Question: During what decade did J.R.R. Tolkien use mythopoeia in his literary works?

Context paragraphs:
The Lord of the Rings (soundtrack): The J.R.R. Tolkien's The Lord of the Rings OST is the soundtrack to Ralph Bakshi's animated film adaptation of J.R.R. Tolkien's "The Lord of the Rings", featuring music composed by Leonard Rosenman.  It was issued as a double-LP in 1978.  In 2001, the album was reissued on CD, with bonus tracks.  The album reached #33 in the Canadian RPM Magazine album charts, February 24, 1979.

Mythopoeia (poem): Mythopoeia (mythos-making) is a term used by J.R.R. Tolkien as a title of a poem.  The term has also been used in English since 1846.

Eucatastrophe: Eucatastrophe is a term coined by English writer J. R. R. Tolkien which refers to the sudden turn of events at the end of a story which ensures that the protagonist does not meet some terrible, impending, and very plausible and probable doom.  Tolkien formed the word by affixing the Greek prefix "eu", meaning "good", to "catastrophe", the word traditionally used in classically inspired literary criticism to refer to the "unraveling" or conclusion of a drama's plot.  For Tolkien, the term appears to have had a thematic meaning that went beyond its literal etymological meaning in terms of form.  In his definition as outlined in his 1947 essay "On Fairy-Stories", eucatastrophe is a fundamental part of his conception of mythopoeia.  Though Tolkien's interest is in myth, it is also connected to the gospel; Tolkien calls the Incarnation of Christ the eucatastrophe of "human history" and the Resurrection the eucatastrophe of the Incarnation.

The Silmarillion: The Silmarillion is a collection of mythopoeic works by English writer J. R. R. Tolkien, edited and published posthumously by his son, Christopher Tolkien, in 1977, with assistance from Guy Gavriel Kay.  "The Silmarillion", along with J. R. R. Tolkien's other works, forms an extensive, though incomplete, narrative that describes the universe of Eä in which are found the lands of Valinor, Beleriand, Númenor, and Middle-earth within which "The Hobbit" and "The Lord of the Rings" take place.

J. R. R. Tolkien: Author of the Century: J.R.R. Tolkien: Author of the Century is a work of literary criticism written by Tom Shippey.  It is about the work of J.R.R. Tolkien.  In it, Shippey argues for the relevance of Tolkien today and attempts to firmly establish Tolkien's literary merits.

Mythopoeia: Mythopoeia (also mythopoesis, after Hellenistic Greek μυθοποιία, μυθοποίησις "myth-making") is a narrative genre in modern literature and film where a fictional or artificial mythology is created by the writer of prose or other fiction.  This meaning of the word "mythopoeia" follows its use by J. R. R. Tolkien in the 1930s.  The authors in this genre integrate traditional mythological themes and archetypes into fiction.

Tolkienmoot: Tolkienmoot (also advertised as Tolkien Moot and TolkienMoot (camel case)) originally began under the name of Merpcon in 2005.  Always a convention focused on J.R.R. Tolkien and gaming in Middle-earth, as the venue expanded to include a broader array of game systems, guest speakers, and special events, it was decided to change the title to Tolkienmoot in 2009.  The convention was founded, and continuous to be funded and run by Hawke Robinson, founder of the Inland Empire Eä Tolkien Society an official Smial of the U.K. Tolkien Society, RPG Research, Other Minds Magazine, Middle-earth Radio, Middle-earth Talk, Eä RPG, and other endeavours, as well as an active member of CAR-PGa (Committee for the Advancement of Role-Playing Games website), WSTRA (Washington State Therapeutic Recreation Association website), and others.

Charles Leslie Wrenn: Charles Leslie Wrenn (1895–1969) was a British scholar.  He became Rawlinson and Bosworth Professor of Anglo-Saxon at the University of Oxford in 1945, the successor in the chair of J.R.R. Tolkien, and held the position until 1963.  Wrenn was a Fellow of Pembroke College, Oxford.  He was also a member of the Oxford literary discussion group known as the "Inklings", which included C. S. Lewis and Tolkien.  Some of the work published by Wrenn includes "The English Language" (1949), "A Study of Old English Literature" (1967)"," and "An Old English Grammar," written with Randolph Quirk (1955, rev. 1957).  His literary interests were primarily comparative literature and later poets including T. S. Elliot.

Eru Ilúvatar: Eru Ilúvatar is a fictional character in J.R.R. Tolkien's Middle-earth legendarium.  He is introduced in "The Silmarillion" as the supreme being of the universe, creator of all existence.  In Tolkien's invented Elvish language Quenya, "Eru" means "The One", or "He that is Alone" and "Ilúvatar" signifies "Father of All".  The names appear in Tolkien's work both in isolation and paired ("Eru Ilúvatar").

Sellic Spell: Sellic Spell (] , an Old English phrase meaning "wondrous tale" and taken from the poem "Beowulf") is a short prose text available in Modern and Old English redactions, written by J.R.R. Tolkien in a creative attempt to reconstruct the folktale underlying the narrative in the first two thousand lines of the Old English poem "Beowulf".  Among other things, it seeks to clarify and integrate a number of narrative strands in the Anglo-Saxon poem.  The resulting text is a loose variant of the "Skilful Companions" type of folktale, in which each of several characters (two or three in Tolkien's text, depending on the redaction) has a valuable but specific skill.  Unlike in folktales of that type, however, the skills of Tolkien's characters do not supplement each other in the resolution of the narrative problem.  Tolkien's recasting of the material also incorporates the sluggish youth motif and the abandonment of the hero at the waterfall, both elements found in the analogous Old Icelandic "Grettis saga".  The suggestion that a waterfall like that of "Grettis saga" was part of the original setting of the pool of monsters in "Beowulf" was made by W.W. Lawrence in 1912.

Supporting paragraphs: The Silmarillion Mythopoeia
Answer: 1930s