Rapakivi Research Articles

New insights on the origin for rapakivi granites: U-Pb and Lu-Hf in zircon from Alto Candeias Intrusive Suite, Amazonian Craton, Brazil

The Southwestern Amazonian Craton, in Rondônia state, Brazil, comprises multiple orogens with ages ranging from 1.8 to 1.0 Ga, where successive magmatic, metamorphic, and deformational processes reworked ancient rocks and produced new complexes and juvenile continental crust. Identification of the geochronological and petrographic characteristics of granitoids and terranes generated during such events is crucial for the recognition and distinction of their magma sources. A total of 64 samples collected from the Alto Candeias Intrusive Suite outcrops in Rondônia state recognized four different groups: (1) Monte Negro unit (rapakivi granites), (2) Buriti unit (equigranular to porphyritic granodiorites), (3) Campo Novo unit (medium to coarse-grained charnockites), and (4) Jacilândia unit (fine-grained granites). U-Pb geochronological data were obtained for each unit, with the following ages: 1350 ± 5 Ma (Monte Negro unit), 1350 ± 2 Ma (Buriti unit), 1349 ± 3 Ma (Campo Novo unit), 1348 ± 3 Ma, and 1349 ± 1 Ma (Jacilândia unit). The ages of the four granitic units are the same within error. Lu-Hf isotopic results presented in this study indicate that the Alto Candeias Intrusive Suite has the mantle as the magmatic source and that the continental crust coeval to the subduction process. This process led to the formation of I-type granitoids generated in the SW margin of the Amazonian Craton around 1350 Ma during San Ignacio orogeny.

Rapakivi granites and associating magmatism during the Aptian development stage of the Siberian craton active continental margin (northeast Asia)

Rapakivi granites and associating magmatism during the Aptian development stage of the Siberian craton active continental margin (northeast Asia)

Rapakivi Granites and Associating Magmatism during the Aptian Development Phase of the Siberian Craton Active Continental Margin (Northeast Asia)

Rapakivi Granites and Associating Magmatism during the Aptian Development Phase of the Siberian Craton Active Continental Margin (Northeast Asia)

Mesoproterozoic Strike-Slip Faulting within the Åland Rapakivi Batholith, Southwestern Finland

Paleostress inversion analysis of outcrop data from brittle fault structures within the Mesoproterozoic 1.58 Ga Åland rapakivi granite, southwestern Finland, revealed two separate strike-slip faulting stages. Stage 1 is dominated by dextral slip along E–W-trending faults under WNW–ESE to NNW–SSE compression, whereas Stage 2 displays less prominent faulting localized in an orthogonal network of N–S and E–W trending faults that developed under NE–SW compression. Relative age constraints indicate that faulting occurred between 1.58 and 0.5 Ga, and further correlation with previously published results indicate a 1.55–1.4 Ga age for Stage 1 faulting, while Stage 2 is compatible with previously described fault reactivations between 1.3–1.2 Ga. To place the results of the fault analyses in a wider framework, we conducted a regional structural interpretation using bathymetric, topographic, and geophysical datasets and reviewed previously published results. Based on the above, we attribute the emplacement of the 1.6–1.5 Ga rapakivi granites and the subsequent development of the Mesoproterozoic sedimentary basins to the reactivation of inherited Paleoproterozoic shear zones during Mesoproterozoic crustal extension. As such, this study contributes towards understanding the relationships between magmatism and strain localisation in continental (failed) rift settings.

Gravity modeling of ore gabbroids Korsun-Novomirhorod pluton

This work concerned three-dimensional gravity modeling of the Gorodishche gabbro-anorthosite massif located within the Korsun-Novomirgorod pluton of the Ukrainian Shield. A three-dimensional model of the upper crust was created using maps of the anomalous gravitational field at a scale of 1:200 000, taking into account data from seismic methods of various modifications. The differences in the structure of the intrusive complex and its gneisses were reflected in seismic wave fields, allowing us to determine the boundaries of the entire intrusive massif: rapakivi granites and basic rocks. Three-dimensional gravity was modeled to separate these complexes of different densities. This made it possible to identify gabbro-anorthosite bodies with a maximum thickness of 5 km in the upper part of the section, and to study the contacts of the intrusive complex and gneisses. In the process of solving inverse problems, various criteria for local optimization of gravitational field sources were implemented. In the iterative process, three different functionals were calculated. The mean square of the difference between the observed and theoretical fields is F1, the average sum of the moduli of the field difference is the functional F2, and the preliminary logarithm of the parameters is the functional F3. The joint use of functionals makes it possible to reduce various types of noise in the observed potential field data. In the process of research, it was found that the use of functionals of various types in the selection method algorithms is quite advisable. This makes it possible to create new algorithms that improve feasible solutions to the inverse problem, which is necessary for the implementation of additive technologies for the quantitative interpretation of gravity survey data. The constructed model, which takes into account all available a priori information about the density and geometric parameters of anome-forming objects, can be used to obtain additional reliable geological information about gabbro-anarthosite massifs.

Quartz Porphyries on the Outer Islands in the Gulf of Finland: Volcanic Comagmates of Rapakivi Granites

Quartz Porphyries on the Outer Islands in the Gulf of Finland: Volcanic Comagmates of Rapakivi Granites

Quartz Porphyries of the Outer Islands of the Gulf of Finland ‒ Volcanic Comagmates of the Rapakivi Granites

The article presents new petrogeochemical data of rocks from the area of the Outer Islands of the Gulf of Finland. Previously, quartz porphyries of Gogland Island were considered as a standard of volcanic comagmates of Rapakivi granite of the Vyborg massif. There are two effusive tolshas on Sommers Island. The “Southern” is composed of quartz porphyries, with an isotopic age of 1.66 Ga old, so they can be considered as the earliest manifestations of Riphean magmatic activity in this area. In addition to quartz porphyries, trachybasalts, andesibasalts, and dacites are present in the “Northern” strata, and its isotopic age is 1.59‒1.57 Ga old, which does not correspond to the values of the nearby Vyborg massif 1.65‒1.63 Ga old. Therefore, despite the pro-ximity of the compositions of quartz porphyry and rapakivi granites, volcanites are not products of differentiation of the magma initial for granites, but were formed independently of them from the same type of source, but in a slightly different structural environment, allowing their free flow to the Earth’s surface.

Petrology and geochemistry of Late Triassic rapakivi-type granites in the Dupangling area, South China: Role of fluid-rock interaction in the origin of rapakivi texture

Rapakivi-type granites not only document magmatic processes but also archive subsolidus interactions between granitic rock and fluid, and thereby provide crucial information about fluid infiltration in the Earth's crust. However, the key process to generate rapakivi texture is still debated. Here, we report comprehensive mineralogical, geochemical and Hf isotopic compositions of the Dupangling rapakivi granites (210.4–214.9 Ma) in the South China Block to investigate the effect of fluid-rock interaction on the origin of rapakivi feldspar. Dupangling rapakivi granites have high SiO2 (72.63–78.21 wt%) and alkali contents (Na2O + K2O = 6.14–9.06 wt%) with high K2O/Na2O ratios (1.37–2.64), characteristic of weakly peraluminous (A/CNK = 1.04–1.10) high-K calc-alkaline granites. Samples have weakly fractionated REE patterns with negative Eu anomalies (δEu = 0.05–0.38). They have negative whole-rock εNd(t) (−8.45 to −7.91), variable zircon εHf(t) (−9.7 to −1.0) and two-stage Hf isotope model ages (1.32–1.84 Ga), due to their derivation from a major early Mesoproterozoic crustal source with a subordinate late Paleoproterozoic component. Rapakivi feldspars in Dupangling granites are composed of an alkali-feldspar core and a plagioclase mantle. Fractures, pores and secondary inclusions (biotite, sericite, epidote and hematite) are closely associated with the mantles and oligoclase patches within alkali-feldspar cores. These pervasive microtextural features and variations of Be, Rb, Ba, Sr and LREE within rapakivi feldspars are interpreted to have formed through subsolidus fluid-induced dissolution-reprecipitation replacement processes. This study highlights that fluid-rock interaction plays an important role in generating rapakivi texture.

Red pyterlite from Virolahti in southeastern Finland: a unique heritage stone with a classic rapakivi texture applied in historic and modern architecture

Red pyterlite from Virolahti in southeastern Finland: a unique heritage stone with a classic rapakivi texture applied in historic and modern architecture

Insights into the petrogenetic evolution of the Khallari layered intrusion and coeval granites of the Paleoproterozoic Dongargarh Supergroup, Bastar Craton, India

Several layered igneous complexes around the globe host ultramafic-mafic lithologies at the base to more evolved lithologies at the roof sections. In this study, we report U-Pb zircon ages and geochemistry of Paleoproterozoic granites and Khallari layered intrusion from the Dongargarh Supergroup of Bastar craton, central India. The Khallari layered intrusion hosts pyroxenites at the base to more evolved lithologies including gabbro, layered gabbro and anorthositic gabbros towards the roof section of the magma chamber. The estimated weighted mean U-Pb zircon ages of granites (2443 ± 13 Ma) and layered intrusion (2494 ± 19 Ma and 2469.2 ± 5.2 Ma) are in conjunction with the major Siderian crust building peak identified at the craton. The granitic plutons of the Dongargarh Supergroup are chemically similar to post-collisional/anorogenic granitic rocks, in which the rapakivi granites exhibit a fractional crystallization relation with the Khallari layered intrusion. The Dongargarh granites and enclaves were derived by a combination of fractional crystallization and mixing of partial melts from the pre-existing crust of the Bastar craton. Petrogenetic modeling indicates Khallari layered intrusion is formed by the fractional crystallization of lithospheric mantle melt followed by crystal accumulation. The parental melt also experienced localized crustal contamination (up to 10%) during its evolution. The layered intrusion and the granites formed in a post-collisional rift setting where magmatism postdates the proposed subduction and collisional orogenesis at 2.5 Ga involves cratonic domains of Eastern and Western Bastar cratons.

Natural Experiment on the Extraction and Quenching of Rapakivi-like Magmas: Traces of Interaction with the Mafic Melts and Their Derivatives, Salmi Batholith (Karelia, Russia)

The origin of the anorthosite-rapakivi granite-bearing rock complexes was a topic of research for geologists for more than a century. Magmatic systems that produce these complexes were widely developed in the Precambrian and have no direct analogues in modern times. The main goal of this study was to characterize the conditions under which primitive granitoids formed and to shed light on the history of ore matter transport during these stages. The object of the research was granite porphyry dikes—a subeffusive analogue of rapakivi granite from the Salmi batholith in the Fennoscandian Shield. Characteristic solid-phase inclusions of a mineral paragenesis of mafic rocks, as well as inclusions of sulfide melts, were found in zircon from this type of rock. These sulfide inclusions were homogenized by heating, and subsequently, the trace element composition was determined by the LA-ICP-MS method. The geochemistry of zircons was studied by the SIMS method, and the temperature of their formation was determined using a Ti-geothermometer. The temperature of the studied zircon grain formation varied from 925 to 765 °C. The values of ƒO2 for the early stages of the rock formation were in the region below the boundary of the FMQ buffer. The presence of two sulfide melts at the time at which the sulfide inclusions were captured by the zircon, pyrrhotite-chalcopyrite, and sphalerite-chalcopyrite compositions was established. The capture of sulfide inclusions from the pyrrhotite-chalcopyrite composition occurred above 841 °C, while in sphalerite-chalcopyrite, they occurred at a lower temperature of 765 °C. The connection between the formation of granite porphyry with mafic melts that form rocks of the gabbro and anorthosite types was established.

Geothermal Potential of Hot Dry Rock in South-East Baltic Basin Countries—A Review

The beginning of 2022 was a time of major changes in the perception of energy availability and security in European countries. The aggression of Russia against Ukraine destabilizing the European energy economy, combined with the withdrawal from fossil fuels which has been going on for a dozen years, has strengthened activities to introduce new energy technologies based on renewable energy sources. One of the most promising and stable sources of renewable energy is geothermal energy, in particular enhanced geothermal systems (EGS) in hot dry rocks (HDR). These deposits occur at a great depth in almost every place on Earth, but due to their low permeability, they require hydraulic fracturing, which results in high investment costs. This technology has been developed for several decades. The current situation in Europe seems to confirm that its rapid development to a level that guarantees stable and profitable operation is crucial. This is of particular importance in the case of former member states of the economic zone of the Council for Mutual Economic Assistance, which until recently were heavily dependent on Russian energy. This review, based on the latest available data, covers potential HDR prospective areas in the countries of the south-eastern Baltic basin, including Lithuania, Latvia, Estonia and Poland. It is specific to this region that the original heat flux density is lower as a result of the paleoclimatic effect associated with the youngest ice age; however, thermal conditions do not deviate too much compared to western Europe, especially Rhine Graben, and significantly exceed the conditions of Finland, where an EGS project is currently being operated. In Lithuania, the most prospective area is the ZNI intrusion (south of Klaipeda), characterized by a geothermal gradient of up to 40 °C/1000 m. In addition, the Precambrian batholith south of Liepāja (Latvia) and the Rapakivi granites in the north and center of Estonia are promising EGS sites. Poland has relatively the most explored EGS potential, in both volcanic, crystalline and sedimentary rocks, especially in the area of the Szczecin Trough, Gorzów Block, Moglino-Łódź Trough and Karkonosze Mountains. Unfortunately, local tectonic conditions, in particular the development of faults and natural fracture zones that affect the directions of fracture propagation during hydraulic fracturing, have not been sufficiently recognized, which is one of the main barriers to the expansion of EGS pilot projects in these countries. These issues present challenges for the researchers, especially in terms of petrophysical analyses of rocks in target zones and local stress conditions, which have a key impact on fracturing operations and profitability of the systems. Despite high investment costs on the one hand and a significant slowdown in the global economy in 2022 on the other, it remains hopeful that the authorities of individual countries will decide to accelerate research work, leading to the implementation of pilot projects of EGS installations, and that this technology will be further improved to ensure a stable clean energy supply.

Geochemistry of Xenoliths in Rapakivi Granites of the Korsun-Novomyrhorod Pluton (Ukrainian Shield)

Rapakivi of the Korsun-Novomyrhorod pluton (KNP), being the latest Precambrian granites of the central part of the Ukrainian shield, contain older acidic and intermediate rocks as xenoliths, the geochemical features of which reflect the Early Proterozoic geodynamic situation. Rapakivi granites, their differentiates and three types of xenoliths in them, represented by plagiogneiss, pink granite and charnockitoid (mangerite), were selected in the northwestern part of the KNP for geochemical studies. Analysis findings were compared with the geochemical characteristics of similar rocks of igneous and metamorphic Precambrian complexes that surround the KNP and could serve as a source of xenoliths. Based on distribution patterns of rare earth elements, lithophile elements content and their ratios relations in the rocks, taking into account their petrographic composition, it was established that plagiogneiss belongs to the upper part of the Inhul-Inhulets series, pink granite belongs to the Kirovohrad complex, and charnokitoid belongs to the intermediate rocks of the Tashlyk complex. In the latter, acid charnockitoids (enderbites) are probably younger than intermediate ones and were formed in another geodynamic setting. Pink granite, like the granites of the Kirovohrad complex, shows collisional geochemical features, in contrast to the rapakivi granites containing these xenoliths, which have predominantly within-plate geochemical characteristics. Thus, in the form of xenoliths in rapakivi those rocks were preserved that had been generated before and during the collision that occurred about 2 billion years ago and constructed a crust thickening at the site of the Inhul megablock, under subsequent extension of which about 1.75 billion years ago the KNP was intruded. Acid charnockitoids of the Tashlyk complex and rocks of the Novoukrainian complex, which are absent in xenoliths, probably were formed after the collision.

Tool for similarity identification of rapakivi granites in heritage buildings

• Building stone similarity to quarry rocks can be evaluated using in-situ measurements. • The similarity evaluation is made based on a specific chemical stone fingerprint. • Chemical fingerprint is developed using multivariate statistical analysis. • SIMCA and NBC are appropriate to evaluate the building-to-quarry stone similarity. The similarity of quarry stone with rapakivi stone of two buildings was assessed based on a 9-element fingerprint. The aim of the present case study was to assess the similarity between stones in buildings: the Kotka City Hall and the Orthodox Church of Kotka, and rocks in three Finnish quarries: Heponiemi, Jumalniemi and Metsola. Similarity assessment of building stones is necessary for effective and aesthetically-appropriate reconstruction. In the case of old buildings with stones of unknown origin, data on stone source quarries may have been lost over time. The present tool proposes a methodology to determine the most similar-to-the-origin stone and quarry for use in cultural heritage restoration . The tool in this study utilizes in-situ chemical analyses of the rock surface measured using a portable X-ray fluorescence (XRF) instrument together with modelling of the stone using multivariate statistical approaches (modified Soft Independent Modelling by Class Analogy , SIMCA) and machine learning ( Naive Bayes Classification , NBC) to determine the fingerprint of the stone in the building and assess its similarity to quarry rock data. The proposed methodology for identification of stone origin was utilised in a case study of rapakivi from the Kotka area in Finland.

Trace element composition of quartz from alkaline granites – A factor supporting genetic considerations: Case study of the Pitinga Sn–Nb–Ta–Th-cryolite deposit

The Madeira pluton, bearing the world-class tin-cryolite deposit of Pitinga, and the closely associated Europa pluton lie in the central part of the Amazon craton, Brazil. The Madeira pluton consists of four principal rock types: early metaluminous porphyritic amphibole-biotite granite with rapakivi texture, metaluminous biotite granite, metaluminous hypersolvus porphyritic granite, and peralkaline albite granite, while the Europa pluton consists of peralkaline riebeckite-biotite alkali feldspar granite. Texture and chemical composition of quartz from all mentioned rock types was evaluated in order: (i) to estimate the contents of trace elements in quartz from peralkaline granites, (ii) to define major differences in the uptake of trace elements into quartz in peraluminous vs. peralkaline conditions, (iii) to better constrain the evolution of the composite Madeira pluton. The contents of Li, Be, B, Na, Al, P, K, Sc, Ti, Mn, Fe, Ga, Ge, Rb, Sr, Zr, Nb, Sn, Sb, Ce, Yb, Hf, Ta, Th, and U in quartz were analyzed using laser-ablation ICP-MS. Quartz from the studied metaluminous and peralkaline granites of the Madeira and Europa plutons is poor in Al (<150 ppm Al) and Li (mostly <20 ppm Li) but enriched in Ge (max. 10 ppm), Sc (max. 6 ppm), and Ga (max. 13 ppm). As suggested by the TitaniQ thermobarometer, the Madeira biotite granite crystallized between ca. 700 and 650 °C at a nearly constant pressure of 3 kbar, while the hypersolvus granite crystallized between 800 and 700 °C at 15–20 to 2 kbar. Textural and chemical data on quartz are in agreement with previous geochronological data: the Madeira pluton comprises two older pulses of less evolved, mostly metaluminous biotite-hornblende and biotite granites, and two younger pulses of mutually mingled metaluminous hypersolvus granite and rare metal-enriched peralkaline albite granite. Differences in texture and composition of quartz do not support direct relations between the hypersolvus granite and the albite granite via magmatic fractionation, but exposure to similar metasomatic processes after their mingling is highly probable. Typical chemical features of quartz from peralkaline granites are relative high contents of Ti and Ge accompanied by low contents of Al and Li, forming an array along the Ti–Ge join in the Ti–Al–Ge ternary diagram.

Earth's anomalous middle-age magmatism driven by plate slowdown

The mid-Proterozoic or "boring billion" exhibited extremely stable environmental conditions, with little change in atmospheric oxygen levels, and mildly oxygenated shallow oceans. A limited number of passive margins with extremely long lifespans are observed from this time, suggesting that subdued tectonic activity—a plate slowdown—was the underlying reason for the environmental stability. However, the Proterozoic also has a unique magmatic and metamorphic record; massif-type anorthosites and anorogenic Rapakivi granites are largely confined to this period and the temperature/pressure (thermobaric ratio) of granulite facies metamorphism peaked at over 1500 °C/GPa during the Mesoproterozoic. Here, we develop a method of calculating plate velocities from the passive margin record, benchmarked against Phanerozoic tectonic velocities. We then extend this approach to geological observations from the Proterozoic, and provide the first quantitative constraints on Proterozoic plate velocities that substantiate the postulated slowdown. Using mantle evolution models, we calculate the consequences of this slowdown for mantle temperatures, magmatic regimes and metamorphic conditions in the crust. We show that higher mantle temperatures in the Proterozoic would have resulted in a larger proportion of intrusive magmatism, with mantle-derived melts emplaced at the Moho or into the lower crust, enabling the production of anorthosites and Rapakivi granites, and giving rise to extreme thermobaric ratios of crustal metamorphism when plate velocities were slowest.

The monotonous intermediate magma system of the Permian Wurzen caldera, Germany: Magma dynamics and petrogenetic constraints for a supereruption

The Lower Permian Wurzen caldera formed during a VEI 8 supereruption that tapped monotonous intermediate magmas in a continental rift. The well-preserved crystal-rich intracaldera ignimbrite (<58 vol%) and its related plutonic facies allow for compositional and textural studies on juvenile fragments and mineral phases, providing a unique opportunity to unravel the caldera's pre-eruptive evolution.The climactic Wurzen ignimbrite contains different fiamme of fine-grained mafic, fine-grained rhyolitic (71.8 to 76.6 wt% SiO2), porphyritic (trachy-) dacitic (64.5 to 67.6 wt% SiO2), and coarse porphyritic rhyodacitic composition (64.7 to 74.3 wt% SiO2), which point to a permanent interplay between rejuvenation, differentiation, and cooling in the Wurzen magma body. The similarity of their trace element concentrations suggests derivation from a shallow magma chamber (Nb and Ta at 22 and 1.6 ppm, respectively). The picture becomes more differentiated when considering mineral composition and thermobarometric estimations. Resorption textures in anorthitic plagioclase (An >45 mol%) are presumably formed by excess heat from underplating magmas. Coarse sieve textures in plagioclase indicate a rapid ascent of magma into the shallow magma body. In contrast, oscillatory zonation and rapakivi texture in quartz, albitic plagioclase, and sanidine indicate convection during crystal growth. The spatially discrete crystallization of augite and pigeonite indicates tapping of anhydrous Ca-saturated and -undersaturated magma. The presence of pigeonite indicates eruption from a superheated anhydrous (trachy-) dacitic magma batch at temperatures of 1010 °C, whereas the occurrence of annite implies simultaneous tapping of hydrous shallow magma chambers at low temperatures (~750 °C). By applied barometers on clinopyroxene and biotite, it suggests a deep-seated magma chamber at depths of 25 to 15 km and a shallow magma chamber at ca. 11 km, respectively.Mineral assemblage of the intracaldera Wurzen ignimbrite (quartz, sanidine, plagioclase, calcic and calcic-sodic clinopyroxene, pigeonite, annite) is more typical for crystal-poor, hot rhyolites like in the Snake River Plain (Idaho, USA) or Messum igneous complex (Namibia), than that of monotonous intermediates at active continental margins.

The role of crystal mush in porphyry systems: A case study from the Baishiya ore field, East Kunlun orogenic belt, northern Qinghai-Tibet plateau

Since a cold storage crystal mush reservoir has been gradually used to describe magmas in shallow crust, traditional mechanisms, such as wall-rock assimilation, melt-crystal separation, as well as magma mixing and mingling, must be used with caution because recycled antecrysts can play a significant role. As a result, magmatic processes accounted for texture, geochemistry, and mineralization diversity among ore-related porphyry, overlying (sub)volcanic rocks, and underlying pluton in porphyry systems remain ambiguous. The Baishiya igneous suite (East Kunlun orogenic belt, China) with porphyry-related skarn mineralization provides an opportunity to resolve this issue. Within the crystal mush concept, we propose a comprehensive model based on the subtle changes. First and foremost, large K-feldspar grains characterized by high Sr/Y ratios (52–134) in the top area of granodiorite have a slightly enriched lead isotopic signature, indicating a previously existed crystal mush equilibrated with K-feldspar. The locked crystal mush was injected by mantle-derived mafic melts, leading to a transfer in heat and volatiles from hot melts to cold crystal mush. The buoyant volatiles and loaded metals introduced by episodic mafic replenishments concentrated on the roof, providing a fluid-rich and thermal cycling condition for K-feldspar coarse graining. Some enlarged K-feldspar grains sunk into the bottom area due to gravity, and subsequently reacted with upwelling hot melts to form rapakivi textures. As a gradually waning of injection of mafic melts, crystallization drove fluid exsolution, forming magmatic-hydrothermal events. The finally solidified granodiorite acted as a host rock for a newly produced magma reservoir, but the following development was different. Catastrophic eruptions induced by tectonic stress transition led to a strong depletion of volatiles and associated metal endowment in the underlying magma reservoir, and subsequently left a barren magma source, terminating potential mineralization events. The residual felsic melts migrated upwards along previously formed magma conduits, and thus emplaced as barren porphyry dike. Our work reveals that recycling of K-feldspar antecryst induced by mafic injection contributes to high Sr/Y ratio in ore-related porphyritic granodiorite. Within a long-lived replenishment of mantle-derived magma, a crystal mush reservoir at shallow crustal levels can act as a ‘cooling pond’ to quench these hot melts, but accept volatiles and loaded ore-forming elements, concentrating metals by volatile buoyancy with the help of a compressional stress, which is presumably essential for late fluid exsolution from the reservoir’s roof.

Age and Geochemical Characteristics of Nansu Rapakivi Granite in Jiaobei Uplift Belt, Qingdao

LA-ICP-MS zircon U-Pb geochronology from Nansu large Rapakivi granite in the Jiaobei uplift belt shows the concordant age is 116.5±0.32Ma and the weighted average age is 116.7±0.89Ma, belonging to the late Yanshanian products of Early Cretaceous. The rock geochemical characteristics show that the SiO2 content of rapakivi granite ranges from 70.30% to 71.65%, with an average of 70.975%, A / CNK is 0.871 ~ 0.895 (average 0.883). K2O content is 4.70 ~ 5.75%, with an average of 5.14%, which is characterized by high potassium. Regarding trace elemental patterns, all the studied samples are enriched in large一ion-lithophile elements, e.g., K and Rb, and depleted in high-field-strength elements, e.g., Nb, Ta, and Ti. In terms of the chondrite-normalized rare earth element patterns, the Nansu samples are characterized by the strong enrichment of light rare earth elements (LREE) compared with heavy rare earth elements (HREE) and the absence of negative Eu anomalies. The Nansu ring porphyry granite is of high Sr and low Yb type, belonging to type I adakite, and formed in a high-pressure medium high-temperature environment of about 23km at depth and about 670oC. It is speculated that it was formed in the island arc environment and is related to the subduction of the Mesozoic Pacific plate.

Study supporting restoration of rapakivi granite in St. Petersburg

The focus of this ongoing study has been on two rapakivi granites, wiborgite and pyterlite, that have been utilized in St Petersburg since the 1760s but originate from south-eastern Finland. The aims of this study have been to describe the two types of rapakivi granites in their geological settings, to assess the needs for restoration of stones utilized in constructions and to establish databases of stones utilized in historical buildings and of the original and alternative quarries. The focus of this study has been on defining the original quarries for the old building stones or finding other similar substitute granite deposits. Chemical analysis with a handheld XRF instrument was found to be the most promising approach when combined with multivariate mathematical tools. In addition, the applicability of chemical treatment of the surface of rapakivi granite for changing the appearance of stones was investigated. The visual appearance and texture of natural stones used in restoration are the key factors, in addition to the stone type and quality. The chemical treatment of stone surfaces using acidic or metal salt treatments altered the colour tone and visual pattern. Thermal treatment was also found to be effective, but it might be harmful to the surface structure. With further optimisation, chemical treatment could be a feasible method to change the visual appearance of fresh stone in the case of substitution of weathered stone. In addition, this project has initiated cross-border activities that aim to create opportunities for establishing first contacts between the authorities, construction companies, stone producers and the manufacturer who produces the needed high-quality stone pieces.