/pdf/insights-into-the-tectonic-evolution-of-the-north-china-4npdhca6nf.pdf

Insights into the tectonic evolution of the North China Craton through comparative tectonic analysis: A record of outward growth of Precambrian continents

An exotic Mesoarchean microcontinent: The Coorg Block, southern India

Formation of Archean (3600-2500 Ma) continental crust in the Dharwar Craton, southern India

Paleo- to Mesoarchean TTG accretion and continental growth in the western Dharwar craton, Southern India: Constraints from SHRIMP U–Pb zircon geochronology, whole-rock geochemistry and Nd–Sr isotopes

### REE-minerals

Monazite, xenotime, and allanite are REE1-minerals sensu stricto because lanthanides (La…Lu) and yttrium are critical constituents in them Apatite does not require REE, but because it contains substantial REE in many rocks, it is included in this review All four minerals also host unusually high radionuclide concentrations, notably Th and U, forming the basis of their utility as geochronometers

This quartet of accessory minerals is playing an increasingly important role in petrochronology because they provide ways to link robust spot ages to petrogenetic ( P–T ) conditions so can lend petrogenetic context to chronology based on other minerals Part I of this review assembles the basic requisites prior to integrative petrochronologic analysis Individual characteristics of the four REE-minerals are addressed first, ie, their crystal chemistry and stability relations Thermobarometers and trace element geochemistry used for tracing petrogenesis are discussed next, and finally their chronology is summarized Part II presents case studies to highlight the specific strengths of REE-minerals used to resolve the dynamics of a broad range of processes, from diagenetic to magmatic conditions Finally, a brief section at the end outlines a few of the current challenges and promising perspectives for future work

To introduce the four REE-minerals in style, let us recall the origins of their names The three phosphates have well respected Greek grandparents, and allanite has solid Scottish roots, yet of all four of them show idiosyncracies in etymology or type material

Apatite had long puzzled naturalists, as it shows great chemical and physical variability and can resemble other minerals Once properly identified, Abraham Gottlieb Werner named it apatite His reasoning referred to the Greek root ἀπατὰω and giving the precise Latin translation: decipio  Taken literally, both mean “I deceive” or “I mislead”, which sounds like an apt confession from this mineral for having fooled …

Petrochronology Based on REE-Minerals: Monazite, Allanite, Xenotime, Apatite

Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

The Ranomena ultramafic complex in NE Madagascar consists of layered gabbro, harzburgite, orthopyroxenite, clinopyroxenite, garnet websterite and chromitite-layered peridotite. This study of the Ranomena chromite chemistry aims to better understand the petrogenesis and palaeotectonic environment of the complex. The chromite from the Ranomena chromitite is unzoned/weakly zoned and has a Cr# (Cr/(Cr + Al)) of 0.59-0.69, a Mg# (Mg/(Fe + Mg)) of 0.37-0.44, and low Al2O3 (15-23 wt %) suggesting derivation from a supra-subduction zone arc setting. Calculation of parental melt composition suggests that the parental magma composition of the Ranomena chromitite was similar to that of a primitive tholeiitic basalt formed at a high degree of mantle melting, suggesting the parental melt composition was equivalent to that of an island-arc tholeiite (IAT). The parental magma of the Ranomena chromite had a FeO/MgO ratio of 0.9 to 1.8, suggesting arc derivation. The parental magma was Al- and Fe-rich, similar to a tholeiitic basaltic magma. The composition of orthopyroxene from the chromitite indicates a crystallization temperature range of 1250-1300 degrees C at 1.0 GPa. The chemistry of the chromite in the Ranomena chromitite further suggests that the complex formed in a supra-subduction zone arc tectonic setting.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/8F12ACE7229C962D7E7255BD9C5D516E/S0016756816000972a.pdf/div-class-title-chromite-chemistry-as-an-indicator-of-petrogenesis-and-tectonic-setting-of-the-ranomena-ultramafic-complex-in-north-eastern-madagascar-div.pdf

Chromite chemistry as an indicator of petrogenesis and tectonic setting of the Ranomena ultramafic complex in north-eastern Madagascar

Petrogenesis and tectonic setting of the Bondla mafic-ultramafic complex, western India: Inferences from chromian spinel chemistry

In this study we present field relations, petrology, whole-rock major, trace and rare earth element geochemistry, zircon U-Pb ages, whole-rock Sr and Nd isotopes, and in situ zircon Hf and O isotopes from the Karwar block, western peninsular India. The rocks consist predominantly of tonalite-trondhjemite-granodiorite (TTG), granite and amphibolite. The felsic rocks are grouped into three: 1. TTG-I characterised by low K2O, high Na2O and Al2O3, low Sr/Y and La/Yb ratios, slightly enriched HREEs, negative Sr, Eu and Ti anomalies, a 3.2 Ga crystallisation age, and 3.60 Ga and 3.47 Ga inherited zircons; 2. TTG-II with lower SiO2, higher Sr/Y and La/Yb ratios, stronger REE fractionation with no HREE enrichment, negative Nb and Ta anomalies, a 3.2 Ga crystallisation age, but no inheritance; 3. Granites with high SiO2 and K2O, low Na2O and Al2O3, very low Sr/Y and La/Yb ratios, weak REE fractionation with enriched REEs, negative Sr, Eu and Ti anomalies and a 2.94 Ga crystallisation age. The TTG-I formed from a mantle source, but with a significant component of older crustal material, whereas the TTG-II originated mostly from a mantle-derived juvenile magma. The granite evolved from an enriched source containing a relatively large amount of older crustal material. The precursors of TTG-I and -II are similar to mid-ocean ridge basalts (MORB), whereas the granites are similar to volcanic arc/within-plate sources and the amphibolites are remnants of gabbros/basalts. An initial 3.6 Ga crust likely formed by the underplating of an accreted oceanic plateau-like or island arc-like crust. TTG-I was produced by subduction and slab melting at a moderate depth, induced melting of mafic lower crust and older upper crust at 3.2 Ga. TTG-II formed at 3.2 Ga by subduction and with a higher degree of slab melting at a greater depth than TTG-1, together with more effective mixing with mantle peridotite, followed by intrusion and induced melting of mafic lower crust. Basaltic magmatism at 3.0 Ga and subsequent metamorphism to amphibolite resulted in extensive and thicker crust. Assimilation and melting of TTG crust at a shallow depth during the emplacement of a mantle-derived magma produced the 2.94 Ga granites. The presence of inherited zircons, combined with whole-rock major and trace elements, Nd isotopes and in situ zircon Hf and O isotopes, indicates that older crustal material was incorporated into the source magma of TTG-I and that the Karwar block originally contained 3.60 to 3.47 Ga crust that was subsequently reworked during the Paleo- and Mesoarchean.

C. Ishwar-Kumar

Papers

Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

Chromite chemistry as an indicator of petrogenesis and tectonic setting of the Ranomena ultramafic complex in north-eastern Madagascar

Petrogenesis and tectonic setting of the Bondla mafic-ultramafic complex, western India: Inferences from chromian spinel chemistry

Paleo- to Mesoarchean crustal growth in the Karwar block, southern India: Constraints on TTG genesis and Archean tectonics

Geological correlations between India and Madagascar in a Gondwanan perspective