Petrogenesis Of Granitic Rocks Research Articles

New insights into the petrogenesis of granitic rocks in southern Thailand, SE Asia tin belt: evidence from petrochemistry and geochronology

ABSTRACT The granitic rocks in the Prachuap Khiri Khan Province, southern Thailand, SE Asia Tin Belt, comprise gneissic biotite monzogranite, porphyritic muscovite–biotite monzogranite, and porphyritic biotite monzogranite. Comprehensive field observations, petrography, mineral chemistry, and geochemistry establish gneissic biotite monzogranites as part of the Central Belt Granites (CBGs), while porphyritic muscovite–biotite monzogranite and porphyritic biotite monzogranite as part of the Western Belt Granites (WBGs). CBG and WBG granitic units exhibit peraluminous, alkali-calcic, and magnesian magmatic series traits, reflecting an S-type granite character resulting from crustal partial melting. Significantly, scatter correlations in variation diagrams, combined with the enrichment of Cs, Rb, Th, U, Pb, Nd, and P, and the depletion of Ba, Nb, and Ti contents, point towards an S-type granite signature formed during collisional events. Crystallization conditions reveal CBG gneissic biotite monzogranite encountered P–T conditions of 2.97–3.85 kbar/680°C–733°C/11.1–14.4 km, while WBG’s porphyritic muscovite–biotite monzogranite and porphyritic biotite monzogranite experienced 2.73–4.15 kbar/628°C–732°C/10.2–15.5 km and 2.47–3.80 kbar/651°C–728°C/9.2–14.2 km, respectively. Geochronological data indicate that CBG’s gneissic biotite monzogranite was emplaced from Early Cretaceous collision (128–119 Ma) of Indochina and Sibumasu terranes, while WBG’s porphyritic muscovite–biotite monzogranite and porphyritic biotite monzogranite were formed during the syn-collision of Sibumasu and West Burma terranes during Early Cretaceous (121–111 Ma) to Paleocene. Mineralogical and geochemical attributes of these granitic rocks exhibit strong relevance to Sn-W mineralization processes, indicative of a profound association.

Petrogenesis of Granitic Rocks in the Hisakajima Island, Goto Archipelago, Southwestern Japan: A Geochemical Study

Whole-rock chemical compositions including rare earth elements for the granitic rocks from the Hisakajima Island, Goto Archipelago, southwestern Japan were measured in order to constrain their origin and petrogenesis. The granites were divided into two types—a granodioritic group (GD) and a high Fe/Mg ratio granitic group (HFG). The granitic magma was formed by the upwelling of high-temperature mantle material, which might be related to the extension of the Japan Sea around the Middle Miocene. The origin of the GD magma was attributed to the mantle material, while the origin of the HFG magma was attributed to partial melting of the crust by upwelling of the high-temperature mantle. The amount of rare earth elements revealed the secondary addition of light rare earth elements through hydrothermal processes for the granites. Chondrite normalized rare earth element patterns revealed that the HFG rocks were not well differentiated.

Petrogenesis of granitic rocks in the Pingtan Island, Fujian Province: Constraints from zircon U-Pb dating, O-Hf isotopes and biotite mineral chemistry

Petrogenesis of granitic rocks in the Pingtan Island, Fujian Province: Constraints from zircon U-Pb dating, O-Hf isotopes and biotite mineral chemistry

Petrogenesis of granitic rocks in the Pingtan Island, Fujian Province: Constraints from zircon U-Pb dating, O-Hf isotopes and biotite mineral chemistry

东南沿海地区发育具有'等同位素组成'特征的晚中生代双峰式火成岩，其成因备受争论。本文选择了福建省平潭岛双峰式杂岩体中的花岗闪长岩、英云闪长岩与花岗岩开展了高精度锆石U-Pb定年、原位O-Hf同位素和黑云母矿物化学方面的研究，以探讨这些花岗质岩石的成因。分析结果显示，花岗闪长岩、英云闪长岩与花岗岩的锆石U-Pb年龄分别为116.8±1.0Ma、116.3±1.0Ma与117.4±1.0Ma，表明它们均侵位于早白垩世。这三类岩石也有较为相似的锆石O-Hf同位素组成。其中，锆石的δ18O分别变化为4.6%~5.3‰、4.8%~5.3‰及5.0%~5.6‰，与地幔的O同位素值基本一致。锆石的eHf（t）变化范围分别为+2.0~+7.1、+2.8~+6.5及+1.8~+5.6，相应的两阶段模式年龄tDM2分别为741~1046Ma、754~995Ma及815~1058Ma。锆石O-Hf同位素数据反映其熔融源区主要为相对较年轻的地壳物质，来自华夏地块古老基底的贡献较少。另外，黑云母矿物化学暗示这三类岩石具有Ⅰ型花岗岩的特征。但是，黑云母种属在不同岩性间存在差异，其中花岗闪长岩与英云闪长岩中的黑云母为镁质类型，花岗岩中的黑云母为铁质类型。从花岗闪长岩、英云闪长岩到花岗岩，黑云母的结晶温度和岩浆体系的氧逸度均逐渐降低，这与钙碱性岩浆分异演化的趋势基本一致。结合前人研究资料及区域地质演化历程，我们认为平潭岛杂岩体中的花岗质岩石形成于古太平洋俯冲背景，其熔融源区主要为新增生地壳物质。花岗质岩石内部岩性的差别主要是母岩浆经历不同程度分异演化的结果。我们的研究结果暗示壳幔岩浆混合在东南沿海早白垩世长英质岩石形成过程中所具有的作用可能较为有限。

Petrogenesis of granitic rocks of the Jabal Sabir area, South Taiz City, Yemen Republic

The Tertiary granitic intrusive body (∼21 Ma) of the Jabal Sabir area was emplaced during the early stages of the Red Sea opening. This intrusive body occupies the southern sector of Taiz City. It is triangular in shape, affected by two major faults, one of which is in parallel to the Gulf of Aden, and the other is in parallel to the eastern margin of the Red Sea coast. The petrogenesis of such a type of intrusion provides additional information on the origin of the Oligo-Miocene magmatic activity in relation to the rifting tectonics and evolution of this part of the Arabian Shield.

Geochronology and petrogenesis of granitic rocks in Gangdese batholith, southern Tibet

Based on petrological and geochemical characteristics such as rock assemblage, petrogeochemistry, Sr-Nd isotope, zircon U-Pb age, and Hf isotope, we studied geochronological framework, magma types, source characters, and petrogenesis of different stages of magmatism of the granitic rocks from the Gangdese batholith in southern Tibet. The magmatic activities of the Gangdese batholith can be divided into three stages. The Mesozoic magmatism, induced by northern subduction of Neotethyan slab, was continuously developed, with two peak periods of Late Jurassic and Early Cretaceous. The Paleocene-Eocene magmatism was the most intensive, and resulted from a complex progress of Neotethyan oceanic slab, including subduction, rollback, and subsequent breakoff. And the Oligocene-Miocene magmatism was attributed to the convective removal of thickened lithosphere in an east-west extension setting after India-Asia collision. Isotopically, zircons from these granitic rocks are characterized by positive ɛ Hf(t) values, suggesting that the magmatic source of the Gangdese batholith might be an arc terrane, which was accreted to the southern margin of Asia during Late Paleozoic. Therefore, the chronological framework and Hf isotopic characteristics of the Gangdese batholith are distinct from the granitic rocks in adjacent areas, which can be served as a powerful tracer in studying source-to-sink relation of sediments during the uplift and erosion of Tibetan Plateau.

Typology and petrogenesis of granitic rocks in the Sanandaj-Sirjan metamorphic belt, Iran: with emphasis on the Alvand plutonic complex

Typology and petrogenesis of granitic rocks in the Sanandaj-Sirjan metamorphic belt, Iran: with emphasis on the Alvand plutonic complex

ALLANITE-(Ce) AS AN INDICATOR OF THE ORIGIN OF GRANITIC ROCKS IN JAPAN: IMPORTANCE OF Sr-Nd ISOTOPIC AND CHEMICAL COMPOSITION

The isotopic compositions of Sr and Nd were analyzed for sixteen samples of allanite-(Ce) from Mesozoic–Cenozoic granitic rocks in Japan (11 samples of an Mn-rich type, and five samples of an Mn-poor type). The Mn-rich allanite-(Ce) crystals have an initial 87Sr/86Sr value in the range 0.70811–0.71398 and an initial 143Nd/144Nd value in the range 0.512148–0.512471, whereas for crystals of Mn-poor allanite-(Ce), the analogous intervals are 0.70499–0.70704 and 0.512547–0.512606. There is a negative correlation between 87Sr/86Sr and 143Nd/144Nd values. The trend of these isotopic data for Mn-rich and Mn-poor allanite-(Ce) is parallel to that for ilmenite- and magnetite-series granitic rocks from Japan, respectively. This parallelism suggests that the genesis of these two groups of allanite-(Ce) is related to that of ilmenite-series and magnetite-series granitic rocks. The characteristics of allanite-(Ce) can shed light on the petrogenesis of granitic rocks.

Geochemistry and petrogenesis of tertiary granitic rocks from the Island of Mull, Northwest Scotland

The anorogenic igneous rocks of Mull consist essentially of a lava pile of predominantly basaltic composition, cut by an intrusive complex. The basement consists of Precambrian metamorphic rocks of the Moine Series underlain by Lewisian gneiss. The intrusive complex contains a significant proportion of granitic intrusions which can be ascribed to three successive centres of activity, Centres 1–3. We report new major and trace element, including rare earth element analyses, 87Sr/86Sr ratios and δ18O values for a comprehensive collection of granitic rocks from the 3 centres. The δ18O values range from +4 to −6 indicating variable extent of interaction between the rocks and heated meteoric groundwater. However, correlations of δ18O with other major and trace element data and 87Sr/86Sr ratios are uniformly low, apart from Fe2O3. It is thus unlikely that the interaction of the rocks with meteoric water has systematically altered the chemical (including Sr isotope) characteristics. The chemical and Sr isotope data reflect magmatic values and can therefore be used to comment on the petrogenesis of the granitic rocks.