Ordo-Silurian assemblage in the Indochina interior: Geochronological, elemental, and Sr-Nd-Pb-Hf-O isotopic constraints of early Paleozoic granitoids in South Laos

Abstract In order to verify the early Paleozoic accretionary assemblage in the Indochina interior and constrain the Prototethyan tectonic evolution in Southeast Asia, this study presents a set of new U-Pb geochronological, elemental, and Sr-Nd-Pb-Hf-O isotopic data for the fifty-two representative granitoids in South Laos. The granitoids from the Kontum terrane, Tam Ky-Phuoc Son tectonic zone, and southern Truong Son igneous zone in South Laos yield the crystallization ages of 464–485 Ma, 455–471 Ma, and 427–446 Ma, respectively, with a northerly younging trend within the Indochina interior. They are mainly monzogranite with A/CNK = 0.96–1.99 and K2O > Na2O, which are marked by enrichment in large-ion lithophile elements and depletion in high field strength elements with remarkable Nb-Ta, Sr-P, and Ti negative anomalies. Their initial 87Sr/86Sr ratios range from 0.70510 to 0.71559, εNd(t) from −9.5 to −3.0, (206Pb/204Pb)i from 18.65 to 19.72, (207Pb/204Pb)i from 15.66 to 15.80, and (208Pb/ 204Pb)i from 38.84 to 39.79. The corresponding zircon ɛHf(t) and δ18O values are in the range of −10.6 to +1.0 and 6.88‰ to 8.94‰, respectively. In addition, their Sr-Nd-Pb and Hf-O isotopic compositions are generally similar with those of time-equivalent granitoids in South Tibet and SW Yunnan, China, and synchronous mafic-intermediate igneous rocks in South Laos, but distinctive from those of the supracrustal sedimentary-derived South China Paleozoic granite and Lincang-Sukhothai S-type granite. The early Paleozoic granitoids in South Laos might have originated from a mixed source of the wedge-derived juvenile crust coupled with supracrustal materials. All these data synthetically suggest the southward subduction of the Tam Ky-Phuoc Son Ocean and the northerly on-growing Ordo-Silurian accretionary orogenesis within the previously defined “single-ancient” Indochina block. The assemblage of the Indochina block might initiate at ca. 430 Ma in the Silurian and terminate in the Early-Middle Devonian.

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Geochronology and geochemistry of igneous rocks in the southeastern Lesser Xing’an Range, northeastern China: petrogenesis and implications for the early Mesozoic tectonic evolution

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2018-0198 ◽

2020 ◽

Vol 57 (4) ◽

pp. 506-523

Author(s):

Jin-hua Qin ◽

Cui Liu ◽

Jin-fu Deng

Keyword(s):

Field Strength ◽

Inductively Coupled Plasma ◽

High Field ◽

Magma Mixing ◽

Tectonic Setting ◽

Alkali Feldspar ◽

Igneous Rocks ◽

Geochemical Data ◽

High Field Strength ◽

Alkaline Granite

We present systematic U–Pb age data collected by laser ablation multi-collector inductively coupled plasma mass spectrometry, precise geochemical data, and Nd isotope data for igneous rocks from the southeastern Lesser Xing’an Range (SE LXR). The results indicate that the formation ages as follows: Maojiatun alkaline granite, 207.2 ± 0.84 Ma and 204.6 ± 0.93 Ma; Diorite porphyrite, 164.5 ± 0.97 Ma; and Tieli syenogranite, 186.7 ± 1.50 Ma. The alkaline granite has high silicon, potassium, alkali, and FeOT contents; it is enriched in high field strength elements, Zr, Hf, Th, Rb, and U; is depleted in Ba, Sr, Nb, Ta, P, Ti, etc.; and has high ratios of 10000Ga/Al. It shows an A2-type granite affinity. The Tieli alkali-feldspar granite has high total alkali contents and is enriched in high field strength elements and rare earth elements and depleted in Sr, Ba, Ti, and P, and shows varying degrees of alkalinity. Rocks from SE LXR display similar εNd (t) values with corresponding to Nd model ages of 1095 to 813 Ma. The igneous rocks from the SE LXR are proposed to be derived from melting of the Neoproterozoic lower crust and potential magma mixing with ancient crystalline basement. The formation of the Maojiatun alkaline granite occurred in response to a postorogenic event following the closure of the Paleo-Asian Ocean. However, the SE LXR exhibited an extensional back-arc tectonic setting in the Early Jurassic. The Middle Jurassic diorite porphyrite could be related to the temporary stagnation of the westward subduction of the Paleo-Pacific plate.

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Geochronology and geochemistry of early Paleozoic igneous rocks from the Zhangguangcai Range, northeastern China: Constraints on tectonic evolution of the eastern Central Asian Orogenic Belt

Lithosphere ◽

10.1130/l639.1 ◽

2017 ◽

Vol 9 (5) ◽

pp. 803-827 ◽

Cited By ~ 13

Author(s):

Zhiwei Wang ◽

Wenliang Xu ◽

Fuping Pei ◽

Peng Guo ◽

Feng Wang ◽

...

Keyword(s):

Tectonic Evolution ◽

Northeastern China ◽

Orogenic Belt ◽

Igneous Rocks ◽

Central Asian Orogenic Belt ◽

Early Paleozoic ◽

Central Asian

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Geochemistry and isotopic evolution of the Mesoproterozoic Cape Meredith Complex, West Falkland

Geological Magazine ◽

10.1017/s0016756800004519 ◽

2000 ◽

Vol 137 (5) ◽

pp. 537-553 ◽

Cited By ~ 19

Author(s):

ROBERT J. THOMAS ◽

JOACHIM JACOBS ◽

BRUCE M. EGLINGTON

Keyword(s):

High Field ◽

Alkaline Basalt ◽

Thin Sheets ◽

Calc Alkaline ◽

Isotopic Data ◽

High Field Strength ◽

Geological Evolution ◽

Isotopic Evolution ◽

Dronning Maud Land ◽

Granitoid Gneisses

Whole-rock major and trace element geochemical and Rb–Sr/Sm–Nd isotopic data are presented for the Mesoproterozoic (∼1.0 Ga) metamorphic and igneous rocks of the Cape Meredith Complex, West Falkland. The data indicate that the oldest rocks, the ∼1.1 Ga supracrustal gneisses of the Big Cape Formation, which form three petrographic and geochemical groups (mafic amphibolite, quartz–plagioclase–biotite–hornblende intermediate gneiss and acid gneiss), probably represent a juvenile calc-alkaline, basalt–andesite–rhyolite volcanic sequence, with epsilon (εNdT) values and NdTDM ages of ∼+3 to +6 and ∼1100 to 1400 Ma respectively. It is argued on geochemical grounds that these metavolcanics were extruded in an island-arc at around 1120 Ma. The Big Cape Formation was intruded by granitoids during and after a collisional orogenic event at around 1090 Ma. The oldest, foliated, (G1) granodiorite was emplaced as thin sheets at approximately 1090 to 1070 Ma and is characterized by εNd values of ∼+1.5 to 4 (TDM = ∼1200 to 1400 Ma), showing its juvenile nature. The ∼1070 Ma (G2) syntectonic granitoid gneisses and ∼1000 Ma G3 post-tectonic granites also exhibit juvenile characteristics (εNd = ∼0 to +5 and TDM = 2200 to 1200 Ma, respectively). The granitoids show a time-composition evolution from Na-rich (G1) granodiorite to potassic, high-High Field Strength Element granites (G3). The geochemical and isotopic characteristics and geological evolution of the Cape Meredith Complex is comparable with that of the adjacent Gondwana crustal blocks in Natal (SE Africa) and Dronning Maud Land (East Antarctica), supporting models that demonstrate these areas evolved in a contiguous, juvenile arc environment prior to, and during, a major orogenic event at ∼1.1 Ga. These events were associated with the birth of the Rodinian supercontinent. The three areas remained juxtaposed during Rodinia break-up and were subsequently incorporated into Gondwana in the same relative positions.

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The Kamusite A2-type granites in the Karamaili tectonic belt, Xinjiang (NW China): tracing staged postcollisional delamination in the eastern Junggar

Geological Magazine ◽

10.1017/s0016756820000813 ◽

2020 ◽

pp. 1-26

Author(s):

Bowen Zhang ◽

Chuan Chen ◽

Xiaoping Gong ◽

Yaxiaer Yalikun ◽

Kadeliya Kaheman

Keyword(s):

Partial Melting ◽

Large Scale ◽

Late Carboniferous ◽

Zircon Geochronology ◽

High Field Strength ◽

Original Source ◽

Type Granite ◽

Juvenile Crust ◽

Tectonic Belt ◽

Extensional Setting

Abstract The Kamusite pluton is located in the eastern Junggar area, the westernmost segment of the Karamaili structural belt, and is predominantly composed of medium granite and microgranite with an exposure area of 30 km2. The U–Pb zircon geochronology of the Kamusite granites indicates that they crystallized in the late Carboniferous period (328–321 Ma). These granites exhibit high contents of SiO2 (76.09–77.85 wt %) and K2O + Na2O (8.01–9.06 wt %), but low MgO (0.01–0.14 wt %), CaO (0.07–0.32 wt %) and TiO2 (0.01–0.13 wt %) contents, showing alkalic–calcic, weakly peraluminous and ferroan features. They are depleted in Ba, Sr, Ti and P and enriched in Rb and some high-field-strength elements (Hf, Nd, Ta and Y); their rare earth element patterns are slightly right-leaning with strongly negative Eu anomalies, high 10 000 * Ga/Al (3.4–5.36, >2.6) and especially high Y/Nb ratios (1.61–10.33, >1.2), showing the geochemical characteristics of A2-type granite. These granites were produced by partial melting in a high-temperature, low-pressure, reduced and anhydrous environment and experienced extensive fractional crystallization, which concomitantly resulted in tin mineralization. Combining the high positive zircon ϵHf(t) values of +10.9 to +15.76 with young Hf (TDM2) model ages (638–330 Ma), it can be suggested that underplating-related mantle-derived materials were the original source of the Kamusite A2-type granites; namely, these granites formed by the partial melting of juvenile crust. The record of large-scale magmatism indicates that the whole tectonic belt was in a postcollisional extensional setting induced by staged delamination from west to east during the late Carboniferous to early Permian periods.

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Nd isotopic compositions of felsic igneous rocks in Cape Breton Island, Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e92-056 ◽

1992 ◽

Vol 29 (4) ◽

pp. 650-657 ◽

Cited By ~ 36

Author(s):

Sandra M. Barr ◽

Ernst Hegner

Keyword(s):

New Brunswick ◽

Small Variation ◽

Igneous Rocks ◽

Northwestern Part ◽

Isotopic Data ◽

Cape Breton Island ◽

Late Precambrian ◽

Cape Breton ◽

Depleted Mantle ◽

Juvenile Crust

Nd isotopic data from 18 felsic plutonic and volcanic units in Cape Breton Island show variations consistent with other geological and geophysical evidence for at least three distinct terranes. A ca. 1.2 Ga syenite considered to be part of Grenvilleage basement exposed in the northwestern part of the island yields an initial εNd value of +0.4 and a depleted-mantle model age (TDM) of 1.66 Ga, suggesting substantial involvement of older (Archean or Early Proterozoic) crust in its petrogenesis. A TDM of 1.38 Ga indicated by Nd isotopic data for a Devonian granite spatially associated with the syenite is also consistent with the presence of older crust in that part of Cape Breton Island. In contrast, Silurian rhyolite and Devonian granites from the Aspy terrane have TDM ranging from 0.7 to 1.1 Ga and initial εNd between +2.8 and −1.2, and overlap in isotopic characteristics with late Precambrian and Early Ordovician plutons in the Bras d'Or terrane that yield TDM of 0.9–1.1 Ga and initial εNd of +1.4 to −1.8. The relatively small variation in εNd and TDM in these terranes suggests that old crust like that under the Blair River Complex may not be present. Granitic plutons and rhyolite in the Mira terrane of southeastern Cape Breton Island have a range in TDM (0.8–1.2 Ga) similar to that of the Aspy and Bras d'Or terranes, but initial εNd values ranging from +0.8 to +5.0 indicate more juvenile crust. This juvenile crust also appears to be present under southern New Brunswick and eastern Newfoundland and may be characteristic of the Avalon terrane.

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