The relationship between irradiation sensitivity of quartz Al and Ti centers and baking temperature by volcanic lava flow: Example of Datong volcanic group, China

The investigation of irradiation sensitivity of electron spin resonance (ESR) centers is a significant part of the study of ESR signal characteristics and helps to gain insight into the physical mechanisms of paramagnetic centers. In this study, we have observed and compared the irradiation sensitivity characteristics of ESR centers under high-temperature baking in natural conditions by lava flow.

Available online 1 July 2022

1350-4487/© 2022 Elsevier Ltd All rights reserved

The relationship between irradiation sensitivity of quartz Al and Ti centers

and baking temperature by volcanic lava flow: Example of Datong volcanic

group, China

Chun-Ru Liua, Hao Jia,*, Wen-Peng Lib, Chuan-Yi Weia, Gong-Ming Yina,**

aState Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, 100029, China

bDepartment of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China

A R T I C L E I N F O

Keywords:

Quartz

Electron spin resonance (ESR)

Al center

Ti center

Lava flow

Datong volcano group

A B S T R A C T The investigation of irradiation sensitivity of electron spin resonance (ESR) centers is a significant part of the study of ESR signal characteristics and helps to gain insight into the physical mechanisms of paramagnetic centers In this study, we have observed and compared the irradiation sensitivity characteristics of ESR centers under high-temperature baking in natural conditions by lava flow Results show that the irradiation sensitivity of the Al and Ti–Li centers increases with the baking temperature, while the irradiation sensitivity of the Ti–H center increases first (up to ~500 ◦C) and then decreases with temperature Moreover, the ESR intensity of the Ti center is more strongly dependent on the annealing history of the samples than the Al center In addition, from the results of the heating experiment, after heating above 1000 ◦C, additional irradiation does not produce new Ti–H signals, which probably indicates that the paleo-temperature of the lava flow in Yujiazhai area did not exceed 1000 ◦C

1 Introduction

Structural defects in solids (charged electron and electron hole traps)

may be produced by radioactive elements decaying in the environment

The increase in defect concentration is positively correlated with the

increase in the accumulation of radiation dose Electron spin resonance

(ESR) is one of the main dating techniques which are based on the

accumulation of radiation defects in solids being the same as

lumines-cence dating (Vyatkin and Koshchug, 2020) In ESR dating, lattice

de-fects with unpaired electrons are analyzed to determine the accumulated

dose of radiation and hence the age (Toyoda and Ikeya, 1991)

Quartz is one of the most abundant minerals on the surface of the

earth which is often used for ESR dating (e.g Grün et al., 1999; Toyoda

et al., 2000), such as for fault gouge (e.g Ikeya et al., 1982), volcanic

tephra (e.g Imai et al., 1985; Suchodoletz et al., 2012), flint (e.g Porat

et al., 1994), and sediment (e.g Yokoyama et al., 1985; Liu et al., 2010)

The recent studies of the signal characteristics are mainly focused on the

feature of light fading (e.g Yokoyama et al., 1985; Toyoda et al., 2000;

Voinchet et al., 2003), thermal behavior (e.g Fukuchi, 1989; Toyoda

and Ikeya, 1991; Toyoda et al., 1993; Falgu`eres et al., 1994; Vyatkin and

Koshchug, 2020), dose-response (e.g Grün and Macdonald, 1989; Grün and Brumby, 1994; Voinchet et al., 2013; Duval and Guilarte, 2015; Tsukamoto et al., 2018), and potential use for sediment provenance tracing (e.g Tissoux et al., 2015; Wei et al., 2017, 2019), etc Changes in ESR heating, bleaching, and irradiation (Poolton et al.,

2000) sensitivity of quartz as a result of laboratory treatments had been studied, however, there are very few studies from natural conditions, in spite of the studies of luminescence dating, which is similar to the ESR principle, many sensitivity studies have been carried out and a lot of reliable results have been achieved (e.g Lai and Wintle, 2006; Zheng

et al., 2009; Lü and Sun, 2011) So it was significantly necessary to check the feature of the sensitivity (mainly irradiation) of ESR centers in nat-ural conditions

The Quaternary Datong volcanic group (DVG) is the most important monogenetic volcanic region in eastern China The volcanic basalt overlays the lacustrine strata, forming the baking strata with different temperatures, and the closer to the basalt, the higher the baking tem-perature The lacustrine strata baked by lava flow provides a good natural sample for the study of sensitivity characteristics of quartz ESR centers because compared with the result of laboratory treatments: 1)

* Corresponding author

** Corresponding author

E-mail addresses: jihao9610@126.com (H Ji), yingongming@ies.ac.cn (G.-M Yin)

Contents lists available at ScienceDirect Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas

https://doi.org/10.1016/j.radmeas.2022.106823

Received 30 November 2021; Received in revised form 15 June 2022; Accepted 29 June 2022

Radiation Measurements 157 (2022) 106823

the characteristics of quartz baked by lava flow are the same because of

the same provenance of sediments (Wang et al., 2002); 2) after

depo-sition the lacustrine strata have been baked at different temperatures

from high (hundreds or even over a thousand) to low (natural

envi-ronment temperature) depending on the depth; 3) the sample was baked

in the air, not in the oven; 4) the raw sediment was baked, not just quartz

grains; 5) the baked time was much longer, days or even months; 6) after

baking, the sample was irradiated at the natural dose rate rather than

artificially irradiated at 8 to 10 orders of magnitude higher than the

natural dose rate; 7) before baking, the lacustrine sediments was

bleached under natural sunlight; 8) judging from the characteristics of

the lacustrine sediments closest to the basalt, water should be involved

in the lava flow baking

Therefore, in the present study, we have observed and compared the

irradiation sensitivity (the amount of signal growth per unit dose)

characteristics of quartz ESR centers in natural conditions by lava flow

In addition, according to the heating experiment, we estimated the

paleo-temperatures of the lava flow and the associated baking layers

2 Samples

The sample site is located in the central part of Nihewan Basin, and

the Sanggan River flows through Nihewan Basin from west to east

Typical lacustrine strata (tens of meters thick) are widely distributed in

Nihewan Basin along the banks of the Sanggan River The sedimentary

deposit studied is considered to be homogeneous and the quartz initially

(before baking) should have the same physical properties The Cetian

Reservoir was built on the Sanggan River in the Nihewan Basin The lava

flow from DVG, located in the eastern part of Datong City, covered the

lacustrine strata at the north bank of Cetian Reservoir (Fig 1)

There are at least 13 volcanic cones in the western part of the DVG,

composed predominantly of alkali basalt produced by central-vent

eruptions, while the eastern part of the DVG is dominated by lava

flow composed mainly of tholeiites produced by fissure eruptions (e.g

Zhang, 1986; Basu et al., 1991; Li and Xu, 1995; Xu et al., 2005)

Volcanism in the western part of the DVG dates from the late Middle

Pleistocene, at ~0.4 Ma, while in the eastern part it dates from the early

Middle Pleistocene, at ~0.76 Ma (e.g Kaneoka et al., 1983; Chen et al.,

1992; Cheng et al., 2006) However, the timing of the ending of

volca-nism in the region has been debated for several decades (e.g Pei, 1981;

Zhou et al., 1982; Li and Sun, 1984; Zhu et al., 1990; Chen et al., 1992;

Zhao et al., 2012; Zhao et al., 2015)

The sampling site is located on the north bank of Cetian Reservoir the southwest of Yujiazhai village, and the southeast of DVG (Fig 2) The upper part of the sample section is covered with basalt which has a thickness of about 4 m Chen et al (1986) used the K–Ar method to determine the average age of basalt in Cetian Reservoir as ~0.4 Ma The baked layer is about 1.2 m and has a distinct red color compared with the unfired layer (Liu et al., 2015) According to the baking color and degree, from high to low, the baked layer can be divided into four parts (Fig 2): (1) sintering layer Indirect contact with lava flow, due to high temperature and pressure, the loose sediments consolidated into hard blocks with brick red color and thickness of ~10 cm, with numerous pores and rolling structure The basalt is inclined upward at the contact surface between the basalt and lacustrine layer (2) High temperature quenched layer, located in the lower part of the sintered layer, between

10 and 20 cm deep It is speculated that water is involved in baking, so it shows the characteristics of high-temperature quenching, gray and looseness, spherical structure, and more pores (Fig 2c) (3) High baking temperature layer at a depth between 20 cm and 80 cm, dense and dark red (4) Low baking temperature layer at a depth between 80 cm and

120 cm, dense and yellow-green, and the grain size of the sediment is smaller than for the upper layers (5) The typical lacustrine layer is located at depths below 120 cm, yellow-white and dense It contains a 5

cm thick calcium carbonate plate at the depth of 160 cm (Fig 2e)

We sampled sediments in these different layers (0–10, 10–20, 30–40, 50–60, 70–80, 90–100, 110–120, 130–140, 150–160, and 170–180 cm) and named them S1-10 to evaluate the impact of the baking temperature

on the quartz ESR centers under natural conditions, and in order to evaluate the dose rates of sample S1 and S2, we also collected a basalt sample (B1) at about 10 cm from the top of the lacustrine layer for analysis (Fig 2)

3 Experimental procedures

3.1 Quartz extraction and irradiation

There is a significant difference in grain size between the upper and lower It is clayey silt at the depth of 0–80 cm, and silty clay below 80

cm So, it is hard to separate the fraction larger than 100 μm below 80

cm For comparing the natural signal intensity of quartz, 80–100 μm fraction in all the samples was chosen to avoid any difference caused by

Fig 1 Location map of the study area and sampling site

C.-R Liu et al

different quartz particle sizes After sieving, pure quartz was obtained

through chemical separation techniques detailed by Liu et al (2010)

For investigating the irradiation sensitivity change, six samples of

different baking characteristics were selected for the study: S1and S2

were selected for different colors and features; S3 and S5 were selected

with 30 cm intervals for S3, S4 and S5 have the same color and features;

S7 was selected to be 30 cm from S5 for S6 and S7 have the same color

and features; S8 was selected because it is hard to extract enough quartz

in S9 and S10 for higher calcium content The quartz grains extracted

from six samples (S1, S2, S3, S5, S7, and S8) were divided into several

200 mg aliquots, seven of them were irradiated using a60Co gamma

source with the dose range of 109–2072 Gy

3.2 ESR measurement

The ESR intensities of both the Al and Ti centers were measured with

a Bruker ER-041-XG X-band spectrometer in a finger dewar cooled to 77

K with liquid nitrogen, in the ESR laboratory of the Institute of Geology, China Earthquake Administration, Beijing The experimental parame-ters were: microwave power 5 mW and modulation amplitude 0.16 mT The Al center intensity was measured from the top of the first peak to the bottom of the 16th peak (Yokoyama et al., 1985) The Ti–Li center in-tensity was taken from the top of the peak at g = 1.979 to the bottom at

g = 1.913 (Rink et al., 2007; Liu et al., 2010) and the average of the two peaks near g = 1.986 to the baseline is used as the signal intensity of the Ti–H center Fig 3 showed the natural S3 sample ESR spectrum at low temperature (77K, liquid nitrogen) Considering the angular depen-dence of the ESR signal due to the sample heterogeneity, each aliquot was measured six times after a rotation of 60◦ angle in the cavity to obtain the average intensity

Fig 2 Sampling profile of Yujiazhai and sample locations on the profile

Radiation Measurements 157 (2022) 106823

3.3 Dose rate

Dose rate is one of the factors to compare ESR signal characteristics

of quartz in different baking layers (see 4.1 section) The external dose

rate consists of the beta and gamma dose rates from the radioactive

el-ements (U, Th, K) in the sediments immediately surrounding the sample,

plus the contribution from cosmic rays However, as a result of the

gamma rays having an average range of 30 cm, the calculation of the

gamma dose rate for samples S1 and S2 should take into account the

contribution of the overlying basalt Considering the depths of samples

S1 and S2, we estimate the contribution ratios of basalt and sediment to

gamma dose rate as 1:1 and 1:3, respectively Radioactive elements (U,

Th, K) concentrations were determined by ICP-OES/MS analysis of the

natural sediments and basalt The external alpha dose rate was not

considered for hydrofluoric acid etching in quartz extraction (Liu et al.,

2010) The external beta and gamma dose rates were derived using the

dose rate conversion factors from Gu´erin et al (2011) We assumed a

grain size of 90 μm for beta ray attenuation, and the attenuation factor is

0.93 (Mejdahl, 1979) Since the sediments were dry at the time of

sampling, current water is more likely underestimated in comparison

with the past water content, and therefore it is estimated to be 10%

concerning previous ESR studies in the Nihewan Basin (The lacustrine

strata are the same set of sedimentary stratigraphy as in the Nihewan

Basin) (Liu et al., 2010, 2013, 2014) In addition, the water content of

basalt is considered to be 0% The cosmic dose rate contributions were

calculated using the formulae proposed by Prescott and Hutton (1988),

with depth, altitude, and latitude corrections (Prescott and Hutton,

1994)

4 Results

4.1 ESR measurement of natural (non-irradiated) aliquots

In this section we want to compare quantificationally the ESR signal intensity of natural quartz because quartz at different depths: 1) theo-retically, has the same provenance and the same transport and deposi-tion process before deposideposi-tion; 2) after deposideposi-tion, was partial or complete thermal bleaching by lava flow depending on the depth; 3) after baking, was irradiated continuously at natural dose rate for hun-dreds of thousands of years

The dose rates were shown in Table 1, range of 2.72–3.17 Gy/ka, low

in the upper layer and high in the lower layer Theoretically, if there is

no change in irradiation sensitivity characteristics of quartz ESR centers

at different depths, the intensity of quartz ESR centers should increase with the depth according to stratigraphic order However, the ESR in-tensity of quartz at different baking layers varies greatly The natural quartz ESR spectrum of several samples (S1, S4, S7, and S10) at low temperature (77K) were shown in Fig 4

4.1.1 The Al center

Fig 5a shows the evolution of the Al center signal intensity versus the depth of sampling It can be divided into three stages: 1) During the first stage, between 180 and 130 cm, the signal intensity does not change significantly 2) The second stage corresponds to a rapid decrease of signal intensity between 130 and 50 cm 3) The third stage corresponds

to a rapid increase of intensity between 50 cm and the top of the sequence

Considering the dose rate and stratigraphic order, the Al center in-tensity of the second stage (130-50 cm) should be equal to or slightly less than that of the first stage (180-130 cm) The Al center intensity of the second stage is much smaller than that of the first stage because the quartz was baked at high temperatures (over 220 ◦C), and the ESR in-tensity of the Al center decrease at 220 ◦C (Toyoda and Ikeya, 1991), and then released

4.1.2 The Ti center

There are three types of Ti centers according with the nature of the compensator cations: Ti–Li center, Ti–H center and Ti–Na center The Ti–Na center is however very rarely observed in natural quartz In this study, we did not observe the presence of this center in middle and lower layer (S5, S6, S7, S8, S9 and S10), so we will just discuss the signal characteristics of the Ti–Li and Ti–H centers

The signal intensity of the Ti–Li center remains basically unchanged for the lower part of the sequence from 180 to 130 cm depth, then de-creases to the minimum value at 90 cm, and then inde-creases slowly with the increasing baking temperature at the depth between 90 and 30 cm, before to lastly grows rapidly until the top of the section, as shown in Fig 5b

The Ti associated donor electrons are recombining predominantly at the [AlO4]0 acceptors The annealing process may lead directly to the

Fig 3 ESR spectrum showing the intensity of the Al, Ti–Li, and Ti–H centers in

natural sample S3 (77K, liquid nitrogen)

Table 1

Dose rates for samples S1–S10 and B1 from the Yujiazhai profile

Sample No Depth (cm) U (ppm) Th (ppm) K (%) Water content (%) Dβ (Gy/ka) Dγ (Gy/ka) Dcos (Gy/ka) Dtotal (Gy/ka) S1 5 1.52 ± 0.08 8.85 ± 0.44 2.33 ± 0.12 10 ± 5 1.900 ± 0.072 1.024 ± 0.026 0.120 ± 0.006 2.72 ± 0.15 S2 15 1.59 ± 0.08 9.83 ± 0.49 2.29 ± 0.11 10 ± 5 1.904 ± 0.074 1.082 ± 0.028 0.119 ± 0.006 2.93 ± 0.16 S3 35 1.62 ± 0.08 10.17 ± 0.51 1.91 ± 0.10 10 ± 5 1.668 ± 0.065 1.015 ± 0.026 0.115 ± 0.006 2.80 ± 0.14 S4 55 1.61 ± 0.08 8.84 ± 0.44 1.90 ± 0.10 10 ± 5 1.630 ± 0.063 0.955 ± 0.028 0.112 ± 0.006 2.70 ± 0.13 S5 75 2.06 ± 0.10 10.62 ± 0.53 1.99 ± 0.10 10 ± 5 1.782 ± 0.069 1.096 ± 0.028 0.108 ± 0.005 2.99 ± 0.15 S6 95 2.27 ± 0.11 9.71 ± 0.49 1.98 ± 0.10 10 ± 5 1.780 ± 0.069 1.075 ± 0.032 0.105 ± 0.005 2.96 ± 0.15 S7 115 2.13 ± 0.11 11.42 ± 0.57 2.11 ± 0.11 10 ± 5 1.887 ± 0.073 1.163 ± 0.030 0.105 ± 0.005 3.16 ± 0.15 S8 135 2.24 ± 0.11 11.75 ± 0.59 2.08 ± 0.10 10 ± 5 1.888 ± 0.073 1.181 ± 0.030 0.099 ± 0.005 3.17 ± 0.16 S9 155 2.19 ± 0.11 10.72 ± 0.54 2.15 ± 0.11 10 ± 5 1.904 ± 0.074 1.148 ± 0.034 0.097 ± 0.005 3.15 ± 0.15 S10 175 2.72 ± 0.14 10.64 ± 0.53 1.89 ± 0.10 10 ± 5 1.796 ± 0.070 1.140 ± 0.034 0.094 ± 0.005 3.03 ± 0.15

C.-R Liu et al

dissociation of Li, H associates (Poolton et al., 2000), rather than first

changing their charge state (Weil, 1984) Thus, the intensity of Ti–Li

center from 50 cm to 0 cm increases (Fig 6), similar to that of Al center

Compared with the Al and Ti–Li centers, the signal intensity of the

Ti–H is very weak As shown in Fig 5c, the signal intensity of Ti–H

center initially remains consistent at the depth of 180–130 cm, then

increases to a maximum at 50 cm and decreases sharply with the

in-crease of baking temperature

It is very interesting to compare Fig 5b and c that there is a good

correspondence between the stage of rapid increase of natural signal

intensity of the Ti–Li center and the stage of rapid decrease of natural

signal intensity of the Ti–H center (40-0 cm) Poolton et al (2000) also

observed this phenomenon by heating quartz samples before artificial

irradiation and proposed the following explanation: beyond 870 ◦C

(temperature of the transition from β-quartz to β-tridymite), the Ti–H

centers become unstable and dissociate, this would leave isolated Ti ions

available for Li capture, and then enhance the Ti–Li center population

At the stage where the natural signal intensity of ESR centers changes

significantly (60-0 cm), compared with the change of less than one time

of the Al center intensity, the signal intensity of the Ti–Li and Ti–H

centers changed by a factor of 7 and 2, respectively It indicates that the

ESR intensity of the Ti center is more strongly dependent on the

annealing history of the samples than the Al center (Poolton et al.,

2000) As there are many potential sources of H+and Li+within the

lattice in quartz, including water inclusions, OH molecules, [H3O4]0

defects, and cations associated with the Al or other centers (Halliburton

et al., 1979; Nuttall and Weil, 1981; Yang and McKeever, 1990), the

observed signal intensity change is much greater for Ti related signal

centers than for Al center

Compared with the signal intensity at the depth of 180–130 cm, the

maximum intensity value of both Ti–Li and Ti–H center has been

increased by two times and one time respectively (Fig 5b and c)

Ac-cording to the measurement results of dose rate (Table 1), we speculated

that the irradiation sensitivity of both Ti–Li and Ti–H centers changed

after high-temperature baking

4.2 ESR measurement of irradiated aliquots

According to the results of natural (non-irradiated) aliquots, we

suggest that high-temperature baking may change the irradiation

sensitivity of Al, Ti–Li, and Ti–H centers in quartz To verify this, we

have conducted an artificial irradiation experiment for six samples (S1,

S2, S3, S5, S7, and S8) to confirm whether the irradiation sensitivities of

ESR centers actually change after baking by lava flow The growth of

ESR intensity with irradiation for the six samples is shown in Fig 6

5 Discussion

In this study, the irradiation sensitivity is defined as the amount of signal growth per unit dose, that is:

K = △E/△Gy Where K is the irradiation sensitivity constant, △E is the intensity of ESR signal growth after received irradiation of △Gy

Recently, the Exponential + linear (EXP + LIN) function and Double saturating exponential (DSE) function have been recommended for dose response behavior fitting of the Al and Ti–Li centers, respectively (e.g Duval, 2012; Duval and Guilarte, 2015) But, in order to facilitate comparison and discussion, linear fitting is adopted in this study because the linear fitting is close to the exponential fitting in the low dose part, the maximum value of artificial irradiation is 2072 Gy in this study (Fig 6) The linear fitting equation is expressed as:

I=K*(D + DE) Where I is the ESR intensity, D is the additional irradiation dose, DE is the equivalent dose The results of fitting see Table 2

5.1 The Al center

According to the results of fitting (Table 2), the order of irradiation sensitivity constant of the Al center can be roughly expressed as KS8 =

KS7 <KS5 <KS3 <KS2 =KS1(Fig 6a), indicating that the change of irradiation sensitivity of the Al center increases with the baking tem-perature The Al center sensitivity of S7 is the same as that of S8, indi-cating that the layer where S7 is located is not affected by baking or the baking temperature is not sufficient to change the irradiation sensitivity

of the Al center As shown in Fig 5a, in the first stage (180-130 cm), the signal intensity of the Al center basically does not vary We interpret it as below 130 cm, the sediments were not affected by baking and the signal intensity of the Al center is the geological original intensity In the second stage (130-50 cm, between S7 and S3) the irradiation sensitivity

of the Al center is increase, but the intensity of it decreases as the rise of baking temperature Therefore, it can be concluded that the signal in-tensity of unbleachable part (during the deposition process) in Al center was released by the baking temperature at this stage, but the baking temperature was not sufficient to change the irradiation sensitivity of this center In the third stage (50-0 cm), the Al signal increases with decreasing depth, corresponding to the irradiation sensitivity of the Al

Fig 4 The natural quartz ESR spectrum of several samples (S1, S4, S7, and S10) at low temperature (77K, liquid nitrogen)

Radiation Measurements 157 (2022) 106823

center increases with the baking temperature (Fig 6a) This suggests that high-temperature baking near to the lava flow is sufficient to alter the irradiation sensitivity of the Al center, and that the higher the temperature rises, the greater the sensitivity increases

The Al center is a defect where an Al3+replaces a Si4+and is asso-ciated with a monovalent cation M+, such as H+, Li+, or Na+ Because of

Fig 5 Variation of signal intensity of ESR centers vs depth (a) Al center, (b)

Ti–Li center, and (c) Ti–H center

Fig 6 Evolution of the signal intensity of ESR centers with accumulated

gamma dose (a) Al center, (b) Ti–Li center, and (c) Ti–H center For Ti–H center, since the signal intensities of Sample S3 and S5 are much greater than the other four samples, two intensity axes were established to compare them together with the accumulated gamma dose S1, S2, S7, and S8 correspond to the left intensity axis and S3 and S5 correspond to the right intensity axis

C.-R Liu et al

the irradiation at room temperature, after trapping a hole, the cation M+

diffuses away Therefore, the increase of the Al center irradiation

sensitivity observed with baking may be due to the diffusion of the

cations within the quartz itself, and further studies are needed

5.2 The Ti center

The order of irradiation sensitivity constant of the Ti–Li center can be

expressed as KS8 =KS7 <KS5 <KS3 <KS1 <KS2(Fig 6b) This indicates

that the irradiation sensitivity of the Ti–Li center also increases with

baking temperature (Although the irradiation sensitivity of sample S2 is

slightly greater than that of S1), just like the behavior of the Al center,

but a little different is that the layer where the minimum signal value of

the Ti–Li center is located (90–100 cm) (Fig 5b) is below the layer

where the minimum signal value of the Al center is located (50–60 cm)

(Fig 5a) This suggests that the thermal stability of the Al center is

higher than that of the Ti–Li center, which is consistent with the results

observed by Toyoda and Ikeya (1991)

The variation of the Ti–H center sensitivity with temperature is

significantly different from that of the Al and Ti–Li centers The

irradi-ation sensitivity constant of samples at different layers can be expressed

as KS1 <KS2 <KS8 =KS7 <KS3 <KS5 (Fig 6c) This indicates that the

irradiation sensitivity of the Ti–H center first increases and then

de-creases with baking temperature, which can well explain the variation of

the Ti–H center’s natural intensity at different layers on the profile

(Fig 5c)

5.3 Estimating annealing temperatures

In order to estimate annealing temperatures for the different layers,

we attempted to perform a heating experiment (each aliquot was heated

for 12 h in the temperature range from 100 to 1100 ◦C at 100 ◦C

in-tervals using a muffle furnace) in the laboratory and then irradiated a

specific dose value (6000 Gy) to observe the change of signal intensity of

ESR centers To ensure that the quartz particles had the same origin, the

sample used was lacustrine sediment 350 cm from the basalt, and the

results are shown in Fig 7

Despite the difference between laboratory simulations and natural

conditions, we can still see that for the same ESR center, the signal

in-tensities at different heating temperatures from laboratory simulations

(the red line in Fig 7) show almost consistent trends with the natural

signal intensities at different depths in the profile (Fig 5) Theoretically,

the change in the net increase in the signal intensity of ESR centers

before and after irradiation of samples (the signal intensity value of the

red line minus the signal intensity value of the blue line) with different

heating temperatures (Fig 7) can be considered to represent a change in

irradiation sensitivity Therefore, it can be clearly seen that the changes

of radiation sensitivity of the three ESR centers observed in the

labo-ratory (Fig 7) are coincident with those observed under natural

con-ditions (volcanic baking) (Section 5.1 and 5.2), which can be seen as

additional evidence for our conclusion

From Fig 5, we can see that for the three ESR centers, there is a

significant inflection point in the signal intensity at 50–60 cm depth

Table 2

The linear fitting results of quartz Al, Ti–Li, and Ti–H centers K = irradiation

sensitivity constant; Adj r2 =goodness-of-fit

Sample No Al center Ti–Li center Ti–H center

S1 0.6450 0.9786 0.5459 0.9898 0.0019 0.9696

S2 0.6498 0.9811 0.6079 0.9906 0.0029 0.9667

S3 0.5171 0.9854 0.3816 0.9639 0.0297 0.9881

S5 0.2951 0.9531 0.1778 0.9783 0.0438 0.9642

S7 0.1070 0.9667 0.0199 0.9730 0.0035 0.9699

S8 0.1188 0.9730 0.0182 0.9760 0.0035 0.9838

Fig 7 The relations between the signal intensity of ESR centers (before and

after gamma irradiation 6000 Gy) and annealing at different temperatures (0–1100 ◦C) for 12 h

Radiation Measurements 157 (2022) 106823

uniformly, and by comparing with the heating curves, the inflection

point represents a temperature perhaps around 400–500 ◦C However,

for middle and lower layers (180-60 cm), the assessment of the

annealing temperatures only by ESR intensities is unreliable due to the

possibility of varying degrees of thermal bleaching of the ESR centers

An interesting phenomenon is that after heating above 1000 ◦C,

addi-tional irradiation does not produce new Ti–H signals, and since Ti–H

signals can be observed in all of our samples, this probably indicates that

the paleo-temperature of lava flow did not exceed 1000 ◦C

It should be noted that according to the results of our heating

experiment, the changing behavior of the natural signal intensity of the

Ti–Li and Ti–H centers in the upper section (40-0 cm) may not be

explained by the quartz phase transition (β-quartz to β2-tridymite,

870 ◦C) proposed by Poolton et al (2000), and we speculate that this

may be related to another phase transition of quartz (α-quartz to

β-quartz, 573 ◦C), which, of course, requires further experiments to

confirm

6 Summary and conclusions

In this paper, we investigated the relationship between irradiation

sensitivity of quartz Al and Ti centers and baking temperature by

vol-canic lava flow The irradiation sensitivity of the Al and Ti–Li centers

increases with the baking temperature, whereas the irradiation

sensi-tivity of the Ti–H center increases first (up to ~500 ◦C) and then

de-creases with temperature The reduction of the Ti–H center sensitivity at

40-0 cm depth may be due to the baking temperature in this depth range

reaching the temperature of the quartz phase transition from α-quartz to

β-quartz (573 ◦C), causing the [TiO4/H+]0 centers become unstable and

dissociate In addition, from our experimental results, the ESR intensity

of the Ti center is more strongly dependent on the annealing history of

the samples than the Al center, because there are many potential sources

of H+and Li+within the lattice in quartz, including water inclusions, OH

molecules, [H3O4]0 defects and cations associated with the Al or other

centers (Yang and McKeever, 1990) Finally, from the results of the

heating experiment, after heating above 1000 ◦C, additional irradiation

does not produce new Ti–H signals, this probably indicates that the

paleo-temperature of the lava flow in Yujiazhai area did not exceed

1000 ◦C

Declaration of competing interest

The authors declare that they have no known competing financial

interests or personal relationships that could have appeared to influence

the work reported in this paper

Data availability

Data will be made available on request

Acknowledgements

This work was supported by the National Natural Science Foundation

of China (Grant No 42172211), and the basic scientific research fund,

Institute of Geology, China Earthquake Administration (Grant No

IGCEA1908)

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