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The Altun orogenic belt, located on the northern margin of the Tibetan Plateau, records the assembly and breakup of the Rodinia supercontinent. In this paper, we report the petrography, zircon U–Pb ages and Hf isotope data, and bulk geochemistry of the Hongliugou alkali feldspar granites from the Altun orogenic belt to constrain their petrogenesis and tectonic implication. Zircon U–Pb dating yielded ages of 857–851 Ma, interpreted as the emplacement ages of the granites. The granites are metaluminous; have high SiO2, K2O, and rare‐earth element (REE) contents; low CaO and P2O5 contents; high FeOt/MgO ratios; and high 10,000 × Ga/Al values. They show marked depletion in heavy REEs, enrichment in light REEs, and pronounced negative Eu anomalies. These rocks are enriched in high‐field‐strength elements, depleted in Ba, Sr, P, and Ti, and lack Nb and Ta anomalies. These petrological and geochemical characteristics are consistent with those of A‐type granites. The samples plot in the A1‐type field in a discrimination diagram for A‐type granites. Zircon εHf(t) values vary from +1.76 to +7.40 with two‐stage Hf model ages of 1.27 to 1.63 Ga, implying that the granites were derived mainly from juvenile crust. On the basis of these and previous results, we propose that the Hongliugou alkali feldspar granites formed in an intraplate rift setting related to the initial breakup of Rodinia. [ABSTRACT FROM AUTHOR]

The Altun orogenic belt in northwest China is part of the northern margin of the Tibetan Plateau. The North Altun ophiolitic mélange belt is an important tectonic unit within the Altun orogenic belt that contains voluminous early Paleozoic granitoids. In this study, we report the petrological features, geochemical compositions, and zircon U Pb and Hf isotope data of three granitic plutons from the western segment of the North Altun ophiolitic mélange belt. Zircon U Pb dating yields magmatic crystallization ages of 499, 493 and 496 Ma for samples of granodiorite, quartz diorite and syenogranite, respectively. The granitoids have metaluminous to weakly peraluminous and medium-K to high-K calc–alkaline characteristics and display relative enrichments in large ion lithophile elements (Rb, Th, U, K) and light rare earth elements (LREE) and relative depletions in Nb, Ta, Sr, P and Ti, suggesting an arc-related origin. The granodiorites (499 Ma) have positive zircon ε Hf (t) values ranging from +1.87 to +6.59 with two-stage Hf model ages (T DMC) of 1.05 to 1.35 Ga, implying that the granodiorites were derived from juvenile crust. The quartz diorites (493 Ma) have similar Hf isotopic characteristics to the granodiorites (ε Hf (t) = +2.59 to +6.04, T DMC = 1.08 to 1.30 Ga), indicating derivation from juvenile crust. The syenogranites (496 Ma) have high total REE and K 2 O contents, and low zircon ε Hf (t) values (−1.69 to +1.54), suggesting that they were derived mainly from juvenile crust mixed with ancient crustal materials. Combined with data from previous studies, we conclude that magmatism in the North Altun ophiolitic mélange belt can be subdivided into three episodes: Episode 1 (520–470 Ma) granitoids are related to subduction; Episode 2 (460–425 Ma) granitoids formed in a continent–continent collisional setting; and Episode 3 (<420 Ma) granitoids are post-collisional granites. Our results are consistent with south-directed subduction of the North Altun oceanic lithosphere beneath the Central Altun Block during the early Paleozoic (520–460 Ma), which was followed by collision with the Dunhuang Block. • The granitoids from the western segment of North Altun formed at 493–499 Ma. • These granitoids belong to I-type granite and have an arc-related origin. • They are derived mainly from juvenile crust. • The granitic magma activity in North Altun can be subdivided into three episodes. [ABSTRACT FROM AUTHOR]

The South Altun orogenic belt (SAOB), consisting of the South Altun block (SAB) and the South Altun continental block (SACB), is one of several important orogenic belts in NW China. Numerous granite bodies are widely distributed in the SAB. However, the petrogenesis and tectonic environment of these granites, and their relationships to those of the SACB, Central Altun Continental block (CACB), North Altun block (NAB), Qilian block (QLB), and North Qaidam block (NQB) remain unclear. In this investigation, we selected the SAB granites for detailed study, and explore the petrogenesis employing bulk-rock geochemistry, zircon U-Pb dating, and Hf isotopic analysis. Zircon U–Pb LA-ICP-MS dating of the granites from the SAB identified seven spatially distinct Paleozoic plutonic suites: (a) Yigan—352–343 Ma; (b) Baiganhu—448–444 Ma; (c) west Mangya—444–435 Ma; (d) Aketishan—265 Ma; (e) Chaishuigou—406 Ma; (f) Changchungou—469 Ma; and (g) north Mangya—462 Ma. Based on previous research combined with our new U-Pb dating and bulk-rock geochemical investigations in the SAB, we identdified six distinct episodes of granitoid emplacement: episodes 1 and 2, quartz diorite + granodiorite + monzogranite with I-type affinities, and ages of 503–497 Ma and 483–458 Ma, respectively; episode 3, granodiorite + monzogranite + syenogranite with I- and S-type affinities, and an age of 456–432 Ma; episode 4, monzogranite + syenogranite + alkali feldspar granite with A-type affinities, and an age of 424–385 Ma; episode 5, granodiorite + monzogranite with S-type affinities, and an age of 352–338 Ma; and episode 6, quartz diorite + monzogranite + syenogranite with I-type affinities, and an age of 265–264 Ma. Zircon Lu-Hf isotope analyses from various episodes show that ε Hf ( t ) values are positive in most cases, but negative for a small number of inherited (xenocrystic) zircons. Source rocks were mainly juvenile crust, evidently mixed with minor ancient continental material. Based on our new results integrated with regional geological data, we conclude that episodes 1 and 2 granitic magma generations were related to the subduction of oceanic crust, episode 3 to post-collisional partial melting, episode 4 to the isostatic adjustment of orogenic blocks after plate suturing, episode 5 to petrotectonic thickening of the Altun crust, and episode 6 to Altun fault transcurrent slip attending Kunlun Paleo Tethys subduction. [ABSTRACT FROM AUTHOR]

The Gonghe geothermal basin is situated in the westernmost part of the western Qinling orogen and possesses the supreme potentials to explore and develop hot dry rock (HDR) geothermal resources in China. The basal rock of HDR reservoir in Gonghe basin is composed of granitoids. In this contribution, in order to constrain the formation mechanism of the Gonghe HDR, granitic samples from outcropping have been collected and drilling core samples data from the archives also been compiled. The studied results show that the obtained zircon U–Pb ages of 255.1 ± 1.9 Ma and 253.9 ± 2.6 Ma for granodiorite and monzogranite, respectively. All granitoids from both outcropping and drilling core have the similar rock associations and their major and trace elements possess the consistent evolved patterns, such as relative enrichment of LILEs (e.g., K, Rb), depletion of HFSEs (e.g., Nb, Ti), and negative Eu anomalies (0.32–0.66), indicating that they share the same magma sources and evolutional processes. And they have the affinity of I-type granites. They were derived from the mixture of partial melting of metabasaltic rocks in the lower crust and a small amount of mantle-derived magma and formed in a subduction-related setting relative to the southward subduction of the Zongwulong oceanic crust beneath the west Qinling terrane. The heat production values of rocks around the Gonghe basin were calculated and all basal granitic rocks ranges from 0.35 to 8.51 μW/m3, yielding an arithmetic mean value of 1.97 μW/m3, indicating that the radioactive heat generation capacity of granitoids in the Gonghe basin is slightly lower. The HDR reservoir in the Gonghe basin was probably due to an allied thermal effect of the radiogenic heat production in the thickening continental crust and the heat contributed by a deep magma chamber below the basin. The early Triassic granitoids with a higher thermal conductivity serve as the conductive medium of the geothermal heat; whilst the sedimentary rocks marked by lower thermal conductivity above the granitic batholiths act as the reservoir cap. This contribution provides a relatively rational understanding for the mechanism of the HDR reservoir in Gonghe geothermal basin from the petrological and geochemical perspectives, which is conducive to the geothermal potential assessment and estimation, and to-be implementation of the Enhanced Geothermal System demonstration project in China. • Granitoids formed between 236 and 255 Ma have same geochemical features, suggesting a prolonged magmatism. • Gonghe basin area has a lower heat production value, 1.97 μW/m3 on average. • HDR reservoir in Gonghe basin was an allied result of the radiogenic heat production and a deep magma chamber. [ABSTRACT FROM AUTHOR]