Geochemistry and U-Pb zircon geochronology of Late-Mesozoic lavas from Xishan, Beijing

Abstract

Zircon U-Pb dating by both SHRIMP and LA-ICP-MS and geochemical study of the Tiaojishan Formation and the Donglintai Formation from Xishan, Beijing, reveal that ages of upper lavas of Tiaojishan Formation and Middle of Donglintai Formation are 137.1±4.5 Ma(2σ ) and 130-134 Ma, respectively. The fomer is slightly older than the latter and the age difference between these two formations is less than 5 Ma. These lines of evidence prove that the two volcanoes erupted within a short time. The age of the Tiaojishan Formation from Xishan, Beijing is distinctively different from that of the Chende Basin. This indicated that the ages of Tiaojishan lavas varied in different regions. The Tiaojishan Formation consists of typical adakite (SiO 2 =56%, Na 2 O = 3.99-6.17, Na 2 O/K 2 O = 2.2 -3.1, Sr = 680-1074×10 −6 , Y = 13.2-16.3×10 −6 , Yb = 1.13-1.52×10 −6 , Sr/Y = 43-66), high-Mg adakite and high-Mg andesite (Mg# = 54-55). Features of continental crust of adakite from the Tiaojishan Formation and its syngeneric middle silicic vocanic rocks, such as typical Nd-Ta negative abnormality and Pb possive abnormality, indicate that these lavas are originated from partial melts of continental crust. These results suggest that the adakite from the Tiaojishan Formation of Xishan, Beijing derived from thickened eclogitic lower crust and lithosphere beneath the North China craton at mesozoic that was foundered into the aesthenosphere, and subsequenctly partially melted and interacted with mantle olivine during melts upward migration. The age of lavas from the Tiaojishan Formation restrained the foundation which should last at least until 137 Ma. Lavas of the Donglintai Formation are rhyolith and andesite with normal Mg# and thus they did not interact with the mantle. These lavas represent remobilized melts of lower crust material caused by mantle aesthenosphere upwelling migration induced by foundation.

Constraints on the upper boundary age of the Tiaojishan Formation volcanic rocks in West Liaoning-North Hebei by LA-ICP-MS dating

“…The Mesozoic volcanic rocks in West Liaoning-NorthHebei have been a major concern of geological study in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] because the magmatic action has a close relationship with the tectonic frame transformation, biological evolvement and Crust dismantling in the east of China [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] .…”

“…In West Liaoning-North Hebei, the Mesozoic volcanic rocks are developed and their dating results obtained had direct influence on the traditional interpretation of geological issues (such as settings of Crust dismantling, tectonic movement, biological evolvement and magmatic action) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] . However, in the study of volcanic rock chronology, the dating results were quite different even in the same bed of strata.…”

“…But, the isotopic data obtained are complicated, and some of them from different strata have apparent overlapping; especially in the Tiaojishan Formation, researchers have obtained the most in number but the most complicated data (too wide age range) [1][2][3][4][5][6][7][8][9][10][11][12][13] . It resulted in dispute over the settings and age of the Tiaojishan Formation volcanic rocks and the settings of the Mesozoic tectonic events in West Liaoning-North Hebei [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] .…”

“…In the study region, there are three key Mesozoic volcanic strata: the Tiaojishan (Lanqi) Formation, the Zhangjiakou Formation, and the Yixian Formation (corresponding bed) volcanic rocks, and their volcanic actions corresponded to the Mesozoic tectonic events in the east of China [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] , the different stages of Crust dismantling in Mesozoic in North China [1,7,8] and the different stages of the biological evolvement in Mesozoic in the east of China, respectively [15,19] . But, the isotopic data obtained are complicated, and some of them from different strata have apparent overlapping; especially in the Tiaojishan Formation, researchers have obtained the most in number but the most complicated data (too wide age range) [1][2][3][4][5][6][7][8][9][10][11][12][13] . It resulted in dispute over the settings and age of the Tiaojishan Formation volcanic rocks and the settings of the Mesozoic tectonic events in West Liaoning-North Hebei [1][2][3][4][5][6][7][8][9][10]<...>…”

Implications of subduction and subduction zone migration of the Paleo-Pacific Plate beneath eastern North China, based on distribution, geochronology, and geochemistry of Late Mesozoic volcanic rocks

“…Zhang et al 2008a;Yang and Li 2008), Xishan Zone (e.g. Yuan et al 2006), and Ludong Zone (e.g. Qiu et al 2002;Zhang et al 2002), but there have so far been no studies of Mesozoic volcanic rocks in the Bohai Bay Basin.…”