Isotopic evidence for the origin of Proterozoic massif-type anorthosites and their relation to rapakivi granites in southern Finland and northern Brazil

The purpose of this study was to apply novel isotopic methods to shed light on the petrogenesis and magmatic evolution of Proterozoic massif-type anorthosites and related rapakivi granites in southern Finland and northern Brazil. Representative rock types from two AMCG (Anorthosite-Mangerite-Charnockite-Granite) complexes of similar age and composition, the 1640 Ma Ahvenisto complex and the 1530 Ma Mucajaí complex, were studied. Zircon U Pb ages from 1642 Ma to 1636 Ma in the Ahvenisto complex and from 1527 Ma to 1519 Ma in the Mucajaí complex were measured. All major rock types (anorthositic and gabbroic rocks, granites, monzodiorites) have overlapping ages. Only the most evolved granitic rocks in both suites are marginally younger than the rest of the rock types. The whole-rock (ID-TIMS) εNd isotope values obtained for all rock-types in both complexes range from +0.4 to 2.1 (at 1640 Ma) in Ahvenisto and 1.9 to 2.8 (at 1525 Ma) in Mucajaí. Zircon Lu Hf isotopes of the Finnish rapakivi suite rocks revealed a depleted mantle signature (initial εHf values up to +9 at ~1640 Ma) in the most primitive rock types, that was not detected in the Repartimento anorthosite of the Mucajaí complex. Rapakivi granites from both study areas displayed homogeneous Hf isotope compositions (~±2 ε units at 2SD) with average εHf values from +1.0 to 0.1 at ~1640 Ma and +0.1 to 2.2 at 1540 Ma in the Finnish suite and from 2.0 to 3.1 at 1525 Ma in the Mucajaí complex. Zircon oxygen isotope studies in both study areas produced relatively low δ18O value estimates for the primary magmas of the anorthositic rocks (δ18Ozir from 5.5 to 7.5 in Ahvenisto and ~6.5 in Mucajaí) and somewhat higher values for the rapakivi granites (~8.0 in Ahvenisto and from 6.0 to 7.5 in Mucajaí). The lowest δ18Ozir values were observed in the Ahvenisto leucotroctolite (δ18Ozir from 5.4 to 7.0 ), which also had the highest initial εHf values (+0.3 to +5.2 at 1640 Ma) within the Ahvenisto complex. This correlation was taken as evidence of a depleted mantle source component in the Finnish AMCG suite, even though most of them display crustal isotope signatures (δ18Ozir from 6.3 to 7.8 ; εHf from 1.5 to +5.1; 1640 Ma). The somewhat higher δ18Ozir values observed in the rapakivi granites from both complexes combined with the Hf isotope results suggest they were derived from crustal sources.Tässä työssä tutkittiin Etelä-Suomesta tunnettujen n. 1600 miljoonaa vuotta vanhojen rapakivigraniittien ja anortosiittien geokemiallisia koostumuksia ja vertailtiin niitä Pohjois-Brasiliasta, syvältä Amazonin sademetsästä, löydettyjen samanlaisten kivien koostumuksiin. Molemmilla alueilla tutkittujen kivien koostumukset todettiin hyvin samankaltaisiksi ja seurueet miltei samanikäisiksi keskenään. Suomalaiset rapakivigraniitit ja niihin kiinteästi liittyvät tummat, anortosiittiset, kivilajit ovat olleet petrologisten tutkimusten kohteena jo 1800-luvun lopulta lähtien. Nykyään rapakiviä tunnetaan kaikilta mantereilta ja niiden syntymekanismeja tutkitaan aktiivisesti ympäri maailman. Uraani-lyijy -iänmääritysmenetelmän perusteella rapakivigraniitit ja anortosiitit ovat saman ikäisiä keskenään molemmilla tutkimusalueilla, Mäntyharjulla sijaitsevassa Ahveniston rapakivikompleksissa ja Pohjois-Brasiliassa, Mucajaín rapakivikompleksissa. Ahveniston kivien iäksi määritettiin n. 1640 ja Mucajaín n. 1525 miljoonaa vuotta. Nuorimmat Lounais-Suomesta tunnetut rapakiviesiintymät ovat saman ikäisiä kuin Mucajaí-kompleksi. Aiemmin kokokivinäytteistä tehtyjen neodyymi- ja strontium-isotooppimittausten perusteella on saatu viitteitä siitä, että Etelä-Suomen anortosiittiset kivilajit olisivat peräisin maapallon vaipasta ja että samaan aikaan syntyneet rapakivigraniitit edustaisivat maapallon kuorikerroksen osittaisia kivisulia. Tässä tutkimuksessa vertailtujen Ahveniston ja Mucajaín kivilajien neodyymi-isotooppikoostumusten havaittiin paitsi tukevan tätä olettamusta myös olevan keskenään hyvin samankaltaiset. Lisäksi kivilajien tutkimukseen sovellettiin uutta menetelmää, joka hyödyntää yksittäisistä zirkoni-mineraalin kiteistä tehtyjä hafnium- ja happi-isotooppimittauksia. Näiden menetelmien avulla saatiin yksityiskohtaisempaa tietoa graniitit ja anortosiitit synnyttäneiden kivisulien kehityksestä ja voitiin vahvistaa kokokivinäytteistä mitatut tulokset. Seurueiden samankaltaisuus tukee myös SAMBA-supermannerteoriaa, jonka mukaan Fennoskandian ja Pohjois-Amazonian mannerlaatat olisivat keskiproterotsooisella ajalla, noin 1500 miljoonaa vuotta sitten, olleet lähellä toisiaan ja mahdollisesti muodostaneet yhtenäisen supermantereen osan

Massiivi-tyypin anortosiittien jäännössulien tasapainoinen kiteytyminen: tapaustutkimus 1.64 miljardia vuotta vanhasta Ahvenisto-kompleksista Kaakkois-Suomessa

Fe–Ti–P-rich mafic to intermediate rocks (monzodiorites and oxide–apatite–gabbronorites, OAGNs) are found as small intrusions in most AMCG (anorthosite–magnerite–charnokite–granite) suites. The origin of the monzodioritic rocks is still debated, but in many studies, they are presumed to represent residual liquid compositions after fractionation of anorthositic cumulates. In the 1.64 Ga Ahvenisto complex, SE Finland, monzodioritic rocks occur as minor dike-like lenses closely associated with anorthositic rocks. We report new field, petrographic, and geochemical (XRF, ICP-MS, EMPA) data complemented with crystallization modeling (rhyolite-MELTS, MAGFRAC) for the monzodioritic rocks, apatite–oxide–gabbronorite, and olivine-bearing anorthositic rocks of the Ahvenisto complex. The presented evidence suggest that the monzodioritic rocks closely represent melt compositions while the apatite–oxide–gabbronorite and olivine-bearing anorthositic rocks are cumulates. The monzodioritic rocks seem to form a liquid line of descent (LLD) from primitive olivine monzodiorites to more evolved monzodiorites. Petrological modeling suggests that the interpreted LLD closely corresponds to a residual melt trend left after fractional crystallization (FC) and formation of the cumulate anorthositic rocks and minor apatite–oxide–gabbronorite in shallow magma chambers. Consequent equilibrium crystallization (EC) of separate monzodioritic residual magma batches can produce the observed mineral assemblages and the low Mg numbers measured from olivine (Fo25–45) and pyroxenes (En48–63, Mg#cpx 60–69). The monzodioritic rocks and apatite–oxide–gabbronorites show similar petrological and geochemical characteristics to corresponding rock types in other AMCG suites, and the model described in this study could be applicable to them as well.Peer reviewe

EKG-kortti ensihoidon ja päivystyksen uusille työntekijöille Tyks Akuuttiin : kirjallisuuskatsaus

Tutkimusten mukaan hoitajien sydänsähkökäyrän rekisteröinnissä on ollut puutteita (Riski 2004). Hoitajat ovat myös itse kokeneet epävarmuutta sydänsähkökäyrän tulkinnassa ja arvioinnissa, mikä he kokevat johtuvan vähäisestä kokemuksesta sydänsähkökäyrien tulkinnasta (Nickasch ym. 2016). Tarkoituksena oli selvittää sydänsähkökäyrän rakenne, sen rekisteröinnin perusteet ja yleisimmin tavatut sydämen rytmihäiriöt sekä niiden tyypillisimmät muutokset. Tavoitteena oli luoda työkalu sydänsähkökäyrän tulkintaan ja rytmihäiriöiden arviointiin, joka tukee hoitajan systemaattista sydänsähkökäyrän tulkitsemista, toimii muistin tukena rytmihäiriöitä arvioitaessa ja näin helpottaa työntekoa. Opinnäytetyö toteutettiin kuvailevana kirjallisuuskatsauksena. Tietoa haettiin useista alalla käytössä olevista tietokannoista ennalta valittujen hakusanojen mukaisesti. Kerätystä tiedosta muodostui ajantasainen kuva sydänsähkökäyrästä, sen rekisteröinnistä ja rytmihäiriöistä. Tämän tiedon pohjalta tuotettiin taskukokoinen EKG-kortti erityisesti ensihoidon ja päivystyksen uusille työntekijöille Varsinais-Suomen sairaanhoitopiirin Tyks Akuuttiin, jonka toimeksiannosta opinnäytetyö tehtiin. EKG-kortti on kaksipuoleinen, jonka toisella puolella on perustiedot sydänsähkökäyrästä, sen osien kestosta ja koosta, elektrodien sijoittelusta, vaurioiden paikantamisesta sydämessä ja sydämen sähköisen akselin määrittämisestä. Toisella puolella on mallikuvia rytmihäiriöistä ja niiden tyypillisimmistä muutoksista.Studies have shown that there have been deficiency in the registration of electrocardiogram by nurses (Riski 2004). Nurses themselves have also experienced uncertainty in the interpretation and evaluation of the electrocardiogram, which they feel is due to limited experience in the interpretation of electrocardiograms (Nickasch et al. 2016). The purpose was to find out the basics of the electrocardiogram and its registration and the most commonly found cardiac arrhythmias, as well as their most typical changes. The aim was to create a tool for the interpretation of the electrocardiogram and the assessment of arrhythmias, which supports the nurses systematic interpretation of the electrocardiogram, acts as a memory aid in the assessment of arrhythmias and thus facilitates work. The thesis was carried out as a descriptive literature review. Information was retrieved from several databases according to preselected keywords. The collected data formed an up-to-date picture of the electrocardiogram, its registration and arrhythmias. Based on this information, a pocket-sized ECG card was produced, especially for new emergency and acute care personnel to The Hospital District of Southwest Finland for Tyks Acute, on whose commission by the thesis was made. The ECG card is double-sided, with the other side providing basic information about the electrocardiogram, the duration and size of its parts, the placement of the electrodes, locating the lesions in the heart and determining the electrical axis of the heart. On the other side are model images of arrhythmias and their most typical changes.Graafinen sisältö on julkaistu CC-BY-SA -lisenssillä (poislukien Tyks Akuutin logo)

Tracing the styles of mafic-felsic magma interaction : A case study from the Ahvenisto igneous complex, Finland

The 1.64 Ga Ahvenisto complex, southeastern Finland, is an anorthosite-mangerite-charnokite-granite (AMCG) suite in which diverse interaction styles of coeval mafic and felsic magmas are observed. Commingling, resulting in mafic pillows and net-veined granite dykes, and chemical mixing producing hybrid rocks, are the most common interaction types. Detailed description of the factors that controlled the interaction styles and relationships between involved rock types are provided using targeted mapping, petrography, and geochemical analyses complemented by chemical mixing and melt viscosity modeling. Interaction occurred at intermediate stages in the magmatic evolution of the complex: when the last fractions of mafic (monzodioritic) melts and the earliest fractions of felsic (hornblende granitic) melts existed simultaneously. Differentiation of mafic magma has produced three monzodioritic rock types: 1) olivine monzodiorite (most mafic, Mg# 49-40), 2) ferrodiorite (Mg# 42-33), and 3) massive monzodiorite (most evolved, Mg# 28-27). The types form an evolutionary trend, and each exhibits different style of interaction with coeval hbl-granite resulting from contrasting conditions and properties (temperature, viscosity, composition). The variation in these properties due to magma evolution and relative proportions of interacting magmas dictated the interaction style: interaction between olivine monzodiorites and granite was almost negligible; ferrodiorites intermingled forming pillows with granitic veins intruding them; and chemical mixing of massive monzodiorite and hbl-granite produced hybrid rocks.Peer reviewe

Termodynaamiset rajat massiivi-tyypin anortosiittien ja niiden kantamagmojen synnylle

Development of computational modeling tools has revolutionized studies of magmatic processes over the last four decades. Their refinement from binary mixing equations to thermodynamically controlled geochemical assimilation models has provided more comprehensive and detailed modeling constraints of an array of magmatic systems. One of the questions that has not yet been vigorously studied using thermodynamic constraints is the origin of massif-type anorthosites. The parental melts to these intrusions are hypothesized to be either mantle-derived high-Al basaltic melts that undergo crustal contamination or monzodioritic melts derived directly from lower crust. On the other hand, many studies suggest that the monzodioritic rocks do not represent parental melts but instead represent crystal remnants of residual liquids left after crystal fractionation of parental melts. Regardless of the source or composition, magmas that produce massif-type anorthosites have been suggested to have undergone polybaric (~1000–100 MPa) fractional crystallization while ascending through the lithosphere. We conducted lower crustal melting, assimilation-fractional crystallization, and isobaric and polybaric fractional crystallization major element modeling using two thermodynamically constrained modeling tools, the Magma Chamber Simulator (MCS) and rhyolite-MELTS, to test the suitability of these tools and to study the petrogenesis of massif-type anorthosites. Comparison of our models with a large suite of whole-rock data suggests that the massif-type anorthosite parental melts were high-Al basalts that were produced when hot mantle-derived partial melts assimilated lower crustal material at Moho levels. These contaminated basaltic parental magmas then experienced polybaric fractional crystallization at different crustal levels (~40 to 5 km) producing residual melts that crystallized as monzodioritic rocks. Model outcomes also support the suggestion that the cumulates produced during polybaric fractional crystallization likely underwent density separation, thus producing the plagioclase-rich anorthositic rocks. The modeled processes are linked to a four-stage model that describes the key petrogenetic processes that generate massif-type anorthosites. The presented framework enables further detailed thermodynamic and geochemical modeling of individual anorthosite intrusions using MCS and involving trace element and isotope constrains.Peer reviewe

OpenFIRE – A Web GIS Service for Distributing the Finnish Reflection Experiment Datasets

Non peer reviewe

High-aluminum orthopyroxene megacrysts (HAOM) in the Ahvenisto complex, SE Finland, and the polybaric crystallization of massif-type anorthosites

The occurrence of high-aluminum orthopyroxene megacrysts (HAOMs) in several massif-type Proterozoic anorthosite complexes has been used as evidence of their polybaric crystallization. Here, we report such petrographic and geochemical (XRF and EMPA) evidence from HAOMs discovered in the 1.64 Ga Ahvenisto rapakivi granite-massif-type anorthosite complex in southeastern Finland. Two different types of HAOMs were recognized: type 1 HAOMs are individual, euhedral-to-subhedral crystals, and up to 15 cm in diameter, and type 2 HAOMs occur in pegmatitic pockets closely associated with megacrystic (up to 30 cm long) plagioclase. The type 1 megacrysts in particular are surrounded by complex corona structures composed of plagioclase, low-Al orthopyroxene, iddingsite (after olivine), and sulfides. Orthopyroxene crystallization pressure estimates based on an Al-in-Opx geobarometer reveal a three-stage compositional evolution in both textural HAOM types. The Al content decreases significantly from the core regions of the HAOM (4.4-7.6 wt% Al2O3), through the rims (1.3-3.6 wt%), into the host rock (0.5-1.5 wt%). Enstatite compositions overlap, but are generally higher in the cores (En(similar to 60-70)) and rims (En(similar to 50-70)) of the HAOMs than in the host rock (En(similar to 45-60)) orthopyroxenes. The highest recorded Al abundances in the HAOM cores correspond to crystallization pressures of up to similar to 1.1 GPa (similar to 34 km depth), whereas the HAOM rims have crystallized at lower pressures (max. similar to 0.5 GPa, 20 km depth). The highest pressure estimates for the host rock orthopyroxene were similar to 0.2 GPa (<7 km depth). These observations confirm the polybaric magmatic evolution of the Ahvenisto anorthosites and suggest that the entire 1.65-1.55 Ga Fennoscandian rapakivi suite was emplaced at a relatively shallow level (<7 km depth) in the upper crust. Global comparison to similar rock types reveals remarkable similarities in the petrogenetic processes controlling HAOM composition and evolution of anorthosite parental magmas.Peer reviewe