Fission Track Analysis Research Articles

Exhumation of the Late Cretaceous Ore‐forming Porphyries in Zhongdian Area, Northwestern Yunnan: Evidence from Fission Track Analysis

Acta Geologica Sinica - English EditionVolume 95, Issue 5 p. 1786-1787 Research Advance Exhumation of the Late Cretaceous Ore-forming Porphyries in Zhongdian Area, Northwestern Yunnan: Evidence from Fission Track Analysis Xuelong LIU, Corresponding Author Xuelong LIU xuelongliu@foxmail.com Kunming University of Science and Technology, Kunming, 650093 China Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037 ChinaCorresponding author. E-mail: xuelongliu@foxmail.comSearch for more papers by this authorZhiming YANG, Zhiming YANG Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037 ChinaSearch for more papers by this authorYingxiang LU, Yingxiang LU Kunming University of Science and Technology, Kunming, 650093 China Yunnan Geological Survey, Kunming, 650051 ChinaSearch for more papers by this authorNa ZHANG, Na ZHANG Kunming University of Science and Technology, Kunming, 650093 ChinaSearch for more papers by this authorLeilei DONG, Leilei DONG Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037 ChinaSearch for more papers by this authorQianqian JIAO, Qianqian JIAO Kunming University of Science and Technology, Kunming, 650093 ChinaSearch for more papers by this authorJianhang CHEN, Jianhang CHEN Kunming University of Science and Technology, Kunming, 650093 ChinaSearch for more papers by this authorFucheng YANG, Fucheng YANG China University of Geosciences, Beijing, 100083 ChinaSearch for more papers by this author Xuelong LIU, Corresponding Author Xuelong LIU xuelongliu@foxmail.com Kunming University of Science and Technology, Kunming, 650093 China Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037 ChinaCorresponding author. E-mail: xuelongliu@foxmail.comSearch for more papers by this authorZhiming YANG, Zhiming YANG Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037 ChinaSearch for more papers by this authorYingxiang LU, Yingxiang LU Kunming University of Science and Technology, Kunming, 650093 China Yunnan Geological Survey, Kunming, 650051 ChinaSearch for more papers by this authorNa ZHANG, Na ZHANG Kunming University of Science and Technology, Kunming, 650093 ChinaSearch for more papers by this authorLeilei DONG, Leilei DONG Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037 ChinaSearch for more papers by this authorQianqian JIAO, Qianqian JIAO Kunming University of Science and Technology, Kunming, 650093 ChinaSearch for more papers by this authorJianhang CHEN, Jianhang CHEN Kunming University of Science and Technology, Kunming, 650093 ChinaSearch for more papers by this authorFucheng YANG, Fucheng YANG China University of Geosciences, Beijing, 100083 ChinaSearch for more papers by this author First published: 31 May 2021 https://doi.org/10.1111/1755-6724.14752Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume95, Issue5October 2021Pages 1786-1787 RelatedInformation

Formation mechanism of the Beidagang Uplift, Bohai Bay Basin, Eastern China: Insights from apatite fission track analysis and seismic data

The formation of uplifts in rift basins is generally controlled by fault-block tilting and/or regional uplift. The Beidagang Uplift, located in the middle part of the Qikou Sag of the Bohai Bay Basin, is an important hydrocarbon accumulation zone that has experienced a complex evolutionary history since the Cenozoic. In this study, we conducted apatite fission track (AFT) analysis and structural analysis of seismic data to distinguish the processes of fault-block tilting and regional uplift, and unravel the uplifting history and formation mechanism of the Beidagang Uplift. The results show that the Beidagang Uplift experienced two stages of tectonic uplift and exhumation mainly in the early Cenozoic (65–45 Ma) and a late depositional stage of early Eocene to the early Miocene (40–18 Ma). The uplift and exhumation substages of 40–38 Ma, 26–24 Ma and 24–18 Ma were caused by regional uplift, whereas those of 38–32 Ma and 32–26 Ma were mainly due to fault-block tilting. These rapid tectonic uplift and exhumation events recorded by the AFT data were closely related to the regional dynamic background as evidenced by a wide range of responses in eastern China. This study provides a good case for distinguishing between the effects of tilting and regional uplift in the formation of uplifts within rift basins, and has profound implications for regional dynamics.

Pulsed Mesozoic exhumation in Northeast Asia: New constraints from zircon U-Pb and apatite U-Pb, fission track and (U-Th)/He analyses in the Zhangguangcai Range, NE China

Northeast Asia located at the margin of the Paleo-Pacific/Pacific plate provides a detailed record of subduction-related orogenic activity. In order to shed light on Mesozoic-Cenozoic tectonic processes arising from the complex interaction and juxtaposition of multiple tectonic domains, we performed zircon U-Pb and apatite U-Pb, fission-track (FT) and (U-Th)/He analyses in the Zhangguangcai Range, a major mountain range in northeastern Asia. Our zircon and apatite U-Pb results indicate that most granites in the Zhangguangcai Range were emplaced at shallow crustal levels in the early Jurassic (~200–173 Ma) along with a minor amount of Triassic granites (~232 Ma). Volcanic rocks of the Maoershan and Ningyuancun formations were erupted at ~190–175 Ma and ~182–177 Ma, respectively. This Early Mesozoic magmatic activity is related to subduction of the Mudanjiang oceanic plate that separated the Jiamusi and Songliao blocks. Apatite FT analysis of granites and volcanic rocks reveals three groups of cooling ages clustering at ~193–171 Ma, ~158–129 Ma and ~118–102 Ma, while AHe analysis of granites yielded three groups of cooling ages at ~149–135 Ma, ~106–85 Ma and ~57–48 Ma. Based on these data and thermal history modelling, we propose that the central Zhangguangcai Range experienced episodic, multi-stage exhumation at shallow crustal levels since the Jurassic. Early-Middle Jurassic exhumation took place during the closure of the Mudanjiang Ocean, which resulted in unroofing of granites in the central Zhangguangcai Range and topographic growth of the Songliao block. Late Jurassic-Early Cretaceous exhumation occurred within an extensional tectonic setting, which has previously been documented across northeast Asia. Such exhumation could have been linked to lithosphere delamination and resulted in basin and range topography style, prior to the change in subduction parameters of the Paleo-Pacific plate and/or collision and strike-slip translation of the Okhotomorsk block in the Late Cretaceous.

Mesozoic Intracontinental Orogeny in the Tectonic History of the Kolyvan’– Tomsk Folded Zone (Southern Siberia): a Synthesis of Geological Data and results of Apatite Fission Track Analysis

Abstract —The Kolyvan’–Tomsk folded zone (KTFZ) is a late Permian collisional orogen in the northwestern section of the Central Asian Orogenic Belt. The Mesozoic history of the KTFZ area includes Late Triassic–Early Jurassic and Late Jurassic–Early Cretaceous orogenic events. The earlier event produced narrow deep half-ramp basins filled with Early–Middle Jurassic molasse south of the KTFZ, and the later activity rejuvenated the Tomsk thrust fault, whereby the KTFZ Paleozoic rocks were thrust over the Early–Middle Jurassic basin sediments. The Mesozoic orogenic events induced erosion and the ensuing exposure of granitoids (Barlak complex) that were emplaced in a within-plate context after the Permian collisional orogeny. Both events were most likely associated with ocean closure, i.e., the Paleothetys Ocean in the Late Triassic–Early Jurassic and the Mongol–Okhotsk Ocean in the Late Jurassic–Early Cretaceous. The apatite fission track (AFT) ages of granitoids from the Ob’ complex in the KTFZ range between ~120 and 100 Ma (the Aptian and the Albian). The rocks with Early Cretaceous AFT ages were exhumed as a result of denudation and peneplanation of the Early Cretaceous orogeny, which produced a vast Late Cretaceous–Paleogene planation surface. The tectonic pattern of the two orogenic events, although being different in details, generally inherited the late Paleozoic primary collisional structure of the Kolyvan’–Tomsk zone.

Thermal history of the East European Platform margin in Poland based on apatite and zircon low-temperature thermochronology

Abstract. The Phanerozoic tectonothermal evolution of the SW slope of the East European Platform (EEP) in Poland is reconstructed by means of thermal maturity, low-temperature thermochronometry, and thermal modelling. We provide a set of new thermochronometric data and integrate stratigraphic and thermal maturity information to constrain the burial and thermal history of sediments. Apatite fission track (AFT) analysis and zircon (U-Th)/He (ZHe) thermochronology have been carried out on samples of sandstones, bentonites, diabase, and crystalline basement rocks collected from 17 boreholes located in central and NE Poland. They penetrated sedimentary cover of the EEP subdivided from the north to south into the Baltic, Podlasie, and Lublin basins. The average ZHe ages from Proterozoic basement rocks as well as Ordovician to Silurian bentonites and Cambrian to lower Carboniferous sandstones range from 848 ± 81 to 255 ± 22 Ma with a single early Permian age of 288 Ma, corresponding to cooling after a thermal event. The remaining ZHe ages represent partial reset or source ages. The AFT ages of samples are dispersed in the range of 235.8 ± 17.3 Ma (Middle Triassic) to 42.1 ± 11.1 Ma (Paleogene) providing a record of Mesozoic and Cenozoic cooling. The highest frequency of the AFT ages is in the Jurassic and Early Cretaceous prior to Alpine basin inversion. Thermal maturity results are consistent with the SW-ward increase of the Paleozoic and Mesozoic sediments thickness. An important break in a thermal maturity profile exists across the base Permian–Mesozoic unconformity. Thermal modelling showed that significant heating of Ediacaran to Carboniferous sedimentary successions occurred before the Permian with maximum paleotemperatures in the earliest and latest Carboniferous for Baltic–Podlasie and Lublin basins, respectively. The results obtained suggest an important role of early Carboniferous uplift and exhumation at the SW margin of the EEP. The SW slope of the latter was afterward overridden in the Lublin Basin by the Variscan orogenic wedge. Its tectonic loading interrupted Carboniferous uplift and caused resumption of sedimentation in the late Viséan. Consequently, a thermal history of the Lublin Basin is different from that in the Podlasie and Baltic basins but similar to other sections of the Variscan foreland, characterized by maximum burial at the end of Carboniferous. The Mesozoic thermal history was characterized by gradual cooling from peak temperatures at the transition from Triassic to Jurassic due to decreasing heat flow. Burial caused maximum paleotemperatures in the SW part of the study area, where the EEP was covered by an extensive sedimentary pile. However, further NE, due to low temperatures caused by shallow burial, the impact of fluids can be detected by vitrinite reflectance, illite/smectite, and thermochronological data. Our new results emphasize the importance of using multiple low-temperature thermochronometers and thermal modelling in connection with thermal maturity analysis to elucidate the near-surface evolution of platform margins.

Multiproxy provenance analysis of Lower to Upper Cretaceous synorogenic deposits in the Southern Andes (34–35°S): Evidence of coeval volcanism during the onset of the Andean orogeny

The combination of detrital low-temperature thermochronology with previous U–Pb geochronology, petrological and sedimentological analyses, has proven to be a valuable approach to constrain the provenance of non-marine Lower to Upper Cretaceous synorogenic deposits in the northern Neuquén Basin. This work focuses on the study of the Diamante Formation, a fluvial succession that represents the first synorogenic products of the Andean foreland basin at 34–35°S. The results indicate that the deposition of the Diamante Formation occurred simultaneously with the existence of an active western volcanic arc during the onset of the foreland basin. The facies associations evidence the transition between the backarc and the foreland basin stages as well as the inception of fluvial sedimentation in the foredeep. Petrographic analyses, together with changes in the paleocurrents and the record of limestone clasts suggest a regional detrital source shift. Apatite fission-track analyses (AFT) of a sample collected from the lower part of the Diamante Formation indicate an Albian central cooling age. This sample also evidences a remarkable presence of angular apatite and zircon crystals with subordinated rounded and subangular grains. Zircon fission-track analyses (ZFT) of a sample from the upper part of the Diamante Formation yield two discrete populations of cooling ages, both reflecting source-cooling during the Late Jurassic (∼161 Ma) and the Permian (∼265 Ma). Finally, a comparison between the AFT and the U–Pb maximum depositional zircon-age reveals a short lag time (ca. 3 ma), likely related to the rapid magmatic cooling of a coeval volcanic source at ∼110 Ma (Albian).

Preservation of late Paleozoic glacial rock surfaces by burial prior to Cenozoic exhumation, Fleurieu Peninsula, Southeastern Australia

The antiquity of the Australian landscape has long been the subject of debate, with some studies inferring extraordinary longevity (>10 8 myr) for some subaerial landforms dating back to the early Paleozoic. A number of early Permian glacial erosion surfaces in the Fleurieu Peninsula, southeastern Australia, provide an opportunity to test the notion of long-term subaerial emergence, and thus tectonic and geomorphic stability, of parts of the Australian continent. Here we present results of apatite fission track analysis (AFTA) applied to a suite of samples collected from localities where glacial erosion features of early Permian age are developed. Our synthesis of AFTA results with geological data reveals four cooling episodes (C1-4), which are interpreted to represent distinct stages of exhumation. These episodes occurred during the Ediacaran to Ordovician (C1), mid-Carboniferous (C2), Permian to mid-Triassic (C3) and Eocene to Oligocene (C4). The interpretation of AFTA results indicates that the Neoproterozoic − Lower Paleozoic metasedimentary rocks and granitic intrusions upon which the glacial rock surfaces generally occur were exhumed to the surface by the latest Carboniferous − earliest Permian during episodes C2 and/or C3, possibly as a far-field response to the intraplate Alice Springs Orogeny. The resulting landscapes were sculpted by glacial erosive processes. Our interpretation of AFTA results suggests that the erosion surfaces and overlying Permian sedimentary rocks were subsequently heated to between c. 60 and 80°C, which we interpret as recording burial by a sedimentary cover comprising Permian and younger strata, roughly 1 km in thickness. This interpretation is consistent with existing thermochronological datasets from this region, and also with palynological and geochronological datasets from sediments in offshore Mesozoic − Cenozoic-age basins along the southern Australian margin that indicate substantial recycling of Permian − Cretaceous sediments. We propose that the exhumation which led to the contemporary exposure of the glacial erosion features began during the Eocene to Oligocene (episode C4), during the initial stages of intraplate deformation that has shaped the Mt Lofty and Flinders Ranges in South Australia. Our findings are consistent with several recent studies, which suggest that burial and exhumation have played a key role in the preservation and contemporary re-exposure of Gondwanan geomorphic features in the Australian landscape.

Burial and exhumation of late paleozoic arc-related rocks in the Tulasu basin, Western Chinese Tianshan: Implication for the preservation of epithermal deposits in old orogenic belts

Epithermal deposits are susceptible to erosion owing to their shallow emplacement depth of 1 to 2 km, resulting in the observation that the majority of epithermal deposits worldwide are generally Cenozoic in age. Several large and super-large epithermal deposits likely associated with Late-Devonian to Carboniferous arc magmatism were recognized in the Tulasu volcanic-clastic sedimentary basin, western Chinese Tianshan. In order to further clarify the preservation processes of these old epithermal orebodies, apatite fission track (AFT) analysis has been undertaken in this study. Our AFT results gave a range of ages from 54.7 ± 6.3 Ma to 272.3 ± 8.7 Ma, and the mean confined fission track lengths are between 12.1 ± 0.2 μm and 13.5 ± 0.1 μm. Our new data, in combination with the 1:50,000 geological mapping, suggest that the ore-hosting Tulasu basin may have undergone multiple burial and exhumation episodes postdating the mineralization. The main burial scenario, probably occurring in the late Early Carboniferous (350–330 Ma) and Permian (300–250 Ma), may be related to subsidence on syn-volcanic faults concurrent with retreat of the Junggar Ocean and strong uplift of the neighboring mountain range induced by final closure of the Paleo-Asian Ocean, respectively. The calculated thickness of ca. 4.83 km of sedimentary rocks deposited during the burial events form a critical shield for the epithermal ore bodies that have been protected from substantial erosion by subsequent geological processes. Exhumation occurred in two episodes: Late Triassic-Cretaceous (ca. 240–100 Ma) and Oligocene (ca. 35 Ma). The Late Triassic-Cretaceous erosion is characterized by a slow exhumation rate (ca. 0.012 mm/y), corresponding to a total unroofing thickness of ca. 1.67 km. In contrast, the Oligocene event exhibits as a higher exhumation rate (up to ca. 0.057 mm/y), with removal of ca. 3.83 km of sedimentary cover. Therefore, the epithermal deposits have undergone a complex geological path from formation to final exposure. Initial burial and the following sluggish exhumation are two fundamental factors for the preservation of epithermal deposits in the old orogenic belts.

Thermo-tectonic development of the Wandel Sea Basin, North Greenland

The Carboniferous–Palaeogene Wandel Sea Basin of eastern North Greenland (north of 80°N, east of 40°W) is an important piece in the puzzle of Arctic geology. It is particularly important for understanding how the Paleocene–Eocene convergence between Greenland, the Canadian Arctic and Svalbard relates to the compressional tectonics in the High Arctic, collectively known as the Eurekan Orogeny. In this study, we present apatite fission-track analysis (AFTA) data and review published vitrinite reflectance data combined with observations from the stratigraphic record to place firmer constraints on the timing of key tectonic events. This research study reveals a long history of episodic burial and exhumation since the collapse of the Palaeozoic fold belts in Greenland. Our results define pre-Cenozoic exhumation episodes in early Permian, Late Triassic, Late Jurassic and mid-Cretaceous times, each involving the removal of kilometre-scale sedimentary covers. Mid-Paleocene exhumation defines the timing of compression along the major fault zones during the first stage of the Eurekan Orogeny, after the onset of sea-floor spreading west of Greenland. Regional exhumation that began at the end of the Eocene led to the removal of most of a kilometre-thick cover that had accumulated during Eocene subsidence and involved a major reverse movement along the Harder Fjord Fault Zone, northern Peary Land. These events took place after the end of sea-floor spreading west of Greenland, and thus, represent post-Eurekan tectonics. Mid–late Miocene exhumation is most likely a consequence of uplift and incision across most of the Wandel Sea Basin study area. The preserved sedimentary sequences of the Wandel Sea Basin represent remnants of thicker strata that likely extended substantially beyond the present-day outline of the basin. We find that the present-day outline of the basin with scattered sedimentary outliers is primarily the result of fault inversion during Eurekan compression followed by deposition and removal of a kilometre-thick overburden.

Thermal history reconstruction from apatite fission-track analysis and vitrinite reflectance data of the Bongor Basin, the Republic of Chad

The Bongor Basin in southern Chad is one of the Cretaceous–Paleogene rift basins developed on the Precambrian crystalline basement and has been confirmed as a petroliferous basin in the last decade. Less than 400 m of Cenozoic unconsolidated sediments are separated by an unconformity from an underlying section of Lower Cretaceous units, in turn separated by another unconformity from underlying Precambrian basement. In addition, there is a locally low-angle unconformity within the Cenozoic section. A synthesis of apatite fission-track analysis data in four wells from the basin reveals two cooling episodes from Late Cretaceous to early Paleocene (beginning between 75 and 60 Ma) and mid-Miocene, respectively. The results suggest that regionally synchronous cooling is a likely scenario. The first exhumation between 75 and 60 Ma affected the whole basin, and the magnitude of uplift and erosion was approximately 1100–1250 m across the whole basin. In contrast, the second exhumation during the Miocene affected mainly the northern part of the basin while the magnitude was weak and could not be detected in the southeast of the basin. Potential trapping structures, for example, fault blocks and synsedimentary anticlines, formed prior to and inverted anticlines as a result of the first cooling phase of exhumation (strong compressional inversion) and were available for hydrocarbon migration and accumulation during the main phase of hydrocarbon generation. The Miocene exhumation was less pronounced and had weak or no impact on the hydrocarbon generation and accumulation.

Measurement of uranium concentrations in tap water samples collected from Muthanna governorate, Iraq using nuclear track detector CR-39

In the current study, uranium concentrations were measured in tap water samples collected from selected regions in Muthanna governorate southern Iraq. Fission track analysis technique with alpha track detector (CR-39) has been applied to determine the uranium content. The results of this experimental investigation showed that the highest value of uranium concentration in tap water samples was 4.05 ± 0.16 μg/l found in Al-Hassan district, while the lowest value was 2.02 ± 0.13 μg/l found in Al-Mualimin district. The average value of uranium content in tap water samples was 3.01 ± 0.15 μg/l. The results of the uranium content were compared with the published data and they were found to be within the safety levels.

Activity of the Baiganhu Fault of the Altyn Tagh Fault System, northern Tibetan Plateau: Insights from zircon and apatite fission track analyses

The geometry and kinematics of first-order structural systems on the Tibetan Plateau (TP) are key to understanding how the continental crust and lithosphere deformed during the India-Asia collision. The Altyn Tagh Fault (ATF), which is a large-scale fault bounding the northern edge of the Tibetan Plateau (NTP), absorbed as much as one-third of the total convergence in the collision between India and Eurasia. The Baiganhu Fault, in the western Qimen Tagh Mountains on the NTP, is recognized as belonging to the ATF and has played an important role in the development of its adjacent region. Due to the high elevation and harsh working conditions, this fault has received little attention, and the timing of its activation has not been thoroughly researched. In this study, we collected granite samples from close to the Baiganhu Fault in the Qimen Tagh Mountains, and used zircon and apatite fission track dating to constrain the timing of activation for this fault. The fission track ages and HeFTy modeling results reveal two rapid cooling stages along the Baiganhu Fault: one during the Jurassic-cretaceous (~180–120 Ma) and the second since the mid-Miocene (~15–10 Ma), consistent with other regions on the NTP. The first fast exhumation event was a far-field response to the Lhasa-Qiangtang collision, and the second stage most likely resulted from crustal thickening, with a connection to the ATF occurring at around ~15–10 Ma.

Differential Phanerozoic evolution of cratonic and non-cratonic lithosphere from a thermochronological perspective: São Francisco Craton and marginal orogens (Brazil)

The São Francisco Craton (SFC) and its marginal Araçuaí and Brasília orogens exhibit a significant diversity in their lithospheric architecture. These orogens were shaped during the Neoproterozoic–Cambrian amalgamation of West Gondwana. The rigid cratonic lithosphere of the SFC and the relatively weak lithosphere of the Araçuaí Orogen were disrupted during the Cretaceous opening of the South Atlantic Ocean, whereas the Brasília Orogen remained in the continental hinterland. In earlier research, the thermal effects of the Phanerozoic reactivations in the shallow crust of the Araçuaí Orogen have been revealed by low-temperature thermochronology, mainly by apatite fission track (AFT) analysis. However, analyses from the continental interior are scarce. Here we present new AFT data from forty-three samples from the Brasília Orogen, the SFC and the Araçuaí Orogen, far from the passive margin of the Atlantic coast (~150 to 800 km). Three main periods of basement exhumation were identified: (i) Paleozoic, recorded both by samples from the SFC and Brasília Orogen; (ii) Early Cretaceous to Cenomanian, recorded by samples from the Araçuaí Orogen; and (iii) Late Cretaceous to Paleocene, inferred in samples from all domains. We compare the differential exhumation pattern of the different geotectonic provinces with their lithospheric strengths. We suggest that the SFC likely concentrated the Meso-Cenozoic reactivations in narrow weak zones while the Araçuaí Orogen displayed a far-reaching Meso-Cenozoic deformation. The Brasília Orogen seems to be an example of a stronger orogenic lithosphere, inhibiting reworking, confirmed by our new AFT data. Understanding the role of the lithosphere rigidity may be decisive to comprehend the processes of differential denudation and the tectonic–morphological evolution over Phanerozoic events.

Technical note: LA–ICP-MS U–Pb dating of unetched and etched apatites

Abstract. The same unetched and chemically etched apatite crystals from five rock samples were dated by the U–Pb method via laser ablation inductively coupled plasma mass spectrometry (LA–ICP-MS). The objective of this study is to test whether chemical etching required for apatite fission track analysis impacts the precision and accuracy of apatite U–Pb geochronology. The results of this experiment suggest that etching has insignificant effects on the accuracy of apatite U–Pb ages obtained by LA–ICP-MS. Therefore, LA–ICP-MS is reliable for U–Pb analysis as part of apatite fission track and U–Pb double dating.

Timing and rates of morpho-tectonic events in a segment of the Central and Western cordilleras of Colombia revealed through low-temperature thermochronology

New zircon and apatite fission-track analyses and aluminium in hornblende thermobarometric data are presented from Cretaceous and Triassic plutons situated along an east-west transect across the Central Cordillera, the Cauca Romeral Fault System and the eastern slopes of the Western Cordillera in the Colombian Andes. The results are combined with published apatite (U–Th)/He ages revealing three episodes of increased cooling during the Late Cretaceous (~110 - 90 Ma), the Eocene (~55-40 Ma) and the Miocene (23-20 Ma). The latter two phases correlate well with the Pre-Andean and Proto-Andean periods previously identified on the basis of stratigraphic unconformities and thermochronology studies in the region. A fourth event, at ~10 Ma, is tentatively recognized in modelled data sets, but not by absolute age values. The thermochronology data imply a total of uplift-driven exhumation (i.e., crustal unroofing) in the study area of up to 10 kms since ~50 Ma at rates of ~0.1 km/Myr and 4 kms since ~23 Ma initially at 0.2 km/Myr. From 10 Ma the rates changed to 0.3–0.33 km/Myr with estimated geothermal gradients of 25–30 °C/km. Thermobarometry data suggest that the crystallization of the Cretaceous intrusions, now at the surface, took place at depths of 8–13 km confirming the amount of exhumation revealed by low-temperature thermochronology.

Late Cretaceous-Cenozoic tectonic-sedimentary evolution and U-enrichment in the southern Songliao Basin

Late Cretaceous-Cenozoic tectonic-sedimentary evolution is fundamental to U (Uranium) migration and U-enrichment in the southern Songliao Basin, northeast China. To establish the genetic connection between tectonic-sedimentary evolution and U-enrichment, this paper presents a mineralogical study, apatite fission-track (AFT) analysis, and SEM-CL analysis of quartz grains. Two stages of mineralization were proposed, including the U pre-enrichment stage during the Late Cretaceous, and the ore-forming stage during the Cenozoic. Based on the density plots of the AFT ages, paleoclimate studies, and SEM-CL analysis of quartz grains, it is inferred that the U pre-enrichment was closely related to the rapid uplift of the Great Xing'an Range and the Zhangguangcai Range, and the O2-rich atmosphere during 97–90 Ma in the southern Songliao Basin. The O2-rich atmosphere increased U mobility and led to the formation of red beds during the Late Cretaceous, which widely developed U pre-enrichment in the basins of Northeast China. The mineralogical study reveals that the Qianjiadian uranium deposit developed in two stages. The diagenetic process experienced the transition from early alkaline to late acidic conditions, to promote the Stage I mineralization (U pre-enrichment). The dominant occurrence spaces for U were the dissolution pores of quartz, tightly packed with calcite cement. U-enrichment during alkaline ambient conditions was mainly via adsorption. With the increase of the buried depth, the early alkaline diagenesis returned to acidic conditions due to the abundant organic material. U(VI) was reduced to pitchblende due to the reducing capacity of the organic matter (OM). Stage II (ore-forming stage) mineralization was strictly related to the hydrocarbon re-concentration. According to the thermal history study of the CC1 and Q2 boreholes, the southern Songliao Basin experienced four episodes of rapid uplift during the Cenozoic at 83–80 Ma, 68–52 Ma, 33–23 Ma, and −8 Ma, respectively. The Cenozoic uplifts led to hydrocarbon migration at 65 Ma, 23 Ma, and present. The re-concentration of hydrocarbon prompted the U mineralization in the Qianjiadian uranium deposit in the southern Songliao Basin during the stable period of tectonic movements. The reducing conditions caused by hydrocarbons promoted U mineralization. The dominant spaces of coffinite were intergranular dissolved pores, formed during the transformation from the feldspar to the kaolinite under acidic conditions. The post-rift phase and structural inversion phase directly controlled the U pre-enrichment stage and the ore-forming stage, respectively. Overall, the tectonic-sedimentary evolution played an important role in controlling the U leaching from granites, the dominant occurrence spaces, and U recycling.

Formation and preservation of the Bayan Obo Fe-REE-Nb deposit, Inner Mongolia: Insights from evidences of petrogenesis, geochemistry and apatite fission track dating

The Bayan Obo ore deposit in Inner Mongolia, North China, the largest-known rare earth element (REE) deposit in the world, has attracted considerable attention over the past decades. However, its genesis has been highly debated, especially whether the host dolomite is of sedimentary or igneous origin. In this study, we present a comprehensive study on field geology, petrographic, geochemical, and apatite fission track analyses on REE-mineralized dolomite (H8) and its wall-rock (H9), in an effort to provide additional insights into the formation and preservation of this giant ore deposit. According to field geology and petrology analyses, the ore-hosted dolomite of the H8 unit in/around the Bayan Obo deposit displays the characteristics of sedimentary carbonates and demonstrates complicated deformation and hydrothermal events that resulted in the complex REE mineralization. The parameter of w(As) in pyrite ranging from 100 to 1600 ppm suggesting that the pyrite of the Bayan Obo deposit was mainly formed in a hydrothermal environment, and the thermal event from pyrite at ~440 Ma may represent the mineralization event of the Bayan Obo deposit, or it is an important disturbance event after the mineralization of the deposit. The geochemical research depicts that the evolution process of carbonatite was originated from calcium carbonatites and magnesio-carbonatites to ferro-carbonatite, indicating that the different genesis models of the Bayan Obo deposit that ranging from sedimentary carbonate to volcano-sedimentary and igneous carbonatites are reasonable. The two apatite ages obtained from granite on the east side of the Bayan Obo deposit and the dolomite in the Bayan Obo deposit are ~173 Ma and ~54 Ma, respectively. Time–temperature (t–T) histories of rocks yield new information about the timing of deformation of the Bayan Obo deposit, implying that the east side of the deposit experienced a rapid cooling process between ~300 Ma to ~54 Ma (especially ~300–180 Ma), this reflects the granite underwent a rapid cooling process which coeval with the plate subduction during the closure of the Palaeo-Asian Ocean, while the tectonic movement has little effect on the broken of the H8 dolomite in the mining area. Although the slate of the H9 unit from the east of the Bayan Obo deposit experienced a strong fragmentation in the later tectonic movement, it still made a great contribution to the mineralization for better preservation of REE-rich fluids, leading to the formation of the giant Fe-REE-Nb deposit.

Intracontinental uplift of the Brazilian Central Plateau linked to continental breakup, orogenies, and basin filling, supported by apatite and zircon fission-track data

Fission-track analysis in zircon and apatite detrital grains from Mesoproterozoic sedimentary sequences show evidence of cooling episodes in central Brazil from Neoproterozoic to Cenozoic. Apatite fission-track ages reveal a main cooling episode during the Late Cretaceous-Early Paleogene, providing important clues on cooling by uplift and denudation during drifting of South America and Africa. Zircon data also suggest 3 distinct cooling events: (i) a Neoproterozoic-Cambrian event, probably related to orogenic exhumation of the Brasilia Belt and the thermal decay of West Gondwana assembly, (ii) a Devonian-Carboniferous event, probably related to the Late Famatinian orogeny and early stages of the Gondwanide orogeny, and (iii) an Early Permian to Triassic event, linked to the Late Gondwanide orogeny. These results indicate that the processes of assembly and breakup of supercontinents might significantly affect the plate interior, especially along with ancient orogenic belts. Zircon data has shown evidence of thermal decay during and after the West Gondwana assembly. Apatite data, on the other hand, has shown evidence of thermal decay during and after the breakup of Pangaea. The processes of assembly as well as the breakup of supercontinents can be tracked in the intracratonic setting, especially along with ancient orogenic belts. These assumptions take us back to the old concept of “mobile belts” as old orogenic regions that represent weak portions of the continental crust, assumed to have a greater tendency for mobility when solicited. In this case, the Brasilia Belt has shown to present great vertical mobility, accommodating tectonic far-field forces by uplift and as a result, feeding the Phanerozoic basins around it.

Effect of gender and occupations on uranium concentration in human blood and soil samples collected from Babylon, Iraq

Abstract Uranium concentrations of human blood and soil samples have been studied at different ages and occupations in Babylon, Iraq. The technique of nuclear track detectors CR 39 with nuclear fission track analysis has been used to determine the uranium concentrations in this study. Results have shown that the concentrations of uranium ranged from 0.56 ± 0.06 to 1.24 ± 0.29 ppb with an average of 0.83 ± 0.18 ppb in blood samples. On the other hand, the concentrations of uranium in soil samples ranged from 0.93 ± 0.20 to 2.59 ± 0.15 ppm with an average of 1.72 ± 0.19 ppm. Moreover, the highest averages of concentration have been found in the city center of Babylon, reaching 1.09 ± 0.22 ppb and 2.10 ± 0.23 ppm in blood and soil samples, respectively. The results have further proved that gender and occupations have an effect in increasing the concentrations of uranium. In addition, the concentrations in blood samples are generally lower than the concentration in soil samples.

Late Cenozoic Activity of the Tashkurgan Normal Fault and Implications for the Origin of the Kongur Shan Extensional System, Eastern Pamir

In the northwest of the Himalayan-Tibetan Orogen, the ~250 km-long Kongur Shan extensional system in the eastern Pamir was formed during the convergence between the Indian and Asian plates. Tectonic activity of the Kongur Shan normal fault and the Tashkurgan normal fault can help to reveal the origin of east-west extension along the Kongur Shan extensional system. The Kongur Shan fault has been extensively studied, while the Tashkurgan fault calls for systemic research. In this study, low-temperature thermochronology including apatite fission track analysis and apatite and zircon (U-Th)/He analyses is applied to constrain the timing of activity of the Tashkurgan fault. Results indicate that the Tashkurgan fault initiated at 10-5 Ma, and most likely at 6-5 Ma. The footwall of the Tashkurgan fault has been exhumed at an average exhumation rate of 0.6-0.9 mm/a since the initiation of the Tashkurgan fault. Combined with previous research on the Kongur Shan fault, we believe that the origin of east-west extension along the Kongur Shan extensional system was driven by gravitational collapse of over-thickened Pamir crust.