On first listen, it seems like Portland trio Menomena might be turning into wimps on their fourth album, “Mines.” This is a band that routinely kicks your ass with killer guitar ramps, rock-solid yet frenetic drumming and by-the-throat lyrics. Why, then, does the album start with a surprisingly basic guitar strum and At War With The Mystics-era Flaming Lips bassline? What’s with the heavily orchestrated chorus? Where is the rock in all of this?

Luckily, this record is Menomena’s most fully realized effort yet. Where they would have thrown together a bombastic three-minute barn-burner on previous albums (see Friend And Foe’s “The Pelican”), “Mines” sees the Rose City boys spend time making their songs count. Most songs are nearly or over five minutes long; in fact, only one is in the three-minute category this time around.

Digging deeper into “Mines” than a single listen may become one of the most rewarding musical experiences of 2010. Let’s return to “Queen Black Acid,” the aforementioned atmospheric opener. The track, which had been previewed during their last year of shows, seems like a necessary homage to lost youth. “I feel like certain times in my life are met with certain times of pain to thrive,” sings co-leader Danny Seim. “And worst of all is when it’s gone cause I know the sea won’t be calm for long.” Maybe Menomena are transitioning into lyrical maturity after several records of confrontational if not particularly deep lyrics. After all, many of those themes—of lost youth, of gaining wisdom, of old regrets—appear in more developed forms later on in the album. If so, this record proves their brilliance.

For much of the record, things veer wildly between doses of the bombast that marked their previous records and this new direction. Second track “TAOS” starts with a drone-ish guitar line that doesn’t properly prepare you for the onslaught that is the next five minutes of your life. Even though Seim is sing-screaming with the same ferocity as on previous records, the lyrics point to a softening of sorts: “I’m not the most cocksure guy, but I get more bold with every smile.”

By turns proggy, ethereal and loud, “Mines” is an excellent illustration of Menomena’s recording process, which begins with recording hundreds of loops in DLR, a computer program written by the other leader, Brent Knopf (also known as Ramona Falls, whose album Intuit was a WRS of its own last summer). DLR explains some of the wilder swings in the album, like in the chorus of “TAOS” which summons horns, handclaps and gospel harmonies in later repetitions.

This record is firmly Seim’s, but some of the most exhilarating songs clearly come from Knopf’s experiences in Ramona Falls. “Killemall” starts with a build that would be right at home in one of the new Tarantino movies, but abruptly drops into an almost-whispered Knopf chorus that seems more like Ramona’s “Russia” than a Menomena track. If anything, the import of ideas from Ramona Falls has given “Mines” a sense of craft that seemed lacking before. Instead of three guys messing around with a computer program, “Mines” sounds like three professionalized musicians sitting down for the first time.

All this talk of Seim and Knopf has made me thirsty for Menomena’s secret weapon: drummer/percussionist Justin Harris. It’s Harris who ties the two halves of Menomena: Seim’s bombastic, almost nautical rock with Knopf’s quiet, almost nautical folk. Harris’s half-time shuffle on “BOTE” glues together the piano interludes and the fire-eyed slide guitar; “Tithe” eventually rips into an epic build that’s only made possible because of Harris. For me, J.H. will always be the hero of Menomena.

Let’s leave with “Oh Pretty Boy, You’re Such A Big Boy.” Can a song have a more exposing opening than “Hold my hands, feel them shake. I fear I’m showing my age”? After a few lines of the same, things get sexy. A low-octave piano build, a ‘70s Motown drumbeat and a reverb-drenched slide line turn what could be an overly maudlin Smiths-esque throwaway into what might be the most replayable song of the year. The clavichord solo in the middle paves the way for an explosion of feeling, rhythm and melody that would sound right at home on Talking Book-era Stevie Wonder. “All my love is just not enough,” they sing. Songs this wrenching are one in a million, and Menomena have created one of the best.

“Mines,” like Menomena’s previous records, doesn’t ask for a second listen. It demands it. Unlike those records, though, this time they’ve created an enduring document of artists transitioning from bold kids to refined adults. Works like this can become bellwether moments for music, and we can only hope that this proves Menomena’s capacity for future genius.