Thermochronologic Constraints on Uplifting Events since the Early Cretaceous in the North Margin of the Luxi Rise, Eastern China

INTRODUCTION

The Luxi rise is one of the key areas for understanding of large scale extension and lithospheric thinning in eastern China during the Mesozoic and Cenozoic. The lithospheric thinning is responsible for the development of basin-range structure and regional extensional uplifting. In recent years, geologists have rebuilt the Cenozoic uplift history of the Luxi rise by means of apatite fission track technology (Tang et al., 2011; Li and Zhong, 2006) and have proved the preferable uplifting-subsidence coupling relationship between the Luxi rise and the Jiyang depression (Wang et al., 2008; Li et al., 2007). However, the uplifting time of Mengshan in the south and Taishan in the central area is of significant difference (Tang et al., 2011; Li et al., 2007; Li and Zhong, 2006), arising a question: whether the Luxi rise is uplifted as a whole Guozhi Wang, Shugen Liu and Can Zou or diverse fault blocks? The purpose of this study is to explore the timing of uplifting events in the north margin by high-quality dating of igneous and sedimentary minerals using ⁴⁰Ar/³⁹Ar and fission track technique.

GEOLOGICAL BACKGROUND

The Luxi rise, located in the east craton of North China and confined by the Tanlu fault zone in the east, the Lankao-Liaocheng fault in the west, the Qihe-Guangrao fault in the north bordering on the Cenozoic Jiyang depression, respectively, appears a sector spreading from NNW to N as a whole (Fig. 1).

Figure  1.  Geological diagram and sampling point of the Luxi rise. F1. Lankao-Liaocheng fault; F2. Qihe-Gangrao fault; F3, F4, F5. Tanlu fault zone.

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The Neoarchean (Taishan Group) and the Cambrian–Middle Ordovician widely expose in the Luxi rise and a few Late Paleozoic (C₂–P) and Mesozoic can also be found there. The Cambrian–Middle Ordovician is dominated by marine limestone and dolomite. The Late Paleozoic (C₂–P) is composed of marine clastic rocks and continental coal-bearing layers. Some of the Mesozoic–Cenozoic sedimentary basins, such as the Zibo, Linqu, Laiwu, Yiyuan, Mengyin, and Pingyi basins, etc., developed in the Luxi rise, by confinement of the NW-trending faults (Fig. 1), are filled with continental clastic and pyroclastic rocks.

The compression in SN direction during the later Indosinian orogen resulted in EW-trending open folds with thrusting; the NW-SE compression in the middle Yanshan orogen produced NE-trending tight to open folds and thrust nappe; NE-trending slip fault and high-angle reverse fault were formed during the late Yanshan orogen (Li et al., 2005). Two large scale extensional movements since the Late Mesozoic are responsible for the development of the steep dipping extensional fault and shallow dipping detachment fault; the NW-striking steep dipping extensional faults defining the boundary between the Mesozoic– Cenozoic basins and the Neoarchean Taishan Group (Fig. 1), have been controlling the evolution of the Mesozoic–Cenozoic basins (Hu et al., 2009; Li L H, 2009; Wang et al., 2008; Li S Z et al., 2005). The shallow level dipping detachment faults distribute between the Lower Cambrian and Archean, Ordovician and Carboniferous (Hu et al., 2009).

The Mesozoic–Cenozoic igneous rocks, elongated in NW-trending extensional faults and in the Mesozoic–Cenozoic basins, are predominantly composed of volcanic rocks dominated by trachybasalt, trachyandesite, and some gabbro and monzonite. The Mesozoic volcanic rocks from Mengyin Basin were dated as 114.8–124.3 Ma by ⁴⁰Ar/³⁹Ar method (Qiu et al., 2002), and the Cenozoic counterpart mainly consists of basalt.

SAMPLE FEATURES AND ANALYTICAL TESTING METHOD

Sample Features

Samples are mainly collected from the Cretaceous Qingshan Formation, Jurassic Fenshuiling Formation, Triassic Fangzi Formation and the Yanshanian monzonite in the Zibo Basin (Fig. 1). Of them, two samples from the Qingshan Formation are gray-white rhyolitic volcanic tuff (Lw17) and gray-white dacitic breccia (Lw14), others from Fenshuiling and Fangzi formations are grey lithic quartz sandstones (Lw19) and red quartz sandstones (Lw9), respectively. The fission track chronology of the apatite extracted from these samples is analyzed. The Yanshanian flesh pink and massive monzonite bandedly exposing in NW direction, chiefly consist of microcline (48%), plagioclase (25%), quartz (12%), biotite (15%) and a few accessory minerals (< 1%). Apatite, zircon, K-feldspar and biotite are extracted from the biotite monzonite (Lw11); the former two are used for fission-track dating and the latter two for ⁴⁰Ar/³⁹Ar dating.

Analytical Testing Method and Procedure

As a very experienced technique, the fissiontrack analysis of apatite and zircon has been widely applying in the study of tectonic geology (Yuan et al., 2007; Ketcham et al., 1999; Green, 1986). The ex-detector is used for apatite and zircon dating (Gleadow and Duddy, 1981) and the detailed analytical procedure is adopted using the description by Yuan et al. (2007). The fission-track analytical results of the apatite and zircon are listed in Table 1 for this study.

Table  1.  Fission-track analytical results of apatite and zircon from the north margin of the Luxi rise, eastern China

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⁴⁰Ar/³⁹Ar dating of the biotite and K-feldspar was conducted in the Key Laboratory of Orogenic Belt and Crustal Evolution of Ministry of Education, Beijing University. The details can be traced in the literature (Gong et al., 2008).

RESULTS

T-t Path of Apatite

The apatite annealing models based on laboratory research have been proposed since 1980s (Carlson et al., 1999; Ketcham et al., 1999; Duddy et al., 1988; Laslett et al., 1987). In this article, the annealing model by Laslett et al. (1987) is selected to simulate the possible thermal history via AFTSolve software (Ketcham et al., 2000). The simulated track length distribution and track age were checked statistically, and the later was checked mathematically by Kolmogorov-Smirnov (K-S). It is an acceptablefitifK-S > 0.05andgoodifK-S > 0.5.

The fission-track ages of all apatite samples are younger than that of the host strata, indicating full annealing for all these samples. Two cases are supposed in simulation: (1) subsidence during the Miocene; (2) denudation during the Miocene. Except for the sample LW11, other three samples are of high fitting (Fig. 2). The T-t path of all the samples can be classified as two groups. The samples near the Jiyang depression are in subsidence during 19.9–16.2 or 18.3–15.4 Ma (Figs. 2a, 2b), which implied that the Guantao Formation (N₁g) were formed during the subsidence when the source areas had been eroded away by late uplifting; but the samples near rise (Lw14, Lw9) indicating a slow uplifting (Figs. 2c, 2d) and the Guantao Formation was absent here in the same period. According to the T-t thermal history of the three high-fitting samples, two stages of rapid uplift with sharp decrease of temperature (cooling) can be recognized. The first stage (53.6–30.1 Ma) from the Luxi rise to the Jiyang depression is a tilted uplift from south to north, and the uplift time gets younger ages from 53.6–46.9 to 39.5–31.8 and 37.1–30.1 Ma (Figs. 2a, 2b, 2d) far away from the Luxi rise to the Jiyang depression. The second stage (13.4–0 Ma) is a tilted uplift from south to north, and the uplift time becomes 13.4–0, 6.5–0 and 2.9–0 Ma (Figs. 2a, 2b, 2d), far away from the Luxi rise to the Jiyang depression.

Figure  2.  T-t path of apatite and rapid cooling time. The rapid cooling time: (a) 37.1–30.1 and 2.9-0 Ma; (b) 39.5–31.8 and 6.5–0 Ma; (c) 62–56.4, 24.1–16.1, and 8.4–0 Ma; (d) 53.6–46.9 and 13.4–0 Ma. The locations of samples refer to Fig. 1.

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Isotope Closure Temperature of Mineral

Closure temperature is an effective and dispersive critical temperature appearing in isotope system (Doddson, 1973). The isotope daughter from radiation will totally get lost if the temperature of minerals is higher than closure temperature while it will almost remain if the temperature is lower than closure temperature and the isotope daughter will lose due to no effects of the diffusion on age testing. The closure temperature is related to the apparent age of minerals, and the temperature of minerals at their apparent age is their closure temperature, which is in line with the conclusion that the age of minerals should be recorded from their closure temperature. The closure temperature is a complicated function of diffusion property, cooling speed, grain size and others of minerals (Chen and Li, 1999; Doddson, 1973).

The ⁴⁰Ar/³⁹Ar closure temperatures have been determined as 500±50 (Harrison, 1981), 350±50 (Hacker and Wang, 1995), 300±50 (Hacker and Wang, 1995) and 150±30 ℃ (McDougall and Harrison, 1999) from hornblende, muscovite, biotitie and K-feldspar, respectively. Recent researches show that, for alkali feldspar, the diffusion loss process of Ar is much more complicated than the model of mono-diffusion domain assumed by Doddson (1973) model. Both mono-diffusion domain and a kind of distribution of diffusion domain in the samples give a birth to the MDD (multiple diffusion domains) model (Lovera et al., 1989). According to MDD diffusion model, a continuous cooling curve between < 350–150 ℃ was obtained from the analysis of alkali feldspar (Chen and Li, 1999). It is the closure temperature differences of diverse minerals from the same monzonite that enable us reconstruct the T-t history.

Isotopic Geochronology of Different Minerals

Biotite, K-feldspar, zircon and apatite are extracted from the same biotite monzonite (Lw11) to conduct ⁴⁰Ar/³⁹Ar dating and fission track dating respectively.

⁴⁰Ar/³⁹Ar isotopic dating results of the biotite and K-feldspar are listed in Tables 2 and 3, respectively. An age plateau of 111.1±2.4 Ma of biotite can be observed (Fig. 3a). The age of 111.2±2.5 Ma (Fig. 3b) could be interpreted as the cooling age of the biotite at 300±50 ℃. Similarly, 111.3±2.4 Ma age plateau and cooling age 109.3±3.3 Ma of the K-feldspar shows in Fig. 3. As mentioned before, the closure temperature of the biotite is 300±50 ℃ (Hacker and Wang, 1995) and that of the K-feldspar is 150±30 ℃ (McDougall and Harrison, 1988). It is obviously contradictory in closure temperature but same in cooling age. It could be a possible result that the rock mass cooled steeply from 300±50 to 150±30 ℃ when fast uplifting. In another hand, the fission track age (75 Ma) and closure temperature (250 ℃) of the zircon suggest that the biotite monzonite was cooled down to 250 ℃ at 75 Ma, impling the biotite monzonite was not cooled to 150±30 ℃ until 111.3±2.4 Ma. There is another possible interpretation that the multi-diffusion domain of the K-feldspar expands its closure temperature to 300–150 ℃ (Chen and Li, 1999), then, the MDD of the K-feldspar results the same cooling age of the biotite and K-feldspar had.

Table  2.  The ⁴⁰Ar/³⁹Ar analytic data of the biotite

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Table  3.  The ⁴⁰Ar/³⁹Ar analytic data of the K-feldspar

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Figure  3.  ⁴⁰Ar/³⁹Ar age of the biotite and K-feldspar. (a) and (b) Biotite; (c) and (d) K-feldspar.

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The fission track dating of zircon and apatite (LW11) from the same biotite monzonite are 75±7 and 40±3 Ma (Table 1), respectively. It is known that the closure temperatures of zircon and apatite are 250 and 120 ℃ respectively (Carlson et al., 1999; Ketcham et al., 1999; Laslett and Galbralth, 1996). Therefore, the fission track ages of zircon and apatite (LW11) from the same biotite monzonite suggest that the biotite monzonite could be cooled to 250 and 120 ℃ at 75±7 and 40±3 Ma (Table 1), respectively.

DISCUSSION

Due to moderate closure temperature, the ⁴⁰Ar/³⁹Ar ages of the biotite and K-feldspar (111 Ma) result in the best estimate of the monzonite at 300±50 ℃ for the cooling time. At lower temperature, fission track of zircon and apatite indicates a rapid cooling of the biotite monzonite at 70 and 40 Ma, respectively. Based on the T-t path of the apatite and cooling age of the biotite, K-feldspar and zircon from the same biotite monzonite, the T-t path was reconstructed for the north margin of the Luxi rise (Fig. 4).

Figure  4.  T-t path on the north margin of the Luxi rise. Curve A. samples Lw17 and Lw19; Curve B. sample Lw9. FT. fission track; Ap. apatite; Zirc. zircon; Kfs. K-feldspar; Bio. biotite; the pane. range of closure temperature.

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As shown as in Fig. 4, it is clear that the north margin of the Luxi rise was rapidly uplifted in two phases: the first occurred during 111–46.9 Ma and the second during 13.4–0 Ma while the first uplifting near the Jiyang depression happened during 11–55.8 Ma and the second during 6.5–0 Ma. Subsequently, slow uplifting and denudation could have taken place between the two rapid upliftings.

The precedent study on the uplift history of the Mengshan (location, see Fig. 1) in the south of the Luxi rise proposed that the Mengshan also has two rapid upliftings during 70–40 and 32–20 Ma, respectively (Tang et al., 2011), whereas the Taishan in the center of the Luxi rise (location, see Fig. 1) has three upliftings during 48, 44–37 and 23–20 Ma (Li et al., 2007). If the first uplifting time (111–46.9 Ma) can matches that of Mengshan (70–40 Ma), the regional tilted uplifting from N to S in the Luxi rise is inferred to have acted during Early Cretaceous–Eocene. The second uplifting time (2.9–0, 6.5–0, 13.4–0 Ma) (Figs. 2a, 2b, 2d) is later in the north margin of the Luxi rise than the third one in the Taishan (23–20 Ma) and the second one (32–20 Ma) in the Mengshan, which implies the uplifting during this period is tilted uplift from S to N; that is, the southern Luxi rise uplifted at first and the northern Luxi rise then followed.

⁴⁰Ar/³⁹Ar ages of the biotite and K-feldspar from biotite monzonite in the northern Luxi rise are respectively 111.2±2.5 and 111.3±2.4 Ma, comparative to those of K/Ar age 119–125 Ma from the Mesozoic basalt in Feixian (Zhang et al., 2002), Rb/Sr age 119.6 Ma from trachyandesite in the Luxi rise (Qiu et al., 2005), ⁴⁰Ar/³⁹Ar age 115 Ma from gabbro in Jinan (Tan and Lin, 1994) and ⁴⁰Ar/³⁹Ar age 114.8–124.3 Ma from volcanic rocks in Mengyin basin (Qiu et al., 2002). K/Ar ages 62–100.5 Ma was also recognized from basalt in central Bohai Sea (Hou et al., 2003). All of the ages suggested that magmatism lasted from 119 to 62 Ma. The K/Ar ages 28.8–36.5 and 10.6–18.9 Ma were analyzed from basalts in central Bohai Sea and Linqu-Changle (Jin, 1985). All ages above indicate the Mesozoic and Cenozoic magmatism was mainly emplaced in 119–67.5 and 36.5–10.6 Ma, respectively, and the magmatism ages of 119–62 Ma match first uplifting ages 111–46.9 Ma, but second uplifting (13.4–0 or 6.5–0 Ma) is a little bit later than the magmatism.

The magmatite geochemistry indicated that the magma source was originated from lithospheric mantle envolved from an enriched one to a depleted one from the Mesozoic to the Cenozoic, and the change of magma source most was likely resulted from an asthenosphere upwelling and a large scale lithospheric delamination (Qiu et al., 2005). The coincidence of the ages between the magmatism and uplifting demonstrates that two phases of uplifting were caused by large scale crust extension and lithospheric thinning.

CONCLUSION

(1) Two phases 111–46.9 and 13.4–0 or 6.5–0 Ma of rapid uplifting were recognized in the north margin of the Luxi rise.

(2) The first rapid uplifting is the tilted uplift during 111–46.9 Ma from N to S in the Zibo and followed southward during 70–40 Ma in the Mengshan.

(3) The second rapid uplifting took place in tilt way during 32–20 Ma from S to N in the Mengshan, and followed in turn during 23–20 and 13.4–0 or 6.5–0 Ma in the Taishan and Zibo, respectively.

(4) The two phases of rapid uplifting were caused by large scale extension and of the lithospheric thinning.