Apatite Fission-Track Thermochronology in the Tamusu Area,Bayingobi Basin,NW China,and its Geological Significance

The Bayingobi basin is located in the middle of Central Asia Orogenic Belt,at the intersection of Paleo-Asian Ocean and Tethys Ocean,as well as the junction of multiple tectonic plates.This unique tectonic setting underpins the basin's intricate history of tectonic activity.To unravel the multifaceted tectono-thermal evolution within the southwestern region of the basin and to elucidate the implications of sandstone-hosted uranium mineralization,granitic and clastic rock samples were collected from the Zongnai Mts.uplift and Yingejing depression,and apatite fission track(AFT)dating and thermal history simulation analysis were performed.AFT dating findings reveal that the apparent ages of all samples fall within the range of 244 Ma to 112 Ma.In particular,the bedrock of the Zongnai Mts.and Jurassic detrital apatite fission tracks have undergone complete annealing,capturing the uplift-cooling age.Meanwhile,the AFT ages of Cretaceous detrital rocks are either equivalent to or notably exceed the age of sedimentary strata,signifying the cooling age of the provenance.A comprehensive examination of AFT ages and palaeocurrent direction analyses suggests that the Cretaceous source in the Tamusu area predominantly originated from the central and southern sectors of the Zongnai Mts.uplift.However,at a certain juncture during the Late Early Cretaceous,the Cretaceous provenance expanded to include the northern part of the Zongnai Mts.uplift.Based on the results of thermal history simulations and previous studies,it is considered that the Tamusu area has undergone four distinct tectonic uplift events since the Late Paleozoic.The first is the Late Permian to Early Triassic(260-240 Ma),which is associated with the closure of the Paleo-Asian Ocean and the accretionary orogeny within the Alxa region.The second uplift event took place in the Early Jurassic(190-175 Ma)and corresponded to intraplate orogeny following the closure of the Paleo-Asian Ocean.The third uplift event is the Late Jurassic to Early Cretaceous(160-120 Ma),which is linked to the East Asia's position as the convergence center of multiple tectonic plates during this period.The fourth uplift event is linked to the Late Early Cretaceous(112-100 Ma),driven either by the westward subduction of the eastern Pacific plate or the mantle upwelling resulting from the Bangong-Nujiang oceanic lithosphere subduction and slab break-off.The primary stress orientation for the first three tectonic uplift phases approximated a nearly SN direction,while the fourth stage featured a principal stress direction of NW.The fourth tectonic uplift event of the Late Early Cretaceous and basaltic eruption thermal event during this period likely exerted a significant influence on the formation of the Tamusu sandstone-hosted uranium deposit.

Thermal and exhumation history of the Songnan Low Uplift,Qiongdongnan Basin:constraints from the apatite fission-track and zircon(U-Th)/He thermochronology

Significant advancements have been made in the study of Mesozoic granite buried hills in the Songnan Low Uplift(SNLU)of the Qiongdongnan Basin.These findings indicate that the bedrock buried hills in this basin hold great potential for exploration.Borehole samples taken from the granite buried hills in the SNLU were analyzed using apatite fission track(AFT)and zircon(U-Th)/He data to unravel the thermal history of the basement rock.This information is crucial for understanding the processes of exhumation and alteration that occurred after its formation.Thermal modeling of a sample from the western bulge of the SNLU revealed a prolonged cooling event from the late Mesozoic to the Oligocene period(~80-23.8 Ma),followed by a heating stage from the Miocene epoch until the present(~23.8 Ma to present).In contrast,the sample from the eastern bulge experienced a more complex thermal history.It underwent two cooling stages during the late Mesozoic to late Eocene period(~80-36.4 Ma)and the late Oligocene period(~30-23.8 Ma),interspersed with two heating phases during the late Eocene to early Oligocene period(~36.4-30 Ma)and the Miocene epoch to recent times(~23.8-0 Ma),respectively.The differences in exhumation histories between the western and eastern bulges during the late Eocene to Oligocene period in the SNLU can likely be attributed to differences in fault activity.Unlike typical passive continental margin basins,the SNLU has experienced accelerated subsidence after the rifting phase,which began around 5.2 Ma ago.The possible mechanism for this abnormal post-rifting subsidence may be the decay or movement of the deep thermal source and the rapid cooling of the asthenosphere.Long-term and multi-episodic cooling and exhumation processes play a key role in the alteration of bedrock and contribute to the formation of reservoirs.On the other hand,rapid post-rifting subsidence(sedimentation)promotes the formation of cap rocks.

Tectonic-thermal history and hydrocarbon potential of the Pearl River Mouth Basin,northern South China Sea:Insights from borehole apatite fission-track thermochronology

The Pearl River Mouth Basin(PRMB)is one of the most petroliferous basins on the northern margin of the South China Sea.Knowledge of the thermal history of the PRMB is significant for understanding its tectonic evolution and for unraveling its poorly studied source-rock maturation history.Our investigations in this study are based on apatite fission-track(AFT)thermochronology analysis of 12 cutting samples from 4 boreholes.Both AFT ages and length data suggested that the PRMB has experienced quite complicated thermal evolution.Thermal history modeling results unraveled four successive events of heating separated by three stages of cooling since the early Middle Eocene.The cooling events occurred approximately in the Late Eocene,early Oligocene,and the Late Miocene,possibly attributed to the Zhuqiong II Event,Nanhai Event,and Dongsha Event,respectively.The erosion amount during the first cooling stage is roughly estimated to be about 455-712 m,with an erosion rate of 0.08-0.12 mm/a.The second erosion-driven cooling is stronger than the first one,with an erosion amount of about 747-814 m and an erosion rate between about 0.13-0.21 mm/a.The erosion amount calculated related to the third cooling event varies from 800 m to 3419 m,which is speculative due to the possible influence of the magmatic activity.

A tectono-thermal perspective on the petroleum generation,accumulation and preservation in the southern Ordos Basin, North China

The southern Ordos Basin has excellent petroleum exploration prospects.However,the tectono-thermal history and the controls on petroleum generation,accumulation and preservation conditions in southern basin are unclear.In this study,we analyzed the present geothermal field,paleo-geothermal gradient,maturity of the hydrocarbon source rocks,uplift and cooling process and tectono-thermal evolution history.In the study area,for the Ordovician,Permain and the Triassic strata,the present temperature is low(3070℃)in the southeastern area but high(80140℃)in the northwestern area.The paleogeothermal gradient varied from 24℃/km to 30℃/km with a heat flow of 58—69 m W/m^(2)(i.e.,a medium-temperature basin).The paleo-temperatures are higher than the present temperatures and the maximum paleo-temperatures controlled the thermal maturity of the source rocks.The vitrinite reflectance(Ro)values of the Triassic strata are>0.7%and the thermal maturity reached the middlemature oil generation stage.The Rovalues of the Permian-Ordovician strata are>1.8%and the thermal maturity reached the over-mature gas generation stage.The southern Ordos Basin has experienced the multiple tectonic events at the Late Ordovician Caledonian(452 Ma),Late Triassic(215 Ma),Late Jurassic(165160 Ma),End-Early Cretaceous(110100 Ma)and Cenozoic(since 40 Ma).A large-scale tectonothermal event occurred at the End-Early Cretaceous(110100 Ma),which was controlled by lithospheric extension,destruction and thinning.This event led to the highest paleo-temperatures and thermal maturities and coeval with the peak period of petroleum generation and accumulation.The southern Ordos Basin has undergone rapid and large-scale uplift since the Late Cretaceous due to expansion of the northeastern margin of the Tibetan Plateau,uplift of the Qinling orogenic belt and thrust faulting in the Liupanshan tectonic belt.The southern Ordos Basin experienced tectonic overprinting that was strong in the south and weak in the north.The strongest overprinting occurred in the southwestern part of the basin.The large-scale uplift,denudation and faulting led to oil and gas loss from reservoirs.The petroleum generation,accumulation and preservation in the southern Ordos Basin were affected by deep lithospheric structures and the tectono-thermal evolution.This work provides a novel tectono-thermal perspective on the petroleum generation,accumulation and preservation condition of the southern Ordos Basin.

Cenozoic Exhumation and Thrusting in the Northern Qilian Shan,Northeastern Margin of the Tibetan Plateau:Constraints from Sedimentological and Apatite Fission-Track Data

The Qilian Shan lies along the northeastern edge of the Tibetan Plateau. To constrain its deformation history, we conducted integrated research on Mesozoic-Cenozoic stratigraphic sections in the Jiuxi Basin immediately north of the mountain range. Paleocurrent measurements, sandstone compositional data, and facies analysis of Cenozoic stratigraphic sections suggest that the Jiuxi Basin received sediments from the Altyn Tagh Range in the northwest, initially in the Oligocene （-33 Ma）, depositing the Huoshaogou Formation in the northern part of the basin. Later, the source area of the Jiuxi Basin changed to the Qilian Shan in the south during Late Oligocene （-27 Ma）, which led to the deposition of the Baiyanghe Formation. We suggest that uplift of the northern Qilian Shan induced by thrusting began no later than the Late Oligocene. Fission-track analysis of apatite from the Qilian Shan yields further information about the deformation history of the northern Qilain Shan and the Jiuxi Basin. It shows that a period of rapid cooling, interpreted as exhumation, initiated in the Oligocene. We suggest that this exhumation marked the initial uplift of the Qilian Shan resulting from the India-Asia collision.

Late Cretaceous-Cenozoic Exhumation History of the L(u|¨)liang Mountains,North China Craton:Constraint from Fission-track Thermochronology

The Lüliang Mountains, located in the North China Craton, is a relatively stable block, but it has experienced uplift and denudation since the late Mesozoic. We hence aim to explore its time and rate of the exhumation by the fission-track method. The results show that, no matter what type rocks are, the pooled ages of zircon and apatite fission-track range from 60.0 to 93.7 Ma and 28.6 to 43.3 Ma, respectively; all of the apatite fission-track length distributions are unimodal and yield a mean length of -13 μm; and the thermal history modeling results based on apatite fission-track data indicate that the time-temperature paths exhibit similar patterns and the cooling has been accelerated for each sample since the Pliocene （c.5 Ma）. Therefore, we can conclude that a successive cooling, probably involving two slow （during c.75-35Ma and 35-5Ma） and one rapid （during c.5 Ma-0 Ma） cooling, has occurred through the exhumation of the Liiliang Mountains since the late Cretaceous. The maximum exhumation is more than 5 km under a steady-state geothermal gradient of 35℃/km. Combined with the tectonic setting, this exhumation may be the resultant effect from the surrounding plate interactions, and it has been accelerated since c.5 Ma predominantly due to the India-Eurasia collision.

Accelerated Exhumation During the Cenozoic in the Dabie Mountains: Evidence from Fission-Track Ages

Abstract: Zircon and apatite fission-track dating indicates that the exhumation of the Dabie Mountains tended to be accelerated in the Cenozoic and that the exhumation of the eastern Dabie Mountains was more and more intense from south to north, which is in accordance with the more and more intense dissection from south to north, as is reflected by the modern geomorphologic features of the Dabie Mountains. The accelerated exhumation during the Cenozoic was related to the high elevation of the Dabie Mountains resulting from Late Cretaceous-Palaeogene detachment faulting and subsequent fault-block uplift and subsidence. The average elevation at that time was at least about 660 m higher than that at the present. The intense exhumation lagged behind intense uplift.

Cenozoic Exhumation of Larsemann Hills,East Antarctica:Evidence from Apatite Fission-track Thermochronology

Does Cenozoic exhumation occur in the Larsemann Hills, East Antarctica？ In the present paper, we conducted an apatite fission-track thermochronologic study across the Larsemann Hills of East Antarctica. Our work reveals a Cenozoic exhumation event at 49.8 ± 12 Ma, which we interpret to be a result of exhumation caused by crustal extension. Within the uncertainty of our age determination, the timing of extension in East Antarctica determined by our study is coeval with the onset time of rifting in West Antarctica at c.55 Ma. The apatite fission-track cooling ages vary systematically in space, indicating a coherent block rotation of the Larsemann Hills region from c.50 Ma to c.10 Ma. This pattern of block tilting was locally disrupted by normal faulting along the Larsemann Hills detachment fault at c.5.4 Ma. The regional extension in the Larsemann Hills, East Antarctica was the result of tectonic evolution in this area, and may be related to the global extension. Through the discussion of Pan-Gondwanaland movement, and Mesozoic and Cenozoic extensions in West and East Antarctica and adjacent areas, we suggest that the protracted Cenozoic cooling over the Larsemann Hills area was caused by extensional tectonics related to separation and formation of the India Ocean at the time of Gondwanaland breakup.

Cenozoic Exhumation History of the East Kunlun Orogenic Belt Constrained by Apatite Fission-Track Thermochronology

Objective The East Kunlun Orogenic belt constitutes the first marked change in the topographic reliefs north of the Qinghai-Tibet Plateau.The Cenozoic tectonic evolution of this orogenic belt is crucial for understanding the remote deformational effects of the Eurasian plate collision and the migration track at the northern margin of the plateau.However,when and how the uplift occurred remains

INVESTIGATION OF THE PALEOGEOTHERMAL TECTONIC HISTORY ON DONGPU DEPRESSION AND OIL/GAS FORMATION BY FISSION-TRACK METHOD

Dongpu depression is a fault basin at residual-mobility period of Diwa stage, it developed on the strata of the Mesozoie and Pre-Mesozoie. It is one of the important oil/gas- bearing basin during Cenozoie era along the East China. The strueture in Dongpu geodepression is very complex. There exists a strueture pattern with east- and west-depression belts and one central swell belt, it is divided into the southern- and northern-division by Gaopingji (orMeng Ju ) -Xieheng fault.

Thermal Evolution of the Tanlu Fault Zone on the Eastern Margin of the Dabie Mountains and Its Tectonic Implications

Five samples of muscovite from mylonites of the earlier Tanlu ductile shear zone on the eastern margin of the Dabie Mountains yield 40Ar/39Ar ages ranging from 178 Ma to 196 Ma. Three of them have reliable plateau ages of 188.7±0.7 Ma, 189.7±0.6 Ma and 192.5±0.7 Ma respectively, which indicates a syn-orogenic, sinistral strike-slip thermal event. This displacement movement derived from the continent-continent collision of the North and South China blocks took place in the Early Jurassic and after uplifting of high-pressure to ultrahigh-pressure slabs to the mid-crust. It is suggested that during the collision the Tanlu fault zone was an intracontinental transform fault caused by differential subduction speeds. The 40Ar/39Ar ages of mylonite whole-rock and muscovite from the later Tanlu ductile shear zone suggest another sinistral strike-slip cooling event at 128 Ma. During this strike-slip faulting, large-scale intrusion and doming uplift occurred in the eastern part of the Dabie orogenic belt. Data of K-feldspar 40Ar/39Ar MDD and apatite fission-track analysis from metamorphic rocks indicate two high-speed cooling events experienced by the Tanlu fault zone, which took place at 90 Ma and 45-58 Ma respectively. They correspond respectively to two phases of extensional activities in the Late Cretaceous and Eogene as well as development of the Qianshan fault-controlled basin to the east of the Tanlu fault zone. The cooling times recorded by K-feldspar and apatite show that the uplifting in the Dabie orogenic belt occured earlier than that on the eastern margin occupied by the Tanlu fault zone. The above phenomena suggest that the uplifting of the Dabie orogenic belt during the Late Cretaceous to Eogene was not controlled by the Tanlu normal faulting, but as a result of the lithospheric delamination.

Radiometric Zircon Ages of a Tuff Sample from the Baishantou Member of Wuyun Formation,Jiayin:A Contribution to the Search for the K-T Boundary in Heilongjian River Area,China

The existence of the Cretaceous-Tertiary （K/T） boundary in the non-marine succession is expected at Jiayin in the Heilongjiang River area, China. Zircons from a tuff sample from the Baishantou Member of Wuyun Formation in Jiayin were analyzed by the laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） U-Pb dating and fission-track dating methods. Ages of 64.1±0.7 Ma （U-Pb） and 61.7±1.8 Ma （fission-track dating） were obtained, which allow reevaluation of a previously reported late Maastrichian age for the tuff layer that was in conflict with the paleontological evidence. These results confirm the Danian age of the section in agreement with the paleontological evidence.

Detrital apatite fission track constraints on Cenozoic tectonic evolution of the northeastern Qinghai-Tibet Plateau, China： Evidence from Cenozoic strata in Lulehe section, Northern Qaidam Basin

The Northern Qaidam Basin is located at the northeastern part of the Qinghai-Tibetan Plateau. It contains very thick Cenozoic terrestrial clastic sediments, which records the formation of the northern Qaidam Basin due to compressional deformation during the Indo-Asian collision. In this paper, we used detrital apatite fission-track thermochronology, including 4 sandstones and 2 conglomerates samples from the Lulehe section, to reveal the Cenozoic evolution of the northern Qaidam Basin. Fission-track dating indicated the source region of the Lulehe section has experiencedimportant cooling and uplifting in the Late Cretaceous(at ~85.1 Ma and ~65 Ma) and the Eocene(~52 Ma), respectively. The AFT age distribution on the section suggested that the provenance of Lulehe section sediments were mainly derived from the south Qilian Shan(Qilian Mountains) and Altun Shan(Altun Mountains), and two significantly provenance changes may occur at 43.4-46.1 Ma and ~37.8 Ma, respectively. The results may have strong constrains on the Cenozoic deformation and tectonic evolution of the northern Qaidam Basin and Qinghai-Tibet Plateau.

Continental accretion and incremental deformation in the thermochronologic evolution of the Lesser Caucasus

Apatite fission-track analysis and thermochronologic statistical modeling of Precambrian-Oligocenc plutonic and metamorphic rocks from the Lesser Caucasus resolve two discrete cooling episodes.Cooling occurred during incremental crustal shortening due to obduction and continental accretion along the margins of the northern branch of the Neotethys.(1)The thermochronometric record of a Late Cretaceous(Turonian-Maastrichtian)cooling/exhumation event,coeval to widespread ophiolite obduction,is still present only in a relatively small area of the upper plate of the Amasia-Sevan-Akera(ASA)suture zone,i.e.the suture marking the final closure of the northern Neotethys during the Paleogene.Such area has not been affected by significant later exhumation.(2)Rapid cooling/exhumation occurred in the Early-Middle Miocene in both the lower and upper plates of the ASA suture zone,obscuring previous thermochronologic signatures over most of the study area.Miocene contractional reactivation of the ASA suture zone occurred contemporaneously with the main phase of shortening and exhumation along the Bitlis suture zone marking the closure of the southern branch of the Neotethys and the ensuing ArabiaEurasia collision.Miocene collisional stress from the Bitlis suture zone was transmitted northward across the Anatolian hinterland,which was left relatively undeformed,and focused along preexisting structural discontinuities such as the eastern Pontides and the ASA suture zone.

Mesozoic Tectonothermal Evolution of the Southern Central Asian Orogenic Belt: Evidence from Apatite Fission-Track Thermochronology in Shalazha Mountain, Inner Mongolia

Mesozoic intracontinental orogeny and deformation were widespread within the southern Central Asian Orogenic Belt(CAOB). Chronological constraints remain unclear when assessing the Mesozoic evolution of the central segment of this region. The tectonic belt of Shalazha Mountain located in the center of this region is an ideal place to decode the deformation process. Apatite fission-track(AFT) thermochronology in Shalazha Mountain is applied to constrain the Mesozoic tectonothermal evolution of the central segment of southern CAOB. The bedrock AFT ages range from 161.8 ± 6.9 to 137.0 ± 7.3 Ma, and the first reported detrital AFT obtained from Lower Cretaceous strata shows three age peaks: P1(ca. 178 Ma), P2(ca. 149 Ma) and P3(ca. 105.6 Ma). Bedrock thermal history modeling indicates that Shalazha Mountain have experienced three stages of differential cooling: Late Triassic–Early Jurassic(~230–174 Ma), Late Jurassic–Earliest Cretaceous(~174–135 Ma) and later(~135 Ma). The first two cooling stages are well preserved by the detrital AFT thermochronological result(P1, P2) from the adjacent Lower Cretaceous strata, while P3(ca. 105.6 Ma) records coeval volcanic activity. Furthermore, our data uncover that hanging wall samples cooled faster between the Late Triassic and the Early Cretaceous than those from the footwall of Shalazha thrust fault, which synchronizes with the cooling of the Shalazha Mountain and implies significant two-stage thrust fault activation between ca. 230 and 135 Ma. These new low-temperature thermochronological results from the Shalazha Mountain region and nearby reveal three main phases of differential tectonothermal events representing the Mesozoic reactivation of the central segment of the southern CAOB. In our interpretations, the initial rapid uplift in the Late Triassic was possibly associated with intracontinental orogenesis of the CAOB. Subsequent Middle Jurassic–Earliest Cretaceous cooling is highly consistent with the Mesozoic intense intraplate compression that occurred in the southern CAOB, and is interpreted as a record of closure of the Mongol-Okhotsk Ocean. Then widespread Cretaceous denudation and burial in the adjacent fault basin could be linked with the oblique subduction of the Izanagi Plate along the eastern Eurasian Plate, creating a northeast-trending normal fault and synchronous extension. However, our AFT thermochronometry detects no intense Cenozoic reactivation information of Shalazha Mountain region.

Exhumation and Deformation of the Daba Shan Orocline as Determined from Modern River Sands Apatite Fission-Track

The Daba Shan orocline is located at the northeastern margin of the Sichuan Basin and has been inferred as a foreland thrust-fold belt of the Qinling Orogen since the Late Triassic.A complete understanding of rock exhumation history is critical to elucidate how and when this typical orocline structure is developed.Detrital apatite fission-track dating of modern river sands is employed to reveal the regional exhumation history of the Daba Shan orocline.Four age peaks are identified and interpreted as the results of tectonic exhumation.Two older age peaks at ~150–140 and ~116–86 Ma are agreement with two main shortening deformation episodes of the Yanshanian Movement in the eastern China.The other two younger age peaks at ~69 and ~37 Ma support that the Daba Shan was reactivated by the Late Cretaceous to Cenozoic deformation which were likely related to the subduction of the Pacific Ocean and eastward growth of the Tibetan Plateau,respectively.It is worth noting that in contrast to the ~150–140 Ma rapid rock uplift and exhumation,the Middle Cretaceous exhumation(~116–86 Ma) shifted southward and continued to spread to southern tips of the Daba Shan.These exhumation variations in temporal and spatial allow a southward thrust deformation with piggyback style during the Yanshanian.

Genesis of Daba arcuate structural belt related to adjacent basement upheavals:Constraints from Fission-track and (U-Th)/He thermochronology

Fission-track, (U-Th)/He thermochronology, and cooling properties indicate that the southern Daba arcuate zone (SDBAZ) underwent a distinctive phase of rapid cooling in 153-100 Ma at a rate of 1.44-1.90°C/Ma. This rapid uplifting strongly contrasts with (1) the previous, rapid foreland subsidence during Early to Middle Jurassic in response to late-orogenic compression from the Qinling belt, (2) the succeeding long, slow cooling phase and relative thermal stability that occurred during the 100-45 Ma period. This rapid cooling event in the SDBAZ parallels those experienced by two adjacent upheavals of Huangling (HLUZ) and Hannan-Micang (HMUZ), with cooling rates of 2.22-3.17°C/Ma for the HLUZ in 160-126 Ma, 4.91°C/Ma for the southern HMUZ in 150-125 Ma, as well as 2.11°C/Ma for the northern HMUZ in 150-105 Ma. Comparing thermal histories among the SDBAZ, the HLUZ, the HMUZ, and the Wudang metamorphic zone (WDMZ), we infer that the Daba arcuate structural belt formed in 153-100 Ma. The combined dating data support a correlation with a low-angle arcuate south-thrusting of the Qinling orogen triggered by northward convergence of the Yangtze Craton, contemporaneously encountering rigid basement obstructions from the HLUZ and the HMUZ, respectively. Both the SDBAZ and neighboring domains additionally underwent a comparatively fast cooling and uplift since about 45 Ma.

Fission-track-age records of the Mesozoic tectonic-events in the southwest margin of the Ordos Basin, China

Based on the analysis of apatite and zircon fission track(FT),the FT age distribution and the peck-ages of the Mesozoic tectonic events in the southwest margin of the Ordos Basin(OB)were discussed.(1)The early event mainly occurred at 213-194 Ma with a peck-age of 205 Ma,and corresponded to the tectonic uplift and the mega-clastic deposit in the southwest OB during the Late Triassic.(2)The middle event included at least two episodes.One was at 165-141 Ma with a peck-age of 150 Ma,and the other was at 115-113 Ma with a peck-age of 114 Ma,corresponding to the over-thrusting and the mega-clastic deposits in the southwest OB during the Late Jurassic to the Early Cretaceous.(3)The late event mainly demonstrated the regional uplifting and included at least two episodes.One was at 100-81 Ma with a peck-age of 90 Ma,and the other was at 66-59 Ma with a peck-age of 63 Ma.Additionally,the relationship analysis of the tectonic event and the mineralizing chronology revealed that the extreme environment of the peck-age event and the subsequent moderate activity could be the key factors of the multiple resources coupling and coexistence in the OB.

Paleomagnetic and Fission-Track Dating of a Late Cenozoic Red Earth Section in the Liupan Shan and Associated Tectonic Implications

The north-trending Liupan Shan （六盘山） is an important tectonic boundary between the Tibetan Plateau and the Ordos platform. The Late Cenozoic red earth deposits of the Liupan Shan record its tectonic history and environmental effects. In this article we report a new Late Cenozoic red earth section from an intermontane basin in the southern part of the Liupan Shan. Lithofacies analysis, paleomagnetic and fission-track chronologies, and paleocurrent analysis have been employed to identi- fy the tectonic uplift events of the Liupan Shan. Based on the age constraints of mammal fossils, the pa- leomagnetic polarity zones of the Huating （华亭） Section can be approximately correlated with the standard polarity zones that lie between C3An.2n and C5n.ln of the Geomagnetic Polar- ity Timescale; the bottom age of this section is approximately 10 Ma. Based on this and the previous studies, we infer that a tectonic event commenced in the southern Liupan Shan in this interval between 8.3 and 8.7 Ma, accompanied by a remarkable increase in sediment accumulation rate. Field observations, fission-track dating, determinations of grain-size frequency distribu- tions and the vertebrate fossils found there suggest that the red earth deposits were reworked by water and mainly transported by fluvial-alluvial processes from the adjacent area.

Fission-Track Age of Bobai County and Baise Basin Tektite in Guangxi

Tektite arouses great concern of the scientists in different fields, mainly because it is a synthesized material produced by impact between terrestrial material and extraterrestrial material, and the falling or forming process of tektite has never