In order to better constrain the evolution of the Tethyan orogenic system, we conducted an integrated investigation involving U-Pb dating of igneous and detrital zircon, geochemical analysis of ...igneous rocks, compositional analysis of sedimentary strata, and a synthesis of existing work across the Qilian Shan, Qaidam Basin, and the Eastern Kunlun Range of central and northern Tibet. This effort reveals five stages of arc magmatism at 1005-910 Ma, 790-720 Ma, 580-500 Ma, 490-375 Ma, and 290-195 Ma, respectively. Arc activities were interrupted by repeated continent-continent collision followed by ocean opening along the older suture zones first created in the Neoproterozoic. This suggests that Wilson cycles have played a controlling role in constructing the southern Asian continent. The magmatic history and regional geologic constraints allow us to construct a coherent tectonic model that has the following key features. (1) The linked South Qilian suture in the west and North Qinling suture in the east formed the northern boundary of the coherent Kunlun-Qaidam-North Qinling Terrane in the early Paleozoic. (2) The Songpan-Ganzi Terrane has been the western part of the Yangtze craton since the Neoproterozoic. (3) Development of the wide (>700 km) Permian-Triassic arc across the Kunlun-Qaidam Terrane was induced by flat subduction and rapid slab rollback, which also caused extreme extension of the Songpan-Ganzi Terrane. (4) The formation of the Anymaqen-Kunlun-Muztagh Ocean (= the Neo-Kunlun Ocean in this study) was created within Laurasia rather than being a preexisting ocean between Gondwana and Laurasia as postulated by most early studies.
Our understanding of the assembly history of Asia depends critically on the tectonic relationships between its major cratons, including Siberia, North China, South China, and Tarim. The intervening ...microcontinents between these cratons can provide insight into the paleogeographic and paleotectonic relationships of the cratons, but there is currently a general lack of knowledge regarding the basement geology of these microcontinents. Here we present results from systematic geologic mapping, U-Pb zircon dating, whole-rock geochemical analysis, and synthesis of existing data to establish the Proterozoic to early Paleozoic evolution of the central Qilian basement to the south of the North China craton in northwest China. Our results indicate that the region underwent three major periods of magmatic activity at 960-880, 877-710, and 550-375 Ma. Our geochemical analysis suggests that the ca. 900 Ma plutons were generated during arc magmatism and/or syncollisional crustal melting, whereas the ca. 820 Ma plutons are A-type granitoids, which are typically associated with extensional tectonism. Igneous zircons from a high- and ultrahigh-pressure eclogite in the north-central Qilian Shan have a U-Pb age of ca. 916 Ma, whereas dating of the recrystallized rims suggests that eclogite facies metamorphism occurred at ca. 485 Ma. Our detrital zircon geochronology also indicates that a widespread metasedimentary unit in the region was deposited between ca. 1200 and ca. 960 Ma, prior to the onset of a rift-drift event at ca. 750 Ma. Based on regional geologic constraints and the magmatic history, we propose the following tectonic history: (1) the paleo-Qilian Ocean bound the combined North Tarim-North China craton to the south (present-day coordinates) in the Mesoproterozoic; (2) the paleo-Qilian Ocean closed between 900 and 820 Ma following the collision of North Tarim-North China craton and the South Tarim-Qaidam-Kunlun continent; (3) the younger Qilian Ocean opened at ca. 775 Ma along the previous suture trace of the paleo-Qilian Ocean as a marginal sea within southern Laurasia; and (4) this ocean closed by ca. 445-440 Ma as a result of collision between the Tarim-North China cratons and the Qaidam-Kunlun continent along a south-dipping subduction system.
Abundant Early Paleozoic magmatism is preserved in northern Tibet and has important implications for continental crustal growth in response to continental collisions. To better constrain the ...evolution of the northern margin of the Tibetan Plateau and the resulting closure of the North Qilian Ocean, we conducted an integrated investigation involving U-Th-Pb zircon geochronology, whole-rock geochemistry, and syntheses of existing data sets across the North Qilian orogenic belt. Zircon U-Pb dating indicates that the Early Paleozoic intrusive rocks in the study area can be divided into two stages: 460-480 Ma and 440 Ma. The 478-480 Ma meta gabbro-diorite samples belong to the calc-alkaline series and show a fractional crystallization trend in the Harker diagrams. These samples have relatively high La/Nb (2.08-3.26) and low La/Ba (0.05-0.06) ratios, indicating a subduction-modified continental-lithospheric mantle source. The 460-480 Ma meta-granite samples are I-type and classified as high-K calc-alkaline series. Both the meta gabbro-diorite and meta-granite samples are characterized by negative Nb, Ta, and Ti anomalies and enriched LILEs, and showing arc signatures that may be related to the southward subduction of the North Qilian oceanic crust. The 441 Ma hornblende syenite samples have high contents of alkalis (K2O + Na2O = 7.80%-12.07%) and belong to the alkaline series, suggesting an extensional geological setting. The 440 Ma syenogranite samples are classified as high Ba-Sr granites and belong to the shoshonitic series. The syenogranite samples were most likely generated by partial melting of lithospheric mantle that had been metasomatized by slab-derived fluids, and mixed by the crust derived granitic magmas during the ascent of the magma. Both the hornblende syenite (441 Ma) and the syenogranite (440 Ma) samples were emplaced in a post-collisional tectonic setting associated with the closure process of the North Qilian Ocean.
The Eastern Kunlun Range in north Tibet, located along the northern margin of the eastern Tethyan orogenic system, records evidence for continental break‐up and ocean development in the ...Neoproterozoic, Paleozoic‐early Mesozoic subduction and continental collision, Mesozoic intracontinental extension, and Cenozoic contractional deformation. The Kunlun region is marked by active left‐lateral strike‐slip deformation of Kunlun fault system, one of the major intracontinental strike‐slip faults in Tibet that developed in response India‐Asia. To better constrain the tectonic evolution of the Eastern Kunlun Range and the closure of the various Kunlun oceans, we conducted detailed investigation integrating new geologic mapping, geochronology, and whole‐rock geochemistry with a synthesis of existing datasets across north Tibet. The Eastern Kunlun Range experienced three major deformation events in the Neoproterozoic, early Paleozoic, and Late Paleozoic‐early Mesozoic, which were associated with collision of the Proto‐, Paleo‐, and Neo‐Kunlun arcs, respectively. Our new detrital zircon analyses from Mesoproterozoic‐Cenozoic strata constrain stratigraphic age and sediment provenance and highlight the importance of three periods of arc activity. Our stratigraphic synthesis, including new field observations, provides new insights into connections between sediment dispersal and changes in tectonism and paleogeography. Miocene‐to‐present strike‐slip activity on the Kunlun fault and the associated strain pattern can be explained by clockwise rotation of the Kunlun fault and its wall rock as a bookshelf‐fault system, which has been proposed for northern Tibet as a result of distributed north‐south right‐lateral shear. The development of this fault system was facilitated by the presence of a Triassic suture that provided a preexisting weakness.
Plain Language Summary
The Eastern Kunlun Range in northern Tibet is located within the interior high‐elevation Tibetan Plateau. Its current morphology and geologic structure reflect Cenozoic faulting related to India‐Asia convergence since the early Cenozoic. Active deformation across the Eastern Kunlun Range reactivates complex older geologic relationships that record prior oceanic subduction and continental collision events. We present field and analytical observations from key sites along the Kunlun and Xiangride Rivers across the Eastern Kunlun Range to establish the pre‐Cenozoic geologic history of this region. Our dating of arc‐related intrusions and sedimentary rocks reveals that three distinct ocean‐closure‐related collisions occurred here over the last billion years. This repeated focused deformation has been reactived most recently in the Cenozoic to for the left‐slip Kunlun fault.
Key Points
The Eastern Kunlun Range, north Tibet, experienced three arc‐collision events in the Proterozoic through Mesozoic
New detrital zircon data from Mesoproterozoic‐Cenozoic better constrain their stratigraphic age and provenance in the Kunlun region
This site of repeated continental collision was reactivated by Cenozoic deformation during India‐Asia convergence
Zircon U–Pb dating and whole-rock geochemical analysis have been performed on Late Jurassic – Early Cretaceous intrusive rocks of the Ulanhot area, NE China, with the aim of constraining the tectonic ...evolution of the central and southern Da Xingan Range. Zircon U–Pb dating indicates that Late Jurassic – Early Cretaceous magmatic events experienced four stages at: c. 155 Ma; c. 144 Ma; 135–130 Ma; and c. 126 Ma. The c. 155 Ma magmatic event consists of quartz diorite and granite-porphyryp with the geochemical characteristic of high Sr and Sr/Y or high A/CNK (1.38), implying the primary magma was derived from partial melting of a thickened lower crust which induced the closure of the Mongol–Okhotsk Ocean. The c. 144 Ma magmatic event consists of quartz monzodiorite with the geochemical characteristics of alkaline series, and indicates the delamination of a thickened crust. The 135–130 Ma magmatic event consists of syenogranite and granite-porphyry with characteristics of both I-type and A-type granites, which induced both the subduction of the Palaeo-Pacific oceanic plate and the post-orogenic extension of the Mongol–Okhotsk Orogenic Belt. The c. 126 Ma magmatic event consisted of highly fractionated I-type biotite granite and alkaline series gabbro, marking the end of the Mongol–Okhotsk Orogen, and implying that the study area was controlled by the circum-Pacific tectonic system during this stage.
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•Gold mineralization in the Daxiyingzi ore distract is associated with quartz veins hosted by volcanic rocks.•Fluid inclusion and stable isotope data suggest magmatic origin of the ...mineralizing fluids.•The mineralization is classified as epithermal-mesothermal gold deposit.•The gold mineralization took place during 149–158 Ma.
The Daxiyingzi gold deposit is located in the Chifeng-Chaoyang gold ore concentration area, toward the northern margin of the North China Craton. The ore bodies of the Daxiyingzi gold deposit are mainly hosted in the Manitu volcanic rocks, which are intruded on by the Mesozoic granite porphyry. The ore formation consists of four main stages: magnetite-hematite (Ⅰ), quartz-metal sulfide (II), gold-bearing polymetallic sulfide-quartz (III), and pyrite-carbonate (IV). The homogenization temperatures of the fluid inclusion range from 189.5 to 310.0 °C, while the salinity ranges from 0.53 to 13.55 wt% NaCl equiv., corresponding to entrapment depths of 0.1–1.0 km below the paleowater table. The quartz from the stage II and III veins from Daxiyingzi have δDV-SMOW values range from −62.1 to −82.8‰, while the δ18OH2O values range from 0.46 to 1.26‰. The samples for galena, sphalerite, and pyrite from the Daxiyingzi veins have approximate S isotopic compositions, with δ34S values ranging from 3.5 to 3.9‰, 3.9 to 4.2‰ and 3.5 to 5.0‰, respectively. The S-H-O isotopic data suggest that the ore-forming fluid had originated from magmatic sources. The zircon U-Pb ages of the volcanic rocks and granite porphyry are ca. 157–158 and 149 Ma, respectively, which suggests that the gold mineralization took place from 149 to 158 Ma. The volcanic rocks are belong to the high-K calc-alkaline to alkaline series, while the granite porphyry is belongs to A-type granite, which suggests an extensional tectonic setting. Our new data indicates that the Daxiyingzi gold deposit is a typical epithermal-mesothermal deposit formed by a Late Jurassic magmatic-hydrothermal system.
One of the ophiolites that record the Proto-Tethys Ocean’s episodic closure is the Munabulake ophiolitic mélange, which is situated in the middle of the Kunlun–Qaidam and Altun–Qilian blocks. ...Detailed field mapping revealed that the Munabulake ophiolitic mélange comprises local (ultramafic rocks, basalts, andesites, gabbros, diorites, and plagiogranites) and exotic (marble, gneiss, schist, and amphibolite) blocks, many of which are in the schist matrix (Qimantage Group). Based on geochronological, geochemical, and petrological observations, the mafic rocks in the Munabulake ophiolitic mélange can be categorized into three categories: 498-Ma OIB-like gabbros, 468-Ma Hawaiian alkaline basalt-like dolerite and pillow basaltic slices, and 428 Ma massive SSZ-like ultramafic rocks. The 501–452 Ma I-type granites exhibit arc affinities due to the oceanic crust subduction. These findings, along with spatial relationships, suggest that the Early Paleozoic ophiolite complex, island arc rocks, and accretionary complex generated as an intra-oceanic arc system as a result of obduction of the south Altun Ocean’s onto the Central Altun block within a north-directed subduction event. A dextral strike–slip was evident throughout the Early Paleozoic oceanic crust subduction based on the whole set of planar and linear structural data, and the subduction polarity was likely to the north. According to the ophiolitic mélange’s youngest rocks and the existence of 413 Ma granite dykes that are widely exposed in the Munabulake ophiolitic mélange, the Munabulake ophiolitic mélange was most likely emplaced during the Middle Silurian. This Munabulake ophiolitic mélange is similar in age and petrochemical characteristics to the other ophiolites in the South Altun subduction–collision belt, indicating that the Manabulak ophiolite mélange is a westward extension of the Apa–Mangya subduction–collision belt, which formed during the northward subduction of the South Altun Ocean slab during the Early Paleozoic. Thus, the final closing time of the South Altun Ocean is between 413 and 428 Ma.
Abstract
Background
This study aimed to determine the predictive factors for post-conization of residual disease in subsequent hysterectomy for cervical intraepithelial neoplasia grade 2 or 3.
...Methods
This retrospective study included 267 patients with histologically confirmed cervical intraepithelial neoplasia grade 2 or 3 who underwent hysterectomy within 7 months after conization. Clinical data (e.g., age, menopausal status, gravidity, parity, type of transformation zone, conization method) as well as pathological data pertaining to conization and hysterectomy were collected from medical records. A logistic regression model was used to analyze the relationship between the variables and risk of residual lesions in hysterectomy samples.
Results
Overall, 70 (26.2%) patients had residual lesions in their hysterectomy specimens. Univariate analyses revealed that age ≥ 50 years (
p
=0.019), endocervical gland involvement(
p
=0.013), positive margin(
p
< 0.001), and involvement of 3–4 quadrants(
p
< 0.001) were risk factors for residual lesions. Conversely, postmenopausal status, gravidity ≥ 3, parity ≥ 2, loop electrosurgical excision procedure, and type III transformation zone were not risk factors for residual lesions. A positive margin(
p
< 0.001) and multiple-quadrant involvement(
p
< 0.001) were identified as independent risk factors for residual lesions on multivariate analysis.
Conclusions
Multiple-quadrant involvement and a positive cone margin were reliable predictive factors for residual disease. Total hysterectomy or repeated cervical conization should be considered for patients with these two risk factors. The identification of high-risk patients with extensive lesions by colposcopic examination before conization is indispensable, as it will enable surgeons to perform conization with consideration of risk factors and possibly improve the approach used for the excisional procedure. For high-risk patients, colposcope-guided cold-knife conization is preferred when resources permit.
The growth of the Tibetan Plateau resulted primarily from Cenozoic India-Asia collision and continued convergence, and thus the deformation timing and geomorphic evolution of northern Tibet are ...critical to understanding the dynamics of orogenic plateau growth. Although previous studies have suggested that the Altyn Tagh Shan and the Eastern Kunlun Range of northern Tibet have experienced differential faulting and exhumation history, our knowledge of the temporal and spatial distribution of the growth of the northwestern Tibetan Plateau is still lacking. In this study, we integrate new geologic mapping, low-temperature themochronometry (18 apatite-fission track ages), and Optically Stimulated Luminescence (OSL) dating to provide constraints on the Cenozoic cooling history of northwestern Tibet and late Quaternary fluvial terrace development. We focus on where Altyn Tagh Shan structures are juxtaposed against Eastern Kunlun Range structures. New fission-track cooling ages from one traverse along the Aksu River yielded three cooling age domains: Paleocene, Miocene, and early Pliocene. With this new knowledge of ~12–10 Ma initiation of Jianxiashan thrusting and exhumation, we suggest a refined N-S shortening rate of this thrust system of 2.0–2.4 mm/yr and strain rates of 8–9 × 10−16 s−1. Thermal history modeling suggests that the study area experienced two broad events, including slow cooling through the AFT PAZ since the early Eocene and rapid cooling during the late Miocene. Our OSL dating results from the Aksu drainage reflect two separate processes of aggradation and incision that occurred during the late Pleistocene and Holocene, respectively, which are interpreted to result from long-term forcing of incision by a constant rate of tectonic uplift modulated by late Quaternary climatic variations. We interpret that this incision occurred at a rate of ~1 mm/yr, which is faster than exhumation rates inferred from the AFT data (0.3–0.5 mm/yr). These Quaternary exhumation rates may reflect faster recent exhumation or uplift associated with the proximal Altyn Tagh fault. In accordance with previous studies, we present a refined Cenozoic tectonic model for the evolution history of northern Tibet. The deformation pattern of northern Tibet results from clockwise rotation of preexisting weaknesses and transpressional deformation along the Kunlun fault and the Haiyuan fault.
•AFT modeling shows slow cooling from the early Eocene and late Miocene rapid cooling.•A refined N-S shortening rates on Jianxiashan thrust system is 2.0–2.4 mm/yr.•Incision occurs at a rate of ~1 mm/yr that is double of exhumation rate inferred from AFT.
ASTER thermal infrared (TIR) data are widely used to detect mafic–ultramafic rock and quartz-rich rock, and several rock indices have been proposed based on emissivity features. However, ASTER TIR ...bands of radiance data correlate highly with each other, which indicates that the independent information derived from different bands may be limited, what's more, ASTER TIR radiance-at-sensor data contain atmospheric effect and temperature information, thus interfering with the availability of these previously proposed indices. In this study, we aim to explain the correlation using a linear approximation of the Planck function and deduce a linear equation that represents the relationship of the radiance between two TIR bands. Theoretical difference indices were deduced based on the linear equation and regression residual characteristics for any two ASTER TIR radiance bands. The study area is located in Qinghai Province, China, and belongs to the Qinghai–Tibet Plateau, where the average elevation is approximately 4200m. A scatter plot of radiance derived from the ASTER image that overlaps the study area indicates that mafic–ultramafic rock and quartz-rich rock can be distinguished from other surface objects well. Two mafic–ultramafic rock indices (MI1=b13−0.9147∗b10−1.4366 and MI2=b13−0.8945∗b11−1.2404) and two quartz-rich rock indices (QI1=b13−0.9261∗b12−1.4623 and QI2=b14−0.844∗b12−1.8971) were proposed; they satisfactorily map these rock units. The atmospheric effect on the indices is weak in arid or high-elevation region, so it will not interfere with the indices obviously in these regions. One-way variance analysis was performed to discuss the stability of the indices with respect to temperature. The mafic–ultramafic rock indices are found to be independent of temperature, whereas the values of quartz-rich rock indices increase with the rising of temperature. We thus conclude that the quartz-rich rock indices are suitable for the high-elevation region only, while the mafic–ultramafic rock indices may be capable of detecting these rocks in regions with different natural conditions.
•The relation of radiances between two ASTER TIR radiance bands was deduced.•Two categories of rock indices were proposed based on the linear equation.•The availability and universality of the indices were discussed.
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