Torres del Paine, day 3, part I
Day 3 of our backpacking tour in Torres del Paine National Park (Chile) was an especially rich one. There's so much material to share that I'm going to divide the day up into three chunks: (I) the area around Los Perros Glacier, (II) the area on the east side of John Gardner Pass, and (III) the area west of John Gardner Pass, including the Grey Glacier.
We begin in Los Perros. As you will recall from our last installment, Lily and I had put in a long day of hiking, essentially pulling double duty by hiking all the way from Seron to Los Perros, and skipping Dickson in between. Because the park only allows camping in certain designated areas, trekkers are often put in the position of either hiking less than they want on a certain day, or more than they want. Day 2 was more than we wanted. We slept heavily, and woke to a drier world. We made coffee (we tried out those new Starbucks "Via" instant coffee packets on this trip and found them reasonably acceptable) and decided that before the day's slog, we should backtrack a bit to the Los Perros Glacier and check it out in more detail. As we were hiking in to camp the previous evening, we only had a 5 minute window of decent weather to view the glacier and its surroundings, so we wanted to see what we had missed.
It was a good call. I really enjoyed poking around there. To start with, check out this perspective view down the valley we had hiked up the previous day, the horseshoe-shaped glacial moraine, and the gray-colored glacial lake backed up behind the moraine:
A closer look at the till making up the moraine:
...And in another direction, too:
Composite stitched together of the moraine-dammed lake, using both of the previous two photos plus three others:
Looking down the axis of the lateral part of the moraine (perspective is towards the glacier, though the ice itself is hidden by the bedrock ridge):
"Lil on till":
We walked towards the glacier, checking out the accumulation of icebergs up against the moraine:
A closer look at the terminus of the glacier:
It was a cool place to look at rocks, too. Everything was so fresh, since the glacier had so recently scraped them clean. In this photo, looking across the lake, you can see the line where the vegetation abruptly stops, showing where the glacier was until relatively recently, when it receded to its present position.
A little lateral moraine clings to the walls of the valley. Where it has been eroded away, you can see details of the bedrock, like the granite dike visible on the left.
If you look carefully in this photo, you will see a large vertical granite dike. Follow along in the direction I am pointing. Hopefully you will be able to find it:
This dike continued out into the space where the glacier eventually carved the valley where the lake now sits. But in the middle of the lake is an island, and right along strike from the big granite dike, you can see a granite dike cutting across the rock of the island:
I'll bet it's the same one.
These dikes had some cool details revealed in the area around Los Perros Glacier. Here's an explosion of dark xenoliths in one intrusion. This is clearly intrusive, because it cuts across several turbidite layers, but I was confused about the texture. I expected granite, but it really looked kind of like... sandstone.
I know there are some clastic dikes in the area, and this may be one of them. I've never seen clastic dikes before, but I guess this is what I would imagine they would look like.
...and how about this???
I think that's two clastic dikes cross-cutting a turbidite bed. A nice relative dating exercise, eh?
Some Z-folds reconfigure quartz-filled tension gashes:
I also found a cool little chunk which showed a nice set of concentric ribs:
Classic slickenlines, lacking those gaudy crystal fiber lineations you usually see on fault surfaces. This is gouging, pure and unadulterated and simple:
Such geological goodies! It's better than instant coffee for perking a fellow up in the morning hours. Energized and invigorated, we headed back to Los Perros Camp for our packs, and hit the trail, heading further up the valley. More on that in part II!
We begin in Los Perros. As you will recall from our last installment, Lily and I had put in a long day of hiking, essentially pulling double duty by hiking all the way from Seron to Los Perros, and skipping Dickson in between. Because the park only allows camping in certain designated areas, trekkers are often put in the position of either hiking less than they want on a certain day, or more than they want. Day 2 was more than we wanted. We slept heavily, and woke to a drier world. We made coffee (we tried out those new Starbucks "Via" instant coffee packets on this trip and found them reasonably acceptable) and decided that before the day's slog, we should backtrack a bit to the Los Perros Glacier and check it out in more detail. As we were hiking in to camp the previous evening, we only had a 5 minute window of decent weather to view the glacier and its surroundings, so we wanted to see what we had missed.
It was a good call. I really enjoyed poking around there. To start with, check out this perspective view down the valley we had hiked up the previous day, the horseshoe-shaped glacial moraine, and the gray-colored glacial lake backed up behind the moraine:
A closer look at the till making up the moraine:
...And in another direction, too:
Composite stitched together of the moraine-dammed lake, using both of the previous two photos plus three others:
Looking down the axis of the lateral part of the moraine (perspective is towards the glacier, though the ice itself is hidden by the bedrock ridge):
"Lil on till":
We walked towards the glacier, checking out the accumulation of icebergs up against the moraine:
A closer look at the terminus of the glacier:
It was a cool place to look at rocks, too. Everything was so fresh, since the glacier had so recently scraped them clean. In this photo, looking across the lake, you can see the line where the vegetation abruptly stops, showing where the glacier was until relatively recently, when it receded to its present position.
A little lateral moraine clings to the walls of the valley. Where it has been eroded away, you can see details of the bedrock, like the granite dike visible on the left.
If you look carefully in this photo, you will see a large vertical granite dike. Follow along in the direction I am pointing. Hopefully you will be able to find it:
This dike continued out into the space where the glacier eventually carved the valley where the lake now sits. But in the middle of the lake is an island, and right along strike from the big granite dike, you can see a granite dike cutting across the rock of the island:
I'll bet it's the same one.
These dikes had some cool details revealed in the area around Los Perros Glacier. Here's an explosion of dark xenoliths in one intrusion. This is clearly intrusive, because it cuts across several turbidite layers, but I was confused about the texture. I expected granite, but it really looked kind of like... sandstone.
I know there are some clastic dikes in the area, and this may be one of them. I've never seen clastic dikes before, but I guess this is what I would imagine they would look like.
...and how about this???
I think that's two clastic dikes cross-cutting a turbidite bed. A nice relative dating exercise, eh?
Some Z-folds reconfigure quartz-filled tension gashes:
I also found a cool little chunk which showed a nice set of concentric ribs:
Classic slickenlines, lacking those gaudy crystal fiber lineations you usually see on fault surfaces. This is gouging, pure and unadulterated and simple:
Such geological goodies! It's better than instant coffee for perking a fellow up in the morning hours. Energized and invigorated, we headed back to Los Perros Camp for our packs, and hit the trail, heading further up the valley. More on that in part II!
Labels: chile, glacial landforms, glaciation, granite, igneous, patagonia, primary structures, sediment, south america, structure, travel, xenoliths
1 Comments:
It is difficult to tell from a picture, but given your proximity to a glacier an alternative hypothesis for the "slickenlines" could be glacial striations. Perhaps a seemingly minor point, but one with significant implications for the final interpretation.
I have worked on a succession of sedimentary rocks that experienced flexural slip in a late Precambrian fold-thrust system and display both "gaudy" slickenfibre packages and slickenlines. These rocks were subsequently glaciated in the Quaternary and it is often impossible to differentiate the fault structures from glacial striations.
If you ever make it to Newfoundland I'd be happy to show you the outcrops.
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