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The subcontinental lithospheric mantle (SCLM) is now suggested by many workers to play a role in the formation of orogenic gold deposits in active continental margins, given that the gold and volatiles may be introduced into the SCLM during plate subduction. The giant Cretaceous Jiaodong gold province within the North China block occurs in a convergent margin setting where there is no terrane accretion, thus eliminating from consideration the commonly accepted metal and fluid source reservoir for orogenic gold--the metamorphosed upper crust of an active orogenic belt. Thus, the auriferous fluids were released below the high-grade Archean cratonic rocks from either enriched SCLM or directly from the subducted oceanic slab. Mercury (Hg) isotopes allow fingerprinting of isotopically distinct reservoirs, discriminating between the two possibilities. We present Hg isotope data for a set of pyrite grains, native gold, and lamprophyres from six main gold districts in the Jiaodong gold province. These samples dominantly yielded near-zero Δ199Hg (0‰ ± 0.1‰), within uncertainty of the mantle Δ199Hg value. The results provide novel evidence that the SCLM predominantly controlled the Hg budget of the Jiaodong gold deposits, implying that the SCLM acted as a buffer for the crustal mass-independent fractionation Hg signatures and a storage reservoir for gold and volatiles. Consequently, during slab subduction, gold and volatiles were recycled and stored within the SCLM and were later released from the mantle during uplift and relaxation of compressional tectonics. [ABSTRACT FROM AUTHOR]

Quantifying the rhythms and rates of magmatic-hydrothermal systems is critical for a better understanding of their controls on ore formation and the dynamics of magmatic reservoirs that feed them. We reconstructed the evolution of ore-forming fluids using hydrothermal quartz from the 17.4 Ma Zhibula skarn, Tibet. Ion probe analysis reveals sharp and dramatic changes in quartz δ18O values between 5‰ and -9.3‰, with fluid δ18O values varying between 2.8‰ and -18.2‰, which are best explained by transient meteoric water incursion into a hydrothermal system dominated by magmatic fluids. Two pulses of magmatic fluids and a meteoric water incursion event are inferred, which operated at the millennium scale (760-1510 yr) as constrained by the aluminum diffusion chronometer. Our results indicate that magmatic reservoirs are likely water unsaturated for most of their lifetime (>105 -106 yr), with transient and episodic fluid exsolutions (-10³ yr) being driven by magma replenishment or crystallization-induced water saturation. With focused and efficient metal deposition, multiple pulses of metallifer- ous fluids favor the formation of giant deposits with high grade. Meteoric water δ18O values (-25.4 ± 2.3‰) derived from Zhibula quartz further suggest a paleo-elevation of 5.9 ± 0.3 km; this transient early Miocene surface uplift plausibly was due to break-off of the oceanic slab attached to the Indian Plate. Our research highlights that ubiquitous hydrothermal quartz in orogenic belts can probe the dynamics of magmatic-hydrothermal systems and also quantify paleo-elevations, which has significant tectonic implications. [ABSTRACT FROM AUTHOR]

We propose a flat-slab subduction model for Mesozoic South China based on both new sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon data and a synthesis of existing structural, geochronological, and sedimentary facies results. This model not only explains the development of a broad (~1300-km-wide) intracontinental orogen that migrated from the coastal region into the continental interior between Ca. 250 Ma and 190 Ma, but can also account for the puzzling chain of events that followed: the formation of a shallow-marine basin in the wake of the migrating foreland fold-and-thrust belt, and the development of one of the world's largest Basin and Range-style magmatic provinces after the orogeny. The South China record may serve as an example of the multiple effects of flat-slab subduction, including migrating orogenesis and foreland flexure, synorogenic sagging behind the active orogen, postdelamination lithospheric rebound, and the development of a Basin and Range-style broad magmatic province. [ABSTRACT FROM AUTHOR]