Baddeleyite from Large Complex Deposits: Significance for Archean-Paleozoic Plume Processes in the Arctic Region (NE Fennoscandian Shield) Based on U-Pb (ID-TIMS) and LA-ICP-MS Data

Baddeleyite is an important mineral geochronometer. It is valued in the U-Pb (ID-TIMS) geochronology more than zircon because of its magmatic origin, while zircon can be metamorphic, hydrothermal or occur as xenocrysts. Detailed mineralogical (BSE, KL, etc.) research of baddeleyite started in the Fennoscandian Shield in the 1990s. The mineral was first extracted from the Paleozoic Kovdor deposit, the second-biggest baddeleyite deposit in the world after Phalaborwa (2.1 Ga), South Africa. The mineral was successfully introduced into the U-Pb systematics. This study provides new U-Pb and LA-ICP-MS data on Archean Ti-Mgt and BIF deposits, Paleoproterozoic layered PGE intrusions with Pt-Pd and Cu-Ni reefs and Paleozoic complex deposits (baddeleyite, apatite, foscorite ores, etc.) in the NE Fennoscandian Shield. Data on concentrations of REE in baddeleyite and temperature of the U-Pb systematics closure are also provided. It is shown that baddeleyite plays an important role in the geological history of the Earth, in particular, in the break-up of supercontinents.

The Oldest Grey Gneisses and Tonalite-Trondhjemite Granodiorites in the Fennoscandian Shield: ID-TIMS and SHRIMP Data

Genesis of the oldest continental crust retains a marked trace in the Earth’s evolution over its 4.5 Ga history. Despite ample isotope data on the role of the continental crust in the Earth’s evolution, there has been much debate on the origin of grey gneisses and tonalite-trondhjemite-granodiorites (TTG). Precise U-Pb (ID-TIMS) and SHRIMP data on single zircon for paragneisses and TTG (3158.2 ± 8.2 Ma) have indicated the Central-Kola and Belomorian (White Sea) megablocks of the Fennoscandian Shield to be 3.16 Ga and 3.70 Ga, respectively. The newly obtained ages of zircon from these megablocks indicate the origin of the discrete continental crust to be 3.16 and 3.70 Ga. It is close to the Nordsim zircon data on the Siurua TTG (Finland), which are 3.45 and 3.73 Ga in the core. The new summarized data on the Earth’s oldest rocks (basement and continental crust) indicate the younger age of the rocks in the Fennoscandian Shield as compared to those in Australia (Kronendonk et al., 2019).

New U-Pb and Sm-Nd Data and REE Distribution in Sulphides of Paleoproterozoic PGE Layered Intrusions in the Arctic Part of the Fennoscandian Shield

The U-Pb (on zircon) and Sm-Nd analysis is a popular isotope-geochronological tool for estimating the age of rocks from PGE mafic-ultramafic intrusions. Sulphides can be used to study the geochronology of ore processes as well, since they should indicate the time of ore mineralization. Gabbronorite has been sampled from the Passivaara reef at the Penikat layered intrusion (Finland) for U-Pb and Sm-Nd isotope single zircon analyses in order to separate sulphide minerals. The Sm-Nd isotope age of gabbronorite has been dated at 2426 ± 36 Ma;eNd(T) = −1.4 ± 0.4. The Sm-Nd isotope age on sulphides and rock-forming minerals reflects the crystallization time of the ore-bearing gabbronorite from the Passivaara reef of the Penikat layered intrusion. The mass-spectrometer analytical environment and modes of operation have been adjusted to detect REE in sulphide minerals on example of pyrite from the PGE Penikat layered intrusion (Finland) and chalcopyrite from the Talnakh deposit (Norilsk area, Russia) has been estimated. The total REE content in pyrite is ca. 3.5 ppm, which is enough to define the Sm-Nd age of pyrite. The study shows how to use the mineral/chondrite spectra to evaluate the accuracy of the REE analytical results on example of State Standard Sample 2463 (Russia).

Mesoarchean Gridino Mafic Dykes Swarm of the Belomorian Eclogite Province of the Fennoscandian Shield(Russia)

Two eclogite associations have been recognized within Belomorian TTG gneisses:(1)the subduction-type Salma association and(2)Gridino eclogitized mafic dykes.Protoliths of the Salma eclogites represent a sequence

Mafic Dykes on Bornholm(Denmark) as Indicators of Precambrian to Permian Extensional Events at the SW Margin of the Fennoscandian Shield

About 200 mafic dykes intruded Mesoproterozoic gneisses and granites of Bornholm,a Danish island situated in the southern Baltic Sea between Sweden,Germany and Poland.Field studies along the northern coast document

芬兰的冰川作用与冰川地貌(英文)

芬兰是一个地形比较平缓,由差异风化、侵蚀和冰川活动改造过的古准平原,平均海拔高度152m,其基岩主要由前寒武纪岩石组成。第四纪沉积盖层平均厚约8m,在芬兰南部最厚可能超过100m。芬兰在更新世至少曾两次被巨大的芬兰斯堪的纳维亚大冰盖完全覆盖,但其地貌却无例外地代表了80000—9000年B.P.的末次冰川作用。在芬兰没有现代冰川发育。 芬兰最近一次冰期是Weichsel冰期,早在110000年B.P.可能就开始了,但肯定不会晚于75000—70000年B.P.在末次冰期间阶段,曾出现过冰川退缩过程,芬兰北部的冰碛下泥炭的^(14)C年代为40000—58000年B.P.。在芬兰,大冰盖的冰退开始于约12000年B.P.,而冰后期定于大约10000年B.P.。全新世早期的冰川退缩速率平均约100m/a到260m/a。大约到了9000年B.P.,冰川边缘己全部退出芬兰到达瑞典北部的冰中心区。 芬兰的地形特征受冰川侵蚀的影响不大,但在构造控制的冰期前谷地,却受到较大的侵蚀。常见的侵蚀地貌是羊背石,其余还有山原侵蚀面、刻槽、条痕等,而冰斗、U形谷及其它典型的山谷冰川侵蚀地形仅在芬兰最北部见到有限数量。 芬兰97％以上的基岩被第四纪沉积物覆盖,冰碛通常以粘质底碛盖层及消融碛形式出现,富含巨砾。最明显的冰碛地形是鼓丘和DeGeer冰碛垅,常成群出现。鼓丘可达上?