Petrogenesis and tectonic implications of A-type granites in the Dabie orogenic belt, China: geochronological and geochemical constraints

Abstract

The Dabie orogenic belt is characterized by the presence of large volumes of intrusive and volcanic rocks that formed in Late Mesozoic times. Most of the intrusive bodies are I-type granites but it is still unclear whether there are contemporary A-type granites. Here, we report the first unambiguous discovery of A-type granite from Baiyashan in the North Dabie tectonic belt. The crystallization age of the body has been fixed as 120.4 ± 1.2 Ma using U–Pb analysis of zircons by LA-ICPMS. The Baiyashan granite is enriched in Si, K, Na, Rb and REE, has elevated FeOtot/(FeOtot + MgO) and Ga/Al ratios, and is depleted in Mg, Ca, Mn, Ba, Sr, P and Ti. The REE composition shows highly fractionated patterns with (La/Yb)N = 6.95–16.68 and Eu*/Eu = 0.33–0.59. Its crystallization age, field relationships, petrographic and geochemical data show beyond doubt that the Baiyashan granite is an Early Cretaceous A-type granite. Sr–Nd isotope systematics are characterized by a high ISr of 0.708–0.714 and a low ɛNd of −7.5 to −19.4, with TDM2 = 1.5–2.5 Ga, and these data indicate that the magmas were dominantly sourced from partial melting of middle to lower crustal intermediate-felsic igneous rocks and mingling with mafic to intermediate magmas, during rift-related magmatism associated with subduction of the Palaeo-Pacific Plate beneath Eastern China in Early Cretaceous times.

Multi-chronometric dating of the Huarong granitoids from the middle Yangtze Craton: Implications for the tectonic evolution of eastern China

“…K-Ar biotite ages range from 165 to 110 Ma (Table 1, IGSH, 1974;HGSB, 1977), suggesting a prolonged cooling history. However, distinct Jurassic and Cretaceous magmatic episodes have recently been identified by SHRIMP and LA-ICP-MS U-Pb zircon and 40 Ar/ 39 Ar hornblende and biotite data (Table 1, Wu et al, 2005;Xie et al, 2006;Chen et al, 2009;Li et al, 2010a and references therein). The Huarong granitoids intrude the Mesoproterozoic Lengjiaxi Formation that is dominated by low-grade phyllite, schist, and granulitite.…”

“…These magmatic rocks are economically important due to their Cu-Au-Mo mineralization. They also serve as geodynamic tracers of the regional tectonic evolution (Li, 2000;Davis et al, 2002;Liu et al, 2004;Wu et al, 2005;Hiseh et al, 2008;Chen et al, 2009;Pirajno et al, 2009;Li et al, 2009Li et al, , 2010aZhu et al, 2010b). The petrogenesis and geodynamic setting of these magmatic rocks are still controversial with three models.…”

“…The third model suggests that specifically the adakitic magmatism traces either partial melting of thickened lower crust or lithospheric thinning due to lower crust delamination (Xu et al, 2002;Wang et al, 2004Wang et al, , 2006Li et al, 2009Li et al, , 2010aHe et al, 2010). The last two scenarios were related to paleo-Pacific subduction beneath the eastern China Continent (Zhang et al, 2002;Wu et al, 2005;Zhao et al, 2005;Huang et al, 2007;Chen et al, 2009;Li et al, 2009;Zhu et al, 2010b). Paleo-Pacific subduction scenarios comprise (He et al, 2010): (1) subduction since the Early Jurassic (Jahn et al, 1990;Martin et al, 1994;Lan et al, 1996;Lapierre et al, 1997;Sewell and Campbell, 1997); (2) slab steepening from shallow Early Jurassic to intermediate Late Cretaceous dip (Zhou and Li, 2000); (3) flat-slab subduction and slab-foundering .…”

Deformation features of garnet-bearing granites from Huwan, western Dabie Mountains

“…Current research has not reached consensus on many problems, such as the petrogenesis, age of formation, tectonic setting and geodynamic significance of the foliated granites and their relationship with the UHP metamorphic unit. This hampers our understanding of the formation and structural evolution of the principal rock units in the Dabie-Sulu orogenic belt.There are several theories about the origin of these foliated garnet granites: (1) their protoliths were Jinningian granites that experienced UHP metamorphism along with eclogites during continental subduction [8][9][10][11] , subsequent to intrusion and crystallization into previously regionally metamorphosed country rocks [3] ; (2) their protoliths were feldspathic rocks in the Dabie regional metamorphic complex that did not undergo UHP metamorphism, but were emplaced by mixing or remelting in the middle and lower crust during exhumation of UHP metamorphic rocks [12,13] ; and (3) their protoliths were products of partial melting during exhumation of retrograde UHP rocks and were deformed later [2,[5][6][7][14][15][16][17] . These theories might explain existing chronological data from the foliated garnet granites as…”

“…There are several theories about the origin of these foliated garnet granites: (1) their protoliths were Jinningian granites that experienced UHP metamorphism along with eclogites during continental subduction [8][9][10][11] , subsequent to intrusion and crystallization into previously regionally metamorphosed country rocks [3] ; (2) their protoliths were feldspathic rocks in the Dabie regional metamorphic complex that did not undergo UHP metamorphism, but were emplaced by mixing or remelting in the middle and lower crust during exhumation of UHP metamorphic rocks [12,13] ; and (3) their protoliths were products of partial melting during exhumation of retrograde UHP rocks and were deformed later [2,[5][6][7][14][15][16][17] . These theories might explain existing chronological data from the foliated garnet granites as follows: (1) a zircon U-Pb upper intercept age of 773-727 Ma could represent the intrusion and crystallization ages of the protoliths, while lower intercept ages of 231-219 Ma could be peak metamorphic age of Indosinian UHP rocks, indicating that the foliated garnet granites underwent UHP metamorphism [8,18 -21] or at least fluid infiltration [3] ; or alternatively, (2) a zircon U-Pb concordant age of 234-227 Ma could be the magmatic intrusion age [22,23] , whereas the zircon age of 773-727 Ma represents an inherited zircon age.…”