Two anomalous metastable phases have been recently reported from ultrahigh pressure metamorphic (UHPM) rocks: α-quartz incipiently amorphized under pressure (IAUP quartz) found in eclogites from Antarctica and lonsdaleite, a hexagonal polytype of sp3-bonded carbon, observed in diamond bearing genesis from the Kokchetav Massif, Kazakhstan. Incipiently, amorphized α-quartz and lonsdaleite are anomalous phases that cannot crystallize at equilibrium in metamorphic rocks. They form in place of coesite/stishovite and diamond, respectively, if crystallization of the latter minerals is impeded by kinetics during a shock or at low temperatures. Besides impactites, these metastable phases have been observed thus far in a few UHPM rocks but they could be more common. Indeed, they remain difficult to put in evidence, because they can be identified only by high-resolution in situ techniques, they are preserved in narrow μm-sized zones, and they show a spatial transition toward normal α-quartz and diamond. For these reasons, they have almost completely escaped notice so far. © 2011 Elsevier Inc. All rights reserved.

Godard, G., Frezzotti, M., Palmeri, R., Smith, D. (2011). Origin of High-Pressure Disordered Metastable Phases (Lonsdaleite and Incipiently Amorphized Quartz) in Metamorphic Rocks: Geodynamic Shock or Crystal-Scale Overpressure?. Elsevier [10.1016/B978-0-12-385144-4.00004-7].

Origin of High-Pressure Disordered Metastable Phases (Lonsdaleite and Incipiently Amorphized Quartz) in Metamorphic Rocks: Geodynamic Shock or Crystal-Scale Overpressure?

FREZZOTTI, MARIA LUCE;
2011

Abstract

Two anomalous metastable phases have been recently reported from ultrahigh pressure metamorphic (UHPM) rocks: α-quartz incipiently amorphized under pressure (IAUP quartz) found in eclogites from Antarctica and lonsdaleite, a hexagonal polytype of sp3-bonded carbon, observed in diamond bearing genesis from the Kokchetav Massif, Kazakhstan. Incipiently, amorphized α-quartz and lonsdaleite are anomalous phases that cannot crystallize at equilibrium in metamorphic rocks. They form in place of coesite/stishovite and diamond, respectively, if crystallization of the latter minerals is impeded by kinetics during a shock or at low temperatures. Besides impactites, these metastable phases have been observed thus far in a few UHPM rocks but they could be more common. Indeed, they remain difficult to put in evidence, because they can be identified only by high-resolution in situ techniques, they are preserved in narrow μm-sized zones, and they show a spatial transition toward normal α-quartz and diamond. For these reasons, they have almost completely escaped notice so far. © 2011 Elsevier Inc. All rights reserved.
Monografia o trattato scientifico - Monografia di Ricerca - Prima edizione
Quartz, coesite, diamond, subduction, metamorphism
English
2011
978-0-12-385144-4
Elsevier
24
Godard, G., Frezzotti, M., Palmeri, R., Smith, D. (2011). Origin of High-Pressure Disordered Metastable Phases (Lonsdaleite and Incipiently Amorphized Quartz) in Metamorphic Rocks: Geodynamic Shock or Crystal-Scale Overpressure?. Elsevier [10.1016/B978-0-12-385144-4.00004-7].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/53883
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