Geochronological, elemental and Sr-Nd-Hf-O isotopic constraints on the petrogenesis of the Triassic post-collisional granitic rocks in NW Thailand and its Paleotethyan implications

This study was jointly funded by the National Science Foundation of China (41190073), National Basic Research Program of China (2014CB440901 and 2016YFC0600303) and the Fundamental Research Funds for the Central Universities to SYSU.New U-Pb geochronological, petrologic, elemental and Sr-Nd-Hf-O isotopic data for the granites from the Inthanon and Sukhothai zones in NW Thailand in conjunction with correlations with SW China are presented to constrain the age and position of the Paleotethys Ocean in this region and the associated assembly of Southeast Asia. The geochronological data show that the granitic rocks in the Inthanon and Sukhothai zones, herein named Group 1 and Group 2 granites, respectively, yield similar crystallization ages of 230-200 Ma. Group 1 samples are characterized by monzogranite and granite with I- and S-type geochemical affinity and Group 2 samples by I-type monzogranite and granodiorite. They have generally similar chondrite-normalized REE and PM- normalized multi-element patterns but distinct Sr-Nd-Hf-O isotopic compositions. Group 1 samples have slightly higher initial 87Sr/86Sr ratios (0.7111- 0.7293) but lower εNd(t) values (-11.1 ~ -14.1) than those of Group 2 samples (87Sr/86Sr(i)=0.7073-0.7278 and εNd(t)=-8.3 ~ -11.0). Group 1 samples show the lower εHf(t) values (-5.4 ~ -18.2), older TDM (1.62-2.40 Ga) and higher δ18O values (+ 7.95-+9.94) than those of Group 2 samples (εHf(t) of -11.1-+4.80, TDM of 0.96-1.95 Ga and δ18O of + 4.95 ~+7.98) for the Triassic crystallization zircons. These geochemical signatures are similar to the Kwangsian and Indosinian granites in the South China and Indochina blocks but distinct from those of the Gangdese I-type granite and Sibumasu Paleozoic granite. Our data suggest that Group 1 samples mainly originated from the early Paleozoic supracrustal rocks containing metapelite and metavolcanic components, which had previously experienced the surface weathering. Group 2 samples were derived from a hybridized source of an old metamorphic and a newly underplated mafic component. Synthesis of our data with available regional observations indicate that the Inthanon zone represents the main suture zone of the eastern Paleotethyan Ocean in NW Thailand and links with the Changning-Menglian suture zone in SW Yunnan (SW China). In NW Thailand, a switch from the eastward subduction of the Paleotethyan oceanic plate to the collision of the Sibumasu with Indochina blocks occurred at ~ 237 Ma, and syn- and post-collisional time being at ~ 237-230 Ma and ~ 200-230 Ma, respectively. The late Triassic granites in the Inthanon and Sukhothai zones are representative of the post-collisional magmatic products.PostprintPeer reviewe

A Mesozoic Andean-Type Orogenic Cycle in Southeastern China as Recorded by Granitoid Evolution

Petrology, magnetic susceptibilities, zircon U-Pb ages, zircon Hf isotopes and whole-rock geochemical data are used to constrain the evolution of Mesozoic high-potassium granitic rocks that record an Andean-type orogenic cycle in the southeastern China segment of the Western Pacific. Decreasing melting pressures of the granitic magmas from the Late Triassic to the Early Cretaceous, as reflected by decreasing Sm/Yb ratios, point to a general trend of crustal attenuation with time in western Zhejiang Province. Five distinct stages of granitic magmatism are identified: (1) 230 to 215 Ma: high-temperature, high-pressure dehydration melting in a reduced and thickened crust caused by flat-slab subduction of the paleo-Pacific Plate; (2) 170 to 150 Ma: low-temperature, high-pressure water-fluxed melting in an oxidized and thickened crust caused by the foundering of the paleo-Pacific Plate; (3) 140 to 130 Ma: low-temperature, low-pressure dehydration melting of the continental crust caused by extension of the lithosphere; (4) 130 to 125 Ma: high-temperature, low-pressure dehydration melting of the refractory materials in the continental crust caused by further extension of the lithosphere and possibly basaltic underplating; and (5) 115 to 100 Ma: emplacement of fractionation products of hydrous basalts from the enriched continental lithospheric mantle

Introduction to Journal of South American Earth Sciences special issue on “Magmatism of southernmost South America”

complex magmatic history due to the occurrence of multiple large-scalegeological processes that include mantle plumes impingements, slabwindows opening, collisional episodes, normal and flat subductionevents, mantle transition zone-derived melts ascent, slab break-offevents, etc. (e.g., Mpodozis and Kay, 1992; Gorring et al., 1997; Rileyet al., 2001; Pankhurst et al., 2006; Kay et al., 2007; Ramos, 2008;Breitsprecher and Thorkerlson, 2009; Arag´on et al., 2013; Gianni et al.,2018; Navarrete et al., 2019; 2020; Iannelli et al., 2020). Although thismagmatic history began during the Neoproterozoic, the igneous activityof the last 300 Myr has been remarkably intense and voluminous,constituting one of the most distinctive geological features of this region.So much so that three Phanerozoic Large Igneous Provinces (LIPs) havebeen proposed (Kay et al., 1989; Pankhurst et al., 1998; Kay et al., 2007;Bastías-Mercado et al., 2020 ? this special issue). The first of them linkedto the Permian-Triassic subduction events (Choiyoi SLIP - Bastías-Mercado et al. this especial issue, and references therein; Oliveroset al., 2019), although there are also proposals that have suggested anorigin related to slab-breakoff episodes (e.g., Mpodozis and Kay, 1992;Pankhurst et al., 2006). The second would have been generated by theJurassic Karoo mantle plume impingement added to the paleo-pacificsubduction during the beginning of the Gondwana breakup (ChonAike SLIP - e.g., Kay et al., 1989; Pankhurst et al., 1998), whereas theorigin of the Oligocene-Miocene third province (Somuncura LIP ? Kayet al., 2007) is still under discussion. There are proposals that invoke amantle plume impingement (Kay et al., 2007), a lithospheric delaminationevent (Remesal et al., 2012), as well as the mantle transitionzone-derived melts ascent due to the Farallon slab stagnation (Navarreteet al., 2020), between others. In this special issue, most of the articles arelinked to these Permian-Triassic, Jurassic and mid-Cenozoic LIPs(Fig. 1), although multiple subduction-related magmatic events are alsoincluded, such as the formation of the Patagonian Batholith (e.g., Pankhurstet al., 1999) and the eruption of the volcanic products linked tothe magmatism of the Andean subduction zone (e.g., Rapela et al., 1984;1988).From the economic point of view, the socio-economic developmentof Chile and Argentina was marked by the magmatism of the southernmostSouth American region. In this sense, the Jurassic magmatismof Patagonia gave rise to numerous precious metals hydro-thermal largemineral deposits (e.g., Schalamuk et al., 1997; Echavarría et al., 2005;Guido and Campbell, 2011; Permuy Vidal et al., 2016; Tassara et al.,2017), whereas the Cenozoic intraplate magmatism of Patagoniafavored the hydrocarbon maturation in Patagonian oil and gas producingMesozoic basins (e.g., Rodriguez and Littke, 2001; Spacapan et al.,2018). Also, giant porphyry copper deposits were produced by theMeso-Cenozoic subduction-related magmatism in the Andean region (e.g., Mpodozis and Cornejo, 2012; Lee and Tang, 2020).Therefore, new contributions that improve the comprehension of thelarge magmatic episodes of southernmost South America are highlyrelevant for the general geological knowledge of this region, and theirinterest exceeds that of the academic geological community.Fil: Navarrete Granzotto, César Rodrigo. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zaffarana, Claudia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentin

Petrogenesis of Paleozoic–Early Mesozoic Granites and Pegmatites in the Yuechengling Pluton of South China

AbstractAlthough pegmatites are volumetrically minor in the upper continental crust, these rocks host abundant rare metal deposits (e.g., Li, Be, Rb, Ta, and Nb). Pegmatites can be formed either by extensive fractional crystallization of granitic magmas or by low-degree partial melting of metasedimentary rocks. The Mao’ershan–Yuechengling composite batholith in the Nanling Range in the South China Block (SCB) is of early Paleozoic–Triassic age (440–381 and 236–204 Ma, respectively). Recently, hundreds of pegmatites associated with Nb, Ta, Be, Rb, and Li mineralization have been identified in this batholith. These pegmatites are hosted by granitic wall rocks. However, the relationships between the pegmatites and granitic wall rocks are not well constrained. To address this, we investigated the Mao’antang (MAT) and Tongzuo (TZ) pegmatites and their biotite granite wall rocks in the middle part of the Yuechengling pluton. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb ages revealed that the MAT pegmatites formed during the Permian (269 Ma) and Triassic (231 Ma) and that the MAT biotite granite wall rock records two stages of magmatic activity (271 and 231 Ma) that are coeval with the pegmatites. The TZ pegmatites probably formed during the Triassic (235 Ma), and the TZ biotite granite wall rock formed during the Silurian (435 Ma). The MAT biotite granite and pegmatites (εNdt=−12.0 to −10.6; εHft=−8.0 to −1.0), TZ pegmatites (εNdt=−10.4 to −6.1), and TZ biotite granites (εNdt=−9.1 to −8.7; εHft=−7.7 to −4.1) have enriched whole-rock Nd and zircon Hf isotopic compositions that are similar to those of early Paleozoic and Triassic S-type granites in the SCB. In addition, the whole-rock Pb isotopic compositions of the MAT and TZ pegmatites and granites are distributed along the upper crust evolution line. We suggest that the MAT and TZ biotite granites were mainly derived from Paleoproterozoic metasedimentary rocks in the middle crust. The MAT pegmatites are fractional crystallization products of the MAT biotite granites, whereas the TZ pegmatites were formed by fractional crystallization of hidden parental S-type granites. We propose that the MAT and TZ pegmatites have potential for rare metal (Nb, Ta, Be, and Li) mineralization, as they record high degrees of fractional crystallization. The MAT and TZ areas in the middle of the Yuechengling pluton are promising targets for rare metal exploration

MAGNETIC SUSCEPTIBILITIES DISTRIBUTION AND ITS POSSIBLY GEOLOGICAL SIGNIFICANCE OF SUBMERGED BELITUNG GRANITE

An appraisal of the marine magnetic anomalies over the Belitung water provides information on the distribution of the magnetic susceptibility values. The 0.001 to 0.003 cgs unit contour values charac- terize the zone of submerged Belitung granite coincides with the zone of less than 50 nT total mag- netic anomaly contour value. Susceptibilities distribution analyses reveal a strong correlation between magnetic susceptibility and type of granites. The nature of submerged Belitung intrusive is suggested to be granitic pluton of biotite-granite that is associated with cassiterite minerals

Characteristics of Radiogenic Heat Production of Widely Distributed Granitoids in Western Sichuan, Southeast Tibetan Plateau

AbstractInvestigating the genesis of geothermal resources requires a thorough understanding of the heat source mechanism, which is also a vital basis for the efficient exploration and utilization of geothermal resources. Situated in the eastern Himalayan syntax, western Sichuan is considered to be one of the main concentration regions of high-temperature geothermal resources in China. To date, various studies have been carried out to reveal the heat source and genesis of the abundant high-temperature resources in this area; however, studies on the contribution of the radioactive heat generated by the widely distributed granitoids to the high-temperature geothermal resources remain scarce. In order to resolve this knowledge gap, we attempted to obtain evidence from the geochemical data published in the literature in the past few decades. A total of 548 radiogenic heat production rate data were determined. The statistical data indicate that the average concentrations of the heat-producing elements U, Th, and K are 6.09±5.22 ppm, 26.74±16.78 ppm, and 3.51±0.82%, respectively. The calculated heat production values of the granitoids vary from 0.52 to 10.86 μW/m3, yielding an arithmetic average value of 3.74±2.15 μW/m3, which is higher than that of global Mesozoic–Cenozoic granites (3.09±1.62 μW/m3). Based on the heat production values, the capacity of the granitic batholiths to store heat was assessed, and the Dongcuo pluton was found to be the largest heat reservoir (382.88×1013 J/a). The distribution of the crustal heat flow was examined using the calculated heat production data and the stratigraphic structure obtained via deep seismic sounding in the study area. The results indicate that the crustal heat flow is 48.3–56.2 mW/m2, which is mainly contributed by the radioactive decay in the granitoids in the upper crust. The fact that it accounts for nearly half of the regional background heat flow indicates that the radiogenic heat from the granitoids is an important heat source for the formation of the thermal anomaly and the high-temperature geothermal resources in the study area. Thus, the results obtained in this study highlight the importance of the widely distributed granitoids to high-temperature geothermal resources in western Sichuan

Early Paleozoic and Early Mesozoic intraplate tectonic and magmatic events in the Cathaysia Block, South China

The authors acknowledge financial supports provided by the National Basic Research Program of China (973 program, 2012CB416701), National Natural Science Foundation of China (41330208 and 41272226), and the Bureau of China Geological Survey (201211093-1).The geodynamic framework of the South China Craton in the Early Paleozoic and Early Mesozoic has been modeled as developing through either oceanic convergence or intracontinental settings. On the basis of an integrated structural, geochemical, zircon U-Pb and Hf isotopic, and mica 40Ar/39Ar geochronologic study we establish that an intracontinental setting is currently the best fit for the available data. Our results suggest that widespread tectonomagmatic activity involving granite emplacement and mylonitic deformation occurred during two distinct stages: ~435-415 Ma and ~230-210 Ma. The coeval nature of emplacement of the plutons and their ductile deformation is corroborated by the subparallel orientation of the mylonitic foliation along the pluton margins, gneissose foliation in the middle part of pluton, the magmatic foliation within the plutons, and the schistosity in the surrounding metamorphosed country rocks. The 435-415 Ma granitoids exhibit peraluminous, high-K characteristics, and zircons show negative εHf(t) values (average -6.2, n = 66), and Paleoproterozoic two-stage model ages of circa 2.21-1.64 Ga (average 1.84 Ga). The data suggest that the Early Paleozoic plutons were derived from the partial melting of the Paleoproterozoic basement of the Cathaysia Block. The 230-210 Ma granites are potassic and have zircons with εHf(t) values of -2.8 - 8.7 (average -5.4, n = 62), corresponding to TDM2 ages ranging from 2.0 to 1.44 Ga (average 1.64 Ga), suggesting that the Early Mesozoic partial melts in Cathaysia were also derived from basement. The geochemical distinction between the two phases of granites traces continental crustal evolution with time, with the Early Mesozoic crust enriched in potassium, silicon, and aluminum, but deficient in calcium, relative to the Paleozoic crust. Kinematical investigations provide evidence for an early-stage ductile deformation with a doubly vergent thrusting pattern dated at 433 ± 1 to 428 ± 1 Ma (40Ar/39Ar furnace step-heating pseudoplateau ages obtained on muscovite and biotite from mylonite and deformed granite) and a late-stage strike-slip movement with sinistral sense of ductile shearing at 232 ± 1 to 234 ± 1 Ma (40Ar/39Ar furnace step-heating pseudoplateau ages) along an E-W direction. The geological, geochemical, and isotopic signatures likely reflect far-field effects in response to continental assembly events at these times.Publisher PDFPeer reviewe

Compression to extension switch during the Middle Triassic orogeny of Eastern China: the case study of the Jiulingshan massif in the southern foreland of the Dabieshan

The Jiulingshan massif is an E–W trending anticlinorium in the South China Block (SCB) that forms the southern foreland of the Qinling–Dabie orogen. The Jiulingshan consists of Middle Proterozoic (ca. 1 Ga–800 Ma) metamorphic and plutonic rocks unconformably overlain by Sinian to Triassic rocks. In these cover rocks, two episodes of deformation of pre-Late Triassic age are recognized. Namely, a N–S compressional phase characterized by south verging thrusts, upright folds and vertical cleavage followed by an extensional phase characterized by layer parallel slip, collapse folds and extensional allochthons of Proterozoic slate on top of Carboniferous to Middle Triassic carbonates. The extensional tectonics appears to be a mechanical consequence of the compressional tectonics. On a regional scale, the Jiulingshan massif forms one of the domed crustal scale shear zones of the SCB that accommodated the continuing convergence that immediately followed the Qinling–Dabie collision