The Pengguan tectonic dome of Longmen Mountains, Sichuan Province: Mesozoic denudation of a Neoproterozoic magmatic arc-basin system

Abstract

Neoproterozoic igneous and metamorphic complexes occur as tectonic domes in the LongmenMountains of the western margin of the Yangtze Block, and are important in reconstructing the Rodinian supercontinent and constraining the timing and mechanism of tectonic denudational processes. The Pengguan dome consists of granitic intrusions and metamorphic rocks of the Huangshuihe Group and is tectonically overlain by ductilly deformed Sinian to Paleozoic strata. The plutonic intrusions consist of granites with abundant amphibolite enclaves. New LA-ICP-MS zircon U-Pb dating yielded an emplacement age of 809±3 Ma and a protolith age of 844±6 Ma for the granite. The granitic rocks have geochemical signatures typical of A-type granites, indicating their formation under an extensional environment, by melting of newly formed tonalite-trondhjemite-granodiorite (TTG) rocks. A detachment fault, characterized by variable ductile shear deformation of S-C fabric and ESE-ward kinematics, separates the Pengguan dome from the Sinian-Paleozoic cover. 40 Ar/ 39 Ar dating of muscovite from the mylonite in the detachment fault of the dome demonstrates that ductile deformation occurred at ~160 Ma. This study indicates the existence of a Neoproterozoic magmatic arc-basin system, which was denudated by a Jurassic middle crustal ductile channel flow along the Longmenshan thrust belt.

New geochronology constraints on timing and depth of the ancient earthquakes along the Longmen Shan fault belt, eastern Tibet

“…The LSFB experienced a protracted tectonic history with multiple deformations during the Indosinian orogeny. Here we compiled 40 Ar/ 39 Ar mica, U‐Pb zircon, and U‐Pb monazite ages of the Mesozoic magmatic and ductile deformation events (110–250 Ma) in the LSFB from the literature (Table S3) [ Arne et al ., ; Kirby et al ., ; Huang et al ., ; Roger et al ., ; Zhang et al ., ; Xiao et al ., ; Xu et al ., ; Yuan et al ., ; Yan et al ., , ; Weller et al ., ; Jolivet et al ., ]. Figure a is a probability histogram of all these data, which display several age peaks, four of which are most prominent, at 220–240 Ma, 180–200 Ma, 150–170 Ma, and 110–140 Ma.…”

“…As illustrated in Figure , the detrital illite ages are 896 ± 34 Ma, 868 ± 47 Ma, and 843 ± 68 Ma, respectively. These results are consistent with the Neoproterozoic intruding time of the Pengguan complex within error [ Ma et al ., ; Yan et al ., ]. The authigenic illite age is 193 ± 4 Ma for PS05, 198 ± 7 Ma for PS09, and 196 ± 13 Ma for SLY.…”

“…The 206 Pb/ 238 U ages derived from LA‐ICP‐MS analyses are characterized by a large range of 703–901 Ma ages (Figure a), indicating the presence of inherited zircons in the grains. These ages are consistent with the U‐Pb ages derived from sensitive high‐resolution ion microprobe for the Pengguan complex [ Yan et al ., ], which are considered as the generation time of the Yangtze basement as mentioned above. The ZFT pooled ages of the two pseudotachylyte samples are 404 ± 46 Ma (PS11) and 398 ± 39 Ma (PS12), and one host rock sample is 472 ± 93 Ma (SLY).…”

“…Among them, the Pengguan complex is exposed at the core of a large extensional dome, which is separated from the similar Xuelongbao crystalline complex by the WMF to the west (Figures b and c). As obtained by U‐Pb dating, the Pengguan crystalline basement is considered as the result of Neoproterozoic magmatism, mainly consisting of biotite granite, plagiogranite, pyroclastic rocks, volcanics, and some mafic‐ultramafic intrusive rocks, which are locally affected by mylonite [ Ma et al ., ; Yan et al ., ]. The mylonite is only well developed along the WMF and is contemporaneous to the metamorphism changing from amphibolites to greenschist facies.…”

Fault‐related fold styles and progressions in fold‐thrust belts: Insights from sandbox modeling

“…Fault-related folds include decollement folds, fault-propagation folds, and fault-bend folds and are commonly associated with thrust assemblages including imbricate thrusts and duplexes [e.g., Boyer and Elliot, 1982;Berger, 1984;Banks and Warburton, 1986;Jamison, 1987;Lacombe et al, 1999;Pfiffner, 2006;Yan et al, 2003aYan et al, , 2008Yan et al, , 2009Yan et al, , 2011 Decollement folds form when displacement along a bedding-parallel decollement fault is transferred into folding of the hanging wall layers. Decollement folds are characterized by a decollement that defines the downward termination of the fold and an incompetent, ductile basal unit thickened in the core of the fold with no visible thrust ramp (Figure 1a) [Suppe and Medwedeff, 1990;Erslev, 1991;Shaw et al, 2003].…”