Lajishankou Ophiolite Complex: Implications for Paleozoic Multiple Accretionary and Collisional Events in the South Qilian Belt

The Lajishan ophiolite complex in the Qilian Orogen is one of several ophiolites situated between the Qaidam and North China blocks that record episodic closure of the Proto-Tethyan Ocean. Detailed field relations and geochemical and geochronological studies are critical to unraveling the tectonic processes responsible for an extensive period of intraoceanic subduction that produced juvenile ophiolite/island arc terranes, which were obducted onto continental margins during ocean closure. The Lajishankou ophiolite complex crops out along the northern margin of the South Qilian belt and was thrust over a Neoproterozoic-Ordovician passive margin sequence that was deposited upon the Proterozoic Central Qilian block. The mafic rocks in Lajishankou ophiolite complex are the most abundant slices and can be categorized into three distinct groups based on petrological, geochemical, and geochronological characteristics: massive island arc tholeiites, 509-Ma back-arc dolerite dykes, and 491-Ma pillow basaltic and dolerite slices that are of seamount origin in a back-arc basin. These results, together with spatial relationships, indicate that the Cambrian island arc rocks, ophiolite complex, and accretionary complex developed between 530 and 480 Ma as a single, intraoceanic arc-basin system as a result of south directed subduction of the Proto-Tethyan Ocean prior to Early Ordovician obduction of this system onto the Central Qilian block. Final continental amalgamation involved continental collision of the Central Qilian block with the Qaidam block during the Late Ordovician. This model solves the long-lasting discussion on the emplacement of the Lajishan ophiolite and contributes to an improved understanding of multiple accretionary and collisional processes in the Qilian Orogen

Loss-based structures and frequency dependencies of giant magnetostrictive materials for rotary ultrasonic machining applications

This paper investigates rotating magnetostrictive ultrasonic transducers (RMUT) with eddy current losses to enhance the stability requirements of high-power ultrasonic vibration processing in defense and military industries. A nonlinear amplitude prediction model for RMUT has been developed by integrating the ultrasonic excitation system with magnetostriction and magnetization phenomena based on the substructure system's ultrasonic vibration transmission characteristics and laws. By delving into the mechanism of energy conversion and dynamic characteristics of eddy current loss in ultrasonic vibration systems, the influence of eddy losses on RMUT's output amplitude and frequency stability can be unveiled. Simulations and experiments have been conducted to verify the nonlinear prediction model with a given loss structure. Verifications show that the mechanical quality factor of RMUT can be adjusted to achieve strength-toughness matching of vibration energy in terms of internal structure by modifying the heat loss of the excitation system. Especially, radially slit treatments (RS) led to a higher mechanical quality factor and larger vibration amplitude, while radially sliced treatments (RSE) resulted in a higher energy transfer characteristic. Compared to the RSE structure, RS exhibits a 218% decrease in stability and a 47.1% increase in amplitude

Simulation and experimental study of ultrasonic vibration-assisted milling of GH4169 high-temperature alloy

GH4169 high-temperature alloy is widely used in aerospace and other fields because of its excellent fatigue, radiation, oxidation, and corrosion resistance. However, milling forces, high temperatures, and machining hardening can occur during milling processing. To explore the machining characteristics of GH4169 high-temperature alloy, an ultrasonic vibration-assisted milling model was established to study the effect of ultrasonic milling parameters on the milling process. The simulation results show that: the increase of ultrasonic amplitude can effectively reduce the machining stress, improve the chip-breaking effect and reduce the milling force; with the rise of milling speed, the separation characteristic is weakened, which is not conducive to chip breaking; the increase of radial cutting width will increase the machining stress and improve the milling force. Finally, by comparing the actual machining and simulation results, the error is within 10%, which verifies the feasibility of the simulation study and provides guidance for ultrasonic milling of GH4169 high-temperature alloy

Paleozoic HP Granulite-facies Metamorphism and Anatexis in the Dulan Area of the North Qaidam UHP Terrane, Western China: Constraints from Petrology, Zircon U–Pb and Amphibole Ar-Ar Geochronology

HP mafic and felsic adakitic granulite bodies in the Dulan area of the North Qaidam ultrahigh-pressure (UHP) terrane record high-pressure (HP) granulite-facies metamorphism and anatexis and provide temporal and tectonic constraints on deep subduction of continental crust and its subsequent exhumation. Mafic HP granulite components dominate the main outcrop and preserve features diagnostic of anatexis and locally may be described as migmatite. The HP mafic granulites comprise garnet, clinopyroxene, plagioclase and quartz. The felsic granulite (leucosome) is mainly composed of K-feldspar + plagioclase + quartz + kyanite + garnet. Detailed zircon U–Pb and amphibole Ar–Ar geochronology, combined with trace element geochemistry, indicate peak metamorphism for the mafic HP granulite at 434 ± 3 to 435 ± 3 Ma and peak metamorphism and partial melting for the felsic HP granulite at 433 ± 5 to 438 ± 4 Ma, which overlaps the ages of UHP metamorphism for adjacent eclogite (430–446 Ma). 40Ar/39Ar amphibole ages of 423 to 432 Ma represent amphibolite-facies retrograde metamorphism and indicate rapid cooling during exhumation of the HP granulite bodies. Our geochronological data, combined with field relationships, petrology and geochemistry suggest that HP granulite-facies metamorphism and the partial melting that produced adakitic melts represent the same tectonic event. In this case, the felsic HP granulites (leucosome) formed from an adakitic melt derived from partial melting of mafic HP granulite in the overriding plate in a relatively higher geothermal gradient (15–18 °C/km), leaving garnet-cumulate and/or meta-ultramafic (mainly garnet pyroxenite) as the residual component. In contrast, the nearby UHP eclogite is thought to have formed in the subducted plate in a relatively lower geothermal gradient (6–10 °C/km). Penecontemporaneous metamorphic ages but different geothermal gradients between HP granulites and related UHP eclogite define a possible paired metamorphic belt generated in a subduction–collision setting associated with the North Qaidam continental collisional orogeny during the Late Ordovician–Early Silurian

Two contrasting accretion v. collision orogenies: insights from Early Paleozoic polyphase metamorphism in the Altun–Qilian–North Qaidam orogenic system, NW China

The Altun–Qilian–North Qaidam (AQQ) orogenic system in northern Tibet is considered to be the northernmost orogenic collage of the Prototethyan domain. It is regarded as resulting from collisions between various continental terranes derived from the northern margin of Gondwana, although the AQQ orogenic system also includes abundant ophiolites, arc magmatic rocks and subduction–accretion complexes. Some researchers regard the orogenic system of north Tibet as a typical accretionary orogen built by the development of an evolving arc–accretion complex growing southwards along the margin of the Tarim and North China cratons during the Paleozoic. We propose, based on both published data and our new data, that two distinct accretion and collision orogenies developed in the AQQ during the early Paleozoic. The diagnostic marks are HP–LT metamorphic rocks in the North Altun–North Qilian Mountains and UHP metamorphic rocks in the South Altun–North Qaidam Mountains. A review of metamorphic, geochronological, geochemical and structural data indicates that the North Altun–North Qilian HP–LT metamorphic belt is related to early Paleozoic subduction–accretion and, together with ophiolite mélanges and arc metamorphic–magmatic complexes, forms an early Paleozoic accretionary orogen. By contrast, the South Altun–North Qaidam UHP metamorphic belt is associated with continental subduction and collision, accompanied by Barrovian-type metamorphic overprinting and collision-related magmatism, reflecting an early Paleozoic collisional orogeny

Physiological functions of IPCs derived from BMMSCs.

<p>A. The expression of C-peptide from differentiated IPCs was analyzed with FCM. (a. BMMSCs were cultured in the growth medium as negative controls. b. The expression of C-peptide from traditional group was analyzed. c.The expression of IPCs from pancreatic extract group was analyzed. d. The expression of IPCs from Mixed group was analyzed. The respective immunoglobulin isotypes were used as isotype controls). B. Differentiated IPCs release insulin in response to glucose. Glucose-induced insulin release data correspond to the amount of insulin secreted for 1 h after 5.5mM and 25mM glucose stimulation. Data presented are means ± SD of the triplicate wells of the same IPCs culture. C. IPCs showed secretary vesicles with a dense core and a peripheral, electron-lucent halo, and mitotic activity was detected by conventional electron microscopy (Scale bar: 500 nm).</p