Neoarchean sanukitoid series in the Karelian Province, Finland

Sanukitoid series intrusions can be found throughout the Archean Karelian Province of the Fennoscandian shield. All sanukitoids share the same controversial elemental characteristics: they have high content of incompatible elements such as K, Ba, and Sr as well as high content of the compatible elements Mg, Cr, and Ni, and high Mg#. This composition is explained by an enriched mantle wedge origin in a Neoarchean subduction setting. This study concentrates on sanukitoid intrusions and tonalite-trondhjemite-granodiorite series (TTGs) from Finnish part of the Karelian Province. The collected rock samples have been studied in the field and under microscope as well as for their whole-rock (including isotopes) and mineral compositions. The new data together with previously published analyses help us to better understand the petrogenesis, tectonic setting and reworking of the Archean rock units. TTGs from the Karelian Province form a voluminous series of granitoids and reworked migmatites. This study divides TTG series into two subgroups based on their elemental composition: low-HREE (heavy rare earth element) TTGs and high-HREE TTGs indicating pressure differences in their source. Sanukitoid series is a minor, divergent group of intrusions. These intrusions are variable sized, and the texture varies from even-grained to K-feldspar porphyritic. The elemental composition differentiates sanukitoids from more voluminous TTG groups, the SiO2 in sanukitoids varies to include series of gabbro, diorite, and granodiorite. U Pb age determinations from sanukitoid series show temporally limited emplacement between ~ 2745 2715 Ma after the main crust forming period in the area. Hafnium, neodymium, common lead, and oxygene isotopes indicate well homogenized characteristics. Recycled crust has made a variable, yet minor, contribution to sanukitoids, as evidenced by oxygene isotopes and inherited zircon cores. A proposed tectonic setting for the formation of the sanukitoid series is slab breakoff of oceanic lithosphere in subduction setting, with sanukitoids deriving from an enriched mantle wedge. The proposed setting explains some of the peculiar features of sanukitoids, such as their temporally limited occurrence and controversial elemental composition. Sanukitoids would occur after cessation of the regional growth of Archean crust, and they could be derived from mantle wedge previously enriched by melts and fluids from oceanic crust and sediments. A subsequent event during the Paleoproterozoic Svecofennian orogeny at ~1.9 Ga affected the appearance and microstructures of the rocks as well as caused redistribution of lead between minerals and whole rock. However, the deformation was not able to obliterate the original geochemical characteristics of these sanukitoids.Laattatektoniikka on perustavanlaatuinen geologinen teoria, jota voi merkityksessä verrata biologian evoluutioteoriaan. Laattatektoniikkateorialla pystytään selittämään suurin osa maapallon merkittävistä geologisista ilmiöistä. Maankuori jaetaan mantereiseen ja merellisiin laattoihin, jotka liikkuvatoistensa suhteen laattatektoniikkateorian mukaan. Näiden mantereisen ja merellisen laatan törmätessä toistensa suhteen merellinen laatta painuu maan vaippaan. Törmäys vyöhykkeillä esiintyy maanjäristyksiä, tulivuoren purkauksia ja samalla kun uutta mantereista kuorta syntyy. On kuitenkin ollut epäselvää milloin ja miten tämä prosessi on alkanut toimia 4,5 miljardia vuotta vanhalla Maapallolla. Tässä tutkimuksessa on kuvattu sanukitoidi-nimistä kivilajiryhmän Itä-Suomesta sekä tutkittu kyseisen ryhmän koostumusta, ikää, lähdettä ja sitä synnyttänyttä tektonista prosessia. Sanukitoidien poikkeuksellinen koostumus todistaa laattatektoniikan toimineen jo 2,7 miljardia vuotta sitten maamme alueella. Kuitenkin sen luonne poikkesi nykyisestä, merellisen laatan törmätessä mantereiseen katkesi upotessaan maan vaippaan. Sanukitoidien koostumus ja isotooppi suhteet todistavat niiden lähteen olevan vaipassa johon on sekoittunut mannerkuorta vaihtelevissa määrin. Nuoremmat prosessit ovat muodostaneet Etelä-Suomen kallioperän 1,9 miljardia vuotta sitten, samalla Itä-Suomen kallioperä mukaan lukien sanukitoidit lämpenivät 400 500 ºC asteeseen. Tämä lämpötila ei ole muuttanut tutkittujen kivien alkuaine koostumusta, vaikka lyijy isotooppi pitoisuuksissa havaittiin muutoksia

Both plume and arc : origin of Neoarchaean crust as recorded in Veligallu greenstone belt, Dharwar craton, India

Several profound changes, including those involving formation of the continental crust, occurred on Earth during the Neoarchaean Era. However, the tectonic settings associated with Neoarchaean crustal growth are not well understood and vigorously debated. The Neoarchaean Veligallu greenstone belt, eastern Dharwar craton hosts a variety of ultramafic, mafic and felsic volcanic rocks. Whole-rock elemental and Nd isotope data along with zircon U-Pb dating on these rocks provide significant insights into the origin and tectonic setting of Neoarchaean crust formation. The volcanism in the Veligallu belt started with similar to 2.67 Ga tholeiitic basalts derived from shallow melting of a slightly depleted mantle (epsilon(Ndt) = + 0.6 to + 1.1). Moderate negative Nb anomalies, slightly elevated Th/Yb and LREE, and an absence of evidence for crustal contamination are consistent with extraction of these basalts from a mantle source weakly metasomatized by subducted slab-derived fluids in an incipient oceanic arc setting. As the arc matured, clastic sediments started forming with concurrent emplacement of komatiites, komatiitic basalts and ferropicrites showing strong signatures of contamination with continental crust (negative Nb and Ti anomalies, LREE enrichment and negative epsilon(Ndt)). In the final stage (similar to 2.58 Ga), a variety of felsic volcanic rocks (sodic trachyandesite, high Mg# andesite, rhyolite, calc-alkaline andesite) formed. The rock association and distinct geochemical signatures (enrichment of LILE, negative Nb and Ti anomalies, Mesoarchaean Nd model ages and inherited older zircons) suggest a continental margin arc environment which contained older crust. The evolutionary history of the Veligallu belt implies that both the arcand plume-related processes, and their interplay contributed significantly to the growth of Neoarchaean crust.Peer reviewe

Constraints over the age of magmatism and subsequent deformation for the Neoarchean Kukkola Gneiss Complex, northern Fennoscandia

The Archean crust in northern Fennoscandia preserves a fragmentary geological record, making direct correlation among Archean domains challenging. This study presents two new zircon U-Pb age determinations from the Archean Kukkola Gneiss Complex (KGC) that straddles the border between Finland and Sweden. The results indicate that crystallization of tonalites within the magmatic core of the complex occurred at 2711 +/- 8 Ma, somewhat earlier than previously considered. A new pulse of magmatism occurred at 2675 +/- 10 Ma as demonstrated by hornblende-tonalites cutting the 2.71 Ga rocks. The results further indicate that the first deformation event responsible for development of penetrative foliations occurred after the first magmatic event at 2.71 Ga and prior to the subsequent tectonothermal event at 2.68 Ga. These findings are in concert with the known major periods of magmatism (2.8-2.7 Ga) and deformation (2.7 Ga) within better-known Archean domains in northern Fennoscandia, and hence support their correlation with KGC. Three complementary age determinations on the Haparanda-suite granites and tonalites were conducted: the results indicate crystallization ages of 1.90-1.89 Ga, overlapping with the known age range of the suite and supporting its predominance over the 1.8 Ga Lina suite granites in the Tornio-Haparanda area.Peer reviewe

Constraints over the age of magmatism and subsequent deformation for the Neoarchean Kukkola Gneiss Complex, northern Fennoscandia

The Archean crust in northern Fennoscandia preserves a fragmentary geological record, making direct correlation among Archean domains challenging. This study presents two new zircon U-Pb age determinations from the Archean Kukkola Gneiss Complex (KGC) that straddles the border between Finland and Sweden. The results indicate that crystallization of tonalites within the magmatic core of the complex occurred at 2711 +/- 8 Ma, somewhat earlier than previously considered. A new pulse of magmatism occurred at 2675 +/- 10 Ma as demonstrated by hornblende-tonalites cutting the 2.71 Ga rocks. The results further indicate that the first deformation event responsible for development of penetrative foliations occurred after the first magmatic event at 2.71 Ga and prior to the subsequent tectonothermal event at 2.68 Ga. These findings are in concert with the known major periods of magmatism (2.8-2.7 Ga) and deformation (2.7 Ga) within better-known Archean domains in northern Fennoscandia, and hence support their correlation with KGC. Three complementary age determinations on the Haparanda-suite granites and tonalites were conducted: the results indicate crystallization ages of 1.90-1.89 Ga, overlapping with the known age range of the suite and supporting its predominance over the 1.8 Ga Lina suite granites in the Tornio-Haparanda area

Alkaline-rich quartz syenite intrusions of the Western Karelia subprovince

Tables detailing geochemical analyses, analytical data for the five age samples and oxygen-isotope analyses from this stud

The tectonomagmatic significance of Neoarchaean variably alkali-enriched gabbro and diorite intrusions of the western Karelia Province

Table detailing oxygen-isotope analyses from this study

Evidence of crustal growth during the Svecofennian orogeny : New isotopic data from the central parts of the Paleoproterozoic Central Finland Granitoid Complex

Peer reviewe