Hard Rock Taipei 硬石台北
要如何進行這個地質寶?
公館區域存有不同種類的石頭，這些石頭是從台北各個區域收集而來，正好可以見證台北豐富的地質組成。前往公館三個地點辨識不同種類的石頭，從頁面中與現場介紹牌的資訊來區辨地層的地質性質。
題目在最下面。
背景知識：台灣的起源
臺灣島約略在中新世晚期(2300萬至533萬年前)開始上升，各理論均同意臺灣島受到菲律賓海板塊與歐亞板塊碰撞影響而上升，菲律賓海板塊擠壓歐亞板塊而上升，呂宋島弧屬於菲律賓海板塊，擠壓後上升成為海岸山脈，歐亞板塊則上升成為中央山脈，兩個板塊邊緣相撞區域則是台東縱谷的所在地。地層活動在板塊相撞時相當活躍，其實直到今日台灣的板塊活動仍持續活躍。
台北的地質
台北有很獨特的地質特性，兩百萬年前台北其實是丘陵，約略在四十萬年前與林口相接的山腳斷層發生地質活動而陷落成台北盆地。二十萬年前時，岩漿逐漸冷卻並封住了古淡水河的出海口，導致台北形成堰塞湖好長一段時間。後來，淡水河終於在三萬年前在水力侵蝕作用下突破阻擋的岩石，湖水才逐漸消退。臺北盆地實質上受到火山與河流活動的影響。
更特別的是台北也受到地層活動的影響，台北的東南方受到菲律賓海板塊、歐亞板塊與琉球島弧的影響，即是受到雪山山脈的作用而提供了岩石變質的良好環境。
臺北盆地北接陽明山，西連林口台地，東南方由雪山山脈推擠界定範圍。流經臺北盆地的主要河流為大漢溪、淡水河與基隆河。這樣的地質環境讓台北擁有豐富的地質組成。
岩石分類
火成岩
噴發的岩漿冷卻後透過凝固作用形成火成岩。凝固作用可能發生在表面下形成侵入性岩石，也可能發生於表面上形成噴出岩。火成岩可能透過結晶化作用形成顆粒狀結晶岩石，或是沒有結晶化作用形成自然界中的玻璃。常見的侵入岩例子像是花崗岩，常見的火山噴出岩則像是玄武岩或是安山岩。
Cited from web
沉積岩
沉積岩主要由小碎石堆積後，由海底或地表礦物、生物殘骸膠結化後形成岩石，沉積岩可以依照其組成成分區分成不同種類的沉積岩，如：碎屑沉積岩、生物沉積岩、化學沉積岩…等等。常見的沉積岩像是沙岩、石灰岩、或泥岩。沉積岩有獨特可鑑別的岩石特性 -- 波痕，波痕代表著在成岩過程中曾受到水流或是風的擾動。
cited from web
變質岩
變質岩由已成形的岩石受到不同的溫度與壓力環境影響而使原來的石頭發生質變，質變作用導致岩石發生顯著的物理與化學特性變化，變質岩可能會有完全不同的顏色、紋理與外形，變質岩透過再結晶過程而發生質地的變化，變質作用受到不同因素的影響，包含：溫度、壓力、溫度與壓力兩者。變質作用主要可分為兩種，一種是接觸變質作用，這種變質作用跟侵入性岩漿有關，岩漿的高溫讓周遭的石頭發生變質作用，另一種則是廣域變質作用，這種變質作用跟溫度與壓力都有關，經常發生在地質活動旺盛區，像是造山運動頻繁的區域。除了前面兩種主要的變質作用以外，還有一種變質作用主要跟壓力比較相關、溫度扮演比較小角色的變質作用，這種變質作用可能會產生像是玉這類較為特別的岩石，這種變質作用稱為埋藏變質作用。
葉理是在岩石中的纖維狀平面組織，常作為變質岩鑑定特徵的依據，依照變質岩的結構大致可以分為兩個類別，有葉理的變質岩與葉理不顯著的變質岩。
cited from web
台北的岩石
台北的岩石組成受到台北盆地地層與台灣北部的地層活動影響
台北的火成岩
火成岩座落在台北地層下方，分布在陽明山與台北北部海岸線，這樣分布的原因可能跟大屯火山群活動相關，大屯火山群最早在280萬至250萬年前開始活動噴發，這些火山活動的地質顯露在台北的北部區域。不過，台北的中心區域其實有更古遠的火成岩，像是公館凝灰岩，這些火成岩可能在8500萬年前的南澳造山運動時就已經成形。海底火山噴發後形成噴發岩與火山灰，隨著火山噴發後噴發岩顆粒與火山灰沉積在海底地表，這些火成岩可以在台北盆地下的地層之中找到。閱讀下方圖片的內容可以知道不同地層的時序關係，也可以知道台北的發展時間表 (Teng et al., 2001)。
從圖中可知，台北最早的地層是五指山層，年輕的地層會在古老的地層之上，從古老至年輕地層依序排列為五指山層、木山層、大寮層、石底層、南港層、南莊層、桂竹林層、板橋層、五股層、景美層、和松山層。依據這個時間軸可發現大屯活山群活動落在相對年輕的地層，公館凝灰岩出現的時間遠比大屯火山群的火成岩來得更早。
台北的沉積岩
因河流活動與曾經是堰塞湖的緣故，整個台北盆地被沉積物覆蓋住，沉積岩也是台北的主要組成，特別是西北方、北方等沿著淡水河流經區域，像是北投或是唭哩岸。台北有一種特別的沉積岩稱作唭哩岸岩，依被發現的地點命名，唭哩岸岩屬於富含石英的沙岩，唭哩岸岩硬度佳可作為建築的良好材料，所以一些台北的歷史建築使用這種石頭作為牆面。
台北的變質岩
變質岩也是台北岩石的組成之一，台北變質岩形成的主因可能受到雪山山脈、板塊擠壓的影響，在台北東方、東南方區域菲律賓海板塊與歐亞板塊相撞影響形成大量的造成區域，這些區域有不同的壓力與溫度提供岩石變質作用良好的環境條件，這些區域較常見的變質岩可能為板岩，也有一些特別的變質岩可以在這些區域發現，像是大理岩或是玉。
台灣變質岩分布圖
下圖為台灣岩石分佈圖，從圖可以看到台北的岩石組成相當豐富，有現代沉積區塊、西半部沉積岩區塊、火成岩區塊，還有中央山脈板岩變質岩區塊。（註：台北東南方的中央山脈板岩變質區塊其實已經屬於雪山山脈的範圍了。）
cited and adapted from web
Hard Rock Taipei
What to do with this earth cache?
There are placed with different types of rocks in Gongguan. These rocks were collected from all regions from Taipei as evidence to see the plentiful rock composition in Taipei. Go to three points in Gongguan to recognize different rocks. Distinguish the Formation of geological properties from the information on the listing page and the virtual introduction board.
The questions are at the end of article.
Background Knowledge : Origin of Taiwan
The beginning formation of Taiwan Island was approximately at late Miocene (23.03 to 5.333 million years ago). The formation theories all agree that the uplift of Taiwan Island results from the collision of Philippine (PH) Sea Plate and Eurasian (EU) Plate. The EU Plate is sliding under the PH Sea Plate, resulting a convergent boundary lifting up Taiwan. Luzon Volcanic Arc belongs to PH Sea Plate becomes the Coastal Range or Haian Range. And the margin of EU Plate becomes the Central Mountain Range. Taitung Longitudinal Valley is the special contact between two Plates. The tectonic boundary was active while the collision occurred and it remains active nowadays.
Geology of Taipei
Taipei is a unique place because it was originally a hill at two millions years ago and became a basin due seismic activity on the Sanchiao fault between Linkou and Taipei at four hundred thousand years ago. At two hundred thousand years ago, volcanic lava cooled down and blocked Tamsui river’s gate to the sea. Taipei Basin became a dammed lake for a long while. Then, Tamsui River went through the rocks with water erosion at northern Taipei into the sea at approximately thirty thousand years ago. Taipei Basin is actually influenced by volcanic and river activities.
Moreover, Taipei is also affected by the tectonic activities with PH plate, EU Plate and Ryukyu Arc at southeast of Taipei city or New Taipei city. Southeast Taipei is affected by Xueshan Mountain Range with a suitable condition for the process of metamorphism.
Taipei basin is bounded by Yangmingshan to the north, Linkou mesa to the west, and Xueshan Mountain Range to the southeast. The main rivers in the basin include Dahan, Tamsui and Keelung. The geological environment makes plentiful rock composition in Taipei.
Classification of rocks
Igneous Rocks
Explosive lava cooled down and through solidification into igneous rocks. The process of solidification into rock occurs below the surface as intrusive rocks. If the process occurs on the surface, lava becomes extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks. Or, it may be formed without crystallization into natural glasses. A common example of intrusive type is granite. Extrusive rocks, which result from magma on surface, turn into basalt or andesite.
cited from web
Sedimentary rocks
Sedimentary rocks are formed by the accumulation or deposition of small particles. Subsequent cementation of mineral or organic particles occurs on the ground of oceans or other bodies of water at the Earth's surface. Sedimentary rocks can be classified by composition, including Siliciclastic sedimentary rocks, Carbonate sedimentary rocks, Evaporite sedimentary rocks, Organic-rich sedimentary rocks, Siliceous sedimentary rocks, Iron-rich sedimentary rocks, or Phosphatic sedimentary rocks. Common sedimentary rocks includes sandstone, limestone, or mudstone.
Sedimentary rocks may have a unique feature. It might be distinguished with ripple marks. Ripple marks are sedimentary structures and indicate the activity of water or wind. Ripple marks make some sedimentary rocks with very unique texture.
cited from web
Metamorphic rocks
Metamorphic rocks are formed by subjecting rocks to different temperature and pressure conditions than those in which the original rock was formed. The metamorphism results in significant change in physical properties and chemistry of the stone. Metamorphic rocks can be totally changed into different color, texture, or appearance. Metamorphism has two main different types including Contact metamorphism and Regional metamorphism. Contact metamorphism is temperature-dominate metamorphism. It may be related to intrusive magma affecting surrounding rocks. The temperature is the main reason caused the minerals into the process of metamorphism. Regional metamorphism, also known as dynamic metamorphism, is majorly influenced by the pressure relating to tectonic activities. Regional metamorphism precisely is related to both temperature and pressure. The process often occurs at the mountain-building regions. Besides contact and regional metamorphism, there is another type of metamorphism. Pressure-dominate metamorphism, and temperature plays a small role, may produce unique rocks, such as jade. This mechanism termed burial metamorphism.
Foliation is a specific feature belongs to metamorphic rocks. The layering within metamorphic rocks is called foliation. The texture occurs when a rock is shortened during recrystallization. The structure of metamorphic rocks can be divided into two categories, foliated and non-foliated.
Rocks in Taipei
Rock composition in Taipei is influenced by the formation of Taipei basin and the tectonic activities in northern Taiwan.
Igneous Rock in Taipei
Igneous rocks are the main type under the surface in Taipei and located at Yangmingshan or northern coastline. The reason is related to the activity of Tatun Volcanic Group at northern Taiwan. Tatun volcanic group first explored at 2.8 Ma lasting to 2.5 Ma. Outcrops of this activity can be found at northern Taipei. However, there are some more ancient igneous rocks being found in the center of Taipei, such as Gongguan tuff. It may be formed after the Nanao Orogeny around 85 Ma. Volcano under surface explored into ancient sea forming extrusive rocks and volcanic ash. Following ejection and deposition, the ash and small particles are in the process of consolidation forming tuffs. It may be found in the era of Formation under the Taipei Basin. Read the picture from an article (Teng et al., 2001) to see each era of Formation and the timeline of Taipei. The most ancient Formation in Taipei is Wuchihshan Formation. Younger Formation is covered on the older Formation. Old Formation to young Formation under Taipei Basin is in sequence with Wuchihshan Formation, Mushan Formation, Taliao Foramtion, Shiti Formation, Nankang Formation, Nanchuang Formation, Kueichulin Formation, Banchiao Formation, Wugu Formation, Jingmei Formation, and Sungshan Formaiotn. From the indication of time line, Tatun volcanic activity is relatively young compared to other old Formations. The time of Gongguan tuffs should be much earlier than igneous rocks of Tatun.
Sedimentary rocks in Taipei
Due to the river activities and dammed lake ever, a layer of sedimentary deposit covered whole Taipei Basin. Sedimentary rocks are also the main type in Taipei, especially northwest and northern Taipei along the Tamsui River, like Beitou or Qilian. A special sedimentary rock, which is “Qilian Rock”, is discovered at Qilian in Taipei. The type of Qilian Rock is sandstone composed of much quartz. Qilian Rocks is hard enough and is a great material for buildings. Therefore, some historical sites still have this kind of rock material on the wall.
Metamorphic rocks in Taipei
Metamorphic rock is a type of rocks in Taipei. Metamorphic rocks is much fewer than the two other types of rocks. However, some metamorphic rocks can be found in southeast of Taipei. It might be due to the tectonic activities, resulting in the Xueshan Mountain Range, at southeast and east area of Taipei. The collision of PH Plate and EU Plate caused a huge mountain-building region in Taiwan. The region creates a condition for metamorphism of both temperature and pressure. Many different types of metamorphic rocks can be found in Taiwan. And the most prevalence type in Taipei might be slate. Though, some unique metamorphic rock can be found in southern Taipei, such as jade and marble.
Rock distribution in Taipei
The photo below shows the distribution of different rocks in Taiwan. As the indication, rocks in Taipei are plentiful with different types of rocks. The area in Taipei is covered with recent sedimentary layer, west sedimentary rocks, igneous, and slate in central mountain range.
(p.s. The light green region is “Slate in Central Mountain Range” as indicated. However, the region near southeast Taipei is actually belonging to the region of Xueshan Range.)
cited and adapted from web
問題：
地點一
前往圖片(照片變色處理)中的地點。這裡的建築使用在台北發現的岩石建成。
1.1 請回答區塊A和B的岩石種類(A和B是相同的)。 1.2 請回答區塊C的岩石種類。
選擇題：A. 板岩 B. 泥岩 C. 砂岩 D. 花崗岩 E. 安山岩 F. 不是岩石
2. 你有發現波痕嗎?
地點二
找到圖片中的岩石群 (照片變色處理)
3.1 這些岩石群的種類是什麼?
選擇題：A. 火成岩 B. 沉積岩 C. 變質岩
3.2 觀察到什麼特徵?
4.這些岩石都被分類為同一種岩石，但外貌型態、顏色、質地卻大不相同，請試著解釋原因。
地點三
找到說明指示牌
5. 此處的岩石稱作公館凝灰岩，他們坐落在特定的地層。請閱讀指示牌上的年代，對照頁面中的資料推測特定的地層年代。
6. 自由選擇: 附上你在現場的照片、GPS位置圖、或是你的旅行蟲，感激不盡。
線上登錄這個地質寶，請寄到Geocaching.com的信箱，若有什麼問題，會再回覆給你。
Question
Stage 1
Go to spot in the picture below. (Photo discoloration) Building here is made with a type of rock discovered in Taipei.
1.1 What is the type of rocks in area A and B (A is equal to B)? 1.2 What is the type of rocks in area C?
Answer from the options : A. Slate B. Mudstone C. Sandstone D. Granite E. Andesite F. Not Rock
2. Do you find the ripple marks?
Stage 2
Find the group of rocks in the picture below. (Photo discoloration)
3.1 What are the types of these rocks?
Answer from the options : A. Igneous rock B. Sedimentary rock C. Metamorphic rock
3.2 What kind of features do you find?
4. Look deep. Rocks here are classified as the same category. How do their appearances looks so different? Try to explain it.
Stage 3
Find the introduction board
5. The rocks here is called Gongguan Tuff. They were formed at a specific era of Formation. Read the specific time on the board, and compare to the listing page to figure out which specific Formation under Taipei Basin.
6. Optional: a photo of you, your GPS or your TB at WP would be appreciated
Log this cache "Found it" and send me your suggested answers either via my profile, or via geocaching.com (Message Center) messaging, and I will contact you if there is a problem.
Reference
Sibuet & Hsu, 2004 How was Taiwan created?
Geology of Taiwan from wiki
Su et al., 2018 Tectonic controls on the stratigraphic development of the rifted Taipei Basin
台灣大百科全書 頁岩
Teng et al., 2001 Origin and Geological Evolution of the Taipei Basin
https://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/basalt.html
台灣變質岩的分布