Geochemistry, zircon U–Pb and molybdenite Re–Os dating of the Taolaituo porphyry Mo deposit in the Central Great Hinggan Range: implications for the geodynamic evolution of northeastern China

The Taolaituo porphyry‐type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. The mineralization occurs mainly as veins, lenses and layers within the host porphyry. To better understand the link between the mineralization and the host igneous rocks, we studied samples from the underground workings and report new SHRIMP II zircon U–Pb and Re–Os molybdenite ages, and geochemical data from both the molybdenites and the porphyry granites. Five molybdenite samples yield a Re–Os isochron weighted mean age of 133.0 ± 0.82 Ma, whereas the porphyry granitoids samples yield crystallization ages of 133 ± 1 Ma and 130.4 ± 1.3 Ma. The U–Pb and Re–Os ages are similar, suggesting that the mineralization is genetically related to the Early Cretaceous porphyry emplacement. Re contents of the molybdenites range from 21.74 to 42.45 ppm, with an average of 32.69 ppm, whereas δ34S values vary between 3.7‰ and 4.2‰, which is typical of mantle sulphur. The 206Pb/204Pb, 207Pb/ 204Pb and 208Pb/204Pb vary in the ranges of 18.276–18.385, 15.566–15.580 and 38.321–38.382, respectively. The Taolaituo Early Cretaceous granitoids are A‐type granites. These observations indicate that the molybdenites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lithospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Taolaituo deposit occurred contemporaneously with the Early Cretaceous tectonothermal events associated with lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere associated with intra‐continental extension in northeast China. Copyright © 2015 John Wiley & Sons, Ltd.

Wake-up call from the Hayward Fault

During a brief visit to California this week, I, along with a metroregionfull of people, was treated to a rattling little temblor from the Hayward Fault. The quick jolt struck conveniently just before everyone’s morning alarms went off, serving as a wakeup call for the day, and as this season’s broader “wakeup call” reminder that there are big active seams in the crust inching along around and below our cities. …

Latest Devonian to earliest Carboniferous conodont and carbon isotope stratigraphy of a shallow‐water sequence in South China

To improve regional and intercontinental correlation of the uppermost Devonian–lowermost Carboniferous, we examined the conodont faunas and carbon isotopic records of the Tangbagou Formation in the Qilinzhai section, southern Guizhou, South China. The Tangbagou Formation is a succession of mixed carbonate–siliciclastic rocks that accumulated on a shallow‐water platform under normal marine conditions. Seven conodont zones for shallow‐water biofacies in South China, the Cl. gilwernensis–Cl. unicornis Zone, the Po. spicatus Zone, the Si. homosimplex Zone, the Si. sinensis Zone, the Si. eurylobata Zone, the Ps. multistriatus Zone and the Po. co. porcatus Zone in ascending order, are recognized in the Tangbagou Formation. Although apparently limited in its value for global correlation, this conodont zonation is more applicable to shallow‐water biofacies in South China. Carbonate samples have yielded carbon isotopic signatures consistent with those recorded in Euroamerica sections, in particular showing four distinct characteristics: (1) the peak values of Hangenberg Carbon Isotope Excursion (HICE) during the latest Devonian, (2) a minor positive shift (P1) in the Si. homosimplex Zone during the early Tournaisian, (3) a second minor positive shift (P2) in the Si. sinensis Zone and (4) the middle Tournaisian Carbon Isotope Excursion (TICE) in the middle part of the Tangbagou Formation. The similarity in peak values (~5.5‰) and magnitude of TICE for the Qilinzhai and Belgian sections indicates that the Euro‐asia δ13Ccarb trends may reflect the changes in global mean ocean δ13CDIC, rather than having been overprinted by local carbon cycling. Integration of conodont biostratigraphy and δ13C stratigraphy provides a powerful tool for stratigraphic correlation. Copyright © 2015 John Wiley & Sons, Ltd.

Dip variations of the North American and North Caribbean Plates dominate the tectonic activity of Puerto Rico–Virgin Islands and adjacent areas

The M 7.0 Haiti earthquake of 2010 in the Greater Antilles is a reminder that the northeastern Caribbean is at a high risk for seismic and tsunami hazards. The Greater Antilles consist of the Hispaniola microplate to the west and Puerto Rico–Virgin Islands to the east and are situated between two subduction zones with the Puerto Rico Trench to the north and the Muertos Trough to the south. Although there is no active volcanism on Puerto Rico, earthquake depths and previous seismic tomography results imply that the slabs of Caribbean and North American Plates exist at depth. However, how far the east Muertos Trough subduction of the North Caribbean Plate has extended has not been fully addressed. In addition, the Puerto Rico–Virgin Islands are bounded by extensional regimes to both the west (Mona Rift) and east (Anegada Passage). The cause of the extension is still under debate. In this paper, we use new 3D seismic tomography and gravity data to carry out an integrated study of the geometry of the subducting slabs of the North American and North Caribbean Plates in the Puerto Rico–Virgin Islands area. The results indicate that both slabs have an increase of dip westward, which is strongly controlled by the subduction rollback of the North American Plate. These variations affected the tectonic evolution of the Puerto Rico–Virgin Islands. Thus, the results of this research advance our understanding of the kinematic evolution of the Puerto Rico–Virgin Islands and associated natural hazards. Copyright © 2015 John Wiley & Sons, Ltd.