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Research Article
Liang Tianyi, Li Mengmeng*, Wang Li, Wang Guanhong, Tang Xinglong, and Li Zhuang
Geochronology and geochemistry of late
Paleozoic volcanic rocks in eastern Inner
Mongolia and their geological significance
https://doi.org/10.1515/geo-2025-0786
received September 10, 2024; accepted February 28, 2025
Abstract: The Daxing’anling region in Inner Mongolia has
always been the most active area of tectonic magmatic
activity in the Xingmeng orogenic belt. This study investi-
gated the rock geochemistry of trachyandesite and rhyolite
tuffof the Late Carboniferous Gegen Aobao Formation in
eastern Inner Mongolia. This study presents new petro-
graphy, zircon U-Pb age, and whole-rock geochemical data
for the Late Carboniferous Gegenaobao Formation in vol-
canic rocks in order to constrain their petrogenesis and
geodynamic setting. The results indicate that the aluminum
content of trachyandesite is relatively high, and the calcium
and magnesium content is higher than that of rhyolite tuff,
showing a sodium-rich characteristic. It is a quasi-aluminum
peraluminous rock, and the europium anomaly is not
obvious. The formation age is 304.4 ±2.3 Ma. The calcium
and magnesium content of the rhyolite tuffis relatively low,
exhibiting characteristics of calcium alkali and weak pera-
luminous rocks. It has more obvious characteristics of light
and heavy rare earth fractionation and negative europium
anomalies, with a formation age of 307.6 ±2.0 Ma.
Comprehensive analysis shows that the magma of Late
Carboniferous volcanic rocks in eastern Inner Mongolia
mainly originates from the crust, with a deeper source of
andesite and partial melting of the mantle material. Both are
tectonic environments of continental margin arc volcanic
rocks. The Xing’an Block and the Songnen Block completed
collision assembly in the Early Carboniferous and were in a
post-orogenic extension environment in the Late
Carboniferous. The ancient Asian Ocean in the northern
part of the Erlian Hegenshan Zhalantun Heihe tectonic
belt had already closed in the Late Carboniferous, and the
Xingmeng orogenic belt began to enter the orogenic exten-
sion stage.
Keywords: U-Pb chronology, rock geochemistry, Xingmeng
orogenic belt, magmatic genesis
1 Introduction
The Xingmeng orogenic belt in eastern Inner Mongolia is
one of the most significant regions for continental accre-
tion and mountain building between the two major plates
[1]. The study of its tectonic evolution has always been a
focus of attention for scholars both domestically and inter-
nationally [2]. According to the latest research, the Xing-
meng orogenic belt completed the collision and collage of
the Siberian and North China plates through the assembly
of numerous microcontinents within the ancient Asian
Ocean [3]. By studying the evolution of tectonic zones
between numerous microplates, numerous theories on
the evolution of the ancient Asian Ocean have gradually
emerged [4,5]. The Erlian Hegenshan Heihe tectonic belt is
an important tectonic belt in the Xingmeng region, located
between the Xing’an and Songnen blocks. It is also
Liang Tianyi: Chemical Geological Prospecting Institute of Liaoning
Province Co. LTD, No. 6, Section 3, Helanshan Road, Jinzhou Economic
and Technological Development Zone, Jinzhou, Liaoning Province,
121007, China, e-mail: 327251026@qq.com
* Corresponding author: Li Mengmeng, School of Computer Science
and Engineering, Guilin University of Aerospace Technology, No. 2 Jinji
Road, Qixing District, Guangxi, Guilin, 541004, China,
e-mail: 710423866@qq.com
Wang Li: Chemical Geological Prospecting Institute of Liaoning Province
Co. LTD, No. 6, Section 3, Helanshan Road, Jinzhou Economic and
Technological Development Zone, Jinzhou, Liaoning Province, 121007,
China, e-mail: 373519089@qq.com
Wang Guanhong: Chemical Geological Prospecting Institute of Liaoning
Province Co. LTD, No. 6, Section 3, Helanshan Road, Jinzhou Economic
and Technological Development Zone, Jinzhou, Liaoning Province,
121007, China, e-mail: 178272736@qq.com
Tang Xinglong: Chemical Geological Prospecting Institute of Liaoning
Province Co. LTD, No. 6, Section 3, Helanshan Road, Jinzhou Economic
and Technological Development Zone, Jinzhou, Liaoning Province,
121007, China, e-mail: 463272@qq.com
Li Zhuang: Chemical Geological Prospecting Institute of Liaoning
Province Co. LTD, No. 6, Section 3, Helanshan Road, Jinzhou Economic
and Technological Development Zone, Jinzhou, Liaoning Province,
121007, China, e-mail: 949631246@qq.com
Open Geosciences 2025; 17: 20250786
Open Access. © 2025 the author(s), published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 International License.
considered one of the six major subduction zones in Inner
Mongolia [6]. Some scholars initially believed that this tec-
tonic zone was the final closure position of the ancient
Asian Ocean, but others believed that it was only the colli-
sion closure position between the Xing’an Block and the
Songnen Block [7–9] and did not represent the final posi-
tion of the ancient Asian Ocean. At the same time, dif-
ferent views have been put forward on the formation
time limit of this tectonic belt. Some scholars believe
that the Xing’an and Songnen blocks completed collision
and assembly during the Late Devonian Early Carboni-
ferous [7,10–12]. Some scholars also believe that the
Xing’an and Songnen blocks were still active during the
Early Permian, and the magmatic activity in the Late
Paleozoic was mainly caused by the subduction of oceanic
crust [13]. In summary, further research is needed on the
tectonic magmatic evolution of the Xingmeng orogenic
belt in the late Paleozoic era.
The research area is located in the middle section of
the Greater Khingan Range, with the Erenhot Hegenshan
Heihe ophiolite belt passing through the southern part of
the studied area. The Late Paleozoic volcanic rocks widely
distributed in the study area are important research
objects for studying the evolution of the Xingmeng oro-
genic belt. Through field systematic geological surveys
and sampling work, systematic petrographic, zircon U-Pb
geochronology, and geochemical analysis were conducted
on the combination of intermediate to felsic volcanic rocks
to explore their age, petrogenetic, and tectonic back-
ground. Further analysis was conducted on the combina-
tion process of the Late Paleozoic Xing’an Block and the
Songnen Block in the middle section of the Greater
Figure 1: Geologic map in the study area.
2Liang Tianyi et al.
Khingan Range, providing reliable basic data for studying
the evolution of the Paleozoic Xingmeng orogenic belt and
improving the research level of the tectonic magmatic evo-
lution of the Xingmeng orogenic belt in the Late Paleozoic.
2 Geological overview
The research area is locatedat the contact point betweenthe
Xing’an block and the Songnen block. The regional geolo-
gical structure is located on the Dongwuqi Duobaoshan
island arc, and the Erenhot Hegenshan suture zone is
located in the southern part of the working area (Figure
1a). The Paleozoic rocks are widely distributed in the
research area, accompanied by a certain scale of Mesozoic
volcanic rock strata and intrusive rocks. The Paleozoic strata
are mainly composed of the Late Carboniferous Gegenaobao
Formation (C
2
g), which is a set of marine felsic volcanic lava/
volcanic debris rock combinations. It is in angular uncon-
formity contact with the overlying Linxi Formation (P
3
l). The
Linxi Formation (P
3
l) is a set of marine land interaction
facies clastic rock combinations, mainly composed of sand-
stone, siltstone, and interbedded limestone. The Mesozoic
volcanic rocks are mainly the Manketou Ebo Formation
(J3m) of the Jurassic system, which is composed of terrestrial
felsic volcanic rocks, and the Baiyin Gaolao Formation (K1b)
of the Cretaceous system, which is mainly composed of felsic
volcanic rocks. The intrusive rocks are mainly of the Cretac-
eous period (Figure 1b and c).
The Carboniferous Gegen Aobao Formation is the main
stratigraphic unit in the work area, which is widely spread.
Through detailed field research and profile measurements,
the lower part of this formation is found to be mainly
composed of marine, terrestrial clastic rocks, including meta-
morphic quartz sandstone, feldspar sandstone, metamorphic
siltstone, and mudstone slate, which have obvious meta-
morphic phenomena such as sericite and chloritization. The
central region is mainly composed of intermediate volcanic
rocks, including trachyandesite (including pores), trachyte,
breccia lava, andesite tuff, and a small amount of felsic tuff.
The upper part is mainly composed of felsic rocks such as
rhyolite tuff, rhyolite, and a small amount of breccia lava.
Trachyandesite is mainly gray-brown in color, with a
spotted structure and a spotted crystal content of 10%. It is
mainly composed of plagioclase and a small amount of
biotite, with a spotted grain size of 0.30–2.00 mm. The
matrix is mainly composed of plagioclase and a small
amount of opaque minerals. Plagioclase is mostly needle-
shaped with a particle size of 0.02–0.06 mm. Rocks have a
small amount of developed pores, which are mainly filled
Figure 2: Field outcrop and microphotographs of volcanic rocks in the study area. Pl, Plagioclase; Qtz, quartz; and Kfs, K-feldspar.
Geochronology and geochemistry of late Paleozoic volcanic rocks 3
with epidote. It can be seen that the rock has undergone
strong epidote and silicification, with developed fractures
filled with iron and epidote (Figure 2a and c).
The color of rhyolite tuffis mainly gray, with a tuffac-
eous structure and blocky structure. Volcanic breccia is
composed of tuff, which is angular or irregular in shape,
with a gravel diameter of 2.00–15.00 mm and a content of
about 8%. The main components of rock debris are tuffand
andesite, which are subrounded or subangular in shape,
with a particle size of 0.05–2.00 mm and a content of about
5%. The main components of crystal fragments are plagio-
clase, potassium feldspar, and a small amount of quartz,
which are irregular in shape. The grain size of crystal
fragments is 0.05–2.00 mm, and individual crystal frag-
ments can reach 3.00 mm, with a content of about 35%.
The glass shards are irregular in shape, with most of
them undergoing devitrification. Some undergo slight
polarization reactions, while others crystallize into small
quartz crystals, accounting for about 52% (Figure 2b and d).
3 Materials and methods
This work mainly focuses on the study of trachyandesite
and rhyolitic tuffin the volcanic rock suit of the
Gegenaobao Formation, including petrology, chronology,
and rock geochemistry. The zircon chronology samples
are numbered trachyandesite (TW5) and rhyolitic tuff
(TW16), and the rock geochemical samples are numbered
trachyandesite (G1–G8) and rhyolitic tuff(H1–H7). The
sampling locations are shown in Figure 1b.
Single mineral sorting was conducted at the Regional
Geological Survey and Research Institute of Langfang City,
Hebei Province. First, each sample is crushed to an appro-
priate particle size, cleaned, dried, and screened, and
zircon crystals of different particle sizes are separated
using magnetic and heavy liquid separation methods. CL
image (cathodoluminescence image) shooting and LA-ICP-
MS U-Pb dating were completed at Beijing Kehui Testing
Technology Co., Ltd. The laser ablation inductively coupled
plasma mass spectrometer was used (Jena Elite, Germany),
and the laser model was Newwave 193-UC (USA). Based on
the cathodoluminescence and transmission light images of
zircon, suitable zircon positions without inclusions and
cracks were selected [14]. A 193 mm excimer laser was
used to etch the surface of the zircon, with a laser ablation
diameter of 25 μm, and the erosion frequency is 10 Hz.
Using He as a carrier for erosion material, transport the
erosion material to a mass spectrometer for testing and
analysis. The high-frequency transmitter power of ICPMS
is 1200w, the cooling gas (Ar) flow is 9 L/min, and the mate-
rial of the cone is nickel. The integration time for analysis
is a total of 40 s, and the blank collection time is 30 s. The
Table 1: LA-ICP-MS U–Pb isotope analysis results of zircon from trachyandesite (TW5) in the study area
Tested point Isotope ratios and errors Age and error (Ma/σ)
207
Pb/
206
Pb 1σ
207
Pb/
235
U1σ
206
Pb/
238
U1σ
207
Pb/
206
Pb 1σ
207
Pb/
235
U1σ
206
Pb/
238
U1σ
TW5-01 0.0515 0.0036 0.3382 0.0234 0.0483 0.0008 261.2 158.3 295.8 17.8 303.9 4.7
TW5-02 0.0540 0.0032 0.3618 0.0212 0.0491 0.0008 372.3 133.3 313.6 15.8 309.0 4.7
TW5-03 0.0545 0.0032 0.3589 0.0215 0.0476 0.0008 390.8 131.5 311.4 16.1 300.0 4.6
TW5-04 0.1085 0.0062 0.6200 0.0321 0.0424 0.0007 1775.9 99.1 489.9 20.2 267.6 4.6
TW5-05 0.0746 0.0095 0.2120 0.0274 0.0215 0.0006 1058.3 253.2 195.2 22.9 137.0 3.5
TW5-06 0.0575 0.0035 0.3889 0.0244 0.0488 0.0007 522.3 133.3 333.6 17.8 307.0 4.5
TW5-07 0.0563 0.0033 0.3739 0.0211 0.0483 0.0008 464.9 129.6 322.5 15.6 303.9 5.1
TW5-08 0.0506 0.0033 0.3368 0.0220 0.0482 0.0008 220.4 150.0 294.7 16.7 303.4 4.8
TW5-09 0.0537 0.0022 0.3563 0.0137 0.0483 0.0006 366.7 94.4 309.4 10.3 304.0 4.0
TW5-10 0.0562 0.0026 0.3672 0.0158 0.0478 0.0007 461.2 103.7 317.6 11.7 301.1 4.3
TW5-11 0.0853 0.0043 0.5544 0.0248 0.0478 0.0007 1324.1 97.8 447.9 16.2 301.1 4.5
TW5-12 0.0598 0.0044 0.3961 0.0288 0.0482 0.0008 598.2 159.2 338.8 20.9 303.2 4.6
TW5-13 0.0594 0.0039 0.3852 0.0246 0.0477 0.0008 581.2 143.3 330.8 18.0 300.2 4.7
TW5-14 0.0531 0.0029 0.1589 0.0084 0.0218 0.0003 331.5 121.3 149.7 7.4 139.3 2.0
TW5-15 0.0495 0.0030 0.3268 0.0193 0.0481 0.0006 172.3 137.9 287.2 14.8 302.9 3.9
TW5-16 0.0650 0.0036 0.4136 0.0195 0.0469 0.0007 772.2 116.7 351.5 14.0 295.6 4.5
TW5-17 0.0561 0.0033 0.3795 0.0219 0.0491 0.0007 457.5 132.4 326.7 16.1 308.8 4.3
TW5-18 0.0500 0.0038 0.3422 0.0259 0.0501 0.0009 198.2 177.8 298.8 19.6 314.9 5.3
TW5-19 0.0599 0.0031 0.3985 0.0203 0.0485 0.0006 598.2 112.9 340.6 14.7 305.3 3.9
TW5-20 0.0485 0.0035 0.3276 0.0235 0.0483 0.0009 124.2 159.2 287.8 18.0 304.1 5.2
4Liang Tianyi et al.
sample data were processed using NIST 610 and GJ-1 as
internal zircon standards, and the software was analyzed
and plotted using the ICPMSData program and the Isopolot
program [15].
A total of 15 samples were analyzed for major and
trace elements geochemistry. First, the samples were sub-
jected to weathering shell removal and then crushed and
ground into powder using a ball mill. The testing and ana-
lysis of major and trace elements were completed by the
laboratory of the Hebei Provincial Institute of Regional
Geological and Mineral Resources Survey. The major ele-
ments were tested using the Axios Max X-ray fluorescence
spectrometer, with an accuracy better than 5%. Trace ele-
ments were tested using an inductively coupled plasma
mass spectrometer, with an analysis accuracy better
than 5%.
4 Analysis results
4.1 Zircon U–Pb geochronology
The results of zircon U–Pb isotope analysis in the study
area are shown in Tables 1 and 2. The zircon U–Pb age
harmony diagram and some zircon cathodoluminescence
diagrams are shown in Figure 3. The selected zircon sam-
ples are mostly in the shape of long columns or squares
with good transparency. The diameter of zircon particles is
mostly between 100 and 200 μm. Zircons have distinct
rhythmic bands of magmatic origin. According to previous
research, the corresponding Th and U content and Th/U of
zircons vary depending on their genesis [16,17]. Generally,
magmatic zircons have Th/U greater than 0.4, while meta-
morphic zircons have lower Th and U content, with Th/U
often less than 0.07 [18]. The Th/U of TW5 zircon sample
ranges from 0.47 to 2.01, while the Th/U of TW16 ranges
from 0.44 to 0.76, both of which are greater than 0.4,
showing obvious magmatic zircon characteristics.
A total of 20 zircon measurement spots were obtained
from the trachyandesite (TW5) sample. On the 206Pb/238U-
207Pb/235U harmonic map, the measurement points TW5-
04, TW5-05, and TW5-14 have poor harmony, so they were
not included in the final calculation. The weighted mean
age of the remaining measurement points is 304.4 ±2.3 Ma,
with MSWD =0.63, which represents the age of the forma-
tion of trachyandesite. A total of 19 zircon measurement
points were obtained from the rhyolitic tuff(TW16) sample,
which was shown on the 206Pb/238U-207Pb/235U harmonic
map. All 19 measurement points were included in the pro-
jection calculation, with an age-weighted average of 307.6 ±
2.0 Ma and MSWD =0.25, which represents the age of the
formation of rhyolite tuff.
Table 2: Zircon LA-ICP-MS U-Pb data for Rhyolitic tuff(TW16) in the study area
Tested point Isotope ratios and errors Age and error (Ma/σ)
207
Pb/
206
Pb 1σ
207
Pb/
235
U1σ
206
Pb/
238
U1σ
207
Pb/
206
Pb 1σ
207
Pb/
235
U1σ
206
Pb/
238
U1σ
TW16-01 0.0599 0.0036 0.4005 0.0237 0.0484 0.0007 611.1 123.1 342.0 17.2 304.5 4.3
TW16-02 0.0605 0.0031 0.3975 0.0194 0.0481 0.0006 633.4 109.2 339.9 14.1 302.9 4.0
TW16-03 0.0529 0.0026 0.3560 0.0167 0.0492 0.0006 324.1 113.0 309.3 12.5 309.5 3.8
TW16-04 0.0523 0.0030 0.3510 0.0198 0.0491 0.0006 298.2 133.3 305.5 14.9 308.9 3.6
TW16-05 0.0535 0.0038 0.3510 0.0234 0.0488 0.0007 350.1 156.5 305.5 17.6 307.4 4.4
TW16-06 0.0531 0.0026 0.3533 0.0169 0.0486 0.0006 344.5 111.1 307.2 12.7 306.2 3.8
TW16-07 0.0522 0.0029 0.3517 0.0198 0.0487 0.0006 300.1 125.9 306.0 14.9 306.6 3.8
TW16-08 0.0570 0.0026 0.3855 0.0172 0.0494 0.0006 500.0 101.8 331.1 12.6 310.7 3.8
TW16-09 0.0552 0.0027 0.3678 0.0172 0.0485 0.0006 420.4 107.4 318.0 12.8 305.5 3.8
TW16-10 0.0506 0.0036 0.3401 0.0250 0.0487 0.0010 220.4 166.6 297.3 18.9 306.6 5.9
TW16-12 0.0524 0.0036 0.3542 0.0241 0.0494 0.0011 301.9 157.4 307.9 18.1 310.8 6.6
TW16-13 0.0576 0.0030 0.3837 0.0192 0.0488 0.0007 522.3 119.4 329.7 14.1 307.1 4.6
TW16-14 0.0493 0.0025 0.3337 0.0166 0.0491 0.0007 164.9 116.7 292.4 12.7 309.0 4.3
TW16-15 0.0484 0.0035 0.3226 0.0212 0.0488 0.0008 120.5 159.2 283.9 16.3 307.0 4.9
TW16-16 0.0517 0.0053 0.3420 0.0329 0.0493 0.0011 333.4 233.3 298.7 24.9 310.0 6.9
TW16-17 0.0523 0.0024 0.3525 0.0153 0.0493 0.0007 298.2 103.7 306.6 11.5 310.0 4.4
TW16-18 0.0536 0.0035 0.3599 0.0217 0.0492 0.0007 353.8 148.1 312.2 16.2 309.4 4.5
TW16-19 0.0512 0.0029 0.3400 0.0189 0.0487 0.0008 250.1 126.8 297.2 14.3 306.6 4.6
TW16-20 0.0484 0.0040 0.3281 0.0278 0.0492 0.0012 116.8 185.2 288.1 21.2 309.8 7.1
Geochronology and geochemistry of late Paleozoic volcanic rocks 5
4.2 Geochemistry
4.2.1 Major element characteristics
The main elemental analysis results of trachyandesite are
shown in Table 3. The SiO
2
content ranges from 55.40 to
58.02%, with a high Al
2
O
3
content of 14.89–19.29%, MgO
content of 1.52–3.26%, CaO content of 3.33–7.57%, P
2
O
5
con-
tent of 0.24–0.52%, total alkali (ALK) content of 4.41–7.64%,
and a mean of 6.36%. The rocks exhibit sodium-rich char-
acteristics, with Na
2
O content of 3.19–5.20%, an aluminum
saturation index (A/CNK) of 0.83–1.05, and a Rittman index
(σ) of 0.83–1.05, ranging from 1.42 to 3.71, with an average
of 2.82, exhibiting calc-alkaline characteristics. The Mg#
value ranges from 30.23 to 49.53, with an average of
41.98. According to the TAS diagram of volcanic rocks
(Figure 4), most of the samples fall within the range of
trachyandesite, with two samples falling within the range
of andesite. According to the SiO
2
–K
2
O diagram (Figure 5),
the samples are mostly calcium-alkaline (high potassium)
series rocks, with one sample located within the range of
potassium basalt. Due to the complex genesis and diversity
of volcanic rocks, they may form rock types with subtle
differences due to different geological environments and
magmatic processes. According to the A/CNK–A/NK dia-
gram (Figure 6), it is shown that the trachyandesite has
semialuminous to peraluminous characteristics.
The analysis results of major elements in felsic rocks
are shown in Table 4. The SiO
2
content is between 72.44 and
75.24%, and the aluminum content is moderate, ranging
from 12.88 to 14.39%. The content of MgO is 0.27–0.31%,
and the content of CaO is 0.26–0.35%. The P
2
O
5
content is
Figure 3: Zircon U–Pb age harmony map and partial zircon cathodoluminescence (CL) map of trachyandesite (TW5) and rhyolite tuff(TW16) in the
study area.
6Liang Tianyi et al.
Table 3: Analysis results of major elements (%) and trace elements (ppm) in coarse Anite in the study area
Sample
number
G1 G2 G3 G4 G5 G6 G7 G8
Lithology Trachy-
andesite
Trachy-
andesite
Andesite Trachy-
andesite
Trachy-
andesite
Trachy-
andesite
Andesite Trachy-
andesite
SiO
2
57.62 55.58 55.40 58.02 56.72 56.70 56.42 55.42
TiO
2
0.86 0.90 1.17 1.60 1.45 1.01 1.55 0.97
Al
2
O
3
18.30 19.29 18.17 14.89 16.71 16.23 14.92 16.25
Fe
2
O
3
3.33 3.43 2.36 4.45 4.89 3.33 3.64 3.47
FeO 3.63 3.66 4.13 3.92 2.19 2.87 4.20 2.80
MnO 0.11 0.11 0.27 0.12 0.12 0.15 0.11 0.13
MgO 3.18 3.18 1.52 2.61 2.89 2.58 2.74 3.26
CaO 4.51 5.03 7.57 3.33 4.58 3.59 5.40 4.28
Na
2
O 5.00 5.10 3.55 5.20 4.56 3.19 3.78 5.14
K
2
O 1.28 1.36 0.86 2.44 2.25 3.37 1.71 2.09
P
2
O
5
0.24 0.26 0.37 0.44 0.52 0.29 0.41 0.28
LOI 1.17 1.02 4.00 2.32 2.40 6.02 4.43 5.59
TOTAL 99.23 98.92 99.37 99.32 99.31 99.32 99.32 99.69
ALK 6.28 6.46 4.41 7.64 6.81 6.56 5.49 7.23
Na
2
O/K
2
O 3.91 3.75 4.13 2.13 2.03 0.95 2.21 2.46
A/CNK 1.03 1.02 0.89 0.86 0.92 1.05 0.83 0.88
DI 59.49 56.83 50.43 68.92 62.10 64.66 58.22 63.77
σ2.61 3.16 1.42 3.68 3.17 2.77 2.03 3.71
SI 19.39 19.04 12.25 14.06 17.40 16.88 17.05 19.53
Mg
#
46.10 45.66 30.23 36.99 43.87 43.94 39.52 49.53
V 74.20 83.77 159.13 244.04 181.86 125.48 225.46 144.19
Cr 9.40 4.72 2.24 6.94 14.32 6.17 14.52 5.31
Ni 3.71 5.36 3.82 9.62 13.46 5.86 11.84 5.80
Ga 22.34 19.10 21.04 22.73 23.18 21.92 22.20 19.30
Rb 38.66 34.69 17.26 47.55 40.35 83.65 36.05 55.51
Sr 558.96 475.58 1028.39 714.10 1018.49 578.32 637.26 559.11
Zr 226.02 174.50 161.54 232.00 220.08 181.42 208.17 154.40
Nb 7.67 8.01 6.14 9.10 11.64 7.82 8.61 6.75
Ba 834.27 579.98 650.88 820.80 901.32 1700.93 937.14 621.23
Hf 5.85 4.70 4.66 6.60 5.78 5.22 6.11 4.68
Ta 0.42 0.38 0.36 0.58 0.62 0.51 0.48 0.45
W 0.03 0.44 0.26 0.37 0.45 0.43 0.35 0.26
Pb 17.31 11.74 12.18 15.43 14.74 15.77 12.92 11.53
Th 3.11 2.48 2.78 4.28 3.68 4.13 3.99 3.43
U 0.72 0.60 0.68 1.17 1.11 1.29 1.11 0.83
La 25.40 19.70 22.00 27.80 33.50 25.20 24.90 21.60
Ce 43.40 44.40 45.00 59.50 68.00 48.50 51.70 41.00
Pr 5.81 4.57 6.08 7.97 8.96 6.61 7.10 5.47
Nd 24.10 19.00 26.50 33.80 36.10 27.80 31.50 23.20
Sm 4.76 3.85 5.23 7.03 7.10 5.44 6.35 4.73
Eu 1.46 1.15 1.67 1.96 2.10 1.92 1.71 1.47
Gd 3.84 3.07 4.39 5.80 5.77 4.76 5.21 4.01
Tb 0.60 0.48 0.67 0.88 0.80 0.71 0.78 0.61
Dy 3.46 2.79 3.55 4.92 4.15 3.78 4.25 3.34
Ho 0.64 0.51 0.61 0.89 0.71 0.68 0.78 0.62
Er 1.70 1.40 1.73 2.40 1.94 1.91 2.11 1.77
Tm 0.26 0.22 0.29 0.39 0.33 0.31 0.37 0.30
Yb 1.58 1.32 1.65 2.34 1.89 1.82 2.11 1.74
Lu 0.25 0.22 0.25 0.36 0.28 0.29 0.32 0.27
Y 19.90 15.80 18.00 24.40 22.50 20.90 21.60 17.10
ΣREE 117.26 102.68 119.62 156.04 171.63 129.73 139.19 110.13
La
N
/Yb
N
11.53 10.71 9.56 8.52 12.71 9.93 8.46 8.90
(Continued)
Geochronology and geochemistry of late Paleozoic volcanic rocks 7
low, and the total alkali (ALK) content is high, ranging from
7.66% to 9.13%, with an average of 8.71%. The rocks exhibit
sodium-rich characteristics, with the aluminum supersa-
turation index (A/CNK) ranging from 0.99 to 1.15 and the
Rittman index (σ) ranging from 1.81 to 2.81, with an average
of 2.46, exhibiting calc-alkaline characteristics. The Mg #
value ranges from 17.98 to 22.68, with an average of 20.18.
According to the TAS diagram of volcanic rocks (Figure 4),
all samples fall within the range of rhyolite. According to
the SiO
2
-K
2
O diagram (Figure 5), all seven samples are high
in potassium/calcium alkaline series rocks. According to
the A/CNK-A/NK diagram (Figure 6), it is shown that felsic
rocks are mostly weakly peraluminous rocks.
4.2.2 Characteristics of trace and rare earth elements
The analysis results of trace and rare earth elements in
trachyandesite are shown in Table 3, and the spider web
diagram (Figure 7a) shows the relative enrichment of large
ion lithophile elements such as Ba, Rb, and K (LILE) and
loss of the high-field-strength elements such as Nb (HFSE).
Table 3: Continued
Sample
number
G1 G2 G3 G4 G5 G6 G7 G8
Lithology Trachy-
andesite
Trachy-
andesite
Andesite Trachy-
andesite
Trachy-
andesite
Trachy-
andesite
Andesite Trachy-
andesite
δEu 1.04 1.02 1.07 0.94 1.00 1.15 0.91 1.03
δCe 0.88 1.15 0.95 0.98 0.96 0.92 0.95 0.92
Figure 4: TAS diagram of volcanic rocks in the study area.
Figure 5: SiO
2
–K
2
O diagram of volcanic rocks in the study area.
Figure 6: A/CNK–A/NK diagram of volcanic rocks in the study area.
8Liang Tianyi et al.
Table 4: Analysis results of major elements (%) and trace elements (ppm) of Rhyolitic tuffin the study area
Sample number H1 H2 H3 H4 H5 H6 H7
Lithology Rhyolitic tuff
SiO
2
75.24 73.18 73.10 72.56 72.44 74.82 74.92
TiO
2
0.13 0.09 0.12 0.17 0.12 0.15 0.16
Al
2
O
3
13.08 14.39 12.88 14.15 13.64 13.27 13.05
Fe
2
O
3
0.86 0.50 0.64 0.66 0.63 0.56 0.72
FeO 1.11 1.54 1.55 1.64 1.22 1.62 1.28
MnO 0.04 0.03 0.08 0.09 0.10 0.09 0.09
MgO 0.31 0.28 0.27 0.28 0.27 0.29 0.30
CaO 0.35 0.35 0.29 0.30 0.30 0.26 0.30
Na
2
O 4.32 3.87 4.85 4.66 5.07 4.62 4.61
K
2
O 3.34 5.11 4.17 4.10 4.07 4.05 4.11
P
2
O
5
0.03 0.03 0.05 0.06 0.05 0.05 0.06
LOI 1.34 0.77 1.32 0.54 0.26 1.73 1.21
TOTAL 100.15 100.14 99.32 99.21 98.17 101.53 100.81
LAK 7.66 8.98 9.02 8.76 9.13 8.67 8.72
Na
2
O/K
2
O 1.29 0.76 1.16 1.14 1.25 1.14 1.12
A/CNK 1.15 1.15 0.99 1.12 1.03 1.07 1.04
DI 92.94 92.33 94.5 92.55 94.51 93.64 94.23
σ1.81 2.67 2.68 2.58 2.81 2.36 2.38
SI 3.12 2.48 2.36 2.43 2.39 2.57 2.72
Mg
#
22.68 20.05 18.47 17.98 21.09 19.351 21.62
V 7.42 6.07 6.94 4.35 6.82 4.65 5.92
Cr 2.23 1.98 1.47 1.85 2.05 1.42 1.99
Ni 0.96 0.85 0.88 1.12 0.89 1.00 1.05
Ga 18.71 15.96 18.95 18.91 20.75 17.49 20.47
Rb 91.54 104.67 89.97 95.25 96.01 93.02 86.69
Sr 74.47 158.31 121.38 82.58 80.94 73.36 80.10
Zr 236.82 135.28 182.58 211.66 157.99 148.53 147.82
Nb 11.30 6.66 12.15 14.11 12.51 7.82 9.15
Ba 930.84 1217.76 718.20 1123.00 887.00 999.91 894.06
Hf 7.14 4.07 4.84 5.79 5.40 5.05 5.30
Ta 0.74 0.39 0.95 0.74 0.85 1.04 0.75
W 1.09 0.70 0.44 0.73 0.93 0.89 0.75
Pb 9.03 15.79 12.56 21.31 19.88 13.75 14.49
Th 8.57 4.51 8.78 9.73 9.51 7.80 7.04
U 2.61 1.29 1.88 1.71 1.97 2.83 2.30
La 41.40 15.40 19.31 29.30 21.61 29.46 21.01
Ce 73.70 28.30 45.16 48.01 42.76 62.69 40.81
Pr 9.62 3.46 3.98 3.86 6.27 6.37 6.56
Nd 37.80 13.80 21.67 20.87 26.66 22.99 22.62
Sm 7.65 2.84 3.16 3.39 6.15 3.17 2.92
Eu 1.65 0.62 0.97 0.97 1.51 0.96 0.83
Gd 6.43 2.61 3.04 2.77 4.96 4.74 2.32
Tb 1.13 0.44 0.94 0.87 0.93 0.82 0.78
Dy 7.02 2.85 3.46 5.34 6.16 5.82 5.50
Ho 1.30 0.57 1.12 0.36 0.34 0.80 0.95
Er 3.90 1.70 3.10 1.02 2.03 2.89 3.20
Tm 0.61 0.32 0.34 0.46 0.42 0.30 0.45
Yb 3.90 1.95 2.55 2.38 3.79 2.63 1.94
Lu 0.62 0.32 0.33 0.28 0.47 0.46 0.54
Y 42.50 16.20 36.23 30.73 31.71 19.17 28.54
ΣREE 196.73 75.18 109.13 119.89 124.04 144.10 110.43
La
N
/Yb
N
7.61 5.66 5.42 8.84 4.09 8.03 7.76
δEu 0.72 0.70 0.96 0.97 0.83 0.76 0.98
δCe 0.91 0.95 1.26 1.11 0.90 1.12 0.85
Geochronology and geochemistry of late Paleozoic volcanic rocks 9
ΣREE =102.68 ×10
−6
–171.63 ×10
−6
, (La/Yb) N=8.46–12.71,
LREE/HREE (the ratio of the sum of La, Ce, Pr, Nd, Sm, and
Eu to the sum of Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) =
7.68–9.81 (enrichment of light rare earth and depletion of
heavy rare earth). Figure 7b shows a clear right-leaning
feature. The abnormality of europium is not obvious,
with δEu =0.91–1.15 and an average value of 1.02.
The trace and rare earth element analysis results of rhyo-
lite tuffare shown in Table 4, and the spider of the primitive
mantle of the rock web diagram (Figure 7a) shows enrichment
of large ion lithophile elements such as Ba, Rb, K, and U and the
loss of Nb, Sr, P, and Ti. ∑REE =75.18 ×10
−6
to 196.73 ×10
−6
,(La/
Yb) N=4.09–8.84, and some samples have poor heavy rare
earth fractionation. Figure 7b shows a clear right-leaning fea-
ture. The negative europium anomaly is relatively weak, with a
δEu value of 0.70–0.98 and an average value of 0.85, which
should be the result of plagioclase crystal differentiation.
During the formation process of rhyolite tuff,differences in
the magma composition, cooling rate, crystallization condi-
tions, and other factors result in variations in the chemical
composition, mineral composition, and physical properties of
the rock. This difference may manifest in the distribution and
dispersion of different data points, as shown in Figure 7b.
5 Discussion
5.1 Zircon chronology
The Late Paleozoic volcanic activity in the Greater Khingan
Mountains has always been a focus of research for
geologists. In recent years, especially with the continuous
advancement of chronological technology, reliable geolo-
gical chronological data have been provided for the Late
Paleozoic volcanic activity and magmatic evolution in the
central part of the Xingmeng orogenic belt.
On the Erlian Hegenshan Heihe tectonic belt, a large
amount of volcanic and intrusive rocks occurred in the
Late Paleozoic era. The measured ages of the intrusive
rocks in the Ma Mai Wenduer area of Dongwuqi were
307 ±1.9 and 299.7 ±5.3 Ma, and it was believed that they
were products of the early extensional structures of the
collision between the Siberian plate and the North China
plate. The measured age of the intrusive complex was 319.6
±4.1 Ma in the Sonazha lead–zinc silver deposit area of
Dongwu Banner, which also exhibited an extensional
environment [19]. The measured ages of granite in the
Dabaoshan area of the Greater Khingan Mountains were
309.0 ±3.0 and 299.3 ±2.8 Ma [20]. A study was conducted
on the volcanic rocks of the Carboniferous Benbatu Forma-
tion in the Chagan Nur area between 313 and 308 Ma and
suggested that they may have formed in an extensional
environment after the collision, inferring that the Soren
suture zone had closed before the Late Carboniferous [21].
In this study, zircon U–Pb dating was carried out on
moderately felsic volcanic rocks, avoiding the meta-
morphic clastic rocks in the lower part. Zircon particles
with good crystallization and obvious magmatic zircon
characteristics were selected. The zircon U–Pb age of inter-
mediate trachyandesite was 304.4 ±2.3 Ma, and that of
rhyolite tuffwas 307.6 ±2.0 Ma, representing the age of
volcanic rock formation. There is a certain time interval
between the two. Based on a comprehensive analysis of the
profile, it is believed that the region experienced a
Figure 7: Standardized spider diagram of trace elements in the primitive mantle of trachyandesite and standardized distribution pattern diagram of
rare earth element of chondrite meteorites.
10 Liang Tianyi et al.
relatively complete sedimentary eruption cycle in the Late
Carboniferous. First, a marine sedimentary layer domi-
nated by terrestrial debris was formed in low-lying areas
in the early stages, followed by the strongest period of
volcanic activity. Alkaline magma erupted effusively on a
large scale, accompanied by jet eruptions of medium felsic
magma, forming a rock combination mainly composed of
trachyandesite and trachyte interbedded with andesitic
tuff. Then, felsic magma erupted on a large scale, mainly
consisting of rhyolite tuff. Based on zircon U–Pb chron-
ology, this volcanic rock group was determined to be the
Late Carboniferous Gegenaobao Formation.
5.2 Source characteristics
The volcanic rocks in the northwest region of Zhalaite
Banner are mainly composed of intermediate trachyande-
site, felsic rhyolite, and tuff. Compared to felsic rocks, inter-
mediate trachyandesite has higher MgO, CaO, and P
2
O
5
content, while felsic rocks have higher total alkali (ALK)
content and higher K
2
O/Na
2
O values with similar alu-
minum content. The content of intermediate rocks is
similar to that of trachyandesite measured, while the con-
tent of felsic rocks is similar to that of rhyolite in Tonglu,
Zhejiang, and Xiangshan, Jiangxi [22]. According to the
measured content of major elements in the volcanic rocks,
the values of the high potassium/calcium alkaline series
rocks in the island arc volcanic rocks are similar [23], sug-
gesting that the volcanic rocks are related to a volcanic arc
magmatic activity.
According to the spider diagram of trace elements and
the rare earth element distribution diagram (Figure 7), the
volcanic rocks are relatively enriched in light rare earth
elements and large ion lithophilic elements such as Ba, K,
and Rb, significantly losing high field strength elements
such as Nb, especially felsic rocks that strongly lose Sr, P,
and Ti. In island arc or active continental margin environ-
ments, volcanic rocks are enriched in light rare earth ele-
ments and large ion lithophile elements, while they are
depleted in high field strength elements, are often formed
due to magmatic activity caused by plate subduction, sug-
gesting that magma may have originated from crustal
melting [24,25]. The volcanic rocks and intermediate rocks
in the research area have subtle Eu anomalies, δEu =
0.91–1.15, the average value is 1.02, and the Sr anomaly is
not obvious, while the felsic rock shows a more obvious Eu
anomaly with an average value of 0.63. At the same time,
the Sr anomaly is also significantly deficient compared to
the intermediate rock, which is consistent with the
observation data under the petrological microscope in a
previous report. The plagioclase content of the inter-
mediate rock is significantly lower than that of the felsic
rock. The negative anomaly of P may manifest as the crys-
tallization separation of apatite, while the depletion of Ti
may be controlled by the separation crystallization of ilme-
nite. The negative anomalies of Sr and Ba indicate that
plagioclase may have undergone fractional crystallization.
Similarly, the separation and crystallization of plagioclase
can lead to a strong depletion of Eu and Sr, which are
strongly compatible elements with plagioclase. The nega-
tive anomaly of Pindicates the separation and crystalliza-
tion of apatite during magma evolution, while the negative
anomaly of Nb suggests the possible involvement of crustal
material in magma evolution. The intersecting phenom-
enon of the trace-element bead network curves is due to
the varying degrees of enrichment of individual elements
in different rocks, reflecting the addition or contamination
of external substances during magma migration and diag-
enesis. These are typical characteristics of crustal magma
being contaminated by upper crustal materials [26].
The average Nb/U value of intermediate volcanic rocks
is 9.16, while that of felsic rocks is 5.33, which is lower than
the continental crust [25]. The average Nb/Ta ratio is 16.45
(except for a lower sample), which is significantly higher
than the average value of the continental crust [27] and
closer to the corresponding value of 17.8 in the original
mantle, suggesting the presence of mantle-derived magma
involvement. The average Ba/Th values of trachyandesite
are 250.10, Ba/La values are 35.27, La/Nb values are 3.08,
and Ba/Nb values are 109.15, which are all higher than
those of oceanic ridge basalt (N-MORB) originating from
the depleted mantle, with values of 60, 4, 1.07, and 4.3,
respectively, and generally higher than the average level
of continental crust. It is generally believed that the La/Nb
ratio is high, which is also a distinct feature of contamina-
tion [28,29]. The average Rb/Sr ratio of felsic rocks is 1.05
(greater than 0.5), the average Ti/Zr ratio is 4.72 (less than
20), and the average Ti/Y ratio is 29.65 (mostly less than
100), all of which belong to the characteristics of crustal
magma products.
Compared with basalt magma, andesite magma has a
more complex source and can be formed through partial
melting of the metasomatic mantle. This type of magma
has not undergone significant evolution, so its rare earth
element chondrite standardization map shows a U-shaped
curve. It can also be directly melted through the subduc-
tion of the oceanic crust [30]. In this case, the rare earth
element distribution map of volcanic rocks will have a
steep right-leaning feature, with strong light and heavy
rare earth fractionation, especially the loss of heavy rare
Geochronology and geochemistry of late Paleozoic volcanic rocks 11
earth elements [31]. If the solution produced by oceanic
crust melting interacts with mantle rocks during the ascent
process, it will form high magnesium andesite, and the
content of heavy rare earth elements will significantly
increase. Basalt, andesite, and even felsic rocks produced
under the background of island arcs are mostly caused by
the crystallization differentiation of basic magma. Under
the background of land arcs, the thickness of the crust is
large, which provides a longer crystallization differentiation
time for a large amount of basic magma to rise. The rocks
produced under these conditions have obvious negative
europium anomalies, mainly due to the crystallization dif-
ferentiation of plagioclase. The traditional belief is that
rhyolite rocks are products of crustal material melting. In
recent years, research has found that felsic island arc
magmas can also be formed by the melting process of sub-
ducting oceanic crust [32]. The Y value content of felsic rocks
in this study is relatively high, averaging 29.30, and the
degree of differentiation between light and heavy rare
earths is low, averaging 6.49. Therefore, the volcanic rocks
in the study area are more likely to come from partial
melting of the crust. At the same time, according to the C/
MF–A/MF diagram of volcanic rocks (Figure 8), most of the
intermediate trachyandesite comes from the partial melting
of basic rocks with deeper sources. Felsic rocks originate
from the partial melting of metamorphic mudstone.
In order to distinguish the source of magma, the Mg#
value is an ideal parameter. Studies have shown that the
typical midocean ridge tholeiitic basalt (MORB) has an Mg#
value of about 60. However, according to experimental
petrological research, the Mg# value of lower crust-derived
solutions is relatively low and has little correlation with
the degree of melting, generally less than 40. Only with the
participation of mantle material can the Mg# value be
greater than 40. The Mg# values of the intermediate tra-
chyandesite studied in this study are 30.23–49.53, with an
average of 41.98, indicating that it is mainly a product of
crustal magma with slight involvement of mantle material.
Mg# values of felsic rocks are 17.98–22.68, with an average
of 20.18, indicating typical characteristics of crustal
magma.
Based on comprehensive analysis, it is believed that
the volcanic rocks in the study area mainly originate from
the crust, but the composition of intermediate rocks should
be partially melted by mantle material. The formation age
of intermediate rocks is 304.4 ±2.3 Ma, and the formation
age of felsic rocks is 307.6 ±2.0 Ma. The two are relatively
close. At the same time, according to the actual occurrence
of the field strata, both have continuity in time and space,
and the two should be a relatively continuous eruption
sedimentary environment.
5.3 Construction environment
The Xingmeng orogenic belt in central Inner Mongolia is
characterized by strong Paleozoic accretion and strong
Mesozoic Cenozoic transformation and is an important
component of the eastern section of the Central Asian oro-
genic belt in China. The formation and development of the
Xingmeng orogenic belt are closely related to the evolution
of the ancient Asian Ocean. This study area is located in the
northwest of Zhalaite Banner in eastern Inner Mongolia,
slightly west of the contact zone between the Xing’an block
and the Songnen block, and is an ideal place for studying
the magmatic activity of the Xingmeng orogenic belt.
The ancient Asian Ocean did not simply continue to
subduct until the end of the collision but went through long
and multiple stages of subduction extension before finally
colliding and closing, completing the transition toward the
continental crust [33]. The Songnen block merged with the
Duobaoshan Island Arc along the Heihe Zhalantun line
during the Late Carboniferous, gradually forming a land
area with the Xing’an Songnen block in the middle. The
structural pattern of the Okhotsk Ocean to the north and
the Paleo-Asian Ocean to the south continued until the
Middle Permian. Early Carboniferous metamorphic basic
volcanic rocks were discovered in the Xilinhot area, sug-
gesting that the controlled primitive magma formation of
this volcanic rock originated from the depleted mantle of
Figure 8: Harker diagram of volcanic rocks in the study area.
12 Liang Tianyi et al.
the subduction plate dehydration metasomatism and was a
product of magmatic activity in the island arc environ-
ment. They inferred that the ancient Asian Ocean was
not closed during the Early Carboniferous but was still in
the stage of subduction and subduction of the oceanic
crust [34].
The volcanic rocks in this study area were formed
during the Late Carboniferous, and according to zircon
U–Pb dating data, they were formed between 304 and
308 Ma. Similarly, there have been numerous reports of
volcanic magmatism during the Late Carboniferous in
areas such as Xilinhot, Suzuoqi, and Dongwuqi in the
Greater Khingan Mountains [35], suggesting that the occur-
rence of volcanic magmatism during the Late Carboni-
ferous had a certain degree of isochronicity.
According to data, there are a total of six ancient sub-
duction zones in Inner Mongolia, among which the
Hegenshan Zhalantun accretion complex belt is located
in the southern part of the study area, extending northeast.
This is also an extension of the Erlian Hegenshan Heihe
ophiolite complex belt, with an overall trend of NE, which
is consistent with the direction of the main structural line
in the area. There are a large number of A-type granites
distributed around this tectonic zone; therefore, there is
also a certain spatial connection between the Late
Carboniferous magmatic rocks.
According to the latest chronological and geochemical
data, A-type granite in the Xing’an Island Arc was formed
during the Late Carboniferous. The measured age of alka-
line granite in the Ulan Tolgoi area was 317 Ma [36], and the
Figure 9: Structure diagram of volcanic rocks in the study area: (a) lg σ–lg τ; (b) Hf–Ta–Th; (c) Yb+Ta–Rb; and (d) Ta/Yb–Th/Yb.
Geochronology and geochemistry of late Paleozoic volcanic rocks 13
age of alkali feldspar granite in the Duobao Mountain area
was 309 Ma. The measured age of potassium feldspar
granite in the Twelve Stations rock mass in the Heihe
area of the northeastern part of the Daxing’an Mountains
was 298 Ma. The measured age of granite in the Jinggetai
area of Inner Mongolia was 301 Ma [37]. At the same time,
there is also a distribution of I-type granite with high dif-
ferentiation on a certain scale in the Zhalantun area, such
as the 322 Ma syenogranite in Quansheng Forest Farm and
the 317–314 Ma syenogranite in the Tayuan area [38], indi-
cating that the intrusive rocks formed during this period
have a post-orogenic extensional background. The felsic
volcanic rocks in this study also exhibit high differentiation
characteristics, suggesting that they may also have exten-
sional backgrounds. They found in their study of the Nen-
jiang area on the southeastern edge of the Xing’an block
that the age of the intermediate felsic intrusive rocks in the
area was between 315 and 298 Ma, formed during the Late
Carboniferous. They also compared the magmatic activity
of the Early Carboniferous and concluded that the Xing-
meng orogenic belt experienced two distinct periods of
magmatic activity during the Carboniferous, belonging to
Figure 10: Late Paleozoic regional tectonic evolution model. (a) The closure stage of the ancient Asian Ocean from the Late Devonian to the
Carboniferous; (b) the stage of land–land collision in the Late Carboniferous; and (c) the fold orogeny stage of the Early Middle Permian.
14 Liang Tianyi et al.
different tectonic backgrounds. The Early Carboniferous
was in a subduction environment, while the Late Carboni-
ferous was in an extensional tectonic environment after
plate collision [39]. It is believed that the differentiated
I- and A-type granites distributed in the Zhalantun area
are a sign of vertical crustal thickening in the region,
with strong post-collisional magmatic activity [40].
At the end of the Early Carboniferous, the Siberian
Plate and the North China Plate contracted and eventually
collided, forming a large amount of Early Carboniferous
magmatic rocks in the Hegenshan Heihe tectonic zone.
Subsequently, the ancient Asian oceanic crust in the
middle of the Late Carboniferous subducted and subducted
northwestward along the Hegenshan Zhalantun line,
causing the collision and merging of the Xing’an Block
and the Songnen Block on the southern edge of the
Siberian Plate. To the north of the subduction zone, a vol-
canic rock combination related to subduction gradually
formed in the Yiershi Diannan area, reflecting the conti-
nental margin volcanic arc environment. Subsequently, in
the late Carboniferous to early Permian of the Xing’an
Island Arc, magmatic rocks with highly differentiated
Type I and Type A and post-orogenic collision extensional
environments gradually formed.
The lg σ–Lg τdiagram shows that the volcanic rocks in
the study area are mainly located within the range of the
subduction zone (Figure 9a). According to the Hf Ta Th and
Yb +Ta Rb diagrams, the volcanic rocks belong to the range
of island arc rocks, especially felsic volcanic rocks with
post-collision characteristics (Figure 9b and c). The Ta/Yb
and Th/Yb diagrams show an active continental margin
arc, indicating that subduction is still ongoing (Figure
9d). Based on comprehensive analysis, it is believed that
the volcanic rocks in the study area should be related to
volcanic magmatic events with continental arc character-
istics during the subduction process of the oceanic crust. At
the same time, volcanic rocks have crustal characteristics,
while intermediate rocks have deeper magma sources and
the participation of mantle-derived materials. Felsic rocks
have high heterogeneity, indicating a post-collision exten-
sional environment background. This indicates that in the
late Carboniferous, the Songnen block and Xing’an block
have completed integration, and the Xingmeng orogenic
belt gradually transitioned toward a post-collision exten-
sional environment.
In summary, the study area underwent three stages of
development during the Late Paleozoic era. The first
stage is the closure stage of the ancient Asian Ocean
from the Late Devonian to the Carboniferous, character-
ized by a tectonic environment based on oceanic crust and
an active continental margin environment with magma
development (Figure 10a). The second stage is the land–
land collision stage of the Late Carboniferous, during
which the study area received intermediate and felsic vol-
canic rock deposits with island arc properties from the
Gegen Aobao Formation. Analysis suggests that this should
be a product of further activation of land–land collision by
the movement of the two major plates in the north and
south (Figure 10b). In the folding and orogeny stage of the
Early Middle Permian in the third stage, the crust under-
went folding and orogeny, causing the volcanic rock layers
of the Gegen Aobao Formation to fold and then the crust to
rise, resulting in sedimentary interruptions in the Early
Middle Permian (Figure 10c).
6 Conclusions
1. The zircon LA-ICP-MS U–Pb ages of the intermediate
felsic volcanic rock combination in the Zhalaiteqi area
of eastern Inner Mongolia are 304.4 ±2.3 Ma and 307.6 ±
2.0 Ma, respectively. The formation period is the Late
Carboniferous.
2. The Late Carboniferous volcanic rocks in this study area
are relatively enriched in light rare earth elements and
large ion lithophile elements such as Ba, K, and Rb while
significantly losing high field strength elements such as
Nb. Particularly, felsic rocks strongly lose Sr, P, and Ti. It
is believed that the magma of this volcanic rock combi-
nation mainly originates from the crust, but the compo-
sition of intermediate rocks should be partially melted
by mantle material, and felsic rocks may have been
contaminated by shallow crustal material. Both are tec-
tonic environments of continental margin arc volcanic
rocks, exhibiting magmatic activity events related to
subduction extension.
3. The felsic volcanic rocks of the Gegenaobao Formation
in the northwest of Zhalaite Banner are located on the
Late Paleozoic A-type magmatic rock belt along the
Erlian Hegenshan Zhalantun Heihe line. Based on rock
assemblages, chronology, and geochemical characteris-
tics, comprehensive analysis suggests that the Xing’an
block and Songnen block have completed collision and
assembly in the Early Carboniferous and were in a tec-
tonic environment of subducted continental arc volca-
noes in the Late Carboniferous with post-orogenic
extension characteristics. The Late Carboniferous
ancient Asian Ocean has closed along the Erlian
Hegenshan Zhalantun Heihe rock structural belt in the
north, and the Xingmeng orogenic belt has begun to
enter the stage of orogenic extension.
Geochronology and geochemistry of late Paleozoic volcanic rocks 15
Acknowledgments: This work was funded by the basic
Geological Survey Project of Shenyang Geological Survey
Center “Inner Mongolia 1:50000 Diaoyutai (L51E006006),
Chuludaba (L51E006007), Dongbayan Ulan (L51E006008),
Taladaba (L51E005008) regional geological survey.”The
authors thank Dr. Wei Zhou and Dr. Kunyu Wu from the
School of Earth and Environmental Sciences of the University
of Queensland for help in the revision of the main part of this
manuscript. The authors also thank the editor and reviewers
for their assistance with this manuscript.
Funding information: This work was supported by 2024
Guangxi University Young and Middle aged Teachers’
Basic Scientific Research Ability Improvement Project
(2024KY0813); and the Doctor and Professor Foundation of
Guilin University of Aerospace Technology (KX202204801).
Author contributions: Drawing of graphics: Wang Li,
Wang Guanhong. Data processing: Tang Xinglong, Li
Zhuang. Writing –original draft: Liang Tianyi. Writing –
review & editing: Li Mengmeng.
Conflict of interest: Authors state no conflict of interest.
Data availability statement: Data sharing is not applicable
to this article as no datasets were generated or analysed
during the current study.
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Geochronology and geochemistry of late Paleozoic volcanic rocks 17
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