A new method for extraction of alteration information using the Landsat 8 imagery in a heavily vegetated and sediments‐covered region: A case study from Zhejiang Province, E. China

Ore prediction based on the Operational Land Imager (ETM+) image within the heavily vegetated and sediments‐covered areas is always a difficulty for geological remote sensing. Here, we report a new scheme for extraction of near‐ore alteration information in such localities: Terrain Analysis → principal component analysis →Fractal → Spatial Overlay and the Fe3+–OH− integrated anomalies that are punctate and probably ore‐caused were reasonably exposed. Findings showed a satisfactory result that the spatial, if not genetic, dependency relationship between the remotely sensed anomalies and geochemical anomalies, as well as the ore‐controlling geological bodies, is significant. However, no substantial spectral anomalies of vegetation immediately responsible for local mineralization and alteration were detected. This study may have contributed a useful case study for in‐depth remote sensing exploration.

Provenance and tectonic setting of the Early and Middle Devonian Xueshan Formation, the North Qilian Belt, China

The North Qilian orogenic belt is the key in the exploration of the formation and assembly of Asia. The Early–Middle Devonian Xueshan Formation, which is deposited in the north area of North Qilian Orogenic Belt, is the most important for revealing the evolution basin–mountain transition of the North Qilian Belt. In order to reveal the tectonic evolution of the central orogenic belt in China and Paleozoic global plate reconstruction, it is necessary to perform provenance analysis of the Xueshan Formation. Eighteen samples were collected from Yumen and Yongchang profiles in the west of North Qilian Belt (WN), and 16 samples were obtained from Gulang and Jingtai profiles in the east of North Qilian Belt (EN). The compositions of clastic conglomerates and the sandstones suggested that felsic volcanic was the main source of the WN Xueshan Formation deposits and that the sedimentary and metamorphic rocks were the main source of the EN sediments. According to major geochemistry indexes, such as Al2O3/SiO2 ratio ranging from 0.08 to 0.37 and the chemical index of alteration less than 80, the source rocks were moderately weathered and of moderately matured. The samples from the EN were relatively enriched in Cr, Ni, Sc, and V elements and depleted in Hf element. However, those from the WN were enriched in Hf without the enrichment of Cr, Ni, Sc, or V. The samples from WN showed a strong negative Eu anomaly, but the samples from EN showed a weak negative Eu anomaly or a positive Eu anomaly. All the above geochemical characteristics suggested the prominent input of felsic clasts with granitic rocks into the WN. Meanwhile, the discrimination diagrams of trace elements implied that WN rocks were derived from continental island arc and that the EN rocks were derived from orogenic belt and the passive continental margin. The North China Plate subducted southwards and formed subduction‐related arc magmatism along the southern margin of the North Qilian Terrane during the Early–Middle Devonian. In conclusion, the WN is a fore‐arc basin, but EN is a foreland basin.

Geochronology, geochemistry, and petrogenesis of the late Mesozoic Luoyang volcanics: Implications for the geodynamic evolution of the Zhejiang–Fujian region, SE China

The Zhejiang–Fujian region, situated along the southeastern coast of China and in the eastern part of the Cathaysia Block, is characterized by large volumes of late Mesozoic granitoid volcanics. We present new zircon U–Pb ages, whole‐rock geochemistry, and Sr─Nd─Hf‐isotope data for 3 rhyolite porphyries from the Luoyang region (LY‐1, LY‐2, and LY‐3). We identify 2 magmatic events. In Stage 1 (146 Ma), rhyolite porphyry LY‐1 was produced by the partial melting of Proterozoic Mayuan Group amphibolites and metasediments. In Stage 2 (130–126 Ma), rhyolite porphyries LY‐2 and LY‐3 were generated by the continued melting of amphibolites but with only a minor contribution from metasedimentary rocks. The fractionation of plagioclase, biotite, titanite, and allanite (degree of fractionation 0.7–0.5) from an LY‐2 parent magma produced LY‐3. Our new data, together with other published data, indicate that minor volcanism, related to the initial northwestward subduction of the Paleo‐Pacific Plate beneath SE China, occurred in a continental arc setting in the Zhejiang–Fujian coastal region from 160 to 140 Ma but that the major period of volcanism took place from 140 to 120 Ma in a back‐arc setting and occurred because of rollback of the subducting slab.

Origin of ooids in ooidal‐muddy laminites: A case study of the lower Cambrian Qingxudong Formation in the Sichuan Basin, South China

Ooids have been considered the most intriguing component of carbonate rocks, but the formation mechanism of carbonate ooids remains a matter of intense discussion. The lower Cambrian Qingxudong Formation in the southeastern Sichuan Basin contains abundant ooidal‐muddy laminites. Petrographic and sedimentological analyses revealed that these laminites formed in a shallow‐marine environment (preferably along the windward side of the reef‐shoal). Changing energy conditions caused variable supplies of grainy and muddy accumulation. A wide variety of ooids developed in grainy intervals. The normal ooids (2 mm in diameter) in the upper portion of the laminites developed in a deepening and moderate‐energy subtidal environment but were influenced by episodic hydrodynamic events. Petrographic and geochemical analyses suggest that microbes played an important role in ooid formation. High carbonate‐supersaturated and alkaline conditions that were mediated by microbial activity (e.g., bacterial sulfate reduction and photosynthesis) and agitated seawater conditions were the most important factors that mediated the formation of the Qingxudong ooids. This study provides new insights into paleooceanographic conditions during the Early Cambrian and offers a perspective on the formation of ancient normal and giant ooids.