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The Cambrian Period is the first period of the Phanerozoic Eon and witnessed the explosive appearance of the metazoans, representing the beginning of the modern earth-life system characterized by animals in contrary to the Precambrian earth-life system dominated by microbial life. However, understanding Cambrian earth-life system evolution is hampered by regional and global stratigraphic correlations due to an incomplete chronostratigraphy and consequent absence of a highresolution timescale. Here we briefly review the historical narrative of the present international chronostratigraphic framework of the Cambrian System and summarize recent advances and problems of the undefined Cambrian stage GSSPs, in particular we challenge the global correlation of the GSSP for the Cambrian base, in addition to Cambrian chemostratigraphy and geochronology. Based on the recent advances of the international Cambrian chronostratigraphy, revisions to the Cambrian chronostratigraphy of China, which are largely based on the stratigraphic record of South China, are suggested, and the Xiaotanian Stage is newly proposed for the Cambrian Stage 2 of China. We further summarize the integrative stratigraphy of South China, North China and Tarim platforms respectively with an emphasis on the facies variations of the Precambrian-Cambrian boundary successions and problems for identification of the Cambrian base in the different facies and areas of China. Moreover, we discuss stratigraphic complications that are introduced by poorly fossiliferous dolomite successions in the upper Cambrian System which are widespread in South China, North China and Tarim platforms.

Subduction zones are unique to Earth and fundamental in its evolution, yet we still know little about the causes and mechanisms of their initiation. Numerical models show that far-field forcing may cause subduction initiation at weak pre-existing structures, while inferences from modern subduction zones suggest initiation through spontaneous lithospheric gravitational collapse. For both endmembers, the timing of subduction inception corresponds with initial lower plate burial, whereas coeval or delayed extension in the upper plate are diagnostic of spontaneous or forced subduction initiation, respectively. In modern systems, the earliest extension-related upper plate rocks are found in forearcs, but lower plate rocks that recorded initial burial have been subducted and are inaccessible. Here, we investigate a fossil system, the archetypal Semail Ophiolite of Oman, which exposes both lower and upper plate relics of incipient subduction stages. We show with Lu–Hf and U–Pb geochronology of the lower and upper plate material that initial burial of the lower plate occurred before 104 million years ago, predating upper plate extension and the formation of Semail oceanic crust by at least 8 Myr. Such a time lag reveals far-field forced subduction initiation and provides unequivocal, direct evidence for a subduction initiation mechanism in the geological record.

Granitoids of the tonalite–trondhjemite–granodiorite (TTG) series dominate Earth’s earliest continental crust. The geochemical diversity of TTGs is ascribed to several possible geodynamic settings of magma formation, from low-pressure differentiation of oceanic plateaus to high-pressure melting of mafic crust at convergent plate margins. These interpretations implicitly assume that the bulk-rock compositions of TTGs did not change from magma generation in the source to complete crystallization. However, crystal–liquid segregation influences the geochemistry of felsic magmas, as shown by the textural and chemical complementarity between coeval plutons and silicic volcanic rocks in the Phanerozoic Eon. We demonstrate here that Paleoarchean (ca. 3,456 million years old) TTG plutons from South Africa do not represent liquids but fossil, crystal-rich magma reservoirs left behind by the eruption of silicic volcanic rocks, being possibly coeval at the million-year scale as constrained by high-precision uranium–lead geochronology. The chemical signature of the dominant trondhjemites, conventionally interpreted as melts generated by high-pressure melting of basalts, reflects the combined accumulation of plagioclase phenocrysts and loss of interstitial liquid that erupted as silicic volcanic rocks. Our results indicate that the entire compositional diversity of TTGs could derive from the upper crustal differentiation of a single, tonalitic magma formed by basalt melting and/or crystallization at <40 km depth. These results call for a unifying model of Hadean–Archean continent nucleation by intracrustal production of TTG magmas.The chemical diversity of Earth’s early continental building blocks can be explained by differentiation of a single melt, without complex geodynamic settings, according to petrological and geochemical analysis of samples from South Africa.

Understanding the relationship between mineral occurrences and host granitic rocks can be controversial. The Zaozigou Au-Sb deposit (118 t Au, 0.12 Mt Sb), hosted in metasedimentary rocks and dacitic to granodioritic sills and dikes, is one such example of a large gold deposit argued to have formed from either magmatic or metamorphic hydrothermal processes. Two populations of monazite are identified within a mineralized dacite located along a major shear zone. Magmatic monazite commonly occurs within magmatic biotite and quartz phenocrysts and is characterized by uniform and high Th concentrations. It has a crystallization age of 238.3 ± 2.6 Ma, consistent with the zircon U-Pb age of 238.0 ± 1.8 Ma from the same dacite. Hydrothermal monazite is associated with sulfides and sericite, and has a 207Pb-corrected 206Pb/238U age of 211.1 ± 3.0 Ma. The amount of Th in hydrothermal monazite is widely variable. The low Th content of some monazite grains reflects direct precipitation from a metamorphic hydrothermal fluid. Furthermore, the elevated Th content in other hydrothermal monazite grains is likely due to the release of Th (and U) into hydrothermal fluids by dissolution of pre-existing Th-rich minerals in the country rock during ore-related alteration events. The magmatism, which overlaps Middle-Late Triassic terrane subduction-accretion in the West Qinling orogen, thus pre-dates the ore-forming event by about 30 m.y. The δ34S values of pyrite, arsenopyrite, stibnite, marcasite, and chalcopyrite from disseminated- and vein-type ores range from − 12.0 to − 5.5‰. Such negative values are distinct from those measured for other deposits in the northwestern part of the orogen that are genetically related to Triassic magmatism, including the Xiekeng-Jiangligou-Shuangpengxi Cu-Au-Fe-Mo skarn, Laodou reduced intrusion-related Au, and Gangcha epithermal Au ores. The Zaozigou deposit is best classified as an epizonal orogenic Au-Sb deposit. Our results demonstrate the usefulness of high-precision in situ geochronology on monazite for deciphering age relationships in ore deposits that have spatial associations with granitic rocks, thus aiding in the testing of the veracity of ore formation models.

Northeastern China is an important Mo resource region in China, with more than 80 Mo deposits and occurrences. The Huojihe deposit located in the Lesser Xing’an Range represents one of the many Mesozoic porphyry Mo deposits in NE China and has been selected for investigation attempting to clarify the possible mechanisms controlling Mo mineralization. In this study, accessory minerals, including zircon and apatite from the causative intrusions (biotite monzogranite and granodiorite), have been analyzed to reveal their chemical and isotopic compositions, which provide insights into the nature of the source magmas and a better understanding of the factors affecting their mineralization potential. Zircon U-Pb dating shows that the biotite monzogranite from the Huojihe deposit formed at 181.6 ± 0.6 Ma, which is identical to the previously reported molybdenite Re-Os age (~181 Ma), indicating that the Mo mineralization is probably genetically related to the intrusion. The intrusion samples share homogeneous geochemical and Sr-Nd isotopic compositions, with initial Sr/ Sr ratios of 0.7072–0.7075 and slightly negative ε (t) values from –2.3 to –1.4, reflecting a uniform magma source. The least-altered apatites show similar (or slightly enriched) initial Sr/ Sr ratios (0.7080–0.7108) and ε (t) values (–4.0 to –1.8), whereas the hydrothermally altered apatites are characterized by significantly higher initial Sr/ Sr ratios (0.7091–0.7119) and more negative ε (t) values (–4.9 to –4.4), probably due to the interaction between the hydrothermal fluids and wall rocks. The zircon ε (t) values vary from –0.9 to 1.7, corresponding to a restricted range of T ages from 1279 to 1120 Ma. The Sr-Nd-Hf isotope results suggest that the primary magmas associated with the Mo mineralization could be generated from a dominantly Mesoproterozoic lower crust source, with rare contributions from the depleted mantle. The low Ga and Ce and high Eu contents in the magmatic apatite demonstrate that the original magmas have a relatively high oxygen fugacity, which is also supported by the high zircon Ce /Ce * (22–568) and Eu /Eu * (0.38–0.71) values. Estimates of absolute sulfur concentrations in the mineralization-related melt using available partitioning models for apatite return relatively low magmatic sulfur concentrations in Huojihe (20–100 ppm), indistinguishable from those of larger or smaller deposits or even barren magmatic bodies. Using the sulfur concentration data, a minimum volume of 10–50 km magma has been suggested to be necessary to produce the Huojihe Mo deposit based on mass balance modeling. Besides, the Mo concentration in the original magma has also been roughly estimated based on the magma size (10–50 km ) and the contained Mo in Huojihe (0.275 Mt). The magmatic Mo concentrations (2–10 ppm) are similar to many other porphyry Mo systems (e.g., the Climax-type porphyry Mo deposits), and are also comparable to subeconomic to barren magma systems. This study suggests that pre-degassing enrichments of Mo and S in the original magma is not necessarily important in the formation of the Huojihe Mo deposit; rather, factors other than melt composition may be more critical in forming a porphyry Mo deposit. This understanding might also apply to other porphyry Mo mineralized systems worldwide.

The prevailing view of the formation of porphyry copper deposits along convergent plate boundaries involves deep crustal differentiation of metal-bearing juvenile magmas derived from the mantle wedge above a subduction zone. However, many major porphyry districts formed during periods of flat-slab subduction when the mantle wedge would have been reduced or absent, leaving the source of the ore-forming magmas unclear. Here we use geochronology and thermobarometry to investigate deep crustal processes during the genesis of the Late Cretaceous–Palaeocene Laramide Porphyry Province in Arizona, which formed during flat-slab subduction of the Farallon Plate beneath North America. We show that the isotopic signatures of Laramide granitic rocks are consistent with a Proterozoic crustal source that was potentially pre-enriched in copper. This source underwent water-fluxed melting between 73 and 60 Ma, coincident with the peak of granitic magmatism (78–50 Ma), porphyry genesis (73–56 Ma) and flat-slab subduction (70–40 Ma). To explain the formation of the Laramide Porphyry Province, we propose that volatiles derived from the leading edge of the Farallon flat slab promoted melting of both mafic and felsic pre-enriched lower crust, without requiring extensive magmatic or metallogenic input from the mantle wedge. Other convergent plate boundaries with flat-slab regimes may undergo a similar mechanism of volatile-mediated lower-crustal melting. Laramide flat-slab subduction releases fluids into the overlying crust that mediate water-fluxed melting of precursor arc lower crust, ultimately forming porphyry copper deposits, according to a geochronology and thermobarometry study.

This work was funded by the CSIRO Flagship Marine & Coastal Carbon Biogeochemical Cluster (Coastal Carbon Cluster), the Spanish Ministry of Economy and Competitiveness (projects EstresX CTM2012-32603, MedShift CGL2015-71809-P), the Generalitat de Catalunya (MERS 2017 SGR – 1588), the Australian Research Council LIEF Project (LE170100219), the Edith Cowan University Faculty Research Grant Scheme and the King Abdullah University of Science and Technology (KAUST) through baseline funding to Carlos M. Duarte. This work contributes to the ICTA Unit of Excellence (MinECo, MDM2015-0552)

Andradite-rich garnet is a common U-bearing mineral in a variety of alkalic igneous rocks and skarn deposits, but has been largely neglected as a U–Pb chronometer. In situ laser ablation-inductively coupled plasma mass spectrometry U–Pb dates of andradite-rich garnet from a syenite pluton and two iron skarn deposits in the North China craton demonstrate the suitability and reliability of the mineral in accurately dating magmatic and hydrothermal processes. Two hydrothermal garnets from the iron skarn deposits have homogenous cores and zoned rims (Ad 86 Gr 11 to Ad 98 Gr 1 ) with 22–118 ppm U, whereas one magmatic garnet from the syenite is texturally and compositionally homogenous (Ad 70 Gr 22 to Ad 77 Gr 14 ) and has 0.1–20 ppm U. All three garnets have flat time-resolved signals obtained from depth profile analyses for U, indicating structurally bound U. Uranium is correlated with REE in both magmatic and hydrothermal garnets, indicating that the incorporation of U into the garnet is largely controlled by substitution mechanisms. Two hydrothermal garnets yielded U–Pb dates of 129 ± 2 (2 σ ; MSWD = 0.7) and 130 ± 1 Ma (2 σ ; MSWD = 0.5), indistinguishable from zircon U–Pb dates of 131 ± 1 and 129 ± 1 Ma for their respective ore-related intrusions. The magmatic garnet has a U–Pb age of 389 ± 3 Ma (2 σ ; MSWD = 0.6), consistent with a U–Pb zircon date of 388 ± 2 Ma for the syenite. The consistency between the garnet and zircon U–Pb dates confirms the reliability and accuracy of garnet U–Pb dating. Given the occurrence of andradite-rich garnet in alkaline and ultramafic magmatic rocks and hydrothermal ore deposits, our results highlight the potential utilization of garnet as a powerful U–Pb geochronometer for dating magmatism and skarn-related mineralization.