High-Grade Contact Metamorphism in the Kochumdek River Valley (Podkamennaya Tunguska Basin, East Siberia): Evidence for Magma Flow

Abstract

—Spurrite-merwinite marbles on the right bank of the Kochumdek River in the Podkamennaya Tunguska basin formed along the top margin of a flood basalt intrusion (Kuzmovka complex) from a marly limestone protolith of the Rhuddanian Lower Kochumdek Subformation, at a pressure of ~200 bars. The contact metamorphic aureole comprises four zones of successively decreasing temperatures marked by the respective mineral assemblages: T ≥ 900 °C (merwinite, spurrite and gehlenite (±rankinite, bredigite); T ≥ 750 °C (spurrite); T ≥ 700 °C (tilleyite, wollastonite, and melilite (Gehl<50)); and ~500–550 °C (diopside, amphibole, and grossular). Very high temperatures at the contact (Tcont > 2/3 Tmelt) result from magma flow along a conduit. The temperature profiles for the Kochumdek metamorphic complex show good fit between measured and geothermometer-derived values at a magma temperature of 1200 °C, an intrusion thickness of ≥ 40 m, a heating time of six months, and a magma flow lifespan within one month. Stagnant magma in a conduit of any thickness cools down and crystallizes rapidly and fails to heat up sediments to the temperatures required for spurrite–merwinite metamorphism (above 790 °C).

Mineralogical Diversity of Ca2SiO4-Bearing Combustion Metamorphic Rocks in the Hatrurim Basin: Implications for Storage and Partitioning of Elements in Oil Shale Clinkering

“…Bredigite hydrates very slowly at 20 °C and is thus considered as an undesirable constituent of cement clinker (though more preferable than MgO periclase) [103]. In this respect, the presence/absence of bredigite in rocks of complex compositions is potentially of practical value: the Bredigite Ca 7 Mg(SiO 4 ) 4 is quite frequently found in high-temperature contact aureoles that formed after the precursor Mg-enriched (usually dolomite-bearing) sediments, but is a relatively rare mineral [97][98][99][100][101]. On the other hand, this constituent is typical of periclase refractories, high-Mg cement clinker and metallurgical slags.…”

“…-Ca 2 (SiO 4 ). First Tilley and Vincent (1948) [97] discovered bredigite in the Scawt Hill contact aureole in Northern Ireland and identified it as Bredigite Ca7Mg(SiO4)4 is quite frequently found in high-temperature contact aureoles that formed after the precursor Mg-enriched (usually dolomite-bearing) sediments, but is a relatively rare mineral [97][98][99][100][101]. On the other hand, this constituent is typical of periclase refractories, high-Mg cement clinker and metallurgical slags.…”

Sulfide Minerals as Potential Tracers of Isochemical Processes in Contact Metamorphism: Case Study of the Kochumdek Aureole, East Siberia

“…Diverse sulfide mineralization was reported in the spurrite marbles of the Kochumdek contact aureole [31][32][33][34][35] located in the western termination of the Tunguska basin (the Podkamennaya Tunguska River catchment, East Siberia) [1,2,30,36]. The Tunguska basin is composed of thick sequences (3-7 km in thickness) of Middle Proterozoic to Paleozoic volcano-sedimentary rocks (PR 2 -P 2 ), which are interbedded with mafic sills and buried under flood basalts over a large part of the basin territory.…”

“…This idea was tested on the Silurian marly limestones (the Tunguska basin, East Siberia), which was metamorphosed by the Early Triassic Kochumdek gabbro-dolerite sill. According to available data on critical mineral assemblages and numerical simulations [29,30], the Kochumdek aureole results from a single brief thermal event of up to 900 • C and a yearlong peak stage of metamorphism. Therefore, thermal history reconstructions for the Kochumdek area may be relatively simple, more so because it was not subject to any significant later alteration.…”

The Role of Magmatic Heat Sources in the Formation of Regional and Contact Metamorphic Areas in West Sangilen (Tuva, Russia)

“…Вместе с тем имеются до конца не исследованные вопросы, связанные с изучением поясов HT/LP-метаморфизма: какова природа тепловых источников, каким образом работают механизмы теплопереноса и транспорта магмы/расплава, всегда ли обоснована генетическая связь с интрузивными комплексами? Имеются примеры приповерхностных проявлений контактового метаморфизма, где эта связь достоверно установлена [Sokol et al, 2019]. Сложнее дело обстоит в случае «скрытых» интрузий, признаками которых являются высокотемпературные зонально-метаморфические комплексы.…”