# Geochronology and Tectonic Evolution of the Lincang Batholith in Southwestern Yunnan, China

Authors: Hongyuan Zhang; Junlai Liu; Wenbin Wu
Journal: Journal of Geological Research
 (2012)

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## Abstract

Geochronological research of the Lincang Batholith is one key scientific problem to discuss the tectonic evolution of the Tethys. Two granitic specimens were selected from the Mengku-Douge area in the Lincang Batholith to perform the LA-ICPMS Zircon U-Pb dating based on thorough review of petrological, geochemical, and geochronological data by the former scientists. Rock-forming age data of biotite granite specimen from Kunsai is about 220 Ma, the Norian age. However, the west sample from Mengku shows 230 Ma, the Carnian age. The later intrusion in Kunsai area located east to the Mengku area shows directly their uneven phenomena in both space and time and may indirectly reflect the space difference of the contraction-extension transformation period of the deep seated faults. Considering the former40Ar/39Ar data and the outcrop in Mengku, the Lincang Batholith should have experienced one tectonic exhumation and regional subsidence cycle. The regional subsidence cycle has close relations to the expansion of the Meso Tethys.


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## Body

## 1.  Introduction

The Sanjiang-Indochina region is one key area to study the evolution of the Tethys [1–10] (Figure 1). The Changning-Menglian zone was considered as the major faunal break between Gondwanan assemblage to the west and Cathaysian to the east [11, 12]. The subduction-related magmatism occurred along the western edge of the Lanping-Simao-Indochina terrane throughout the Triassic and the closure of Palaeo-Tethys  [12, 13]. The Lincang Batholith extends ~370 km from north to south, covering the Chiangrai-Chiang Mai region of Thailand, with an area of more than 10000 km2 (Figure 2). It has been shown by many authors that there is great mineral potential  [14].Figure 1
Map of plate tectonics and ore-forming metals in the southern Sanjiang and Indochina peninsula. (a) Scope of Tethys and zone divisions; (b) research area and distribution of major metals: (1) Changning-Menglian-Chiangmai PaleoTethys Suture (time and space after [1, 21, 22]); (2) Ailaoshan-Song Ma Paleo-Tethys Suture (time and space after [2, 6, 8]); (3) Bangong Co-Nujiang Meso-Tethys Suture (time and space after [5]); (4) Yanlung Tsangpo-Naga-Arakan New-Tethys Suture (time and space after [22, 23]); (F1) Nujiang-Saging Fault Zone; (F2) Ranong Fault Zone; (F3) Three Tower Fault Zone; (F4) Tonle Sap Fault Zone; (F5) Đà Lat-Bianhe Fault Zone; (F6) Điên Biên Phú Fault Zone; (F7) Changshan-Da Nang Fault Zone; (F8) Lanjiang Fault Zone; (F9) Ailaoshan-Red River Fault Zone; (F10) Xianshuihe-Xiaojiang Fault Zone; (F11) Lancang-Jinghong Fault Zone.Figure 2
Regional map of Indian Period and research locality in western Yunnan. The distribution of metal deposits also indicates that there is an important boundary along the Lincang Granite Batholith. Stereographic maps of lower hemisphere projection indicating the initial occurrence of Lincang granite Batholith are also plotted in the regional map. L, S, Q  refer to joints parallel to the initial foliation, parallel to the flow direction but upright to the initial foliation, upright to both the flow direction and initial foliation. Orientation of shear fractures can be generated by local stress system of the Batholith with emplacements [24].The Lingcang Batholith was divided into three lithologic intervals by previous authors,  the Xiaojie, Lincang, and Menghai intervals (Figure2) [15–17]. The major intrusion is porphyritic monzonitic granite, which mainly contains quartz, zonal plagioclase, K-feldspar, and biotite. In addition, geochemical studies have shown that the granite mainly has source features of the crust mixing origin [16, 18].The Lingcang Batholith was proposed to form in a passive continental margin according to geochemical research [19]. The intrusive timing spans from late Permian to late Triassic based on whole-rock Rb-Sr, mineral 40Ar/39Ar, whole-rock 87Sr/86Sr, Rb-Sr, Sm-Nd, and some other methods (Table 1).Table 1
Isotopic age data for the Lincang Batholite in the earlier stage.
Lithologic section
Lithology
Measured objects and methods
Dating results, Ma
Sample positions
Testers and the time
Xiaojie
Granite porphyry
Whole-rock (Rb-Sr)
169
±
5
Laomaocun
Zhang et al., 2006 [25]
Xiaojie
Monzonitic granite
Whole-rock (87Sr/86Sr)
279
Yun County
Chen, 1991 [26]
Lincang
Biotite granite
Biotite (40Ar/39Ar)
201.1
±
2.7
Near the Lancangjiang River
Dai et al., 1986 [27]
Lincang
Monzonitic granite
Whole-rock (Rb-Sr)
279
Lincang
Chen, 1991 [26]
Lincang
Medium-grained equigranular granodiorite
Whole-rock (Rb-Sr)
263.8
Milestone along Lincang-Mengku road 327–387 km
Zhang et al., 1990 [28]
Lincang
Unequal-sized biotite granite
Whole-rock (Rb-Sr)
193
Shangyun-Xiaotang
Zhang et al., 1990 [28]
Lincang
Monzonitic granite
Whole-rock (Rb-Sr)
275
±
59
Lincang
Liu et al., 1989 [18]
Menghai
Monzonitic granite
Whole-rock (87Sr/86Sr)
279
Menghai
Chen, 1991 [26]
Menghai
Monzonitic granite
Biotite (Rb-Sr)
256
Menghai
Wang, 1984 [29]But there are also some understanding differences on the crystallization period and evolution time of the Lincang Batholith. Many predecessors discussed mineral diagenesis and tectonic evolution through traditional data [16, 20], although, not from the viewpoint of the plate tectonics. On scientific problems of the Lincang Batholith, some solutions were put forward such as single period of mixed granite [16], quasi-situ metasomatic granite [20], or Neoproterozoic type I granite complex batholith with multiperiod transforming events [19].Therefore, the formation and evolution of the Lincang Batholith is still the key to discuss the regional tectonic evolution of the Baoshan and Lanping-Simao-Indochina block. In this study, we conducted petrographic analysis of the Lincang Batholith and provide new LA-ICP-MS U-Pb data in order to constrain the tectonic evolution of the Batholith. We discuss these results of dating in the context of regional tectonic evolution.


## 2. Dating Methods, Specimens, and Results

### 2.1. Dating Methods

The U-Pb zircon age dating of monzonitic granite samples selected from the Mengku-Douge research area in Lincang segment (Figures2 and 3) was designed and completed in the Institute of Geology and Geophysics, Chinese Academy of Sciences. Jobs of single zircon grain micro-area U-Pb geochronological analysis were taken through Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) of 7500a-type producted by Agilient Co. Ltd., with which the laser beam diameter is 60 μm, the erosion frequency is 8 Hz, the energy density is 15~20 J·cm−2, the erosion time is about 60 s. For detailed analysis procedures, please see Xu et al. [32]. The Zircon U-Pb isotope and the U, Th data processing are finished by software Glitter4. 0 [33], and computing of U-Pb concordia diagrams, weighted average ages and graphics were completed by software Isoplot3.0 [34].Figure 3
Geological sketch map in Mengku-Douge area (revised after [15–17, 30, 31]) (1) Area of ingression sea of the Meso-Tethys; (2)  Jurassic terrigenous sediments; (3) Early Jurassic volcanic sedimentary rocks; (4) Lincang Triassic granite rock; (5) deep metamorphic wedge with local granodiorite quality migmatization Late Paleozoic; (6) schistosity occurrence; (7) bedding occurrence.


### 2.2. Specimens

#### 2.2.1. Specimen from Kunsai Quarries

The biotite monzonitic granite samples were selected from the Kunsai quarries to the east of Quannei-Douge migmatite rock belt (Figures3 and 4(a)). The north part of the rock unit is plunged into the Jurassic basin (Figure 3). Field study shows that both the rock unit and the Jurassic basin have experienced a period of ductile transformation events. The microstructure study shows brittle deformed feldspar (Figures 4(b) and 4(c)), dynamically recrystallized quartz (Figure 4(c)), microdeflected biotite (Figure 4(d)), zircon grains with relatively intact crystal, long column, some rounded output and a higher degree of porosity which is symbiotic to microcline grains (Figure 4(b)). The cathode luminescence (CL) images show that the typical magmatic zircon characteristics are colorless and transparent here with oscillatory zoning, the length of about 120 μm–420 μm and the aspect ratio of 1.2 to 4.1 (Figure 4(e)). Totally, for 22 points of 22 zircon grains of sample biotite granodiorite KS-2 from the Kunsai quarries we performed U-Pb isotope analysis in order to statistically gain a feasible dating result (Figure 4(f)). All points were selected on the edge of long- column euhedral grains where the magmatic zircon oscillatory zoning is clear.Geochronological research of granite sample KS-2. (a) Position photo of the biotite monzonitic granite sample in the field of Kunsai Quarry. (b) The zircon grows together with the microcline CPL. (c) The microstructure of complete recrystallized quartz indicates the rock once experienced high-greenschist facies of deformation, CPL. (d) One biotite crystal is folded, PPL. (e) Magmatic zircon is shown by the SEM cathodoluminescence (CL) image. The circled area is deduced to form during the crystallization of granite and is just the measured area by laser-ICPMS (f) Zircon La-ICPMs U-Pb dating figure, and the average age is about 220 Ma.
(a)
(b)
(c)
(d)
(e)
(f)


#### 2.2.2. Specimens from Mengku Quarries

The monzonitic granite sample MK-4 is selected from the Mengku East Quarry at the eastern side of the Mengku Town in the Shuangjiang County, which separates Jurassic red clastic rocks with one bedding bottom granitic conglomerate by the paleo-weathering crust in between (Figures5(a), 5(b), and 5(c)). Figure 5(a) shows the position photo of the biotite monzonitic granite sample in the Mengku East Quarry. From the field outcrop, both granitic intrusion (lower left) and its weathering top can be found to be cleavaged which had been covered by the upper Jurassic red detrital sediments with terrigenous origin, namely, the Huakaizuo Formation. The MK-4 zircon grains (Figure 5(d)) change greatly and have different shapes and sizes, such as long column, fan, and irregular granular. However, size of zircon grains is uniform with length between 90 μm and 150 μm and length-width ratio in 1.1 : 1–1.8 : 1. Zircon grains develop with quartz, plagioclase in rocks. The rock sample has been affected by weathering, showing retrograde metamorphism (Figure 5(e)). Characteristic oscillatory zoning of typical magmatic zircon is rendered on the cathode CL image. The idiomorphic degree of zircon is high, but some fragmented. On the sample of MK-4, 18 zircon grains and 18 points were analyzed by ICP-MS. Edge of the long-column idiomorphic or the chipped-hypidiomorphic zircon grains, and the clear zone of magmatic zircon oscillatory were always selected to perform the micro isotope analysis (Figure 5(f)).Geochronological research of the granite sample MK-4. (a) Position photo of the biotite monzonitic granite sample in a field Quarry of east Mengku. (b) Granitic intrusion (lower left) and its fossil weathering were cleavaged. (c) The red detrital material of terrigenous origin, Huakaizuo Formation in Jurassic, was normal gradational. (d) Granitic intrusions are selected as sample. (e) The micro  characteristics of MK-4 and the zircon setting are shown. The zircon grains are associated with quartz and plagioclase and have been degraded by some weathering process, CPL, (f) Magmatic zircon is shown by the SEM cathodoluminescence (CL) image. The circled area is deduced to form during the crystallization of granite and is just the measured area by laser-ICPMS. (g) Zircon La-ICPMs U-Pb dating figure, and the average age is about 245 Ma.
(a)
(b)
(c)
(d)
(e)
(f)
(g)


#### 2.2.3. Dating Results

As shown in Figure4(f) and Table 2, the overall harmony values of KS-2 zircon age data range from 195 Ma to 245 Ma, but some of them are below the U-Pb harmonic line and deviated from the harmony line. This is probably because  the micro region selected is too close to the boundary of the zircon grain. Some zircon grains (Figure 5(f)) also have some cracks in and this may also affect the dating result. From the harmonic visible figure, zircon dating values are focused to a range from 210 Ma to 230 Ma, and the average age is about 220 Ma. This means that the crystallization age of the Kunsai quarries biotite granite is about in the late Triassic Norian period.Table 2
U-Pb isotopic dating for the single grain Zircon from granite of Kunsai.
No.
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
A77
0.05789
0.00231
0.25961
0.00949
0.03251
0.00089
0.01383
0.00076
526
38
234
8
206
6
278
15
A78
0.05188
0.00244
0.23562
0.00953
0.03294
0.00079
0.01035
0.00025
280
110
215
8
209
5
208
5
A79
0.05273
0.00141
0.24329
0.00604
0.03345
0.00081
0.01108
0.00055
317
26
221
5
212
5
223
11
A80
0.05213
0.00216
0.23471
0.00801
0.03265
0.00077
0.01025
0.00024
291
97
214
7
207
5
206
5
A81
0.05209
0.00131
0.25938
0.00608
0.0361
0.00086
0.01177
0.00034
289
25
234
5
229
5
237
7
A82
0.05014
0.00118
0.24192
0.00531
0.03498
0.00082
0.01113
0.00044
201
24
220
4
222
5
224
9
A83
0.05126
0.00122
0.24287
0.00541
0.03435
0.00081
0.01155
0.0006
253
24
221
4
218
5
232
12
A84
0.05027
0.00114
0.24534
0.00525
0.03539
0.00083
0.01176
0.00041
207
24
223
4
224
5
236
8
A89
0.0521
0.00237
0.22575
0.00875
0.03143
0.00075
0.00987
0.00023
290
107
207
7
199
5
199
5
A90
0.05305
0.00182
0.2649
0.0084
0.03621
0.00094
0.01376
0.00075
331
33
239
7
229
6
276
15
A91
0.05739
0.00113
0.23972
0.00441
0.03029
0.0007
0.00946
0.00032
507
23
218
4
192
4
190
6
A92
0.05076
0.00135
0.24604
0.00612
0.03515
0.00085
0.01173
0.00045
230
26
223
5
223
5
236
9
A93
0.05089
0.00279
0.24455
0.01197
0.03485
0.00086
0.01098
0.00025
236
127
222
10
221
5
221
5
A94
0.05114
0.00155
0.24377
0.00683
0.03457
0.00087
0.01167
0.00055
247
29
222
6
219
5
235
11
A95
0.05055
0.00109
0.24175
0.00488
0.03469
0.00081
0.01181
0.00045
220
24
220
4
220
5
237
9
A96
0.05018
0.00134
0.23857
0.00594
0.03448
0.00084
0.01149
0.00049
203
26
217
5
219
5
231
10
B02
0.05115
0.00119
0.24774
0.00541
0.03514
0.00084
0.01297
0.00054
248
25
225
4
223
5
260
11
B03
0.05067
0.00224
0.24165
0.00903
0.03459
0.00082
0.0109
0.00025
226
104
220
7
219
5
219
5
B04
0.05104
0.00235
0.24163
0.00953
0.03433
0.00082
0.01081
0.00025
243
109
220
8
218
5
217
5
B05
0.05079
0.00153
0.24968
0.00699
0.03567
0.0009
0.01274
0.00067
231
29
226
6
226
6
256
13
B06
0.05039
0.00095
0.24525
0.00437
0.03531
0.00082
0.01121
0.00038
213
25
223
4
224
5
225
8
B07
0.05429
0.00243
0.27463
0.01035
0.03669
0.00089
0.01147
0.00027
383
103
246
8
232
6
230
5
B08
0.05014
0.00223
0.24399
0.00913
0.0353
0.00085
0.01114
0.00026
201
104
222
7
224
5
224
5
B09
0.05141
0.00105
0.25807
0.00495
0.03643
0.00086
0.01414
0.00053
259
25
233
4
231
5
284
11As shown in Figure5(g) and Table 3, the overall harmony values of MK-4 zircon age data range between 190 Ma and 315 Ma. The values are somewhat scattered mainly because the granite of the Mengku quarries has been heavily weathered (Figure 5(d)). During the weathering process, chemical bonds of ZrO2 in zircon grains of our MK-4 sample would be broken. Therefore, some zircon isotope escaped. The average age of 245 Ma might indicate that the late Permian to early-middle Triassic magmatic event happened in the Mengku Quarries area of the Lincang Batholith.Table 3
U-Pb isotopic dating for the single grain Zircon from granite of Mengku.
Analysis
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
no.
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
1
0.05174
0.00244
0.32303
0.0139
0.04528
0.00108
0.01152
0.00053
274
56
284
11
285
7
232
11
2
0.09115
0.00288
2.96352
0.08448
0.23585
0.0053
0.08061
0.00287
1450
25
1398
22
1365
28
1567
54
3
0.11509
0.00332
0.50952
0.01225
0.03212
0.00066
0.02102
0.00068
1881
19
418
8
204
4
420
13
4
0.04837
0.00265
0.22077
0.01108
0.03312
0.00085
0.01153
0.00063
117
69
203
9
210
5
232
13
5
0.04837
0.0022
0.27295
0.01145
0.04095
0.00092
0.01223
0.0006
117
57
245
9
259
6
246
12
6
0.05351
0.00279
0.29775
0.01415
0.04038
0.00104
0.01371
0.00078
350
62
265
11
255
6
275
16
7
0.0806
0.00218
2.27431
0.05585
0.2048
0.00394
0.05968
0.00155
1212
22
1204
17
1201
21
1172
30
8
0.0802
0.00341
2.36577
0.09085
0.2141
0.00577
0.05352
0.00277
1202
37
1232
27
1251
31
1054
53
9
0.05928
0.00248
0.29959
0.01132
0.03668
0.00082
0.00966
0.00046
577
45
266
9
232
5
194
9
10
0.04989
0.00375
0.23793
0.0163
0.03461
0.00119
0.00907
0.00072
190
96
217
13
219
7
182
14
11
0.07866
0.00333
0.34683
0.01279
0.032
0.00079
0.01233
0.00063
1164
37
302
10
203
5
248
13
12
0.0406
0.00217
0.22437
0.01119
0.04011
0.00095
0.01052
0.00055
−255
72
206
9
254
6
212
11
13
0.0639
0.00299
0.31538
0.01317
0.03582
0.00089
0.01126
0.00067
738
48
278
10
227
6
226
13
14
0.07481
0.00441
0.3517
0.01817
0.03412
0.00108
0.01178
0.00078
1063
56
306
14
216
7
237
16
15
0.06821
0.00263
0.97745
0.03376
0.10399
0.00236
0.03233
0.00106
875
37
692
17
638
14
643
21
16
0.05116
0.00255
0.26673
0.01227
0.03784
0.00088
0.01057
0.00052
248
64
240
10
239
5
213
10
17
0.05025
0.00304
0.25181
0.01395
0.03636
0.00102
0.01037
0.00064
207
77
228
11
230
6
209
13
18
0.05379
0.003
0.27018
0.01369
0.03645
0.00098
0.00965
0.0006
362
67
243
11
231
6
194
12
19
0.05083
0.00373
0.26778
0.01802
0.03823
0.00125
0.00987
0.00055
233
96
241
14
242
8
199
11
20
0.06022
0.00487
0.2998
0.0217
0.03612
0.00142
0.01137
0.00113
611
90
266
17
229
9
229
23
21
0.0473
0.00214
0.20932
0.0087
0.0321
0.0007
0.00892
0.00038
64
55
193
7
204
4
179
8
22
0.05405
0.00334
0.28442
0.01602
0.03817
0.00111
0.00858
0.0006
373
75
254
13
241
7
173
12
23
0.05907
0.0024
0.66212
0.02439
0.08128
0.00181
0.03438
0.00121
570
43
516
15
504
11
683
24
24
0.05064
0.00245
0.21459
0.00944
0.03072
0.00072
0.00797
0.00046
224
59
197
8
195
5
160
9
25
0.05594
0.00261
0.26352
0.01113
0.03415
0.0008
0.00964
0.00045
450
53
237
9
216
5
194
9
26
0.06769
0.00524
0.32217
0.02212
0.0345
0.00134
0.01049
0.0009
859
80
284
17
219
8
211
18
27
0.06354
0.00206
0.75553
0.02205
0.08618
0.00166
0.02056
0.00084
726
32
571
13
533
10
411
17
28
0.05014
0.00296
0.33191
0.01801
0.04797
0.00129
0.02068
0.0011
201
77
291
14
302
8
414
22
29
0.23782
0.00377
6.55914
0.08439
0.19984
0.00325
0.01824
0.00075
3105
12
2054
11
1174
17
365
15


## 2.1. Dating Methods

The U-Pb zircon age dating of monzonitic granite samples selected from the Mengku-Douge research area in Lincang segment (Figures2 and 3) was designed and completed in the Institute of Geology and Geophysics, Chinese Academy of Sciences. Jobs of single zircon grain micro-area U-Pb geochronological analysis were taken through Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) of 7500a-type producted by Agilient Co. Ltd., with which the laser beam diameter is 60 μm, the erosion frequency is 8 Hz, the energy density is 15~20 J·cm−2, the erosion time is about 60 s. For detailed analysis procedures, please see Xu et al. [32]. The Zircon U-Pb isotope and the U, Th data processing are finished by software Glitter4. 0 [33], and computing of U-Pb concordia diagrams, weighted average ages and graphics were completed by software Isoplot3.0 [34].Figure 3
Geological sketch map in Mengku-Douge area (revised after [15–17, 30, 31]) (1) Area of ingression sea of the Meso-Tethys; (2)  Jurassic terrigenous sediments; (3) Early Jurassic volcanic sedimentary rocks; (4) Lincang Triassic granite rock; (5) deep metamorphic wedge with local granodiorite quality migmatization Late Paleozoic; (6) schistosity occurrence; (7) bedding occurrence.


## 2.2. Specimens

### 2.2.1. Specimen from Kunsai Quarries

The biotite monzonitic granite samples were selected from the Kunsai quarries to the east of Quannei-Douge migmatite rock belt (Figures3 and 4(a)). The north part of the rock unit is plunged into the Jurassic basin (Figure 3). Field study shows that both the rock unit and the Jurassic basin have experienced a period of ductile transformation events. The microstructure study shows brittle deformed feldspar (Figures 4(b) and 4(c)), dynamically recrystallized quartz (Figure 4(c)), microdeflected biotite (Figure 4(d)), zircon grains with relatively intact crystal, long column, some rounded output and a higher degree of porosity which is symbiotic to microcline grains (Figure 4(b)). The cathode luminescence (CL) images show that the typical magmatic zircon characteristics are colorless and transparent here with oscillatory zoning, the length of about 120 μm–420 μm and the aspect ratio of 1.2 to 4.1 (Figure 4(e)). Totally, for 22 points of 22 zircon grains of sample biotite granodiorite KS-2 from the Kunsai quarries we performed U-Pb isotope analysis in order to statistically gain a feasible dating result (Figure 4(f)). All points were selected on the edge of long- column euhedral grains where the magmatic zircon oscillatory zoning is clear.Geochronological research of granite sample KS-2. (a) Position photo of the biotite monzonitic granite sample in the field of Kunsai Quarry. (b) The zircon grows together with the microcline CPL. (c) The microstructure of complete recrystallized quartz indicates the rock once experienced high-greenschist facies of deformation, CPL. (d) One biotite crystal is folded, PPL. (e) Magmatic zircon is shown by the SEM cathodoluminescence (CL) image. The circled area is deduced to form during the crystallization of granite and is just the measured area by laser-ICPMS (f) Zircon La-ICPMs U-Pb dating figure, and the average age is about 220 Ma.
(a)
(b)
(c)
(d)
(e)
(f)


### 2.2.2. Specimens from Mengku Quarries

The monzonitic granite sample MK-4 is selected from the Mengku East Quarry at the eastern side of the Mengku Town in the Shuangjiang County, which separates Jurassic red clastic rocks with one bedding bottom granitic conglomerate by the paleo-weathering crust in between (Figures5(a), 5(b), and 5(c)). Figure 5(a) shows the position photo of the biotite monzonitic granite sample in the Mengku East Quarry. From the field outcrop, both granitic intrusion (lower left) and its weathering top can be found to be cleavaged which had been covered by the upper Jurassic red detrital sediments with terrigenous origin, namely, the Huakaizuo Formation. The MK-4 zircon grains (Figure 5(d)) change greatly and have different shapes and sizes, such as long column, fan, and irregular granular. However, size of zircon grains is uniform with length between 90 μm and 150 μm and length-width ratio in 1.1 : 1–1.8 : 1. Zircon grains develop with quartz, plagioclase in rocks. The rock sample has been affected by weathering, showing retrograde metamorphism (Figure 5(e)). Characteristic oscillatory zoning of typical magmatic zircon is rendered on the cathode CL image. The idiomorphic degree of zircon is high, but some fragmented. On the sample of MK-4, 18 zircon grains and 18 points were analyzed by ICP-MS. Edge of the long-column idiomorphic or the chipped-hypidiomorphic zircon grains, and the clear zone of magmatic zircon oscillatory were always selected to perform the micro isotope analysis (Figure 5(f)).Geochronological research of the granite sample MK-4. (a) Position photo of the biotite monzonitic granite sample in a field Quarry of east Mengku. (b) Granitic intrusion (lower left) and its fossil weathering were cleavaged. (c) The red detrital material of terrigenous origin, Huakaizuo Formation in Jurassic, was normal gradational. (d) Granitic intrusions are selected as sample. (e) The micro  characteristics of MK-4 and the zircon setting are shown. The zircon grains are associated with quartz and plagioclase and have been degraded by some weathering process, CPL, (f) Magmatic zircon is shown by the SEM cathodoluminescence (CL) image. The circled area is deduced to form during the crystallization of granite and is just the measured area by laser-ICPMS. (g) Zircon La-ICPMs U-Pb dating figure, and the average age is about 245 Ma.
(a)
(b)
(c)
(d)
(e)
(f)
(g)


### 2.2.3. Dating Results

As shown in Figure4(f) and Table 2, the overall harmony values of KS-2 zircon age data range from 195 Ma to 245 Ma, but some of them are below the U-Pb harmonic line and deviated from the harmony line. This is probably because  the micro region selected is too close to the boundary of the zircon grain. Some zircon grains (Figure 5(f)) also have some cracks in and this may also affect the dating result. From the harmonic visible figure, zircon dating values are focused to a range from 210 Ma to 230 Ma, and the average age is about 220 Ma. This means that the crystallization age of the Kunsai quarries biotite granite is about in the late Triassic Norian period.Table 2
U-Pb isotopic dating for the single grain Zircon from granite of Kunsai.
No.
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
A77
0.05789
0.00231
0.25961
0.00949
0.03251
0.00089
0.01383
0.00076
526
38
234
8
206
6
278
15
A78
0.05188
0.00244
0.23562
0.00953
0.03294
0.00079
0.01035
0.00025
280
110
215
8
209
5
208
5
A79
0.05273
0.00141
0.24329
0.00604
0.03345
0.00081
0.01108
0.00055
317
26
221
5
212
5
223
11
A80
0.05213
0.00216
0.23471
0.00801
0.03265
0.00077
0.01025
0.00024
291
97
214
7
207
5
206
5
A81
0.05209
0.00131
0.25938
0.00608
0.0361
0.00086
0.01177
0.00034
289
25
234
5
229
5
237
7
A82
0.05014
0.00118
0.24192
0.00531
0.03498
0.00082
0.01113
0.00044
201
24
220
4
222
5
224
9
A83
0.05126
0.00122
0.24287
0.00541
0.03435
0.00081
0.01155
0.0006
253
24
221
4
218
5
232
12
A84
0.05027
0.00114
0.24534
0.00525
0.03539
0.00083
0.01176
0.00041
207
24
223
4
224
5
236
8
A89
0.0521
0.00237
0.22575
0.00875
0.03143
0.00075
0.00987
0.00023
290
107
207
7
199
5
199
5
A90
0.05305
0.00182
0.2649
0.0084
0.03621
0.00094
0.01376
0.00075
331
33
239
7
229
6
276
15
A91
0.05739
0.00113
0.23972
0.00441
0.03029
0.0007
0.00946
0.00032
507
23
218
4
192
4
190
6
A92
0.05076
0.00135
0.24604
0.00612
0.03515
0.00085
0.01173
0.00045
230
26
223
5
223
5
236
9
A93
0.05089
0.00279
0.24455
0.01197
0.03485
0.00086
0.01098
0.00025
236
127
222
10
221
5
221
5
A94
0.05114
0.00155
0.24377
0.00683
0.03457
0.00087
0.01167
0.00055
247
29
222
6
219
5
235
11
A95
0.05055
0.00109
0.24175
0.00488
0.03469
0.00081
0.01181
0.00045
220
24
220
4
220
5
237
9
A96
0.05018
0.00134
0.23857
0.00594
0.03448
0.00084
0.01149
0.00049
203
26
217
5
219
5
231
10
B02
0.05115
0.00119
0.24774
0.00541
0.03514
0.00084
0.01297
0.00054
248
25
225
4
223
5
260
11
B03
0.05067
0.00224
0.24165
0.00903
0.03459
0.00082
0.0109
0.00025
226
104
220
7
219
5
219
5
B04
0.05104
0.00235
0.24163
0.00953
0.03433
0.00082
0.01081
0.00025
243
109
220
8
218
5
217
5
B05
0.05079
0.00153
0.24968
0.00699
0.03567
0.0009
0.01274
0.00067
231
29
226
6
226
6
256
13
B06
0.05039
0.00095
0.24525
0.00437
0.03531
0.00082
0.01121
0.00038
213
25
223
4
224
5
225
8
B07
0.05429
0.00243
0.27463
0.01035
0.03669
0.00089
0.01147
0.00027
383
103
246
8
232
6
230
5
B08
0.05014
0.00223
0.24399
0.00913
0.0353
0.00085
0.01114
0.00026
201
104
222
7
224
5
224
5
B09
0.05141
0.00105
0.25807
0.00495
0.03643
0.00086
0.01414
0.00053
259
25
233
4
231
5
284
11As shown in Figure5(g) and Table 3, the overall harmony values of MK-4 zircon age data range between 190 Ma and 315 Ma. The values are somewhat scattered mainly because the granite of the Mengku quarries has been heavily weathered (Figure 5(d)). During the weathering process, chemical bonds of ZrO2 in zircon grains of our MK-4 sample would be broken. Therefore, some zircon isotope escaped. The average age of 245 Ma might indicate that the late Permian to early-middle Triassic magmatic event happened in the Mengku Quarries area of the Lincang Batholith.Table 3
U-Pb isotopic dating for the single grain Zircon from granite of Mengku.
Analysis
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
no.
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
1
0.05174
0.00244
0.32303
0.0139
0.04528
0.00108
0.01152
0.00053
274
56
284
11
285
7
232
11
2
0.09115
0.00288
2.96352
0.08448
0.23585
0.0053
0.08061
0.00287
1450
25
1398
22
1365
28
1567
54
3
0.11509
0.00332
0.50952
0.01225
0.03212
0.00066
0.02102
0.00068
1881
19
418
8
204
4
420
13
4
0.04837
0.00265
0.22077
0.01108
0.03312
0.00085
0.01153
0.00063
117
69
203
9
210
5
232
13
5
0.04837
0.0022
0.27295
0.01145
0.04095
0.00092
0.01223
0.0006
117
57
245
9
259
6
246
12
6
0.05351
0.00279
0.29775
0.01415
0.04038
0.00104
0.01371
0.00078
350
62
265
11
255
6
275
16
7
0.0806
0.00218
2.27431
0.05585
0.2048
0.00394
0.05968
0.00155
1212
22
1204
17
1201
21
1172
30
8
0.0802
0.00341
2.36577
0.09085
0.2141
0.00577
0.05352
0.00277
1202
37
1232
27
1251
31
1054
53
9
0.05928
0.00248
0.29959
0.01132
0.03668
0.00082
0.00966
0.00046
577
45
266
9
232
5
194
9
10
0.04989
0.00375
0.23793
0.0163
0.03461
0.00119
0.00907
0.00072
190
96
217
13
219
7
182
14
11
0.07866
0.00333
0.34683
0.01279
0.032
0.00079
0.01233
0.00063
1164
37
302
10
203
5
248
13
12
0.0406
0.00217
0.22437
0.01119
0.04011
0.00095
0.01052
0.00055
−255
72
206
9
254
6
212
11
13
0.0639
0.00299
0.31538
0.01317
0.03582
0.00089
0.01126
0.00067
738
48
278
10
227
6
226
13
14
0.07481
0.00441
0.3517
0.01817
0.03412
0.00108
0.01178
0.00078
1063
56
306
14
216
7
237
16
15
0.06821
0.00263
0.97745
0.03376
0.10399
0.00236
0.03233
0.00106
875
37
692
17
638
14
643
21
16
0.05116
0.00255
0.26673
0.01227
0.03784
0.00088
0.01057
0.00052
248
64
240
10
239
5
213
10
17
0.05025
0.00304
0.25181
0.01395
0.03636
0.00102
0.01037
0.00064
207
77
228
11
230
6
209
13
18
0.05379
0.003
0.27018
0.01369
0.03645
0.00098
0.00965
0.0006
362
67
243
11
231
6
194
12
19
0.05083
0.00373
0.26778
0.01802
0.03823
0.00125
0.00987
0.00055
233
96
241
14
242
8
199
11
20
0.06022
0.00487
0.2998
0.0217
0.03612
0.00142
0.01137
0.00113
611
90
266
17
229
9
229
23
21
0.0473
0.00214
0.20932
0.0087
0.0321
0.0007
0.00892
0.00038
64
55
193
7
204
4
179
8
22
0.05405
0.00334
0.28442
0.01602
0.03817
0.00111
0.00858
0.0006
373
75
254
13
241
7
173
12
23
0.05907
0.0024
0.66212
0.02439
0.08128
0.00181
0.03438
0.00121
570
43
516
15
504
11
683
24
24
0.05064
0.00245
0.21459
0.00944
0.03072
0.00072
0.00797
0.00046
224
59
197
8
195
5
160
9
25
0.05594
0.00261
0.26352
0.01113
0.03415
0.0008
0.00964
0.00045
450
53
237
9
216
5
194
9
26
0.06769
0.00524
0.32217
0.02212
0.0345
0.00134
0.01049
0.0009
859
80
284
17
219
8
211
18
27
0.06354
0.00206
0.75553
0.02205
0.08618
0.00166
0.02056
0.00084
726
32
571
13
533
10
411
17
28
0.05014
0.00296
0.33191
0.01801
0.04797
0.00129
0.02068
0.0011
201
77
291
14
302
8
414
22
29
0.23782
0.00377
6.55914
0.08439
0.19984
0.00325
0.01824
0.00075
3105
12
2054
11
1174
17
365
15


## 2.2.1. Specimen from Kunsai Quarries

The biotite monzonitic granite samples were selected from the Kunsai quarries to the east of Quannei-Douge migmatite rock belt (Figures3 and 4(a)). The north part of the rock unit is plunged into the Jurassic basin (Figure 3). Field study shows that both the rock unit and the Jurassic basin have experienced a period of ductile transformation events. The microstructure study shows brittle deformed feldspar (Figures 4(b) and 4(c)), dynamically recrystallized quartz (Figure 4(c)), microdeflected biotite (Figure 4(d)), zircon grains with relatively intact crystal, long column, some rounded output and a higher degree of porosity which is symbiotic to microcline grains (Figure 4(b)). The cathode luminescence (CL) images show that the typical magmatic zircon characteristics are colorless and transparent here with oscillatory zoning, the length of about 120 μm–420 μm and the aspect ratio of 1.2 to 4.1 (Figure 4(e)). Totally, for 22 points of 22 zircon grains of sample biotite granodiorite KS-2 from the Kunsai quarries we performed U-Pb isotope analysis in order to statistically gain a feasible dating result (Figure 4(f)). All points were selected on the edge of long- column euhedral grains where the magmatic zircon oscillatory zoning is clear.Geochronological research of granite sample KS-2. (a) Position photo of the biotite monzonitic granite sample in the field of Kunsai Quarry. (b) The zircon grows together with the microcline CPL. (c) The microstructure of complete recrystallized quartz indicates the rock once experienced high-greenschist facies of deformation, CPL. (d) One biotite crystal is folded, PPL. (e) Magmatic zircon is shown by the SEM cathodoluminescence (CL) image. The circled area is deduced to form during the crystallization of granite and is just the measured area by laser-ICPMS (f) Zircon La-ICPMs U-Pb dating figure, and the average age is about 220 Ma.
(a)
(b)
(c)
(d)
(e)
(f)


## 2.2.2. Specimens from Mengku Quarries

The monzonitic granite sample MK-4 is selected from the Mengku East Quarry at the eastern side of the Mengku Town in the Shuangjiang County, which separates Jurassic red clastic rocks with one bedding bottom granitic conglomerate by the paleo-weathering crust in between (Figures5(a), 5(b), and 5(c)). Figure 5(a) shows the position photo of the biotite monzonitic granite sample in the Mengku East Quarry. From the field outcrop, both granitic intrusion (lower left) and its weathering top can be found to be cleavaged which had been covered by the upper Jurassic red detrital sediments with terrigenous origin, namely, the Huakaizuo Formation. The MK-4 zircon grains (Figure 5(d)) change greatly and have different shapes and sizes, such as long column, fan, and irregular granular. However, size of zircon grains is uniform with length between 90 μm and 150 μm and length-width ratio in 1.1 : 1–1.8 : 1. Zircon grains develop with quartz, plagioclase in rocks. The rock sample has been affected by weathering, showing retrograde metamorphism (Figure 5(e)). Characteristic oscillatory zoning of typical magmatic zircon is rendered on the cathode CL image. The idiomorphic degree of zircon is high, but some fragmented. On the sample of MK-4, 18 zircon grains and 18 points were analyzed by ICP-MS. Edge of the long-column idiomorphic or the chipped-hypidiomorphic zircon grains, and the clear zone of magmatic zircon oscillatory were always selected to perform the micro isotope analysis (Figure 5(f)).Geochronological research of the granite sample MK-4. (a) Position photo of the biotite monzonitic granite sample in a field Quarry of east Mengku. (b) Granitic intrusion (lower left) and its fossil weathering were cleavaged. (c) The red detrital material of terrigenous origin, Huakaizuo Formation in Jurassic, was normal gradational. (d) Granitic intrusions are selected as sample. (e) The micro  characteristics of MK-4 and the zircon setting are shown. The zircon grains are associated with quartz and plagioclase and have been degraded by some weathering process, CPL, (f) Magmatic zircon is shown by the SEM cathodoluminescence (CL) image. The circled area is deduced to form during the crystallization of granite and is just the measured area by laser-ICPMS. (g) Zircon La-ICPMs U-Pb dating figure, and the average age is about 245 Ma.
(a)
(b)
(c)
(d)
(e)
(f)
(g)


## 2.2.3. Dating Results

As shown in Figure4(f) and Table 2, the overall harmony values of KS-2 zircon age data range from 195 Ma to 245 Ma, but some of them are below the U-Pb harmonic line and deviated from the harmony line. This is probably because  the micro region selected is too close to the boundary of the zircon grain. Some zircon grains (Figure 5(f)) also have some cracks in and this may also affect the dating result. From the harmonic visible figure, zircon dating values are focused to a range from 210 Ma to 230 Ma, and the average age is about 220 Ma. This means that the crystallization age of the Kunsai quarries biotite granite is about in the late Triassic Norian period.Table 2
U-Pb isotopic dating for the single grain Zircon from granite of Kunsai.
No.
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
A77
0.05789
0.00231
0.25961
0.00949
0.03251
0.00089
0.01383
0.00076
526
38
234
8
206
6
278
15
A78
0.05188
0.00244
0.23562
0.00953
0.03294
0.00079
0.01035
0.00025
280
110
215
8
209
5
208
5
A79
0.05273
0.00141
0.24329
0.00604
0.03345
0.00081
0.01108
0.00055
317
26
221
5
212
5
223
11
A80
0.05213
0.00216
0.23471
0.00801
0.03265
0.00077
0.01025
0.00024
291
97
214
7
207
5
206
5
A81
0.05209
0.00131
0.25938
0.00608
0.0361
0.00086
0.01177
0.00034
289
25
234
5
229
5
237
7
A82
0.05014
0.00118
0.24192
0.00531
0.03498
0.00082
0.01113
0.00044
201
24
220
4
222
5
224
9
A83
0.05126
0.00122
0.24287
0.00541
0.03435
0.00081
0.01155
0.0006
253
24
221
4
218
5
232
12
A84
0.05027
0.00114
0.24534
0.00525
0.03539
0.00083
0.01176
0.00041
207
24
223
4
224
5
236
8
A89
0.0521
0.00237
0.22575
0.00875
0.03143
0.00075
0.00987
0.00023
290
107
207
7
199
5
199
5
A90
0.05305
0.00182
0.2649
0.0084
0.03621
0.00094
0.01376
0.00075
331
33
239
7
229
6
276
15
A91
0.05739
0.00113
0.23972
0.00441
0.03029
0.0007
0.00946
0.00032
507
23
218
4
192
4
190
6
A92
0.05076
0.00135
0.24604
0.00612
0.03515
0.00085
0.01173
0.00045
230
26
223
5
223
5
236
9
A93
0.05089
0.00279
0.24455
0.01197
0.03485
0.00086
0.01098
0.00025
236
127
222
10
221
5
221
5
A94
0.05114
0.00155
0.24377
0.00683
0.03457
0.00087
0.01167
0.00055
247
29
222
6
219
5
235
11
A95
0.05055
0.00109
0.24175
0.00488
0.03469
0.00081
0.01181
0.00045
220
24
220
4
220
5
237
9
A96
0.05018
0.00134
0.23857
0.00594
0.03448
0.00084
0.01149
0.00049
203
26
217
5
219
5
231
10
B02
0.05115
0.00119
0.24774
0.00541
0.03514
0.00084
0.01297
0.00054
248
25
225
4
223
5
260
11
B03
0.05067
0.00224
0.24165
0.00903
0.03459
0.00082
0.0109
0.00025
226
104
220
7
219
5
219
5
B04
0.05104
0.00235
0.24163
0.00953
0.03433
0.00082
0.01081
0.00025
243
109
220
8
218
5
217
5
B05
0.05079
0.00153
0.24968
0.00699
0.03567
0.0009
0.01274
0.00067
231
29
226
6
226
6
256
13
B06
0.05039
0.00095
0.24525
0.00437
0.03531
0.00082
0.01121
0.00038
213
25
223
4
224
5
225
8
B07
0.05429
0.00243
0.27463
0.01035
0.03669
0.00089
0.01147
0.00027
383
103
246
8
232
6
230
5
B08
0.05014
0.00223
0.24399
0.00913
0.0353
0.00085
0.01114
0.00026
201
104
222
7
224
5
224
5
B09
0.05141
0.00105
0.25807
0.00495
0.03643
0.00086
0.01414
0.00053
259
25
233
4
231
5
284
11As shown in Figure5(g) and Table 3, the overall harmony values of MK-4 zircon age data range between 190 Ma and 315 Ma. The values are somewhat scattered mainly because the granite of the Mengku quarries has been heavily weathered (Figure 5(d)). During the weathering process, chemical bonds of ZrO2 in zircon grains of our MK-4 sample would be broken. Therefore, some zircon isotope escaped. The average age of 245 Ma might indicate that the late Permian to early-middle Triassic magmatic event happened in the Mengku Quarries area of the Lincang Batholith.Table 3
U-Pb isotopic dating for the single grain Zircon from granite of Mengku.
Analysis
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
207Pb/206Pb
207Pb/235U
206Pb/238U
208Pb/232Th
no.
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
Ratio
Error (1σ)
1
0.05174
0.00244
0.32303
0.0139
0.04528
0.00108
0.01152
0.00053
274
56
284
11
285
7
232
11
2
0.09115
0.00288
2.96352
0.08448
0.23585
0.0053
0.08061
0.00287
1450
25
1398
22
1365
28
1567
54
3
0.11509
0.00332
0.50952
0.01225
0.03212
0.00066
0.02102
0.00068
1881
19
418
8
204
4
420
13
4
0.04837
0.00265
0.22077
0.01108
0.03312
0.00085
0.01153
0.00063
117
69
203
9
210
5
232
13
5
0.04837
0.0022
0.27295
0.01145
0.04095
0.00092
0.01223
0.0006
117
57
245
9
259
6
246
12
6
0.05351
0.00279
0.29775
0.01415
0.04038
0.00104
0.01371
0.00078
350
62
265
11
255
6
275
16
7
0.0806
0.00218
2.27431
0.05585
0.2048
0.00394
0.05968
0.00155
1212
22
1204
17
1201
21
1172
30
8
0.0802
0.00341
2.36577
0.09085
0.2141
0.00577
0.05352
0.00277
1202
37
1232
27
1251
31
1054
53
9
0.05928
0.00248
0.29959
0.01132
0.03668
0.00082
0.00966
0.00046
577
45
266
9
232
5
194
9
10
0.04989
0.00375
0.23793
0.0163
0.03461
0.00119
0.00907
0.00072
190
96
217
13
219
7
182
14
11
0.07866
0.00333
0.34683
0.01279
0.032
0.00079
0.01233
0.00063
1164
37
302
10
203
5
248
13
12
0.0406
0.00217
0.22437
0.01119
0.04011
0.00095
0.01052
0.00055
−255
72
206
9
254
6
212
11
13
0.0639
0.00299
0.31538
0.01317
0.03582
0.00089
0.01126
0.00067
738
48
278
10
227
6
226
13
14
0.07481
0.00441
0.3517
0.01817
0.03412
0.00108
0.01178
0.00078
1063
56
306
14
216
7
237
16
15
0.06821
0.00263
0.97745
0.03376
0.10399
0.00236
0.03233
0.00106
875
37
692
17
638
14
643
21
16
0.05116
0.00255
0.26673
0.01227
0.03784
0.00088
0.01057
0.00052
248
64
240
10
239
5
213
10
17
0.05025
0.00304
0.25181
0.01395
0.03636
0.00102
0.01037
0.00064
207
77
228
11
230
6
209
13
18
0.05379
0.003
0.27018
0.01369
0.03645
0.00098
0.00965
0.0006
362
67
243
11
231
6
194
12
19
0.05083
0.00373
0.26778
0.01802
0.03823
0.00125
0.00987
0.00055
233
96
241
14
242
8
199
11
20
0.06022
0.00487
0.2998
0.0217
0.03612
0.00142
0.01137
0.00113
611
90
266
17
229
9
229
23
21
0.0473
0.00214
0.20932
0.0087
0.0321
0.0007
0.00892
0.00038
64
55
193
7
204
4
179
8
22
0.05405
0.00334
0.28442
0.01602
0.03817
0.00111
0.00858
0.0006
373
75
254
13
241
7
173
12
23
0.05907
0.0024
0.66212
0.02439
0.08128
0.00181
0.03438
0.00121
570
43
516
15
504
11
683
24
24
0.05064
0.00245
0.21459
0.00944
0.03072
0.00072
0.00797
0.00046
224
59
197
8
195
5
160
9
25
0.05594
0.00261
0.26352
0.01113
0.03415
0.0008
0.00964
0.00045
450
53
237
9
216
5
194
9
26
0.06769
0.00524
0.32217
0.02212
0.0345
0.00134
0.01049
0.0009
859
80
284
17
219
8
211
18
27
0.06354
0.00206
0.75553
0.02205
0.08618
0.00166
0.02056
0.00084
726
32
571
13
533
10
411
17
28
0.05014
0.00296
0.33191
0.01801
0.04797
0.00129
0.02068
0.0011
201
77
291
14
302
8
414
22
29
0.23782
0.00377
6.55914
0.08439
0.19984
0.00325
0.01824
0.00075
3105
12
2054
11
1174
17
365
15


## 3. Tectonic Implications

Previous petrological and geochemical studies [18, 26, 28, 35] indicate that the Lincang granite mainly shows two types of granite with an initial strontium isotope ratio ranging from 0.71 to 0.78 and therefore it belongs to S-type granite and once may have been formed in an environment of tectonic collision. Combined with previous chronological data, we propose a three-stage model on the tectonic evolution between late Permian and Jurassic (Figure 6).Figure 6
Isotopic age histogram showing the major tectonic event in the area east to the Tibet Peateau (after [8]).(1)  Regional Collision and Contraction before the Formation of the Lincang Batholith
Before the formation of the Lincang Batholith, the Paleo-Tethys Ocean and many intraoceanic islands distributed between the Baoshan and the Lanping-Simao-Indosinian blocks [36]. In a regional contractional environment of subduction and collision, it is extremely common to find folding, thrusting, and uplifting phenomena (Figure 7(a)).Figure 7
Formation and tectonic evolution model for the Lincang Batholith.(2)  Time Heterogeneity of In Situ Hybrid of the Lincang Batholith
The Lincang Batholith was controlled by one deep-seated fault along the Lancang Jiang River and proposed in situ hybrid origin of the Batholith in the early to middle Triassic collision between the Baoshan-Shantai and Lanping-Simao-Indochina Blocks [16]. Our study shows an ununiform law result in the aspect of mixing time of the Batholith (Figure 7(b)). The intrusion time in the east Qunsai area was later than in the Mengku area, indicating that the regional contraction in Mengku area was weakened or stopped, and triggered magma poured at ~230 Ma, however, the contraction pattern may still remain in the Qunsai area to the east.(3)  Tectonic Denudation and Regional Exhumation Happened between Late Triassic and Middle Jurassic, Which Is Supported by ~201 Ma Biotite40Ar/39Ar Age from the Lincang Batholith [27]
This paper research shows that the upper part of the Lincang Batholith experienced long-term denudation, resulting in the development of the weathering crust (Figure7(a)). The upper crust is the Jurassic Huakaizuo Formation, characterized by carbonate rocks of shallow sea facies, together with some volcano clastic rocks (Figure 5(b)). Unconformity relationship is shown between the Batholith and the Huakaizuo Formation (Figures 3, 5(a), 5(b), 5(c), and 7(c)). Apparently, the Meso-Tethys expansion also happened in this era and left some effect in the Lincang Area.



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*Source: 287962-2012-08-08.xml*