A 25‐Year History of Volcano Magma Supply in the East Central Aleutian Arc, Alaska

2020 ◽  
Vol 47 (15) ◽  
Author(s):  
Xueming Xue ◽  
Jeffrey T. Freymueller
Keyword(s):  
East Central ◽  
Magma Supply ◽  
Aleutian Arc ◽  
History Of

scholarly journals Low Nucleotide Diversity in Chimpanzees and Bonobos

Genetics ◽  
2003 ◽  
Vol 164 (4) ◽  
pp. 1511-1518 ◽  
Author(s):  
Ning Yu ◽  
Michael I Jensen-Seaman ◽  
Leona Chemnick ◽  
Judith R Kidd ◽  
Amos S Deinard ◽  
...  
Keyword(s):  
Nucleotide Diversity ◽  
Nuclear Dna ◽  
Demographic History ◽  
Nuclear Genome ◽  
Limited Data ◽  
Effective Population ◽  
East Central ◽  
Dna Diversity ◽  
History Of ◽  
Mtdna Diversity

Abstract Comparison of the levels of nucleotide diversity in humans and apes may provide much insight into the mechanisms of maintenance of DNA polymorphism and the demographic history of these organisms. In the past, abundant mitochondrial DNA (mtDNA) polymorphism data indicated that nucleotide diversity (π) is more than threefold higher in chimpanzees than in humans. Furthermore, it has recently been claimed, on the basis of limited data, that this is also true for nuclear DNA. In this study we sequenced 50 noncoding, nonrepetitive DNA segments randomly chosen from the nuclear genome in 9 bonobos and 17 chimpanzees. Surprisingly, the π value for bonobos is only 0.078%, even somewhat lower than that (0.088%) for humans for the same 50 segments. The π values are 0.092, 0.130, and 0.082% for East, Central, and West African chimpanzees, respectively, and 0.132% for all chimpanzees. These values are similar to or at most only 1.5 times higher than that for humans. The much larger difference in mtDNA diversity than in nuclear DNA diversity between humans and chimpanzees is puzzling. We speculate that it is due mainly to a reduction in effective population size (Ne) in the human lineage after the human-chimpanzee divergence, because a reduction in Ne has a stronger effect on mtDNA diversity than on nuclear DNA diversity.

Timing of fluorite mineralization and exhumation events in the east Central Alborz Mountains, northern Iran: constraints from fluorite (U–Th)/He thermochronometry

2021 ◽  
pp. 1-17
Author(s):  
Behnam Shafiei Bafti ◽  
István Dunkl ◽  
Saeed Madanipour
Keyword(s):  
Thermal Relaxation ◽  
Geothermal Gradient ◽  
Source Rocks ◽  
Lower Amount ◽  
Mining District ◽  
Northern Iran ◽  
East Central ◽  
Central Alborz ◽  
Ore Mineralization ◽  
History Of

Abstract The recently developed fluorite (U–Th)/He thermochronology (FHe) technique was applied to date fluorite mineralization and elucidate the exhumation history of the Mazandaran Fluorspar Mining District (MFMD) located in the east Central Alborz Mountains, Iran. A total of 32 fluorite single-crystal samples from four Middle Triassic carbonate-hosted fluorite deposits were dated. The presented FHe ages range between c. 85 Ma (age of fluorite mineralization) and c. 20 Ma (erosional cooling during the exhumation of the Alborz Mountains). The Late Cretaceous FHe ages (i.e. 84.5 ± 3.6, 78.8 ± 4.4 and 72.3 ± 3.5 Ma) are interpreted as the age of mineralization and confirm an epigenetic origin for ore mineralization in the MFMD, likely a result of prolonged hydrothermal circulation of basinal brines through potential source rocks. Most FHe ages scatter around the Eocene Epoch (55.4 ± 3.9 to 33.1 ± 1.7 Ma), recording an important cooling event after heating by regional magmatism in an extensional tectonic regime. Cooling of the heated fluorites, as a result of thermal relaxation in response to geothermal gradient re-equilibration after the end of magmatism, or exhumation cooling during extensional tectonics characterized by lower amount of erosion are most probably the causes of the recorded Eocene FHe cooling ages. Oligocene–Miocene FHe ages (i.e. 27.6 ± 1.4 to 19.5 ± 1.1 Ma) are related to the accelerated uplift of the whole Alborz Mountains, possibly as a result of the initial collision between the Afro-Arabian and Eurasian plates further to the south.

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