Nb and Ta anomalies, positive ε Nd (t) (4.47 to 4.88) and variable ε Hf (t) values (–3.65 to 11.91), suggesting that they were generated by partial melting of an asthenospheric mantle source. The ca. 165 Ma Jiangyong lamprophyre dyke has relatively high SiO 2 content (51.70 wt%) and arc-like trace elemental affinities with significantly negative Nb and Ta anomalies and variable ε Hf (t) values (–9.10 to 2.65). They were derived from a lithospheric mantle source previously modified by subducted component, along with a contribution from the asthenospheric mantle. Granites from the ca. 146–137 Ma Taibao granitic pluton have high SiO 2 contents (63.41–66.66 wt%), variable (La/Yb) N and Sr/Y values, and negative to positive ε Hf (t) values (−4.16 to 0.86). These granites have compositions transitional from adakite to arc-type rocks and were likely generated by partial melting of Mesoproterozoic meta -igneous rocks, with an addition of a mantle-derived component. Compared with those granites, diorites of the ca. 99 Ma Eryue pluton exhibit moderate SiO 2 contents (59.90–60.30 wt%), a wide range of zircon ε Hf (t) values (−12.04 to 0.50) and negative ε Nd (t) values (–8.61 to –8.57), and they were probably formed by magma mixing of crust-mantle materials associated with back-arc extension. Our new data, together with other geological evidence, provide further insights for the evolution of the Tethyan and Paleo-Pacific tectonic domains during the Late Triassic to Late Cretaceous in the SCB. In the early stage, the Tethyan tectonic domain, ultramafic–mafic rocks from the Ludong and Fuchuan plutons in the Nanling Range was related to the post-orogenic extension. This domain was gradually changed to the Paleo-Pacific domain during the period from Late Triassic to Early Jurassic and the tectonic transition was accomplished at ∼ 170 ± 5 Ma. In the later stage, the Paleo-Pacific tectonic domain, the Jiangyong lamprophyre, Taibao granites and Eryue diorites were produced via the crustal thickening, localized extension, and large-scale lithospheric extension due to the advancing, slab-foundering, and rollback of the oceanic slab during the period from Middle Jurassic to Late Cretaceous.