Fission-track Ages Research Articles

U-Pb and fission-track data from zircon and apatite resolve latest- and post-Alleghanian thermal histories along the Fall Line of the Atlantic margin of the southeastern United States

Abstract Although the Atlantic continental margin of the eastern United States is an archetypal passive margin, episodes of rejuvenation following continental breakup are increasingly well documented. To better constrain this history of rejuvenation along the southern portion of this continental margin, we present zircon U-Pb (ZUPb) age, zircon fission-track (ZFT) age, apatite U-Pb (AUPb) age, and apatite fission-track (AFT) age and length data from six bedrock samples. The samples were collected along the boundary between the exposed Appalachian hinterland (Piedmont province) and the updip limit of passive margin strata (Coastal Plain province). The samples were collected from central Virginia southward to the South Carolina–Georgia border. ZUPb age distributions are generally consistent with geologic mapping in each of the sample areas. The AUPb data are highly discordant owing to high common-Pb abundances, but for two plutons at the northern and southern ends of the sample area, they define a discordia regression line that indicates substantial Permo-Triassic exhumation-driven cooling. ZFT age distributions are highly dispersed but define central values ranging from Permian to Jurassic. AFT data mostly appear to define a singular underlying cooling age, generally approximately Jurassic or Early Cretaceous. Apatite fission tracks are moderately long (mean lengths in the range of ~13.5 µm), however track lengths for one sample in central North Carolina are shorter (~12.5 µm). To interpret the post-breakup thermal history, we present inverse models of time-temperature history for the five plutonic samples. The models show a history of (1) rapid cooling (>10 °C/m.y.) from deep-crustal to near-surface temperatures by the Triassic, (2) hundreds of degrees of Triassic reheating, (3) Jurassic–Early Cretaceous cooling (at rates of 1–10 °C/m.y.), and (4) slow Late Cretaceous–Cenozoic cooling (~1 °C/m.y.). An additional suite of forward models is presented to further evaluate the magnitude of maximum Triassic reheating at one sample site that is particularly well constrained by thermal maturity data. The model results and geologic reasoning suggest that the inverse models may overestimate Triassic paleotemperatures but that other aspects of the inverse modeling are robust. Overall, this thermal history can be reconciled with several aspects of the lithostratigraphy of distal parts of the continental margin, including the lack of Jurassic–earliest Cretaceous strata beneath the southern Atlantic coastal plain and Cretaceous–Cenozoic grain-size trends.

Cenozoic two-phase topographic growth of the northeastern Tibetan Plateau derived from two thermochronologic transects across the southern Qilian Shan thrust belt

The formation of high topography on the northeastern margin of the Tibetan Plateau (the Qilian Shan) constrains the evolutionary history of the plateau. Although prominent exhumation occurred in the middle–late Miocene, the time at which deformation and relief development began in the Qilian Shan during the Cenozoic remains highly debated. Here, we use low-temperature thermochronology to reveal the histories of topographic growth in the Qilian Shan. Two transects were sampled in two primary thrust belts (Qaidam Shan and Danghenan Shan) in the southern Qilian Shan. New apatite fission track ages range from 16.6 to 113 Ma, and apatite (U-Th)/He ages range from 8.4 to 63.5 Ma. Age–elevation relationships and thermal modeling show enhanced rock exhumation in the late Paleocene–early Eocene and middle–late Miocene in both transects. The results indicate two pulses of enhanced thrusting on the major thrust belts in the southern Qilian Shan in the late Paleocene–early Eocene and middle–late Miocene. Our findings imply an early Cenozoic onset of topographic growth in the northeastern Tibetan Plateau, which was quasi-synchronous with the India–Asia collision.

Denudation Process of Crystalline Nappes in a Continental Collision Zone Constrained by Inversion of Fission‐Track Data and Thermokinematic Forward Modeling: An Example From Eastern Nepalese Himalaya

AbstractThermochronological methods were applied to the Higher Himalayan Crystalline (HHC) nappe and the underlying Lesser Himalayan Sequences (LHS) to elucidate the denudation process for the middle‐ and upper‐crust of eastern Nepal over millions of years. Thermochronological inverse modeling was undertaken for new results of fission‐track (FT) age and FT length data of zircon and apatite in order to reconstruct the time‐temperature (t‐T) paths in the temperature range of 60–350°C. Eight t‐T paths calculated along the across‐strike section show that the cooling process of the HHC nappe in this study area is characterized by the following three aspects: (a) gradual cooling followed by rapid cooling and subsequent gradual cooling, (b) northward‐younging of the timing of the rapid cooling, and (c) gradual cooling followed by <2 Myr rapid cooling in the frontmost part of the HHC nappe. The observed FT ages and t‐T paths were then compared with those predicted by forwarding thermokinematic modeling. The results of the thermokinematic modeling for the “Flat‐Ramp‐Flat MHT model”, in which the HHC and the underlying LHS are denudated in direct proportion to the uplift of rocks transported along the Main Himalayan Thrust (MHT), reproduced the observed t‐T paths and FT ages in eastern Nepal. This indicates that the observed FT ages and t‐T paths reflect a denudation process driven by the movement of the MHT with a flat‐ramp‐flat geometry and that the denudation rate and its spatial distribution have roughly been constant in eastern Nepal since ca. 9 Ma.

Spatially focused erosion in the High Himalaya and the geometry of the Main Himalayan Thrust in Central Nepal (85°E) from thermo-kinematic modeling of thermochronological data in the Gyirong region (southern China)

The subsurface structure of the Himalaya is dominated by the seismically active Main Himalayan Thrust fault, which accommodates about half of the plate convergence between India and Asia. In Central Nepal, geological, geophysical, and geodetic studies indicate that the Main Himalayan Thrust has a flat-ramp-flat geometry, which causes cooling, erosion, and exhumation of rocks to be faster above the mid-crustal ramp than above the adjacent upper and lower flats. However, in the northern High Himalaya the ramp geometry, in particular its width and depth are not well resolved. To place further constraints on the northward extent and depth of the ramp, we present for the first time low-temperature thermochronological data and U-Pb zircon ages from the Gyirong region, China (northern High Himalaya). Our zircon U-Pb data show that the protolith of the High Himalayan orthogneisses is 478 ± 4 Ma old, and was intruded by a large leucogranite at 19.5 ± 0.7 Ma. The Pliocene-Quaternary cooling of the study area is constrained by apatite fission track ages and apatite and zircon (U-Th)/He ages between ~5 Ma and ~ 0.5 Ma, which show a marked trend of southward-younging ages. Together with published cooling ages from Nepal farther south, the ages define a U-shaped pattern across the Main Himalayan Thrust, with ages increasing to the north and south from a minimum in the High Himalaya. A thermo-kinematic model, in which the geometry of the mid-crustal ramp was varied, explains the age data and suggests that the ramp has a dip of ~22°N. Compared to previous models, our new ages require that the ramp has a greater width (~55 km) and reaches a greater depth (~34 km) below the northern High Himalaya. Still farther north, the fault is presumably developed as a gently-dipping ductile shear zone, which forms the prominent reflector visible in seismic reflection data.

Late Mesozoic-Cenozoic multistage exhumation of the central Bangong-Nujiang Suture, Central Tibet

The Cenozoic rise of the Tibetan Plateau has significantly altered global climate change and the biological redistribution of Asia. However, there remain great controversies about its detailed topographical evolution, especially in the hinterland of the Plateau, such as around the Bangong-Nujiang Suture (BNS). Here, we choose the Gaize Basin, which is located in the central BNS, as our target research area. New low-temperature thermochronology data have been used to quantify the cooling history of the intrusive rocks and sedimentary strata from the N-S edges of the Gaize Basin. Our thermochronology results show that 1) zircon (UTh)/He ages range from 54 ± 3.7 to 113 ± 8.4 Ma, 2) apatite fission track ages mostly cluster around ~55 Ma, and 3) apatite (UTh)/He ages are between 34 ± 3.3 and 63 ± 4.4 Ma. Combined with the results from thermochronology modelling, we suggest that there were three cooling stages recorded around the Gaize Basin: 1) the late Mesozoic (120–100 Ma), which was probably due to the BNS closure and subsequent Qiangtang-Lhasa collision, 2) the Late Cretaceous-early Paleogene (85–55 Ma), which was perhaps related to the far-field effects of the Neo-Tethyan oceanic subduction, and 3) 47–30 Ma, in response to the continuous India-Asian collision. Similar to today, low relief topography has finalized in the central Tibetan Plateau after the last cooling stage and is mainly aided by river incision and erosion on both sides of the BNS.

Pulsed rise and growth of the Tibetan Plateau to its northern margin since ca. 30 Ma

The onset of mountain building along margins of the Tibetan Plateau provides a key constraint on the processes by which the high topography in Eurasia formed. Although progressive expansion of thickened crust underpins most models, several studies suggest that the northern extent of the plateau was established early, soon after the collision between India and Eurasia at ca. 50 Ma. This inference relies heavily on the age and provenance of Cenozoic sediments preserved in the Qaidam basin. Here, we present evidence in the northern plateau for a considerably younger inception and evolution of the Qaidam basin, based on magnetostratigraphies combined with detrital apatite fission-track ages that date the basin fills to be from ca. 30 to 4.8 Ma. Detrital zircon-provenance analyses coupled with paleocurrents reveal that two-stage growth of the Qilian Shan in the northeastern margin of the Tibetan Plateau began at ca. 30 and at 10 Ma, respectively. Evidence for ca. 30 and 10 to 15 Ma widespread synchronous deformation throughout the Tibetan Plateau and its margins suggests that these two stages of outward growth may have resulted from the removal of mantle lithosphere beneath different portions of the Tibetan Plateau.

The preservation mechanism of the Duolong ore district in northwest Tibet: Evidence from the low temperature thermochronological study

The Early Cretaceous Duolong porphyry-epithermal copper ore district is one of the largest copper ore districts in the central Tibetan Plateau. In order to investigate the preservation mechanism of Early Cretaceous porphyry-epithermal mineralization, new apatite and zircon fission track dating and (U-Th)/He dating of pre-ore sandstone, ore-related and barren intrusive rocks, and post-ore igneous rock, thermal modeling together with previous thermochronological data of the Duolong ore district were combined to study the burial and exhumation processes. Apatite fission track ages range from 68 ± 4 to 40 ± 4 Ma, with mean track lengths varying from 12.1 ± 2.0 to 12.8 ± 2.4 μm. Zircon fission track ages range from 106 ± 4 to 86 ± 4 Ma. In addition, apatite (U-Th)/He yields average age ranging from 62.7 ± 4.2 to 22.6 ± 1.2 Ma, and zircon (U-Th)/He yields average age of 112.3 ± 5.1 Ma. The thermal modeling shows that the Duolong ore district experienced two periods of exhumation and two stages of burial. The first period of exhumation with rate of 0.14 km/m.y. took place immediately after the ore formation which caused the erosion of orebody. Two periods of burial are thought to be related to northeast-southwest striking fault and thrust nappe structure induced by Lhasa-Qiangtang collision between 110 and 65 Ma when the overlying rocks of orebodies were thickened to 4 km. The last period of exhumation with rate of 0.062 km/m.y. (since 65 Ma) is attributed to lithospheric delamination related to India-Asia collision. The preservation of the Duolong ore district mainly benefited from the burial related to the Lhasa-Qiangtang collision. The exhumation and uplift of Duolong ore district was mainly attributed to the India-Asia collision since Paleocene.

Uplift and Expansion of the North Qilian Shan Recorded by Detrital Fission Tracks in the Jiudong Basin, NW China

The North Qilian Shan, located in the northeastern front of the Tibetan Plateau, is an ideal region to study the expansion process of the plateau, which is not clearly revealed due to the lack of direct evidence and an accurate age control. In the Jiudong Basin (foreland basin of the North Qilian Shan), a continuous late Cenozoic sedimentary sequence and a reliable chronostratigraphic framework (post-7 Ma) provide us the material to study this process. In this study, we first analyzed the provenance changes of the sediment by detrital apatite fission track age distributions and apatite particle textures. The result shows that the first provenance change occurred at 4.6–3.6 Ma, when the sediment source changed from the southern to the northern parts of the North Qilian Shan, and it indicates that the North Qilian Shan Fault had propagated to its modern location. The second provenance change occurred at 3.0–2.4 Ma, at when the Yumu Shan and its south region began to provide sediments for the Jiudong Basin, and it indicates that the tectonic deformation in the North Qilian Shan had expanded to the North Yumu Shan Fault. Our finding suggests that two significant expansion events happened since the Pliocene for the North Qilian Shan.

Low-temperature thermochronology of active arc-arc collision zone, South Fossa Magna region, central Japan

The South Fossa Magna region, central Japan, has been an active collision zone between the Honshu Arc and the Izu-Bonin Arc since the middle Miocene and provides an excellent setting for reconstructing the earliest stages of continent formation. Multi-system geo-thermochronometry was applied to different domains of the South Fossa Magna region, together with some previously published data, to reveal mountain formation processes, i.e., vertical crustal movements. Nine granitic samples yielded zircon U–Pb ages of 10.2–5.8 Ma (n = 2), apatite (U–Th)/He (AHe) ages of 42.8–2.6 Ma (n = 7), and apatite fission-track (AFT) ages of 44.1–3.0 Ma (n = 9). Thermal history inversion modeling based on the AHe and AFT data suggests rapid cooling events confined within the study region at ~6–2 Ma. The Kanto Mountains may have undergone a domal uplift in association with their collision with the Tanzawa Block at ~5 Ma. However, this uplift may have slowed down following the southward migration of the plate boundary and late Pliocene termination of the Tanzawa collision against Honshu Island. The Minobu Mountains and adjacent mountains may have been uplifted when motion of the Philippine Sea plate changed from northward to northwestward at ~3 Ma. Therefore, mountain formation in the South Fossa Magna region was mainly controlled by collisions of the Tanzawa and Izu Blocks and motional change of the Philippine Sea plate. Earlier collisions of the Kushigatayama Block at ~13 Ma and Misaka Block at ~10 Ma appear to have had little effect on mountain formation. Together with a clockwise rotation of the Kanto Mountains at 12–6 Ma, these observations suggest that horizontal deformation predominated during the earlier stage of arc-arc collision, and vertical movements due to buoyancy of the accreted crust resulting from crustal shortening and thickening developed at a later stage.

Lithofacies paleogeography restoration and its significance of Jurassic to Lower Cretaceous in southern margin of Junggar Basin, NW China

In view of the difficulties in the study of lithofacies paleogeography and the low reliability of the distribution range of sedimentary sand bodies in the prototype basin caused by less deep drilling, complex seismic imaging and low degree of exploration in the southern margin of Junggar Basin, NW China. A new method based on the source to sink idea was used to restore lithofacies paleogeography and predict glutenite distribution. In the restoration, apatite fission track age was used to define range and uplift time of macro-provenance; the range of provenance area and the migration process of lake shoreline were restored based on the quantitative relationship between gravel diameter and transportation distance, tectonic shortening and other geological parameters; drilling cores and field outcrop sedimentary structures were analyzed, and a series of maps of lithofacies paleogeographic evolution and distribution range of glutenite bodies were compiled. It is concluded that from Early Jurassic to Early Cretaceous, in the southern margin of Junggar Basin, the provenance area gradually expanded from south to north, the lake basin expanded, shrunk and expanded, and the paleoclimate changed from humid to drought to humid. The western section always had proximal fan delta deposits from the southern ancient Tianshan provenance developed, and in the middle and eastern sections, the provenance areas evolved from far source to near source, mainly river-delta, braided delta, fan delta and other sediments developed. The boundary between provenance areas of the western and middle sections is speculated to be Hongche fault zone. In an angle open to the northwest with the current basin edge line, the restored ancient lake shoreline controlled the heterogeneity of reservoirs in the delta plain belt and delta front belt on its both sides. The ancient lake shoreline, current stratigraphic denudation line and current basin margin line limit the types and scope of favorable reservoirs. This understanding provides an important geological basis for oil and gas exploration in the deep lower source-reservoir assemblage at the southern margin of Junggar Basin.

Zircon (U-Th)/He Closure Temperature Lower Than Apatite Thermochronometric Systems: Reconciliation of a Paradox

Here, we present seven new zircon (U-Th)/He (ZHe) ages and three new zircon fission track (ZFT) ages analyzed from an age-elevation profile (Machu Picchu, Peru). ZFT data present ages older than those obtained with other thermochronological data, whereas the ZHe data interestingly present ages similar to those obtained with apatite (U-Th)/He (AHe). It has been proposed that He retention in zircon is linked to the damage dose, with an evolution of the closure temperature from low values associated with a low α-dose (<1016 α/g), subsequently increasing before decreasing again at a very high α-dose (>1018 α/g). Studies have focused on He diffusion behavior at high α-dose, but little is known at low doses. We propose that the ZHe closure temperature at α-dose ranging from 6 × 1015 to 4 × 1016 α/g is in the range of ~60–80 °C. This value is lower than that proposed in the current damage model ZRDAAM and demonstrates that the ZHe and AHe methods could have similar closure temperatures at low α-dose (i.e., similar ages). These new data strengthen our previous geological conclusions and even highlight a cooling rate approximately twice as important as that deduced from AHe and apatite fission track data alone at Machu Picchu.

A multi-method approach to constrain the age of eruption and post-depositional processes in a Lower Jurassic ignimbrite from the Marifil Volcanic Complex, eastern North Patagonian Massif

In the eastern North Patagonian Massif, the Marifil Volcanic Complex corresponds to an Early Jurassic magmatic event. In this study, we evaluate new geochronological and thermochronological data obtained from an ignimbrite of the complex. U–Pb zircon ages from the pumice fraction reveal a Concordia age of 184.4 ± 1.1 Ma. Conversely, U–Pb zircon ages from the whole-rock sample evidence a Concordia age of 190.4 ± 0.6 Ma. Fission track techniques were applied on the same whole-rock sample. Zircon fission track performed on the same zircon-crystals dated by U–Pb yielded an age of 172.5 ± 8.1 Ma, while apatite fission track evidenced a cooling age of 179.1 ± 13.5 Ma. Apatite and zircon crystals describe uniform morphologies with unaltered euhedral to subhedral grains and well-developed crystalline forms. The results suggest that the age of eruption and deposition of the ignimbrite is better explained by the pumice zircon age rather than the whole-rock zircon age. Inherited grain-ages and petrographic evidence support provenance from older, probably cogenetic, magmatic products. Fission track ages reflect a post-depositional process probably related to diagenetic mineral changes.

Petrological characteristics and zircon fission-track ages of Chibanian (middle Pleistocene) tephra layers on the Odamaki Hill in the Chichibu Basin, Saitama Prefecture, eastern Japan

Petrological characteristics and zircon fission-track ages of Chibanian (middle Pleistocene) tephra layers on the Odamaki Hill in the Chichibu Basin, Saitama Prefecture, eastern Japan

Comments on “Devonian to Permian post-orogenic denudation of the Brasília Belt of West Gondwana: Insights from apatite fission track thermochronology” by Fonseca et al. (2020)

In a recent paper published in the Journal of Geodynamics (vol. 137, June 2020, 101733), Fonseca et al. (2020) proposed a thought-provoking model aiming to elucidate the exhumation history of the Neoproterozoic Brasília Fold Belt (BFB) between the Devonian and Cretaceous periods. Exclusively based on information from the literature and new thermochronological data, Fonseca et al. (2020) presented an alternative model that tries to bind tectonic uplift, erosion, and the influx of clastic material coming from the BFB into the intracratonic Paraná Basin. Although the welcome proposal and reliable quality of the analytical data, the hypothesis presented diverges from several previously published works. In the light of the presented apatite fission-track ages, we disagree with their paleogeographical model, which puts the Brasília Fold Belt as a major source for clastic detritus to the Paraná Basin between the Devonian to Permian. The primary goal of our comments is to clarify the state-of-art of the intricate source-to-sink system of the Paraná Basin. Secondarily, we try to demonstrate why the model proposed by Fonseca et al. (2020) presents some geodynamic and interpretative problems and do not characterize an adequate paleogeographic scenario for southwest Gondwana between the Devonian to Permian periods.

Characterization of Lower and Middle Pleistocene tephra beds in the southern plains of western Canada

Wellsch Valley tephra, near Swift Current, southwestern Saskatchewan, and Galt Island tephra, near Medicine Hat, southeastern Alberta, have been referenced in the literature since the 1970s, but little is available on their physical and chemical attributes — necessary information if they are to be recognized elsewhere. This study seeks to remedy this situation. Both have a calc-alkaline rhyolitic composition with hornblende, biotite, plagioclase, pyroxene, and Fe–Ti oxides being dominant. They have a similar composition but are not the same. Wellsch Valley tephra has a glass fission-track age of 0.75 ± 0.05 Ma, a reversed magnetic polarity, and was deposited at the close of the Matuyama Chron. Galt Island tephra has an age of 0.49 ± 0.05 Ma, a normal magnetic polarity, and was deposited during the early Brunhes Chron. Rich fossil vertebrate faunas occur in sediments close to them. Major- and trace-element concentrations in their glass shards indicate a source in the Cascade Range of the Pacific Northwest, USA, but differences in trace-element ratios suggest they are not consanguineous.

Accessories in Kaiserstuhl carbonatites and related rocks as accurate and faithful recorders of whole rock age and isotopic composition

The accessories perovskite, pyrochlore, zirconolite, calzirtite and melanite from carbonatites and carbonate-rich foidites from the Kaiserstuhl are variously suited for the in situ determination of their U–Pb ages and Sr, Nd- and Hf-isotope ratios by LA-ICP-MS. The 143Nd/144Nd ratios may be determined precisely in all five phases, the 176Hf/177Hf ratios only in calzirtite and the 87Sr/86Sr ratios in perovskites and pyrochlores. The carbonatites and carbonate-rich foidites belong to one of the three magmatic groups that Schleicher et al. (1990) distinguished in the Kaiserstuhl on the basis of their Sr, Nd and Pb isotope ratios. Tephrites, phonolites and essexites (nepheline monzogabbros) form the second and limburgites (nepheline basanites) and olivine nephelinites the third. Our 87Sr/86Sr isotope data from the accessories overlap with the carbonatite and olivine nephelinite fields defined by Schleicher et al. (1990) but exhibit a much narrower range. These and the εNd and εHf values plot along the mantle array in the field of oceanic island basalts relatively close to mid-ocean ridge basalts. Previously reported K–Ar, Ar–Ar and fission track ages for the Kaiserstuhl lie between 16.2 and 17.8 Ma. They stem entirely from the geologically older tephrites, phonolites and essexites. No ages existed so far for the geologically younger carbonatites and carbonate-rich foidites except for one apatite fission track age (15.8 Ma). We obtained precise U–Pb ages for zirconolites and calzirtites of 15.66, respectively 15.5 Ma (± 0.1 2σ) and for pyrochlores of 15.35 ± 0.24 Ma. Only the perovskites from the Badberg soevite yielded a U–P concordia age of 14.56 ± 0.86 Ma while the perovskites from bergalites (haüyne melilitites) only gave 206Pb/238U and 208Pb/232Th ages of 15.26 ± 0.21, respectively, 15.28 ± 0.48 Ma. The main Kaiserstuhl rock types were emplaced over a time span of 1.6 Ma almost 1 million years before the carbonatites and carbonate-rich foidites. These were emplaced within only 0.32 Ma.

The Tectonic event of the Zaire-Hala’alate thrust belt in Junggar Basin,China

The Yanshanian tectonic activity intensity effect of The Zaire- Hala’alate thrust belt, which is located in the northwest margin of Junggar Basin, have been in dispute for a long time. The distribution characteristics of the FT peak age in the narrower time domain is the key to understanding the dynamic mechanism of this important intracontinental deformation. In this study, apatite fission track dating and thermal history simulation analysis were carried out on 6 samples collected from this area. The results show that the fission track ages are mainly distributed in three intervals, corresponding to the geological ages of 130∼128Ma, 92∼89Ma and 72Ma, reflecting the obvious cooling and uplifting events in the three periods. At the same time, the thermal history simulation shows that the region experienced three rapid uplift events in the Early Cretaceous, the Early Late Cretaceous and the Late Cretaceous-Eocene. The comprehensive study shows that the main thrust fold in this area started from the end of Early Cretaceous, and the tectonic movement was the most intense in Late Cretaceous. As a whole, Tectonic activity migrated from south to north, which shows a retro-thrust expansion from the basin to the orogenic belt.

Combined Zircon/Apatite U-Pb and Fission-Track Dating by LA-ICP-MS and Its Geological Applications: An Example from the Egyptian Younger Granites

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) is classically used in U-Pb dating to measure U and Pb isotopic concentrations. Recently, it has become frequently used in fission-track (FT) chronometry too. As an advantage, the U-Pb and FT double dating will enable efficiently determining the crystallization ages and the thermo-tectonic history concurrently as samples volume, analytical time, efforts, and cost will be greatly reduced. To demonstrate the validity of this approach, a Younger granite (Ediacaran age) sample from North Eastern Desert (NED), Egypt was analyzed for U-Pb and FT double dating. The integration of multiple geochronologic data yielded a zircon U-Pb crystallization age of 599 ± 30 Ma, after emplacement, the rock cooled /uplifted rapidly to depths of 9–14 km as response to the post-Pan African Orogeny erosional event as indicated by apatite U-Pb age of 474 ± 9 Ma. Afterwards, the area experienced a slow cooling/exhumation for a short period, most-likely as response to denudation effect. During the Devonian, the area was rapidly exhumed to reach depths of 1.5–3 km as response to the Hercynian tectonic event, as indicated by a zircon FT age of 347 ± 16 Ma. Then the studied sample has experienced a relatively long period of thermal stability between the Carboniferous and the Eocene. During the Oligocene-Miocene, the Gulf of Suez opening event affected the area by crustal uplift to its current elevation. This integration of Orogenic and thermo-tectonic information reveals the validity, efficiency, and importance of double dating of U-Pb and FT techniques using LA-ICP-MS methodology.

Differential post-mineralization thermal evolution of the Jiaodong and Liaodong Areas, Eastern China: An indicator of regional tectonic activity

Post-mineralization thermal evolution is an integral part of the process of formation of ore deposits. However, as two important gold mineralization regions in eastern China, the thermal histories after ore formation of the Jiaodong area is debated while that of the Liaodong area are scarce. Given that the two areas are not only in similar tectonic settings but also have gold deposits that formed in association with the thinning and destruction of the North China Craton, a comparative study can be made. Here new zircon and apatite (U–Th)/He and apatite fission track ages are presented to reconstruct the post-mineralization geological evolution. Four periods of rapid uplift and denudation happening during the 110–100 Ma, 80–70 Ma, 42–38 Ma and 35–32 Ma are defined in Liaodong, and two such periods happening during the 100–95 Ma and 80–72 Ma in Jiaodong. The small timing difference of the rapid uplift (110–100 Ma versus 100–95 Ma) can be explained by the elevation difference of the respective samples. Hence, the evolution processes between the Jiaodong and Liaodong areas are very similar during the Cretaceous, but show marked differences during the Cenozoic. After ore-formation, the erosion amount in Liaodong and Jiaodong is estimated at ∼4.8 and ∼4.7 km, respectively. Moreover, the denudation intensity in Liaodong shows an increase from southeast to northwest. The westward convergence of the Pacific Plate and associated multi-stage activity of the Tanlu and Yalujiang faults are inferred to have induced the regional-scale rapid uplift of the Jiao-Liao areas.

Transition from slab roll-back to slab break-off in the central Apennines, Italy: Constraints from the stratigraphic and thermochronologic record

ABSTRACTStratigraphic and thermochronologic data are used to study the processes that shaped the topography of the central Apennines of Italy. These are part of a major, active mountain belt in the center of the Mediterranean area, where several subduction zones control a complex topography. The Apennines were shaped by contraction at the front of the accretionary wedge overlying the subducting Adria microplate followed by extension at the wedge rear in response to eastward slab roll-back. In the central Apennines, intermontane extensional basins on the western flank rise eastward toward the summit. We contribute with new data consisting of 28 (U-Th-Sm)/He and 10 fission track ages on apatites to resolve a complex pattern of thermal histories in time and space, which we interpret as reflecting the transitional state of the orogen, undergoing a two-phase evolution related to initial slab retreat, followed by slab detachment. Along the Tyrrhenian coast, we document cooling from depths ≥3–4 km occurring between 8 and 5 Ma and related to the opening of marine extensional basins. Post–5 Ma, a broader region of the central Apennines exhibits cooling from variable depths, between <2 km in most areas and ≥3–4 km in the northeast, and with different onset times: at ca. 4 Ma in the west, at ca. 2.5 Ma in the center and northeast, and at ca. 1 Ma in the southeast. Between 5 and 2.5 Ma, exhumation is associated with modest topographic growth during the late stages of thrusting. Since 2.5 Ma, exhumation has concurred with the opening of intermontane basins in the west and in the east, with regional topographic growth and erosion, that we interpret to be associated with the locally detaching slab.