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.

Geochronologic and thermobarometric constraints on the metamorphic history of the Fairbanks Mining District, western Yukon-Tanana terrane, Alaska

2002 ◽  
Vol 39 (7) ◽  
pp. 1107-1126 ◽  
Author(s):  
Thomas A Douglas ◽  
Paul W Layer ◽  
Rainer J Newberry ◽  
Mary J Keskinen
Keyword(s):  
Thrust Fault ◽  
White Mica ◽  
Mining District ◽  
East Central ◽  
Diamond Drill ◽  
Metamorphic History ◽  
Structural History ◽  
History Of ◽  
Radiogenic Argon ◽  
Single Grain

This study presents new petrologic and thermochronologic information from the Fairbanks district of east central Alaska that indicate a complex metamorphic and structural history for the western Yukon–Tanana terrane. Garnet–biotite and garnet–pyroxene thermometry and jadeite barometry yield prograde temperatures and pressures for the Chatanika eclogite (523°C, 14–15 kbar (1 kbar = 100 MPa)). Cooling from peak eclogitization is estimated from 40Ar/39Ar single grain geochronology at ~210–180 Ma. Secondary white mica ages of 140–115 Ma along the fault contact between eclogite and underlying lower amphibolite-facies rocks constrain the age of the event that placed the Chatanika eclogite over the Fairbanks schist. Based on observations from field mapping and diamond drill samples, we interpret this structural contact as a thrust fault. Garnet–biotite mineral pairs are reset by as much as 200°C within this fault zone. Biotite and white mica ages of ~100–110 Ma, combined with Jurassic amphibole ages in Fairbanks schist samples, indicate the Fairbanks schist and Chatanika eclogite cooled through biotite and white mica argon closure temperatures in the early Cretaceous. Intrusion of mid-Cretaceous, calc-alkalic, gold-related granitic plutons in the Fairbanks district are evidenced by loss of radiogenic argon in many of the 40Ar/39Ar age fractions. Eocene basalt is visible in six widely separated localities within the eastern part of the Fairbanks district. However, the pervasiveness of a 50 Ma resetting event in samples as far as 30 km from present day basalt localities indicates the Eocene flows were either deposited throughout the Fairbanks area or are associated with large plutons at depth.

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.

Low-temperature thermal history of the Gilmore Dome area, Fairbanks Mining District, Alaska

1993 ◽  
Vol 30 (4) ◽  
pp. 764-768 ◽  
Author(s):  
John M. Murphy ◽  
Arne Bakke
Keyword(s):  
Gold Deposit ◽  
Fission Track ◽  
Hydrothermal Fluids ◽  
Mining District ◽  
Cooling Path ◽  
Alteration Assemblage ◽  
Zircon Fission Track ◽  
History Of ◽  
Maximum Temperatures ◽  
Fission Track Ages

Eight apatite and two zircon fission-track ages provide evidence of complex Tertiary thermal overprinting by hydrothermal fluids in the Gilmore Dome area. Five ages on apatite from the Fort Knox gold deposit average 41 Ma, one from the Stepovich prospect is 80 Ma, and two from Pedro Dome average 67 Ma. Elevations of these samples overlap but their ages do not, indicating that each area experienced a different thermal history.Ages of apatite from the Fort Knox gold deposit decrease with elevation from 42 to 36 Ma but have data trends indicative of complex cooling. Two ~51 Ma ages on zircon indicate that maximum temperatures approached or exceeded ~180 °C. An alteration assemblage of chalcedony + zeolite + calcite + clay in the deposit resulted from deposition by a paleo-hydrothermal system. The data suggest that the system followed a complex cooling path from > 180 to < 110 °C between 51 and 36 Ma, and that final cooling to below 60 °C occurred after ~25 Ma.The 80 Ma age from Stepovich prospect either resulted from cooling after intrusion of the underlying pluton (~90 Ma) or records postintrusion thermal overprinting sometime after ~50 Ma. The 67 Ma samples from Pedro Dome may also have experienced partial age reduction during later heating. The differences in the data from the different areas and the presence of a late alteration assemblage at Fort Knox suggest that the fluids responsible for heating were largely confined to the highly fractured and porous Fort Knox pluton.

The Ismaili Tradition in Iran: 13th Century to the Present

2021 ◽  
Author(s):  
Daniel Beben
Keyword(s):  
20Th Century ◽  
Future Research ◽  
Early 20Th Century ◽  
13Th Century ◽  
Complete Understanding ◽  
Northern Iran ◽  
Minority Community ◽  
History Of ◽  
The 19Th Century ◽  
To Receive

The Ismailis are a minority community of Shiʿi Muslims that first emerged in the 8th century. Iran has hosted one of the largest Ismaili communities since the earliest years of the movement and from 1095 to 1841 it served as the home of the Nizārī Ismaili imams. In 1256 the Ismaili headquarters at the fortress of Alamūt in northern Iran was captured by the Mongols and the Imam Rukn al-Dīn Khūrshāh was arrested and executed, opening a perilous new chapter in the history of the Ismailis in Iran. Generations of observers believed that the Ismailis had perished entirely in the course of the Mongol conquests. Beginning in the 19th century, research on the Ismailis began to slowly reveal the myriad ways in which they survived and even flourished in Iran and elsewhere into the post-Mongol era. However, scholarship on the Iranian Ismailis down to the early 20th century remained almost entirely dependent on non-Ismaili sources that were generally quite hostile toward their subject. The discovery of many previously unknown Ismaili texts beginning in the early 20th century offered prospects for a richer and more complete understanding of the tradition’s historical development. Yet despite this, the Ismaili tradition in the post-Mongol era continues to receive only a fraction of the scholarly attention given to earlier periods, and a number of sources produced by Ismaili communities in this period remain unexplored, offering valuable opportunities for future research.

The dire straits of Paratethys: Gateways to the anoxic giant of Eurasia

2021 ◽  
pp. SP523-2021-73
Author(s):  
D. V. Palcu ◽  
W. Krijgsman
Keyword(s):  
Carbon Sink ◽  
Global Climate ◽  
Water Masses ◽  
Source Rocks ◽  
Global Ocean ◽  
Tectonic Processes ◽  
Anoxic Environments ◽  
Geological Evolution ◽  
History Of ◽  
Tethys Ocean

AbstractA complex interplay of palaeoclimatic, eustatic and tectonic processes led to fragmentation and dissipation of the vast Tethys Ocean in Eocene-Oligocene times. The resulting Paratethys Sea occupied the northern Tethys region on Eurasia, grouping water masses of various subbasins, separated from each other and from the open ocean through narrow and shallow gateways and land bridges. Changes in marine gateway configuration and intra-basinal connectivity affected the regional hydrology, shifting most Paratethyan basins to extreme carbon-sink anoxic environments, anomalohaline evaporitic or brackish conditions or even endorheic lakes. Paratethys gateway restriction triggered the onset of a long-lasting (∼20 Myr) giant anoxic sea, characterised by stratified water masses and anoxic bottom water conditions, resulting in thick hydrocarbon source rocks. Here, we review the geological evolution of the “dire straits” of Paratethys that played a crucial role in the Eocene-Oligocene connectivity history of the Central Eurasian seas and we show that the main anoxic phases (Kuma and Maikop) correspond to restricted connectivity with the global ocean and a period of CO2 depletion in the atmosphere. Paratethys represents one of the largest carbon sinks of Earth's history and may thus have played a prominent role in global climate change.

scholarly journals Evaluation of hydrocarbons generated from the Permo-Carboniferous source rocks in Huanghua Depression of the Bohai Bay Basin, China

2018 ◽  
Vol 36 (5) ◽  
pp. 1229-1244
Author(s):  
Xiao-Rong Qu ◽  
Yan-Ming Zhu ◽  
Wu Li ◽  
Xin Tang ◽  
Han Zhang
Keyword(s):  
Oil And Gas ◽  
Source Rocks ◽  
Bohai Bay ◽  
Hydrocarbon Generation ◽  
Burial History ◽  
Bohai Bay Basin ◽  
Important Conclusion ◽  
The North ◽  
Huanghua Depression ◽  
History Of

The Huanghua Depression is located in the north-centre of Bohai Bay Basin, which is a rift basin developed in the Mesozoic over the basement of the Huabei Platform, China. Permo-Carboniferous source rocks were formed in the Huanghua Depression, which has experienced multiple complicated tectonic alterations with inhomogeneous uplift, deformation, buried depth and magma effect. As a result, the hydrocarbon generation evolution of Permo-Carboniferous source rocks was characterized by discontinuity and grading. On the basis of a detailed study on tectonic-burial history, the paper worked on the burial history, heating history and hydrocarbon generation history of Permo-Carboniferous source rocks in the Huanghua Depression combined with apatite fission track testing and fluid inclusion analyses using the EASY% Ro numerical simulation. The results revealed that their maturity evolved in stages with multiple hydrocarbon generations. In this paper, we clarified the tectonic episode, the strength of hydrocarbon generation and the time–spatial distribution of hydrocarbon regeneration. Finally, an important conclusion was made that the hydrocarbon regeneration of Permo-Carboniferous source rocks occurred in the Late Cenozoic and the subordinate depressions were brought forward as advantage zones for the depth exploration of Permo-Carboniferous oil and gas in the middle-northern part of the Huanghua Depression, Bohai Bay Basin, China.

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