Rock Associations Research Articles

Hualgayoc mining district, northern Peru: Testing the use of zircon composition in exploration for porphyry-type deposits

The Hualgayoc district in the Cajamarca region, northern Peru, hosts several deposits, including the Cerro Corona Au + Cu porphyry deposit (0.55 Mt Cu, 99 t Au) and the Tantahuatay high-sulfidation epithermal Au deposit (74 t Au), plus other Au, Cu, Ag and base metal prospects. Previous studies have documented that zircon in igneous rocks associated with porphyry systems elsewhere in the world shows large positive Ce anomalies and small negative Eu anomalies, which reflect both the oxidized and hydrous nature of their parental magmas. This study presents the trace element compositions of magmatic zircon from igneous rocks associated with porphyry-style mineralization, as well as barren stocks, sills and volcanic rocks in the district, in order to investigate the usefulness of zircon composition in exploration for porphyry-type deposits. The compositions of the zircon suggest that all parental magmas in the Hualgayoc district are oxidized, and that the magnitude of Ce and Eu anomalies is independent of the spatial and/or temporal association of igneous rocks with mineralization. Although zircon composition is not sufficient to recognize specific intrusions as fertile to generate hydrothermal ore deposits, the composition, properly applied, may be useful to target areas containing oxidized igneous rocks for further detailed exploration.

Contrasting high-Mg, high-K rocks in Central Iberia: the appinite—vaugnerite conundrum and their (non-existent) relation with arc magmatism

The central zone of the Iberian Massif contains abundant granitic batholiths, mostly consisting of peraluminous granodiorites to granites, with minor volumes of high-Mg and high-K ultramafic, mafic, and intermediate rocks (UMI rocks), belonging to two associations: vaugnerites and appinites. The UMI rocks crop out as small stocks within anatectic domains or granite bodies, as enclaves (scattered, clusters or swarms), even as syn-plutonic dikes. SHRIMP zircon U–Pb ages range from ~ 291 Ma to ~ 328 Ma, being broadly coeval with the granites and slightly younger than the anatexites that host them. The vaugnerites are alkaline, with Na2O + K2O concentrations similar to shoshonites, whereas the appinites are comparable to high-K calc-alkaline series, but in no way can they be considered arc-rocks indicative of subduction. Compared with arc-related shoshonites and high-K calc-alkaline rocks, the Iberian UMI rocks, especially the vaugnerites, are much more enriched in mica-compatible elements such as Li, Rb, Cs, Be, Sn, Nb, etc. as well as in Th and U. They also have extraordinarily elevated production of radiogenic heat, the appinites about 1.5 µWm−3, and the vaugnerites about 3.9 µWm−3. These values contrast with the average heat production of the upper mantle (0.02 µWm−3) and the lower continental crust (0.6 µWm−3) and are even higher than the average continental crust (1.4 µWm−3) indicating extensive crustal contamination. The negative whole-rock eNdt, usually between − 2 and – 6, the elevated initial 87Sr/86Sr, usually > 0.706, and the old Nd model ages (1 Ga to 1.5 Ga), i.e., much higher than the zircon crystallization ages, reinforces this idea. Despite both rock associations being affected by crustal contamination, the processes that operated were different. Whereas appinites may have resulted from bulk contamination with anatexites plus crystal fractionation, the vaugnerites require contamination with supercritical fluids resulting from biotite breakdown. Accordingly, we propose that the production of appinites or vaugnerites depends on the fertility of the metamorphic rocks they traversed en route from the mantle to the middle crust: if the host rock was fertile and partially molten, the intrusion of mafic magma increased the melt fraction so permitting bulk contamination to produce hybrid appinite magmas; if the rock was infertile, the fluids released from micas breakdown during the metamorphism could migrate as such to the mafic magmas, contaminating them to yield vaugnerite magmas.

Breed Associations of the Gaisin Block of the Ukrainian Shield

The Gaysins block is characterized by a wide range of both metamorphic and ultrametamorphic formations. Ultrametamorphic formations are represented by an association of rocks with a transition from charnockitoids to two-feldspar granites. Remnants of metamorphic rocks are composed of diafluorinated varieties to varying degrees. Geological surveys of the last decades have discovered on the territory of the Gaysin block structures of variegated composition, which are represented by both metamorphic and ultrametamorphic rocks. The most studied are structures in the area of the settlements of Chagiv, Tyagun, Sitkovtsi, Naraevka, Tsibuliv and Popudnya. The wide variety of the mineral composition of the rocks of the Gaysinsky block is due to the metamorpho-metasomatic transformations of the primary parageneses formed under the conditions of the granulite facies. These transformations are taking place against the background of a decrease in the PT parameters of regional metamorphism.

A review and appraisal on the study progress of the geological evolution of Sri Lanka: Rock associations, metamorphism and their relations with Gondwana

地球表生环境的演变及生命演化过程，与地球构造过程密切相关，新元古代-寒武纪时期的冈瓦纳大陆汇聚过程见证了一系列剧变。东非造山带（ca.650~620Ma）和Kuunga造山带（ca.600~500Ma）是冈瓦纳大陆块体汇聚过程中形成的两条主要造山带，二者在斯里兰卡所在的区域十字交叉。因此斯里兰卡地质演化历史的准确梳理，对理解新元古代时期全球构造过程的重要意义不言而喻。斯里兰卡的四个前寒武纪地质体（Wanni、Kadugannawa、Highland和Vijayan杂岩地体）中，中部的Highland杂岩地体最古老（ca.2000~1800Ma）、变质程度最高（普遍麻粒岩相，局部为超高温麻粒岩相），其余三个地质体主要岩石的形成时代为中元古代晚期-新元古代（ca.1100~700Ma），岩石记录的变质级别略低于Highland地体，为角闪岩相-麻粒岩相。现有研究表明斯里兰卡几个地质体在新元古代-寒武纪时期（ca.610~500Ma）的变质作用记录最为显著，并伴随有广泛的陆壳重熔再造。该构造热事件晚于东非造山带的变质时代（ca.650~620Ma），与Kuunga造山带活动时间（ca.600~500Ma）吻合度较高，这与前人提出的莫桑比克缝合带（东非造山带）穿过斯里兰卡的认识相矛盾。斯里兰卡的高级变质作用究竟是单次造山作用的结果，还是代表了两期造山事件的叠加效应，目前尚无定论。高温-超高温变质作用是斯里兰卡前寒武纪基底岩系的显著特征，其中超高温麻粒岩具有假蓝宝石+石英、紫苏辉石（Al₂O₃含量可达~13%）+夕线石、尖晶石+石英等的矿物组合，不同研究者给出超高温峰期变质温度在950~1150℃的范围内，峰期变质压力在10~16kbar的范围内，多显示顺时针演化<i>P</i>-<i>T</i>轨迹。斯里兰卡中东部地区的基性麻粒岩，发育由斜方辉石+斜长石、角闪石+斜长石或单斜辉石+斜长石组成的环绕石榴石的蠕虫状后成合晶结构，指示近等温降压的<i>P</i>-<i>T</i>演化样式，以及峰期变质作用之后地体相对快速抬升的演化过程。紫苏花岗岩在斯里兰卡不同地体中都很常见，与所有的高级变质岩（如泥质、基性麻粒岩和钙硅酸盐岩等）密切伴生，是研究斯里兰卡地质演化不可忽视的岩石类型。紫苏花岗岩的原岩成因较为复杂，其最古老部分的形成时代可能为太古宙或古元古代（~1850Ma），但是没有很好的年代学限定。部分紫苏花岗岩原岩时代为ca.1100~750Ma，具有钙碱性弧岩浆的地球化学特征，并记录ca.580~500Ma的变质作用，还有一部分紫苏花岗岩时代与区域麻粒岩相变质作用的峰期时代相当，为ca.580~550Ma。在一些地区的角闪片麻岩中，还可以观察到补丁状分布的初始紫苏花岗岩，其形成时代多被认为晚于峰期麻粒岩相变质时代。斯里兰卡四个前寒武纪地质体在岩石组合、变质级别、地质年代学格架等方面的差异被普遍认同，暗示这些地质体具有不同的演化历史。但是斯里兰卡不同地质体的汇聚过程是否对应于莫桑比克洋的闭合，以及Kuunga造山带如何改造斯里兰卡的基底岩石，目前并不清楚。本文综述了前人发表的研究结果，主要从斯里兰卡不同地质体岩石组合、高温-超高温变质作用（Highland地体）、变质地质年代学及其对冈瓦纳大陆重建的启示等几个方面，对斯里兰卡地质演化研究进行归纳和小结。在此基础上提出，在斯里兰卡基底构造框架、新元古代晚期-寒武纪高温-超高温变质作用、紫苏花岗岩成因、地质演化的年代学格架、斯里兰卡在冈瓦纳大陆重建中的位置和作用、下地壳热状态和热源机制等诸多方面，还存在问题和争议，是值得未来开展深入研究的方向。

ОСОБЛИВОСТІ ЛОКАЛІЗАЦІЇ УРАНОВОГО ЗРУДЕНІННЯ В МЕЖАХ ТЕРЕЙНУ ТАЗІАСТ-ТІДЖІРІТ, РЕГІБАТСЬКИЙ ЩИТ

The Reguibat Shield is an area of intensive uranium exploration and about 80 ore occurrences have been discovered in recent decades within its borders. The region of the study is located within the Tasiast-Tijirit terrane, which represents a northwestern part of Archean domain of the Reguibat Shield. The rocks of the terrane are of Mesoarchean age. The main types of rocks are migmatites, gneisses and amphibolites, greenstone associations, granitic intrusions and pegmatites. Samples of pegmatites, granites, ferruginous quartzites and sedimentary rocks that showed an increased radiation level after conducting a ground-based radiometric survey were selected for laboratory studies from the host rocks of the Tasiast-Tijirit terrane. The following types of laboratory analyses were used for the study: 1) spectral analysis by laser-luminescence method to determine the uranium content in samples; 2) atomic emission spectroscopy for the general estimation of concentrations of chemical elements in samples; 3) X-ray fluorescence analysis to determine the chemical composition of samples and its trace elements; 4) electron microprobe analysis to determine the morphology of mineralization and the chemical composition of uranium minerals. Among the Tasiast-Tijirit terrane rocks the increased uranium content was found in the following rock associations: pegmatites and granites; ferruginous quartzites within the banded iron formation; calcretes in sedimentary rocks. According to the results of field and laboratory studies, the main factors of the localization of uranium mineralization in calcretes of the OumDherua area were established. The main geological, physical and chemical conditions essential for the formation of uranium mineralization of the calcrete type within the study region were established. It was found that granites and pegmatites could provide source of uranium for ore mineralization in sedimentary formations, such as surficial and calcrete types. The latter are studied and mined quite intensively in the world including the Reguibat Shield. The study results show the high potential for prospecting and exploration of new uranium occurrences within the Tasiast-Tijirit terrane.

The U-Pb Zircon Geochronology (LA-ICP-MS) of Geological Processes in Granulites of Middle Bouh Area. Article 3. Rock association in the lower reaches of the Yatran river

LA-ICP-MS method was applied to investigate U-Pb and Lu-Hf isotope systematics of zircon crystals from charnockitic gneiss and biotite-garnet-hypersthene enderbite that occur in the lower reaches of the Yatran river (Yatran block of the Bouh river area). According to the obtained isotope data, charnockitic gneiss hosts three zircon populations. The oldest one is represented by three crystals that have isotope age between 3125 and 3300 Ma, and εHf values between –2.3 and –7.5. The next population is well-defined, it has an age of 2038±25 Ma and large variations of Hf isotope composition: 176Hf/177Hf — from 0.28122 to 0.28261, εHf — from –9.3 до 4.6. However, the ages of most of the analyzed zircons spread along the concordia between 2300 and 2800 Ma. All zircons in this population have a similar Hf isotope composition 176Hf/177Hf = 0.28072 to 0.28092, which does not depend on the age. It is characteristic that the oldest (with preserved U-Pb isotope systematics) crystals have positive or slightly negative εHf values. Most of the U-Pb isotope analyses of zircons from enderbite fall on the discordia line that has an upper interception age of 2029 ± 18 Ma. A small number of discordant grains have 207Pb/206Pb ages up to 2500 Ma. Hafnium isotope composition in zircons from enderbite varies widely: 176Hf/177Hf = 0.28131 to 0.28151, and εHf from –6.2 to 1.8.

Petrogenesis of Late Cretaceous volcanic-plutonic complex from Xiaoxiong caldera in East Zhejiang

破火山内出露的火山岩与浅成侵入岩为硅质岩浆演化研究提供了一个重要窗口，从而备受关注。小雄破火山内的火山-侵入杂岩是中国东南沿海晚白垩世岩浆活动的典型代表，包括小雄组火山岩（K₂x）与两类侵入岩（花岗斑岩、正长斑岩）。本文以小雄火山-侵入杂岩为研究对象，开展了系统的锆石U-Pb年代学、岩石学和地球化学研究，旨在深入探讨破火山内火山岩与侵入岩之间的成因联系和岩浆演化过程。系统的LA-ICP-MS 锆石U-Pb年代学研究表明，小雄组火山岩形成于98~88Ma，并具有多期次喷发的特点，可分为下段、中段和上段，年龄分别为98~96Ma（K₂x¹）、95~92Ma（K₂x²）、~ 88Ma（K₂x³）。小雄花岗斑岩形成年龄为90Ma；正长斑岩形成稍晚，约88Ma。与下段流纹质玻屑凝灰岩的Nd-Hf同位素组成[ε_Nd（t）=-8.3~-7.2， ε_Hf（t）=-11.8~-7.2]相比，中段流纹岩要更为亏损[ε_Nd（t）=-5.84~-5.32， ε_Hf（t）=-10.1~-0.5]。研究表明，小雄组流纹质火山岩的母岩浆可能起源于发生在深部岩浆房中渐进的壳幔相互作用，中段流纹岩的源区混入了更多的亏损幔源组分。中段流纹岩与花岗斑岩具有相似的Nd-Hf同位素组成，以及 互补的微量元素地球化学特征，由发生在浅部岩浆房的分离结晶作用和堆晶作用所制约。值得注意的是，正长斑岩与花岗斑岩并不存在直接的成因演化关系，两者应是不同的起源。不同的正长斑岩岩株具有高度一致的结晶年龄、微量元素特征以及Nd-Hf同位素组成，以上特征均表明小雄破火山内的正长斑岩具有相同的起源。正长斑岩母岩浆起源于富集岩石圈地幔的部分熔融，岩浆源区混入了来自亏损的软流圈地幔组分，其地球化学成分变化主要受普通辉石+磷灰石+钛铁矿的分离结晶所控制。;The association of volcanic and shallow plutonic rocks in calderas may provide important clues to the geochemical evolution of silicic magma systems, and thus it has received a lot of attention. The Xiaoxiong caldera, mainly composed of volcanic rocks of the Xiaoxiong Formation (K₂x) and two types of plutonic rocks (granite-porphyry and syenite-porphyry), is a typical product of Late Cretaceous magmatism in SE China. In this paper, we conducted petrological and geochemical studies, as well as zircon dating and trace element analysis for the coexisting volcanic and plutonic rocks from the Xiaoxiong caldera, aiming to constrain the magmatic origin and evolution processes and evaluate the petrogenetic relationship between the volcanism and plutonism. LA-ICP-MS zircon U-Pb dating results revealed that the Xiaoxiong Formation was formed in 98~88Ma with characteristics of multi-staged eruptions. The ages of the Ⅰ-, Ⅱ-, Ⅲ-cycle volcanic rocks are constrained at 98~96Ma (K₂x¹), 95~92Ma (K₂x²) and ~88Ma (K₂x³), respectively. Meanwhile, zircon U-Pb dating provides crystallization ages of ca. 90Ma for granite-porphyry and ca. 88Ma for syenite-porphyry. However, in terms of Nd-Hf isotopic compositions, the rhyolites from the middle section [ε_Nd(t)=-8.3~-7.2, ε_Hf(t)=-11.8~-7.2] record increasingly depleted characteristics to the rhyolitic vitric tuffs from the lower section [ε_Nd(t)=-5.84~-5.32, ε_Hf(t)=-10.1~-0.5], implying a progressive crust-mantle interaction, and more juvenile, Nd-Hf isotopically depleted materials were involved into the source of these rhyolites. The rhyolites from the middle section and the granite-porphyry show cogenetic and complementary geochemical signatures. Therefore, we suggest that they could be closely linked by fractional crystallization and crystal accumulation in a shallow magma chamber, i.e., these rhyolites are formed by the extraction of interstitial melt from crystal mush, while the granite-porphyry represents the residual crystal mush. It is worth to note that there is no directly evolutional relationship between granite-porphyry and syenite-porphyry, and they are more likely to have different magmatic origins. In addition, the syenite-porphyries of different stocks in the Xiaoxiong caldera have a highly consistent crystallization ages, trace element characteristics and Nd-Hf isotope compositions, which indicates that they have the same magmatic origins. The syenite-porphyry was generated probably by pyroxene+apatite+ilmenite -dominated fractional crystallization from basaltic magma that was produced by magma mixing between melts derived from depleted asthenosphere and subduction-related enriched lithospheric mantle.

Chapter 3.1a Antarctic Peninsula and South Shetland Islands: volcanology

Abstract The voluminous continental margin volcanic arc of the Antarctic Peninsula is one of the major tectonic features of West Antarctica. It extends from the Trinity Peninsula and the South Shetland Islands in the north to Alexander Island and Palmer Land in the south, a distance of c. 1300 km, and was related to east-directed subduction beneath the continental margin. Thicknesses of exposed volcanic rocks are up to c. 1.5 km, and the terrain is highly dissected by erosion and heavily glacierized. The arc was active from Late Jurassic or Early Cretaceous times until the Early Miocene, a period of climate cooling from subtropical to glacial. The migration of the volcanic axis was towards the trench over time along most of the length of the arc. Early volcanism was commonly submarine but most of the volcanism was subaerial. Basaltic–andesitic stratocones and large silicic composite volcanoes with calderas can be identified. Other rock associations include volcaniclastic fans, distal tuff accumulations, coastal wetlands and glacio-marine eruptions. Other groups of volcanic rocks of Jurassic age in Alexander Island comprise accreted oceanic basalts within an accretionary complex and volcanic rocks erupted within a rift basin along the continental margin that apparently predate subduction.

Metamorphism of the Dizi Series Rocks (the Greater Caucasus): Petrography, Mineralogy and Evolution of Metamorphic Assemblages

The Dizi Series is exposed within the Southern Slope zone of the Greater Caucasus, in the core of the Svaneti anticlinorium. It is mainly composed of terrigenous, volcanogenic and carbonate rocks faunistically dated from the Devonian to the Triassic inclusive. Regional and contact metamorphism of the Dizi Series rocks was studied. It is stated that the degree of regional metamorphism corresponds to the chlorite-sericite subfacies of the greenschist facies, occurring at a temperature of 300–350°C and a pressure of 1.5–2.3 kbar. As a result of the action of the Middle Jurassic intrusive rock bodies, the regionally metamorphosed rocks of the Dizi Series underwent contact metamorphism. Three zones of contact metamorphism were distinguished corresponding to albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels subfacies. Contact metamorphism took place at a significantly higher temperature and lower pressure than the preceding regional metamorphism. The maximum temperature of the contact metamorphism reached ≈ 570°С, while pressure varied within the range of ≈ 0.3–0.8 kbar. The evolution of rock associations of regional and contact metamorphism of the Dizi Series was studied. The fields of facies and subfacies of regional and contact metamorphism are shown in the Ps-T diagram. Three age populations of zircons were identified using U-Pb LA-ICP-MS dating of the diorite-porphyrite intrusion in the Dizi Series: Zrn1 (ca. 2200 Ma) and Zrn2 (458 ± 29 Ma) that were captured by the diorite-porphyrite magma from the ancient magmatic and metamorphic rocks of the crystalline basement, and Zrn3 (166.5 ± 4.6 Ma) that corresponds to the age of diorite-porphyrite crystallization.

Crystallization ages of the basic intrusive Ediacaran magmatism in the southeastern Dom Feliciano Belt, southernmost Brazil: Implications in the belt geodynamic evolution

The participation of mantle-derived magmas, especially hydrous basaltic liquids, in the evolution of granitic belts in both orogenic and post-collisional environments is crucial to evaluate both mantle and crustal evolution, as well as the material transference processes between these two reservoirs. Besides, this transition in the geodynamic context creates specific conditions, promoting the generation of voluminous magmatism. The Dom Feliciano Belt is a mobile belt in southernmost Brazil, generated during the Brasiliano-Pan-African Orogeny. It comprises an eastern unit, the Pelotas Terrane, essentially formed by Cryogenian and Ediacaran granitoids, with minor dioritic and gabbroic rocks in the southeast of the area. This paper presents geochronological studies to determine the crystallization ages (zircon U-Pb SHRIMP) of the most representative bodies of two associations of basic rocks, the Passo da Fabiana Gabbros (PFG), and the Alto Alegre Diorite (AAD). Besides, two granites in the PFG region were analyzed (zircon U-Pb LA-ICP-MS) to evaluate its emplacement, when compared to those of the basic magmas. The results show that PFG yield a crystallization age of 591.2 ± 3.5 Ma (MSWD = 1.3), while the AAD presented a crystallization age of 562 ± 3.7 Ma (MSWD = 0.73). In the PFG region, a biotite monzogranite, included in the Cerro Grande Suite, yielded an age of 612 ± 1 Ma (MSWD = 0.00083), and a leucosyenogranite of the Dom Feliciano Suite, showed crystallization age of 588 ± 2 Ma (MSWD = 0.00037). Considering the tectonic context of the Dom Feliciano Belt, it is necessary to highlight that an important mantle component, responsible for the generation of water-rich high-alumina calc-alkaline basaltic liquids, was involved in the belt late evolution (590-560 Ma). In this period, the belt was already in post-collisional settings, in a geodynamic context where compressive tensions were cessing, followed by an extensional regime. These conditions enabled mantle-partial melting, which was responsible for the basic rocks generation, with deep regional structures controlling its evolution and emplacement.

Middle Triassic diorites from the Loei Fold Belt, NE Thailand: Petrogenesis and tectonic implications in the context of Paleotethyan subduction

Two Early-Middle Triassic magmatic arc belts occur in the Indochina Block within Thailand, namely the Lampang Volcanic Belt and the Loei-Phetchabun Volcanic Belt, which are about 150 km apart and run parallel to each other. The Lampang Volcanic Belt has been extensively studied and suggested to be induced by eastward Paleotethyan subduction, whereas the Loei-Phetchabun Volcanic Belt has not been well constrained due to the scarcity of geochronological and geochemical data. Here we report a detailed study on zircon U–Pb dating, elemental geochemistry and Sr–Nd isotopes for the Phu Rai diorites recently identified in Loei Province, NE Thailand. The Phu Rai diorites yield Middle Triassic (ca. 239 Ma) emplacement ages. They are calc-alkaline rocks characterized by arc-like trace element patterns and depleted Sr–Nd isotopic compositions ((87Sr/86Sr)i = 0.70371–0.70392; εNd(t) = +1.65 to +2.54). These geochemical and isotopic signatures reveal that the Phu Rai diorites were most likely derived from a depleted mantle wedge metasomatized by subducted sediment-derived melts and slab-derived fluids, and modified by limited degree of fractional crystallization involving clinopyroxene, amphibole and Fe–Ti oxides combined with weak plagioclase accumulation. Based on our results and others from the literature, we suggest the existence of an Early-Middle Triassic (ca. 250–239 Ma) magmatic arc belt in NE Thailand, which is not directly linked to eastward Paleotethyan subduction, but is possibly associated with eastward subduction of the Nan back-arc basin. Specifically, the ca. 239 Ma Phu Rai diorites and ca. 245–241 Ma adakites nearby form a rock association in response to slab break-off at that time, immediately after the initial stage of the Sukhothai-Indochina collision. The occurrence of this rock association could mark not only the cessation of eastward subduction of the Nan back-arc basin but also the initiation of the Sukhothai-Indochina collision.

Main and rare earth elements of amphibolites of the Ray-Iz massif (Polar Urals)

Relevance. The Ray-Iz massif contains the Tsentralnoye chromium ore deposit and is unique in terms of variety of metamorphic rock associations. It has been studied since 1932. However, some aspects of geology and petrology in the literature are not fully covered. One of these areas is a vein series of rocks localized in ultramafic rocks. The spatial confinement of amphibolites to the Central zone of metamorphism, which is consistent with the zone of distribution of deposits and ore occurrences of chromites, determines the need for a detailed study. Purpose of work. Study of mineralogical and petrographic characteristics, as well as the geochemistry of lanthanides of amphibolites of the Ray-Iz massif (Polar Urals). Results. The study of the nature of REE distribution in rock-forming minerals made it possible to determine that the variation in the amount of REE (33–75 g/t) within one rock is associated with the quantitative content of the main minerals-concentrators. The main mineral concentrator lanthanides in garnet amphibolites is garnet, while amphibole is in garnet-free pyroxene-bearing amphibolites. Based on the results of the chemical composition of amphibole and coexisting plagioclases and amphibolite garnets, the temperature was calculated using amphiboleplagioclase by T. Holland, J. Blundy, as well as the garnet amphibolite by L. L. Perchuk geothermometers and pressure based on amphibole geobarometer by M. W. Schmidt. Conclusion. The nature of the distribution of lanthanides in the main rock-forming minerals, amphibole and garnet, has been revealed. Comparison of parameters and compositional features of amphiboles made it possible to conclude that there is a direct relationship between temperature, pressure, the sum of REE and TiO2 , as well as (La/Yb)n , in the mineral.

THE PHENOMENON OF RAPID ACCUMULATION OF SEDIMENTS BELONGING TO THE UDOKAN GROUP AND THE FORMATION OF THE UNIQUE UDOKAN COPPER DEPOSIT (ALDAN SHIELD, SIBERIAN CRATON)

We analyzed new geological and geochronological data on sedimentation and metamorphism in the junction area of the Aldan and Stanovoy Superterranes comprising the southern flank of the Siberian craton. The analysis was focused on early Proterozoic deposits belonging to the Udokan group. It is confirmed that highly metamorphosed rocks at the base of the Udokan group (Kolar subgroup of the Stanovoy suture zone) differ sharply from other rock associations included in this group (Chiney and Kemen subgroups of the Aldan Superterrane). They differ in the degree of metamorphic alterations, style of tectonic deformation, igneous complexes intruding them, and show a complete lack of copper mineralization. There are thus grounds to exclude the Kolar subgroup from the Udokan group. According to our data, the age of the sediments in the Udokan group, including the Chiney and Kemen subgroups, is 1.90‒1.87 Ga, i.e. in the study area, sedimentation lasted for no more than 30 Ma and proceeded simultaneously with the copper mineralization within the intracontinental extensional basin at the stage of collapse of the early Proterozoic orogen.

Multistage Magmatism in Ophiolites and Associated Metavolcanites of the Ulan-Sar’dag Mélange (East Sayan, Russia)

We present new whole-rock major and trace element, mineral chemistry, and U-Pb isotope data for the Ulan-Sar’dag mélange, including different lithostratigraphic units: Ophiolitic, mafic rocks and metavolcanites. The Ulan-Sar’dag mélange comprises of a seafloor and island-arc system of remnants of the Paleo-Asian Ocean. Detailed studies on the magmatic rocks led to the discovery of a rock association that possesses differing geochemical signatures within the studied area. The Ulan-Sar’dag mélange includes blocks of mantle peridotite, podiform chromitite, cumulate rocks, deep-water siliceous chert, and metavolcanic rocks of the Ilchir suite. The ophiolitic unit shows overturned pseudostratigraphy. The nappe of mantle tectonites is thrusted over the volcanic-sedimentary sequence of the Ilchir suite. The metavolcanic series consist of basic, intermediate, and alkaline rocks. The mantle peridotite and cumulate rocks formed in a supra-subduction zone environment. The mafic and metavolcanic rocks belong to the following geochemical types: (1) Ensimatic island-arc boninites; (2) island-arc calc-alkaline andesitic basalts, andesites, and dacites; (3) tholeiitic basalts of mid-ocean ridges; and (4) oceanic island basalts. U–Pb dating of zircons from the trachyandesite, belonging to the second geochemical type, yielded a date of 833 ± 4 Ma which is interpreted as the crystallization age during mature island-arc and intra-arc rifting stages. The possible influence of later plume magmatic-hydrothermal activities led to the appearance of moderately alkaline igneous rocks (monzogabbro, trachybasalt, trachyandesite, subalkaline gabbro, and metasomatized peridotites) with a significant subduction geochemical fingerprint.

Evolution of a Cambro-Ordovician active margin in northern Gondwana: Geochemical and zircon geochronological evidence from the Góry Sowie metasedimentary rocks, Poland

The Góry Sowie Massif (GSM) in Poland represents a Devonian high-pressure–ultrahigh-pressure (HP–UHP) terrane dominated by paragneiss, with subordinate orthogneiss, metabasite and felsic granulite. Whole-rock geochemistry of four migmatitic paragneiss and five granulite samples from the northern part of the GSM was combined with U–Pb–Lu–Hf isotopic data on zircon in order to constrain the sedimentary provenance, tectonic setting and paleogeographic location of the sedimentary paleo-basins now forming the GSM. Granulite and paragneiss protoliths are geochemically analogous to flysch-like graywacke and point either to a continental arc or an active continental margin setting dominated by Cambrian felsic arc detritus. Detrital zircon age spectra record a dominant Ediacaran to Cambrian population (493–600 Ma) with rare clusters of Palaeoproterozoic to Neoarchean age (1900–2100 Ma and 2400–2700 Ma). These reflect a peri-Gondwana provenance in the vicinity of the Trans-Saharan belt and place firm constraints on the age of sedimentary protolith of paragneisses at the middle to late Cambrian. Except one sample, the felsic granulites show only late Cambrian depositional ages. The zircon overgrowth rims give two age clusters, one at c. 397–402 Ma that possibly records a HP metamorphic event, and the other at c. 379–393 Ma that probably records the timing of a high-temperature event including migmatization during exhumation. This tectono-thermal event was coeval with emplacement of Devonian ophiolitic rocks that surround the GSM. The GSM rock association, degree and timing of metamorphism and coeval ophiolite emplacement resemble closely the Galicia-Trás-os-Montes middle and upper allochthonous units in NW Iberia and in the Münchberg Massif in Germany. We suggest that all these massifs were in close spatial proximity before the Devonian and may form part of a single, now tectonically dismembered, terrane or archipelago, which was located along the northern periphery of the Gondwana margin during the Cambro–Ordovician.

Eoarchean rock association in the Dniester-Bouh Domain of the Ukrainian Shield: A suite of LILE-depleted enderbites and mafic granulites

We present the results of a study of an Eoarchean rock assemblage in the Dniester-Bouh Domain of the Ukrainian Shield. This comprises granulite-facies granitoids intercalated with mafic and ultramafic granulites. Zircon U-Pb geochronology indicates enderbite crystallisation at 3786 ± 32 Ma, followed by a subsequent event at ca. 3500 Ma. Several events can be tentatively identified that affected these rocks between ca. 3000 and 2700 Ma. The last zircon growth event took place in response to granulite facies metamorphism and included two separate episodes at ca. 2000 and ca. 1900 Ma. The oldest two zircon populations in enderbites have εHf values around 0, indicating their crystallisation from a protolith with a short crustal residence time. Zircons that crystallised during the 3000–2700 Ma event(s) vary in Hf isotope systematics from εHf ~ 1 at ca. 3000 Ma to εHf ~ −14 at c. 2700 Ma. Paleoproterozoic zircons reveal even more significant variations in εHf value from +6 to –22. Such variations are indicative of juvenile input and mixing with old non-radiogenic Hf.All Eoarchean rocks are depleted in incompatible trace elements and have negative Ta-Nb, P, and Ti anomalies. Compared to the typical TTG associations, enderbites record depletion in felsic components (SiO2, Na2O, K2O, Rb, Th), and enrichment in mafic ones (TiO2, MgO, CaO, V), allowing them to be defined as “mafic” or “depleted” TTG.Geochemical data indicate that mafic and ultramafic rocks of the Dniester-Bouh Domain formed by shallow high-degree melting of the mantle, with the absence of garnet in their source, and the presence of residual Ti-bearing minerals and/or amphibole. In contrast, enderbites were formed from a mixed garnet-bearing amphibolite – eclogite source, i.e. melting over a range of pressures/depths. Our preferred model for the formation of the Eoarchean rock association involves the shallow melting of mantle and formation of basalts and accompanying ultramafic cumulates at a spreading centre, with subsequent underthrusting of one segment of oceanic crust beneath the other, and partial melting of hydrated metamorphosed (eclogitized) mafic rocks in the underthrust plate, leading to the formation of the TTG melts.

Geochemistry and Sr–Nd–Pb isotope characteristics of Miocene basalt–trachyte rock association in transitional zone between the Outer Western Carpathians and Bohemian Massif

Representative samples covering all petrographic types of the Miocene subvolcanic (dykes and sills) basalt-trachyte rock association from the Uherský Brod area (UB, Moravia) in the Czech Republic were studied. The UB area is associated with the Klippen Zone in the neighbourhood of the contact of the Carpathian-Pannonian Block with the Bohemian Massif. The petrographic and geochemical features of the subvolcanic rocks from the UB area only partly resemble those of the calc-alkaline rocks in a similar structural position in the coeval Pieniny area in Poland as well as of the transitional calc-alkaline rocks from the Central Slovakian volcanic field. The Miocene subvolcanic rocks were generated by melting of the variably metasomatised sub-lithospheric source and subsequent fractional crystallisation of the primary basaltic magma. The compositional characteristics of this rock series straddle the alkaline and subalkaline volcanic rock fields, while the rocks from the Pieniny area and from the Central Slovakian volcanic field are predominantly calc-alkaline andesites. The distribution of incompatible elements such as U, Th, REE, Nb, Ta, Sr, Ba as well as LaN/YbN ratios and Sr-Nd-Pb isotope composition of the rocks from the UB and Pieniny areas differ substantially, whereas the geochemical patterns of the UB rocks are slightly similar to those of the transitional rocks from the Central Slovakian volcanic field. The modest contents of incompatible trace elements in the andesitic rocks from the Pieniny area share several characteristics of the prevalent calc-alkaline andesitic rocks from the Carpathian-Pannonian region. Basaltic-trachytic series from the UB area are characterised by higher epsilon Nd (similar to 2.5) and lower Sr-87/Sr-86 (similar to 0.704) and Pb-207/Pb-204 (similar to 15.65) initial values in comparison with the calc-alkaline rocks from the Carpathian-Pannonian region including the Pieniny area. Nevertheless, the basaltic-trachytic rocks from the UB, richer in some of the incompatible trace elements (e.g., U, Th, REE, Sr and Ba) partly resemble (including Sr-Nd-Pb isotopes) the Na-alkaline Miocene volcanic rock series of the NE shoulder of the Cheb-Domažlice Graben in the Bohemian Massif.

The nature of the interface between basalts and serpentinized mantle in oceanic domains: Insights from a geological section in the Alps

The association of mafic extrusive rocks and serpentinized mantle rocks is a common feature encountered in numerous ultra-distal magma-poor rifted margins as well as in (ultra)slow-spreading oceanic settings where detachment faulting and mantle exhumation occur. Although seismic imaging and high-resolution TOBI radar allow imaging this association, the nature of this interface is poorly understood (e.g. nonconformity vs. tectonic channelized vs. diffuse fluid flow along the interface). The timing between magmatism and active detachment faulting is often poorly constrained and it remains difficult to decipher if mafic extrusives are pre-, syn- or post-exhumation of mantle rocks at the seafloor. In this study, we characterize the nature of this interface from a section of a Jurassic ultra-distal margin preserved in the Platta nappe, SE Swiss Alps. We show that the basalt-serpentinized mantle contact does neither correspond to an Alpine thrust system, nor to a nonconformity or a detachment plane exhuming mantle rocks from underneath already emplaced basalts. Rather, the basalt-serpentinite interface corresponds to a weak decoupling level formed by conjugate low-angle normal faults onto which conjugate high-angle normal faults branch. These structures are diagnostic of co-axial extensional tectonics occurring during and after emplacement of basalts over a formerly exhumed serpentinized mantle. Carbonate extensional and shear veins and foliated ophicalcites formed during this Jurassic extensional event. Their distribution across and along the basalt-serpentinite interface demonstrates that this decoupling interface was a high-permeability layer that channelized high fluid flow responsible for the widespread hydrothermal alteration. A positive feedback between fluid flow and extensional deformation is proposed.

Magmatism of the Devonian Altai-Sayan Rift System: Geological and geochemical evidence for diverse plume-lithosphere interactions

The geodynamic environment of the 407–392 Ma Altai-Sayan Rift System is characterized using previously published and new original data on whole rock, trace and Sr-Nd isotopic compositions, along with U-Pb zircon ages. Five magmatic associations are present: basalt (basalts and basaltic trachyandesites), continuous (basalts, andesites, dacite-rhyolites), alkaline (basalts, nephelinite, tephrite, phonotephrite, phonolite, teralite, ijolite-urthite, foyaite, nepheline and alkaline syenite), bimodal (trachybasalts, trachyrhyolites-pantellerites and peralkaline granites) and ultramafic-mafic (picrites and picrodolerites). Mafic rocks of basalt, continuous, alkaline, and bimodal associations exhibit a wide variation of TiO2 (from 1.05 to 4.05 wt%) and are compositionally intermediate between intraplate basalts of OIB type and basalts of active continental margins IAB type. The TiO2 content in these mafic rocks correlates directly with the content of large ion lithophile elements (LILE), rare-earth elements (REE), high field strength elements (HSFE), and particularly with Nb and Ta. The basaltic samples have positive εNd(395) values (+3.4 to +7.7) and a large range of εSr(395) values (−13.6 to +12.6). εSr(395) decreases with increasing TiO2 abundance. Pantellerites and alkaline granites have ore-level concentrations of Nb, Ta, Zr, Hf, REE; and they have similar Sr and Nd isotope parameters to those of the high-Ti basalts. This indicates their origin via fractionation of mantle magmas. Rhyolite samples are depleted in rare incompatible elements, but have low positive εNd(395) values (+1.5 to +1.8), and εSr(395) values (+16.6 to +20.6), and they compositionally resemble the rocks produced from anatectic magmas of crustal origin.Whole-rock elemental and isotopic data suggest that the mafic rocks were likely derived from lithospheric mantle that was metasomatized during the prior Caledonian accretion/subduction event. In combination with the field relationship and regional geology, our study suggests that the rock associations from the Devonian Altai-Sayan Rift System were derived by the activity of mantle plumes.

High-K granites between the Archean Gavião and Jequié blocks, São Francisco Craton, Brazil: Implications for cratonization and amalgamation of the Rhyacian Atlantica continent

Precambrian terrane boundaries are sites of diverse rock associations and structural complexity. Motions along the boundary zones are commonly related to the construction of ancient large continental masses. This seems to be the case in the São Francisco Craton, Brazil, where three major blocks (Gavião, Jequié and Serrinha) collided in the Paleoproterozoic to form the northern part of the craton. This manuscript presents zircon U-Pb ages and whole-rock geochemistry for rock associations on the western border of the Jequié Block, which is defined by the north-trending left-lateral 600-km long Contendas-Jacobina fault zone. The studied rocks are granulite to amphibolite facies Neoarchean orthopyroxene-hornblende granite gneisses of the Jequié block, which also occur tectonically imbricated within Paleoproterozoic metavolcanosedimentary rocks of the Contendas-Mirante belt. The rocks are 2.65-2.63 Ga high-K ferroan, metaluminous to slightly peraluminous syeno-monzogranite in composition, with negative ƐNd(2650) and Nd model ages of 3.05-2.88 Ga. They are depleted in Sr and Ti, enriched in Th, Ba and Pb enrichment, and have marked negative Eu/Eu*. This geochemical signature coupled with the Nd-isotope data indicate that the parental granitic magma was generated by crustal reworking of felsic Mesoarchean crust distinct from the western-sitting >3.3 Ga Gavião Block. The investigated granitic gneisses are similar to other potassic granitoids that occur in the São Francisco Craton, which mark the thermal stabilization of the Archean lithosphere. The westward thrusting of the Neoarchean hornblende granitic gneiss and associated high-Mg tremolitite (meta-basalts) onto Paleoproterozoic volcano-sedimentary sequences establishes field evidence of Paleoproterozoic nappe stacking before lateral displacement during block collision. The crustal amalgamation is related to the assembly of the São Francisco-Congo Craton, a major landmass established before the Columbia supercontinent.