Cenozoic Thrust Research Articles

Long live the fault! Double inversion of a Mesozoic rift‐related fault system in the central Apennines

AbstractThe San Potito area in central Apennines (Italy), enclosed within the Latium‐Abruzzi carbonate platform, exposes anomalously pelagic carbonates filling an intraplatform basin formed during Jurassic rifting. Oriented obliquely to the regional NW‐SE trend of Cenozoic thrusts and extensional faults, the basin's eastern boundary fault system, striking N‐S, played a pivotal role in structuring orogenic and post‐orogenic features. Large tracts of the fault experienced double reactivation: positive inversion during Miocene shortening, and negative during post‐orogenic extension. Double reactivation is evidenced by older‐on‐younger extensional contacts, and by the change in orientation of thrusts and recent extensional faults from NW‐SE to NNW‐SSE, the latter being consistent with the trend of Jurassic rift‐related structures of the area. This structural interplay highlights the importance of Jurassic faults and their ability in forcing the structural trends, by surviving across multiple deformation stages, even controlling active extensional seismicity.

Late Cenozoic thrust propagation within the Keping fold-and-thrust belt along the southern foreland of Chinese Tian Shan: Evidence from apatite (U[sbnd]Th)/He results

The Keping fold-and-thrust belt (FTB) is located along the southern foreland of the Chinese Tian Shan, consisting of 3–6 rows of E- to NE-trending thrusts. Determining the time of thrusting and folding within the Keping FTB is crucial to understand the process and characteristic of tectonic deformation along the southern Tian Shan foreland. Here, we present new deformation ages of four thrusts within the Keping FTB by using the apatite (UTh)/He thermochronometer. Based on analyses of 59 single-grain apatite (UTh)/He ages of 13 sandstone samples collected from the hanging-walls of the four thrusts, the deformation ages of two thrusts located at the northern part of the western Keping FTB were constrained to be ~12 Ma and ~ 11 Ma, respectively; while those of two thrusts located at the southern part of the eastern Keping FTB were interpreted to be ~14 Ma and ~ 13 Ma, respectively. The above deformation ages, together with previous studies, suggest that the Cenozoic deformation across the southern Tian Shan foreland initiated at ~16–12 Ma, and the propagation process of the Keping thrust system is laterally non-synchronous. Additionally, the million-year-scale crustal shortening rates of the Keping FTB were recalculated to be ~2.2–3.9 mm/yr in its western segment and ~ 1.3–3.6 mm/yr in its eastern segment, based on the new age constraints of initial tectonic deformation and published shortening estimates.

Late Mesozoic–Cenozoic cooling history of the northeastern Tibetan Plateau and its foreland derived from low-temperature thermochronology

AbstractThe growth history and formation mechanisms of the Cenozoic Tibetan Plateau are the subject of an intense debate with important implications for understanding the kinematics and dynamics of large-scale intracontinental deformation. Better constraints on the uplift and deformation history across the northern plateau are necessary to address how the Tibetan Plateau was constructed. To this end, we present updated field observations coupled with low-temperature thermochronology from the Qaidam basin in the south to the Qilian Shan foreland in the north. Our results show that the region experienced a late Mesozoic cooling event that is interpreted as a result of tectonic deformation prior to the India-Asia collision. Our results also reveal the onset of renewed cooling in the Eocene in the Qilian Shan region along the northern margin of the Tibetan Plateau, which we interpret to indicate the timing of initial thrusting and plateau formation along the plateau margin. The interpreted Eocene thrusting in the Qilian Shan predates Cenozoic thrust belts to the south (e.g., the Eastern Kunlun Range), which supports out-of-sequence rather than northward-migrating thrust belt development. The early Cenozoic deformation exploited the south-dipping early Paleozoic Qilian suture zone as indicated by our field mapping and the existing geophysical data. In the Miocene, strike-slip faulting was initiated along segments of the older Paleozoic suture zones in northern Tibet, which led to the development of the Kunlun and Haiyuan left-slip transpressional systems. Late Miocene deformation and uplift of the Hexi corridor and Longshou Shan directly north of the Qilian Shan thrust belt represent the most recent phase of outward plateau growth.

The Cenozoic thrusting sequence of the Longmen Shan fold-and-thrust belt, eastern margin of the Tibetan plateau: Insights from low-temperature thermochronology

The 2008 MW 7.8 Wenchuan earthquake in China led to intensive studies on the development and dynamic mechanisms of the Longmen Shan fold-and-thrust belt. To construct the uplift history of the Longmen Shan, previous works had undertaken numerous low-temperature thermochronological studies in mountainous area, in particular apatite and zircon (U–Th)/He dating, which provided valuable evidence for understanding phases of uplift in the Longmen Shan during the Cenozoic. However, few (U–Th)/He ages have been obtained from the Sichuan Basin, which leaves a blank in our understanding of the link between the Wenchuan earthquake and the out-of-sequence Longmen Shan. In this study, we carried out (U–Th)/He dating on apatite and zircon separated from samples collected in the Sichuan Basin and the frontal southern Longmen Shan. Together with previous low-temperature thermochronological studies, we reconstructed the thrusting sequence of the Longmen Shan. The results of dating of apatite suggest that thrusting in the Longmen Shan is temporally and spatially variable. After continuous thrust propagation into the Sichuan Basin (over several to tens of Myr), deformation migrated back into the mountain range, which in this case termed “out-of-sequence” style of deformation.

Structural analysis and tectonic evolution of the western domain of the Eastern Kunlun Range, northwest Tibet

AbstractThe Tibetan Plateau, the largest highland on Earth, formed due to the collision of India-Asia over the past 50–60 m.y., and the evolution of the Tibetan Plateau impacts our knowledge of continental tectonics. Examination of the northernmost margin of the Tibetan Plateau is key to unravelling the deformation mechanisms acting in northern Tibet. The left-slip Altyn Tagh fault system defines the northwest margin of the Tibetan Plateau, separating the Western and Eastern Kunlun Ranges in the southwest. Both Cenozoic and pre-Cenozoic crustal deformation events at this junction between the Altyn Tagh and Kunlun Ranges were responsible for the construction of northwestern Tibet, yet the relative contribution of each phase remains unconstrained. The western domain of the Eastern Kunlun Range is marked by active NE-trending, left-slip deformation of the Altyn Tagh fault and an E-striking Cenozoic thrust system developed in response India-Asia collision. To better constrain the Paleozoic Altyn Tagh and Kunlun orogens and establish the Cenozoic structural framework, we conducted an integrated investigation involving detailed geologic mapping (∼1:50,000 scale), U-Pb zircon geochronology, and synthesis of existing data sets across northwestern Tibet. Our new zircon analyses from Paleoproterozoic–Cretaceous strata constrain stratigraphic age and sediment provenance and highlight Proterozoic–Paleozoic arc activity. We propose a tectonic model for the Neoproterozoic–Mesozoic evolution of northwestern Tibet wherein restoration of an ∼56-km-long balanced cross section across the western domain of the Eastern Kunlun suggests that Cenozoic minimum shortening strain was ∼30% (∼24 km shortening). Field evidence suggests this shortening commenced after ca. 25–20 Ma, which yields an average long-term shortening rate of 1.2–0.9 mm yr–1 and strain rates of 4.7 × 10–16 s–1 to 2.3 × 10–16 s–1. Geometric considerations demonstrate that this contractional deformation did not significantly contribute to left-slip offset on the Altyn Tagh fault, which has ∼10 mm/yr slip rates.

Paleomagnetic and Geochronologic Results of Latest Cretaceous Lava Flows From the Lhasa Terrane and Their Tectonic Implications

AbstractTo position the Asian southern margin before the India‐Asia collision, paleomagnetic and geochronologic studies were performed on the Dianzhong Formation lava flows from the Shiquanhe area of the westernmost Lhasa terrane (LT). Zircon U‐Pb analyses dated the lava flows to ~69.5 ± 2.5 Ma. The characteristic remanent magnetization directions contain antipodal polarities and pass fold tests, implying that they are primary magnetizations; this interpretation is supported by rock‐magnetic analyses and petrographic observations. Forty‐four site‐mean directions were divided into 17 statistically independent direction groups. The group‐mean direction after tilt correction is Ds = 43.3°, Is = 30.3°, k = 28.0, α95 = 6.9°. The corresponding paleopole at 47.8°N, 181.4°E (A95 = 6.4°) yields a paleolatitude of 16.6° ± 6.4°N for the Shiquanhe area of westernmost Tibet (32.34°N, 80.12°E). Consistent paleolatitudes for the southern margin of the LT calculated from the western and central part of the LT indicate that the leading edge of the LT was aligned relatively W‐E. When compared with the reference pole at 70 Ma for Eurasia, this new paleopole suggests that crustal shortening between the Shiquanhe area and stable Asia was 1,500 ± 800 km. This is supported by the crustal shortening (600–1,000 km) absorbed by Cenozoic thrust and fold belts within this area, indicating that the magnitude of crustal shortening within Asia north of the India‐Asia suture zone was similar in the central and western part of the plateau.

Geology, Fluid Inclusions, and Isotopic Geochemistry of the Jinman Sediment‐Hosted Copper Deposit in the Lanping Basin, China

AbstractThe Jinman Cu polymetallic deposit is located within Middle Jurassic sandstone and slate units in the Lanping Basin of southwestern China. The Cu mineralization occurs mainly as sulfide‐bearing quartz–carbonate veins in faults and fractures, controlled by a Cenozoic thrust–nappe system. A detailed study of fluid inclusions from the Jinman deposit distinguishes three types of fluid inclusions in syn‐ore quartz and post‐ore calcite: aqueous water (type A), CO2–H2O (type B), and CO2‐dominated (type C) fluid inclusions.The homogenization temperatures of CO2–H2O inclusions vary from 208°C to 329°C, with corresponding salinities from 0.6 to 4.6 wt.% NaCl equivalent. The homogenization temperatures of the aqueous fluid inclusions mainly range from 164°C to 249°C, with salinities from 7.2 to 20.2 wt.% NaCl equivalent. These characteristics of fluid inclusions are significantly different from those of basinal mineralization systems, but similar to those of orogenic or magmatic mineralization systems. The H and O isotope compositions suggest that the ore‐forming fluid is predominantly derived from magmatic water, with the participation of basinal brine. The δ34S values are widely variable between −9.7 ‰ and 9.7 ‰, with a mode distribution around zero, which may be interpreted by the variation in physico‐chemical conditions or by compositional variation of the sources. The mixing of a deeply sourced CO2‐rich fluid with basinal brine was the key mechanism responsible for the mineralization of the Jinman deposit.

Late Cenozoic thrusting of major faults along the central segment of Longmen Shan, eastern Tibet: Evidence from low-temperature thermochronology

The Cenozoic orogenic process of the Longmen Shan (LMS) and the kinematics of major faults along the LMS are crucial for understanding the growth history and mechanism of the eastern Tibetan Plateau. Three major faults, from west to east, are present in the central segment of the LMS: the Wenchuan-Maoxian Fault (WMF), the Beichuan-Yingxiu Fault (BYF), and the Jiangyou-Guanxian Fault (JGF). Previous researchers have placed great impetus on the Pengguan Massif, between the WMF and BYF. However, limited low-temperature thermochronology data coverage in other areas prevents us from fully delineating the tectonic history of the LMS. In this study, we collect 22 samples from vertical profiles in the Xuelongbao Massif and the range frontal area located at the hanging walls of the WMF and JGF respectively, and conduct apatite and zircon fission track analyses. New fission track data reveal that the Xuelongbao Massif has been undergoing rapid exhumation with an average rate of ~0.7–0.9mm/yr since ~11Ma, and the range frontal area began rapid exhumation at ~7.5Ma with total exhumation of ~2.5–4.5km. The exhumation histories indicate that the three major faults (WMF, BYF and JGF) in the central LMS are all reverse faults, and show a basinward in-sequence propagation from middle Miocene to present-day. Such a pattern further implies that upper crustal shortening is the primary driver for the LMS' uplift during the Late Cenozoic. Nevertheless, middle-lower crustal deformation is difficult to be constrained by the exhumation histories, and its contribution to LMS' uplift cannot be ruled out.

Contrasting terrace systems of the lower Moulouya river as indicator of crustal deformation in NE Morocco

The Moulouya river has the largest catchment in Morocco and drains an area characterized by active crustal deformation during the Late Cenozoic due to the N–S convergence between the African and Eurasian plates. As yet, its Pleistocene terrace sequence remains poorly documented. Our study focuses on the lowermost reach of the river in north-eastern Morocco, which drains the Zebra-Triffa sedimentary basin directly upstream of the estuary. New field observations, measurements and sedimentological data reveal contrasting fluvial environments on each side of a newly identified, W–E striking thrust zone disrupting the sedimentary basin. On the one hand, long-lasting fluvial aggradation, materialized by 37 m-thick stacked terraces, has occurred in the footwall of the thrust. On the other hand, the hanging wall is characterized by a well-preserved terrace staircase, with three Pleistocene terrace levels. Whilst the identification of this thrust zone question some previous interpretations about the local (hydro-)geology, it is consistent with the statement that most of the Plio-Quaternary deformation in the eastern Rif mountains has concentrated in this region of Morocco. Our new data and interpretations also agree with morphometric indicators showing that the whole Moulouya catchment is at desequilibrium state (i.e. several knickzones in its longitudinal profile), showing several knickzones in its longitudinal profile, is at disequilibrium state. We also suggest that the knickzone in the Beni Snassen gorge, located directly upstream of the Zebra-Triffa sedimentary basin, could (partly) result from a transient fluvial reaction to Late Cenozoic thrusting activity and correlated uplift in the hanging wall.

Noble Gas and Stable Isotopic Constraints on the Origin of the Ag–Cu Polymetallic Ore Deposits in the Baiyangping Area, Yunnan Province, SW China

AbstractThe Lanping basin, Yunnan province, SW China, is located at the juncture of the Eurasian and Indian Plates in the eastern part of the Tibetan Plateau. The Lanping basin, in the Sanjiang Tethyan metallogenic province, is a significant Cu–Ag–Zn–Pb mineralized belt in China that includes the largest sandstone‐hosted Zn–Pb deposit in the world, the Jinding deposit, as well as several Ag–Cu deposits (the Baiyangping and Jinman deposits). These deposits, with total reserves of over 16.0 Mt Pb + Zn, 0.6 Mt Cu, and 7,000 t Ag, are mainly hosted in Meso‐Cenozoic clastic rocks and are dominantly controlled by two Cenozoic thrust systems developed in the western and eastern segments of the basin.The Baiyangping, Babaoshan, and Hetaoqing ore deposits are representative of the epithermal base metal deposits in the Lanping basin. The microthermometric data show that the ore‐forming fluids for these deposits were low temperature (110–180 °C) and had bimodal distribution of salinity at moderate and mid to high salinities (approximately 2–8 wt.% and 18–26 wt.% NaCl equivalent). The C and O isotope data indicate that the ore‐forming fluids were related to hot basin brines. We present new He and Ar isotope data on volatiles released from fluid inclusions contained in sulfides and in barite in these three deposits. 3He/4He ratios of the ore‐forming fluids are 0.01 to 0.14 R/Ra with a mean of 0.07 Ra (where R is the 3He/4He ratio and Ra is the ratio for atmospheric helium). This mean value is intermediate to typical 3He/4He ratios for the crust (R/Ra = 0.01 to 0.05) and the ratio for air‐saturated water (R/Ra = 1). The mean ratio is also significantly lower than the ratios found for mantle‐derived fluids (R/Ra = 6 to 9). The 40Ar/36Ar ratios of the ore‐forming fluids range from 298 to 382 with a mean of 323. This value is slightly higher than that for the air‐saturated water (295.5). The 3He/4He ratios of fluids from the fluid inclusions imply that the ore‐forming fluid for the Baiyangping, Babaoshan, and Hetaoqing deposits was derived from the crust and that any mantle‐derived He was negligible. The content of the radiogenic Ar ranges between 0.2 to 20.4%, and the proportion of air‐derived 40Ar averages 94.1%. This indicates that atmospheric Ar was important in the formation of these deposits but that some radiogenic 40Ar was derived from crustal rocks. Based on these observations coupled with other geochemical evidence, we suggest that the ore‐forming fluids responsible for the formation of the Ag–Cu–Pb–Zn polymetallic ore deposits in the Baiyangping area of the Lanping basin were mainly derived from crustal fluids. The fluids may have mixed with some amount of air‐saturated water, but there was no significant involvement of mantle‐derived fluids.

Moho depth inferred from gravity and topography in an intraplate area (Iberian Chain)

This paper discusses variations in Moho depth beneath an intraplate area, including the Iberian Chain thrust belt and the surrounding Cenozoic basins, based on topography and Bouguer anomaly data analysis. Two models of Moho depth mapping were used: Airy Moho depth maps and a Moho depth map derived from the Bouguer anomaly map. According to these models, a minimum Moho depth of 32 to 36km was calculated beneath the Iberian Chain and the Central System, and a maximum Moho depth ranging from 37 to 44km for the central part of the Iberian Chain. This crustal thickening (at least 5 to 7km) was generated during the Cenozoic contraction. Subsequent to these analyses, a new 2D density model was built across the entire Iberian Chain. This model showed a thickening of the upper crust, which is consistent with a Cenozoic thrust system involving only the upper crust.

The Bogeda Shan uplifting: Evidence from multiple phases of deformation

The current topography of Central Asia is considered to have resulted from crustal shortening related to the ongoing India–Asia collision that started in the Early Tertiary period. The Bogeda Shan, a northeastern branch of the Tian Shan located in northwest China, has several summits higher than 5000m. The northern piedmont of the Bogeda Shan exhibits remarkable deformation features that remain poorly studied. This study documents three phases of tectonic deformation in the Bogeda Shan that are related to the far-field effects of collisions along the southern Eurasian margin. Detailed field observations show that the intensively folded Upper Permian strata are covered by a subhorizontal Lower Jurassic layer, thus indicating a Triassic tectonic event that is probably related to the onset of the uplift in the Bogeda Shan during a Cimmerian orogenic episode (D1). A seismic profile suggests that this deformation episode was followed by the Late Jurassic–Early Cretaceous deformation (D2), which is characterized by wide wavelength folds overlaid by undeformed Cretaceous layers. Cenozoic thrusts were also observed in the northern piedmont of the Bogeda Shan (D3). This study demonstrates that the onset of uplift in the Bogeda Shan began in the Early Mesozoic and separated the Turfan–Hami Basin from the Junggar Basin. A new tectonic evolution model of the Bogeda Shan was reconstructed by these three tectonic phases. This work indicates that the current topography of the Bogeda Shan and its surrounding area was the result of multiple phases of deformation related to successive collisions at the southern Eurasian margin.

Distribution of the Late-Quaternary deformation in Northwestern Himalaya

Three main Cenozoic thrusts at the front of Northwestern Himalaya have accommodated most of the India–Eurasia convergence across the belt over the last million years and produced the present relief. Their recent tectonic activity is poorly known because of the long period of inaccessibility of the Jammu and Kashmir state, and because the latest and only large earthquake recorded in the region occurred in 1555 AD. We show where the deformation is localized during the Late-Quaternary, and determine shortening rates across the structures by analyzing the geometry and chronology of geomorphic markers. The Main Boundary Thrust in this region ceased moving at least ∼30 ka ago. On the contrary, the more external Medlicott–Wadia Thrust and Main Frontal Thrust, both merging at depth on the sub-flat detachment of the Main Himalayan Thrust, exhibit hectometric-scale deformations accumulated during the last thousands of years. The total shortening rate absorbed by these faults over the last 14–24 ka is between 13.2 and 27.2 mm/yr (11.2±3.8 and 9.0±3.2 mm/yr, respectively). Part of this deformation may be associated to the geometry of the Chenab reentrant, which could generate an extra oblique component. However, the lower bound of our shortening rates is consistent with previously determined geodetic rates. Active deformation on these structures follows an in-sequence/out-of-sequence pattern, with breaking of both ramps being possible for earthquakes triggered on the main detachment.

Influence of pre-Andean crustal structure on Cenozoic thrust belt kinematics and shortening magnitude: Northwestern Argentina

The retroarc fold-and-thrust belt of the Central Andes exhibits major along-strike variations in its pre-Cenozoic tectonic configuration. These variations have been proposed to explain the considerable southward decrease in the observed magnitude of Cenozoic shortening. Regional mapping, a cross section, and U-Pb and (U-Th)/He age dating of apatite and zircon presented here build upon the preexisting geological framework for the region. At the latitude of the regional transect (24–25°S), results demonstrate that the thrust belt propagated in an overall eastward direction in three distinct pulses during Cenozoic time. Each eastward jump in the deformation front was apparently followed by local westward deformation migration, likely reflecting a subcritically tapered orogenic wedge. The first eastward jump was at ca. 40 Ma, when deformation and exhumation were restricted to the western margin of the Eastern Cordillera and eastern margin of the Puna Plateau. At 12–10 Ma, the thrust front jumped ∼75 km toward the east to bypass the central portion of a horst block of the Cretaceous Salta rift system, followed by initiation of new faults in a subsystem that propagated toward the west into this preexisting structural high. During Pliocene time, deformation again migrated >100 km eastward to a Cretaceous synrift depocenter in the Santa Barbara Ranges. The sporadic foreland-ward propagation documented here may be common in basement-involved thrust systems where inherited weaknesses due to previous crustal deformation are preferentially reactivated during later shortening. The minimum estimate for the magnitude of shortening at this latitude is ∼142 km, which is moderate in magnitude compared to the 250–350 km of shortening accommodated in the retroarc thrust belt of southern Bolivia to the north. This work supports previous hypotheses that the magnitude of shortening decreases significantly along strike away from a maximum in southern Bolivia, largely as a result of the distribution of pre-Cenozoic basins that are able to accommodate a large magnitude of thin-skinned shortening. A major implication is that variations in the pre-orogenic upper-crustal architecture can influence the behavior of the continental lithosphere during later orogenesis, a result that challenges geodynamic models that neglect upper-plate heterogeneities.

Constructing the Longmen Shan eastern Tibetan Plateau margin: Insights from low‐temperature thermochronology

AbstractContrasting models of upper crustal shortening versus lower crustal flow have been proposed to explain the formation of thickened crust in the Longmen Shan (LMS), eastern Tibetan Plateau (TP) margin. These models require different structural kinematics along the LMS, whose structural geometry is defined by three parallel NW‐dipping fault zones. From foreland (southeast) to hinterland (northwest), they are the Guanxian‐Anxian Fault, Yingxiu‐Beichuan Fault (YBF), and Wenchuan‐Maowen Fault (WMF). Newly derived and previously published low‐temperature thermochronology data from the LMS were synthesized to constrain the spatial exhumation and test previous models. The results show that (1) exhumation increases abruptly across the range‐bounding YBF, suggesting the fault being the main thrust boundary between the LMS and the Sichuan Basin to the east; (2) Younger Late Cenozoic cooling ages are found on the hinterland WMF, where a dichotomy of ages on the hanging wall versus footwall suggests Late Cenozoic thrust activity; and (3) toward the hinterland to the west, exhumation rates decrease twofold over a distance of ~30–40 km. This exhumation pattern indicates a westward decrease of tectonic uplift, providing the regional topography approached a steady state, whereby exhumation is in balance with tectonic uplift. The observed exhumation estimates support an upper crustal configuration where thrusts in the LMS merge gradually into a gentle detachment seated at a depth of ~20–30 km. Results of this study support a revised upper crustal thrusting model.

Ages of sediment-hosted Himalayan Pb–Zn–Cu–Ag polymetallic deposits in the Lanping basin, China: Re–Os geochronology of molybdenite and Sm–Nd dating of calcite

The Lanping basin is a significant Pb–Zn–Cu–Ag mineralization belt of the Sanjiang Tethyan metallogenic province in China. Over 100 thrust-controlled, sediment-hosted, Himalayan base metal deposits have been discovered in this basin, including the largest sandstone-hosted Pb–Zn deposit in the world (Jinding), and several Cu±Ag±Co deposits (Baiyangping, Baiyangchang and Jinman). These deposits, with total reserves of over 16.0 Mt Pb+Zn, 0.6 Mt Cu, and 7000 t Ag, are mainly hosted in Meso-Cenozoic mottled clastic rocks, and strictly controlled by two Cenozoic thrust systems developed in the western and eastern segments of the Lanping basin.To define the metallogenic history of the study area, we dated nine calcite samples associated with copper sulfides from the Jinman Cu deposit by the Sm–Nd method and five molybdenite samples from the Liancheng Cu–Mo deposit by the Re–Os method. The calcite Sm–Nd age for the Jinman deposit (58±5Ma) and the molybdenite Re–Os age for the Liancheng deposit (48±2Ma), together with previously published chronological data, demonstrate (1) the Cu–Ag mineralization in the western Lanping basin mainly occurred in three episodes (i.e., ∼56–54, 51–48, and 31–29Ma), corresponding to the main- and late-collisional stages of the Indo–Asian orogeny; and (2) the Pb–Zn–Ag (±Cu) mineralization in the eastern Lanping basin lacked precise and direct dating, however, the apatite fission track ages of several representative deposits (21±4Ma to 32±5Ma) may offer some constraints on the mineralization age.

Early Cenozoic Multiple Thrust in the Tibetan Plateau

Recently completed regional geological mapping at a scale of 1 : 250,000 or larger across all of the Tibetan Plateau coupled with deep seismic surveys reveals for the first time a comprehensive depiction of the major early Cenozoic thrust systems resulting from the northward subduction of the Indian Continental Plate. These systems define a series of overlapping north-dipping thrust sheets that thickened the Tibetan crust and lead to the rise of the plateau. The few south-dipping thrusts present apparently developed within a sheet when the back moved faster than the toe. Many of the thrusts are shown to extend to the middle-lower crustal depths by seismic data. The regional thrust systems are the Main Central, Renbu-Zedong, Gangdese, Central Gangdese, North Gangdese, Bangoin-Nujiang, Qiangtang, Hohxil, and South Kunlun Thrusts. The minimal southward displacements of the South Kunlun, Hohxil, South Qiangtang, and Central Gangdese Thrusts are estimated to be 30 km, 25 km, 150 km and 50 km, respectively. Deep thrusting began in the Himalaya-Tibetan region soon after India-Eurasia continental collision and led to crustal thickening and subsequent uplift of the Tibetan Plateau during Late Eocene-Early Miocene when the systems were mainly active. The major thrust systems ceased moving in Early Miocene and many were soon covered by lacustrine strata. This activity succeeded in the late Cenozoic to crustal extension and strike-slip movement in the central Tibetan Plateau. The revelation of the full array of the early Cenozoic thrust systems provides a much more complete understanding of the tectonic framework of the Tibetan Plateau.

Factors controlling selective abandonment and reactivation in thick-skin orogens: a case study in the Magdalena Valley, Colombia

Abstract The initial stages of tectonic inversion and the mechanisms of selective reactivation and abandonment of pre-existing normal faults during contractional orogenesis are explored in a partially buried Cenozoic thrust belt in the Andes of Colombia. A multidisciplinary approach that includes subsurface structural mapping, multimethod thermochronometry and detrital zircon U–Pb geochronology reveals the extent of a Palaeogene thrust belt buried underneath the Cenozoic strata of the Middle Magdalena Valley Basin. A less oblique orientation with respect to compressive stress and shorter traces in faults of the Middle Magdalena Valley Basin with respect to faults in the western part of the Eastern Cordillera, apparently acted as deformation inhibitors of the Magdalena faults in advanced Neogene stages of inversion. Protracted Cenozoic eastwards tilting of the Central Cordillera and the tectonic load from the uplifting Eastern Cordillera favoured the accumulation of a thick Cenozoic sedimentary sequence in an, at least episodically, closed basin. All the above-mentioned conditions helped to block deformation in the Magdalena Basin, favouring deformation to be taken up by structures in the western Eastern Cordillera. These relationships underscore the importance of buried structural records in elevated hinterland basins, in which the low-relief stratigraphic cover overlies a complex subsurface record, potentially including large magnitudes of deformation during early orogenesis. Supplementary material: Tables and figures on the laboratory methods for the thermochronometrical and geochronometrical analyses are available at http://www.geolsoc.org.uk/SUP18601 .

Cenozoic thrust system, basin evolution, and uplift of the Tanggula Range in the Tuotuohe region, central Tibet

New field mapping reveals a large Cenozoic thrust system in the Tanggula Range and Tuotuohe region, central Tibet. The thrust system is parallel to the Tanggula Range, and it is termed the Tanggula thrust system (TTS). Three thrust belts can be identified in this thrust system. From south to north, they are the Geraddong-Esuima thrust belt (GEB), the Quemocuo-Gaina fold-thrust belt (QGB), and the Baqing-Wulwl thrust belt (BWLB). The deformation styles can be classified as high-angle imbricate thrust, fold thrust and lower-angle imbricate thrust, respectively. The initiation of sedimentation in the Tuotuohe Basin and stratigraphic unconformities indicate that the thrust system was developed during 52–23Ma. Sequential filling patterns, sedimentary facies and paleocurrents indicate that the Tuotuohe Basin was a foreland basin in front of the TTS. Restored structural sections suggest 89km (60%) of N–S shortening in the TTS and 96km (48%) shortening in the Tuotuohe Basin. The thrust system has not only influenced the development of this Cenozoic basin, but also resulted in the rapid uplift of the Tanggula Range during the Eocene and Oligocene.

Formation of the Dongmozhazhua Pb–Zn Deposit in the Thrust‐Fold Setting of the Tibetan Plateau, China: Evidence from Fluid Inclusion and Stable Isotope Data

AbstractThe Dongmozhazhua deposit, the largest Pb–Zn deposit in south Qinghai, China, is stratabound, carbonate‐hosted and associated with epigenetic dolomitization and silicification of Lower–Middle Permian—Upper Triassic limestones in the hanging walls of a Cenozoic thrust fault system. The mineralization is localized in a Cenozoic thrust‐folded belt along the northeastern edge of the Tibetan plateau, which was formed due to the India–Asia plate collision during the early Tertiary. The deposit comprises 16 orebodies with variable thicknesses (1.5–26.3 m) and lengths (160–1820 m). The ores occur as dissemination, vein, and breccia cement. The main sulfide assemblage is sphalerite + galena + pyrite + marcasite ± chalcopyrite ± tetrahedrite, and gangue minerals consist mainly of calcite, dolomite, barite, and quartz. Samples of pre‐ to post‐ore stages calcite yielded δ13C and δ18O values that are, respectively, similar to and lower than those yielded by the host limestones, suggesting that the calcite formed from fluids derived from carbonate dissolution. Fluid inclusions in calcite and sphalerite in the polymetallic sulfidization stage mostly comprise liquid and gas phases at room temperature, with moderate homogenization temperatures (100–140°C) and high salinities (21–28 wt% NaCl eq.). Micro‐thermometric fluid inclusion data point to polysaline brines as ore‐forming fluids. The δD and δ18O values of ore fluids, cation compositions of fluid inclusions, and geological information suggest two main possible fluid sources, namely basinal brines and evaporated seawater. The fluid inclusion data and regional geology suggest that basinal brines derived from Tertiary basins located southeast of the Dongmozhazhua deposit migrated along deep detachment zones of the regional thrust system, leached substantial base metals from country rocks, and finally ascended along thrust faults at Dongmozhazhua. There, the base‐metal‐rich basinal brines mixed with bacterially‐reduced H2S‐bearing fluids derived from evaporated seawater preserved in the Permo–Triassic carbonate strata. The mixing of the two fluids resulted in Pb–Zn mineralization. The Dongmozhazhua Pb–Zn deposit has many characteristics that are similar to MVT Pb–Zn deposits worldwide.