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The Munsungun--Winterville Belt (MWB) is a major Ordovician lithotectonic belt developed on the leading edge of the ensialic Ganderia in northern Maine. Recent mapping reveals a much wider extent of [...]

The Bohai Bay Basin, located on the eastern Asian margin, is the second largest oil-production basin in China. It contains numerous depressions and sags, among which Nanpu Sag has become particularly important because of significant oil discoveries in recent years. Geologically and tectonically, however, the rifting mechanism and geodynamic evolution of the basin remain uncertain. This paper uses detailed volcanic and stratigraphic records obtained through extensive drilling and sampling in Nanpu Sag to interpret tectono-stratigraphic sequences and discuss basin dynamic evolution and crust-mantle interactions of the Bohai Bay Basin. Nanpu Sag contains voluminous volcanic rocks of dominantly alkaline basalts. Drill core samples, well logs, and seismic profiles reveal three volcanic cycles between the Eocene and Miocene Epochs. These basalts were created during a transition from garnet- to spinel-peridotite. Five tectono-stratigraphic sequences produced by episodic continental rifting have been identified, each composed of a basal coarse clastic sequence, a lower volcanic sequence, a middle deep-water clastic sequence, and an upper infilling sequence. Tectonically, Nanpu Sag experienced four evolutionary phases. The first three corresponded to three rifting events revealed by cyclic volcanism and sedimentary depositional features. The fourth phase was marked by extreme thermal subsidence and prograding fluvial deposition fallowed by tectonic inversion. A diapiric upper-mantle upwelling model is proposed to explain the dynamics that controlled the multiple rifting processes, the cyclic volcanism, and the periodic tectonic evolution of Nanpu Sag and the greater Bohai Bay Basin. doi: 10.1130/B30041.1

Evidence for post-Acadian through Alleghanian deformation in eastern Maine: multiple brittle reactivation of the Norumbega Fault system Please note that Figure 6 of Wang and Ludman, published in Atlantic Geology, [...]

ABSTRACT Detailed mapping in eastern and east-central Maine reveals a complex history of multiple brittle reactivations along the Norumbega fault system (NFS) following initial late Acadian (380 Ma) ductile shearing. [...]

The article focuses on Uranium–lead (U-Pb) geochronology of hydrothermal zircons from the Nyainqentanglha ductile shear zone. Topics include the ductile shear zones has considered to be the western boundary faults of the Yadong-Gulu rift system, the potential to provide critical temporal constraints for the large-scale East–West extension event in the Tibetan Plateau and the high precision geochronological analysis of hydrothermal zircons from the northern Nyainqentanglha ductile has collected.

The Hahaigang W–Mo polymetallic skarn deposit is located in the central-eastern part of Gangdese tectono-magmatic belt in Lhasa terrane, Tibet. The deposit was discovered in 2007 with currently proven 46milliontons of WO3 ores, 12milliontons of Mo ores, and 1.31milliontons of combined Cu–Pb–Zn ores, at an average grade of 0.20% WO3, 0.07% Mo, 0.026% Cu, 0.49% Pb, and 3.1% Zn. Ore bodies occur in veins or disseminations, and are confined within the NE-striking Dalong fault zone which is hosted by the Lower-Permian Pangna Group of dominantly quartz sandstone and slate. Several granitic plutons are exposed in the area or known from drill-holes. Ages of these granitic plutons are determined by using zircon U–Pb LA–ICP–MS method. For example, the biotite monzogranite yields a 206Pb/238U–207Pb/238U concordia age of 58.66±0.90Ma and a weighted mean 206Pb/238U age of 57.02±0.42Ma. The granite porphyry yields a 206Pb/238U–207Pb/238U concordia age of 109.1±8.9Ma and a weighted mean 206Pb/238U age of 114.0±2.6Ma. The biotite monzogranite yields a weighted mean 206Pb/238U age of 56.1±1.1Ma. Re–Os isochron age of 63.2±3.2Ma from 5 molybdenite samples collected from the W–Mo skarn ores is also obtained in this study. The zircon U–Pb and molybdenite Re–Os geochronological data suggest that the W–Mo mineralization was not temporally associated with any of the dated igneous plutons. However, the molybdenite Re–Os age of 63.2±3.2Ma indicates that the W–Mo mineralization might have occurred during the main India–Eurasia collision that was initiated around 65Ma. Microprobe analysis of ilvaite that occurs in two generations in the W–Mo skarn ores reveals a close relationship to Ca–Fe–F-rich hydrothermal fluids, which were probably derived from deeply-seated magmas. We suggest that ascent of the fluids was strictly controlled by the ore-controlling Dalong fault zone, and that chemical interaction and metasomatism between the fluids and the Lower-Permian Pangna quartz-feldspathic host rocks produced the ilvaite and the W–Mo polymetallic skarn deposit during the main India–Eurasia collision. Although the majority of the polymetallic deposits in the Gangdese belt are reported to be either pre- or post-main collision, it is evident from this study that the main collision also produced W–Mo polymetallic mineralization within the belt. [ABSTRACT FROM AUTHOR]