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Post-collisional granites are generally generated by partial melting of continental crust during orogenic extension. The occurrence of normal calc-alkaline granites following adakitic granites in a collisional orogen is frequently supposed as a sign of tectonic regime transition from compression to extension, which has been debated yet. In this paper, we present a comprehensive study of zircon U–Pb ages, Hf–O isotopes, as well as whole-rock major and trace elements and Sr–Nd isotopes, for Tongbai and Jigongshan post-collisional granitic plutons in the Tongbai orogen. Zircon U–Pb dating yields intrusion ages of ca. 140 and 135 Ma for the Tongbai and Jigongshan plutons, respectively, suggesting they are post-collisional granites. These granites are high-K calc-alkaline series, metaluminous to weakly peraluminous with A/CNK ratios of 0.85–1.08. The Tongbai gneissic granites are normal calc-alkaline granite, having variable SiO2 (61.93–76.74 wt%) and Sr/Y (2.9–38.9) and (La/Yb)N (1.7–30.1) ratios with variably negative Eu anomalies (0.41–0.92). They have relatively high initial Sr isotope ratios of 0.707571 to 0.710317, and low eNd(t) (− 15.74 to − 11.09) and eHf(t) (− 17.6 to − 16.9) values. Their Nd and Hf model ages range from 2.2 to 1.8 Ga and 2.3 to 2.2 Ga. On the contrary, the Jigongshan granites show higher SiO2 (66.56–72.11 wt%) and Sr/Y (30.1–182.0) and (La/Yb)N (27.4–91.4) ratios with insignificant Eu anomalies (0.73–1.00), belonging to adakitic granite. They have Isr = 0.707843–0.708366, eNd(t) = − 19.83 to − 17.59, and eHf(t) = − 26.0 to − 23.5. Their Nd and Hf model ages vary from ca. 2.5 to 2.4 Ga and ca. 2.8 to 2.6 Ga. The Tongbai and Jigongshan granites are characterized by mantle-like zircon δ18O values (5.17–5.46‰). These geochemical features suggest that the Tongbai and Jigongshan granites were derived from partial melting of Paleoproterozoic and Archean continental crust, respectively. Fractional crystallization affected the geochemical compositions of the Tongbai gneissic granites, while the compositions of the Jigongshan granites were mainly controlled by partial melting. The adakitic signatures of the Jigongshan granites were either inherited from their source or ascribed to more garnet in their residues. The voluminous post-collisional granites might form by the collapse of the thickened Tongbai orogenic root. The normal Tongbai gneissic granites occurred slightly earlier than the Jigongshan adakitic granites in the Tongbai orogen, suggesting that it is not a mandate to sign the tectonic transition from adakitic to normal calc-alkaline granites in post-collisional settings. Therefore, this study provides another example supporting the burst of voluminous post-collisional granites with different compositions as a consequence of the collapse of the thickened orogenic roots of collisional orogens.

S-type peraluminous granite can crop out in various tectonic settings. The Paleozoic Piaochi granitic intrusion is a large S-type peraluminous intrusion located in the North Qinling orogen, and has important implication for its tectonic evolution. Though intensively studied, the age and tectonic setting of this intrusion are still controversial. In this study, we carried out an integrated study of zircon U–Pb age, major and trace elements, and Sr–Nd–Hf–O isotope compositions for the Piaochi intrusion, with aims to constrain its petrogenesis and tectonic significance. SIMS and LA-ICPMS U–Pb zircon data obtained from magmatic zircons indicate that the Piaochi intrusion was emplaced at 473 ± 4 Ma, and contained ca. 490 Ma inherited zircons. The granite samples from the Piaochi intrusion show typical S-type characteristics, such as the relatively moderate aluminum saturation index (1.00–1.08), low zirconium saturation temperatures, occurrences of muscovite, and high zircon δ 18 O values (8.70 to 9.54‰). The relatively low Sm/Nd (0.13–0.20) and FeO T /MgO ratios (2.21–3.9) suggest that the granites are unfractionated. The geochemical compositions reveal that they were derived from partial melting of a clay-poor, but plagioclase- and biotite-rich psammitic source, similar to metasedimentary rocks outcropping in the North Qinling unit. Moreover, the Piaochi granites are moderately depleted in Eu and heavy rare earth elements, and have relatively high (La/Yb) N values (22.8–56.8), implying a high-pressure, plagioclase-poor and garnet-rich residual assemblage. The Piaochi granites have high and variable initial 87 Sr/ 86 Sr ratios (0.72167–0.72511) and low e Nd (t) (from − 10.23 to − 8.71) values with two-stage Nd model ages (T DM2 ) of 1.91–2.03 Ga, which are comparable with those of supracrustal materials in the North Qinling unit. In addition, our results show that the ca. 470 Ma magmatic zircons display a narrow e Hf (t) array within those of the inherited cores. These imply that the Piaochi granites inherited their isotopic characteristics wholly from their sources, and the Hf isotopes might have been differently homogenized during the partial melting. Our new zircon U–Pb ages indicate that the Piaochi granites were emplaced after the climax of the UHP metamorphism, coeval with later retrograde metamorphism during exhumation. Therefore, we suggest that the formation of the early Paleozoic Piaochi intrusion was triggered by the exhumation of the UHP rocks.

Potassium (K)-rich mafic rocks are viewed as being derived from partial melting of an enriched mantle source, but it is controversial about which processes cause the mantle enrichment. The Fushui intrusive complex is the largest early Paleozoic K-rich intrusive complex in the eastern Qinling orogen. Therefore, detailed studies on the Fushui complex can contribute not only to understanding of the petrogenesis of K-rich mafic rocks, but also to unraveling the Paleozoic evolution of the Qinling orogen. In this study, we provide an integrated investigation of in situ zircon U–Pb dating and Hf–O isotopes, in combination with whole-rock major and trace elements, as well as Sr–Nd–Hf isotopes, for the Fushui intrusive complex. In situ zircon secondary ion mass spectrometry (SIMS) / laser ablation induction coupled plasma mass spectrometry (LA-ICPMS) U–Pb dating reveals that different rock types of the Fushui complex have identical formation ages of 488–484 Ma. The Fushui complex belongs to the shoshonitic series, and is characterized by extreme large ion lithophile element (LILE, e.g., Ba, U, Th and Sr) and Pb enrichment and depletion of high field-strength elements (HFSEs, e.g. Nb, Ta, Zr, Hf, P and Ti). It shows high initial Sr isotopic ratios (0.7100–0.7151), negative whole-rock e Nd(t) (−3.97 to −5.68) and negative to slight positive whole-rock (−2.24 to 2.38) and zircon (−2.85 to 0.34) e Hf(t) values, as well as high zircon δ18O values (6.86 ± 0.13 ‰). The Hf–Nd isotopic systems are decoupled with positive Δe Hf values (3.85–5.37). These geochemical features indicate that the mantle source has incorporated subducted zircon–barren oceanic sediments. A simple two-end-members mixing model constrains the amount of subducted sediments in the Fushui mantle source to 5–8 %. The Fushui complex originated from 1 to 6 % equilibrium melting of a phlogopite-bearing garnet lherzolite by non-modal melting. As shoshonitic magmas have been discovered in modern nascent arcs, we suggest that the generation of the Fushui complex was induced by the subduction of the Paleotethyan Ocean, when it jumped from the northern to the southern boundary of the North Qinling microcontinent.

The tectonic properties of the Erlangping unit and the subduction polarity of oceanic basins in the North Qinling–Tongbai orogen have been the focus of debate for more than twenty years. The resolution of these controversies hinges on the refined constraints on the location and nature of subduction-related magmatism. In this contribution, we provide a combined study of zircon U–Pb ages, major and trace element geochemistry, and Sr–Nd–Hf isotope compositions of gabbroic rocks from the Erlangping unit in the Tongbai orogen. U–Pb dating of zircons from two gabbroic diorite samples yielded two weighted mean ages of 443 ± 3 and 440 ± 4 Ma. The Erlangping gabbroic rocks are tholeiitic in composition with variable MgO (4.48–8.17%), and low K 2 O (0.25–1.01%) and TiO 2 (0.60–1.79%) contents. They are characterized by enrichment of LILEs, depletion of HFSEs, and highly positive whole-rock e Nd (t) (3.76–5.68) and zircon e Hf (t) (12.0–12.1) values. The geochemical features indicate that the Erlangping gabbroic rocks were derived from a depleted lithospheric mantle that had been exposed to metasomatism by slab-derived fluid shortly before their generation. Their occurrence, coupled with coeval granitoids with highly positive e Nd (t) values, manifest significant crustal growth in the North Qinling–Tongbai orogen during the late Ordovician–Silurian. In addition, the Erlangping gabbroic rocks have low Sr/Y (7.32–26.2) and (La/Yb) N (1.34–4.07) ratios, but high HREEs, Y and Sc contents. This implies that their mantle source had no residual garnet, and thus partial melting of the lithospheric mantle occurred under relatively low-pressure conditions. The generation of the Erlangping gabbroic rocks might result from incipient rifting of the Erlangping back-arc basin induced by the northward subduction of the Paleotethyan Shangdan Ocean. Taking into account the ca. 490 Ma collision between the Erlangping arc and North Qinling microcontinent, we suggested that the evolution of the North Qinling belt from an arc to a back-arc realm involved a prolonged period of underplating of basaltic magma, granulite-facies metamorphism, and anatexis of precursor rocks. Consequently, the Qinling–Tongbai orogenic belt provides a key place for better understanding the Phanerozoic crustal growth and differentiation.

To investigate the molecular chaperone function of trigger factor (TF) and its relationship with isomerase activity in vivo, the assisted folding of adenylate kinase (AK) by TF in Escherichia coli was examined by measuring the amounts of soluble AK produced during co-expression. When the mutant of chicken AK, P17G, is expressed in plasmid pBVAK, 95% of the protein is found in inclusion bodies. Co-expression of AK with TF was achieved using a plasmid pBVAT that allowed expression of TF and AK in the same plasmid under separate control. Co-expression with TF resulted in an increase in the amount of soluble AK, with a higher increase when TF was expressed at higher levels in the cell. Co-expression of AK with the two TF mutants, Y221G and F233Y, in which peptidyl-prolyl cis/trans isomerase activity was 1% of wild-type, gave the same results as wild-type TF. This provides in vivo evidence that the molecular chaperone activity of TF is distinct from its isomerase activity.

Covalent joining of the two half molecules of tRNA Ala by T 4 RNA ligase to form a reconstituted whole molecule was investigated. The two half molecules consisting, respectively, of residues 1–35 and 36–75 were prepared by partial degradation of tRNA Ala with RNAase T 1 . The 5′-half molecule was treated with alkaline phosphatase to remove the 3′-terminal phosphate group, and the 5′-OH group of the 3′-half molecule was phosphorylated with [γ- 32 P]ATP by polynucleotide kinase. The two terminal nucletides to be joined were identified as Guo and Cyd. Prior to the covalent joining reaction, the two modified half molecules in an equimolar mixture were annealed, and the rejoined half molecules, separated by gel electrophoresis, served as the substrate for T 4 RNA ligase. Optimum conditions for this ligation, such as RNA ligase concentration, pH, Mg 2+ concentration, reaction temperature and time of reaction, were investigated. Under the optimum conditions a yield of about 70% joining of the reconstituted whole molecule was obtained as shown by gel electrophoresis, resistance to hydrolysis by alkaline phosphatase, nearest neighbour analysis and alanine acceptor activity.