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Multiple high- and ultrahigh-pressure orogenies in the Qin Mountains: boundary conditions permitting their formation and exhumation

Fachliche Zuordnung Mineralogie, Petrologie und Geochemie
Förderung Förderung von 2006 bis 2011
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 24431055
 
Erstellungsjahr 2013

Zusammenfassung der Projektergebnisse

The overriding goals of this project were the establishment of the boundary conditions that permitted the formation and the exhumation of high- and ultrahigh-pressure rocks in the Qinling orogen of Central China and to make a first-order contribution to the understanding of the centerpiece of Chinese geology, the Qin Mountains; the Qinling-Dabie orogenic collage constitutes the geographic, geologic, and cultural heart of China. First, we show that the Qinling orogen plays a key role in the understanding the amalgamation and breakup of the Rodinia supercontinent. For this, we investigated the Proterozoic evolution of the Qinling-Dabie orogenic collage and surrounding segments of the bounding South China craton and North China craton, employing U/Th–Pb geochronology. Our scenario suggests that the Qinling-Dabie orogenic collage records the final stages of the assemblage of the core of Rodinia, and this was completed not earlier than ~825 Ma, and its breakup, which was most active at ~750 Ma. Then, we focused on the Early Paleozoic (ultra)high-pressure and (ultra)high-temperature metamorphic Qinling orogenic collage. Orogens with multiple (ultra)high-pressure ((U)HP) and (ultra)high-temperature ((U)HT) metamorphic events provide a complex but telling record of oceanic and continental interaction. The Early Paleozoic history of the Qinling orogenic collage offers snapshots of at least three (U)HP and two (U)HT metamorphic events. We argued that a Meso-Neoproterozoic crustal fragment - the Qinling complex - localized subduction-accretion events that involved subduction, oceanic-arc formation, and back-arc spreading along its northern margin, and mantle-wedge exhumation and spreading-ridge subduction along its southern margin. Next, we addressed the Late Paleozoic subduction and high-pressure metamorphism in the Qinling orogen, resolving the long-standing discussion about the Late Paleozoic–Early Mesozoic location of the suture between the South and North China cratons in the Qinling. We also work on the connection between the two Triassic ultrahigh orogenic remnants in central China, the Dabie and Sulu, establishing, which micro-continents were involved in the collision from Qinling to Sulu and what P-T-d-t paths were achieved. In a series of papers, we report results on the foreland of the Qinling orogen. First, we addressed the timing of the final foreland growth of China’s largest orogens: the Mesozoic Qin Mountains (Qinling) and the Cenozoic Tibetan Plateau. In particular, we asked when the front of the Qinling orogen foldthrust belt was emplaced, and when the northern Sichuan Basin was affected by the eastward growth of the Tibetan Plateau. We employ zircon and apatite fission-track and (U-Th)/He dating in the Proterozoic crystalline rocks of the Hannan-Micang massifs (the frontal basement massifs of the Qinling orogen) and the sedimentary rocks of the northern Sichuan Basin. We extended the work on the eastward growth of the Tibet Plateau and addressed the Late Cretaceous–Cenozoic exhumation of the Qin, Daba, and Wudang Mountains from apatite fission-track and (U-Th)/He data. Data from field investigation, structural analysis, and 40Ar–39Ar and fission-track geochronology synthesized the structural architecture, stress fields, and tectonic evolution of the Dabashan orocline, southwestern Qinling. This study provided an example of intra-continental orogeny when terminal deformation is governed by foreland heterogeneities. Studies on the foreland massifs and basins of the north-central Yangtze craton (southern Qinling foreland) recorded the deformation and the tectonic–thermal history, provenance and hinterland exhumation of the Qinling foreland. A methodologically interesting aspect of this work was the double dating approach (U-Pb and FT on detrital zircon). A final aspect of the project comprised a methodologic study, addressing the potential of the mineral monazite for reconstructing the low-temperature thermal histories of geological samples from confined fissiontrack length measurements.

Projektbezogene Publikationen (Auswahl)

 
 

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