American Journal of Science最新文献

{"title":"Post-depositional transformations in sedimentary rocks and implications for paleoenvironmental studies: evidence from the Mesoproterozoic (∼1.1 Ga) of the Taoudeni Basin, Mauritania","authors":"Mohamed Ghnahalla, A. El Albani, Ahmed Abd Elmola, O. Bankole, C. Fontaine, Mohamed Salem Sabar, A. Trentesaux, Claude Laforest, A. Meunier, Céline Boissard, Chenyi Tu, T. Lyons","doi":"10.2475/07.2022.02","DOIUrl":"https://doi.org/10.2475/07.2022.02","url":null,"abstract":"Understanding paleoenvironmental dynamics linked to biological evolution in Earth history is a major goal within the geological community. The difficulty of achieving this goal, at least in part, lies with the secondary transformations experienced by a majority of ancient rocks, especially through metamorphism and hydrothermal activity. The Mesoproterozoic (∼1.1 Ga) shallow-marine deposits from the Taoudeni Basin, Mauritania, have suffered a complex, multiphase tectonic, and thermal evolutionary history. Representative samples from two drill cores (a background site [S2] and a dolerite intrusion-bearing drill core [S1]) from the El Mreiti Group were evaluated for transformations and overprints of original mineralogies and geochemical compositions. Our results show that the drill core hosting the dolerite intrusion (S1) is characterized by a suite of minerals (that is, pyroxene, graphite, pyrrhotite, garnet, zeolite, and authigenic clay minerals) resulting from contact metamorphism and associated hydrothermal activity. However, compared to the S1, the S2 core shows no evidence of post-depositional transformation. The geochemical data obtained from S1 reveal a striking elevation of iron contents likely delivered from the hydrothermal fluids. Moreover, concentrations of redox-sensitive trace elements (molybdenum, uranium, and vanadium) increased dramatically during hydrothermal and metamorphic activity. This study demonstrates that need for caution when assessing paleoenvironmental conditions in ancient sedimentary rocks, particularly for iron and trace metal approaches commonly used in reconstructions of paleo-redox.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"898 - 937"},"PeriodicalIF":2.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43682764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Determination of an intracontinental transform system along the southern Central Asian orogenic belt in the latest Paleozoic","authors":"Jin Zhang, J. Qu, Beihang Zhang, Heng Zhao, Ronggou Zheng, Jianfeng Liu, Jie Hui, Pengfei Niu, Long Yun, Shuo Zhao, Yiping Zhang","doi":"10.2475/07.2022.01","DOIUrl":"https://doi.org/10.2475/07.2022.01","url":null,"abstract":"Intracontinental transform structures are important forms of continental deformation, such as the Altyn Tagh fault on Tibetan Plateau. Although many intracontinental transform structures have developed throughout geological history, their identification is relatively difficult due to later deformation and sedimentary covering. Strike-slip faults played an important role in the formation and subsequent transformation of the Central Asian orogenic belt (CAOB). In this study, a group of nearly EW-trending dextral shear zones along the southern CAOB in the Beishan, Alxa, northern margin of the North China Craton and the Great Xing'an Mountains to the east, is reported. Regional strike-slip duplex systems were developed and strongly superimposed on the CAOB in the Beishan and Alxa regions. Meanwhile, to the west of the Beishan, coeval ductile shear zones with the same kinematics also developed along the CAOB. The ages of the shear zones range from 280 Ma to 230 Ma and become younger to the east. This megashear system may also connect with the shortening in the Ural Orogenic belt to the west and the convergence along the eastern margin of the Eurasian continent, which is approximately more than 9000 km long in the Asian continent and consists of an intracontinental transform structure in the central Pangea continent. Further west, the dextral shear system may also connect with the coeval shear zones with the same kinematics along the southern Variscan orogenic belt in Europe and even the South Appalachian Orogenic Belt in the southeastern North America, which we call the Intra-Pangean Megashear (IPM) after Irving (2004). The rotation and approach of the Baltic Craton and Siberian Craton and the northern Pangean lithosphere heated by mantle plumes and its lat.eral (eastward) spreading may have caused the development of the IPM and intracontinental deformation from Pangea B to Pangea A.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"851 - 897"},"PeriodicalIF":2.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69325513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The LSU campus mounds, with construction beginning at ∼11,000 BP, are the oldest known extant man-made structures in the Americas","authors":"B. Ellwood, S. Warny, Rebecca A. Hackworth, Suzanne H. Ellwood, Jonathan H. Tomkin, S. Bentley, D. Braud, G. Clayton","doi":"10.2475/06.2022.02","DOIUrl":"https://doi.org/10.2475/06.2022.02","url":null,"abstract":"Radiocarbon dating of the two LSU Campus Mounds (16EBR6) indicates that the construction of one, Mound B, began at ∼11,000 BP, making Mound B the oldest known and intact manmade structure in the Americas. The age analyses presented here are based on thirty one 14C dates. The older (deeper) parts of both of the LSU Campus Mounds contain many thin, burned ash lenses, suggesting that the Mounds may have been used for ceremonial or cremation purposes. These ash layers are composed mainly of phytoliths, bio-silicate (SiO2) structural compounds in plants that remained after burning of these plants. Analysis of the abundant ash lenses indicates that the plants burned were mainly C4 hydrophilic grasses that are dominated by 90-98% reed and cane plants. The ash layers also contain microscopic fragments of burned, large mammal osteons (bone). The layers of reed and cane phytoliths, containing very small numbers of osteons, are indicative of very hot fires. This finding supports the argument that the fires were used for ceremonials or cremations. No ash beds later than 5,000 BP are known from either LSU Campus Mound A or B, although at ∼800 calBP, a wooden post (now charcoal) was planted and burned on the top of Mound B. It appears that construction of Mound B began during the climate amelioration that followed the Younger Dryas climate event, which ended at ∼11,700 BP. Construction of Mound A appears to have begun at ∼9,500 calBP. Building of the LSU Campus Mounds shows a hiatus when climate deteriorated during the 8200 Climate Event, which defined the end of the Holocene Greenlandian Stage and the beginning of the Northgrippian Stage. Construction began again at ∼7,500 BP, when both mounds continued construction until ∼6,000 BP, with one apparently anomalous date in Mound A at ∼5,100 calBP.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"795 - 827"},"PeriodicalIF":2.9,"publicationDate":"2022-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42365039","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of source compositions on adakitic features: A case study from the Buya granite, in western Kunlun, NW China","authors":"Peng Wang, Guochun Zhao, Qian Liu, Jinlong Yao, Yigui Han, Jianhua Li","doi":"10.2475/06.2022.03","DOIUrl":"https://doi.org/10.2475/06.2022.03","url":null,"abstract":"Characterized by high Sr/Y (> 40) and La/Yb (> 20) ratios, the adakitic features are, generally, attributed to a garnet-bearing residue. However, adakitic features may be inherited from an adakitic source. In this contribution, we take the Buya granite as an example to demonstrate the effect of source on adakitic features through petrology, zircon U-Pb geochronology and Lu-Hf isotopes, whole-rock geochemistry, and Sr-Nd-Pb isotopes. The 445 Ma Buya granite contains many coeval microgranular magmatic enclaves (MMEs), and some late fine-grained granitic dikes. The host granite and the MMEs display sub-parallel to parallel trace-element patterns characterized by enrichments in LREE and LILE, and depletions in HREE and HFSE, typical of adakitc features. Importantly, the two lithologies possess comparable zircon Hf and whole rock Sr-Nd-Pb isotopic compositions that plot along a mantle array. The MMEs are interpreted as cognate fragments of early-formed crystals and the parental magma was sourced from overriding mantle wedge metasomatized by fluids derived from the subducted Proto-Tethys slab. Comparatively, the dikes, with positive εNd(t) (∼2) values and lower (87Sr/86Sr)t (∼0.705), were products of the partial melting of a plagioclase-rich crustal source. Although the host granite and the MMEs possess adakitic features, the latter have higher La/Yb ratios and relatively lower Sr/Y ratios, which are inconsistent with garnet effect because of similarly high DY/DSr (∼1900) and high DYb/DLa ratios (∼2300) for garnet/melt. Instead, this feature is attributed to the fractional crystallization of hornblende and allanite. Therefore, the host granite and the MMEs may inherit adakitic features from the source. Likewise, the adakitic features of the dikes are attributed to a plagioclase-rich source due to the enrichment in Sr element. The early fractional crystallization of amphibole and biotite in the MMEs can elevate Zr/Sm and lower Nb/Ta ratios, respectively, in the residual liquid to form evolved magma similar to adakites and TTGs. The Buya granite displays an arc affinity, demonstrating the northward subduction of the Proto-Tethys oceanic plate.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"828 - 850"},"PeriodicalIF":2.9,"publicationDate":"2022-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47036038","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A giant sand injection complex: Processes and implications for basin evolution and subsurface fluid flow","authors":"M. Vigorito, A. Hurst, A. Scott, Olivier Stanzione, A. Grippa","doi":"10.2475/06.2022.01","DOIUrl":"https://doi.org/10.2475/06.2022.01","url":null,"abstract":"Giant sand injection complexes form, intricate, basin-scale fluid plumbing systems and document the remobilisation and intrusion of several tens of cubic kilometres of sand within the shallow crust in stratigraphic units 100's metres thick. This is the first detailed and extensive account of the Panoche Giant Injection Complex (PGIG), a regionally significant outcrop (>300 km2) and part of a larger subsurface development (>4000 km2) identified in boreholes and on seismic reflection data. Magnificent exposure of the PGIC occurs along the north western margin of the San Joaquin Valley and presents the opportunity to examine the regional geological significance of a giant sand injection complex and its origin in the context of a late Cretaceous – early Paleocene forearc basin. Between 25 and 49 km3 of sand were remobilised and injected, at least 0.35 km3 of which extruded onto the paleo-seafloor. Large sandstone intrusions often >10 m thick and laterally extensive on a kilometer scale formed saucer-shaped intrusions, wing-like intrusions and a variety of sill geometries along with volumetrically smaller randomly oriented dikes in a 200–300 m thick interval. Dikes prevail below and above this interval, some reaching the paleo seafloor and extruding sand. Networks of propagating hydrofractures form intensely brecciated host strata, some of which were intruded by sand. All intrusions formed in a single pulsed event in which the most intense hydrofracturing caused by supra-lithostatic fluid pressure occurred approximately 600 to 800 m below the paleo seafloor. A crudely orthogonal arrangement of dikes is preserved with most oriented normal, and less commonly oriented parallel to the oceanic trench associated with the late Mesozoic to early Tertiary North Pacific subduction. Dikes orthogonal to the trench opened against the minimum horizontal stress, which was parallel to the trench. Dikes parallel to the trench opened against the regional maximum horizontal stress along minor faults formed in extension caused by shallow crustal deformation. There is no evidence that compressional tectonics influenced the onset of elevated pore fluid pressure necessary to promote sand injection. However, tectonic compression was responsible for creating the basin physiography that locally increased subsidence and accelerated chemical diagenesis in the basin centre. PGIC outcrop, located along the basin margins, was unlikely to have experienced heating above 70 °C, equivalent about 2 km burial, so the effects of chemical diagenesis in the host strata of the injection complex had negligible potential to evolve significant pore water volume. In a deeper part of the basin approximately 150 km to the south, lateral equivalents of the host strata were subjected to heating >100 °C and would expel significant volumes of water displaced by quartz cementation and clay dehydration that caused lateral pressure transfer to the north and western margin of the basin where the PGIC form","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"729 - 794"},"PeriodicalIF":2.9,"publicationDate":"2022-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43318231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Partial molar volumes of metal oxides in silicate melts: Effects of Coulombic interactions","authors":"H. Nesbitt, P. Richet, G. Bancroft, G. Henderson","doi":"10.2475/05.2022.02","DOIUrl":"https://doi.org/10.2475/05.2022.02","url":null,"abstract":"Alkaline, alkaline earth, many 3d and most 4f modifier oxides dissolved in siliceous melts mix non-ideally with SiO2 to produce linear, density-compositional mixing trends from which partial molar volumes of modifier oxides (V*) are determined. An analysis of these experimental data reveals that the partial molar volumes of alkali, alkaline earths, most 4f and many 3d modifier oxides partial molar volumes are accurately reproduced by: where FC = (z+•z−)/d2 (Coulomb's Law) and z indicates charge. The bond length ‘d’ is the sum of the radii of the cation (M+, M2+, M3+ or M4+) and oxide ion (O2−) observed in ionic crystals. The coefficients ‘m’ and ‘b’ are 0.325 and 1.38 Å/atom respectively. Partial molar volumes of network-forming oxides also conform to the above equation where ‘m’ = ∼3.25 and ‘b’ is 1.68 Å/atom. Coulomb's force of attraction (FC) is the product of the cationic field strength (z+/d2) and the charge on an anion, where ‘d’ is the distance separating the centers of the two charges. In silicate melts containing modifier cations, apical O atoms of Si tetrahedra are negatively charged and are displaced toward the cations due to Coulombic attraction. The resulting collapse around the cations is referred to as ‘electrostriction’. Partial molar volumes (V*) of modifier oxides are thus composed of two terms, the volume of the polyhedron of the modifier cation (VPoly) and a volume associated with collapse of tetrahedra around the cation (VCol): VCol is negative for all modifier oxides and becomes increasingly negative with increased charge on the cation and with increased coordination number (CN). VPoly is itself composed of two terms, an intrinsic volume (VInt) and an excluded volume (VEx). The intrinsic volume can be calculated using cationic and O2− radii evaluated from ionic crystals. VEx reflects the state of packing around cationic polyhedra. It is equal to 6.83 Å3/atom for all modifier oxides so that the expression for VPoly is: A linear relationship exists between VPoly and VCol which results in the observed linear density-composition trends from which partial molar volumes are determined. In spite of their linearity, these trends are the result of non-ideal mixing of modifier oxide and SiO2 components in siliceous melts. Our finding that tetrahedra collapse around modifier cations differs from the traditional perspective where modifier cations were considered to occupy voids within the silicate network but otherwise had limited effect on melt structure. These results demonstrate that modifier cations affect the network substantially by causing surrounding tetrahedra to rotate, twist, tilt and flex during their collapse toward modifier cations.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"683 - 704"},"PeriodicalIF":2.9,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46402195","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Weathering intensity and lithium isotopes: A reactive transport perspective","authors":"M. Winnick, J. Druhan, K. Maher","doi":"10.2475/05.2022.01","DOIUrl":"https://doi.org/10.2475/05.2022.01","url":null,"abstract":"Lithium isotopes have emerged as a powerful tool to probe the response of global weathering to changes in climate. Due to the preferential incorporation of 6Li into clay minerals during chemical weathering, the isotope ratio δ7Li may be used to interrogate the balance of primary mineral dissolution and clay precipitation. This balance has been linked to relative rates of chemical and physical denudation, such that dissolved δ7Li (δ7Lidiss) is highest at moderate weathering intensities when chemical and physical denudation are comparable. However, we argue that current theory linking δ7Li to weathering regimes through fluid travel times are unable to explain observations of low δ7Li and high Li concentrations in rapidly eroding settings. In this study, we re-examine the relationships between δ7Li, Li concentration, and weathering regime by incorporating Li isotopes into simulations of weathering profiles using a reactive transport model (CrunchFlow) that includes advective fluxes of regolith to simulate variable erosion rates in response to uplift. In these simulations, fractionation is implemented through a kinetic fractionation factor during clay precipitation, which allows the δ7Li of dissolved and suspended loads in the model to vary as a function of Li/Al ratios in primary and secondary minerals. When the model is run over a range of infiltration and erosion rates, simulations reproduce observed global patterns of δ7Lidiss and suspended load δ7Li as a function of weathering intensity, controlled primarily by water travel times and mineral residence times in weathered bedrock. We find that reduced water travel times at low weathering intensity, however, are inconsistent with observations of high Li concentrations. As an alternative, we demonstrate how the rapid weathering of soluble, Li-rich minerals such as chlorite under low weathering intensities may resolve this apparent discrepancy between data and theory. We also suggest that observed patterns are consistent with geothermal Li sources under low weathering intensities. This work offers a foundation guiding future studies in testing potential mechanisms underlying global riverine δ7Lidiss.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"647 - 682"},"PeriodicalIF":2.9,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44313854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Proterozoic-Mesozoic development of the Quanji block from northern Tibet and the cratonic assembly of eastern Asia","authors":"Chao Wang, D. Evans, Meng Li, Ji-Heng Zhang, Jian Han, Bin Wen, J. Wang, Junming Zhao","doi":"10.2475/05.2022.03","DOIUrl":"https://doi.org/10.2475/05.2022.03","url":null,"abstract":"Unraveling the timing, location, and mechanisms of cratonic aggregation in Earth's continental jigsaw puzzle is a key factor for plate tectonic reconstructions. The Quanji Block (QB) is a sliver of anomalously old and well-preserved continental crust embedded within the Paleozoic-Mesozoic tectonic collage of the northeastern Tibetan Plateau and has played a critical role in Proto-/Paleotethys paleogeographic reconstructions. New geological mapping, stratigraphic logging, and geochronological analysis lead to a refined understanding of QB's history from Paleoproterozoic to present. Deposited atop a largely Paleoproterozoic basement, the Quanji Group records rifting and epicratonic cover at 1.7 to 1.6 Ga. The Quanji Group is unconformably overlain by the Xiaogaolu Group, which preserves black shale, Ediacaran-type Charnia, ribbon-shaped fossils and a late Ediacaran glaciation. U-Pb detrital zircon ages from Cambrian Olongbuluke Group marine platform deposits are quite different from ages in underlying units, with a minor component of Neoproterozoic (880–815 Ma) ages. The apparent change in detrital zircon sources coincides with a regionally expressed Great Unconformity during the Precambrian–Cambrian transition. The new stratigraphy and U-Pb geochronology of QB suggest that the late Paleoproterozoic to Cambrian history of QB has a remarkable similarity to that of the southern margin of North China Block (NCB), indicating that the QB has been displaced dextrally from an initial location adjacent to NCB. The transform motion occurred in stages between ca. 350 and 200 Ma, which suggests that transform tectonism appears to be an essential element of any viable model for kinematic development of the Paleo-Tethyan oceanic domains and the ultimate cratonic assembly of eastern Asia.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"705 - 727"},"PeriodicalIF":2.9,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49037081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New Idria serpentinite protrusion, Diablo Range, California: From upper mantle to the surface","authors":"R. Coleman, J. Gooley, R. Gregory, S. Graham","doi":"10.2475/04.2022.01","DOIUrl":"https://doi.org/10.2475/04.2022.01","url":null,"abstract":"The New Idria serpentinite body in the Coast Ranges of California is a diapir that resulted from the interaction of the migrating Mendocino trench-ridge-transform fault triple junction, transpression, metasomatic fluids, and previously subducted oceanic crust and mantle. Northward propagation of the San Andreas fault progressively eliminated the original subduction zone, allowing seawater to penetrate into the formerly subducting abyssal peridotite mantle, triggering serpentinization. The associated physical changes in density, volume, and strength yielded an expanding, buoyantly rising serpentinite protrusion, facilitated by transpression along the San Andreas fault. Sedimentary facies and intrusion of minor cross cutting syenite and alkali basalt dikes indicate that the serpentinization-driven diapir buoyantly rose and widely breached the surface by ca. 14 Ma, attending migration of the Mendocino Triple Junction past the latitude of New Idria.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"533 - 560"},"PeriodicalIF":2.9,"publicationDate":"2022-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43198975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"From Gondwana rifting to Alpine orogeny: Detrital zircon geochronologic and provenance signals from the Kopet Dagh Basin (NE Iran)","authors":"A. Mohammadi, J. Ruh, M. Guillong, O. Laurent, L. Aghajari","doi":"10.2475/04.2022.02","DOIUrl":"https://doi.org/10.2475/04.2022.02","url":null,"abstract":"The Kopet Dagh mountains in NE Iran exhibit a 7-km-thick continuous sedimentary sequence recording detritus from exposed surrounding terranes from the last 175 Ma. This work presents a multi-disciplinary geochronologic and provenance analysis in an attempt to identify and date major geologic events along the northern segment of the Tethys and reconstruct the regional tectonic history from Gondwana-related rifting until the Alpine orogeny. Sandstone framework, heavy mineral analysis, U-Pb dating of detrital zircons, and Hf-isotope ratio measurements on dated zircons from Triassic to Paleocene sandstones indicate three main tectonic events that include Early Silurian intracontinental rifting (opening of Paleo-Tethys), Early Carboniferous rifting of a back-arc basin (Aghdarband Complex), and Late Triassic collisional to post-collisional magmatism (Paleo-Tethys collision). Mineralogical and age peak considerations indicate that detritus was supplied from the south into the extensional Kopet Dagh Basin during Middle Jurassic, while Cretaceous to Paleocene sandstones show signs of increasing recycling.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"561 - 592"},"PeriodicalIF":2.9,"publicationDate":"2022-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43277084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}