Late Cretaceous Magmatism Research Articles

NEW DATA ON THE AGE OF MAGMATIC ROCKS OF THE ALPHA-MENDELEEV RISE (ARCTIC OCEAN): RESULTS OF ISOTOPIC U/Pb DATING OF ZIRCONS

The age of magmatic rocks of the basic composition sampled at the Alpha-Mendeleev Rise in the Arctic Ocean with the help of a research submarine was studied, based on the measurement of the U/Pb age of zircons separated from them. Early Cretaceous rocks of the moderately alkaline series, formed at the turn of 112 million years, are most common on the Rise. These rocks contain a large number of ancient xenogenic zircons, the age analysis of which shows that the subalkaline melts interacted with the crust at two levels: with the horizon of Early Cretaceous sandstones and with rocks of the Late Archean crystalline basement with an age of 2675.1 ± 11.6 million years. They also contain a small number of younger zircons with an age of 83–87 million years, which probably arose during the recrystallization of Early Cretaceous zircons under the influence of Late Cretaceous magmatism.

New Data on the Age of Magmatic Rocks in the Alpha–Mendeleev Rise (Arctic Ocean) Based on the Results of Isotope U/Pb Dating of Zircons

The age of magmatic rocks of basic composition sampled at the Alpha–Mendeleev Rise in the Arctic Ocean by a research submarine was studied based on the measurement of the U/Pb age of zircons separated from them. Early Cretaceous rocks of the moderately alkaline series, which had been formed at the turn of 112 million years, are most common on the Rise. These rocks contain a large number of ancient xenogenic zircons the age analysis of which shows that the subalkaline melts interacted with the crust at two levels including the horizon of Early Cretaceous sandstones and with rocks of the Late Archean crystalline basement aged 2675.1 ± 11.6 Ma. They also contain a small number of younger zircons aged 83 to 87 Ma, which probably arose during the recrystallization of Early Cretaceous zircons under the influence of Late Cretaceous magmatism.

Post-rift magma plumbing system in the northern Great South Basin, New Zealand

Late Cretaceous magmatism has been widely documented in the Great South Basin (GSB) of New Zealand, which is mainly relevant to the Gondwana break-up (105–83 Ma) and the separation of Zealandia from Australia and Antarctica (83–66 Ma). However, the magma plumbing system in the GSB is still poorly understood. In this study, we used a high-resolution 3D seismic reflection data to investigate the igneous intrusions that developed in the northern part of GSB. These igneous intrusions occurred from ∼75 Ma to ∼58 Ma that corresponded to the spreading of the Tasman Sea and the Southern Ocean. Most of the igneous intrusions developed above listric faults which formed during rifting stage. Moreover, dykes are also observed between the listric faults and igneous intrusions. Listric faults, dykes and sills formed the magma plumbing system of GSB. This study explored the possible origin of post-rift magmatism in the GSB, and addressed the post-rift magma plumbing system in detail, which greatly promoted the understanding of GSB’ evolution, resource exploration and marine geological hazard assessment.

Early Jurassic and Late Cretaceous magmatism on Horseshoe Island, Antarctic Peninsula: New U-Pb and microstructural data

Early Jurassic U-Pb age is obtained for both foliated and undeformed granites on Horseshoe Island, Antarctic Peninsula. Some microstructures in the foliated granites/orthogneisses indicate high-temperature greenschist or low- to medium-temperature amphibolite facies deformation conditions. Additionally, a Late Cretaceous age is yielded for a gabbro intruding the deformed granitoids.

Exotic vs local Caribbean origin for the arc-related Mabujina Amphibolite Complex (Cuba): implications for segmentation of the Caribbean arc during the Cretaceous

ABSTRACT The Mabujina Complex exposed in south-central Cuba consists of an elongated body of metamorphosed volcanic and subvolcanic mafic rocks and tonalitic gneisses. The complex is largely composed of greenschist facies rocks (Porvenir Formation) directly below the Cretaceous volcanic arc section and of a deeper sequence of deformed amphibolite facies rocks (Mabujina Amphibolite Complex). The origin of the protolith of the Mabujina Complex has been the subject of intense debate in the past. While some authors consider the Mabujina Complex to represent the deepest and oldest (Early Cretaceous) exposed section (root) of the Cretaceous Caribbean volcanic arc others suggested an exotic (non-Caribbean related) Early Cretaceous volcanic arc section. The later proposal implies the tectonic emplacement underneath the Caribbean arc of a segment of the Pacific-related Early Cretaceous Mexican Guerrero volcanic arc terrane. A new set of whole-rock geochemical analyses presented in this study shows that the protoliths of the Mabujina Amphibolite Complex constitute an island-arc sequence with a) less abundant island-arc tholeiitic mafic rocks similar to the Early Cretaceous tholeiitic island arc of the Caribbean and b) dominant transitional to calc-alkaline mafic and felsic igneous rocks that resemble the Early to Late Cretaceous magmatism of the Caribbean arc. The high initial Nd ratios of the rocks from the Mabujina Amphibolite Complex are indistinguishable from the tholeiitic to calc-alkaline sequences from the Caribbean arc, reflecting a depleted MORB mantle source with limited subduction-related component input. The present data, together with published geochemical and geochronological data of the protoliths, allow identifying a Caribbean origin for the Mabujina Complex instead of an exotic provenance in the Guerrero Arc of western Mexico. However, even if the interpretation of the geochemical data favours a Caribbean origin, the Mabujina Amphibolite Complex cannot represent the root of the volcanic arc. Here, we propose that the Mabujina Amphibolite Complex is a fragment of the Early to Mid-Cretaceous Caribbean arc that was tectonically emplaced below this same arc as a likely consequence of arc segmentation and strike-slip trans-compression triggered by oblique subduction during the mid-Cretaceous.

Magmatic Processes of Granitoids in the Hongniu-Hongshan Porphyry-Skarn Copper Deposit, Southern Yidun Terrane, China: Evidence from Mineral Geochemistry

The Hongniu-Hongshan porphyry-skarn deposit is located in the southern Yidun terrane in the Sanjiang Tethyan Metallogenic Domain (STMD). Although its metallogenesis has been well constrained in the past decade, the magmatic processes for granitoids in the Hongniu-Hongshan deposit are still poorly understood. Herein, we provide new geochemical data on magmatic minerals (plagioclase, amphibole, and clinopyroxene) in the Hongniu-Hongshan granitoids to get a better insight into these processes. The complex zoning patterns of plagioclase phenocrysts indicate magma recharge and mixing. Physiochemical estimations indicate that clinopyroxenes were crystallized in hotter (919 ± 11 °C) and more mafic (FeO: 2.8–4.6 wt.%, MgO: 0.8–1.8 wt.%) magmas in a deep chamber (18.6 ± 0.9 km) compared with the colder (819 ± 29 °C), more felsic (FeO: 0.9–2.2 wt.%, MgO: 0.3–0.6 wt.%) and shallow magma chamber (13.4 ± 1.6 km) in which amphiboles crystallized. Therefore, we suggest that magmatic minerals in the Hongniu-Hongshan granitoids were produced by multistage magmatic processes within the upper–middle crust range. In this model, the deep-seated magmas recharged into the shallow reservoir and mixed with the shallow magmas therein. The recharged hot magmas may provide heat sources and rejuvenate the shallow magma reservoirs. On this basis, we further infer that ore-forming materials could be pre-concentrated in the crustal range and mobilized by the Late Cretaceous magmatism in the southern Yidun terrane.

Late Cretaceous Transition From Calc-Alkaline to Alkaline Magmatism in the Eastern Anatolian Plateau: Implications for Microblock Collision Timing

Abstract In convergent belts, a collision between two blocks can reshape upper mantle geometry and processes responsible for a change in mechanisms of magma generation with distinct geochemical compositions. Therefore, identifying the turning point of a magma compositional shift can provide key constraints on collision timing, which is decisive in building a framework of regional tectonic evolution. The Eastern Anatolian Plateau is composed of a mosaic of rifted blocks assembled through successive collisional events, culminating with the terminal collision of Arabia with Eurasia and the closure of the southern branch of the Neotethys in the Cenozoic. The timing of the microblock collision of the Bitlis–Pütürge Massifs with the Eastern Taurides Block, the southern Eastern Anatolian Plateau, is a matter of debate due to limited constraints on the timing and petrogenesis of the (post-)collision-related magmatism during the Late Cretaceous. This study identifies three compositionally distinct intrusive suites aged from ~87 to ~69 Ma in the Eastern Taurides Block, the southern Eastern Anatolian Plateau. Group 1 intrusive rocks were emplaced in the southern Eastern Taurides Block at ~87–77 Ma and are characterized by high-K calc-alkaline compositions with predominantly depleted Hf and Nd isotope compositions [εHf(t) = 0.9 to +16.5 and εNd(t) = −2.3 to +6.9]. In contrast, the younger (~77–69 Ma) Group 2A comprises nepheline (Ne)-normative alkaline compositions, and Group 2B consists of shoshonitic compositions; both groups are mainly distributed in the central and northern Eastern Taurides Block. Groups 2A and 2B overlap in age between ~77 and 69 Ma and show relatively enriched Hf–Nd isotope compositions [Group 2A: εHf(t) = −1.0 to +4.7 and εNd(t) = −2.3 to +1.2; Group 2B: εHf(t) = −4.0 to +4.0 and εNd(t) = −6.5 to −1.3]. Group 1 intrusive rocks relate to the sub-arc asthenosphere-derived melts that differentiated toward the granite minimum by fractional crystallization. Parental melts of Group 2A intrusive rocks are interpreted to be derived from metasomatized subcontinental lithospheric mantle and differentiated toward the phonolite minimum. Crustal assimilation during magma ascent pushed the initially silica-undersaturated magma (Group 2A) into silica-(over)saturated compositions (Group 2B) through fractional crystallization that ultimately evolved toward the granite minimum. We propose that the Group 1 magmatism was related to northward subduction and closure of the Berit oceanic lithosphere, whereas the Group 2 magmatism results from collision-induced lithospheric delamination ± slab rollback. Together with the P–T–t evolution of the high-pressure metamorphic rocks from the Bitlis Massif and the spatiotemporal and geochemical variations of the Late Cretaceous magmatism in the Eastern Taurides Block, this study suggests that microblock collision of the Bitlis–Pütürge Massifs with the Eastern Taurides Block (Eurasia) most likely occurred at ~84–77 Ma. This study provides an example to constrain collision timing through a perspective of magmatic transition from calc-alkaline to alkaline series.

Genesis and Significance of Late Cretaceous Granitic Magmatism in Xianghualing Tin–Polymetallic Orefield, Nanling Region, South China

Typical stratiform-like cassiterite–sulfide orebodies formed at 160–150 Ma cut by a steep hydrothermal vein-type orebody were discovered in the Xianghualing tin–polymetallic orefield, which implied a new phase of magmatism and mineralization later than the Late Jurassic stage. Hence, a systematic study of the characteristics and genesis of the concealed Laohuya granite, including U–Pb age, trace elements, Lu–Hf isotopes of zircons, and whole-rock major- and trace-elements, is examined in this paper. The zircon U–Pb dating yielded a Concordia age of 87.75 ± 1 Ma, confirming the existence of Late Cretaceous magmatism in the Xianghualing tin–polymetallic orefield. The Laohuya granite is classified as syenogranite and belongs to the peraluminous, high K calc-alkaline series. It is a highly evolved A2-type granite with εHf(t) values ranging from −14.97 to −7.59 and two-stage model ages (TDM2) ranging from 2939 to 2280 Ma. Combining chronology, petrochemistry, isotopic geochemistry, and previous tectonic studies, we believe that the Laohuya granite originated from the partial melting of a reworked ancient crust composed of TTGs, and its weathered sediments formed in subduction or collision zones at 2.5 Ga, controlled by the reactivation of the Chenzhou–Linwu deep fault in the extensional setting of South China during the Late Cretaceous.

Late Jurassic and Early Cretaceous magmatism along the northeastern margin of the Inner Mongolia Plateau and its tectonic significance

The Inner Mongolia Plateau is located in the north of the Late Palaeozoic Hegenshan ophiolitic mélange belt, and its Mesozoic magmatism impacts our understanding of the tectonic evolution affected by the closing of the Mongol‐Okhotsk Ocean and Palaeo‐Pacific Ocean. Here, we present new U–Pb ages, whole‐rock geochemistry and Hf isotopes from the Late Mesozoic magmatic rocks in the Dalai area along the northeastern margin of the Inner Mongolia Plateau. The Late Jurassic rock types include medium‐fine‐grained phenocryst‐bearing and porphyritic monzogranites as well as medium‐fine‐grained monzogranites with the precise age range of 167.7–159.8 Ma. The Early Cretaceous rock types consist of fine‐grained biotite monzogranite and medium‐fine‐grained biotite monzogranite with the precise age range of 140.9–130.7 Ma. The geochemistry data show that the Late Jurassic and Early Cretaceous rocks are peraluminous granites and high‐K calc‐alkaline series and can be classified as A‐type granite. These granites are enriched in large‐ionlithophile elements such as Rb, Th and U, depleted in the high‐field‐strength elements such as Nb, Sr, P, and Ti. Rare earth elements have high total concentrations and present the light rare earth elements enriched with the heavy rare earth elements depleted. Zircon Hf isotopes show that εHf(t) ranges from +8.0 to +15.9 from the Late Jurassic rocks and +6.9 to +13.5 from the Early Cretaceous rocks. Our new results reveal that the Late Jurassic and the Early Cretaceous magmas were derived from partial melting of the younger lower crust, and the Early Cretaceous rocks are more strongly contaminated than the Jurassic intrusions. The Late Jurassic rocks in the Dalai area were formed from a post‐collisional setting related to the closure of the Mongol‐Okhotsk Ocean in the Early‐Middle Jurassic. The Early Cretaceous intrusions were formed from a transition setting from post‐collision to syn‐collision associated with the superposition of the Mongol‐Okhotsk Ocean and the Palaeo‐Pacific Ocean tectonic domain.

Petrogenesis of the late Cretaceous Budongla Mg-rich monzodiorite pluton in the central Lhasa subterrane, Tibet, China: Whole-rock geochemistry, zircon U-Pb dating, and zircon Lu-Hf isotopes

Mg-rich monzodiorite are found in the Budongla gold ore district, Zhongba County, Xizang (Tibet) Autonomous Region, P.R. China. Studying the petrogenesis of this intermediate pluton can provide effective information to explore the geological evolution of the Lhasa terrane. One monzodiorite sample yielded a weighted mean 206Pb/238U age of 92.7 ± 1.1 Ma (mean square weighted deviation=0.33) using LA-ICP-MS zircon U-Pb dating, which represents the late phase of Late Cretaceous magmatism. The rock-forming minerals in the Budongla Mg-rich monzodiorite mainly include K-feldspar, plagioclase, quartz, biotite augite, and amphibole, and its accessory minerals mainly include magnetite, titanite, zircon, and apatite. The rocks are rich in K2O+Na2O and K2O with medium contents of SiO2, CaO, and A12O3,, suggesting these rocks belong to the high-K calc-alkaline series. These rocks have high MgO, Fe2O3, and FeO, with high Mg# values and low DI, which implies they are Mg-rich intermediate intrusive rocks. The rocks are enriched in LREEs and LILEs and depleted in HREEs and HFSEs. They have negative Eu anomalies, no obvious negative Ce anomalies, and slightly negative εHf(t). We infer that the Budongla pluton is a high-K calc-alkaline metaluminous Mg-rich monzodiorite and intruded during the post-collisional period of the Lhasa and Qiangtang terranes.

Late cretaceous magmatism in the Northern Lhasa subterrane, central Tibet: geodynamic implications

ABSTRACT Compositional changes of successively emplaced magmatites can be used to infer changes in their petrogenetic evolution and geodynamic setting. The central-northern Lhasa terrane hosts extensive Late Cretaceous magmatism, however, the mechanism that triggered the magmatism and its relationship to the directly preceding Late Cretaceous tectonic transition in the central Tibetan Plateau is still unresolved. Therefore, we conducted a detailed petrological, geochronological, geochemical, and isotopic study on recently identified Late Cretaceous doleritic and granodioritic rocks in the Xiongmei area, northern Lhasa subterrane. The potassic (K2O/Na2O ratios >1) dolerites (ca. 80 Ma) display a post-collisional basaltic shoshonitic signature with uniform moderately enriched whole-rock Sr–Nd and zircon–Hf isotopic compositions ((87Sr/86Sr)t = 0.7070 to 0.7095, whole-rock εNd(t) = – 2.4 to – 1.3, and zircon εHf(t) = – 5.9 to +1.9), suggesting that they evolved from a similar parental magma and were likely derived by partial melting of an enriched lithospheric mantle metasomatized by hydrous fluids. The granodiorites are geochemically divided into medium-K and high-K calc-alkaline rocks. The medium-K samples (ca. 80 Ma) are generally characterized by low K2O/Na2O ratios <1, whereas the high-K samples (78–76 Ma) display high K2O/Na2O ratios >1. The medium-K samples have positive zircon εHf(t) values from +4.8 to +6.5 and uniform whole-rock ɛNd(t) values from – 2.4 to – 1.3, which significantly differ from those of the high-K samples that have negative to positive zircon εHf(t) values from – 1.9 to +2.8 and negative whole-rock ɛNd(t) values from – 8.4 to – 5.1. The medium-K samples are characterized by high Sr contents and Sr/Y ratios, coupled with low Y and HREE contents, similar to adakitic compositions, and were interpreted to have been derived from deep partial melting of the foundering juvenile garnet-bearing mafic lower crust at relatively low temperatures. Compared to the medium-K samples, the high-K samples have lower Sr/Y and (La/Yb)N ratios, coupled with flat HREE patterns and distinct negative Eu, Sr and Ti anomalies and are most likely derived from shallower partial melting of the K-rich juvenile lower crust at relatively high temperatures. Considering the occurrence of variable magmatism in the central-northern Lhasa subterrane during the Late Cretaceous, the change in magma composition and lower crustal melting conditions (cold-deep vs. hot-shallow) suggest that the lithospheric mantle keel was partially detached by small-scale mantle convection in response to the low-angle Neo-Tethys-associated subduction between 85 and 70 Ma.

New evidence of Late Cretaceous magmatism on the offshore central West Iberian Margin (Estremadura Spur) from potential field data

The West Iberian Margin (WIM) is a key example of a magma-poor passive margin, punctuated by several post-rift magmatic manifestations that are part of the Late Cretaceous Atlantic Alkaline Province. In this work, potential field (gravity and magnetics) data, constrained by 3D multichannel seismic reflection data, are used to describe and characterise the geometry and nature of magmatic features located offshore the central segment of the margin, the Estremadura Spur. The estimated geometry and nature of the magmatic features was achieved through the integration of 3D gravity and magnetic inversion and 2D magnetic forward modelling. The results provide an insightful 3D subsurface model revealing that: 1) the Estremadura Spur Intrusion represents a 28 × 15 km wide laccolith with an overall granitic nature and an estimated density of 2490–2640 kg/m3 and 0.01–0.05 SI magnetic susceptibility, 2) the 26 × 17 km Fontanelas buried volcano is dominantly basaltic, with density values of 2500–2821 kg/m3 and magnetic susceptibility of 0.01 to 0.0875 SI, and 3) multiple sill complexes intruded the region, thus producing a higher magnetic background on otherwise inconspicuous anomalies The models allowed achieving a confident fit suggesting that both the ESI and the Fontanelas volcano are coeval with the outcropping magmatic features from this same magmatic event. Additionally, the results support that Late Cretaceous alkaline magmatism on the West Iberian Margin is more significant than anticipated and provide further evidence to clarify unclear geometrical aspects of similar intrusions observed onshore. Acknowledging the geometry and nature of these magmatic entities allows to better understand the role of post-rift intra-plate magmatism on continental hyper-extended rifted margins by clarifying how shallow plumbing systems evolve in these settings.

LA–ICP–MS U–Pb Dating, Elemental Mapping and In Situ Trace Element Analyses of Cassiterites from the Gejiu Tin Polymetallic Deposit, SW China: Constraints on the Timing of Mineralization and Precipitation Environment

As a major constituent in magmatic–hydrothermal ore deposits, cassiterites, with moderate amounts of U and low Pb, can be dated with U–Pb geochronology. The tetragonal lattice structure makes cassiterites capable of incorporating dozens of elements within its crystal lattice (e.g., Fe, Ti, W, Zr, Hf, Ta, Nb, Mn, Sc, V, and Sb). Variations of these elements record information of potential elemental substitution mechanisms and precipitation environments of cassiterites. In this study, we collected cassiterite grains from four different ore styles of the Gejiu tin polymetallic deposit to perform LA–ICP–MS U–Pb dating, multiple element mapping, and in situ trace element analysis on these cassiterites. Systematic U–Pb dating yielded Tera–Wasserburg lower intercepted ages at around 85 Ma, coinciding with zircon U–Pb ages of regional Late Yanshanian granitoids, within their respective analytical uncertainties. Such age coincidence, combined with the spatial association, suggests that tin mineralization may be genetically related to the Late Cretaceous granitic magmatism. Multielemental mapping shows that the distribution of Nb, Ta, and Ti in the cassiterite grains correlates well with the regular oscillatory zoning patterns in cathodoluminescence (CL) images. The relatively high Sb, Fe, W, Ga, and U concentrations control the dark luminescing domains in these cassiterite grains. The systematic variations in chemical compositions suggest that trace elements such as Sc, V, Fe, and Ga incorporate in cassiterites via coupled substitutions of Sc3+ + V5+ ↔ 2 (Sn, Ti)4+, Fe3+ + Ga5+ ↔ 2 (Sn, Ti)4+ and Fe3+ + OH– ↔ Sn4+ + O2– or Fe3+ + H+ ↔ Sn4+. The covariation of redox sensitive elements such as W, U, Fe, and Sb indicates that the ”tin-granite” type of cassiterites were formed under an oxidized state whereas cassiterites from skarn, massive sulfide, and oxidized ore styles were precipitated in a reducing environment.

Late Cretaceous granitoids of the Sikhote–Alin orogenic belt, southeastern Russia: implications for the Mesozoic geodynamic history of the eastern Asian continental margin

We present new U–Pb age data for granitoids in the Central Sikhote–Alin orogenic belt in SE Russia, which refute the established opinion about the absence of the Late Cretaceous magmatism at the eastern margin of the Palaeo-Asian continent. It was previously thought that a period of magmatic quiescence occurred from 88 to 50 Ma, related to subduction of the Palaeo-Pacific plate under the eastern margin of the Palaeo-Asian continent, although this is inconsistent with evidence from the Sikhote–Alin, Sakhalin and Japan regions. Three suites of plutonic rocks with different ages were identified in this study. The first suite has ages of 105–92 Ma and formed in a syn-orogenic setting. The second (86–83 Ma) and third ( c. 73 Ma) suites formed during the post-orogenic stage of the Sikhote–Alin orogenic belt. The second and third suites were coeval with Late Cretaceous granitoids that formed in a supra-subduction continental arc known as the Eastern Sikhote–Alin volcanic–plutonic belt. However, the studied rocks are located far inland from the Eastern Sikhote–Alin volcanic–plutonic belt. The ages of the studied granitoids coincide with the timing of a change in the angle of convergence between the Palaeo-Pacific plate and eastern margin of the Palaeo-Asian continent. This change in motion of the oceanic plate with respect to the continental plate was probably caused by a rupture in the subducted slab (i.e. a slab tear), followed by asthenospheric upwelling and partial melting of the overlying crust, which ultimately generated post-orogenic intrusive magmatism. Supplementary material: Laser ablation–inductively coupled plasma–mass spectrometry zircon U–Pb data of the Bikin–Bol. Ussurka granitoid suites are available at https://doi.org/10.6084/m9.figshare.c.5738616

Geochronology and geochemistry of the PiaOac granites: Implication for Late Cretaceous magmatism and metallogeny in NE Vietnam

Sn-W deposits have recently been found in NE Vietnam, which has been considered as southwestern extension of the South China Block. The timing and relationships between the Sn-W mineralization and associated granitic magmatism in this area have not been well understood. This study presents new zircon and cassiterite U-Pb geochronology, whole-rock geochemistry, and zircon Hf-isotope data for the PiaOac granites, greisens, and cassiterite veins in NE Vietnam. The PiaOac granites are characterized by high Na2O + K2O, and K2O/Na2O, and low Fe2O3T and Mg#. The presence of primary muscovite, and high A/CNK (1.23–1.26), Rb/Sr (20–25), and P2O5 (0.33–0.35%) suggest that they are strongly peraluminous S-type granites. Low K/Rb, Zr/Hf, Nb/Ta, and Eu/Eu* indicate that the granitic magma experienced strong fractional crystallization. The PiaOac granites have homogeneous zircon Hf-isotope compositions with average εHf(t) values of −9.6 to −8.7 and two-stage Hf model ages of 1.76–1.71 Ga. They probably were sourced from Neoproterozoic metasedimentary rocks with late Paleoproterozoic model ages in NE Vietnam. Low CaO/Na2O (<0.3) and high Rb/Sr and Rb/Ba ratios further suggest a clay-rich pelitic source. Zircons from greisen have significantly unradiogenic Hf-isotope compositions (εHf (t) = -12.2) and large variations, implying strong interaction with wall rocks in late fluid-rich stage during magmatic evolution. Extended magmatic differentiation was followed by interaction with wall rocks, which has altered the redox environment, facilitating the Sn-W mineralization.Zircon U-Pb dating results reveal that the PiaOac granites formed in the Late Cretaceous (89–88 Ma), coincident with the ∼ 89 Ma mineralization constrained by cassiterite U-Pb dating, suggesting that the Sn-W mineralization is closely related to the granitic magmatism and greisenization. Late Cretaceous magmatism and mineralization in NE Vietnam are similar to those in SW South China in terms of formation age, rock association, deposit type, source composition, and tectonic setting, all together constituting an E-W trending Late Cretaceous metallogenic belt. The Late Cretaceous granites and associated deposits in the belt were probably formed in an intracontinental orogenic setting in response to the combined action of the subduction of Pacific and Neo-Tethys Plates.

Late Cretaceous Magmatism in the Northern Lhasa Subterrane, Central Tibet: Geodynamic Implications

Late Cretaceous Magmatism in the Northern Lhasa Subterrane, Central Tibet: Geodynamic Implications

The birth of the Sava Suture Zone: The early geological observations and the context of bimodal magmatism (southern Belgrade outskirts; Andjelkovic, 1973)

This paper presents one of the significant results of the research of Prof. Dr. Milodrag Andjelkovic. The study underlines the first field record providing the evidence of the Upper Cretaceous bimodal magmatism that eventually led towards the definition of the Late Cretaceous ?Sava?Vardar Zone? in 2002 (Pamic, 2002). Currently, the 20-years old ?Sava?Vardar Zone? i.e., the Sava Suture Zone regarded as a crustal assembly formerly intervening the amalgamated Adria and south Eurasian affinities. The pioneering field mapping- based observations contributing the debuted Sava Suture Zone, are in the underestimated report of Prof. Dr. Milodrag Andjelkovic, presenting his observations of the typifying Late Cretaceous bimodal magmatism (published in 1973 in the regional XIX-century established journal ?Annales geologiques de la peninsule Balkanique?; Title: ?Geologija mezozoika okoline Beograda?, translated: The geology of Mesozoic assembly: vicinity of the Belgrade area). in that time, during early 1970?s, the entire geoscience community of former Yugoslavia for a long time denying any Late Cretaceous magmatism within the Vardar Zone, offering a counterargument grounded onto the geosyncline tectonic framework. The 1973 paper was published much prior the constraints on the Late Cretaceous bimodal magmatic intrusions, discussed as the ?Peri Adriatic Sava magmatic arc? or Peri Adriatic Lineament, but only three decades later. The Andjelkovic?s 1973 report represents the first published record, interpreting a number of the Late Cretaceous bimodal magmatic mini-occurrences distributed in the modern-day Sava Suture Zone belt. Despite using the previous tectonic model, the often-neglected descriptions of the Jurassic?Late Cretaceous biostratigraphy and their spatial relationship with the confined magmatic entities, allow the important correlation of a number of Late Cretaceous smallscale basins, positioned to the northwest (Bosnia &amp; Herzegovina, Croatia), and to the south of Belgrade (Central Serbia, North Macedonia). The understanding of this suture zone, bending in the vicinity of Belgrade, is of primary importance, providing the characterization of the terminal Alpine collisional mechanism in the area.

Rock-Forming (Biotite and Plagioclase) and Accessory (Zircon) Minerals Geochemistry as an Indicator of the Metal Fertility of Magmas by the Example of Au-Cu-Fe-Skarn Deposits in Eastern Transbaikalia

Many gold and gold-bearing complex deposits related to the Late Jurassic and Early Cretaceous magmatism are known in Eastern Transbaikalia. The largest deposits are the Lugokan, the Kultuma and the Bystrinsky. These deposits are in a paragenetic relationship with the Late Jurassic magmatic rocks of the Shakhtama complex. According to the available data, the total resources of gold in these three deposits are estimated to be approximately 443 tons: the Lugokan, Au~53 tons, Cu~302 thousand tons; the Kultuma, Au~121 tons, Cu~587 thousand tons, Fe~33 mln t; the Bystrinsky, Au~269 tons, Cu~2070 thousand tons, Fe~67 mln t. One of the main aims of this work was to reveal the criteria of fertility for the classical porphyry type, based on the specific geochemical features of rock-forming and accessory minerals. A comparison of the obtained results with other data on the large porphyry and skarn deposits of the world showed that the magmatic rocks of the Bystrinsky massif, specifically porphyry species dated 159.6–158.6 Ma, are potentially ore-bearing for the porphyry type mineralization. The magmatic rocks that widely occur at the Lugokan and Kultuma deposits are most close to the Fe-skarn deposits. The best indicators of the magma fertility for the porphyry rocks are Ce/Ce*, Eu/Eu*, Yb/Dy, (Ce/Nd)/Y in zircons. Thus, magmatic rocks characterized by Ce/Ce* &gt; 100, Eu/Eu* &gt; 0.4, Yb/Dy &gt; 5.0 and (Ce/Nd)/Y &gt; 0.01 may be classified as high fertile for the classical porphyry mineralization in Eastern Transbaikalia. The plagioclase and biotite chemistry data also showed that the magmatic rocks that occurred at the Bystrinsky deposit are the most fertile for the porphyry type mineralization. The magmatic rocks classified as ore-bearing porphyry type have Al* &gt; 1 in plagioclase, high values of IV(F) and IV(F/Cl) and low ratios of X(F)/X(OH) in biotites. The assessment of the metal fertility of magmatic rocks is most effective in combination with data on both the composition of rock-forming and accessory minerals. The obtained data may be used to develop the methods of prediction and search for gold, copper and iron mineralization.

Nature, timing and magnitude of buried Late Cretaceous magmatism on the central West Iberian Margin

AbstractThe magma‐poor West Iberian Margin (WIM), as part of the Peri‐Atlantic alkaline province, records multiple evidence for intra‐plate post‐rift magmatism. Based on high‐resolution multichannel seismic data, this work discusses the presence of large volcanic and intrusive features in the Estremadura Spur, providing evidence for important magmatic activity during the drifting of the continental margin. Our observations reveal distinct voluminous fissure‐fed effusive sequences and the details of the 2800 m‐high Fontanelas compound volcano, including its external and internal architecture, secondary vents and associated lava flows, all of which were probably extruded at intermediate water depths. Numerous and morphologically diverse sills and sill complexes are also described, attesting to the presence of a Late Cretaceous shallow magmatic plumbing system in the area. Magmatism in this region is interpreted as having occurred during two main pulses and types of activity: (1) Coniacian to lower Campanian(?) age, characterised by fissural and fault‐controlled volcanism, which mostly extruded massive lobate/sheet lava flows; and (2) a second voluminous intrusive and extrusive event of mid to late Campanian age, which includes the intrusion of the Estremadura Spur laccolith and the prominent Fontanelas compound volcano with associated dendritic lava flows. The inferred volumes of the first fissure‐fed effusive event suggest a large eruption magnitude, comparable to some of the largest historical effusive eruptions. The second magmatic pulse led to the emplacement of discrete clusters of sills and sill complexes, as well as the construction of the ca. 2.8‐km‐high Fontanelas volcano, suggesting a syn‐rift structural inheritance that controlled the location of the Estremadura Spur Intrusion and the Fontanelas volcanic area. Altogether, a total volume of rock exceeding 1.452 km3 is estimated to have been emplaced or extruded in this region in a relatively short period, attesting to the prominence of the magmatism in this sector of the WIM.

Hafnium isotopes in zircons track the changing sources for the Late Cretaceous magmatism in Eastern Srednogorie, Bulgaria

We present new Hf isotopic data of magmatic zircons from the Eastern Srednogorie zone. The data outline two clear temporal trends: rising initial εHf from the initiation of the magmatism at ~95 Ma to 81 Ma, followed by a rapid decline in the initial εHf in the 81–78 Ma time period. The first trend highlights the increasing participation of mantle melts in the formation of magmatic products in the East Balkan and Strandzha regions, which is likely dictated by the southward retreat of the subducting slab. This trend is also evident in published Hf isotopic data on zircons from Central Srednogorie zone. The second trend of rapidly decreasing initial εHf of zircons is interpreted to reflect increased proportion of lower crustal melts in an intra-arc rift extensional environment (the Yambol-Burgas region) between 81 and 78 Ma; this trend is not observed in the Central Srednogorie zone.