While you visit Matsu, have you ever noticed that there’s a giant “zebra” lying beside the coastal line? The local residents called it “the zebra rock” due to the black and white colors on the rock. But it’s not just about the color of the rock! This earthcache will bring you to visit a special geological spot that you could observe and learn how the dykes formed, and how it became the way you see now.
當你造訪馬祖時，你是否有注意到海岸線旁躺著一隻大『斑馬』？當地的人們因為岩石上黑白相間的顏色而稱它為『斑馬岩』。但這不僅僅是關於岩石的顏色這麼簡單而已喔！這個地質寶將帶你拜訪這個特殊的地質景觀，你將可以從中觀察並且學習岩脈是如何形成的，又是如何變成你現在看到的樣子。
The origin of Matsu Islands / 馬祖列島的起源
About 165 million years ago, along the southeastern coast of China, due to the push and shove of the Eurasian plate and the Philippine Sea plate, volcanic activity is frequent, and the collision of plates between plates has led to the melting of plates and the formation of hot magma.
約一億六千五百萬年前開始。在中國大陸東南沿岸一帶，因歐亞大陸板塊與菲律賓海板塊的推擠，使火山活動頻繁。板塊間的互相碰撞促使了板塊融化、炙熱岩漿的生成，這些蘊含大量二氧化矽成份的岩漿隨即沿著歐亞大陸板塊的裂隙上升。
Because the magma viscosity cools the rock formation sits below the surface and crystallizes, forming a vast deep rock body-granite.In the later part of the sea,because of the island-type climate temperature and the erosion of the surface by rain and the lift movement of the earth’s crust, it became the hills of the sea surface. At the end of the ice age 18 million years ago, the sea was flooded into low-lying areas, creating this beautiful island, Matsu.
由於岩漿過於黏稠的特性，未及擠出地表即在地表下就逐漸冷卻結晶，形成了以花崗岩為主的廣大深成岩體，而後配合著海島型氣候的高溫和雨水對地表岩層的侵蝕沖刷及地殼的抬升運動，才使得花崗岩體露出地表，成為中國大陸東南沿海地區一帶高低起伏的丘陵。約在一萬八千年前冰河期的結束，高漲的海水，開始向陸地淹沒低窪的區域，於是地勢較高的丘陵地也被海水一一阻隔，在歷經漫長的大地變革之後，馬祖列島才終於變至今日的面貌。
The formation of igneous rocks / 火成岩的形成
Igneous rock refers to a kind of rock formed after magma or lava has cooled and solidified (magma ejected from the earth's crust, or existing rocks that have been melted). Igneous rocks are one of the three main rock types, and the other two types are sedimentary rocks and metamorphic rocks.
火成岩，是指岩漿或熔岩冷卻和凝固後（地殼裡噴出的岩漿，或者被熔化的現存岩石）所成形的一種岩石。火成岩是三種主要岩石類型之一，其他兩種類型分別是沉積岩和變質岩。
Igneous rocks are divided into two types according to their formation methods: If magma condenses into igneous rocks deep underground, we call it Intrusive igneous rocks, like granite. If magma erupts to the surface and becomes a lava flow, these hot fluids will cause a sharp drop in temperature due to contact with air, sea water or surrounding rocks and condense, turning from molten molten liquid to solid rock, we call it Extrusive igneous rocks, like basalt.
火成岩依形成方式分為兩種類型：岩漿如果在地底下深處凝結成火成岩，我們就稱為侵入岩(Intrusive igneous rocks)，像是花崗岩。如果岩漿噴發至地表成為熔岩流，這些熾熱流體因接觸空氣、海水或圍岩而使得溫度急遽下降凝結，由融熔液態轉為固態的岩石，我們就稱為噴出岩(Extrusive igneous rocks)，像是玄武岩。
The main rock masses of Nangan are mainly shells and granodiorite, which belong to intrusive rocks. In addition, dark gray porphyritic rhyolite volcanic rocks can be seen on the island. In the bedrock of granite type, there are dyke intrusions generated earlier that penetrate or cut through.
南竿的主要岩體以花崗岩與花崗閃長岩為主，屬於侵入岩類，另外在島上尚可見到深灰色的斑狀流紋岩質火山岩出露。在花崗岩類的基岩中，有較晚期生成的岩脈侵入體貫入或切穿。
The intrusion of magma / 侵入地層的岩漿
The hot magma rises from the magma reservoir and fills the cracks, gaps or structural folds in the crust, melting the surrounding rocks to form magma clusters. When the magma cools, minerals with high melting points begin to crystallize, such as olivine (mafic mineral) And anorthite (feldspar minerals) crystallized first at almost the same temperature, and then other minerals were formed according to the melting point, and finally these minerals were composed into igneous rocks.
熾熱的岩漿由岩漿庫上升而填充於地殼的裂縫、缺口或構造褶曲地區，將周圍的岩石融化形成岩漿團，當岩漿冷卻時，熔點高的礦物便開始結晶，如橄欖石(鎂鐵礦物)和鈣長石(長石礦物)幾乎在相同溫度下最早結晶，接著再依熔點高低先後生成別種礦物，最後這些礦物分別組成形成火成岩。
According to the relation between these igneous rocks and the strata, the igneous rocks are roughly parallel to the stratum and the concordant is roughly parallel to the stratum. The unconcordant is obviously not parallel to the stratum. According to the appearance of igneous rock bodies, they are divided into six categories. The integrated rock masses include laccolith, lopolith, and sill; unconformity penetrates into batholith, stock and dyke.
依據這些火成岩與地層的關係區分為火成岩體與地層面約略平行的整合貫入(concordant)與地層面明顯不平行的不整合貫入 (disconcordant)。再按照火成岩體的外觀區分為六類，整合貫入的岩體有岩蓋(laccolith)、岩盆 (lopolith)與岩床(sill)；不整合貫入有岩基 (batholoth)、岩株(stock)與岩脈(dyke)。
Laccolith mostly occurs in acidic magma, and the viscosity is high and it is not easy to flow to both sides, so they form caps. The lopolith is basin-shaped, and because it is formed at a deeper level, the crystal grains are larger. The sill is a magma intrusion along the stratum plane to form a plate-like intrusion parallel to the plane. It occurs more often in basic magma, which is easy to expand to both sides and is formed in a shallower place below the ground. Dikes are vein-like intrusions obliquely intersecting with the surrounding rock bedding or schistosity. They are the products of magma rising along the fractures and often appear in groups.
岩蓋大多發生於酸性岩漿，粘度大不易向兩側流動，所以形成蓋狀。岩盆為盆狀，由於形成於較深處，因此結晶顆粒較大。岩床是岩漿沿地層層面侵入，形成與層面平行的板狀侵入體，較常發生於基性岩漿，易向兩側擴展，形成於地底下較淺處。岩脈則是與圍岩層理或片理斜交的脈狀侵入體，為岩漿沿裂縫上升的產物，常群體出現。
The formation of dykes / 岩脈的形成
The dyke is formed by magma intruding into the adjacent rock and then being cooled and solidified. There are two ways to intrude into the adjacent rock:
(1) The adjacent rock itself has fissures. Magma flows into the adjacent rock through the original fissures. However, if the fissures are located below a certain depth underground, they will be closed due to static rock pressure. The dykes formed in this way only occur Partial area
(2) When the fluid pressure caused by magma is greater than the minimum principal stress of the lithostatic pressure and the tensile strength of the adjacent rock, the parallel maximum principal stress and the intermediate stress will be formed due to hydraulic fracturing. In the fracture plane of the principal stress, magma intrudes into the adjacent rock along this fracture plane by forceful injection, which is a common form of formation.
岩脈為岩漿侵入圍岩(adjacent rock)後，經冷卻凝固所形成，其侵入圍岩方式有2種：(1) 圍岩本身具有裂隙(fissure)，岩漿即透過原有的裂隙流入圍岩，但裂隙若位於地底某深度以下，會因靜岩壓力而閉合，此種方式形成的岩脈僅發生於局部區域。(2) 當岩漿造成的流體壓力(fluid pressure)大於靜岩壓力(lithostatic pressure)的最小主應力及圍岩的張力強度時，將因水力開裂作用(hydraulic fracturing)而形成平行最大主應力及中間主應力的裂理面，岩漿則沿此裂理面以強力貫入(forceful injection) 的方式侵入圍岩，此為較常見的形成方式。
To log this cache, please answer the following questions:
- According to your observation, what kinds of the rock that the dark rocks and light-colored rocks is? Please explain your thought.
- According to your observation, what is the order of formation of dark rocks and light-colored rocks? Please explain your thought.
- According to the picture below, what is the order of formation of the two dykes A and B in the picture? Please explain your thought
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Take a photo in front of the zebra rock, the photos must contain either you (no face required), your personal item, a piece of paper with your geocaching name, or any else that would makes your photos unique.
Notes:
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Please don’t post any answers in your log.
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Please send the answers to the owner via message system of geocaching.com. Only the accounts that sent the answers could log as found, so please make sure you sent your own answers even you’re in the group-hunting.
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You MUST visit the earthcache location to claim a find. I’ll delete the logs of people who clearly didn’t visit the earthcache or who didn't complete the logging tasks.
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You don’t have to wait the permission to log after you send the answers. Any logs without all of the answers will be deleted.
REF: 連江縣海洋教育資源中心, 地質季刊, 臺灣地質知識服務網
