Mineral Chemical Characteristics of Gabbro-diorite for Shulouqiu Uranium Deposit in Northern Guangdong, China: Constraint on the Magmatic Source

1 Introduction The uranium deposits related with Indosinian and Yanshanian granite have provided the abundant resource of uranium during the past several decades in China.The deposits are mainly distributing in the Guidong granite

Magma source and evolution law in Yueshan ore field, Anhui Province, China

Major elements, trace elements and sulfur, oxygen isotopic compositions of the main intrusions were studied in Yueshan area. The fact that intrusions enriched in Th and Sr, and depleted in Rb and Ba in this area, suggests that the original magma roots in alkali basalt magma of upper mantle, with deep characteristics. It can be seen that the diagenesis environments are the island arc and active continental margin areas from the lg τ to lg σ diagram of intrusions. With the increase of SiO2, Fe2O3, MnO and P2O5 decrease, which shows that the magma of Yueshan area endured crystal fractionation of ferromanganese mineral and apatite in early evolution stage. With the further rise and evolution of magma, magma composition of calcium increased, meanwhile enriched in Zr, and depleted in Nb and Ta. This indicates that crustal component is gradually added, the assimilation and contamination occur between magma and crustal material, which includes the magma evolving, from calc-alkaline series to alkaline series. The results show that crystal fractionation, assimilation and contamination are the main evolution law of magma in this area.

Multi-isotope and geochemical approach to the magma source and tectonic setting of Proterozoic anorthosite massifs and AnorthositeMangerite-Charnockite-Granite(AMCG)suites

The occurrence of massif-type anorthosite intrusions is a widespread Proterozoic phenomenon.They are usually associated with gabbroic,charnockitic,and granitic rocks,comprising the so-called anorthositemangerite-charnockite-granite(AMCG)suite.Although these rocks have been extensively studied worldwide,several aspects concerning their formation remain unsettled.Among them,the magma source and the tectonic setting are the most important.To evaluate these issues,we first compiled geochemical and isotopic data of Proterozoic anorthosite massifs and AMCG suites worldwide and stored it in a database named datAMCG.This plethora of data allows us to make some important interpretations.We argue that the wide-ranging multi-isotopic composition of this group of rocks reflects varying proportions of juvenile mantle-derived melts and crustal components.We interpret that the precursor magmas of most massive anorthosite bodies and associated mafic rocks have a mantle-dominated origin.However,we highlight that a crustal component is indispensable to generate these lithologies.Adding variable amounts of this material during succeeding multi-stage assimilation-fractional crystallization(AFC)processes gives these intrusions their typical mantle-crustal hybrid isotopic traits.In contrast,a crustaldominant origin with a complementary mantle component is interpreted for most MCG rocks.In summary,the isotopic information in datAMCG indicates that both sources are necessary to generate AMCG rocks.Therefore,we suggest that hybridized magmas with different mantle-crust proportions originate these rocks.This interpretation might offer a more nuanced and accurate depiction of this phenomenon in future work instead of choosing a single-sourced model as in the past decades.Finally,tectonomagmatic diagrams suggest that the rocks under study were likely generated in a tectonic environment that transitioned between collision and post-collisional extension,sometimes involving subduction-modified mantle sources.This interpretation is supported by geological and geochronological information from most complexes,thus challenging the Andean-type margins as an ideal tectonic setting.

Geochronology and geochemistry of lithium-rich tuffs in the Sichuan basin,western Yangtze:Implication for the magmatic origin and final closure of eastern Paleo-Tethys

The felsic volcanogenic tuffs named"green-bean rocks"(GBRs),characterized by a green or yellowish green color,are widely distributed in the western Yangtze platform and have a high lithium content(286-957 ppm).This paper studies the ages,origin and tectonic setting of the GBRs in the Sichuan basin on the western margin of the Yangtze platform through the whole-rock geochemistry and zircon trace elements by using U-Pb dating and Hf-O isotopes.The GBR samples from the Quxian and Beibei sections yielded zircon U-Pb ages of 245.5±1.8 Ma and 244.8±2.2 Ma.These samples can be used as the isochronous stratigraphic marker of the Early-Middle Triassic boundary(EMTB)for regional correlation.The whole-rock and zircon geochemistry,and zircon Hf-O isotopes exhibited S-type geochemical affinities with high positiveδ^(18)0 values(9.28‰-11.98‰),low negativeε_(Hf)(t)values(-13.87 to-6.79),and T_(DM)^(2)ages of 2150-1703 Ma,indicating that the lithium-rich GBRs were generated by the remelting of the pre-existing ancient Paleoproterozoic layer without mantle source contamination in the arcrelated/orogenic tectonic setting.The results of this study demonstrate that the lithium-rich GBRs in the western Yangtze platform were derived from arc volcanic eruptions along the Sanjiang orogen,triggered by the closure of the eastern Paleo-Tethys Ocean and the syn-collision between the continental Indochina and Yangtze blocks at ca.247 Ma.This was marked by a major shift from I-type magmas with intermediateε_(Hf)(t)values to S-type magmas with low negativeε_(Hf)(t)values.Collectively,our results provide new insights into the origin of the GBRs and decodes the closure of the eastern Paleo-Tethys.

Geochemistry, Monazite U–Pb Dating, and Li–Nd Isotopes of the Madi Rare Metal Granite in the Northeastern Part of the North China Craton

The Madi rare metal granite is a complex massif,which contains a variety of rare metals,such as Nb,Ta,Li,and Be.In this paper,the geochemical characteristics of the granite were obtained by multi-collector inductively coupled mass spectrometry(MC-ICP-MS).The precise crystalline age of the granite was obtained from monazite U-Pb dating,and the source of the granite was determined using Li-Nd isotopes.The Madi rare metal granite is a high-K(calc-alkaline),peraluminous,S-type granite.The U-Pb monazite age indicates that the crystalline age of the granite is 175.6 Ma,which is Early Jurassic.The granite is characterized by a relatively wide range ofδ7 Li values(+2.99‰to+5.83‰)and high lithium concentrations(181 ppm to 1022 ppm).The lithium isotopic composition of the granite does not significantly correlate with the degree of magmatic differentiation.An insignificant amount of lithium isotope fractionation occurred during the granitic differentiation.The lithium isotopic composition of the granite significantly differs from that of the wall rock,but it is very similar to that of a primitive mantle peridotite xenolith(meanδ7 Li value+3.5‰).The plot of Li concentration versusδ7 Li indicates that the Li isotopic composition of the granite is similar to that of island arc lavas.Based on the above-described evidence,the granite was mainly derived from the crust,but it was contaminated by a deep granitic magma.