The distribution and varve thickness data of Late Weichselian varved clay were analyzed to describe the proglacial sedimentary environment, ice recession and water-level changes in the Baltic Ice Lake at the distal position of Pandivere–Neva (13.5–13.1 ka BP) icerecessional formations in western Estonia. According to vertical changes in natural water content, fabric and varve thickness, four clay units were distinguished, reflecting a change in the sedimentary environment from ice-proximal to distal conditions. The varved clay complex is locally interrupted by a massive silty-clay unit, interpreted as an icedrift material during the stagnation of the glacier margin at the Pandivere–Neva line. Varve correlation gave a 294-year-long floating varve chronology. According to total varve thickness and the relation between thicknesses of seasonal layers, an about 130year period of ice-proximal conditions in the study area was followed by a rapid (within ca 20 years) change to more distal conditions. The presented varve chronology does not cover the entire period of proglacial conditions in the area, as all studied clay sections displayed an erosional discontinuity at the upper contact. In total, ca 4 m of selective post-sedimentary erosion of clay is attributed to wave erosion due to a water-level drop after the final drainage of the Baltic Ice Lake. It is concluded that the Yoldia Sea minimum level in the Pärnu area was 0 to –2 m a.s.l.
分析了晚Weichselian期变粘土的分布和厚度资料，以描述爱沙尼亚西部Pandivere-Neva (13.5 ~ 13.1 ka BP)冰退地层远端波罗的海冰湖的前冰期沉积环境、冰退和水位变化。根据天然含水量、组构和阀厚的垂直变化，划分出4个粘土单元，反映了沉积环境从冰近端到远端条件的变化。破碎的粘土复合体在局部被一个巨大的粉质粘土单元打断，这被解释为pandiva - neva线冰川边缘停滞期间的冰漂物质。瓣膜相关性给出了294年的浮动瓣膜年表。根据总厚度和季节层厚度之间的关系，研究区冰-近端条件在约130年的周期后迅速(约20年)向远端条件转变。所提出的年代学并不能涵盖该地区前冰期的整个时期，因为所有研究的粘土剖面在上部接触处都显示出侵蚀不连续。总的来说，约4米的选择性沉积后粘土侵蚀可归因于波罗的海冰湖最终排水后水位下降造成的波浪侵蚀。推断Pärnu地区约迪亚海最低水位为0 ~ 2 m a.s.l。
{"title":"Glacial varves at the distal slope of Pandivere-Neva ice-recessional formations in western Estonia","authors":"P. Talviste, T. Hang, M. Kohv","doi":"10.17741/BGSF/84.1.001","DOIUrl":"https://doi.org/10.17741/BGSF/84.1.001","url":null,"abstract":"The distribution and varve thickness data of Late Weichselian varved clay were analyzed to describe the proglacial sedimentary environment, ice recession and water-level changes in the Baltic Ice Lake at the distal position of Pandivere–Neva (13.5–13.1 ka BP) icerecessional formations in western Estonia. According to vertical changes in natural water content, fabric and varve thickness, four clay units were distinguished, reflecting a change in the sedimentary environment from ice-proximal to distal conditions. The varved clay complex is locally interrupted by a massive silty-clay unit, interpreted as an icedrift material during the stagnation of the glacier margin at the Pandivere–Neva line. Varve correlation gave a 294-year-long floating varve chronology. According to total varve thickness and the relation between thicknesses of seasonal layers, an about 130year period of ice-proximal conditions in the study area was followed by a rapid (within ca 20 years) change to more distal conditions. The presented varve chronology does not cover the entire period of proglacial conditions in the area, as all studied clay sections displayed an erosional discontinuity at the upper contact. In total, ca 4 m of selective post-sedimentary erosion of clay is attributed to wave erosion due to a water-level drop after the final drainage of the Baltic Ice Lake. It is concluded that the Yoldia Sea minimum level in the Pärnu area was 0 to –2 m a.s.l.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"84 1","pages":"7-19"},"PeriodicalIF":0.7,"publicationDate":"2012-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67630525","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The coversands distributed in the Blonie glaciolacustrine basin, west of Warsaw (Central Poland) were investigated. Textural features including grain size, rounding and frosting of quartz grains and mineralogical-petrographic composition in the sandy fractions (0.5– 0.8 and 0.8–1.0 mm) were examined and the types, dynamics, regime and variation in processes during the formation of the coversands were determined. The sands are characterized by the prevalence of quartz and lack of micaceous minerals. Moreover, the relatively high content of partially rounded, matt (EM/RM) and well-rounded (RM) quartz grains, typical of aeolian sedimentary conditions, was certified. Hence, the results show a high aeolization degree of the investigated sediments, thus correlating them with aeolian deposition in dry, periglacial conditions after drying up of the Warsaw icedammed lake.
{"title":"Geological setting and sedimentary characteristics of the coversands distributed in the western part of the Blonie glaciolacustrine basin (Central Poland) - preliminary results","authors":"E. Kalińska","doi":"10.17741/BGSF/84.1.003","DOIUrl":"https://doi.org/10.17741/BGSF/84.1.003","url":null,"abstract":"The coversands distributed in the Blonie glaciolacustrine basin, west of Warsaw (Central Poland) were investigated. Textural features including grain size, rounding and frosting of quartz grains and mineralogical-petrographic composition in the sandy fractions (0.5– 0.8 and 0.8–1.0 mm) were examined and the types, dynamics, regime and variation in processes during the formation of the coversands were determined. The sands are characterized by the prevalence of quartz and lack of micaceous minerals. Moreover, the relatively high content of partially rounded, matt (EM/RM) and well-rounded (RM) quartz grains, typical of aeolian sedimentary conditions, was certified. Hence, the results show a high aeolization degree of the investigated sediments, thus correlating them with aeolian deposition in dry, periglacial conditions after drying up of the Warsaw icedammed lake.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"84 1","pages":"33-44"},"PeriodicalIF":0.7,"publicationDate":"2012-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67630167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Geologic position of the Younger Dryas subfossil forest in the Warta River valley, central Poland","authors":"D. Dzieduszyńska, J. Petera-Zganiacz","doi":"10.17741/BGSF/84.1.006","DOIUrl":"https://doi.org/10.17741/BGSF/84.1.006","url":null,"abstract":"","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"84 1","pages":"69-79"},"PeriodicalIF":0.7,"publicationDate":"2012-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67630290","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Paleoproterozoic Oripää granite in the Loimaa area in southwestern Finland (Fig. 1a; Nironen, 1999) is a small, heterogeneous leucogranite pluton that was emplaced within the synorogenic (1.89–1.87 Ga) plutonic and supracrustal rocks of the Arc complex of southern Finland at ~1.85 Ga (Kurhila et al., 2005, 2011). The Oripää granite has been considered to belong to the “microcline granites” (leucogranites) of the Late Svecofennian granite–migmatite zone (LSGM zone; Ehlers et al., 1993). In terms of its relatively radiogenic Nd isotope character (positive initial ε Nd value) and relatively old age (Rämö & Nironen, 2001; Kurhila et al., 2005) it is, however, rather different from the main leucogranite bodies of the LSGM farther south. We have analyzed new samples from the Oripää granite and its country rocks (tonalite, quartz diorite, amphibolite) for Nd isotopes and elemental geochemistry in order to further characterize the Oripää granite and the bedrock around it. Our results show that the Oripää granite is consanguineous with its immediate country rocks and that the terrane boundary marking transition from the Arc complex of western Finland to the Arc complex of southern Finland is located just north of the Oripää granite at this longitude.
芬兰西南部Loimaa地区古元古代Oripää花岗岩(图1a;Nironen, 1999)是一种小型的非均质浅花岗岩体，位于芬兰南部~1.85 Ga的同生(1.89-1.87 Ga)深成岩和壳上岩石中(Kurhila et al.， 2005, 2011)。Oripää花岗岩被认为属于晚斯韦芬世花岗岩-杂岩带(LSGM带)的“微斜长花岗岩”(浅色花岗岩);Ehlers et al.， 1993)。相对放射性成因的Nd同位素特征(正初始ε Nd值)和相对年老(Rämö & Nironen, 2001;Kurhila et al.， 2005)然而，它与LSGM更南边的主要浅花岗岩体有很大不同。我们分析了Oripää花岗岩及其岩石(闪长岩、石英闪长岩、角闪岩)的新样品，用于Nd同位素和元素地球化学，以进一步表征Oripää花岗岩及其周围的基岩。研究结果表明，Oripää花岗岩与其邻近的农村岩石紧密相连，标志着芬兰西部弧形杂岩向芬兰南部弧形杂岩过渡的地体边界位于该经度Oripää花岗岩的正北。
{"title":"The Oripää granite revisited: Elemental geochemistry, Nd isotopes, and implication to terrane boundary","authors":"M. Nironen, O. T. Rämö","doi":"10.17741/BGSF/83.2.003","DOIUrl":"https://doi.org/10.17741/BGSF/83.2.003","url":null,"abstract":"The Paleoproterozoic Oripää granite in the Loimaa area in southwestern Finland (Fig. 1a; Nironen, 1999) is a small, heterogeneous leucogranite pluton that was emplaced within the synorogenic (1.89–1.87 Ga) plutonic and supracrustal rocks of the Arc complex of southern Finland at ~1.85 Ga (Kurhila et al., 2005, 2011). The Oripää granite has been considered to belong to the “microcline granites” (leucogranites) of the Late Svecofennian granite–migmatite zone (LSGM zone; Ehlers et al., 1993). In terms of its relatively radiogenic Nd isotope character (positive initial ε Nd value) and relatively old age (Rämö & Nironen, 2001; Kurhila et al., 2005) it is, however, rather different from the main leucogranite bodies of the LSGM farther south. We have analyzed new samples from the Oripää granite and its country rocks (tonalite, quartz diorite, amphibolite) for Nd isotopes and elemental geochemistry in order to further characterize the Oripää granite and the bedrock around it. Our results show that the Oripää granite is consanguineous with its immediate country rocks and that the terrane boundary marking transition from the Arc complex of western Finland to the Arc complex of southern Finland is located just north of the Oripää granite at this longitude.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"83 1","pages":"115-122"},"PeriodicalIF":0.7,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67630036","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rock magnetic investigations constraining relative timing for gold deposits in Finland SATU MERTANEN AND FREDRIK KARELL 2) 1) Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland 2) Åbo Akademi University, Department of Geology and Mineralogy, FI-20500 Turku, Finland Bulletin_83_2_s71_94_Mertanen.pmd 19.1.2012, 15:03 75 76 Satu Mertanen and Fredrik Karell
芬兰金矿床的岩石磁学研究及其相对成矿时间[j] .萨图·默塔宁，费德瑞克·卡列尔2)1)芬兰地质调查局，邮政信箱96号，芬兰埃斯波，FI-02151 2) Åbo芬兰科学院大学地质矿物系，FI-20500图尔库2012年1月19日，15:03 75 76 Satu Mertanen和Fredrik Karell
{"title":"Rock magnetic investigations constraining relative timing for gold deposits in Finland","authors":"S. Mertanen, F. Karell","doi":"10.17741/BGSF/83.2.001","DOIUrl":"https://doi.org/10.17741/BGSF/83.2.001","url":null,"abstract":"Rock magnetic investigations constraining relative timing for gold deposits in Finland SATU MERTANEN AND FREDRIK KARELL 2) 1) Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland 2) Åbo Akademi University, Department of Geology and Mineralogy, FI-20500 Turku, Finland Bulletin_83_2_s71_94_Mertanen.pmd 19.1.2012, 15:03 75 76 Satu Mertanen and Fredrik Karell","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"83 1","pages":"75-94"},"PeriodicalIF":0.7,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67629931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A method to estimate the 87Sr/86Sr ratio of a rock based on its age and Rb/Sr ratio is presented. This method, together with data from the Rock Geochemical Database of Finland (n=6544) is used to estimate the 87Sr/86Sr ratios in the Precambrian of Finland and in its different major units. A generalization to cover the whole area of Finland is achieved by smoothing of estimation points. The estimation method is evaluated by comparing its results to published Rb-Sr isotope analyses (n=138) obtained on the Finnish Precambrian. The results show correspondence to different geological units of Finland, but no systematic difference between Archaean and younger areas is evident. Evaluation of the method shows that most of the estimates are reliable and accurate to be used as background material for provenance studies in archaeology, paleontology and sedimentology. However, some granitic rocks may have large (>1.0 %) relative errors. Strontium concentration weighted average of the estimates differs only by 0.001 from the average 87Sr/86Sr ratio (0.730) of the rivers on the Fennoscandian shield.
{"title":"Estimating the distribution of strontium isotope ratios ( 87 Sr/ 86 Sr) in the Precambrian of Finland","authors":"L. Kaislaniemi","doi":"10.17741/BGSF/83.2.002","DOIUrl":"https://doi.org/10.17741/BGSF/83.2.002","url":null,"abstract":"A method to estimate the 87Sr/86Sr ratio of a rock based on its age and Rb/Sr ratio is presented. This method, together with data from the Rock Geochemical Database of Finland (n=6544) is used to estimate the 87Sr/86Sr ratios in the Precambrian of Finland and in its different major units. A generalization to cover the whole area of Finland is achieved by smoothing of estimation points. The estimation method is evaluated by comparing its results to published Rb-Sr isotope analyses (n=138) obtained on the Finnish Precambrian. The results show correspondence to different geological units of Finland, but no systematic difference between Archaean and younger areas is evident. Evaluation of the method shows that most of the estimates are reliable and accurate to be used as background material for provenance studies in archaeology, paleontology and sedimentology. However, some granitic rocks may have large (>1.0 %) relative errors. Strontium concentration weighted average of the estimates differs only by 0.001 from the average 87Sr/86Sr ratio (0.730) of the rivers on the Fennoscandian shield.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"83 1","pages":"95-113"},"PeriodicalIF":0.7,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67630013","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Th.G. Sahama's (1910-1983) volcanological and mineralogical studies in Africa: Part II. Minerals of granitic pegmatites and other mineral occurrences of eastern and southern Africa","authors":"I. Haapala","doi":"10.17741/BGSF/83.1.004","DOIUrl":"https://doi.org/10.17741/BGSF/83.1.004","url":null,"abstract":"","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"83 1","pages":"57-70"},"PeriodicalIF":0.7,"publicationDate":"2011-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67629800","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The alkaline lavas of Mt. Nyiragongo in the Virunga Volcanic Field (western branch of the East African Rift), as well as the granitic pegmatites and hydrothermal mineral deposits of eastern and southern Africa, were the main research topics of Professor Th.G. Sahama (University of Helsinki) during thirty years. During several expeditions 1952–1972 to the Virunga Field, Sahama and his team collected large amounts of samples from the foot plane, flank flows, caldera walls, and the lava lake of Mt Nyiragongo, which were studied in Helsinki University and in Brussels. The lavas turned out to be feldspar-free nephelinites, leucitites and melilitites containing as major constituents nepheline, leucite, melilite, kalsilite, and clinopyroxene in varying proportions. The Nyiragongo lavas are more alkaline than the other volcanics of the Virunga Field. Sahama and his team found and described six new silicate minerals from the Nyiragongo lavas: gotzenite, combeite, kirschsteinite, trikalsilite, delhayelite, and andremeyerite, some of which locally represent the main constituents of the rocks. Sahama concluded that the Nyiragongo lavas crystallized from mantle-derived magmas without significant crustal contamination. The crustal magma chamber was layered, and the eruption started with melilite nephelinite (bergalite) magmas from the top of the chamber, followed by nepheline leucitite magmas and finally by melilite-leucite nephelinite (“nepheline-aggregate lava”) melts. Sahama’s studies aroused great international interest among petrologists and mineralogists, which has activated further systematic geochemical, mineralogical and isotopic studies in the area.
{"title":"Th.G. Sahama's (1910-1983) volcanological and mineralogical studies in Africa: Part I. Expeditions to the Virunga Volcanic Field and petrological- mineralogical studies on the Nyiragongo volcano","authors":"I. Haapala","doi":"10.17741/BGSF/83.1.003","DOIUrl":"https://doi.org/10.17741/BGSF/83.1.003","url":null,"abstract":"The alkaline lavas of Mt. Nyiragongo in the Virunga Volcanic Field (western branch of the East African Rift), as well as the granitic pegmatites and hydrothermal mineral deposits of eastern and southern Africa, were the main research topics of Professor Th.G. Sahama (University of Helsinki) during thirty years. During several expeditions 1952–1972 to the Virunga Field, Sahama and his team collected large amounts of samples from the foot plane, flank flows, caldera walls, and the lava lake of Mt Nyiragongo, which were studied in Helsinki University and in Brussels. The lavas turned out to be feldspar-free nephelinites, leucitites and melilitites containing as major constituents nepheline, leucite, melilite, kalsilite, and clinopyroxene in varying proportions. The Nyiragongo lavas are more alkaline than the other volcanics of the Virunga Field. Sahama and his team found and described six new silicate minerals from the Nyiragongo lavas: gotzenite, combeite, kirschsteinite, trikalsilite, delhayelite, and andremeyerite, some of which locally represent the main constituents of the rocks. Sahama concluded that the Nyiragongo lavas crystallized from mantle-derived magmas without significant crustal contamination. The crustal magma chamber was layered, and the eruption started with melilite nephelinite (bergalite) magmas from the top of the chamber, followed by nepheline leucitite magmas and finally by melilite-leucite nephelinite (“nepheline-aggregate lava”) melts. Sahama’s studies aroused great international interest among petrologists and mineralogists, which has activated further systematic geochemical, mineralogical and isotopic studies in the area.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"83 1","pages":"41-55"},"PeriodicalIF":0.7,"publicationDate":"2011-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67629873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The 1580–1570 Ma old Vehmaa rapakivi granite batholith was studied with the aim to define the geological constraints for localization of natural stone deposits in the batholith. The batholith comprises four roughly concentric granite intrusions from the margin inwards: pyterlite, coarse-grained porphyritic rapakivi granite and two types of mediumgrained porphyritic rapakivi granite. Also porphyry aplite and even-grained rapakivi granite occur. The batholith has intruded as a succession of pulses of subhorizontal sheet-like intrusions conceivably through repeated cauldron subsidence. Natural stone quarries are confined only to certain intrusions within the batholith. We show that the mediumgrained porphyritc granite body in the centre of the batholith comprises two almost identical but different intrusions, with only slightly different appearances: the inner (IG) and the outer (OG) granite. The quarries are confined to the outer intrusion which has an appearance more attractive to the market than that of the inner intrusion. The localization of the natural stone deposits in the Vehmaa batholith is a result of the magmatic history of the batholith, producing intrusions of different appearances with different commercial potential.
{"title":"Magmatic constraints on localization of natural stone deposits in the Vehmaa rapakivi granite batholith, southwestern Finland","authors":"O. Selonen, C. Ehlers, H. Luodes, F. Karell","doi":"10.17741/BGSF/83.1.002","DOIUrl":"https://doi.org/10.17741/BGSF/83.1.002","url":null,"abstract":"The 1580–1570 Ma old Vehmaa rapakivi granite batholith was studied with the aim to define the geological constraints for localization of natural stone deposits in the batholith. The batholith comprises four roughly concentric granite intrusions from the margin inwards: pyterlite, coarse-grained porphyritic rapakivi granite and two types of mediumgrained porphyritic rapakivi granite. Also porphyry aplite and even-grained rapakivi granite occur. The batholith has intruded as a succession of pulses of subhorizontal sheet-like intrusions conceivably through repeated cauldron subsidence. Natural stone quarries are confined only to certain intrusions within the batholith. We show that the mediumgrained porphyritc granite body in the centre of the batholith comprises two almost identical but different intrusions, with only slightly different appearances: the inner (IG) and the outer (OG) granite. The quarries are confined to the outer intrusion which has an appearance more attractive to the market than that of the inner intrusion. The localization of the natural stone deposits in the Vehmaa batholith is a result of the magmatic history of the batholith, producing intrusions of different appearances with different commercial potential.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"83 1","pages":"25-39"},"PeriodicalIF":0.7,"publicationDate":"2011-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67629772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Detrital zircon studies suggest that the few quartzite occurrences in southern Finland are younger than 1.87 Ga and express sedimentation after 1.89–1.87 Ga accretional deformation and metamorphism in the Svecofennian orogenic belt. Detailed field work in the high-grade metamorphic Pyhantaka area allowed to distinguish an overturned formation within metagraywackes (cordierite paragneisses) and psammites. The Pyhantaka formation has a maximum thickness of 1000 meters and consists of quartzite overlain by meta-arkose, metatuff, and metabasalt on top. An uncorformity, expressed by a weathering surface, separates the quartzite from underlying metagraywacke. The metavolcanic rocks within, stratigraphically underlying and overlying the Pyhantaka formation are mostly basalts and basaltic andesites, but a felsic volcanic rock and dacitic fragments in volcaniclastic rocks imply bimodal affinity. The quartzite was deposited during a stable intra-orogenic period probably after accretion but before 1.83–1.80 Ga collisional deformation and metamorphism in the Svecofennian orogen. Rifting during the intraorogenic period and accumulation of variable material in the rift from nearby sources by fluvial processes is a viable scenario for deposition and preservation of the Pyhantaka formation. Geochemical diagrams of the metavolcanic rocks show a scatter that is best explained by source heterogeneity and crustal contamination. Despite their (likely) postaccretion setting the basaltic rocks show arc-type characteristics due to subductionmodified lithospheric mantle sources. Because of recycling, also the paragneisses in the Pyhantaka area are geochemically similar in spite that they represent different tectonic settings. The use of elemental geochemistry alone appears to be insufficient for discriminating tectonic settings of basalts or graywackes in the Svecofennian of southern Finland where accretion and post-accretion settings were largely obliterated by late collision.
{"title":"The Pyhäntaka formation, southern Finland: a sequence of metasandstones and metavolcanic rocks upon an intra-orogenic unconformity","authors":"M. Nironen","doi":"10.17741/BGSF/83.1.001","DOIUrl":"https://doi.org/10.17741/BGSF/83.1.001","url":null,"abstract":"Detrital zircon studies suggest that the few quartzite occurrences in southern Finland are younger than 1.87 Ga and express sedimentation after 1.89–1.87 Ga accretional deformation and metamorphism in the Svecofennian orogenic belt. Detailed field work in the high-grade metamorphic Pyhantaka area allowed to distinguish an overturned formation within metagraywackes (cordierite paragneisses) and psammites. The Pyhantaka formation has a maximum thickness of 1000 meters and consists of quartzite overlain by meta-arkose, metatuff, and metabasalt on top. An uncorformity, expressed by a weathering surface, separates the quartzite from underlying metagraywacke. The metavolcanic rocks within, stratigraphically underlying and overlying the Pyhantaka formation are mostly basalts and basaltic andesites, but a felsic volcanic rock and dacitic fragments in volcaniclastic rocks imply bimodal affinity. The quartzite was deposited during a stable intra-orogenic period probably after accretion but before 1.83–1.80 Ga collisional deformation and metamorphism in the Svecofennian orogen. Rifting during the intraorogenic period and accumulation of variable material in the rift from nearby sources by fluvial processes is a viable scenario for deposition and preservation of the Pyhantaka formation. Geochemical diagrams of the metavolcanic rocks show a scatter that is best explained by source heterogeneity and crustal contamination. Despite their (likely) postaccretion setting the basaltic rocks show arc-type characteristics due to subductionmodified lithospheric mantle sources. Because of recycling, also the paragneisses in the Pyhantaka area are geochemically similar in spite that they represent different tectonic settings. The use of elemental geochemistry alone appears to be insufficient for discriminating tectonic settings of basalts or graywackes in the Svecofennian of southern Finland where accretion and post-accretion settings were largely obliterated by late collision.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"83 1","pages":"5-23"},"PeriodicalIF":0.7,"publicationDate":"2011-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67630044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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