Geochemical characteristics of sedimentary rocks play an important role in indicating depositional environments and tectonic backgrounds. In this article, the major and trace elements of the Daohugou Formation are measured, which shows that the quartz and silicate minerals are abundant; trace elements, except for Rb, are depleted than that of the upper crust; the rare earth elements (REE) curves incline to the right with Eu negative anomaly and slight Ce negative anomaly. The Daohugou Formation is continental deposits with freshwater and oxic conditions, and the climate changes from warm and humid to hot and dry. The source rock of the Daohugou Formation is granite which experienced an intermediate chemical weathering under wet and warm conditions, and the tectonic background of the Daohugou Formation is a passive continental margin. It is deduced that the provenance of the Daohugou Formation is Archean gneiss in the south of the Daohugou Basin.
Integrated gravity and magnetic prospecting in the Luanchuan ore cluster by the Henan Institute of Geological Survey has led to the recent discovery of the Yuku concealed porphyry Mo–W deposit. This research focuses on the geological, geochemical, and chronological features of the Yuku deposit, and it discusses the genesis of the deposit and its associated concealed granitic batholith. Skarn and/or hornfels occur in the contact zone between the granitic batholith and the wall rocks. The Mo mineralization is mostly hosted in porphyritic granites, whereas the large Mo–W deposits of the area (e.g., the Nannihu–Sandaozhuang Mo–W deposit) are mostly hosted in the skarn and hornfels. The laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) zircon U–Pb dating constrained three episodes of magmatic emplacement: (a) the porphyritic biotite monzogranite at 153.1 ± 1.2 Ma, (b) the ore‐causative porphyritic syenogranite at 147.1 ± 1.3 to 148.0 ± 1.6 Ma, and (c) the last porphyritic monzogranite at 130.0 ± 1.3 Ma. The granitic batholiths have high contents of SiO 2 , Al 2 O 3 , and K 2 O + Na 2 O, obvious fractionation between the light and heavy rare earth elements [(La/Yb) N = 17.3–37.3], a negative Eu anomaly (δEu = 0.62–0.84), enrichment in Rb, Th, U, and Sr, and depletion of P and Ti. These features indicate the fractionation of plagioclase, amphibole, garnet, and rutile from the primary magmas or as residues in the source. The ε Hf ( t ) isotopic values of the zircons are concentrated between −21 and −13, with corresponding two‐stage model ages ( t DM2 ) between 2.1 and 1.7 Ga. The above characteristics indicate that the granitic batholiths were derived from the partial melting of the thickened lower crust during the Mesozoic to Cenozoic. The ore‐forming fluids emplaced in the contact zone between the batholith and the wall rocks resulted in the metasomatic alteration and the deposition of Mo–W mineralization.
Present global compilations of ages and isotopic data suggest insignificant crustal growth after 450 Ma. Previous Nd isotopic studies of whole rocks from the Central Asian Orogenic Belt suggest large volumes of juvenile crustal additions in the Phanerozoic. To test this, we studied detrital zircons from the Xinglonggou Formation of western Liaoning at the northern margin of the North China craton, which was deposited after the collision between the Siberian Plate and the North China craton to form this part of the Central Asian Orogenic Belt. Zircons from the Xinglonggou sandstones are characterized by two major groups of U-Pb ages (2.6-2.4 Ga and 260-220 Ma) except for three grains (1.9-1.6 Ga). The 2.6 to 2.4 Ga zircons have positive ε~Hf~ (t) values up to coeval depleted mantle value, which suggest juvenile crustal addition. The results are consistent with existing data for the North China craton (NCC). ε~Hf~ (t) values of 260 to 220 Ma zircons range widely from −15.4 to 13.3. While zircons with the negative ε~Hf~ (t) values are similar to igneous zircons from intrusive rocks of the North China craton and indicate recycling of ancient continental crustal materials, those with the positive values and young model ages point to a significant period of crustal generation with the source provenance from the eastern Central Asian Orogenic Belt (CAOB) to the north. Mixing of detritus from both the North China craton and the eastern Central Asian Orogenic Belt suggests the ca. 250 Ma closure of the Paleo-Asian ocean and collision between the North China craton and the Siberian Plate along the eastern Solonker zone. The youngest zircons constrain uplift of the eastern Central Asian Orogenic Belt to be no older than 208 Ma. Thus, the 260 to 220 Ma crustal growth is related to the subduction of the Paleo-Asian ocean Plate along the Solonker suture, which records the termination of the Central Asian Orogenic Belt. The Solonker suture occupies an area of 700 km long and 60 km wide and extends from Solonker via Sonid Yuoqi to Linxi in Inner Mongolia and further west and northeast. This implies extensive juvenile crustal additions during this period. It may change our present views of Phanerozoic crustal growth.
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